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Editor Work2016 Vol. 24, No. 6
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2016, 24(6): 1041-1047.
Abstract
1186KB
For predicting a mine's slope deformation so as to adopt timely safety measures, this paper proposes a new dynamic synthetical prediction method. With the help of phase-space reconstruction by substituting different lag time, a new data series from the original monitoring data was get for this method. It took the linear optimization method, which on the condition of the minimum sum of squares of prediction residue error, to calculate the weights of different methods' predictions, such as ARMA time series and GM (1, 1) grey theory. The comparison of the results indicates that, the standard deviation of the synthetical prediction is reduced obviously compared with independent approaches; predictions after the Phase-space reconstruction can improve the average precision. And this provides a reliable method for the forecast and precaution for each kind of landslide.
For predicting a mine's slope deformation so as to adopt timely safety measures, this paper proposes a new dynamic synthetical prediction method. With the help of phase-space reconstruction by substituting different lag time, a new data series from the original monitoring data was get for this method. It took the linear optimization method, which on the condition of the minimum sum of squares of prediction residue error, to calculate the weights of different methods' predictions, such as ARMA time series and GM (1, 1) grey theory. The comparison of the results indicates that, the standard deviation of the synthetical prediction is reduced obviously compared with independent approaches; predictions after the Phase-space reconstruction can improve the average precision. And this provides a reliable method for the forecast and precaution for each kind of landslide.
2016, 24(6): 1048-1055.
The stability of colluvial landslides in the Three Gorges Reservoir is obviously influenced by the fluctuation of water level. So studying the evolutionary process and stability prediction of colluvial landslides under the reservoir water level fluctuation is significant to provide references for disaster management and construction planning. The load-unload response prediction model in which reservoir water level was treated as the load-unload parameter and landslide displacement rate, as the load-unload response parameter was established. The model was based on the relationship between landslide deformation and reservoir water level fluctuation. And the type of landslide seepage field under the reservoir water level fluctuation was determined by revealing the relationship. Then the load-unload interval differences were evaluated by the rate of stability coefficient. Taking Huanglianshu landslide for example, the model was used to predict the development trend. The results show that the relationship between horizontal displacement of the landslide and reservoir water level fluctuation has an obvious hysteretic nature. The hydrodynamic pressure landslide has a loading process of six months and an unloading process of one month. The load-unload response ratio of monitoring sites raises and is more than 1. It reveals that the landslide will be instable and the load-unload response is more obvious due to reservoir water level fluctuation. The application results show that the prediction is well coincident with the macroscopic deformation evidence. Thus the improved model is feasible in the stability prediction of landslides.
The stability of colluvial landslides in the Three Gorges Reservoir is obviously influenced by the fluctuation of water level. So studying the evolutionary process and stability prediction of colluvial landslides under the reservoir water level fluctuation is significant to provide references for disaster management and construction planning. The load-unload response prediction model in which reservoir water level was treated as the load-unload parameter and landslide displacement rate, as the load-unload response parameter was established. The model was based on the relationship between landslide deformation and reservoir water level fluctuation. And the type of landslide seepage field under the reservoir water level fluctuation was determined by revealing the relationship. Then the load-unload interval differences were evaluated by the rate of stability coefficient. Taking Huanglianshu landslide for example, the model was used to predict the development trend. The results show that the relationship between horizontal displacement of the landslide and reservoir water level fluctuation has an obvious hysteretic nature. The hydrodynamic pressure landslide has a loading process of six months and an unloading process of one month. The load-unload response ratio of monitoring sites raises and is more than 1. It reveals that the landslide will be instable and the load-unload response is more obvious due to reservoir water level fluctuation. The application results show that the prediction is well coincident with the macroscopic deformation evidence. Thus the improved model is feasible in the stability prediction of landslides.
2016, 24(6): 1056-1063.
Reasonable selection of rheological parameters may play a role in delineating the runout process mobility behavior of debris flow and high speed and long distance landslide. In this study, three-dimensional continuum model simulation method is applied using voellmy model and analysis of variance, to study the dynamic process under different rheological parameters, and to a compare the sensitivity degree of rheological parameters to runout behavior. The results show that dynamic basal friction angle and turbulence coefficient can influence the dynamic characteristics of debris flow and high speed and long distance landslide to a different degree. The higher dynamic basal friction angle will produce bigger and faster energy dissipation process, making the whole movement process lag; the higher turbulence coefficient increased strength momentum exchange between the fluid layers, with great ability to mix media around, and increased entrainment effect. The basal topography is an important factor influencing the debris transportation and deposition processes. The underlying surface conditions, particles of debris, pore water pressure has a very close connection with velocity, runout distance and deposition area, volume, and can affect the debris intensity and disaster area and scale to a large extent. The proposed suggestions can be estimated conveniently in general geotechnical practices and can provide the scientific basis for regional disaster prevention and reduction and scientific research.
Reasonable selection of rheological parameters may play a role in delineating the runout process mobility behavior of debris flow and high speed and long distance landslide. In this study, three-dimensional continuum model simulation method is applied using voellmy model and analysis of variance, to study the dynamic process under different rheological parameters, and to a compare the sensitivity degree of rheological parameters to runout behavior. The results show that dynamic basal friction angle and turbulence coefficient can influence the dynamic characteristics of debris flow and high speed and long distance landslide to a different degree. The higher dynamic basal friction angle will produce bigger and faster energy dissipation process, making the whole movement process lag; the higher turbulence coefficient increased strength momentum exchange between the fluid layers, with great ability to mix media around, and increased entrainment effect. The basal topography is an important factor influencing the debris transportation and deposition processes. The underlying surface conditions, particles of debris, pore water pressure has a very close connection with velocity, runout distance and deposition area, volume, and can affect the debris intensity and disaster area and scale to a large extent. The proposed suggestions can be estimated conveniently in general geotechnical practices and can provide the scientific basis for regional disaster prevention and reduction and scientific research.
2016, 24(6): 1064-1071.
Identifying such earthquake-damaged risk elements is the foundation to the safety evaluation and scientific prevention for underground engineering. With the application of system theory, the comprehensive risk system was carried into structure decomposition and element integration for earthquake-damaged underground engineering, which erected the three supportting formal structure description with task, event and element, and took the multi risk elements into all consideration. From the geological conditions, topography and geomorphology, engineering effect, environmental conditions, monitoring performance and other point of view, the risk element was respectively interpretted; the risk logical association and mechanism was explored between the disaster causing elements and the hazard bearing elements for earthquake-damaged underground engineering. Finally, the concept system and methodological framework was erected for earthquake-damaged risk analysis science, which provides the basis for exploring the essential elements of the earthquake-damaged risk system, and carrying on the comprehensive integrated system analysis and assessment for underground engineering.
Identifying such earthquake-damaged risk elements is the foundation to the safety evaluation and scientific prevention for underground engineering. With the application of system theory, the comprehensive risk system was carried into structure decomposition and element integration for earthquake-damaged underground engineering, which erected the three supportting formal structure description with task, event and element, and took the multi risk elements into all consideration. From the geological conditions, topography and geomorphology, engineering effect, environmental conditions, monitoring performance and other point of view, the risk element was respectively interpretted; the risk logical association and mechanism was explored between the disaster causing elements and the hazard bearing elements for earthquake-damaged underground engineering. Finally, the concept system and methodological framework was erected for earthquake-damaged risk analysis science, which provides the basis for exploring the essential elements of the earthquake-damaged risk system, and carrying on the comprehensive integrated system analysis and assessment for underground engineering.
2016, 24(6): 1072-1079.
Tanggudong landslide which is huge lies among the pre-selected upper, middle and lower dam of Lenggu hydropower station. It has a decisive effect on the selection of hydropower station dam site and construction and layout. Studying formation mechanism of landslide has a very important influence on analyzing deformation and evolutionary of similar slopes in this river. On the basis of analyzing geo-environmental conditions and characteristics of landslide, the author analyzes formation mechanism of landslide by means of bottom friction test method and discrete element numerical calculation. The results show:Tanggudong landslide is a giant and rock landslide, of which the deformation and failure model is slipping-cracking. It cuts off layers and moves along the ladder-like sliding surface which is composed of the steeply inclined outside joints and gently inclined outside joints in the strongly weathered layers. Instability and failure of these front slopes firstly occur, which is then followed by the continuous deformation of the upper slopes. Consequently, instability and failure of the whole upper slope in the rear part ultimately occurs.
Tanggudong landslide which is huge lies among the pre-selected upper, middle and lower dam of Lenggu hydropower station. It has a decisive effect on the selection of hydropower station dam site and construction and layout. Studying formation mechanism of landslide has a very important influence on analyzing deformation and evolutionary of similar slopes in this river. On the basis of analyzing geo-environmental conditions and characteristics of landslide, the author analyzes formation mechanism of landslide by means of bottom friction test method and discrete element numerical calculation. The results show:Tanggudong landslide is a giant and rock landslide, of which the deformation and failure model is slipping-cracking. It cuts off layers and moves along the ladder-like sliding surface which is composed of the steeply inclined outside joints and gently inclined outside joints in the strongly weathered layers. Instability and failure of these front slopes firstly occur, which is then followed by the continuous deformation of the upper slopes. Consequently, instability and failure of the whole upper slope in the rear part ultimately occurs.
2016, 24(6): 1080-1087.
The red beds is wide distributed in Enshi Basin with a large number of slopes or man-made high and steep slopes. Because of the specialities of the engineering geological properties, the deformation and failure of the slopes under the natural geological process and human engineering activities always cause casualties and property losses, which has greatly influences and restrictions on the construction of urban municipal engineering and road engineering. According to the field engineering geological investigation, drilling, field test (water pressure and infiltration test), sample collection and laboratory rock mass parameters test, the engineering geological property, hydraulic characteristics and slope deformation characteristics of red beds are investigated. The red beds in Enshi Basin can be divided into "hard sandstone" and "soft sandstone", the former ones are relatively impermeable layers composed by better consolidated silt-stone and sandstone with high strength, lower permeability; the latter ones are aquifer layer composed by poor consolidated sandstone with low strength, strong permeability. The scale of deformation and failure of slope is small, but the quantity is big and the harmfulness is heavy. This paper have researched on the deformation and failure mode of slopes from two aspects:the motion mode and influencing factors. According to the movement modes of the slope rock mass, the deformation and failure of the red bed slopes are divided into three kinds:the bedding rock landslide, the falling collapse, and the dumping collapse. Based on the deformation and failure influencing factors, the deformation and failure of the slopes also are divided into three kinds:soft and hard sandstone layers with different weathering functions, the disadvantageous combination of the bedding planes and the cutting structure planes, the artificial excavation disturbance. The characteristics and the processes of the various types of deformation and failure modes are analyzed, which has significant guiding and reference value for the prevention and control of the deformation and damage of the red bed slopes in Enshi Basin and areas of the same kind.
The red beds is wide distributed in Enshi Basin with a large number of slopes or man-made high and steep slopes. Because of the specialities of the engineering geological properties, the deformation and failure of the slopes under the natural geological process and human engineering activities always cause casualties and property losses, which has greatly influences and restrictions on the construction of urban municipal engineering and road engineering. According to the field engineering geological investigation, drilling, field test (water pressure and infiltration test), sample collection and laboratory rock mass parameters test, the engineering geological property, hydraulic characteristics and slope deformation characteristics of red beds are investigated. The red beds in Enshi Basin can be divided into "hard sandstone" and "soft sandstone", the former ones are relatively impermeable layers composed by better consolidated silt-stone and sandstone with high strength, lower permeability; the latter ones are aquifer layer composed by poor consolidated sandstone with low strength, strong permeability. The scale of deformation and failure of slope is small, but the quantity is big and the harmfulness is heavy. This paper have researched on the deformation and failure mode of slopes from two aspects:the motion mode and influencing factors. According to the movement modes of the slope rock mass, the deformation and failure of the red bed slopes are divided into three kinds:the bedding rock landslide, the falling collapse, and the dumping collapse. Based on the deformation and failure influencing factors, the deformation and failure of the slopes also are divided into three kinds:soft and hard sandstone layers with different weathering functions, the disadvantageous combination of the bedding planes and the cutting structure planes, the artificial excavation disturbance. The characteristics and the processes of the various types of deformation and failure modes are analyzed, which has significant guiding and reference value for the prevention and control of the deformation and damage of the red bed slopes in Enshi Basin and areas of the same kind.
2016, 24(6): 1088-1095.
Landslide is a critical geological disaster that has drawn general concern of the society. Earthquakes, rainfalls, reservoir operations and construction activities frequently induce large movements of high slopes and even trigger landslides or debris flows, which poses a significant threat to human lives and properties. In recent years, the monitoring technologies of slope deformation have been rapidly developed and played an increasingly important role in ensuring slope stability, verifying the effect of reinforcing measures, enhancing early warning of landslides, et al. This paper briefly introduces the conventional slope deformation monitoring technologies and their shortcomings. The latest development and applications of slope deformation monitoring technologies at home and abroad in the past few decades are presented in detail, followed by a comparison of the features of these technologies, especially the distributed fiber optic sensing technology. Finally, some research suggestions are proposed for future development of slope deformation monitoring technologies.
Landslide is a critical geological disaster that has drawn general concern of the society. Earthquakes, rainfalls, reservoir operations and construction activities frequently induce large movements of high slopes and even trigger landslides or debris flows, which poses a significant threat to human lives and properties. In recent years, the monitoring technologies of slope deformation have been rapidly developed and played an increasingly important role in ensuring slope stability, verifying the effect of reinforcing measures, enhancing early warning of landslides, et al. This paper briefly introduces the conventional slope deformation monitoring technologies and their shortcomings. The latest development and applications of slope deformation monitoring technologies at home and abroad in the past few decades are presented in detail, followed by a comparison of the features of these technologies, especially the distributed fiber optic sensing technology. Finally, some research suggestions are proposed for future development of slope deformation monitoring technologies.
2016, 24(6): 1096-1102.
The occuring of debris flow in the valley needs three basic conditions at the same time which are rich loose deposits, enough water and slope terrain. In view of the shortage of the gravity flow drainage technology and the need for the rapid drainage of the storm, then it uses the siphon drainage technology of self-dredging ability and water separation. So it can improve efficiency and durability of debris flows control. To choose the diameter of the barrier grid and design the siphon drainage system is the key to ensuring the dredging capability of drainage pool. Using computational fluid dynamics software CFD, a three-dimensional numerical model is established to analyze the hydraulic characteristics of the flow in the drainage pool first. Then mathematical model of sediment incipient motion and suspension is established. It can use the hydraulic characteristics of the flow in the drainage pool to analyze sediment incipient motion and suspension. So the evaluation index about dredging ability of siphon drainage pool is established. Besides, it analyses three essential conditions for sediment to be drained out of the pool with water. It suggests that when installing the siphon for the engineering, the water head difference between inlet and outlet should be above 5m, and the diameter of the barrier grid should be no more than 10mm. This can guide the design of siphon drainage pool in practical debris flow prevention engineering.
The occuring of debris flow in the valley needs three basic conditions at the same time which are rich loose deposits, enough water and slope terrain. In view of the shortage of the gravity flow drainage technology and the need for the rapid drainage of the storm, then it uses the siphon drainage technology of self-dredging ability and water separation. So it can improve efficiency and durability of debris flows control. To choose the diameter of the barrier grid and design the siphon drainage system is the key to ensuring the dredging capability of drainage pool. Using computational fluid dynamics software CFD, a three-dimensional numerical model is established to analyze the hydraulic characteristics of the flow in the drainage pool first. Then mathematical model of sediment incipient motion and suspension is established. It can use the hydraulic characteristics of the flow in the drainage pool to analyze sediment incipient motion and suspension. So the evaluation index about dredging ability of siphon drainage pool is established. Besides, it analyses three essential conditions for sediment to be drained out of the pool with water. It suggests that when installing the siphon for the engineering, the water head difference between inlet and outlet should be above 5m, and the diameter of the barrier grid should be no more than 10mm. This can guide the design of siphon drainage pool in practical debris flow prevention engineering.
2016, 24(6): 1110-1117.
A slope model was conducted in the laboratory and a special strain sensing cable was buried in the soil mass. The sensing cable strain at different position of the slope model was measured by the pulse-prepump Brillouin optical time-domain analysis (PPP-BOTDA) technology during the loading and cut the slope. Then the test processing was simulated by the finite element analysis software Geo-studio. The measurement data under the loading have been analyzed to discuss the co-deformation between the sensing cable and the soil mass. The results show that the co-deformation was affected by the confining pressure significantly. The measurement data of the sensing cable during cut slope showed that there was strain concentration area in the soil mass. When the slope failed, the position of the sliding surface was consistent with the strain anomaly area of the sensing cable. The results provide a guiding to evaluate slope stability and perform early warning of landslides.
A slope model was conducted in the laboratory and a special strain sensing cable was buried in the soil mass. The sensing cable strain at different position of the slope model was measured by the pulse-prepump Brillouin optical time-domain analysis (PPP-BOTDA) technology during the loading and cut the slope. Then the test processing was simulated by the finite element analysis software Geo-studio. The measurement data under the loading have been analyzed to discuss the co-deformation between the sensing cable and the soil mass. The results show that the co-deformation was affected by the confining pressure significantly. The measurement data of the sensing cable during cut slope showed that there was strain concentration area in the soil mass. When the slope failed, the position of the sliding surface was consistent with the strain anomaly area of the sensing cable. The results provide a guiding to evaluate slope stability and perform early warning of landslides.
2016, 24(6): 1118-1125.
As a kind of distributed fiber optic sensing technology based on Brillouin back-scattering, BOTDR was used to monitor the deformation of overburden during the coal mining. Taking a working face in Huainan mining area as an example, distributed optical sensing cables were implanted into the overburden of coal seam by drilling. By grouting the borehole with cement, it is assumed that the deformation of sensing cable and the overburden should be the same. During the mining, strain distribution of sensing cables was obtained periodically. By analyzing the strain distribution and its variation, the deformation and failure of overburden were investigated during the mining. The maximum tensile strain along the borehole is about 5m depth with the value of 8350με.The maximum compressive strain is -550με at the borehole depth of 37m. Strain distribution shows a good correlation with the structure of the strata. A relatively larger tensile strain can be observed in the soft strata, such as mudstone. However, the strain in the hard strata, such as sandstone, the cable strain is smaller and usually ompressive. The maximum deformation of the strata along the borehole is 34mm. The loosened circle of roadway is about 6m. The results show that distributed optical fiber sensing technology can obtain the deformation and its variation of the overburden, which can provide reliable data for the safe and efficient mining.
As a kind of distributed fiber optic sensing technology based on Brillouin back-scattering, BOTDR was used to monitor the deformation of overburden during the coal mining. Taking a working face in Huainan mining area as an example, distributed optical sensing cables were implanted into the overburden of coal seam by drilling. By grouting the borehole with cement, it is assumed that the deformation of sensing cable and the overburden should be the same. During the mining, strain distribution of sensing cables was obtained periodically. By analyzing the strain distribution and its variation, the deformation and failure of overburden were investigated during the mining. The maximum tensile strain along the borehole is about 5m depth with the value of 8350με.The maximum compressive strain is -550με at the borehole depth of 37m. Strain distribution shows a good correlation with the structure of the strata. A relatively larger tensile strain can be observed in the soft strata, such as mudstone. However, the strain in the hard strata, such as sandstone, the cable strain is smaller and usually ompressive. The maximum deformation of the strata along the borehole is 34mm. The loosened circle of roadway is about 6m. The results show that distributed optical fiber sensing technology can obtain the deformation and its variation of the overburden, which can provide reliable data for the safe and efficient mining.
2016, 24(6): 1126-1135.
In earthquake-prone areas, seismic load can significantly influence the stability of rock slope. Therefore, accurately and effectively estimate the stability is very important in seismic design of rock slope. Safety coefficient method has its limitation as this method ignores the uncertainties of seismic load and other influential factors. Under the condition that the smooth flow gap is uncongested and congested, this paper calculated the anti-overturning safety factor of rock slope by pseudo-dynamic method, and analyzed the influence of the seismic load, surcharge and depths of water in the tensile crack on anti-overturning safety factors of rock slope. Based on the deterministic calculation model of anti-overturning stability and in consideration of the variability of seismic load, surcharge and the depth of water in tension crack, the reliability analysis of anti-overturing stability of rock slope is developed. The mean values and coefficients of variation of seismic load, surcharge and depths of water in the tensile crack on anti-overturning reliability index were analyzed. Based on the study of this paper, it can be found that the anti-overturning safety factor of rock slope decreased rapidly when the smooth flow gap is congested. Besides, the variability of seismic load and other influential factors can significantly influence the stability of rock slope. Therefore, safety factor and reliability index are combined to estimate the anti-overturning stability is benefical to the safety of seismic design of rock slope by appropriately considering the amplification factor.
In earthquake-prone areas, seismic load can significantly influence the stability of rock slope. Therefore, accurately and effectively estimate the stability is very important in seismic design of rock slope. Safety coefficient method has its limitation as this method ignores the uncertainties of seismic load and other influential factors. Under the condition that the smooth flow gap is uncongested and congested, this paper calculated the anti-overturning safety factor of rock slope by pseudo-dynamic method, and analyzed the influence of the seismic load, surcharge and depths of water in the tensile crack on anti-overturning safety factors of rock slope. Based on the deterministic calculation model of anti-overturning stability and in consideration of the variability of seismic load, surcharge and the depth of water in tension crack, the reliability analysis of anti-overturing stability of rock slope is developed. The mean values and coefficients of variation of seismic load, surcharge and depths of water in the tensile crack on anti-overturning reliability index were analyzed. Based on the study of this paper, it can be found that the anti-overturning safety factor of rock slope decreased rapidly when the smooth flow gap is congested. Besides, the variability of seismic load and other influential factors can significantly influence the stability of rock slope. Therefore, safety factor and reliability index are combined to estimate the anti-overturning stability is benefical to the safety of seismic design of rock slope by appropriately considering the amplification factor.
2016, 24(6): 1136-1144.
Prediction of landslides is very important for mitigating geo-hazards but is scientifically very challenging. Based on the deformation characteristics and the data measured by monitoring of Baishuihe landslide, Three Gorges Reservoir, a time series addition model was established for the landslide displacement prediction. In the model, the accumulative displacement is divided into three parts:trend, periodic and random terms, which can be explained by the internal factors (geological environment, gravity, et al.), external factors (rainfall, reservoir water level, et al.), random factors (uncertainties).After statistically analyzing the displacement data, a cubic polynomial model was proposed for the trend term displacement prediction. And using multi algorithm to find the optimal support vector regression (SVR) model to train and predict the periodic term. The results show that based on Genetic algorithm (GA-SVR) and the time series model, the displacements prediction of Baishuihe landslide are better than the landslide displacements based on the particle swarm optimization (PSO-SVR) and the grid search (GS-SVR) model. Therefore, the coupling model based on the time series and GA-SVR can be used to predict the landslide displacement. GA-SVR will have broad application prospects in the prediction of the "step type" landslide displacement.
Prediction of landslides is very important for mitigating geo-hazards but is scientifically very challenging. Based on the deformation characteristics and the data measured by monitoring of Baishuihe landslide, Three Gorges Reservoir, a time series addition model was established for the landslide displacement prediction. In the model, the accumulative displacement is divided into three parts:trend, periodic and random terms, which can be explained by the internal factors (geological environment, gravity, et al.), external factors (rainfall, reservoir water level, et al.), random factors (uncertainties).After statistically analyzing the displacement data, a cubic polynomial model was proposed for the trend term displacement prediction. And using multi algorithm to find the optimal support vector regression (SVR) model to train and predict the periodic term. The results show that based on Genetic algorithm (GA-SVR) and the time series model, the displacements prediction of Baishuihe landslide are better than the landslide displacements based on the particle swarm optimization (PSO-SVR) and the grid search (GS-SVR) model. Therefore, the coupling model based on the time series and GA-SVR can be used to predict the landslide displacement. GA-SVR will have broad application prospects in the prediction of the "step type" landslide displacement.
2016, 24(6): 1145-1156.
In early morning of July 6, 2016, there took place a large debris flow disaster in Liucun, Yecheng county of Xinjiang. The event made serious villagers death and property loss. The paper, adopting the methods of in-situ investigation, witness interviewing and remote sensing explanation, based on the topography and morphology, lithologies and geological structure, as well as the climate and hydrology, analyzes the characteristics and formation of the landslides, the conditions and hazard chains and disaster mechanism of the debris flow. It also predicts the trend of landslide/debris flow in this area. The in-situ investigation shows (1) in the adjacent area between Liucun and Qichun of the northern slope of West Kunlun Mountains, 38 landslides were triggered by a rainstorm in that day. The landslides are shallow, loess type with the mechanism of Creeping-Tension, and some big landslides have the characteristics of long-runout. (2) the landslide debris accumulated in the gully of "V-shape" to form dams. Among which, there were 15 landslides and 2 dams in the upstream of Liuchun. Under the action of rainfall and small debris flow upwards, the dams are outbreak to form debris flow.(3) there exist more than 227 loess slopes under deforming in the both sides of "V-shape" gully, in the condition of climate change and the increasing of extremely climate events, those slopes would take place similar landslides. The size could be much larger than that of this time. At last, it is suggested to promote advanced research to the mechanism of the shallow loess landslides, the critical rainfall strength, and the movement of mud flow, and strengthen the study of the monitoring, prediction and early alarming of such landslide-debris flow geohazard chains.
In early morning of July 6, 2016, there took place a large debris flow disaster in Liucun, Yecheng county of Xinjiang. The event made serious villagers death and property loss. The paper, adopting the methods of in-situ investigation, witness interviewing and remote sensing explanation, based on the topography and morphology, lithologies and geological structure, as well as the climate and hydrology, analyzes the characteristics and formation of the landslides, the conditions and hazard chains and disaster mechanism of the debris flow. It also predicts the trend of landslide/debris flow in this area. The in-situ investigation shows (1) in the adjacent area between Liucun and Qichun of the northern slope of West Kunlun Mountains, 38 landslides were triggered by a rainstorm in that day. The landslides are shallow, loess type with the mechanism of Creeping-Tension, and some big landslides have the characteristics of long-runout. (2) the landslide debris accumulated in the gully of "V-shape" to form dams. Among which, there were 15 landslides and 2 dams in the upstream of Liuchun. Under the action of rainfall and small debris flow upwards, the dams are outbreak to form debris flow.(3) there exist more than 227 loess slopes under deforming in the both sides of "V-shape" gully, in the condition of climate change and the increasing of extremely climate events, those slopes would take place similar landslides. The size could be much larger than that of this time. At last, it is suggested to promote advanced research to the mechanism of the shallow loess landslides, the critical rainfall strength, and the movement of mud flow, and strengthen the study of the monitoring, prediction and early alarming of such landslide-debris flow geohazard chains.
2016, 24(6): 1157-1169.
Tunnel located in hipparion red clay region encountered many engineering geological problems in the construction process. In order to make sure construction safe and smooth traffic, a series of experiments and methods was carried out in the tunnel construction, such as laboratory test, field test and permeability test in situ, et al. Taking the surrounding rock section of the typical hipparion red clay in Shilou tunnel below the underground water level as an example, several aspects about the surrounding rock of hipparion red clay will be analyzed, including volume moisture content, pore water pressure, stress of surrounding rock (soil pressure), vault subsidence and horizontal convergence through the field monitoring. Based on this, a series of works will be done:the reliable situ shear strength parameters of surrounding rock will be obtained by shear tests, three dimensional finite element numerical model of tunnel will be built, the deformation law of the hipparion red clay surrounding rock will be investigated respectively for the water-force coupling effect and without considering it, the variation of the pore water pressure during excavation, the influence degree about the displacement field and stress field of water-stress coupling on red clayrock will be analyzed, and the mechanism of the surrounding rock deformation will be proposed. The results show that:(1) The site monitoring vault settlement is greater than horizontal convergence, and the stress level of surrounding rock is higher on the whole, which can be described by using three different stages, the growth period ( < 20 days), the adjustment period (20~60 days), the stable period (>60 days).Water content of the lower stage is higher than the top, the pore water pressure has experienced the process from negative to positive. (2) The cohesion determined by situ shear test C is 64.0kPa, the angle of internal φ is 27.7°. (3) Numerical analysis shows that, the change of pore water pressure is very obvious after the tunnel excavation, which is caused by the change of the underground water flow velocity field, the hydraulic gradient near lining surface, and the soil hydrodynamic seepage pressure are larger; considering the water-stress coupling, the surrounding rock shear stress, maximum shear strain, crown settlement, horizontal convergence, floor heave are all larger. (4) Groundwater appears seepage influenced by the excavation and support, and passing through the crown, side wall, ending in the tunnel bottom; rock joints appears the further expansion affected by the excavation and groundwater seepage, and becoming the good migration pathway of groundwater; the decrease of the surrounding rock pore water pressure enlarges the effective stress, and the mechanical strength is plunge as the soil tending to the saturated state. In turn, high effective stress, low strength of surrounding rock and through joint fracture together change the groundwater seepage field state. (5) In order to guarantee the whole stability of the surrounding rock, timely discharging water of the tunnel bottom and making construction of inverted arch are suggested.
Tunnel located in hipparion red clay region encountered many engineering geological problems in the construction process. In order to make sure construction safe and smooth traffic, a series of experiments and methods was carried out in the tunnel construction, such as laboratory test, field test and permeability test in situ, et al. Taking the surrounding rock section of the typical hipparion red clay in Shilou tunnel below the underground water level as an example, several aspects about the surrounding rock of hipparion red clay will be analyzed, including volume moisture content, pore water pressure, stress of surrounding rock (soil pressure), vault subsidence and horizontal convergence through the field monitoring. Based on this, a series of works will be done:the reliable situ shear strength parameters of surrounding rock will be obtained by shear tests, three dimensional finite element numerical model of tunnel will be built, the deformation law of the hipparion red clay surrounding rock will be investigated respectively for the water-force coupling effect and without considering it, the variation of the pore water pressure during excavation, the influence degree about the displacement field and stress field of water-stress coupling on red clayrock will be analyzed, and the mechanism of the surrounding rock deformation will be proposed. The results show that:(1) The site monitoring vault settlement is greater than horizontal convergence, and the stress level of surrounding rock is higher on the whole, which can be described by using three different stages, the growth period ( < 20 days), the adjustment period (20~60 days), the stable period (>60 days).Water content of the lower stage is higher than the top, the pore water pressure has experienced the process from negative to positive. (2) The cohesion determined by situ shear test C is 64.0kPa, the angle of internal φ is 27.7°. (3) Numerical analysis shows that, the change of pore water pressure is very obvious after the tunnel excavation, which is caused by the change of the underground water flow velocity field, the hydraulic gradient near lining surface, and the soil hydrodynamic seepage pressure are larger; considering the water-stress coupling, the surrounding rock shear stress, maximum shear strain, crown settlement, horizontal convergence, floor heave are all larger. (4) Groundwater appears seepage influenced by the excavation and support, and passing through the crown, side wall, ending in the tunnel bottom; rock joints appears the further expansion affected by the excavation and groundwater seepage, and becoming the good migration pathway of groundwater; the decrease of the surrounding rock pore water pressure enlarges the effective stress, and the mechanical strength is plunge as the soil tending to the saturated state. In turn, high effective stress, low strength of surrounding rock and through joint fracture together change the groundwater seepage field state. (5) In order to guarantee the whole stability of the surrounding rock, timely discharging water of the tunnel bottom and making construction of inverted arch are suggested.
2016, 24(6): 1170-1176.
By means of the vibration test system as well as the ultrasonic testing device and dynamic signal analysis system, the experiment on rock mass with weak intercalation fatigue damage are performed under cyclic loading. The acoustic parameters during defect rock fatigue damage are real-time measured and analyzed in detail. Results show that the ultrasonic wave velocity varies particularly sensitive to the fatigue cycle and reduces with an inversed S-shaped line. The waveform changes from an approximate semicircle to malformation, and the waveform correlation coefficient is descending as a whole with the cyclic times increasing. The ultrasonic wave amplitude has an intense fluctuation in the middle of the fatigue damage. And the rules of frequency-domain characteristics is not obvious, only when sample is nearly damaged, the maximum value of frequency domain and frequency decline sharply, which lead to a hard effective analysis and recognition of the frequency-domain characteristics. Finally, a damage variable is defined based on the transverse ultrasonic wave velocity and the Logistic inverse function equation and the nonlinear quartic polynomial are used to describe the growth law of rock mass with weak intercalation fatigue damage. The results may offer theoretical references for slope fatigue stability evaluation and reinforcement engineering under different kinds of vibration environment.
By means of the vibration test system as well as the ultrasonic testing device and dynamic signal analysis system, the experiment on rock mass with weak intercalation fatigue damage are performed under cyclic loading. The acoustic parameters during defect rock fatigue damage are real-time measured and analyzed in detail. Results show that the ultrasonic wave velocity varies particularly sensitive to the fatigue cycle and reduces with an inversed S-shaped line. The waveform changes from an approximate semicircle to malformation, and the waveform correlation coefficient is descending as a whole with the cyclic times increasing. The ultrasonic wave amplitude has an intense fluctuation in the middle of the fatigue damage. And the rules of frequency-domain characteristics is not obvious, only when sample is nearly damaged, the maximum value of frequency domain and frequency decline sharply, which lead to a hard effective analysis and recognition of the frequency-domain characteristics. Finally, a damage variable is defined based on the transverse ultrasonic wave velocity and the Logistic inverse function equation and the nonlinear quartic polynomial are used to describe the growth law of rock mass with weak intercalation fatigue damage. The results may offer theoretical references for slope fatigue stability evaluation and reinforcement engineering under different kinds of vibration environment.
2016, 24(6): 1177-1181.
Grouting simulation test is an effective way for determining the grouting engineering parameters and revealing the impacts of various parameters on the grouting efficiency. Existing grouting simulation test devices are not integrated. Thus, they cannot simulate the whole grouting process and cannot represent the confining pressure boundary under the filling and compaction of the grouting body, and cannot detect and evaluate the grouting efficiency soundly. After analyzing the grouting technology and theory, an advanced grouting simulation test device is developed in this research for treating the loose strata. This new device is an integrated system and can completely simulate the whole processes under various grouting technique. The loosen strata is filled into the rigid disassemble high-pressure vessel for simulating multi-hole (row) grouting. Confining pressure environment that corresponding to the strata of different depth can be simulated by adjusting the pressure of the gasbag in the inner wall of the vessel. This new devise also provides controllable hydraulic head for water injection experiment and quality evaluation after grouting. Functional verification results demonstrate that this new device can simulate the whole field grouting process really. And, the relationship between grouting parameters (e.g.grouting pressure and grouting quantity) and the grouting efficiency (e.g.diffusion distance, physical properties, et al.) can also be measured during grouting simulation test. This new device makes a foundation for the research on grouting mechanism and the parameter design for field grouting operation.
Grouting simulation test is an effective way for determining the grouting engineering parameters and revealing the impacts of various parameters on the grouting efficiency. Existing grouting simulation test devices are not integrated. Thus, they cannot simulate the whole grouting process and cannot represent the confining pressure boundary under the filling and compaction of the grouting body, and cannot detect and evaluate the grouting efficiency soundly. After analyzing the grouting technology and theory, an advanced grouting simulation test device is developed in this research for treating the loose strata. This new device is an integrated system and can completely simulate the whole processes under various grouting technique. The loosen strata is filled into the rigid disassemble high-pressure vessel for simulating multi-hole (row) grouting. Confining pressure environment that corresponding to the strata of different depth can be simulated by adjusting the pressure of the gasbag in the inner wall of the vessel. This new devise also provides controllable hydraulic head for water injection experiment and quality evaluation after grouting. Functional verification results demonstrate that this new device can simulate the whole field grouting process really. And, the relationship between grouting parameters (e.g.grouting pressure and grouting quantity) and the grouting efficiency (e.g.diffusion distance, physical properties, et al.) can also be measured during grouting simulation test. This new device makes a foundation for the research on grouting mechanism and the parameter design for field grouting operation.
2016, 24(6): 1182-1190.
There is a clear effect of hydro-mechanical path on the deformation of swelling rock. For the deformation behavior of compacted swelling rock under soaking-cyclicing loading and unloading, 1D swelling-circulating compression tests were conducted on Yanji swelling rock with different initial water content. On the basis of compression-rebound curves after swelling, Compression index, swelling index and their difference were obtained and the accumulative total and residual deformation rates were proposed to measure the deformation characteristics under cycling loading and unloading. The study results show that there is a significant negative liner relationship between the swelling ratio and the initial water content. The slope of loading and unloading curve is smaller with the increasing cycles, and the area of hysteresis loop decreases gradually. The compression index, swelling index and their difference increase with the growing cycles. The more the number of cycles, the less the total and residual deformation, and the accumulative total and residual deformation increase firstly, then tend to be stable. The smaller the initial water content, the larger the compression index and swelling index, and the more the accumulative total and residual deformation. The mechanical properties of specimens with different initial water content will be enhanced and normalized by the cycling loading and unloading process.
There is a clear effect of hydro-mechanical path on the deformation of swelling rock. For the deformation behavior of compacted swelling rock under soaking-cyclicing loading and unloading, 1D swelling-circulating compression tests were conducted on Yanji swelling rock with different initial water content. On the basis of compression-rebound curves after swelling, Compression index, swelling index and their difference were obtained and the accumulative total and residual deformation rates were proposed to measure the deformation characteristics under cycling loading and unloading. The study results show that there is a significant negative liner relationship between the swelling ratio and the initial water content. The slope of loading and unloading curve is smaller with the increasing cycles, and the area of hysteresis loop decreases gradually. The compression index, swelling index and their difference increase with the growing cycles. The more the number of cycles, the less the total and residual deformation, and the accumulative total and residual deformation increase firstly, then tend to be stable. The smaller the initial water content, the larger the compression index and swelling index, and the more the accumulative total and residual deformation. The mechanical properties of specimens with different initial water content will be enhanced and normalized by the cycling loading and unloading process.
2016, 24(6): 1191-1198.
To study the strength and deformation characteristic of unbound granular materials of high-speed railway, a granular flow model is established with the internal FISH language of three-dimensional particle flow code PFC3D. Meanwhile, the micro parameters of unbound granular materials are calibrated with the conventional triaxial test results. Considering the influence of the curvature coefficient and the uniformity coefficient on the grain size distribution, five kinds of different grain composition of unbound granular materials are simulated under three different confining pressures. The results show that:There is a predominant factor in the curvature coefficient of unbound granular materials. The differences between the effective size, median diameter and constrained size can't be allowed too large, because the strength behaviors of the unbound granular materials with large curvature coefficient and uneven coefficient performances are higher than the others, and the deformation behaviors become more and more large. The non-uniformity coefficient is another important factor on the strength and deformation behavior of unbound granular materials. With the larger non-uniformity coefficient and well-graded granular materials won't changing the force chain distribution under the different stress condition, and the extrusion becomes more obvious and the transfer and distribution of force are more uniform.
To study the strength and deformation characteristic of unbound granular materials of high-speed railway, a granular flow model is established with the internal FISH language of three-dimensional particle flow code PFC3D. Meanwhile, the micro parameters of unbound granular materials are calibrated with the conventional triaxial test results. Considering the influence of the curvature coefficient and the uniformity coefficient on the grain size distribution, five kinds of different grain composition of unbound granular materials are simulated under three different confining pressures. The results show that:There is a predominant factor in the curvature coefficient of unbound granular materials. The differences between the effective size, median diameter and constrained size can't be allowed too large, because the strength behaviors of the unbound granular materials with large curvature coefficient and uneven coefficient performances are higher than the others, and the deformation behaviors become more and more large. The non-uniformity coefficient is another important factor on the strength and deformation behavior of unbound granular materials. With the larger non-uniformity coefficient and well-graded granular materials won't changing the force chain distribution under the different stress condition, and the extrusion becomes more obvious and the transfer and distribution of force are more uniform.
2016, 24(6): 1199-1206.
Using the WF Automatic Triaxial System, conventional triaxial tests under consolidated undrained condition have been carried out on the dredger fill of Tianjin Binhai New Area. And the tests of different stress paths under K0 consolidation condition were carried out. Scanning electron microscopy (SEM) tests also have been carried out. The test results showed that the structure yield when the strain exceed 2%.The structural yielding stress of INP is bigger than KCP, and DEP is the smallest. The yielding stress is increasing with the confining pressure, but maintain a certain value with the increase of cumulative deformation. Analysis of microstructure test showed that the effect of stress paths and damage degree on the microstructure of dredger fill is significant. The soil microstructure is quite different before and after the yield of soil structure.
Using the WF Automatic Triaxial System, conventional triaxial tests under consolidated undrained condition have been carried out on the dredger fill of Tianjin Binhai New Area. And the tests of different stress paths under K0 consolidation condition were carried out. Scanning electron microscopy (SEM) tests also have been carried out. The test results showed that the structure yield when the strain exceed 2%.The structural yielding stress of INP is bigger than KCP, and DEP is the smallest. The yielding stress is increasing with the confining pressure, but maintain a certain value with the increase of cumulative deformation. Analysis of microstructure test showed that the effect of stress paths and damage degree on the microstructure of dredger fill is significant. The soil microstructure is quite different before and after the yield of soil structure.
2016, 24(6): 1207-1213.
The permeability coefficient decreases in the range of foundation pit after post grouting in bored piles, which has a significant impact on the seepage field of deep foundation pit during dewatering. Taking a plaza-style architecture comprising five towers and underground garage for example, the piles used in the project is bored piles with post grouting technique, the excavation depth of foundation pit is 21 meters, and the thickness of strong permeable confined aquifer groups is 10meters. The open fully penetrating wells are adopted in dewatering engineering which are mainly distributed along the periphery of the foundation pit. Based on the summarization of hydrogeological conditions, a three dimensional unsteady-flow numerical model of underground water is built, which is used to simulate the seepage field under heterogeneous environments. Simultaneously, comparison has been made to the seepage field in homogeneous environments. The model prediction results show that, on the premise of the same dewatering depth, the total water inflow in foundation pit is almost unchanged, while the water inflow in the individual well decreases due to a steeper hydraulic gradient in the post grouting area when the permeability coefficient reduces because of post grouting of pile foundation in pit. Therefore, the number of wells should be increased appropriately. Moreover, the supplied strength will be seriously reduced and the total water inflow in foundation pit will be underestimated if the permeability coefficient is considered as the smaller value after post grouting in the whole calculation domain. The research results have supplied a reference for the optimization plans of underground water control projects and it can also be used for reference in the similar projects of groundwater control.
The permeability coefficient decreases in the range of foundation pit after post grouting in bored piles, which has a significant impact on the seepage field of deep foundation pit during dewatering. Taking a plaza-style architecture comprising five towers and underground garage for example, the piles used in the project is bored piles with post grouting technique, the excavation depth of foundation pit is 21 meters, and the thickness of strong permeable confined aquifer groups is 10meters. The open fully penetrating wells are adopted in dewatering engineering which are mainly distributed along the periphery of the foundation pit. Based on the summarization of hydrogeological conditions, a three dimensional unsteady-flow numerical model of underground water is built, which is used to simulate the seepage field under heterogeneous environments. Simultaneously, comparison has been made to the seepage field in homogeneous environments. The model prediction results show that, on the premise of the same dewatering depth, the total water inflow in foundation pit is almost unchanged, while the water inflow in the individual well decreases due to a steeper hydraulic gradient in the post grouting area when the permeability coefficient reduces because of post grouting of pile foundation in pit. Therefore, the number of wells should be increased appropriately. Moreover, the supplied strength will be seriously reduced and the total water inflow in foundation pit will be underestimated if the permeability coefficient is considered as the smaller value after post grouting in the whole calculation domain. The research results have supplied a reference for the optimization plans of underground water control projects and it can also be used for reference in the similar projects of groundwater control.
2016, 24(6): 1214-1221.
To explore the mechanical behavior of loess under excavation of high slopes, the linear finite element method was first utilized to obtain the stress paths of loess on the potential failure zone of an artificial high slope of 150m in Huanneng Country, Huan Town, Qingyang City, Gansu Province. Based on the stress path above, undrained triaxial tests were then performed on soils with natural and saturate water content. By comparison, conventional loading stress path tests (CTC) with the consolidation stress identical with the tests above were also performed. Results show that under the excavation condition, the stress-strain curves of saturate loess are strain-soften and those of soil with natural water content are slightly strain-harden. Under the conventional loading condition, the stress-strain curves of saturate samples have the same characteristic with the tests above. While the natural water content samples display great strain-harden characteristics. In the two types of tests, the effective stress paths, strength envelope and the effective strength parameters are almost the same for the saturate samples. But for the loess with natural water content, the strength envelops are paralleled with the effective internal friction angle almost the same and the higher cohesion for the stress path tests.
To explore the mechanical behavior of loess under excavation of high slopes, the linear finite element method was first utilized to obtain the stress paths of loess on the potential failure zone of an artificial high slope of 150m in Huanneng Country, Huan Town, Qingyang City, Gansu Province. Based on the stress path above, undrained triaxial tests were then performed on soils with natural and saturate water content. By comparison, conventional loading stress path tests (CTC) with the consolidation stress identical with the tests above were also performed. Results show that under the excavation condition, the stress-strain curves of saturate loess are strain-soften and those of soil with natural water content are slightly strain-harden. Under the conventional loading condition, the stress-strain curves of saturate samples have the same characteristic with the tests above. While the natural water content samples display great strain-harden characteristics. In the two types of tests, the effective stress paths, strength envelope and the effective strength parameters are almost the same for the saturate samples. But for the loess with natural water content, the strength envelops are paralleled with the effective internal friction angle almost the same and the higher cohesion for the stress path tests.
2016, 24(6): 1222-1229.
On the basis of the single parameter method recommended by the specification of foundation excavations, the finite difference method of bi-parameter elastic foundation for cantilever retaining piles in excavations was proposed. The cantilever retaining pile was regarded as a whole rather than be divided into two segments-cantilever segment and anchored segment as usual. Meanwhile, the soil reaction which exceeded the limit of passive earth pressure stress was corrected, so the accuracy and efficiency of the calculation was improved. Taking the practical project as an example, the subgrade resistances bi-parameters m and n were obtained through inverting the field data. And the result showed that the calculated value by the method and the measured data were in good agreement. Thus it could be proved that finite difference method has a good advantage under the same condition. At the same time, the effects of shear strength parameters and embedded depth on stress correction were discussed, and some conclusions which were beneficial to the projects were obtained.
On the basis of the single parameter method recommended by the specification of foundation excavations, the finite difference method of bi-parameter elastic foundation for cantilever retaining piles in excavations was proposed. The cantilever retaining pile was regarded as a whole rather than be divided into two segments-cantilever segment and anchored segment as usual. Meanwhile, the soil reaction which exceeded the limit of passive earth pressure stress was corrected, so the accuracy and efficiency of the calculation was improved. Taking the practical project as an example, the subgrade resistances bi-parameters m and n were obtained through inverting the field data. And the result showed that the calculated value by the method and the measured data were in good agreement. Thus it could be proved that finite difference method has a good advantage under the same condition. At the same time, the effects of shear strength parameters and embedded depth on stress correction were discussed, and some conclusions which were beneficial to the projects were obtained.
2016, 24(6): 1230-1239.
The foundation pit project of Tianhan Grand Theatre's underground commercial construction is located above Line 1 of Changsha Metro and the minimum distance between the pit's bottom and the tunnel's roof is about 6.2m. The pit's bottom is situated in the round gravel layer in which the groundwater is rather abundant. Considering the impacts of dewatering on the surrounding environment, the enclosed water-resisting curtain combined with anti-floating anchor wires was applied to this project. The influence factors of the bottom soil resilience include soil unloading induced by the excavation and dewatering, the groundwater seepage and the application of anti-floating anchor cable. Thus, how to calculate and analyze the impact on underlying metro tunnels becomes the emphasis and difficulty in this project. Two common methods for estimating the spring back deformation were used to calculate the bottom's resilience value and tunnel uplift displacement. Then, the finite element software MIDAS GTS was employed to established a three-dimensional numerical model to simulate three types of engineering conditions. Case 1 took no account of the effect of groundwater seepage and didn't adopt anti-floating anchor wires. Case 2 considered the coupling of seepage and stress but didn't adopt anti-floating anchor wires. Case 3 considered not only the coupling of seepage and stress but the effect of anti-floating anchor wires. The comparative result shows that when the curtain has a lower permeability, the simulation result tends to be uniform regardless the influence of the coupling of seepage and stress. Besides, the calculating result of actual criterion is close to the simulation result, after amending the value and reasonable influence depth of unloading stress. The results can provide a beneficial reference for the design and construction of the similar projects to some extent.
The foundation pit project of Tianhan Grand Theatre's underground commercial construction is located above Line 1 of Changsha Metro and the minimum distance between the pit's bottom and the tunnel's roof is about 6.2m. The pit's bottom is situated in the round gravel layer in which the groundwater is rather abundant. Considering the impacts of dewatering on the surrounding environment, the enclosed water-resisting curtain combined with anti-floating anchor wires was applied to this project. The influence factors of the bottom soil resilience include soil unloading induced by the excavation and dewatering, the groundwater seepage and the application of anti-floating anchor cable. Thus, how to calculate and analyze the impact on underlying metro tunnels becomes the emphasis and difficulty in this project. Two common methods for estimating the spring back deformation were used to calculate the bottom's resilience value and tunnel uplift displacement. Then, the finite element software MIDAS GTS was employed to established a three-dimensional numerical model to simulate three types of engineering conditions. Case 1 took no account of the effect of groundwater seepage and didn't adopt anti-floating anchor wires. Case 2 considered the coupling of seepage and stress but didn't adopt anti-floating anchor wires. Case 3 considered not only the coupling of seepage and stress but the effect of anti-floating anchor wires. The comparative result shows that when the curtain has a lower permeability, the simulation result tends to be uniform regardless the influence of the coupling of seepage and stress. Besides, the calculating result of actual criterion is close to the simulation result, after amending the value and reasonable influence depth of unloading stress. The results can provide a beneficial reference for the design and construction of the similar projects to some extent.
2016, 24(6): 1240-1246.
Natural loess, possessing strong structural characteristic, will suffer inevitable disturbance in the process of sampling, transportation and sample preparation. Based on the principle of Carlo Monte, non-cohesive materials-quartz powder and sand and cohesive materials-bentonite, gypsum and industrial salt were chosen to prepare artificial collapsible loess with the air fall method. Vertical consolidation pressure was applied to the soil with 5kPa, 10kPa and 15kPa separately, and after 9months soil samples were taken to conduct geotechnical test and electron microscope scanning test. The geotechnical test results show that:with increase of consolidation pressure, shear strength parameters are improved, and the peak coefficient of collapsibility is reduced. Analysis on SEM microstructure shows that consolidation pressure has great effect on overhead pore, while inter-granular pore is influenced relatively slightly by the consolidation pressure; with the increase of consolidation pressure, particle anisotropy, area ratio and equivalent diameter increase, while particle oblate degree and fill ratio decrease. There is a good relationship between soil mechanical parameters such as internal friction angle, cohesion strength and coefficient of collapsibility and microstructure parameters such as area ratio, fill ratio, equivalent, anisotropy, and oblate degree. From the microscopic point of view, it is proved that the artificial collapsible loess is a relatively ideal similar material for the collapsible loess model test.
Natural loess, possessing strong structural characteristic, will suffer inevitable disturbance in the process of sampling, transportation and sample preparation. Based on the principle of Carlo Monte, non-cohesive materials-quartz powder and sand and cohesive materials-bentonite, gypsum and industrial salt were chosen to prepare artificial collapsible loess with the air fall method. Vertical consolidation pressure was applied to the soil with 5kPa, 10kPa and 15kPa separately, and after 9months soil samples were taken to conduct geotechnical test and electron microscope scanning test. The geotechnical test results show that:with increase of consolidation pressure, shear strength parameters are improved, and the peak coefficient of collapsibility is reduced. Analysis on SEM microstructure shows that consolidation pressure has great effect on overhead pore, while inter-granular pore is influenced relatively slightly by the consolidation pressure; with the increase of consolidation pressure, particle anisotropy, area ratio and equivalent diameter increase, while particle oblate degree and fill ratio decrease. There is a good relationship between soil mechanical parameters such as internal friction angle, cohesion strength and coefficient of collapsibility and microstructure parameters such as area ratio, fill ratio, equivalent, anisotropy, and oblate degree. From the microscopic point of view, it is proved that the artificial collapsible loess is a relatively ideal similar material for the collapsible loess model test.
2016, 24(6): 1247-1254.
Jointed rockmass is common in the southwestern mountain area, which is also a earthquake-prone area. Strong earthquake and jointed rock mass structure are the two main factors of geological disasters in the near field of Wenchuan earthquake. The coupling of the factors makes complex causes of landslides along Minjiang triggered by earthquake and difficult research process of landslides. Furthermore, due to the complexity of jointed rock mass and early lack of understanding of seismic P-wave, there is none research progresses made in deformation-failure mechanisms under strong P-wave. Research progresses in deformation-failure mechanisms of jointed rock mass induced by P-wave were summarized systematically in this paper. Then the correct thinking and effect way to solving the core problems is discussed, which is designed to play an important role in the research on the macro dynamic response and the micro mechanism of rock mass under P-wave. Also, the research on seismic response of jointed rock mass and the failure pattern of jointed rock slopes induced by near field P-wave would be deepened, indicating the direction for further study on the seismic geological hazards.
Jointed rockmass is common in the southwestern mountain area, which is also a earthquake-prone area. Strong earthquake and jointed rock mass structure are the two main factors of geological disasters in the near field of Wenchuan earthquake. The coupling of the factors makes complex causes of landslides along Minjiang triggered by earthquake and difficult research process of landslides. Furthermore, due to the complexity of jointed rock mass and early lack of understanding of seismic P-wave, there is none research progresses made in deformation-failure mechanisms under strong P-wave. Research progresses in deformation-failure mechanisms of jointed rock mass induced by P-wave were summarized systematically in this paper. Then the correct thinking and effect way to solving the core problems is discussed, which is designed to play an important role in the research on the macro dynamic response and the micro mechanism of rock mass under P-wave. Also, the research on seismic response of jointed rock mass and the failure pattern of jointed rock slopes induced by near field P-wave would be deepened, indicating the direction for further study on the seismic geological hazards.
2016, 24(6): 1255-1261.
Structures at the ground surface and underground structures may be destroyed when overlying soil is significantly deformed by bedrock fault movement during an earthquake. Currently no analytical solution is available for estimation of soil deformation at the surface and subsurface that induced by faulting. Moreover, the influences of key factors on the deformation mechanism of the overlying soil are not yet fully understood. In this paper, complimentary error function is adopted and used to represent soil vertical displacement profile at different depths. A soil deformation mechanism, which consist a stationary zone, a shearing zone and a rigid body zone, is adopted. By applying reasonable boundary conditions for the deformation mechanism, a theoretical model is then developed to predict the undrained deformation of the overlying soil induced by reverse faulting of bedrock fault. The theoretical model is further verified by independent centrifuge and numerical data. Comparison between calculated data from the proposed model, measured data from the centrifuge tests and computed results from numerical simulation show that both surface and subsurface deformation can be fairly well represented by the complimentary error function. Parametric studies show that the influences of the magnitude of the bedrock fault movement on the locations of heaving deformation zone at the ground surface are not significant. Increasing in shape parameter results in a narrower zone of heaving deformation. In addition, bedrock fault with larger dip angle drives the heaving deformation zone move towards the side of bedrock hanging wall.
Structures at the ground surface and underground structures may be destroyed when overlying soil is significantly deformed by bedrock fault movement during an earthquake. Currently no analytical solution is available for estimation of soil deformation at the surface and subsurface that induced by faulting. Moreover, the influences of key factors on the deformation mechanism of the overlying soil are not yet fully understood. In this paper, complimentary error function is adopted and used to represent soil vertical displacement profile at different depths. A soil deformation mechanism, which consist a stationary zone, a shearing zone and a rigid body zone, is adopted. By applying reasonable boundary conditions for the deformation mechanism, a theoretical model is then developed to predict the undrained deformation of the overlying soil induced by reverse faulting of bedrock fault. The theoretical model is further verified by independent centrifuge and numerical data. Comparison between calculated data from the proposed model, measured data from the centrifuge tests and computed results from numerical simulation show that both surface and subsurface deformation can be fairly well represented by the complimentary error function. Parametric studies show that the influences of the magnitude of the bedrock fault movement on the locations of heaving deformation zone at the ground surface are not significant. Increasing in shape parameter results in a narrower zone of heaving deformation. In addition, bedrock fault with larger dip angle drives the heaving deformation zone move towards the side of bedrock hanging wall.
2016, 24(6): 1262-1268.
The inclination angle of the failure plane of rock mass is the angle between the fracture surface and the maximum principal stress, it is an important parameter in the design of the rock engineering projects, and serves as an important basis for the security warning in engineering projects. The inclination angle of the failure surface of rock mass is influenced by the stress, fabric, water and other factors, giving rise to great uncertainty in the determination of the inclination angle of the failure surface, especially for weak rock mass. The inclination angle of failure surface is 45°+φ/2 as given by the Mohr-Coulomb failure criterion and it is a constant. In fact, the inclination angle of failure surface is found to fall in a range instead of being constant, so it is necessary to carry out a study on the inclination angle of failure surface. By focusing on the failure of the silty mudstones under the hydraulic-mechanical coupling condition, which is a typical soft rock in the red beds in South China, this paper has derived a mathematical expression of the inclination angle of failure surface of rock mass, with the use of the probability distribution function of micro cracks in the rock mass. Three axial compression tests have been done under the hydraulic-mechanical coupling condition in the TAW-100(hydro-mechanical coupling and mciro-mechanical triaxial test equipment with servo-control loading system).According to the derived mathematical expression, the range of the inclination angle of failure surface is determined to be 50.3°~80.2° with the confining pressure being 0 and 1MPa. Furthermore current results are compared with the prediction of the Mohr-Coulomb theory, as well as the experimental results. It is found that the results obtained by the method of probability is close to the experimental results, suggesting that this method is reasonable and reliable.
The inclination angle of the failure plane of rock mass is the angle between the fracture surface and the maximum principal stress, it is an important parameter in the design of the rock engineering projects, and serves as an important basis for the security warning in engineering projects. The inclination angle of the failure surface of rock mass is influenced by the stress, fabric, water and other factors, giving rise to great uncertainty in the determination of the inclination angle of the failure surface, especially for weak rock mass. The inclination angle of failure surface is 45°+φ/2 as given by the Mohr-Coulomb failure criterion and it is a constant. In fact, the inclination angle of failure surface is found to fall in a range instead of being constant, so it is necessary to carry out a study on the inclination angle of failure surface. By focusing on the failure of the silty mudstones under the hydraulic-mechanical coupling condition, which is a typical soft rock in the red beds in South China, this paper has derived a mathematical expression of the inclination angle of failure surface of rock mass, with the use of the probability distribution function of micro cracks in the rock mass. Three axial compression tests have been done under the hydraulic-mechanical coupling condition in the TAW-100(hydro-mechanical coupling and mciro-mechanical triaxial test equipment with servo-control loading system).According to the derived mathematical expression, the range of the inclination angle of failure surface is determined to be 50.3°~80.2° with the confining pressure being 0 and 1MPa. Furthermore current results are compared with the prediction of the Mohr-Coulomb theory, as well as the experimental results. It is found that the results obtained by the method of probability is close to the experimental results, suggesting that this method is reasonable and reliable.
2016, 24(6): 1269-1277.
In the past 30 years, the population in Beijing has got a sharp increase leading to the rapid expansion of the city, the extraction of groundwater resources increases year by year, aggravates the land subsidence, forms subsidence center, the activity of the ground fissures has significantly accelerated which becomes the important geological problem for the city development planning. At present, the knowledge of Beijing ground fissures are still limited to the investigation and evaluation of the individual space and a single crack evaluation, we still lack the understanding of the regional law. By collecting and summarizing related literature and survey data, conjointly fracture site surveying, we find that ground fissures in Beijing have obvious regional characteristics, the development of most ground fissures are closely associated with deep fault belt. Therefore, according to the relationship between the fault zone and ground fissures, the author divides the ground fissure zones into six regions, summarizes the distributions、occurrences、extension and the phenomena of destruction about the ground fissures, analyzes briefly about the reason of the ground fissures. Finally, several suggestions for future researches of ground fissures are put forward.
In the past 30 years, the population in Beijing has got a sharp increase leading to the rapid expansion of the city, the extraction of groundwater resources increases year by year, aggravates the land subsidence, forms subsidence center, the activity of the ground fissures has significantly accelerated which becomes the important geological problem for the city development planning. At present, the knowledge of Beijing ground fissures are still limited to the investigation and evaluation of the individual space and a single crack evaluation, we still lack the understanding of the regional law. By collecting and summarizing related literature and survey data, conjointly fracture site surveying, we find that ground fissures in Beijing have obvious regional characteristics, the development of most ground fissures are closely associated with deep fault belt. Therefore, according to the relationship between the fault zone and ground fissures, the author divides the ground fissure zones into six regions, summarizes the distributions、occurrences、extension and the phenomena of destruction about the ground fissures, analyzes briefly about the reason of the ground fissures. Finally, several suggestions for future researches of ground fissures are put forward.
2016, 24(6): 1278-1285.
Beiluntai fault is a Holocene active fault. The fault total length is 70km. It is a line of south Tianshan and piedmont alluvial fan. Beiluntai fault activity is obvious and generating a series of apparent geomorphic traces on the surface. The fault had dislocated proluvial fan and terrace form fault escarpment. The fault strike is near EW, extending length is about 2.5km in Beiluntai fault Akeaiken part. The maximum height of the fault escarpment is 18.5m and the minimum height is 5.1m. We find different level geomorphic surfaces had different vertical displacement and the formation age of geomorphic surfaces older, the cumulative displacement greater. The dispalcemengt of fault is a process that accumulates over time. Based on the field geological investigation and surveying the deformation microtopography in order to accurate analysis the characteristics of paleoearthquake. We are surveying the deformation of alluvial fan near the Beiluntai fault. Use excavator to excavate two large paleoearthquake exploratory trench at Akeaiken part and Dihe agriculture part in Beiluntai fault. We had maked photo mosaics of the trench profile and inverted the paleoearthquake event to analysis the times of paleoearthquake. The conclusion shows the paleoearthquake event is frequently occurred in Beiluntai fault. We use the theory of erosion unconformity on the hanging wall, growth strata on the footwall and and sudden change of maker strata position between the hanging wall and footwall to inverting the times of paleoearthquake event. And the result shows that not less than three times paleoearthquake evet had been happened in the Beiluntai fault Akeaiken part, the cumulation amount of vertical displacement is 4.5m, the co-seismic displacement is 1.2 to 1.5m. The fault is dislocate the second terrace in Beiluntai fault Dihe agriculture part and formed the 1.6m faultscarp. We were analysis the photo of trench profile recorded two times paleoearthquake event and the latest paleoearthquake event caused 1.5m vertical displacement. It makes the surface layer bending deflection near the fault. Beiluntai fault have never been occurred large-scale earthquake since the earliest recorded history, this indicates that energy accumulation of the fault has reached a high level, large-scale earthquake may occurred in the future.
Beiluntai fault is a Holocene active fault. The fault total length is 70km. It is a line of south Tianshan and piedmont alluvial fan. Beiluntai fault activity is obvious and generating a series of apparent geomorphic traces on the surface. The fault had dislocated proluvial fan and terrace form fault escarpment. The fault strike is near EW, extending length is about 2.5km in Beiluntai fault Akeaiken part. The maximum height of the fault escarpment is 18.5m and the minimum height is 5.1m. We find different level geomorphic surfaces had different vertical displacement and the formation age of geomorphic surfaces older, the cumulative displacement greater. The dispalcemengt of fault is a process that accumulates over time. Based on the field geological investigation and surveying the deformation microtopography in order to accurate analysis the characteristics of paleoearthquake. We are surveying the deformation of alluvial fan near the Beiluntai fault. Use excavator to excavate two large paleoearthquake exploratory trench at Akeaiken part and Dihe agriculture part in Beiluntai fault. We had maked photo mosaics of the trench profile and inverted the paleoearthquake event to analysis the times of paleoearthquake. The conclusion shows the paleoearthquake event is frequently occurred in Beiluntai fault. We use the theory of erosion unconformity on the hanging wall, growth strata on the footwall and and sudden change of maker strata position between the hanging wall and footwall to inverting the times of paleoearthquake event. And the result shows that not less than three times paleoearthquake evet had been happened in the Beiluntai fault Akeaiken part, the cumulation amount of vertical displacement is 4.5m, the co-seismic displacement is 1.2 to 1.5m. The fault is dislocate the second terrace in Beiluntai fault Dihe agriculture part and formed the 1.6m faultscarp. We were analysis the photo of trench profile recorded two times paleoearthquake event and the latest paleoearthquake event caused 1.5m vertical displacement. It makes the surface layer bending deflection near the fault. Beiluntai fault have never been occurred large-scale earthquake since the earliest recorded history, this indicates that energy accumulation of the fault has reached a high level, large-scale earthquake may occurred in the future.
2016, 24(6): 1286-1293.
Weathering is one of the most important diseases in the surrounding rocks of Mogao Grottoes, which seriously affects the purpose for long-term preservation. To study the weathering characteristics of Yumen glutenite in Mogao Grottoes, a test point on the south side of Mogao Grottoes is selected. The method of step by step dissection is adopted and a series of experiments are conducted, such as X-Ray diffraction test, soluble salt test, field acoustic wave test and rebound test at different distances from the surface, which are 0、3、5、8 and 10cm. The results illustrate that the main salts involve Na2SO4、NaCl、CaSO4, and the main minerals are quartz, feldspar, calcite, dolomite while clay mineral is chlorite; the mechanical strength reduced due to the influence of weathering, which is confirmed by the field acoustic wave test and rebound test. Both of the results rise with the increase of depth. By analyzing Meteorological data and the results, the main effects on weathering are determined and the mechanism of rock weathering is discussed. Weathering includes that (1) temperature stress causes damage on the rock mass structure and fracture. (2) the main mineral calcite in the cement is easy to convert into soluble Ca (HCO3)2, which could affect the cementation of rock mass structure. (3) salt weathering is another important rock weathering. Salts migrate and enrich with moisture migration and hydrate with water, which causes damage to the cohesion between different particles and result in the breakdown of rock mass.
Weathering is one of the most important diseases in the surrounding rocks of Mogao Grottoes, which seriously affects the purpose for long-term preservation. To study the weathering characteristics of Yumen glutenite in Mogao Grottoes, a test point on the south side of Mogao Grottoes is selected. The method of step by step dissection is adopted and a series of experiments are conducted, such as X-Ray diffraction test, soluble salt test, field acoustic wave test and rebound test at different distances from the surface, which are 0、3、5、8 and 10cm. The results illustrate that the main salts involve Na2SO4、NaCl、CaSO4, and the main minerals are quartz, feldspar, calcite, dolomite while clay mineral is chlorite; the mechanical strength reduced due to the influence of weathering, which is confirmed by the field acoustic wave test and rebound test. Both of the results rise with the increase of depth. By analyzing Meteorological data and the results, the main effects on weathering are determined and the mechanism of rock weathering is discussed. Weathering includes that (1) temperature stress causes damage on the rock mass structure and fracture. (2) the main mineral calcite in the cement is easy to convert into soluble Ca (HCO3)2, which could affect the cementation of rock mass structure. (3) salt weathering is another important rock weathering. Salts migrate and enrich with moisture migration and hydrate with water, which causes damage to the cohesion between different particles and result in the breakdown of rock mass.
2016, 24(6): 1294-1301.
Hardening soil small model (HSS) can consider not only soil shear and compression hardening, but also account for shear modulus attenuating in tiny strain range. Therefore, it has a good application for numerical analysis of excavations. To study the sensitivity of HSS model's stiffness parameters E50ref, G0ref and γ0.7 on the excavation's numerical analysis results in Xiamen area, based on sensitivity analysis theory and orthogonal experiment theory, representative residual sandy sticky clay, silty clay and mucky soil are chosen to serve as research objects, and take surface subsidence value of excavation and enclosure wall's maximum moment value as a control index. Single control on soil layer's parameters sensitivity study is applied respectively. The result shows that to calculate surface subsidence and enclosure wall's moment accurately in excavation numerical analysis. Firstly, control the value of soil's G0ref; secondly, E50ref impacts less than γ0.7; with the deepening of the excavation depth, the impact of G0ref for surface subsidence becomes less, while E50ref and γ0.7 impacts more; E50ref impacts less on enclosure wall's moment with the deepening of the excavation, while G0ref and γ0.7 tend to impact more, especially for G0ref. The results show that small strain behavior of soil is of great importance to excavation construction and deserves more attention in relevant design and construction. The analysis results could provide references for the acquirement of more reasonable stratum deformation and structure inner force in deep excavation finite element analysis.
Hardening soil small model (HSS) can consider not only soil shear and compression hardening, but also account for shear modulus attenuating in tiny strain range. Therefore, it has a good application for numerical analysis of excavations. To study the sensitivity of HSS model's stiffness parameters E50ref, G0ref and γ0.7 on the excavation's numerical analysis results in Xiamen area, based on sensitivity analysis theory and orthogonal experiment theory, representative residual sandy sticky clay, silty clay and mucky soil are chosen to serve as research objects, and take surface subsidence value of excavation and enclosure wall's maximum moment value as a control index. Single control on soil layer's parameters sensitivity study is applied respectively. The result shows that to calculate surface subsidence and enclosure wall's moment accurately in excavation numerical analysis. Firstly, control the value of soil's G0ref; secondly, E50ref impacts less than γ0.7; with the deepening of the excavation depth, the impact of G0ref for surface subsidence becomes less, while E50ref and γ0.7 impacts more; E50ref impacts less on enclosure wall's moment with the deepening of the excavation, while G0ref and γ0.7 tend to impact more, especially for G0ref. The results show that small strain behavior of soil is of great importance to excavation construction and deserves more attention in relevant design and construction. The analysis results could provide references for the acquirement of more reasonable stratum deformation and structure inner force in deep excavation finite element analysis.
2016, 24(6): 1302-1308.
As the rapid development of highway, railway and urban rail transit project, soft ground settlement caused by the long-term cyclic dynamic load has been paid more and more attention. The dynamic triaxial tests to measure the dynamic characteristic of muddy soil were conducted on samples from Fuzhou. A series of changing regulations of dynamic stress, dynamic strength, dynamic shear modulus and damping ratios were analyzed. The effects of consolidation pressure and dynamic stress amplitude on the dynamic strength of muddy soil were investigated respectively. A relationship among dynamic strength, consolidation pressure and vibration numbers is developed, by which the dynamic strength of soil in different depth can be estimated. The experimental results show that, the dynamic strength falls as the cycle of the dynamic loading increases, and it increases as consolidation pressure increases. It should be noticed that the values of dynamic strength is low. Finally, the values of dynamic shear modulus and damping ratios are given.
As the rapid development of highway, railway and urban rail transit project, soft ground settlement caused by the long-term cyclic dynamic load has been paid more and more attention. The dynamic triaxial tests to measure the dynamic characteristic of muddy soil were conducted on samples from Fuzhou. A series of changing regulations of dynamic stress, dynamic strength, dynamic shear modulus and damping ratios were analyzed. The effects of consolidation pressure and dynamic stress amplitude on the dynamic strength of muddy soil were investigated respectively. A relationship among dynamic strength, consolidation pressure and vibration numbers is developed, by which the dynamic strength of soil in different depth can be estimated. The experimental results show that, the dynamic strength falls as the cycle of the dynamic loading increases, and it increases as consolidation pressure increases. It should be noticed that the values of dynamic strength is low. Finally, the values of dynamic shear modulus and damping ratios are given.
2016, 24(6): 1309-1317.
Rapid long run-out landslide usually moves in high speed and travels for a long distance, therefore it trends to cause catastrophic effects on its overlong travelling path. In the study area of the Jingyang south loess tableland in this paper, this kind of landslide occurred frequently in last few decades and resulted in serious disasters. Since the destructive properties of this kind of landslide, to study its moving process and mechanism is necessary and of great significance for both study and construction purpose. Spatial prediction is a sort of effective methods to prevent landslide hazards. To make spatial prediction for rapid long run-out landslides accurately, making back analysis of the previous events is indispensable. For above reasons, this article choose a typical rapid long run-out loess landslide named "Dabaozi" in the south bank of Jinghe river, Shanxi, as study target to simulate its moving process and analyze its moving mechanism. Detailed field surveying was conducted, which reveals the landslide's matter source is mainly made up of loess stratum from L1 to L9 in the slope and sand gravel in terrace in front of the slope. Sand gravel layer was apparently entrained by the original loess landslide mass which is shown by the over-thrust of sand gravel in the front of the landslide, so it was regarded as potential landslide mass in order to take entrainment into account in building the Digital Elevation Model (DEM) of the landslide and simulation. In addition, 2groups of undisturbed loess and sand gravel samples were taken from the landslide area to conduct consolidated undrained (CU) triaxial tests and ring shear tests and some common indoor tests to get the physical and mechanical parameters needed in the simulation. On this basis, we utilized a software LS-RAPID which is developed from Sassa's geotechnical model to study the kinematic behaviors of this landslide. As a results, the moving speed, travelling path, thick of deposition mass and some other important kinematic indexes of the landslide were obtained. The simulation results show that the max average velocity of the landslide is about 9.56m·s-1 when it has moved 5.7s, and the whole moving process lasts about 24.5 seconds, and the topography obtained by simulation shows good accordance with fact in respect of the travelling distance and depositional forms. The moving process can be divided into two stage according to the transformation of motion state based on average velocity obtained from simulation, one is the starting accelerated stage (0s-5s) which has an acceleration of 1.68m·s-2, the other one is the moving decelerated stage which has an acceleration of -0.51m·s-2, and the topography of simulation shows that the transformation occurs when the whole landslide mass just reaches the terrace in front of the slope. By summarizing, we find that the initial steep topography condition in the study area and Q2 loess's high constructive strength play pivotal roles in making the landslide moves fast, and the landslide surface liquefaction occurred in the horizon terrace which mainly makes up of saturated sand-gravel contributes to a long travel distance, and this article can provide beneficial reference to the later study of loess rapid long run-out landslide.
Rapid long run-out landslide usually moves in high speed and travels for a long distance, therefore it trends to cause catastrophic effects on its overlong travelling path. In the study area of the Jingyang south loess tableland in this paper, this kind of landslide occurred frequently in last few decades and resulted in serious disasters. Since the destructive properties of this kind of landslide, to study its moving process and mechanism is necessary and of great significance for both study and construction purpose. Spatial prediction is a sort of effective methods to prevent landslide hazards. To make spatial prediction for rapid long run-out landslides accurately, making back analysis of the previous events is indispensable. For above reasons, this article choose a typical rapid long run-out loess landslide named "Dabaozi" in the south bank of Jinghe river, Shanxi, as study target to simulate its moving process and analyze its moving mechanism. Detailed field surveying was conducted, which reveals the landslide's matter source is mainly made up of loess stratum from L1 to L9 in the slope and sand gravel in terrace in front of the slope. Sand gravel layer was apparently entrained by the original loess landslide mass which is shown by the over-thrust of sand gravel in the front of the landslide, so it was regarded as potential landslide mass in order to take entrainment into account in building the Digital Elevation Model (DEM) of the landslide and simulation. In addition, 2groups of undisturbed loess and sand gravel samples were taken from the landslide area to conduct consolidated undrained (CU) triaxial tests and ring shear tests and some common indoor tests to get the physical and mechanical parameters needed in the simulation. On this basis, we utilized a software LS-RAPID which is developed from Sassa's geotechnical model to study the kinematic behaviors of this landslide. As a results, the moving speed, travelling path, thick of deposition mass and some other important kinematic indexes of the landslide were obtained. The simulation results show that the max average velocity of the landslide is about 9.56m·s-1 when it has moved 5.7s, and the whole moving process lasts about 24.5 seconds, and the topography obtained by simulation shows good accordance with fact in respect of the travelling distance and depositional forms. The moving process can be divided into two stage according to the transformation of motion state based on average velocity obtained from simulation, one is the starting accelerated stage (0s-5s) which has an acceleration of 1.68m·s-2, the other one is the moving decelerated stage which has an acceleration of -0.51m·s-2, and the topography of simulation shows that the transformation occurs when the whole landslide mass just reaches the terrace in front of the slope. By summarizing, we find that the initial steep topography condition in the study area and Q2 loess's high constructive strength play pivotal roles in making the landslide moves fast, and the landslide surface liquefaction occurred in the horizon terrace which mainly makes up of saturated sand-gravel contributes to a long travel distance, and this article can provide beneficial reference to the later study of loess rapid long run-out landslide.
2016, 24(6): 1318-1326.
Jinping Ⅰ hydropower station is a double-curvature arch dam, the designed height of which is 305m. The foundation rock masses are mainly assigned to class Ⅱ, Ⅲ1. The rock masses are damaged in different degrees during the blasting excavation. For assessing the degree of rock mass damage quantitatively, the detection results of blasting excavation are used, in which rock mass relaxation depth and single-hole sonic attenuation of the relaxation rock after excavation are applied as an indicator to classify the degree of rock mass damage. A rapid detection method and classification standard of rock mass damage are proposed. Evaluation of rock mass damage after dam excavation is completed and treatment suggestion is proposed for the rock mass under different degree damage.
Jinping Ⅰ hydropower station is a double-curvature arch dam, the designed height of which is 305m. The foundation rock masses are mainly assigned to class Ⅱ, Ⅲ1. The rock masses are damaged in different degrees during the blasting excavation. For assessing the degree of rock mass damage quantitatively, the detection results of blasting excavation are used, in which rock mass relaxation depth and single-hole sonic attenuation of the relaxation rock after excavation are applied as an indicator to classify the degree of rock mass damage. A rapid detection method and classification standard of rock mass damage are proposed. Evaluation of rock mass damage after dam excavation is completed and treatment suggestion is proposed for the rock mass under different degree damage.
2016, 24(6): 1327-1332.
For studying the anisotropy of intact loess in Xining, through triaxial test with consolidated undrained at different angles in every depth, analyzing the relationship between deviatoric stress and angles in loess, meanwhile, exploring the law about the degree in anisotropy with the strain increasing. The results show that the deviatoric stress-strain relationship of loess which is near the optimum water content is strain-hardening, the most failure modes is bulging in middle part; the deviatoric stress-strain relationship of intact loess in different depths present obvious anisotropy, at the same strain, the deviatoric stress have the maximum value in the vertical direction and have the minimum value in the angle of 45°or 90°to the vertical direction. The degree in anisotropy of intact loess with the strain is connected with the stress history. When the preconsolidation pressure is small, the degree in anisotropy of intact loess decreases with the increase of the strain, and conversely, the degree in anisotropy increases with the increase of strain.
For studying the anisotropy of intact loess in Xining, through triaxial test with consolidated undrained at different angles in every depth, analyzing the relationship between deviatoric stress and angles in loess, meanwhile, exploring the law about the degree in anisotropy with the strain increasing. The results show that the deviatoric stress-strain relationship of loess which is near the optimum water content is strain-hardening, the most failure modes is bulging in middle part; the deviatoric stress-strain relationship of intact loess in different depths present obvious anisotropy, at the same strain, the deviatoric stress have the maximum value in the vertical direction and have the minimum value in the angle of 45°or 90°to the vertical direction. The degree in anisotropy of intact loess with the strain is connected with the stress history. When the preconsolidation pressure is small, the degree in anisotropy of intact loess decreases with the increase of the strain, and conversely, the degree in anisotropy increases with the increase of strain.
2016, 24(6): 1333-1343.
Geophysical non-uniqueness are everywhere. Faced with this situation we usually tend to combine geological data to calibrate the interpretation results. However, the information on geology and deep drilling are deficiency in remote areas, and field existing wells are often difficult to obtain information on lithology catalog, which will cause that the inversion results are difficult to interpret. Whether hydraulic characteristics of the water level and water quality information contained in the geological body can be used to assist the geophysical inversion? Based on this idea, a method for interpreting ERT data based on groundwater numerical modeling is provided in this article. In this article, Magneto-telluric method is a way to accomplish numerical simulation of geophysical forward and inversion. Firstly, by studying the known geological model and multiple geological models interpreted from ERT data, a set of groundwater numerical models can be set up. Then numerical simulation of groundwater flow and solute transport were conducted. Lastly, the optimal geological model can be obtained by comparing the result of numerical simulation of groundwater. Sensitivity analysis were also conducted to verify the method.
Geophysical non-uniqueness are everywhere. Faced with this situation we usually tend to combine geological data to calibrate the interpretation results. However, the information on geology and deep drilling are deficiency in remote areas, and field existing wells are often difficult to obtain information on lithology catalog, which will cause that the inversion results are difficult to interpret. Whether hydraulic characteristics of the water level and water quality information contained in the geological body can be used to assist the geophysical inversion? Based on this idea, a method for interpreting ERT data based on groundwater numerical modeling is provided in this article. In this article, Magneto-telluric method is a way to accomplish numerical simulation of geophysical forward and inversion. Firstly, by studying the known geological model and multiple geological models interpreted from ERT data, a set of groundwater numerical models can be set up. Then numerical simulation of groundwater flow and solute transport were conducted. Lastly, the optimal geological model can be obtained by comparing the result of numerical simulation of groundwater. Sensitivity analysis were also conducted to verify the method.
2016, 24(6): 1344-1353.
The NSFC proposals and grants of engineering geology in 2016 were analyzed. The number of proposals has been increasing. The number of Young Scientists Fund proposals increased significantly in this year. The peer-review referees well handled the scale of peer-review on the proposals, especially the NSFC Young Scientists Fund. The age distribution of the General Program applicant tends to be double-peak structure. The age distribution of the Young Scientists Fund applicant tends to be reasonable. There are reasonable varieties of funded ratio among different age group. The young scientists have not actively participated in the grants of National Science Fund for Distinguished Young yet. Although the applicants of Key Program are older in age than average but tend to become younger than last year.
The NSFC proposals and grants of engineering geology in 2016 were analyzed. The number of proposals has been increasing. The number of Young Scientists Fund proposals increased significantly in this year. The peer-review referees well handled the scale of peer-review on the proposals, especially the NSFC Young Scientists Fund. The age distribution of the General Program applicant tends to be double-peak structure. The age distribution of the Young Scientists Fund applicant tends to be reasonable. There are reasonable varieties of funded ratio among different age group. The young scientists have not actively participated in the grants of National Science Fund for Distinguished Young yet. Although the applicants of Key Program are older in age than average but tend to become younger than last year.
2016, 24(6): 1103-1109.
The data mining techniques were used to predict shear strength of slip zone soil. In order to define the qualitative and quantitative factors affecting the shear strength, the CHAID (Chi-squared Automatic Interaction Detector) method and correlation analysis were used to pretreat data. According to the result obtained by CHAID method the landslides are classified by sedimentary environment of slip bed. Based on the classification, the influencing factors were selected in the light of Pearson correlation coefficient. The correlation analysis result shows that the internal friction angle of slip zone is affected by different factors as the slip bed of different sedimentary environment. The cohesive force has no obvious relationship with the factors. Stepwise regression was carried out to establish regression model for internal friction angle. The regression equations are passed statistical test and of good fitting degree and prediction accuracy. The forecast equations for the actual project data have good performances.
The data mining techniques were used to predict shear strength of slip zone soil. In order to define the qualitative and quantitative factors affecting the shear strength, the CHAID (Chi-squared Automatic Interaction Detector) method and correlation analysis were used to pretreat data. According to the result obtained by CHAID method the landslides are classified by sedimentary environment of slip bed. Based on the classification, the influencing factors were selected in the light of Pearson correlation coefficient. The correlation analysis result shows that the internal friction angle of slip zone is affected by different factors as the slip bed of different sedimentary environment. The cohesive force has no obvious relationship with the factors. Stepwise regression was carried out to establish regression model for internal friction angle. The regression equations are passed statistical test and of good fitting degree and prediction accuracy. The forecast equations for the actual project data have good performances.
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