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Editor Work2014 Vol. 22, No. 1
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2014, 22(1): 1-7.
Abstract
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On 13th August 2010, large numerous debris flows occurred due to high intensity rainfall in Longchi area of Dujiangyan city. These disastrous debris flows brought heavy damage to reconstruction of the earthquake damaged region. It is very important to study the formative mechanism and early mitigation warning of the debris flows in this area. Based on the research achievements of predecessors such as occurrence and rainfall condition, this paper reveals that the water content of sediments and the depth of surface runoff are important factors to the initiation of debris flows. According to the characteristics of antecedent rainfall and effective rainfall intensity when debris flows occur, this paper establishes an initiation model of debris flow in this region. It is related to three grades of soil particle initiation processes. They are individual, partial, and whole grades. The different rainfall conditions are divided into blue, yellow and red three risk levels for this area of debris flow monitoring and early warning.
On 13th August 2010, large numerous debris flows occurred due to high intensity rainfall in Longchi area of Dujiangyan city. These disastrous debris flows brought heavy damage to reconstruction of the earthquake damaged region. It is very important to study the formative mechanism and early mitigation warning of the debris flows in this area. Based on the research achievements of predecessors such as occurrence and rainfall condition, this paper reveals that the water content of sediments and the depth of surface runoff are important factors to the initiation of debris flows. According to the characteristics of antecedent rainfall and effective rainfall intensity when debris flows occur, this paper establishes an initiation model of debris flow in this region. It is related to three grades of soil particle initiation processes. They are individual, partial, and whole grades. The different rainfall conditions are divided into blue, yellow and red three risk levels for this area of debris flow monitoring and early warning.
The monitoring of ground fissures plays an important role in the prevention and control of the ground fissure hazard. In this paper, BOTDR-based distributed monitoring technology is used to monitor the development process of ground fissures. The principle of distributed optical fiber sensing technology and the distributed monitoring method are introduced. The field monitoring of ground fissures located in Wuxi is studied. The results show that BOTDR-based distributed monitoring technology can be effectively used to the deformation monitoring of ground fissures. Its monitoring accuracy and measuring range can be improved by the fixed-point layout of optical fiber. The monitoring accuracy can reach 0.1mm and the measuring range can raise 30mm. The multiple ground fissures within a certain area can be monitored by the gridded laying of optical fiber. The positioning accuracy of the ground fissure monitoring can be improved by setting up the different lengths between two fixed-points along the same direction.
The monitoring of ground fissures plays an important role in the prevention and control of the ground fissure hazard. In this paper, BOTDR-based distributed monitoring technology is used to monitor the development process of ground fissures. The principle of distributed optical fiber sensing technology and the distributed monitoring method are introduced. The field monitoring of ground fissures located in Wuxi is studied. The results show that BOTDR-based distributed monitoring technology can be effectively used to the deformation monitoring of ground fissures. Its monitoring accuracy and measuring range can be improved by the fixed-point layout of optical fiber. The monitoring accuracy can reach 0.1mm and the measuring range can raise 30mm. The multiple ground fissures within a certain area can be monitored by the gridded laying of optical fiber. The positioning accuracy of the ground fissure monitoring can be improved by setting up the different lengths between two fixed-points along the same direction.
2014, 22(1): 14-23.
Statistical analysis is a basic method to study the spatial distribution of earthquake induced geo-hazards. Many scholars have analyzed spatial distribution characteristics for the earthquake induced geo-hazards by selecting different evaluation indexes. Among all of these indexes, the hazards number and hazards number density are unreliable until field investigation to confirm the accuracy of the hazards data. Thus, this paper presents a method to study the spatial distribution law of earthquake induced geo-hazards in the Baisha river basin of Dujiangyan county by using three parameters. They are Pa, Ph and Pn. They can reduce the negative influence of geo-hazards numbers. The statistical results show that this method is simple and effective for revealing the general characteristics of hazards distribution and more information about hazards scales. In addition, the method uses a new index [C] to measure the extent of ground damaged in small watershed. Findings are as follows. The main distribution area of geo-hazards is not equal to the zones damaged worst. The main distribution area of seismic induced geo-hazards is 30～50 in slope gradient, 1540～2740m in slope elevation, and E-SW in slope aspect. By the contrast analysis of this results and other scholars' statistical results, it can be found that the distribution area exists upper limit in slope gradient and elevation, 50 and 3000m respectively. Besides, the main distributed slope aspect is closely relate to the strike direction of Beichuan-Yingxiu Fault, but there is no back-slope effects in Baisha river basin. The distribution of geo-hazards is less relates to the stratum lithology.
Statistical analysis is a basic method to study the spatial distribution of earthquake induced geo-hazards. Many scholars have analyzed spatial distribution characteristics for the earthquake induced geo-hazards by selecting different evaluation indexes. Among all of these indexes, the hazards number and hazards number density are unreliable until field investigation to confirm the accuracy of the hazards data. Thus, this paper presents a method to study the spatial distribution law of earthquake induced geo-hazards in the Baisha river basin of Dujiangyan county by using three parameters. They are Pa, Ph and Pn. They can reduce the negative influence of geo-hazards numbers. The statistical results show that this method is simple and effective for revealing the general characteristics of hazards distribution and more information about hazards scales. In addition, the method uses a new index [C] to measure the extent of ground damaged in small watershed. Findings are as follows. The main distribution area of geo-hazards is not equal to the zones damaged worst. The main distribution area of seismic induced geo-hazards is 30～50 in slope gradient, 1540～2740m in slope elevation, and E-SW in slope aspect. By the contrast analysis of this results and other scholars' statistical results, it can be found that the distribution area exists upper limit in slope gradient and elevation, 50 and 3000m respectively. Besides, the main distributed slope aspect is closely relate to the strike direction of Beichuan-Yingxiu Fault, but there is no back-slope effects in Baisha river basin. The distribution of geo-hazards is less relates to the stratum lithology.
2014, 22(1): 24-29.
The formation and development of landslide are often associated with the activity of surface water and groundwater. This paper analyzes the deformation mechanism of a water-saturated landslide in the Shitian Highway in Qin-ba mountain area, predicts the failure mode of the landslide after excavation, and formulates the control scheme. The monitoring data analysis at the construction stage and the study of engineering effect are used to verify the deformation and failure mode. Deformation features of the landslide at each construction stage are summarized. The large-scale overburden landslide has plentiful groundwater. The creep characteristics are associated with the rheological property and the stress states of cohesive soil. Higher clay content, larger plasticity index and higher water content of sliding mass cause stronger rheology of soil and more obvious effects on creep deformation in landslide body. It is difficult to control the deformation development of the water-saturated landslide only to take surface drainage engineering and supporting measures. Underground drainage engineering such as discharge tunnel to change the groundwater seepage field and improve the slide zone's effective stress must be complemented when treating the water-saturated landslide. With the deepening of excavation, the strain energy of the slope has been released and the new plastic zone can be formed. Based on the theory of progressive failure, the sliding surface of the large deep overburden landslide reinforcement with anti-slide pile can be enhanced. The treatment project should consider the influence of multilayer surface.
The formation and development of landslide are often associated with the activity of surface water and groundwater. This paper analyzes the deformation mechanism of a water-saturated landslide in the Shitian Highway in Qin-ba mountain area, predicts the failure mode of the landslide after excavation, and formulates the control scheme. The monitoring data analysis at the construction stage and the study of engineering effect are used to verify the deformation and failure mode. Deformation features of the landslide at each construction stage are summarized. The large-scale overburden landslide has plentiful groundwater. The creep characteristics are associated with the rheological property and the stress states of cohesive soil. Higher clay content, larger plasticity index and higher water content of sliding mass cause stronger rheology of soil and more obvious effects on creep deformation in landslide body. It is difficult to control the deformation development of the water-saturated landslide only to take surface drainage engineering and supporting measures. Underground drainage engineering such as discharge tunnel to change the groundwater seepage field and improve the slide zone's effective stress must be complemented when treating the water-saturated landslide. With the deepening of excavation, the strain energy of the slope has been released and the new plastic zone can be formed. Based on the theory of progressive failure, the sliding surface of the large deep overburden landslide reinforcement with anti-slide pile can be enhanced. The treatment project should consider the influence of multilayer surface.
2014, 22(1): 30-37.
Taking the landslides of Langao County as the object of study, R-factor analysis is used to analyze the influential factors of landslide development. The results are as follow. According to its degree of influence, the dominant factors which contribute to landslide development from great to small are respectively the distance from the slope forward to the river, human engineering activities, landform and structural plane. The secondary factors which contribute to landslide development from great to small are respectively the distance from the slope forward to the river, the excavation of slope toe, aspect of slope, dip of structural plane, topsoil(the percentage of slope area) and the detritus content of sliding mass. Combining the dominant terms and the secondary factors analysis, the main controlling factors, in turn, are the distance from the slope forward to the river, aspect of slope and dip of structural plane. This research provides not only a new analyzed method for landslide hazard, but also gives a new idea for prevention and mitigation landslide hazard.
Taking the landslides of Langao County as the object of study, R-factor analysis is used to analyze the influential factors of landslide development. The results are as follow. According to its degree of influence, the dominant factors which contribute to landslide development from great to small are respectively the distance from the slope forward to the river, human engineering activities, landform and structural plane. The secondary factors which contribute to landslide development from great to small are respectively the distance from the slope forward to the river, the excavation of slope toe, aspect of slope, dip of structural plane, topsoil(the percentage of slope area) and the detritus content of sliding mass. Combining the dominant terms and the secondary factors analysis, the main controlling factors, in turn, are the distance from the slope forward to the river, aspect of slope and dip of structural plane. This research provides not only a new analyzed method for landslide hazard, but also gives a new idea for prevention and mitigation landslide hazard.
2014, 22(1): 38-45.
A torrential rainfall came to Kumamoto prefecture of Japan in mid-July 2012,which initialed floods in the main city area and countless geologic hazards in Aso. They mainly include slope failures, landslides and mud-rock flows. The geographical environment there added too much inconvenience to the restoration work conducted by the related department. Thus compared to the operation of restoration work afterwards, erection of protective facilities in the potentially dangerous area prone to geologic hazards before-hand seems more practical and economical. RESS,risk evaluation system for slope failure based on geographical data base, developed independently by the Department of Civil and Environmental Engineering in Kumamoto University. Seven categories, relief energy, cross section, slope angle, water catchment, land use, geology, change of hazards location, together with risk evaluation were resolved in the forms of data and three-dimensional images. Quantification Theory Ⅱ method then was used to calculate and evaluate the potential risk of the Sakanashi area in Aso. Both the accuracy ratio of risk evaluation and hazards location discrimination were the research requirements. Finally a hazards map of the studied area for prediction was able to be plotted, in which the dangerous locations were marked out clearly by different colors, and which consequently is easy to be understood and be accepted by both the public and professionals.
A torrential rainfall came to Kumamoto prefecture of Japan in mid-July 2012,which initialed floods in the main city area and countless geologic hazards in Aso. They mainly include slope failures, landslides and mud-rock flows. The geographical environment there added too much inconvenience to the restoration work conducted by the related department. Thus compared to the operation of restoration work afterwards, erection of protective facilities in the potentially dangerous area prone to geologic hazards before-hand seems more practical and economical. RESS,risk evaluation system for slope failure based on geographical data base, developed independently by the Department of Civil and Environmental Engineering in Kumamoto University. Seven categories, relief energy, cross section, slope angle, water catchment, land use, geology, change of hazards location, together with risk evaluation were resolved in the forms of data and three-dimensional images. Quantification Theory Ⅱ method then was used to calculate and evaluate the potential risk of the Sakanashi area in Aso. Both the accuracy ratio of risk evaluation and hazards location discrimination were the research requirements. Finally a hazards map of the studied area for prediction was able to be plotted, in which the dangerous locations were marked out clearly by different colors, and which consequently is easy to be understood and be accepted by both the public and professionals.
2014, 22(1): 46-55.
On May 12, 2008, a MS8.0 earthquake occurred in the Longmenshan fault zone in Sichuan province of China. It induced large amounts of geo-hazards. Comprehensive and accurate disasters catalog and the development pattern analysis are the foundation of research in disaster prevention and control. The Mianyuan river basin is one of the typical areas where seismic disasters well developed. This paper used two SPOT5 remote sensing images which took after the earthquake, combined with the aerial image took before the earthquake, automatically identified the geo-hazards spots and connected with the field investigation and visual check. It catalogued the slope geological disasters accurately. By comparison and contrast between the results of the previous researches in the study area and the method used in this paper, this geological disasters extraction method has a lot of advantages. The results are more completely and accurately. On the basis of the disaster development regularity of spatial analysis, we obtained some new understanding different from the previous ones. (1)Paying more attention to the choice and contrast of the times when RS images took and using RS image are an effective method for extraction of coseismic geological disasters, so as to obtain accurate and complete interpretation results; (2)the extracted area of disasters is 85.5km2,about two times the research by predecessors. Visual results show that the area of disasters mainly distribute in Beichuan-Yingxiu surface rupture zone and along the both sides of the Mianyuan river; (3)the main factors influencing the distribution of geological disasters in Wenchuan earthquake are elevation, slope, slope-shape, surface ruptures and stratigraphic lithology. Near the elevation of 1500m and 4100m, the geo-hazards area percentages are large, above 31% and 25%respectively. The distribution is positively related to the slope. The geo-hazards area percentage is mainly concentrated in the vicinity of 50. Disasters mainly distribute in the concave slope units, followed by convex slopes. The disasters have big relationships with the active faults complexity characteristics of activity in the region. On the hard rock or the soft stratums with hard under is the main sliding area of disasters, its area percentage up to 49.6%.
On May 12, 2008, a MS8.0 earthquake occurred in the Longmenshan fault zone in Sichuan province of China. It induced large amounts of geo-hazards. Comprehensive and accurate disasters catalog and the development pattern analysis are the foundation of research in disaster prevention and control. The Mianyuan river basin is one of the typical areas where seismic disasters well developed. This paper used two SPOT5 remote sensing images which took after the earthquake, combined with the aerial image took before the earthquake, automatically identified the geo-hazards spots and connected with the field investigation and visual check. It catalogued the slope geological disasters accurately. By comparison and contrast between the results of the previous researches in the study area and the method used in this paper, this geological disasters extraction method has a lot of advantages. The results are more completely and accurately. On the basis of the disaster development regularity of spatial analysis, we obtained some new understanding different from the previous ones. (1)Paying more attention to the choice and contrast of the times when RS images took and using RS image are an effective method for extraction of coseismic geological disasters, so as to obtain accurate and complete interpretation results; (2)the extracted area of disasters is 85.5km2,about two times the research by predecessors. Visual results show that the area of disasters mainly distribute in Beichuan-Yingxiu surface rupture zone and along the both sides of the Mianyuan river; (3)the main factors influencing the distribution of geological disasters in Wenchuan earthquake are elevation, slope, slope-shape, surface ruptures and stratigraphic lithology. Near the elevation of 1500m and 4100m, the geo-hazards area percentages are large, above 31% and 25%respectively. The distribution is positively related to the slope. The geo-hazards area percentage is mainly concentrated in the vicinity of 50. Disasters mainly distribute in the concave slope units, followed by convex slopes. The disasters have big relationships with the active faults complexity characteristics of activity in the region. On the hard rock or the soft stratums with hard under is the main sliding area of disasters, its area percentage up to 49.6%.
2014, 22(1): 56-63.
Bailong river basin is one of the four regions with high incidences of landslide and debris flow in China. Thus it is of vital importance to carry out hazard mapping of the landslides in this region to provide references for disaster management and construction planning. Using slope units as the basic assessment units, this research firstly gets the 6most contributing factors of landslides by means of principal component analysis and independence test. Then, the methods of Logistic Regression(LR) and Support Vector Machine(SVM) are conducted for landslide hazard mapping. Results show that (1) both LR and SVM can effectively evaluate the hazards of landslides in the region; (2)the SVM has a better ability in classification, predicting accuracy and model stability. According to the results of the two models, the study area are classified into five categories,i.e., very high dangerous zone, high dangerous zone, moderate dangerous zone, low dangerous zone and very low dangerous zone, taking an area proportion of 38.76%、14.48%、9.40%、11.28%、26.07% and 13.49%、21.61%、8.17%、26.70%、30.04%,respectively.
Bailong river basin is one of the four regions with high incidences of landslide and debris flow in China. Thus it is of vital importance to carry out hazard mapping of the landslides in this region to provide references for disaster management and construction planning. Using slope units as the basic assessment units, this research firstly gets the 6most contributing factors of landslides by means of principal component analysis and independence test. Then, the methods of Logistic Regression(LR) and Support Vector Machine(SVM) are conducted for landslide hazard mapping. Results show that (1) both LR and SVM can effectively evaluate the hazards of landslides in the region; (2)the SVM has a better ability in classification, predicting accuracy and model stability. According to the results of the two models, the study area are classified into five categories,i.e., very high dangerous zone, high dangerous zone, moderate dangerous zone, low dangerous zone and very low dangerous zone, taking an area proportion of 38.76%、14.48%、9.40%、11.28%、26.07% and 13.49%、21.61%、8.17%、26.70%、30.04%,respectively.
2014, 22(1): 64-70.
The causal link of underground mining and landslides is the focus of attention recently. Considering the limitations of previous undermining induced landslide research, the stochastic medium theory has been used widely in ground surface movement and deformation forecast in diggings. It tries to illuminate the slope movement and deformation principle resulted from underground mining with the stochastic medium theory. Taking Jiweishan landslide in Wulong, Chongqing for example, two models of undermining section in the slope are built. With computer aided calculation, the slope movement and deformation principles induced by undermining are analyzed. The different undermining conditions are also considered. The conclusion is as follow. The undermining-induced differential settlements aggravate the tendency to slip of the Jiweishan slope. The analysis indicates the stochastic medium theory is applicable to analyze slope movement and deformation principles induced by underground mining.
The causal link of underground mining and landslides is the focus of attention recently. Considering the limitations of previous undermining induced landslide research, the stochastic medium theory has been used widely in ground surface movement and deformation forecast in diggings. It tries to illuminate the slope movement and deformation principle resulted from underground mining with the stochastic medium theory. Taking Jiweishan landslide in Wulong, Chongqing for example, two models of undermining section in the slope are built. With computer aided calculation, the slope movement and deformation principles induced by undermining are analyzed. The different undermining conditions are also considered. The conclusion is as follow. The undermining-induced differential settlements aggravate the tendency to slip of the Jiweishan slope. The analysis indicates the stochastic medium theory is applicable to analyze slope movement and deformation principles induced by underground mining.
2014, 22(1): 71-77.
Great earthquakes in mountainous areas usually cause large numbers of landslide dams. For example, at least 257 landslide dams formed during Wenchuan Earthquake in 2008. Lots of aftershocks occurred after the major shock, which might influence the safety of these landslide dams. This paper presents the studies of large-scale shaking table tests on the breach mechanism and process of landslide dams under the coupled effect of aftershocks and water. Two groups of shaking table tests were conducted to simulate the behaviors of two types of landslide dams：one with cohesive materials and small particle size(Dam I) and the other without cohesive materials and with large particle size(Dam Ⅱ). The shaking table tests were conducted under different water depths. The following conclusions are drawn：(1)The main failure mode of landslide dams under the coupled effect of aftershocks and water is overtopping. The breach process is that：seismic force causes the subsidence of the loose landslide dams, seepage of water enlarges the subsidence value, finally, water level rises and overtops the dam crest and the dam fails by water erosion. (2)Earthquakes may not directly cause the failure of landslide dams. The main influence of earthquakes on landslide dams is causing subsidence of dam crest. The subsidence value under the coupled effect of aftershocks and water is larger than that under the effect of either factor. The subsidence induced by the earthquakes may bring forward the overtopping of landslide dams.(3)The subsidence of Dam Ⅰ is larger than that of Dam II under the coupled effect of earthquakes and water, which shows that landslide dams composed of rock and soils with larger particle size are more stable.
Great earthquakes in mountainous areas usually cause large numbers of landslide dams. For example, at least 257 landslide dams formed during Wenchuan Earthquake in 2008. Lots of aftershocks occurred after the major shock, which might influence the safety of these landslide dams. This paper presents the studies of large-scale shaking table tests on the breach mechanism and process of landslide dams under the coupled effect of aftershocks and water. Two groups of shaking table tests were conducted to simulate the behaviors of two types of landslide dams：one with cohesive materials and small particle size(Dam I) and the other without cohesive materials and with large particle size(Dam Ⅱ). The shaking table tests were conducted under different water depths. The following conclusions are drawn：(1)The main failure mode of landslide dams under the coupled effect of aftershocks and water is overtopping. The breach process is that：seismic force causes the subsidence of the loose landslide dams, seepage of water enlarges the subsidence value, finally, water level rises and overtops the dam crest and the dam fails by water erosion. (2)Earthquakes may not directly cause the failure of landslide dams. The main influence of earthquakes on landslide dams is causing subsidence of dam crest. The subsidence value under the coupled effect of aftershocks and water is larger than that under the effect of either factor. The subsidence induced by the earthquakes may bring forward the overtopping of landslide dams.(3)The subsidence of Dam Ⅰ is larger than that of Dam II under the coupled effect of earthquakes and water, which shows that landslide dams composed of rock and soils with larger particle size are more stable.
2014, 22(1): 78-85.
This paper studies the stability and failure mode of cave-roof under pile foundation. It uses the finite element software DIANA's phase analysis to simulate the plastic deformation and displacement field characteristics of foundation soil in the process of karst cave expanding gradually. Also it sets up five different load levels in contrast. It takes the ultimate bearing capacity with no cave as a benchmark to analyze the coupled effects of cave development and load level on the stability of surrounding rock and summarizes cave failure mode and mechanism. The following conclusions are draw: cave development and pile load both exist critical safe value. When the load is small, cave plays a role of main influence to foundation. The development of cave unceasingly makes plastic strain expanding downward along pile. When load level is higher, the plastic strain of same cave developmental stage increases significantly, even within the safe cave development can lead to ahead of security phase and early damage. Finally this paper simulates practice mechanical characteristics of surrounding rock better as karst growing with time in the evolution process, which has important reference value for stability study of karst-roof.
This paper studies the stability and failure mode of cave-roof under pile foundation. It uses the finite element software DIANA's phase analysis to simulate the plastic deformation and displacement field characteristics of foundation soil in the process of karst cave expanding gradually. Also it sets up five different load levels in contrast. It takes the ultimate bearing capacity with no cave as a benchmark to analyze the coupled effects of cave development and load level on the stability of surrounding rock and summarizes cave failure mode and mechanism. The following conclusions are draw: cave development and pile load both exist critical safe value. When the load is small, cave plays a role of main influence to foundation. The development of cave unceasingly makes plastic strain expanding downward along pile. When load level is higher, the plastic strain of same cave developmental stage increases significantly, even within the safe cave development can lead to ahead of security phase and early damage. Finally this paper simulates practice mechanical characteristics of surrounding rock better as karst growing with time in the evolution process, which has important reference value for stability study of karst-roof.
2014, 22(1): 86-90.
Leachate can have some effect on the mechanical properties of compacted clay liner and subsoil in landfill, although there is not a consistent viewpoint. This paper takes CaCl2 and phenol solutions as the representative of inorganic and organic contaminants in leachate. It conducts compression and strength tests on compacted clay liner with 10% Na-bentonite as addition. With the effect of the two solutions, the soils are of higher compressibility and lower shear strength. Phenol solution results in more remarkable changes in mechanical properties. Its undrained shear strength is 55% of tap water and 0.05molL-1 CaCl2. Under the condition of the same pore ratio, solutions decrease the thickness of diffuse double layer and enlarge the pores, which can be the source of the shear strength reduction. Simulate solutions have an adverse impact on compacted clay liner and subsoil.
Leachate can have some effect on the mechanical properties of compacted clay liner and subsoil in landfill, although there is not a consistent viewpoint. This paper takes CaCl2 and phenol solutions as the representative of inorganic and organic contaminants in leachate. It conducts compression and strength tests on compacted clay liner with 10% Na-bentonite as addition. With the effect of the two solutions, the soils are of higher compressibility and lower shear strength. Phenol solution results in more remarkable changes in mechanical properties. Its undrained shear strength is 55% of tap water and 0.05molL-1 CaCl2. Under the condition of the same pore ratio, solutions decrease the thickness of diffuse double layer and enlarge the pores, which can be the source of the shear strength reduction. Simulate solutions have an adverse impact on compacted clay liner and subsoil.
2014, 22(1): 91-97.
The self-boring pressure-meter(SBMP) has little to no disturbance to the surrounding soil and has a long measurement depth. It can determine the stress and strain curve of soil at depth and has an extensive application prospect in the determination of soil parameters and foundation bearing capacity. However, because of the limitations of the analytical tools and research level, the deformation response of surrounding soil during loading process in SBMP test with probes of different length-to-diameter ratio (L/D) has seldom been studied up to present. At the same time, the determination of the soil parameter is closely related to its deformation mechanism. Based on this, the self-boring pressure-meter(SBPM)test with different length-to-diameter ratio(L/D=6, 10, 15, 20) is simulated by PFC3D(Particle Flow Code in Three Dimensions) program in this study. The development and distribution of the displacement and stress field of the soil surrounding the probe are studied. The results of numerical experiments show that the distribution of the displacement and radial-stress field can be divided into two forms according to the size of the L/D. When L/D equals 6,the distribution shape of the displacement and stress field shows an arc-shaped lanterns appearance; the deformation of the surrounding soil along the height of the probe dose not satisfy with the plane strain and axial symmetry conditions. And the soil stress of L/D=6 is smaller than the later three. However, when L/D has a value of 10, 15 and 20,the distribution shape shows a straight wall lanterns appearance; the deformation of the surrounding soil along the height of the probe basically satisfies with the plane strain and axial symmetry conditions. The stress distribution along the height of the probe is relatively uniform than that of the L/D=6, and the soil stress decreases with the increase of the L/D. Several radial stress cores which are approximately symmetrical distribution have formed near both sides of the probe. In addition, the radial-stress at the borehole wall descends in a negative exponential form with the increase of the L/D when the radial strain of the probe is constant.
The self-boring pressure-meter(SBMP) has little to no disturbance to the surrounding soil and has a long measurement depth. It can determine the stress and strain curve of soil at depth and has an extensive application prospect in the determination of soil parameters and foundation bearing capacity. However, because of the limitations of the analytical tools and research level, the deformation response of surrounding soil during loading process in SBMP test with probes of different length-to-diameter ratio (L/D) has seldom been studied up to present. At the same time, the determination of the soil parameter is closely related to its deformation mechanism. Based on this, the self-boring pressure-meter(SBPM)test with different length-to-diameter ratio(L/D=6, 10, 15, 20) is simulated by PFC3D(Particle Flow Code in Three Dimensions) program in this study. The development and distribution of the displacement and stress field of the soil surrounding the probe are studied. The results of numerical experiments show that the distribution of the displacement and radial-stress field can be divided into two forms according to the size of the L/D. When L/D equals 6,the distribution shape of the displacement and stress field shows an arc-shaped lanterns appearance; the deformation of the surrounding soil along the height of the probe dose not satisfy with the plane strain and axial symmetry conditions. And the soil stress of L/D=6 is smaller than the later three. However, when L/D has a value of 10, 15 and 20,the distribution shape shows a straight wall lanterns appearance; the deformation of the surrounding soil along the height of the probe basically satisfies with the plane strain and axial symmetry conditions. The stress distribution along the height of the probe is relatively uniform than that of the L/D=6, and the soil stress decreases with the increase of the L/D. Several radial stress cores which are approximately symmetrical distribution have formed near both sides of the probe. In addition, the radial-stress at the borehole wall descends in a negative exponential form with the increase of the L/D when the radial strain of the probe is constant.
2014, 22(1): 98-105.
Coal has been widely mined in China to support the rapidly developing economy. A great number of gob zones have appeared in almost all provinces of China, especially some provinces with rich coal resources such as Shanxi province, Shaanxi province and Xinjiang province. Gob is dangerous to construction, especially to highways and high speed railways. At present, grouting filling is the main way to reduce engineering hazards in gob area. Fly ash cement slurry is the most commonly used materials in goaf management. Because of lack of fly ash in some goaf treatment project, it is necessary to look for another low-cost grouting material. Loess cement slurry has the advantages of both simple process and reserves of local material. It is considered to be one of the best alternative grouting materials for grouting filling. The property of loess cement slurry is studied in this paper. Firstly, loess samples are collected in Jingyang city of Shaanxi province, Lanzhou city of Gansu province and Lvliang city of Shanxi province. They are taken as experimental materials. Secondly, a large number of loess cement slurry tests on slurry viscosity, stone rate and consolidation strength are performed. Finally, the factors affecting the characters of loess cement grouting material are discussed. They include cement content, water solid ratio and loess type. Results show that with the increase of loess content, the consolidation strength and the liquidity of slurry are reduced, and the setting time is extended. The early consolidation strength of cement loess slurry is low, and the later strength grows larger. The main reason that leads to the difference of loess cement slurry properties lies in regional distribution of loess. The consolidation strength becomes higher as the average grain size becomes coarser. Compared with the Lishi loess slurry, Malan loess slurry performance is stable and intensity is higher. For this reason, Malan loess is more suitable for grouting filling. With the increase percentage of sodium silicate, the viscosity and concretion rate increased, the setting time shortened, and the strength decreased. This research provides a new material of goaf grouting filling and has important practical values.
Coal has been widely mined in China to support the rapidly developing economy. A great number of gob zones have appeared in almost all provinces of China, especially some provinces with rich coal resources such as Shanxi province, Shaanxi province and Xinjiang province. Gob is dangerous to construction, especially to highways and high speed railways. At present, grouting filling is the main way to reduce engineering hazards in gob area. Fly ash cement slurry is the most commonly used materials in goaf management. Because of lack of fly ash in some goaf treatment project, it is necessary to look for another low-cost grouting material. Loess cement slurry has the advantages of both simple process and reserves of local material. It is considered to be one of the best alternative grouting materials for grouting filling. The property of loess cement slurry is studied in this paper. Firstly, loess samples are collected in Jingyang city of Shaanxi province, Lanzhou city of Gansu province and Lvliang city of Shanxi province. They are taken as experimental materials. Secondly, a large number of loess cement slurry tests on slurry viscosity, stone rate and consolidation strength are performed. Finally, the factors affecting the characters of loess cement grouting material are discussed. They include cement content, water solid ratio and loess type. Results show that with the increase of loess content, the consolidation strength and the liquidity of slurry are reduced, and the setting time is extended. The early consolidation strength of cement loess slurry is low, and the later strength grows larger. The main reason that leads to the difference of loess cement slurry properties lies in regional distribution of loess. The consolidation strength becomes higher as the average grain size becomes coarser. Compared with the Lishi loess slurry, Malan loess slurry performance is stable and intensity is higher. For this reason, Malan loess is more suitable for grouting filling. With the increase percentage of sodium silicate, the viscosity and concretion rate increased, the setting time shortened, and the strength decreased. This research provides a new material of goaf grouting filling and has important practical values.
2014, 22(1): 106-111.
Influences of dry density and volumetric water content on permeability characteristics of unsaturated Baode Fm. laterite are studied by adopting Van Genuchten model on basis of measured results. The results show that with different dry density, unsaturated permeability coefficient is accelerated monotonically and increasing with increase of volumetric water content in semilogarithmic coordinates. Unsaturated permeability coefficient is approximate linear related to volumetric water content. The permeability coefficient of dense unsaturated laterite is relatively sensitive to change of volumetric water content. With different dry density, the unsaturated permeability coefficient has an exponential function relationship with the matric suction in semilogarithmic coordinates. The unsaturated permeability coefficient is monotonically decreasing with increase of matric suction. When dry density of soil is relatively high, the permeability coefficient of unsaturated laterite is changing more violently with change of matric suction. The permeability coefficient of dense unsaturated laterite is considerably sensitive to change of dry density.
Influences of dry density and volumetric water content on permeability characteristics of unsaturated Baode Fm. laterite are studied by adopting Van Genuchten model on basis of measured results. The results show that with different dry density, unsaturated permeability coefficient is accelerated monotonically and increasing with increase of volumetric water content in semilogarithmic coordinates. Unsaturated permeability coefficient is approximate linear related to volumetric water content. The permeability coefficient of dense unsaturated laterite is relatively sensitive to change of volumetric water content. With different dry density, the unsaturated permeability coefficient has an exponential function relationship with the matric suction in semilogarithmic coordinates. The unsaturated permeability coefficient is monotonically decreasing with increase of matric suction. When dry density of soil is relatively high, the permeability coefficient of unsaturated laterite is changing more violently with change of matric suction. The permeability coefficient of dense unsaturated laterite is considerably sensitive to change of dry density.
2014, 22(1): 112-123.
Rock and soil aggregate(RSA) is a special kind of geological materials, which is different from soil and fractured rock mass. Recently, RSA is drawn more and more attention from engineering and academia circles. Deep research on the meso-structure, physical and mechanical properties of RSA is not only the need of the engineering construction, but also the inevitable result of theory rock and soil mechanics, calculation of geotechnical mechanics, experimental rock and soil mechanics. Based on the current research for RSA about mesoscopic characteristic home and abroad, the research status of RSA is summarized in term of meso-structure characteristics, meso-structure model and the meso-mechanics characteristic. On the basis of this, shortcomings of meso-scale characteristic research are summarized, point out that carrying out different meso-scale real-time loading tests to analysis local deformation characteristics for RSA is the future direction. The trends of the future research include establishing meso-scale damage evolution equation and the constitutive equation, strengthening research about environment-dependence of RSA, and establishment full-field structure model on meso-scale tests revealing the microstructure evolution under real-time loading condition.
Rock and soil aggregate(RSA) is a special kind of geological materials, which is different from soil and fractured rock mass. Recently, RSA is drawn more and more attention from engineering and academia circles. Deep research on the meso-structure, physical and mechanical properties of RSA is not only the need of the engineering construction, but also the inevitable result of theory rock and soil mechanics, calculation of geotechnical mechanics, experimental rock and soil mechanics. Based on the current research for RSA about mesoscopic characteristic home and abroad, the research status of RSA is summarized in term of meso-structure characteristics, meso-structure model and the meso-mechanics characteristic. On the basis of this, shortcomings of meso-scale characteristic research are summarized, point out that carrying out different meso-scale real-time loading tests to analysis local deformation characteristics for RSA is the future direction. The trends of the future research include establishing meso-scale damage evolution equation and the constitutive equation, strengthening research about environment-dependence of RSA, and establishment full-field structure model on meso-scale tests revealing the microstructure evolution under real-time loading condition.
2014, 22(1): 124-129.
Relaxation and its relaxation zone of excavated foundation rock mass is a kind of common phenomenon in hydropower project. They have important influence on the foundation rock mass quality. The foundation rock mass after excavation is bound to produce new blasting cracks along with the excavation unloading and stress release. Although it has not been further weathered, rock mass can form a relaxation zone in the superficial depth, with its relaxation and unloading. Therefore, determination of relaxation zone thickness is of great significance in engineering. The paper is based on the field of geological environment condition survey and acoustic test and the indoor synthetic analysis. It studies a relaxation zone thickness and characteristics of layered foundation rock mass and analyze the foundation rock causes of deep relaxation. On the basis, it analyses the relaxation zone that has influence on the engineering properties of the foundation rock, which has instructive function for dam foundation excavation practice of similar projects.
Relaxation and its relaxation zone of excavated foundation rock mass is a kind of common phenomenon in hydropower project. They have important influence on the foundation rock mass quality. The foundation rock mass after excavation is bound to produce new blasting cracks along with the excavation unloading and stress release. Although it has not been further weathered, rock mass can form a relaxation zone in the superficial depth, with its relaxation and unloading. Therefore, determination of relaxation zone thickness is of great significance in engineering. The paper is based on the field of geological environment condition survey and acoustic test and the indoor synthetic analysis. It studies a relaxation zone thickness and characteristics of layered foundation rock mass and analyze the foundation rock causes of deep relaxation. On the basis, it analyses the relaxation zone that has influence on the engineering properties of the foundation rock, which has instructive function for dam foundation excavation practice of similar projects.
2014, 22(1): 130-136.
Dolerite argillic alteration is an important geological flaw in Dagangshan hydropower station. This paper takes advantage of geological survey and laboratory experiment, combined with regional geological environment to analyze distribution, mineralogical, structural features, physical mechanics properties and formation mechanism of the altered-rock. The study reveals that the dolerite dykes along SN direction commonly develop altered argillic band. The band mainly concentrates in contact surface of the dykes and granite or internal schistosity crack. The altered-argillic rocks are loose and crumbly and have the following physical characteristics: high water content, low specific gravity, high plasticity and medium compression. Results of X ray diffraction and scanning electron microscope show that they have a lot of chlorite and pore void microstructure characteristics. Pyroxene darkly minerals enrichment, multi-period hydrothermal metasomatism and tectonic stress action constitute the formation mechanism of the dolerite argillic alteration.
Dolerite argillic alteration is an important geological flaw in Dagangshan hydropower station. This paper takes advantage of geological survey and laboratory experiment, combined with regional geological environment to analyze distribution, mineralogical, structural features, physical mechanics properties and formation mechanism of the altered-rock. The study reveals that the dolerite dykes along SN direction commonly develop altered argillic band. The band mainly concentrates in contact surface of the dykes and granite or internal schistosity crack. The altered-argillic rocks are loose and crumbly and have the following physical characteristics: high water content, low specific gravity, high plasticity and medium compression. Results of X ray diffraction and scanning electron microscope show that they have a lot of chlorite and pore void microstructure characteristics. Pyroxene darkly minerals enrichment, multi-period hydrothermal metasomatism and tectonic stress action constitute the formation mechanism of the dolerite argillic alteration.
2014, 22(1): 144-151.
This paper examines the data of 201 projects for the tertiary mudstone in Nanning. The statistics for physical, mechanical and swelling indexes are obtained. A reference for parameters selection of underground engineering in Nanning is provided. The results show that the physical indexes can be used as constants for its low variability, in particular in the 95%confidence interval statistics. Mechanical indexes and swelling indexes data variability are bigger, which need to consider the variability. The tertiary mudstone in Nanning is a typical expansive rock and soil. It has high compressive strength, low compressibility, large shearing strength, and especially large cohesion force. In swelling indexes, the free swelling ratio of the mudstone in Nanning is lower compared with those in other cities. So it can be identified as weak swelling rock and soil. The swelling force is larger differently due to the rock composition and the difference of weathering degree. The parameters selection should be considered specifically when parameters selection.
This paper examines the data of 201 projects for the tertiary mudstone in Nanning. The statistics for physical, mechanical and swelling indexes are obtained. A reference for parameters selection of underground engineering in Nanning is provided. The results show that the physical indexes can be used as constants for its low variability, in particular in the 95%confidence interval statistics. Mechanical indexes and swelling indexes data variability are bigger, which need to consider the variability. The tertiary mudstone in Nanning is a typical expansive rock and soil. It has high compressive strength, low compressibility, large shearing strength, and especially large cohesion force. In swelling indexes, the free swelling ratio of the mudstone in Nanning is lower compared with those in other cities. So it can be identified as weak swelling rock and soil. The swelling force is larger differently due to the rock composition and the difference of weathering degree. The parameters selection should be considered specifically when parameters selection.
2014, 22(1): 152-159.
Based on Shanxi highway engineering geological zoning map, the most typical loess hilly and gully area(I) is further divided into the Northern Shanxi(Ia),Jin West(Ib), and Jin Southwest(Ic). The three sub-regions are distinguished according to the elements of the slope types, stratigraphic combination and slope failure mode loess. The parameter values of peak intensities, start strengths and residual strengths are obtained from different direct shear test methods after experimental study on the area(I) of 53 highway slopes. An analogy between the geological characteristics of the slope and the real engineering surveys is drawn. Statistic and numerical analysis of slope stability under the three intensity parameters in the three sub-regions are made. It is then found that the strength parameters have significant differences in different geographical characteristics. The Jin Northwest(Ia) has less rainfall and less tectonic activity. For slope to slope failure, the peak intensity slope design is more appropriate. The Jin West End(Ib) has structural development. Its seismic activity makes the relative decline in the strength of the soil. It has more old landslides. The residual strength should be used as the strength of the highway slope design parameters. There is a higher security guarantee. The Shanxi South West(Ic) has more rainfall. The start strength should be used in order to avoid geological disasters.
Based on Shanxi highway engineering geological zoning map, the most typical loess hilly and gully area(I) is further divided into the Northern Shanxi(Ia),Jin West(Ib), and Jin Southwest(Ic). The three sub-regions are distinguished according to the elements of the slope types, stratigraphic combination and slope failure mode loess. The parameter values of peak intensities, start strengths and residual strengths are obtained from different direct shear test methods after experimental study on the area(I) of 53 highway slopes. An analogy between the geological characteristics of the slope and the real engineering surveys is drawn. Statistic and numerical analysis of slope stability under the three intensity parameters in the three sub-regions are made. It is then found that the strength parameters have significant differences in different geographical characteristics. The Jin Northwest(Ia) has less rainfall and less tectonic activity. For slope to slope failure, the peak intensity slope design is more appropriate. The Jin West End(Ib) has structural development. Its seismic activity makes the relative decline in the strength of the soil. It has more old landslides. The residual strength should be used as the strength of the highway slope design parameters. There is a higher security guarantee. The Shanxi South West(Ic) has more rainfall. The start strength should be used in order to avoid geological disasters.
2014, 22(1): 160-165.
Determination of soil probability model parameters is the foundation of reliability design in geotechnical engineering. In order to promote the reliability design of geotechnical engineering, regional probability model of soil index should be established firstly. As a reflection of autocorrelation characteristic of soil index-correlation distance, it's necessary to study its regional distribution characteristics and establish the probability distribution model. This paper collects 176 drilling CPT data of Xi'an loess. It uses the resistance value qc as sample and calculates the correlation distance of Xi'an loess by spatial recursive method. It analyzes the statistical characteristics, estimates the unilateral confidence interval of average value. Representative value of Xi'an loess correlation distance in each layer is put forward. Probabilistic model of Xi'an loess correlation distance is established. The model parameters are estimated. The goodness- of -fit test on the model is conducted using the Pearson chi-square method. The test results show that the model complies with the Beta distribution.
Determination of soil probability model parameters is the foundation of reliability design in geotechnical engineering. In order to promote the reliability design of geotechnical engineering, regional probability model of soil index should be established firstly. As a reflection of autocorrelation characteristic of soil index-correlation distance, it's necessary to study its regional distribution characteristics and establish the probability distribution model. This paper collects 176 drilling CPT data of Xi'an loess. It uses the resistance value qc as sample and calculates the correlation distance of Xi'an loess by spatial recursive method. It analyzes the statistical characteristics, estimates the unilateral confidence interval of average value. Representative value of Xi'an loess correlation distance in each layer is put forward. Probabilistic model of Xi'an loess correlation distance is established. The model parameters are estimated. The goodness- of -fit test on the model is conducted using the Pearson chi-square method. The test results show that the model complies with the Beta distribution.
2014, 22(1): 166-172.
The N-sandstone, of which with the characters of poor diagenetic grade, liable to weathering and disintegration, is the extremely soft rock. The N-sandstone is widely distributed in Lanzhou Basin, Gansu Province, China. The structure of the huge thickness N-sandstone will be easily disturbed under the effect of ground water and then softening. That would lead to the instability happened in the engineering basement, especially in the tunnel structure. For studying the engineering geological condition of N-sandstone, the investigation and test data of the Lanzhou to Chongqing Railway and Lanzhou to Zhongchuan Railway was studied and then obtained the physico-mechanical properties of the sandstone. Additionally, through applying scanning electron microscope technology the microstructure change character under the effect of different water content was studied also. Finally, the main effect factors of the engineering geological condition were determined and as follows: water content, clay content, anion concentration of groundwater and porosity. The catastrophe progression method was adopted to establish the engineering geological condition quantitative evaluation model of sandstone. The engineering geological condition of N-sandstone can be divided into five grades: severe(S0.64),bad(0.64 S0.71),general(0.71 S0.79),well(0.79 S0.87) and perfect(S0.87). The evaluation result about the Taoshuping Tunnel of Lanzhou-Chongqing Railway was between 0.57 to 0.77. The engineering geological condition was sever and general. The evaluation result was in keeping with the actual situation.
The N-sandstone, of which with the characters of poor diagenetic grade, liable to weathering and disintegration, is the extremely soft rock. The N-sandstone is widely distributed in Lanzhou Basin, Gansu Province, China. The structure of the huge thickness N-sandstone will be easily disturbed under the effect of ground water and then softening. That would lead to the instability happened in the engineering basement, especially in the tunnel structure. For studying the engineering geological condition of N-sandstone, the investigation and test data of the Lanzhou to Chongqing Railway and Lanzhou to Zhongchuan Railway was studied and then obtained the physico-mechanical properties of the sandstone. Additionally, through applying scanning electron microscope technology the microstructure change character under the effect of different water content was studied also. Finally, the main effect factors of the engineering geological condition were determined and as follows: water content, clay content, anion concentration of groundwater and porosity. The catastrophe progression method was adopted to establish the engineering geological condition quantitative evaluation model of sandstone. The engineering geological condition of N-sandstone can be divided into five grades: severe(S0.64),bad(0.64 S0.71),general(0.71 S0.79),well(0.79 S0.87) and perfect(S0.87). The evaluation result about the Taoshuping Tunnel of Lanzhou-Chongqing Railway was between 0.57 to 0.77. The engineering geological condition was sever and general. The evaluation result was in keeping with the actual situation.
2014, 22(1): 173-179.
Based on the analysis of floor heave disaster appeared in the Shilin tunnel, and the survey of the field geology of the section, the induction factors of floor heave, such as characteristic of surrounding rock, formation pressure, underground water, supporting conditions and the rheology property are demonstrated. Through analyzing the formation mechanism caused by different induction factors deeply, it is indicated that the disaster appeared in Shilin Tunnel is comprehensive floor heave, which posses the characteristics of water swell, extrusion flow and time effect. Considering the influence of the horizontal fault, the tunnel floor is treated as shell structure, and the estimate formula of the displacement for it is suggested. Moreover, the formula is in the consideration of non-associate inducible factors. The important conclusion is that the bending displacement of the tunnel floor takes up a significant proportion of the total displacement. The above results can further deepen the understanding about the formation mechanism of the floor heave disaster induced by the horizontal fault. And it also provides a reliable reference to the disaster prevention of tunnel floor heave.
Based on the analysis of floor heave disaster appeared in the Shilin tunnel, and the survey of the field geology of the section, the induction factors of floor heave, such as characteristic of surrounding rock, formation pressure, underground water, supporting conditions and the rheology property are demonstrated. Through analyzing the formation mechanism caused by different induction factors deeply, it is indicated that the disaster appeared in Shilin Tunnel is comprehensive floor heave, which posses the characteristics of water swell, extrusion flow and time effect. Considering the influence of the horizontal fault, the tunnel floor is treated as shell structure, and the estimate formula of the displacement for it is suggested. Moreover, the formula is in the consideration of non-associate inducible factors. The important conclusion is that the bending displacement of the tunnel floor takes up a significant proportion of the total displacement. The above results can further deepen the understanding about the formation mechanism of the floor heave disaster induced by the horizontal fault. And it also provides a reliable reference to the disaster prevention of tunnel floor heave.
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