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Editor Work2008 Vol. 16, No. 4
Previous Issue
2008, 16(4): 433-444.
Abstract
Wenchuan Earthquake triggered landslides, rock collapses and debris flows at more than 15000 sites, which directly caused about 20,000 fatalities.There are more than 10,000 sites of potential geo-hazards, where an increase in slope collapses is mostly noticeable, which shows the earthquake has substantially abnormal actions on steep slopes in the mountains. In particular, the amplifications at mountain peaks is extremely evident. A comprehensive analysis of quake lake volumes, landslide dam heights and their debris compositions and structures was carried out. An assessment on the 33 landslide dames of dam heights great than 10 m formed by the earthquake was further conducted. Consequently, the landslide dams were classified into four types of the dam burst potential : extremely high, high, intermediate and low. The sliding beds of the landslides induced by the earthquake usually have non-continuous flat sliding beds. Sharp point collision is a common and major characteristic. The sliding beds can be classified into spoon-shaped, raised-shaped and staircase-shaped. Site investigations demonstrate that the vertical vibrations in buildings destroyed by the earthquake adjacent to the landslides were evident. The landslides have three stages: throwing out of ground shocking, collision and collapsing and broken, and high-speed sliding flow. During the high-speed sliding flow, three effects were occurring: (1) high-speed air-bed effect, landslide debris were comprised with larger rock blocks and soils, had enough thickness and the flying distance of 1 to 3 km. (2) Broken debris flow effect, collision broken soils and rocks were in a flowing state, especially they contained abundant water, forming long distance flow sliding. (3) Shovel and scraping, huge collision forces induced collapse of rocks at lower portion, which formed new landslides and collapses, however, their thicknesses are not large and the sliding beds were non-smooth and irregular. The two landslides at western Beichuan county and Dongheko of Qingchuan county were analyzed in detail. They are used as examples to analyze the mechanism of the high speed and long distance sliding and hazard formation of earthquake landslides. The landslide at western Beichuan county buried 1,600 people and destroyed several hundreds houses and buildings, which is the severest landslide disaster triggered by the earthquake and is a rear event in the world. The Donghekou landslide at Qingchuan: Debris flow is a typical high speed and long distance landslide triggered by the earthquake. Its distrace is about 2,400 m. Its high-speed debris flew to the left bank of Qingjiang river and formed landslide dam, resulted 7 villages buried and about 400 fatalities.
Wenchuan Earthquake triggered landslides, rock collapses and debris flows at more than 15000 sites, which directly caused about 20,000 fatalities.There are more than 10,000 sites of potential geo-hazards, where an increase in slope collapses is mostly noticeable, which shows the earthquake has substantially abnormal actions on steep slopes in the mountains. In particular, the amplifications at mountain peaks is extremely evident. A comprehensive analysis of quake lake volumes, landslide dam heights and their debris compositions and structures was carried out. An assessment on the 33 landslide dames of dam heights great than 10 m formed by the earthquake was further conducted. Consequently, the landslide dams were classified into four types of the dam burst potential : extremely high, high, intermediate and low. The sliding beds of the landslides induced by the earthquake usually have non-continuous flat sliding beds. Sharp point collision is a common and major characteristic. The sliding beds can be classified into spoon-shaped, raised-shaped and staircase-shaped. Site investigations demonstrate that the vertical vibrations in buildings destroyed by the earthquake adjacent to the landslides were evident. The landslides have three stages: throwing out of ground shocking, collision and collapsing and broken, and high-speed sliding flow. During the high-speed sliding flow, three effects were occurring: (1) high-speed air-bed effect, landslide debris were comprised with larger rock blocks and soils, had enough thickness and the flying distance of 1 to 3 km. (2) Broken debris flow effect, collision broken soils and rocks were in a flowing state, especially they contained abundant water, forming long distance flow sliding. (3) Shovel and scraping, huge collision forces induced collapse of rocks at lower portion, which formed new landslides and collapses, however, their thicknesses are not large and the sliding beds were non-smooth and irregular. The two landslides at western Beichuan county and Dongheko of Qingchuan county were analyzed in detail. They are used as examples to analyze the mechanism of the high speed and long distance sliding and hazard formation of earthquake landslides. The landslide at western Beichuan county buried 1,600 people and destroyed several hundreds houses and buildings, which is the severest landslide disaster triggered by the earthquake and is a rear event in the world. The Donghekou landslide at Qingchuan: Debris flow is a typical high speed and long distance landslide triggered by the earthquake. Its distrace is about 2,400 m. Its high-speed debris flew to the left bank of Qingjiang river and formed landslide dam, resulted 7 villages buried and about 400 fatalities.
2008, 16(4): 445-449.
Stability of the accumulation body at Xiazanri is very important to the establishments of the Liyuan hydropower station on the Jinsha River. This station is to be built. . Based on field reconnaissance material of the Xiazanri accumulation body, the paper studies its formation mechanism and stability. The results show that it is a complex accumulation body which comprises moraine, alluvium, lake sediment and colluvium and has gone through 2 ice ages, i.e., the Jinjiang ice age in middle pleistocene and the Lijiang ice age in middle Pleistocene. The results of stability assessment show the Xiazanri accumulation body is stable as a whole despite it can have some partial fallings. The key factors controlling whether it will be stable or instable are the stabilities of the loose gravel layer at the slope toe and the lake sediments.
Stability of the accumulation body at Xiazanri is very important to the establishments of the Liyuan hydropower station on the Jinsha River. This station is to be built. . Based on field reconnaissance material of the Xiazanri accumulation body, the paper studies its formation mechanism and stability. The results show that it is a complex accumulation body which comprises moraine, alluvium, lake sediment and colluvium and has gone through 2 ice ages, i.e., the Jinjiang ice age in middle pleistocene and the Lijiang ice age in middle Pleistocene. The results of stability assessment show the Xiazanri accumulation body is stable as a whole despite it can have some partial fallings. The key factors controlling whether it will be stable or instable are the stabilities of the loose gravel layer at the slope toe and the lake sediments.
2008, 16(4): 450-458.
Ya'an to Lugu expressway is a part of the Beijing to Kunming expressway. The Lama stream is spanned by the Lama Stream Bridge along the Ya'an to Lugu expressway. To investigate engineering geological conditions at the bridge, a geological survey and field reconnaissance were conducted prior to the bridge construction. It was found that the geo-environmental conditions near and around the planned bridge site were very complicated. The so-called Xigeda strata have low strength and collapsing characteristics, which can be strongly affected by water. Under the action of water and geological structure, landslide can easily occur in slopes comprising the Xigeda strata. Base on the ground investigations at the Wenwu slope on the Lama stream along the Ya'an to Lugu expressway, this paper presents the engineering geologic and hydrogeological conditions of the landslides comprising the Xigeda strata. The paper gives results on the properties of Xigeda strata, the geological structure and groundwater. It analyzes the causes and contributing factors, finds the optimal slope gradients, the optimal slope shapes, the angle and height of slopes sensitive to landslide. It grades the dangerous degrees according to angle of slope. It provides a basis for further evaluation of slope stability. Finally, it presents some reasonable reinforcements, fill and compression and drainage measures adaptable to the geological conditions.
Ya'an to Lugu expressway is a part of the Beijing to Kunming expressway. The Lama stream is spanned by the Lama Stream Bridge along the Ya'an to Lugu expressway. To investigate engineering geological conditions at the bridge, a geological survey and field reconnaissance were conducted prior to the bridge construction. It was found that the geo-environmental conditions near and around the planned bridge site were very complicated. The so-called Xigeda strata have low strength and collapsing characteristics, which can be strongly affected by water. Under the action of water and geological structure, landslide can easily occur in slopes comprising the Xigeda strata. Base on the ground investigations at the Wenwu slope on the Lama stream along the Ya'an to Lugu expressway, this paper presents the engineering geologic and hydrogeological conditions of the landslides comprising the Xigeda strata. The paper gives results on the properties of Xigeda strata, the geological structure and groundwater. It analyzes the causes and contributing factors, finds the optimal slope gradients, the optimal slope shapes, the angle and height of slopes sensitive to landslide. It grades the dangerous degrees according to angle of slope. It provides a basis for further evaluation of slope stability. Finally, it presents some reasonable reinforcements, fill and compression and drainage measures adaptable to the geological conditions.
2008, 16(4): 459-464.
A detailed surveying on the deformation of a large rockmass slope at Tongxin Village in Wushan Town of Wangxia county indicates the slope is unstable and danger. This paper presents the finding that a 1 m thick coal seam at the bottom of the slope was mined. The slope has two deformatiom phenomena: subsiding and rockmass cracking. The two phenomena continue to develop. They are closely related to the coal mining. Engineering geological comparison indicates that the subsiding and declining due to the coal mining are the main factor causing slope deforming. The UDEC was used to make the simulation of the slope deformation. The numerical results show that after the coal seam was mined, the displacement is transferred from the lower to the upper portions of the slope. The surface subsiding in the front is larger than other places, also is horizontal displacement. The deformation of the upper slope is controlled by the vertical joints, while the deformation of the lower slope is controlled by the horizontal bedding planes and the coal-mining seam. They in whole form the subsiding-declining deformation of the rock mass slope. The calculated deformation curves suggest that deformation has two phases: Sudden quick deformation and slower deformation. I If no new coal-mining activity is carried out, as the time goes on, the mountain slope itself will become stable. The isolated rock columniation in the front slope still has high movement speed after the slope system has balanced. It is instable and has to be trimmed.
A detailed surveying on the deformation of a large rockmass slope at Tongxin Village in Wushan Town of Wangxia county indicates the slope is unstable and danger. This paper presents the finding that a 1 m thick coal seam at the bottom of the slope was mined. The slope has two deformatiom phenomena: subsiding and rockmass cracking. The two phenomena continue to develop. They are closely related to the coal mining. Engineering geological comparison indicates that the subsiding and declining due to the coal mining are the main factor causing slope deforming. The UDEC was used to make the simulation of the slope deformation. The numerical results show that after the coal seam was mined, the displacement is transferred from the lower to the upper portions of the slope. The surface subsiding in the front is larger than other places, also is horizontal displacement. The deformation of the upper slope is controlled by the vertical joints, while the deformation of the lower slope is controlled by the horizontal bedding planes and the coal-mining seam. They in whole form the subsiding-declining deformation of the rock mass slope. The calculated deformation curves suggest that deformation has two phases: Sudden quick deformation and slower deformation. I If no new coal-mining activity is carried out, as the time goes on, the mountain slope itself will become stable. The isolated rock columniation in the front slope still has high movement speed after the slope system has balanced. It is instable and has to be trimmed.
2008, 16(4): 465-469.
This paper embarks from the earthquake geology viewpoint and discusses the earthquake stability of the catchment basin of Jin Ping Hydroelectricity Engineering on Yalongjiang River. The paper focuses on the seismic geologic condition, the historical earthquake situation, the pleistoseismic zone distribution and the seismic activity situation at the key areas of the Jinping I and Jinping II hydroelectric power stations. It further discusses the regional stability of the Jinping hydroelectricity project. The geologic conditions during the construction period are further analyzed. They include the Jin Ping fault discovered from two assistance transportation tunnels across the Jinping mountain and the faults f13, f14, f5, f8 and the fault F1 at the dam sites of Jinping I discovered from both tunnel excavations and slope excavations. The characteristics of the faults were in some expected conditions. The faults did not show any active signs. This paper therefore concludes the Jinping Ⅰ and Jinping Ⅱ hydroelectricity project is earthquake stable and should maintain invariability.
This paper embarks from the earthquake geology viewpoint and discusses the earthquake stability of the catchment basin of Jin Ping Hydroelectricity Engineering on Yalongjiang River. The paper focuses on the seismic geologic condition, the historical earthquake situation, the pleistoseismic zone distribution and the seismic activity situation at the key areas of the Jinping I and Jinping II hydroelectric power stations. It further discusses the regional stability of the Jinping hydroelectricity project. The geologic conditions during the construction period are further analyzed. They include the Jin Ping fault discovered from two assistance transportation tunnels across the Jinping mountain and the faults f13, f14, f5, f8 and the fault F1 at the dam sites of Jinping I discovered from both tunnel excavations and slope excavations. The characteristics of the faults were in some expected conditions. The faults did not show any active signs. This paper therefore concludes the Jinping Ⅰ and Jinping Ⅱ hydroelectricity project is earthquake stable and should maintain invariability.
2008, 16(4): 470-475.
Taking the TBM performance in four tunnels as case examples, this paper analyzes the two reasons that there are problems in using the conventional rock mass quality classification systems to predict the TBM performance. The first reason is the factors which control the rock mass quality are not the factors that influence the rock mass boreability. The second is that most of the factors in rock mass classification systems are semi-quantitative. As a result of the two reasons, the value of the rock mass quality cannot reflect the rock mass boreabilty. According to the purpose of the rock mass classification for tunnels tunneling by TBM and the features of the TBM cutting process, this paper suggests two systems to classify the rock mass: (a) the rock mass boreability classification system for estimating how difficulty the rock mass are bored by TBM and (b) the rock mass quality classification system for estimating the stability of surrounding rock mass. The factors which are used to classify the rock mass boreability group in the system (a) are lithology, weathering degree and joint characters. The factors which are used to classify the rock mass quality in the system (b) are factors which will cause geological problems in the cutting process. The system (a) predicts the net penetration rate (PR) of the TBM, the system (b) evaluates the utilization (U) of the TBM, then the advance rate (AR) of the TBM is calculated by PR and U.
Taking the TBM performance in four tunnels as case examples, this paper analyzes the two reasons that there are problems in using the conventional rock mass quality classification systems to predict the TBM performance. The first reason is the factors which control the rock mass quality are not the factors that influence the rock mass boreability. The second is that most of the factors in rock mass classification systems are semi-quantitative. As a result of the two reasons, the value of the rock mass quality cannot reflect the rock mass boreabilty. According to the purpose of the rock mass classification for tunnels tunneling by TBM and the features of the TBM cutting process, this paper suggests two systems to classify the rock mass: (a) the rock mass boreability classification system for estimating how difficulty the rock mass are bored by TBM and (b) the rock mass quality classification system for estimating the stability of surrounding rock mass. The factors which are used to classify the rock mass boreability group in the system (a) are lithology, weathering degree and joint characters. The factors which are used to classify the rock mass quality in the system (b) are factors which will cause geological problems in the cutting process. The system (a) predicts the net penetration rate (PR) of the TBM, the system (b) evaluates the utilization (U) of the TBM, then the advance rate (AR) of the TBM is calculated by PR and U.
2008, 16(4): 476-481.
At a transformer substation in northeastern Yunnan Province, a slope was filled for sufficient constructing areas. The fill slope was composed of Quaternary accumulative formation and underlain Triassic detrital rock. The materials of the upper layer were predominated with accumulative formation such as landfill, gardening soil and silty clay The upper layer was underlain by a thin layer composed of completely to highly weathered mudstone. It was prone to become softer and its strength could be reduced significantly when moisturized. The lower layer was composed of packsand. After a period of heavy rainfalls, the fill slope started to creep and deform, which threatened the safety of the transformer substation, dead end tower of 110 kv output power. This paper described the geological environmental background of the northern slope on the 220kV Yanjin transformer substation. It further presented a detailed analysis of deformation mechanism through field investigation and laboratory testing. The slope deformation was probably caused by a combination effect of unfavorable topographic, geological and hydro geological conditions, and external loading due to filling. It was concluded that the creep deformation of the slope was triggered by external loading applied at the back of the slope.
At a transformer substation in northeastern Yunnan Province, a slope was filled for sufficient constructing areas. The fill slope was composed of Quaternary accumulative formation and underlain Triassic detrital rock. The materials of the upper layer were predominated with accumulative formation such as landfill, gardening soil and silty clay The upper layer was underlain by a thin layer composed of completely to highly weathered mudstone. It was prone to become softer and its strength could be reduced significantly when moisturized. The lower layer was composed of packsand. After a period of heavy rainfalls, the fill slope started to creep and deform, which threatened the safety of the transformer substation, dead end tower of 110 kv output power. This paper described the geological environmental background of the northern slope on the 220kV Yanjin transformer substation. It further presented a detailed analysis of deformation mechanism through field investigation and laboratory testing. The slope deformation was probably caused by a combination effect of unfavorable topographic, geological and hydro geological conditions, and external loading due to filling. It was concluded that the creep deformation of the slope was triggered by external loading applied at the back of the slope.
2008, 16(4): 482-488.
This paper examines a high slope at the portal of a compressed highway tunnel with shallow depth in south Anhui province. The construction design of zero excavation is proposed to maximally protect the geological environment and prevent the large-scale geological disasters. The necessary reinforcement measures are used by taking intco consideration of the site engineering geological conditions. The site engineering geological conditions are investigated systematically. Then the types and causes of rock mass structures and the combination between structural planes and slope surface are studied in detail so as to analyze the slope deformation mechanism. A geological model of this high slope is described with engineering geological profile. The detailed descriptions of the geological sketches are conducted. It is demonstrated that the slope deformation is always initiated by the non-uniform compression of the unconsolidated rock mass, leading to ladder sliding along the combination between structure planes with high dip angles and structure planes with low dip angles paralleling with slope. The ladder sliding makes greater stress to the structures and surrounding rocks of the tunnel. Failures can occur when the supplementary pressure exceeds their strengths, which will induce great geohazards. The result of FLAC3D numerical modeling indicates that the stress concentration distributes along the unconsolidated rock mass near the inside of this tunnel. The tensile stress zone can occur in the upper rock mass. Based on the analysis, before tunnel excavation, reinforcement measures should to be implemented to avoid stress concentrations on the tunnel structure and surrounding rocks.
This paper examines a high slope at the portal of a compressed highway tunnel with shallow depth in south Anhui province. The construction design of zero excavation is proposed to maximally protect the geological environment and prevent the large-scale geological disasters. The necessary reinforcement measures are used by taking intco consideration of the site engineering geological conditions. The site engineering geological conditions are investigated systematically. Then the types and causes of rock mass structures and the combination between structural planes and slope surface are studied in detail so as to analyze the slope deformation mechanism. A geological model of this high slope is described with engineering geological profile. The detailed descriptions of the geological sketches are conducted. It is demonstrated that the slope deformation is always initiated by the non-uniform compression of the unconsolidated rock mass, leading to ladder sliding along the combination between structure planes with high dip angles and structure planes with low dip angles paralleling with slope. The ladder sliding makes greater stress to the structures and surrounding rocks of the tunnel. Failures can occur when the supplementary pressure exceeds their strengths, which will induce great geohazards. The result of FLAC3D numerical modeling indicates that the stress concentration distributes along the unconsolidated rock mass near the inside of this tunnel. The tensile stress zone can occur in the upper rock mass. Based on the analysis, before tunnel excavation, reinforcement measures should to be implemented to avoid stress concentrations on the tunnel structure and surrounding rocks.
2008, 16(4): 489-494.
A new laboratory equipment called High Pressure Permeability Testing Machine is used in this study. The Static Servo Valve is the main control apparatus. It can make the inlet water pressure of the sample stable when this is no computer control. The sample seepage outlet water pressure value can be controlled by speed control valve. The long time water and rock interaction test under high seepage pressure is then achieved. On the basis of this machine, this paper puts forward the different phase ion concentration studying method of water-rock reaction seepage solution. The penetrability change rule of the sample in different phases can be acquired. In order to study the rock strength characteristics influenced by water and rock reaction, with almost the same conditions, the conventional triaxial experiments under high seepage pressure have been conducted for the samples of passing and not passing by long time water and rock interaction. The effective confining pressure which approaches the sample destroying condition has been proposed to analyze the strength characteristics. In order to contrast the study, this paper also presents the conventional triaxial experiments of satiety water sample under the same actual and effective confining pressure values. On basis of the test results, the studied altered rocks have the similar characteristics under high seepage pressure, normal temperature and pressure. The reaction between altered rock and reservoir water is feebleness, which will not affect the rock mass penetrability and mechanics characteristics.
A new laboratory equipment called High Pressure Permeability Testing Machine is used in this study. The Static Servo Valve is the main control apparatus. It can make the inlet water pressure of the sample stable when this is no computer control. The sample seepage outlet water pressure value can be controlled by speed control valve. The long time water and rock interaction test under high seepage pressure is then achieved. On the basis of this machine, this paper puts forward the different phase ion concentration studying method of water-rock reaction seepage solution. The penetrability change rule of the sample in different phases can be acquired. In order to study the rock strength characteristics influenced by water and rock reaction, with almost the same conditions, the conventional triaxial experiments under high seepage pressure have been conducted for the samples of passing and not passing by long time water and rock interaction. The effective confining pressure which approaches the sample destroying condition has been proposed to analyze the strength characteristics. In order to contrast the study, this paper also presents the conventional triaxial experiments of satiety water sample under the same actual and effective confining pressure values. On basis of the test results, the studied altered rocks have the similar characteristics under high seepage pressure, normal temperature and pressure. The reaction between altered rock and reservoir water is feebleness, which will not affect the rock mass penetrability and mechanics characteristics.
2008, 16(4): 495-501.
Based on a series of one-dimensional consolidation tests, the characteristics of creep deformation and secondary consolidation of Shanghai undisturbed soft soils were studied for different load ratios, different load velocity and overload pre-pressure. The test results showed that, creep deformation increased along with the increase of stress level and load velocity. For a constant stress level, the creep deformation decreased with the increase of load ratios. The creep deformation presented non-line characteristic and transferred from visco-elasticity to visco-plasticity while stress increased. When load ratios were high, the transformation was obviously. The parameter of Metchell one-dimensional model could be gotten by simulating experimental data and the curves tally with experimental data.It could be drawn from the analysis of testing data that for normally consolidated soils, the coefficient of secondary consolidation Ca wasn't affected by stress level and load ratios obviously, but it was related to load velocity closely. When the load velocity increased, Ca increased rapidly and then decreased slightly with stress rising. In addition, surcharge preloading can decrease the value of Ca and thereby is propitious for reducing the construction settlement.
Based on a series of one-dimensional consolidation tests, the characteristics of creep deformation and secondary consolidation of Shanghai undisturbed soft soils were studied for different load ratios, different load velocity and overload pre-pressure. The test results showed that, creep deformation increased along with the increase of stress level and load velocity. For a constant stress level, the creep deformation decreased with the increase of load ratios. The creep deformation presented non-line characteristic and transferred from visco-elasticity to visco-plasticity while stress increased. When load ratios were high, the transformation was obviously. The parameter of Metchell one-dimensional model could be gotten by simulating experimental data and the curves tally with experimental data.It could be drawn from the analysis of testing data that for normally consolidated soils, the coefficient of secondary consolidation Ca wasn't affected by stress level and load ratios obviously, but it was related to load velocity closely. When the load velocity increased, Ca increased rapidly and then decreased slightly with stress rising. In addition, surcharge preloading can decrease the value of Ca and thereby is propitious for reducing the construction settlement.
2008, 16(4): 502-506.
The dynamic modulus tests of cyclical tri-axial loading with increasing and decreasing amplitudes were carried out for silty soils from one site in Taiyuan city and five sites in Handan city. The test results show that the speed of decrease in the dynamic modulus with the increase of the shear strain for the silty soils from different sites was slower, compared with sandy soil. The plastic threshold is found to be equal to 85% of Emax. So the amplitudes of cyclical loading were reduced just before the dynamic modulus gets to 85% Emax. As a result, the dynamic modulus would mostly return to the initial value. Variations of the clay contents have different functions. The dynamic strength of silty soils at their original conditions decreases with the increase of clay contents when the clay content is less than 10%. The dynamic strength of silty soil at their original conditions increases with the increase of clay contents when the clay content is more than 10%.
The dynamic modulus tests of cyclical tri-axial loading with increasing and decreasing amplitudes were carried out for silty soils from one site in Taiyuan city and five sites in Handan city. The test results show that the speed of decrease in the dynamic modulus with the increase of the shear strain for the silty soils from different sites was slower, compared with sandy soil. The plastic threshold is found to be equal to 85% of Emax. So the amplitudes of cyclical loading were reduced just before the dynamic modulus gets to 85% Emax. As a result, the dynamic modulus would mostly return to the initial value. Variations of the clay contents have different functions. The dynamic strength of silty soils at their original conditions decreases with the increase of clay contents when the clay content is less than 10%. The dynamic strength of silty soil at their original conditions increases with the increase of clay contents when the clay content is more than 10%.
2008, 16(4): 507-511.
Marine sediment clay has higher creep characteristic. Traditional rheological constitutive models built under each level loading are impractical and hard to describe the nonlinear properties of rheology of rock and soil really. So, the BP neural network is introduced in the text. It has strong nonlinear mapping ability and fault-tolerance ability. Through improving the algorithm of BP, the BP constitutive model is built directly. The model is based on the creep data of laboratory direct shear experiment. It could avoid building a necessary complex constitutive equation in order to meeting the variable law of trial curve and creep character. At the end, the modeling method is tested by the creep experimental data of soft clay of Shanghai and the features of BP neural network rheological model on describing creep curves of soft clay are discussed. It is shown that the rheological model is simple and can effectively describe nonlinear creep of soil clay with better prediction.
Marine sediment clay has higher creep characteristic. Traditional rheological constitutive models built under each level loading are impractical and hard to describe the nonlinear properties of rheology of rock and soil really. So, the BP neural network is introduced in the text. It has strong nonlinear mapping ability and fault-tolerance ability. Through improving the algorithm of BP, the BP constitutive model is built directly. The model is based on the creep data of laboratory direct shear experiment. It could avoid building a necessary complex constitutive equation in order to meeting the variable law of trial curve and creep character. At the end, the modeling method is tested by the creep experimental data of soft clay of Shanghai and the features of BP neural network rheological model on describing creep curves of soft clay are discussed. It is shown that the rheological model is simple and can effectively describe nonlinear creep of soil clay with better prediction.
2008, 16(4): 512-517.
It is very necessary to determine reasonable reinforced area and no reinforced area in slope engineering. Design scheme is often verified and adjusted in the process of construction. The reinforcement demand degree analysis is a new method. It can combine major factors of affecting slope stability with actual displacement monitoring results at the site, and also can find adequate design results by expert experience and knowledge. This reinforcement demand degree analysis is applied to the slope stability on the right bank of a hydropower station. The analysis adopts affecting weight values, and reaches reinforcement demand degree for each part of the slope during the period of construction. The application has obtained the best results.
It is very necessary to determine reasonable reinforced area and no reinforced area in slope engineering. Design scheme is often verified and adjusted in the process of construction. The reinforcement demand degree analysis is a new method. It can combine major factors of affecting slope stability with actual displacement monitoring results at the site, and also can find adequate design results by expert experience and knowledge. This reinforcement demand degree analysis is applied to the slope stability on the right bank of a hydropower station. The analysis adopts affecting weight values, and reaches reinforcement demand degree for each part of the slope during the period of construction. The application has obtained the best results.
2008, 16(4): 518-521.
Deformation monitoring is one of the main contents in slope monitoring. Deformation prediction is one of the main technical problems. The current deformation prediction models have limitations. For example, the neural network predicting model needs massive data as study pieces and grey model requests that the original data must meet the exponent rule. A back propagation neural network prediction model and grey system GM(1,1) model for slope deformation are built. In order to gain more accurate prediction results, a weighted function combining forecasting model of neural network and grey system on slope deformation is developed and a dynamic programming method is used to solve multi-step decision problem, which can minimize the square sum of the relative errors and gain the combination weight. So, the predicting result can greatly enhance the precision and make up the limitation of single method. Through calculating an actual slope the predicting results develop greatly and consistent with the monitoring data. The combining predicting model enriches the slope deformation prediction theory.
Deformation monitoring is one of the main contents in slope monitoring. Deformation prediction is one of the main technical problems. The current deformation prediction models have limitations. For example, the neural network predicting model needs massive data as study pieces and grey model requests that the original data must meet the exponent rule. A back propagation neural network prediction model and grey system GM(1,1) model for slope deformation are built. In order to gain more accurate prediction results, a weighted function combining forecasting model of neural network and grey system on slope deformation is developed and a dynamic programming method is used to solve multi-step decision problem, which can minimize the square sum of the relative errors and gain the combination weight. So, the predicting result can greatly enhance the precision and make up the limitation of single method. Through calculating an actual slope the predicting results develop greatly and consistent with the monitoring data. The combining predicting model enriches the slope deformation prediction theory.
2008, 16(4): 522-527.
Based on the strength reduction theory, the factor of safety K of high slope structure is calculated using finite element method (FEM) (software -MIDAS/GTS). The sliding strip of slope structure is found at first. The input data and the output data used in the FEM are disposed again. Then the relation f1 (and f3) between basic random variables c,f and 1 (and 3), which are most (and least) main stress, may be found. So, the high slope structural function Z can be changed into explicit form from the original implicit form using above relation f1 and f3. Based on this explicit function Z, the reliability index 1 of each failure element within a sliding strip is computed using Monte Carlo method. The area Ai of above element is taken as weight coefficient. Then the slope structural whole reliability index can be given based on the mean value, which is the result of all the failure elements i multiplied by Ai . The result of example shows that the present method is reasonable and feasible. It may simplify the computation program of slope structural whole reliability. And it can also be taken as a theory reference in high slope structural stability analysis.
Based on the strength reduction theory, the factor of safety K of high slope structure is calculated using finite element method (FEM) (software -MIDAS/GTS). The sliding strip of slope structure is found at first. The input data and the output data used in the FEM are disposed again. Then the relation f1 (and f3) between basic random variables c,f and 1 (and 3), which are most (and least) main stress, may be found. So, the high slope structural function Z can be changed into explicit form from the original implicit form using above relation f1 and f3. Based on this explicit function Z, the reliability index 1 of each failure element within a sliding strip is computed using Monte Carlo method. The area Ai of above element is taken as weight coefficient. Then the slope structural whole reliability index can be given based on the mean value, which is the result of all the failure elements i multiplied by Ai . The result of example shows that the present method is reasonable and feasible. It may simplify the computation program of slope structural whole reliability. And it can also be taken as a theory reference in high slope structural stability analysis.
2008, 16(4): 528-532.
Firstly, the Shanxi formation coal seam sections and hydrogeological features were analysed. Based on characteristic of the associated mining of multi-coal seams and the engineering geological characteristics of overburden, the mining impact pattern of multi-coal seam mining and the dynamic fracture mechanism of overburden were characterized. A comprehensive research method combining engineering geological mechanical model test and finite element numerical simulation was applied. The related strata movement parameters, stress distribution and influence area of multi-coal seam mining were obtained as follows: strike boundary angle=62, full extraction coefficient=0.95, the greatest subsidence angle=82, horizontal movement factor=0.39, and deviation of inflection point /mining deep=0.12. The stress distribution of multi-coal seam mining was analysed. The stress concentrated locations at the roof, bottom and surround rocks were determined. The maximum stress concentrations were on the coal wall lines. The bottom stresses tended to transfer into the coal pillar. The development height of caving zone and water flowing fractured zone of multi-coal seam mining were calculated. They were 32 m and 81.5m respectively. The assess of influence degree of coal layer safety mining was that, for the area of influence of height of crack belt reached to the belt of weathering, which didn't form the transfixion, and it penetrated the clay layer partially, there existed the possibility of sand boil when stoping. Some measures for mine water prevention and control should be used. The method of small work face, mining separate layers, mining thickness below the local strictly limit should be adopted. The results were confirmed with the field tests and assured that no geologic hazard would occur.
Firstly, the Shanxi formation coal seam sections and hydrogeological features were analysed. Based on characteristic of the associated mining of multi-coal seams and the engineering geological characteristics of overburden, the mining impact pattern of multi-coal seam mining and the dynamic fracture mechanism of overburden were characterized. A comprehensive research method combining engineering geological mechanical model test and finite element numerical simulation was applied. The related strata movement parameters, stress distribution and influence area of multi-coal seam mining were obtained as follows: strike boundary angle=62, full extraction coefficient=0.95, the greatest subsidence angle=82, horizontal movement factor=0.39, and deviation of inflection point /mining deep=0.12. The stress distribution of multi-coal seam mining was analysed. The stress concentrated locations at the roof, bottom and surround rocks were determined. The maximum stress concentrations were on the coal wall lines. The bottom stresses tended to transfer into the coal pillar. The development height of caving zone and water flowing fractured zone of multi-coal seam mining were calculated. They were 32 m and 81.5m respectively. The assess of influence degree of coal layer safety mining was that, for the area of influence of height of crack belt reached to the belt of weathering, which didn't form the transfixion, and it penetrated the clay layer partially, there existed the possibility of sand boil when stoping. Some measures for mine water prevention and control should be used. The method of small work face, mining separate layers, mining thickness below the local strictly limit should be adopted. The results were confirmed with the field tests and assured that no geologic hazard would occur.
2008, 16(4): 533-538.
It is to predict the settlement of soft soil foundation under reservoir dam and to study the law of settlement of soft soil foundation and the law of dissipation of pore water pressure. A plane-strain FEM model was established to analyze the settlement of soft soil foundation for reservoir dam. The results showed that the settlement of soft soil foundation included initial stages, quick stages and slow stages. The laws governing the settlement and the dissipation of pore water pressure could be described with the Hill model and the Expdec2 model, respectively. The maximum of settlement and the additional settlement due to dam mass and the maximum of horizontal displacement were obtained. The results can offer an important reference to the construction of dam and the subsidence of similar soft soil foundation.
It is to predict the settlement of soft soil foundation under reservoir dam and to study the law of settlement of soft soil foundation and the law of dissipation of pore water pressure. A plane-strain FEM model was established to analyze the settlement of soft soil foundation for reservoir dam. The results showed that the settlement of soft soil foundation included initial stages, quick stages and slow stages. The laws governing the settlement and the dissipation of pore water pressure could be described with the Hill model and the Expdec2 model, respectively. The maximum of settlement and the additional settlement due to dam mass and the maximum of horizontal displacement were obtained. The results can offer an important reference to the construction of dam and the subsidence of similar soft soil foundation.
2008, 16(4): 539-545.
Based on the distinct element method of particle flow, a specimen with weak seam of Particle Flow Code (PFC) model is made by using the contact-bond model and the slip model. The numerical model test is carried on with different weak seam parameters. Then the paper discusses contrasting failure process and form under different weak seam thickness as well as different inclination angle conditions, and analyzes the influence to specimen strength. Simulation result indicates that fissures are produced first in weak seam and then are expanded with loading, which presents the typical progressive failure process. When the weak seam is thicker and its obliquity is steeper, the specimen presenting the feature to slide along with the weak seam becomes more obvious. But if it is thin and small, the weak seam doesn't dominate the destroying of the specimen. The thickness and obliquity of the weak seam have influence on the specimen peak strength. The peak strength is decreased when the thickness and obliquity are increased. The relation between the kind of failure characteristic and the geometric parameters is obtained from the numerical simulation. This relation offers a further understanding about mechanical property of weak seam and progressive failure.
Based on the distinct element method of particle flow, a specimen with weak seam of Particle Flow Code (PFC) model is made by using the contact-bond model and the slip model. The numerical model test is carried on with different weak seam parameters. Then the paper discusses contrasting failure process and form under different weak seam thickness as well as different inclination angle conditions, and analyzes the influence to specimen strength. Simulation result indicates that fissures are produced first in weak seam and then are expanded with loading, which presents the typical progressive failure process. When the weak seam is thicker and its obliquity is steeper, the specimen presenting the feature to slide along with the weak seam becomes more obvious. But if it is thin and small, the weak seam doesn't dominate the destroying of the specimen. The thickness and obliquity of the weak seam have influence on the specimen peak strength. The peak strength is decreased when the thickness and obliquity are increased. The relation between the kind of failure characteristic and the geometric parameters is obtained from the numerical simulation. This relation offers a further understanding about mechanical property of weak seam and progressive failure.
2008, 16(4): 546-550.
The tunnel rock mass has a complex stress state. It is important for tunnel rock mass stability analysis that the rock mass failure region distribution during construction is evaluated appropriately. The yield approach index is proposed in the paper to evaluate the rock mass failure extent, which is suitable for the rock mass stress failure probability under complex stress state. The Mohr-Coulomb type rockmass material is used in the paper to deduce corresponding calculation equations for yield approach index. The numerical method for the calculation of yield approach index is implemented in nonlinear finite element software user subroutine. In the Ganzhou-Longyan mongline railway tunnel construction process between DKl33+095 and DKl38+237, the wet-sprayed fiber reinforced concrete lining structure is used as the first stage lining structural and the step tunnel excavation lining construction process is used. To evaluate the tunnel rock mass failure zone evolution during tunnel construction, the nonlinear finite element analysis with consideration of rock mass yield approach index is performed for the railway tunnel first stage lining construction process using the wet-sprayed fiber reinforced concrete lining structure. The rock mass failure index evolution during construction process is analyzed and the tunnel rock mass stability is determined during step tunnel excavation lining construction process. The numerical result shows that the rock mass failure zone mainly exists during the bottom step construction process. The yield approach index for rock mass failure estimation provides more information than that of common rock mass plastic zone distribution. This index is useful for the engineers to evaluate the tunnel excavation and lining plan quantitatively.
The tunnel rock mass has a complex stress state. It is important for tunnel rock mass stability analysis that the rock mass failure region distribution during construction is evaluated appropriately. The yield approach index is proposed in the paper to evaluate the rock mass failure extent, which is suitable for the rock mass stress failure probability under complex stress state. The Mohr-Coulomb type rockmass material is used in the paper to deduce corresponding calculation equations for yield approach index. The numerical method for the calculation of yield approach index is implemented in nonlinear finite element software user subroutine. In the Ganzhou-Longyan mongline railway tunnel construction process between DKl33+095 and DKl38+237, the wet-sprayed fiber reinforced concrete lining structure is used as the first stage lining structural and the step tunnel excavation lining construction process is used. To evaluate the tunnel rock mass failure zone evolution during tunnel construction, the nonlinear finite element analysis with consideration of rock mass yield approach index is performed for the railway tunnel first stage lining construction process using the wet-sprayed fiber reinforced concrete lining structure. The rock mass failure index evolution during construction process is analyzed and the tunnel rock mass stability is determined during step tunnel excavation lining construction process. The numerical result shows that the rock mass failure zone mainly exists during the bottom step construction process. The yield approach index for rock mass failure estimation provides more information than that of common rock mass plastic zone distribution. This index is useful for the engineers to evaluate the tunnel excavation and lining plan quantitatively.
2008, 16(4): 551-556.
With respect to the characteristics of the special soft-soil along an expressway in northern Jiangsu province, the CMSC firming agent was synthesized with ingredient method of full powder by adopting two projects and added into soil with given proportion. Meanwhile, considering the local hydrologic and climatic factors and aiming at the conservative soaking condition, a new hit canister was invented. The soils improved with the CMSC firming agent were compacted in the new hit canister. The compacted samples were taken out and cured. When the curing time was mature, they should be soaked into the water with the new soaking equipment. At last, the pluging test was conducted. It indicated that the compacted samples were saturated within three-dimensional soaking condition. The CBR value was ensured its credibility within this new soaking condition which was closer to the actual situation. The engineering properties of soil improved with CMSC firming agent were better than lime-improved soil. The optimum proportion of CMSC firming agent could be obtained and the improving mechanism of CMSC soil firming agent were studied further more. The results could be used for reference to further study and engineering application.
With respect to the characteristics of the special soft-soil along an expressway in northern Jiangsu province, the CMSC firming agent was synthesized with ingredient method of full powder by adopting two projects and added into soil with given proportion. Meanwhile, considering the local hydrologic and climatic factors and aiming at the conservative soaking condition, a new hit canister was invented. The soils improved with the CMSC firming agent were compacted in the new hit canister. The compacted samples were taken out and cured. When the curing time was mature, they should be soaked into the water with the new soaking equipment. At last, the pluging test was conducted. It indicated that the compacted samples were saturated within three-dimensional soaking condition. The CBR value was ensured its credibility within this new soaking condition which was closer to the actual situation. The engineering properties of soil improved with CMSC firming agent were better than lime-improved soil. The optimum proportion of CMSC firming agent could be obtained and the improving mechanism of CMSC soil firming agent were studied further more. The results could be used for reference to further study and engineering application.
2008, 16(4): 557-562.
Physical and mechanical properties of loess are very poor. The loess has big aperture, strong wet subsidence, and low intensity. The complex and varied terrains and landforms of loess regions can result in a lot of disease of road tunnels in loess during construction. According to the characteristics of distresses in the road tunnel in Qijia mountain, the thickness, cavity distribution, crevice water were detected with geo-radar. Material of lining was nondestructively detected with sound locater. Limiting structure of the tunnel was detected with a circumscription apparatus. Based on detected results, causes of the distresses were analyzed. Three treatment schemes were put forward by slurry injection from the back of lining structure, lining reinforcement, treating the water proof system. Stability of surrounding rock and the state of forces of the lining structure were analyzed before and after the treatment. It is showed that the treatment scheme of the tunnel is feasible. Taken construction and cost estimate into account, an optimal scheme is obtained.
Physical and mechanical properties of loess are very poor. The loess has big aperture, strong wet subsidence, and low intensity. The complex and varied terrains and landforms of loess regions can result in a lot of disease of road tunnels in loess during construction. According to the characteristics of distresses in the road tunnel in Qijia mountain, the thickness, cavity distribution, crevice water were detected with geo-radar. Material of lining was nondestructively detected with sound locater. Limiting structure of the tunnel was detected with a circumscription apparatus. Based on detected results, causes of the distresses were analyzed. Three treatment schemes were put forward by slurry injection from the back of lining structure, lining reinforcement, treating the water proof system. Stability of surrounding rock and the state of forces of the lining structure were analyzed before and after the treatment. It is showed that the treatment scheme of the tunnel is feasible. Taken construction and cost estimate into account, an optimal scheme is obtained.
2008, 16(4): 563-566.
The composite grid foundation is a type of lateral confined structure composite grid foundation. This paper presents some loading experiments and other tests on the composite grid foundations. The test the results show that the deformation of grid structure is restricted. The deformation of grid structure foundation is reduced. The deformation of the foundation soil is restricted. The stress in the foundation soil has the regulation of the concentration and the increment with respect to the ratio of stress sharing.
The composite grid foundation is a type of lateral confined structure composite grid foundation. This paper presents some loading experiments and other tests on the composite grid foundations. The test the results show that the deformation of grid structure is restricted. The deformation of grid structure foundation is reduced. The deformation of the foundation soil is restricted. The stress in the foundation soil has the regulation of the concentration and the increment with respect to the ratio of stress sharing.
2008, 16(4): 567-571.
The marine soft soils in coastal area of Shenzhen region were generally exhibited characteristics of high water content, high compressibility, low strength, low bearing capacity and strong structural characteristics. The theory of consolidation and the calculation of settlement were analysed preliminarily. Some critical problems such as soil parameters, overloading and differential settlement, requiring attention during the theoretical calculations, were then presented. Several technical measures such as preloading, composite foundation and riprap and displacement methods can be adopted for reinforcing the marine soft soil under corresponding special engineering conditions. These measures have been testified to be very effective.
The marine soft soils in coastal area of Shenzhen region were generally exhibited characteristics of high water content, high compressibility, low strength, low bearing capacity and strong structural characteristics. The theory of consolidation and the calculation of settlement were analysed preliminarily. Some critical problems such as soil parameters, overloading and differential settlement, requiring attention during the theoretical calculations, were then presented. Several technical measures such as preloading, composite foundation and riprap and displacement methods can be adopted for reinforcing the marine soft soil under corresponding special engineering conditions. These measures have been testified to be very effective.
2008, 16(4): 572-576.
A new technique of two times adding quicklime for improving soft-soils was developed and used during Jiangsu expressway construction. It not only settled effectively the problems of soft soil smashed difficulty, gray-doped uneven, and slow construction, and in-effect of quicklime, but also increased the strength of quicklime mixed -soft soils. The test results show that the CBR value of lime-soil mixtures increases by 6% to 8%. This paper examines the mechanism of the technique. At the first time, when it is added to soft soils, the quicklime absorbs the soil moisture and evaporates the soil moisture by the heat of quicklime degradation, and leads to ions exchange. At the second time, when it is further added to the pre-treated soft-soils, the quicklime increases further the volcanic ash and ion exchange, forms new crystals and structure, and subsequently, improves the strength and stability of the lime-soil mixture through the compaction of lime and soft soil.
A new technique of two times adding quicklime for improving soft-soils was developed and used during Jiangsu expressway construction. It not only settled effectively the problems of soft soil smashed difficulty, gray-doped uneven, and slow construction, and in-effect of quicklime, but also increased the strength of quicklime mixed -soft soils. The test results show that the CBR value of lime-soil mixtures increases by 6% to 8%. This paper examines the mechanism of the technique. At the first time, when it is added to soft soils, the quicklime absorbs the soil moisture and evaporates the soil moisture by the heat of quicklime degradation, and leads to ions exchange. At the second time, when it is further added to the pre-treated soft-soils, the quicklime increases further the volcanic ash and ion exchange, forms new crystals and structure, and subsequently, improves the strength and stability of the lime-soil mixture through the compaction of lime and soft soil.
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