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Editor Work2011 Vol. 19, No. 2
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2011, 19(2): 145-151.
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It was 3 years since the Wenchuan earthquake.A lot of domestic and foreign scholars have conducted a great deal of work on the development and distribution patterns,formation mechanisms and prevention strategies of the geohazards triggered by the Wenchuan earthquake,and have published a lot of research results.Since the frequency and scale of increased markedly,especially in 2010,many researchers are beginning to pay close attention to the occurrence rules,activity trends and duration of geohazards triggered by rainfalls after the Wenchuan earthquake.This paper collected the data pre-and post-earthquake,and analyzed the characteristics and occurrence rules of major geohazards triggered by rainfalls in the last 3years in the Wenchuan earthquake area.Based on this,the duration,activity trends and high risk areas of geohzards in the Wenchuan earthquake areas were analyzed.The preliminary study results indicate geohazard activity in theWenchuan erathquake area will keep still intense in future 20-25 years.In this period of time,geohazard activity level appeared to decline in shock with the cycle of every four or five years.After that,the geological condition will be gradually stable.The high geohazards risk areas will be mainly distributed along the Yingxiu-Beichuan fault,especially in the sections of Genda-Yingxiu in Wenchuan county,Xiaoyudong in Pengzhou county,Hongbai,Shifang county-Chaping,Anxian county,Leigu-Chenjiaba in Beichuan county and Donghekou-Woqian in Qingchuan county.
It was 3 years since the Wenchuan earthquake.A lot of domestic and foreign scholars have conducted a great deal of work on the development and distribution patterns,formation mechanisms and prevention strategies of the geohazards triggered by the Wenchuan earthquake,and have published a lot of research results.Since the frequency and scale of increased markedly,especially in 2010,many researchers are beginning to pay close attention to the occurrence rules,activity trends and duration of geohazards triggered by rainfalls after the Wenchuan earthquake.This paper collected the data pre-and post-earthquake,and analyzed the characteristics and occurrence rules of major geohazards triggered by rainfalls in the last 3years in the Wenchuan earthquake area.Based on this,the duration,activity trends and high risk areas of geohzards in the Wenchuan earthquake areas were analyzed.The preliminary study results indicate geohazard activity in theWenchuan erathquake area will keep still intense in future 20-25 years.In this period of time,geohazard activity level appeared to decline in shock with the cycle of every four or five years.After that,the geological condition will be gradually stable.The high geohazards risk areas will be mainly distributed along the Yingxiu-Beichuan fault,especially in the sections of Genda-Yingxiu in Wenchuan county,Xiaoyudong in Pengzhou county,Hongbai,Shifang county-Chaping,Anxian county,Leigu-Chenjiaba in Beichuan county and Donghekou-Woqian in Qingchuan county.
2011, 19(2): 152-161.
On March 10, 2011,a Ms5.8 earthquake,focal depth 10km,struck Yingjiang county locating on Dehong Autonomous Prefecture of Yunnan province closed to Sino-Burna border,induced 25 persons killed, 250 injured,about 130 thousand people affected,many institutions(building)damaged,extensive liquefaction developed,about 19km Yingjiang embankment cracked.Such greater secondary disasters trigged by a Ms 5.8 earthquake is rare in recent seismic events.By analyzing the geological background of the earthquake and investigating geological hazards,this paper obtained an initial understanding of geo-hazards: (1)This earthquake is the results of continue enhance of Yingjiang scale 4 earthquake swarm beginning in 2011; in recent years,seismic swarm in Yingjiang region present a gradual migration from north to south along Sudian Fault; this earthquake is a continuation of this trend; the main shock and aftershocks show that Yingjing co-seismic rupture is a conjugate rupture between Shudian Fault and Dayingjing Fault.(2)Sand liquefaction is one of main reasons that this earthquake induced so severe loss.Sand liquefaction products lots of secondary geo-hazard phenomenon,sand and water blasting to the surface,sliding along the lateral ramp,ground cracking and subsidence,et al., which results in greater damages to houses,river banks,roads,water facilities and electric poles and other agencies.(3)Sand liquefaction are mainly developed in Dayingjiang Holocene alluvial deposits of fine sand,serious liquefied area is the Dayingjiang old river channel,construction(building)damaged area and degree is better accord with the extent and degree of liquefaction.The late Pleistocene as the second terrace of Yingjiang is not only high altitude,better flood resistance capacity,but also strong engineering geological conditions for non-liquefaction,so where is the better place as the planning development area of the local towns.
On March 10, 2011,a Ms5.8 earthquake,focal depth 10km,struck Yingjiang county locating on Dehong Autonomous Prefecture of Yunnan province closed to Sino-Burna border,induced 25 persons killed, 250 injured,about 130 thousand people affected,many institutions(building)damaged,extensive liquefaction developed,about 19km Yingjiang embankment cracked.Such greater secondary disasters trigged by a Ms 5.8 earthquake is rare in recent seismic events.By analyzing the geological background of the earthquake and investigating geological hazards,this paper obtained an initial understanding of geo-hazards: (1)This earthquake is the results of continue enhance of Yingjiang scale 4 earthquake swarm beginning in 2011; in recent years,seismic swarm in Yingjiang region present a gradual migration from north to south along Sudian Fault; this earthquake is a continuation of this trend; the main shock and aftershocks show that Yingjing co-seismic rupture is a conjugate rupture between Shudian Fault and Dayingjing Fault.(2)Sand liquefaction is one of main reasons that this earthquake induced so severe loss.Sand liquefaction products lots of secondary geo-hazard phenomenon,sand and water blasting to the surface,sliding along the lateral ramp,ground cracking and subsidence,et al., which results in greater damages to houses,river banks,roads,water facilities and electric poles and other agencies.(3)Sand liquefaction are mainly developed in Dayingjiang Holocene alluvial deposits of fine sand,serious liquefied area is the Dayingjiang old river channel,construction(building)damaged area and degree is better accord with the extent and degree of liquefaction.The late Pleistocene as the second terrace of Yingjiang is not only high altitude,better flood resistance capacity,but also strong engineering geological conditions for non-liquefaction,so where is the better place as the planning development area of the local towns.
2011, 19(2): 162-167.
The common two-dimensional(2D)methods for the driving forces of landslides don't consider the lateral variation and confinements,which can make the stabilization design un-precisely.Three-dimensional(3D)method can reflect the spatial distribution of the driving force of landslide.So it can resolve the problem of 2D methods.This paper provides a general formula for calculating the driving force of 3D landslide.It is based on the method of the general form of 3D equilibrium proposed by the authors. The paper presents case studies and a comparison between the 2D and 3D methods. Then,it obtains a distribution function of the lateral variation. This function reflects the spatial distribution of the driving force of 3D landslides,and makes slope stabilization design more reasonable.
The common two-dimensional(2D)methods for the driving forces of landslides don't consider the lateral variation and confinements,which can make the stabilization design un-precisely.Three-dimensional(3D)method can reflect the spatial distribution of the driving force of landslide.So it can resolve the problem of 2D methods.This paper provides a general formula for calculating the driving force of 3D landslide.It is based on the method of the general form of 3D equilibrium proposed by the authors. The paper presents case studies and a comparison between the 2D and 3D methods. Then,it obtains a distribution function of the lateral variation. This function reflects the spatial distribution of the driving force of 3D landslides,and makes slope stabilization design more reasonable.
2011, 19(2): 168-175.
Large rock slides e and then subsequent broken rock mass avalanches are one of the most destructive geological hazards in the world.Especially,the rock avalanches have intensive run-out ability and destructive power.This paper mainly studies the flow and deposition mechanism of rock landslide induced avalanche.Using a two-dimensional particle flow method,this paper numerically examines the influence of the original height,volume,slope angle and depositing substrate's frictional coefficient and waviness to avalanches.Numerical test results reveal that: (a)the flow and deposition process of a rock avalanche present a discrete and fluid-like nature; (b)increasing in the original height,the volume of rock avalanche and the slope angle would increase the maximum run-out length; and (c)increasing in the frictional coefficient and waviness of the deposition substrate would decrease the maximum run-out length.
Large rock slides e and then subsequent broken rock mass avalanches are one of the most destructive geological hazards in the world.Especially,the rock avalanches have intensive run-out ability and destructive power.This paper mainly studies the flow and deposition mechanism of rock landslide induced avalanche.Using a two-dimensional particle flow method,this paper numerically examines the influence of the original height,volume,slope angle and depositing substrate's frictional coefficient and waviness to avalanches.Numerical test results reveal that: (a)the flow and deposition process of a rock avalanche present a discrete and fluid-like nature; (b)increasing in the original height,the volume of rock avalanche and the slope angle would increase the maximum run-out length; and (c)increasing in the frictional coefficient and waviness of the deposition substrate would decrease the maximum run-out length.
2011, 19(2): 176-180.
In order to calculate and compare with the traditional rigid critical equilibrium method, this paper puts forward a new method of upper bound limit analysis for plane sliding of rock slope on the basis of limit analysis theory. By taking into consideration of the equivalent condition between the internal energy dissipation produced in the slip surface and the outer work done by external force, the upper bound solution for plane sliding of rock slope stability analysis can be deduced by means of strength reduction method. The new method can analyze different influencing factors including the hydrostatic pressure in back fissure, uplift pressure along slip surface, self-weight, horizontal seismic inertia force and anchorage force. The approaching channel inside slope of the spillway tunnel in the right bank of Jinping First Stage Hydropower Station is a typical multilevel step-shaped rock slope. The rock mass structure of the slope is stratified structure, and the potential mode of failure is plane sliding. The calculation results show that the new method of upper bound limit analysis is applicable to plane sliding of rock slope stability and is consistent with the rigid critical equilibrium method. Furthermore, it is a useful checking calculation approach for traditional method.
In order to calculate and compare with the traditional rigid critical equilibrium method, this paper puts forward a new method of upper bound limit analysis for plane sliding of rock slope on the basis of limit analysis theory. By taking into consideration of the equivalent condition between the internal energy dissipation produced in the slip surface and the outer work done by external force, the upper bound solution for plane sliding of rock slope stability analysis can be deduced by means of strength reduction method. The new method can analyze different influencing factors including the hydrostatic pressure in back fissure, uplift pressure along slip surface, self-weight, horizontal seismic inertia force and anchorage force. The approaching channel inside slope of the spillway tunnel in the right bank of Jinping First Stage Hydropower Station is a typical multilevel step-shaped rock slope. The rock mass structure of the slope is stratified structure, and the potential mode of failure is plane sliding. The calculation results show that the new method of upper bound limit analysis is applicable to plane sliding of rock slope stability and is consistent with the rigid critical equilibrium method. Furthermore, it is a useful checking calculation approach for traditional method.
2011, 19(2): 181-186.
More than one local minimum of the factor of safety can be encountered in stability analysis of complex slopes. So, how to obtain minimal factor of safety remains a significant issue in stability analysis of complex slopes. Based on simplified Bishop method, a new heuristic global optimization algorithm called Intelligent Single Particle Optimizer (ISPO) is proposed to search for the critical slip surface of complex slope in this paper. The simulated annealing mechanism is considered so as to help ISPO to escape from local minimums quickly. The ISPO with simulated annealing (SA) mechanism combines the merits of the two algorithms. The proposed algorithm is applied to searching for the critical slip surfaces of two complex slopes in the paper. Comparing with other methods, the results demonstrate that the combined SA-ISPO algorithm has sufficient calculating precision and stability, as well as high searching efficiency. And also the SA-ISPO has efficient global searching ability because the result is independent of searching range.
More than one local minimum of the factor of safety can be encountered in stability analysis of complex slopes. So, how to obtain minimal factor of safety remains a significant issue in stability analysis of complex slopes. Based on simplified Bishop method, a new heuristic global optimization algorithm called Intelligent Single Particle Optimizer (ISPO) is proposed to search for the critical slip surface of complex slope in this paper. The simulated annealing mechanism is considered so as to help ISPO to escape from local minimums quickly. The ISPO with simulated annealing (SA) mechanism combines the merits of the two algorithms. The proposed algorithm is applied to searching for the critical slip surfaces of two complex slopes in the paper. Comparing with other methods, the results demonstrate that the combined SA-ISPO algorithm has sufficient calculating precision and stability, as well as high searching efficiency. And also the SA-ISPO has efficient global searching ability because the result is independent of searching range.
2011, 19(2): 187-192.
It is very typical that wind erosion controls and influences the instability process of steep slope comprising layered soils at the mesa of Jiaohe Ruins in Turpan. Wind erosion caverns can be formed in the layered slope soils. They can further cause the slope to deform and failure. They are typically formed in the slopes with low anti-wind erosion capacity and together with the local climate characteristic of frequent gales. The paper employs the methods of engineering geology, experiment of wind tunnel, physical simulation and numerical simulation to analyze the slope instablity characteristics in terms of particularity, diversity and stages. It further validates the presence of forming and developing wind erosion caverns.It reveals the mechanism of differential wind erosions and deformation and failure mechanism of suspended soil masses. It provides some useful references for the controlling and monitoring of the deformation and failure in such steep slopes.
It is very typical that wind erosion controls and influences the instability process of steep slope comprising layered soils at the mesa of Jiaohe Ruins in Turpan. Wind erosion caverns can be formed in the layered slope soils. They can further cause the slope to deform and failure. They are typically formed in the slopes with low anti-wind erosion capacity and together with the local climate characteristic of frequent gales. The paper employs the methods of engineering geology, experiment of wind tunnel, physical simulation and numerical simulation to analyze the slope instablity characteristics in terms of particularity, diversity and stages. It further validates the presence of forming and developing wind erosion caverns.It reveals the mechanism of differential wind erosions and deformation and failure mechanism of suspended soil masses. It provides some useful references for the controlling and monitoring of the deformation and failure in such steep slopes.
2011, 19(2): 193-198.
This paper presents a study on the precision and reliability of landslide deformation monitoring with GPS-RTK technology.Some monitoring points were set on the landslide body.The GPS RTK technology,the three-dimension surveying technology by total station and the GPS single epoch positioning technology were used to monitor the deformation process from stable state to the failure of the landslide in real time. The results are further combined with large physical model experiment of one kind of landslides.The processing and analysis on the monitored data of the landslide have resulted in the technique parameters about reliability and precision of landslide deformation monitoring with the RTK technology.That is,the precision of plane and height from RTK can be controlled within 15mm and 20mm respectively,under the conditions that there are more than seven satellites observed synchronous and the data link can work normally.The experimental results indicate that the GPS-RTK technology can be used to monitor the dynamic and real time deformation of this type of landslides when the observation conditions are favorable.
This paper presents a study on the precision and reliability of landslide deformation monitoring with GPS-RTK technology.Some monitoring points were set on the landslide body.The GPS RTK technology,the three-dimension surveying technology by total station and the GPS single epoch positioning technology were used to monitor the deformation process from stable state to the failure of the landslide in real time. The results are further combined with large physical model experiment of one kind of landslides.The processing and analysis on the monitored data of the landslide have resulted in the technique parameters about reliability and precision of landslide deformation monitoring with the RTK technology.That is,the precision of plane and height from RTK can be controlled within 15mm and 20mm respectively,under the conditions that there are more than seven satellites observed synchronous and the data link can work normally.The experimental results indicate that the GPS-RTK technology can be used to monitor the dynamic and real time deformation of this type of landslides when the observation conditions are favorable.
2011, 19(2): 199-204.
Stress analysis is done to the soil arch between piles.It is based on existing research of anti-slide pile spacing.Pile spacing is calculated by two conditions.They are side resistance and soil arch strength.Unified strength theory is introduced to analyze soil arch strength.On the basis of this analysis,the front and posterior arch roof and arch foot are respectively judged that the soil is or is not in critical state.Then the values of three pile spacing can be obtained.The corresponding minimum pile spacing is taken as the design one.The method is suitable for slide thrust distribution with the form of either rectangle,or triangle or trapezoid.Soil self-weight stress can be also considered.It can be simultaneously applied to the anchored anti-slide pile spacing.Two calculation examples are analyzed by the presented method.The comparison between the calculation results and the existing or design results shows that the effect of proposed method is satisfactory.When specific calculation is done,the suitable value of unified strength parameter b is between 0.2and 0.7.When slide thrust is rectangular distribution,b is about 0.3.For triangular distribution,b is about 0.6.For trapezium distribution,b lies between 0.3and 0.6.
Stress analysis is done to the soil arch between piles.It is based on existing research of anti-slide pile spacing.Pile spacing is calculated by two conditions.They are side resistance and soil arch strength.Unified strength theory is introduced to analyze soil arch strength.On the basis of this analysis,the front and posterior arch roof and arch foot are respectively judged that the soil is or is not in critical state.Then the values of three pile spacing can be obtained.The corresponding minimum pile spacing is taken as the design one.The method is suitable for slide thrust distribution with the form of either rectangle,or triangle or trapezoid.Soil self-weight stress can be also considered.It can be simultaneously applied to the anchored anti-slide pile spacing.Two calculation examples are analyzed by the presented method.The comparison between the calculation results and the existing or design results shows that the effect of proposed method is satisfactory.When specific calculation is done,the suitable value of unified strength parameter b is between 0.2and 0.7.When slide thrust is rectangular distribution,b is about 0.3.For triangular distribution,b is about 0.6.For trapezium distribution,b lies between 0.3and 0.6.
2011, 19(2): 205-212.
The Wenchuan 8.0 earthquake triggered a huge number of rockfall hazards. The hazards most happened in cataclastic rock mass. The respective stability of the back wall and the front accumulation of the slope and the influence of the back wall upon the stability of accumulation are problems that are faced by people after the earthquake. This paper takes the Ganhekou rockfalling accumulation as a example. It is based on analysis of the structure feature and genetic mechanism of the slope. It uses the 2D Discrete Element MethodUDEC to simulate the stability status and possible failure process of the slope under nature or earthquake condition.It uses the limit equilibrium theory based models and analyse the stability of accumulation before or after loaded by new substance generated by new rockfall. The results show that the genetic process of rockfalling accumulation can divided to stress redistribution, the formation of potential rockfall mass and rockfall induced by earthquake three phases. Before loading function, the accumulation is relatively stable both under nature or earthquake condition. But after considering the function of loading, it may fail under earthquake. The combined use of discrete element method and limit equilibrium method are practicable way for solving similar problem of similar slopes.
The Wenchuan 8.0 earthquake triggered a huge number of rockfall hazards. The hazards most happened in cataclastic rock mass. The respective stability of the back wall and the front accumulation of the slope and the influence of the back wall upon the stability of accumulation are problems that are faced by people after the earthquake. This paper takes the Ganhekou rockfalling accumulation as a example. It is based on analysis of the structure feature and genetic mechanism of the slope. It uses the 2D Discrete Element MethodUDEC to simulate the stability status and possible failure process of the slope under nature or earthquake condition.It uses the limit equilibrium theory based models and analyse the stability of accumulation before or after loaded by new substance generated by new rockfall. The results show that the genetic process of rockfalling accumulation can divided to stress redistribution, the formation of potential rockfall mass and rockfall induced by earthquake three phases. Before loading function, the accumulation is relatively stable both under nature or earthquake condition. But after considering the function of loading, it may fail under earthquake. The combined use of discrete element method and limit equilibrium method are practicable way for solving similar problem of similar slopes.
2011, 19(2): 213-218.
The red bedrock mass examined in this paper has a bedding structure of easily slided strata.Its shear zones or weak intercalations are present among the relatively hard rock strata such as sand stone and soft rock strata such as silt-mud stone.The slope at the powerhouse site of Wawu Mountain Hydropower Project in particular is a day lighting slope whose bedding dip direction is almost the same as the slope dip direction.The sand stone strata and the silt mudstone strata are developed alternatively with low bedding dip angles of 10to 20.Shear zones or weak intercalations usually exist between the sand stone and silt mudstone under the action of tectonic movement,hyper-gene weathering and unloading.Landslides often take place along the shear zone or weak intercalation.It is under this geological background that the paleo-landslides such as Yanwan and Miaoziyan landslide at the powerhouse site came into being during the geological times.Eventually,the landslides are almost stable under the natural conditions.After their formation,the geomorphy of the landslides was changed because of the weathering and erosion.Or simply it was buried by slope debris.So it is not easy to find them using landslide geomorphic features alone.The Miaoziyan landslide is a buried paleo-landslide and was revived for the toe cutting and rainfall during the excavation.The stability of the Miaoziyan landslide under all work-condition was calculated.The calculation is based on the repeat shear test of the weak intercalation by the energy method upper bound limit analysis.Some treatments were used to prevent it from sliding further.Such re-landsliding would have side effect to the powerhouse construction.This paper can be used as a reference for the investigation and analysis of similar red bedrock mass paleo-landslides.
The red bedrock mass examined in this paper has a bedding structure of easily slided strata.Its shear zones or weak intercalations are present among the relatively hard rock strata such as sand stone and soft rock strata such as silt-mud stone.The slope at the powerhouse site of Wawu Mountain Hydropower Project in particular is a day lighting slope whose bedding dip direction is almost the same as the slope dip direction.The sand stone strata and the silt mudstone strata are developed alternatively with low bedding dip angles of 10to 20.Shear zones or weak intercalations usually exist between the sand stone and silt mudstone under the action of tectonic movement,hyper-gene weathering and unloading.Landslides often take place along the shear zone or weak intercalation.It is under this geological background that the paleo-landslides such as Yanwan and Miaoziyan landslide at the powerhouse site came into being during the geological times.Eventually,the landslides are almost stable under the natural conditions.After their formation,the geomorphy of the landslides was changed because of the weathering and erosion.Or simply it was buried by slope debris.So it is not easy to find them using landslide geomorphic features alone.The Miaoziyan landslide is a buried paleo-landslide and was revived for the toe cutting and rainfall during the excavation.The stability of the Miaoziyan landslide under all work-condition was calculated.The calculation is based on the repeat shear test of the weak intercalation by the energy method upper bound limit analysis.Some treatments were used to prevent it from sliding further.Such re-landsliding would have side effect to the powerhouse construction.This paper can be used as a reference for the investigation and analysis of similar red bedrock mass paleo-landslides.
2011, 19(2): 219-224.
Modulated potassium silicate solution(PS)has been applied widely for the protection of heritage soil in the arid area of northwestern China and obviously succeeded.However,protection of such site soil in the moist area is remained as one of research subjects.Based on the data of laboratory tests,the strengthening effect of PS for soil with relative higher water content is presented in this paper.The soil samples taken from Liangzhu civilization site(3000 B.C.)were modulated to obtain higher water content up to 13％ ~25％ and strengthened by PS infiltration.Some important findings were revealed in the comparison of consolidation and shear strength properties for original and PS strengthened soils.The PS strengthening effect can be observed even for soil with water content as higher as 25%.The PS filtration may increase the consolidation property and shear strength,and the laboratory study revealed some important findings in plasticity-brittleness transition.The test data show,that the PS strengthening may result in the stabilization of soil structure framework and secondary support to the pores.This work should give a support to the further application of PS strengthening technology for heritage site soil.
Modulated potassium silicate solution(PS)has been applied widely for the protection of heritage soil in the arid area of northwestern China and obviously succeeded.However,protection of such site soil in the moist area is remained as one of research subjects.Based on the data of laboratory tests,the strengthening effect of PS for soil with relative higher water content is presented in this paper.The soil samples taken from Liangzhu civilization site(3000 B.C.)were modulated to obtain higher water content up to 13％ ~25％ and strengthened by PS infiltration.Some important findings were revealed in the comparison of consolidation and shear strength properties for original and PS strengthened soils.The PS strengthening effect can be observed even for soil with water content as higher as 25%.The PS filtration may increase the consolidation property and shear strength,and the laboratory study revealed some important findings in plasticity-brittleness transition.The test data show,that the PS strengthening may result in the stabilization of soil structure framework and secondary support to the pores.This work should give a support to the further application of PS strengthening technology for heritage site soil.
2011, 19(2): 225-230.
The threshold pressure gradient is defined as the initiation condition of occurring seepage flow in low permeable rock mass.This value is an important factor in oil production and engineering against leakage,because of the existence of nonlinear infiltration phenomenon in the rock mass.This paper presents a laboratory test method and associated test results to determine the threshold pressure gradient value.During the test,the inlet water pressure of the test sample is stably controlled for long time.The outlet water volume change quantity is exactly measured.When the quantity of seeped water volume change is linear with respect to the time,the corresponding infiltration features are satisfied the Darcy's law.On the base of the new permeability test method,the different permeability soft rocks have been systemically tested.According to the positive correlation of the measured permeability coefficient and the pressure gradient,the Averaged Three Times Method has been put forward to calculate quasi-threshold pressure gradient.At first,the measured permeability coefficient values are adjusted uniformly.Then the absolute permeability coefficient value is determined.Thirdly,the V0 value is specified by taking the three times if the average value.Subsequently,the value of quasi-threshold pressure gradient is determined.On the basis of test data analysis,the quasi-threshold pressure gradient increases as the confining pressure increases.It increases as the rock absolute permeability coefficient decreases.Furthermore,the quasi-threshold pressure gradient is larger during the infiltration pressure increase process than that during the infiltration pressure decrease process.These results are similar to the theory,which showed that the Averaged Three Times Method is better for the quasi-threshold pressure gradient.This method put forward a new thinking about determination of the infiltration threshold pressure gradient of rock mass in Laboratory.
The threshold pressure gradient is defined as the initiation condition of occurring seepage flow in low permeable rock mass.This value is an important factor in oil production and engineering against leakage,because of the existence of nonlinear infiltration phenomenon in the rock mass.This paper presents a laboratory test method and associated test results to determine the threshold pressure gradient value.During the test,the inlet water pressure of the test sample is stably controlled for long time.The outlet water volume change quantity is exactly measured.When the quantity of seeped water volume change is linear with respect to the time,the corresponding infiltration features are satisfied the Darcy's law.On the base of the new permeability test method,the different permeability soft rocks have been systemically tested.According to the positive correlation of the measured permeability coefficient and the pressure gradient,the Averaged Three Times Method has been put forward to calculate quasi-threshold pressure gradient.At first,the measured permeability coefficient values are adjusted uniformly.Then the absolute permeability coefficient value is determined.Thirdly,the V0 value is specified by taking the three times if the average value.Subsequently,the value of quasi-threshold pressure gradient is determined.On the basis of test data analysis,the quasi-threshold pressure gradient increases as the confining pressure increases.It increases as the rock absolute permeability coefficient decreases.Furthermore,the quasi-threshold pressure gradient is larger during the infiltration pressure increase process than that during the infiltration pressure decrease process.These results are similar to the theory,which showed that the Averaged Three Times Method is better for the quasi-threshold pressure gradient.This method put forward a new thinking about determination of the infiltration threshold pressure gradient of rock mass in Laboratory.
2011, 19(2): 231-237.
Past studies have shown that the macroscopic mechanical properties and performance of soil depend on its microstructure essentially. Driving pile into a soft soil would cause a significant change in the internal structure of the soft soil surrounding the pile. The strength and deformation characters are the macroscopic expression of this change. The relationship between soil microstructure and its change of macroscopic mechanical behavior is of great theoretical and practical significance. It can not only reveal the mechanical properties, but also understand its mechanism of effect of driving pile from microcosmic viewpoint. It further provides guidance to the practice. To obtain the microstructural and mechanical parameters, microstructural tests and consolidated undrained triaxial tests were carried out respectively. In addition, the soil specimens of different sites around the piles were obtained at different times during pile driven according the actual engineering in Tianjin's Binhai New Area. Through analysis of the representative components, three representative components were extract to describe the microstructural characteristics of the squeezed soil.The paper has the following findings. The three representative components have a good corresponding relationship with the soil cohesive strength and a weaker association with the soil internal friction angle. The first representative component contains nearly all the information. The second and third representative components make further additions to those properties that cannot be extracted from the first representative component. Besides, analysis shows that the soil microstructural properties control the strength character. There is an inverse relationship on the macro mechanical property between the soil near ground surface and the lower soil layers during pile driving. These results provide strong supports to the argument that the microstuctural parameters are the crucial factors of mechanical character by the representative component analysis.
Past studies have shown that the macroscopic mechanical properties and performance of soil depend on its microstructure essentially. Driving pile into a soft soil would cause a significant change in the internal structure of the soft soil surrounding the pile. The strength and deformation characters are the macroscopic expression of this change. The relationship between soil microstructure and its change of macroscopic mechanical behavior is of great theoretical and practical significance. It can not only reveal the mechanical properties, but also understand its mechanism of effect of driving pile from microcosmic viewpoint. It further provides guidance to the practice. To obtain the microstructural and mechanical parameters, microstructural tests and consolidated undrained triaxial tests were carried out respectively. In addition, the soil specimens of different sites around the piles were obtained at different times during pile driven according the actual engineering in Tianjin's Binhai New Area. Through analysis of the representative components, three representative components were extract to describe the microstructural characteristics of the squeezed soil.The paper has the following findings. The three representative components have a good corresponding relationship with the soil cohesive strength and a weaker association with the soil internal friction angle. The first representative component contains nearly all the information. The second and third representative components make further additions to those properties that cannot be extracted from the first representative component. Besides, analysis shows that the soil microstructural properties control the strength character. There is an inverse relationship on the macro mechanical property between the soil near ground surface and the lower soil layers during pile driving. These results provide strong supports to the argument that the microstuctural parameters are the crucial factors of mechanical character by the representative component analysis.
2011, 19(2): 238-243.
In theory,there is a rigorous deducing process for the Laslett algorithm and the generalized H-H algorithm under the mean trace length estimation of discontinuities.However,they have different accuracies of estimated values on different trace length levels.This study carries out tests on the accuracy of estimated values from both algorithms and evaluates their applicability, based on the full-trace length data of excavated slopes.Because the height of test windows in engineering are small,this paper has amended the estimated values of the generalized H-H algorithm.The values are calculated under the conditions of small test window and long trace length level.The research results indicate that(1)under the conditions of small test window and short trace length level, the Laslett algorithm is adopted; (2)under the conditions of small test window and long trace length level,the generalized H-H algorithm is adopted. A modified coefficient 2 is suggested.
In theory,there is a rigorous deducing process for the Laslett algorithm and the generalized H-H algorithm under the mean trace length estimation of discontinuities.However,they have different accuracies of estimated values on different trace length levels.This study carries out tests on the accuracy of estimated values from both algorithms and evaluates their applicability, based on the full-trace length data of excavated slopes.Because the height of test windows in engineering are small,this paper has amended the estimated values of the generalized H-H algorithm.The values are calculated under the conditions of small test window and long trace length level.The research results indicate that(1)under the conditions of small test window and short trace length level, the Laslett algorithm is adopted; (2)under the conditions of small test window and long trace length level,the generalized H-H algorithm is adopted. A modified coefficient 2 is suggested.
2011, 19(2): 244-249.
The characteristics of the development of plastic strain and the process of unstable failure for embankment of heterogeneous soils are studied with the strength reduction FEM.The unstable mechanism for embankment is analyzed according to the stress field of unstable state and formation of the critical slip surfaces.The results indicate that the strength reduction FEM is applied to stability analysis of embankments of heterogeneous soils in the theory and numeric simulation.Furthermore,the numerical non-convergence of FEM global equilibrium and displacement can be taken as a failure criterion of embankment slope.The unstable failure state can be evaluated correctly using the criterion.The relationship between the nodal displacement in the slip surface and the load increment can be investigated with reference to the plastic zone deformed from slope toe to slope crest at the same time.In addition,the stress field of unstable state in the embankment shows that it is necessary to adopt the tension-shear composite failure criterion for stability analysis of embankments to reflect the mechanism for formation of critical slip surfaces.
The characteristics of the development of plastic strain and the process of unstable failure for embankment of heterogeneous soils are studied with the strength reduction FEM.The unstable mechanism for embankment is analyzed according to the stress field of unstable state and formation of the critical slip surfaces.The results indicate that the strength reduction FEM is applied to stability analysis of embankments of heterogeneous soils in the theory and numeric simulation.Furthermore,the numerical non-convergence of FEM global equilibrium and displacement can be taken as a failure criterion of embankment slope.The unstable failure state can be evaluated correctly using the criterion.The relationship between the nodal displacement in the slip surface and the load increment can be investigated with reference to the plastic zone deformed from slope toe to slope crest at the same time.In addition,the stress field of unstable state in the embankment shows that it is necessary to adopt the tension-shear composite failure criterion for stability analysis of embankments to reflect the mechanism for formation of critical slip surfaces.
2011, 19(2): 250-253.
A new method with use of normal vector unit cycle to assess rock fracture roughness on linear profiles is proposed. A new concept of orientation roughness is put forward to reduce data dimension from 2D to 1D. The roughness quantitative description takes the form of weight mean value and weight variance of orientation. The two parameters can reflect contribution of each differential length. The bigger the orientation roughness, the rougher the linear profile. The new method with other exiting methods, are used to assess several regular and irregular linear profiles. The results show good uniformity, which indicates the new method is right and can be used to assess rock fracture roughness.
A new method with use of normal vector unit cycle to assess rock fracture roughness on linear profiles is proposed. A new concept of orientation roughness is put forward to reduce data dimension from 2D to 1D. The roughness quantitative description takes the form of weight mean value and weight variance of orientation. The two parameters can reflect contribution of each differential length. The bigger the orientation roughness, the rougher the linear profile. The new method with other exiting methods, are used to assess several regular and irregular linear profiles. The results show good uniformity, which indicates the new method is right and can be used to assess rock fracture roughness.
2011, 19(2): 254-261.
The expansive soil in Panzhihua region was generated during the Pleistocene glacial period of the second late glacial period.Based on physical and mechanical tests and analysis of laboratory and field,this paper reveals the physical and mechanical properties of the expansive soil.The properties have a great dispersion and are related with many factors including soil mineral composition,moisture content,fracture surface,buried depth,gradation,test conditions.Experimental results show that the fracture surface of the expansive soil can be divided into two types with different smooth degrees.They are the types of smooth fracture surface and smooth surface scratches.Coarse-grained minerals have little effect on the expansion and shrinkage.But fine-grained minerals have a greater impact on the expansion and shrinkage.For exposed or near-surface soils,they have been weathered intensely,,developed more cracks,have larger expansion efforts.For the expansion soil from same site with higher montmorillonite content,it has a greater freedom of expansion,a higher level of expansion.The physical and mechanical property indices of the expansive soils from different sites have limited differences.The clay contents in the expansion soil is not significant.The shear strength values of the expansive soil from different sites can change greatly.The shear strength values of the expansive soil from the same site can have some fluctuations.A majority of the expansive soils are hard plastic to hard state.Their compressive deformation at natural state is small.Their bearing capacity at natural state can be doubly reduced when they are fully saturated.
The expansive soil in Panzhihua region was generated during the Pleistocene glacial period of the second late glacial period.Based on physical and mechanical tests and analysis of laboratory and field,this paper reveals the physical and mechanical properties of the expansive soil.The properties have a great dispersion and are related with many factors including soil mineral composition,moisture content,fracture surface,buried depth,gradation,test conditions.Experimental results show that the fracture surface of the expansive soil can be divided into two types with different smooth degrees.They are the types of smooth fracture surface and smooth surface scratches.Coarse-grained minerals have little effect on the expansion and shrinkage.But fine-grained minerals have a greater impact on the expansion and shrinkage.For exposed or near-surface soils,they have been weathered intensely,,developed more cracks,have larger expansion efforts.For the expansion soil from same site with higher montmorillonite content,it has a greater freedom of expansion,a higher level of expansion.The physical and mechanical property indices of the expansive soils from different sites have limited differences.The clay contents in the expansion soil is not significant.The shear strength values of the expansive soil from different sites can change greatly.The shear strength values of the expansive soil from the same site can have some fluctuations.A majority of the expansive soils are hard plastic to hard state.Their compressive deformation at natural state is small.Their bearing capacity at natural state can be doubly reduced when they are fully saturated.
2011, 19(2): 262-270.
Wenjia gully is located at the epicenter area of the 2008 Wenchuan Earthquake.A huge landslide was ever triggered by the earthquake.During the passed three flood seasons,at least five typical debris flows occurred at Wenjia gully.In particular,a severest debris flow occurred on Aug.13, 2010. It had a volume up to 3.1107m3.Five residents lost their lives unfortunately and hundreds of new-built houses were buried during the catastrophic event.However,it was fortunate that almost all the residents evacuated successfully before the debris flow occurred.In this paper,on the basis of tracking investigation,the mechanism and characteristics of the Wenjia-gully debris flows were discussed and some suggestions were put forward.The acknowledges obtained after investigation and analysis are as follows: (1)The debris flows were caused by both Wenchuan earthquake and strong rainfall.As the debris flow formation is concerned,a circle was presented as runoff-erosion-collapse-engulfment-erosion-collapse-enlargement-,and so on; (2)The critical rainfall initiated debris flow was significantly decreased and a power-law relation is existed between debris flow magnitude and daily rainfall,which can be used to predict the volume of debris flow on the basis of weather forecasting; (3)As the occurrence process is concerned,the debris flow lasted for a long duration and moved a far distance; (4)In terms of destroying process,a clear chain characteristic was taken on with several damage ways; (5)Debris flow magnitude was enlarged and the frequency was higher obviously.
Wenjia gully is located at the epicenter area of the 2008 Wenchuan Earthquake.A huge landslide was ever triggered by the earthquake.During the passed three flood seasons,at least five typical debris flows occurred at Wenjia gully.In particular,a severest debris flow occurred on Aug.13, 2010. It had a volume up to 3.1107m3.Five residents lost their lives unfortunately and hundreds of new-built houses were buried during the catastrophic event.However,it was fortunate that almost all the residents evacuated successfully before the debris flow occurred.In this paper,on the basis of tracking investigation,the mechanism and characteristics of the Wenjia-gully debris flows were discussed and some suggestions were put forward.The acknowledges obtained after investigation and analysis are as follows: (1)The debris flows were caused by both Wenchuan earthquake and strong rainfall.As the debris flow formation is concerned,a circle was presented as runoff-erosion-collapse-engulfment-erosion-collapse-enlargement-,and so on; (2)The critical rainfall initiated debris flow was significantly decreased and a power-law relation is existed between debris flow magnitude and daily rainfall,which can be used to predict the volume of debris flow on the basis of weather forecasting; (3)As the occurrence process is concerned,the debris flow lasted for a long duration and moved a far distance; (4)In terms of destroying process,a clear chain characteristic was taken on with several damage ways; (5)Debris flow magnitude was enlarged and the frequency was higher obviously.
2011, 19(2): 271-276.
In Kuan-cheng county of Hebei province,a railway to be built will cut across an ancient landslide mass of about 77104m3,and in the form of a cutting channel in front of the ancient landslide mass. Excavation of the cutt slope in the mass could lead to re-activity of the ancient landslide. To ensure the safety of railway operation in the future,a complete treatment is necessary.Based on geological survey in the field and experiment,the stability of the ancient landslide mass is calculated along the existing and ancient sliding surface with different working conditions and combining with specific characteristics of the revival landslide.Two treatment schemes were put forward.They are the anti-slide pile scheme and the cleanup+earthwork+anti-slide pile+retaining wall between piles scheme.Through an integrated comparison,the second scheme was adopted and completed.Works include cleanup earthwork,anti-slide piles,drainage system,and slope protection.
In Kuan-cheng county of Hebei province,a railway to be built will cut across an ancient landslide mass of about 77104m3,and in the form of a cutting channel in front of the ancient landslide mass. Excavation of the cutt slope in the mass could lead to re-activity of the ancient landslide. To ensure the safety of railway operation in the future,a complete treatment is necessary.Based on geological survey in the field and experiment,the stability of the ancient landslide mass is calculated along the existing and ancient sliding surface with different working conditions and combining with specific characteristics of the revival landslide.Two treatment schemes were put forward.They are the anti-slide pile scheme and the cleanup+earthwork+anti-slide pile+retaining wall between piles scheme.Through an integrated comparison,the second scheme was adopted and completed.Works include cleanup earthwork,anti-slide piles,drainage system,and slope protection.
2011, 19(2): 277-283.
In Shanghai land area,many ancient river beds developed in the Quaternary period.The ancient river channel beds since late Pleistocene have substantial effects on construction.Based on large amount of drillhole and test datum,this paper presents the genesis,distribution,and sediment characters of the ancient river channels in late Pleistocene,Holocene,and present years.This paper further analyzes the effects of ancient river channels on construction,especially underground projects.The results of this paper can be used as the basis of investigation,design,and construction of new projects.
In Shanghai land area,many ancient river beds developed in the Quaternary period.The ancient river channel beds since late Pleistocene have substantial effects on construction.Based on large amount of drillhole and test datum,this paper presents the genesis,distribution,and sediment characters of the ancient river channels in late Pleistocene,Holocene,and present years.This paper further analyzes the effects of ancient river channels on construction,especially underground projects.The results of this paper can be used as the basis of investigation,design,and construction of new projects.
2011, 19(2): 284-288.
The purpose of landslide monitoring is to obtain the characteristics and evolutionary process of landslides.For some important sites,monitoring in deep ground is the most direct and effective means to determine whether or not potential landslide exists,in this paper,five boreholes for underground monitoring are set on two profiles of a slope behind a hydropower plant.Slide area,slope activity,sliding direction,sliding surface and types of the landslide are discussed and analyzed.The monitoring results reveal that it is a retrogressive landslide with obvious activity.The displacement velocity of the landslide is large and it has accelerated in the rainy seasons.Sliding surface in the slope front has been locally penetrated.It alsohas creep deformation in the upslope.
The purpose of landslide monitoring is to obtain the characteristics and evolutionary process of landslides.For some important sites,monitoring in deep ground is the most direct and effective means to determine whether or not potential landslide exists,in this paper,five boreholes for underground monitoring are set on two profiles of a slope behind a hydropower plant.Slide area,slope activity,sliding direction,sliding surface and types of the landslide are discussed and analyzed.The monitoring results reveal that it is a retrogressive landslide with obvious activity.The displacement velocity of the landslide is large and it has accelerated in the rainy seasons.Sliding surface in the slope front has been locally penetrated.It alsohas creep deformation in the upslope.
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