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Editor Work2011 Vol. 19, No. 6
Previous Issue
2011, 19(6): 795-801.
Abstract
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The reactive mechanism of large landslide is complicated and is a key point of landslide research.The Baozha landslide is a typical large landslide in Enshi.Its stability is urgent to be evaluated in order to keep safety for people. Thid paper is based on the engineering geological condition investigation and analyses the formation mechanism.A 2D model is developed.With the FLAC software and based on the borehole displacement data,this paper inverses the rational calculation parameter of the soils and rocks forming the landslide.Considering landslide natural state and river trenching,three-simulations are done.The results show the following three points: (1)Baozha landslide is a pulling landslide.It is developed in easy-sliding strata-sandstone and muddy stone of Silurian System.Laogou river erosion and rainfall are the main induction factor.The slope front edge failed at the beginning.Then the deformation developed to middle and back of the slope.At last,the landslide happened.(2) at present,the main factors that influence the deformation and stability of the landslide are the Laogouhe river cutting and rainfall.(3)the Baozha landslide is stable now.With the river cutting deeper,this landslide is possible to have a progressive failure.The suggestion is that the front toe of the landslide should be improved as soon as possible.
The reactive mechanism of large landslide is complicated and is a key point of landslide research.The Baozha landslide is a typical large landslide in Enshi.Its stability is urgent to be evaluated in order to keep safety for people. Thid paper is based on the engineering geological condition investigation and analyses the formation mechanism.A 2D model is developed.With the FLAC software and based on the borehole displacement data,this paper inverses the rational calculation parameter of the soils and rocks forming the landslide.Considering landslide natural state and river trenching,three-simulations are done.The results show the following three points: (1)Baozha landslide is a pulling landslide.It is developed in easy-sliding strata-sandstone and muddy stone of Silurian System.Laogou river erosion and rainfall are the main induction factor.The slope front edge failed at the beginning.Then the deformation developed to middle and back of the slope.At last,the landslide happened.(2) at present,the main factors that influence the deformation and stability of the landslide are the Laogouhe river cutting and rainfall.(3)the Baozha landslide is stable now.With the river cutting deeper,this landslide is possible to have a progressive failure.The suggestion is that the front toe of the landslide should be improved as soon as possible.
2011, 19(6): 802-808.
Landslide statistics and research findings have shown that the occurrence time of landslides has the feature of evident period distribution.In addition to rainfall,the moon and sun gravitational tide is recognized as another apparent factor.In this paper,the statistical diagram of landslides in days is gained by analyzing the data of a certain number of slides.Further efforts is made on the deduction of the formulas of tidal stress at surface of the Earth,by modifying a simplified elastic earth model based on the earth tide theory.The mechanism of landslide triggered by tidal stress is discussed in further.Moreover,a rock slope in Nanjing is taken as a example,based on the planar failure surface method,to discuss the correlation between tidal stress and time,and how the safety factor of stability change with time.The results show that,the tidal stress and the factor of slope stability change with time at daily period.Therefore,the characteristic with daily successive variation of landslides and the mechanism triggered by earth tide are elaborated quantitatively.
Landslide statistics and research findings have shown that the occurrence time of landslides has the feature of evident period distribution.In addition to rainfall,the moon and sun gravitational tide is recognized as another apparent factor.In this paper,the statistical diagram of landslides in days is gained by analyzing the data of a certain number of slides.Further efforts is made on the deduction of the formulas of tidal stress at surface of the Earth,by modifying a simplified elastic earth model based on the earth tide theory.The mechanism of landslide triggered by tidal stress is discussed in further.Moreover,a rock slope in Nanjing is taken as a example,based on the planar failure surface method,to discuss the correlation between tidal stress and time,and how the safety factor of stability change with time.The results show that,the tidal stress and the factor of slope stability change with time at daily period.Therefore,the characteristic with daily successive variation of landslides and the mechanism triggered by earth tide are elaborated quantitatively.
2011, 19(6): 809-815.
The geological event of long runout rockfall-landslide can cause great damages and broader coverage,which are followed closely by engineering and technical personnel.The Wenchuan Earthquake,happened in May 12, 2008,induced tens of thousands of landslides.Though the number of long runout rockfall-landslides was not high,they did greater damage than the other types of landslides.Comparing with general landslides,the forming conditions of the long runout rockfall-landslide are studied.In order to predict its severity and range and provide basis for homeland planning and preventive treatment design,this paper summarizes its characteristic and comprehensively analyses the factors influencing its high speed and long distance.The paper is based on practical engineering experience and widely collection of studies about the long runout rockfall-landslides at home and abroad.Earthquake,ground water,and mining activities can cause the landslide instability and make it active.The paper proposes that the long runout rockfall-landslide must exist the following three conditions: namely large-scale sliding masses,cut export overhang and the terrain available for geology body to movement.It provides important research contents for further prediction of the space distribution of the long runout rockfall-landslide.
The geological event of long runout rockfall-landslide can cause great damages and broader coverage,which are followed closely by engineering and technical personnel.The Wenchuan Earthquake,happened in May 12, 2008,induced tens of thousands of landslides.Though the number of long runout rockfall-landslides was not high,they did greater damage than the other types of landslides.Comparing with general landslides,the forming conditions of the long runout rockfall-landslide are studied.In order to predict its severity and range and provide basis for homeland planning and preventive treatment design,this paper summarizes its characteristic and comprehensively analyses the factors influencing its high speed and long distance.The paper is based on practical engineering experience and widely collection of studies about the long runout rockfall-landslides at home and abroad.Earthquake,ground water,and mining activities can cause the landslide instability and make it active.The paper proposes that the long runout rockfall-landslide must exist the following three conditions: namely large-scale sliding masses,cut export overhang and the terrain available for geology body to movement.It provides important research contents for further prediction of the space distribution of the long runout rockfall-landslide.
2011, 19(6): 816-822.
In consideration of the physical,chemical and mechanical effects of groundwater to landslides around the Three Gorge Reservoir,this paper demonstrates that the mechanical effect of groundwater on the stability of the landslides in the area of the Three Gorge Reservoir is much greater than the physical and chemical effects of groundwater.Based on this knowledge,the total pressure head in a landslide body is introduced.Different mechanical effects of groundwater are simplified into a total water pressure head.Landslide prediction model of rainfall,reservoir level fluctuation are established with load and unload response theory(LURT).Numerical simulation results of landslide process indicate that this method can estimate the stability state and evolution stage of a landslide quantitatively.Take LURT leaping as the failure boding of a landslide,the sliding time of the landslide can be predicted.Analysis of Badong landslide monitoring data also indicate that LURT method can judge the steady-state and sliding time of landslide directly.
In consideration of the physical,chemical and mechanical effects of groundwater to landslides around the Three Gorge Reservoir,this paper demonstrates that the mechanical effect of groundwater on the stability of the landslides in the area of the Three Gorge Reservoir is much greater than the physical and chemical effects of groundwater.Based on this knowledge,the total pressure head in a landslide body is introduced.Different mechanical effects of groundwater are simplified into a total water pressure head.Landslide prediction model of rainfall,reservoir level fluctuation are established with load and unload response theory(LURT).Numerical simulation results of landslide process indicate that this method can estimate the stability state and evolution stage of a landslide quantitatively.Take LURT leaping as the failure boding of a landslide,the sliding time of the landslide can be predicted.Analysis of Badong landslide monitoring data also indicate that LURT method can judge the steady-state and sliding time of landslide directly.
2011, 19(6): 823-830.
In August 2010,serious deformation occurred in the Wangxia dangerous rock mass.The local residents and river channel safety are in high risk.This paper is based on detailed investigation of the new cracks,deformation history,GPS observations,total station monitoring and crack displacement monitoring data analysis.It analyses comprehensively the deformation and reasons of the unstable rock mass.The results show that the overall displacement direction of the rock mass was towards to SW with obvious subsidence deformation.The T10 crack controlled cracking and the back edge of the deformation zone that mainly manifested as crack opening and settlement deformation.The overall displacement direction of the block between the T11and T12 cracks was towards to SW and accompanied with settlement deformation more than horizontal displacement.Serious deformation occurred in the block near the T13 crack,caused by the block squeezing action between the T11and T12 cracks.A group of structural planes with large and straight persistence and good apertures were developed due to connected joint surfaces in the formations of the dangerous rock mass.The planes controlled the destruction of the rock that were parallel to the failure surface.The dangerous rock mass and its weak base rock formed a typical hard to soft to hard lithologic layers,which provided a combined condition of the geological structure for the interlayer-gliding of the rock mass.The expansion of the cracks and collapse pits were formed on the basis of previous deformation.They had very close relationship with the mining activities at the bottom of the rock mass.Subsided extrusion type collapse had formed so that the dangerous rock mass undertook rotational sliding to the free face after rainfall.
In August 2010,serious deformation occurred in the Wangxia dangerous rock mass.The local residents and river channel safety are in high risk.This paper is based on detailed investigation of the new cracks,deformation history,GPS observations,total station monitoring and crack displacement monitoring data analysis.It analyses comprehensively the deformation and reasons of the unstable rock mass.The results show that the overall displacement direction of the rock mass was towards to SW with obvious subsidence deformation.The T10 crack controlled cracking and the back edge of the deformation zone that mainly manifested as crack opening and settlement deformation.The overall displacement direction of the block between the T11and T12 cracks was towards to SW and accompanied with settlement deformation more than horizontal displacement.Serious deformation occurred in the block near the T13 crack,caused by the block squeezing action between the T11and T12 cracks.A group of structural planes with large and straight persistence and good apertures were developed due to connected joint surfaces in the formations of the dangerous rock mass.The planes controlled the destruction of the rock that were parallel to the failure surface.The dangerous rock mass and its weak base rock formed a typical hard to soft to hard lithologic layers,which provided a combined condition of the geological structure for the interlayer-gliding of the rock mass.The expansion of the cracks and collapse pits were formed on the basis of previous deformation.They had very close relationship with the mining activities at the bottom of the rock mass.Subsided extrusion type collapse had formed so that the dangerous rock mass undertook rotational sliding to the free face after rainfall.
2011, 19(6): 831-838.
Landslide geohazards induced by underground mining in mountainous areas have caused a serious influence to human activities.Aimed at the mechanism of underground mining-induced landslides,typical work and researches over the past several decades at home and abroad are analysed in this paper.Previous investigations can be summarized into three parts: field monitoring,physical modelling and numerical modelling.The findings are: 1)there is no clear understanding about the patterns of rock mass moving induced by underground mining.Underground mining activity is believed just one of the factors influencing the slope stability.The impacts of different aspects such as the mining method and goaf management technique resulted in the ignorance of underground mining effect.2)in-situ monitoring: most of the data is the deformation of the ground surface.There are no corresponding records about the relationship between the undermining process and rock mass movement; 3)Based on the assumptions of the geological background,constitution relationship,and other parameters,modelling researches are always excessively simplified,and the conclusions are primary and simple.This paper puts forward that further studies will focus on the detailed analysis of underground mining effect,monitor the underground mining process and rock mass deformation,and build the large-scale three dimension numerical model that can reflect geological condition better.
Landslide geohazards induced by underground mining in mountainous areas have caused a serious influence to human activities.Aimed at the mechanism of underground mining-induced landslides,typical work and researches over the past several decades at home and abroad are analysed in this paper.Previous investigations can be summarized into three parts: field monitoring,physical modelling and numerical modelling.The findings are: 1)there is no clear understanding about the patterns of rock mass moving induced by underground mining.Underground mining activity is believed just one of the factors influencing the slope stability.The impacts of different aspects such as the mining method and goaf management technique resulted in the ignorance of underground mining effect.2)in-situ monitoring: most of the data is the deformation of the ground surface.There are no corresponding records about the relationship between the undermining process and rock mass movement; 3)Based on the assumptions of the geological background,constitution relationship,and other parameters,modelling researches are always excessively simplified,and the conclusions are primary and simple.This paper puts forward that further studies will focus on the detailed analysis of underground mining effect,monitor the underground mining process and rock mass deformation,and build the large-scale three dimension numerical model that can reflect geological condition better.
2011, 19(6): 839-843.
The meteorological early warning of geo-hazards has worked for eight years since 2003.The China Institute of Geo-Environmental Monitoring has gained 1281 early warning products.Based on the former products and accuracy methods,this paper establishes an integrated evaluation system for the effectiveness of geological hazard early warning in China.The warning has three elements including early warning time,space and magnitude.Three models are established.The accuracies of geo-hazards early warning in the July of 2008 and the July of 2009 are 16.57% and 24.51%,respectively.These results are just the same as the fact nowadays or in the near future.The integrated evaluation system model includes the time,space,and magnitude of geological hazard early warning effectiveness.This model introduced in this paper is feasible and practicable,which accords with the current level of national and provincial.Therefore it can be applicable to evaluating the level of geo-hazard early warning.
The meteorological early warning of geo-hazards has worked for eight years since 2003.The China Institute of Geo-Environmental Monitoring has gained 1281 early warning products.Based on the former products and accuracy methods,this paper establishes an integrated evaluation system for the effectiveness of geological hazard early warning in China.The warning has three elements including early warning time,space and magnitude.Three models are established.The accuracies of geo-hazards early warning in the July of 2008 and the July of 2009 are 16.57% and 24.51%,respectively.These results are just the same as the fact nowadays or in the near future.The integrated evaluation system model includes the time,space,and magnitude of geological hazard early warning effectiveness.This model introduced in this paper is feasible and practicable,which accords with the current level of national and provincial.Therefore it can be applicable to evaluating the level of geo-hazard early warning.
2011, 19(6): 844-851.
A 20m high slope lies in construction site of an energy company.The mine slag was stacked 10 to 50 years ago and wholly belongs to Triassic soft sandstone and mudstone.The slag shows weathered earthy and strong weathering state.The sandstone fragments can be promptly crushed by hand.The mine slag shows loose structure,poor sorting,weak adhesion and strong permeability.The slag composing the slope was treated with dynamic compaction.But,many positions of the slag slope still slid and collapsed during the rainy season in 2010.The landslide sites were located in the lower slope.This paper examines the landslide mechanism and deformation characteristics of the dynamically compacted slope highly filled with slag under rainfall infiltration.It uses elastic-plastic mechanics finite element method,unsaturated fluid mechanics and other theories.The corresponding numerical model for displacement-unsaturated seepage coupling is set up.Based on the numerical model,displacement field,seepage pressure distribution,volume water content and safety factor are studied in detailed.The numerical results indicate: (a)with continuous rainfall,the slope safety factor significantly reduces; (b)because of the lower permeability after dynamic compaction,seepage positive pressure focuses on the top of the slope within a certain depth and gradually increases and tends to stabilize under continuous rainfall.But the maximum negative seepage pressure value basically keeps stable and negative pressure zone shows diminishing.This shows negative pressure has a limited impact on slope filled with slag after dynamic compaction.Emphasis is to take good drainage measures within a certain depth range at the top of slope to reduce seepage positive pressure; (c)vol.water content gradually increases to saturated status; (d)shear failure occurs at the toe of slope under continuous rainfall,leading to collapse in the lower part of slope.The research results have an important reference value for studying on stability of slag-soil mixed slope,such as gangue hill,tailing dam,roadbed primed with gravel,et al.
A 20m high slope lies in construction site of an energy company.The mine slag was stacked 10 to 50 years ago and wholly belongs to Triassic soft sandstone and mudstone.The slag shows weathered earthy and strong weathering state.The sandstone fragments can be promptly crushed by hand.The mine slag shows loose structure,poor sorting,weak adhesion and strong permeability.The slag composing the slope was treated with dynamic compaction.But,many positions of the slag slope still slid and collapsed during the rainy season in 2010.The landslide sites were located in the lower slope.This paper examines the landslide mechanism and deformation characteristics of the dynamically compacted slope highly filled with slag under rainfall infiltration.It uses elastic-plastic mechanics finite element method,unsaturated fluid mechanics and other theories.The corresponding numerical model for displacement-unsaturated seepage coupling is set up.Based on the numerical model,displacement field,seepage pressure distribution,volume water content and safety factor are studied in detailed.The numerical results indicate: (a)with continuous rainfall,the slope safety factor significantly reduces; (b)because of the lower permeability after dynamic compaction,seepage positive pressure focuses on the top of the slope within a certain depth and gradually increases and tends to stabilize under continuous rainfall.But the maximum negative seepage pressure value basically keeps stable and negative pressure zone shows diminishing.This shows negative pressure has a limited impact on slope filled with slag after dynamic compaction.Emphasis is to take good drainage measures within a certain depth range at the top of slope to reduce seepage positive pressure; (c)vol.water content gradually increases to saturated status; (d)shear failure occurs at the toe of slope under continuous rainfall,leading to collapse in the lower part of slope.The research results have an important reference value for studying on stability of slag-soil mixed slope,such as gangue hill,tailing dam,roadbed primed with gravel,et al.
2011, 19(6): 852-858.
The slope progressive failure process has impacts on slope stability.Slope destruction can be considered as the extension of local failure to the entire failure with the progressive process.They have the dual characteristics of fuzziness and randomness.The progressive failure fuzzy stochastic method can well reflect the partial slope body failure including its emergence,its extension and its influence to the entire slope reliability.This study is based on the spatial variation of geotechnical body.It considers the fuzziness of random variable and limit state function.It further establishes the fuzzy limit state equation of the slope progressive destruction with basic variables.It then calculates the slope fuzzy probabilities for the partial failure and the extended failure.It then obtains the progressively failure fuzzy probability.The example shows that the slope asymptotic failure analysis method in association with the fuzzy stochastic theory can reflect the actual state of the slope better.The result provides a new thinking to the slope reliability.
The slope progressive failure process has impacts on slope stability.Slope destruction can be considered as the extension of local failure to the entire failure with the progressive process.They have the dual characteristics of fuzziness and randomness.The progressive failure fuzzy stochastic method can well reflect the partial slope body failure including its emergence,its extension and its influence to the entire slope reliability.This study is based on the spatial variation of geotechnical body.It considers the fuzziness of random variable and limit state function.It further establishes the fuzzy limit state equation of the slope progressive destruction with basic variables.It then calculates the slope fuzzy probabilities for the partial failure and the extended failure.It then obtains the progressively failure fuzzy probability.The example shows that the slope asymptotic failure analysis method in association with the fuzzy stochastic theory can reflect the actual state of the slope better.The result provides a new thinking to the slope reliability.
2011, 19(6): 859-864.
The Danshan artificial landscape hill is to be located in Zhenjiang city.The hill will be constructed on the base of the abandoned quarry and will be filled with the construction waste.The maximum of thickness of the fill soil will be 50m.The thick soft clay with low strength and high compressibility in the west foundation of the hill will have great effect on the deformation and stability of the new hill.In this paper,the stability of the artificial hill slope is calculated with numerical analysis method.The results show that foundation soil and groundwater have greater impact on the artificial slope stability.As the artificial hill height increases,the excess porewater pressure and displacement in the slope body increase.The maximum change rate of the porewater pressure values is at the middle of the slope.Near the sliding surface,the excess pore pressure will reach to 150 kPa,and reduce the soil effective stress,which does not benefit to slope stability.The dissipation of pore pressure during post-construction is about 71%after construction,which is very slow.Deformation and stability of soil consolidation will require more than one year.After the deformation is stable,the maximum horizontal displacement of the foundation soil is to be 91.2cm,the vertical displacement to 70cm.The total settlement amount of the numerical results is consistent with that from the layer-wise summation method.The stability coefficient of the slope is 1.28and is calculated with FEM strength reduction method.This value is close to the result of the Limit equilibrium method.The numerical results are reliable,which can be used as the basis for engineering design and construction.
The Danshan artificial landscape hill is to be located in Zhenjiang city.The hill will be constructed on the base of the abandoned quarry and will be filled with the construction waste.The maximum of thickness of the fill soil will be 50m.The thick soft clay with low strength and high compressibility in the west foundation of the hill will have great effect on the deformation and stability of the new hill.In this paper,the stability of the artificial hill slope is calculated with numerical analysis method.The results show that foundation soil and groundwater have greater impact on the artificial slope stability.As the artificial hill height increases,the excess porewater pressure and displacement in the slope body increase.The maximum change rate of the porewater pressure values is at the middle of the slope.Near the sliding surface,the excess pore pressure will reach to 150 kPa,and reduce the soil effective stress,which does not benefit to slope stability.The dissipation of pore pressure during post-construction is about 71%after construction,which is very slow.Deformation and stability of soil consolidation will require more than one year.After the deformation is stable,the maximum horizontal displacement of the foundation soil is to be 91.2cm,the vertical displacement to 70cm.The total settlement amount of the numerical results is consistent with that from the layer-wise summation method.The stability coefficient of the slope is 1.28and is calculated with FEM strength reduction method.This value is close to the result of the Limit equilibrium method.The numerical results are reliable,which can be used as the basis for engineering design and construction.
2011, 19(6): 865-874.
Shear strength of unsaturated soil increases as its matric suction increases and the degree of saturation decreases.However,effect of matric suction to shear strength can be greatly different for different types of unsaturated soils.In this paper,the relationship between matric suction and shear strength of the unsaturated remoulded loess soil is examined with experimental approach.It is found that as matric suction increases,the soil shear strength varies nonlinearly.The variation has clear four stages: increasing,decreasing and keeping relatively constant.Particularly,the four stages can be identified based on the correlations between matric suction and shear strength,consistent with those shown on the soilwater characteristic curve.Matric suction of 5 kPa, 60 kPa, 170 kPa are critical values for the four stages.Notably,shear strength of the soils attain their peak values at matric suction of 60 kPa.Variation of apparent cohesions of the soils with matric suction shows the same trend as those of shear strengths,whereas variation of apparent internal friction angles of the soils increases stage by stage.It is also found that shear strength parameter b of the unsaturated loess soil is not a constant.
Shear strength of unsaturated soil increases as its matric suction increases and the degree of saturation decreases.However,effect of matric suction to shear strength can be greatly different for different types of unsaturated soils.In this paper,the relationship between matric suction and shear strength of the unsaturated remoulded loess soil is examined with experimental approach.It is found that as matric suction increases,the soil shear strength varies nonlinearly.The variation has clear four stages: increasing,decreasing and keeping relatively constant.Particularly,the four stages can be identified based on the correlations between matric suction and shear strength,consistent with those shown on the soilwater characteristic curve.Matric suction of 5 kPa, 60 kPa, 170 kPa are critical values for the four stages.Notably,shear strength of the soils attain their peak values at matric suction of 60 kPa.Variation of apparent cohesions of the soils with matric suction shows the same trend as those of shear strengths,whereas variation of apparent internal friction angles of the soils increases stage by stage.It is also found that shear strength parameter b of the unsaturated loess soil is not a constant.
2011, 19(6): 875-881.
Evaporation of water saturated in soil is a time-dependent process of decreasing water content.It is always accompanied by the evolution of soil fabric,stress-strain state as well as soil engineering properties.It is also an initiator of many geotechnical engineering problems.In this investigation,desiccation tests under different temperatures(25~45℃)were carried on initially saturated clayey soil with various layer thicknesses(5~11mm).The water loss of the specimen during drying was monitored and the corresponding evaporation curve was obtained.The results show that the evaporation process of soil water occurs in three fairly distinct stages: constant rate stage,falling rate stage and residual stage.After analyzing the evaporation characteristics and the intrinsic mechanism involved in each stage,it is found that the constant rate stage generally occurs at the initial drying period,where the water content is relative high and the specimen is still saturate.During the constant rate stage,the profile moisture transfer is dominated by liquid flow and mainly controlled by capillary force,and the evaporation rate significantly depends on environmental factors or limited by the amount of energy available to vaporize soil moisture in the upper layer of the soil.The decrease of vapor pressure gradient on the evaporation surface,transfer velocity of profile moisture,profile suction gradient,availability of water amount and the increase of pore air are the primary factors that result in the evaporation transition from constant rate stage to falling rate stage.During the falling rate stage,the profile moisture moves in both liquid and vapor forms and the later one gradually dominates the evaporation process,the evaporation rate is mainly limited by the soil conditions and pore structure.In addition,it is also found that higher temperature corresponds to higher initial evaporation rate and shorter drying period,while the initial evaporation rate is less sensitive to specimen thickness changes; thicker specimen needs longer drying period.
Evaporation of water saturated in soil is a time-dependent process of decreasing water content.It is always accompanied by the evolution of soil fabric,stress-strain state as well as soil engineering properties.It is also an initiator of many geotechnical engineering problems.In this investigation,desiccation tests under different temperatures(25~45℃)were carried on initially saturated clayey soil with various layer thicknesses(5~11mm).The water loss of the specimen during drying was monitored and the corresponding evaporation curve was obtained.The results show that the evaporation process of soil water occurs in three fairly distinct stages: constant rate stage,falling rate stage and residual stage.After analyzing the evaporation characteristics and the intrinsic mechanism involved in each stage,it is found that the constant rate stage generally occurs at the initial drying period,where the water content is relative high and the specimen is still saturate.During the constant rate stage,the profile moisture transfer is dominated by liquid flow and mainly controlled by capillary force,and the evaporation rate significantly depends on environmental factors or limited by the amount of energy available to vaporize soil moisture in the upper layer of the soil.The decrease of vapor pressure gradient on the evaporation surface,transfer velocity of profile moisture,profile suction gradient,availability of water amount and the increase of pore air are the primary factors that result in the evaporation transition from constant rate stage to falling rate stage.During the falling rate stage,the profile moisture moves in both liquid and vapor forms and the later one gradually dominates the evaporation process,the evaporation rate is mainly limited by the soil conditions and pore structure.In addition,it is also found that higher temperature corresponds to higher initial evaporation rate and shorter drying period,while the initial evaporation rate is less sensitive to specimen thickness changes; thicker specimen needs longer drying period.
2011, 19(6): 882-886.
Based on the theory of solving over-determined equations with the least square method and parameters back analysis methods,this paper discusses the approach to quickly determine the compressive moduli of multi-layered soft ground.The approach contains CPTU tests data together with corresponding ground settlement data.It is aimed to establish the empirical relationship formula between compressive modulus and cone tip resistance according to kinds of soils.Finally,the CPTU tests results of soft ground in Chong-qi Bridge are present.The results of the compressive modulus are compared with data of laboratory oedometer tests and other situ tests.Comparisons of the results indicate that the compressive modulus determined with CPTU tests are twice as much as that measured in the laboratory consolidation tests and are in good agreement with that from CPT and SPT.When the compressive modulus from CPTU tests were used directly for design,it would be better in practice.
Based on the theory of solving over-determined equations with the least square method and parameters back analysis methods,this paper discusses the approach to quickly determine the compressive moduli of multi-layered soft ground.The approach contains CPTU tests data together with corresponding ground settlement data.It is aimed to establish the empirical relationship formula between compressive modulus and cone tip resistance according to kinds of soils.Finally,the CPTU tests results of soft ground in Chong-qi Bridge are present.The results of the compressive modulus are compared with data of laboratory oedometer tests and other situ tests.Comparisons of the results indicate that the compressive modulus determined with CPTU tests are twice as much as that measured in the laboratory consolidation tests and are in good agreement with that from CPT and SPT.When the compressive modulus from CPTU tests were used directly for design,it would be better in practice.
2011, 19(6): 887-892.
Analysis of joint occurrence in rock mass is an important and basic task in rock mechanics and rock hydraulics.This paper analyzes the merits and demerits of the traditional plots analysis method,the fuzzy equivalence clustering method and the fuzzy C-means clustering method(FCM).Then it proposes a synthetical method.This method is more accurate and reasonable according to the merits and demerits mentioned above when the above three methods are used alone.This synthetical method is applied to the group number and the superiority trends of joint occurrence in the rock mass at-555 levels in SanShandao Gold Mine.
Analysis of joint occurrence in rock mass is an important and basic task in rock mechanics and rock hydraulics.This paper analyzes the merits and demerits of the traditional plots analysis method,the fuzzy equivalence clustering method and the fuzzy C-means clustering method(FCM).Then it proposes a synthetical method.This method is more accurate and reasonable according to the merits and demerits mentioned above when the above three methods are used alone.This synthetical method is applied to the group number and the superiority trends of joint occurrence in the rock mass at-555 levels in SanShandao Gold Mine.
2011, 19(6): 893-901.
The surface features in urban areas are very complex and have significant spatial variations.As a result,the subsidence monitoring measures without differentiating surface features can hardly precisely reflect the subsidence characters of urban area since they are influenced by various factors.Previous subsidence monitoring with the PS-InSAR technique is unable to conduct attribute classification for PS monitoring points due to the low spatial resolution of SAR images.In this paper,the high density PS monitoring points in Tanggu research area are firstly extracted using the 1m spatial resolution TerraSAR-X images.Based on various industrial classification standards,the PS attributes for different urban surface features are then divided into different categories to facilitate complex urban subsidence analysis.SAR tomography technique is adopted to deal with the classification error of PS monitoring points for high buildings.The attribute of each PS monitoring point is automatically recognized with spatial analysis and the specific subsidence characters of each kind of surface feature are discussed.As a result,the subsidence rate of soil surface is the highest while the residential area and bridges are the lowest.This preliminary research shows that 1)high spatial resolution TerraSAR-X images make it possible to carry out attribute classification on PS monitoring points and further to carry out subsidence monitoring on different surface feature; 2)it helps us understand the mechanism and hazard of different surface features induced by their own influencing factors, and present us the scientific references to land subsidence monitoring,warning and risk assessment during urban constructions.
The surface features in urban areas are very complex and have significant spatial variations.As a result,the subsidence monitoring measures without differentiating surface features can hardly precisely reflect the subsidence characters of urban area since they are influenced by various factors.Previous subsidence monitoring with the PS-InSAR technique is unable to conduct attribute classification for PS monitoring points due to the low spatial resolution of SAR images.In this paper,the high density PS monitoring points in Tanggu research area are firstly extracted using the 1m spatial resolution TerraSAR-X images.Based on various industrial classification standards,the PS attributes for different urban surface features are then divided into different categories to facilitate complex urban subsidence analysis.SAR tomography technique is adopted to deal with the classification error of PS monitoring points for high buildings.The attribute of each PS monitoring point is automatically recognized with spatial analysis and the specific subsidence characters of each kind of surface feature are discussed.As a result,the subsidence rate of soil surface is the highest while the residential area and bridges are the lowest.This preliminary research shows that 1)high spatial resolution TerraSAR-X images make it possible to carry out attribute classification on PS monitoring points and further to carry out subsidence monitoring on different surface feature; 2)it helps us understand the mechanism and hazard of different surface features induced by their own influencing factors, and present us the scientific references to land subsidence monitoring,warning and risk assessment during urban constructions.
2011, 19(6): 902-908.
In order to know the mechanical effect and the stability of the adjacent gas pipeline,the optimum elastic modulus scheme of the loose soil,grouting reinforcement soil and primary support are back-analyzed with utilization of the orthogonal experiment design and on the basis of in-situ measured deformation.The safety impact evaluation on the gas pipeline during the construction process of the hydraulic tunnel are carried out with the back-calculated optimum parameters.The results show that the elastic modulus values for the primary support,the grouting reinforcement soil and the loose soil are 26000MPa, 50MPa and 40MPa,respectively.The adjacent gas pipeline was safe and stable during the construction process of the hydraulic tunnel.
In order to know the mechanical effect and the stability of the adjacent gas pipeline,the optimum elastic modulus scheme of the loose soil,grouting reinforcement soil and primary support are back-analyzed with utilization of the orthogonal experiment design and on the basis of in-situ measured deformation.The safety impact evaluation on the gas pipeline during the construction process of the hydraulic tunnel are carried out with the back-calculated optimum parameters.The results show that the elastic modulus values for the primary support,the grouting reinforcement soil and the loose soil are 26000MPa, 50MPa and 40MPa,respectively.The adjacent gas pipeline was safe and stable during the construction process of the hydraulic tunnel.
2011, 19(6): 909-916.
As a style of anchoring the cable of suspension bridge,the gravity anchor is one of the most important elements for the safe of the bridge.The displacement of the anchorage buttress is the key factor for the stability.This paper examines the stability of the anchorage for a Super Cable-stayed Bridge planned to be built over Longjiang river in Yunnan Province.It is located in the place with complex stratum condition.The soil strength and modulus parameters are very small at the construction site.Therefore,predicting the displacement of anchorage buttresses under various conditions is very important to design the proposal of foundation treatment and determine treatment parameters reasonably.This paper presents the large-scale numerical models with FLAC3D-fast lagranian analysis of continua in three-dimensions.The models are developed in strict accordance with the construction steps.They include foundation pit excavation,main body of anchorage construction,backfill and weights construction,and cable connection.The results indicate that the displacement of the anchorage buttress in the last two steps is about 5cm,lower than the allowable value 15cm.The settlement of foundation pit is in the allowable limits,too.The soil needn't to be strengthened.Because the displacement is largely dependent on the soil parameters,we also conduct the parameters sensitivity analysis.Results indicate that the deformation modulus E is ought to be assured through enough tests for its big sensitivity value.
As a style of anchoring the cable of suspension bridge,the gravity anchor is one of the most important elements for the safe of the bridge.The displacement of the anchorage buttress is the key factor for the stability.This paper examines the stability of the anchorage for a Super Cable-stayed Bridge planned to be built over Longjiang river in Yunnan Province.It is located in the place with complex stratum condition.The soil strength and modulus parameters are very small at the construction site.Therefore,predicting the displacement of anchorage buttresses under various conditions is very important to design the proposal of foundation treatment and determine treatment parameters reasonably.This paper presents the large-scale numerical models with FLAC3D-fast lagranian analysis of continua in three-dimensions.The models are developed in strict accordance with the construction steps.They include foundation pit excavation,main body of anchorage construction,backfill and weights construction,and cable connection.The results indicate that the displacement of the anchorage buttress in the last two steps is about 5cm,lower than the allowable value 15cm.The settlement of foundation pit is in the allowable limits,too.The soil needn't to be strengthened.Because the displacement is largely dependent on the soil parameters,we also conduct the parameters sensitivity analysis.Results indicate that the deformation modulus E is ought to be assured through enough tests for its big sensitivity value.
2011, 19(6): 917-921.
Sandstone and slate are the main rock types in the west route area of the South-to-North Water Transfer Project.The strength of slates is anisotropic obviously.It plays a significant role in the choice of the diversion dam site and the design and construction of the deep and long tunnelsThis paper studies the strength characters and deformation law of slates,and confirms the reasonable strength parameters of slates.The uniaxial compression deformation tests and triaxial compression tests are carried out on slate samples drilled in the west route area.The study considers the various laws of the slate strength with the dips of bedding planes.The anisotropy of the slate strength is obtained with the Hoek-Brown criterion and based on these test results.The shear strength of the rock mass is confirmed and becomes the foundation for engineering design.
Sandstone and slate are the main rock types in the west route area of the South-to-North Water Transfer Project.The strength of slates is anisotropic obviously.It plays a significant role in the choice of the diversion dam site and the design and construction of the deep and long tunnelsThis paper studies the strength characters and deformation law of slates,and confirms the reasonable strength parameters of slates.The uniaxial compression deformation tests and triaxial compression tests are carried out on slate samples drilled in the west route area.The study considers the various laws of the slate strength with the dips of bedding planes.The anisotropy of the slate strength is obtained with the Hoek-Brown criterion and based on these test results.The shear strength of the rock mass is confirmed and becomes the foundation for engineering design.
2011, 19(6): 922-927.
Coal mining has caused a variety of mining-affected zones including old mined-area,present mined-area and future mined-area.The 1000 kV UHV transmission line of Southeast Shanxi to Nanyang passes through the mined out space and layout area of Shanxi coalfield.This paper appraises the influence of mining of coalfield layout area to the foundation stability of the transmission towers.Based on the locally collected data,it used the FLAC3D numerical method.The mining simulation of the coal seam 3# under the N177 tower of the 1000 kV UHV transmission line is presented.After the coal seam 3# has been conducted,the numerical simulation of coal seam 9# is established.The results are as follows: The mining of the coal seam 9# can bring influence on the stability of the transmission tower foundation.The most subsidence of the ground is 1.15m and the most inclination of the transmission tower foundation along the power line is 5.7.Without taking anti-deformation measures,the inclination of the tower foundation will endanger the stability of 1 000 kV UHV transmission line.
Coal mining has caused a variety of mining-affected zones including old mined-area,present mined-area and future mined-area.The 1000 kV UHV transmission line of Southeast Shanxi to Nanyang passes through the mined out space and layout area of Shanxi coalfield.This paper appraises the influence of mining of coalfield layout area to the foundation stability of the transmission towers.Based on the locally collected data,it used the FLAC3D numerical method.The mining simulation of the coal seam 3# under the N177 tower of the 1000 kV UHV transmission line is presented.After the coal seam 3# has been conducted,the numerical simulation of coal seam 9# is established.The results are as follows: The mining of the coal seam 9# can bring influence on the stability of the transmission tower foundation.The most subsidence of the ground is 1.15m and the most inclination of the transmission tower foundation along the power line is 5.7.Without taking anti-deformation measures,the inclination of the tower foundation will endanger the stability of 1 000 kV UHV transmission line.
2011, 19(6): 928-934.
Many sensors usually are installed in a landslide body.So,their comprehension information can be extracted.Only one key monitoring sensor instead of the others is usually used in the prediction model at the same time in the landslide at present.The present prediction model can't make a full use of the monitoring data from the many sensors.The errors from the sensors cannot be considered in the model too.In order to overcome the above shortcomings,multi-sensor valuation fusion theory has been developed and used.The fusion efficiency of multi-sensor is theoretically proved to be better than that of any single sensor.Analysis of landslide is carried out by using a pixel-level fusion method.The result identifies that the landslide had experienced slowly deformation stage form July 2006 to September 2007and uniform motion deformation stage form September 2007 to September 2008and accelerated deformation stage form September 2008 to August 2009and rapidly deformation stage form August 2009 to February 2010.Such result is consistent with the law of nature.Two different periods of transitional,happened in August and September,which reflected the rain is the main factors caused landslide sliding.And the feasibility and effectiveness of the method is also proved at the same time.
Many sensors usually are installed in a landslide body.So,their comprehension information can be extracted.Only one key monitoring sensor instead of the others is usually used in the prediction model at the same time in the landslide at present.The present prediction model can't make a full use of the monitoring data from the many sensors.The errors from the sensors cannot be considered in the model too.In order to overcome the above shortcomings,multi-sensor valuation fusion theory has been developed and used.The fusion efficiency of multi-sensor is theoretically proved to be better than that of any single sensor.Analysis of landslide is carried out by using a pixel-level fusion method.The result identifies that the landslide had experienced slowly deformation stage form July 2006 to September 2007and uniform motion deformation stage form September 2007 to September 2008and accelerated deformation stage form September 2008 to August 2009and rapidly deformation stage form August 2009 to February 2010.Such result is consistent with the law of nature.Two different periods of transitional,happened in August and September,which reflected the rain is the main factors caused landslide sliding.And the feasibility and effectiveness of the method is also proved at the same time.
2011, 19(6): 935-940.
The No.3 line of Nanjing Metro would cross a valley and karst area,which is one of the several major geotechnical problems during the construction.A preliminary survey showed that there were many caves in the area.It's located in the downtown area where has heavy traffic and dense buildings,many underground pipelines and complicated geological conditions.In order to find out the karst development situation in a certain place for the engineering,the high-density resistivity method was used for karst prospecting after combination of geological structure and comprehensive election.The WN measurement was carried out.The electrical sense points are located on asphalt or cement concrete pavements.The condition of the sense contact to the ground surface was poor.So it had substantial errors in the back analysis process.For this reason,the electrode with ground coupling conditions were improved in the measurement.The power supply voltage was also increased to improve the current penetration.During testing,the isolines were rendered on the test data directly.According to the characteristics of low resistivity distribution from the isolines,the karst development situation was inferred.The results coincide with the drilling results relatively.The results were successful.After the contrast analysis between field engineering geological investigation and the borehole data,the spatial distribution of the karsts was identified.The results show that the geophysical method has multiple solutions.Before the geophysical work,a field investigation should be carried out for the geological and tectonic conditions in study area.Then geological analysis of the karst characteristics should be carried out in order to guide the work of geophysical wiring and data interpretation well.When the ground conditions are poor,the methods of piling soil up and watering can be undertaken to solve the problem of electrode coupling.To the existence of error of the back analysis,the isoline map of apparent resistivity can be used directly to infer the locations of karsts.
The No.3 line of Nanjing Metro would cross a valley and karst area,which is one of the several major geotechnical problems during the construction.A preliminary survey showed that there were many caves in the area.It's located in the downtown area where has heavy traffic and dense buildings,many underground pipelines and complicated geological conditions.In order to find out the karst development situation in a certain place for the engineering,the high-density resistivity method was used for karst prospecting after combination of geological structure and comprehensive election.The WN measurement was carried out.The electrical sense points are located on asphalt or cement concrete pavements.The condition of the sense contact to the ground surface was poor.So it had substantial errors in the back analysis process.For this reason,the electrode with ground coupling conditions were improved in the measurement.The power supply voltage was also increased to improve the current penetration.During testing,the isolines were rendered on the test data directly.According to the characteristics of low resistivity distribution from the isolines,the karst development situation was inferred.The results coincide with the drilling results relatively.The results were successful.After the contrast analysis between field engineering geological investigation and the borehole data,the spatial distribution of the karsts was identified.The results show that the geophysical method has multiple solutions.Before the geophysical work,a field investigation should be carried out for the geological and tectonic conditions in study area.Then geological analysis of the karst characteristics should be carried out in order to guide the work of geophysical wiring and data interpretation well.When the ground conditions are poor,the methods of piling soil up and watering can be undertaken to solve the problem of electrode coupling.To the existence of error of the back analysis,the isoline map of apparent resistivity can be used directly to infer the locations of karsts.
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