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Editor Work2012 Vol. 20, No. 4
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2012, 20(4): 471-477.
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This paper examines the law of the deformation and failure of slopes associated with weak planes under earthquake effects. Experiments with a single three group weak surface slope model is carried out under simulated earthquake deformation and failure in shaking table. The digital speckle correlation method is used to process the experimental results. The displacement and strain of model slope are obtained. From the experimental results, it can be found that the displacement and strain are concentrated in the weak surface slope with the continuous vibration, eventually leading to the slope damage. It can be found from the experimental model comparisons that the deeper the weak surface in the slope body, the more stable the slope. The longer of the weak surface in the body, the less stable the slope. The test model first appeared fractures in the top, and then damaged along a weak surface, which is analyzed for the cause of the slope failure.
This paper examines the law of the deformation and failure of slopes associated with weak planes under earthquake effects. Experiments with a single three group weak surface slope model is carried out under simulated earthquake deformation and failure in shaking table. The digital speckle correlation method is used to process the experimental results. The displacement and strain of model slope are obtained. From the experimental results, it can be found that the displacement and strain are concentrated in the weak surface slope with the continuous vibration, eventually leading to the slope damage. It can be found from the experimental model comparisons that the deeper the weak surface in the slope body, the more stable the slope. The longer of the weak surface in the body, the less stable the slope. The test model first appeared fractures in the top, and then damaged along a weak surface, which is analyzed for the cause of the slope failure.
2012, 20(4): 478-482.
The inter-slice action of transmitting coefficient method is classified according to its properties and the relationship among the inter-slice action and active earth pressure and passive earth pressure. This paper reveals that the three types of calculation results discord with the real stress state, which is more dangerous. The reason for the problem is analyzed. The limit value of the inter-slice stress is solved with the Mohr-Coulomb yield criterion. The finding shows that the rear slice can occur active destruction when the inter-slice action is less than the active earth pressure. So the inter-slice action should take active earth pressure. The anterior slice can occur passive destruction when the inter-slice action is more than the passive earth pressure. So the inter-slice action should take passive earth pressure. The research results are applied to engineering cases.
The inter-slice action of transmitting coefficient method is classified according to its properties and the relationship among the inter-slice action and active earth pressure and passive earth pressure. This paper reveals that the three types of calculation results discord with the real stress state, which is more dangerous. The reason for the problem is analyzed. The limit value of the inter-slice stress is solved with the Mohr-Coulomb yield criterion. The finding shows that the rear slice can occur active destruction when the inter-slice action is less than the active earth pressure. So the inter-slice action should take active earth pressure. The anterior slice can occur passive destruction when the inter-slice action is more than the passive earth pressure. So the inter-slice action should take passive earth pressure. The research results are applied to engineering cases.
2012, 20(4): 483-490.
This paper is based on dynamic shear modulus formula and correlative parameters of loess gained from three triaxial tests. The tests were acted by random seismic load. A subprogram of MSC.Marc was programmed. Finite element model acted by artificial earthquake wave was built to study dynamic response of loess slope. So, the displacement, velocity and stress transformation law of loess slope were analyzed when excellent frequency, amplitude and action direction of input seismic wave was changed. The results show that excellent frequency of slope displacement, velocity response time-history is much smaller than the input wave. A large number of high frequency wave was filtered when seismic wave transmit in slope soil. And dynamic response of loess slope was affected by the predominant frequency of seismic wave strongly. A giving slope was exceptional sensitive to certain seismic wave with predominant frequency. In addition, the changing of amplitude of seismic wave could alter the dynamic response amplitude of slope linearly, but couldn't transform the spectrum character of dynamic response of slope. The result also shows that the dynamic response time-history of slope contains more high frequency components when acting earthquake wave with certain action angle. Response amplitude of displacement and velocity reduced more quickly more close to the top when action angle increasing. Different effect law of stress response amplitude was shown in the top, middle and toe of slope. The changing of seismic wave acting direction affects dynamic response amplificatory coefficient also, which decreases with the increase of seismic wave acting angle when direction is un-vertical.
This paper is based on dynamic shear modulus formula and correlative parameters of loess gained from three triaxial tests. The tests were acted by random seismic load. A subprogram of MSC.Marc was programmed. Finite element model acted by artificial earthquake wave was built to study dynamic response of loess slope. So, the displacement, velocity and stress transformation law of loess slope were analyzed when excellent frequency, amplitude and action direction of input seismic wave was changed. The results show that excellent frequency of slope displacement, velocity response time-history is much smaller than the input wave. A large number of high frequency wave was filtered when seismic wave transmit in slope soil. And dynamic response of loess slope was affected by the predominant frequency of seismic wave strongly. A giving slope was exceptional sensitive to certain seismic wave with predominant frequency. In addition, the changing of amplitude of seismic wave could alter the dynamic response amplitude of slope linearly, but couldn't transform the spectrum character of dynamic response of slope. The result also shows that the dynamic response time-history of slope contains more high frequency components when acting earthquake wave with certain action angle. Response amplitude of displacement and velocity reduced more quickly more close to the top when action angle increasing. Different effect law of stress response amplitude was shown in the top, middle and toe of slope. The changing of seismic wave acting direction affects dynamic response amplificatory coefficient also, which decreases with the increase of seismic wave acting angle when direction is un-vertical.
2012, 20(4): 491-507.
Study on the hazard of water surge induced by landslide is an important content in the chain of reservoir landslide hazard. The surge hazard is a difficult and hot problem in landslide and hydropower project fields. In this paper, the coupling of Euler and Lagrange (CEL) algorithm and the orthogonal numerical method are used to study the influence of landslide body shape, landslide front morphology, landslide volume, friction factor of slide surface and the water surface width on the surge. The results are as follows. For the slide body with the same volume, the wedge shape formats the largest surge. The larger of the front angle of the wedge the higher of the surge height. This kind of effect is more significant in the near field. Secondly, the volume of landslide has a greater influence on the surge height. With the increasing of the volume the surge height increases too. Thirdly, under the same conditions, the surge height decreases with the increasing of the friction coefficient of sliding surface. Fourthly due to the blocking effect, as the water surface width decreases, the surge height shows an increasing tendency. Especially the climbing height of the surge increases significantly.
Study on the hazard of water surge induced by landslide is an important content in the chain of reservoir landslide hazard. The surge hazard is a difficult and hot problem in landslide and hydropower project fields. In this paper, the coupling of Euler and Lagrange (CEL) algorithm and the orthogonal numerical method are used to study the influence of landslide body shape, landslide front morphology, landslide volume, friction factor of slide surface and the water surface width on the surge. The results are as follows. For the slide body with the same volume, the wedge shape formats the largest surge. The larger of the front angle of the wedge the higher of the surge height. This kind of effect is more significant in the near field. Secondly, the volume of landslide has a greater influence on the surge height. With the increasing of the volume the surge height increases too. Thirdly, under the same conditions, the surge height decreases with the increasing of the friction coefficient of sliding surface. Fourthly due to the blocking effect, as the water surface width decreases, the surge height shows an increasing tendency. Especially the climbing height of the surge increases significantly.
2012, 20(4): 508-513.
Information value model is a widely used landslide susceptibility assessment method. However, it neglects the weights of different factors. This paper proposes the weighted information value model based on AHP.The impact of terrain, fault, river and lithology types on landslide in Enshi City is assessed with GIS spatial analysis. According to the weighted information value of these controlling factors, the study area can be divided into high, intermediate, low and very low susceptible areas for landslide occurrence.
Information value model is a widely used landslide susceptibility assessment method. However, it neglects the weights of different factors. This paper proposes the weighted information value model based on AHP.The impact of terrain, fault, river and lithology types on landslide in Enshi City is assessed with GIS spatial analysis. According to the weighted information value of these controlling factors, the study area can be divided into high, intermediate, low and very low susceptible areas for landslide occurrence.
2012, 20(4): 514-521.
The Qingjiang River Valley is the high susceptible area of landslide in Hubei Province, where the landslides have caused a great deal of economic loss and have great threats to local people. The geological environment of the studying area is complicated. There are deep rivercut valleys and steep bank slopes. The geological structure is developed. There were large-scale intermittent ascending motions in the aspect of neotectonic movement. There are 2843 landslide hazards in the studying area. They include 2275 landslides and 568 collapse-landslides. Most of the landslides are small-scale and are mainly distributed at the region with frequent human activities. According to the statistics analysis, the space distribution law of the landslides in the Qingjiang River Valley depends on the geological environmental and dynamic factors. The dynamic factors include natural dynamic factors and human dynamic factors. The former is mainly the rainfall. The later is the increasing cutting slope work by human activities. The time law of the landslides is synchronous, hysteresis and unstable period. The self-action law of landslides is inheritance, concealment, burstiness and diversity. Based on the investigation on the geological environmental conditions and the basic characteristics of the landslides in the studying area, the mitigation strategies for landslide hazards in the studying area are are proposed correspondingly. They include monitoring and early warning, relocation and movement, engineering improvement, and geological environment protection.
The Qingjiang River Valley is the high susceptible area of landslide in Hubei Province, where the landslides have caused a great deal of economic loss and have great threats to local people. The geological environment of the studying area is complicated. There are deep rivercut valleys and steep bank slopes. The geological structure is developed. There were large-scale intermittent ascending motions in the aspect of neotectonic movement. There are 2843 landslide hazards in the studying area. They include 2275 landslides and 568 collapse-landslides. Most of the landslides are small-scale and are mainly distributed at the region with frequent human activities. According to the statistics analysis, the space distribution law of the landslides in the Qingjiang River Valley depends on the geological environmental and dynamic factors. The dynamic factors include natural dynamic factors and human dynamic factors. The former is mainly the rainfall. The later is the increasing cutting slope work by human activities. The time law of the landslides is synchronous, hysteresis and unstable period. The self-action law of landslides is inheritance, concealment, burstiness and diversity. Based on the investigation on the geological environmental conditions and the basic characteristics of the landslides in the studying area, the mitigation strategies for landslide hazards in the studying area are are proposed correspondingly. They include monitoring and early warning, relocation and movement, engineering improvement, and geological environment protection.
2012, 20(4): 522-531.
This paper selects typical study area in epicenter area of the Beichuan as the site for the landslides interpretations induced after the Wenchuan Earthquake on May 12, 2008 and the strong rainfall on September 24, 2009.It bases on high-resolution aerial photographs and remote sensing SPOT 5 imagery. The results are as follows.the number of the earthquake-induced landslides is 1999.the number of the rainfall-induced landslides is 828.the rainfall enlarged the 150 earthquake-induced landslides. The earthquake and the rainfall are powerful causes for the occurrence of landslides.the rainfall-induced landslide area is 25% larger than the earthquake-induced landslide area. So, the landslide number in the study areais increased by 41.4%.The strong rainfall not only induced new landslides but also made the original earthquake landslides raise, and to expand the area so that the landslide area increased by68.7%.Meanwhile, on the basis of remote sensing data interpretation, the paper further analyse the induced landslides, carries out the trends, hazard and risk evaluation, which provides a scientific prediction basis. The findings in this paper can be useful to the Wenchuan Earthquake restoration and reconstruction in disaster mitigation and preparedness and provide the decision-makers to carry out earthquake-induced landslides and rainfall-induced landslides scale contrast and control factor coupling analysis and the earthquake and rainfall coupling disasters chain mode.
This paper selects typical study area in epicenter area of the Beichuan as the site for the landslides interpretations induced after the Wenchuan Earthquake on May 12, 2008 and the strong rainfall on September 24, 2009.It bases on high-resolution aerial photographs and remote sensing SPOT 5 imagery. The results are as follows.the number of the earthquake-induced landslides is 1999.the number of the rainfall-induced landslides is 828.the rainfall enlarged the 150 earthquake-induced landslides. The earthquake and the rainfall are powerful causes for the occurrence of landslides.the rainfall-induced landslide area is 25% larger than the earthquake-induced landslide area. So, the landslide number in the study areais increased by 41.4%.The strong rainfall not only induced new landslides but also made the original earthquake landslides raise, and to expand the area so that the landslide area increased by68.7%.Meanwhile, on the basis of remote sensing data interpretation, the paper further analyse the induced landslides, carries out the trends, hazard and risk evaluation, which provides a scientific prediction basis. The findings in this paper can be useful to the Wenchuan Earthquake restoration and reconstruction in disaster mitigation and preparedness and provide the decision-makers to carry out earthquake-induced landslides and rainfall-induced landslides scale contrast and control factor coupling analysis and the earthquake and rainfall coupling disasters chain mode.
2012, 20(4): 532-539.
Wenchuan Earthquake happened in weak geological environment of the mountainous area. Both internal and external earthquake vulnerable geologic forces can accelerate the geological environment change in the disaster area. Changes in the process can appear different geological effects and geohazards. People have paid full attentions to the earthquake secondary geological hazards. In the disaster reconstruction process, they notice the geological hazard survey and evaluation, and site selection from fault zone. They can avoid major geological disaster and bad geological, major geological disasters to the management. However, after the earthquake, disaster geological hazards on the lag of the damage still beyond the people's imagination. The Zhouqu debris flow, Qingpping debris flow, the 213 national highway destroyed by the earthquake are warned us that geological disaster prevention and control of the situation are still severe. The need is increased for attention to disaster geological environment, the present situation and the prevention of geological disasters science and technology research. Early effective means of disaster are also needed. This paper studies the disaster area landscape change, the surface damage, mountain earthquake cracked, hydrogeology conditions change, geological disasters such as development features of geological environment situation. It analyzes the evolution process of the earthquake, the surface slope geological environment change process, the influence of the external factors, collapse, landslide and debris flow relationship geological disasters. It summarizes the geological environment changing process of the development of the geological disaster distribution characteristics. It proposes the rebuilding after the geological disaster prevention and control measures to stage. Conclusions are as follows.(1)After the changes of the geological environment speeding up, all kinds of surface slope destruction of geological environment evolution of external factors in a highly sensitive period.(2)the earthquake and its aftershocks of repeated impact damage, outside the moment of load overlay, decades, geological disaster on high frequency, multiple, an unexpected period.(3)After the reconstruction phase should strengthen the investigation of geological hazard assessment, and to pay attention to the special period and the important section of disaster prevention and control, to take the investigation and assessment of predicting+the crowd monitoring to prevent+monitoring and warning+move geological hazards+engineering management and so on.the many kinds of combination prevention and control measures have to be adopted after geological disasters.
Wenchuan Earthquake happened in weak geological environment of the mountainous area. Both internal and external earthquake vulnerable geologic forces can accelerate the geological environment change in the disaster area. Changes in the process can appear different geological effects and geohazards. People have paid full attentions to the earthquake secondary geological hazards. In the disaster reconstruction process, they notice the geological hazard survey and evaluation, and site selection from fault zone. They can avoid major geological disaster and bad geological, major geological disasters to the management. However, after the earthquake, disaster geological hazards on the lag of the damage still beyond the people's imagination. The Zhouqu debris flow, Qingpping debris flow, the 213 national highway destroyed by the earthquake are warned us that geological disaster prevention and control of the situation are still severe. The need is increased for attention to disaster geological environment, the present situation and the prevention of geological disasters science and technology research. Early effective means of disaster are also needed. This paper studies the disaster area landscape change, the surface damage, mountain earthquake cracked, hydrogeology conditions change, geological disasters such as development features of geological environment situation. It analyzes the evolution process of the earthquake, the surface slope geological environment change process, the influence of the external factors, collapse, landslide and debris flow relationship geological disasters. It summarizes the geological environment changing process of the development of the geological disaster distribution characteristics. It proposes the rebuilding after the geological disaster prevention and control measures to stage. Conclusions are as follows.(1)After the changes of the geological environment speeding up, all kinds of surface slope destruction of geological environment evolution of external factors in a highly sensitive period.(2)the earthquake and its aftershocks of repeated impact damage, outside the moment of load overlay, decades, geological disaster on high frequency, multiple, an unexpected period.(3)After the reconstruction phase should strengthen the investigation of geological hazard assessment, and to pay attention to the special period and the important section of disaster prevention and control, to take the investigation and assessment of predicting+the crowd monitoring to prevent+monitoring and warning+move geological hazards+engineering management and so on.the many kinds of combination prevention and control measures have to be adopted after geological disasters.
2012, 20(4): 540-546.
Due to lacking of knowledge of geological conditions in the survey and design stage, or requirements to improve the road line, highway tunnels can be constructed in large ancient landslide mass. For example, the Chuanzhusi tunnel is constructed in a large ancient landslide. This paper bases on the geological conditions of landslide occurrence and the tunnel. A detailed analysis is done on the system characteristics of the ancient landslide. Through investigation and by the construction of geological and mechanical methods, this paper studies the tunneling in through the ancient landslide. It turns up the geological characteristics of the problem, such as holes, rocks and collapse and deformation and failure mechanisms, and suggests remediation measures. The research result for the construction of the tunnel passing through the ancient landslide has an important significance.
Due to lacking of knowledge of geological conditions in the survey and design stage, or requirements to improve the road line, highway tunnels can be constructed in large ancient landslide mass. For example, the Chuanzhusi tunnel is constructed in a large ancient landslide. This paper bases on the geological conditions of landslide occurrence and the tunnel. A detailed analysis is done on the system characteristics of the ancient landslide. Through investigation and by the construction of geological and mechanical methods, this paper studies the tunneling in through the ancient landslide. It turns up the geological characteristics of the problem, such as holes, rocks and collapse and deformation and failure mechanisms, and suggests remediation measures. The research result for the construction of the tunnel passing through the ancient landslide has an important significance.
2012, 20(4): 547-555.
In order to explore rainfall response mechanism of loess-bedrock landslide, the paper has discussed ground water level response characteristics of Lingnan landslide under rainstorm and successive rain and soil stress-strain characteristics under corresponding stress path. It takes the Lingnan landslide in Linyou county as an example. It combines macroscopic deformation and failure data of landslide, geotechnical test and analog computation. Moreover, the failure mechanism of the loess-bedrock landslide has been studied in the paper. The paper shows the preliminary results as follows. Firstly, the landslide mass is silty loessial clay. The landslide bed is glutenite. The mass and bed are featured by lower osmotic coefficient and high imperviousness. Secondly, the muddy loess flow and block slide are the main models of motion instability of Lingnan landslide. Upon rainstorm, the muddy loess flow breaks out frequently. In this sense, the block slide is in connection with successive cloudy-rainy weather. Thirdly, the ground water level of the slope has increased drastically in 235.5 mm successive rain compared with 103 mm rainstorm. Fourthly, the silty loess of landslide mass is characterized with dilatancy. In case of a rainstorm, surface soil pore water pressure easily diffuses, subsequently, induces low-speed muddy loess flows. Under successive cloudy-rainy weather, dilating pores are timely replenished by ground water during shear breakdown of slide planes below ground water level. Drastic block slide arising from this cause can make great hazards.
In order to explore rainfall response mechanism of loess-bedrock landslide, the paper has discussed ground water level response characteristics of Lingnan landslide under rainstorm and successive rain and soil stress-strain characteristics under corresponding stress path. It takes the Lingnan landslide in Linyou county as an example. It combines macroscopic deformation and failure data of landslide, geotechnical test and analog computation. Moreover, the failure mechanism of the loess-bedrock landslide has been studied in the paper. The paper shows the preliminary results as follows. Firstly, the landslide mass is silty loessial clay. The landslide bed is glutenite. The mass and bed are featured by lower osmotic coefficient and high imperviousness. Secondly, the muddy loess flow and block slide are the main models of motion instability of Lingnan landslide. Upon rainstorm, the muddy loess flow breaks out frequently. In this sense, the block slide is in connection with successive cloudy-rainy weather. Thirdly, the ground water level of the slope has increased drastically in 235.5 mm successive rain compared with 103 mm rainstorm. Fourthly, the silty loess of landslide mass is characterized with dilatancy. In case of a rainstorm, surface soil pore water pressure easily diffuses, subsequently, induces low-speed muddy loess flows. Under successive cloudy-rainy weather, dilating pores are timely replenished by ground water during shear breakdown of slide planes below ground water level. Drastic block slide arising from this cause can make great hazards.
2012, 20(4): 556-563.
Landslide hazard is the most serious type of geological hazards in Lanzhou city. It has the characteristics of large quantity and scale, abruptness, short duration and damaging. in the authors use the support of MapGIS and design and develop the landslide hazard meteorological early-warning system for the disaster prevention and mitigation service in Lanzhou city. On the basis of the collected information, internal and external factors which lead to landslide are quantified in GIS, the authors get the relatively stationary landslide hazard potential risk assessment figure of Lanzhou city. By analyzing the relationship between rainfall and landslide hazard, the authors get the rainfall threshold expression. The system provides four rainfall models and two early-warning models, which achieves the diversification of models. Rainfall is quantified by four rainfall models. Potential probability value of landslide hazard in Lanzhou city is coupled with rainfall probability value, which is based on two early-warning models. Each model of early-warning system provides three, four and five limits of threshold for the final mapping selection. Through MapGIS k9 IMS secondary development platform, the system realizes Web publishing of real-time information of landslide hazards. The system realizes the automatic process from data acquisition to analysis and calculation, finally site released, which provides the basis for decision-making of disaster prevention and mitigation of Lanzhou city.
Landslide hazard is the most serious type of geological hazards in Lanzhou city. It has the characteristics of large quantity and scale, abruptness, short duration and damaging. in the authors use the support of MapGIS and design and develop the landslide hazard meteorological early-warning system for the disaster prevention and mitigation service in Lanzhou city. On the basis of the collected information, internal and external factors which lead to landslide are quantified in GIS, the authors get the relatively stationary landslide hazard potential risk assessment figure of Lanzhou city. By analyzing the relationship between rainfall and landslide hazard, the authors get the rainfall threshold expression. The system provides four rainfall models and two early-warning models, which achieves the diversification of models. Rainfall is quantified by four rainfall models. Potential probability value of landslide hazard in Lanzhou city is coupled with rainfall probability value, which is based on two early-warning models. Each model of early-warning system provides three, four and five limits of threshold for the final mapping selection. Through MapGIS k9 IMS secondary development platform, the system realizes Web publishing of real-time information of landslide hazards. The system realizes the automatic process from data acquisition to analysis and calculation, finally site released, which provides the basis for decision-making of disaster prevention and mitigation of Lanzhou city.
2012, 20(4): 564-569.
The creep characteristic of rock mass discontinuity has important practical significance for the analysis of rheological properties of the rock engineering. Based on the shear creep test of dentate discontinuity on the condition of shear stress, this paper studies the creep characteristics of discontinuities with different slope ratios and normal stresses. According to the creep test results, the shear creep empirical formula of discontinuity is obtained, and the long-term strength characteristics of discontinuities are studied. In this paper, Burgers model is selected to describe the shear creep deformation characteristics of discontinuities. The paper gives a discussion of the Burgers model for describing the shear creep characteristics of structural parameters of discontinuities.
The creep characteristic of rock mass discontinuity has important practical significance for the analysis of rheological properties of the rock engineering. Based on the shear creep test of dentate discontinuity on the condition of shear stress, this paper studies the creep characteristics of discontinuities with different slope ratios and normal stresses. According to the creep test results, the shear creep empirical formula of discontinuity is obtained, and the long-term strength characteristics of discontinuities are studied. In this paper, Burgers model is selected to describe the shear creep deformation characteristics of discontinuities. The paper gives a discussion of the Burgers model for describing the shear creep characteristics of structural parameters of discontinuities.
2012, 20(4): 570-575.
The discontinuities such as cracks, joints and faults can have the varying degrees of developments. The permeability of fractured rock can show the characteristics of anisotropy and discontinuity. The traditional finite element method encounters difficulty in the solution of the seepage field for intensive fractured rocks. This paper proposes the solution of seepage problems with free surface. It is obtained through meshless Galerkin method.the corresponding basic equations and integration schemes are derived. Applications of penalty function method to the processing procedure of seepage boundary condition and free surface boundary are also put forward. Two-dimensional meshless method software LIDAREFM is developed with IDL language. Research on seepage field characteristics and distribution of free surface under different discontinuity combinations are carried out, taking the fractured rock slope at Qiaozi town, Huairou County in Beijing as an example. The seepage field features under different degrees of opening and connectivity are discussed. Results show that the meshless method has certain advantages in solving seepage field of intensive fracture problem. The layout independence of gridding nodes on integration points is achieved. The re-processing of free surface and sub-domain with cracks crossing is avoided. The process of solving the seepage problem is simplified.
The discontinuities such as cracks, joints and faults can have the varying degrees of developments. The permeability of fractured rock can show the characteristics of anisotropy and discontinuity. The traditional finite element method encounters difficulty in the solution of the seepage field for intensive fractured rocks. This paper proposes the solution of seepage problems with free surface. It is obtained through meshless Galerkin method.the corresponding basic equations and integration schemes are derived. Applications of penalty function method to the processing procedure of seepage boundary condition and free surface boundary are also put forward. Two-dimensional meshless method software LIDAREFM is developed with IDL language. Research on seepage field characteristics and distribution of free surface under different discontinuity combinations are carried out, taking the fractured rock slope at Qiaozi town, Huairou County in Beijing as an example. The seepage field features under different degrees of opening and connectivity are discussed. Results show that the meshless method has certain advantages in solving seepage field of intensive fracture problem. The layout independence of gridding nodes on integration points is achieved. The re-processing of free surface and sub-domain with cracks crossing is avoided. The process of solving the seepage problem is simplified.
2012, 20(4): 576-584.
This paper reveals the dissolution gritty mechanism of dolomite. Some dissolution tests are carried out under different solution conditions and dolomite structures to analyze the factor of dissolution rate. It uses the casting thin sections and the scanning electron microscope methods to analyze the microstructure of dolomite at different dissolution stages.the test findings are that: (1)the rock microstructure dominates dissolution rate. The relations of different dolomite structures with its dissolution rate rateare as follows: (a) the dissolution rates for medium-fine grain dolomite, fine-powder crystal dolomite and powder dolomicrite are greatest and medium and lowest, respectively; (2)Specific surface area is connected with the total dissolution amount but not the dissolution rate in unit area; (3)the dissolution starts at the inter grain, the inter crystal void, the tectonic micro-fracture and the cleavage. It extends gradually to make sure that the voids and fractures are connected each other; (4)the dissolution worsens the microstructure of Dolomite gradually, weakens the connecting force of crystals. It couples with the disintegration and falling off of crystals. And finally it breaks up into fine particles and results in the gritting of dolomite.
This paper reveals the dissolution gritty mechanism of dolomite. Some dissolution tests are carried out under different solution conditions and dolomite structures to analyze the factor of dissolution rate. It uses the casting thin sections and the scanning electron microscope methods to analyze the microstructure of dolomite at different dissolution stages.the test findings are that: (1)the rock microstructure dominates dissolution rate. The relations of different dolomite structures with its dissolution rate rateare as follows: (a) the dissolution rates for medium-fine grain dolomite, fine-powder crystal dolomite and powder dolomicrite are greatest and medium and lowest, respectively; (2)Specific surface area is connected with the total dissolution amount but not the dissolution rate in unit area; (3)the dissolution starts at the inter grain, the inter crystal void, the tectonic micro-fracture and the cleavage. It extends gradually to make sure that the voids and fractures are connected each other; (4)the dissolution worsens the microstructure of Dolomite gradually, weakens the connecting force of crystals. It couples with the disintegration and falling off of crystals. And finally it breaks up into fine particles and results in the gritting of dolomite.
2012, 20(4): 585-590.
The 3D joint surface network simulation is based on Monte-Carlo theory. It is the most common method to study growth regulation of rock mass joints, and joint volume frequency,v. v is determined by that is measured in the field. It is one of the key parameters which affect the result of joint network simulation. Using the 3D joint surface network simulation program, a new method is promoted to determine v. This method is based on the back analysis from line frequency to volume frequency. A value to a joint set is given as the initial joint volume frequency.the 3D joint surface network simulation program is adopted to generate a 3D network model which just contains the joint set. Then line frequency along the survey line's trend of the model can be calculated. Therefore, a series line frequency(v) can be got from the series volume frequency.Then the functional relationship can be built up between the line frequency and the volume frequency. Lastly, the actual volume frequency can be determined using the line frequency measured in survey line trend. This paper further takes the rock mass of Yujianhe dam site in Xifeng county, Guizhou province as an example. The results show that there are a good linear relation between v and .The ratio between v and max is 0.4~1.0 when the joint radius obeys to the lognormal distribution. The ratio is about 1.3~3.5 when the radius does negative index distribution. Eventually, the rock mass integrality at the Yujianhe dam site is appraised using and v respectively. The result shows that the latter is more precise than the former.
The 3D joint surface network simulation is based on Monte-Carlo theory. It is the most common method to study growth regulation of rock mass joints, and joint volume frequency,v. v is determined by that is measured in the field. It is one of the key parameters which affect the result of joint network simulation. Using the 3D joint surface network simulation program, a new method is promoted to determine v. This method is based on the back analysis from line frequency to volume frequency. A value to a joint set is given as the initial joint volume frequency.the 3D joint surface network simulation program is adopted to generate a 3D network model which just contains the joint set. Then line frequency along the survey line's trend of the model can be calculated. Therefore, a series line frequency(v) can be got from the series volume frequency.Then the functional relationship can be built up between the line frequency and the volume frequency. Lastly, the actual volume frequency can be determined using the line frequency measured in survey line trend. This paper further takes the rock mass of Yujianhe dam site in Xifeng county, Guizhou province as an example. The results show that there are a good linear relation between v and .The ratio between v and max is 0.4~1.0 when the joint radius obeys to the lognormal distribution. The ratio is about 1.3~3.5 when the radius does negative index distribution. Eventually, the rock mass integrality at the Yujianhe dam site is appraised using and v respectively. The result shows that the latter is more precise than the former.
2012, 20(4): 591-598.
The analysis of occurrence of discontinuities is a basic work for further study on mechanical analysis and stability of rock mass. Traditional analysis of the plot method is insufficient and inadequate. And they are unable to analyze occurrence data of discontinuities accurately. Although the fuzzy cluster method can achieve accurate dominant occurrences, the initial cluster centroids must be given in advance. And the method uses a local optimized algorithm. Different choices of initial guesses of cluster centroids can lead to different partitions of the same data. In order to obtain objective results of classification and the dominant occurrence, a fuzzy c-means cluster analysis method based on the Particle Swarm Optimization(PSO)algorithm is proposed. This hybrid method uses the PSO algorithm to solve the problem. So it can avoid the subjectivity of the initial cluster centroids specified manually, overcome the defects of the fuzzy c-means algorithm such as the local optima and sensitivity to initialization, and analyse the occurrence data efficiently, even if there are a large number of discontinuities. Meanwhile, the optimal cluster number can be determined automatically during the operational process of the algorithm. On the basis of the field measured data from the real rock mass, the proposed approach has been testified to be reliable and reasonable. And the classification and dominant occurrences are more realistic.
The analysis of occurrence of discontinuities is a basic work for further study on mechanical analysis and stability of rock mass. Traditional analysis of the plot method is insufficient and inadequate. And they are unable to analyze occurrence data of discontinuities accurately. Although the fuzzy cluster method can achieve accurate dominant occurrences, the initial cluster centroids must be given in advance. And the method uses a local optimized algorithm. Different choices of initial guesses of cluster centroids can lead to different partitions of the same data. In order to obtain objective results of classification and the dominant occurrence, a fuzzy c-means cluster analysis method based on the Particle Swarm Optimization(PSO)algorithm is proposed. This hybrid method uses the PSO algorithm to solve the problem. So it can avoid the subjectivity of the initial cluster centroids specified manually, overcome the defects of the fuzzy c-means algorithm such as the local optima and sensitivity to initialization, and analyse the occurrence data efficiently, even if there are a large number of discontinuities. Meanwhile, the optimal cluster number can be determined automatically during the operational process of the algorithm. On the basis of the field measured data from the real rock mass, the proposed approach has been testified to be reliable and reasonable. And the classification and dominant occurrences are more realistic.
2012, 20(4): 599-606.
Porosity is one of the important characteristics of rock mass. It can reflect the effect of weathering and altering for the physical and mechanical characteristics of rock mass. Therefore, the functional relationship of porosity and the other physical and mechanical parameters is established through indoor experiments. The effect of weathering and altering for the physical and mechanical characteristics of granite-porphyry also is analyzed. The results show that the dry density and compressive strength of the weathered and altered granite-porphyry decrease as porosity increases, which presents the power function relationship. Their correlation coefficient are greater than 0.83.The water absorption increases with increasing in porosity, which presents the binomial functional relationship. Their correlation coefficient are greater than 0.90.All the weathering and altering can weaken the physical and mechanical characteristics of granite-porphyry. As increasing in weathering and altering, the physical and mechanical characteristics of granite-porphyry can gradually reduce. The influence of altering and weathering for the steep-inclined structural face is stronger than for the gently dipping structural face.
Porosity is one of the important characteristics of rock mass. It can reflect the effect of weathering and altering for the physical and mechanical characteristics of rock mass. Therefore, the functional relationship of porosity and the other physical and mechanical parameters is established through indoor experiments. The effect of weathering and altering for the physical and mechanical characteristics of granite-porphyry also is analyzed. The results show that the dry density and compressive strength of the weathered and altered granite-porphyry decrease as porosity increases, which presents the power function relationship. Their correlation coefficient are greater than 0.83.The water absorption increases with increasing in porosity, which presents the binomial functional relationship. Their correlation coefficient are greater than 0.90.All the weathering and altering can weaken the physical and mechanical characteristics of granite-porphyry. As increasing in weathering and altering, the physical and mechanical characteristics of granite-porphyry can gradually reduce. The influence of altering and weathering for the steep-inclined structural face is stronger than for the gently dipping structural face.
2012, 20(4): 607-613.
Microstructure and micromechanics of granular soils have been of interest to many researchers because of their significant role in the macroscale response. Discrete element method(DEM) is usually simpler, faster, and cheaper than the traditional experimental method and able to obtain some information that is difficult or inaccessible in the experimental method. In this paper, some new developments of the microscale study on granular soil using DEM are briefly reviewed. Some issues in numerical modeling such as density(mass) scaling and membrane boundary simulation are discussed. The new developments on microstructure study such as particle rotation and displacement and mesoscale void ratio distribution using DEM are analyzed. It is concluded that DEM is a powerful tool that can capture the discrete characteristics of the granular materials.
Microstructure and micromechanics of granular soils have been of interest to many researchers because of their significant role in the macroscale response. Discrete element method(DEM) is usually simpler, faster, and cheaper than the traditional experimental method and able to obtain some information that is difficult or inaccessible in the experimental method. In this paper, some new developments of the microscale study on granular soil using DEM are briefly reviewed. Some issues in numerical modeling such as density(mass) scaling and membrane boundary simulation are discussed. The new developments on microstructure study such as particle rotation and displacement and mesoscale void ratio distribution using DEM are analyzed. It is concluded that DEM is a powerful tool that can capture the discrete characteristics of the granular materials.
2012, 20(4): 614-620.
This paper is based on the SWCC obtained from the test with the triaxial test instrument for unsaturated soils controlled by stress and strain(WF)in the laboratory.The test results show that the SWCCs of two kind of soils are different greatly.The state of the soil in the foundation under the reservoir changes form nature state to unsaturated state,and further to saturated state,because of the increase of water content after sluice of the reservoir.The change course of soil saturation is analysed with FEM for seepage of unsteady and unsaturated conditions.The laboratory test results are further used in the numerical analysis.The engineering geology is influenced greatly by the change course.It is found that the provision of cut seepage ditch can diminish the influence of the change course.From the analysis,the effect of the measure of seepage control can reduce the groundwater level and reduce the water content of the soils up the groundwater level.This is important to reduce immerge and salt-basify for the project.
This paper is based on the SWCC obtained from the test with the triaxial test instrument for unsaturated soils controlled by stress and strain(WF)in the laboratory.The test results show that the SWCCs of two kind of soils are different greatly.The state of the soil in the foundation under the reservoir changes form nature state to unsaturated state,and further to saturated state,because of the increase of water content after sluice of the reservoir.The change course of soil saturation is analysed with FEM for seepage of unsteady and unsaturated conditions.The laboratory test results are further used in the numerical analysis.The engineering geology is influenced greatly by the change course.It is found that the provision of cut seepage ditch can diminish the influence of the change course.From the analysis,the effect of the measure of seepage control can reduce the groundwater level and reduce the water content of the soils up the groundwater level.This is important to reduce immerge and salt-basify for the project.
2012, 20(4): 621-626.
This paper investigates the effect of chlorate salt on the stress-strain characteristics of cement stabilized soils. The clay with various sodium chloride salt concentrations is prepared artificially and stabilized by ordinary portland cement with different contents. A series of unconfined compressive strength tests of cement stabilized clay specimens after various curing periods are carried out in laboratory. The test results show that the chloride salt has adverse effects to the cement stabilized clay. The unconfined compression strength and deformation modulus of the cement treated clays decrease as the chloride salt content increases. The failure strain of cement treated clays increases as the chloride salt content increases. The stress-strain curves of cement stabilized clay change from brittle failure to ductile failure as the chloride salt content increases. However, the ratio of deformation modulus to the unconfined compressive strength of cement clay is independent to the chloride salt content.
This paper investigates the effect of chlorate salt on the stress-strain characteristics of cement stabilized soils. The clay with various sodium chloride salt concentrations is prepared artificially and stabilized by ordinary portland cement with different contents. A series of unconfined compressive strength tests of cement stabilized clay specimens after various curing periods are carried out in laboratory. The test results show that the chloride salt has adverse effects to the cement stabilized clay. The unconfined compression strength and deformation modulus of the cement treated clays decrease as the chloride salt content increases. The failure strain of cement treated clays increases as the chloride salt content increases. The stress-strain curves of cement stabilized clay change from brittle failure to ductile failure as the chloride salt content increases. However, the ratio of deformation modulus to the unconfined compressive strength of cement clay is independent to the chloride salt content.
2012, 20(4): 627-632.
Huge amounts of dredged clays are inevitably produced during the processes of river dredging and widening and port construction and expanding. Consequently, how to deal with the great amounts of dredged clays has become a hot issue in hydraulic engineering and geotechnical engineering. It is usual to treat the dredged clays with solidification method. The treated soils are usually used for engineering construction. So its mechanical properties should be considered as engineering materials. In order to study the compression properties and the structure yield stress, a series of compression tests with different mixing proportions are performed on the soils. As many natural sedimentary structural clays and cement-stabilized soil, there is a notable structure yield point for all compression curves of the solidified soil in many one-dimensional compression experiment results. When the upper load is less than the structure yield stress, the compressibility of solidified soil is very small. But the compressibility increases dramatically once the upper load is over the structure yield stress. Some factors affecting the structure yield stress are analyzed. Expression about the relationship between Py and qu is proposed by comparing the results of the one-dimensional compression tests and the unconfined compression tests. Compression properties of the solidified soil are significantly different between pre-yield and post-yield states, which is very useful for its application in engineering. The upper load cannot exceed the structure yield stress to avoid the sudden destruction without warning.
Huge amounts of dredged clays are inevitably produced during the processes of river dredging and widening and port construction and expanding. Consequently, how to deal with the great amounts of dredged clays has become a hot issue in hydraulic engineering and geotechnical engineering. It is usual to treat the dredged clays with solidification method. The treated soils are usually used for engineering construction. So its mechanical properties should be considered as engineering materials. In order to study the compression properties and the structure yield stress, a series of compression tests with different mixing proportions are performed on the soils. As many natural sedimentary structural clays and cement-stabilized soil, there is a notable structure yield point for all compression curves of the solidified soil in many one-dimensional compression experiment results. When the upper load is less than the structure yield stress, the compressibility of solidified soil is very small. But the compressibility increases dramatically once the upper load is over the structure yield stress. Some factors affecting the structure yield stress are analyzed. Expression about the relationship between Py and qu is proposed by comparing the results of the one-dimensional compression tests and the unconfined compression tests. Compression properties of the solidified soil are significantly different between pre-yield and post-yield states, which is very useful for its application in engineering. The upper load cannot exceed the structure yield stress to avoid the sudden destruction without warning.
2012, 20(4): 633-638.
The exposed carbonate limestone area at Guilin has red clay of high plastic limit. The clay was formed by laterization from limestone. Its pores are large and have high water contents It has the character of strong two layer structure. The upper layer is hard and the lower layer is soft. The upper clay has the rigid and hard plastic condition and high bearing capacity. The lower clay is soft plastic, has flowing plastic condition and weak bearing capacity. It needs treatment. This papers uses the soil-cement mixing method to treat the soft red clay. Laboratory tests are done on the mechanical properties of the cemented soils. The test results include the deformation of character and strength of the cemented clays taking into account the effects of cement-soil ratio and age.
The exposed carbonate limestone area at Guilin has red clay of high plastic limit. The clay was formed by laterization from limestone. Its pores are large and have high water contents It has the character of strong two layer structure. The upper layer is hard and the lower layer is soft. The upper clay has the rigid and hard plastic condition and high bearing capacity. The lower clay is soft plastic, has flowing plastic condition and weak bearing capacity. It needs treatment. This papers uses the soil-cement mixing method to treat the soft red clay. Laboratory tests are done on the mechanical properties of the cemented soils. The test results include the deformation of character and strength of the cemented clays taking into account the effects of cement-soil ratio and age.
2012, 20(4): 639-648.
This paper uses the Dynamic Biot's equation as the governing equation, and adopts the finite element method for space discretization and the generalized Newmark- for time discretization. A computational program PORO-WSSI 2D is developed for the consolidation and dynamic response analysis of seabed foundation. It is based on the program SWANDYNE which is for earthquake analysis. The consolidation modulus in PORO-WSSI 2D is validated by the Terzaghi 1D consolidation theory. Applying the PORO-WSSI 2D,the consolidation process and the final consolidation status of seabed foundation under a large-scale composite breakwater and hydrostatic water pressure are intensively investigated. The computational results indicate the PORO-WSSI 2D can effectively analyze and evaluate the consolidation process, and predict the shear failure of seabed foundation under marine structures.the final consolidation status determined also can provide the initial conditions as true as possible for the later analysis of liquefaction and shear failure in seabed foundation under the ocean wave or earthquake loading in engineering.
This paper uses the Dynamic Biot's equation as the governing equation, and adopts the finite element method for space discretization and the generalized Newmark- for time discretization. A computational program PORO-WSSI 2D is developed for the consolidation and dynamic response analysis of seabed foundation. It is based on the program SWANDYNE which is for earthquake analysis. The consolidation modulus in PORO-WSSI 2D is validated by the Terzaghi 1D consolidation theory. Applying the PORO-WSSI 2D,the consolidation process and the final consolidation status of seabed foundation under a large-scale composite breakwater and hydrostatic water pressure are intensively investigated. The computational results indicate the PORO-WSSI 2D can effectively analyze and evaluate the consolidation process, and predict the shear failure of seabed foundation under marine structures.the final consolidation status determined also can provide the initial conditions as true as possible for the later analysis of liquefaction and shear failure in seabed foundation under the ocean wave or earthquake loading in engineering.
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