2011 Vol. 33 No. 1
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Abstract：
This paper presents (a) constitutive models such as hypo-elastic models and elastic visco-plastic models, (b) methods for calculating the settlement of clayey soils in one-dimensional (1D) straining, (c) equations for nonlinear creep and compression of clayey soils in 1D straining, (d) development of lab testing facilities such as a double cell triaxial apparatus, a true-triaxial loading device, a direct shear box for testing the interface of a structural element and an unsaturated soil with suction control, and a soil nail pullout box, and (e) development of optical fiber sensing technologies for geotechnical monitoring. From the above presentation, the main conclusions are summarized in this paper.
This paper presents (a) constitutive models such as hypo-elastic models and elastic visco-plastic models, (b) methods for calculating the settlement of clayey soils in one-dimensional (1D) straining, (c) equations for nonlinear creep and compression of clayey soils in 1D straining, (d) development of lab testing facilities such as a double cell triaxial apparatus, a true-triaxial loading device, a direct shear box for testing the interface of a structural element and an unsaturated soil with suction control, and a soil nail pullout box, and (e) development of optical fiber sensing technologies for geotechnical monitoring. From the above presentation, the main conclusions are summarized in this paper.
Abstract：
Dynamic response of pile foundation-structure interaction is reproduced under earthquakes in the shaking table model tests and numerical simulation tests using software MARC. The results show that the effect of deformation of high-rise structures is large because of changed pile-type. The most shear force and overturning moment of high-rise structure in squeezed branch pile interaction system are smaller than those in straight pile interaction system. The deformation energy of the structure is reduced on account of considerable seismic energy in the interaction system of squeezed branch piles and is diffused to the soil through the branch or disk, while considerable seismic energy in the interaction system of straight piles and is converted into deformation energy of the structure, resulting in greater structural damage. At the same time, the results of shaking table tests and numerical simulation show that the squeezed branch pile-foundation has more damping energy, effectively enhances seismic capability of the structure system, and reduces seismic response of the structure under earthquakes. The study is of great significance to the reduction of earthquake damage.
Dynamic response of pile foundation-structure interaction is reproduced under earthquakes in the shaking table model tests and numerical simulation tests using software MARC. The results show that the effect of deformation of high-rise structures is large because of changed pile-type. The most shear force and overturning moment of high-rise structure in squeezed branch pile interaction system are smaller than those in straight pile interaction system. The deformation energy of the structure is reduced on account of considerable seismic energy in the interaction system of squeezed branch piles and is diffused to the soil through the branch or disk, while considerable seismic energy in the interaction system of straight piles and is converted into deformation energy of the structure, resulting in greater structural damage. At the same time, the results of shaking table tests and numerical simulation show that the squeezed branch pile-foundation has more damping energy, effectively enhances seismic capability of the structure system, and reduces seismic response of the structure under earthquakes. The study is of great significance to the reduction of earthquake damage.
Abstract：
There are limitation and short comings by using the fuzzy judgment method to evaluate the roadbed stability in karst area at present. Based on the consideration of the fuzziness and hierarchy of the chief factors for the roadbed stability, a two-stage fuzzy synthesis judgment model for the roadbed stability in karst area is presented. The interval features of the subordinate degrees and the weight vectors on the factors as well as the nonlinear features of weighting operation of fuzzy matrices are discussed. By use of the nonlinear composition operator on fuzzy matrix, the interval mathematics theory and the relative superiority degree method to interval number matrix, the interval fuzzy judgment theory for roadbed stability in karst area is suggested. It can reduce the effect of subjectivity of judgment and reflect the effect of the bad factors on the judgment results. It is more rational and maneuverable. The calculated results and a comparison with other methods show that the proposed method is reliable and reasonable.
There are limitation and short comings by using the fuzzy judgment method to evaluate the roadbed stability in karst area at present. Based on the consideration of the fuzziness and hierarchy of the chief factors for the roadbed stability, a two-stage fuzzy synthesis judgment model for the roadbed stability in karst area is presented. The interval features of the subordinate degrees and the weight vectors on the factors as well as the nonlinear features of weighting operation of fuzzy matrices are discussed. By use of the nonlinear composition operator on fuzzy matrix, the interval mathematics theory and the relative superiority degree method to interval number matrix, the interval fuzzy judgment theory for roadbed stability in karst area is suggested. It can reduce the effect of subjectivity of judgment and reflect the effect of the bad factors on the judgment results. It is more rational and maneuverable. The calculated results and a comparison with other methods show that the proposed method is reliable and reasonable.
Abstract：
Based on the unified strength theory and the shear strength of unsaturated soil in terms of two state stress variables, the unified solution of shear strength for unsaturated soil under the plane strain condition is derived by taking into consideration the effect of the intermediate principal stress rationally. Analytical solutions for unsaturated soil of the active earth pressure, the passive earth pressure and the critical bearing capacity for strip foundation suitable for any lateral pressure coefficient are presented by considering the intermediate principal stress, particularly different influences of high and low matric suctions. The analytical solutions obtained in this paper have very broad theoretical values. More choices can be made according to the actual engineering situations. The results show that in the low matric suction region, the passive earth pressure and the critical bearing capacity for strip foundation increase as the unified strength theory parameter and matric suction increase, while the active earth pressure decreases. In the high matric suction region, the passive earth pressure and the critical bearing capacity gradually decrease and reach some constants. The influence of over-consolidation ratio on the critical bearing capacity for strip foundation is less significant.
Based on the unified strength theory and the shear strength of unsaturated soil in terms of two state stress variables, the unified solution of shear strength for unsaturated soil under the plane strain condition is derived by taking into consideration the effect of the intermediate principal stress rationally. Analytical solutions for unsaturated soil of the active earth pressure, the passive earth pressure and the critical bearing capacity for strip foundation suitable for any lateral pressure coefficient are presented by considering the intermediate principal stress, particularly different influences of high and low matric suctions. The analytical solutions obtained in this paper have very broad theoretical values. More choices can be made according to the actual engineering situations. The results show that in the low matric suction region, the passive earth pressure and the critical bearing capacity for strip foundation increase as the unified strength theory parameter and matric suction increase, while the active earth pressure decreases. In the high matric suction region, the passive earth pressure and the critical bearing capacity gradually decrease and reach some constants. The influence of over-consolidation ratio on the critical bearing capacity for strip foundation is less significant.
Abstract：
Based on the digital model which can greatly reflect the actual objects with considering the characteristics of the underground construction process, a new and practical modeling method (CDIM model transformation method) is put forward combing the digital and numerical geological models with relevant structural ones. This method is implemented using the following procedures: (1) cutting the 3D digital model according to numerical domain; (2) extracting control data from the cut model which includes holes to reconstruct the model mesh; (3) forming the numerical model automatically by the attribute; (4) importing the model into numerical analysis system and finishing the modeling work. All the above procedures are carried out rapidly by programming. In the method, the construction process can be simulated conveniently and the complex model can be used in different numerical systems. The present method is proved to be more accurate and simple and the efficiency of preprocessor is highly improved. The transformed model can be used by different numerical systems and provide the best technological support for the construction simulation.
Based on the digital model which can greatly reflect the actual objects with considering the characteristics of the underground construction process, a new and practical modeling method (CDIM model transformation method) is put forward combing the digital and numerical geological models with relevant structural ones. This method is implemented using the following procedures: (1) cutting the 3D digital model according to numerical domain; (2) extracting control data from the cut model which includes holes to reconstruct the model mesh; (3) forming the numerical model automatically by the attribute; (4) importing the model into numerical analysis system and finishing the modeling work. All the above procedures are carried out rapidly by programming. In the method, the construction process can be simulated conveniently and the complex model can be used in different numerical systems. The present method is proved to be more accurate and simple and the efficiency of preprocessor is highly improved. The transformed model can be used by different numerical systems and provide the best technological support for the construction simulation.
Abstract：
The generalization of anisotropic constitutive models is more complex than that of isotropic constitutive models. Using the g(θ) method to generalize the anisotropic constitutive models will result in the discontinuousness and concavity of yield surfaces. But the yield surfaces can be continuous and the critical state surfaces can consist with the adopted failure criterion if the transformed stress (TS) method is used. The modified Cam-clay model with initial stress-induced anisotropy is generalized using the TS method as an example. The proportionality constant and the stress gradient of the generalized model are defined, and the tangent stiffness matrix used in finite element analysis is given. It is seen from the comparison between the test data and the model predictions that the generalized anisotropic constitutive model using the TS method can reasonably describe the strength and deformation characteristics of the K0-consolidation soils.
The generalization of anisotropic constitutive models is more complex than that of isotropic constitutive models. Using the g(θ) method to generalize the anisotropic constitutive models will result in the discontinuousness and concavity of yield surfaces. But the yield surfaces can be continuous and the critical state surfaces can consist with the adopted failure criterion if the transformed stress (TS) method is used. The modified Cam-clay model with initial stress-induced anisotropy is generalized using the TS method as an example. The proportionality constant and the stress gradient of the generalized model are defined, and the tangent stiffness matrix used in finite element analysis is given. It is seen from the comparison between the test data and the model predictions that the generalized anisotropic constitutive model using the TS method can reasonably describe the strength and deformation characteristics of the K0-consolidation soils.
Abstract：
Based on numerical analysis and previous study results, a unified analysis model is established to estimate the ultimate bearing capacity of uplift piles with enlarged base. Under the limit state, it is supposed to form an elliptic local failure mode on the enlarged base, while in the straight shaft, a power function of slip surface is assumed. The failure curve is related to the soil properties and the pile sizes. A concept of H1 is presented, which is the height influenced by the enlarged base. It is an important part in the present method. Then, a formula applicable to the soft soil region such as Shanghai area is proposed to estimate H1. The calculated results are in good accordance with the field ones, proving that the present method is feasible. Moreover, it is also practical in calculating the ultimate bearing capacity of straight-shaft uplift piles.
Based on numerical analysis and previous study results, a unified analysis model is established to estimate the ultimate bearing capacity of uplift piles with enlarged base. Under the limit state, it is supposed to form an elliptic local failure mode on the enlarged base, while in the straight shaft, a power function of slip surface is assumed. The failure curve is related to the soil properties and the pile sizes. A concept of H1 is presented, which is the height influenced by the enlarged base. It is an important part in the present method. Then, a formula applicable to the soft soil region such as Shanghai area is proposed to estimate H1. The calculated results are in good accordance with the field ones, proving that the present method is feasible. Moreover, it is also practical in calculating the ultimate bearing capacity of straight-shaft uplift piles.
Abstract：
Based on ANN model and reliability theory the limit state function of liquefaction and the probability function of liquefaction are established. In terms of the reference value of SPT in China code a simplified probabilistic procedure for liquefaction evaluation is proposed. The assessment of soil liquefaction potential is based on the liquefied reference value of SPT which is the liquefaction critical value of SPT for given ground acceleration, the depth of soil layers and ground water levels, and is also related to earthquake magnitude and liquefaction probability. The two corrections factors for earthquake magnitudes, and the depth of soil layers and ground water levels, are respectively given for estimating liquefaction potential at any soil layer and various earthquake magnitudes. In addition, based on the procedure another liquefaction criterion according to the design earthquake groups is also given to be convenient to engineering practice in China.
Based on ANN model and reliability theory the limit state function of liquefaction and the probability function of liquefaction are established. In terms of the reference value of SPT in China code a simplified probabilistic procedure for liquefaction evaluation is proposed. The assessment of soil liquefaction potential is based on the liquefied reference value of SPT which is the liquefaction critical value of SPT for given ground acceleration, the depth of soil layers and ground water levels, and is also related to earthquake magnitude and liquefaction probability. The two corrections factors for earthquake magnitudes, and the depth of soil layers and ground water levels, are respectively given for estimating liquefaction potential at any soil layer and various earthquake magnitudes. In addition, based on the procedure another liquefaction criterion according to the design earthquake groups is also given to be convenient to engineering practice in China.
Abstract：
With the development of national economy and the drying up of shallow resources, the embedded depth of rock mass engineering becomes more and more deep. The phenomenon of zonal disintegration appears and is monitored in surrounding rock mass of deep tunnels. The special geological engineering phenomenon has attracted scholars' great attention in the field rock mechanics. However, the knowledge on the fracture shape and forming mechanism of the zonal disintegration is not quite enough. There is doubt about whether or not the connection on the in-situ TV observation can represent the whole tunnel impersonally. There is argument that the fractured zones are the concentric circle of the cavity or the spirals and slip lines. The issue determines the essence of the zonal disintegration and whether or not it is an unexplained new phenomenon by using the theory in existence. In order to know about the phenomenon in substance, geo-mechanical model tests are carried out on the deep mine tunnel of Dingji Coal Mine in Huainan Mine area. Comparing the results of in-situ monitoring with those of model tests, the main characteristics and changing laws of the zonal disintegration are summarized. The zonal disintegration is the circular pull fracture which is concentric to the cavity. The research results are important for understanding the failure modes and revealing the deformation and failure mechanism of surrounding rock mass in deep tunnels.
With the development of national economy and the drying up of shallow resources, the embedded depth of rock mass engineering becomes more and more deep. The phenomenon of zonal disintegration appears and is monitored in surrounding rock mass of deep tunnels. The special geological engineering phenomenon has attracted scholars' great attention in the field rock mechanics. However, the knowledge on the fracture shape and forming mechanism of the zonal disintegration is not quite enough. There is doubt about whether or not the connection on the in-situ TV observation can represent the whole tunnel impersonally. There is argument that the fractured zones are the concentric circle of the cavity or the spirals and slip lines. The issue determines the essence of the zonal disintegration and whether or not it is an unexplained new phenomenon by using the theory in existence. In order to know about the phenomenon in substance, geo-mechanical model tests are carried out on the deep mine tunnel of Dingji Coal Mine in Huainan Mine area. Comparing the results of in-situ monitoring with those of model tests, the main characteristics and changing laws of the zonal disintegration are summarized. The zonal disintegration is the circular pull fracture which is concentric to the cavity. The research results are important for understanding the failure modes and revealing the deformation and failure mechanism of surrounding rock mass in deep tunnels.
Abstract：
The integral safety of high arch dams mainly depends on the stability of supporting rock system. There is no standard for the instability criteria for high arch dams due to its complexity. The instability criteria for the FEM stability analysis of high arch dam and its cusp catastrophe model are discussed firstly. Then the advantages of plastic zone connection criteria, catastrophe criteria of plastic strain energy and displacement are analyzed. The case shows that the plastic zone connection criteria are affected obviously by dam local factor and artificial factor, and that the displacement catastrophe criteria may produce different stability analysis results due to different monitoring points. Whereas the plastic strain energy is unique and reflected correctly for high arch dams under typical load condition, the catastrophe of the plastic strain energy of high arch dams is a better criterion.
The integral safety of high arch dams mainly depends on the stability of supporting rock system. There is no standard for the instability criteria for high arch dams due to its complexity. The instability criteria for the FEM stability analysis of high arch dam and its cusp catastrophe model are discussed firstly. Then the advantages of plastic zone connection criteria, catastrophe criteria of plastic strain energy and displacement are analyzed. The case shows that the plastic zone connection criteria are affected obviously by dam local factor and artificial factor, and that the displacement catastrophe criteria may produce different stability analysis results due to different monitoring points. Whereas the plastic strain energy is unique and reflected correctly for high arch dams under typical load condition, the catastrophe of the plastic strain energy of high arch dams is a better criterion.
Abstract：
Unequal settlements between the piles and the soil will result in soil arching of embankments. Pressure test results (or monitoring in situ) show that the fill load concentrates toward the pipe pile cap and the mixed piles, the earth pressure on the pile cap platform is 4.5 times the average one on the soil-area between piles, and that on the mixed pile top is 1.7 times that on the soil-area between piles. The pile cap platform, the soil-area between piles and the mixed piles share 25%, 69% and 6% of the total fill load. The bearing capacity of the piles and the soil-area between piles do not give full play, that is, the bearing load on the pipe piles is only 40 % of their capacity, and the soil-area between piles is only 25 %, indicating that there is still potential to be tapped. The replacement ratio is the main factor for the increase of proportion of pile bearing load, and the main way is to raise the replacement ratio of piles and the size of the pile cap.
Unequal settlements between the piles and the soil will result in soil arching of embankments. Pressure test results (or monitoring in situ) show that the fill load concentrates toward the pipe pile cap and the mixed piles, the earth pressure on the pile cap platform is 4.5 times the average one on the soil-area between piles, and that on the mixed pile top is 1.7 times that on the soil-area between piles. The pile cap platform, the soil-area between piles and the mixed piles share 25%, 69% and 6% of the total fill load. The bearing capacity of the piles and the soil-area between piles do not give full play, that is, the bearing load on the pipe piles is only 40 % of their capacity, and the soil-area between piles is only 25 %, indicating that there is still potential to be tapped. The replacement ratio is the main factor for the increase of proportion of pile bearing load, and the main way is to raise the replacement ratio of piles and the size of the pile cap.
Abstract：
A modified CKC cyclic triaxial apparatus is used to monitor the evolution of granular soil microstructures during cyclic triaxial tests. Micro digital screening techniques are used to capture the change of microstructures of sand samples during liquefaction induced by cyclic loading. Digital images at certain stages of the tests are cut from the videos and further processed by self-developed software named GeoDIP. The microfabric evolutions including particle orientation, contact normal and number of contacts are analyzed. Labeled particles are traced to study the micro mechanism of soil deformation. It is found that there is no preferred orientation of the long axes of particles in liquefied samples. The main direction of contact normal between particles orients vertically whether the sample is liquefied or not. The samples experience a significant loss of contact number during liquefaction, but the number regains a lot after post-liquefaction drainage. Soil particles exhibit obvious translational motion before liquefaction, but start to move relatively and rotate when liquefaction occurs. The results of this study can not only explore the micro mechanism of sand liquefaction, but also provide an experimental basis for numerical modeling of sand liquefaction.liquefaction, but the number regained a lot after post-liquefaction drainage. Soil particles exhibited obvious translational motion before liquefaction, but start to move relatively and rotate when liquefaction occurs.
A modified CKC cyclic triaxial apparatus is used to monitor the evolution of granular soil microstructures during cyclic triaxial tests. Micro digital screening techniques are used to capture the change of microstructures of sand samples during liquefaction induced by cyclic loading. Digital images at certain stages of the tests are cut from the videos and further processed by self-developed software named GeoDIP. The microfabric evolutions including particle orientation, contact normal and number of contacts are analyzed. Labeled particles are traced to study the micro mechanism of soil deformation. It is found that there is no preferred orientation of the long axes of particles in liquefied samples. The main direction of contact normal between particles orients vertically whether the sample is liquefied or not. The samples experience a significant loss of contact number during liquefaction, but the number regains a lot after post-liquefaction drainage. Soil particles exhibit obvious translational motion before liquefaction, but start to move relatively and rotate when liquefaction occurs. The results of this study can not only explore the micro mechanism of sand liquefaction, but also provide an experimental basis for numerical modeling of sand liquefaction.liquefaction, but the number regained a lot after post-liquefaction drainage. Soil particles exhibited obvious translational motion before liquefaction, but start to move relatively and rotate when liquefaction occurs.
Abstract：
The rheological parameters of cement-based grout is time-dependent, which has an important influence on building grout diffusion model. Based on the assumption of Bingham fluid and narrow plate model of grouting diffusion, a formula for calculating the diffusion radius in soil is developed considering the time-varying behaviors of grout. It shows that the grouting diffusion radius of Bingham fluid is related to the grouting pressure difference, gap width, flow velocity and time-dependent behaviors of rheological parameters. The law of fracture pressure of grouting is affected by the gap width notably, and the rheological parameters of grout play a key role in computing the diffusion radius. So it is unreasonable to neglect the time-dependent behaviors of grout in computing the diffusion radius. Based on the grouting tests on strong-weathered granite tunnel in Xiamen Airport, the application of the formula of grouting diffusion has proved to be successful in practice. Furthermore, some available results are gained, beneficial to the design and construction of fracture grouting in strong-weathered granite.
The rheological parameters of cement-based grout is time-dependent, which has an important influence on building grout diffusion model. Based on the assumption of Bingham fluid and narrow plate model of grouting diffusion, a formula for calculating the diffusion radius in soil is developed considering the time-varying behaviors of grout. It shows that the grouting diffusion radius of Bingham fluid is related to the grouting pressure difference, gap width, flow velocity and time-dependent behaviors of rheological parameters. The law of fracture pressure of grouting is affected by the gap width notably, and the rheological parameters of grout play a key role in computing the diffusion radius. So it is unreasonable to neglect the time-dependent behaviors of grout in computing the diffusion radius. Based on the grouting tests on strong-weathered granite tunnel in Xiamen Airport, the application of the formula of grouting diffusion has proved to be successful in practice. Furthermore, some available results are gained, beneficial to the design and construction of fracture grouting in strong-weathered granite.
Abstract：
For the rock slope with planar failure surface, the structural plane plays a controlling role in the stability of slope. In the process of design and analysis, if the planar failure appears without fixed plane in rock slope, the critical inclination of failure face can be used as the basis for analyzing the slope stability. The traditional estimation formula is optimized. Considering the effects of gravity and earthquakes, two formulae for calculating the critical inclination of failure face are given respectively. One is based on the limit height of slope, and the other is based on the limit factor of safety. Through comparison and analysis, their advantages and disadvantages are obtained.
For the rock slope with planar failure surface, the structural plane plays a controlling role in the stability of slope. In the process of design and analysis, if the planar failure appears without fixed plane in rock slope, the critical inclination of failure face can be used as the basis for analyzing the slope stability. The traditional estimation formula is optimized. Considering the effects of gravity and earthquakes, two formulae for calculating the critical inclination of failure face are given respectively. One is based on the limit height of slope, and the other is based on the limit factor of safety. Through comparison and analysis, their advantages and disadvantages are obtained.
Abstract：
Loading devices and displacement and stress measurement systems are installed on the geotechnical centrifuge. A centrifugal model in line with the actual stress is established. Considering different conditions, the treatment techniques for new and old roadbeds as well as the improvement efficiency of prestressed pile composite foundation treatment in differential settlement deformation of road widening are studied. The differential deformation features of the widening project and the effectiveness and mechanism of the treatment techniques are simulated. The results show that for the road widening laid with geotextile materials in different strata, although uneven settlement of new and old roadbeds may reduce, the effeciency is not obvious. With the help of reinforced treatment, the lateral displacement of shallow soil greatly decreases, while that of deep soil changes little, indicating that the reinforcement has limited effect on the lateral displacement of soft soil, Using prestressed pipes to handle road widening can control the uneven settlement, greatly accelerate the construction schedule and shorten the construction period, indicating that the composite piled foundation in soft soil is suitable for road widening projects with urgent construction time and high settlement control requirements. The study also shows that the pipe piles produce upward penetration deformation, and due to pile caps and reinforced cushions, the penetration depth is effectively alleviated.
Loading devices and displacement and stress measurement systems are installed on the geotechnical centrifuge. A centrifugal model in line with the actual stress is established. Considering different conditions, the treatment techniques for new and old roadbeds as well as the improvement efficiency of prestressed pile composite foundation treatment in differential settlement deformation of road widening are studied. The differential deformation features of the widening project and the effectiveness and mechanism of the treatment techniques are simulated. The results show that for the road widening laid with geotextile materials in different strata, although uneven settlement of new and old roadbeds may reduce, the effeciency is not obvious. With the help of reinforced treatment, the lateral displacement of shallow soil greatly decreases, while that of deep soil changes little, indicating that the reinforcement has limited effect on the lateral displacement of soft soil, Using prestressed pipes to handle road widening can control the uneven settlement, greatly accelerate the construction schedule and shorten the construction period, indicating that the composite piled foundation in soft soil is suitable for road widening projects with urgent construction time and high settlement control requirements. The study also shows that the pipe piles produce upward penetration deformation, and due to pile caps and reinforced cushions, the penetration depth is effectively alleviated.
Abstract：
The consistency in position and time of segregation ice in frozen soils is obtained by use of dynamic photograph and image processing in continuously freezing experiments of one-dimensional open system with different temperature gradients. According to the binarization images of frozen soils, the initiation time, position, thickness and evolving rules of segregation ice can be obtained quantitatively. The thickness of segregation ice obtained from the image analysis is consistent with the frost heave tested by displacement transducer. Three phases of evolving process in the ice segregation can be divided according to the results of the image processing: the early freezing, the growth of thin and discontinuous segregation ice and the final ice lens. There is nearly a linear relationship between the initiation time of the final ice lens and the temperature gradient in continuously freezing experiments. The initiation time of the final ice lens will move up with the increase of the temperature gradient.
The consistency in position and time of segregation ice in frozen soils is obtained by use of dynamic photograph and image processing in continuously freezing experiments of one-dimensional open system with different temperature gradients. According to the binarization images of frozen soils, the initiation time, position, thickness and evolving rules of segregation ice can be obtained quantitatively. The thickness of segregation ice obtained from the image analysis is consistent with the frost heave tested by displacement transducer. Three phases of evolving process in the ice segregation can be divided according to the results of the image processing: the early freezing, the growth of thin and discontinuous segregation ice and the final ice lens. There is nearly a linear relationship between the initiation time of the final ice lens and the temperature gradient in continuously freezing experiments. The initiation time of the final ice lens will move up with the increase of the temperature gradient.
Abstract：
The shield technology has been widely used in underground construction. The face stability is the key problem in the shield tunneling. Large-scale model tests on the face stability of tunnels with the ratios of tunnel depth to diameter C/D = 0.5，1.0 and 2.0 are conducted in the dry sand. The influence of C/D on the ultimate support pressure and the settlement of ground surface are obtained. The support pressure decreases sharply with the increase of the face displacement. However, the settlement of the ground surface is not sensitive to the support pressure before the residual support pressure. Both the support pressure and the ground settlement are essential to the monitoring of the face stability in the shield tunnelling.
The shield technology has been widely used in underground construction. The face stability is the key problem in the shield tunneling. Large-scale model tests on the face stability of tunnels with the ratios of tunnel depth to diameter C/D = 0.5，1.0 and 2.0 are conducted in the dry sand. The influence of C/D on the ultimate support pressure and the settlement of ground surface are obtained. The support pressure decreases sharply with the increase of the face displacement. However, the settlement of the ground surface is not sensitive to the support pressure before the residual support pressure. Both the support pressure and the ground settlement are essential to the monitoring of the face stability in the shield tunnelling.
Abstract：
When the composite piled foundation reaches the general ultimate bearing capacity status, an increment of the ultimate bearing capacity for natural foundation is induced by “barrier effect” of piles. The analysis of the problem can be simplified for both the sum of the vertical ultimate bearing capacity of foundation and the increment of the ultimate bearing capacity of foundation soil horizontally sliding around piles. Based on the finite element plastic lower bound limit method, the numerical solutions for the vertical ultimate bearing capacity of foundation and the horizontal resistance sliding around piles varying with soil depth are obtained, and the sliding resistance formula is also established. The sliding resistance coefficient ks reduces with the increase of pile spacing. The increment of the ultimate bearing capacity Δfu decreases with the increase of pile spacing. The results indicate that the resistance sliding around piles in the composite piled foundation is being and can not be ignored, and that the ultimate bearing capacity of the composite piled foundation has certain increment, which can be regarded as the security reserve of foundation.
When the composite piled foundation reaches the general ultimate bearing capacity status, an increment of the ultimate bearing capacity for natural foundation is induced by “barrier effect” of piles. The analysis of the problem can be simplified for both the sum of the vertical ultimate bearing capacity of foundation and the increment of the ultimate bearing capacity of foundation soil horizontally sliding around piles. Based on the finite element plastic lower bound limit method, the numerical solutions for the vertical ultimate bearing capacity of foundation and the horizontal resistance sliding around piles varying with soil depth are obtained, and the sliding resistance formula is also established. The sliding resistance coefficient ks reduces with the increase of pile spacing. The increment of the ultimate bearing capacity Δfu decreases with the increase of pile spacing. The results indicate that the resistance sliding around piles in the composite piled foundation is being and can not be ignored, and that the ultimate bearing capacity of the composite piled foundation has certain increment, which can be regarded as the security reserve of foundation.
Abstract：
Among the triggering factors of post-earthquake rock landslide, the rainfall water plays a most important role. However, different from that of soil slope, the mechanism of its effect on rock landslide failure is not clear. From the view of fracture mechanics and based on the characters of post-earthquake rock, the mechanism of crack propagation, the way of water infiltration and the development process of sliding face are studied. By using the upper bound theorem, the influence of fissure water on the stability of rock slope is quantitatively studied. Finally, an example is given to prove the theory. The results show that the propagation and coalescence of fissures and the softening of sliding face are the main reason for the failure of post-earthquake rock landslide under rainfall.
Among the triggering factors of post-earthquake rock landslide, the rainfall water plays a most important role. However, different from that of soil slope, the mechanism of its effect on rock landslide failure is not clear. From the view of fracture mechanics and based on the characters of post-earthquake rock, the mechanism of crack propagation, the way of water infiltration and the development process of sliding face are studied. By using the upper bound theorem, the influence of fissure water on the stability of rock slope is quantitatively studied. Finally, an example is given to prove the theory. The results show that the propagation and coalescence of fissures and the softening of sliding face are the main reason for the failure of post-earthquake rock landslide under rainfall.
Abstract：
By surveying the damages of termites infesting the dikes at the Qiantang River estuary, it is found that the dikes and dams with saline soil can prevent termite invasion. Based on the findings, experiments are performed for the physical and mechanical indices of anti-seepage earth samples by adding salt and the penetrating ability of termites. The results show that (a) when the soil salinity is less than 2%, the fluctuation of physical and mechanical indices is subtle; (b) when the soil salinity reaches 0.6%, the dikes and dams can effectively prevent termites. According to the dam types and nest-building characteristics of termites, a scientific method of specifying paving locations of saline soil, soil salinity and operating details are developed. The technology is applied to the dams suffering from severe termite infestation, and the effect of termite prevention is remarkable. The technology provides new thinking and method for dam termite prevention.
By surveying the damages of termites infesting the dikes at the Qiantang River estuary, it is found that the dikes and dams with saline soil can prevent termite invasion. Based on the findings, experiments are performed for the physical and mechanical indices of anti-seepage earth samples by adding salt and the penetrating ability of termites. The results show that (a) when the soil salinity is less than 2%, the fluctuation of physical and mechanical indices is subtle; (b) when the soil salinity reaches 0.6%, the dikes and dams can effectively prevent termites. According to the dam types and nest-building characteristics of termites, a scientific method of specifying paving locations of saline soil, soil salinity and operating details are developed. The technology is applied to the dams suffering from severe termite infestation, and the effect of termite prevention is remarkable. The technology provides new thinking and method for dam termite prevention.
Abstract：
How to estimate the settlement caused by pressure-relief of confined water has been a research focus in the academic and engineering fields. During the process of pumping confined water, the drop of hydraulic head leads to the decrease of uplift force, and produces extra stress on overlaying soil, resulting in the settlement of the ground. As the permeability coefficient is very small, the roof of the confined aquifer is supposed to be impermeable. By calculating steady flow of fully penetrated well of confined water, the additional force acting on the overlaying soil, which is caused by pressure-relief of confined water, is studied. Above all, the effects of some parameters on the settlement are studied, such as the thickness, modulus of the overlaying soil, head difference and transmissibility of the confined aquifer. Through an example, the settlement of the ground caused by decompression of confined water is small and agrees with the actual one.
How to estimate the settlement caused by pressure-relief of confined water has been a research focus in the academic and engineering fields. During the process of pumping confined water, the drop of hydraulic head leads to the decrease of uplift force, and produces extra stress on overlaying soil, resulting in the settlement of the ground. As the permeability coefficient is very small, the roof of the confined aquifer is supposed to be impermeable. By calculating steady flow of fully penetrated well of confined water, the additional force acting on the overlaying soil, which is caused by pressure-relief of confined water, is studied. Above all, the effects of some parameters on the settlement are studied, such as the thickness, modulus of the overlaying soil, head difference and transmissibility of the confined aquifer. Through an example, the settlement of the ground caused by decompression of confined water is small and agrees with the actual one.
Abstract：
The apparatus for static and dynamic universal triaxial and torsional shear soil tests is employed to perform stress-controlled coupling vertical and torsional shear tests under different three-dimensional initial anisotropic consolidation stress conditions. Through experimental tests the effects of the initial orientation angle of the major principal stress, the ratio of the two stress components and the cyclic stress level on the pore water pressure and the strength of the saturated marine clay are examined. The initial orientation angle of the major principal stress has a significant influence on the characteristics of pore water pressure: as the angle increases, both the residual pore water pressure and the amplitude of fluctuated pore water pressure increase. Meanwhile, the relations between the normalized residual pore water pressure ratio and the cyclic number ratio with different initial orientation angles of the major principal stress are established. Under the conditions of keeping the area bounded by the elliptical stress path unchanged, there exists a certain critical value for the ratio of the axial and torsional shear stresses. At this critical value, the residual pore water pressure is the lowest. Both the fluctuated pore water pressure and the residual pore water pressure increase with increasing cyclic stress ratio. However, there is great difference between the high and the low stress levels. Furthermore, the critical cyclic stress ratio is determined according to the time history curves of pore water pressure under different cyclic stress ratios. The initial orientation angle of the major principal stress has a significant influence on the dynamic strength: as the angle increases, the dynamic strength decreases. The dynamic strength curve indicates that there is basically a linear relationship between the cyclic stress ratio and the logarithm of the cyclic number required at failure.
The apparatus for static and dynamic universal triaxial and torsional shear soil tests is employed to perform stress-controlled coupling vertical and torsional shear tests under different three-dimensional initial anisotropic consolidation stress conditions. Through experimental tests the effects of the initial orientation angle of the major principal stress, the ratio of the two stress components and the cyclic stress level on the pore water pressure and the strength of the saturated marine clay are examined. The initial orientation angle of the major principal stress has a significant influence on the characteristics of pore water pressure: as the angle increases, both the residual pore water pressure and the amplitude of fluctuated pore water pressure increase. Meanwhile, the relations between the normalized residual pore water pressure ratio and the cyclic number ratio with different initial orientation angles of the major principal stress are established. Under the conditions of keeping the area bounded by the elliptical stress path unchanged, there exists a certain critical value for the ratio of the axial and torsional shear stresses. At this critical value, the residual pore water pressure is the lowest. Both the fluctuated pore water pressure and the residual pore water pressure increase with increasing cyclic stress ratio. However, there is great difference between the high and the low stress levels. Furthermore, the critical cyclic stress ratio is determined according to the time history curves of pore water pressure under different cyclic stress ratios. The initial orientation angle of the major principal stress has a significant influence on the dynamic strength: as the angle increases, the dynamic strength decreases. The dynamic strength curve indicates that there is basically a linear relationship between the cyclic stress ratio and the logarithm of the cyclic number required at failure.
