The commercial FEM software ANSYS was used to analyze the failure characteristics of overburden strata under the conditions of different lengths of mining faces. It was shown that the parameters of mining faces, espec...The commercial FEM software ANSYS was used to analyze the failure characteristics of overburden strata under the conditions of different lengths of mining faces. It was shown that the parameters of mining faces, especially the length was the important factor to the failure heights and shapes of overburden strata. Fuzzy mathematics and statistical methods were used to analyze the forecasting method of the failure height of overburden strata influenced by the parameters of mining face based on the measured data under the conditions of fully-mechanized mining of general hardness cover rocks. On the basis of these analyses, a new forecasting formula was gotten. The forecasting result conforms to the in situ measured value. The result has a very important application value in safe and high-efficient mining, and has a very important advancing function to theoretical studies.展开更多
As a critical mechanical characteristic of rock,brittleness significantly influences fracture modes and damage evolution processes.Accurate quantitative evaluation of brittleness is essential for ensuring the stabilit...As a critical mechanical characteristic of rock,brittleness significantly influences fracture modes and damage evolution processes.Accurate quantitative evaluation of brittleness is essential for ensuring the stability of various engineering applications.Based on the pre-peak and post-peak stages of the rock stress-strain curve,this study constructed a brittleness index BI^(*).The index quantifies the ability of rock to resist plastic deformation during the pre-peak crack growth stage and evaluates the intensity of strength drop during the post-peak softening stage.Another index,BII,was established based on the degree of pre-peak elastic energy accumulation and the instability characteristics of post-peak dissipated energy.This index reflects the essential properties of rock failure by revealing the energy evolution mechanism.Furthermore,by defining a damage variable from the energy dissipation over the entire deformation process,an index B_(D)was introduced to evaluate brittleness from the perspective of internal damage development.Triaxial compression and cyclic loading tests were conducted on rocks of different lithologies to evaluate the new index.The influences of confining pressure and lithology on rock brittleness were analyzed,along with the sensitivity analysis of various brittleness index parameters.The results indicated that the proposed brittleness indices accurately distinguish the brittleness differences among various lithologies and show effective consistency with the failure modes of specimens under different confining pressures.Meanwhile,different brittleness indices were affected by confining pressure and lithology to different degrees.The post-peak softening stage of rock played a particularly significant role in brittleness analysis.A brittleness classification system under different confining pressures and lithologies was established.The research results contribute to the enhancement and refinement of the rock brittleness evaluation system.展开更多
The deteriorated bearing capacity and nonlinear expansion deformation of weakly cemented Xiyu conglomerate under complex water environments and stress disturbances pose significant risks to the safety of stratum engin...The deteriorated bearing capacity and nonlinear expansion deformation of weakly cemented Xiyu conglomerate under complex water environments and stress disturbances pose significant risks to the safety of stratum engineering construction.In this study,to precisely comprehend the influences of pore pressure(P_(w))and stress path on the deformation characteristics,dilation behavior,and damage evolution of Xiyu conglomerate,a series of triaxial monotonic loading and cyclic loading-unloading tests were conducted on saturated Xiyu conglomerate with varied confining pressures(σ_(3))and pore pressures.The results indicate that as P_(w)increases,the secant modulus,unloading modulus,and loading modulus decrease,but increase with risingσ_(3).Additionally,P_(w)accelerates the onset of dilatancy,whereasσ_(3)delays it.Asσ_(3)increases,the peak stress,crack damage stress,and residual strength increase,while these parameters decrease with increasing P_(w).A positive correlation exists between the effective confining pressure and the effective axial stress.Furthermore,an increase in P_(w)results in a greater maximum dilation angle,which decreases with increasingσ_(3).The failure mode is mainly a tensile-shear mixed failure mode.The high pore pressure and cyclic loading stress path aggravate the deterioration of strength and failure mode of the weakly cemented Xiyu conglomerate.Finally,a new damage variable and conceptual model are proposed and discussed.The findings provide insight into the damage and failure mechanism of the Xiyu conglomerate under pore pressure and cyclic disturbance,offering a crucial experimental foundation for the design and construction of hydropower projects in the Xiyu conglomerate layer.展开更多
To assess the effectiveness of vacuum preloading combined electroosmotic strengthening of ultra-soft soil and study the mechanism of the process, a comprehensive experimental investigation was performed. A laboratory ...To assess the effectiveness of vacuum preloading combined electroosmotic strengthening of ultra-soft soil and study the mechanism of the process, a comprehensive experimental investigation was performed. A laboratory test cell was designed and applied to evaluate the vacuum preloading combined electroosmosis. Several factors were taken into consideration, including the directions of the electroosmotic current and water induced by vacuum preloading and the replenishment of groundwater from the surrounding area. The results indicate that electroosmosis together with vacuum preloading improve the soil strength greatly, with an increase of approximately 60%, and reduce the water content of the soil on the basis of consolidation of vacuum preloading, howeve~ further settlement is not obvious with only 1.7 mm. The reinforcement effect of vacuum preloading combined electroosmosis is better than that of electroosmosis after vacuum preloading. Elemental analysis using X-ray fluorescence proves that the soil strengthening during electroosmotic period in this work is mainly caused by electroosmosis-induced electrochemical reactions, the concentrations of Al2O3 in the VPCEO region increase by 2.2%, 1.5%, and 0.9% at the anode, the midpoint between the electrodes, and the cathode, respectively.展开更多
This paper reports a series solution of wave functions for two-dimensional scattering and diffraction of plane SH waves induced by a symmetrical V-shaped canyon with different shape ratios. A half-space with a symmetr...This paper reports a series solution of wave functions for two-dimensional scattering and diffraction of plane SH waves induced by a symmetrical V-shaped canyon with different shape ratios. A half-space with a symmetrical V-shaped canyon is divided into two sub-regions by using a circular-arc auxiliary boundary. The two sub-regions are represented by global and local cylindrical coordinate systems, respectively. In each coordinate system, the wave field satisfying the Helmholtz equation is represented by the separation of variables method, in terms of the series of both Bessel functions and Hankel functions with unknown complex coefficients. Then, the two wave fields are described in the local coordinate system using the Graf addition theorem. Finally, the unknown coefficients are sought by satisfying the continuity conditions of the auxiliary boundary. To consider the phase characteristics of the wave scattering, a parametric analysis is carried out in the time domain by assuming an incident signal of the Ricker type. Surface and subsurface transient responses demonstrate the characteristics and mechanisms of wave propagating and scattering.展开更多
Monotonic lateral load model tests were carried out on steel skirted suction caissons embedded in the saturated medium sand to study the bearing capacity. A three-dimensional continuum finite element model was develop...Monotonic lateral load model tests were carried out on steel skirted suction caissons embedded in the saturated medium sand to study the bearing capacity. A three-dimensional continuum finite element model was developed with Z_SOIL software. The numerical model was calibrated against experimental results. Soil deformation and earth pressures on skirted caissons were investigated by using the finite element model to extend the model tests. It shows that the ＂skirted＂ structure can significantly increase the lateral capacity and limit the deflection, especially suitable for offshore wind turbines, compared with regular suction caissons without the ＂skirted＂ at the same load level. In addition, appropriate determination of rotation centers plays a crucial role in calculating the lateral capacity by using the analytical method. It was also found that the rotation center is related to dimensions of skirted suction caissons and loading process, i.e. the rotation center moves upwards with the increase of the ＂skirted＂ width and length; moreover, the rotation center moves downwards with the increase of loading and keeps constant when all the sand along the caisson＇s wall yields. It is so complex that we cannot simply determine its position like the regular suction caisson commonly with a specified position to the length ratio of the caisson.展开更多
When variations occur in the water content or dry bulk density of soil,the contact angle hysteresis will affect the soil-water characteristic curve(SWCC).The occurrence of the contact angle hysteresis can be divided i...When variations occur in the water content or dry bulk density of soil,the contact angle hysteresis will affect the soil-water characteristic curve(SWCC).The occurrence of the contact angle hysteresis can be divided into slipping and pinning.It is difficult to determine the effect of pinning existence on SWCC by tests.In this study,the effect of contact angle hysteresis on SWCC was analyzed either in the case of no variations in soil dry bulk density with changes in soil water content or no variations in soil water content with changes in soil dry bulk density.In both cases,soil particles were simplified to the spherical particle model.Based on the geometrically mechanic relationship between the particles and connecting liquid bridges,a physical model for predicting the SWCC was derived from the spherical particle model.Adjusting parameters made the model applicable to various soils,that is,the cohesive soil was considered as micron-sized spherical particles.Through the simulations on SWCC test data of sand,silt,clay,and swelling soil,it was confirmed that the physical model possessed good reliability and practicability.Finally,the analysis of rationality of contact angle was performed based on the basic assumptions of the model.展开更多
Pile foundation is widely used in the offshore engineering. The pile can be seriously destroyed by the soil liquefaction during strong earthquakes. The potentials of liquefaction and damages of pile foundation due to ...Pile foundation is widely used in the offshore engineering. The pile can be seriously destroyed by the soil liquefaction during strong earthquakes. The potentials of liquefaction and damages of pile foundation due to the liquefaction can be reduced by the implementation of the drainage in the liquefiable foundation. A patented pile technology, named rigidity-drain pile, was introduced. The partial section of the pile body was filled by materials with higher penetrability which forms some effective drainage channels in the pile. The principles and construction methods were presented. 3D models for both rigidity-drain pile and ordinary pile were built in FLAC3D code. The dynamic loadings were applied on the bottom of the model. According to the numerical results, in the case of the rigidity-drain pile, the water in the relevant distance range around the pile flows toward the pile drainage, the contour of the pore pressure shows a funnel form. Contrast to the ordinary pile, the rigidity-drain pile can dissipate the accumulated excess pore water, maintain effective stress and obviously reduce the possibility of surrounding soil liquefaction.展开更多
There are many fracture zones crossing the dam foundation of the Xiangjiaba Hydropower Project in southwestern China. Clastic rock is the main media of the fracture zone and has poor physical and mechanical properties...There are many fracture zones crossing the dam foundation of the Xiangjiaba Hydropower Project in southwestern China. Clastic rock is the main media of the fracture zone and has poor physical and mechanical properties. In order to investigate the creep behavior of clastic rock, triaxial creep tests were conducted using a rock servo-controlling rheological testing machine. The results show that the creep behavior of clastic rock is significant at a high level of deviatoric stress, and less time-dependent deformation occurs at high confining pressure. Based on the creep test results, the relationship between axial strain and time under different confining pressures was investigated, and the relationship between axial strain rate and deviatoric stress was also discussed. The strain rate increases rapidly, and the rock sample fails eventually under high deviatoric stress. Moreover, the creep failure mechanism under different confining pressures was analyzed. The main failure mechanism of clastic rock is plastic shear, accompanied by a significant compression and ductile dilatancy. On the other band, with the determined parameters, the Burgers creep model was used to fit the creep curves. The results indicate that the Burgers model can exactly describe the creep behavior of clastic rock in the Xiangjiaba Hydropower Project.展开更多
The behavior of soil-structure interface plays a major role in the definition of soil-structure interaction. In this paper a bi-potential surface elasto-plastic model for soil-structure interface is proposed in order ...The behavior of soil-structure interface plays a major role in the definition of soil-structure interaction. In this paper a bi-potential surface elasto-plastic model for soil-structure interface is proposed in order to describe the interface deformation behavior,including strain softening and normal dilatancy. The model is formulated in the framework of generalized potential theory,in which the soil-structure interface problem is regard as a two-dimensional mathematical problem in stress field,and plastic state equations are used to replace the traditional field surface. The relation curves of shear stress and tangential strain are fitted by a piecewise function composed by hyperbolic functions and hyperbolic secant functions,while the relation curves of normal strain and tangential strain are fitted by another piecewise function composed by quadratic functions and hyperbolic secant functions. The approach proposed has the advantage of deriving an elastoplastic constitutive matrix without postulating the plastic potential functions and yield surface. Moreover,the mathematical principle is clear,and the entire model parameters can be identified by experimental tests. Finally,the predictions of the model have been compared with experimental results obtained from simple shear tests under normal stresses,and results show the model is reasonable and practical.展开更多
Coarse aggregates are the major infrastructure materials of concrete-faced rock-fill dams and are consolidated to bear upper and lateral loads.With the increase of dam height,high confining pressure and complex stress...Coarse aggregates are the major infrastructure materials of concrete-faced rock-fill dams and are consolidated to bear upper and lateral loads.With the increase of dam height,high confining pressure and complex stress states complicate the shear behavfor of coarse aggregates,and thus impede the high dam's proper construction,operation and maintenance.An experimental program was conducted to study the shear behavior of dam coarse aggregates using a large-scale triaxial shear apparatus.Through triaxial shear tests,the strain-stress behaviors of aggregates were observed under constant confining pressures:300 kPa,600 kPa 900 kPa and 1200 kPa.Shear strengths and aggregate breakage characteristics associated with high pressure shear processes are discussed.Stress path tests were conducted to observe and analyze coarse aggregate response under complex stress states.In triaxial shear tests,it was found that peak deviator stresses increase along with confining pressures,whereas the peak principal stress ratios decrease as confining pressures increase With increasing confining pressures,the dilation decreases and the contraction eventually prevails.Initial strength parameters(Poisson's ratio and tangent modulus)show a nonlinear relationship with confining pressures when the pressures are relatively low.Shear strength parameters decrease with increasing confining pressures.The failure envelope lines are convex curves,with clear curvature under low confining pressures.Under moderate confining pressures,dilation is offset by particle breakage.Under high confining pressures,dilation disappears.展开更多
Swelling and shrinkage due to moisture-change is one of the characteristics of the expansive soil,which is similar to the behavior of most materials under thermal effect,If the deformation is restricted,stress in expa...Swelling and shrinkage due to moisture-change is one of the characteristics of the expansive soil,which is similar to the behavior of most materials under thermal effect,If the deformation is restricted,stress in expansive soil is caused by the swell-shrinking.The stress is defined as "moisture-change stress" and is adopted to analyze swell-shrinkage deformation based on the elasticity mechanics theory.The state when the total stress becomes equal to the soil tensile strength is considered as the cracking criterion as moisture-change increases.Then,the initial cracking mechanism due to evaporation is revealed as follows:Different rates of moisture loss at different depths result in greater shrinkage deformation on the surface while there is smaller shrinkage deformation at the underlayer in expansive soil;cracks will grow when the nonuniform shrinkage deformation increases to a certain degree.A theoretical model is established,which may be used to calculate the stress caused by moisture-change.The depth of initial cracks growing is predicted by the proposed model in expansive soil,A series of laboratory tests are carried out by exposing expansive soil samples with different moisture-changes.The process of crack propagation is investigated by resistivity method.The test results show good consistency with the predicted results by the proposed theoretical model.展开更多
A new model to simulate spatially correlated earthquake ground motions is developed. In the model, the main factors that characterize three distinct effects of spatial variability, namely, the incoherency effect, the ...A new model to simulate spatially correlated earthquake ground motions is developed. In the model, the main factors that characterize three distinct effects of spatial variability, namely, the incoherency effect, the wave-passage effect and the site-response effect, are taken into account, and corresponding terms/parameters are incorporated into the well known model of uniform ground motions. Some of these terms/parameters can be determined by the root operation, and others can be calculated directly. The proposed model is first verified theoretically, and examples of ground motion simulations are provided as a further illustration. It is proven that the ensemble expected value and the ensemble auto-/cross-spectral density functions of the simulated ground motions are identical to the target spectral density functions. The proposed model can also be used to simulate other correlated stochastic processes, such as wave and wind loads.展开更多
The earth’s surface irregularities can substantially affect seismic waves and induce amplifi cations of ground motions. This study investigates whether and how the source characteristics affect the site amplifi catio...The earth’s surface irregularities can substantially affect seismic waves and induce amplifi cations of ground motions. This study investigates whether and how the source characteristics affect the site amplifi cation effects. An analytical model of a line source of cylindrical waves impinging on an alluvial valley is proposed to link the source and site. The analytical solution to this problem proves one aspect of the strong effect of source on site amplifi cation, i.e., the wave curvature effect. It is found that the site amplifi cation depends on the source location, especially under conditions of a small source-to-site distance. Whether the displacement is amplifi ed or reduced and the size of the amplifi cation or reduction may be determined by the location of the source. It is suggested that traditional studies of site responses, which usually ignore the source effect, should be further improved by combining the source with site effects.展开更多
The construction process and load-bearing behaviors of Cast-in-place concrete thin-wall pipe piles are analyzed based on its application on Yantong Expressway Project. The low strain test, static load test and field e...The construction process and load-bearing behaviors of Cast-in-place concrete thin-wall pipe piles are analyzed based on its application on Yantong Expressway Project. The low strain test, static load test and field excavation were also carried out, and the bearing capacity of the new pile can meet the requirements of design. With the increase of pile diameter, the bearing capacity is increased. The settlement of composite foundation is decreased, when the replacement ratio of pile is increased. The test results also show that the load carried by inner soils is neglectable. According to the tests and application, it can be concluded that the new type of pile is convenient to construction with high bearing capacity and reliable quality, which has great potential in practical engineering.展开更多
Through laboratory test, the relationships among change of compactibility, liquid/plastic limit, free swell, swell ratio without load, california bearing ratio (CBR) and soakage (after being soaked in water), and mix-...Through laboratory test, the relationships among change of compactibility, liquid/plastic limit, free swell, swell ratio without load, california bearing ratio (CBR) and soakage (after being soaked in water), and mix-ratio of quick lime and time were studied. The results show that optimum water content, plastic limit and CBR of high liquid limit clay improved by quick lime increase with the increase of mix-ratio of quick lime, while the maximum dry density, liquid limit, plasticity index, soakage (after being immersed in water), free swell, and swell ratio without load decrease with the increase of mix-ratio of quick lime. Plastic limit of high liquid clay improved by quick lime gradually increases with time, while the liquid limit, plasticity index, free swell and swell ratio without load gradually decrease with time. When the mix-ratio of quick lime exceeds 2%, after 14 d, swell ratio without load of the improved clay is zero, its free swell is about 30% of that of untreated soil, and its plasticity index is less than 26 for sub-grade material, satisfying the requirement by 'Specifications for Design of Highway Subgrade'.展开更多
The success of a tunnel-boring machine （TBM） in a given project depends on the functionality of all components of the system, from the cutters to the backup system, and on the entire rolling stock. However, no part ...The success of a tunnel-boring machine （TBM） in a given project depends on the functionality of all components of the system, from the cutters to the backup system, and on the entire rolling stock. However, no part of the machine plays a more crucial role in the efficient operation of the machine than its cutterhead. The design of the cutterhead impacts the efficiency of cutting, the balance of the head, the life of the cutters, the maintenance of the main bearing/gearbox, and the effectiveness of the mucking along with its effects on the wear of the face and gage cutters/muck buckets. Overall, cutterhead design heavily impacts the rate of penetration （ROP）, rate of machine utilization （U）, and daffy advance rate （AR）. Although there has been some discussion in commonly available publications regarding disk cutters, cutting forces, and some design features of the head, there is limited literature on this subject because the design of cutter- heads is mainly handled by machine manufacturers. Most of the design process involves proprietary algorithms by the manufacturers, and despite recent attention on the subject, the design of rock TBMs has been somewhat of a mystery to most end-users. This paper is an attempt to demystify the basic concepts in design. Although it may not be sufficient for a full-fledged design by the readers, this paper allows engineers and contractors to understand the thought process in the design steps, what to Look for in a proper design, and the implications of the head design on machine operation and life cycle.展开更多
The dynamic stress introduced in half elastic space by wave loading is characterized by the equation between the magnitude of half cyclic axial stress and cyclic torsion shear stress and the principal stress, whose di...The dynamic stress introduced in half elastic space by wave loading is characterized by the equation between the magnitude of half cyclic axial stress and cyclic torsion shear stress and the principal stress, whose direction rotates continuously and compression stress on seabed can be calculated by the use of small amplitude wave theory. With relationship curves of saturated silt of liquefaction cycles and cyclic stress ratios obtained by cyclic triaxial-torsional coupling shear tests and curve fitting method to different data points of relative density, it is suggested that the cyclic stress ratio corresponding to constant liquefaction impedance be taken as the critical cyclic stress ratio which implies liquefaction. There exists a linear relationship between critical cyclic stress ratio and relative density under different relative densities. Empirical formula for critical cyclic stress ratios of seabed liquefaction induced by wave loading under different relative densities is established. The possibility of seabed silt liquefaction and its influence factors are analyzed based on the small-amplitude wave theory and the data acquired in laboratory tests.展开更多
The development of fissures in expansive soils has a great effect on the stability of slope. Of the three phases of soils,the gas phase and solid phase are relatively insulated,so the average resistivity of soils can ...The development of fissures in expansive soils has a great effect on the stability of slope. Of the three phases of soils,the gas phase and solid phase are relatively insulated,so the average resistivity of soils can be calculated from the resistivity of the liquid phase. On this basis,the two-part model of resistivity changing with the water saturation of the expansive soil can be deduced. A 2-D resistance grid model is established based on simulating the resistance of ver-tically developed fissures. Variation in measured resistance of vertically developed fissures at different positions can be calculated from this model. Fissure development can be inversely determined from the variation in the measured resis-tance. Finally,the model is verified by an indoor resistivity test for remolded soil samples,indicating that the test result agrees well with that of the model established.展开更多
文摘The commercial FEM software ANSYS was used to analyze the failure characteristics of overburden strata under the conditions of different lengths of mining faces. It was shown that the parameters of mining faces, especially the length was the important factor to the failure heights and shapes of overburden strata. Fuzzy mathematics and statistical methods were used to analyze the forecasting method of the failure height of overburden strata influenced by the parameters of mining face based on the measured data under the conditions of fully-mechanized mining of general hardness cover rocks. On the basis of these analyses, a new forecasting formula was gotten. The forecasting result conforms to the in situ measured value. The result has a very important application value in safe and high-efficient mining, and has a very important advancing function to theoretical studies.
基金support from the National Natural Science Foundation of China(Grant Nos.12072102 and 12102129).
文摘As a critical mechanical characteristic of rock,brittleness significantly influences fracture modes and damage evolution processes.Accurate quantitative evaluation of brittleness is essential for ensuring the stability of various engineering applications.Based on the pre-peak and post-peak stages of the rock stress-strain curve,this study constructed a brittleness index BI^(*).The index quantifies the ability of rock to resist plastic deformation during the pre-peak crack growth stage and evaluates the intensity of strength drop during the post-peak softening stage.Another index,BII,was established based on the degree of pre-peak elastic energy accumulation and the instability characteristics of post-peak dissipated energy.This index reflects the essential properties of rock failure by revealing the energy evolution mechanism.Furthermore,by defining a damage variable from the energy dissipation over the entire deformation process,an index B_(D)was introduced to evaluate brittleness from the perspective of internal damage development.Triaxial compression and cyclic loading tests were conducted on rocks of different lithologies to evaluate the new index.The influences of confining pressure and lithology on rock brittleness were analyzed,along with the sensitivity analysis of various brittleness index parameters.The results indicated that the proposed brittleness indices accurately distinguish the brittleness differences among various lithologies and show effective consistency with the failure modes of specimens under different confining pressures.Meanwhile,different brittleness indices were affected by confining pressure and lithology to different degrees.The post-peak softening stage of rock played a particularly significant role in brittleness analysis.A brittleness classification system under different confining pressures and lithologies was established.The research results contribute to the enhancement and refinement of the rock brittleness evaluation system.
基金This work was supported by the Central University Basic Research Fund of China(B230201059and No.B240201155)the water science and technology special fund of Xinjiang Uygur Autonomous Region(No.XSKJ-2023-30)funded by China Power Construction Group research project(Grant No.DJ-HXGG-2023-16).
文摘The deteriorated bearing capacity and nonlinear expansion deformation of weakly cemented Xiyu conglomerate under complex water environments and stress disturbances pose significant risks to the safety of stratum engineering construction.In this study,to precisely comprehend the influences of pore pressure(P_(w))and stress path on the deformation characteristics,dilation behavior,and damage evolution of Xiyu conglomerate,a series of triaxial monotonic loading and cyclic loading-unloading tests were conducted on saturated Xiyu conglomerate with varied confining pressures(σ_(3))and pore pressures.The results indicate that as P_(w)increases,the secant modulus,unloading modulus,and loading modulus decrease,but increase with risingσ_(3).Additionally,P_(w)accelerates the onset of dilatancy,whereasσ_(3)delays it.Asσ_(3)increases,the peak stress,crack damage stress,and residual strength increase,while these parameters decrease with increasing P_(w).A positive correlation exists between the effective confining pressure and the effective axial stress.Furthermore,an increase in P_(w)results in a greater maximum dilation angle,which decreases with increasingσ_(3).The failure mode is mainly a tensile-shear mixed failure mode.The high pore pressure and cyclic loading stress path aggravate the deterioration of strength and failure mode of the weakly cemented Xiyu conglomerate.Finally,a new damage variable and conceptual model are proposed and discussed.The findings provide insight into the damage and failure mechanism of the Xiyu conglomerate under pore pressure and cyclic disturbance,offering a crucial experimental foundation for the design and construction of hydropower projects in the Xiyu conglomerate layer.
基金Project(2009B13014) supported by the Fundamental Research Funds for the Central Universities of ChinaProject(IRT1125) supported by the Program for Changjiang Scholars and Innovative Research Team in University,China
文摘To assess the effectiveness of vacuum preloading combined electroosmotic strengthening of ultra-soft soil and study the mechanism of the process, a comprehensive experimental investigation was performed. A laboratory test cell was designed and applied to evaluate the vacuum preloading combined electroosmosis. Several factors were taken into consideration, including the directions of the electroosmotic current and water induced by vacuum preloading and the replenishment of groundwater from the surrounding area. The results indicate that electroosmosis together with vacuum preloading improve the soil strength greatly, with an increase of approximately 60%, and reduce the water content of the soil on the basis of consolidation of vacuum preloading, howeve~ further settlement is not obvious with only 1.7 mm. The reinforcement effect of vacuum preloading combined electroosmosis is better than that of electroosmosis after vacuum preloading. Elemental analysis using X-ray fluorescence proves that the soil strengthening during electroosmotic period in this work is mainly caused by electroosmosis-induced electrochemical reactions, the concentrations of Al2O3 in the VPCEO region increase by 2.2%, 1.5%, and 0.9% at the anode, the midpoint between the electrodes, and the cathode, respectively.
基金National Natural Science Foundation of China Under Grant No.51278382
文摘This paper reports a series solution of wave functions for two-dimensional scattering and diffraction of plane SH waves induced by a symmetrical V-shaped canyon with different shape ratios. A half-space with a symmetrical V-shaped canyon is divided into two sub-regions by using a circular-arc auxiliary boundary. The two sub-regions are represented by global and local cylindrical coordinate systems, respectively. In each coordinate system, the wave field satisfying the Helmholtz equation is represented by the separation of variables method, in terms of the series of both Bessel functions and Hankel functions with unknown complex coefficients. Then, the two wave fields are described in the local coordinate system using the Graf addition theorem. Finally, the unknown coefficients are sought by satisfying the continuity conditions of the auxiliary boundary. To consider the phase characteristics of the wave scattering, a parametric analysis is carried out in the time domain by assuming an incident signal of the Ricker type. Surface and subsurface transient responses demonstrate the characteristics and mechanisms of wave propagating and scattering.
基金financially supported by the National Natural Science Foundation of China(Grant No.51078227)Shandong Natural Science Foundation(Grant No.ZR2009FM003)
文摘Monotonic lateral load model tests were carried out on steel skirted suction caissons embedded in the saturated medium sand to study the bearing capacity. A three-dimensional continuum finite element model was developed with Z_SOIL software. The numerical model was calibrated against experimental results. Soil deformation and earth pressures on skirted caissons were investigated by using the finite element model to extend the model tests. It shows that the ＂skirted＂ structure can significantly increase the lateral capacity and limit the deflection, especially suitable for offshore wind turbines, compared with regular suction caissons without the ＂skirted＂ at the same load level. In addition, appropriate determination of rotation centers plays a crucial role in calculating the lateral capacity by using the analytical method. It was also found that the rotation center is related to dimensions of skirted suction caissons and loading process, i.e. the rotation center moves upwards with the increase of the ＂skirted＂ width and length; moreover, the rotation center moves downwards with the increase of loading and keeps constant when all the sand along the caisson＇s wall yields. It is so complex that we cannot simply determine its position like the regular suction caisson commonly with a specified position to the length ratio of the caisson.
基金Supported by the National Natural Science Foundation of China(No.50979028)the Program of the Chinese Ministry of Water Resources(No.200801065)
文摘When variations occur in the water content or dry bulk density of soil,the contact angle hysteresis will affect the soil-water characteristic curve(SWCC).The occurrence of the contact angle hysteresis can be divided into slipping and pinning.It is difficult to determine the effect of pinning existence on SWCC by tests.In this study,the effect of contact angle hysteresis on SWCC was analyzed either in the case of no variations in soil dry bulk density with changes in soil water content or no variations in soil water content with changes in soil dry bulk density.In both cases,soil particles were simplified to the spherical particle model.Based on the geometrically mechanic relationship between the particles and connecting liquid bridges,a physical model for predicting the SWCC was derived from the spherical particle model.Adjusting parameters made the model applicable to various soils,that is,the cohesive soil was considered as micron-sized spherical particles.Through the simulations on SWCC test data of sand,silt,clay,and swelling soil,it was confirmed that the physical model possessed good reliability and practicability.Finally,the analysis of rationality of contact angle was performed based on the basic assumptions of the model.
基金Project (50639010) supported by the National Natural Science Foundation of China
文摘Pile foundation is widely used in the offshore engineering. The pile can be seriously destroyed by the soil liquefaction during strong earthquakes. The potentials of liquefaction and damages of pile foundation due to the liquefaction can be reduced by the implementation of the drainage in the liquefiable foundation. A patented pile technology, named rigidity-drain pile, was introduced. The partial section of the pile body was filled by materials with higher penetrability which forms some effective drainage channels in the pile. The principles and construction methods were presented. 3D models for both rigidity-drain pile and ordinary pile were built in FLAC3D code. The dynamic loadings were applied on the bottom of the model. According to the numerical results, in the case of the rigidity-drain pile, the water in the relevant distance range around the pile flows toward the pile drainage, the contour of the pore pressure shows a funnel form. Contrast to the ordinary pile, the rigidity-drain pile can dissipate the accumulated excess pore water, maintain effective stress and obviously reduce the possibility of surrounding soil liquefaction.
基金supported by the National Natural Science Foundation of China(Grants No.51409261 and 11172090)the Natural Science Foundation of Shandong Province(Grants No.ZR2014EEQ014)the Applied Basic Research Programs of Qingdao City(Grant No.14-2-4-67-jch)
文摘There are many fracture zones crossing the dam foundation of the Xiangjiaba Hydropower Project in southwestern China. Clastic rock is the main media of the fracture zone and has poor physical and mechanical properties. In order to investigate the creep behavior of clastic rock, triaxial creep tests were conducted using a rock servo-controlling rheological testing machine. The results show that the creep behavior of clastic rock is significant at a high level of deviatoric stress, and less time-dependent deformation occurs at high confining pressure. Based on the creep test results, the relationship between axial strain and time under different confining pressures was investigated, and the relationship between axial strain rate and deviatoric stress was also discussed. The strain rate increases rapidly, and the rock sample fails eventually under high deviatoric stress. Moreover, the creep failure mechanism under different confining pressures was analyzed. The main failure mechanism of clastic rock is plastic shear, accompanied by a significant compression and ductile dilatancy. On the other band, with the determined parameters, the Burgers creep model was used to fit the creep curves. The results indicate that the Burgers model can exactly describe the creep behavior of clastic rock in the Xiangjiaba Hydropower Project.
基金supported by the National Natural Science Foundation of ChinaYalona River Hydropower Development of Ertan Hydropower Development Company (No.50639050)
文摘The behavior of soil-structure interface plays a major role in the definition of soil-structure interaction. In this paper a bi-potential surface elasto-plastic model for soil-structure interface is proposed in order to describe the interface deformation behavior,including strain softening and normal dilatancy. The model is formulated in the framework of generalized potential theory,in which the soil-structure interface problem is regard as a two-dimensional mathematical problem in stress field,and plastic state equations are used to replace the traditional field surface. The relation curves of shear stress and tangential strain are fitted by a piecewise function composed by hyperbolic functions and hyperbolic secant functions,while the relation curves of normal strain and tangential strain are fitted by another piecewise function composed by quadratic functions and hyperbolic secant functions. The approach proposed has the advantage of deriving an elastoplastic constitutive matrix without postulating the plastic potential functions and yield surface. Moreover,the mathematical principle is clear,and the entire model parameters can be identified by experimental tests. Finally,the predictions of the model have been compared with experimental results obtained from simple shear tests under normal stresses,and results show the model is reasonable and practical.
基金supported by the National Natural Science Foundation of China(Grant No.50639050)
文摘Coarse aggregates are the major infrastructure materials of concrete-faced rock-fill dams and are consolidated to bear upper and lateral loads.With the increase of dam height,high confining pressure and complex stress states complicate the shear behavfor of coarse aggregates,and thus impede the high dam's proper construction,operation and maintenance.An experimental program was conducted to study the shear behavior of dam coarse aggregates using a large-scale triaxial shear apparatus.Through triaxial shear tests,the strain-stress behaviors of aggregates were observed under constant confining pressures:300 kPa,600 kPa 900 kPa and 1200 kPa.Shear strengths and aggregate breakage characteristics associated with high pressure shear processes are discussed.Stress path tests were conducted to observe and analyze coarse aggregate response under complex stress states.In triaxial shear tests,it was found that peak deviator stresses increase along with confining pressures,whereas the peak principal stress ratios decrease as confining pressures increase With increasing confining pressures,the dilation decreases and the contraction eventually prevails.Initial strength parameters(Poisson's ratio and tangent modulus)show a nonlinear relationship with confining pressures when the pressures are relatively low.Shear strength parameters decrease with increasing confining pressures.The failure envelope lines are convex curves,with clear curvature under low confining pressures.Under moderate confining pressures,dilation is offset by particle breakage.Under high confining pressures,dilation disappears.
基金Project(2006BAB04A10) supported by the National Science and Technology Pillar Program during the 11th Five Year Plan of ChinaProject(51008117) supported by the National Natural Science Foundation of China
文摘Swelling and shrinkage due to moisture-change is one of the characteristics of the expansive soil,which is similar to the behavior of most materials under thermal effect,If the deformation is restricted,stress in expansive soil is caused by the swell-shrinking.The stress is defined as "moisture-change stress" and is adopted to analyze swell-shrinkage deformation based on the elasticity mechanics theory.The state when the total stress becomes equal to the soil tensile strength is considered as the cracking criterion as moisture-change increases.Then,the initial cracking mechanism due to evaporation is revealed as follows:Different rates of moisture loss at different depths result in greater shrinkage deformation on the surface while there is smaller shrinkage deformation at the underlayer in expansive soil;cracks will grow when the nonuniform shrinkage deformation increases to a certain degree.A theoretical model is established,which may be used to calculate the stress caused by moisture-change.The depth of initial cracks growing is predicted by the proposed model in expansive soil,A series of laboratory tests are carried out by exposing expansive soil samples with different moisture-changes.The process of crack propagation is investigated by resistivity method.The test results show good consistency with the predicted results by the proposed theoretical model.
基金National Natural Science Foundation of China Under Grant No.90815020 and No.50639010
文摘A new model to simulate spatially correlated earthquake ground motions is developed. In the model, the main factors that characterize three distinct effects of spatial variability, namely, the incoherency effect, the wave-passage effect and the site-response effect, are taken into account, and corresponding terms/parameters are incorporated into the well known model of uniform ground motions. Some of these terms/parameters can be determined by the root operation, and others can be calculated directly. The proposed model is first verified theoretically, and examples of ground motion simulations are provided as a further illustration. It is proven that the ensemble expected value and the ensemble auto-/cross-spectral density functions of the simulated ground motions are identical to the target spectral density functions. The proposed model can also be used to simulate other correlated stochastic processes, such as wave and wind loads.
基金National Natural Science Foundation of China under Grant Nos.51479050 and 51338009National Key Basic Research Program of China under Grant No.2015CB057901+2 种基金the Public Service Sector R&D Project of Ministry of Water Resource of China under Grant No.201501035-03the Fundamental Research Funds for the Central Universities under Grant Nos.2013B05814,2014B06814 and 2015B01214the 111 Project under Grant No.B13024
文摘The earth’s surface irregularities can substantially affect seismic waves and induce amplifi cations of ground motions. This study investigates whether and how the source characteristics affect the site amplifi cation effects. An analytical model of a line source of cylindrical waves impinging on an alluvial valley is proposed to link the source and site. The analytical solution to this problem proves one aspect of the strong effect of source on site amplifi cation, i.e., the wave curvature effect. It is found that the site amplifi cation depends on the source location, especially under conditions of a small source-to-site distance. Whether the displacement is amplifi ed or reduced and the size of the amplifi cation or reduction may be determined by the location of the source. It is suggested that traditional studies of site responses, which usually ignore the source effect, should be further improved by combining the source with site effects.
基金Project(50679017) supported by the National Natural Science Foundation of China
文摘The construction process and load-bearing behaviors of Cast-in-place concrete thin-wall pipe piles are analyzed based on its application on Yantong Expressway Project. The low strain test, static load test and field excavation were also carried out, and the bearing capacity of the new pile can meet the requirements of design. With the increase of pile diameter, the bearing capacity is increased. The settlement of composite foundation is decreased, when the replacement ratio of pile is increased. The test results also show that the load carried by inner soils is neglectable. According to the tests and application, it can be concluded that the new type of pile is convenient to construction with high bearing capacity and reliable quality, which has great potential in practical engineering.
文摘Through laboratory test, the relationships among change of compactibility, liquid/plastic limit, free swell, swell ratio without load, california bearing ratio (CBR) and soakage (after being soaked in water), and mix-ratio of quick lime and time were studied. The results show that optimum water content, plastic limit and CBR of high liquid limit clay improved by quick lime increase with the increase of mix-ratio of quick lime, while the maximum dry density, liquid limit, plasticity index, soakage (after being immersed in water), free swell, and swell ratio without load decrease with the increase of mix-ratio of quick lime. Plastic limit of high liquid clay improved by quick lime gradually increases with time, while the liquid limit, plasticity index, free swell and swell ratio without load gradually decrease with time. When the mix-ratio of quick lime exceeds 2%, after 14 d, swell ratio without load of the improved clay is zero, its free swell is about 30% of that of untreated soil, and its plasticity index is less than 26 for sub-grade material, satisfying the requirement by 'Specifications for Design of Highway Subgrade'.
文摘The success of a tunnel-boring machine （TBM） in a given project depends on the functionality of all components of the system, from the cutters to the backup system, and on the entire rolling stock. However, no part of the machine plays a more crucial role in the efficient operation of the machine than its cutterhead. The design of the cutterhead impacts the efficiency of cutting, the balance of the head, the life of the cutters, the maintenance of the main bearing/gearbox, and the effectiveness of the mucking along with its effects on the wear of the face and gage cutters/muck buckets. Overall, cutterhead design heavily impacts the rate of penetration （ROP）, rate of machine utilization （U）, and daffy advance rate （AR）. Although there has been some discussion in commonly available publications regarding disk cutters, cutting forces, and some design features of the head, there is limited literature on this subject because the design of cutter- heads is mainly handled by machine manufacturers. Most of the design process involves proprietary algorithms by the manufacturers, and despite recent attention on the subject, the design of rock TBMs has been somewhat of a mystery to most end-users. This paper is an attempt to demystify the basic concepts in design. Although it may not be sufficient for a full-fledged design by the readers, this paper allows engineers and contractors to understand the thought process in the design steps, what to Look for in a proper design, and the implications of the head design on machine operation and life cycle.
基金Project supported by the National Natural Science Foundation o China(No.51578214)the Jiangsu Provincial Natural Science Foun dation of China(No.BK20150814)+1 种基金the China Postdoctoral Science Foundation(No.2015M581714)the Jiangsu Provincial Post doctoral Science Foundation of China(No.1501026C)
基金supported by the National Natural Science Foundation of China(Grant Nos.50639010 and 50909039)the Fundamental Research Funds for the Central Universities(Grant No. 2010B04514)
文摘The dynamic stress introduced in half elastic space by wave loading is characterized by the equation between the magnitude of half cyclic axial stress and cyclic torsion shear stress and the principal stress, whose direction rotates continuously and compression stress on seabed can be calculated by the use of small amplitude wave theory. With relationship curves of saturated silt of liquefaction cycles and cyclic stress ratios obtained by cyclic triaxial-torsional coupling shear tests and curve fitting method to different data points of relative density, it is suggested that the cyclic stress ratio corresponding to constant liquefaction impedance be taken as the critical cyclic stress ratio which implies liquefaction. There exists a linear relationship between critical cyclic stress ratio and relative density under different relative densities. Empirical formula for critical cyclic stress ratios of seabed liquefaction induced by wave loading under different relative densities is established. The possibility of seabed silt liquefaction and its influence factors are analyzed based on the small-amplitude wave theory and the data acquired in laboratory tests.
基金Project 50579017 supported by the National Natural Science Foundation of China
文摘The development of fissures in expansive soils has a great effect on the stability of slope. Of the three phases of soils,the gas phase and solid phase are relatively insulated,so the average resistivity of soils can be calculated from the resistivity of the liquid phase. On this basis,the two-part model of resistivity changing with the water saturation of the expansive soil can be deduced. A 2-D resistance grid model is established based on simulating the resistance of ver-tically developed fissures. Variation in measured resistance of vertically developed fissures at different positions can be calculated from this model. Fissure development can be inversely determined from the variation in the measured resis-tance. Finally,the model is verified by an indoor resistivity test for remolded soil samples,indicating that the test result agrees well with that of the model established.
