黄土路堑边坡变形破坏机理的三轴试验研究

通过原状黄土的减压三轴压缩试验,研究了黄土边坡不同深度不同含水量土体的应力-应变关系,并与原状黄土的常规三轴试验结果进行了比较,发现减压三轴试验能合理地模拟和解释开挖卸荷作用下黄土边坡土体的变形与破坏过程。试验结果表明:坡脚开挖卸荷时,黄土边坡中浅层非饱和黄土易出现应变软化或塑性流动,强度较低,易产生较大变形,而深层饱和黄土仅在高围压下发生应变硬化,强度增加,在中低围压时均发生应变软化现象。分析认为黄土边坡特殊的工程地质条件,使得黄土边坡的特定部位在开挖卸荷作用下常形成了不利于土体稳定的含水量和围压组合,导致坡体特定部位的土体变形破坏,进而诱发边坡的变形破坏;开挖卸荷作用下黄土边坡变形破坏的力学机制应为蠕滑-压致拉裂或"牵引式滑坡"。     

结构性饱和黄土动力特性试验研究

基于室内不排水动三轴试验，研究了5种因素，即围压、超固结比、偏压固结比、动剪应力比、加载频率等对饱和黄土动力特性的影响。本文强调了结构性在饱和黄土动力特性研究中的重要性，结构性的破坏是影响土体动力力学特性的一个重要转折点。并阐明了用塑性残余变形来表征土体内部结构的变化并以此作为孔压增长函数自变量的合理性。     

陕西泾阳南塬黄土滑坡灾害与引水灌溉的关系

陕西泾阳南塬塬边黄土滑坡频繁发生，造成的经济损失和人员伤亡极为惨重。本文讨论了区内黄土滑坡灾害形成的地貌地形及地质环境特征，着重分析了人类不合理的引用地表水灌溉，改变了地下水文条件，从而降低了土体的抗剪强度，导致黄土滑坡形成的过程和机制。通过研究认为，合理进行灌溉，控制地下水位是改善塬边地质环境和防治滑坡灾害的关键措施。     

地下水位上升下黄土斜坡稳定性分析

黄土高原一些地区,由于塬上引水灌溉使得地下水位不断抬升,造成黄土滑坡频繁发生。地下水位变化严重影响着黄土斜坡的稳定性。基于饱和-非饱和渗流理论和延伸的摩尔-库伦破坏准则,结合室内饱和和非饱和试验结果,针对泾阳南塬一典型黄土斜坡,考虑地下水位上升情况下,对其进行了瞬态饱和-非饱和渗流分析;然后将计算得到的瞬态孔隙水压力分布用于斜坡的极限平衡分析。结果表明:地下水位上升对暂态渗流场和斜坡稳定性有明显影响;考虑非饱和渗流和吸力强度的边坡稳定分析方法更加符合实际情况。     

恒定主应力偏转角下黏土不排水剪切特性分析

天然土的结构性、各向异性对其强度有影响.进行固结压力100kPa、主应力轴恒定偏转角为0°,15°,30°,45°,60°的恒定主应力轴偏转角的固结不排水剪切试验,分析了不同恒定主应力轴偏转角对饱和软黏土固结不排水剪切强度影响;推导了总应力控制恒定主应力轴偏转角剪切试验总应力路径,编制了总应力控制剪切三维点积分程序,对比恒定主应力轴偏转角饱和软黏土固结不排水剪切强度计算值与试验结果,表明程序能很好地反应各向异性对土剪切强度影响.     

陕西宝鸡地区千阳县塌山黄土滑坡稳定性分析

通过对宝鸡塌山黄土滑坡详细调查和钻探结果表明：具有特殊性的黄土为塌山黄土滑坡形成提供了物质基础；斜坡地形地貌、顺向斜坡结构、黄土节理等为塌山黄土滑坡提供了边界条件；人类活动、降水等是塌山黄土滑坡形成的主导诱发因素；多种因素相辅相成，导致塌山黄土滑坡发生发展。其次，采用SARMA法和FLAC法对滑坡稳定性进行了计算和模拟分析，通过对滑坡体土体应力的分析与滑坡安全系数计算表明，在天然状态下塌山黄土滑坡现今整体稳定，局部(滑坡前缘左侧)有失稳可能，这与野外调查塌山黄土滑坡现今变形特征以及整体稳定局部可能失稳的结论基本一致。而在饱和状态、天然状态＋地震、饱和状态＋地震3种工况下，塌山黄土滑坡整体失稳的可能性较大。     

聚丙烯纤维加筋绍兴非饱和黏土的剪切特性研究

为了研究纤维加筋非饱和土的剪切特性，以绍兴地区广泛分布的非饱和黏土为研究对象，聚丙烯纤维为加筋材料，通过一系列非饱和直剪试验，探讨了纤维长度对加筋土剪切变形特性、抗剪强度及其指标的影响规律，并简要分析了聚丙烯纤维的增强机理，最后得出了0.2%掺量下补强效果最佳的纤维长度．研究结果表明：随着净法向应力的增大，土体的剪应力-剪切位移曲线由软化型逐渐向硬化型转化，纤维长度L为12 mm的加筋土样表现出的剪切硬化特性最明显；不同净法向应力下，纤维加筋非饱和土的抗剪强度均高于素土；随着纤维长度的增加，纤维加筋土的黏聚力呈先增加后减小，内摩擦角先增加后趋于平缓；当纤维长度L为12 mm时，聚丙烯纤维对土体抗剪强度指标的补强效果能够最大程度得到发挥．     

香港大屿山残坡积土的残余强度试验研究

粘性土的残余强度是边坡稳定性评价、桩基与土的相互作用机理研究及填土边坡设计中的重要参数。本文在综述大量文献的基础上，结合香港大屿山火山岩风化残坡积土的残余强度试验研究，分析了残余强度的测试方法和影响残余强度的因素。研究结果表明，残余强度与有效法向应力间具有明显的非线性关系；与单剪测试结果相比，多级剪测试结果明显偏高。     

土剪破坏次声监测试验研究

土质滑坡临滑会产生次声波,次声监测可以作为判断土质滑坡临滑的一种技术手段.在考虑到滑坡的力学方式是以剪切破坏为主的前提下,为了探明土质滑坡过程中的次声信号响应特征,设计了土体直剪实验次声-力-位移联合监测系统,开展了土体剪破坏次声监测试验,在次声事件自动拾取的基础上,结合黏性土渐进性破坏理论,分析了剪切过程中的微观声学机理,结果表明:(1)黏性土剪切破坏时发出的次声信号主要来源于弹性阶段中黏土颗粒的相互挤压、弹塑性阶段中以黏土胶体团粒本身的拉张破裂和应变软化阶段中土颗粒间的摩擦;(2)在土体剪切载荷的不同阶段,次声信号的幅值大小呈现出应变软化阶段弹性阶段弹塑性阶段的规律;(3)剪切力与次声信号之间存在较强的相关性,次声事件的峰值包络线与剪切力趋势线相当吻合,并且次声信号的均方功率峰值都在推力峰值之前,平均提前为22.95 s.研究对进一步利用次声开展土质滑坡的监测和稳定性评价具有重要的理论参考价值.     

土剪破坏次声监测试验研究

土质滑坡临滑会产生次声波, 次声监测可以作为判断土质滑坡临滑的一种技术手段. 在考虑到滑坡的力学方式是以剪切破坏为主的前提下, 为了探明土质滑坡过程中的次声信号响应特征, 设计了土体直剪实验次声-力-位移联合监测系统, 开展了土体剪破坏次声监测试验, 在次声事件自动拾取的基础上, 结合黏性土渐进性破坏理论, 分析了剪切过程中的微观声学机理, 结果表明: (1)黏性土剪切破坏时发出的次声信号主要来源于弹性阶段中黏土颗粒的相互挤压、弹塑性阶段中以黏土胶体团粒本身的拉张破裂和应变软化阶段中土颗粒间的摩擦; (2)在土体剪切载荷的不同阶段, 次声信号的幅值大小呈现出应变软化阶段<弹性阶段<弹塑性阶段的规律; (3)剪切力与次声信号之间存在较强的相关性, 次声事件的峰值包络线与剪切力趋势线相当吻合, 并且次声信号的均方功率峰值都在推力峰值之前, 平均提前为22.95 s. 研究对进一步利用次声开展土质滑坡的监测和稳定性评价具有重要的理论参考价值.      

三趾马红土与西北黄土高原滑坡

本文在前人和作者以往研究成果的基础上总结了黄土高原大中型滑坡的形成发育规律;滑坡发生的土体结构效应;指出三趾马红土（N2）是控制和影响黄土高原滑坡形成的重要因素,并对其物质成分、工程特性及古风化带（不整合面）与滑坡的关系,及其在滑坡发生中的作用进行探讨。     

ROTATIONAL RESISTANCE AND SHEAR-INDUCED ANISOTROPY IN GRANULAR MEDIA

This paper presents a micromechanical study on the behavior of granular materials under confined shear using a three-dimensional Discrete Element Method （DEM）. We consider rotational resistance among spherical particles in the DEM code as an approximate way to account for the effect of particle shape. Under undrained shear, it is found rotational resistance may help to increase the shear strength of a granular system and to enhance its resistance to liquefaction. The evolution of internal structure and anisotropy in granular systems with different initial conditions depict a clear bimodal character which distinguishes two contact subnetworks. In the presence of rotational resistance, a good correlation is found between an analytical stress-force-fabric relation and the DEM results, in which the normal force anisotropy plays a dominant role. The unique properties of critical state and liquefaction state in relation to granular anisotropy are also explored and discussed.     

Thermal Responses of Saturated Silty Clay During Repeated Heating–Cooling Processes

The thermal responses of the saturated silty clay to repeated heating–cooling are studied in laboratory. Results show that the pore pressure induced by undrained heating increases with increasing temperature, but the peak pore pressure appears a degradation trend with increasing temperature cycles. During the consolidation process at an elevated temperature, the specimen contracts due to the dissipation of the pore pressure; however, the thermally induced pore pressure is under no conditions fully dissipated to zero, therefore, there always exists a residual pore pressure in the specimens once a thermal loading higher than the ambient temperature is applied. During the undrained cooling, pore pressure continues to decline and eventually falls below zero. During the isothermal consolidation at the original temperature, the specimen begins to expand due to water absorption caused by the negative pore pressure, and eventually reaches a steady value. In addition, the consolidation volumetric strain generated during the drainage process at 50°C is greater than that during the water absorption process at 25°C, the difference seems to be most obvious for the first three cycles, and begins to diminish gradually thereafter.     

Discrete simulation and micromechanical analysis of two-dimensional saturated granular media

In this study, a novel approach to incorporate the pore water pressure in the discrete element method (DEM) to comprehensively model saturated granular media was developed. A numerical model was constructed based on the DEM by implanting additional routines in the basic DEM code; pore water pressure calculations were used with a two-dimensional (2D) model to simulate the undrained behavior of saturated granular media. This model coupled the interaction of solid particles and the pore fluid in saturated granular media. Finally, several 2D undrained shear tests were simulated. The test results showed that the model could predict the response of the saturated granular soil to shear loading. The effect of initial compaction was investigated. Biaxial tests on dense and loose specimens were conducted, and the effect of the initial density on the change in shear strength and the volume change of the system was investigated. The overall behavior of loose and dense specimens was phenomenologically similar to the real granular material. Constant volume tests were simulated, and the results were compared to those from the coupled model. Induced anisotropy was micromechanically investigated by studying the contact force orientation. The change in anisotropy depended on the modeling scheme. However, the overall responses of the media obtained using the coupled and constant volume methods were similar.     

Discrete simulation and micromechanical analysis of two-dimensional saturated granular media

In this study, a novel approach to incorporate the pore water pressure in the discrete element method （DEM） to comprehensively model saturated granular media was developed. A numerical model was constructed based on the DEM by implanting additional routines in the basic DEM code; pore water pressure calculations were used with a two-dimensional （2D） model to simulate the undrained behavior of satu- rated granular media. This model coupled the interaction of solid particles and the pore fluid in saturated granular media. Finally, several 2D undrained shear tests were simulated. The test results showed that the model could predict the response of the saturated granular soil to shear loading. The effect of initial compaction was investigated. Biaxial tests on dense and loose specimens were conducted, and the effect of the initial density on the change in shear strength and the volume change of the system was inves- tigated. The overall behavior of loose and dense specimens was phenomenologically similar to the real granular material. Constant volume tests were simulated, and the results were compared to those from the coupled model. Induced anisotropy was micromechanically investigated by studying the contact force orientation. The change in anisotropy depended on the modeling scheme. However, the overall responses of the media obtained usinz the couoled and constant volume methods were similar.     

Steady state and stability of a beam on a damped tensionless foundation under a moving load

In the first part of this paper we study the effect of damping on the multiple steady state deformations of an infinite beam resting on a tensionless foundation and under a point load moving with a sub-critical speed. Due to the non-linear characteristics of the problem, a guess on the deformed shape has to be made before a numerical search can be initiated. It is found that when the damping is present, all the steady state solutions are asymmetric. As the damping approaches zero, some of the steady state solutions become symmetric, while some others remain asymmetric. In the second part of the paper we propose to test the stability of these steady state deformations by a transient analysis on a long finite beam. Our numerical experiment indicates that among all these multiple steady state solutions only one of them is stable. This stable steady state deformation reduces to a symmetric solution when the damping approaches zero. Furthermore, it is found that this stable solution is also the one among all steady state solutions closest in shape to the linear solution based on a bilateral foundation model.     

Multi-mechanism anisotropic model for granular materials

By representing the assembly by a simplified column model, a constitutive theory, referred to as sliding–rolling theory, was recently developed for a two-dimensional assembly of rods subjected to biaxial loading, and then extended to a three-dimensional assembly of spheres subjected to triaxial (equibiaxial) loading. The sliding–rolling theory provides a framework for developing a phenomenological constitutive law for granular materials, which is the objective of the present work. The sliding–rolling theory provides information concerning yield and flow directions during radial and non-radial loading. In addition, the theory provides information on the role of fabric anisotropy on the stress–strain behavior and critical state shear strength. In the present paper, a multi-axial phenomenological model is developed within the sliding–rolling framework by utilizing the concepts of critical state, classical elasto-plasticity and bounding surface. The resulting theory involves two yield surfaces and falls within the definition of the multi-mechanism models. Computational issues concerning the solution uniqueness for stress states at the corner of yield surfaces are addressed. The effect of initial and induced fabric anisotropy on the constitutive behavior is incorporated. It is shown that the model is capable of simulating the effect of anisotropy, and the behavior of loose and dense sands under drained and undrained loading.     

Thermo-mechanically coupled investigation of steady state rolling tires by numerical simulation and experiment

In this contribution, a numerical framework for the efficient thermo-mechanical analysis of fully 3D tire structures (axisymmetric geometry) in steady state motion is presented. The modular simulation approach consists of a sequentially coupled mechanical and thermal simulation module. In the mechanical module, the Arbitrary Lagrangian Eulerian (ALE) framework is used together with a 3D finite element model of the tire structure to represent its temperature-dependent viscoelastic behavior at steady state rolling and finite deformations. Physically computed heat source terms (energy dissipation from the material and friction in the tire–road contact zone) are used as input quantities for the thermal module. In the thermal module, a representative cross-sectional part of the tire is employed to evaluate the temperature evolution due to internal and external heat sources in a transient thermal simulation. Special emphasis is given to an adequate material test program to identify the model parameters. The parameter identification is discussed in detail. Numerical results for three different types of special performance tires at free rolling conditions are compared to experimental measurements from the test rig, focusing especially on rolling resistance and surface temperature distribution.     

黄土斜坡最危险滑裂面的遗传算法确定及稳定性分析

黄土滑坡尤其是地震作用下的黄土滑坡历来是我国西部广大地区一种突出而严重的地质灾害。本文研究了一种采用遗传算法基本思想和原理确定黄土斜坡“最危险滑裂面”、并以此为基础进行稳定性分析的新方法。实例的验证表明,与传统方法相比,该方法更准确、更高效,具有较好的实用性。