地铁荷载下隧道周围粉性土孔压的单因素试验

为了研究地铁荷载作用下饱和粉性土的孔隙水压力特性,针对上海地铁10号线国权路附近的饱和粉性土进行多功能GDS循环三轴试验,考虑了振动频率、动应力幅值及固结比等因素对孔隙水压力的影响。试验结果表明:土体遭受地铁振动荷载作用下,孔隙水压力经过三个阶段的变化过程,即快速增长-缓慢增加-衰减稳定。相同振动频率及固结比条件下,动应力幅值越大,产生的孔隙水压力越大;相同动应力幅值及固结比条件下,频率越小,产生的孔隙水压力越大;相同动应力幅值及振动频率条件下,固结比越大,产生的孔隙水压力越大。采用单因素设计法及方差分析,得到振动频率、动应力幅值及固结比等因素均对孔隙水压力有非常显著的影响。     

有效应力原理表达式的推导和理解

基于应力的定义,推导出了有效应力原理的表达式,并通过颗粒的受力分析,证明由于土颗粒之间的接触可以看成点接触,有效应力与颗粒之间接触点上的作用力直接相关,而与孔隙水压力无关。另外由于土颗粒可看成是不可压缩的,孔隙水压力并不会使土颗粒产生移动或明显的压缩变形,因此有效应力决定了饱和土的变形和强度。     

水泥搅拌桩复合地基的应用实例与分析

水泥搅拌桩在处理正常固结的淤泥与淤泥质土、粉土、饱和黄土、素填土、粘性土以及无流动地下水的饱和松散砂土等地基中非常适用。通过上海地区一工程实例,介绍该技术的一些特点,并提出一些看法及建议。     

强震触发黄土滑坡发生机制试验

为了进一步研究不同地震破坏程度后黄土的变形特性及稳态强度,通过MTS土动三轴仪进行了不同围压(100、150、200 k Pa)、不同动应变(0,1%、2%、3%)条件下的饱和黄土静力剪切试验。结果表明:在相同试样条件下,应力路径对稳态强度影响极小,不同震动破坏程度的试样在试验结束后的残余强度几乎相等;黄土液化后的稳态强度随着初始孔隙比的减小而增加;饱和度主要对黄土的黏聚力产生影响;初始有效固结压力与稳态强度有良好的拟合关系。比较震后斜坡重力驱动剪应力与稳态强度的关系,可判断斜坡会否发生破坏。     

饱和粉土振动孔隙水压力的试验研究

本文通过饱和粉土的动三轴试验,总结和分析了饱和粉土的振动孔隙水压力发展规律,提出了振动孔压力比与振次比之间满足幂函数关系的孔压发展模式,说明了饱和少粘性土振动初期孔压急剧上升随之逐渐趋于稳定的特点,并分析了产生的原因及其粘粒的影响,验证了Lee提出的振动孔压比U/σ0'可以表示为大主应变ξ1的单一函数这一结论,推导出振动孔压发展极限值与团结比民间的关系,为实际工程和进一步的研究提供了参考依据．     

梯度饱和土层的一维固结度的计算

研究了梯度饱和土层在外荷载下的固结作用,利用Biot理论给出了固结的基本微分方程,一些材料常数假设为指数模型,当梯度系数为零时,退化为一维均匀饱和土层的固结,利用分离变量等方法,得到透水和不透水边界条件下孔隙压力,给出了固结度曲线。当梯度系数不为零时,给出了梯度饱和土在外荷载下的孔隙压力,利用固结度的定义,数值算例出了梯度饱和土层的固结度变化曲线,分析和讨论了梯度系数等对固结度的影响。这些结果对地基下沉量计算和预测有一定的理论价值和意义。     

谈谈土力学中有效应力的定义和分类

笔者在《土力学》课程的教学中,发现各教材对“土的有效应力”的定义不尽一致。且对有效应力的产生原因未作分析。 罗家枢、周文哲合编《土力学》关于土的有效应力是这样定义的:“由土骨架承担的压力,即外加压力在土骨架引起的应力。称为有效应力”。该定义出现在“土的压缩性”这一节中,这样定义的话,在“地基沉降的时间过程”这节中就可根据有效应力的定义,讲述孔隙水压力与有效应力在饱和土层的渗透固结过程中的关系:但在“土的自重应力”的计算中,就难以说明自重应力是什么性质的力,为什么计算地下水位以下土的自重应力要用浮容重指标等等一系列相关问题。     

沥青路面内动空隙水压力的数值模拟(英文)

为了研究沥青路面内的动水压力,基于Biot固结方程,将沥青混合料看作多孔介质,并考虑了它和水体的惯性力及两者之间的耦合作用,对饱水沥青路面进行了快速Lagrange有限差分分析.结果表明,水压的产生和消散在轮载作用过程中同时存在,导致面层内正负水压力及渗透力随时间交替出现,这证实了水损坏过程中的水力反复泵吸作用.动孔隙水压力随车速的增大而增大,而且由于水压力的存在路面弯沉和面层内的有效应力减小,但水对沥青膜的乳化和置换作用加强.动水压力的最大值出现在面层底部,所以建议在面层底部设一排水层,将排水状态由单面排水变为双面排水,有效抑制水损坏的发生.     

降雨作用下排水钉的性能及其对渗流场的影响

为探究降雨入渗作用下排水钉的排水性能及其对土体渗流场的影响,通过开展室内试验、建立排水钉数值模型、定义流量函数模拟降雨入渗过程,分析排水钉排水量及土体中体积含水率和孔隙水压力的变化规律。 结果表明:随着降雨时间的增加,排水钉排水量不断增大直至最大值,排水量处于最大值一段时间后,土体表面积水入渗完成,排水量开始大幅减小。 随着降雨入渗的发展,各监测点处体积含水率均达到土体饱和体积含水率,各处孔隙水压力值由负变正,降雨停止后,由于排水钉的排水作用,各处体积含水率均不断减小,最终,各监测点处体积含水率均小于初始状态,孔隙水压力值由正变负。 数值模拟结果能与室内试验结果具有良好的一致性。 研究结果说明排水钉具有良好的排水效果,可有效解决工程中降水的排出问题,能够为工程的排水设计提供借鉴。     

结构性对黏性土渗透性状的影响研究

利用改进的固结渗透仪,通过对天然沉积软黏土原状样及重塑样进行固结渗透试验,对比分析了压缩过程中天然沉积土原状样与重塑样在同一孔隙比和同一应力水平下的渗透性状。研究结果表明,天然沉积土原状样e-log kv曲线位于重塑样的右边,但是两者差别不大;原状样的log kv-logσ’v关系曲线位于重塑样的上方,天然沉积土原状样与重塑样同一应力水平下的渗透系数的比值随着应力水平的增大而先增大后减小,在原状样固结屈服压力时达到最大值。     

Instability of saturated soil under axial load

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考虑孔压梯度和应变梯度影响的饱和土剪切稳定性分析

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A strength degradation model of saturated soft clay and its application in caisson breakwater

In this paper we propose a degradation model to describe the damage-dependent behavior of saturated soft clay under cyclic loading, which is then applied to the analysis of a caisson breakwater. The degree of damage and remolding of soft clay is quantified by a damage parameter related to the accumulated plastic deviatoric strain. Through the correlation between the maximum pore pressure and the undrained strength of soft clay, we obtain a damage-dependent degradation model that employs the post-cyclic undrained strength degradation coefficient in terms of the cyclic stress ratio and the number of cycles. Based on the Tresca yield criterion, the degradation model of undrained strength of soft clay is numerically implemented in the user interface USDFLD of ABAQUS. The performance of this model is verified by a comparison between numerical results (finite element method) and experimental data (cyclic triaxial test). The model is applied to the numerical simulation of a caisson breakwater resting on a partially sand-filled soft clay seabed under cyclic wave loading. The cyclic stress distribution, pore pressure development, and strength degradation of the seabed soil are presented to illustrate the applicability and efficiency of the model in the analysis of the interaction between offshore structures and soft ground.     

Development of the shear bands in saturated soil

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轴向扩散下不可压饱和多孔简支弹性杆的弯曲

Based on the mathematical model of the bending of the incompressible saturated poroelastic beam with axialdiffusion, the quasi-static bendings of the simply supported poroelastic beam subjected to a suddenly applied constant loadwere investigated, and the analytical solutions were obtained for different diffusion conditions of the pore fluid at the beamends. The deflections, the bending moments of the solid skeleton and the equivalent couples of the pore pressures werepresented in figures. It is also shown that the behavior of the saturated poroelastic beams depends closely on the diffusionconditions at the beam ends, especially for the equivalent couples of the pore pressures. It is found that the Mandel-Cryereffect also exists in the bending of the saturated poroelastic beams under specific diffusion conditions at the beam ends.     

Torsional oscillations of a rigid disc bonded to multilayered poroelastic medium

INTRODUCTION The dynamic response of foundations resting onthe surface of a half space is of significant importancein soil-foundation interactions and machine founda-tion designs. Observation of earthquake damage in-dicated that the local soil properties, foundation ge-ometries, etc., play a central role in the dynamic be-havior of the soil-foundation system. Ever-increasing research has been devoted to theproblem of an elastic half space indented by a rigidfooting by employi…     

饱和土中压缩带的演化

The development of compaction bands in saturated soils, which is coupling-rate, inertial and pore-pressure-dependent, under axisymmetric loading was discussed, using a simple model and a matching technique at the moving boundary of a band. It is shown that the development of compaction bands is dominated by the coupling-rate and pore-pressure effects of material. The soil strength makes the band shrinking, whilst pore pressure diffusion makes the band expand. Numerical simulations were carried out in this paper.