A study on water film in saturated sand

Water film can serve as a sliding surface and cause landslides on gentle slopes. The development of "water film" in saturated sand is analyzed numerically and theoretically based on a quasi-three-phase model. It is shown that stable water films initiate and grow if the choking state (where the fluid velocity decreases to near zero) remains steady in a liquefied sand column. Discontinuity can occur in pore water velocity, grain velocity and pore pressure after the initiation of a water film. However, the discontinuity and water film can disappear once the choking state is changed. The key to the formation of water film is the choking in the sand column caused by eroded fine grains.     

3D scattering of obliquely incident plane SV waves by an alluvial valley embedded in a fluid-saturated,poroelastic layered half-space

The indirect boundary element method is used to study the 3D dynamic response of an infinitely long alluvial valley embedded in a saturated layered half-space for obliquely incident SV waves. A wave-number transform is first applied along the valley’s axis to reduce a 3D problem to a 2D plane strain problem. The problem is then solved in the section perpendicular to the axis of the valley. Finally, the 3D dynamic responses of the valley are obtained by an inverse wave-number transform. The validity of the method is confirmed by comparison with relevant results. The differences between the responses around the valley embedded in dry and in saturated poroelastic medium are studied, and the effects of drainage conditions, porosity, soil layer stiffness, and soil layer thickness on the dynamic response are discussed in detail resulting in some conclusions.     

二维格子气自动机模拟孔隙介质的电传输特性

本文应用2-D格子气自动机模拟饱和油水两相的多孔介质的导电特性。在油水两相界面处,引入反射与透射系数来决定粒子的运动状态,通过调节反射与透射系数就可以改变油水两相的导电性差异。用模拟结果考察Archie公式的地层因素F=R0/Rw和电阻率增大系数I=Rt/R0,其中,R0为百分之百饱和水时的岩石电阻率,Rw为水的电阻率,Rt为不同流体饮和度时的岩石电阻率。结果表明F与孔隙度φ间,I与含水饱和度间都存在幂关系,并可以表示为F=aφ-m,I=bS-nw模拟结果同时证实：公式中的参数a、m的变化反映了孔隙微观结构的变化,参数b、n主要受孔隙度大小和油相分布状态的影响。     

Micro- and macro-observations of liquefaction of saturated sand around buried structures in centrifuge shaking table tests

A novel experimental method was designed to study the micro-behavior of saturated sand around a buried structure in centrifuge shaking table tests under strong simulated earthquake loading, in addition to the traditional macro-measurements. One free field test was first carried out as a reference, followed by one test with a deep buried structure and one with a shallowly buried structure. During the tests with the buried structure, high quality pictures of moving sand around the structure were recorded by a newly developed image acquisition system. By analyzing the interesting pictures at reasonable intervals using an image analysis software, the evolutions of microstructural features were obtained such as the orientations of the long axes of particles, the orientations of contact normals between particles and the average contact number of the interesting group of particles. The results showed that the evolutions of the micro-features were consistent with those of the macro-measurements such as excess pore pressures and accelerations, which help illuminate the mechanism of sand liquefaction.     

饱和土沉积谷场地对平面SV波的散射问题的解析解

把波函数展开方法用于饱和多孔介质中波的传播的研究中,给出了不同土层界面条件（透水条件和不透水条件）下具有饱和土沉积层的圆弧形沉积河谷场地对平面SV波散射问题的解析解. 其中沉积谷软土场地用饱和多孔介质的Biot动力学理论模拟,半空间场地用单相介质弹性动力理论模拟. 对于入射角大于临界入射角时,产生的面波的波函数用有限Fourier级数展开,这种方法适用于较大的入射波频率范围,这是现存的数值方法所不能比拟的一大优点. 文中算例分析了入射波频率和入射角对地震地面运动的影响.     

Carbone organique total (COT) et magnésium (Mg2+) : deux traceurs complémentaires du temps de séjour dans l'aquifère karstique

The Total Organic Carbon (TOC) is an interesting tracer of fast infiltration within karstic systems [3,7]. Regular sampling on several aquifers, from the experimental site of Vaucluse, made it possible to demonstrate the high sensitivity of this tracer compared with other commonly used chemical and isotopic tracers in karstic hydrogeology. The complementarity of magnesium, indicator of the residence time of water within the system, and TOC appears as a relevant tool in order to characterize the behaviour of the aquifer, to differentiate the water types which participate to the karstic flow (fast infiltration, unsaturated zone, saturated zone) and then, to evaluate their vulnerability.     

水饱和土层中骨架波速的获取与分析

本文较详细地研究了水饱和状态下土体的波速性质，提出了由饱水土体波速值计算土体骨架波速值的方法。用本文的方法可以解决在工程地质工作中波速测试方面存在的一些问题。     

Condition for liquefaction instability in fluid-saturated granular soils

High-porosity granular materials such as loose sands can implode when subjected to compressive stresses. The mechanism of deformation is diffuse in that the jump in the strain rate tensor has three independent eigenvalues (full rank), in contrast to the jump in the strain rate tensor for a deformation band-type instability that has one eigenvalue (rank one). Recently, the mechanism of volume implosion has been studied in the context of material instability. In this paper we move one step further and consider the effect of a volume constraint associated with the presence of fluids in the pores of granular materials that have a tendency to implode. The upshot of this constraint is that at the onset of liquefaction the solid matrix deforms in a nearly isochoric fashion at the same time that the pore fluid pressure increases. The corresponding eigenmode (e-mode) is represented by jumps in the strain rate tensor and rate of pore fluid pressure. The framework presented in this work is used to analyze the onset of liquefaction instability in very loose Hostun RF sand tested in undrained triaxial compression and extension.     

引潮力作用下饱和地质岩体的力学响应

本文应用孔隙弹性理论,探讨了引潮力作用下饱和地质岩体的力学响应.首先通过引潮力作用下饱和岩体的自由能表达式,得到岩体孔压与应力、应力与应变之间的关系;然后从引潮力作用下饱和岩体的平衡微分方程出发,结合流-固耦合理论,分析了饱水岩体应变与引潮位之间的关系;最后推导出饱和岩体的两大力学物理量--孔压和潮汐应力(平均应力)与引潮位之间的物理关系.模型表明:饱和岩体孔压与引潮位成反比,平均潮汐应力与引潮位成正比;比例系数不仅与岩体骨架的Lame系数有关,而且与Biot模量有关.将模型应用于会理川-18井水位变化分析,估计出水位响应系数D,并以此为基础,求得岩体孔压、潮汐应力与引潮位的相关系数(A和C)及Skempton系数B.最后对比分析了耦合条件下与不考虑耦合时得到的各参数之间的差异,分析表明:对饱和地质岩体而言,应力、孔压对引潮力的响应是流-固耦合作用的产物;研究其力学响应时必须充分考虑耦合效应.模型的建立,为研究引潮力作用下井-承压含水层系统力学、水动力学、与地震有关的断层力学以及引潮力触发机制的定量研究提供了基础.     

半空间饱和介质内圆形洞室对平面P1波的散射

考虑土颗粒和孔隙流体的压缩性以及孔隙流体与土骨架之间的粘性耦合作用,采用修正的Biot模型,假定半空间表面不透水,得到了平面P1波(快压缩波)在半空间表面的反射P1波、P2波(慢压缩波)和SV波(剪切波)的幅值.采用大圆弧假定将半空间内圆形洞室的散射问题转化为大圆弧和圆形洞室的多重散射问题,运用波函数展开法将入射波、反射波以及半空间表面和洞室的散射波的势函数展开成Fourier-Bessel函数的无穷级数形式,由Graf加法定理得到同一坐标系下的势函数的表达式,根据半空间表面和洞室完全自由的边界条件得到了待定复系数的理论解.通过数值计算,着重分析了平面P1波垂直向上入射时无量纲入射频率和洞室埋藏深度等对洞室的动应力集中因子和半空间表面的归一化水平和竖向位移的影响.