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1.
A model of chemo-osmotic consolidation of clays in multi-dimensional domains is presented, with volumetric strains induced by both changes in the chemistry and osmotically driven pore water flow considered. Three fully coupled governing equations considering force equilibrium, pore water transport and chemical transport are presented and solved using the transient finite element method. The proposed approach is verified via consideration of chemo-osmotic consolidation of a compacted clay landfill liner and then applied to investigation of a hypothetical case with a local leachate leak in the compacted clay liner. An assessment of the impact of the two-dimensional nature of the system is made. The consolidation process is found to be dominated by osmotic consolidation in the early stages and subsequently by chemical consolidation. It is found that the surface settlement and the leachate concentration in the compacted clay liner may be highly overestimated by a one-dimensional analysis. Moreover, the peak negative excess pore pressure predicted by the two-dimensional solution remains in a shallow region under the leak while in the one-dimensional solution it moves progressively downwards. 相似文献
2.
为进一步深入研究弹性饱和黏性土地基的二维固结机制,引入Hansbo渗流方程描述固结过程中的非达西渗流,修正Biot二维固结方程。基于加权残数法,给出相应的有限元数值求解格式。通过和饱和黏性土一维非达西渗流固结理论有限体积法数值结果的对比,证明数值计算方法的有效性。在此基础上,探讨Hansbo渗流参数对二维地基固结进程的影响。计算结果表明,在固结初期,Hansbo渗流将增强Mandel-Cryer效应,增大孔压的峰值,并延长孔隙水压力达到峰值的时间;在固结中后期,整个土层存在孔隙水压力滞后现象。同时,Hansbo渗流将阻碍地基沉降的发展。而且,上述影响会随着Hansbo渗流参数的增大而更加明显。 相似文献
3.
软黏土层一维有限应变固结的超静孔压消散研究 总被引：1，自引：0，他引：1
根据土力学固结理论计算分析软黏土层固结过程的超静孔隙水压力值,确定软黏土体固结过程的强度增长,对排水固结法处理软土地基至关重要。软黏土层固结过程中土体变形较大时,有限应变固结理论和小应变固结理论计算分析软黏土固结所得结果差异较大。利用非线性有限元法及程序,通过对软黏土层固结工程算例的计算结果分析,研究了有限应变固结理论和小应变固结理论计算分析软黏土层一维固结超静孔压值消散的差异;探讨了软黏土体一维固结过程中,几何非线性、土体渗透性变化和压缩性变化对超静孔隙水压力消散的影响。研究结果表明,当土体的变形较大时,有限应变固结理论计算出的超静孔压要比小应变固结理论得到的值消散的更快。考虑土体固结过程中渗透性的变化时,超静孔压消散变慢;可用软黏土渗透性变化指数ck 反映渗透性变化对超静孔压消散的影响,渗透性变化指数ck值越小、超静孔压消散越慢。固结过程中软黏土压缩性的大小及变化也影响超静孔压的消散,可用软黏土的压缩指数cc反映固结过程中压缩性的大小及变化对超静孔压消散的影响,软黏土的压缩指数cc越小,固结过程软黏土层中的超静孔压消散越快。 相似文献
4.
F. E. analysis of field consolidation curves obtained with the modified borehole shear device (BHSD)
A modified version of the bore hole sheat device (BHSD) was used to obtain field consolidation curves in a soft sensitive clay. The Porewater pressure dissipation was monitored at the centre of one of the shear plates. This paper describes briefly the in situ device employed and demonstrates the basic features of the linearelastic F. E. program ‘SOL’. A detailed study is made to simulate the field behaviour with the finite element approach. Comparisons are made between the field and analytical consolidation behaviour. Difficulties in predicting the value of the coefficient of consolidation of a sensitive clay using the BHSD consolidation curves are discussed. 相似文献
5.
Columnar inclusion is one of the effective and widely used methods for improving the engineering properties of soft clay ground. This article investigates the consolidation behavior of composite soft clay ground using both physical model tests under an axial-symmetry condition and finite element simulations using the PLAXIS 2D program. It was determined that the final settlement and the rate of consolidation of the composite ground depended on the stress state. For an applied stress that is much lower than the failure stress, the final settlement of the composite ground was lower, and the consolidation was rapid. When the soil–cement column failed, the stress on the column suddenly decreased (due to strain-softening); meanwhile, the stress on the soil increased to maintain the force equilibrium. Consequently, the excess pore pressure in the surrounding clay increased immediately. The cracked soil–cement column acted as a drain, which accelerated the dissipation of the excess pore pressure. The consolidation of the composite ground was mainly observed in the vertical direction and was controlled by the area ratio, which is the ratio of the diameter of the soil–cement column to the diameter of the composite ground, a. The stress on the column was shown to be low for a composite ground with a high value of a, which resulted in less settlement and fast consolidation. For a long soil–cement column, the excess pore pressures in the surrounding clay and the column were essentially the same at a given consolidation time throughout the improvement depth. It is proposed that the soil–cement column and surrounding clay form a compressible ground, and the consolidation occurs in the vertical direction. The composite coefficient of consolidation (cv(com)) that was obtained from the physical model test on the composite ground can be used to approximate the rate of consolidation. This approximation was validated via a finite element simulation. The proposed method is highly useful to geotechnical engineers because of its simplicity and reliable prediction. 相似文献
6.
电渗固结是促进低渗透性软土排水固结的有效方法。为了揭示不同电势梯度影响高岭土电渗固结的基本规律,在自制电渗试验装置上对高岭土进行电渗试验。试验过程中测量电流、排水量、沉降量以及有效电压随时间的变化,并进行单位排水能耗分析。基于电渗固结多场耦合控制方程,实现土体电渗固结全耦合分析的有限元数值方法,计算结果与解析解吻合良好,验证了程序的有效性。为预测不同电势梯度下土体沉降量随时间的变化关系,分别对0.5,1.0,1.5 V/cm 3种电势梯度电渗固结试验进行数值模拟分析,获得模型表面沉降量分布、阳极超静孔隙水压力时空发展规律、阳极位置固结度等曲线,计算结果和试验结果吻合良好,可为实际电渗试验提供理论指导。 相似文献
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某软土深基坑工程时间效应有限元分析 总被引：2，自引：0，他引：2
软土地区的深基坑因土体的固结作用和流变性而具有了时间效应。本文以Biot固结有限元法为基础,用三元件模型中的第一个线性弹簧模拟固结作用,弹性模量考虑了开挖应力路径和应力历史的影响;另外一部分(KELVIN模型)来模拟土体的流变性,以实际变形的反演来得到两个参数的大致取值,再对基坑的变形情况以及进一步开挖进行分析。假定为正常固结饱和粘土,平面应变问题。通过对某饱和软粘土地基深基坑开挖工程实例的分析,得到的挡墙水平位移曲线与实测曲线很吻合,表明程序较好地反映出基坑的时间效应。 相似文献
9.
考虑土中指数形式渗流定律以及土体的非线性固结特性,以超静孔隙水压力为变量在拉格朗日坐标系内建立了软土一维大变形固结问题的控制方程及其求解条件,并运用有限差分法获取其数值解答。在指数形式渗流定律退化为达西定律下,通过将差分解与已有的半解析解进行对比,验证了数值计算的可靠性。最后对指数形式渗流定律下软土一维非线性大变形固结性状进行计算分析,结果表明： 1时,软土的非线性大变形固结速率会随外载增大而减慢; 1时,软土的非线性大变形固结速率会随着外荷载的增加而加快;软土非线性大变形固结速率要比非线性小变形固结速率快,且差别会随荷载增大而加剧;此外,大变形固结理论的最终沉降值要小于小变形固结理论,且差别会随着荷载的增大而加剧。 相似文献
10.
Bryan A. McCabe Brian G. Sexton Barry M. Lehane 《Geotechnical and Geological Engineering》2013,31(1):183-197
Although finite element packages facilitating coupled consolidation analyses are increasingly in use, many practitioners still favour linear uncoupled analysis out of familiarity with the use of coefficients of consolidation. However, coefficients of consolidation measured by any single means tend to exhibit significant variation, with mean results from different laboratory and field tests also varying widely, leaving uncertainty over the correct values to apply to field problems. In this paper, a finite difference approach is used to back-calculate operational coefficients of consolidation from pore pressure measurements pertinent to a pile group driven in clay–silt. The research shows that this method is capable of successfully capturing the process of pore pressure dissipation, and that the operational coefficient of consolidation around the pile group is higher than that derived from piezocone dissipation tests in the same material. 相似文献
11.
Application of an optimum design technique for determining the coefficient of consolidation by using piezocone test data 总被引：4，自引：0，他引：4
For normally consolidated clay, several researchers have developed a number of theoretical time factors to determine the coefficient of consolidation from piezocone test results. However, depending on assumptions and analytical techniques, it could vary considerably, even for a specific degree of consolidation. In this paper a method is proposed to determine a consistent coefficient of consolidation by applying the concept of an optimum design technique over all ranges of the degree of consolidation. Initial excess pore pressure distribution is assumed to be capable of being obtained by the successive spherical cavity expansion theory. The dissipation of pore pressure is simulated by means of a two-dimensional linear-uncoupled axi-symmetric consolidation analysis. The minimization of differences between measured and predicted excess pore pressure was carried out by the BFGS unconstrained optimum design algorithm with a one-dimensional golden section search technique. By analyzing numerical examples and in-situ test results, it was found that the adopted optimum design technique gives consistent and convergent results. 相似文献
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袋装砂井爆夯法处理软土地基是利用炸药在设置有排水通道的软土中爆炸产生冲击和振动而使土体加固的方法。针对该法进行理论研究,提出了一种将袋装砂井爆夯处理软土地基的三维问题转化为二维平面应变问题的数值模拟方法：袋装砂井转化为等价砂墙;利用等效冲量原理,炮孔爆炸压力则转化为等效压力墙。数值模拟中考虑了土体骨架变形与孔隙水非达西渗流的耦合。对数值模拟的现场试验验证分析表明,沉降数值分析的结果与铁路宁启线软基处理现场测试结果具有很好的可比性。所提出的数值分析方法可模拟袋装砂井爆夯处理软土地基的超静孔隙水压产生和消散以及土体沉降变形的动态过程。 相似文献
14.
Presented in this paper is a study of the one-dimensional consolidation process under haversine repeated loading with and
without rest period. The analysis was carried out using a hybrid coupled, analytical and numerical implicit finite difference
technique. The rate of imposition of excess pore-water pressure was determined analytically, and the remaining part of the
governing differential equation was solved numerically. The clay deposit considered was a homogeneous clay layer with permeable
top and/or impermeable bottom hydraulic boundary conditions with constant coefficients of permeability and of consolidation.
The study reveals that although the loading function is positive for all times, the excess pore-water pressure at the base
of the clay deposit with permeable top and impermeable bottom oscillates with time reaching a ‘steady state’ after few cycles
of loading depending on whether there is a rest period or not. An increase in the rest period causes a decrease in the number
of cycles required to achieve the steady state. The paper shows also that the rest period in the haversine repeated loading
decelerates the consolidation process. Similarly, the paper reveals that the effective stress at the bottom of the clay layer
with permeable top and impermeable bottom increases with time but showing mild fluctuations that do not change the sign. The
maximum positive effective stress achieved depends on the rest period of the haversine repeated loading. A haversine repeated
loading without a rest period gives the highest value for the positive effective stress. 相似文献
15.
为进一步探讨饱和黏性土的弹黏塑性和变渗透性对一维固结进程的影响,引入考虑时间效应的统一硬化（UH）本构模型描述饱和黏土的弹黏塑性,并用Taylor的经验关系式表示其渗透系数与孔隙比的关系,修正了太沙基一维固结理论,并利用有限差分法对方程进行求解。通过与一维流变固结试验结果对比,验证本文计算方法的有效性以及UH模型的适用性。在此基础上,讨论了UH模型参数、压缩指数与渗透指数的比值以及荷载强度等对固结过程的影响。计算结果表明:饱和黏土的黏滞性使得在固结初期地基内部出现了孔压升高现象,并减缓了固结中后期地基孔压的整体消散,增大了地基的沉降量,并且这种现象随着初始超固结参数的增大而更明显;另外,随着压缩指数与渗透指数比值的减小,地基固结进程会加快,但地基最终沉降量不受影响;同时,在固结后期,当压缩指数不大于渗透指数时,较小荷载强度对应的地基内孔压消散较慢,然而,当压缩指数大于渗透指数时,荷载强度对孔压消散的影响则相对很小。 相似文献
16.
The construction of diaphragm wall panels can cause the stress change and soil movements in adjacent ground. In this paper, the construction sequence of a typical diaphragm wall panel in saturated soft clay is simulated with a 3D finite element program. The soil is assumed to behave as an isotropic linear elastic/Mohr–Coulomb plastic material with a soil–water coupled consolidation response. Influence of the pore water pressure is concerned to consider the consolidation behavior of the saturated soft clay. The analysis shows that the changes in effective horizontal stress and pore water pressure during diaphragm wall installation depend on arching mechanism and permeability. The variation in stresses and movements of ground computed by the coupled consolidation analysis and the total stress analysis are compared. Influences of the permeability coefficient on the installation effects are discussed by parametric studies. Finally, a case study of a diaphragm wall construction in Shanghai, in which the ground settlements were monitored, is presented to illustrate the prediction procedure of coupled consolidation analysis. 相似文献
17.
In this paper, a numerical solution for the electro-osmosis consolidation of clay in multi-dimensional domains at large strains is presented, with the coupling of the soil mechanical behaviour, pore water transport and electrical fields being considered. In particular, the Modified Cam Clay model is employed to describe the elasto-plastic behaviour of clay, and some empirical expressions are used to consider the nonlinear variation of the hydraulic and electrical conductivities of the soil mass during the consolidation processes. The implementation of the theoretical model in a finite element code allows for analysis of the evolution of the transient response of the clay subjected to electro-osmosis treatment. The proposed model is verified via comparison with data from a large strain electro-osmosis laboratory test, to demonstrate its accuracy and effectiveness. Various numerical examples are also investigated to study the deformation characteristics and time-dependent evolution of the excess pore pressure. Finally, a well-documented field application of electro-osmosis is simulated to provide further verification. The results show that the numerical solution is effective in predicting the nonlinear behaviour of clay during electro-osmosis consolidation. 相似文献
18.
对饱水软粘土的预压排水主固结研究应从其排水的本质出发, 即从软土在预压过程的含水量变化上研究主固结量的变化规律, 利用土的基本性质指标导出主固结比基本公式及主固结量(沉降量)、绝对主固结量、绝对固结度等理论计算方法.与传统的算法不一样的地方是这些算法与预压荷载(即固结应力) 无关系, 直接计算出主固结的效果及评价预压排水固结地基处理卸载的可行性.利用上述基本公式亦可导出剩余主固结量、主固结速率等计算式.通过实例的分析, 证明上述理论方法与观测的数据基本相符. 相似文献
19.
利用自行研制的高压固结试验系统,对重塑黏土试样进行了竖向压力从0.25 MPa到12.00 MPa的一维固结试验;并利用三轴设备对该土样进行了0.3～2.5 MPa的等向固结试验。试验结果表明：一维固结试验获得的各级压力固结曲线均有明显的次固结阶段,重塑黏土的次固结系数随竖向压力增大而非线性变化;具体而言,当固结压力小于2 MPa,次固结系数随竖向压力增大而显著减小,当固结压力大于2 MPa后,次固结系数则几乎不变;等向固结试验获得的次固结系数则远小于一维固结试验获得的相应值,其随固结压力的变化规律也与一维固结不同。此外,从微观角度对试验结果进行的分析表明,高压下黏土次固结变形的物理机制不同于低压。即低压下黏土次固结变形的主因是颗粒间的相对滑移,而高压下则是结合水膜的蠕变;而且低压下偏应力对次固结变形有控制性影响,但高压下其影响很小。 相似文献