非饱和粘弹性地基在加荷随时间指数变化作用下的一维固结半解析解

研究了非饱和粘弹性地基在加荷随时间指数变化作用下的一维固结特性。针对粘弹性地基土最基本的merchant模型,采用李氏比拟法,依据Fredlund固结理论及Cayley-Hamilton数学方法得到Laplace变换域内的超孔隙压力的解;再根据Crump方法编制程序进行Laplace逆变换得到了时间域内的超孔隙压力及土层沉降的半解析解。最后,本文给出了一个典型算例,揭示了在加荷随时间指数变化下非饱和粘弹性地基的固结特性,扩展了非饱和土固结理论在工程实际中的适用性。     

饱和块状混合回填土地基的一维固结分析

用块状渣土置换软弱地基和回填低洼谷地等是处置工程渣土的有效途径。为了分析饱和块状混合回填土地基的固结性状,运用混合物理论建立了其一维固结模型。首先,假定块状土固相和充填土固相之间满足等应变条件,获得了饱和块状混合回填土中各相应变与块状土孔隙变形和充填土孔隙变形的关系式。其次,在小应变条件下,根据自由能势函数方程建立了饱和块状混合回填土的一维线弹性本构方程,再结合达西定律和应力平衡方程获得了一维固结控制方程。再次,利用分离变量法得到一维固结解析解,通过退化本文模型与已有模型进行对比,验证了本文模型的正确性。最后,基于所得解析解,分析了充填土孔隙渗透系数、块状土孔隙渗透系数以及流体交换参数等因素对饱和块状混合回填土地基固结性状的影响。分析结果表明：充填土孔隙渗透系数对饱和块状混合回填土地基整体固结性状起主导作用;在固结初期,块状土超孔压会有一定程度的上升,且3个参数具有相似的作用机理。     

悬浮长芯劲性搅拌桩复合地基固结解析解

推导出瞬时加荷情况下悬浮长芯劲性搅拌桩复合地基的固结方程和相应的定解条件,利用三层地基一维固结理论,建立了相应的固结解析解,包括桩间土和下卧层土中超静孔隙水压力解答和复合地基整体平均固结度解答。通过固结速率解析解与有限元数值解的比较,证明了解析解的合理性。利用解析解进行复合地基固结速率影响因素分析,研究了悬浮长芯劲性搅拌桩复合地基的固结性状。结果表明:悬浮长芯劲性搅拌桩复合地基的固结速率主要受桩的贯入比和下卧层刚度的影响。复合地基的固结速率随桩的贯入比和下卧层土压缩模量的增加而增大。搅拌桩壳长度、厚度和刚度以及芯桩截面含心率的变化对复合地基固结速率没有影响。增加芯桩的压缩模量只会使固结前期复合地基的固结速率略微减小,不会影响固结后期复合地基的固结速率。     

悬浮长芯劲性搅拌桩复合地基固结解析解

推导出瞬时加荷情况下悬浮长芯劲性搅拌桩复合地基的固结方程和相应的定解条件,利用三层地基一维固结理论,建立了相应的固结解析解,包括桩间土和下卧层土中超静孔隙水压力解答和复合地基整体平均固结度解答。通过固结速率解析解与有限元数值解的比较,证明了解析解的合理性。利用解析解进行复合地基固结速率影响因素分析,研究了悬浮长芯劲性搅拌桩复合地基的固结性状。结果表明:悬浮长芯劲性搅拌桩复合地基的固结速率主要受桩的贯入比和下卧层刚度的影响。复合地基的固结速率随桩的贯入比和下卧层土压缩模量的增加而增大。搅拌桩壳长度、厚度和刚度以及芯桩截面含心率的变化对复合地基固结速率没有影响。增加芯桩的压缩模量只会使固结前期复合地基的固结速率略微减小,不会影响固结后期复合地基的固结速率。     

外荷载随时间变化下考虑起始电势梯度的一维电渗固结解析解

将起始电势梯度的概念引入电渗固结理论，基于相关假定建立了外荷载随时间变化下考虑有效电势衰减的一维电渗固结控制方程，利用变量代换和分离变量法获得了电渗固结通解，并给出了常见加荷形式下解析解的表达式。将退化解与已有解析解进行比较，并将所提解与有限差分解展开对比，验证了所提解答正确性。基于所提解析解，分析了相关参数对软土地基电渗固结特性的影响。结果表明：起始电势梯度的存在降低了超孔隙水压力绝对值和沉降量；水力渗透系数的减小有利电渗排水固结过程的进行，且电渗透系数与水力渗透系数比值越大，沉降量越大、电渗排水固结效果越好；当采用电渗联合堆载预压法加固时，电渗作用可降低因外荷载引起的正超孔隙水压力的最大值，提高固结排水时土体的稳定性。     

地表温度周期波动的饱和土一维热固结解析解

针对地表温度周期波动的饱和土一维热固结问题,建立相应的热固结模型。利用偏微分理论,得到土层内部超静孔隙水压、温度增量的解析解,并进而得到地基沉降的表达式,由此分析饱和土的一维热固结性状,并与Terzaghi解进行比较。结果表明:热固结性状与温度增量、热传导速率、温度波动周期等有关;受地表温度周期波动的影响,超静孔隙水压、沉降也会出现波动性。     

双层地基超载预压固结理论及应用

针对未打穿竖井地基传统固结计算方法的不足 ,将深厚软土未打穿竖井地基合理转化为双层地基 ;分析了双层地基超载预压的固结、沉降机理 ,给出了多级等速加、卸载条件下双层地基一维固结孔压解析解。考虑时间因素的影响 ,提出了反映土结构性的固结沉降计算方法。最后 ,结合工程实例计算 ,发现采用超载预压法处理深厚软土地基 ,对于控制工后沉降是不利的 ;工后沉降主要是下卧层的压缩变形造成的 ,约占工后总沉降的 74%左右。     

非饱和土中单桩的横向瞬态响应研究

基于非饱和土的动力控制方程,对非饱和土中单桩的水平瞬态响应进行分析.先利用Laplace变换,再对方程进行无量纲化,建立了变换域内非饱和土的水平波动方程,通过分离变量法及算子分解理论得到了Laplace变换域内的位移解;根据桩-土接触面的边界条件求解桩的动力平衡方程,得到变换域内的桩身位移和内力的解析解,再通过Lapl...     

变荷载下劲性搅拌桩复合地基固结分析

采用劲性搅拌桩加固地基的复合地基技术越来越多地被用于实际工程,而对其固结理论的研究有待深入。基于等应变假定,推导出劲性搅拌桩复合地基在变荷载作用下桩间土的固结方程,采用双层地基一维固结理论求解该固结方程,得到了桩间土中的平均超静孔隙水压力和复合地基整体平均固结度的解析表达式。通过与固结度有限元分析结果的比较,评价了固结度解析表达式的计算精度。利用该固结度解析表达式进行参数分析,研究了劲性搅拌桩复合地基的固结特性。研究结果表明,劲性搅拌桩复合地基的固结速率远大于传统的水泥搅拌桩复合地基,它随着劲性搅拌桩的置换率、芯桩芯长比和水泥土外壳材料压缩模量的增大而增大。芯桩的截面含芯率和压缩模量对复合地基固结速率影响很小。     

循环荷载作用下地基一维非线性固结解析解

将孔隙比e与有效应力σ关系（e-lgσ）引入循环荷载作用下单层地基的一维非线性固结问题的研究之中，通过假定土体中的初始有效应力沿深度均匀分布和固结过程中土体渗透性的降低与压缩性的减小成正比，建立了低频循环荷载作用下单层地基的一维非线性固结问题的固结方程。由ω-σ变换得出了低频梯形循环荷载作用下单层地基的一维非线性固结问题的解析解，采用Fortran语言编制了相应的计算程序，并通过将其特例情况下的解分别与目前已有的解析解和半解析解进行对比的方法对文中解作了验证。现有单层地基的一维非线性固结解析解均为文中解的特例。     

One-dimensional consolidation of unsaturated soils considering self-weight: Semi-analytical solutions

For the newly deposited soil, the consolidation will occur under the self-weight and external load jointly if the soil is treated by the stack pre-pressure method. The soil stress caused by self-weight has a significant influence on its consolidation process no matter the soil is either saturated or unsaturated. However, the soil’s self-weight is ignored in the one-dimensional (1D) consolidation theory for unsaturated soils (Fredlund and Hasan, 1979). In this paper, we derived the semi-analytical solutions for excess pressures and normalized settlement in 1D dimensional consolidation of unsaturated soils considering self-weight. The analytical solutions were obtained by Crump’s method (Crump, 1976), through a computing program coupling the calculation of initial excess pore pressures with the inverse Laplace transform of the obtained solutions. Then, the proposed solutions are verified through a degradation case. Several 2D charts are presented to visualize the solutions, and various examples are employed to discuss the key factors that affect one-dimensional consolidation behavior of unsaturated soils when self-weight is considered. It can be found that the relative excess pore pressure will be restrained for the one-dimensional consolidation when considering self-weight.     

Coupled consolidation via vertical drains in unsaturated soils induced by time-varying loading based on continuous permeable boundary

Considering continuous permeable boundary and coupled radial-vertical flow in this paper, a generalized semi-analytical solution for the consolidation enhanced by vertical drains (VDs) in unsaturated soils under time-varying loading is proposed. Firstly, the continuous permeable boundary is introduced into the axisymmetric consolidation model. Afterwards, the coupled controlling governing equations of excess pore pressures (EPPs) are solved by mathematical methods such as the decoupling technology, the Laplace transformation and inversion. Then, the validity of the current solution is verified by special cases with double-permeable boundary conditions (BCs) and instantaneous loading. The case analyses eventually were carried out, and the results show that the smear effects slow down the consolidation process but that is not obvious when the smear parameter is great than five. The effect of vertical flow on consolidation becomes insignificant when the ratio of radial to vertical permeability coefficient is greater than five; conversely, when its value is less than five, the above effect increases with the enhancement of the permeability properties at the top (or bottom) boundary. Moreover, the new solution can be applied to time-varying loadings, and different distributions of top and bottom boundary permeability.     

Consolidation of partially saturated ground improved by impervious column inclusion: Governing equations and semi-analytical solutions

This study focuses on the consolidation behavior and mathematical interpretation of partially-saturated ground improved by impervious column inclusion. The constitutive relations for soil skeleton, pore air and pore water for partially saturated soils are proposed in the context of partially-saturated ground improved by impervious column inclusion. Settlement equation and dissipation equations of excess pore air/water pressures for a partially saturated improved ground are then derived. The semi-analytical solutions for ground settlement and pore pressure dissipation are then obtained through the Laplace transform and validated by the existing solutions for two special cases in the literature and the numerical results obtained from the finite difference method. A series of parametric studies is finally conducted to investigate the influence of some key factors on consolidation of partially saturated ground improved by impervious column inclusion. Based on the parametric study, it can be found that a higher value of the area replacement ratio or modulus of the pile results in a longer dissipation time of excess pore air pressure (PAP), a shorter dissipation time of excess pore water pressure (PWP), and a lower normalized settlement.     

A simple solution for prefabricated vertical drain with surcharge preloading combined with vacuum consolidation

Prefabricated vertical drains (PVDs) with the surcharge preloading and vacuum consolidation has become considerably popular for ground improvement projects. A simple solution that incorporates the fundamental embankment features, such as the average degree of consolidation and excess pore pressure, are essential for the design of soft ground improvements by PVDs with vacuum preloading. However, most of the solutions for vertical drains with vacuum consolidation require numerical simulations, whose implementation tends to be laborious. In contrast, a simple solution for vacuum consolidation under time-dependent loading has not yet been proposed. In this study, a simple solution that can be easily incorporated into a conventional spreadsheet is derived for PVDs with vacuum preloading by applying the Laplace transform technique. The proposed solution accounts for several actual construction conditions, such as initial surcharge load, vacuum pump trial period, variations of radial permeability, and time-dependent loading. The results obtained from this proposed approach were validated with those from the finite element method and field data from the case study of the Cai Mep International Terminal project in southern Vietnam. The derived solutions, including the excess pore pressures and average degrees of consolidation, were in good agreement with the predicted and observed data.     

双层砂井地基大变形固结方程差分解

基于砂井地基轴对称大变形固结控制方程,综合考虑双层砂井地基软土的压缩性与渗透性非线性幂函数变化、分级加荷、径向与竖向同时渗流排水、初始超静孔压几种分布模式等实际条件,采用交替方向隐式（ADI）差分法编程求解了建立的双层砂井地基大变形固结控制方程,通过算例分析验证了建立的方程与差分解法及编制程序的合理性。将本文方法应用于围海造陆工程吹填淤泥与海相沉积淤泥组成的双层砂井地基固结计算,预测的固结沉降过程较经典固结理论更接近于实测值,对双层砂井地基固结沉降过程预测进行了有益的探讨。     

软黏土一维非线性大应变固结解析理论

给出了软黏土一维大应变固结中土体总应力、有效应力、孔隙水压力、孔隙比和沉降等一般相互关系,通过对土体压缩性和渗透性的假定得到了拉格朗日坐标下以超静孔压为变量的一维非线性大应变固结方程及其解析解。利用此解分析了土体一维非线性大应变固结性状,并与传统的小应变固结理论作了比较。此解也可用于对大应变固结问题的各种数值解法的验证。     

Fully coupled solution for the consolidation of poroelastic soil around geosynthetic encased stone columns

The paper presents an extension of a recently developed fully coupled elastoplastic method (Pulko and Logar, 2016) for the analysis of a poroelastic thick-walled soil cylinder around an elastoplastic end-bearing stone column to account for the influence of an elastic geosynthetic encasement. The method was developed in the framework of Biot's consolidation theory (Biot, 1941) and is based on a unit cell concept, wherein the column encasement is modeled as a thin elastic membrane, which can only sustain tension and acts in the radial direction. Analytical closed-form expressions for excess pore pressures, stresses, strains, displacements and encasement forces were derived in the Laplace domain. The final elastoplastic solution in time domain was obtained numerically by using efficient numerical scheme for the inverse Laplace transform. The validity of the solution was checked against finite element analyses and compared with previously developed analytical methods. The results showing the influence of column encasement on transient state of settlements, strains, excess pore pressures and encasement forces under instantaneous or time dependent load are presented and discussed.