结构性土一维非线性大应变固结半解析解

以结构性较强的天然饱和软黏土为研究对象,考虑了沉积作用对其自重应力的影响,以及压缩性和渗透性的非线性变化,推导了任意加载条件下结构性土一维大应变固结控制方程,并采用半解析的方法对方程进行求解计算。再将其退化为无结构性的饱和软黏土固结解,与已有的大应变固结解进行了对比,验证了该解的正确性。最后将该半解析解计算结果与小应变固结理论解、不考虑结构性的固结理论解计算结果进行对比分析。结果表明:大应变固结理论的沉降计算值大于小应变固结理论的计算值,且二者的差值随着荷载的增加而增加;当考虑土体的结构性时,地表沉降计算值小于不考虑土体结构性的沉降计算值。     

多级线性荷载下饱和软黏土一维大应变固结解析解

在软土地基工程中,荷载往往都是分级施加,随着固结地基强度增加到一定值后,再施加下一级荷载以确保地基稳定。基于谢康和饱和软黏土一维大应变固结解析解,采用数学归纳法推导了任意形式多级线性荷载作用下的解,并编制了相应的通用计算程序,可以方便进行计算分析。通过与线性小应变假定下解的计算对比表明,在实际工程中基于非线性大应变进行计算分析更为合理。     

双层黏弹性地基一维固结分析

软土具有黏滞性,对其固结和变形会产生一定程度的影响。采用现有基于广义Voigt流变模型的单层黏弹性地基一维固结问题求解方法,获得各土层的孔压通解表达式。根据两层土体接触面处孔压和流量连续条件及边界条件,给出了系统的正交关系,进而确定通解中待定系数。广义Voigt模型反映了土体应力应变关系在不同时期的特征,因此该解有广泛的适用性。采用岩土工程中应用较广的Merchant流变模型对一工程算例进行了分析。分析结果表明,土体的黏滞性降低了土体的固结速度,且深度越深,影响幅度越大。     

饱和软土大应变自重固结非线性分析

饱和软土的自重固结涉及许多复杂的非线性问题,而现有分析方法一般基于线性假设,将固结控制方程简化,在沉降变形较大的情况下并不合理。基于Gibson大变形固结方程,推导在单面排水和双面排水条件下的边界条件,综合考虑饱和软土的自重特性与非线性压缩、渗透关系,采用稳定性较好的Crank-Nicolson型差分格式离散并求解非线性控制方程,并从孔隙比、沉降、孔隙水流速3个方面将数值解与CS2固结数值模型进行对比验证。结合工程实例,研究土层不同初始厚度和初始孔隙比对自重固结的影响。结果表明：初始厚度与初始孔隙比较大土层最终沉降也较大。与传统方法相比,该方法所得出的数值解精度较高,实现了高度非线性固结方程的快速求解,其成果更能广泛运用于实际工程的分析之中。     

饱和土体一维复杂非线性固结特性研究

结合大量宁波软土室内固结与压缩试验数据,采用偏微分有限元软件FLEXPDE,同时考虑土体固结过程中材料和几何的复杂非线性,进行了土体固结特性研究。在压缩指数和渗透指数不同比值条件下,进行了解析解推导和有限元数值分析,得出了不同条件下土体有效应力和孔隙比沿高度的变化规律。结果表明,压缩指数和渗透指数比值不等于1时,由于数值解法充分考虑土体的复杂非线性,其结果与实际更加符合;而在比值等于1时所得出的结果与Gibson得出的结果一致;考虑土体材料和几何复杂非线性使得有效应力及固结度预测偏于安全。     

变荷载下双层地基一维非线性固结近似解析解

目前考虑土体非线性压缩及渗透特性的双层地基非线性固结解均假定土体固结系数保持不变,能反映固结系数变化的双层地基非线性固结解还很鲜见。引入经典的e- 和e- 非线性关系描述土体的非线性压缩、渗透特性,在假定双层地基上、下土层压缩指数与渗透指数比值 相等且不等于1的基础上,得到变荷载下考虑土体固结系数变化的双层地基一维非线性固结近似解。该解答在 1条件下可退化为已有的 1时双层地基一维非线性固结解。基于此解探讨了双层地基上、下土层参数的相对比值对非线性固结性状的影响。结果表明：单面排水条件下 越小,下层土与上层土的相对压缩性越低、相对渗透性越高,则双层地基非线性固结速率越快;减小 值,增加双层地基中压缩性小、渗透性高的土层的厚度,会加快地基的固结速率。     

饱和软土成层地基一维非线性固结解析解

假定土体在固结过程中压缩性和渗透性的变化成正比,基于 - 及 - 关系,推导出饱和软土成层地基一维非线性固结解析解,分别给出了按沉降定义和按有效应力定义的每层土平均固结度及整个土层总固结度的计算公式。采用Fortran语言编制了相应的计算程序,将计算得到的结果与已有双层地基一维非线性固结解析解计算结果进行比较,验证该解析解的正确性。利用该程序分析成层地基一维非线性固结性状,分别讨论了初始竖向渗透系数、初始体积压缩系数、荷载值及土层厚度对地基固结性状的影响。分析结果表明：在成层地基一维非线性固结过程中,初始竖向渗透系数对超静孔压的影响较为复杂,对上下层地基固结速率影响不同;初始体积压缩系数增大,超静孔压增大,固结速率变小;所加荷载值越大,超静孔压消散越慢,固结发展越慢;超静孔压消散速率不仅取决于土层厚度,同时取决于各层土渗透性的相对大小。     

考虑起始坡降双层地基的大应变非线性固结

天然软土成层分布特性及土中渗流存在起始水力坡降的现象已被人们熟知。但变荷载下能同时考虑黏土中起始水力坡降、软土非线性压缩渗透特性及大应变特性的双层地基固结理论还鲜见报道。在拉格朗日坐标系中建立以超静孔压为变量的双层软土地基大应变非线性固结模型并给出其有限差分解。通过与考虑起始水力坡降的单层地基大应变非线性固结数值计算结果对比,验证了差分解的可靠性。着重分析了上、下土层起始坡降无量纲参数R1、R2对双层地基固结性状的影响,分析在大应变与小应变假定下双层地基超静孔压消散及固结沉降变形的异同。结果表明：上层土无量纲参数R1对双层地基固结性状的影响程度较下层土无量纲参数R2显著;大应变假定下双层地基渗流前锋的下移速度要快于小应变假定下的移动速度;大应变假定下考虑起始水力坡降的双层软土地基超静孔压消散速率要比小应变假定下快,且大应变假定下考虑起始水力坡降的双层地基最终沉降量要比小应变假定下大。     

变荷载下基于指数渗流双层地基一维固结分析

在土中渗流服从指数形式的前提下,建立了变荷载作用下双层地基的一维固结控制微分方程。利用有限差分法求得孔隙水压力的数值解,并通过与解析解对比对其可靠性进行了验证。对双层地基在指数形式渗流时不同参数下的固结性状进行分析,结果表明：单面排水条件下,双层地基中上层土渗流指数的大小对固结速率起决定性作用,而下层土渗流指数大小对固结速率的影响很小;如果上、下两层土体的压缩性不同,则地基按变形定义的平均固结度和按孔压定义的平均固结度不再相等;地基中下层土与上层土的相对压缩性越低、相对渗透性越高,则地基的固结速率越快;增大压缩性小、渗透性高的土层相对厚度,会加快双层地基的固结速率。     

考虑非达西渗流的双层软土地基大变形非线性固结分析

现有的双层软土地基大变形固结理论均假定土中渗流遵循达西定律,但软黏土中渗流在低水力坡降下会出现偏离达西定律的现象已逐渐为人们认识。综合考虑双层软黏土中的非达西渗流、软土的非线性压缩渗透特性及实际中的变荷载作用,在拉格朗日坐标系中建立以超静孔压为变量的软土大变形非线性固结模型,并给出其有限差分解。在此基础上,通过与已有的非达西定律下单层地基大变形固结数值解计算结果相对比,以验证其差分解的可靠性。最后着重分析上、下层非达西渗流参数m_1、i_(11)及m_2、i_(12)对固结性状的影响,并分析了在大、小变形不同几何假定下对双层地基超静孔压消散及固结沉降影响的异同。结果表明:上层土参数m_1、i_(11)对固结性状的影响要比下层土参数m_2、i_(12)显著;m_2、i_(12)的增大会引起上层土超静孔压消散速率的加快,但双层地基的固结速率会减慢;大变形假定下双层软土地基的固结速率要比小变形假定下快,但两种几何假定下双层地基的最终沉降量是相等的。     

Gibson地基的一维固结解

针对单层Gibson地基模型,运用Laplace变换,求得了单层Gibson地基的一维固结问题,得到了频域内的通解。通过Laplace逆变换,即可计算单层Gibson地基在任意荷载下的一维固结特性。此外,结合工程实例,对解进行了探讨,揭示了单层Gibson地基的固结特性。     

Study of the 1-D consolidation behavior of two-layered soft soils: Parametric studies using a rheological model with viscoplastic body

The governing equations for the coupled processes of consolidation and creep of two-layered soft soils are established. The Nishihara rheological model is adopted to simulate the elasto-viscoplastic characteristics of soft soils, disregarding the effects of the soil self-gravity. A semi-analytical theory combined with numerical and analytical methods is introduced to solve the governing equations of the one-dimensional rheological model. The computational procedure and the approximate solutions for two-layered soft soils subjected to surface loading are obtained for two drainage conditions. The solutions and the computational procedure are used to study the effects of the two layers and constitutive parameters on rheological consolidation behavior of soft soils. It can be concluded that two layers affect the rate of excess pore water pressure dissipation and settlement development. The parametric studies show that when the parameters of the upper layer remain constant, increases in the permeability and elastic modulus in the lower layer accelerate the dissipation of the excess pore water pressure, and meanwhile increases in the viscosity coefficient and viscoplastic limit slows down the dissipation of the excess water pressure.     

软土大变形固结计算中参数识别的遗传算法

含水量很高的饱和软土在外荷载作用下沉降很大,小变形分析误差太大,必须通过大变形非线性固结计算来模拟。遗传算法是一种全局优化和搜索的仿生算法。近年来随着工程领域中复杂的大规模非线性系统的出现,遗传算法日益得到青睐,目前已经广泛应用到各个领域中。本文对遗传算法做了改进,主要体现在杂交算子的选取和轮盘赌模型的模拟退火拉伸,并将其用于饱和软土的大变形固结分析,解决其中的关键参数识别问题。研究表明该方法是行之有效的,值得进一步研究探索。     

Model for large strain consolidation with non-Darcian flow described by a flow exponent and threshold gradient

Many pieces of evidence have confirmed that the seepage in fine-grained soils can deviate from traditional Darcy's law that contributes to the consolidation theory. In this paper, a numerical model, referred to as consolidation with non-Darcian flow 2 (CNDF2), is developed for the 1D large strain consolidation of a saturated porous medium with the non-Darcian flow. The algorithm accounts for vertical strain, general constitutive relationships, the relative velocity of the fluid and solid phases, variable compressibility and permeability relation during consolidation, time-dependent loading, and unload/reload effects. Compared with the CS2 model proposed in previous studies, some parts of the CNDF2 model are modified in order to adapt to the non-Darcian flow, especially the equivalent series hydraulic conductivity and fluid flow. The verification examples of the CNDF2 model demonstrate excellent accuracy for both small strain and large strain consolidation. According to the applicable conditions of non-Darcian flow law, the CNDF2 model is most suitable for the fine-grained soil. The development of CNDF2 is first presented, followed by examples to analyze the influences of the non-Darcian flow on the consolidation behavior.     

Model for large strain consolidation under constant rate of strain

A numerical model, called CCRS1, is presented for one‐dimensional large strain consolidation under constant rate of strain loading conditions. The algorithm accounts for vertical strain, general constitutive relationships, relative velocity of fluid and solid phases, changing compressibility and hydraulic conductivity during consolidation, and an externally applied hydraulic gradient acting across the specimen. Soil compressibility is rate independent, and as such, the current model is most appropriate for less‐structured clays. Verification checks show excellent agreement with analytical and numerical solutions for small and large strain conditions. A series of numeric examples indicates that compressibility and hydraulic conductivity constitutive relationships can have an important effect on constant rate of strain consolidation response. Results also indicate that analytical solutions obtained using small strain theory can be in significant error for large strain conditions with changing coefficient of consolidation. Copyright © 2012 John Wiley & Sons, Ltd.     

Analytical solutions of linear finite‐ and small‐strain one‐dimensional consolidation

Analytical solutions are presented for linear finite‐strain one‐dimensional consolidation of initially unconsolidated soil layers with surcharge loading for both one‐ and two‐way drainage. These solutions complement earlier solutions for initially unconsolidated soil layers without surcharge and initially normally consolidated soil layers with surcharge. Small‐strain solutions for the consolidation of initially unconsolidated soil layers with surcharge loading are also presented, and the relationship between the earlier solutions for initially unconsolidated soil without surcharge and the corresponding small‐strain solutions, which was not addressed in the earlier work, is clarified. The new solutions for initially unconsolidated soil with surcharge loading can be applied to the analysis of low stress consolidation tests and to the partial validation of numerical solutions of non‐linear finite‐strain consolidation. They also clarify a formerly perplexing aspect of finite‐strain solution charts first noted in numerical solutions. Copyright © 2004 John Wiley & Sons, Ltd.     

饱和软土大变形非线性自重固结模型

基于分段线性方法,建立了饱和软土一维自重固结模型（简称SWC模型）。该模型能考虑自重固结过程中土体的大变形效应和材料参数的非线性变化。将该模型的计算结果与相关解析解、现场试验及室内试验结果进行了对比验证,证明了SWC模型能准确计算出大变形和非线性条件下饱和软土的自重固结过程,包括沉降量、平均固结度、孔隙比分布和超孔隙水压力分布等参数随时间的变化过程。随后,以现场试验为基础,采用SWC模型对饱和软土自重固结的4个主要影响因素（即土体初始高度、边界排水条件、初始孔隙比和土粒相对密度）进行了参数分析。结果表明,上述4个参数对软土自重固结过程均具有重要影响：土体初始高度越高,则自重固结沉降量和最终平均应变值越大;边界排水条件对土体自重固结的速度有重要影响,但不影响自重固结的最终沉降量;初始孔隙比越大,则自重固结沉降量越大,其完成自重固结所需时间越短;土粒相对密度越大,则土体的最终沉降量越大,完成自重固结所需时间越短。