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。     

基于Hansbo渗流的理想砂井地基固结分析

室内试验和现场观测表明,许多饱和黏性土中的渗流在小水力梯度时不能用Darcy定律描述,这应该是导致基于Darcy渗流的传统砂井固结理论有时不能很好地解释某些砂井地基固结特性的原因。引入同时考虑低速渗流幂函数曲线段和较高速渗流直线段的Hansbo渗流方程描述非Darcy渗流,在自由竖向应变假定下修正了Barron的理想砂井地基固结方程,并给出了有限差分法数值求解格式。据此探讨了Hansbo渗流参数、地基厚度等对砂井地基固结进程的影响。计算结果表明:和Darcy渗流相比,Hansbo渗流延缓了砂井地基内的孔压消散速度,导致固结速度变慢,并且径向排水对孔压消散的作用会更显著。如将Hansbo渗流方程简化为幂函数形式,则往往会高估砂井地基的固结程度,特别是在固结的初期。最后对比了自由竖向应变假定和等竖向应变假定对计算结果的影响。     

双层砂井地基固结度的概率分析

采用概率统计理论,分析了土工参数不确定性及土体自相关距离对双层砂井地基固结度的影响,推导了当径向固结系数为伽玛分布时平均固结度的特征值计算公式,并以深圳某工程为例采用蒙特卡罗法对双层砂井地基平均固结度进行了概率分析,指出按确定性方法计算达到目标固结度所需的预压时间,并不能满足工程要求,用概率方法预测更为合理。     

考虑井阻随时间变化下砂井地基的非线性固结解

针对砂井地基固结过程中砂井的渗透系数会逐渐降低这一特性,通过引入e-lgσ1和e-Igk对数模型来描述土体的非线性固结特性,同时考虑井阻随时间变化和涂抹区径向渗透系数变化等因素,推导砂井地基非线性固结的控制方程,并采用分离变量法求得该方程的固结解.通过退化研究并与己有的解析解进行对比分析,对该解答的正确性进行验证.基于...     

砂井地基固结概率特性的近似分析方法

利用蒙特卡罗模拟方法计算砂井地基固结度概率特征值。通过正交试验研究不确定性参数变异性对砂井地基固结概率特性的影响。研究了砂井地基固结概率分析的近似方法 ,并探讨了近似方法的精度。推导了砂井地基固结度期望值和方差的计算公式。研究表明 ,砂井地基固结度的概率特性对水平固结系数的不确定性最为敏感。提出了只考虑水平固结系数不确定性的砂井地基固结概率特性的近似分析方法。误差研究进一步证明了近似方法的实用性。砂井地基固结概率设计方法用设计系数将概率设计与常规设计联系起来。     

地基单向和三向排水固结与强度增长的计算及其实际观测

排水固结法加固软基有垫层排水和砂井排水两类方法。采用的计算方法多数仅考虑地基加固层的平均固结度与强度的增长。砂井地基主要是考虑水平向排水固结,对竖向排水不予考虑或考虑竖向排水的平均固结度,故与实际情况有差异。本文改进为计算地基不同部位的任一深度和任一时间的固结度,更符合地基的实际情况。 籍助电算研制出简便的计算图表。对垫层排水处理海堤软基与排水砂井处理深水防波堤软基两项工程,进行计算,并与实际观测资料作比较,结果表明,两者较为接近。     

考虑土体三维强度特性的静压桩周超孔压解析及演变

 将饱和黏性土中静压沉桩过程近视看作柱孔不排水扩张问题,在充分考虑土体三维强度特性的条件下采用SMP准则改进的修正剑桥模型,推导得出柱孔扩张引起超孔压的基本解答。在此基础上,考虑桩周土竖向和径向固结,建立空间轴对称固结方程的定解条件,采用分离变量法求得桩周超静孔隙水压力消散的级数解答。分析桩周土体超静孔隙水压力随时间和空间的演变规律,揭示应力历史、径向和竖向固结系数以及剪切模量等因素对初始超孔压的产生和随后的固结速率的影响规律,并通过实例验证本文解答的合理性和适用性。通过与现场实测对比,本文解答较好地反映了静压桩周土体超静孔隙水压力的演变规律。此外,桩周土体的超静孔隙水压力随距桩侧径向距离增大呈对数衰减。剪切模量和竖向固结系数对桩周土体固结速率影响较小,而土体超固结比和径向固结系数对固结速率影响较为显著,表明超孔压消散主要发生在径向。研究成果对静压桩承载力的确定具有一定的指导意义。     

砂井地基双面排水固结问题的研究

用传统的固结理论分析方法研究了砂井加固软土地基的单向、径向和三维固结问题。探讨了单一砂井双面排水情况下软土地基的平均固结度计算方法，提出了固结度计算的新的修正方法，对软土地基内路基设计具有一定的指导意义。     

考虑涂抹作用的未打穿砂井地基固结理论分析

 在等应变假设和瞬时加载条件下,研究单面和双面排水情况下未打穿砂井地基的固结问题。通过设置虚拟砂井的方法考虑未打穿土层的径竖向组合渗流;同时,为考虑施工对土体的扰动随离砂井的距离增大而逐渐减小的事实,引入一个函数,将土体水平渗透系数统一表达,并在假设的3种模式下(涂抹区水平渗透系数不变、呈线性变化和呈抛物线变化),得到未打穿砂井地基固结解析解。编制计算程序,详细阐述编程过程中要注意的几个问题,对未打穿砂井地基的固结性状进行分析。结果表明,考虑涂抹区水平渗透系数呈抛物线变化时地基固结最快,呈线性变化时次之,不变时最慢;施工扰动范围、程度越大,固结越慢;砂井打入深度越深,固结越快;砂井渗透系数越大,固结越快。     

砂井排水法在镇江电厂三期干煤棚工程中的应用

基于轴对称单井理论,将砂井打设所导致整个地基竖向渗透性增强的影响等效在太沙基单向固结方程的渗透系数上,确定出地基的竖向等效渗透系数,从而将砂井地基转换成无砂井地基的固结排水问题。这样对整个土基进行真三维固结的有限元分析就可以预测砂井地基固结排水所导致的不均匀沉降、土体侧向变形以及土体内的孔压消散,最后,通过某工程实例验证了该方法的有效性。     

General solutions for consolidation of multilayered soil with a vertical drain system

A quasi-analytical method is newly introduced to solve the equal-strain consolidation problem of multilayered soil with a vertical drain system. Both vertical and radial drainage conditions are considered, together with the effects of drain resistance and smear. By using the method of Laplace transform with respect to time, a general explicit analytical solution for the consolidation in transformed space is obtained. Numerical inversion of the Laplace transform in the time domain is then applied to obtain the solution for calculating excess pore-water pressure. This solution is explicitly expressed and conveniently coded into a computer program for ease and efficiency of practical use. Its validity and accuracy are verified by comparing the special cases of the proposed solution with a finite-element solution and an available analytical solution. Moreover, the consolidation behavior of a four-layered soil with a vertical drain is investigated. The order of soil layers is shown to have a significant effect on the behavior of consolidation. This highlights that caution should be exercised when weighted average consolidation parameters of multilayered soil are used to analyze the consolidation behavior.     

等应变条件下的砂井地基固结解析理论

本文建立了等应变条件下较为完善的打穿软粘土层的砂井地基固结解析理论,该理论较同样条件下现有理论更接近自由应变条件下严密的但极其复杂的解析理论。文中对巴隆(R.A.Barron)理论和汉斯(S.Hansbo)理论作了详细的分析和讨论,阐述了考虑井阻作用时巴隆理论的不合理性和汉斯理论的近似性。最后根据本文理论编制了可用于IBM-PC微机的绘图软件,绘制了常用砂井的平均径向固结度-径向固结时间因子等曲线。利用这些曲线,能较方便地进行考虑井阻作用和涂抹作用的砂井地基设计。     

基于排水体椭圆柱假定的井阻非线性竖井地基固结理论

 目前针对塑料排水板处理地基的固结计算均采用传统的砂井固结理论,即需要将扁长的塑料排水板等效为圆柱体之后再进行分析,这种简化过程可能会带来一定误差。为此,将塑料排水板视为与其形状较为接近的椭圆柱体进行研究。首先给出椭圆柱坐标体系下的塑料排水板处理地基固结基本方程,并基于椭圆柱坐标系理论得到超静孔隙水压和固结度的解析解,讨论新的解答与已有经典解答之间的关系,认为经典的排水板周长等效法高估了排水板的排水固结效果。此外,讨论了排水板渗透系数kw随深度线性衰减和随时间指数衰减变化时的固结解析解,通过计算讨论认为,渗透系数随时间的变化对排水板地基固结影响最显著,参数A2值越大,排水板地基固结速率越慢,以致于排水板严重淤堵而丧失排水能力。     

Inflection point method for predicting settlement of PVD improved soft clay under embankments

Prefabricated vertical drains (PVDs) are being used to accelerate the consolidation of subsoil for construction of high embankments on soft ground. The construction is carried out in stages and the height of each stage construction depends on gain in strength of soft subsoil and target factor of safety. The inflection point method for estimating the degree of consolidation for vertical drainage has previously been published. The degree of consolidation was estimated to be 70% at the inflection point. After 70% consolidation, the rate of consolidation reduces to a minimum value and it is economical and technically feasible to allow the second-stage loading. Additional load at this stage would ensure increase in shear strength of the subsoil. In this paper, the authors have extended the procedure of inflection point method for vertical drainage to a three-dimensional drainage when PVDs are adopted for subsoil improvement. Theoretical graphs have been developed which can estimate the percent consolidation at inflection point (% U_i) for different subsoil thickness, drain spacing ratios and C_r/C_v ratios. Different factors viz. smear, drain spacing, depth of clay thickness and well resistance were also considered in the analysis. The degree of consolidation at inflection point is observed in the range of 61–78%. The inflection point method has been applied to a settlement data from a case history of two sites and the estimated percent consolidation at inflection point has been compared with the values predicted from developed theoretical graphs. The total primary settlement estimated from inflection point has been compared with that of Asaoka method, which is widely used in the field. It is concluded that inflection point method has the potential for field application and provides an alternate method for estimating of total settlement in field applications using PVDs and surcharge, and to determine the appropriate required waiting period for stage loading.     

砂井径向排水的不均匀固结效应及简易量化方法

软土的不均匀固结问题普遍存在而且未受到足够的重视，不均匀固结会带来“淤堵”问题，影响单元体径向排水速率。文中利用数值方法研究砂井单元体的径向固结，首先通过分析单元体内部的土体孔隙比和渗透系数的径向分布特征，论证砂井径向排水的不均匀固结特性；对单元体平均固结度的数值模拟结果和理论解析结果进行比较，指出不均匀固结效应对孔压消散速率的影响，并提出可以表征不均匀固结效应影响程度的“等效涂抹效应”的概念（Ke）；最后，文章进一步研究Ke与土体的压缩性、渗透性和应力条件之间的关系。基于文中的研究结果，提出利用土体基本的物理力学指标和工程设计参数对“等效涂抹效应”（Ke）进行计算的简易量化方法。     

路堤下等应变复合地基的固结分析

 路堤下等应变复合地基固结沉降时,桩间土承担的荷载向桩体转移,桩土总应力不断变化,超静孔压增减量不等于有效应力增减量。考虑桩土总应力的变化、竖向排水体的压缩和孔隙水压力、桩体的排水性能、桩与排水体的距离等对复合地基的固结产生的影响。推导考虑桩体排水性能、桩土荷载转移、排水体压缩性和井阻的路堤下复合地基孔压、固结度、桩土应力比的解析解。固结分析表明,不透水桩可以加速地基固结,透水桩可能减缓固结,复合地基固结的快慢受桩身固结系数影响很大,高固结系数桩复合地基固结度大于小固结系数桩复合地基。     

Numerical Analyses on Consolidation of Clayey Ground Improved by Vertical Drain System Based on 3-D Elasto-Viscous Model

This paper addresses a proposal on the three-dimensional elasto-viscous consolidation theory and discusses on its applicability. In order to predict the three-dimensional consolidation behavior of clayey ground improved by vertical drain system, one-dimensional consolidation theory based on an elasto-viscous liquid model proposed by Yoshikuni et al. (1994), which can express secondary consolidation without considering any distinction between normally consolidated and overconsolidated regions, is extended to three-dimensional condition. This theory is applied to the consolidation of a hollow cylindrical body that models a clayey ground improved by a vertical drain system. Then, a rigorous solution of elastic consolidation theory, a FEM solution based on elasto-plastic theory and a FDM solution using three-dimensional elasto-viscous theory are compared with the test results obtained using the three-dimensional consolidation test apparatus developed by the authors (Baek and Moriwaki, 2004). Based on the results of analyses, it is evident that the three-dimensional consolidation theory proposed by authors could simulate the consolidation behavior of clayey ground improved by vertical drains, such as the secondary consolidation and the radial displacement during the three-dimensional consolidation process.     

成层未打穿砂井地基固结Lagrange插值解法

考虑井阻和涂抹区的影响,建立成层未打穿砂井地基固结的数值模型和算法。将未打穿砂井底面下的软土层视为虚拟排水井,同时将未打穿砂井转化为打穿的多段砂井,使得土层边界条件和数值计算过程简单化。对超孔隙水压力用Lagrange插值多项式等结点插值近似,把砂井打设区固结方程转化为结点的超孔隙水压力的简单微分方程组,砂井固结方程转化为一线性代数方程组,以4层土为例,导出详细的计算公式。如增加土层数,仅需改变边界结点系数公式。最后,把该解法与相关近似方法的计算结果进行分析比较,并给出一个多层软土路基预压加固工程案例。结果表明,将下卧层简化为一维固结与考虑其三维固结对计算结果影响很小。     

变附加应力条件下考虑桩体二维井阻作用的复合地基固结解析理论研究

 通过在现有解的形式基础上增加一个二次多项式,提出一种新的复合地基固结解的形式及解答方法,推导得到地基附加应力既随时间变化也随深度变化条件下考虑桩体竖向及径向二维井阻作用的散体材料桩复合地基固结解析解,通过退化、与已有解的比较等方法对解进行分析验证。结果表明,现有的瞬时荷载下考虑桩体径竖向渗流的解、考虑桩体竖向渗流与变形协调的解、太沙基一维固结解等都是本文解的特例,这说明本文解的正确合理性。地基加载历时越长,固结越慢;地基底部附加应力越小,固结越快;考虑桩体径竖向二维井阻时地基固结比只考虑竖向井阻时慢,桩径比越小,桩体渗透系数越小,两者的差异越大。本文解的表达形式及解答方法,为复合地基固结度的求解提供一种新的思路,发展和完善了现有的复合地基固结理论。