考虑桩体固结变形的散体材料桩复合地基固结解析计算

将单个散体材料桩截面和单桩影响范围内的桩周土截面作为一个研究单元考虑,由固结过程中孔隙水排出量等于单元体体积减小量,并引入平均超孔隙水压力的概念,考虑桩体的固结变形,推得散体材料桩复合地基的固结方程。通过等应变假设和初始边界条件,由分离变量法对该固结方程进行求解,得到了桩体和桩间土的平均超孔隙水压力、平均固结度、复合地基整体固结度。通过某工程实例计算,将计算结果与已有解析解进行了比较分析。当散体材料桩复合地基的井径比较大时,两者计算结果十分相近;当井径比较小时,两者差别较大。     

考虑加载过程及桩体固结变形的碎石桩复合地基固结解析解

为了完善碎石桩复合地基固结理论,通过假设从桩体排出的水量等于流入桩体的水量与桩体体积变化之和以及地基扰动区土体水平渗透系数呈线性变化,并考虑上部荷载逐渐施加,推导了考虑桩体体积变化的碎石桩复合地基超静孔压及固结度解析解。当加载时间趋于零时,本文解可退化为瞬时加载情况下的解;当加载时间及桩径同时趋于零时,本文解可进一步退化为Terzaghi一维固结解,这证明了本文解的正确性。通过与已有解的比较,对地基固结性状进行了分析。结果表明,加载过程对地基固结度影响显著,加载历时越长,固结越慢;在各种条件下,不考虑桩体固结变形时地基固结始终比考虑桩体变形时快,并且其影响随着加载历时变小、桩径比变小、桩土模量比变小、桩土渗透系数变小而逐渐增大,这说明在实际工程固结计算中不考虑桩体固结变形是偏于不安全的。     

考虑砂石桩固结的混凝土芯砂石桩复合地基固结解析解

考虑了混凝土芯砂石桩复合地基中砂石桩的环形排水通道、砂石桩体内的径、竖向渗流和土体施工扰动,并采用桩土共同分担荷载的初始条件,得到了混凝土芯砂石桩复合地基固结问题的控制方程,给出了控制方程的解答;并分别给出了复合地基按应力和按变形定义的总平均固结度,分析了砂石桩桩体渗透系数、芯桩与砂石桩直径比对地基固结性状的影响。结果表明：对于混凝土芯砂石桩复合地基按应力定义的固结度与按变形定义的固结度表达式不同;地基的固结随着砂石桩桩体渗透系数增加而加快;砂石桩直径一定的情况下,固结速率随芯桩直径增大先增大后减小。最后对本文解和以往的两种解做了比较,与以往解相比本文解能够同时考虑环形通道和桩土荷载分担,给出的固结度介于以往的两种解之间。     

碎石桩复合地基非线性固结解析解

通过引入土体的e-lgσ和e-lgk对数模型,考虑了土体固结过程中压缩模量非线性增长和渗透系数非线性减小的特征,给出了一种碎石桩复合地基非线性固结解析解,并对复合地基的非线性固结性状进行了分析。结果表明,按应力和按变形定义的两种固结度不相等,按变形定义的固结度一般大于按应力定义的固结度;当压缩指数小于渗透指数时,不考虑土体的非线性特征会低估地基的固结度,而当压缩指数大于渗透指数时,不考虑土体的非线性则会高估地基的固结度;对于按应力定义的固结度来说,当压缩指数小于渗透指数时,随着附加应力的增大,地基固结速度加快,而当压缩指数大于渗透指数时,附加应力增大,地基固结减慢;对于按变形定义的固结度来说,不论压缩指数大于还是小于渗透指数,附加应力增大,地基固结速度总是加快。     

双层散体材料桩复合地基固结理论

研究了考虑涂抹效应和应力集中效应的双层散体材料桩复合地基固结解析解及其工程应用,分不同情况讨论了特征根的可能变化规律,也讨论了解析解转化为双层竖井地基以及双层天然地基的普遍适用性。研究发现,固结速率随井径比的减小、水平向渗透系数比的增大和桩体刚度的增大而增加;底面排水条件对双层散体材料桩复合地基的固结影响,在井径比不是很大的情况下影响不大;是否考虑应力集中效应对计算结果影响较大。     

考虑土体非线性的CCSG桩复合地基固结解

混凝土芯砂石桩（CCSG）桩复合地基是一种新型多元复合地基。通过引入地基土体的e-lgσ和e-lgk对数模型,考虑地基土体固结过程中压缩模量和渗透系数非线性变化的特征,推导出基于等应变假设的CCSG桩复合地基非线性固结解析解,且现有的考虑土体非线性的砂井固结解和碎石桩复合地基固结解均是文中解的特例。根据该解析解得到桩土模量比、土体压缩指数与渗透指数比、荷载增量等无量纲参数变化时,CCSG桩复合地基的固结度曲线。分析结果表明,按应力和按变形定义的两种固结度不相等,通常按变形定义的固结速度较快;土体压缩模量和渗透系数的非线性变化对固结影响较大。最后通过和由实测数据获得的固结度曲线对比,验证了解析解的正确性。     

砂井联合水泥土搅拌桩复合地基固结解析解

砂井联合水泥土桩复合地基是一种新型的复合地基加固技术,既可以加快软土地基固结时间,又可以增强软土地基的强度。针对该组合型复合地基的布桩特点,该类复合地基可以简化成以水泥土搅拌桩为中心的轴对称固结模型,并假定孔隙水沿径向渗流到砂井体内的流量等同于砂井体内排出的水量,考虑砂井的涂抹效应,推导出该类型下砂井联合水泥土搅拌桩复合地基固结方程。根据实际工程荷载多数单级施加和地基附加应力呈梯形分布的特点,得出了砂井联合水泥土桩复合地基固结解析解。通过对单级荷载情况下的复合地基固结解析解的退化,得出了瞬时施加荷载下的解析解。最后分别针对井径比、加荷历时、桩-土模量比、砂井渗透系数等影响因素,对复合地基固结性状进行了分析。该解答对提高此类复合地基的设计和计算水平有一定的理论指导意义。     

未打穿散体材料桩复合地基固结简化解研究

利用平均固结度普遍解,将未打穿散体材料桩复合地基转化为等效双层地基,推导出未打穿散体材料桩复合地基固结简化解,给出其平均固结度计算简化公式。根据简化解、现有解和有限单元法编制程序,绘制考虑贯入比、桩体渗透系数、土体扰动区渗透系数和土体扰动区影响因子等因素对固结的影响曲线图,分析了各因素对未打穿散体材料桩复合地基固结性状的影响,并对3种计算方法所求出的平均固结度进行了比较研究,进而探讨了简化解的适用性。研究结果表明,无论是在单面排水还是在双面排水条件下,简化解求出的平均固结度总体上是介于现有解和有限单元法二者之间,尤其在固结过程的“中后期”（即固结度≥50%时）。从实用角度来看,简化解的计算结果具有足够精度,且简便、实用;在各种影响因素中,散体材料桩长度和桩体渗透系数对固结过程的影响最大。     

考虑桩体刺入变形的透水混凝土桩复合地基固结理论研究

现有的多元复合地基利用两种或者两种以上的桩型对地基土进行加固,以期提高地基承载力、加速地基固结。提出了一种兼具散体材料桩和刚性不排水桩自身优点的透水混凝土桩复合地基固结模型。工程中刚性桩与土体的压缩量并不相等,这与等应变条件存在着不一致的地方。为此,抛弃传统等应变假设,考虑桩体向垫层和下卧层的刺入变形,对传统等应变假定进行修正,同时考虑了扰动区土体水平渗透系数的抛物线变化和水在桩体内的径向、竖向渗流,给出了此类固结问题的控制方程和解答以及复合地基固结度的表达式,并对复合地基固结度的解进行了讨论。最后与其他复合地基解做了比较并对固结性状进行了分析,并针对透水混凝土桩孔隙引起的桩阻作用对地基固结速度的影响进行了验证。     

考虑影响区真实形状的竖向排水井地基固结解

针对现有竖向排水井地基固结解析理论对影响区一律采用圆形等效假定的缺陷,研究了影响区真实形状为正六边形的按梅花形布置的竖向排水井地基的固结问题。通过建立新固结方程和引入新的边界条件,并考虑土体水平渗透系数变化,得到了相应的解析解。对于土体水平渗透系数的3种变化模式,分别给出了各种模式下的特殊解。在此基础上,分析了3种模式下3个主要的无量纲参数对地基固结性状的影响,并比较了计算结果和现有理论结果。分析结果表明,影响区和涂抹扰动区范围越大,固结越慢;土体的最大与最小水平渗透系数之比越小,固结越快;在相同条件下,考虑扰动区渗透系数线性变化的模式2固结最快,而假定扰动区渗透系数不变的模式1的解与现有理论解相当接近,验证了现有竖向排水井地基固结解析理论中对影响区采用圆形等效假定的合理性     

Analytical solutions for the consolidation of unsaturated foundation with prefabricated vertical drain

Based on the consolidation theory raised by Fredlund, the solutions for the equal-strain consolidation of unsaturated foundation with the prefabricated vertical drain considering smear effect and drain resistance are analytically formulated in this paper. Firstly, governing equations for excess pore pressures (i.e., excess pore-air and pore-water pressures) under the equal-strain hypothesis are derived with the introduction of radial boundary conditions. Afterwards, the obtained coupled equations are solved by applying general integration, decoupling process, and Fourier sine series expansion. The smear coefficients and factors of drain resistance corresponding to air and water phases are both captured explicitly in the final solutions. Furthermore, the degenerated solutions are employed to verify the reliability of the current solutions. Finally, a parametric study is conducted to study the consolidation characteristics of the proposed foundation model against modeling sizes (S and N), smear coefficients (α_a and α_w), and drain resistance factors (G_a and G_w).     

Analytical models for consolidation of combined composite ground improved by impervious columns and vertical drains

In recent years, a new technique of ground improvement, which involves the combined use of impervious column and vertical drains, has been proposed and utilized in many field projects to accelerate consolidation and increase bearing capacity of soft soil ground. To cover the possible distribution patterns of impervious columns and vertical drains, 2 analytical models, including Model A with outward flow and Model B with inward flow within the soils, are proposed to predict the consolidation of combined composite ground by considering the following factors: (1) disturbance effects of both impervious columns and vertical drains, (2) the well resistance of vertical drains, and (3) time‐variant loadings. The average degrees of consolidation predicted by the proposed analytical models are compared with several existing solutions and then against the measured data in the literature. The consolidation behavior of a combined composite ground is investigated by the proposed analytical solutions. The results show that the combined use of impervious columns and vertical drains can remarkably accelerate the consolidation rate of soft soils compared with the single use of either of them. The average degrees of consolidation predicted by both analytical models agree well with the measured data. Compared with Model B, Model A usually predicts a faster consolidation rate because of a shorter drainage path. Many factors can influence consolidation behavior of combined composite ground, such as loading scheme, distribution patterns and the disturbance effects of impervious columns and vertical drains, and compression modulus ratio of impervious column to soil.     

考虑径向渗透系数变化的真空预压竖井地基固结解析解

针对真空预压条件下竖井地基固结问题,考虑竖井地基扰动区土体径向渗透系数变化的3种模式(扰动区渗透系数为常数、线性变化、抛物线变化)和竖井井阻随时间变化等因素影响;建立数学计算模型,采用解析解法,推导了考虑径向渗透系数因施工扰动而变化的真空预压竖井地基固结问题的解析解。基于此解,编制了计算程序,绘制出了考虑扰动区土体径向渗透系数变化和竖井井阻随时间变化影响的真空预压竖井地基固结曲线图。研究表明:井阻变化率对固结速率有较大影响;在土体扰动区径向渗透系数变化的3种模式中,渗透系数为抛物线变化时固结速率最快,渗透系数为线性时次之,渗透系数为常数时固结速率最慢。     

Analytical solutions for consolidation aided by vertical drains

Soil disturbance caused during the installation of vertical drains reduces the in situ hydraulic conductivity of soft deposits in the immediate vicinity of the drains, resulting in a slower rate of consolidation than would be expected in the absence of disturbance. Experimental investigations have revealed the existence of two distinct zones, a smear zone and a transition zone, within the disturbed zone around the vertical drain. The degree of change in the hydraulic conductivity in the smear and transition zones is difficult to assess without performing of laboratory tests. Based on the available literature, four different profiles of hydraulic conductivity versus distance from the vertical drain were identified. Closed-form solutions for the rate of consolidation for each of these four hydraulic conductivity profiles were developed. It is found that different variations of the hydraulic conductivity profiles in the disturbed zone result in different rates of consolidation.     

透水桩与不透水桩组合型复合地基固结解析分析

在深厚软土地基处理中,联合使用透水与不透水桩,既可以加速地基固结,又能较大地提高地基的承载力,具有广泛的应用价值。基于轴对称固结模型,并考虑透水桩的体积压缩,建立了透水与不透水桩组合型复合地基的固结微分方程,利用边界条件和初始条件,得到了外部荷载瞬时施加情况下的地基固结解析解,并将该解与现有解析解进行对比分析,验证其合理性;同时,对桩的扰动效应、井阻效应、压缩模量等影响因素进行了分析,探讨了该复合地基的固结特性。结果表明:不考虑透水桩体积变化将高估组合型复合地基的固结速率;减小透水桩的井阻效应和施工扰动效应,增大置换率及桩体模量,将加快组合型复合地基的固结速率,实际工程中可以从这些方面减少地基的工后沉降。