变化荷载下散体材料桩复合地基固结解析解

研究了实际工程中荷载逐渐施加情况下的散体材料桩复合地基固结问题，建立了相应的数学模型，并给出了解析解，探讨了加载历时和一些地基物理、几何参数尤其是桩体刚度对复合地基固结过程的影响，并将竖井地基与分别按两种渗流模型计算的复合地基的固结特性进行了比较，两者有较大差别。     

半透水边界的散体材料桩复合地基孔隙水压力变化规律

针对半透水边界的散体材料桩复合地基孔隙水压力变化规律,建立了数学模型,给出了半透水边界的散体材料桩复合地基孔隙水压力解析解.根据解析解结果,编制相应的计算程序,绘制了孔隙水压力变化曲线图.研究显示,复合地基的顶、底面的透水性能参数Rv1和Rv2均对孔隙水压力变化产生影响,Rv1和Rv2值越大,孔隙水压力下降会越快.     

刚性基础下水泥土桩复合地基固结分析

为了掌握刚性基础下水泥土桩复合地基的固结性状，建立了复合地基的固结解析式.根据固结过程中孔隙水排出量等于单元体体积减小量的关系和平均超孔隙水压力的概念，推得水泥土桩复合地基的固结方程.通过等应变假设和初始边界条件，由分离变量法针对该固结方程进行了求解，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和固结沉降.研究结果表明，该解析式所得的计算结果与有限元分析结果相吻合，且水泥搅拌桩复合地基固结速率大于天然地基固结速率，并与现场观测的水泥土桩复合地基固结度变化趋势一致.     

真空—堆载联合预压不排水桩复合地基固结简化解研究

针对不排水桩复合地基固结问题,考虑到真空-堆载联合预压荷载的瞬时施加和桩体未打穿等因素对复合地基固结的影响,采用双层地基法将未打穿复合地基转化为等效双层地基,推导出真空-堆载联合预压不排水桩复合地基固结简化解,并绘制出贯入比、桩-土压缩模量之比、加固区和下卧层的土体渗透系数之比以及压缩模量之比对固结的影响曲线图。研究结果表明,在单面排水条件下,随着贯入比、桩-土压缩模量之比、加固区和下卧层土体压缩模量之比的增大,复合地基固结速率随之加快;加固区和下卧层的土体渗透系数之比对固结速率的影响不显著。在各种影响因素中,贯入比对固结速率的影响最大,加固区和下卧层土体压缩模量之比对固结速率的影响较为明显。     

层状土中考虑剪切变形的单桩水平振动解析解

针对桩基水平振动分析问题，建立了能够同时考虑桩体弯曲和剪切变形的桩土计算模型.采用与频率相关的刚度系数和阻尼系数来模拟土对桩的动反力，简化桩体为Timoshenko梁，得到了层状黏弹性地基中能同时考虑桩体弯曲和剪切变形的单桩的水平振动解析解.研究了桩土模量比、桩体长径比、地基成层性以及激振频率对桩基动力响应的影响.并且在给定桩土参数的情况下，把同时考虑桩体弯曲和剪切变形的解析解与只考虑弯曲变形的解进行了比较.结果表明，忽略桩体水平振动时的剪切变形可能会带来较大的误差.     

长板-短桩复合地基的固结解析解

为了研究长板-短桩复合地基施工后的固结问题,通过采用不透水桩联合砂井的组合桩模型并考虑竖井的体积变化和涂抹效应,提出了塑料排水板和水泥土搅拌桩共同作用下的土体固结控制方程,得出了孔压和固结度的解析表达式.结果表明：本文解与现有解的固结方程形式一致,只有参数具有差异,表明本文解的固结度慢于现有解;当井径比较大和竖井扰动区影响较大时,本文解与实际情况相符,所得结果更精确.     

复合地基承载力深度修正研究

目的 提出一种简单适用的复合地基承载力深度修正方法和修正参数.方法 通过对复合地基的不同分类,研究加固体的工作机理和复合地基的破坏特征,探讨复合地基承载力的影响因素和深度修正相关问题.对散体桩复合地基采用Plaxis有限元软件进行数值模拟分析验证.结果 散体桩单桩承载力的发挥受桩周土的应力水平约束,复合地基承载力深度修正可按桩体和地基土分别进行,桩体部分深度修正系数为土层的被动土压力系数与桩体材料被动土压力系数的乘积的1/4.结论 散体材料桩复合地基承载力的深度修正包含桩体修正和桩周土修正两部分,刚性桩、柔性桩宜只对桩周土进行修正.复合地基承载力深度修正系数可根据已有规范取值,深度修正可按照笔者推导出的公式计算.     

散体材料复合地基承载力分析方法研究

目的研究长短桩复合地基这一新型的地基处理技术，解决其承载力计算方法问题．方法首先从试验出发，全面分析散体材料桩复合地基的承载机理．在此基础上，引进圆孔扩张理论，充分考虑散体材料桩与桩土间相互作用．结果导出了桩体与土体承载过程中的应力应变计算公式，并针对以往承载力计算方法主观参数众多难以确定以及未能考虑布桩方式影响的缺陷，提出了一套散体材料桩复合地基面积比承载力计算方法．结论通过工程算例，验证了文中计算方法的可行性．     

连续排水边界下成层地基一维非线性固结解析解（英文）

为了研究边界排水时间效应对固结过程的影响,引入连续排水边界研究成层地基一维非线性固结问题。通过引入孔隙比与有效应力之间的非线性关系,建立了瞬时荷载作用下成层地基固结问题的控制方程,进而获得按沉降定义和按超静孔隙水压力定义的平均固结度以及成层地基沉降的解析解。通过与有限差分解析解对比以及现有解析解对比验证了所得解析解的正确性。基于所得解,通过详细的参数分析研究了成层地基一维非线性固结特性。结果表明,排水界面参数对成层地基的固结性状有很大影响,固结速率随界面参数的增大而增大。在连续排水边界条件下,按沉降定义的平均固结度随有效应力比的增大而增大,而按超静孔隙水压力定义的平均固结度随有效应力比的增大而减小。     

路堤荷载作用下透水性混凝土桩减压降沉效应研究

透水混凝土桩兼具了刚性桩的高强度特性和散体桩良好透水性的特点,适用于地基的加固处理。为了研究透水性混凝土桩地基处理技术对地基的减压降沉效应,基于有限元法和Biot固结理论对路基荷载作用下透水性混凝土桩复合地基的超静孔隙水压力、桩土应力比、水平位移、沉降等进行研究,并与散体桩和刚性桩进行了对比分析。研究发现透水性混凝土桩复合地基内累积的超静孔隙水压力能够迅速消散,说明透水性混凝土桩具有显著的减压效应;同时发现,透水性混凝土桩复合地基的水平位移和工后沉降较小,证明透水性混凝土桩在降低地基沉降方面具有显著的作用。因此,透水性混凝土桩特别适用于加固透水性差、工后沉降大的地基。     

半透水边界砂井地基的真空预压固结解

针对砂井地基顶部存在垫层和底部存在下卧层的现状,采用半透水边界来反映它们对砂井地基固结的影响。假定地基变形符合等应变条件,考虑水平向渗透系数沿半径发生变化,建立了上下边界为半透水边界时真空预压砂井地基的固结理论,通过分离变量法获得固结度和沉降的级数解析解答,分析了底部透水系数、顶部透水系数、井阻、渗透系数沿半径分布特性对砂井地基固结度和沉降的影响规律。研究表明,当底部半透水时,最终负孔压和有效应力呈现出沿地基深度衰减的变化规律。当其它条件相同时,底部透水系数越大的地基固结度越大,但最终沉降和径向固结时间因子相同时的固结沉降却越小。当底部边界不透水时,最终沉降不会随着顶部透水系数改变而改变。但当底部边界半透水或完全透水时,最终沉降随着顶部透水系数增大而增大。顶部透水系数越大的地基固结度越大,径向固结时间因子相同时的固结沉降也越大。均匀井阻的大小不会影响负压最终竖向分布特性,也不会改变最终沉降,但会明显降低砂井地基固结度,延长固结完成时间。渗透系数径向分布模式会对砂井地基的固结度产生影响。工况一计算的固结度最大,工况二计算的固结度最小,工况三计算的固结度介于工况一和工况二之间。半透水边界对真空预压砂井地基固结过程的影响规律与堆载预压砂井地基相比存在明显不同。     

A general solution for vertical-drain consolidation with impeded drainage boundaries

An analytical solution is derived from the generalized governing equations of equal-strain consolidation with vertical drains under multi-ramp surcharge preloading. The hydraulic boundary conditions at both top and bottom of the consolidating soil are modelled as impeded drainage. The impeded drainage is described by using the third type boundary condition with a characteristic factor of drainage efficiency. Fully drained and undrained boundary conditions can also be modelled by applying an infinite and a zero characteristic factor, respectively. Simultaneous radial and vertical flow conditions are considered, together with the effects of drain resistance and smear. An increase in total stress due to multi-ramp loading is reasonably modelled as a function of both time and depth. A solution to calculate excess pore-water pressure at any arbitrary point in soil is derived, and the overall average degree of consolidation is obtained. It shows that the proposed solution can be used to analyze not only vertical-drain consolidation but also one-dimensional consolidation under either one-way or two-way vertical drainage conditions. The characteristic factors of drainage efficiency of top and bottom boundaries have a potentially important influence on consolidation. The boundary may be considered fully drained when the characteristic factor is greater than 100 and fully undrained when the characteristic factor is less than 0.1. The stress distribution along depth induced by the surcharge loading has a limited effect on the overall average degree of consolidation. However, it has a significant effect on the dissipation of excess pore-water pressure.     

One-dimensional consolidation of double-layered soil with non-Darcian flow described by exponent and threshold gradient

Based on non-Darcian flow law described by exponent and threshold gradient within a double-layered soil, the classic theory of one-dimensional consolidation of double-layered soil was modified to consider the change of vertical total stress with depth and time together. Because of the complexity of governing equations, the numerical solutions were obtained in detail by finite difference method. Then, the numerical solutions were compared with the analytical solutions in condition that non-Darcian flow law was degenerated to Dary’s law, and the comparison results show that numerical solutions are reliable. Finally, consolidation behavior of double-layered soil with different parameters was analyzed, and the results show that the consolidation rate of double-layered soil decreases with increasing the value of exponent and threshold of non-Darcian flow, and the exponent and threshold gradient of the first soil layer greatly influence the consolidation rate of double-layered soil. The larger the ratio of the equivalent water head of external load to the total thickness of double-layered soil, the larger the rate of the consolidation, and the similitude relationship in classical consolidation theory of double-layered soil is not satisfied. The other consolidation behavior of double-layered soil with non-Darcian flow is the same as that with Darcy’s law.     

变荷载下半透水边界成层黏弹性地基的一维固结分析

基于Kelvin黏弹性地基模型，研究了半透水边界饱和成层黏弹性地基在循环荷载作用下的一
维固结问题。利用Laplace变换，得到了问题在变换域内的通解。通过数值Laplace逆变换，获得了黏弹性
成层饱水地基在变荷载下的有效应力及固结曲线图。结果表明，在变荷载下黏弹性地基的固结速率慢于弹
性地基，其有效应力呈振荡增长；地基的上部垫层和下卧土层的透水性能对固结速率具有较大的影响。     

Consolidation analysis of composite foundation with partially penetrated cement fly-ash gravel(CFG) piles under changing permeable boundary conditions

Based on the double-layered foundation theory, the composite ground with partially penetrated cement fly-ash gravel(CFG) piles was regarded as a double-layered foundation including the surface reinforced area and the underlying untreated stratum. Due to the changing permeability property of CFG piles, the whole consolidation process of the composite ground with CFG piles was divided into two stages, i.e., the early stage(permeable CFG pile bodies) and the later stage(impermeable pile bodies). Then, the consolidation equation of the composite foundation with CFG piles was established by using the Terzaghi one-dimensional consolidation theory. Consequently, the unified formula to calculate the excess pore water pressure was derived with the specific solutions for the consolidation degree of composite ground, reinforced area and underlying stratum under instant load obtained respectively. Finally, combined with a numerical example, influencing rules by main factors(including the replacement rate m, the treatment depth h1, the permeability coefficient Ks1, Kv2 and compression modulus Es1, Es2 of reinforced area and underlying stratum) on the consolidation property of composite ground with CFG piles were discussed in detail. The result shows that the consolidation velocity of underlying stratum is slower than that of the reinforced area. However, the consolidation velocity of underlying stratum is slow at first then fast as a result of the transferring of effective stress to the underlying stratum during the dissipating process of excess pore water pressure.     

基于双剪统一强度理论的碎石桩复合地基承载及变形性状研究

基于双剪统一强度理论，并利用复合地基中碎石桩与桩周土的竖向位移相等，侧向变形协调与连续的条件，通过弹塑性理论，对碎石桩复合地基的承载及变形性状进行了分析研究，讨论了权系数b的大小对复合地基承载及变形性状的影响，推出了作用在复合地基上的荷载、碎石桩所分担的荷载及加固区压缩量与桩周土的塑性区半径的关系的系列解析算式。提出了对于碎石桩复合地基的设计应该实行承载力和沉降双重控制的设计思想。为验证本方法的可行性，将模型试验的结果与计算结果进行了对比。     

循环荷载作用下双层地基的一维固结

本文对循环荷载作用下双层地基一维团结作了研究．基于Ｔｅｒｚａｇｈｉ假设，利用Ｌａｐｌａｃｅ变换推导了任意荷载作用下一维固结方程的通解，并对特例情况下几种常见循环荷载下地基有效应力和沉降的解析算式作了详细推导，经典Ｔｅｒｚａｇｈｉ一维固结理论解是本文的一个特例．文中给出了算例分析并对所得解答作了有益的讨论，提出了进一步研究的内容．     

基于双剪统一强度理论的碎石桩复合地基承载及变形性状研究

基于双剪统一强度理论,并利用复合地基中碎石桩与桩周土的竖向位移相等,侧向变形协调与连续的条件,通过弹塑性理论,对碎石桩复合地基的承载及变形性状进行了分析研究,讨论了权系数b的大小对复合地基承载及变形性状的影响,推出了作用在复合地基上的荷载、碎石桩所分担的荷载及加固区压缩量与桩周土的塑性区半径的关系的系列解析算式。提出了对于碎石桩复合地基的设计应该实行承载力和沉降双重控制的设计思想。为验证本方法的可行性,将模型试验的结果与计算结果进行了对比。     

Simplified method for predicating consolidation settlement of soft ground improved by floating soil-cement column

A simplified method is presented for predicting consolidation settlement of soft ground improved by floating soil-cement column on the basis of double soil-layer consolidation theory. Combining the axisymmetric consolidation model and equal strain assumption, the governing equation was derived for the consolidation of clayey subsoil reinforced by soil-cement column. By modifying the boundary condition of the interface between the improved layer and underlying layer on seepage and pore-water pressure, the analytical solution of consolidation of soft ground improved by floating soil-cement column was developed under depth-dependent ramp load. The results of the parameter analysis of consolidation behavior show that the consolidation rate is closely related with the depth replacement ratio by the column and the permeability of upper layer. The influence of column-soil constrained modulus ratio and radius ratio of the influence zone to the column on consolidation is also affected by depth replacement ratio. The column-soil total stress ratio increases with time and approaches the final value accompanied with the dissipation of excess pore water pressure.     

考虑土体水平渗透系数变化的复合地基固结解

为了体现桩体施工扰动对桩周土体造成的负面影响,考虑了排水影响区土体水平渗透性的3种变化模式,即扰动区渗透系数不变、扰动区渗透系数线性变化和整个影响区渗透系数线性变化.采用由平衡条件和等应变假设得到的新的初始条件,分别给出了在各种模式下桩体和土体中的超静孔压的解.将桩体的固结引入复合地基按应力定义的固结度,并分别给出了复合地基按应力和变形定义的总平均固结度.最后分析了4个参数对地基固结性状的影响,并比较了计算结果和文献结果.结果表明,分别按应力和变形定义的总平均固结度相等;土体的最大与最小水平渗透系数之比越大,固结越慢;扰动区范围越小,固结越快;桩体越硬,固结越快.