竖向排水井地基工后沉降预测

预测工后沉降是排水固结预压加固软土地基的关键问题之一。根据等应变竖向排水井地基固结理论,提出了沉降曲线的近似计算方法。通过实测沉降资料与近似理论曲线的拟合,获得竖向排水井地基的最终沉降量和平均固结度,从而预估其工后沉降量。将该方法分别应用于真空预压和堆载预压处理的竖井地基,进行工后沉降预测,结果表明该方法是可行的     

库内层状软土地基的联合处理方法研究

介绍了利用重锤夯实法加固表层填土与排水固结法加固深层软土联合处理库内层状软土地基的方法,在填土静荷载和塑料排水板作用下淤泥质软土很快完成主固结沉降,重锤夯实法使表层填土受到动力压密,软土和填土强度得以提高.试验结果表明,排水固结过程中填土层的单位沉降量远小于淤泥质软土,重锤夯实法的有效加固深度可以达到地表下3.5 m,影响深度可达6.0 m.联合采用两种地基处理方法可以有效提高层状地基承载力.     

真空排水预压下土体变形的应力路径分析

通过室内试验, 对真空排水预压下土体变形特性进行了应力路径分析, 测定软土地基在真空预压加固后应力路径的改变对沉降量的影响, 论证真空排水预压加固软土地基不能消除其剪应力引起的剪切变形, 结合实例, 计算其后期沉降量与固结沉降量的比值, 并推算软土地基在真空预压下其最终沉降量计算公式的修正系数。     

真空排水预压下土体变形的应力路径分析

通过室内试验,对真空排水预压下土体变形特性进行了应力路径分析,测定软土地基在真空预压加固后应力路径的改变对沉降量的影响,论证真空排水预压加固软土地基不能消除其剪应力引起的剪切变形,结合实例,计算其后期沉降量与固结沉降量的比值,并推算软土地基在真空预压下其最终沉降量计算公式的修正系数.     

短程超载真空预压动力排水固结法加固深厚淤泥软基工法研究

针对沿海地区深厚淤泥软土的特点和工程建设时效性的要求,本文在总结软土排水固结S-T曲线规律的基础上提出应用短程超载真空预压动力排水固结法加固深厚淤泥的方法,发现深厚淤泥软土在真空负压、超载正压和动力冲击三者优化组合的作用下,主固结沉降可在短时间内完成,土体强度提高的同时地表吹填土在动力冲击作用下形成超固结的硬壳层。深厚淤泥软土加固后能够满足地基承载力的要求并且能够有效控制工后沉降和不均匀沉降。并通过工程实例,对地基处理后的效果进行分析评价,证明了该工法的可行性和有效性,为沿海地区广泛分布的深厚淤泥软土地基的加固提供了新的途径。     

固结排水中排水带通水量的影响及选择

井阻作用影响地基的固结速率,排水带的通水量与井阻作用有直接关系,过小通水量的排水带在地基中产生较大的井阻,通水量较大的排水带又使生产成本提高。笔者分析了通水量对地基固结的影响,并提出根据被加固地基的性状来选择通水量的方法。建议用公式 来确定所使用排水带的容许通水量下限值。     

既有建筑新近填土欠固结地基加固处理方法探讨

欠固结土地基固结沉降引起的地基变形,危害着建筑物正常使用和安全,解决欠固结土沉降变形问题一直是岩土工程界探索和研究的课题。针对既有建筑物下新近填土欠固结地基引发建筑物不均匀沉降进行了深入探究,查找、分析引发不均匀沉降的原因,并根据地基土固结程度及建筑物结构类型提出了合理的地基加固处理方法,为既有建筑新近填土欠固结地基加固处理提供参考。     

静动力排水固结法中孔压、土压的响应特征及应用研究

在静动力排水固结法处理饱和软黏土地基处理的场地进行现场的数据测试,分析了该条件下的孔隙水压力和土压力的响应规律,提供在一定的施工条件下沉降规律及与孔压、土压响应关系的求解方法,为静动力排水固结法加固淤泥类软土地基的研究和工程实践提供了一定的参考依据。     

动力排水固结法的加固机理及工艺特征

在分析动力排水固结法加固软粘土地基的机理和特点的基础上,提出了适用于处理软粘土地基的动力排水固结法施工工艺。     

真空预压法在连云港潮间带软基加固工程中的应用

以实际工程为例,论述了真空预压排水固结法加固连云港沿海地区潮间带软土地基的原理和施工要点,对工程实际的观测结果进行了深入分析。实践证明,使用真空预压法,对地基施加相当于80kPa荷载的真空压力,100d后地基的总沉降量可达到1m,地基土的平均固结度超过80％,经过加固的地基土抗剪强度明显增加,地基承载力基本满足后续施工要求。表明真空预压法适用连云港沿海潮间带软基加固,效果明显。     

离心模型试验模拟塑料排水板处理软土地基的方法和应用

采用大型土工离心机对某工程近海软土地基上堤坝施工期及运行期进行了模拟。试验中采用停机加载法模拟分级施工加载过程, 原型中采用塑料排水板固结法处理软土地基, 模型中则根据固结过程相似的原理, 换算成等效圆截面排水体, 在模型制作中采用等效透水滤芯进行模拟。根据激光位移传感器和孔隙水压力传感器数据可以得出相应原型软土地基的沉降特性和孔隙水压力变化情况。根据试验得到的沉降曲线, 采用"经验双曲线法"推算出了地基最终沉降, 然后得出按沉降推算的分层地基平均固结度随时间的变化。对比试验模拟得到的软土地基固结度和理论计算结果, 二者基本接近, 表明塑料排水板模拟方法用于离心模型试验是可行的。      

塑料板排水法加固软基技术

阐述了塑料板排水法加固地基的原理，并对抗剪强度的增长计算和地基沉降的机理进行了分析，对其今后发展方向作了展望。     

任意附加应力下竖井径竖向耦合固结等应变解

竖向排水体包括砂井和塑料排水板已广泛应用于加速软黏土地基的固结。不同形式的轴对称条件下含竖向排水体均质各向同性地基的固结解析解答也相继被提出,而各种解答均假定地基中附加应力在竖向排水体的深度范围内是均匀分布的。显然,当竖向排水体深度与地面堆载区宽度的比值相对较高,或竖向排水体的影响区域靠近地面堆载区的边缘时,这个假定并不适用。为此,在现有径竖向耦合固结等应变解的基础上,提出任意分布的地基附加应力条件下的解答,并分析附加应力分布形式和线性加载速率对地基固结的影响。结果表明,均匀分布的附加应力条件下的解答低估了地基的固结速率,而瞬时加载条件下的解答则高估了地基的固结速率。     

堆载预压联合强夯加固软土地基的试验研究

通过某软土回填地基加固工程现场试验,论证只要合理地确定施工参数和工艺,完全可用塑料板排水分级堆填压载并联合强夯的静态——动力预压法加固软土地基。此外,就不同排水板间距、不同填料及不同夯击能时静态、动力排水固结过程中地基的变形、孔隙水压力分布、固结状态及地基的强度增长规律等进行对比分析。也与检测结果作了比较。     

Consolidation behavior of soft deposits considering the variation of prefabricated vertical drain discharge capacity

This paper is primarily focused on why and how to consider the varied discharge capacity during simulations of consolidation via prefabricated vertical drains (PVDs) for soft soil deposits. First, the existing studies regarding discharge capacity are summarized and discussed. These studies conclude that the discharge capacity of PVDs at sites vary with the confining pressure and consolidation time. Next, a series of analytical solutions that consider the variation of discharge capacity with ground depth, consolidation time or both simultaneously are presented and compared. Applications of these solutions and of the newly introduced parameters are described. Then, a well-documented case history on ground treatment with PVDs is analyzed, in which the parameters related to the time-dependent discharge capacity were obtained from laboratory tests. A comparison between a classical solution and the newly presented method indicates that consideration of the varied discharge capacity in the consolidation theory can better predict the consolidation process of PVD-improved ground.     

Probabilistic analyses of soil consolidation by prefabricated vertical drains for single‐drain and multi‐drain systems

Natural soils are one of the most inherently variables in the ground. Although the significance of inherent soil variability in relation to reliable predictions of consolidation rates of soil deposits has long been realized, there have been few studies that addressed the issue of soil variability for the problem of ground improvement by prefabricated vertical drains. Despite showing valuable insights into the impact of soil spatial variability on soil consolidation by prefabricated vertical drains, available stochastic works on this subject are based on a single‐drain (or unit cell) analyses. However, how the idealized unit cell solution can be a supplement to the complex multi‐drain systems for spatially variable soils has never been addressed in the literature. In this study, a rigorous stochastic finite elements modeling approach that allows the true nature of soil spatial variability to be considered in a reliable and quantifiable manner, both for the single‐drain and multi‐drain systems, is presented. The feasibility of performing an analysis based on the unit cell concept as compared with the multi‐drain analysis is assessed in a probabilistic context. It is shown that with proper input statistics representative of a particular domain of interest, both the single‐drain and multi‐drain analyses yield almost identical results. Copyright © 2016 John Wiley & Sons, Ltd.     

Assessment of Marine Clay Improvement Under Reclamation Fills by in-situ Testing Methods

In ground improvement projects with prefabricated vertical drains, the duration of the preloading period is set in advance based on the predetermined time rate of consolidation of the compressible layer. If prediction is accurately done, the required degree of consolidation is met at the pre-determined preloading time. As such, there is a requirement for in-situ tests to be carried out just prior to the removal of surcharge to assess the degree of consolidation of the improved ground. In-situ tests were carried out after 23 months of surcharge loading at the In-Situ Test Site within the Changi East Reclamation Project in the Republic of Singapore. In-situ testing works in this research study comprises the use of field vane shear, piezocone, flat dilatometer and self-boring pressuremeter. The in-situ tests were carried out to determine the shear strength and degree of consolidation of the Singapore marine clay at Changi after 23 months of surcharge loading. The In-Situ Test Site consisted of a Vertical Drain Area as well as an untreated Control Area. Both areas were located adjacent to each other and were surcharged simultaneously to the same level and surcharge left in place for a period of 23 months. Comparison was made between the in-situ test results of the Vertical Drain Area and the untreated Control Area.     

修正等应变假定下刚性桩复合地基固结特性分析

刚性桩复合地基固结特性是影响工程进度的重要因素。为研究外荷载作用下刚性桩复合地基固结特性，结合刚性桩和桩间土应力?应变特点对等应变假定进行修正。在此基础之上，考虑涂抹效应、桩间土和下卧层土体固结特性的影响，推导得到桩间土和下卧层土体固结微分方程。基于双层地基固结理论，考虑单级匀速施加荷载和附加应力沿深度变化等边界条件，推导得到其固结度解析解。最后，利用数值模拟方法对解析解进行验证，并对影响刚性桩复合地基固结特性的因素进行分析。结果表明：理论计算与数值模拟结果较为吻合；刚性桩复合地基固结速率受到贯入比影响较大，当贯入比较小时，与天然地基相比，其固结速率较小，贯入比较大且桩端阻力系数较小时，复合地基固结速率大于天然地基；随着贯入比、桩?土相对刚度和垫层?土体相对刚度的增大，复合地基整体固结速率加快；随着置换率的增大，复合地基整体固结速率降低。     

打桩引起的基坑开挖问题及处理

通过某电厂桩基处理工程实例,介绍了打桩引起的预制桩偏位及开挖问题。在不加外荷载情况下,采用塑料排水板方法消散打桩引起的超静孔隙水压力的处理措施,解决了高孔隙水压力下主厂房的开挖问题。分析了塑料排水板消散孔隙水压力的影响因素。观测结果及工程实践表明,塑料排水板处理桩基工程快速经济,可不需加载,但处理效果与水平排水系统有关。