考虑桩基影响的基坑突涌模型试验研究

软土地区承压水深基坑工程常常遇到基坑突涌问题,针对有较多工程桩的多层地下室深基坑,进行了有桩基坑突涌模型试验研究。分析了基坑突涌破坏模式为土体表面涌水涌砂破坏,属于流土破坏类型,揭示了桩土相互作用机理,桩身轴力和桩侧摩阻力分布规律。研究结果表明:随着承压水压力的增加,桩顶与土体竖向位移呈现相似的变化规律,均呈抛物线分布。由于桩基的作用,黏土层破坏时的水力梯度明显提高,对比无桩软土深基坑在承压水压力作用下的土体变形规律,坑内工程桩的抗拔效应对坑底土体隆起变形起到较明显的抑制作用。     

Axisymmetric fundamental solutions for a finite layer with impeded boundaries

Axisymmetric fundamental solutions that are applied in the consolidation calculations of a finitecaly clay layer with impeded boundaries were derived. Laplace and Hankel integral transforms were utilized with respect to time and radial coordinates, respectively in the analysis. The derivation of fundamental solutions considers two boundary-value problems involving unit point loading and ring loading in the vertical. The solutions are extended to circular distributed and strip distributed normal load. The computation and analysis of settlements, vertical total stress and excess pore pressure in the consolidation layer subject to circular loading are presented. Project (No. 500117) supported by the National Natural Science Foundation of Zhejiang Province     

Axisymmetric fundamental solutions for a finite layer with impeded boundaries

INTRODUCTIONBiot’sconsolidationtheorywasproposedin1 941fromcontinuousmediumfundamentalequations.Thetheorytakingintoaccountthecouplingbetweenthesolidstrainsandporepres suredissipationiscalled“coupledconsolidationtheory” .Thesolutionofgoverningequationso…     

桩-土界面扭剪剪切与直剪剪切的差异性研究

直剪试验在剪切过程中桩-土的剪切面积逐渐减小,导致垂直应力发生偏心,剪应力不能保持均匀分布,并不能反映土体的实际软弱剪切面,而扭转剪切能够保持剪切过程中桩-土的接触面积始终不变,避免了垂直应力发生偏心。针对新出现的界面扭剪试验和常规直剪试验在桩-土界面研究中的差异,探讨了两种剪切方式下的桩-土界面的摩擦特性,设计了桩-土界面摩擦单元,并基于相同剪切速率和桩-土界面接触条件,进行不同含水率和法向应力下的扭剪试验和直剪试验。试验结果表明扭剪和直剪试验的不同之处为:(1)扭转剪切的桩-土界面剪切强度为直剪剪切强度的1.5～2.1倍,扭剪剪切的剪应力达到最大值后会呈现出不同程度的软化或保持基本不变,而直剪剪切的剪应力表现为硬化趋势;(2)同一法向应力下,随着含水率的增加,扭剪试验的极限剪切位移逐渐增加而直剪试验的极限剪切位移呈现出微弱的降低;(3)直剪剪切界面摩擦角明显低于同条件下扭剪剪切的界面摩擦角。试验结果可以为桩-土界面研究中扭剪试验和直剪试验剪切强度的转换提供参考。