均质黏性土中静压沉桩桩土界面孔压增量及有效土压室内试验研究

研究饱和黏性土中静压沉桩引起的桩土界面孔压增量及有效径向应力的变化规律对工程实践具有重要意义。利用自制的大比例模型试验系统,通过双壁开口和闭口管桩,实现了开口和闭口桩桩身表面嵌入式安装微型测试元件,得到了考虑孔压增量的桩土界面有效径向应力的变化规律。研究结果表明:入土深度越大,桩土界面孔压增量及有效径向应力越大,闭口桩桩土界面超孔压大于开口桩;桩身上部桩土界面超孔压和有效径向应力小于桩身下部;同一入土深度,随着桩身h/L的增加,桩土界面土压力存在侧压力“退化”的现象;特定试验条件下,闭口和开口桩桩土界面超孔压与上覆有效土体自重比值最大值分别是61.2%和52.1%,桩土界面有效径向应力是超孔压的3.76~5.46倍。桩土界面超孔压和有效径向应力与桩身h/L位置有关。

考虑渗流效应的土压力计算

地下水产生的渗流效应具有两重性 ,其对水压力的影响大于对有效土压力的影响。该概念若能在深基坑工程中得到应用 ,将会使设计更加合理 。

阻滑桩加固土坡稳定性分析的上限解法

从极限分析机动学方法出发, 利用土的抗剪强度折减系数概念, 建立了土坡的极限平衡状态方程, 由此确定土坡的临界稳定安全系数及其相应的潜在破坏模式。对于典型问题, 通过与现有极限平衡解和有限元数值解的对比分析, 验证了这种上限解法的合理性。进而对于在给定的荷载条件下不能满足抗滑稳定性要求的土坡, 考虑采用阻滑桩加固方式, 根据桩侧有效土压力的合理分布模式确定桩体与滑动面相交的截面上等效抗滑力和抗滑力矩, 利用极限分析上限定理建立了阻滑桩加固土坡的极限平衡状态方程, 将桩侧土压力作为目标函数, 运用数学规划方法确定了极限平衡状态时的临界桩侧土压力,以此为土坡加固中阻滑桩设计提供依据。通过数值计算与分析探讨了阻滑桩加固位置的优化布置等问题。

基于孔压静力触探试验方法确定砂土的内摩擦角研究

在岩土工程设计中,砂土的内摩擦角作为重要的输入参数之一,可用于计算土压力和确定地基承载里,其准确性直接关系到建造成本和安全,因此确定砂土的内摩擦角是岩土工程勘察中的重要工作内容。在常用的测试手段中,一般采用室内试验进行土体的内摩擦角测试,比如三轴压缩试验和直接剪切试验等,然而由于砂土取土较为困难,采用静力触探手段获取砂土的内摩擦角具有原位性、真实性、快速可靠等特点,在工程勘测中得到越来越多的应用。本文依托实际工程项目,分析总结目前采用孔压静力触探试验成果确定砂土内摩擦角的三种常用方法,并开展实测进行验证对比。研究结果表明,相对于采用锥尖阻力与有效上覆土压力的确定方法、采用有效上覆土压力和相对密实度的确定方法,Senneset提出的计算方法具有明显的优势,计算结果可靠性高、适用性广。

对设抗浮锚杆的基础底板受力分析与讨论

对于基础持力层为岩石的地区,独立柱基础构造底板被广泛应用于有地下室的工程中。地下水较浅时,整个基础底板承受水浮力,此时应对建筑物进行抗浮验算。若在地基内均匀设置锚杆抗浮,基础底板的设计内力应考虑在水浮力、锚杆等效荷载、基础及覆土自重作用下的筏板与在有效土压力作用的柱下独立柱基作用之和。文中分析了在水浮力与等效锚杆作用下筏板的受力情况。

Initiation and Development of Water Film by Seepage

When water seeps upwards through a saturated soil layer,the soil layer may become instability and water films occur and develop.Water film serves as a natural sliding surface because of its very small friction.Accordingly,debris flow may happen.To investigate this phenomenon,a pseudothree-phase media is presented first.Then discontinuity method is used to analyze the expansion velocity of water film.Finally,perturbation method is used to analyze the case that a water flow is forced to seep upwards through the soil layer while the movement of the skeleton may be neglected relative to that of water.The theoretical evolutions of pore pressure gradient,effective stress,water velocity,the porosity and the eroded fine grains are obtained.It can be seen clearly that with the erosion and redeposited of fine grains,permeability at some positions in the soil layer becomes smaller and smaller and,the pore pressure gradient becomes bigger and bigger,while the effective stress becomes smaller and smaller.When the effective stress equals zero,e.f.liquefaction,the water film occurs.It is shown also that once a water film occurs,it will be expanded in a speed of U(t)(1-ε).

Analysis on effective stress formula and consolidation of gassy muddy clay

In order to found an applicable equation of consolidation for gassy muddy clay, an effective stress formula of gas-charged nearly-saturated soils was introduced. And then, a consolidation equation was derived. Subsequently, supposing soils were under tangential loading, the expressions of pore water pressure were presented. The analytic solution of pore water pressure was attempted to be validated by the measured values in a real embankment. The parameters in the expressions of pore water pressure were gotten by the method of trial. The result shows that the consolidation model is rational and the analytic solution of pore water pressure is correct. The following conclusions can be made: 1) the influence of bubbles on the compressibility of pore fluid should be considered; 2) the effective stress would be influenced by bubbles, and the consolidation would depend on the compressibility of soil skeleton: the softer the soils are, the more distinct the influence of bubbles is; for normal clay, the influence of bubbles on the effective stress may be commonly neglected.

层状黏性土中静压桩沉贯特性现场试验

为探讨层状黏性土中静压桩的沉贯特性,依托山东东营某桩基工程开展了现场静压桩足尺试验,分析开闭口静压桩压桩力的变化规律,明确开闭口静压桩桩端阻力和桩侧摩阻力在贯入过程中的分布形式,揭示桩土界面径向土压力和孔隙水压力的分布特征以及有效径向土压力对单位桩侧摩阻力的影响机制。试验结果表明:压桩力的变化规律基本反映了土层性质的变化,土层的软硬程度制约着压桩力的变化,开口桩压桩力明显小于闭口桩压桩力,沉桩结束时开口桩占闭口桩的33.9%~79.7%;土层的软硬程度对桩端阻力的影响较大,并且闭口桩对桩端土层软硬程度的敏感性高于开口桩;桩侧摩阻力的发挥与土层的性质密切相关,受到土层变化的原因桩侧摩阻力临近深度并不明显,并且单位桩侧摩阻力出现明显的退化现象;桩土界面桩侧土压力的增长幅度与土层性质密切相关;孔隙水压力和超孔隙水压力的分布形式与土层的渗透性有关,基于水力压裂理论结合圆柱孔扩张理论推导的超孔隙水压力计算公式能较好地反映超孔隙水压力的分布特征;粉土层中有效径向土压力与单位桩侧摩阻力的比值为0.28左右,在粉质黏土层的比值为0.3,桩侧摩阻力的退化实质上是桩侧有效径向土压力的退化。