深厚软土地基锥形-有孔柱形组合管桩静压沉桩机制及沉桩效应研究

As the vertical reinforcement of composite ground，Pre-stressed Tubular Concrete piles are adapted to treat the deep soft soil ground, but the serious problems arise during the sinking-pile for the surroundings. In order to alleviate these negative effects, and improve the capacity of composite ground of rigid pile, the taper-cylinder with holes combined pipe-pile technique has been put forward. The key scientific problems of the sinking-pile penetration mechanism and the sinking-pile effect during the static sinking-pile have been covered closely in this research. By the use of the three methods of model test, theoretical analysis and numerical simulation, the pile-soil interaction mechanism of the taper-cylinder with holes combined pipe-pile has been researched during the static sinking-pile, especially, the change rules of the sinking-pile effects about both the space-time dissipation of excess pore water pressure and the displacement of soil during the static sinking-pile process of the taper-cylinder with holes combined pipe-pile. By introducing the parameters of pile diameter, hole diameter, depth and sinking-pile velocity，the penetration equations on the base of cavity expansion theory have been established during the static sinking pipe-pile with holes on the condition of three-dimensional axial symmetry,the analytic expressions of the expression of excess pore water pressure and the radius of plastic zone have been deduced. The simplified calculation of excess pore water pressure and soil displacement have also been perfected. The physical and mechanical indexes of the soil around the pile are studied before and after the static sinking pile.How such factors as taper angle, disposal-hole mode, hole diameter and hole distance affect the change rules of the sinking-pile effect has been studied. The main influence factors have been also analysed and its sensitivity. At last, the research aim has been achieved that the sinking-pile mechanism and the sinking-pile effect have been fully revealed for the taper-cylinder with holes combined pipe-pile in deep soft soil ground. The research results can establish the reliable base for the theoretical study of the composite ground of the taper-cylinder with holes combined pipe-pile, and its application in the future.

作为复合地基竖向增强体，混凝土管桩适合于处理深厚软土地基，但其静压沉桩效应将对周围环境产生严重影响。为减轻这种不利影响和提高复合地基承载力，提出锥形-有孔柱形组合管桩新技术。本项目紧紧围绕这种组合管桩静压沉桩贯入机制和沉桩效应等关键科学问题，采用模型试验、理论分析和数值模拟方法，研究这种组合管桩静压沉桩过程桩土相互作用内在机理，特别是超孔隙水压力时空消散、土体位移等沉桩效应变化规律；通过引入桩径、孔径、深度、沉桩速率等参数，建立三维轴对称条件下锥形-有孔柱形组合管桩静压沉桩贯入方程，推导出组合管桩静压沉桩超孔隙水压力、塑性区半径等解析表达式，完善超孔隙水压力和土体位移简化计算；研究静压沉桩前后桩周土体物理力学指标变化规律；研究沉桩效应变化规律的主要影响因素，并分析其敏感性；达到揭示锥形-有孔柱形组合管桩静压沉桩机制目的，为今后开展锥形-有孔柱形组合管桩复合地基理论研究及其应用奠定可靠基础。

本项目采用模型试验、理论分析和数值模拟方法，研究锥形-有孔柱形组合管桩静压沉桩机制和沉桩效应问题。基于圆孔扩张理论，推导出锥形-有孔柱形组合管桩超孔隙水压力与开孔孔径、径向距离、深度、沉桩速率关系之间的解析解。下沉深度相同时，超孔隙水压力随径向距离增加逐渐减小，随沉桩速率减慢而呈递减趋势；径向距离相同时，超孔隙水压力随深度加深逐渐增大，随沉桩速率加快而逐渐增大；相同的径向距离且同等深度处，超孔隙水压力随开孔孔径减小缓慢增大，说明开孔的孔径对锥形-有孔柱形组合管桩超孔压的影响较小。设计了7种锥形-有孔柱形组合管桩模型，进行了相应的室内模型试验。试验表明：这种组合管桩有很好的排水效果，桩周土体含水率在锥形-有孔柱形组合管桩静压沉桩后明显降低，土体含水率降幅随着沉桩位置中心径向距离和竖向深度的增加有所减小。随着径向距离增大，土体抗剪抗剪强度指标增幅减小，竖向深度方面中层土体抗剪强度指标增幅最为明显。在其它试验参数相同的情况下，双向对穿锥形-有孔柱形组合管桩静压沉桩后60h后桩周土体各项力学指标变化幅度最大，星状对穿开孔次之，单向对穿影响最小。桩身开孔数量越多，土体物理力学性质改变越明显。而在开孔方式、桩径大小相同的情况下，1/70锥度大小的锥形-有孔柱形组合管桩物理力学指标变化幅度相较于1/80、1/90锥度稍有提升，锥形-有孔柱形组合管桩在静压沉桩过程中能有效提高超孔隙水压力消散率。单根组合管桩静压沉桩时，在沉桩深度保持不变的情况下，随着测点离桩芯距离的增加，位移逐渐减小，最大影响范围约为9R（R为管桩半径）；随着管桩贯入软黏土的深度增加，桩周土体竖向位移越来越大。研究了桩间距、施工顺序、施工间歇期、开孔方式和桩数等主要因素对组合管桩群桩沉桩效应的影响，分析了其敏感性。通过本项目研究，达到揭示锥形-有孔柱形组合管桩静压沉桩机制目的，为今后开展锥形-有孔柱形组合管桩复合地基理论研究及其应用奠定可靠基础。