【作者】 邓学支；

【导师】 卫龙武；

【作者基本信息】 东南大学 ， 岩土工程， 2006， 硕士

【摘要】 静压桩技术在我国很多地区得到了空前发展和广泛应用,但是静压桩的研究明显落后于应用。国内对静压桩的研究多采用与静力触探相类似的研究理论和方法,主要研究了静压桩的挤土效应,在一定程度上解决了静压桩施工对周围环境的影响问题。本文主要研究静压桩沉桩机理、压桩力与承载力计算及二者间的关系,这对于沉桩可能性、施工机具选择、压桩力和承载力估算等问题具有重要工程应用价值。论文的主要工作有:分析了粘性土和砂土层中的沉桩特性,比较了沉桩过程中平面圆孔扩张经典解答和空间圆柱形扩张解析解的优缺点,平面圆孔扩张解答推导简单,结果明了,但所求得的位移、应力和超孔压值与z坐标无关,显然与事实不符;空间圆柱形孔扩张归结为空间轴对称问题,考虑z轴方向的变化、τrz和土体自重的影响,但未对桩端和桩侧进行区分。有鉴于此,提出桩端用球形孔扩张、桩侧滑动摩擦计算模式来模拟沉桩过程来获取沉桩后在桩周产生的应力场是可行的。静压桩沉桩过程中超静孔隙水压力的产生和消散对沉桩施工、桩周土体再固结及其后承载力发展具有重要意义。本文系统地分析了国内外专家学者对沉桩引起的超孔隙水压力的研究情况,包括理论分析计算和实测经验总结,然后采用空间圆柱孔扩张理论的空间应力解答,根据Henkel超孔压公式,从理论上对弹性区和塑性区超孔压径向和竖向分布规律进行了分析。分析了桩侧和桩尖阻力的特性,假定土体为均质、各向同性的理想弹塑性材料,采用摩尔-库仑模型,根据球孔扩张理论求得其解析解,考虑桩身滑动摩擦,确定沉桩过程中不同深度压桩力计算公式,最后用有限元分析软件Ansys8.0对沉桩过程采用位移贯入法进行模拟和计算分析,分析(计算)结果与实际工程实测结果有较好的一致性。根据桩—土作用分析承载力的影响因素和规律,特别考虑了承载力的时间效应,分析归纳了静压桩承载力间效应现象、研究意义和估算方法。最后对于终压力与承载力关系,结合南京地区数个静压桩工程资料,用专业统计分析软件DPS定量或定性分析了二者间的影响因素,以期由终压力直接推算极限承载力。更多还原

【Abstract】 Jacked-in pile is being widely used in many region of our country, and its theory study lag behind its application. Domestic experts pay more attention to eliminate the geological environment influence caused by jacked-in pile’s soil compacting effect, some beneficial conclusions are obtained by adopting some theories and methods similar to CPT study. The mechanism of pile penetration, simulation and computation of resistance & the ultimate bearing capacity of jacked-in pile are be discussed, as well as their relations. Following are the main results in this paper.First, jacked-in pile penetration characteristic of cohesive soil and the sandy soil are analyzed, then giving the merits and faults between traditional plane Cavity Expansion Method(CEM) and spatial cylindrical CEM , it is put forward that the former reasoning simple, easy to be understood, but the displacement, stress and excess pore pressure obtained do nothing with the z coordinates, it’s obviously against with the fact, and the latter considers it as an spatial axisymmetric problem, which considering the change of z value along z axis direction, influence ofτrzand the soil self-weight, but neglecting the discrimination of pile end and the pile side. Taking into the above considerations, a simulation & computation pattern that spherical cavity expansion method and sliding friction are adopted to pile end and pile side respectively are proposed to get the stress field around pile, it’s proved to be feasible.The generation and dissipation of excess pore pressure during pile penetration are discussed in this paper, which have great significance of jacked-in pile’s installation, soil around pile’s reconsolidation and the bearing capacity development of pile. As well as domestic and international experts’study of excess pore pressure caused by pile jacking, including theory analysis, calculation and field survey. Then theoretical analysis of the law of excess pore pressure‘s radial and vertical distribution in the elastic and plastic zone are given by adopting the spatial stress answer of spatial cylinder cavity expansion, and formula according to Henkel excess pore pressure theory.According to the analysis of the trait of the resistance in the pile side and pile end , it is assumed that the soil is homogeneous , isotropic and perfect material of elasticity and plasticity. Mohr-Cloumb model is adopted in this paper. Then the analytic solve is got based on the cavity expansion method, And considering the sliding friction on the pile side , the calculating formula of pile jacking force is confirmed while the pile is in different depth. At last the process of pile jacking is simulated and calculated by using the displacement penetration method in FEM software Ansys8.0. The analysis result accords well to the project .更多还原