支护桩桩间临空土体破坏机理与稳定性分析方法

发布时间：2018-09-09 18:11

【摘要】：在众多类型的支挡结构中,支护桩因侧向抗力大、施工方便、对周边地质体扰动相对较小等优点,被广泛应用于各类边坡治理、基坑支护工程中。支护桩是一种水平方向不连续的支挡结构,这种不连续的目的一方面在于合理利用土体的自承能力;另一方面使其可以有较深的嵌固段,从而将荷载传递至相对稳定的深部地层中。当支护桩存在临空段时,如何确保桩间临空土体的稳定性成为工程技术人员需要解决的问题。国内外学者针对支护桩等非连续挡土系统开展了卓有成效的研究,但关于桩间临空土体局部破坏现象的研究尚不充分,对桩间临空土体局部破坏机理及影响因素的认识并不全面,而且缺乏便于工程应用的桩间临空土体稳定性分析方法。本文采用理论分析、数值模拟和振动台模型试验手段对相邻两支护桩间临空土体破坏机理和稳定性分析方法展开研究,主要内容及成果包括:①从工程案例和模型试验现象入手,归纳出桩间临空土体的三种破坏模式,并对每种破坏模式的诱发因素、形成机制、识别特征、工程应对措施进行论述,为系统研究桩间临空土体破坏规律和机理、有针对性地建立桩间临空土体稳定性分析方法奠定基础。②基于力学分析方法获得土体中支护应力场的空间分布规律;根据支护作用的发生机制和支护应力场的不均匀特性,将被支护土体分为“直接约束区”和“间接约束区”两部分,从应力扩散和土拱效应的角度研究了“间接约束区”土体的力学特征;提出桩间临空土体潜在局部破坏区域的界定方法。③在综合考虑土体应变局部化特性和剪切带扩展机理的基础上,分析了桩间三维滑动土楔的形成机制,建立了一种空间滑动楔形体模型;提出桩间临空土体稳定性评价指标体系与相应的判据;针对桩间临空土体滑塌失稳破坏模式,基于能量平衡原理和极限分析上限定理提出一种能够考虑地震作用的桩间临空土体稳定性分析方法;采用三维有限差分法结合强度折减法获得了桩间临空土体稳定性系数数值解。④采用单一变量法研究了桩间临空面几何尺寸、被支护土体强度参数以及地震作用对桩间临空土体稳定性的影响;对理论计算结果和数值模拟结果进行了详细对比,明确了两种方法的适用范围。研究发现,桩间临空土体稳定性系数随着土体黏聚力、内摩擦角的增大而增大;随着桩间临空面宽度的增大而降低,但下降的趋势逐渐变缓;随着临空面高度的增大而降低,且降低的趋势逐渐减缓。当临空面高宽比位于4/1~1/1区间时,三维理论分析方法得到的临空土体稳定性系数随桩间临空面几何尺寸、被支护土体强度参数的变化规律与三维有限差分法数值模拟结果基本保持一致,且略偏于安全。⑤采用拟静力法研究了水平地震作用与竖向地震作用对桩间临空土体稳定性的影响。研究发现,水平地震作用与竖向地震作用均会降低桩间临空土体的稳定性;同时考虑水平地震作用与竖向地震作用时求得的桩间临空土体地震稳定性系数小于单独考虑水平地震作用或竖向地震作用时求得的地震稳定性系数;不论是桩间临空面宽度增大或是临空面高度增大,桩间临空土体地震屈服加速度系数均有所降低。⑥考虑到拟静力法将地震过程用施加在滑动土楔上的惯性力来表征,存在高估或低估地震作用的可能,进一步采用小型精密地震模拟振动台系统和自行开发的刚性边界支护桩模型试验装置开展了共计40组破坏性试验,探究了桩间临空土体动力破坏特征,以及临空面高度、临空面宽度、土体强度参数、地震波峰值加速度、加载波形等因素对桩间临空土体动力破坏性状的影响,并将试验结果与理论分析结果进行了对比。
[Abstract]:In many types of retaining structures, retaining piles are widely used in slope treatment because of their large lateral resistance, convenient construction and relatively small disturbance to surrounding geological bodies. On the other hand, it can have a deeper embedded section, so that the load can be transferred to a relatively stable deep stratum. How to ensure the stability of the empty soil between piles becomes a problem that engineers and technicians need to solve. However, the research on the local failure of the soil between piles is still insufficient. The understanding of the mechanism and influencing factors of the local failure of the soil between piles is incomplete, and the stability analysis method of the soil between piles is lacking. In this paper, theoretical analysis, numerical simulation and shaking table model test methods are used. The failure mechanism and stability analysis method of the aerial soil between adjacent two supporting piles are studied. The main contents and achievements include: (1) Starting with engineering cases and model test phenomena, three failure modes of the aerial soil between piles are summarized, and the inducing factors of each failure mode, forming mechanism, identifying characteristics and engineering countermeasures are discussed. In order to systematically study the failure law and mechanism of the soil near the empty between piles, the stability analysis method of the soil near the empty between piles is established. The soil mass is divided into two parts: the direct restraint zone and the indirect restraint zone. The mechanical characteristics of the soil mass in the indirect restraint zone are studied from the point of stress diffusion and soil arching effect. On the basis of the analysis of the formation mechanism of the three-dimensional sliding soil wedge between piles, a spatial sliding wedge model is established, and the evaluation index system and corresponding criteria for the stability of the soil in the air between piles are proposed. In this paper, the stability analysis method of the soil between piles is used, and the numerical solution of the stability coefficient of the soil between piles is obtained by using the three-dimensional finite difference method and the strength reduction method. It is found that the coefficient of stability increases with the increase of soil cohesion and internal friction angle, decreases with the increase of the width of the free surface between piles, but the decreasing trend gradually slows down with the increase of the height of the free surface between piles. When the ratio of height to width is in the range of 4/1~1/1, the stability coefficient of the soil near the empty surface obtained by the three-dimensional theoretical analysis method is in accordance with the geometric size of the empty surface between piles, and the variation law of the strength parameters of the retained soil is basically consistent with the numerical simulation results of the three-dimensional finite difference method, and is slightly safe. Quasi-static method is used to study the influence of horizontal and vertical seismic action on the stability of the soil near the pile space.It is found that both horizontal and vertical seismic action can reduce the stability of the soil near the pile space. The qualitative coefficient is smaller than the seismic stability coefficient obtained when the horizontal or vertical seismic action is considered alone; the seismic yield acceleration coefficient of the empty soil between piles decreases with the increase of the width of the empty surface or the height of the empty surface. Inertia force indicates that there is the possibility of overestimating or underestimating earthquake action. A total of 40 groups of destructive tests were carried out by using a small precision shaking table system and a self-developed rigid boundary supporting pile model test device. The characteristics of dynamic failure of the soil near the pile, as well as the height, width and width of the soil near the pile, were investigated. The influence of strength parameters, peak acceleration of seismic wave, loading waveform and other factors on the dynamic destructive behavior of aerial soil between piles is studied. The experimental results are compared with the theoretical results.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU473.1

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