【作者】 白若虚；

【导师】 郑刚；

【作者基本信息】 天津大学 ， 结构工程， 2012， 硕士

【摘要】 深基坑工程中防治底部承压水突涌的问题逐渐成为一个非常严峻的课题。承压水问题处理难度大,并且处理不当可能造成极其严重的工程危害。因此,如何准确判断含承压水基坑的抗突涌稳定已越来越引起工程上的重视。目前已有的基坑抗突涌稳定计算理论主要有以下几种:压力平衡理论、均质连续梁、板分析法、带预应力均质连续梁、板分析法、均质连续体法、统计预测法等等,这些方法从不同角度研究基坑突涌破坏的机理,但是均存在一些不足或缺陷,对基坑突涌破坏的过程和破坏机理都没有深入认识。我们可以发现基坑突涌破坏和土石坝粘土心墙劈裂这两个不同工程领域现象的发生机理非常相似:都是存在高水压作用,都是在粘土层(弱透水层)产生渗漏通道,都是张拉破坏,两者发生都具有突然性,裂缝扩展过程与水力劈裂伸展的现象也非常相似,二者在发生机理、发生条件及计算方法方面应该存在共通之处。本文即借鉴土石坝粘土心墙的水力劈裂理论来解释基坑突涌破坏机理。为了观测基坑突涌破坏过程并验证突涌破坏机理,本文利用适用于研究粒状集合体的破裂和破裂发展问题、以及颗粒的流动(大位移)问题的微/细观力学程序颗粒流PFC(Particle Flow Code)建立数值模型。通过一系列参数分析和试验,最终实现模拟基坑突涌的全过程。更多还原

【Abstract】 Protecting from Bottom piping in deep foundation pit engineering has been gradually a very severe subject. It is difficult to solve the problem connected with confined water, and it might cause great damage to the project if the solution is not proper. Hence, how to estimate exactly the stability of anti-bottom-piping of foundation pit under the confined water becomes more and more important. The existing calculation theories of stability of anti-piping for foundation pit are summarized as followed: simple balance of the water pressure and the soil’s weight, considering the shearing and cementation strength of soil, considering the stiffness of the pit, overall consideration of the stiffness and the strength of the pit and statistics and anticipation based on neural network model. These methods have studied the mechanism of piping in different views, but all of them have some drawbacks and have not acquired a clear and deeply acknowledge to the mechanism of piping.We can find that the bottom piping of foundation pit and the hydraulic fracturing of clay core in fill dam, which are two different engineering fields’phenomenon, is very similar in their mechanism. They both have the existence of high water pressure; have formed leak path in clay pan (low permeable layer) and broken due to tension. They both happen abruptly and the phenomenon of crack progressing and hydraulic fracture extension is exactly similar. Therefore there must be some common properties in their occurrence mechanism and condition and calculation method. In this paper, we are attempting to use the hydraulic fracture theory in fill dam engineering for reference to explain the mechanism of piping in foundation pit.To observe the failure process of piping and verify the mechanism, we will use PFC (Particle Flow Code), which is suitable for studying problem with flow (large deformation) and fracture, to build numerical model. We will eventually achieve the simulation of the entire process of piping via a series of parameter analysis and test.更多还原