【作者】 梁超；

【导师】 刘齐建； 万智；

【作者基本信息】 湖南大学 ， 土木水利， 2023， 硕士

【摘要】 桩锚支护结构是一种常见的基坑支护形式,因其独特优势,目前已被广泛应用于复杂深基坑支护。新建建筑基坑附近存在地下室、建筑群桩等地下结构时,支护桩与邻近地下结构之间形成多层有限土体。传统基坑支护设计采用基于半无限土体的主动土压力会使得支护结构设计偏保守。因此,对多层有限土体主动土压力进行研究具有重要意义。此外,对于邻近桩基础建筑的桩锚支护基坑,基坑开挖对周围造成的影响如何,开挖过程中支护桩与建筑桩的响应情况也有待研究。本文首先根据长沙市某桩锚支护基坑工程,提出了刚性挡墙平动模式下多层有限土体主动土压力计算模型,推导出多层有限土体主动土压力计算理论,探究了土体参数变化对多层有限土体主动土压力分布的影响。其次,建立成层有限土体土压力作用下的桩锚结构受力变形计算模型,利用传递矩阵法和Laplace变换求解支护桩受力和变形。然后,采用数值方法探究桩锚支护结构参数及建筑群桩参数变化对支护桩和建筑桩的影响。最后,对长沙市某桩锚支护基坑开挖过程开展了工程实践。本文通过上述研究,获得如下结论:(1)多层有限土体主动土压力随着土体宽深比的增大而增大,但主动土压力的增长幅度会随宽深比的增大而逐渐减小;土的内摩擦角、墙土界面摩擦角、土的黏聚力的增大均会使多层有限土体主动土压力减小;墙土界面摩擦角的变化会影响有限土体主动土压力分布的非线性程度,即当墙土界面摩擦角越大,有限土体主动土压力分布曲线的弯曲弧度越大。(2)本文提出了多层有限土体作用下的支护桩受力变形计算理论,可以准确预测支护桩桩顶最大位移,能够对复杂地层下基坑支护桩的桩身受力变形进行计算。(3)在紧群桩基础的桩锚支护体系中,提高锚索预应力、增大建筑桩直径、增加建筑桩桩长和增加建筑桩密度,均有利于提高建筑群桩基础整体的挡土效果,减小支护桩和建筑桩的水平位移变形。但单纯增大支护桩桩径对减小支护桩桩身位移效果不好。距离基坑越近,建筑桩鼓曲变形现象越明显。当建筑桩的桩长较短时,群桩基础底部压力会使支护桩的桩身位移和弯矩显著增大。(4)长沙市某桩锚支护基坑开挖过程中,支护桩桩顶最大水平位移和沉降均在控制值范围内,但部分建筑沉降较大。长沙市某紧邻群桩基础建筑桩锚支护基坑开挖过程中会影响基坑周围环境,但施工现场的出现突发情况且不及时采取措施所造成的破坏性影响更严重。在本工程中,采用水循环全套管跟管钻进法进行锚索施工是可行的,并取得了较好的施工效果。更多还原

【Abstract】 The pile-anchor support structure is a common form of excavation support,and it has been widely used in complex deep foundation support because of its unique advantages.When underground structures such as basement and building group piles exist near the foundation pit of a new building,a multi-layer finite soil is formed between the supporting piles and the adjacent underground structures.The use of a traditional excavation support design based on the active soil pressure of semi-infinite soil will result in a conservative sup port structure design.Therefore,studying the active soil pressure of multi-layer finite soil is of great significance.In addition,for pile anchor supported pits adjacent to pile foundation buildings,how the excavation of the pit affects the surrounding area and the response of the supporting piles to the building piles during the excavation also needs to be studied.This paper proposes a calculation model for the active soil pressure of multi-layer finite-width soil under the rigid retaining wall slidi ng mode based on the Changsha pile-supported excavation project.The calculation theory of active soil pressure of multi-layer finite viscosity and multi-layer finite viscosity-free soil is derived,and the influence of changes in soil parameters on the di stribution of active soil pressure in multi-layer finite soil is explored.Secondly,the calculation model of the force and deformation of the pile-anchor structure under the action of layered finite soil pressure is established.The transfer matrix method and Laplace transform are used to solve the force and deformation of the supporting pile.Then,numerical methods are used to investigate the influence of pile-anchor support structure parameters and building pile parameters on the support pile and buildi ng pile.Finally,engineering practice was carried out on the excavation process of a pile-anchor supported foundation pit in Changsha.In this paper,the following conclusions were obtained from the above study :(1)The active soil pressure of multi-layered finite soil increases with increasing soil width-to-depth ratio,but the growth rate of active soil pressure gradually decreases with increasing width-to-depth ratio.The increase of the internal friction angle of the soil,the wall-soil interface friction angle,and the soil cohesion will decrease the active soil pressure of the multi-layered finite soil.The change of wall-soil interface friction angle affects finite soil’s nonlinear degree of active soil pressur e distribution,that is,when the angle of friction at the interface between the wall and the soil is larger,the arc of curvature of the active earth pressure distribution curve of the finite soil is larger.(2)This paper proposes a theory for calculatin g the force deformation of supporting piles under the action of multi-layer finite soil,which can accurately predict the maximum displacement of the top of supporting piles and can calculate the force deformation of piles supported by foundation piles und er complex strata.(3)In the pile-anchor support system of an adjacent existing pile foundation,increasing the pre-stress of the anchor cable,increasing the diameter of the building pile,increasing the length of the building pile,and increasing the density of the building pile is beneficial to improve the soil retention effect of the building pile foundation as a whole and reduce the horizontal displacement and deformation of the support pile and building pile.However,simply increasing the diameter of the support pile is not effective in reducing the displacement of the support pile.The closer to the foundation pit,the more obvious the building pile bulge deformation phenomenon.When the pile length of the construction pile is short,the bottom pressure of the group pile foundation will cause the pile displacement and bending moment of the supporting pile to increase significantly.(4)During the excavation process of the pile-anchor support excavation project in Changsha,the maximum horizontal displacement and settlement of the support pile top are within the control range,but the settlement of some buildings is large.The excavation process of the pile-anchor support excavation project of an adjacent existing pile foundation building pile in Changsha will affect the surrounding environment of the pit,but the destructive impact caused by emergencies that occur during the construction process and are not dealt with promptly is more serious.In this project,it is feasible to use the water circulation full set of pipe following drilling method for anchor cable construction,and has achieved good construction results.更多还原