陡坡与桥梁桩基相互影响及稳定性分析

发布时间：2018-10-23 15:23

【摘要】：陡坡段双桩柱式桥梁与平地常规桥梁的基桩相比,在受荷机理和受力情况上都有很大的差异,基桩受到陡坡土体传递来的横向荷载及桩顶组合荷载的共同作用,同时桩身对桩侧岩土体产生抗力,构成繁杂的陡坡土体-基桩互相影响的系统。本文结合江西省交通运输厅科技项目(编号:2016C0006)进行双桩柱式桥梁的基桩对陡坡安全性及桩身屈曲稳定性的研究。(1)对于陡坡段的均质岩土体,构建一个陡坡岩土体与双桩柱式桥墩及横梁的计算模型,分析其受力情况得出系统势能,并基于最小势能理论可得到下滑土体发生位移后达到稳定时产生的虚位移,以此计算安全系数用于评价陡坡稳定性。在系统总势能中,本文着重考虑了双桩柱式桥墩及横梁的应变能及桩土摩擦的能量。研究表明,本文结果稍大于边坡安全系数,说明双桩柱式桥墩对陡坡安全性是有利影响。在对陡坡安全性系数进行敏感性分析中,发现弹性模量对安全系数的增长影响不大;桩径增大,桩土相互作用面积增大,导致安全系数增大;将基桩布置于坡顶至跛脚水平距离一半的位置时安全系数最大,此位置两侧布置安全系数逐渐减小;陡坡段土体粘聚力和内摩擦角增大,陡坡安全系数随之增大。(2)通过改进的遗传算法对临界滑裂面进行确定。通过五个参数进行控制所构建的三维椭球面,以安全系数作为目标函数,计算最小安全系数所对应的参数最优值构成的最危险滑移面,完成滑移面搜索。为避免局部最优解情况,本文采用优化后的遗传算法进行操作,即通过加入小生境技术,极大限度的避免了局部最优解的出现,保证了搜索滑裂面结果的可靠性。通过在设定区域范围内改变参数进行搜索,结果表明参数对滑移面的形状影响并不大。(3)对于陡坡段桥梁基桩容易发生屈曲稳定的问题,通过滑移面与基桩的模型确定不同受荷类型区域长度,并根据每段受力情况计算包括桩身自重产生能量在内的系统能量,基于能量法可求变分特征方程特征根,得出一种用桩身临界荷载判断桩身屈曲稳定性的方法。通过对桩身屈曲稳定敏感性研究,发现嵌固段长度增长,临界荷载增大;在桩身自由段长度过长和桩径过小的情况下,基桩极易发生屈曲稳定性破坏。
[Abstract]:Compared with the foundation pile of the conventional bridge on the flat ground, there are great differences in the mechanism of loading and the stress on the foundation pile in the steep slope. The pile is subjected to the lateral load transmitted by the steep slope soil and the combined load on the top of the pile. At the same time, the pile body has the resistance to the soil on the side of the pile, forming a complicated system of interaction between the steep slope soil and the foundation pile. In this paper, the safety and buckling stability of foundation piles of double-piling bridge on steep slopes are studied in conjunction with the Science and Technology Project of Jiangxi Provincial Communications and Transportation Department (No. 2016C0006). (1) for homogeneous rock and soil mass in steep slope, A calculation model of steep slope rock soil and double pile column bridge piers and beams is constructed, and the system potential energy is obtained by analyzing its stress. Based on the theory of minimum potential energy, the fictitious displacement of sliding soil can be obtained when the displacement is stable. The safety factor is calculated to evaluate the stability of steep slope. In the total potential energy of the system, the strain energy of piers and beams and the energy of pile-soil friction are considered in this paper. The results show that the safety factor of the slope is slightly larger than that of the bridge piers, which indicates that the double-piling bridge piers have a beneficial effect on the safety of steep slopes. In the sensitivity analysis of the safety coefficient of steep slope, it is found that the elastic modulus has little effect on the increase of safety factor, and the increase of pile diameter and pile-soil interaction area leads to the increase of safety factor. When the pile is arranged at the half of the horizontal distance from the top of the slope to the crippling foot, the safety factor is maximum, and the safety factor on both sides of the position decreases gradually, and the cohesive force and the angle of internal friction of the soil in the steep slope increase. The safety factor of steep slope increases accordingly. (2) the critical slip surface is determined by improved genetic algorithm. The three dimensional ellipsoid is controlled by five parameters and the safety factor is taken as the objective function to calculate the most dangerous slip surface formed by the optimum value of the parameters corresponding to the minimum safety factor and to complete the search of the slip surface. In order to avoid the situation of local optimal solution, this paper uses the optimized genetic algorithm to operate, that is, by adding niche technology, the appearance of local optimal solution is avoided to a great extent, and the reliability of the result of searching slip surface is ensured. The results show that the parameters have little effect on the shape of slip plane. (3) for the bridge pile in steep slope section, buckling stability is easy to occur. Based on the model of sliding plane and pile, the length of different types of load is determined, and the system energy, including the energy generated by pile weight, is calculated according to the stress condition of each section, and the characteristic root of variational characteristic equation is obtained based on energy method. A method for judging the buckling stability of pile body by critical load is obtained. Through the study of the stability sensitivity of pile buckling, it is found that the length of the fixed block increases and the critical load increases, and the buckling stability of the pile is easily destroyed when the length of the free section of the pile is too long and the diameter of the pile is too small.
【学位授予单位】：江西理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U443.15

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