失效桩基原因分析与处理方案

通过对南宁盆地泥岩上某失效桩基工程7根桩静载试验结果的综合评定,认为规范规定的单桩竖向极限承载力统计值按照依次去掉高值后取平均,直至满足极差不超过30%的条件,不利于充分发挥桩基的承载力,按工程的特点与荷载等对失效桩基工程进行处理,并按变形进行控制是可行的办法。同时根据南宁盆地泥岩的物质组成、工程特性和力学性质具有的特殊性和复杂性,如独特的互层性地层构造使泥岩软硬相间难以进行风化带划分,在包括水、岩相互作用、机械扰动及时间效应等各种不确定因素的作用下,泥岩地基上的钻孔桩失效的概率比较高的特点,对泥岩地基工程桩基失效与泥岩的诸多特殊工程性质进行分析,指出桩基承载力不足是由于桩端与嵌岩段泥岩承载力下降造成的。钻孔桩成功与否并不因为桩端承载力取值低而会得到保证。

FAILURE CAUSE ANALYSIS OF A AXIAL CAPACITY BORING PILE FOUNDATION ENGINEERING AND TREATMENT SCHEME

After comprehensive assessing on seven static loading tests results of one failure piles engineering on mudstone subgrade in Nanning basin,the criterion,whose statistical value of axial single pile ultimate capacity adopts the average value after cancelling the peak value in turn until satisfy the condition that the relative difference between the peak value and minimum value won't exceed 30 percent,is pointed that do not make enough use of piles potential bearing capacity.And it is a feasible way to treat the failure piles engineering problem by deformation control based on structural properties and loading and main factor of piles failure on the mudstone foundation is brought about by the decline of pile point capacity and pile side friction embedded in rock,which makes the piles bearing capacity deficient,which is also approved in the laboratory model test.Therefore,the success of boring pile will not only rely on adopting very low value of pile's bearing capacity and pile side friction embedded in rock in piles foundation design.