黏性土中大直径超长钻孔灌注桩承载性状及单桩沉降分析

ANALYSIS OF BEARING PROPERTIES OF LARGE-DIAMETER AND SUPER-LONG BORED PILE IN COHESIVE SOIL AND SINGLE PILE SETTLEMENT

基于太湖湖沼相沉积土地区某在建轨道交通工程的4根试桩现场静荷载和桩身应力测试试验,研究该地区大直径超长钻孔灌注桩竖向荷载下的侧、端阻力发挥特点,并利用一维杆系结构有限单元法与剪切位移法相耦合的混合法分析大直径超长钻孔灌注单桩沉降。研究结果表明:大直径超长钻孔灌注桩单桩受竖向荷载时,侧、端摩阻力发挥呈现从上到下逐步发挥的特点,且侧、端阻力非同步发挥,相互影响;侧摩阻力发挥极限值所需桩土相对位移为4~7 mm;应用可考虑桩周介质的非均质性、边界上剪切滑移非线性等复杂性质的有限元法和剪切位移法相耦合的混合法,可成功预测分析单桩沉降。

Based on the measuring data of static load test and pile stress measurement of 4 test piles in the rail transit engineering in Taihu lacustrine-swamp sedimentary soils area,the characteristics of skin friction and tip resistance of large-diameter and super-long bored piles in cohesive soil are analyzed. The hybrid method of finite element analysis of rod structure coupling with the shear displacement method for single pile is utilized to simulate and predict the single pile settlement. The test results show that,when the load on single pile is vertical,the skin friction and tip resistance of large-diameter and super-long bored pile in soil layer are gradually exerted from top to bottom;and the two above resistances do not play simultaneously but have mutual influence on each other. The pile-soil displacement is 4-7 mm when skin friction reaches to ultimate value. It is verified that the settlement calculation hybrid method in which the anisotropy of rock and soil around pile and nonlinearity of shear sliding on boundary are considered can predict the settlement of single pile successfully.