基于桩土界面应力测试的开闭口桩静力沉桩室内试验对比研究

Laboratory test comparative study on open-close piles during jacked pile-jacking based on pile-soil interface stress measurement

为了探究黏性土中静力沉桩力学机制,开展饱和黏性土中开口桩和闭口桩静力沉桩大型室内模型试验,获得开口桩和闭口桩静力沉桩引起的桩土界面超孔压和土压力的变化规律。同时,根据有效应力原理计算桩土界面有效土压力,将有效土压力与水平自重应力之比视为桩土之间的贴紧系数,建立静力沉桩过程中桩土之间贴紧程度的判定方法。研究结果表明:闭口桩桩土界面超孔压和土压力比开口桩的大,随着桩身贯入深度的增加,开口桩和闭口桩桩土界面超孔压和土压力逐渐增大,且距离桩端越近,桩土界面超孔压与土压力越大;在相同深度处,开口桩和闭口桩桩土界面土压力和有效土压力均存在"侧压力退化"的现象;入土深度越大,桩土之间的贴紧系数越大,桩土之间的贴紧程度越高。桩土之间贴紧程度的判定与沉桩引起的超孔压和土压力相关,判定结果较好地反映了饱和黏性土中静力沉桩的力学机制。

In order to explore the mechanical mechanism of pile-jacking in clay soil,a large-scale laboratory model test of pile-jacking in open and closed pile in saturated clay soil was carried out,and the change law of excess pore pressure and earth pressure at pile-soil interface caused by pile-jacking in open and closed pile was obtained.At the same time,the effective earth pressure at the pile-soil interface was calculated according to the principle of effective stress,and the ratio of effective earth pressure to horizontal dead weight stress was regarded as the adhesion coefficient between pile and soil,and the determination method of the degree of adhesion between pile and soil during pile jacking was established.The results show that the excess pore water pressure and earth pressure at the pile-soil interface of closed pile are larger than that at the open pile.With the increase of pile depth,the excess pore water pressure and earth pressure of open-close piles at the pile-soil interface increase gradually,and the closer the pile is to the pile end,the greater the excess pore water pressure and earth pressure at the pilesoil interface are.The phenomenon of"lateral pressure degradation"exists in the earth pressure and effective earth pressure of open and closed pile interface at the same depth.The greater the depth of burial,the greater the coefficient of adhesion between piles and soil,and the higher the degree of adhesion between piles and soil.The determination of the degree of adhesion between piles and soils is related to the excess pore water pressure and earth pressure caused by jacking piles,which reflects the mechanical mechanism of jacking piles in saturated clay.