黏土-砂交互地层沉井下沉阻力研究

Research on Caisson Sinking Resistance in Clay-Sand Intersected Stratum

为明确交互地层中沉井下沉阻力特征,以常泰长江大桥6号墩沉井基础为背景,基于实测数据对黏土-砂交互式地层中大型沉井下沉过程中的刃脚踏面反力、侧壁压力及侧摩阻力的大小与分布规律进行研究。结果表明:沉井下沉阻力集中在外圈井壁,外圈井壁刃脚踏面反力与踏面埋置深度的相关性较高,且受沉井自重的影响显著,因下部粉质黏土层与粉砂、细砂层的极限承载力相当,随沉井底口由砂土层进入粉质黏土层,外圈井壁刃脚踏面反力均值并无显著变化;在第2次浇筑井壁混凝土阶段,沉井底面位于粉砂、细砂层与下部粉质黏土层分界面,随着沉井自重增大,砂土层内的刃脚踏面反力显著增加,粉质黏土层内的刃脚踏面反力因受土层的超孔隙水压力消散的影响反而有所减小;刃脚踏面由砂层进入粉质黏土层后,位于砂土层内的沉井侧壁压力及下沉侧摩阻力显著增大。

Based on the construction of the caisson foundation of pier No.6 of Changtai Changjiang River Bridge,the characteristics of caisson sinking resistance in the clay-sand intersected stratum are studied.The monitored data of upthrust force at the tip of the cutting toe,pressure imposed on caisson surfaces and lateral friction as well as the distribution law of lateral friction were analyzed.The results show that the resistance during caisson sinking concentrates on the outer caisson walls,the upthrust forces at the tip of the cutting toe of the outer caisson wall is highly correlated with the burying depth of the tip,and also the selfweight of the caisson.Due to that the ultimate load bearing capacity of the silty clay stratum is equivalent to that of the silty sand stratum and the fine sand stratum,as the bottom of the caisson is going through the silty sand stratum into the silty clay stratum,the average upthrust force at the tip of the cutting toe of the outer caisson wall shows no significant variation.During the second-phase caisson wall concreting,the caisson base was located at the interface of the silty clay stratum and the overlying silty sand and fine sand strata,the upthrust force at the tip of the cutting toe in the sand stratum significantly increased as the selfweight of the caisson rose,whereas the upthrust force at the tip of the cutting toe in the silty clay stratum decreased on account of the loss of the excess pore water pressure.Once the tip of the cutting toe entered the silty clay stratum,the caisson walls in the sand stratum endured larger pressure and the lateral friction significantly increased.