深厚软土狭长基坑地连墙变形特性

Deformation Characteristics of Diaphragm Wall in Deep andNarrow Foundation Pit in Soft Soil

为研究南沙港地区软土深基坑内支撑式地连墙变形特性,以广州南沙港铁路明挖隧道深基坑为工程背景,通过大量实测数据统计分析,对比已有研究成果,探讨狭长基坑开挖墙体测斜、墙后地表沉降及其因素影响。结果表明:墙体测斜呈“两头小、中间大”的内凸型,最大侧移量主要分布在20~35 mm,占比高达83.6%,最大侧移变化范围为(0.07%H,0.38%H),平均值为0.22%H,相比宽大基坑的墙体抗侧移变形能力要强,其中H为基坑开挖深度。墙体最大侧移所在位置深度范围为(H-6,H+3),且大多数位于开挖面附近,墙体侧移主要影响深度范围约为2H,深度效应显著。墙后地表沉降主要影响范围为(0.17δ_(hm),1.60δ_(hm)),平均值为0.864δ_(hm),其中δ_(hm)为墙体最大侧移量。墙体最大侧移随墙底以上软土厚度增加呈缓慢增长趋势,随插入比和支撑刚度的增大而缓慢减小,当插入比和支撑刚度超出某一量值,继续增加对墙体变形控制无明显作用。可见,合理的围护体系设计对基坑变形控制至关重要。

In order to study the deformation characteristics of the diaphragm wall with internal bracing in the deep foundation pit of soft soil in Nansha Port area,based on the measured data of the deep foundation pit of the open cut tunnel of Guangzhou Nansha Port Railway and existing research results,the diaphragm wall inclination measurement of the narrow and long foundation pit,the ground settlement behind the diaphragm wall and its influence factors were discussed.The results show that the distribution of diaphragm wall inclination shows a convex shape of“small at both ends and large in the middle”,the maximum lateral displacement is mainly distributed in 20~35 mm,accounting for 83.6%,the maximum lateral displacement range is(0.07%H,0.38%H),with an average value of 0.22%H,where H is the excavation depth of the foundation pit,compared with the diaphragm wall of a wide foundation pit,the diaphragm wall of the narrow and long foundation pit has a stronger resistance to lateral displacement deformation.The depth range of the maximum lateral displacement of the wall is(H-6,H+3),and most of them are located near the excavation face,and the main influence depth range of diaphragm wall deformation is about 2 H,showing a significant depth effect.The main influence range of surface settlement behind the diaphragm wall is(0.17δhm,1.60δhm),and the average value is 0.864δhm,whereδhm is the maximum lateral displacement of the diaphragm wall.The maximum lateral displacement of the diaphragm wall increases slowly with the increase of the thickness of the soft soil above the diaphragm wall bottom,and decreases slowly with the increase of the insertion ratio and the support stiffness.When the insertion ratio and the support stiffness exceed a certain value,further increase has no obvious effect on the diaphragm wall deformation control.It can be seen that a reasonable design of the enclosure system is crucial to the deformation control of the foundation pit.