红黏土地区深基坑变形特性的时空效应研究

为消除地下空间施工安全隐患,针对人为诱导作用下深基坑施工过程中产生的沉降变形问题,研究红黏土地区深基坑施工监测与变形特性的规律。通过在深基坑开挖和拆撑施工过程中对支护结构水平、竖向位移,深层水平位移、内支撑轴力、地下水位和孔隙水压力等进行监测,对高层建筑深基坑变形监测的工作流程、监测方法及监测数据等进行研究。结果表明:特殊的红黏土大型深基坑工程受分步和分阶段开挖作用的综合影响,基坑开挖扰动作用的范围和程度极大不同。伴随基坑开挖力度的加深,基坑坑顶水平位移、竖向沉降位移、周边建筑物沉降位移等均逐步增大,直至基坑开挖至基底后,累积变化数值将稳定于某一具体数值。基坑的开挖导致的周边土体应力释放,同时基坑底部由于上部土体的严重卸荷导致的底部土体产生隆起,致使基坑周围土体进一步向基坑应力损伤方向滑移,为加重地表沉降、水平位移及坑底隆起等不良工程问题的主要原因;孔隙水压力随基坑开挖沿深度基本呈线性变化,时间越长,孔隙水压力值越小,且稳定在某一具体区间内,这与地下水位的补给和基坑底部的土体物理力学参数的规律性变化相关。

Study on temporal-spatial effect of deformation characteristics of deep foundation pit in red clay soil region

In order to eliminate the potential safety hazards of the construction in underground space，the laws of the construction monitoring and the deformation characteristics of the deep foundation pit in red clay region are studied herein for the settlement deformation occurred during the construction of deep foundation pit under the artificial inductive effect． Through the monitorings of the horizontal and vertical displacements of the supporting structures，the deep horizaontal displacement，the internal support axial force，the groundwater level，the pore water pressure，etc． during the excavation and the support removing of deep foundation pit，the working processes，the monitoring methods and the monitoring data of the deformation monitorings of the deep foundation pit for high-rise buildings are studied． The results show that the special large-scale red clay deep foundation pit project is comprehensively influenced by the effects of the staged and phased excavations，for which the range and degree of the disturbing effect from the foundation pit excavation are quite different． Along with the increase of the excavation strength，the horizontal displacement at the top of foundation pit，the vertical displacement，the settlement displacements of the surrounding buildings are all gradually increased and the accumulative changing values are to be stabilized at certain specific values until the foundation pit being excavated to the pit floor． The stress release of the surrounding soil mass caused by the foundation pit excavation and the pit bottom soil mass upheaval caused by the serious unloading of the upper soil mass lead to the further slipping of the soil mass around the foundation pit towards to the direction of stress damage，which are the main causations to worsen the undesirable engineering problems of the surface settlement，horizaontal displacement，pit bottom soil mass upheaval，etc． ，while the pore water pressure basically exhibits a linear change along the excavation depth of foundation pit，for which the longer the time is，the smaller the pore water pressure value is to be and is to be stabilized within a specific interval，which is related to regular changes of groundwater recharge and the physical and mechanical parameters of the soil mass at the bottom of foundation pit．