关键词: 深基坑预降水, 支护墙侧移, 软土地基, 有限元计算, 土层渗透性

Abstract: Recently, field data shows that considerable wall deflection can be induced by pre-excavation dewatering. A numerical model was established and verified based on field data, and a parametric study was carried out to investigate the effect of soil permeability on wall deflection. The results indicate that the wall deflection, in a prescribed dewatering time, will be more obvious with the better soil permeability, the larger anisotropy coefficient of soil permeability within the dewatering depth. That is because, in this case, greater pore pressure decrease will appear at the soil layers, and larger total stress redistribution will appear at the soil-wall interface. Moreover, the depth of wall deflection has relation with the permeability of soil below the bottom of dewatering depth. If the soil below the bottom of dewatering depth is aquiclude and the center of the aquiclude thickness is deeper than the dewatering depth, the wall deflection will roughly appear within the dewatering depth. If the soil below the bottom of dewatering depth is well-drained soils, the wall deflection may reach the location of another aquiclude below the well-drained soils. Besides, when dewatering wells enter the well-drained soils, greater deflection increment will occur with the dewatering depth increase, and over dewatering should be avoided strictly. However, when thick and poorly drained soils appear below the bottom of dewatering depth, wall deflection increment induced by increasing dewatering depth is not apparent.

Key words: pre-excavation dewatering of deep foundation pit, wall deflection, soft ground, finite element calculation, soil permeability