中文摘要：

最新工程案例表明,在基坑开挖前,现场预降水可引起支护墙发生显著初始侧移。依托工程实测资料,建立并验证了数值分析模型,通过一系列参数分析研究了软土地基渗透性条件对基坑开挖前预降水过程中支护墙侧移的影响规律及机制。结果表明,基坑预降水深度范围内土层渗透系数越大,渗透性各向异性越明显;在相同的预降水时间内,被降水土层中将会发生更大程度的孔隙水压力减小;在更强的墙-土界面总压力重分布下,预降水引起的支护墙侧移更大。预降水过程中支护墙侧移沿深度的分布范围与预降水深度底部及其以下土层渗透性有关,若为渗透性较差的深厚弱透水层,则当预降水深度位置不超过0.5倍该弱透水层厚度位置时,支护墙侧移将主要发生在预降水深度范围内;若为渗透性较好的透水层,预降水引起的支护墙侧移深度范围可能达到该层以下的另一弱透水层单元位置处。另外,当预降水深度底端紧邻透水性较好土层时,再增大预降水深度会引起支护墙发生较大增量的侧移,此时,应严防＂超降＂;当预降水深度底面以下为深厚弱透水层时,再增大预降水深度引起的支护墙侧移增量并不明显。

英文摘要：

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.