疏干降水引起坑后地面沉降的一种简化计算方法

Simplified analysis of settlement due to dewatering of foundation pits

在地下水位较高地区进行深基坑开挖,必须进行工程降水为开挖和施工提供干燥环境,大多数基坑位于浅层潜水层,疏干降水时在基坑周围形成地下水的降落漏斗,从而造成地基的不均匀固结沉降,对周围建筑物造成危害。降水(抽取地下水)引起地层压密而引起地面沉降是由于有效应力增加的结果,已经有较多的地面沉降计算理论。在忽略土体侧向变形的情况下,可以采用分层总和法计算地面沉降量,在裘布依假定的前提下求出基坑降水引起周围地下水位降落曲线方程,然后分别计算水位降落曲线以上和降落曲线以下地层的有效应力增量,在此基础上,采用分层总和法求出地面沉降量,同时考虑围护结构对地面沉降的约束作用,在经验假定的基础上利用剪切-位移关系求出其对地面沉降量的影响值,叠加后得到坑后地面沉降的计算公式,并结合工程实例进行计算,表明该方法具有较高的实用价值。

When excavating in the regions with high groundwater level,dewatering is necessary,and it can provide a dry environment for the excavation and construction.Most excavation lie in the phreatic water,so a depression-cone comes into being,which can bring the non-uniform consolidation settlement and is danger to the buildings around the excavation.The settlement due to the dewatering is the result of the increasing of the effective stress in the soil layer,many theories about the settlement calculation have been put forward.When the lateral displacement is ignored,the layer-wise summation method can be used to calculate the settlement.The equation of the cone of water-table depression was obtained on the supposition of Dupuit presupposition,so the increment of effective stress of the soil layers above and under the cone of water-table depression could be calculated,then the settlement could be calculated by the layer-wise summation method.The restriction to the settlement by diaphragm(pile) was also taken into account,the settlement influenced by the restriction of the diaphragm(pile) was calculated by use of the relationship of the shear-displacement on the experiential assumption,and the actual settlement was the sum of the both.The settlement of a foundation pit was obtained,showing that the simplified analysis is feasible.