西安地铁穿越地裂缝的抽水试验研究

查清地裂缝水文地质情况可以为西安地铁设计和施工提供科学依据。根据西安地铁勘察工作需要,2008年7月～9月选择地裂缝穿过的西安市劳动路小学院内场地首次尝试进行跨地裂缝水文地质专项现场试验。试验内容包括试坑渗水试验、钻孔注水和抽水试验,并以1号抽水井的稳定流抽水试验为典型,研究地裂缝对地下水渗流的影响。采用带1个观测孔的稳定流潜水完整井公式、带2个观测孔的稳定流潜水完整井公式以及潜水完整井水位恢复速度计算公式等3个渗透系数计算方法,得到了地表浅层土体沿地裂缝走向和垂直于地裂缝走向的渗透系数,分析了渗透系数的差异性;最后利用MADIS有限元软件模拟场地内建筑物对地基土施加应力,探讨了建筑物对场地土体的影响。结果表明:利用上述3个公式计算,都得到沿地裂缝方向土体的渗透系数比垂直地裂缝方向的土体稍大;在同一落程中,利用潜水完整井水位恢复速度公式计算得到的渗透系数最大,利用带2个观测孔的稳定流潜水完整井公式计算得到的渗透系数次之,利用带1个观测孔的稳定流潜水完整井公式计算得到的渗透系数最小,这主要是由井损造成的;建筑物对场地土体的影响主要集中在素填土层、黄土层和古土壤层,粉质黏土层以下影响则逐渐减弱,影响深度在18m左右;由于建筑物长期对地裂缝上盘土体施加荷载,附加应力作用使地基土固结压密,导致地裂缝上盘土体的渗透系数较下盘小。

Study on Pumping Test for Xi'an Metro Crossing Ground Fracture

Measuring hydrogeological condition of ground fissure could provide a basis for the design and construction of Xi'an Metro. Hydrogeological test around the ground fracture was done in Laodonglu primary school of Xi'an City, which located above the ground fracture, from July to September, 2008. It included water penetration, drilling hole injected with water and pumping tests, and the stationary flow pumping test in No.1 pumping well was taken as a special example. Effect of ground fracture on seepage action of ground water was studied. The three formulas(stationary flow dive fully penetrating well with one or two observation wells, water level reset rate fully penetrating well)were used to calculate the permeability coefficients of shallow soils, which were parallel or vertical to the ground fracture. The differences of permeability coefficients were discussed. Finally, effect of stress application of building on foundation soil was simulated by finite element software MADIS. The results showed that the permeability coefficients of soil body parallel to the ground fracture was a little bigger than that vertical to the ground fracture based on the above mentioned three formulas; the permeability coefficient calculated by the three formulas decreased in the order of water level reset rate fully penetrating well, stationary flow dive fully penetrating well with two observation wells and stationary flow dive fully penetrating well with one observation well under the same height of drop,and well loss caused the difference; the influence of building on soil body mainly focused on plain fill, loess and paleosol strata, gradually decreased under silty clay strata, and the influence depth was approximately 18 m; because of the load application of building to the upper side of ground fracture for a long time, effect of subsidiary stress caused foundation soil consolidation, and the permeability coefficients in the upper side of ground fracture was smaller than that in the lower side.