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高水位地区深基坑工程实践中,多以止水帷幕辅以基坑降水的方式进行地下水的处理。场地水文地质参数的选取、降水方法的选择,以及止水帷幕是否达到良好止水效果等是关系到基坑降水成功与否的几个重要因素。莫桑比克马普托大桥南锚碇基坑直径50m,挖深超过36m,止水帷幕为地下连续墙,墙深56m。在地下连续墙嵌岩的情况下,基坑土方开挖实施过程中屡发承压水突涌事故,导致无法正常开挖施工。首先,通过在坑外进行抽水试验获取场地的水文地质参数,结合有限差分数值模拟软件,建立三维渗流模型,进行基坑渗流场的模拟,预测基坑施工过程中的水位变化情况,与实际坑外降水水位变化进行对比,验证三维渗流模拟计算的合理性与适用性。其次,基于三维渗流计算结果,采取坑内外同时降水的方式将基坑外部承压水水头控制在开挖面以下,使得基坑顺利实施。
In the practice of deep foundation pit in high-water area, the treatment of groundwater is mostly done by means of water curtains combined with foundation pit dewatering. The selection of site hydrogeological parameters, the choice of precipitation methods, and whether the water-stopping veil has a good water-stopping effect are several important factors that affect the success of foundation pit precipitation. Mozambique Maputo Bridge south anchor pit diameter of 50m, dig deeper than 36m, water curtains for the diaphragm wall, wall depth 56m. In the case of underground continuous wall inlaid rock, excavation of earth-rock excavation in the course of implementation of frequent occurrence of sudden pressure water surge accident, resulting in normal excavation can not be constructed. Firstly, the hydrogeological parameters of the site were obtained by pumping tests outside the pit. Combined with the finite difference numerical simulation software, a three-dimensional seepage model was established to simulate the seepage field in the foundation pit and predict the water level change during the construction of the foundation pit. Comparison of external precipitation and water level changes verify the rationality and applicability of 3D seepage simulation. Secondly, based on the three-dimensional seepage calculation results, the water pressure outside the excavation pit is controlled below the excavation face by means of simultaneous precipitation inside and outside the pit, so that the foundation pit can be successfully implemented.