【作者】 金小荣；

【导师】 俞建霖；

【作者基本信息】 浙江大学 ， 岩土工程， 2004， 硕士

【摘要】 在粉砂性土地基中，为增加基坑的稳定性，降低地下水位、减少基坑内外水头差是比较常用、有效且经济的措施。但降低地下水位将引起周围建(构)筑物和地下管线产生附加沉降，对周围环境产生不良影响。基坑降水对周围环境的影响已经引起人们的重视，但总体而言，目前国内外对这方面的研究尚未深入，有必要对此进行系统的研究。 首先介绍了二维非稳定渗流有限元方程，讨论了潜水含水层的自由边界处理问题，建议采用初流量法处理潜水含水层的自由面计算问题，该方法的优点是对自由面处理过程中，可以不必修改计算单元的结点坐标，这对于应力场与渗流场的耦合分析计算非常有利。 其次根据土体的平衡微分方程、质量守恒定律、有效应力原理以及达西定律建立了考虑源汇项的渗流场与应力场耦合数学模型，并且提出了直接耦合有限元计算方法。利用有限元软件ABAQUS对基坑降水环境效应的耦合性状进行分析。 通过二维有限元计算分析表明：降水后基坑周围水位线、降水影响范围和地表沉降的分布规律受基坑周围土体弹性模量、渗透系数和降水深度等因素影响。对基坑周围水位线、降水影响范围性状和周围土体沉降性状依次进行了分析。考虑回灌作用的有限元模型计算分析表明：设置回灌井或者回灌排水沟都可减小回灌处以外的地表总的沉降和不均匀沉降，随着排水沟离开基坑边距离的增加，回灌点以外的总沉降量和不均匀沉降都减少，回灌井埋设深度对周围地表沉降影响较小；通过考虑止水帷幕的有限元模型计算分析表明：设置止水帷幕可大大减小基坑周围土体总沉降和不均匀沉降，随着打设止水帷幕深度的增加，基坑周围地表总沉降和不均匀沉降都减小。 最后将直接耦合有限元模型应用于杭州大剧院基坑降水工程，并将计算结果和现场实测数据进行对比，验证了渗流耦合模型的在工程应用中的合理性和正确性，具有一定的理论意义和实用价值。更多还原

【Abstract】 At present, it is usually effective and economical in excavation in silt-sand soil layer that draining ground water or reducing the difference of water head by light pumping wells or other equipments in order to increase the stability of the pit. However, the lowering of water table will cause harmful subsequent settlement and influence the building and municipal facilities which are near the pit. This problem has caused the attention of many technicians and scholars, but it has not been deeply studied or successfully attacked. Therefore, it is necessary to systemically study the mechanics of the influence induced by dewatering. In this paper, some aspects of this problem were studied as followed.Based on the two-dimensional unsteady seepage flow theory, a finite element equation was present, then the Initial Flow Method which is very beneficial for the coupled analysis problem was introduced for the computation of the phreatic surface because the same FEM grid had been used for stress and seepage calculation.By the law of conservation of mass, the principle of effective stress and the Darcy’s law as well as the equilibrium differential equations, a coupled mathematic model that included the terms of source and sink, and its corresponding direct coupled FEA model, for the analysis of groundwater seepage and stress were developed. The coupled characteristics of the pit’s environment induced by dewatering were analyzed by the software ABAQUS.By the two-dimensional FEA, the law of the fall head curve, the radius of the influence and the settlement were thought to be related with the Young’s module, permeability and the depth of dewatering, etc. then the characteristics of the fall head curve, the radius of the influence and the settlement were analyzed in sequence. By the FEA model that the recharge effect had been taken into account, the surface settlement and the surface differential settlement of the ground surface which was out of the recharge position could be greatly reduced, the recharge effect at far foundation pit wasmuch more apparent than at the near position. By the FEA model that the water-seal effect had been taken into account, the surface settlement and surface differential settlement of the ground surface could be largely reduced; the reduction of the total settlement and the differential settlement increased as the length of water-seal wall grew.The two-dimensional FEA model was applied to the computation of a case project. The measured results compared favorably with the numerical results that verified the feasibility of the coupled model.更多还原