| At present, it is often used in excavation in silt-sand soil layer that draining ground water by light pumping well. However, the system of light pumping wells will cause harmful land subsidence and influence the building and municipal facilities along with the ground water being lowered. Although, Recirculation, one of the methods to reduce this kind of influence, has its own advantage which cannot be replaced by others, its theory develops very slows. Even though, there are some achievements about Recirculation, which are based on steady seepage, none of them can really find out the true relationship between soakage face and time. As a result, the popularization of Recirculation in foundation pit faces encumbrance.In this paper, according to the good permeability of this soil layer and the thickness of aquifer, a finite element software-SEEP2, based on two-dimensional unsteady equivalent full penetrating well flow theory, is presented by applying Ritz method, and numeric simulation of dewatering in unconfined aquifer during its unsteady process is made. Validated by some certain project, this finite element program can fully simulate the dynamic process of the change of soakage face in any time of unsteady stage, and has such precision that it can be used to provide theory evidence to design, construction and management of pit project.Moreover, in this paper, according to the traditional construction methods of recirculation pit project, fall-water wells and recharge wells starting working together, a new optimized method that fall-water wells start working first is provided. In addition, the feasibility and benefit are evaluated by numeric simulation, all of that would be benefit to the development of optimization of recirculation foundation pit projects.Finally, based on the analysis of the foundation pit project in Shanghai, some misleading about the influence of recharge wells and insufficiencies in location of supervised wells are pointed out. It is reasonable that the location of supervised wells should be determined after numeric simulation. |
