Research On The Land Subsidence And Its Numerical Simulation Of Shallow Strata In The Central Area Of Shanghai City

As the most serious geological environmental problem at the present stage, the development of land subsidence in Shanghai has been an important factor restricting the sustainable development of Shanghai. In recent years, Measures of artificial recharge and reduction of pumpage has been effectively taken. Because of this, the ground levels of Shanghai go up obviously. The compression of deep soil layers reduce and the influence weight of shallow soil layers continue to increase. Hence, we mainly research the subsidence in/of shallow ground in this study. The statistical analysis of monitoring data and the land subsidence model (a three-dimensional ground water flow model coupling with a one-dimensional subsidence model) are used to investigated the effects of the shallow ground subsidence generated by the variance of regional groundwater lever. Conclusions are as blow:(1) The research shows that the first and second soft soil layers are the main compression layers in Shanghai’s ground. The deformation rate of the two confined aquifers keeps stable although the groundwater levels increase in the confined aquifers. The main reasons of the continuous compaction under shallow soft soil layers with the increase of the ground water levels in deep confined aquifers are (a) the response of the pore water pressure in the aquifer lags behind the one in the neighboring aquifers (b) the creep behavior under long duration happens with the deformation of mostly shallow confined aquifers response to the changes of water level and always exhibit elasto-plasticity characteristic. Because of the existence of the clay interlayer and the influence of creep behavior, the shallow confined aquifers of some areas also have the deformation hysteresis phenomenon similar to the soft soil.(2) The regional land subsidence model for shallow strata established in this study can well-reflect the real law of seepage and deformation. Based on the results of simulation and prediction using the model built in this study, it is discovered that assuming the regional groundwater level changes are considered only, then under the present groundwater exploitation and recharge conditions, the shallow land subsidence of central area in Shanghai can be well controlled, which has a subsidence rate below4mm/yr in most areas. The subsidence funnels mainly distribute on the edge of the central area. Both the existence of groundwater funnels and large soft soil thickness are the main reasons that lead to the subsidence funnels of marginal areas.(3) Engineering-related subsidence has great impact to the existing subsidence pattern of central area. Since lack of engineering data, obvious is the pragmatic limitation on the land subsidence model built in this thesis. To expedite the research of land subsidence model and simulation study in these areas, more factors, which affect the soil deformation, should be taken into consideration such as foundation pit dewatering and high-rise building loads.