| The underground constructions in urban area has attracted more and more attentions.However,due to the high ground water level in the Yangtze River Delta,the dewatering is necessary in most of the constructions of excavation.If using the conventional drainage technique in the soils with low permeability,the dewatering effect is not so significant,addition to prolonging the excavation construction and leading to a poor soil consolidation.In addition,the drainage may cause ground surface subsidence and other secondary hazards in the area existing confined aquifers.Therefore,it is very important to reduce the surface subsidence by using effective protection measures and dewatering methods.In this thesis,by using laboratory test,field test and numerical simulation methods,the researches and developments were performed on the vacuum dewatering technique,the optimum design method of dewatering and the intelligent control system of dewatering in deep excavation engineering for the solution of the aforementioned problems in the dewatering of excavation construction.The main content of this research contains:(1)A new method with a higher dewatering efficiency was proposed on low permeability soils.In order to solve the problem of dewatering on low permeability soils,including the leakage,the low efficiency and the poor reinforcement effect,a new vacuum dewatering method with a higher efficiency was proposed on low permeability soils,by improving the conventional well pipe to double well pipes based on the vacuum principles.In the numerical simulations,the effect of vacuum degree was analyzed on the flow rate of single well,the pore water pressure and the ground surface subsidence.In the field tests,the efficiency of new method on the vacuum dewatering and the soil consolidation was validated.(2)An optimum design method of dewatering was proposed on the drainage of artesian in deep excavation engineering.In order to study the drainage of artesian in deep excavation engineering,a typical engineering project was selected to perform a deep study based on the analysis results on the hydrogeological conditions of Shanghai.Based on the numerical simulation and field test results,the evolution of seepage field was studied with different dewatering models.The quantitative evaluation on the influence area and the decrement of ground water level reveals the effect of the space enclosing structure on the seepage of ground water,showing that,the ground surface subsidence is smaller with a deeper space enclosing structure and the depth of space enclosing structure should be larger thant 1/3 of the confined aquifers.The evolution of the ground surface subsidence is divided into two stages or six phases based on the subsidence rate: the dewatering stage including the lag phase,the accelerated phase and the moderated phase;and the recovering stage indluding the rebound phase,the gentle phase and the steady phase.The influence area is divided into the violent change area,the significant change area and the minor change area.Based on the analysis results on the drainage in confined aquifers,it is suggested that the multiple well dewatering method should be used,the depth of well should be smaller than that of the space enclosing structure,and the well arrangement should be optimized with a distance of 2-6 m from the space enclosing structure.(3)The intelligent control system of dewatering in deep excavation engineering was proposed.In order to reduce the risk of engineering accidents caused by improper dewatering confined aquifers or even a failure in aquifers,a intelligent control system was devaloped based on the analysis results on the environmental effect of dewater by using Visual Basic.The intelligent control system was assembled by using SQL Server to create the database system and applying the information management technology to vacuum dewatering engineering.This system can do the data management and provide the 3D simulation of ground surface subsidence.A preliminary validation of the system was conducted on an engineering project. |
