Environmental Impact Induced By Excavation Group And Deformation Control In Soft Soil Region

With the national economic develops rapidly,the sharp increase of the city population continuously put forward new requirements to the city bearing capacity.Making full use of urban underground space is a hot spot in recent years because of the limited land in the city.In recent years,the utilization of underground space has shown new features,namely largearea-excavation and multi-block-excavation.The design and construction of excavation group is becoming more and more common in engineering application.In the construction of excavation group there will be some problems: for instance,repeated earth pressure unloading,superposition of earth pressure and deformation,long construction period and significant temporal and spatial effects compared with the single excavation construction.But it becomes sticking out in research and practice that the limitation accompanied by existing analytical theories and methods.Therefore,it is necessary to carry out the research on the mechanism of the environmental influence of the excavation gourp construction.Basic analysis models have been established in this paper by means of numerical simulation and field measurement.The environmental impact superposition mechanism of the single excavation has been revealed and environmental deformation induced by excavation group such as lateral deformation of retaining structure,ground settlement,deformation of nearby buildings and pipes has been expounded in this research.Excavation group design and construction method has been proposed which provides the theoretical support and technical means to solve the problem of excavation group construction.The main contents and conclusions of this paper include:(1)The distribution of strata deformation field induced by single excavation has been analyzed by means of numerical simulation.Then the affected zone adjacent to excavation is partitioned to different parts according to the difference deformation distribution and the degree of environmental impact.Based on environmental influence partitions,the influence of adjacent buildings has been analynized and a practical analysis method has been proposed according to the different characteristics of shallow foundation buildings,pile foundation buildings and shield tunnels and their position in the partition.(2)The distribution characteristics of the environment deformation caused by excavation construction in the corner and the middle part of the excavation are discussed in the research using numerical analysis method combined with engineering mesurement results.And the distribution of the spatial effect of excavation has been summarized.The study found that the spatial effect distribution of the excavation outer space varies with the distance to the excavation.The spatial effect distribution can be expressed by the Gauss curve in the position at the edge of the excavation.The area behind the excavation can be divided into three parts namely the main influence part,sub-influence part and non-influence part.(3)The deformation characteristics of the soil inducend by the adjacent excavations has been analynized in the research using numerical analysis method combined with engineering mesurement results,and variation of soil deformation in horizontal and vertical directions has been revealed.The study found that different construction sequence has great influence on the deformation characteristics of the soil in each construction stage.Synchronous construction has remarkable effect on controlling soil horizontal displacement but soil settlement will increase significantly in this case because of strong superposition of soil deformation field.The distance between adjacent excavation has distinct influence on the deformation superposition of adjacent excavations: When the distance between the excavation is larger than 4H,the soil deformation behaves more as the deformation behavior of the single excavation.Based on the analysis of deformation,a practical analysis method is proposed for the construction of shallow foundation buildings,pile foundation buildings and shield tunnels.(4)By means of the numerical calculation method,the superposition effect of the surrounding environment deformation caused by the excavation is analyzed and the distribution of deformation field around the excavation of different distances is discussed in detail.The difference of the surrounding environmental deformation induced by excavation group and the single excavation has been summarized from repeated earth pressure unloading,superposition of earth pressure and deformation,long construction period and significant temporal and spatial effects which provides the starting point for the subsequent deformation control method.In this paper,the control method of environmental deformation in excavation group construction is put forward from three aspects namely deformation source controling and blocking deformation superposition & transfer path,object protection,which can effectively provide theoretical support and technical guidance for the follow-up construction.(5)The research provides theoretical basis and technical guidance for practical engineering design and construction by applied the method of environmental deformation control in the construction of several practical projects such as Shanghai Civil Aviation Hospital expansion project,Project of Shanghai International Air Service Center,Shanghai Longhua Grand Large Hotel expansion project and so on,which also verifies the effectiveness of the proposed practical analysis method.