Study On Construction Suitability Evaluation Of Nanchang Metro Line 4

With the increase of population and the needs of economic,political and cultural exchanges,China is facing great traffic pressure in the process of urbanization.With the gradual improvement of the transportation system,the traditional travel mode not only reduces the traffic pressure,but also brings noise pollution,air pollution,fossil energy consumption and a large occupation of land resources.As a result,the subway has gradually become an important part of the urban transportation system with small area and strong pollution.In the process of urban subway construction,it is inevitable to face different kinds of geological environment.When the subway crosses rivers and other water rich environments,due to the abundant water supply in the stratum,the engineering construction safety and economy of the subway line are facing great pressure.In particular,there are a large number of high permeability soil layers such as sand gravel layer in the stratum,so special attention should be paid to the risks of water inrush and stratum settlement.In order to ensure the excavation safety of high permeability and water rich stratum,it is necessary to carry out simulation calculation and analysis in combination with the actual engineering geological environment.Taking the engineering construction planning area of Nanchang as the background,this paper selects the typical section of Nanchang Metro Line 4,checks the main construction risks in combination with the specifications,establishes the stratum model,and uses the finite difference software Flac^3d to simulate the excavation.The influence of shield construction on the stratum under the high permeability and water rich stratum is analyzed.By comparing and analyzing the influence of shield excavation on stratum settlement in pure force field environment and seepage field force field coupling environment.In addition,different factors affecting the engineering construction are selected based on geological data,and the weight of different factors for the engineering construction suitability is determined by analytic hierarchy process.Finally,the weighted calculation and evaluation are carried out,and the engineering construction suitability is evaluated by geographic information system from the perspectives of engineering geological environment,hydrogeological environment and adverse geological process.The main research work of this paper is as follows:（1）Based on the industry specifications and in combination with the stratum parameters and groundwater distribution along Nanchang Metro Line 4,the most likely engineering risks are judged.Carry out zoning checking calculation along the subway,and put forward targeted engineering risk prevention suggestions according to the checking calculation results and the actual geological conditions of the checking calculation area;（2）Since the permeability coefficient parameters of the stratum in the simulated excavation area cannot be obtained,it is proposed to establish a data set with the relevant parameters of the rock and soil layer in the nearby stratum,train the BP neural network,obtain the prediction model suitable for the stratum parameters in the simulated excavation area,and predict and study the permeability coefficient;（3）According to the typical geological environment and groundwater distribution of Nanchang Metro Line 4,the stratum model is established.The finite difference program is used to simulate the subway excavation process in the pure mechanical environment,and the settlement distribution of the top and surface of the tunnel under different excavation steps is obtained;（4）Considering the coupling of seepage field and force field,when water inrush occurs at the top and bottom of the tunnel,the settlement distribution of the top and surface of the tunnel under different excavation steps is obtained;（5）The analytic hierarchy process is used to determine the structure of the analytic hierarchy process model.Combined with the engineering geological conditions,hydrogeological conditions and adverse geological effects in the study area,the quantitative evaluation of different elements is carried out based on the industry specifications,and the engineering geological conditions,hydrogeological conditions,adverse geological effects and comprehensive suitability of engineering construction in the study area are evaluated by weighted calculation,And provide construction suggestions for different suitability zones.