| As long as the increase of the subway operating mileages in China,people start to pay more and more attention to the subway project.Meanwhile the convenience and aesthetic degree of subway stations start to get more and more attention from people.In order to improve the space utilization of the underground structure and provide a more convenient transportation to passengers,the structure of the subway station without pillars was proposed.Compared with the regular subway stations,the subway station without pillars has the advantage of optimizing spatial layout which can provide convenient pipeline arrangement and make sure the wide open passenger flow at the same time.At present,many non-columned subway stations have been built in China.But all of them have the smaller span which is unable to satisfy the requirement of the increasing passenger travel.Therefore,the construction of the subway station without pillars which have a large span has been put on the agenda.It is the primary project which can relieve the traffic jam and make life more convenient for people.As a kind of bad geological condition,the round grave layer has a lot of characteristics,such as coarse particle,poor uniformity,loose structure and strong water permeability.In the southwest region,especially in Nanning,The round grave layer is the primary underground which is widespread with large thickness.And in the local area,the depth is almost more than 30 meters.This layer has loose structure and strong water permeability.Usually,it can result in the plenty of the ground water.So the structure which passing through this underground has the general problem of the erosion from the ground water.With the perennial function of the erosion from the ground water,the structural damage start to accumulate gradually.It is the significant threat factor for the whole structure ’s reliability.The Nanning subway station belongs to the deep underground engineering.The condition ofpassing through the round grave rich water layer,the problem of the erosion from the ground water and the degradation mechanism of the structure are all unable to be avoid.This is the chief factor which is the restriction of the progress of the non-columnar subway station.So,it is urgent to carry out the research of the structure design,the construction optimization and the structure durability about the non-columned subway station which is passing through the water-rich round gravel stratum.Based on this,the method of combining the theoretical analysis,experimental research and numerical analysis together is adopt on the background of the water-rich round gravel stratum at Nanning.The research of the structural optimizing and the durability about the non-column large-span subway station structures are carried out.The main research work is included as follows:The in-situ soil test and the laboratory experiment about the rich-water round gravel layer are carried out.The basic physical and mechanical parameters are test.The inversion analysis using coefficient proportional coefficient of m value about round gravel layer is carried out by the method of beam on elastic.Using the mathematical statistics and fuzzy analysis theory,and with the comparison of the data coming from the geological survey,the proposed value of the shear strength and the suggestive value of coefficient of subgrade reaction about the rich-water round gravel layer in Nanning area are obtained by the comprehensive analysis.(2)Based on soil grain size distribution characteristics and nonlinear relation between field pumping test results,this article through to the water-rich round gravel stratum soil particles screening particle size grading features,According to the nonlinear coupling response relation between soil permeability coefficient and effective stress increment,a comprehensive evaluation of significant engineering practice significance is deduced for water-rich round gravel layer soil permeability coefficient calculation model by using the model can be computed with sufficient accuracy of soil infiltration parameters.(3)According to the existing research result about the subway station,the structure selection about the subway Which is across the rich-water round gravel layer is dictated in this paper,such as the ribbed beam scheme,the arched roof scheme and the variable cross-section scheme.And the comparative analysis of three kinds of structure scheme are carried out through the numerical method.The result is that the ribbed beam scheme can effectively reduce the roof and the thickness of the plate and it can reduce the engineering quantity of the reinforced concrete.Although the ribbed beam structure has a great rigidity,but the beam is too high.Then the floor height need to be increased in order to satisfy the requirements of various equipment pipeline arrangement,the construction project become more complex and slow in this way;The roof arch scheme can effectively improve the structure stress and decrease the size of roof section and thereinforcement,but it result in the increase of the structure foundation embedded depth and cause the increased construction difficulty.Therefore this scheme only applies to the large buried depth of the station structure;The variable cross-section plate scheme can reduce the plate thickness and the quantities of the reinforced concrete beam and slab column under the requirement of the structure strength and stiffness.Therefore,the total construction period is greatly saved.(4)Based on the real-time monitoring data of the surrounding system deformation of foundation pit in Guangxi university station,the interaction mechanism between soil body and structure in water-rich gravel stratum is analyzed,and based on the coordination of the deformation of the contact surface between coarse soil and structure,an elastic and plastic damage model of contact surface is established.Then,the method of numerical method is used to optimize the construction scheme of the large strapless subway station.The analysis shows that the structure of the soil in the formation of water-rich boulder is obviously frictional.The ground wall which adopting the rigid joint can significantly control the penetration of the foundation pit.The maximum horizontal displacement of the wall can be controlled at about 2mm by subsection construction.The topsoil with light one can reduce the displacement of the station roof plate by 54%.(5)According to the structure design scheme of Nanning railway traffic engineering and the date of the composition and the concentration of corrosive substances groundwater along the railway engineering,the modeling analysis is set up under the aggressive CO2 environment and the chlorine salt environment.The key areas which can determine the durability and service life about the influence rail engineering concrete structure(namely the durability of concrete structures controlled area)are fixed.The damage cracking of concrete structure under different load conditions and its influence on the control parameters of concrete erosion are studied.The control parameters of the concrete structure of Nanning rail transit engineering is fixed.Based on the correlation and sensitivity analysis of the parameters of corrosion control parameters and concrete mix parameters,the calculation model of concrete erosion control parameters is established.Combined with the structural design material performance and the design years of the structure of the durability control area of the rail transit engineering structure,the corrosion resistance and technical conditions of concrete materials are fixed.And the ratio requirement of the concrete can be confirmed by using the calculation model of concrete erosion control parameters. |
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