Study On Settlement Law And Mechanical Behavior Of Pile-Beam-Arch Method Subway Station In Loess Stratum

Subway station construction is faced with the problems of busy traffic,dense surrounding pipelines,large depth of station and poor geological conditions in the construction section.The pile-beam-arch method has gradually become the preferred method for subway station construction in complex urban environments because of its strong stratum applicability,small construction area and small disturbance to the stratum.Hejiaying station is the deepest station in the loess stratum and is first constructed by pile-beam-arch method.The stress mechanism of the bearing structure of the station and the deformation law caused by the construction are not clear.Therefore,this paper takes the subway Hejiaying station in the loess stratum of Xi’an as the background and uses numerical simulation,theoretical analysis and field monitoring to study the stratum settlement,structural stress and the distribution law of the surrounding rock pressure of the pilot tunnel caused by the construction in the key stage of the station.The main work and conclusions are as follows.(1)Through the numerical simulation of the whole construction process of the station,the ground settlement and the stress law of the supporting structure under the construction of each key stage are obtained:the ground settlement ratio caused by the guide tunnel construction is the largest,followed by the arch buckle construction.After the completion of the main construction of the station,due to the excavation and unloading of the soil in the station,the ground above the station has a rebound phenomenon of reduced settlement.The lining internal force of the guide tunnel is seriously affected by the excavation of the group tunnels.The closer the construction distance of the rear guide tunnel is to the first guide tunnel,and the larger the excavation area of the adjacent guide tunnel is,the greater the increase of the structural internal force of the first tunnel is,and the maximum position of the structural internal force of the guide tunnel is always at the arch foot.(2)In view of the excessive settlement of pilot tunnel construction,the disturbance of pilot tunnel construction on the stratum can be effectively reduced by optimizing the construction sequence of the pilot tunnel.Among them,the stratum settlement caused by the construction sequence of ’first edge and then middle,first upper and then lower’ is the smallest.In view of some special projects with high requirements for settlement control,by reducing the number of guide holes and the total excavation area of guide holes,the scheme of optimizing the type of station guide holes can effectively control the maximum settlement of strata caused by the construction of pile-beam-arch method.Among them,the 4-type tunnel pile method has the best settlement control effect.In the case of no support,the excavation amount of the pilot tunnel has a linear relationship with the corresponding maximum ground settlement.(3)On the basis of the existing theory,the calculation formula of the surrounding rock pressure of the pilot tunnel considering the construction sequence of the pilot tunnel in the pilot tunnel stage is summarized.The influence of the parameters such as the depth of the pilot tunnel,the spacing of the pilot tunnel,the strength of the soil and the size of the pilot tunnel on the surrounding rock pressure of each tunnel is analyzed.From the field monitoring values and the theoretical calculation values of surrounding rock pressure,it can be seen that the surrounding rock pressure of the first tunnel is much larger than that of the second tunnel,and the ratio of the surrounding rock pressure on the left and right sides of each tunnel is much larger than 1,and each tunnel is obviously indigenous to the bias load.(4)The surrounding rock pressure values obtained by the theory in this paper are compared with the field measured values and the surrounding rock pressure values of the existing theory.The vertical and lateral surrounding rock pressures of each tunnel calculated by the theory in this paper are close to and greater than the field measured values,but the theoretical pressure values in this paper can better reflect the bias state of the surrounding rock pressure of each tunnel measuring point.