Pre-reinforcement Method And Stability Analysis Of Subway Passing Through Ultra-shallow Buried Soft Formation

With the acceleration of urbanization,the construction of urban rail transit has gradually become an effective means to solve urban traffic congestion and traffic accidents.The construction of urban rail transit can greatly improve the efficiency of the city,make the city more energetic,bring more space for the development of the city and provide better living conditions for the urban residents.In the process of urban subway construction,the main structure of the subway and its subsidiary structure are very shallow,and the formation conditions are poor,and the underground pipeline,the surface road and the urban building environment are complex.It has brought great difficulties to the construction of the subway.The existing tunnel excavation method and support method cannot guarantee the stability and safety of tunnel excavation.In view of the shallow buried soft strata in the process of urban subway construction,the reinforcement effect characteristics of different pre reinforcement materials are studied through laboratory tests.Through numerical simulation and field test,the pre reinforcement method and stability of tunnel excavation under the condition of extremely shallow buried weak stratum in the construction process of urban subway are studied,and the research indexes are surface deformation,internal convergence and internal force of support.The main work and innovation results in this paper are as follows:Through the analysis and study of the excavation method and the advance support method of shallow buried tunnel,and based on the universal pressure arch theory,a full section pre grouting pre-grouting method is put forward in the tunnel construction of extremely shallow and weak stratum.It is suggested that CRD excavation method,large pipe shed,small catheter and full section pre grouting pre grouting control method should be adopted in the construction of dark excavation tunnel in very shallow and weak stratum.The stability of tunnel excavation can be ensured.The gel properties of the new phosphate water glass and cement water glass grouting material and the physical and mechanical properties of sand and solids were studied through the proportioning test.The results of the study show that:Phosphate water glass slurry ratio and gel time are easy to control.In engineering application,the ratio between pH value of 4-5 and gel time of 15min to 1H should be chosen.The strength of the sand solid is low.Cement and sodium silicate materials are controllable in gel time and have high strength.Numerical simulation experiments show that:The vertical displacement of the tunnel vault,the vertical displacement of underground pipeline,the vertical displacement of the ground and the side wall convergence are in accordance with the relevant standards when the thickness of the pre grouting pre reinforcement design is 2?3M under the condition of extremely shallow and weak stratum,which can guarantee the stability of the tunnel structure and the surrounding rock during the tunnel excavation and support.Numerical simulation experiments show that:The vertical displacement of the tunnel vault,the vertical displacement of underground pipeline and the vertical displacement of the surface of the tunnel conforms to the relevant standards when the excavation step of the CRD excavation method is designed under the condition of extremely shallow and weak stratum,and the length of the tunnel is 62.9 of the 0.5m excavation step.It can ensure the stability of tunnel structure and surrounding rock in the process of tunnel excavation and support,and can greatly improve construction efficiency and engineering efficiency.Relying on Qingdao Metro Line 2 Shilaoren station B exit pedestrian passageway advance grouting pre reinforcement and excavation site test.The 2M reinforcement ring thickness and phosphoric sodium silicate and cement water glass composite grouting material were used for pre grouting pre reinforcement construction,and CRD excavation method was adopted.The construction method is suitable for tunnel construction in extremely shallow soft strata.