Prediction Of Surface Settlement And Construction Plan Evaluation For Shallow Buried Tunnel Considering The Stratum Slip Crack

With the acceleration of urban modernization,underground engineering has entered a period of high-speed construction.Urban underground projects are mostly located in areas with large flow of people and vehicles,facing high safety risks.The difficulty and progress of engineering construction are affected by geological conditions and surrounding environment.During the underground tunnel excavation construction,it is always inevitable to disturb the stratum,resulting in land subsidence,resulting in the destruction of the ground,pipelines and buildings,and the overall collapse of the stratum,sudden collapse and other safety accidents.According to the field monitoring,the deformation and settlement of the ground surface are often consistent with the shape of the ground sliding surface.Therefore,it is necessary to study the law and prediction method of the ground settlement caused by the excavation of the shallow tunnel,and study the influence of the excavation scheme of the shallow tunnel on the law of the ground settlement and the ground sliding surface.Based on this,the main research contents and results are as follows:(1)A correction formula for the width coefficient of surface subsidence trough considering formation slip fracture is proposed.By analyzing the characteristics of formation sliding crack caused by tunnel excavation,the influence of sliding crack surface parameters on formation deformation is studied,the relationship between surface settlement groove formula and formation sliding crack theory is established,and the correction formula of surface settlement groove width coefficient is put forward.The results show that under the condition of shallow burial,the width K of settlement tank is related to the friction angle in the formation φ It satisfies the approximate linear relationship,which can be verified by the measured data.(2)The law of surface settlement and the characteristics of stratum slip during the construction process of Cross Diaphragm(CRD)method is revealed.Relying on the shallow buried tunnel project of Shenzhen Metro,the three-dimensional simulation analysis of the whole process of tunnel CRD method construction is carried out,the formation deformation law and formation slip characteristics of the whole process of construction are studied,and the simulation results are compared with the field monitoring data.The results show that during the construction of double-layer tunnel with CRD method,the surface and vault settlement have experienced several stages,such as micro deformation stage,rapid deformation stage and deformation stability stage respectively.Among them,the settlement change is the most obvious in the excavation stage of upper and lower caverns,and the middle partition wall can reduce the span.After the completion of tunnel construction,the surface settlement is normally distributed,and the stratum slip angle is slightly larger than the result of the modified formula,which shows that CRD method can control and reduce the width of surface settlement trough and reduce the influence range of surface settlement.(3)The evaluation method of shallow tunnel construction scheme is established.Based on the consideration of surface settlement and stratum sliding crack,different construction schemes are designed to study the influence of different schemes adopted by shallow buried tunnel on surface settlement and stratum sliding crack.The results show that the middle partition wall plays a key role in the control of surface and vault settlement and sliding crack angle,and can reduce the maximum surface settlement by about 30%,And it can reduce the influence range of construction on surface settlement.On the premise of giving consideration to safety and progress,CRD simple method can be used as the optimal construction scheme of the project.