Mechanics Response Mechanism And Safety Evaluation Of Subway Tunnel Oblique Crossing Active Fault

In China,in order to create a comfortable and environmentally friendly way of travel,the construction of subways in large cities is in a period of rapid development.In an urban environment known for its complex and sensitive nature,large-scale subway construction will inevitably pass through unfavorable geological conditions,and active faults are one of them.The stick-slip movement of the fault causes not only large deformation of the rock layer along the fault plane,but also permanent deformation of the subway tunnel structure across the fault,resulting in huge damage to the structure.If the active fault is a causative fault,its dislocation process will also release huge seismic energy,causing secondary damage to the subway tunnel structure.Studies have shown that compared with the structure response to ground motion the near the fault zone,those of the far field are different.It is of great scientific and practical significance to study the mechanical behavior of cross-active fault subway tunnel structures under the stick-slip displacement and the dynamic response under near-fault ground motion.Therefore,this paper takes Urumqi Rail Transit Line 4 as the research object and studies it in the following aspects:(1)The method of data investigation is used to summarize the current theory of fault displacement theory,the characteristics of near-fault ground motion,including the upper plate effect,the directional effect,the sliding effect,the velocity pulse effect and the vertical effect are also summarized,which lays a theoretical foundation for subsequent fault dislocation and vibration analysis.(2)In this paper,numerical analysis is also used to establish a three-dimensional computational analysis model of the surrounding rock-fault-tunnel interaction.The contact model is adopted between the fault plane,the lining and the surrounding rock.The primary steel supporting arch is equivalent to the concrete effect.Two types of lining are considered: integral type and sectional type,and the secondary lining steel adopts the integrated model.Considering the reinforcement effect of the anchor,this paper analyses the deformation,force behavior and failure characteristics of the tunnel structure under the oblique fault.(3)This paper discusses the influence on tunnel structure with the intersection angle between the active fault and the axial direction of the tunnel,considering the deformation and stress of the lining structure under four working conditions: 20°,30°,40°,50°;This paper also discusses the key factors of the activity rate of active faults in the rate-shifting reaction.And the deformation and stress characteristics of the lining structure at the five kinds of displacement rates of 0.1m/s,0.2m/s,0.4m/s,0.5m/s and 1m/s.(4)The dynamic response of a cross-active fault subway tunnel structure under near-fault ground motion is studied.In this paper,four examples of near-fault and ordinary ground motion are selected,and the differences in frequency characteristics,response spectrum and velocity time history are analyzed.The difference between dynamic response of the lining structure under earthquake action is compared and analyzed under the same peak acceleration.The influence of the vertical effect of the near fault on the dynamic response of the trans-active fault tunnel is also discussed.