Mechanical Characteristics Of Surrounding Rock Deformation And Support Force In Soft Rock Highway Tunnel During Construction

The deformation control of surrounding rock is very important to build a tunnel in soft rock environment. In depth study of the mechanical properties and deformation characteristics of soft rock, selection of reliable and effective support system is an important guarantee for construction safety and economic rationality. This paper relies on the Oupala tunnel in built which belongs to the Ganzi Babai road, which goes through the soft rock area. On the basis of full understanding of the engineering geological conditions of the site, this article takes in situ monitoring measurement means as the core, to indoor numerical simulation method for auxiliary, in-depth study of the tunnel surrounding rock deformation and support force characteristic, the change rule and analysis of its influence factors and to evaluate the support system of the validity and rationality. The main conclusions are as following:(1) Design of monitoring measurement scheme. Based on the actual geological conditions, combined with the design parameters and construction methods, and according to the relevant norms, the design of the monitoring of the measurement program was planned, including: monitoring of the project selection, monitoring equipment selection and arrangement of the measuring point, etc…(2) Based on the roof subsidence, surrounding rock displacement, internal displacement of surrounding rock and surrounding rock loose circle monitoring results, the deformation characteristics of surrounding rock and its variation law are analyzed. The deformation of surrounding rock in lower part of tunnel is the largest, and the main deformation occurs in the 0-3.5m range. The surrounding rock deformation can be roughly divided into three stages: the stress release stage of the tunnel excavation, the deformation adjustment stage of the inverted arch construction, and the stable stage of the surrounding rock deformation. Deformation of surrounding rock occurs mainly in the first two stages.(3) Through the results of surrounding rock and initial support pressure, axial force of anchor bolt and steel support internal force monitoring, the characteristics and changes of the surrounding rock and support stress were analyzed. The surrounding rock pressure of the tunnel can be divided into two types: deformation pressure and flow pressure. Deformation pressure is the main part of the surrounding rock pressure of the tunnel. Anchor force changes in the development and construction schedule has good correlation, axial force of anchor with tunnel face excavation advance gradually increased, but with distance from the tunnel face, the axial force changes gradually stabilized, the anchors play a positive role in the restraint of the surrounding rock deformation. Steel arches quickly played a key supporting role in start and embodied the skeleton effect in the supporting system, steel arch stress to pressure stress, top arch to arch shoulder range compression stress are larger. In general, the supporting system of tunnel is effective and reasonable, but the optimization space is not large.(4) Based on numerical simulation results, the characteristics of deformation of surrounding rock and supporting force in the whole process of tunnel excavation are summarized. The maximum principal stress of surrounding rock in the tunnel is about symmetrical distributed, in the vault formed a clear low stress zone, and in the arch shoulder and arch foot formed a significant stress concentration area. Displacement field of surrounding rock in tunnel is basically symmetrical distributed, the displacement is growing gradually as the excavation footage increases. The most obvious part of displacement is arch and arch foot. All axial force of anchor is tension, initial excavation anchor force significant changes and with increasing excavation footage, the maximum axial force of anchor gradually stabilized at last.