A Study On Mechanism Of Soft Rock Big Deformation In Diversion Tunnels Of The Dongsong Hydropower Station

As a tough problem, soft rock big deformation is a long-term puzzle in tunneling. Especially in the area with high stress, the harm of soft rock big deformation is prominent. Because the big deformation mechanism of soft rock is complex and lack of effective measures, it is very important to fully understand the mechanism of soft rock big deformation to prevent the big deformation effectively.Based on the construction of diversion tunnels in DongSong Hydropower Station, this thesis is to investigate the soft rock big deformation mechanism in order to prevent big deformation. Firstly, the rock mechanical characteristics is obtained from experimental and theoretical analysis, the deformation of tunnels with no support at different conditions is calculated by theoretical analysis. Secondly, through numerical analysis, actual excavation of tunnel in different geological conditions is simulated to study plastic zone and law of surrounding rock’displacement. To optimize the reasonable method of supporting and excavation, this thesis simulates the time and space effect of surrounding rock in the actual process of excavation. In the fourth chapter, the use of advanced geological forecast in tunneling is proposed to establish a set of forecast system to deal with geological disaster in the area of soft rock. In the fifth chapter, the deformation and force of surrounding rock and supporting structure is monitored through On-site test. Finally, the theoretical analysis, numerical simulation and On-site monitoring are presented for a method to determine the deformation amount of surplus of soft rock tunnel in different geological conditions.Study finds that:the mechanical characteristic of soft rock at DongSong Hydropower Station is of highly disintegrating and rheology. High stress and low strength are the main factors to influent the plastic zone and displacement of soft rock. Support with closed steel can effectively reduce the plastic zone and improve the force applied on the support. The deformation amount of surplus of soft rock tunnel is determined at the range of10-35cm. It is proved through practice and theory that geological forecast based on geological radar can predict a variety of harmful geological bodies which may exist and effectively prevent big deformation and collapse in the soft rock tunnel.