Study On Mechanical Properties Of Surrounding Rock In Soft Carbonaceous Slate Tunnel

With the rapid development of Chinese economy,existing infrastructure facilities have been unable to meet people’s travel requirements.In order to let the people enjoy more convenient transportation,our country has vigorously developed the basic traffic facilities such as high-speed railway,highway and urban subway.Railway or high-speed railway pass through a wide area,with different geological,climatic and environmental conditions.The carbonaceous slate is one of the representative geological conditions.Owing to the carbonaceous slate has low shear strength,it is easy to lose stability,deformation and collapse,so the research of carbonaceous slate tunnel in theory and construction method faces more problems.Therefore,through the method of theoretical analysis and numerical simulation,the deformation and stress of carbonaceous slate tunnel surrounding rock under different rock dip angles and different construction methods are discussed,and the deformation and stress characteristics of surrounding rock under different step parameters are systematically studied.The main research results are as follows:(1)In addition to the engineering geology and hydrologic conditions,the excavation method and support parameters will also affect the mechanical properties of the carbonaceous slate tunnel’s surrounding rock,and summarize the advantages and disadvantages of various tunnel excavation methods.The deformation mechanism of slate tunnel is analyzed,and the position between the direction of the interaction of surrounding rock and the direction of the structural plane is the main factor affecting the stability of slate tunnel;(2)Under the same construction method,the rock layer angle is different,the vertical stress state of the surrounding rock is obviously different,the whole performance is along the rock stratum direction,and the stress concentration is produced at the end of the sliding surface.The vertical stress of the 0 degree angle rock appears symmetrical distribution,and the vertical stress of 30 and 60 degree rock strata shows the low left high right and the stress concentration in the lower left corner,indicating that the interlayer slipping will be produced by the weak interlayer during the excavation of the layered rock mass.With the increase of the inclination angle,the vertical stress of surrounding rock increases first and then decreases,so the stress at the periphery of the tunnel with 30 degree is the largest;(3)Comparing the layered rock mass and the homogeneous rock mass,the numerical simulation results show that the deformation and stress of homogeneous rock mass and layered rock mass are obviously different.The deformation of the surrounding rock of homogeneous rock mass is symmetrical and the layered rock mass inclining along the strata.The deformation of the homogeneous rock mass is less than that of the layered rock;(4)The different angles,under the three construction methods,the deformation of surrounding rock produced by the whole section method is the largest,which can not meet the requirements of construction for deformation.The deformation of the three step method and the CD method meet the requirements of the standard.The CD method is slightly better than the three step method in controlling the settlement of the vault and the uplift of the inverted arch,but the construction of the CD method is very difficult,the construction cost is high,and the efficiency is lower than the three step method.Therefore,the three step method is chosen as the construction method for the carbonaceous slate tunnel;(5)Under the three step construction method,the cyclic footage for 1m,2m and 3m surrounding rock’s plastic zone distributes around the right wall corner,and the whole distribution direction of the plastic zone is in accordance with the rock strata direction.During tunnel support,we should pay attention to key reinforcement in the corresponding position of surrounding rock,prevent plastic deformation of surrounding rock and affect tunnel stability.(6)Under the three step construction method,cyclic footage for 3m deformation of surrounding rock is the largest,beyond the prescribed limits,which can not meet the requirements of construction for deformation.The deformation of the surrounding rock of 2m is close to the maximum limit specified by the tunnel gauge.In the actual project,the deformation of the surrounding rock is generally greater than the simulation result of the numerical calculation software.Therefore,select cyclic footage for 1m as the final length.