Research On Deformation Control Technology Of Surrounding Rock During Construction Of Large-section Tunnel In Soft Rock Stratum By ADECO-RS Method

Large-section tunnels are prone to large deformations and even collapse accidents when built in soft rock formations.Instead,the ADECO-RS has advantage of constructing fast with lower price.In order to study the surrounding rock deformation control mechanism of the ADECO-RS method and provide suggestion for on-site construction,theoretical analysis,numerical simulation and field monitoring are used to analyze the surrounding rock deformation controlling effects of NATM and ADECO-RS.And ADECO-RS method’s construction parameters are optimized.The main research contents and conclusions are as follows:(1)First the theory of the ADECO-RS was introduced.Then the mechanism of ADECO-RS was studied.The results show that the essence of the deformation control of ADECO-RS is to improve the stiffness of the surrounding rock through various measures;The numerical simulation results show that two main measures’ control effect of ADECO-RS is almost the same,but when the two are combined,the tunnel vault settlement is reduced by 10%,and the horizontal convergence is reduced by 28%.(2)The surrounding rock pressure formula was introduced.The formula considered the pre-convergence deformation.The reinforcement density of advanced core soil formula is derived.The calculation results of the formula are close to the actual parameters(The error is 7.4%).The reinforcing length and the connection length of the anchor bar were defined by the instability mechanism of the tunnel face.The formula and simulation is used to calculat the ADECO-RS parameters.(3)Flac3D software is used to compare ADECO-RS and NATM.The numerical result is analyzed from four aspects: the tunnel crown settlement,the horizontal convergence and the stress of surrounding rock and primary support.ADECO-RS(Pipe roof + FGT)has the best effect.Three-step and reserved core soil excavation method is worst.By comparing the monitoring data and simulation results,the rationality of the numerical simulation is confirmed.Base on comprehensive comparison,it is suggested that the ADECO-RS method(Pipe shed + FGT)is better for the construction of large-section tunnels in soft rock formations.(4)Numerical simulation is used to analyze the influence of four construction parameters of the ADECO-RS(Pipe roof + FGT).The results show that the excavation step distance and the deformation of the surrounding rock are positive.While the others are negative.When the bolt spacing(density)is less than 1m,the Control effect is obvious.When the bolt length is greater than 18 m,the Control effect is not obvious.(5)Based on orthogonal test,the sensitivity of the four parameters to the three indexes of surrounding rock deformation is obtained by the range analysis and variance analysis.After Comprehensive analysis,the best construction method is: 1m excavation step,0.5m bolt spacing,14 m bolt length,and 6m lap length.(6)For studying the deformation of surrounding rock in water-rich fault fracture zone of the soft rock stratum,other ADECO-RS methods were introduced.The numerical simulation method is used to compare the ADECO-RS method(Precutting tunnel +FGT),the ADECO-RS method(Honeycomb arch+FGT),the ADECO-RS(Horizontal jetting pile+FGT),the ADECO-RS method(Pipe shed+FGT)and the double side drift method.The results show that the first three ADECO-RS methods behave better in controlling the surrounding rock deformation.And the deformation value of surrounding rock is about 1/10 of that of the double side drift method.