Research On The Theory And Application Of Large Deformation And Support In Deep Buried Soft Rock Tunnels

Deeply buried soft rock tunnels often have characteristics such as high structural stress,complex geological structure,and large deformation,which seriously restrict tunnel engineering construction.Therefore,research on the application of the theory of large deformation and support in deeply buried soft rock tunnels is of great value.Based on the deformation and failure of on-site tunnels,monitoring of surrounding rock deformation,and geostress testing,this paper conducts an in-depth analysis of the deformation characteristics and influencing factors of deeply buried soft rock tunnels under different conditions of engineering.Numerical simulations are used to study the optimization effects of tunnel structures,rigid support structures,and radial pressure relief support structures.The main research content and conclusions are as follows:(1)Analyzing the deformation characteristics and influencing factors of deeply buried soft rock tunnels in practical engineering,this study examines the degree and location of initial support cracking and failure,steel arch distortion and failure,and bottom uplift failure in tunnels with gently inclined rock layers and high-stress soft rock.It also examines the deformation patterns of the tunnel face and cross-section,the deformation patterns of the main and secondary shaft cross-sections,the three-dimensional displacement and deformation patterns,and the analysis of ground stress measured by hydraulic fracturing.The results indicate that the deformation and failure of deeply buried soft rock tunnels are affected by various factors,including ground stress,surrounding rock properties,support structures,groundwater,tunnel depth,and on-site construction.When using traditional rigid support structures,the deformation and failure exhibit characteristics such as large deformation,long duration,diverse forms of failure,and strong destructive power.When excavating adjacent tunnel spaces in deeply buried soft rock,there may be a “group hole effect”.After the arch is installed,the stress of the surrounding rock is released in the first layer of support deformation and failure,and the deformation of the surrounding rock in the arch section is effectively controlled without cracking or blockage.(2)Based on a gently dipping rock layer tunnel with a dip angle of 15°,the effects of tunnel flatness ratio,adding an inverted arch,the span ratio of the inverted arch,and the thickness of the inverted arch on improving tunnel section stress and controlling surrounding rock deformation are analyzed.The results show that the tunnel structure can effectively restrain and optimize the deformation of the surrounding rock in a certain degree of optimization.When the flatness ratio exceeds 0.9238,its inhibitory effect on the uplift of the inverted arch gradually weakens.When the span ratio of the inverted arch is in the range of 0.163 to 0.184,its inhibitory effect on the uplift of the inverted arch weakens.As the thickness of the inverted arch increases,the constraint effect gradually weakens.(3)Based on a high ground stress soft rock tunnel,a numerical model is established,and the effects of the steel arch model,spacing,and lining thickness on controlling surrounding rock deformation and stress release are analyzed and verified through engineering applications.The results show that after optimization of the steel arch model and spacing,the initial support stiffness increases slightly,but the effect on controlling surrounding rock deformation is not significant.When the lining thickness exceeds 47 cm,the trend of vertical displacement reduction slows down.In the engineering application,it is found that when the spacing between arches is reduced from 0.8 m to 0.6 m,the maximum vertical displacement of the surrounding rock is reduced by 4.5 mm,and the maximum horizontal convergence is reduced by 21.8 mm.The enhanced support structure can effectively restrain the deformation of surrounding rock.However,due to the rheological characteristics of soft rock,the surrounding rock deformation continues to develop in the later stage of the project.Therefore,an arch jacket is constructed,and arch failure occurs after the construction.(4)Based on the Zhong yi Tunnel,a numerical model was established to analyze the effect of the cushion layer filling position and cushion layer thickness at different depths on the relaxation effect.The results showed that when both the inner and outer cushion layers were laid simultaneously,the maximum reduction rates of surrounding rock deformation and minor principal stress were 67.27 % and 67.24 %,respectively.When only the inner or outer cushion layer was laid separately,the maximum reduction rates of surrounding rock deformation were9.46% and 34.19%,respectively,and the maximum reduction rates of minor principal stress were 13.62 % and 44.08 %,respectively.Compared with laying the inner or outer cushion layer separately,laying them simultaneously had a more excellent relaxation effect.The relaxation effect of the cushion layer thickness at 600 m and 800 m depths was reflected in two aspects:from the perspective of surrounding rock deformation,the thicker the outer cushion layer,the greater the relaxation deformation,and the trend of increasing relaxation slowed down when the thickness of the outer cushion layer reached 60 cm;from the perspective of stress reduction amplitude,the reduction amplitude of the minor principal stress was limited when the thickness of the outer cushion layer reached 45 cm.(5)Combined with field tests,the application effect of the cushion layer in deep soft rock tunnels was analyzed by comparing and analyzing the deformation and failure characteristics,surrounding rock deformation rules,and structural stress characteristics of the sections without and with the cushion layer.It was found that the section without the cushion layer showed various failure characteristics such as concrete cracking,steel arch distortion,fracture,overlap,and local deformation,and the maximum convergence deformation in the section was 869 mm,with a maximum deformation rate of 210 mm/d on the upper-middle bench,and the arch change rate reached 49.6 %.After the relaxation support of the cushion layer was constructed,the deformation rate at each position in the tunnel was generally less than 5 mm/d after the inverted arch was filled.Compared with the maximum stress of the steel arch at the DK42+078 section under the corresponding geological conditions,which was 279 MPa,the maximum stress of the steel arch after stress release was reduced by 75 % to 69.56 MPa.The results showed that when the inner and outer cushion layers worked together with the surrounding rock and support structure,they could effectively control surrounding rock deformation,absorb surrounding rock pressure,and reduce the surrounding rock pressure within the range of the support structure.