Study On Instability Mechanism And Treatment Measures Of Super-large Cross-section Tunnel Crossing Potential Landslide

With the continuous development of my country's infrastructure construction,there are more and more engineering cases of double-tunnel crossing landslide bodies.The proportion of two-way six-lane and eight-lane highway tunnels in newly-built expressways has gradually increased,which results in the project of double-tunnel crossing potential landslide bodies is gradually developing in the direction of small clear distance and super-large cross-section.However,there are still few academic studies on the double-hole super-large cross-section tunnel crossing potential landslide bodies.Therefore,based on the Hanshankou Tunnel Project,this paper analyzes the instability mechanism of the super-large-section parallel double-hole tunnel orthogonally crossing the potential landslide body and the remediation effect of the remedial measures through ways of numerical simulation,model test,and on-site monitoring.At the same time,the slope stability safety factor F_st of the two-way six-lane super-large cross-section tunnel orthogonally crossing the slope is modified.Finally,the safety factor of different original slopes under the shallow-buried,biased and small-distance two-way six-lane highway tunnel is proposed Corresponding rectification measures.The main conclusions are as follows:(1)Through field investigation and numerical simulation analysis,two main reasons for the landslide in the Hanshankou Tunnel have been obtained:the superimposed effect of the double-tunnel excavation and the disturbance of the surrounding rock caused by the excavation of the super-large section.The slope stability safety factor F_st before the excavation of tunnels of different cross-section sizes is modified by means of increasing strength.The modification results show that the larger the cross-section,the higher the modified stability safety factor,and the easier the slope is to lose stability,the greater the safety reserve;(2)Through numerical simulation,the stability of the comparative working conditions of different clear distances,different buried depths of the left hole,and horizontal distance from the slope toe are compared and analyzed.The calculation results show the degree of influence on the stability of the tunnel-slope under the three influencing factors is:buried depth>clear distance>horizontal distance from the toe of the slope.At the same time,the stability safety factors under the three factors are revised.The results show that the smaller the buried depth of the left hole and the larger the clear distance,the smaller the modified stability safety factor,and the horizontal distance from the slope toe has little effect on the result of the revised stability safety factor.The model test results also verified the instability mechanism of the relying project again;(3)After the stability analysis of the comparative working conditions of different construction sequences and construction methods,the results show that when the CD method is selected to construct the right tunnel first,the disturbance to the slope is smaller,but according to the safety factor and the maximum shear strain increment,different construction sequences and construction methods do not significantly improve the slope stability;calculations show that different support thicknesses and support strengths basically have no effect on the slope stability;(4)Numerical simulation is used to compare the remediation effects of different remediation measures,and the corresponding safety factor range under different remediation measures is determined by means of strength reduction or growth.The results show that when the"anti-slide pile+anchor cable frame beam"is adopted,the remediation effect after the joint reinforcement measures is the best,and the remediation effect is also verified again based on the on-site monitoring data.Finally,curve fitting is performed on the calculated value of the modified stability safety factor mentioned above to obtain the stability safety factor correction relationship under the section,clear distance,and buried depth correction,which is F=?₁?₂?₃F_st(?₁is the section correction coefficient,?₂is the clear distance correction coefficient,and?₃is the buried depth correction coefficient),and then according to the modified stability relationship,the anti-slip improvement measures table corresponding to different original slope safety factors under the shallow buried bias and small clear distance two-way six-lane working condition is obtained.