| The stability of surrounding rock of highway tunnels not only affects the safety of the tunnel and the cost of tunnel construction,but also has a close relationship with the safety of the highway construction and the construction period.The study of tunnel stability and support becomes an important issue.In this paper,the Guigala tunnel No.1 and No.2 inclined shafts are used as the research object to establish a numerical model with FLAC3 D finite difference method numerical simulation software,and perform numerical simulation on the actual working conditions of the tunnel’s grade IV rock section.Through the numerical simulation results and the actual monitoring results on site Compare and determine the rationality of the model.Through a reasonable model,the tunnel’s buried depth,lateral pressure coefficient,excavation footage and other influencing factors are numerically simulated,and its influence on the surrounding rock stability is evaluated from the changes of the surrounding rock stress field,displacement field and plastic zone.In the aspect of support research,the influence of different bolt spacing,bolt length and bolt diameter on the surrounding rock deformation,spray stress and its own axial force is analyzed to determine reasonable bolt support parameters.The results of numerical simulation show that:With the increase of the buried depth of the tunnel,there is a strong stress concentration at the arch foot,arch top and bottom of the tunnel,the stress of the surrounding rock also increases linearly,and the stress value at the stress concentration location is greater;the vertical displacement,horizontal displacement,and plastic zone of the tunnel section Both increase with the increase of the buried depth of the tunnel.The lateral pressure coefficient increased from 1.0 to 1.8,and the stress concentration area shifted from the arch legs on both sides to the top and bottom of the tunnel;and with the increase of the lateral pressure coefficient,the horizontal convergence of the tunnel cross-section gradually increased,but the amount of arch settlement Gradually smaller.With the increase of lateral pressure,the plastic zone develops towards the top and bottom of the tunnel,but it has little effect on the lateral plastic zone.When the lateral stress coefficient increases by 0.2,the plastic zone increases at a rate of 20.3%,22.4%,22.9%,and 22.2%,respectively.When the excavation footage is increased by 0.5m,the maximum shear stress value increases by1.23%,4.43%,1.62%,and 1.02% respectively.The larger the maximum shear stress value of the tunnel section,the greater the possibility of tunnel damage.With the increase of the excavation footage,the maximum settlement rate of the vault increased from1.81mm/d to 3.76mm/d,and the horizontal maximum convergence rate increased from2.41mm/d to 4.55mm/d.The larger the excavation rule,the greater the displacement rate of the surrounding rock,and the greater the possibility of inducing instability of the surrounding rock.The smaller the circumferential distance of the anchor rod,the smaller the settlement and horizontal convergence of the tunnel vault,and the smaller the spray-mixing stress,the more beneficial it is to control the deformation of the tunnel surrounding rock.In addition,the axial force of the anchor rod with a circumferential distance of 1.2m is the smallest and the axial force distribution of the anchor rod is the best.For the consideration of construction costs,it is recommended that the circumferential distance of the anchor rod be 1.2m.With the increase of the length and diameter of the anchor rod,the axial force of the anchor rod gradually increases,and the displacement and blasting stress of the surrounding rock of the tunnel both decrease,which is beneficial to control the deformation of the surrounding rock,but the effect is not particularly obvious,combined with the construction cost Taking into account comprehensively,the length of the anchor rod is 3m and the diameter is 19 mm. |
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