Analysis And Application Of Surrounding Rock Damage Of Slate Tunnel Under Blasting Loa

With the implementation of national strategies such as’western development’,’poverty alleviation’and’transportation power’,expressway construction has developed rapidly.Drilling and blasting method is the main method of tunnel construction at present.However,due to the existence of faults,bedding and other structural planes,the propagation and attenuation law of explosion stress wave is significantly affected,resulting in serious over-break and under-break of the tunnel,and it is difficult to form a better tunnel contour line.According to the traditional blasting parameter design,it can not meet the needs of safe and efficient construction of mountain tunnels with serious faults and relatively developed joints.Reasonable layout of surrounding holes can effectively control over-break and under-break of tunnels.There is an urgent need to propose a new method for blasting construction of layered tunnel tunnels.In this paper,the calculation method of surrounding hole spacing under the action of bedding is proposed,and the layout of surrounding hole network is optimized.Through on-site drilling core sampling,static test and impact dynamics test are carried out to obtain the static and dynamic parameters of surrounding rock.LS-DYNA software is used to establish numerical simulation of slate tunnel with different bedding dip angles.The damage analysis of surrounding rock is carried out,and the field application is carried out.It is verified that this method can effectively reduce over-excavation.This paper relies on Baizhushan Tunnel of Leirong Expressway as the engineering background.The main research work is as follows:(1)According to the theory of damage mechanics and the theory of rock blasting energy distribution,the propagation and attenuation law of stress wave,the constitutive model of surrounding rock damage and the evaluation index of surrounding rock damage are analyzed.The influencing factors and control measures of surrounding hole blasting effect are studied.(2)The mechanical parameters of slate with different bedding angles were measured by uniaxial compression test,triaxial compression test and Brazilian splitting test.The SHPB test was carried out based on high-speed camera.The failure mode and energy dissipation principle of slate with different bedding angles under dynamic impact load were obtained,and the strain rate influence coefficient C was determined.The parameters of HJC model of slate with different bedding angles were calculated,which provided data basis for numerical simulation.(3)By using the finite element software ANSYS/LS-DYNA,the blasting model of tunnel with and without bedding is established,and the influence of bedding on stress wave propagation is obtained.The single hole blasting model of single hole diameter of charge with radius R was established,and the value range of damage variable D corresponding to crushing zone,fracture zone and elastic zone was obtained.The blasting numerical models of slate tunnels with different bedding dip angles(0°,30°,45°,60°,90°)were established.The damage of the reserved rock mass of slate tunnels with different bedding dip angles was studied,and the layout of the hole network around the slate tunnels with different bedding dip angles was optimized.(4)The field blasting test was carried out in the study section of Baizhushan tunnel.The results show that the average explosive consumption is reduced by 0.08kg/m~3.The total station is used to measure the over-break and under-break of each part of the upper step.The site is over-break and there is no under-break.The average thickness of over-break and under-break is controlled within 20cm,which reduces over-break and has better blasting effect.Acoustic damage monitoring and blasting vibration monitoring were carried out.The structure shows that when the hole depth exceeds 3.5m,the change of acoustic wave velocity is within 10%,which will not damage the new tunnel face.The maximum vibration velocity of blasting vibration is0.58cm/s,which meets the safety allowable standard of lining vibration velocity.