| The frequency and scale of high ground stress soft rock tunnels in the western region are increasing year by year.During the blasting excavation of such tunnels,blasting seismic waves and ground stress loads interact with each other and local areas are prone to stress concentration.In addition,excavation unloading leads to loosening and strength reduction of the nearby rock masses.When the mechanical properties of the rock mass are poor,the local rock mass is easily yielded and damaged,which leads to difficulties in support and safety hazards in the later construction period.In this paper,we mainly discuss such problems with literature,theoretical derivation and numerical simulation,and focus on the key points of initial ground stress and blasting seismic wave superimposed effect stress field,with the purpose of proposing the safety criterion of blasting seismic wave damage to high ground stress soft rock,and carry out systematic and in-depth research from different initial ground stress,different rock strength and blasting seismic wave vibration speed,etc.The main contents and conclusions are as follows:(1)Based on the blasting seismic wave medium damping attenuation law and the blasting seismic wave dynamic equation,the stress equation generated on the plane longitudinal wave front is derived.The expressions of the positive stress and particle elastic modulus and particle vibration velocity are established through the dimensional analysis and the relationship between Young’s modulus and wave velocity.(2)By literature research method,the relationship equations between burial depth and vertical ground stress,horizontal ground stress and lateral pressure coefficient were obtained,and the superposition law of different ground stresses and the stress field of the same blasting seismic wave was analyzed by using Flac3 d software.The results show that: the influence range of blasting seismic waves decreases with the increase of initial stress,and the maximum displacement gradually moves in the direction outside the tunnel profile;the ground stress shows a suppression effect on the stress field generated by seismic waves.(3)Based on the existing rock damage model,the existing damage model was modified by combining the linear relationship between ground stress and burial depth.And using Flac3 d software,numerical simulation and theoretical analysis of Hoek-Brown criterion under different strength conditions of rock mass,the damage law of rock mass with different mechanical properties was initially determined after superposition of the two.The results show that: when tunnel blasting excavation,the stress field will increase with the strengthening of the rock mass and the stress will be gradually concentrated;when the rock mass strength is too low,the blasting seismic wave will change the initial stress distribution and the ground stress will promote the range and degree of rock damage,leading to large deformation at a later stage.(4)Through the existing natural seismic evaluation method,peak velocity evaluation method,combined with the characteristics of rock damage damage,the different blasting seismic wave vibration speed of high ground stress soft rock damage was discriminated and divided: complete,minor damage,severe damage,destabilization damage.The results show that: different ground stress on different strength of the seismic wave damping size is significantly different,when the vibration speed is too large,the seismic wave energy is also too large,in the closer to the blast source media damping effect and stress suppression effect is also implicit;vibration speed of 100 cm /s for the paper selected the safety threshold of high ground stress soft rock tunnel,and the joint action of ground stress in the seismic wave stress field is divided into three categories: ground stress dominated,ground stress and blasting seismic wave together dominated(vibration speed of 100cm/s～180cm/s),blasting seismic wave dominated. |
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