Study On Damage And Dynamic Influence Zoning Of Blasting Surrounding Rock In Railway Tunnel With Small Angle

With the rapid development of national economy,the total demand for transportation infrastructure is increasing.Large-scale rapid railway passenger transport network construction,especially the line must be as straight as possible high-speed railway,there will be more and more space cross or even cross angle very small railway tunnel.The research on blasting construction dynamics of small-angle adjacent railway tunnels is not sufficient and in-depth,and the blasting influence zoning cannot be solved.There is no standard and standard for design and construction,and the mechanical mechanism of blasting surrounding rock damage has not been systematically expounded.The influence law of blasting power on the structure of existing railway tunnel under small angle is analyzed,and then the zoning index of blasting construction dynamic influence is proposed.It is an urgent problem to divide the scope of strong influence zone,weak influence zone and no influence zone of railway tunnel.This paper relies on the Tashiling tunnel project of Quzhou-Ningde railway undercrossing the completed construction at a small angle of Tashi highway tunnel in Longquan City.Different blasting parameters,surrounding rock level,cross angle and cross spacing will affect the dynamic influence law of the existing railway tunnel structure.According to the blasting construction parameters,the optimization scheme of tunnel blasting design parameters is proposed.The weight of different influencing factors is comprehensively analyzed,and the influence zoning and control countermeasures of existing railway tunnel blasting based on analytic hierarchy process are proposed.Therefore,in this paper,through theoretical analysis,numerical simulation,analytic hierarchy process and monitoring measurement methods,the damage mechanism and damage effect of surrounding rock in the near-middle area of rock blasting,and the dynamic response law and influence partition of existing railway tunnel structure in the far area are systematically studied.The main research results are as follows:（1）According to the microscopic mechanical mechanism of rock explosion and damage fracture,the mechanical mechanism of rock damage fracture at the early stage of explosion stress wave and the late stage of explosion gas quasi-static action are analyzed respectively,and the damage variables,the average radius of micro cracks and the size of the damage area of the surrounding rock near the middle area of the two different stages of blasting are calculated.（2）In order to evaluate the damage of surrounding rock caused by rock blasting,the whole process of blasting crack propagation is numerically simulated and analyzed,and the mathematical statistics of main crack and branch crack are carried out.The effect of shock wave and stress wave generated by blasting on crack propagation is summarized.（3）The numerical simulation analysis of the dynamic response of the existing railway tunnel structure under different blasting parameters,surrounding rock levels,cross angles and cross spacing was carried out,and the following conclusions were obtained:the vibration velocity,lining stress and structural displacement of the existing tunnel structure caused by blasting construction under different blasting parameters and cross spacing were significantly greater than those without surrounding rock levels and cross spacing;The maximum value mainly appears on the blasting side of tunnel structure,and the minimum value mainly appears on the back blasting side.The maximum section charge of the cutting hole and the distance between the blasting center are the main influencing factors of the dynamic response law of the existing tunnel structure,which should be paid attention to in the control of different zones affected by blasting.（4）The contribution weights of blasting parameters,surrounding rock grade,cross angle and cross net distance factors on the influence zoning index of railway tunnel are analyzed respectively.The following conclusions are obtained:The vibration velocity P₁ is selected as the optimal index of the influence zoning of the existing railway tunnel structure.The vibration velocity of existing tunnel structure is 5.65cm/s as the upper limit of vibration velocity control,4.80cm/s as the dividing point of strong and weak influence area,4.08cm/s as the dividing point of weak and no influence area.The distance cross center of the strong influence area of the existing tunnel structure is 26.05m,the distance cross center of the weak influence area is26.05m～31.83m,and the distance cross center of the non-influence area is more than 31.83m.（5）The control points of blasting construction countermeasures in non-affected zone are vibration velocity of tunnel lining structure,convergence of clearance displacement,lining cracking and development monitoring,timely analysis of monitoring data,feedback of construction parameters and adjustment,and blasting informatization construction.The control points of blasting construction countermeasures in weak influence area are as follows:the maximum section charge of cutting hole is less than 13.14 kg,the circular footage of tunnel excavation is reduced to less than 2.00 m,the step method excavation and the increase of excavation face,the increase of detonator section,and the superposition of blasting wave.The control points of blasting construction in strong influence area are the control points of comprehensive application of weak influence area and no influence area,and the scheme layout and optimization of monitoring points of blasting vibration velocity are strengthened.Based on the comprehensive analysis of the research results,it can be concluded that in the blasting construction of the existing railway tunnel under the small angle,it is necessary to strictly control the variation of the maximum section charge of the cutting hole less than 13.14kg and the distance value of the blasting center between 16.90 m and 24.97 m.The control countermeasures and control points of different influence areas should be timely feedback,correction and adjustment according to the on-site monitoring data,so as to realize the informatization construction of blasting control and ensure the safety of the dynamic response of the existing tunnel structure.