Research On The Influence Of Drilling And Blasting Construction Of Mountain Highway Tunnel On Overlying Rock Mass And Railwa

With the implementation of China ’s transportation power strategy,many traffic engineering constructions have been carried out in the southwest region.Due to the limitation of topography and geological conditions in the region and the strict requirements of route selection and space resource utilization,the drilling and blasting construction of mountain highway tunnels under the existing railway is becoming more and more common,and the impact on the existing lines is worthy of attention.The mechanical behavior of rock mass in tunnel drilling and blasting construction is complex,and it is difficult to control the disturbance degree of adjacent structure,which leads to great challenges in undercrossing drilling and blasting construction.It has certain theoretical and application value to study the influence of tunnel blasting construction on overlying rock mass and existing railway.Therefore,based on the Xiaba tunnel project of Guizhou Naqing expressway,based on the theory of stress wave and rock damage,the three-dimensional cyclic blasting numerical simulation is used as the research method,combined with the field monitoring data,the vibration and damage of rock mass,the disturbance degree of rock mass under different geological conditions,the additional stress and displacement of adjacent bridge pile foundation under blasting construction conditions are systematically studied.The main work and achievements are as follows :(1)Based on the theory of blasting stress wave propagation,the propagation law of blasting stress wave in rock mass and its influencing factors are expounded.At the same time,according to the disturbance degree of rock mass from different blasting sources,the rock mechanical behavior in the near,middle and far areas of the blasting source is clarified.Finally,the rock damage constitutive model under blasting load is introduced,which provides a theoretical basis for subsequent research.(2)Through the numerical simulation of tunnel cyclic blasting construction process under different geological factors,it is found that the greater the initial stress of surrounding rock,the greater the peak value of particle vibration and the smaller the damage degree.Bedding has little effect on the internal vibration velocity and damage of rock mass;the higher the level of surrounding rock,the greater the peak particle velocity and damage degree.Based on the multiple linear regression method,it is found that the initial stress field is the dominant factor affecting the vibration velocity of rock mass in the near and far areas of the explosion source.In addition,the grade of surrounding rock is the dominant factor affecting rock mass damage and promotes rock mass damage.(3)In order to quantitatively give the degree of disturbance of different tunnel excavation methods to the railway and surface,the numerical simulation tests of drilling and blasting excavation and cold excavation schemes were carried out with the settlement of surface and pier as the investigation index.Before crossing the railway bridge,compared with drilling and blasting excavation,the settlement values of each stage under cold excavation are larger.After crossing the railway bridge,the cumulative settlement value of drilling and blasting excavation is very significant,and the shallower the tunnel buried depth,the settlement gap between the two will further expand.Among them,under the excavation of drilling and blasting,the settlement tends to be stable after the tunnel face passes through the bridge 30 ～ 40 m;under cold excavation,the settlement tends to be stable after the tunnel face passes through the bridge for 10 ～ 30 m.Therefore,when the buried depth of the tunnel is shallow,it is necessary to use drilling and blasting excavation carefully,and cold excavation should be adopted.(4)According to the simulation analysis results of tunnel blasting under the existing bridge under the most unfavorable conditions,the variation law of additional stress and displacement of pile foundation caused by construction is revealed.The research shows that the proximity of the tunnel face to the pile foundation will increase the additional stress,and the pile will move away from the explosion source.After the tunnel face passes through the pile foundation,the additional stress and displacement gradually weaken.Finally,according to the existing research results,the corresponding control measures are put forward according to the stress characteristics of pile foundation.(5)Based on the actual situation of the site,different rock mass vibration velocity monitoring schemes are formulated,and the attenuation of the vibration velocity of the explosion stress wave along different propagation paths is revealed.At the same time,the error between the numerical simulation results and the measured data is discussed.Finally,the construction countermeasures of different railway adjacent areas are proposed.