Study On Safety Evaluation Of Blasting Vibration Of Double-Arch Tunnel Passing Through Military Tunnel

With the rapid development of China's economy,the efforts of various local governments to build transportation infrastructure are also increasing.In order to improve the transportation network,various types of tunnels need to be built in various cities.Newly built tunnels will affect the safety of nearby buildings.This thesis relies on the Beifeng tunnel in the reconstruction project of Daishan section of National Power Construction Group 526 National Highway,combined with the numerical simulation software ANSYS / LS-DYNA,to study the blasting vibration characteristics of the double arch tunnel adjacent to the existing military tunnel.Mainly entered the following work:(1)By consulting the literature,a certain number of publicly published measured data were selected as the test samples.Compare different forms of regression formulas.Investigate the characteristics and application scope of different formulas.It is concluded that the multiple linear regression formula has higher fitting accuracy,but it is not applicable to the case where the distribution range of the dose or burst distance is small and the sample repetition rate is high.The cubic root scale or square root scale formula can be used to predict when the distribution of the dose or burst distance is small and the sample repeat rate is high.When the average value of the cube root scale ratio dose is less than 0.07,the cube root scale formula can be used,otherwise the square root scale formula is used.(2)Through the existing engineering cases,study the feasibility of using ANSYS to directly establish an explosive model for calculation.It proves that the numerical simulation method adopted in the subsequent research on the effect of double-arch tunnel excavation and blasting on the existing military tunnel structure is reliable.(3)According to the characteristics of the newly-built Beifeng tunnel and the existing military tunnels,the vibration response characteristics of the existing military tunnels during the blasting construction of the newly-built Beifeng tunnel are studied in depth.The blasting vibration velocity and maximum principal stress at various points of the tunnel lining section are analyzed.Study the propagation law of blasting seismic waves in surrounding rock and military tunnel lining.It is concluded that in the case of Grade III surrounding rock,the three-step method of pilot tunnel blasting has a greater impact on the existing military tunnel lining.Vibration velocity is not only related to the burst distance,but also to other factors such as structural shape.There is no relationship between the peak value of the vibration velocity of the inner and outer linings of the same measurement point of the military tunnel in each working condition.The peak value of the maximum principal stress at the bottom of the lining arch is the largest.Key monitoring should be carried out at the base of the arch.(4)Under the condition of different blasting lengths,conduct numerical simulation on the pilot tunnel of the newly built Beifeng tunnel.Perform dynamic response characteristics analysis and structural vibration safety assessment of existing military tunnels.The optimization of the blasting vibration damping method of the newly built Beifeng tunnel was carried out at different time intervals.It is concluded that the vibration velocity threshold of the existing military tunnel lining under the blasting of Beifeng Tunnel is calculated.Blasting with a time interval of 25 ms can significantly reduce the speed of blasting vibration.