Study on blasting vibration damage effect and overbreak and underbreak control of deep buried tunnel surrounding rock

In order to explore the blasting vibration damage effect of deep buried tunnel and the control law of overbreak and underbreak, taking the No.2 cross tunnel of Wufeng tunnel of Yifu high speed railway as the engineering background, a three-dimensional numerical model was established by using ANSYS/LS-DYNA and HJC constitutive model to systematically simulate the blasting vibration response, damage evolution and overbreak and underbreak characteristics of surrounding rock. Combined with three-dimensional laser scanning, the quantitative evaluation of blasting forming quality of surrounding rock was carried out, and the construction optimization scheme was proposed and verified on site. The results show that the peak vibration velocity of surrounding rock particles near the blasting zone presents the distribution characteristics of "vertical>horizontal radial>axial", and the vertical direction is the dominant direction of vibration energy transfer; The blasting damage evolution of surrounding rock can be divided into three stages: cutting into cavity, step-by-step excavation, and peripheral hole penetration; Affected by the energy superposition and stress concentration between blastholes, the side walls and footings on both sides near the blasting area have high vibration velocity, large damage and significant overbreak. The maximum overbreak of the right footings is 34.7 cm, which is the key control part of overbreak and underbreak. The field measured data show that the maximum average overbreak is 53.3 cm, the maximum average underbreak is 6.9 cm, and the average linear overbreak is 22.5 cm, both exceeding the specification limit, which are quite different from the numerical simulation results. The field investigation found that the actual layout spacing of peripheral holes was uneven, and the number of holes was insufficient, which led to the imbalance of blasting energy distribution in the section. Based on this, a correction scheme with drilling control as the core, intelligent equipment positioning as the guarantee and dynamic feedback as the closed loop is proposed. The field application shows that the under excavation in the test section is eliminated, the maximum average over excavation and the average linear over excavation are reduced by 31.7% and 31.6%, respectively, and the over excavation and under excavation are significantly improved. Aiming at the problem of local overbreak after optimization, through the analysis of three-dimensional geological reconstruction model, it is revealed that it is mainly caused by local wedge falling, and then the dynamic optimization measures of blast hole considering geological factors are put forward.