Study on different influence factors of in-situ stress unloading by dynamic excavation in circular tunnel

Abstract

With the depth of underground mining increase, the in-situ stress is more and more high, which may causes strong disturbance to surrounding rock. To study in-situ stress unloading in blasting excavation of roadway. The unloading influence factors with wave velocity, excavation radius and unloading time are discussed by defining unloading rate. The in-situ stress unloading experiments are performed by impacting different material models. And consider the unloading influence factors with axial stress, excavation radius and lithology in experiment. The results show that unloading stress is fluctuate during in-situ stress unloading, unloading stress decrease first, then increase, and tend to be stable finally. During in-situ stress unloading process, the unloading rate increases with the increase of rock wave velocity, and the more disturb severely of different rock velocity with the unloading rate increases. The unloading rate increases with the increase of rock excavation radius, and the larger scale disturb of different excavation radius with the unloading rate increases. The unloading rate increases with the decrease of unloading time, and the more dynamic disturb intensely of different unloading time with the unloading rate increases. The experiments show that radial cracks are generated by impact stress wave and circular cracks are generated by unloading stress wave. Comparing unloading result, hard rock material generate more damage area than soft rock material, unloading damage of soft rock material focus near excavation face and generate more cracks. Smaller excavation radius are not generate circular crack, it also shows that rock storage energy release completely need enough unloading space.