Strain Evolution and Failure Mode of Straight Wall-Arch Cavern under Impact Load

In order to study the effect of impact load on straight-wall arch cavern and surrounding rock, large-scale steel fiber reinforced concrete specimens were prepared, and a self-developed pendulum impacting system with biaxial stresses was used to carry out impact tests. A super-dynamic information acquisition system was used to record the impact force and internal strain, and digital image correlation technology was used to characterize the surface strain field. 0.6 MPa stress was applied vertically, and the height of 2000 kg pendulum was raised to 150 mm. The results show that: The shock wave with amplitude attenuation was a typical low-frequency shock wave. Four cracks appeared in the spandrel and foot of the straight wall arch specimen, and the cracks at the spandrel were connected by a circumferential crack on the vault of the cavern. The internal peak strain and plastic strain are mainly tensile strain, compressive strain distributed near the left foot of the tunnel. The peak strain was larger in the circumferential direction, smaller in the radial and axial direction. And the plastic strain in the left spandrel was the largest. And the vault was prone to plastic deformation which can not be recovered through peak or plastic strain, but the ratios of plastic strain to peak strain in the vault were all larger. DIC strain cloud map showed that within less than 200 μs, the four cracks of spinner and foot of the sample were formed and connected, and the vertical strain changed the most, the vertical strain concentration area was consistent with the fracture morphology, the horizontal strain concentration area mainly appeared at the spinner position, and the shear strain concentration area was mainly distributed at the bend of each crack.