Dynamic response analyses and improvement countermeasures of shed-tunnel destruction under rolling stone impact: a case study of the shed-tunnel in the southern foot of the Anjiula Mountain on the Sichuan-Tibet Highway

The door-type anti-rolling stone shed-tunnel located at the southern foot of the Anjiula Mountain of the Sichuan-Tibet Highway was seriously damaged under the impact of rolling rocks on the high and steep side slope of the roadside. The huge impact force caused by rolling rocks led to the destruction of the stress concentrated parts of the longitudinal beam, roof and beam-column connection of the shed-tunnel, and after the impact of rolling rocks, a large number of rocks accumulated on the roof of the shed and became permanent loads. The structural dimensions of the shed-tunnel were measured with the tape gauge, and the maximum diameter D=1 m and the maximum falling height H=20 m of the accumulated rolling stones on the roof were measured with a range finder. In order to solve the safety problems of the door-type shed-tunnel, the original structure was reformed by setting grooves on the roof and laying rubber cushion with a thickness of 10-70 cm in the groove and an outward slope of 6 degrees. With the help of LS-DYNA dynamic finite element software, the finite element models of the improved shed-tunnel are established according to the actual size, and the dynamic response of the shed-tunnel under the most disadvantageous conditions (H=20 m, D=1 m) is simulated. The stress performance of the improved shed-tunnel is verified by comparing the numerical simulation results. It is found that the maximum equivalent stress decreases by 72%, the maximum deflection of the roof decreases by 45%, the impact force of falling rocks decreases by 62%, and the probability of rolling rocks accumulating on the roof of the shed-tunnel decreases significantly. The results indicate that the measures of installing rubber cushion on the roof can effectively solve the safety problems existing in the door-type shed-tunnel.