Study and application of strengthening mechanism of square confined concrete arch with grouting holes

The new support way-square confined concrete (SQCC) arch in complex-condition underground engineering applications has higher supporting strength and post-bearing capacity. The grouting holes become key parts of the arch with local weakening and stress concentration effects and greatly influence the bearing capacity of the whole arch. As such, it is necessary to reinforce this area. In laboratory tests and numerical experiments on SQCC test specimens with grouting holes, the strengthening mechanism was investigated by comparative analysis of the mechanical properties, including the deformation and failure patterns, load displacement curve, and ultimate bearing capacity. To compare the different reinforcing effects, strength and economic indexes were established. The results show the ultimate bearing capacity of a short column with grouting holes to be reduced by 29.9% compared to the SQCC short column. In a case study of the SQCC150×8 short column, the reinforcement method using two-angle steel exhibited better reinforcing effect, improving both the strength and economic indexes of short columns up to 148.7% and 90.8%, respectively. When the length of the reinforcement plate ranges from 180-240 mm and the plate thickness is 8 mm, the reinforcement effect is best, and the economic index also reaches its peak value. Moreover, the angle steel strengthening (ASS) experiments was conducted in a full-scale laboratory test. The application of SQCC arches in roadway supports has a good effect, and these research results provide a basis for the design of confined concrete support.