Failure mechanism of surrounding rock with high stress and confined concrete support system

Surrounding rock control is a big challenge in roadway with high stress in deep underground engineering. To address this issue, Zhaolou coal mine - a typical kilometer deep well is taken as engineering background to monitor and analyze the original support scheme. The analysis shows that the following main reasons lead to the support failure in roadway with high stress in deep underground coal mine. Roadway deformation is large and lasts longer with a large extent of damage; all anchor bolts are in severely damaged surrounding rock zone without reliable adhesive basis; and U-shaped steel arch unevenly contacts with surrounding rock without sufficient bearing capacity. With summary of support failure mechanisms on-site, a concept of “high-strength and integrity support” is put forward; a support system with square steel confined concrete (SQCC) is developed; and a full scale in-door comparative test is conducted on its core component - SQCC arch and also on the conventional U29 arch. The research shows the bent and damaged legs of U29 arch result in dramatic reduction of bearing capacity of arch. However, the SQCC arch with similar steel content has a bearing capacity of 2.15 times of that of U29 arch and still has a higher post bearing capacity even after the arch is deformed dramatically. Quantitative evaluation index is established such as vault displacement control rate and bolt strength utilization rate; comparative analysis is made on surrounding rock control mechanism and the mechanical properties of support components under the influence from the four factors - arch strength, geostress, lateral pressure coefficient and surrounding rock mechanical parameters; and good control effect on surrounding rock of SQCC support is verified. Comparative tests are conducted on site. The monitoring results show the roadway surrounding rock deformation on the test section of SQCC support is only 21.2% of that on test section of U29 arch support; and no yield and damage occurs on the test section of SQCC support. Therefore, the SQCC support system is proved to be effective on surrounding rock control.