Study on the range test and evolution law of surrounding rock loose circle in cross-layer roadway

In order to explore the development and expansion law of surrounding rock loose circle in cross-layer roadway, this paper takes the return air uphill in Qingdong No.7 mining area of Huaibei as the background, the development and expansion characteristics of surrounding rock loose circle in roadway are studied by theoretical analysis, laboratory test, numerical simulation and field measurement, and a similar simulation method for testing the development characteristics of loose circle by optical fiber is proposed. The results show that when the surrounding rock of roadway is mudstone, sandy mudstone, fine sandstone and siltstone based on Mohr-Coulomb criterion, the radius of loose circle is 1.72R₀, 1.65R₀, 1.41R₀ and 1.42R₀, respectively. The development range of loose circle is negatively correlated with the strength of surrounding rock. The similar simulation test shows that the failure range of the roadway section is positively correlated with the stress. Under high stress, the section is easy to be destroyed and the fracture development range is approximately semi-circular. The results of DIC digital speckle show that the displacement of surrounding rock around the roadway is gradient distribution, and the range of surrounding rock loose circle is 2 m surrounding rock displacement boundary area around the roadway. Distributed optical fiber monitoring shows that there are two strain mutation inflection points in the process of entering the surrounding rock. The first strain mutation point is the range of surrounding rock loose circle, and the second strain mutation point is the range of surrounding rock plastic zone. The range of surrounding rock loose circle develops from 1.24 m to 1.84 m under gradient stress. The increase of stress leads to the expansion of the development range of loose circle and the gradual decrease of surrounding rock stability. The numerical simulation results show that the development range of the excavation loose circle of the cross-layer roadway is 0.62-1.86 m, and the expansion range of the loose circle is determined by the adjacent surrounding rock. The field geological radar is measured from 10 m to 200 m from the working face, and the range of the floor loose circle is developed from 1.45 m to 1.95 m. The method of distributed optical fiber monitoring loose circle in similar simulation experiment is consistent with the test results of other methods, which can provide the basis for the test of roadway loose circle and the stability control of surrounding rock.