Quality testing of bolt support in deep roadways of mining districts(3)

5. Conclusions

Through plenty of non-destructive testing of axial bolt load in deep roadways of mining districts, the use of pre-warning indicators of axial bolt load in the initial support stage, pre-mining stage and mining disturbance stage is proposed. This provides a new, simple but reliable technique to judge the effectiveness of bolt support and the stress state of surrounding rock. The main conclusions are as follows:

(1)The axial bolt load in different roadways changes with basically the same rules. In the initial support stage, the axial force of the newly-installed bolts increases rapidly; the increase tends to slow down at a certain distance from the working face. In the pre-mining stage, roadway deformation goes into a stable state and the axial bolt load changes slightly. In the mining disturbance stage, the axial bolt load is generally greater. Even within the forepole support zone, the axial bolt load fluctuates drastically.

(2)The change of axial bolt load corresponds to the stress adjustment of surrounding rock. The axial bolt load and its change can reflect the roadway deformation and stability. Through testing the axial bolt load in different zones, abnormal axial bolt loads can be detected, thus taking corresponding pre-warning measures to eliminate the potential safety hazards. Meanwhile, the axial bolt load and its change can indicate whether the bolt support design is reasonable or not, thus providing reference for bolting parameters optimization.

(3)The pre-warning indicators of axial bolt load in different mining service stages are proposed, so is the prediction technique of roadway surrounding rock stability. In the initial support stage, bolt pre-tension should be set at 30% of its yield load and the axial bolt load should be kept between 30%-50% of its yield load (Ps); the pre-warning indicator of axial bolt load is 50% Ps. In the pre-mining stage, the axial bolt load should be kept between 50%-60% of its yield load; the pre-warning indicator of axial bolt load is 60%-80% Ps. In the mining disturbance stage, the axial bolt load should be kept below 80% of its yield load; the pre-warning indicator of axial bolt load is 80% Ps.