The in situ hydraulic properties of fault zones in mine roadway floor

Abstract

In this study, we explored the hydraulic properties of the fault zone at different positions of roadway floor using in situ high-pressure water injection tests under controlled water injection. During the test, injecting water flow rate and pressure as well as water pressure in the monitor borehole were continuously measured and recorded. The test results showed that changes of injecting water pressure in the fault zone obey the changing characteristics of the typical hydraulic fracturing pressure. Analysis of the test results showed that the hydraulic process could be divided into original and post-fracture stages at the breakdown pressure. In the original stage, the flow dimension (v) continuously increased. In the post-fracture stage, the equivalent hydraulic fracture aperture (b) also continuously increased even when the flow rate decreased. The fracturing-induced fractures were scoured during water injection. In addition, the original hydraulic conductivity (K) of the fault zone decreased while the hydraulic fracturing breakdown pressure (P0) increased with the distance (D) of the test point to the roadway floor increasing. The main cause for these phenomena was the difference in the stress states of the fault zone at different locations of the roadway floor.