Influence of structure and water pressure on the hydraulic conductivity of the rock mass around underground excavations

• Hydraulic properties of the rock mass were investigated using in situ tests.
• We used a numerical model to analyze the influence of the damage zone.
• Hydraulic conductivity is strongly related to rock structure and water pressure.
• Hydraulic characteristics are substantially influenced by the damage zone.

In this study, in situ water injection tests and numerical modeling in conjunction with core logs and television image measurements were applied for an investigation of the hydraulic properties of the rock mass around underground excavations. The aim of our work was to investigate the influence of rock structure and water pressure on the hydraulic conductivity of the rock mass around underground excavations. Thus, water injection tests were conducted in four boreholes that were drilled in the rock mass in underground tunnels in China. Seepage connection initiation and steady state seepage were proposed to identify the seepage evolution course within the rock mass by combining the results of pressure and hydraulic conductivity. Generally, hydraulic conductivity is strongly related to rock structure and water pressure. The results also revealed that a rearrangement of rock structure would occur in the damage zone, resulting in an increase in hydraulic conductivity of nearly one to several orders of magnitude. The results from the modified numerical model showed that the pore water distribution and the groundwater inflow rate are affected by both the hydraulic conductivity and the thickness of the damage zone and they are influenced more by the thickness of this zone.