Representativeness of jointed rock mass hydraulic conductivity obtained from packer tests for tunnel inflow rate estimate

In current engineering practice, groundwater inflow into a tunnel in a jointed rock mass is estimated using the equivalent hydraulic conductivity, which is often estimated from packer tests. In a jointed rock mass, however, the flow rate out of a packer interval is controlled mainly by the hydraulic conductivity of joints intersecting the packer interval, which in turn depends on joint characteristics and effective joint normal stress. If the state of stress, or the geological conditions, of joints intersecting a packer interval are significantly different from those intersecting the tunnel, the equivalent hydraulic conductivity estimated from the test might not be representative in estimating groundwater inflow rate into the tunnel. In this study, the potential impact of different stress distribution and geological characteristics of joints around a packer interval from that around a tunnel is discussed on the basis of the concept of hydro-mechanically coupled behavior of joints. The effect of anisotropic characteristics of the jointed rock mass around a packer interval is also discussed through numerical parametric study using the distinct element method. Based on the numerical analysis results and literature review, subsequent guidelines and recommendations in performing packer tests are provided.

Highlight
► Flow rate out of a packer interval is controlled mainly by joint permeability.
► Joint stress and flow conditions around packer interval and tunnel are different.
► Performing packer tests with low internal pressures is suggested.
► Influence of anisotropy of a jointed rock mass on the permeability is not significant.
► Volume engaged by packer test needs to be similar to that by the tunnel excavation.