What is the purpose of Lugeon tests in hydrogeological investigations?

Lugeon tests are in-situ hydraulic tests performed in boreholes to determine the permeability or hydraulic conductivity of rock masses. The primary purpose is to quantify the water-tightness of the rock formation by measuring the rate at which water is injected into a section of the borehole under a specific pressure. The results are expressed in Lugeon units (LU), where 1 LU corresponds to a water intake of 1 liter per meter of borehole length per minute at an injection pressure of 10 bars. The Lugeon test helps characterize the degree of fracturing and jointing in the rock mass, as these features control the flow of water. Higher Lugeon values indicate greater permeability and more fractured rock. The data obtained from Lugeon tests are used to assess the potential for groundwater inflow into tunnels or other underground excavations. They also help in designing appropriate groundwater control measures, such as grouting, to reduce water inflow and stabilize the ground. Furthermore, Lugeon tests can identify zones of high permeability that may require special attention during construction. The 'permeability' or 'hydraulic conductivity' of a rock mass is a measure of its ability to transmit water. 'In-situ' refers to tests performed in the ground, as opposed to laboratory tests on samples. 'Grouting' is the injection of a pumpable material into soil or rock to improve its strength or reduce its permeability. A 'borehole' is a narrow shaft drilled into the ground for investigation or construction purposes.