Deep lying aquifers are a major hazard in shaft sinking and it is essential to obtain prior knowledge of their location, transmissivity, pressure and nature of porosity in order to assess the potential inflow to the excavated shaft. This helps to determine the most appropriate means of ground treatment to minimize water inflow during the subsequent construction.
Aquifer test methods based on the measurement of the recovery of pressure in a single borehole following a period of controlled flow, such as the petroleum industry ‘drill-stem test’, are generally the most appropriate techniques. Several modifications of the standard drill-stem test are described including a new type of probe-hole test carried out during shaft construction from the advancing excavation face. This test has also been used to assess the effectiveness of a cover grouting operation.