The Effects of Horizontal Drain Holes Near High Temperature Excavation Surfaces

Abstract

The use of drain holes for de-pressurizing the near-wall zone of excavations is well understood when the groundwater is cold. However, in certain high temperature conditions (hot groundwater and potential for boiling), there is little experience in the use of drain holes. The objective of this work is to determine the effectiveness of drain holes when there are high temperatures near an excavation. A three-dimensional model of a typical vertical section through a future excavation site was developed with the TOUGH2 heat and mass transport code. The model was used to assess a number of different excavation scenarios. These included using different temperatures in the model, varying the excavation rates and pit face angles, varying the permeability, and including a vertical steam relief well. The results show that the use of drain holes in the walls of an excavation in a high temperature zone is an effective means of reducing the temperature and pressure. In some cases vigorous boiling occurs when the drain hole is first drilled, which leads to a high flow rate of steam.