Consideration of potential groundwater impacts in rock tunneling

The evaluation and mitigation of the potential groundwater impacts of two rock tunnels in the San Bernardino Mountains in southern California is described. The principal impact considered was dewatering of groundwater, which was a serious concern to the project’s immediate neighbors. In the planning stage the feasibility of allaying this concern was established by modeling anticipated tunnel inflows and a monitoring program was implemented to verify assumptions and performance during construction. In the design stage features to mitigate groundwater effects (impervious lining, pre-excavation grouting) were included. Observations taken during construction permit the refinement of the groundwater control measures. The ability to mitigate groundwater impacts was important in obtaining project acceptance by the local community.