Water Inflow Control In Unlined Rock Cavities

The requirements for water inflow control for the Chicago Intercepting Sewer System are stringent. This posed special problems in grouting the bored and conventionally mined tunnels, shafts and chambers of the system. In adapting conventional grouting techniques to the specific problems encountered in the system's pilot project, numerous field procedures were developed. Careful preand post-grout testing and evaluation identified the most efficient and economical of these procedures. As an example of some of the conclusions reached during the project it was found that the mineralized groundwater in the Chicago area tended to reduce the efficiency of the grout holes, thus limiting their useful life. Pressure washing to remove natural fillings was a critical factor in achieving a permanent grout seal. The value of relatively thin lubricating grout mixes was definitely established. Although not an ideal situation, satisfactory results could be obtained by manifold grouting several grout holes simultaneously if done within specific limits of hole groutability, location and numbers. Caulking proved to be a primary controlling factor in achieving acceptable results. To achieve such a high degree of water inflow control requires close supervision by experienced personnel. "Temporary grouting as a construction expedient" produces seepage conditions which are extremely difficult to treat.