Spillway Void Filling
Large voids were discovered under the spillway slabs on a dam. The dam separated a tidal, brackish swamp from a semi-tidal, brackish retention lake adjacent to a convention center. As part of a water quality improvement project, the engineer specified spillway void filling. The general consensus was that the spillway slabs were pile supported and therefore structurally stable. However, the concern was that erosion under the spillway slabs would extend to the adjacent embankment, destabilizing the embankment.
The designer specified pressure grouting with flowable fill. There was extensive flow through the voids at any water level. Because of the elevation drop in the washout and the high volume of water flow, this posed great difficulty for the high slump of material that would be required due to the necessary pumping distance.
CJGeo proposed polyurethane grouting for filling the void below the spillway slabs. Polyurethane grouts are formulated for injection into flowing water streams without affecting grout integrity. Polyurethane grout can also be pumped long distances without needing to use higher slump mixes.
Polyurethane grouts are lighter than water, so have the potential to be buoyant in aquatic environments. However, the 16″ thick concrete slabs of the spillway compensated for the buoyancy of the polyurethane grout.
CJGeo successfully completed the spillway voids filling in less than a day. Approximately 28 cubic yards of polyurethane grout were installed. The polyurethane grout provided an unfactored bearing capacity of 13ksf.