Grouting and Ground Treatment: Proceedings of the Third International Conference, (ASCE)
Compaction Grouting Used for a Water Treatment Plant Expansion
M. W. Oakland, M. L. Bachand
This paper discusses the selection, design and implementation of compaction grouting to densify a zone of loose sands and silts below a proposed expansion to the Adkins Water Treatment Plant in Six Mile, South Carolina. The water treatment plant is owned and operated by Greenville Water System. The expansion included construction of a duplicate set of sedimentation basins and filters adjacent to the existing basins. Each set of basins is about 183 m (600 ft.) in length and 34 m (110 ft.) in width spanning across a shallow natural valley. Settlements of up to about 27 cm (10.5 inches) were observed following construction of the original basins. To avoid settlement of the new structures and provide a foundation compatible with the existing basins, compaction grouting was selected as a versatile remediation technique to densify areas of loose sands and silts that were identified in the center portion of the natural valley. Compaction grouting allowed remediation of only the problem areas while conventional foundation support could be used to at the ends without special transition features. Special design considerations included using compaction grouting in the silty environment. Slow rates of injection combined with high ultimate pressures were selected to avoid hydrofracturing or the need for wick drains. The high pressures were possible due to a thick layer of overburden from the previous site grading. However, sequencing considerations, allowing the contractor to begin foundation in remediated areas while the compaction grouting was still underway, limited the pressures that could be used in some areas of the program. While the settlement of the existing basins appear to have stabilized, as a precautionary measure, the grouting program was extended to stabilize the loose soils below the existing basins to limit potential future seismically induced settlement. Inclined injection holes were drilled at several angles below the existing basins. Careful monitoring and control of injection pressures and rates were essential to avoid heaving the basins. The paper summarizes the history of the project from identifying the previous settlements, through selection of the remediation technology, to construction performance. The paper discussed evaluation of remediation alternatives, reasons for selection of compaction grouting, construction monitoring and revisions of the program in the field to account for accrual grout performance. The paper also presents a summary of grout takes, pay items and confirmatory testing program to assess the effectiveness of the compaction grouting.
|article #1140; publication #62 (GRT-2003)|