Stone Columns for Control of Power Station Foundation Settlements

At a gas-fired power station site, previously placed fill and loose/soft soils to depths of about 4 m required the use of piles or soil improvement for foundation support. Soil improvement by stone columns was selected because removing and replacing the upper soils was not feasible due to shallow groundwater. Also, cost and schedule considerations indicated that stone columns would be more cost effective than piles. Calculations were performed to optimize stone column grids to improve the subsurface conditions and reduce the anticipated foundation settlements to within tolerable limits. A pre-production, large-scale field load testing program provided additional data to support the grid optimization. Stone columns were then installed using the dry/bottom-feed method at configurations determined from the optimization study. Production installation of stone columns, foundation construction, and detailed settlement monitoring for a period of about 1½ years have indicated excellent foundation settlement performance. The results have also validated the design assumptions and confirmed the adequacy of the selected, cost-effective foundation system.