SuperJet Grouting Reduces Foundation Settlement for La Rosita Power Plant in Mexicali, Mexico

Subsurface conditions at the site of the planned La Rosita power plant in Mexicali, Baja California, Mexico, consisted of approximately 7 to 8 m of very stiff to hard clay overlaying a loose silt layer. Beneath the silt, very-dense sand and medium stiff to very stiff clay layers were encountered. Design calculations indicated that without piled foundations or ground treatment to improve the engineering properties of the silt layer, settlements of the plant foundations would exceed tolerable limits. SuperJet grouting was used to bridge the loose silt layer at depth to provide both foundation support and settlement control, successfully reducing the anticipated settlements to within acceptable values. The basis for the SuperJet program design was that the grout columns would transfer the loading from the upper stiff clay to the underlying dense sands. Optimum column spacing was determined based on the anticipated loading on each column, the estimated diameter of the columns, and the ability of the overlying stiff clay soils to bridge from one column to the next. SuperJet grouting was performed under all heavy foundations, including the stacks, heat recovery steam generators (HRSGs), combustion turbines (CTs), and steam turbine generator (STG). The SuperJet grouting program was successfully conducted between March and May 2001. The power plant is now under construction, and the measured settlements of the foundations have been within the anticipated range based on design calculations.