Building a Better Solution—Combining Water Injection and Stone Columns

The presence of hydro-collapsible soils beneath the proposed Erie Police Station project site led to the successful combination of two ground modification techniques. Normally in the presence of up to 30 ft (9 m) of hydro-collapsible soils, the soils are either over excavated and replaced, or the structure is supported by a deep foundation system. A collaboration between Hayward Baker Inc. (HBI) and GROUND Engineering Consultants (GROUND) resulted in an alternative two step ground modification process. The first step consisted of water injection to pre-collapse, “treat,” the soils to a depth approximately above “perched” water levels, at about 18 ft (5.5 m). Consolidation tests were subsequently conducted on treated soils obtained from across the site to evaluate the effectiveness of the treatment process. In the second step, stone columns were installed to increase the bearing capacity at spread and column footing locations. The combination of these techniques provided the client with a sufficient foundation design that was cheaper and faster to construct when compared to conventional over-excavation and replacement or deep foundation system options.