Geopier's Low-Impact Foundation Support for Poor Soils

Developed by Geopier Foundation Company in 1989 and used on over 4,000 buildings since, a RAP system starts by auguring 30-inch-wide shafts 7–30 feet deep and filling them with crushed rock in small batches. A specially designed hydraulic hammer compacts the aggregate at a rate of several hundred hits per minute at an energy exceeding one million foot-pounds. The ram’s angled shape forces the aggregate down and laterally to compact and stabilize the surrounding soil. The first layer uses clean stone to form a “bottom bulb” that stabilizes the soil at the pier’s base. Each additional layer is made from smaller road-grade aggregate or other materials compacted vertically to a thickness of about one foot until the shaft is completed.

Though there are many options for installing foundation supports in poor to moderately poor soil, one of the most common involves excavating and disposing of the poor soil and bringing in engineered fill to replace it. The removal of these materials through trucking consumes fossil fuels, is logistically difficult in urban areas, and often increases toxic emissions in dense urban neighborhoods. With the RAP system, the small volume of soil that is removed during installation can often be reused onsite, and much less aggregate needs to be trucked in than is typical. (The company’s Impact RAP system does not remove any soil and is used on contaminated sites). According to the company, use of a RAP system could also allow for use of a shallow foundation or floor slab in place of a deep foundation or structural floor slab, requiring fewer materials and less embodied energy—particularly from concrete—to produce and install.