Abstract:
ABSTRACT
Unreinforced displacement augercast piles, or rigid inclusions (RIs), were installed for foundation support of a combined sewer overflow treatment building. The RIs penetrated loose silty sand and soft silt and terminated in medium-dense silty sand, approximately 40 feet below finish grade. The building houses water-holding basins and level-sensitive weirs and equipment. The use of the RIs, in combination with settlement monitoring and water preloading, saved millions in foundation costs compared to more traditional pile foundations.
Strain gauge-instrumented static axial load tests and pile integrity tests (PIT) were conducted on the RIs as part of quality control for this technology, which was relatively new to the Pacific Northwest. Strain gauge monitoring continued during the installation of the remaining production RIs, construction of the building, and water preloading. The PIT, verified by excavation of an RI with a shallow PIT anomaly, indicated that the installation process fractured adjacent RIs which had partially been set, even after several days of curing time. While the composite RI-reinforced ground and load distribution mat system performed as expected for settlement control and was not needed for lateral support, RI fractures as observed in this project might need to be controlled in other situations.
Case history information regarding the subsurface fill and deltaic deposit character, RI installation production rates, RI testing procedures and results, and construction settlement monitoring are presented.