Drilled Displacement Columns as Ground Improvement in San Francisco

Drilled displacement columns (DDCs) can improve loose granular soil and transfer loads through weak soil. DDCs and the improved soil surrounding the DDC act as a composite system supporting structural elements, such as foundations and slabs. DDCs use a displacement drill tool to displace and densify granular soil laterally, resulting in improved soil and fewer spoils during installation. DDCs can increase bearing capacities, reduce settlement, and increase soil’s resistance to liquefaction. This paper discusses the benefits of DDCs as ground improvement elements and provides a case study of a project in San Francisco, California. In this project, DDCs were installed to reduce foundation settlement and transfer building loads to a deeper bearing stratum. To confirm the adequacy of the DDCs, load tests were performed on four test elements to ensure they could support the anticipated loads with an acceptable settlement.