Advances in California - Ground Improvement Support of Heavy Foundations

摘要

Ground improvement has been used extensively in the western United States in recent decades to support heavy foundations, to increase soil stiffness and bearing capacity, to control static and seismic settlement, and to reduce the damaging effects of soil liquefaction. With recent changes in the California Building Code and evolving environmental regulations, engineers are relying more on specialty geo-contractors to provide deep foundations and stiff ground improvement systems to support heavy foundation loads with increased seismic demands. We aim to present agency-accepted ground improvement methods that have been used in California and advances in these methods to meet Code changes and regulatory demands in California with specific emphasis on the Drill Displacement Column™ (DDC) system. This paper describes seismic events and changes to Code that have driven advances in engineering design in California, including recent developments and challenges of ground improvement techniques such as Drill Displacement Column™ and Rammed Aggregate Pier® technologies. Environmental conditions including noise and vibrations, contaminated soil sites, regional groundwater protection zones, and regulatory agency requirements, can often affect the design and delivery of ground improvement systems. The DDC system (a type of rigid inclusion and composite ground system) has received increasing attention in California due to the needs for environmentally safe ground improvement, higher bearing capacity below shallow foundations, reduction of soil off-haul, and no-vibration construction requirements in dense urban areas. Structural considerations for foundation design are presented for Drill Displacement Column™ and Rammed Aggregate Pier® (RAP) systems. For example, in California, the DDC system offers strong, uniform support with very stiff ground improvement that requires specific engineering and construction considerations to eliminate footing hard points and that laterally disconnect the ground improvement from foundations and the mass lateral forces during seismic motion from the structure above. In addition, a summary of agency approvals will be presented for the DDC ground improvement system.