Foundation Design and Construction Challenges with Marsh Deposits in a High Seismic Risk Zone-Paper

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The project involved foundations for a $180 million biosolids-processing and energy-recovery plant built on marshland in Orange County, California, within a high seismic risk zone. The site contained up to 45 feet of extremely soft, compressible peat and organic clay over dense sand and gravel, with shallow groundwater. Because the ground conditions qualified the site as seismic Site Class F, the design required site-specific seismic hazard analysis and response spectra based on six earthquake time histories.<br /><br />Ground improvement and drilled piers were unsuitable, so the team selected driven, 14-inch precast prestressed concrete piles. Working closely with the structural engineer, they evaluated pile-cap and mat-slab foundations; mat slabs proved more economical. More than 3,000 piles supported the major structures, including over 1,200 for the three large digester tanks and associated buildings.<br /><br />An indicator-pile program using a pile-driving analyzer verified pile performance and established production-driving criteria. Test results enabled the design pile lengths to be shortened by more than 52,000 linear feet, reducing material costs and installation work. During construction, some piles still could not reach their design tip elevations. Where full penetration was needed for lateral capacity, contractors predrilled the pile paths. More than 330 piles that encountered refusal were cut off, with a combined cut length of about 750 feet.<br /><br />The project demonstrates the importance of detailed subsurface characterization, coordination between geotechnical and structural engineers, and a well-designed test-pile program for controlling costs and addressing challenging ground conditions.

Keywords

biosolids-processing plant

energy recovery

Orange County California

marshland foundations

seismic Site Class F

soft peat clay

driven precast concrete piles

pile-driving analyzer

indicator-pile program

site-specific seismic analysis