USE OF APG PILES FOR SUPPORT OF NEW HOSPITAL REPLACEMENT WING IN A SITE SUSCEPTIBLE TO EXCESSIVE GROUND SETTLEMENT-Paper

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The Ventura County Medical Center Hospital Replacement Wing was built on ground vulnerable to liquefaction, seismic densification, and hydroconsolidation. Loose to medium-dense soils extend to about 90 feet, and potential earthquake-related settlement was estimated at 20–26 inches; the project used a design settlement of up to 20 inches.<br /><br />Auger pressure grouted (APG) piles were selected over drilled shafts and cement deep soil mixing as a cost-effective, constructible foundation. More than 600 piles, generally 18 inches in diameter and 120–140 feet long, support the hospital and associated structures. They extend through potentially liquefiable soils into competent clay and sand below Elevation 69 feet. Design accounted for substantial downdrag from settling soils, as well as seismic lateral loads.<br /><br />An indicator-pile program and dynamic load testing verified capacity. Testing with a 16-ton drop hammer measured resistance along the pile shaft, distinguishing resistance in soils that could settle from dependable support below the liquefiable zone. Test capacities exceeded design requirements. Some production piles experienced grout settlement; after regrouting to cutoff elevation, additional testing confirmed adequate capacity.<br /><br />Pile installation near an excavation shoring wall caused movement in the shoring and an adjacent hospital building. The team paused work, increased survey monitoring, and then resumed with piles installed in alternating pile caps. Continued monitoring showed movements remained manageable, and no damage to adjacent buildings was observed.<br /><br />The project demonstrates how deep foundations, targeted load testing, close monitoring, and adjustments to construction sequencing can address severe settlement hazards while limiting impacts on nearby structures.

Keywords

Ventura County Medical Center

hospital replacement wing

liquefaction

seismic densification

hydroconsolidation

auger pressure grouted piles

deep foundation

downdrag

dynamic load testing

settlement monitoring