The Monterey Peninsula Desalination project consists of a proposed seawater desalination and treatment facility to be constructed by California American Water Company in Marina, California. The approximately $87M project will be constructed on a 376-acre parcel comprised of ancient sand dune fields near the mouth of the Salinas River. The new facility will include treatment plant facilities, water tanks, pumps, pressure filters and piping networks associated with the operation of the desalination plant. Pacific Crest Engineering performed a design-level geotechnical and geologic investigation in 2014 for this project, which required intense coordination with multiple agencies. This project highlights our experience with complex infrastructure and water works projects, quantitative evaluation of seismically‑induced settlement, development of lateral earth pressures and foundation design criteria, development of general earthwork, materials and utility trench recommendations and evaluation of pertinent seismic and geologic hazards.
As part of the Monterey Regional Water Pollution Control Agency (MRWPCA) Salinas Industrial Wastewater and Storm Water Storage and Recovery project, a new stormwater diversion structure was constructed at the Salinas Pump Station in Monterey County. The structure was constructed at an elevation of approximately 20 feet below existing grades in an area underlain with many existing utilities including sanitary sewer and storm drains. In preparation for the replacement of a 54-inch sewer main and junction structure, an approximately 30 x 30-foot excavation was constructed. The excavation was approximately 15 feet in depth and shored with a system of sheet piling and walers. Persistent, long term leaking from the sewer main and adjacent storm drain pipe resulted in significant softening of the subgrade at the base of the excavation. The exposed subgrade was deemed to be too unstable for adequate support of the proposed vault structure, which was to be founded upon a structural mat foundation system. Pacific Crest Engineering performed on-call geotechnical services to assess the excavation conditions and develop recommendations for improving the supporting subgrade for the new vault. Our services were comprised of several site meetings and discussions with the design team, review of the project plans, advancement of a cone penetrometer sounding (CPT), engineering analysis of the CPT data, and report preparation. In order to characterize the in-situ soil conditions at and below the excavation, the CPT was advanced to a depth of 80 feet. Based on our site observations and subsurface data obtained from the CPT, we developed preliminary geotechnical engineering recommendations for improving the bearing capacity of the soft soils underlying the proposed structural mat foundation system. Our recommendations included placement of a cement-treated base course overlying stabilization fabric. However, due to shoring constraints, the excavation could not be deepened sufficiently to accommodate the subgrade improvements. The design team then elected to support the vault on piles, which would remove the need for further excavation and avoid interference with the sheet pile support beams. Pacific Crest Engineering provided design criteria and recommendations for a driven pile foundation, which was ultimately constructed.
The Villa Del Monte Tank Replacement project was orginally planned for replacing the existing water tank and reusing the existing concrete tank pad. The original tank pad was constructed upon the Villa Del Monte Landslide feture, which mobilized durring the 1989 Loma Prieta Earthquake. Durring the course of the geotechnical investigation, we excavated exploratory trenchs near the existing tank pad and discovered large displacement cracks in the soil below the concrete pad. Given these findings, it was determined that the original tank site was no longer viable, and the decision was made to relocate the tank to an alternate building site approximately 250 feet to the northwest. A separate trenching investigation was performed at the new tank site, and it was determined to be a viable location for the installation of the new tank. Pacific Crest Engineering performed a design level geotechnical investigation report for the project, and also provided construction phase earthwork observation and testing.
444 Airport Blvd, Suite 106, Watsonville, CA 95076 · 831-722-9446
Start the conversation