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Loretta Street Waterline Replacement, Oceanside, CA
Client:  City of Oceanside Water Utilities Department

TGI served as the City’s geotechnical consultant for the Loretta Street Waterline Replacement project in Oceanside, CA.  The project entailed approximately 4,800 linear feet of 15” water main.  The pipeline alignment crossed both the Caltrans Highway 76 right-of-way and the San Luis Rey River.  Approximately 1,400 linear feet of the pipeline was constructed using horizontal directional drilling to minimize traffic and environmental impacts.


In addition to the constraints posed by the highway and river crossings, geologic conditions along the alignment varied from hard conglomerate (San Onofre Breccia) to soft and loose alluvial deposits with high groundwater conditions.  Evaluation of the subsurface conditions and geologic contacts along the alignment were of particular importance to assessing the feasibility of trenchless construction.


TGI initially performed a desktop study to summarize existing available information and data regarding geotechnical conditions affecting design and construction of the proposed project and identifying data gaps to be addressed by a subsequent design investigation. 


TGI’s design study consisted of a field/subsurface investigation program including exploratory boreholes, cone penetrometer tests, geophysical testing (resistivity and seismic refraction surveys), and a geotechnical laboratory testing program to evaluate engineering and index properties for representative samples of the San Mateo Formation, San Onofre Breccia and alluvium encountered along the alignment.  Conventional rotary drilling and sonic drilling methods were utilized.  Minimally intrusive investigation methods (CPT and geophysical testing) were successfully and effectively utilized in environmentally-sensitive areas adjacent to the river due to access and permitting constraints.


TGI prepared a Geotechnical Data Report (GDR) providing all of the available data.  The GDR was incorporated in the bid documents for the project.  The waterline replacement, including the HDD construction was successfully completed in 2007.


This project received an “Award of Merit” from the San Diego Section of the American Society of Civil Engineers in 2007.

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