Protecting a Large Diameter Pipeline System in a Developing County

Abstract

The Calleguas Municipal Water District (Calleguas) is a water wholesaling agency that provides water to over 500,000 customers in Ventura County, California. As a large water purveyor, Calleguas owns and operates approximately 209 km (130 miles) of pipelines ranging from 0.61 meter (24 inches) to 1.98 meter (78 inches) in diameter. The pipe materials are mortar lined and coated welded steel pipe, concrete cylinder pipe, and pre-stressed concrete cylinder pipe. Many of Calleguas' pipelines were originally constructed through farmland and along two-lane roads. As Ventura County has grown, roadway and development projects have increasingly affected Calleguas' pipeline rights-of-way, often resulting in increases or reductions in earth cover and use of heavy construction equipment that are outside the pipeline's original design parameters. In addition, these projects often require additional utility crossings over and under the large-diameter Calleguas pipelines. This paper describes: (1) The development of minimum earth cover standards for large-diameter pipelines; (2) The development and enforcement of loading restrictions for large-diameter pipelines during grading and construction of improvements over the pipeline; (3) The techniques and methodologies that Calleguas has employed to prevent damage to its pipelines from insufficient or excess cover, including construction of concrete caps, alternative pavement sections, use of lightweight fill materials, and relocation; (4) Special considerations for protecting large-diameter Pre-Stressed Concrete Cylinder Pipe (PCCP); and (5) Protection and support of large-diameter pipelines during crossing of utilities over and under the pipeline by both conventional open-cut and trenchless construction methods.