Sustainable Soil Re-Use for a Texas Pipeline Project

The Tarrant Regional Water District (TRWD) with the City of Dallas Water Utilities (DWU), are currently engaged in the planning, design, and implementation of a 350 MGD raw water transmission system, which will run across north central Texas from Lake Palestine to Lake Benbrook, with connections to Cedar Creek Reservoir, Richland Chambers Reservoir and a Dallas delivery point. Collectively, the system consists of: approximately 145 miles of 84-inch to 108-inch pipeline; a 5-mile, 120-inch diameter tunnel; six 100-350 MGD pump stations; one 300 MG balancing reservoir; and ancillary facilities. The program developed by TRWD to accomplish these improvements is called the Integrated Pipeline Project (IPL). As a means to deliver this important infrastructure project in a sustainable manner, the IPL has conducted several specialty studies into the re-use of native soil as pipeline embedment. Specialty studies include: a. Route Characterization - Geophysical and geotechnical investigation to categorize soils by re-use potential and to identify marginal soils, b. Chemical Stabilization - Laboratory treatment of marginal soils to increase engineering properties such as strength and durability, c. Native Soil Flowable Fill - Laboratory and field trials to make flowable fill using native soils found along alignment including sands, clayey sands, limestone and lean-to-fat clay, d. Soil Box Testing - Laboratory investigation of large-diameter steel pipe determining pipe wall stresses and pipe deflection under various embedment configurations. e. Finite Element Analysis - 3-dimensional FEA study to test conventional and alternative embedment options for steel and prestressed concrete pipe, f. Flowable Fill Full Scale Pilot study - 2-mile installation of 108-inch pipe embedded in native soil flowable fill, and g. Cost and Sustainability - Analysis of various embedment options with a focus on the sustainable triple bottom line of people, planet and profit. This paper describes the various studies (with a particular focus on the cost and sustainability aspects), presents initial results, and describes a path forward for an innovative and sustainable approach to soil re-use on a water transmission pipeline project.