Southwest Pipeline Tunnels

The City of Dallas is in the design phase of a new pipeline construction project that will transfer treated water from the expanded East Side Water Treatment Plant (ESWTP) to the south and southwest portions of Dallas. The approximately 32 mile-long transmission line will range in diameter from 96 to 120 inches and include 75 proposed tunnel crossings that vary in length from several hundred feet to about 10,000 ft.

The most significant crossings include tunnels beneath interstates IH-35 and IH-45, four major state highways crossings, four railroad crossings, and the Trinity River. Geological conditions along the route vary from stiff clay soils to soft alluvial soils to hard limestone bedrock. To date, Schnabel has developed preliminary design alternatives for each of the 75 proposed crossings.

In order to determine the feasibility and “best-fit” tunneling method for each crossing, we evaluated the geotechnical conditions at each site, the potential lengths and depths of each tunnel, tunnel excavation advance rates and ground support types, and the surface and subsurface conditions in the vicinity of each crossing. Conditions we accounted for include terrain at the tunnel approaches; locations of utilities, streets, and highways; environmental concerns; and potential impacts of construction methods on nearby residences and businesses. Based on the determined preliminary design alternatives, we prepared cost estimates, construction schedules, and contracting parameters for each crossing to be used in the final design of the work.