Lake Travis is located on the Colorado River near the northwest edge of Austin, Texas and provides the region with a fresh water supply, flood control, and numerous recreational activities. Due to the City’s ever increasing population, a demand for a new water treatment plant was imminent for the area. As part of this demand, the City of Austin constructed: Water Treatment Plant No. 4 , a new lake tap , pump station and conveyance tunnels. Brierley Associates provided a variety of geotechnical, design and construction phase services related to the lake intake, pump station and tunnels.
Raw Water Intake
A 9-ft diameter steel shaft was grouted in place approximately 80-ft into limestone under roughly 130-ft of lake water. Attached to the intake structure are three intake screens with isolation plates at various elevations in Lake Travis which gravity feed the water into the Raw Water Intake Tunnel. The three different elevations were primarily selected to maximize the ability to access high quality raw water given the fluctuating lake level.
Raw Water Intake Tunnel
Excavation of 4,386-ft of tunnel connecting to the Raw Water Intake was completed with an Antraquip AQM150 roadheader. The tunnel was finished with a non-reinforced concrete lining and has an operational diameter of 9-ft. Associated with this tunnel is a Raw Water Pump Station with a 25.5-ft diameter 425 ft deep shaft. The Pump Station site was situated on a hill side which required terracing of the rock surface and construction of soil nail walls to support an adjoining roadway.
Raw Water Transmission Main
A second tunnel was excavated to convey raw water from the pump station to the main plant site. The Raw Water Transmission Main is a 3,872-ft long tunnel lined with a 7-ft diameter welded steel pipe. The welded steel pipe was lined with a cement mortar lining and the annular space was backfilled with a low density cellular grout. This tunnel was also excavated with an Antraquip AQM100 roadheader.