Jollyville Transmission Main

Completed in 2015 by Southland Contracting, the Jollyville Water Transmission Main Project was necessary to transport water from Water Treatment Plant No. 4 to the Jollyville Reservoir where it will be distributed to Austin businesses and residents. The project included the construction of a 120-inch transmission main tunnel approximately 35,000 linear feet long. The tunnel was constructed using three Tunnel Boring Machines. Installation of 35,000 linear feet of 84-inch diameter welded steel pipe with cement mortar lining was performed. The project included four shafts. The WTP4 Access Shaft is approximately 210 foot deep and 40 foot in diameter. The Four Points Area Shaft is approximately 275 foot deep and 45 foot in diameter. The PARD Shaft is approximately 130 foot deep and 31 foot in diameter. The Jollyville Reservoir Shaft is approximately 360 foot deep and 40 foot in diameter. Conditions along the way consisted of uniform limestone and dolomite rock requiring little to no support. Although karst features were present throughout the formation, the depth of the tunnel circumvented these features. The depth of the tunnel was also chosen due to a sensitive aquifer containing endangered cave-dwelling invertebrates. Six species of arachnids and insects thrive in and around the karsts and aquifer. Because of this, no probe grouting could be performed due to the risk of seepage into the water features.