Brushy Creek Regional Interceptor – Contract 21

Completed in 2004 by Mole Constructors, the Brushy Creek Regional Interceptor – Contract 21 project included a tunnel consisting of 10,116 linear feet of 110-inch diameter excavation, from one work shaft, through the Del Rio Clay and Georgetown limestone formations. A 110-inch Lovat Tunnel Boring Machine (TBM) was used for the tunnel excavation. Steel ring beams and lagging were used for support in the Del Rio Clay and rock dowels were used for the majority of the tunnel support in the Georgetown formation. Groundwater was encountered at intersection with fault zones. The final lining consisted of 84-inch and 72-inch diameter FRMP (Hobas) pipe.
A change order was issued to increase the tunnel length by 3,216 linear feet from the original 6,900 linear feet and add a shaft. This was the main increase in the contract cost and time. Four shafts were excavated 40 feet to 50 feet in depth. The shafts were supported by liner plates or soldier piles with wood lagging in the soft ground and dowels, mesh, and shotcrete in the rock. Blasting methods were utilized through the rock. Standard drop structures were constructed within the shafts.