Little Walnut/Buttermilk – South Tunnel

Completed in 2006 by Mole Constructors, the Little Walnut/Buttermilk – South Tunnel project consisted of two shafts and a conveyance tunnel with a grouted in place fiberglass pipe permanent liner. The shafts were 18-foot diameter and 16-foot diameter and were excavated to 36 vertical feet and 75 vertical feet in depth respectively in the Austin Chalk rock formation. The shafts were supported by liner plates in the soft ground and dowels, mesh, and shotcrete in the rock. Controlled Blasting methods were utilized through the rock. Standard drop structures were constructed within the shafts. The tunnel consisted of 9,400 linear feet of 99-inch diameter excavation, from one work shaft, through Austin Chalk, claystone, and shale formations. The 540 linear foot starter tunnel was excavated with a 108-inch diameter Tunnel Boring Machine (TBM). A 99-inch Dosco TBM was used for the remainder of the tunnel. Steel ring beams and lagging were used for the majority of the tunnel support. Groundwater was encountered at intersections with fault zones. The final lining consisted of 60-inch diameter FRMP (Hobas) pipe grouted in place with low density cellular grout.