North MacGregor Relief Tunnel

Completed in 2007 by Southland Contracting, the North MacGregor Relief Tunnel Project consisted of furnishing and installing approximately 3,340 feet of 189-inch nominal cut diameter and 179-inch outside diameter (OD) by 161-1/4-inch inside diameter (ID) precision made (zero tolerance) segmented liners. The project had 3-reverse curves with a storm tunnel shaft located near Brays Bayou. The contract included single pass tunnel construction, an outfall, and several storm water connections. The tunnel terminated at a location that doubled as a receiving shaft and the location of a 40-foot by 40-foot diameter by 48-foot-deep junction structure built around an existing 144-inch storm drain, which was removed and used for activation of storm tunnel. The North Macgregor Tunnel was constructed in predominately mixed face conditions, with soft-low plasticity, silty and sand clays above the tunnel including the upper portion of the tunnel soil ranged from soft in the upper portion of the clays, to hard in the dense silty sands. An 800 linear foot run was constructed in a full face of clay deposits, which ranged in strength from approximately 750 PSF to 4500 PSF. Groundwater was present in the zone between the soft clays and the silty sands.