No Business Creek Tunnel and Lift Station

OWNER: Gwinnett County Department of Water Resources

ENGINEER: Parson Corporation

SOUTHLAND HOLDINGS TEAM:  Southland Contracting Inc.

PROJECT HIGHLIGHTS:

This project consisted of 5 shafts, approximately 16,000 lineal feet of tunnel, a 10 MGD pump station and 2 odor control facilities. Three of Five shafts were 24 foot diameter shafts and were constructed through saturated subsurface conditions using secant piles as the primary support methodology. The rock portions of these shafts were excavated using drill and blast methodologies with rock dowels, mesh and shotcrete as the primary supports. These shafts ranged in depth from 78 vertical feet to 236 vertical feet.

One of the 5 shafts was 32 feet in diameter and was constructed through saturated subsurface conditions using secant piles as the primary support methodology. The rock portion of this shaft was excavated using drill and blast methodologies with rock dowels, mesh and shotcrete as the primary supports. This shaft was 204 vertical feet in depth. A 10 MGD pump station was constructed in this shaft.The final shaft was sunk utilizing open caisson methods through the 120 vertical feet depth of saturated subsurface conditions. The remaining 20 vertical feet of this shaft was excavated using drill and blast methodologies.

The tunnel consisted of 15,954 lineal feet of 12’-0” diameter excavation, from one work shaft, through very hard granitic gneiss. Blasting methods were utilized for the starter tunnel, connecting the first two shafts. A 12’-0” Robbins HP TBM was used for the remainder of the tunnel. Rock dowels were used for the majority of the tunnel support. A cast-in-place tunnel lining was installed at the shaft connections. The project is for sewer interception and conveyance.