Sister Grove Regional
Water Resource Recovery, TX

Owner: North Texas Water Authority
Construction Manager: Garney Company

Summary: Triad was the managing partner of a Joint Venture with C&M McNally and Midwest Mole (TMMJV) in McKinney, Texas for the Sister Grove Regional Water Authority Outfall Tunnel. The TMMJV group was required to submit a complete proposal including pricing, work plan, organization, equipment resources for the project, key personnel and schedule. The JV was then interviewed by the owner and construction manager. TMMJV’s score from the process was the highest of several firms that submitted. The project was awarded to TMMJV.

Triad sent management, key personnel and all of the equipment to the project. The project startup was delayed by the owner. However, TMMJV after beginning work was able to make up the lost time and finish the project by the original completion date.

The tunnel was excavated using Triad’s Lovat full face tunnel boring machine cutting a diameter of 123”. The machine was fully refurbished in Triad’s shop before being sent to McKinney. While the TBM was being refurbished, the site was mobilized. Four shaft sites were set up with laydown areas, utilities and security. Four shafts were then excavated utilizing rib and board shoring.

When the TBM arrived, two shifts worked to excavate the first run of 8,240 feet from shaft 4 to shaft 3. The TBM was removed and reset at shaft 6 where it excavated 1,300 feet through mixed face conditions to shaft 5. The crews were split between work sites when that excavation began. The second crew installed pipe between shaft 4 and shaft 3. A hydraulic powered pipe setter was utilized to set each pipe section at the proper line and grade.

When the first section of pipe setting was completed (8,200’), the TBM had finished the excavation between shaft 6 and 5. The pipe setting crew moved to shaft 6 and installed the pipe to shaft 5. The other crew demobilized the TBM and prepared the first tunnel run for grouting. The grouting of the void between the carrier pipe and the excavated tunnel lining was performed by Pacific International Grout with assistance from TMMJV. Once grouting was completed, TMMJV built the required manholes at each shaft location.

Scope: Two tunnels excavated at 123” diameter lined with ribs and boards; 8,240 ft. run excavated in Austin chalk; 1,200 ft run excavated in mixed soft ground conditions with Austin chalk seams; 96” Hobas pipe installed and fully grouted within the tunnel; Four access shafts excavated and built as manholes; Site work to develop working sites for four locations, including site pads, power, water service and security.