Three times per year, TBM: Tunnel Business Magazine recaps the status of major tunneling projects underway in the United States and Canada. Stiver Engineering worked on projects in Canada, Dallas and Houston, Texas that appeared in the June 2022 issue of the print edition.
In Dallas, Texas, the Mill Creek Drainage Relief Tunnel project involves 26,385 linear feet at a 32 foot excavated diameter tunnel (30-ft ID) and seven shafts ranging from 120 to 200 vf. Tunneling will occur primarily in Austin Chalk with excavation via Main Beam TBM and Roadheader. The unique aspect of this project is that the contractor converted the TBM diameter beginning in January 2021, which took 3-4 months to complete. As of January, 19,500 ft of 26,385 linear feet of tunnel have been complete.
Stiver Engineering provided construction engineering services for the contractor prior to and during the tunnel construction. Our work included shoring designs for access shafts, the TBM starter/gripper wall design, shotcrete trolley system for lining the tunnel, several trench safety plan designs, a sound wall design using steel soldier piles and acoustic panels, and a removable shaft cover and rigging details for several liner plate shafts.
The magazine also provided an update on WHCRWA Surface Water Supply Project. Work recently began on Section C1 of the Surface Water Supply Project for West Harris County Regional Water Authority in Houston. This phase of the water transmission included two microtunnel crossings, including a 625’ crossing underneath Keith Harrow Boulevard. The crossing passes underneath of the roadway, through sand transitioning into lean clay and caliche, beneath the water table. Following construction of the C1 crossings, three microtunnel crossings will be a part of the C2 phase of the project. These crossings will pass underneath three waterways, through lean clay and sand layers under the water table. The tunnels will again be launched and recovered in liner plate shafts.
Stiver Engineering provided a shoring design for the launch and receiving tunnel shafts, including portal design implementing soldier piles and the shaft design implementing sheet piling and wale sets. Calculations and a finite element analysis (FEA) were performed for a 108-inch diameter tunnel steel casing pipe. Calculations for grout pressure used to fill voids outside the casing pipe were also provided.
In Canada, TBM provided an updated on the highly anticipated stormwater management program for The City of Toronto. It’s a $3 billion-plus wet weather program to eliminate combined sewer overflows, reduce inflow and infiltration into sewers, and reduce basement flooding. A critical component of the program is the Ashbridges Bay Treatment Plant Outfall. The project will replace the existing outfall, which was built in 1947 and is at the end of its service life. It includes a 3.5-km tunnel of 7.95-m diameter tunnel, launched from a 16-m diameter, 85-m deep shaft. The completed outfall will connect to the 50 in-lake risers drilled from in-water barges to enable efficient dispersion of treated effluent over a wide area of the lake. The project, the largest outfall in the country, will improve the city’s shoreline, beaches and Lake Ontario’s water quality by replacing the existing outfall. Following completion of the tunnel, connections for the 50 risers need to be made, requiring excavation through the segmental lining and bedrock below the lake. The project is slated for completion in 2024/25.
Stiver is providing riprap placement plans for the riser sections on the lakebed. These cages will be placed at the bottom of Lake Ontario and will be guided in place by divers. The riprap baskets will be installed around each of the fifty – 1-meter diameter risers that extend from the tunnel to the lakebed.
Read more about these projects here: https://www.mydigitalpublication.com/publication/?i=709276
