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This tunnel is part of Akron’s Northside Project to improve the City’s sewer infrastructure. Located along the Cuyahoga River, the entire tunnel is designed to collect and store over 10 million gallons of combined sewer overflows. Challenges of the site conditions included extreme weather and proximity to the river that necessitated strict environmental compliance.

Drill Tech Drilling & Shoring, Inc. successfully completed excavation of three separate tunnels on the Northside Interceptor Tunnel Project under contract with Granite Construction Company. Drill Tech utilized a new Sandvik roadheader, model number MH 621 to excavate the three tunnels.

The Tunnel Overflow Conduit (TOC) consisted of a tunnel excavated from a launch portal to the Tunnel Diversion Structure (TDS) Shaft. The overall length of tunnel was 370 linear feet with excavated dimensions of 23.5′ high by 22.5′ wide (horseshoe). Tunnel support consisted of rock dowels, wire mesh, and shotcrete.

Once at the TDS Shaft, the roadheader was used to excavate a second TBM assembly chamber tunnel. This tunnel had an overall length of 350 linear feet with excavated dimensions and tunnel support similar to the TOC. After completion of the TBM assembly chamber, the roadheader was repositioned within the TDS shaft to excavate a third tunnel identified as Rack 32.

The White Rock Hydroelectric Tunnel is a 5-mile-long conduit that provides electricity by feeding pressurized water from Slab Creek Reservoir to the SMUD (Sacramento Municipal Utilities District) powerhouse. As the tunnel showed signs of aging, Drill Tech performed permanent critical infrastructure maintenance work necessary for repairs. This included retaining walls on remote roads, rope access mass scaling, and excavation of rock highwalls. All rock and steel debris along the tunnel had to be excavated and removed from the rock trap before the rock bolt and shotcrete work could begin.   

Construction was performed concurrently along the tunnel, and the site required compliance with environmental regulations including all CA SWPPP components. As water ran through the tunnel over shotcrete rebound, it was collected then pumped out of the adit to a treatment plant to be tested, treated, and discharged into a ravine feeding the American River. When the outage for repairs started, over 1,000gpm of water ran through the tunnel—dropping to 400gpm by the end of the outage. Drill Tech also developed and implemented all aspects of the tunnel’s safety plan such as communication and ventilation, including the primary ventilation system which was installed at the intake shaft at the dam site. The entire scope of the project was completed in one Winter outage (4.5 months) as opposed to the contractually two, meaning the job was finished one year early. 

This project consisted of new tunnel development to operate as part of a creek flood stormwater diversion for the urban region of Morgan Hill, California. In addition to SEM tunnel construction, Drill Tech designed the temporary shoring (8,700 SF of drilled soldier piles with internal bracing, timber and shotcrete lagging) and perimeter sound wall for the portal. 

Proactive coordination, communication, and monitoring were necessary components to the success of Drill Tech’s operations. Construction of the tunnel took place under existing surface streets in the middle of a narrow easement for the tunnel alignment as granted by the City. These critical areas with low cover (7′ at the shallowest) required monitoring ahead of excavation to establish reliable data records and sequencing plans. Since portions of the tunnel utilized blasting excavation just a few hundred feet from dozens of homes, communicating on blasting times with the client and third parties’ interests were vital to the project. The value engineering that eliminated pre-excavation grouting from the surface street grade to within the tunnel minimized project impacts to local residents.

This new tunnel construction project established a canal irrigation water conveyance from the Tulloch Reservoir to bypass over a mile of existing canal that was subject to seismic and slope failures on steep mountain slopes. Drill Tech performed preconstruction environmental assessment of this project including SWPPP plans and grading. Variable ground conditions were encountered and required multiple different support types. Excavation proceeded from both ends by roadheaders powered by a complex electrical system of generators, high voltage transmission cables, and transformers.  

Both portals involved Drill Tech value engineering redesign to optimize the portal geometry and integrate Drill Tech’s means and methods for subsequent excavation at no cost add to the owner. Tunnel construction was completed with shotcrete and concrete liner to support future irrigation water flow.  

This new pedestrian and bicycle underpass tunnel was jacked under the Union Pacific Railroad mainline tracks. Drill Tech built the concrete box for jack and bore operations, as well as multiple retaining walls. The team used ground freezing to stabilize the mixture of sand and boulders that had been used to backfill an old timber trestle. Drill Tech conducted continuous monitoring surveys during the tunneling and grouting operations.  There was no significant movement of the UPRR track at any point during construction. The rail line remained operational for the duration of the project. The team coordinated with UPRR staff and collaborated with Caltrans and the Federal Highway Administration, as the site required extensive traffic control measures with one lane of traffic always open during construction. Additional features included a bus turnout and transit shelter, new hiking trail, construction of an infiltration basin, and miscellaneous drainage improvements. The project also entailed the relocation of a traffic signal.

The Stillwater Mine, one of the largest underground operations in North America, is a network of levels connected by shafts with hundreds of miles of tunnels and shafts ranging from 2000′ to 9000′ in elevation. The owner issued Purchase Orders that outlined a variety of scopes for this project on an annual basis. Scopes included lateral mine development drill/blast drifts, access tunnel rehabilitation, construction of utility chambers underground, and excavation of ore/muck level connection shafts which were accomplished utilizing air powered Alimak raise climbers during excavation. Every shaft excavated was over 200′, with the longest being a pair of 808′ shafts.  

Drill Tech also mined tunnels ranging from 14′ to 20′ diameter by drill/blast excavation. Although ground support typically consisted of rock bolts (over 100,000 installed in the span of four years) and wire mesh, dry mix shotcrete was installed in several areas of poor ground. Drill Tech’s equipment fleet at Stillwater included multiple high production drill jumbos, bolters, LHDs, and haul trucks.  

Drill Tech’s scope included simultaneous development tunnels, production mining, and Alimak raises miles apart underground that required coordination of equipment and manpower across multiple sites. Coordinating the various crews’ transportation back to the main underground train station at shift change was a significant challenge since some of the work areas required over an hour of travel underground to get to the heading. Drill Tech’s safety program was integrated with that of Stillwater Mine and MSHA.