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The penstocks and adjacent tunnels of PG&E’s Helms Pumped Storage facility exhibited years of damage build up. The facility shutdown enabled this repair project to address those damages, with Drill Tech as the General Contractor performing a variety of scopes including grouting, spalled concrete removal/replacement, and drain/decompression hole installation. Drill Tech also carried all Tunnel Safety Order operations for the project, selecting a dedicated gas tester, safety rep, and 5-man rescue team for the double shift operation. Additionally, Drill Tech provided all tunnel utilities (water, air, power, lighting, etc.) to all companies working inside the tunnel during the outage, and oversaw multiple subcontractors/third-party contractors to PG&E.  

The Helms Pumped Storage System is an extremely remote location at about 7500′ elevation, where the weather and length of narrow wooded roads made deliveries and travel for crew members very difficult. With the penstock sloping at 12%, access, hole layout, drilling, and the grouting sequence were difficult to manage. From scratch, Drill Tech fabricated a scaffold system and modular drill on wheels to break down small enough to fit through the 36″ diameter flange and work inside the penstock. Although the spalled concrete repair work grew about 100% in size due to more damage than previously surveyed years ago, Drill Tech still completed all critical work within the desired window set by PG&E. 

This project consists of two microtunneling drives to (1) bypass an environmentally sensitive area known as Stone Creek, and (2) go underneath active UPRR tracks. Each drive required the use of an MTS 1700 EPB Tunnel Boring Machine to install 78″ ‘triloc’ casing below sea level. The stone creek drive was 180 LF and the UPRR drive was approximately 350 LF. After casing installation, Drill Tech will perform contact grouting on the casing, installation/fitup of the permanent 66″ mortar lined WSP, and backfill the annulus with cellular grout. 

This project was part of the greater JPB effort to electrify all 52 miles of Caltrain from San Francisco to San Jose. Drill Tech was involved in two other projects totaling another $80M as part of this electrification effort. This Tunnel Modification Project specifically consisted of the enlargement and electrification of four existing Caltrain double track train tunnels in the San Francisco and San Francisco area: Tunnel 1 is 1800′ long, Tunnel 2 is 1100′ long, Tunnel 3 is 2360′ long, and Tunnel 4 is 3600′ long. All work was completed during weekend long shutdowns of the train tracks from 7pm Friday night to 5am Monday morning, in efforts to minimize impacts to Caltrain operations during heavy commute windows. All equipment had to be modified significantly to allow for rail access since work was performed on the train tracks.

Drill Tech executed a variety of scopes on all four tunnels, the main scope including the use of a rail mounted roadheader to perform tunnel notching that allowed larger electrified trains to fit a larger envelope and achieve the required additional clearance. Drill Tech installed overhead anchors to hold the future OCS wires into the tunnel liner. At each portal (2 per tunnel; 8 total) a larger steel structure was erected on top of either OCS foundations or micropiles. These OCS Portal structures helped hoist the OCS line running through the tunnels, and the OCS wires and conductor rails were then installed. Naturally occurring asbestos (NOA) was encountered during the drilling of OCS foundations and micropiles at the portals.

This project was part of CADOT’s development of Caldecott’s 4^th bore tunnel on Highway 24 that links the East Bay Valleys and Bay Area. Excavation was performed in the most adverse ground conditions of the tunnel, where a mélange of sandstone, siltstone, and fault materials were identified in the first 200′. The SEM drifts were advanced through an incremental two-pass approach that enabled the appropriate excavation through these faulted zones. Temporary shoring was also performed at the portals as the site location historically experienced landslides.  

There were several challenging aspects to Caldecott’s construction that included compliance with stringent environmental regulations, specially tailored equipment for tunnel safety, and third-party considerations. For instance, blasting was specifically prohibited because of the tunnel’s CalOSHA gassy classification and the existing structures nearby. Drill Tech maintained the proper protocol for the project’s safety and successful completion.

This project is the first phase of dam seismic retrofit that establishes new water supply tunnels, drop shaft, and lake intake structures required prior to rebuilding the dam itself in subsequent phases. With the site located directly adjacent to the operating dam and nearby neighborhoods, there were serval stakeholders to remain in compliance with that included environmental agencies, safety regulators, and federal oversight. Underground coring was performed in advance of tunnel excavation to adequately analyze the rock, which varied from extremely weak to strong, and the variable quantities of groundwater and intermixed saturated soils.

Drill Tech performed the portal construction and utilized SEM techniques for both the shaft and tunnel. Drill Tech also designed the shaft, which was supported by lattice girders and shotcrete, that somewhat varied in depth geometry to facilitate future pipe elbow placement. Coordination of the organization and transportation for onsite shotcrete batching was required due to the 24/7 underground excavation operations. Vadnais, Drill Tech’s subsidiary microtunneling company, constructed the 8′ diameter microtunnel that connects the tunnel to Anderson Lake.

Drill Tech designed and constructed a shaft and shaft station, the headframe and hoist foundations, and starter tunnels on this private energy project for New Era Petroleum’s oil extraction operations. Up to 10′ thick concrete foundations were constructed for the hoists and headframe, as these structures provided shaft access at the surface. Shaft excavation was performed through conventional drill/blast SEM sinking techniques staged from a five-level sinking platform that housed a drill jumbo and a Cryderman mucker. Temporary rock bolt support was installed for the shaft. Drill Tech installed the concrete liner in 20′ lifts from the work deck during sinking, using concrete from a Drill Tech onsite batch plant. The starter tunnels were completed using SEM techniques with jack leg drills and a mini excavator and were supported with rock bolts and shotcrete.