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Drill Tech performed rehabilitation for the Cal Park Tunnel—located between San Rafael and Larkspur—and constructed a multiuse path within the tunnel per the contract awarded by the County of Marin. The 31′ diameter 1100′ long horseshoe shaped railroad tunnel rehabilitation mostly consisted of demolition and replacement of broken tunnel supports in highly fractured rock conditions as well as wet, mixed face conditions with short initial standup time. Additionally, this contract required 160′ of re-mining through a completely collapsed section of tunnel, “cut and cover” operations, and temporary support of existing sink holes that reach to the surface. Construction of the pedestrian pathway had all the elements of building construction (i.e. CMU wall, steel erection, architectural, electrical and mechanical works). 

Many of the logistical challenges required significant planning and coordination, since site access was shared with public right of way (Amtrack and local businesses), and the width and size of access was single lane. The very limited overhead and width access to work made drilling conditions and shoring access difficult. Drill Tech was responsible for managing these operations while maintaining relations with nearby stakeholders.  

The purpose of this project was to replace two existing culverts with fish passage culvert tunnels. Drill Tech utilized various ground support methods, including pre-excavation support ahead of mining to ensure stability through the alluvium type soils encountered. The final tunnel condition included a partial liner of reinforced shotcrete as scour protection for stream flow. A unique challenge of the site conditions included the active rail line that traversed above the excavation and seasonal work schedules to accommodate seasonal fish migration. All in-stream work took place from July 15^th to October 31^st. The work was scheduled over two seasons, with one tunnel to be completed each year, but both tunnels were completed in year one.

The South Coast Water District owns and operates a 2-mile long gravity-fed 24″ sewer line and the tunnel it runs through—both of which were initially constructed in the 1950s. Due to the structure’s deterioration and lack of support, the owner developed a multi (four) phase approach to rehabilitate the existing tunnel, install new sewer pipe, and reconnect the 80+ lateral services. Drill Tech was awarded all four contract phases, each concerning a unique scope. The project included 10,000 LF of reinforced concrete pipeline encasement, 10,000 LF of concrete invert placement, and 24″ sewer main.

There were several environmental accommodations made throughout this project including limited access through the beach due to the grunion run, Paleontologist inspection for fossils every 1,000′ of tunneling, and vibration and noise monitoring on equipment. Excavation occurred next to the live sewer main, requiring careful operations and gas testing. Drill Tech’s active partnering with the client, regulating authorities, and 3^rd party stakeholders enabled the identification of issues in real-time and efficient development of solutions in the field as there were numerous unknowns encountered daily throughout the project.

As part of the Occoquan River Crossing Project, Drill Tech performed tunnel and shaft excavation with the purpose of increasing the existing main’s quality and sustainability while establishing higher water flow capacity for the city’s drinking supply. Drill Tech’s tunneling operations occurred underneath the river, where the blocky rock ground conditions presented difficulties for excavation. Moreover, the existing facilities and structures of a nearby historic community required strict blasting regulation.

Drill Tech installed a concrete tunnel invert, completed pre-excavation grouting for tunnel improvements, and installed two 42″ steel water main pipes in the tunnel. Utilizing raise bore methods, Drill Tech excavated two additional 7ft diameter shafts to a depth of 90′ below grade.