After nearly two years of construction, Silicon Valley Clean Water’s (SVCW) long-anticipated Gravity Pipeline project successfully achieved a major milestone – completing its work tunneling two separate tunnel drives over three miles in length with an excavated tunnel diameter of 16-feet. While utilizing this innovative and top-of-line technology is cause to celebrate on its own, tunneling was completed under extreme conditions throughout the COVID-19 global pandemic without significant delays.
Ten years in the planning, SVCW’s $554 million Regional Environmental Sewer Conveyance System Upgrade (RESCU) program encompasses 11 projects, the largest of which are the Gravity Pipeline, Front of Plant and the Pump Stations Improvements projects. All three projects are being delivered under progressive design-build contract agreements. In the case of the Gravity Pipeline the use of progressive design build as the contract delivery method is a first in the United States for a sewer tunnel project of this size. SVCW partnered with the design build contractor Barnard Bessac Joint Venture (BBJV), along with BBJV’s design engineering firm, Arup, for the design and construction of the Gravity Pipeline project. Kennedy/Jenks serves owner advisor engineering services and Tanner Pacific provides construction quality assurance services associated with the project.
In February 2020, the project team had the opportunity to share information about the Gravity Pipeline Project at the California Water Environment Association, Santa Clara Valley Section event. The Owner’s Quality Assurance Lead and BBJV’s Project Manager presented a summary of the progressive design-build delivery method and how it has been used for this project to over 70 attendees. The presentation included insights on the construction work and the proposed tunnel, and the design processes for connecting the tunnel to existing and new SVCW facilities. Crediting the progressive design-build approach as an avenue for enhanced teamwork that yielded several value engineering opportunities for additional cost and time savings. The team was able to take a moment to reflect on the journey and lessons learned up to that point. Little did anyone know at the time, a global pandemic would become a devastating reality a few weeks later.
For anyone who has followed the work of SVCW under Manager Teresa Herrera’s leadership knows that the safety of the public and of staff has always been a top priority. “With the COVID-19 pandemic, this took on a whole new meaning operating under our motto ‘Day by Day, Safety is the Way!” Herrera shared. In the initial planning phase, the Gravity Pipeline Project team turned to risk assessment to help them understand and manage the additional hazards posed by COVID. The result was a 29-item plan identifying the high-risk areas of the project. Barnard Construction Company Vice President, Dan Schall shared, “There was a lot of involvement and consultation with the workers, unions and health and safety authorities. It came down to the safety culture. Employees have to look after themselves and of each other.”
Noting that local orders changed three times between March and May 2020 the third order was particularly challenging in that third-party safety inspections were required but with very little detail or instruction. Barnard-Bessac and neighboring contractor partner Shea-Parsons – the joint venture leading the design and construction of the Front-of-Plant and Pump Stations Improvements projects – creatively and collaboratively decided to share their respective safety officers with each other to conduct these inspections. Additionally, Barnard began weekly company-wide briefings so that the project team could learn of new procedures and protocols that were showing promise elsewhere on Barnard projects. BBJV brought in outside experts, including a doctor, to brief the site teams on various safety topics related to Covid-19.
Despite the upending effects COVID had in varying aspects around the world, in March 2020, the Gravity Pipeline Project reached a major milestone – Salus, the Tunnel Boring Machine (TBM), arrived at the first of its two destinations. Salus broke into the 50-foot deep TBM retrieval shaft located on the northern end of Inner Bair Island. To prepare for Salus’ arrival, BBJV installed a grout plug in the wall of the retrieval shaft. When it arrived close to its “Tunnel Eye,” Salus bore straight into the grout plug, which is designed to seal off the inside of the vertical receiving shaft from the soil and groundwater surrounding the shaft walls. One final step in preparation for Salus’ arrival was to fill the retrieval shaft with water, allowing for a controlled, safe entry of the TBM into the custom-built receiving cradle that BBJV placed in the bottom of the shaft to protect the TBM.
By May 2020, BBJV continued cross-checking their COVID-19 safety measures to ensure crew safety and compliance with local, state, and federal health and safety requirements. BBJV removed all components of Salus from Inner Bair Island and transported them back to the launch shaft, located at Shoreway Road and Holly Street. Crews carried out inspection of Salus’ components and performed necessary maintenance and cleaning. In late June, Salus was ready to begin her second drive from the launch shaft to SVCW’s wastewater treatment facility – setting out to tackle twice the distance of the first drive. SVCW and BBJV continued to emphasize safety at all stages of the continuous mining process. Daily tunnel taskforce meetings were held, and staff visitations in the tunnel and on the TMB provided safety equipment and operations monitoring. Simulated mine safety rescues also were practiced on a regular basis.
Despite ever-changing health and safety directives and challenges, by the end of 2020, Salus continued to be on target for its alignment and tunneling schedule. BBJV and SVCW continuously monitored tunneling activities, and teams reviewed proactive measures to ensure that tunneling operations were conducted safely. With Salus anticipated to arrive at the Front of Plant in mid-2021, BBJV and SPJV worked closely to coordinate Salus’ arrival and planned the second break through at the Surge-Flow Splitter (SFS) Shaft, which is part of the Front-of-Plant project; the SFS shaft would have a temporary function as a TBM retrieval shaft at the end of Salus’ second drive. The preliminary site preparation included establishing the laydown area and methods used to control subsurface water movement. The laydown area accommodated heavy equipment movement and provided a storage area prior to Salus’ arrival at the SFS shaft. To control subsurface water movement and groundwater ingress into the tunneling operations, a grout plug was set up below grade on the outside of the SFS shaft. As in the case of the retrieval shaft at Bair Island, the grout plug was installed to prevent unwanted water from entering the SFS shaft from the outside when Salus tunneled through the shaft wall. Salus would mine through this “grout plug” as she approached the outside surface of the SFS shaft wall. Because both BBJC and SPJV occupied the same working area adjacent to the SFS shaft concurrently, coordination and communication between the contractors were of the highest priority for safety and effective progress of work for both the Gravity Pipeline and Front of Plant project teams.
In June 2021, Salus successfully completed her second tunneling drive and reached the SFS receiving shaft. Having tunneled approximately 13,000 feet from its launch shaft, Salus once again reached its destination on time and on target. This marked the second major milestone for the Gravity Pipeline project team since Salus’ first break in on Bair Island at the end of March 2020. SVCW’s RESCU Quality Assurance team, working with BBJV, documented that ground settlement recorded above the tunnel alignment over the combined 17,600 feet of tunneling for both drives was within construction-industry limits, with no adverse impacts to subsurface utilities or surface features, such as road and sidewalk pavement.
Approximately two months after successfully breaking into the SFS shaft, BBJV removed all of the TBM pieces and support gantries from the SFS shaft and hauled them offsite for use in other tunneling projects not associated with SVCW’s project. SVCW and BBJV negotiated the salvage value of the TBM as part of the original design-build contract for the gravity tunnel.
Having to work through COVID-19 from the end of the first tunneling drive through the second tunneling drive, SVCW, BBJV and SPJV did extraordinary work keeping up with all health and safety measures and protocols while adjusting work procedures to ensure that tunneling production was safe and on schedule.
SVCW Manager, Teresa Herrera, gives credit to SPJV and BBJV, along with the SVCW project team, for this tremendous achievement. “It is a testament to the camaraderie, professionalism, and mutual respect that these teams worked well together in tight quarters while avoiding any interruptions in timeline,” Herrera said. “BBJV implemented strict COVID-19 safety protocols, including staggering crews, daily symptom checks, and increased cleaning. Because of BBJV’s mitigation efforts, the project continued with no lost time due to COVID-19.”
To learn more about the RESCU program, visit https://svcw-rescu.org.