Turlock Irrigation District (TID) Board of Directors voted unanimously at Tuesday’s Board Meeting to approve a $975,000 project to repair the Upper Main Canal Tunnel #2 by removing a mountaintop and “day-lighting” the tunnel to eliminate the risk of collapse.
In a 2003 assessment, evidence of instability included rock fall, slab delamination, and continual raveling. In 2008, a Mead and Hunt report recommended a detailed investigation of the tunnel. The tunnel went under a full assessment in 2011, performed by SAGE, which included visual inspections, exploratory drilling, and seismic refraction testing.
The assessment found that the tunnel’s crown is mainly comprised of weak gravel conglomerate, and it was therefore recommended to day-light the tunnel. During a 2011 Board Workshop, TID staff presented the findings and recommendations to the board, resulting in the Board giving direction to staff to move forward with the day-light option, which would include removing a mountaintop as to prevent the tunnel from collapsing inward.
SAGE prepared design documents and constructability review, which included 78,000 cubic yard of spoils to be placed in the original Delaney Fill borrow site. The estimated cost of the construction is projected to be approximately $975,000.
While $975,000 may seem like a large sum of money to pay, should the tunnel collapse without the needed repairs, the costs would be much greater.
Requests for Qualifications were sent out to potential bidders on February 10th, 2012, and a pre-qualification site visit was performed on March 1st, so that potential bidders could enter the tunnel prior to the irrigation season.
As TID hopes to complete the project this year, Request for Proposals was sent out on August 14th, 2012. Proposals are due to TID on September 19th, with TID issuing a Conditional Notice of Award on September 24th.
Construction is scheduled to commence on October 8th, with hopes to be completed by mid December 2012. By the end of 2012, Tunnel #2 will have provided TID the last of its 121 years of service, and the risk of a tunnel failure will have been eliminated.