Kings River Surge Shaft Liner

The Kings River Powerhouse, part of the Haas-Kings River Hydroelectric Project (FERC No. 1988), has been in operation since the early 1960’s.

Service water for the Kings River Powerhouse begins at the Balch Afterbay Dam, where a portion of the North Fork Kings River is diverted. The water flows through a series of two tunnels, which are separated by the Dinkey Creek Siphon, and down a 9-foot diameter penstock to the powerhouse. Both tunnels are largely 14-foot horseshoe sections and extend nearly two miles in length. The tail end of Tunnel No. 2, approximately 300 feet upstream of the penstock portal, includes a vertical surge shaft approximately 20-foot in diameter by 165-foot high. The uppermost 35 feet of the surge shaft is lined with reinforced concrete and is relieved by a 60-foot diameter open-top surge tank. Most of the tunnels and shaft are unlined hard, sound metamorphic sedimentary rock.

In 2008, leakage was observed on the hillside between the surge tank and penstock portal. By 2009, the leakage rate had increased substantially to nearly 100 gallons per minute, threatening the stability of the hillside, surge tank, and penstock below. Syblon Reid was contracted, through a select bidders/hard bid process, to cutoff the leakage by means of a reinforced shotcrete liner with contact pressure grouting.

Due to energy demands and power commitments, the project schedule was compressed to allow a 13-week outage during winter months. The work was comprised of:

  • Designing and fabricating a work platform for performing all work in the shaft,
  • Rock scaling of the shaft and tunnel,
  • Excavating 1,800 cubic yards (cy) of tunnel muck from the rock trap,
  • Hanging heavy reinforcing in the shaft and tunnel,
  • Onsite batching of 975 cy of shotcrete concrete mix,
  • Placing shotcrete in a 71-foot long section of a 21-foot horseshoe tunnel,
  • Placing shotcrete in a 105-foot long section of a 19-foot internal diameter shaft, and
  • Drilling and contact pressure grouting the upper 35-feet of the shaft.

There were many challenges to this project that made it unique. Located approximately 1 hour east of Fresno in the beautiful Sierra National Forest at 1,700 feet (USGS), any life-threatening emergency would have required a life flight helicopter. Strict environmental controls and Best Management Practices were implemented to regulate the tunnel leakage water for construction use and downstream bypass. Construction water was carefully captured, filtered, tested, and recycled. Syblon Reid worked closely with Cal/OSHA Mining and Tunneling Unit to develop a safe system for working at heights in the shaft, utilizing twin mine hoists rated at 20,000-pounds each and a single-level work deck. All 975 cy of concrete were batched onsite using heated water and volumetric mixers. The concrete was then pumped 300-feet horizontally through the roll-out section of the penstock before an ultimate 135-feet vertical climb to the top of the liner inside the shaft. A substantial portion of this project required double shifts, seven days a week. Perhaps the most challenging aspect of the project, in addition to the schedule, was logistics. Access to the postage stamp size project site, situated on the side of a mountain, required a 3,000-foot trek up an 11-foot wide, 2:1 grade “goat trail”. Mobilization and demobilization were feats in and of themselves.

Ultimately, the project was a huge success, with the owner, engineer, and Syblon Reid – together with its subcontractors – working in a collaborative manner to solve problems and provide solutions.

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