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Spirit Lake Outlet Tunnel Team Plans to Repair Movement to Tunnel Floor

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Spirit Lake Outlet Tunnel Team Plans to Repair Movement to Tunnel Floor Vol. 39, No. 4 July - August 2015 Spirit Lake Outlet Tunnel team plans to repair movement to tunnel floor R Mountain on the move 1.75”Spirit x 1.25” Lake Outlet Tunnel team plans to repair Pantone 032 = Red CMYK = C0, M100, Y80, K0 movement to tunnel floor By Diana Fredlund, Public Aairs Oce hen mountains move, humans The avalanche created a dam of to rise into the more porous pumice Wcan only watch and figure out sediment, ash and fragmented rock, and ash, it could erode the entire dam how to work with the changes. with heavier, less porous materials and possibly send tons of material and below and more erodible pumice and water downstream.” A massive avalanche of rock and ash from pyroclastic flows above it. debris choked Spirit Lake when Mount Snow and rain continued to feed Spirit In the worst-case scenario, St. Helens erupted May 18, 1980, Lake, but without an outlet, the water communities like Castle Rock, Kelso changing the jewel-like lake forever. level rose dangerously close to the and Longview in the Cowlitz River The avalanche completely blocked the more easily erodible material. Valley would be flooded by more than natural outlet where Spirit Lake flowed 60 feet of water and debris. “The U.S. into the North Fork Toutle River and on “The natural dam is strong enough to Forest Service needed to find a way to into the Toutle, Cowlitz and Columbia withstand the weight of water in Spirit stabilize the lake level and the Federal rivers. Lake until it reaches the top layer,” said Emergency Management Agency Chris Budai, Spirit Lake Outlet Tunnel tasked the Corps with finding it,” project manager. “If water levels were Budai said. Mount St. Helens erupted in southwestern Washington May 18, 1980 10 July - August 2015 Corps’pondent ® R Mount St. Helens and Spirit Lake at the tunnel intake are located within the Gifford Pinchot with shotcrete when National Forest in southwestern we excavated it.” Washington. In 1982, President Ronald 1.75” x 1.25” Reagan declared a state of emergency Shotcrete is a and FEMA requested that the U.S. concrete mix that Pantone 032 = Red Army Corps of Engineers develop is “shot” through a CMYK = C0, M100, Y80, K0 and execute a solution to Spirit Lake’s pressurized hose, Photos of Engineers Corps water level problem. allowing the material to adhere to a variety “The first step was to design an of surfaces. Instead interim plan to maintain the lake’s of using shotcrete, the water level until a long-term solution slopes were protected could be developed,” Budai said. The with chain link fabric Corps established a temporary pumping and rock bolts, but the facility on Spirit Lake in November rock was exposed to 1982, which operated until the Spirit freezing and thawing Lake Outlet Tunnel was completed in conditions that caused 1985. a rapid deterioration of the rock slope, Budai It wasn’t as easy as moving equipment said. in and getting repairs started, however. “Fragments of rock In 1982 President Reagan and would break off and Congress created the Mount St. Helens build up behind the (MSH) Mount St. Helens erupted in southwestern National Volcanic Monument within chain link fabric and Washington May 18, 1980. The eruption forever the Gifford Pinchot National Forest. An eventually fall onto changed the jewel-like Spirit Lake, seen here prior to important objective of the legislation the intake air grating May 1980. was to protect natural features and that allows the tunnel allow the environment to develop to function properly. Toutle, Toutle and Cowlitz rivers as it naturally, according to Peter Frenzen, Additionally, ash, pumice and other flows to the Columbia River. staff scientist for the Monument. volcanic material that surrounded the intake was a constant source of material Geologists knew there were some “Spirit Lake and the surrounding that fell on the air grates and blocked areas along the tunnel’s path that area are very remote now, since roads air flow into the tunnel.” could exert additional pressure on the and infrastructure were destroyed in tunnel. These areas are known as shear the blast. As the best known and most Engineers modified the intake air zones, where the pressures could cause studied eruption of the 20th century, grating to allow this debris to drop into the ground to move if the tunnel was we believe it’s important to learn about the shaft and then wash out through the not adequately supported; they also how nature manages its own recovery,” tunnel, eliminating the problem. contained soft, clay gouge material that Frenzen said. “It does create some flows under pressure. challenges, but within the bounds of The intake shaft drops water about public safety we need to preserve this 40 feet into an 8,465-foot long, 11- “The tunnel had to be designed to important natural laboratory.” foot diameter tunnel that the Corps withstand these varying stresses,” constructed through Harry’s Ridge, Budai said. “We knew routine “It definitely posed a challenge which borders Spirit Lake. The water monitoring would be important so we when the Corps began constructing the flows into South Coldwater Creek, could react if we detected any changes outlet tunnel in 1984,” Budai said. “For Coldwater Creek and the North Fork in the tunnel.” example, we couldn’t protect the slopes www.nwp.usace.army.mil 11 ® R 1.75” x 1.25” Pantone 032 = Red CMYK = C0, M100, Y80, K0 Mount St. Helens erupted in southwestern Washington May 18, 1980. After the eruption, fragmented rock, ash and debris choked nearby rivers, threatening local communities downstream. Since its completion in 1985, the capacity means less water can flow to repair the tunnel before the next Corps has repaired the tunnel many without pressurizing the tunnel – the flood season in January 2016. times; most were small repairs to expansion and contraction that occurs restore tunnel integrity. if water completely fills the smaller Because the Monument is managed tunnel. Pressurization can be seen when by the Forest Service, the Gifford A more significant repair was water flows out of a bottle that’s tipped Pinchot National Forest first needed performed in 1997, when tunnel nearly vertical, causing a back-and- to secure funding from its national movement due to pressure build-up in forth motion. In a concrete structure headquarters. As soon as the situation a shear zone caused a partial failure like the Spirit Lake Outlet Tunnel, that was discovered, senior leaders from of some tunnel supports. Pressure can cause damage and failure, since it the Forest Service and the Corps met build-up from that same shear zone can rapidly erode the tunnel rock and to discuss the needed repairs and has caused gradual movement in an undermine the tunnel supports. formulate a funding strategy. area near the 1997 repairs, causing the tunnel to constrict. For nearly 30 years Budai and her team knew the soft Budai and her team began designing the annual inspections showed only clay material was being forced upward the repair plan. “Under normal a gradual constriction in the tunnel’s into the tunnel. “The movement is circumstances a Corps project moves diameter, which engineers monitored much like that of toothpaste being through the design, review, and but decided no action was necessary; in squeezed from a tube,” Budai said. contracting phases in 12 to 18 months,” October 2014 Budai found that was no “The pressure from the material above Budai said. “Our accelerated schedule longer true. the tunnel was forcing the soft material includes design and review in about up into a weaker section of the tunnel.” six weeks. The construction contract is “Our inspection in October found expected to be awarded by early August; one part of the tunnel’s floor had When sharing her findings with the work is scheduled to begin in September moved upward by about a foot and a Forest Service, Budai emphasized 2015 and finish by February 2016.” half, increasing the possibility of a the need to move quickly. During an tunnel collapse,” Budai said. “Another inspection six months later, Budai Fast-tracking the repair project concern is the decreased water capacity found the floor had moved upward means it receives a higher priority for due to the constriction.” Decreased another six inches, reinforcing the need resources while still conducting all the 12 July - August 2015 Corps’pondent ® R quality assurance checks every project fit current and future requirements.” Lake’s water level sustainably into the undergoes. “We are ensuring all design The long-term project will require future.” and review actions are fully in place. formal studies to ensure the repair It means our team is focusing almost work meets all regulations, she added. Mountains move on their1.75” x 1.25”own exclusively on the Tunnel Outlet schedule and many were surprised in Project for a while in order to get the Water continues to flow into Spirit Pantone 032 = Red 2004 when Mount St. HelensCMYK erupted = C0, M100, Y80, K0 work done on time.” Lake and thanks to a team of Corps again. The Spirit Lake Outlet Tunnel and Forest Service scientists, engineers “It’s important to remember these and biologists, the lake will continue was designed to withstand landslides are interim repairs, designed to provide to flow safely through the tunnel and and mudlfows from future eruptions. us time to make more extensive, long- continue its way to the ocean. It’s possible today’s team members won’t term repairs,” Budai said. be working on the project the next time “The cooperation among the agencies “The Forest Service is the lead is outstanding,” Frenzen said.
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