Akkerman
Eighteen shafts will be utilized for microtunneling installation…
Geology dictates construction methodology
Also known as slurry microtunneling, microtunneling is a remote-controlled, laser-guided, continuously supported pipe-jacking method for installing gravity-flow pipelines requiring precise line and grade in poor soil. It’s typically used in ground conditions below the water table where workers aren’t permitted.
Soil is infused with slurry at the face of the bore to minimize ground surface settlement. Cuttings are forced into slurry inlet holes in the microtunnel boring machine’s (MTBM) crushing cone for circulation to and from a closed slurry system to a separation plant (see the diagram on the next page).
The method is used primarily with reinforced concrete, steel casing, fiberglass, centrifugally cast fiberglass reinforced polymer mortar, polymer concrete, clay, and ductile iron ranging in diameter from 30 inches to 114 inches.
With EPB, spoil is removed from the pressurized cutting chamber through a screw conveyor and placed into a haul unit system. EPB systems install pipe by pipe jacking or segment-erecting methods.
The method is often used for large-diameter tunnels, typically 102 inches and larger, where continuous pressure is necessary to balance groundwater and earth pressures. Common pipe types are reinforced concrete, steel casing, fiberglass, centrifugally cast fiberglass, reinforced polymer mortar, polymer concrete, clay, ductile iron, concrete segments, liner plate, and ring beam and lagging tunnels.
CCWRD is an award-winning utility whose assets are critical to maintaining a desert region’s water supply. The district has used both trenchless methodologies before, but this project required using a new material for the first time: Flowtite fiberglass reinforced pipe (FRP). Manufactured by Thompson Pipe Group of Zachary, La., the pipe is strong enough to withstand jacking via EPB or MTBM equipment through the extremely hard sedimentary rock — called caliche — found in desert regions that morphs into a clayey consistency when mixed with water.
At 25,091 feet, the new interceptor represents the third and most extensive installation of Flowtite FRP in the U.S.
“Fiberglass pipe has been widely accepted throughout the world for decades as a solution to corrosion, but adoption in North America has lagged,” says Thompson Pipe Group Executive Vice President Mike Leathers. “This interceptor is a powerful commitment to sustainability from CCWRD and the engineering teams. They’re leading the way in navigating the most complex infrastructure challenges of today and we’re proud to produce pipe that aligns with both their budget and infrastructure goals.”
Next page: Extremely challenging subsurface conditions
