California’s iconic Highway 1 hugs the central coastline and Santa Lucia Mountains through its scenic Big Sur section. The bridges carrying cars and trucks over the many creeks and canyons are engineering marvels—Rocky Creek, Big Creek, and one of the tallest single-span concrete bridges in the world, spanning 714 feet, the Bixby Creek Bridge.
Besides scenic coastal beauty, the stretch of the highway is also famous for flooding, erosion, and rock and mudslides. Earlier this year sections were closed for months after record rain and storms. California Dept. of Transportation (Caltrans) District Five is quoted as saying the region experienced “12 consecutive atmospheric rivers that really soaked and saturated the soil.”
The bridge over Monterey County’s Limekiln Creek was built in 1957 and has been tapped for replacement as part of a complete realignment of the highway for almost a decade. When maintenance staff noticed gaps in a permeable gravity retaining wall called a cribwall supporting the slope around the bridge’s northern abutment—which in turn supports the highway—they immediately called the engineers at Caltrans.
“Excessive rainfall, stormwater, and surge from the towering waves of king tides caused erosion of the soils and fines in a 160-foot section of the interlocking precast concrete cribwall,” says Cliff Frazao, president of the company Caltrans’ District Five called for help, EagleLIFT. “Caltrans geotechnical engineers needed a solution that would preserve the wall’s integrity and save having to replace it.”
Frazao says their first moves were to assess the size and scope of the voids, drill five-eighths-inch holes both vertically and horizontally then insert half-inch steel probes. Next, they chose a product called Strata-fill™ by US company NCFI’s Geotechnical Polyurethanes Division. “We pump this liquid polyurethane foam through steel rods into the voids. It follows the path of least resistance and finds voids we didn’t even know were there. One void behind that wall was large enough to stand up inside,” says Frazao. He also says the product has other benefits, “It’s lightweight, so it doesn’t add extra pressure on the soil, and has a low exothermic reaction temperature, which means it generates very low heat during the polymerization reaction. That’s an ideal characteristic for closed spaces like these voids where you don’t want overheating or a smoldering fire.”
EagleLIFT injected around 5,000 pounds of Strata-fill through the steel rods. Frazao says they accomplished the job in one-and-a-half days and came in 50 percent under budget. “That comes from experience,” says Frazao. “We’ve been doing this for more than 20 years around California and Nevada, so we know infrastructure rehab, concrete cribwalls, and the right low exotherm system. It’s also why we’re so good at stretching a dollar. Replacing that cribwall would cost millions and take many months. Kudos to the maintenance staff for contacting Caltrans, and to Caltrans for doing proactive, preventive maintenance by calling EagleLIFT. If the check engine light comes on in your car, you can either say ‘I’ll worry about that later’ or drive to the mechanic and get it fixed. That choice can mean the difference in a small repair bill and the cost of a new car.
Frazao says the repair is more just a quick temporary fix, “It will last until they finally get around to building a new bridge over Limekiln Creek.”
[Editor] NCFI is a sponsor of GeoPrac.net. [/Editor]