Drivers who use westbound Highway 18 must detour from 8 p.m. Friday until noon Tuesday as crews repair a washout that occurred in February during heavy rains.

About 13,500 drivers use the lane daily. They’ll have to cancel trips or detour using I-90, I-405, Highway 167 or I-5.

The supporting soil has eroded away from the shoulder of Highway 18 about 1.5 miles south of Tiger Summit. Crews need to occupy the westbound lane while they dig out waterlogged dirt 10 feet below, fill the gap with rock, then repave, the Washington State Department of Transportation (WSDOT) said.

The nearly four-day project is intended to prevent a more severe washout that would force a full closure of Highway 18, said WSDOT spokesman Tom Pearce. Since early February, orange cones have cordoned off the damaged shoulder and guardrail.

People can still drive west on Highway 18 from the I-90 interchange in Snoqualmie as far as the Tiger Summit trailhead, then turn back to Snoqualmie, Pearce said.