US101 Oregon Coast Highway Horizontal Drains

The Problem

Three active landslide zones along US101 in Curry County, Oregon — at milepost locations MP315.89, MP332.55, and MP344.44 — were causing recurring slope failures and roadway damage. The unstable slopes, composed of intermixed landslide debris of clay, silt, sand, gravel, and boulder-sized rock fragments ranging from siltstone to serpentinite, were saturated with groundwater, driving chronic movement. Without intercepting and draining that groundwater, the highway faced ongoing structural failures and potential closure on a critical coastal corridor.

JDC's Solution

Oregon DOT designed a multi-site horizontal drain system targeting the groundwater-bearing zones within each slide mass. Jensen Drilling Company furnished all materials, equipment, and labor to drill and install 13,240 feet of 1.5-inch Schedule 80 PVC horizontal drains across 16 drill pads at the three sites, along with permanent 5-inch steel casings, outlet hose systems, and the full stormwater conveyance network. JDC's proprietary horizontal drilling technology — engineered for the challenging mixed soil-rock conditions anticipated at these sites — was a key factor in maintaining drill alignment, minimizing blowout risk, and achieving full drain lengths in highly variable landslide debris. JDC also constructed and removed all temporary access roads and drill pads required to reach the steep, remote slope locations.

Customer Benefit

Jensen Drilling Company delivered a complete, multi-site horizontal drain installation on one of Oregon's most environmentally sensitive and geotechnically complex corridors. The installed drains actively intercept and discharge groundwater from deep within the slide masses, reducing pore pressure and restoring long-term slope stability. Successful completion protects Oregon's coastal highway from recurring landslide-driven closures and costly emergency repairs.