S-Curves Landslide Evaluation
Cannon Beach, Oregon

Hemlock Street has settled and distorted for decades. Deformations occur with extended intense rainfall, resulting in the need for roadway and sewer force main repair and occasional road closure.

To address roadway safety GSI created a decision tree of slope monitoring and protective action for the City. With that program in place, GSI installed inclinometers and piezometers to evaluate slide movement. Continuous water levels were recorded with digital instruments to capture peak water levels with fast rainfall response times.

Inclinometer, water level, and rainfall data were used in developing stability models of slide response. Stabilization options were developed that include dewatering with horizontal drains and infrastructure improvements.

Initial horizontal drains have lowered water levels, and in combination with flexible shear force main joints, and a geogrid reinforced roadway, damage is already reduced.