The landslide occurred within the northern portion of the top of the slope on this property and extended onto the neighboring property to the north.
The slide removed a significant portion of the backyard area, and created a near-vertical scarp up to approximately 20 feet tall and about 60 feet wide. Some of the slide debris was deposited onto the railroad tracks below.
We performed deep drilled borings to collect soil data and also installed inclinometers to measure any potential movement.
Our recommendations included installing a subsurface retaining wall consisting of large reinforced concrete piers within the landslide area along with buttressing the upper portion of the slope with a geo-grid reinforced earth mass to re-establish the lost area in the backyard.
Landslide debris was then removed from behind the retaining wall to expose competent native material and replaced with large 4-man sized rocks against the retaining wall and 4- to 8-inch spalls within the remaining area.
Geogrid reinforced earth slope was constructed directly on the rock spall bench behind the piers, as well as a new drainage system. The top of the slope and the backyard were re-established to pre-slide conditions.
We monitored the installation of these stabilization and drainage systems during construction.
Location: Everett, WA