Client Solutions / Innovative Technologies / Landslides

Landslides

Every winter many public agencies are faced with the cost of repairing recurrent shallow landslides, which are caused by a combination of wet weather, expansive soils and steep slopes. These landslides often threaten nearby critical structures, cause road closures, require on-going maintenance and can lead to the initiation of larger slope failures.

The typical slope stabilization method used where the slope boundaries are fixed is the removed and replaced earthwork method. This method requires that an area much deeper and wider than the slide limits be excavated to provide access to the site and to accommodate the width of earthwork equipment.

The Plate Pile Slope Stabilization method will stabilize a potential landslide at or nearing failure by dividing the slope into small areas each supported by one plate pile. The plate pile system consists of galvanized steel plates affixed to steel poles or "mini piles" that are driven into stable strata underlying a potential landslide. The mini pile transmits the slide forces captured by the steel plate downward to the stiffer material preventing the shallow landslide from developing.

A rigorous testing program under controlled conditions was performed to confirm the plate pile system's effectiveness. University of California, Berkeley's professors Jonathan Bray and Nick Sitar served as the peer reviewers for this demonstration project.

To test program included the construction of a sloping concrete surface with an imbedded irrigation system where a 3-foot thick fill was placed over the slope. The tow of the slope was cut vertical to remove any passive resistance. Landslide conditions were created in the test slope by applying the equivalent of 7.5 inches of rain and then injecting 400 gallons of subsurface water. In the next step, the slope was recreated with the plate piles installed in the fill.

The test was performed on the plate pile reinforced slope under the same conditions as the first test slope. Care was taken to approximate the same initial density and moisture content of the fill. The plate piles were inserted in sleeved holes in the concrete slab at 4 feet on center horizontally and 10 feet apart vertically. The insertion of the sleeved holes simulated embedment in a soft bedrock formation.

The slope without the plate piles system experienced dramatic failure within 7 minutes of applying subsurface irrigation. The slope with the plate piles remained stable. The test results proved that the plate piles could prevent sliding of the soil layer that would otherwise have failed when the subsurface water was turned on.

The plate pile reinforced slope was left in place for 6 months and allowed to dry and crack in the 100-degree weather at the test site. Then the slope was watered again and the subsurface irrigation reapplied. Again, the plate piles held the slope together.