HOW MUCH CAN IT COST TO REMEDIATE A LARGE LANDSLIDE?

Surface areas of large landslides range from 2 to 20 acres, and efforts to improve the stability of landslides this size can be overwhelming. Before discussing remedial costs, large landslides need to be investigated and engineered one step at a time to minimize the potential for setbacks to the owner and/or the consultant. A phased approach helps the owner of the landslide understand if remediation is feasible and what the potential costs could be. It allows sufficient geotechnical data to be gathered, determines the appropriate remediation technique for both landslide and owner, and sets the stage for engineering design and construction. A cookie cutter approach does not work: every large landslide is unique.

The costs to treat a large landslide are dictated by geometry, site considerations, and the methods that are used to improve the balance of forces within the landslide. Potential methods can involve drainage, earthwork and structures. Drainage techniques often include trenching, relief wells and horizontal drains. Earthwork techniques may include unloading, buttresses and key trenches. Structural techniques for large slides are typically large diameter piles with tieback anchors. A phased approach would determine which technique is appropriate for any given landslide.

Costs for treating a large landslide can range from hundreds of thousands of dollars to many millions. For comparison, consider an 800-foot wide and 60-foot deep slide. Horizontal drains are relatively inexpensive at $15 to $20 per foot of installed drain; however, the number of drains and lengths add up and costs can quickly reach hundreds of thousands of dollars or more. Earthwork quantities for a rockfill shear key in an 800-foot wide slide could be on the order of 150,000 to 200,000 cubic yards. Prices of $3 to $20 per cubic yard for materials that range from waste soil to quality rockfill result in potential costs for construction of a shear key that could be on the order of $2 to $3 million. Conventional soldier pile tieback walls are usually inadequate for remediation of landslides this deep, and a wall of 3- to 4-foot diameter shear piles with tiebacks may be more suitable. Considering that construction costs could range from $400 to $500 per foot for a 4-foot diameter pile, an 800-foot long shear pile wall could cost on the order of $3 to $4 million.