Landslides and Slope Repair
In general, landslides are complicated systems of geology, geomorphology and hydrogeology. Rarely does a single design tool address all of the problems associated with incidences of mass movement such as landslides. As a result, D.J. Scheffler, Inc. is very selective when considering projects where the mediation of active or ancient landslides is included in the scope of work.
Soldier piles, or shear pins, consist of vertical shafts drilled through the unstable zone, and heavily reinforced with steel and high strength concrete. Shear pins can be used to stabilize shallow zones of instability, or in conjunction with tieback anchors for larger masses of unstable soil.
A tieback consists of a small diameter drilled shaft that is fitted with a steel-tensioning element that is centered in the hole. The shaft can be horizontal or drilled at an angle depending on the specifics of the job. Once placed, the steel element is surrounded by cement grout.
Tieback anchor systems are rows of tiebacks. The shaft can be horizontal or drilled at an angle depending on the specifics of the job. Horizontal spacing between the tiebacks is job specific. Vertical spacing between the tieback rows is typically 5 feet. Each tieback is hydraulically tested and tensioned at a specified design load, frequently in excess of 850,000 lbs.
The steel ends that protrude from the earth are then incorporated into a reinforced concrete beam or slab that contains the unstable soil mass. Tiebacks can be drilled to depths beyond 250 feet.
Many projects involve a significant quantity of grading in conjunction with structural repairs. Grading includes the construction of key-ways, drainage systems and re-establishing surface grades. Once graded, proper landscaping can further enhance the slope's stability and enhance the aesthetic appeal of the repairs.
Hydraugers are near horizontal drainage elements drilled into the ground in order to minimize groundwater. The buildup of groundwater can trigger landslides. Under specific conditions, it is more economical to install a drainage system to prevent the buildup of groundwater before the movement of a soil mass, as opposed to constructing some form of structural support system.
Drainage galleries are designed to remove as much water as possible from an unstable soil mass. Drainage galleries consist of closely spaced large diameter vertical shafts. These shafts are filled with gravel.
Groundwater will follow the path of least resistance, and the gravel columns provide less resistance to the flow of water than the surrounding native soil. The bottoms of the gravel columns are provided with outlets for the water to escape, either by gravity with hydraugers, or via a system of electric pumps.