Spanish Peaks

Stabilization System for Spanish Peaks Landslide

Spanish Peaks is a ski resort located in the mountain town of Big Sky, Montana, approximately 45 minutes south of Bozeman. The landslide was originally believed to be an ancient and relatively dormant feature; however, after installing inclinometers, it became evident that the slide was still slowly moving downhill, at a rate of up to 0.71 inches per year. Malcolm Drilling designed and constructed a stabilization system consisting of stitch piers and anchors. A total of 65 vertical shafts, each 5 feet in diameter and 65 feet deep, were drilled, extending 15 feet below the slide slip plane elevation. The fronts of the stitch piers were excavated to a depth of 15 feet to provide access for anchor drilling. Tie-backs with 8 strands, each 122 feet in length, were drilled on either side of each stitch pier, anchoring 30 feet below the slide slip plane elevation. A reinforced, cast-in-place shotcrete waler was constructed in front of the piers, 13 feet below the top of the pier. After successful tie-back load testing, the anchors were locked off against the shotcrete waler, and the area was backfilled up to grade. Malcolm successfully completed this project in one summer season, just before the return of snow.

Malcolm Drilling