Spanish Peaks is a ski resort in the mountain town of Big Sky, Montana, approximately 45 minutes south of Bozeman. The landslide was originally thought to be an ancient and relatively dormant feature, however after installing inclinometers it was quickly realized the slide was still creeping downhill- up to 0.71 inches per year. Malcolm Drilling designed and constructed a stabilization system of stitch piers and anchors. A total of 65 vertical shafts – 5 feet in diameter and 65 feet deep – were drilled, tipping out 15 feet below the slide slip plane elevation. The front of the stitch piers was excavated 15 feet deep to create access for the anchor drilling. Tiebacks with 8 strands and lengths of 122 feet 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 down from top of pier. After successful tieback 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 snow returned.
Big Sky, MT
Big Sky, MT