DESIGN AND CONSTRUCTION OF THE SUMMIT SENIOR CARE FACILITY INTO THE SIDE OF AN UNSTABLE CALIFORNIA HILLSIDE

摘要

With stable building sites becoming scarce in the greater San Francisco Bay Area, the new Summit SeniorCare Facility is being built into the side of an unstable hillside adjacent to the San Ramon Regional MedicalCenter in San Ramon, California. This hillside has had a long history of instability and the site of the newSenior Care Facility required excavation into both a historic old landslide and a more recent active landslide.After a thorough geotechnical study, it was concluded that the best way to build the new facility would beto construct a tied-back retaining wall in the area of the old landslide, since it extended off-site onto twoadjacent properties, and remove the active landslide and replace it with compacted fill before cutting intoits toe area with an additional tied-back retaining wall. The design was further complicated by the proximityof the site to several active faults. In the area of the old landslide, the combination of an ascending slopebehind the wall, landslide forces and seismic forces resulted in total design pressures between 365 to 4,575PSF for a wall with a maximum height of 30 feet. The wall for the old landslide was constructed by firstdrilling and placing steel soldier piles in concrete. The tip of the soldier piles extended a minimum of 12feet below the landslide plane that was up to 36 feet below the bottom of the wall. Permanent doublecorrosion protected tiebacks were then installed through the soldier beams and anchored below the slideplane. A shotcrete facing was then installed on the face of the wall.