Abstract:
The Heights project is located at Fashion Valley North, San Diego, CA. The scope of the project is the replacement of two existing commercial buildings, both having 2 – 3 stories, with a large 7-story multifamily residential building. A 1:1 cut slope was present at north side of the site. A permanent soil nail wall, 1,000 linear ft long, with a maximum height of 100 ft, was needed at the north side of the project to accommodate the development. According to the geotechnical investigations, the stratigraphy of the job site mainly consisted of bedrock (i.e., Stadium Conglomerate, Tst). The existing design of the permanent soil nail wall required up to 115 ft long soil nails with large diameter rebars and 13 in. thick permanent facing. Soil nail design optimization was conducted by PB&A to reduce the construction cost. First, the SnailPlus program was used to check the internal and global stability under static and seismic conditions and to design soil nail lengths and sizes. Then, soil nail head force was extracted from the program to design the permanent facing using FHWA recommended procedure. Another challenge of the project was to evaluate the interaction between a future San Diego Gas and Electric tower and the soil nail wall. Finite element analyses were conducted with PLAXIS program to ensure the deflection of the future tower would be within the acceptable range. The optimized soil nail design reduced the soil nail length to maximum 75 ft with lighter rebar and 10 in. thick permanent facing. The optimization eventually helped the client to save approximately $800,000 in construction cost and improved construction productivity by using shorter and lighter nails and thinner permanent facing.