Rockridge Geotechnical (RG) performed a geotechnical investigation and provided geotechnical services during the construction of an affordable housing community at 5173 Highway 12 in Santa Rosa. The nine-building, 99-unit Mahonia Glen will replace a nursery, which included a residence, commercial building, and storage building, previously on-site. Eight of the nine buildings will be three stories, with the community building being only one story. Each of the buildings will be wood-framed and constructed at-grade.

The primary geotechnical issues affecting the development included: (1) the presence of moderately to highly expansive near-surface soil, (2) the presence of an existing creek running through the site, (3) a high groundwater table, and (4) providing adequate foundation support. RG provided recommendations for the building to be supported on a foundation system that mitigates the negative effects of expansive near-surface clay and fluctuations in moisture content, with the exact foundation recommendations being either deepened spread footings or a post-tensioned slab. RG provided consultation during final design and construction permit application.

RG also provided geotechnical observation and construction services during construction; these services included observation during the backfill of voids resulting from demolition activities, as well as excavation and installation of the buildings’ foundations.