Abstract:
The Many Farms Foundation Stabilization and Site Drainage improvement project was a 2019 DesignBuild project to address serviceability problems at Many Farms Community School and High School Campuses. The project is located in Many Farms, Navajo Nation, Arizona. Complex ground conditions at the school site included shallow groundwater, expansive soils, collapsible soils, and localized moisture weakening due to utility leaks. These conditions were identified in study phase as the root cause of school infrastructure distress characterized as sitewide differential settlement related issues. The highprofile project was designed within a fast-track 120 day schedule, work included conducting site characterization with CPT and seismic refraction arrays. The final design-build drawings and specifications were developed with the intent to stabilize classrooms, dormitories, auditorium, and gymnasiums. Site drainage work included a network of concrete channels to mitigate stormwater ingress. The stabilization started in November of 2018. The stabilization work was specified along perimeters of spread footings and also located at each deep foundation element, with up to five crews working continuously over eight months with school in session during most of the work. The final walk through and project closeout occurred in October 2019. Several innovative methods were used to evaluate, stabilize and monitor the site. The grout injection work was optimized with a test strip establishing a site specific grout take. A site improvement factor was established using a dynamic probing rig with the same energy as SPT (140# hammer and 30" Drop). An array of instruments and independently monitored crack distress throughout the entire design and construction phases. Highlights included the deployment of a specialized rig to expedite the grout injection work and the develop of an alternative stabilization method (Push Piers) underneath the High School Auditorium Stage where access was unavailable for the deep injection required. Overall, this is an intriguing case history for mitigating problematic soils, using a data-integrated project level decision making, and the advantages realized through the Design-Build project delivery method.