Abstract:
In July of 2023, an extreme rainfall event caused a landslide slope failure on Route 2 in Gill, Massachusetts. Route 2 is a major East-West transportation corridor in central Massachusetts. The landslide forced the roadway to shut down and then subsequently reopen with lane restrictions in the area of the landslide. Vehicular traffic had to use alternate routes until a solution was formulated to (1) temporarily re-open the roadway to all traffic without lane restrictions and (2) repair the slope/roadway to prevent future failure events.
Due to the emergency nature of the Project, innovative techniques such as a drone survey and automated monitoring systems were used to facilitate design, construction and roadway safety concerns. Existing soil information and time to perform a subsurface investigation was limited, and therefore, on-site soil observations as well as soil information from a nearby bridge project were used in the initial design. To achieve the temporary roadway stabilization a temporary support of excavation (SOE) consisting of cantilevered soldier piles was designed and installed along the roadway approximately 10 feet from the edge of the existing failed slope. Soil conditions for the permanent slope repair were further confirmed and adjusted using feedback from the inspection of the soldier pile installation. The reinforced slope design consisted of boulder fill with a grout mass reinforced using steel shear pins at the base transitioning to a geogrid reinforced soil slope covered in riprap extending up to existing roadway.
To evaluate the performance of the SOE and monitor the existing slope, an extensive automated monitoring and inspection program was executed by GTR. Due to the time and site constraints, the reinforced slope installation and design could be modified using a combination of engineering judgement and the observational method.  Effective communication throughout the Project Team resulted in efficient design and construction of the slope repair, which was completed in record time for the roadway to be paved and re-opened prior to winter.