A GEOHAZARD REMEDIATION FOR A HISTORIC RAILWAY LINE

Historic infrastructure in parts of the northeastern United States has continued to be impacted by degrading and crumbling cuts and slopes. Repairs and stabilization techniques should evolve with the changing conditions and historical infrastructure. This case study presents the challenges associated with a small passenger rail line supporting a major metropolitan region and the narrow corridor with degrading rock slopes that are impacting it.

The project area is in the Cape Anne Granite formation, which crystallized in a high temperature, low pressure environment, with iron and potassium rich magma. The structure consists of northeast trending, high angle thrust faults, west over east, with some strike-slip component. A prominent basaltic dike traverses the corridor below a historic bridge, resulting in construction concerns from the drilling effort.

Field mapping was performed to identify unfavorable joint orientations prone to rock wall failure with respect to the rail line, and then confirmed with aerial imagery and LiDAR surveys. Kinematic analyses to identify the likely failure mode were performed indicating toppling to be the most common. The recommended repair for the site was a combination of a rock slope drape and a rock bolt stabilized concrete facing, applied to critical areas of the slope. The design and construction of the treatments required intuitive methodologies to consider the timing for construction, the impacts to nearby historic structure, and the need to maintain a safe track gauge for the rail line to operate.