Abstract:
This abstract presents a case history on recent rock blasting, excavation, and bedrock slope stabilization techniques to facilitate development on a 46-acre property in Waltham, Massachusetts. The case history addresses multiple S3 conference themes during site investigations, the design phase, and construction. Permanent bedrock slopes required to develop the site for the new high school varied in height up to 120 ft., unprecedented for new building construction in this complex geological region which was significantly altered from both brittle and ductile deformation events and is characterized by slickensided discontinuities that yield minimal friction and stability for the overlying rock blocks. Site development required design of a variety of permanent and temporary rockfall and rock slope stabilization mechanisms including, but not limited to, anchored wire mesh panels and rock dowels, to mitigate risk to public and property while maximizing developable area.
Subsurface conditions encountered during construction required adjustment to rock stabilization designs, especially in differing weathered rock conditions and kinematically unstable rock areas. Weathered rock, faults, shear zones, and fracture zones characterized by deteriorating rock and soil-silt infilling, were observed to daylight and extend out of final rock slope faces and into the excavation. Supplemental rockfall mitigation solutions to stabilize the exposed rock mass encountered during construction included heavy scaling, reinforced concrete retaining walls, and shotcrete and soil nail walls.
Similar bedrock conditions will present challenges for many development projects planned in the Waltham and Interstate 95 (I-95) area. This presentation will identify the issues Owners, consultants, and contractors should anticipate in project planning and design and explore stabilization alternatives to implement and alleviate construction related issues.