Quarrying a Hillslope in Waltham: Considerations and Lessons Learned from Stabilizing Rock in an Open Excavation-Video

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Chris presented lessons from stabilizing rock slopes during construction of a new high school in Waltham, Massachusetts. The project involved excavating roughly 800,000 cubic yards of rock and creating permanent slopes up to 120 feet high beside school buildings, athletic areas, roads, and nearby homes.<br /><br />Investigations and analyses considered multiple failure mechanisms, including planar, wedge, and toppling failures. Because the site required essentially complete rockfall containment, the design combined drape mesh with anchored pin-mesh systems. The blasting program used pre-blast surveys within 500 feet, incremental test blasts, and early communication with residents; coordination also allowed mesh to be installed during excavation.<br /><br />Unexpectedly weathered rock and shear zones meant that some areas needed anchor-supported shotcrete and a soil-nail wall beyond the original plans. The presenter emphasized verifying competent bedrock, using geophysical investigations strategically, accounting for permanent anchors crossing property boundaries, and maintaining clear communication among project teams.<br /><br />During questions, he noted that shotcrete durability depends on reinforcement and drainage but acknowledged uncertainty about long-term performance. Rock competence had been assessed using RQD and UCS data, though conditions encountered in the field sometimes differed from core results.

Keywords

rock slope stabilization

Waltham Massachusetts

rockfall containment

drape mesh

anchored pin mesh

controlled blasting

soil nail wall