Geotechnical test results at a prehistoric landslide site in Breckenridge, southwestern Quebec

Abstract

Geotechnical field testing was conducted in and around a landslide occurred about 1020 cal BP in Breckenridge, southwestern Quebec. The objective of the study is to investigate the magnitude of an earthquake previously hypothesized to have triggered this and other landslides in the region. The purpose of this Open File is to document the data obtained from the Breckenridge landslide site. The landslide is about 980 m long and 370 m wide. Four cone penetration tests (CPT) were conducted to depths ranging from 37 m to 55 m. Two CPTs were inside the landslide scar and two outside. Field vane shear tests (VST) were carried out at three CPT locations. The CPT cone bearing factor Nkt was calibrated to be 11.5. The soil undrained shear strength (Su) was found to have a correlation of Su = 15 + 2.66 H (kPa), where H is depth in meters from the original ground surface elevation at the head scarp. All the CPT data consistently show the same trend for the undisturbed materials. The slip surface was found to be at about 15 m depth from the original ground surface.