Landslide hazards in Vermont

Abstract

Introduction 1 Natural Slope Processes in Soil and Bedrock 1 Mass Movement of Soils and Debris 1 Mass Movement of Bedrock 1 Human-Induced Slope Instability 2 Active Geomorphic Processes Contributing to Instability 3 Acknowledgments 3 Historical Record of Slope Movement in Vermont 3 Research Investigations 5 Movements of Soil Materials on Slopes 6 Soil Types in Vermont 6 Types of Soils in which Slope Movements Occur in Vermont 6 Natural and Human-Induced Slope Movements in Vermont Soils 8 Differing Rates of Movement in Soils in Vermont 9 Debris Avalanches 10 Slope Remediation 11 Slope Movements in Bedrock 12 Conditions that Promote Rock-Slope Movement 12 Types of Structural Discontinuities in Rock 13 Rock-Slope Movement Types 13 Rockfall 13 Block Slides 14 Topples 14 Slope Movements on Vermont's Interstate Highways 16 History and Construction of the System 16 General Geology 18 Design, Design Changes, and Construction of Rockcuts 18 Analysis of Rockcuts 20 Rockcut Slope Failures 20 Results of the Phase I Project 22 Conclusions 22 References Cited 22 FIGURES 1, 2. Photographs showing: 1. The intensity of jointing in the Cheshire Quartzite 2 2. An example of a vertical joint set with a second set intersecting at a large angle 2 3. Map showing locations of soil landslide sites described in the text 4 4, 5. Photographs showing: 4. A, The 1984 debris flow on East Mountain at Mendon, looking downslope; B, The same slide area, looking upslope, from U.S. Route 4 a year later 6 5. A rhythmite sequence at North Springfield flood-control reservoir 7 Contents Ill 1. Types of discontinuities in rock causing failure of slopes 13 2. Criteria used in the 1977-78 analysis of rockslide-rockfall potential along Vermont's Interstate Highway System 20