A landslide and erosion risk assessment methodology for roadsides

Abstract

The overall objective of this thesis is to investigate a section of highway using the Slope Condition and Risk Rating (SCARR), methodology and subsequently evaluate the predictive capabilities of the technique and thus calibrate it for New Zealand conditions. To meet this objective, three specific aims have been defined: 1. To investigate a section of highway using the SCARR methodology to evaluate the risk that landslides pose to the area. 2. To test the predictive capability of this technique by comparing the results of the Stability and Erosion Risk Ratings with the slope stability and erosional condition of the area, using such methods as the Rock Mass Strength Classification, information from aerial photographs and topographical maps, and detailed field investigation of the actual condition of the area. 3. To calibrate the technique for particular regional conditions based on the geomorphic factors present in the area. These aims are pursued after examining the theory of slope stability and erosion and assessing the importance of the controlling factors. The subsequent examination and testing of the SCARR methodology and the Rock Mass Strength Classification, assesses the risk from instability and erosion of the two study areas: Kakatahi, on State Highway 4, and the Rimutaka Hill Road, on State Highway 2. This consists of an investigation of terrain factors, including the geomorphology, hydrology and geology associated with these particular highway sites. The aim is to find the combination of factors, using existing data and rapid reconnaissance, which best represent the particular highway problems. The SCARR methodology is designed to identify separately the actual slope or erosional condition (condition assessment) and the potential problems (risk ratings). Although the methodology worked well in assessing some sites or particular factors, it was found there were some areas where the methodology could be improved, thus increasing the accuracy and usefulness of the methodology. Compared with the original methodology, the revised SCARR ratings, developed in this study, gave a much more accurate, although not entirely comprehensive, representation of the condition and risk, of each area. The subsequent modification and calibration of the original SCARR methodology for particular regional conditions means the outcome is a landslide and erosion risk assessment methodology, particularly suited to New Zealand roads and conditions.