Rodgers, Nick

Phase 4 Slope Vulnerability Assessments is a continuation of Phases 1-3 previously conducted by WSB and MnDOT to determine the risk of slope failure along state highways. This phase includes 16 counties located in districts 1 and 3 and the Metro. The three main components of the model are 1) identify past slope failures, 2) model the causative factors of past failures and how they vary locally, and 3) model the risk of new slope failures. The vulnerability factors and expected failure types reflect the diverse geomorphology of Northeast Minnesota. Vulnerability factors for the new study area include slope angle, curvature, relief, slope orientation (aspect), and water table depth. The preliminary model developed prior to the field visit was underestimating slope vulnerability and was not effectively capturing all historical failure types. WSB determined the solution was to re-design the historical failures model. The model was refined and led to an improved vulnerability output. Model results were ranked into four proposed risk-management categories: action recommended, further evaluation, monitoring, and no action recommended. The risk estimation process was considered preliminary; further consideration of risk tolerance and consequence definitions should be conducted. Preliminary risk results indicated that 499 management areas and 1.4% of the total area was categorized as action recommended under the proposed risk matrix. The results of this study were intended to be the first step of actions required in minimizing slope failure effects including expensive mitigation and maintenance repairs and threats to public safety.

Phase 3 Slope Vulnerability Assessments is a continuation of Phases 1 and 2 previously conducted by WSB and MnDOT to determine the risk of slope failure along state highways. This phase includes 27 counties located in MnDOT districts 1; 2; 3; and 4. The three main components of the model are 1) identify past slope failures; 2) model the causative factors of past slope failures and how they vary locally; and 3) model the risk of new slope failures. Vulnerability factors; failure types; and model results reflect the geomorphology of this region. Vulnerability factors for the new study area include slope angle; terrain curvature; and water table depth. Field verification validates the model's capability of identifying risk in regions with different geology; geomorphology; and hydrology including deep-seated slides. Model results were ranked into four proposed risk management categories: action recommended; further evaluation; monitoring; and no action recommended. The risk estimation process for this phase is considered preliminary; further consideration of risk tolerance and consequence definitions should be conducted. Preliminary risk results indicate that 370 management areas; and 3% of the total area falls into the action recommended category under the proposed risk matrix. The results of this study are intended to be the first step of actions required in minimizing the effects of slope failure including expensive mitigation and maintenance repairs and threats to public safety.

This project; Phase 2 Slope Vulnerability Assessments; is a continuation of the Phase 1 project previously conducted by WSB and MnDOT to determine the risk of slope failure along state highways. The Phase 2 study area includes 32 counties located in districts 4; 6; 7; 8; and Metro. This reports outlines the methods and results of this project including the new landforms; geomorphic processes; and causative factors influencing slope failures in this part of the state. The three main components of the model are the same 1) identify past slope failures; 2) model the causative factors of past slope failures and how they vary locally; and 3) model the risk of new slope failures. Vulnerability factors; failure types; and model results reflect the geomorphology of this region. Vulnerability factors for the new study area include slope; terrain curvature; incision potential; and local relief. Field verification results validate the model's capability of identifying risk in regions with different geology; geomorphology; and hydrology including ravines and bluffs located along the Minnesota River Valley. Model results are ranked into four proposed risk management categories: action recommended; further evaluation; monitoring; and no action recommended. Risk incorporates the model outputs with consequence to infrastructure including distance to roads and populated areas. The risk estimation process for this phase is considered preliminary; further consideration of risk tolerance and consequence definitions should be conducted. Preliminary risk results indicate that 858 management areas; or 0.7% of the total area; would be recommended for mitigation under the proposed risk matrix. Next steps include field visits and a site-specific mitigation program. The results of this study are intended as the first step of actions required in minimizing the effects of slope failure including expensive mitigation and maintenance repairs and threats to public safety.