2160 - The Effects of Soil Suction on Shallow Slope Stability

Shallow slope failures in roadway cuts and on embankments are frequent problems along Oklahoma highways, and most States for that matter, and represent a significant burden on maintenance budgets. Often these failures are associated with clayey soils having relatively high plasticity. Generally, during construction these soils have relatively high shear strength, a stiff consistency, and produce stable slopes. However, over time the soils experience cyclic wetting and drying resulting in a net increase in soil moisture content and corresponding decrease in shear strength. Eventually, the reduction in shear strength results in a slope failure usually triggered by a rainfall event. Exacerbating the problem are desiccation cracks that develop during extreme drying periods allowing water to penetrate the soil deeper and faster. Research is needed so engineers can better understand the problem, better predict shallow slope stability, and implement preventive measures if necessary. Proposed research will examine the mechanics of the soil as related to matric suction changes, soil type, and expected degree of wetting. Research will involve studying at least two field cases where shallow slope instability has been a problem; at least one case will involve a cut slope section and one case will involve an embankment slope. There are three primary objectives of the proposed research: 1) To provide geotechnical engineers with a method for predicting stability of cut slopes and embankment slopes composed of unsaturated soil, incorporating soil moisture condition and suction into the analysis. 2) To provide geotechnical engineers with methods for predicting changes in soil moisture conditions and suction in slopes as a function of climate changes so that a proper "design moisture condition" can be selected. This will also allow for predicting the slope stability over time based on predicted moisture content changes. 3) To provide recommendations to minimize the climate impacts on slope stability including, as necessary, reducing adverse impacts of desiccation cracking in clayey materials. Successful completion of this research will provide engineers with tools for improved analysis of shallow slope stability and recommendations for preventing landslides. The research will involve field testing and monitoring of suction and moisture content, laboratory testing of unsaturated and saturated strength and flow properties, moisture diffusion modeling based on climate data, and stability analyses. Proposed research will be conducted in three phases extending over three annual budget periods. The first phase of this three-year project is expected to be jointly funded by the Oklahoma Department of Transportation (ODOT) and Oklahoma Transportation Center (OkTC). Proposed work will involve a collaborative effort between the University of Oklahoma (OU) and Oklahoma State University (OSU). Thus, in this proposal three phases of work are identified for each of three years. First year work will be supported by the ODOT and OkTC, with years two and three supported by ODOT. In the event that OkTC funds are not obtained the scope of work for the first year will be modified accordingly. Completed research will have a positive impact on geotechnical practice related to transportation corridors. In short, engineers will be able to better design slopes and reduce costly maintenance associated with slope failures. Additionally, the research will positively impact the careers of at least 3 to 4 graduate students and 2 undergraduate students.

    Language

    • English

    Project

    • Status: Completed
    • Contract Numbers:

      SP&R 2160

      SPRY-0010(54)RS

    • Sponsor Organizations:

      Oklahoma Transportation Center

      Oklahoma State University, 700 N Greenwood Avenue, Suite 127
      Tulsa, OK  United States  74106
    • Project Managers:

      Bowman, John

    • Performing Organizations:

      University of Oklahoma, Norman

      School of Civil Engineering and Environmental Science
      202 West Boyd Street, Room 334
      Norman, OK  United States  73019
    • Principal Investigators:

      Miller, Gerald

    • Start Date: 20111001
    • Expected Completion Date: 20151231
    • Actual Completion Date: 0
    • Source Data: RiP Project 32801

    Subject/Index Terms

    Filing Info

    • Accession Number: 01466713
    • Record Type: Research project
    • Source Agency: Oklahoma Department of Transportation
    • Contract Numbers: SP&R 2160, SPRY-0010(54)RS
    • Files: RiP, STATEDOT
    • Created Date: Jan 3 2013 3:22PM