Biopolymerized slope/subgrade stabilization and advanced field monitoring

Background Nebraska experiences a high number of landslides concentrated along roadside slopes (Eversoll, 2013). Current NDOT research project M-061 (Nebraska Specific Slope Design Manual) discovered that the strength degradation of glacial tills and weathered shales is a major cause of the landslides. Proper remediation techniques, therefore, need to be developed. A typical remediation technique would be one that relies on external structures to support the slope, even when the strength of field soils is severely degraded. Another common option may be to fortify the soils and maintain the initial strength of field soils. Some techniques based on the first principle are earth anchors, soil nailing and berms. These techniques are usually expensive or require extra space at the downstream side of the slope. The techniques based on the second principle are grouting or field mixing and stabilizing agents, and these options are typically more economical. Due to the mineralogy of soils and weather conditions in Nebraska, most grouting liquids are not optimal techniques; many of them may exhibit either injectability issues, environmental issues, or develop premature deterioration in cold weather (Karol, 2003). The M-061 study (Nebraska Specific Slope Design Manual) found that the strength reduction of field soils and associated slope failures may be effectively prevented by applying biopolymers to field soils due to their high tolerance to sub-freezing temperature. In addition, biopolymers are environmentally friendly and sustainable because they are likely food additives. Application of biopolymers is rapidly increasing (De Jong et al. 2010, Chang et al. 2015, 2016). They have not, however, been widely used for stabilization of slopes up to date. In the M-061 study, six different biopolymers were preliminarily tested at UNL's Geotechnical Lab. The biopolymer treated soils demonstrated significant strength gain, with up to a 300% strength increase. Two promising biopolymers, Xanthan and Gellan were further tested under well-controlled, severe weathering conditions. They presented minimal strength degradation over time for glacial tills. Another notable result is that the shear strength of Xanthan-treated soils after 16 weathering cycles is comparable to that of the initial unweathered strength of untreated soils, while the weathered strength of untreated soils was not even in a measurable range at 16 weathering cycles. This implies that once field soils are fortified with Xanthan, they will maintain the initial natural strength, even after an extended period of weathering cycles. In addition to their strength enhancing properties, biopolymers are economical, where 1 lb. of biopolymer costs approximately $20-$50 and can treat approximately 1 ton of soils. Based on the promising laboratory test results, this research proposes a follow-up field application to improve failed slopes in Nebraska and subsequent performance evaluation to confirm the feasibility of the biopolymers as a cost-effective and sustainable slope stabilization/retrofitting technique. Selected biopolymers from this study can be easily applied to slopes and other geotechnical applications such as subgrade stabilization by either field mixing or grouting techniques. The targeted biopolymers can be easily applied to field soils using BoMag field mixers (stabilizers and recyclers) and compactors for large-scale "Remove and Replace" projects, or using flight augers and the wet-mixing technique for small-scale projects. Research outcomes will be the optimum mixing ratio of biopolymers and field soils, one for BoMag mixing and the other for auger mixing. The mixing ratio for the two different application techniques will be different because the auger mixing will require a higher water content than the BoMag technique to facilitate an easy mixing process. In addition, the optimum moisture content and degree of compaction will be studied for the BoMag and compactor based application. Evaluation of the field performance of biopolymer-treated soils will also be accompanied by proper testing and monitoring plan with sophisticated equipment and novel evaluation techniques. The research team plans to utilize laboratory testing (e.g., triaxial tests) and in situ testing techniques (e.g., piezocone with HPT capability, self-boring pressuremeter) to monitor the progression of strength and the modulus of soils throughout the field application process. Surveying, fiber optic cable based deformation measurements, and rapid aerial imaging based deformation measurements will be adapted to monitor the overall deformation configuration of the test sites. Data analysis will then be conducted using modern and sophisticated techniques, such as the upper and lower bound approach (Song et al. 2017). The research team has all the required equipment and expertise to conduct this project effectively. Objective The first objective of this project is to apply laboratory-proven soil modification techniques with biopolymers to field condition and confirm their effectiveness and applicability to slopes and subgrade materials in Nebraska with climate conditions considered. Specifically, this objective is to reduce uncertainties in applying the biopolymer-based ground modification technique. The second objective of this project is to provide guidance on determining optimum application parameters (such as mixing ratio, degree of compaction, water content, etc.) and rational field testing methods for evaluating field performance of these biopolymer-based soil modification techniques. This objective will be achieved by comparing performance resulting from multiple different testing methods. In the process, the following detailed documentation will be developed as supporting materials for retrofitting unstable slopes and subgrade materials in Nebraska. a. Documentation of geotechnical and geochemical-mineralogy data for slopes and subgrades: NDOT engineers can determine adequacy of biopolymerization. b. Documentation of soil properties at the failure site by back-calculation: NDOT engineers can determine target strength for soil improvement. (note: this is not applied for subqrade). c. Documentation of soil properties at weathered and unweathered conditions by experimental testing: NDOT engineers can determine the target weathered strength of biopolymerized soi s. d. Documentation of graphics showing the progression of failure in critical layers due to time-dependent strength loss (for technology transfer). e. Documentation of analysis and testing techniques for maintenance team (laboratory and field techniques). f. Final documentation on design and field application specification of biopolymerization technique (polymer-to-soil mixing ratio, optimum moisture content and degree of compaction for BoMag, water content for auger-based technique).


    • English


    • Status: Completed
    • Funding: $124,386.00
    • Sponsor Organizations:

      Nebraska Department of Transportation

      1500 Nebraska 2
      Lincoln, NE  United States  68502
    • Project Managers:

      Halsey, Lieska

    • Performing Organizations:

      University of Nebraska, Lincoln

      1400 R Street
      Lincoln, NE  United States  68588
    • Principal Investigators:

      Song, Chung

    • Start Date: 20190701
    • Expected Completion Date: 20210415
    • Actual Completion Date: 20210415
    • USDOT Program: Transportation, Planning, Research, and Development

    Subject/Index Terms

    Filing Info

    • Accession Number: 01705865
    • Record Type: Research project
    • Source Agency: Nebraska Department of Transportation
    • Files: RIP, STATEDOT
    • Created Date: May 24 2019 1:45PM