Evaluation of the geomechanical behavior of fiber-reinforced clay soil

• Author / Creator

  Palat, Akhila

• Adding short discrete fibers is recommended as one potential option for the stabilization of mine fine tailings. Discrete fiber-reinforced composites are also applicable for land reclamation projects including oil sands mine reclamation, landfill liners or final covers and enhancing the strength of subgrades.
  This thesis presents a comprehensive study on the role of discrete polymeric fibers in altering the geomechanical behavior of clay soil. The clay soil used in this study is kaolinite clay and polypropylene and nylon fibers are used as reinforcements. The scope of this thesis is to: (1) quantify the influence of changing fiber variables on the undrained geomechanical behavior of the clay soil; (2) determine the role of field placement techniques on the stress-strain behavior and pore pressure response of the fiber-reinforced clay; (3) analyse the fiber-soil interface shear strength; and (4) quantify the amount of tensile stresses mobilized in the fibers when subjected to undrained loading.
  The first component of this research included a series of laboratory investigations performed on the fiber-reinforced clay soil to define the response of this composite to undrained loading. The role of different fiber variables (content and length) in influencing the undrained shear strength and pore pressure response of the clay soil was examined. An optimum fiber combination that results in the maximum strength of the composite was proposed based on the lab testing results.
  The second stage of this research explored the role of different sample preparation techniques (compaction and hydraulic placement as a slurry) on the undrained stress-strain behavior of fiber-reinforced clay soil. A novel transparent fiber-reinforced clay soil was prepared to analyze the orientation of fibers within the compacted and slurry samples. Examination of transparent fiber-reinforced clays confirmed the predominant fiber orientation is horizontal in slurry samples and random in samples prepared using the compaction method.
  The third component of this thesis investigated the impact of changing fiber types on the geomechanical behavior of the fiber-reinforced clay soil. The fiber-soil interface shear strength was determined using a modified direct shear apparatus. The role of the interface friction angle and mobilized fiber tension in influencing the shear strength of the soil-fiber composite was analysed for samples prepared using the compaction and slurry method.
  There exists an important gap in the understanding of fiber-reinforced clays, as no studies were able to quantify the amount of tensile stresses mobilized in the fibers during shearing. The fourth component of this thesis demonstrated the mobilization of tensile stresses within the fibers by performing triaxial extension tests on fiber-reinforced clay composites. The effect of changing fiber variables on the shear strength of the composite was analysed. An empirical model was developed to predict the amount of tensile stresses mobilized in the fibers when the composite is subjected to undrained loading; specifically, how tension in fibers are incorporated into strength and manifest in the mechanism of failure.
  The results from this research are anticipated to increase the understanding on the use of discrete fibers for the stabilization of mine fine tailings. This study also comprehends the undrained anisotropic behavior and strength of fibrous organic soils and soils reinforced with elements that act in tension and is expected to have a significant impact on the construction of infrastructure, as implementing this technique of fiber-reinforcement is an option for enhancing the strength of clay soil that is prevalent in Canada.

• Subjects / Keywords

  • fiber-reinforced clay soil
  • undrained behavior
  • strength
  • stiffness
  • pore pressure response

• Graduation date

  Fall 2022

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-3n73-hg84

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.