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Abstract for presentation (Poster or Podium) with a Paper in the Conference Proceedings

Highway Pavements

Assessment of the Permanent Strain Response of Subgrade Soil

Monday, June 17, 2024
10:15 AM - 11:30 AM ET
Room: Galleria
Abstract:
Subgrade stiffness is a critical parameter for pavement design and for increasing a pavement’s durability. When the subgrade is subjected to repeated traffic loading, the initial nonlinearity behavior and permanent strain per load repetition are high. As the number of load repetitions increases, the strain decreases, and it begins to behave more elastically. This condition allows a more accurate measurement of subgrade soils' resilient modulus (MR) in the laboratory. The stress-strain behavior of the soil depends on several factors such as the index properties, stress history, and confining pressure. In this research, the stress-strain responses of sand and clayey soils are thoroughly investigated via laboratory-resilient modulus tests, the NCHRP concept for the behavior of soil under cyclic loading, and the shakedown theory were adopted. A total of 4 different subgrade soils were tested. The results show that the sandy soil exhibited a quasi-brittle behavior and when the applied stress exceeded the allowable recoverable strain it suddenly failed. The resilient behavior of this material was highly dependent on the confining pressure. The fine-grained materials show stress-softening behavior, and they were less dependent on confining pressure. The clayey soil exhibited the behavior of over-consolidated soils when the material was subjected to cyclic loading at low confining pressure. The permanent strain analysis result shows that the summary resilient modulus (SMR) measured for the soil with the lowest fines content did not represent the actual SMR of the material. This material was still showing high permanent strain when the MR was measured.

Learning Objectives:

Attendees can expect to learn the following from this session:
  • Understand the significance of subgrade stiffness in pavement design and its impact on pavement durability
  • Understand the significance of subgrade stiffness in pavement design and its impact on pavement durability
  • Analyze the transition from nonlinear to elastic behavior in subgrade soils under repeated traffic loading and its implications for measurement
  • Investigate the application of laboratory-resilient modulus tests, NCHRP concepts, and shakedown theory in assessing the stress-strain responses of different soil types
  • Compare and contrast the resilient behaviors of different soil types (e.g., sandy, clayey) under cyclic loading, with a focus on their response to confining pressure and permanent strain