Insitu characterization

Monotonic and Cyclic Response of Well-Graded Coarse-Grained Soils

Researchers: Mitch deJager (ongoing MS), Francisco Humire (graduated PhD, 2022), Rachel Reardon (graduated MS, 2021)

Abstract:

Well-graded coarse-grained soils encompass a broad range of materials that are typically found in natural deposits and man-made fills. Current engineering practice assumes the dynamic response of these soils can be evaluated using sand-based methods, which do not incorporate the effects of median grain size (D50) and gradation (Cu). This generalization may lead to conservative engineering designs and overestimations of the anticipated damage from system level analyses. The aim of this project is to develop an experimental database: (1) to evaluate the effects of grain size and gradation on the monotonic and cyclic behavior, and (2) to develop empirical correlations for the assessment of liquefaction triggering and induced deformations for well-graded coarse-grained soils.

A series of constant-volume monotonic and cyclic direct simple shear (DSS) tests will be performed on soil mixtures with different grain size and gradations (Figure 1), but composed of materials from a single natural deposit to minimize the effect of other grain properties (e.g. mineralogy, particle shape). This testing plan will involve a broad range of relative densities (30-80%), overburden stress levels, static shear stresses, and loading patterns (e.g. constant CSR, irregular loading). Shear wave velocity measurements will be obtained to track the changes in shear modulus and soil fabric during various stages of loading.

The effect of D50 and Cu on the stress-dilatancy behavior within Bolton’s (1986) framework is evaluated based on the outcome of monotonic tests. Results of cyclic tests (Figure 2) will provide insights on the physical mechanisms controlling pore pressure generation, accumulation of shear strains, and post-liquefaction reconsolidation strains on well-graded coarse-grained soils. These results will also be used for the development of liquefaction triggering resistance and shear strain accumulation curves, in addition to overburden (Kσ) and static shear stress ratio (Kα) correction factors for different values of D50 and Cu. Ultimately, experimental results will be contrasted to numerical simulations using advanced constitutive models, and calibration protocols will be proposed to capture the monotonic and cyclic response of well-graded coarse-grained soils.

 

Grain size distributions of the soils studied in this project
Figure 1: Grain size distributions of the soils studied in this project
Example of a DSS test result  obtained for soil 100A
Figure 2: Example of DSS test results obtained for soil 100A

 

References:

  1. Reardon, R. A., Humire, F. A., Ahmed, S. S., Ziotopoulou, K., Martinez, A., and DeJong, J. T. (2022). Effect of Gradation on the Strength and Stress-Dilatancy of Coarse-Grained Soils: A Comparison of Monotonic Direct Simple Shear and Triaxial Tests. ASCE GeoCongress 2022 (in press).
  2. Humire, F. A., Ziotopoulou, K., and DeJong, J. T. (2022). Evaluating shear strain accumulation of sands exhibiting cyclic mobility behavior. 20th International Conference on Soil Mechanics and Geotechnical Engineering (ICSMGE). Sydney, Australia (in press).
  3. Humire, F. A., Ziotopoulou, K., Basson, M. S., and Martinez, A. (2019). Framework for tracking the accumulation of shear strains during cyclic mobility. 7th International Conference on Earthquake Geotechnical Engineering, Silvestri, Moraci, and Antonielli (eds), Rome, Italy. [link]
  4. Humire, F. A., Lee, M., Ziotopoulou, K., Gomez, M. G., and DeJong, J. T. (in press). Development and evaluation of pre-conditioning protocols of sand specimens in constant-volume cyclic direct simple shear tests. ASTM Geotechnical Testing Journal.
  5. Humire, F. A., and Ziotopoulou, K. (2022). Mechanisms of shear strain accumulation in laboratory experiments on sands exhibiting cyclic mobility behavior. Canadian Geotechnical Journal. [doi]
  6. Tasiopoulou, P., Ziotopoulou, Κ., Humire, F., Giannakou, A., Chacko, J., and Travasarou, T. (2020). Development and implementation of semiempirical framework for modeling postliquefaction deformation accumulation in sands. ASCE Journal of Geotechnical & Geoenvironmental Engineering, 146(1). [doi]