Doctoral Dissertations

Keywords and Phrases

camera; constitutive modelling; photogrammetry; triaxial test; Unsaturated soils


"An important step to developing a good understanding of the behavior of unsaturated soils is to adopt a formal and simple constitutive framework and to conduct high-quality and short-time experiments. Barcelona Basic Model (BBM) was the first elastoplastic constitutive model for unsaturated soils. The yield curve, which separates the elastic region from the elastoplastic region, is an important aspect of constitutive modeling for unsaturated soils. Most concepts for unsaturated soils were developed based upon the results from suction-controlled triaxial (SCTX) tests. Though, the SCTX tests on unsaturated soils are costly, time-consuming, and laborious, and their results are questionable. This study intends to develop an alternative method to overcome the limitations of the SCTX tests for the constitutive modeling of unsaturated soils and to determine correctly the shape and the evolution of the loading/collapse (LC) yield curves during yielding. A photogrammetry-based method is used to determine the absolute soil volume during triaxial testing. Further evaluation of triaxial testing is presented by determining the soil specimen misalignment and disturbance at different testing stages. The implication of misalignment on the stress-strain relationship of soils during triaxial testing is investigated. In addition, a study of the requirement of point density in image-analysis methods during triaxial testing is presented. Finally, the Modified State Surface Approach (MSSA) is adopted to calibrate the unsaturated soil parameters on constant water content (undrained) tests and determine the shapes of yield curves for unsaturated soils. A modification to BBM is also proposed to handle the dilatancy observed in the undrained triaxial tests and modified unconfined compression tests on silty soil specimens"--Abstract, p. iv


Zhang, Xiong
Cawlfield, Jeffrey D.

Committee Member(s)

Dagli, Cihan H., 1949-
Olgun, C. Guney
Liu, Jenny
Yin, Zhaozheng


Civil, Architectural and Environmental Engineering

Degree Name

Ph. D. in Civil Engineering


Missouri University of Science and Technology

Publication Date

Summer 2022


xiv, 211 pages

Note about bibliography

Includes_bibliographical_references_(pages 209-210)


© 2022 Sara Fayek, All Rights Reserved

Document Type

Dissertation - Open Access

File Type




Thesis Number

T 12035