Hoyos et al., Soils and Rocks 44(3):e2021066621 (2021) 1 Soils and Rocks An International Journal of Geotechnical and Geoenvironmental Engineering www.soilsandrocks.com ISSN 1980-9743 ISSN-e 2675-5475 https://doi.org/10.28927/SR.2021.066621 This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Behavior of unsaturated cohesive-frictional soils over a whole range of suction/thermo-controlled stress paths and modes of deformation Laureano R. Hoyos 1# , Roya Davoodi-Bilesavar 1 , Ujwalkumar D. Patil 2 , Jairo E. Yepes-Heredia 3 , Diego D. Pérez-Ruiz 4 , José A. Cruz 5  Article 1. Introduction Over the last fve decades, intensive research eforts undertaken worldwide have defned the threshold of the state-of-the-knowledge of unsaturated soil behavior. The adoption of matric suction and the excess of total stress over air pressure, i.e., net normal stress, as the relevant stress state variables, has facilitated the investigation of essential features of unsaturated soil response, via either the axis-translation or the vapor transfer technique, for a wide range of matric and total suction states. It is the relative success of these techniques that has prompted researchers in the discipline to devote countless hours to fne-tuning myriad details of standardized soil testing devices, and thus keep the focus of their eforts on expanding and upgrading the capabilities of such devices for testing unsaturated soil materials. The present work documents some of the most recent experimental evidence of the thermo-hydro-mechanical behavior of compacted soils over a whole range of suction- and/or thermo-controlled stress paths and modes of deformation, including data from a series of triaxial, true triaxial, plane strain, ring shear, and resonant column tests conducted on diferent types of compacted cohesive-frictional soils in the low-to-medium matric suction range under either room temperature or thermally controlled conditions. The work focuses primarily on the following essential features of unsaturated soil behavior: (1) Comparative analysis of loading-collapse and apparent tensile strength loci assessed from both suction-controlled triaxial and true triaxial testing on clayey sand, (2) Critical state lines from suction-controlled plane strain testing on silty soil, (3) Peak and residual failure envelopes from suction-controlled ring Abstract The present work documents some of the most recent experimental evidence of the thermo- hydro-mechanical behavior of compacted soils over a whole range of suction- and/or thermo-controlled stress paths and modes of deformation, including data from a series of triaxial, true triaxial, plane strain, ring shear, and resonant column tests conducted on diferent types of cohesive-frictional soils in the low-to-medium matric suction range under either room temperature or thermally controlled conditions. The work has been accomplished at the Advanced Geomechanics Laboratory of the University of Texas at Arlington, focusing primarily on the following essential features of unsaturated soil behavior: (1) Loading- collapse and apparent tensile strength loci assessed from suction-controlled triaxial and true triaxial testing on clayey sand, (2) Critical state lines from suction-controlled plane strain testing on silty soil, (3) Peak and residual failure envelopes from suction-controlled ring shear testing on clayey soil, (4) Frequency response curves and cyclic stress-strain hysteretic loops from thermo-controlled, constant-water content resonant column testing on clayey soil, and (5) Residual failure envelopes from suction/thermo-controlled ring shear testing on clayey soil. The work is intended to serve as a succinct yet reasonably thorough state-of-the-art paper contribution to PanAm-UNSAT 2021: Third Pan-American Conference on Unsaturated Soils, Rio de Janeiro, Brazil, July 21-25, 2021. Keywords Suction-controlled testing Triaxial testing True triaxial testing Plane strain testing Ring shear testing Resonant column testing # Corresponding author. E-mail address: hoyos@uta.edu 1 University of Texas, Department of Civil Engineering, Arlington, USA. 2 University of Guam, School of Engineering, Mangilao, Guam, USA. 3 Texas A&M University, Department of Civil and Environmental Engineering, Texas, USA. 4 Pontifcia Universid Javeriana, Departamento de Ciencias de la Ingeniería, Cali, Colombia. 5 Universidad Militar Nueva Granada, Facultad de Ingeniería, Bogotá, Colombia. Submitted on April 23, 2021; Final Acceptance on June 10, 2021; Discussion open until November 30, 2021.