L.R. Hoyos*^{,a}, P. Arduino^{b}

^{a}University of Texas at Arlington, Department of Civil and Environmental Engineering, Arlington, TX 76019, USA ^{b}University of Washington, Department of Civil and Environmental Engineering, Seattle, WA 98195, USA

**ABSTRACT**

An implicit integration algorithm has been developed to simulate stress-strain response of unsaturated soil under controlled-suction multiaxial stress states. The algorithm supports numerical analyses in the π-plane using a mixed-control constitutive driver, along with a generalized cam-clay model, incorporating a third stress invariant, Lode angle *θ*, within a constant-suction scheme. True triaxial data (σ_{1} ≥ σ_{2} ≥ σ_{3} ) from constant- suction triaxial extension (TE), triaxial compression (TC), and simple shear (SS) tests, conducted on cubical specimens of silty sand, were used for tuning of the developed algorithm. The Willam-Warnke surface was adapted to the unsaturated case for simulation of soil response in three-invariant stress space (p: q: *θ*). Agreement between the observed and predicted soil responses highlight the potential of the developed algorithm for analyses of boundary-value problems involving unsaturated soil deposits.

*Keywords: *
Unsaturated soil; Matric suction; Constitutive modeling; Axis translation; True triaxial testing; Implicit integration; Deviatoric plane