The drained response of loose sand (relative density of 30%) under simultaneous increase in principal stress ratio (R = σ'1/σ'3) and the inclination of major principal stress to the vertical (ασ) is examined using data from hollow cylinder torsional shear testing. The study specifically pertains to the behaviour of loose sand subject to monotonic linear stress path loadings in the R–ασ space, within the domain of R ≤ 2, ασ < 45°, while intermediate principal stress parameter (b) and effective mean normal stress (σ'm) are held constant. The relationship between horizontal shear stress (τzt) and horizontal shear strain (γzt) of loose sand under such loadings is shown to be unique and stress-path independent. At any stress state, the horizontal shear stiffness (dτzt/dγzt) for a given σ'm depends only on the current value of τzt, and not on the value of individual components of normal effective stress, or their increments. When R and ασ are increased simultaneously in a linear manner, loose sand initially exhibits linear strain paths, suggesting no significant changes to the inherent anisotropy during the early stages of such loading. The directions of principal stress increment (αΔσ) and principal strain increment (αΔε) are found coincident, when αΔσ < 45°. An approach to predict the response of loose sand under simultaneous increase in R and ασ with constant b and σ'm has been developed based on these findings.
Flow liquefaction potential of loose sand: stress path envelope and energy–based evaluation
