Strength Anisotropy of Cemented Granular Materials in Low- and High-Stress True Triaxial Tests

Abstract Understanding the mechanical behavior of cemented granular materials under multiaxial stress conditions is essential for the safe and efficient design of filtered tailings disposal systems, yet their anisotropic response remains insufficiently characterized. This study examines the strength anisotropy of iron ore tailings and natural sand blends stabilized with ordinary portland cement through low- and high-pressure true triaxial testing. Mixtures were designed using the porosity-to-volumetric cement content index <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:mi>η</mml:mi> <mml:mo>/</mml:mo> <mml:msubsup> <mml:mi>C</mml:mi> <mml:mrow> <mml:mi>i</mml:mi> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.16</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> <mml:mo stretchy="false">)</mml:mo> </mml:math> to achieve equivalent initial conditions across varying dry unit weights and cement contents. The experimental program comprised unconfined compressive strength tests and true triaxial tests covering stress paths ( b = 0, 0.5, and 1), mean effective stresses (100, 2,000, and 4,000 kPa), and loading orientations ( θ = 0°–180°). The results show that cementation can suppress compaction-induced anisotropy under stresses below the yield threshold, promoting near-isotropic behavior in all directions; however, anisotropy reappears when cement bonds degrade beyond yielding. While both strength and stiffness improved with increasing cement content and dry density, stiffness was controlled primarily by cement dosage and strength by confining stress. Iron ore tailings displayed a larger normalized yield surface ( q / p ′ = 1.2) compared with natural sand ( q / p ′ = 0.8 at 2 MPa). These findings validate the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>η</mml:mi> <mml:mo>/</mml:mo> <mml:msubsup> <mml:mi>C</mml:mi> <mml:mrow> <mml:mi>i</mml:mi> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.16</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> index as a practical design parameter, enabling engineers to balance compaction effort and cement content to meet performance targets under complex field stress paths.