Development of a polyaxial platen for testing true triaxial behavior of rocks

Mining at greater depths can lead to stress-induced failure, especially in areas of high horizontal in-situ stress. The induced stresses around the opening are known be a poly-axial stress state where, σ_1≠ σ_2≠ σ_3 with special case σ_3= 0 and σ_1, σ_2 ≠ its boundary. conventional triaxial testing does not represent actual strength rock regions stress, as it ignores influence intermediate principal (σ_2). typical (biaxial true-triaxial tests) intact mostly requires sophisticated expensive loading systems. This study investigated mechanical behavior under using simple cost-effective design. apparatus consists biaxial frame confining device. has two platens that apply equal both directions (σ_1=σ_2) on 50.8 mm cubical specimen when placed inside uniaxial device performed separate tests constant (σ_2 = constant) used along frame. then compared failure modes peak Berea Sandstone specimens other biaxial/triaxial devices validate design apparatus. We also standard cylindrical samples prismatic different slenderness ratios. These provided complete understanding mode transition from compressive conditions specimen. Additionally, this determined best-fitted envelopes for state. Based regression analysis, we found quadratic polynomial good fit envelope. For envelope, 3D criterion by Nadai (1950) R^2 0.964