Rock Triaxial Tests: Global Deformation vs Local Strain Measurements—Implications

Abstract Accurate stress–strain measurements in triaxial tests are critical to compute reliable mechanical parameters. We focus on compliance at the interfaces between specimen and endcaps, test specimens under various conditions using different instrumentation protocols. The tested materials include aluminum, Eagle Ford shale, Berea sandstone, Jubaila carbonate. Results obtained following common practice reveal that surface roughness specimen-endcap leads marked seating effects, affects all cap-to-cap based hinders ultrasonic energy transmission. In particular, deformation accentuate hysteretic behavior, magnify biases caused by bending tilting (triggered uneven surfaces misalignment), affect estimation of rock parameters, from stiffness Biot’s ?-parameter. Higher confining pressure diminishes effects. Local specimen-bonded strain gauges preferred (Note: mounting sleeves is ill-advised). confirm elastic moduli derived wave propagation higher than quasi-static determined local gauges, probably due lower level preferential high-velocity travel path for first arrivals.