UNDRAINED MONOTONIC AND CYCLIC STRENGTH OF COMPACTED ROCKFILL MATERIAL FROM TRIAXIAL AND TORSIONAL SIMPLE SHEAR TESTS

This report investigates the dynamic strength of materials by cyclic l oading triaxial and torsional simple shear testing in the laboratory. The effect of cyclic number, shear strain, relative density, confining pressure, and initial shear stress on dynamic strength is investigate d. The dynamic strength obtained by cyclic loading tests is compared w ith the static strength obtained by monotonic loading tests. The resul ts show that during an undrained cyclic loading test, an increase in c ycle number is accompanied by increasing axial strain and a rapid buil dup of the pore-water pressure to between 90% and 100% of the confinin g pressure, but that liquefaction or flow failure does not occur. The cyclic shear stress ratio increases as (1) the relative density become s higher, (2) the mean principal stress declines, and (3) the initial shear stress rises, and these tendencies conform qualitatively to the results of research on dense sand. The cyclic shear stress ratio obtai ned from a torsional simple shear test is smaller than that obtained f rom a triaxial test, regardless of the mean principal stress or initia l shear stress.