Monotonic and cyclic simple shear response of gravel-sand mixtures

Understanding the factors that affect the monotonic and cyclic response of gravelly soils during earthquake events is critical to infrastructure design. In this study a large-size Cyclic Simple Shear (CSS) device was utilized to perform monotonic and cyclic shear tests on mixtures of either subrounded 9 mm Pea Gravel or angular 8 mm Crushed Limestone (CLS8) with subrounded Ottawa C109 sand. Tests were performed in constant volume conditions and shear wave velocity was measured for each specimen. Monotonic and cyclic test results at D, = 47% show that there is an optimum mixture percentage that results in the greatest shear strength and resistance to liquefaction (40% Sand for Pea Gravel Mixtures and 60% Sand for CLS8 Mixtures). The effects of particle angularity, cyclic stress ratio, and initial vertical stress on monotonic and cyclic response of loose and dense gravel mixtures were investigated and are presented. Comparison of the results from the cyclic simple shear tests with existing liquefaction triggering charts suggests the need for improved charts for gravelly soil liquefaction evaluation.