Effects of small scaling on the stress dilatancy response of coarse gravel soil

Stress strain behavior of oversized soils is usually assessed after tests on small-scale specimens, where grading is altered due to size restrictions imposed by the available testing devices. It is well known that particle size distribution (PSD) has a strong effect on the mechanical behavior of granular soils, however, most studies reported on this topic are related to sands. This study presents an experimental study of triaxial shearing on coarse soil at different size specimen scales. The scope is to evaluate the impact of small scaling through scalping grading on the stress strain behavior of coarse alluvial gravels. Conventional triaxial compression tests were performed on specimens of 100, 150 and 800 mm in diameter. Grading and size effects are presented and discussed. The results show that dilatancy strongly increases when reducing the specimen size, and the critical state line shifts to higher void ratios. This outcome is due to PSD and packing properties, because small scale specimens are more uniformly graded than coarser ones. The paper addresses the implications of small scaling in gravelly materials.