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The strength and stress-dilatancy of uniform sands has been studied extensively in geotechnical investigations, and practitioners can draw on a wealth of previously reported data for the estimation of their volumetric response. However, the suitability of accepted stressdilatancy theory and empiricism has not been evaluated for well-graded gravelly soils. Axisymmetric, isotropically consolidated drained compression, and pure shear, plane strain quasi-K 0 consolidated drained tests were performed on well-graded Kanaskat gravel using confining pressures ranging over three orders of magnitude to determine its stiffness, strength, and stress-dilatancy response. The plane strain stiffness, strength, and stress-dilatancy of Kanaskat gravel is observed from tests performed using a large cubical true-triaxial device with flexible bladders. The observed response is interpreted with a view of experimental boundary conditions and their impact on the volumetric response. The observed plane strain shear modulus and friction, and dilation angles of well-graded sandy gravel soils commonly used in practice are significantly higher than those measured in the triaxial compression stress path. Existing empirical and modified stress-dilatancy expressions proposed for low confining pressures underestimate the observed dilation response; however, another common empirical approach appears to adequately capture the dilatancy. The data reported herein should help practitioners estimate plane strain behavior of sandy gravel mixtures.

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Shallow foundations derive their support from near surface soils and are extensively used to support structures of all sizes. Existing methods to estimate bearing capacity invoke an assumed failure surface developed within rigid-perfectly plastic soil, and require various semi-empirical modifications to the failure surface to account for geometrical effects. However, the global accuracy and uncertainty associated with the general bearing capacity equation and its modifications has not been sufficiently characterized with respect to observed full-scale footing load tests on plastic fine-grained soils. To assess the global accuracy and uncertainty in the general bearing capacity formula, a load test database consisting of 30 full-scale footings was developed from loading tests reported in the literature. The computed bearing capacity was compared to the capacity extrapolated from the load displacement curves in the database, then statistically characterized using the bias, or the ratio of the extrapolated and computed capacities. On average, the general bearing capacity formula under-predicted the extrapolated bearing capacity with a mean bias of 1.25 and exhibited a moderate to significant amount of variability (i.e., COV = 37%). In order to provide a reliability-based ultimate limit state model, varying levels of uncertainty associated with the undrained shear strength were used in the development of resistance factors for use with AASHTO load statistics. The use of risk-informed design approaches, such as those presented herein, should help to increase more efficient, and therefore sustainable, engineering practices.