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Backward erosion piping (BEP) is a major risk factor for both dams and levees. A significant amount of work has been performed to examine the likelihood of initiation of BEP through examination of critical gradients for sand boil formation and the development of semi-empirical approaches to assess the likelihood of erosion continuing and progressing to a breach. Recently, numerical analyses have been developed to model the BEP process and these tools offer a means to incorporate more complex geometries and soil conditions than can be assessed within the semi-empirical approaches. These simulation methods have been primarily applied to laboratory tests and physical models with uniform properties, but there is a need to validate these models using case histories and explore how variability in stratigraphy and properties influences the BEP process. This study will apply numerical approaches for simulating BEP to the case history of the Bois Brule levee breach that occurred during flooding in July 1993. This paper first describes the Bois Brule levee and observations during flooding. Numerical simulations of piping progression are used to explore the effect of reasonable variations in properties and stratigraphy on the likelihood of failure and the sensitivity of the results to the river level at the time of failure. The paper highlights challenges in modeling BEP and provides guidance on which factors have the largest impact of the results. 

This paper presents a study on the impact of rigid awns and their deployment on interface friction. Awns are appendages attached to the exterior surface of a geo-system and bio inspired by grass seeds. Awns provide frictional anisotropy and assist the seed in self-embedding into the soil or clinging to animal hair. In geo-systems, like piles, deployable awns can provide frictional anisotropy reducing installation effort and increasing global capacity. In addition, flexible awns can be folded up to enable space saving for transportation. This paper presents the results from a set of interface shear tests in a modified direct shear device. Single rigid awns were tested at various angles, from horizontal, as a pseudo-static simulation of deployment, in loose and dense sand, in both the cranial (towards the head) and caudal (towards the tail direction). It is shown that awns opened at larger angles provide higher interface friction and that shearing in the cranial direction provided more resistance than in the caudal direction. This demonstrates that deployable awns could be used in geosystems to provide friction anisotropy and increase capacity.