Experimental and field studies related to the behavior of granular mass flows and the characteristics of their deposits.

摘要

This dissertation combines experimental and field studies of granular mass flows and was undertaken because, despite an intensive study of deposits, the behavior and mechanics of naturally occurring granular mass flows are poorly understood.; Steady uniform flows of dry granular particles down an inclined chute behave in a way that can be modelled semi-empirically by balancing the driving force with the sum of the Coulomb frictional drag and collisional drag calculated from kinetic theory, then solving for average velocity in terms of depth of flow, slope, bed friction and dynamic internal friction. For avalanches down an incline onto a horizontal runout, a depth-averaged, Lagrangian, finite difference scheme using the Mohr-Coulomb constitutive relation and a Coulomb basal friction sliding law gives good agreement with experiments for the shape of the pile and runout distance even though it does not account for the deformation which occurs in experiments.; Uniform steady flows segregate particles more strongly by size than by density. Steady uniform flow of small and large particles show segregation patterns and have velocity profiles that contradict the dispersive stress hypothesis but are compatible with the kinetic sieve hypothesis for size segregation. Avalanches of randomly mixed large and small particles will sort the large ones to the top and front of the flow and the small ones to the base and rear of the flow. If deposition of such a flow occurs en mass, then graded bedding in the deposit reflects the vertical segregation of the moving flow, but if deposition occurs by accretion at the base of the flow during a significant time interval, then the graded bedding reflects longitudinal segregation of the moving flow.; The sedimentology of the 5,700 year old Osceola Mudflow at Mount Rainier, Washington, shows that the normally graded deposits accreted slowly from a debris wave that was coarse grained at its front and progressively finer grained toward its tail. Inundation-limit deposits are emplaced rapidly and thus are ungraded.