Motohiko Hakuno

Granular assembly simulation for ground collapse

Summary Using Cundalls simulation method, the present work aims at study in the mechanism of slope collapse, non-linear dynamic response of structural foundation, liquefaction of loose ground under vibrational excitations, and rupture of earthquake fault. Results are presented from several numerical experiments done on dense sphere assemblies in three dimensions. The experiments are intended for comparison with physical experiments, described by Ishibashi and Chen (ref. 1) and the theoretical results of Jenkins (ref. 2). Periodic boundaries are used to eliminate boundary effects; the effect of sample size is studied in one series of tests, using linear contact stiffnesses. In another test series, contact stiffnesses are nonlinear, according to the Hertz theory. In general, numerical and physical results agree, except for the volume strain observed in a triaxial extension test: this discrepancy may indicate the presence of an initial fabric in the physical sample.Results achieved using the model idealized as a continuous medium, which have been widely applied in the past, differ from those gained by using the granular assembly model adopted in this study. Ignoring the influence of movements of soil particles, including subsidence and rotation of particles, in the former method seems to be the cause of such differences.

Simulations of the Collapse of Concrete Frames and Volcanic Eruption

Abstract Using the Extended Distict Element Method, we constructed models of multi-degrees-of-freedom systems for particles of concrete frames and made a series of numerical simulations of the process by which they collapsed due to seismic forces. When a concrete frame collapses, it is reduced into a pile of debris, but, if the debris could be rejoined to be the original concrete frame, the original shape would be restored. i. e., the frame prior to collapse is considered to be an assembled body of concrete debris. Because the EDEM is a means for analyzing discontinuous bodies, we here report an analysis in which concrete debris is considered to contain the elements of a discontinuous body. For convenience, we assumed that the shape of the debris is circular and that its parts are connected by springs that would satisfy the yielding conditions of Mohr-Coulomb. The results obtained from our simulations are in good agreement with the records of damage done by past earthquakes.