Crack Propagations on the Rock Face at Glacier Point of the Yosemite National Park After the 1999 Rockfall
This study applies finite element analysis to examine the mechanism of crack propagations observed at the Glacier Point of the Yosemite National Park following the June 13, 1999 rockfall event. Extensive crack propagations were observed on a rectangular area of about 18 m by 23 m of rock exfoliation sheet on a rock face about 550 m above the Yosemite Valley 54 days following the rockfall by helicopter flights and by photographs taken by from the valley. This paper models the crack pattern on the hook-shaped rock sheet by using a plane stress analysis subjected to various ratios of vertical to horizontal strain increments. The present finite element analysis uses a code called RFPA that adopts a reduced modulus approach to model the damage process of rock. A mesh of 160 by 160 elements was used to model a rock face of about 35 m by 35 m, and a Weibull distribution is used to model the heterogeneity of the rock face. We found that when the vertical to horizontal strain ratio is smaller than one, the crack pattern closely resembles that observed at the Glacier Point. Thus, the present paper provides a plausible mechanism for the observed crack propagation.
KeywordsRockfall Progressive crack propagation Yosemite National Park Finite element analysis Damage
This study is fully supported by the Hong Kong Polytechnic University (Project No. 1-BBZF of PolyU). The author is grateful to Prof. C.A. Tang in providing the computer program RFPA and Dr. Wieczorek of USGS in providing related materials on the rockfall at Glacier Point of the Yosemite National Park.
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