Yukika Miyashita

Effects of Excess Pore Water Pressure on the Displacement of Failed Dip Slopes in 2004 Niigata-Ken Chuetsu Earthquake

The effects of excess pore water pressure on the behavior of earthquake-induced dip slope failure were evaluated by field investigation, laboratory tests and numerical calculation. Two dip slopes which failed in the 2004 Niigata-ken Chuetsu Earthquake were investigated intensively. One is at Yokowatashi, Ojiya, and the other is at Yamakoshi Village (currently Nagaoka City). In both cases, the sliding plane was mainly along a weak thin layer. Laboratory test results showed that excess pore water pressure possibly increased during earthquake and/or during sliding. The displacement calculation was executed by using extended Newmark and Janbu method which considers the effects of irregular geometry of the sliding plane and the excess pore water pressure increase or the strain softening property of the weak layer. The calculation results showed very significant effects of excess pore pressure or strain softening.

Observation of Shear Banding Characteristics of Sand in Torsional Shear Test Using Image Analysis Technique

Accurate measurement in shear banding and strain localization studies is critical in characterizing the microstructural behavior within failure area. This research is aimed to investigate the effects of initial relative density on the shear banding behavior of sand. A series of tests on Toyoura sand with different initial relative densities were conducted using a hollow cylinderical torsional shear apparatus under drained condition. Unlike the tests conducted on prismatic specimens on plane strain condition, the tests conducted on hollow cylinderical specimens require more complex data analysis due to the curvature of their outer side surface. The test results both dilatancy rate and shear band expansion magnitude are found to have unique relationships with the specimen initial relative density.