Nonlinear Earthquake Response Characteristics of a Central Clay Core Rockfill Dam

Abstract

The eŠect of the 2008 Iwate-Miyagi Nairiku earthquake (MJ 7.2), Japan on the Aratozawa dam, which is a 74.4 m high rockˆll dam with a central clay core located in the area, was studied with a main focus on the change in the vibration period, shear wave velocity, shear modulus, and pore-water pressure. In a vertical section of the central part of the dam, three sets of 3-component accelerometers and 15 pore water pressure meters were installed. During the main shock, the acceleration exceeded 10 m/s 2 at the gallery, inducing large shear strains in excess of 10 -3 and a sudden build-up of the excess pore water pressure in the core. Due to the large strains, the shear wave velocity and shear modulus showed a signiˆcant decrease from their initial values and the vibration period was elongated. The decreased shear wave velocity gradually recovered toward the end of the main shock, and continued to recover with the passage of time. The full recovery of the wave velocity was found to take at least one year, while the dissipation of the excess pore water pressure proceeded more quickly than the recovery of the wave velocity.

Nonlinear dynamics induced in a structure by seismic and environmental loading

“…In solids, granular materials and structures, the effect is a transientinduced disequilibrium, where the material modulus decreases and the dissipation increases, and which may become permanent if deformations are large or frequent. Materials also commonly exhibit a fascinating, slow dynamical recovery from disequilibrium to the original or a new equilibrium of the system's elastic properties after strong wave deformations terminate, observed in the laboratory on rocks (e.g., Guyer and Johnson, 1999;Johnson and Sutin, 2005;TenCate, 2011;Renaud et al, 2012;Renaud et al, 2014), in concrete materials (e.g., Lacouture et al, 2003;Bentahar et al, 2006;Bui et al, 2013), at the Earth's surface in soils (e.g., Field et al, 1997;Sawazaki et al, 2009;Wu et al, 2009a;Ohmachi and Tahara, 2011;Johnson et al, 2009;Renaud et al, 2014) and at the scale of the Earth's crust (Peng and Ben-Zion, 2006;Karabulut and Bouchon, 2007;Brenguier et al, 2008;Wu et al, 2009b). Between laboratory and crustal scales, we studied an intermediate scale system: a civil engineering structure.…”

Modulus reductions of dam embankment materials based on downhole array time series

“…Shear modulus data extracted from the downhole time series were compared with the empirical models based on numerical simulations (Cao et al, 2010; Feng et al, 2010), data extracted from downhole time series (Ohmachi and Tahara, 2011), and laboratory test results (Park and Kishida, 2019b). Modulus reduction curves are known to be influenced by prior straining due to changes in the fabric and void ratios in laboratory tests (e.g.…”

“…Figures 10a and b present a comparison between the normalized modulus reduction data for the Kejyonuma Dam and Aratozawa Dam, respectively, and the empirical models based on numerical simulations to fit the observed dam responses (Cao et al, 2010; Feng et al, 2010), the data extracted from downhole time series (Ohmachi and Tahara, 2011), and laboratory test results using undisturbed samples (Park and Kishida, 2019b). The extracted normalized modulus data for the Kejyonuma Dam and Aratozawa Dam differed and showed dam-dependent characteristics, with the dams being earthfill and rockfill dams, respectively (Table 2).…”

“…Several studies have extracted the dynamic properties of embankment dams using these time series. Ohmachi and Tahara (2011) showed the reduction and recovery of the dynamic shear modulus in the Aratozawa Dam using a downhole time series from a sequence of the 2008 Iwate–Miyagi Nairiku Earthquake. The researchers calculated the apparent shear wave velocities ( V s ) and shear strains ( γ ) between two sensors from the recorded acceleration time series and extracted the dynamic properties during strong shakes.…”

“…Representative modulus reduction data are extracted for the embankment core materials using the apparent V s and the amplitudes of γ between sensors. These data are compared with empirical models from past studies that are based on numerical analyses by fitting the dam responses to the observations (Cao et al, 2010; Feng et al, 2010), inference from the downhole time series (Ohmachi and Tahara, 2011), and laboratory test results of undisturbed dam core materials (Park and Kishida, 2019b). A methodology to update existing modulus reduction models given observed data is proposed to develop a dam-specific empirical model.…”