Induced Dynamic Nonlinear Ground Response at Garner Valley, California

Abstract

We present results from a prototype experiment in which we actively induce, observe, and quantify in situ nonlinear sediment response in the near surface. This experiment was part of a suite of experiments conducted during August 2004 in Garner Valley, California, using a large mobile shaker truck from the Network for Earthquake Engineering Simulation (NEES) facility. We deployed a dense accelerometer array within meters of the mobile shaker truck to replicate a controlled, laboratory-style soil dynamics experiment in order to observe wave-amplitudedependent sediment properties. Ground motion exceeding 1g acceleration was produced near the shaker truck. The wave field was dominated by Rayleigh surface waves and ground motions were strong enough to produce observable nonlinear changes in wave velocity. We found that as the force load of the shaker increased, the Rayleighwave phase velocity decreased by as much as ∼30% at the highest frequencies used (up to 30 Hz). Phase velocity dispersion curves were inverted for S-wave velocity as a function of depth using a simple isotropic elastic model to estimate the depth dependence of changes to the velocity structure. The greatest change in velocity occurred nearest the surface, within the upper 4 m. These estimated S-wave velocity values were used with estimates of surface strain to compare with laboratory-based shear modulus reduction measurements from the same site. Our results suggest that it may be possible to characterize nonlinear soil properties in situ using a noninvasive field technique.

In situ observations of velocity changes in response to tidal deformation from analysis of the high‐frequency ambient wavefield

“…The in situ nonlinearity across the differential strain range of ∼6 × 10 −8 is consistent with the response induced by similar strains in the laboratory [ TenCate et al , ; Pasqualini et al , ]. Thus, our results extend the compatibility between field and laboratory observations at large strain amplitudes [ Lawrence et al , ; Renaud et al , ] toward a smaller deformation regime.…”

Influence of vibration amplitude on dynamic triggering of slip in sheared granular layers

“…Their model suggests that triggering may be caused by a shear modulus reduction (softening) due to the passage of seismic waves and is based on laboratory experiments [63][64][65]. In situ field experiments with induced ground motions have also demonstrated that seismic waves can cause material softening [66][67][68]. These laboratory and field experiments suggest that triggering may not be due to the very small increase in the shear stress by the propagating elastic waves, but rather may be due to the reduction in the shear modulus of the fault gouge material, leading to failure.…”

In SituAssessment of theG–γCurve for Characterizing the Nonlinear Response of Soil: Application to the Garner Valley Downhole Array and the Wildlife Liquefaction Array

“…Stokoe and Darendeli (1998) performed laboratory tests to extract the G-γ curve of the surficial sediments; these results will be used as a reference for our analysis. Moreover, Lawrence et al (2008) studied the nonlinear response of GVDA using induced vibration with acceleration of more than 1g. By inverting the dispersion curves, they observed the greatest change in S-wave velocity nearest the surface (up to a depth of 4 m) related to the nonlinear response of the uppermost layers.…”