Total Stress Analysis of Soft Clay Ground Response in Centrifuge Models

Abstract

This paper presents one-dimensional ground response simulations of centrifuge models involving soft clay deposits subjected to ground motions of varying intensity. Total stress ground response simulations were performed using equivalent-linear (EL) and nonlinear (NL) methods. Shear strains higher than 10% were mobilized during large ground motions, therefore undrained shear strength of the clay is an important parameter for the simulations. Testing shows that the Bay Mud materials used in centrifuge modeling have monotonic shear strengths that increase by 13% per log cycle of shear strain rate. Comparison of simulation results to observations reveals the importance of incorporating shear strength into the development of stress-strain backbone curves, with appropriate consideration of rate-adjustments to shear strength and stiffness. NL ground response simulations provide a good match to observed pseudo-spectral accelerations only when rate-adjusted shear strengths are properly accounted for, otherwise the NL simulations have significant under-prediction bias at oscillator periods less

Evaluation of vertical effective stress and pile tension capacity in sands considering scour-hole dimensions

“…The influence of local scour on the free-field soil properties is considered to be negligible (Meymand, 1998;Shang et al, 2016). The nonlinear SRA employs the general quadratic/hyperbolic (GQ/H) model (Groholski et al, 2016) with the shear strength and damping controls (Afacan et al, 2019;Yee et al, 2013). The GQ/H model uses the reference modulus reduction and damping curves proposed by Darendeli…”

Integration of Viscoplastic Effects in Nonlinear Ground Response Analysis

“…In order to provide a shear strength corrected modulus reduction curve, Afacan et al (2014b) modified the modulus reduction curves obtained through the empirical relationships introduced by Darendeli (2001) to match a target shear strength using the procedure from Yee et al (2013).…”

“…The curves were further modified to match a target rate-adjusted shear strength, and Afacan et al (2014b) showed that the use of strain-rate-adjusted profiles of undrained shear strength allows to obtain more accurate predictions in ground response analysis. The centrifuge model was shaken with 19 earthquake ground motions with peak accelerations varying from 0.02g to 0.6g.…”

“…This formulation removes several of Rayleigh Damping limitations and does not require to select modes or frequencies (Phillips and Hashash 2009). Simulations were done and compared to the results of the centrifuge tests (Afacan et al 2014b).…”

Estimating epistemic uncertainty in soil parameters for nonlinear site response analyses: Introducing the Latin Hypercube Sampling technique

“…Furthermore, this study utilizes an improved modeling of site response at large strains by adjusting the backbone curves and incorporates epistemic uncertainties in soil parameters considering NL constitutive modeling. Note that prior researchers, such as Yee et al (2013) and Afacan et al (2019), have demonstrated the importance of shear strength in the modeling of site response at large strains and that researchers, such as Yee et al (2013) and Groholski et al (2016), have provided methods to adjust the backbone curve to account for it. Finally, another key aspect of this work is to quantify site response uncertainty using both the actual recordings at a geotechnical downhole array (Yazdi et al, 2022; Yee et al, 2013; Zogh et al, 2021) and the predicted median response spectra for different levels of intensity to assess the reliability of using the predicted median response spectra in case the actual recordings at the location of site are not available.…”