Sand response to a large number of loading cycles under zero-lateral-strain conditions: evolution of void ratio and small-strain stiffness

J Park,J C Santamarina

doi:10.1680/jgeot.17.p.124

J Park, J C Santamarina

Open Access

https://doi.org/10.1680/jgeot.17.p.124

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Abstract

Geotechnical structures often experience a large number of repetitive loading cycles. This research examines the quasi-static mechanical response of sands subjected to repetitive loads under zero-lateral-strain boundary conditions. The experimental study uses an automatic repetitive loading frame operated with pneumatic pistons. Both vertical deformation and shear wave velocity are continuously monitored during 10 000 repetitive loading cycles. The void ratio evolves towards the terminal void ratio eT as the number of load cycles increases. The terminal void ratio eT is a function of the initial void ratio e0 and the stress amplitude ratio Δσ/σ0. The number of cycles N* required to reach half of the final volume contraction ranges from N*→1 for densely packed sands (e0→emin) to N→103 for loosely packed sands (e0→emax). As the soil approaches terminal density at a large number of cycles, peak-to-peak strains are dominated by elastic deformations, and the minute plastic strains that remain in every cycle reflect local and sequential contact events. The shear wave velocity increases during cyclic loading with data suggesting a gradual increase in the coefficient of earth pressure K0 during repetitive loading. Changes in shear wave velocity track the evolution of the constrained modulus M; in fact, the constrained modulus can be estimated from the shear wave velocity to compute soil deformation in a given cycle. A simple procedure is suggested to estimate the potential settlement a layer may experience when subjected to repetitive mechanical loads.

Highlights

Geotechnical structures often experience repetitive loading cycles
This paper extends a previous study by the authors (Chong & Santamarina, 2016) to address a large number of load cycles (i.e. N = 104), various stress amplitude ratios Δσ/σ0 and the analysis of elastic cyclic deformation and the accumulation of plastic strain
The ratio M/Gmax is explored, between the constrained modulus M preferred for 1D deformation analysis and the maximum shear stiffness Gmax obtained from shear wave velocity

Summary

Introduction

Geotechnical structures often experience repetitive loading cycles. Previous studies have explored the soil response to all kinds of repetitive loads, including: mechanical cycles associated with wind, waves, pavements, railroads and foundations (Monismith et al, 1975; Poulos, 1989; Jardine, 1991; Brown, 1996; White & Lehane, 2004; Wichtmann et al, 2005, 2010a; Andersen, 2009; LeBlanc et al, 2010; Indraratna et al, 2013; Wu et al, 2017; Guo et al, 2018); chemical cyclic changes in pore fluid (Di Maio, 1996; Musso et al, 2003); thermal cycles (Viklander, 1998; Pasten & Santamarina, 2014; Di Donna & Laloui, 2015); drying and wetting sequences (Albrecht & Benson, 2001; Alonso et al, 2005; Tripathy & Rao, 2009); freeze–thaw cycles (Chamberlain et al, 1990; Viklander, 1998; Qi et al, 2008); and repetitive changes in pore water pressure (Orense et al, 2004; Nakata et al, 2013; Huang, 2016).The design of geo-structures needs to consider the influence of repetitive loads on long-term performance, serviceability and safety. This paper extends a previous study by the authors (Chong & Santamarina, 2016) to address a large number of load cycles (i.e. N = 104), various stress amplitude ratios Δσ/σ0 and the analysis of elastic cyclic deformation and the accumulation of plastic strain.

Results

Conclusion