Effect of Suction on the Drained Seismic Compression of Unsaturated Sand

Rong, Wenyong; McCartney, John S.

doi:10.1051/e3sconf/20199208004

Cited by 3 publications

(2 citation statements)

References 9 publications

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“…However, there are cases where unsaturated soils with relatively high initial degrees of saturation can still liquefy under seismic excitation (Unno et al 2008). In unsaturated soils with lower initial degrees of saturation, seismic compression is expected during strong shaking by earthquakes with shear strain amplitudes greater than the cyclic threshold shear strain (Stewart et al 2004, Rong and McCartney 2019, 2020b. Earthquakes and aftershocks often have rapid shearing with short durations that can lead to undrained conditions even for sands.…”

Section: Seismic Compression Of Unsaturated Soils In Literaturementioning

confidence: 99%

Hyperbolic Hydro-mechanical Model for Seismic Compression Prediction of Unsaturated Soils in the Funicular Regime

Kinikles¹,

McCartney²

2022

PEER Reports

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A semi-empirical elasto-plastic constitutive model with a hyperbolic stress-strain curve was developed with the goal of predicting the seismic compression of unsaturated sands in the funicular regime of the soil-water retention curve (SWRC) during undrained cyclic shearing. Using a flow rule derived from energy considerations, the evolution in plastic volumetric strain (seismic compression) was predicted from the plastic shear strains of the hysteretic hyperbolic stress-strain curve. The plastic volumetric strains are used to predict the changes in degree of saturation from phase relationships and changes in pore air pressure from Boyle’s and Henry’s laws. The degree of saturation was used to estimate changes in matric suction from the transient scanning paths of the SWRC. Changes in small-strain shear modulus estimated from changes in mean effective stress computed from the constant total stress and changes in pore air pressure, degree of saturation and matric suction, in turn affect the hyperbolic stress-strain curve’s shape and the evolution in plastic volumetric strain. The model was calibrated using experimental shear stress-strain backbone curves from drained cyclic simple shear tests and transient SWRC scanning path measurements from undrained cyclic simple shear tests. Then the model predictions were validated using experimental data from undrained cyclic simple shear tests on unsaturated sand specimens with different initial degrees of saturation in the funicular regime. While the model captured the coupled evolution in hydro-mechanical variables (pore air pressure, pore water pressure, matric suction, degree of saturation, volumetric strain, effective stress, shear modulus) well over the first 15 cycles of shearing, the predictions were less accurate after continued cyclic shearing up to 200 cycles. After large numbers of cycles of undrained shearing, a linear decreasing trend between seismic compression and initial degree of saturation was predicted from the model while a nonlinear increasing-decreasing trend was observed in the cyclic simple shear experiments. This discrepancy may be due to not considering post shearing reconsolidation in the model, calibration of model parameters, or experimental issues including a drift in the position of the hysteretic shear-stress strain curve. Nonetheless, the trend from the model is consistent with predictions from previously- developed empirical models in the funicular regime of the SWRC. The developments of the new mechanistic model developed in this study will play a key role in the future development of a holistic model for predicting the seismic compression across all regimes of the SWRC.

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Section: Seismic Compression Of Unsaturated Soils In Literaturementioning

confidence: 99%

Hyperbolic Hydro-mechanical Model for Seismic Compression Prediction of Unsaturated Soils in the Funicular Regime

Kinikles¹,

McCartney²

2022

PEER Reports

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“…Such solutions will improve the accuracy of predictions of the loads that are transferred between structural elements and unsaturated soils. Furthermore, if coupled with appropriate constitutive models, these numerical solutions can facilitate accurate assessments of ratcheting of unsaturated soils under cyclic interactions as well as the ability (or inability) of these soils to reach the shakedown state (Rong and McCartney, 2019). Also, such solutions can assist in improving ground compaction practices to ensure serviceability and reasonable performance during cyclic loading.…”

Section: Introductionmentioning

confidence: 99%

Improving Efficiency, Stability, and Accuracy of Finite Element Solutions for Solving Dynamic Contact Problems Involving Unsaturated Soils

Ghorbani

Chen

Kodikara

et al. 2022

Challenges and Innovations in Geomechanics

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The paper investigates the efficiency, stability, and accuracy of finite element solutions based on the mortar approach in solving dynamic contact problems that involve unsaturated soils. We employ a fully coupled finite element solution and a recently developed bounding surface model for describing the hydro-mechanical hysteresis of unsaturated soils. The paper discusses a key source of instability in numerical simulations of this class of problems which is stress overshooting. We evaluate the efficiency of a solution for this problem and discuss the impact of this solution on improving the accuracy and stability of numerical simulations. Numerical simulations are presented for verification and analysis of efficiency, stability, and accuracy.

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Methodology to Characterize the Seismic Compression of Unsaturated Sands under Different Drainage Conditions

Rong

McCartney

2021

Geotechnical Testing Journal

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This study focuses on a new experimental setup and methodology to characterize 5 the volumetric contraction of unsaturated sands during cyclic shearing under different drainage 6 conditions. A new cyclic simple shear device was developed with suction-saturation control using 7 a hanging column suitable for testing unsaturated granular soils with a maximum suction of 11 8 kPa. The pore water and pore air pressures are monitored during cyclic shearing using an 9 embedded tensiometer and a gauge pressure transducer protected by a hydrophobic filter, 10 respectively. In addition to describing the specimen preparation techniques and testing 11 methodology, typical results for the seismic compression of nearly-saturated, dry, and unsaturated 12 sand specimens during cyclic shearing under different drainage conditions are compared. The 13 differences in the response of these sand specimens were interpreted using the changes in mean 14 effective stress and secant shear modulus during cyclic shearing. The unsaturated sand specimen 15 showed lower seismic compressions than the dry sand specimen and the nearly-saturated sand 16 specimen in drained conditions. A greater contraction observed for the unsaturated sand specimen 17 in undrained conditions was attributed to decreases in mean effective stress and secant shear 18 modulus associated with a decrease in matric suction due to different rates of pore water and air 19 pressure generations and an increase in degree of saturation due to volumetric contraction.

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Effect of Suction on the Drained Seismic Compression of Unsaturated Sand

Cited by 3 publications

References 9 publications

Hyperbolic Hydro-mechanical Model for Seismic Compression Prediction of Unsaturated Soils in the Funicular Regime

Hyperbolic Hydro-mechanical Model for Seismic Compression Prediction of Unsaturated Soils in the Funicular Regime

Improving Efficiency, Stability, and Accuracy of Finite Element Solutions for Solving Dynamic Contact Problems Involving Unsaturated Soils

Methodology to Characterize the Seismic Compression of Unsaturated Sands under Different Drainage Conditions

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