A parameter calibration method in two-surface elastoplastic model for sand-structure interface under monotonic shear loading

Abstract

A new method is proposed to calibrate the key parameters of a two-surface elastoplastic model to simulate the sand-structure interface under monotonic shear loading. A series of DEM simulations, in which a few sand-structure interface parameters and boundary conditions are considered, are conducted to guide the establishment of a calibration method. The simulation results, together with other researchers’ test results, are used to provide semiempirical and empirical equations for parameter calibration using the two-surface elastoplastic constitutive model. Numerical calculations are performed using the new method and the model’s performance is evaluated for dense and loose sands, under constant normal load and constant normal stiffness conditions by comparison with experimental results, which are shown to be in good agreement with the experimental data.

Introduction

Soil-structure systems such as retaining walls, piles, embankment dams and underground tunnels exist widely across engineering applications. The thin layer on the contact face between soil particles and structures is known as the interface shear zone; most of the shear behavior takes place here, such as particle sliding, rolling, breakage and separation during shearing. Thus, it is important to study the interface shear zone to understande the response of sand-structure systems.

Many researchers have tried to simulate the behavior of interface shearing and proposed different models mainly based on the theory of elastoplasticity. These models can be classified as disturbed state concept (DSC) (Fakharian and Evgin, 2000), damage plasticity (Zhang and Zhang, 2004, Zhang and Zhang, 2006), two-surface plasticity (Manzari and Dafalias, 1997, Mortara et al., 2007, Dejong and Westgate, 2009, Lashkari, 2009, Saberi et al., 2016), hypoplasticity (Herle and Arnold, 2006, Stutz et al., 2016, Stutz et al., 2017, Stutz and Wuttke, 2018) and generalized potential theory (Aizhao and Tinghao, 2009; Aizhao et al., 2012) models. Among them, the theory of hypoplasticity is relatively simple and can accurately predict responses to shear stress (Wichtmann et al., 2019). The theory of the DSC and damage plasticity considers that the behavior is caused by disturbance or damage, and generalized potential theory reduces the number of parameters needed to make the model simpler and more practical. The two-surface plasticity theory is suitable for simulating soil-structure behavior under monotonic and cyclic loading with a complex loading history in the plastic range (Saberi et al., 2016, Saberi et al., 2018). Moreover, the concept of critical state soil mechanics (CSSM) is often introduced as a general framework for the two-surface plastic model to capture volumetric changes during shearing (Hachey et al., 1991, Li et al., 1999, Liu et al., 2006, Liu and Ling, 2008, Lashkari, 2009, Saberi et al., 2016). However, the physical parameters in two-surface plastic models need to be calibrated through standard interface shear tests (Shahrour and Rezaie, 1997, Lashkari, 2012, Saberi et al., 2018) using relatively subject data-processing methods such as fitted lines, empirical hypotheses, trial and error approach, etc. Moreover, for different kinds of soils and interfaces, it is inconvenient to perform a large number of tests and data processing. Therefore, a theoretical calibration method needs to be proposed to make two-surface plasticity theory effective and applicable.

Usually, the proposed interface shearing theories can also be implemented in commercial simulation software to simulate the shearing process under different conditions using FDM (Belen et al., 2011, Anubhav, 2015), and FEM (Saberi et al., 2016, Saberi et al., 2018, Saberi et al., 2019, Wichtmann et al., 2019), which have shown good agreement with experimental results in terms of the stress–strain response. Recently, a micropolar continuum approach (Ebrahimian and Bauer, 2012, Ebrahimian and Bauer, 2015; Ebrahimian et al., 2017) was proposed to model the soil-structure interface, which provided a new method to simulate granular soil behavior under shearing in contact with a continuum of differing surface roughness values. However, soils are known to be highly discontinuous media and are well suited to be modeled using the DEM method (Jensen et al., 1999). A number of DEM simulations have been performed to explore the behavior of the soil-structure interface at microscopic scales (Jensen et al., 1999, Gu et al., 2017, Jing et al., 2018, Feng et al., 2019, Huang et al., 2019). Thus, the DEM method is adopted in this paper to study the effect of basic parameters on the sand-structure interface, such as particle diameters, void ratios, surface roughness values, etc.

The present study conducted a series of DEM simulations of sand-structure interfaces under shear loading under different conditions, aiming to establish theoretical procedure for calibrating key parameters in a two-surface elastoplastic model with basic parameters, i.e., the void ratio $e_0$, mean particle diameter $D_{50}$, internal friction angle ${\varphi }_{\mathit{peak}}$ of soil, normalized surface roughness $R_n$ and normal stress ${\sigma }_n$ of boundary conditions.

Together with other research test results, DEM simulation results are used to provide empirical equations and semiempirical equations. Sand-structure behavior curves are derived with the new calibration method and introduced into the computer code numerical calculation software. The model predictions are compared to the measured sand-structure interface response using other researchers’ test results. Moreover, a parametric numerical analysis is performed to better understand the influence of the basic parameters on the soil-structure.