Calibration of a Hypoplastic Constitutive Model with Elastic Strain Range for Firoozkuh Sand
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ORIGINAL PAPER
Calibration of a Hypoplastic Constitutive Model with Elastic Strain Range for Firoozkuh Sand Bahareh Mohammadi-Haji . Alireza Ardakani
Received: 3 May 2019 / Accepted: 13 May 2020 Springer Nature Switzerland AG 2020
Abstract A series of laboratory experiments on Firoozkuh sand were conducted followed by a set of numerical simulations to determine the parameters of a general hypoplastic constitutive model for sand. This model describes inelastic and incrementally nonlinear material properties without a yield surface and detached strain increments in the elastic and plastic portions that is used to accurately simulate soil behavior for small and large strains and unloading– reloading paths. The general models are salient and the model requires unique constitutive constant values for all densities of a particular soil at all pressures. The 13 hypoplastic parameters used were calibrated through standard laboratory monotonic and cyclic triaxial and oedometer tests. Additional undrained triaxial and cyclic triaxial testing data that had not been used in the calibration process were used to validate the parameters. Keywords Hypoplasticity Intergranular strain Calibration Firoozkuh sand Tri-axial tests
B. Mohammadi-Haji A. Ardakani (&) Department of Civil Engineering, Imam Khomeini International University, Qazvin, Iran e-mail: [email protected] B. Mohammadi-Haji e-mail: [email protected]
1 Introduction The need to accurately simulate soil behavior through numerical simulation has led to the development of advanced soil constitutive models. Among these, hypoplastic models are comprehensive and ratedependent and can properly describe the nonlinear stress–strain behavior of soil (Mohammadi-Haji and Ardakani 2018). The initial hypoplastic model was introduced by Gudehus (1996) and Bauer (1996) using the current stress and void ratio in their constitutive relations for granular material. Afterwards, a mathematical formulation of the model was improved by von Wolffersdorf (1996) for sand by altering the earlier equations to obtain more suitable values for critical and limit states. It has been reported that this model does not only properly predict rearrangement of the grain skeleton, which causes soil deposit deformation (Bauer 1996), but describes the dependence of the material behavior on both the density and pressure levels using a single set of material constants with a simple formulation (Wu and Bauer 1993; Wu et al. 1993; Bauer and Wu 1995). Despite its significant aspects, the hypoplastic model improved by von Wolffersdorf is deficient in describing the behavior of soil for specific applications (Masin 2019). The most substantial shortcoming of the model is that it has not been able to predict the high initial stiffness of soil and the accumulation of plastic deformation resulting from small stress cycles, called
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ratcheting (Masin 2019). This means that the basic model is not capable of reproducing
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