Constitutive model with reversal surfaces for granular soils under monotonic and cyclic loading

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4. Constitutive model with reversal surfaces for granular soils under monotonic and cyclic loading

This paper outlines the formulation and verification of a new constitutive model, named LiPa model, that simulates the monotonic and cyclic shearing of granular soils with the same set of soil-specific model constants. It is a SANISAND-type model and employs the last stress reversal point for defining both the elastic and the plastic strain rates. The updating of this point is specially treated to mitigate stress-strain overshooting. Macroscopic sand fabric evolution indices that scale the plastic modulus and dilatancy functions are incorporated, targeting accurate strain accumulation with cycles during shearing, both before and after liquefaction. Model performance is verified against sand-specific monotonic and cyclic shearing tests on Toyoura sand, while the validation is complemented with comparisons against empirical relations targeting generic aspects of the cyclic response: small - strain shear modulus degradation and hysteretic damping increase, volumetric and shear strain accumulation with cycles, effect of stress level on liquefaction resistance. A variety of loading conditions is included in the verification process, i.e., drained/undrained, monotonic/cyclic, to demonstrate the simulative potential of the model. It is shown that a single set of soil-specific constants may be used for both monotonic and cyclic shearing of any strain level, irrespective of stress level and relative density.

10th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE2023)

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