An elastoplastic and viscoplastic model for porous geomaterials

Abstract : Chalk rocks have been used for centuries as strong building materials and for the production of lime. The shallow underground room-and-pillar quarries where chalk rocks were extracted are now abandoned and are enduring the effects of time and weathering which increases their risk of collapse. A large campaign of laboratory tests under different Relative Humidity values (from 90 to 98%) was undertaken to describe the short and long term behavior of two chalks. These laboratory tests clearly show an elastoplastic behavior with strain-hardening/softening, a relative humidity-dependent strength, a pore collapse and matrix densification even if the stress level is much higher than that prevailing in situ as well as a time-dependent shear and volumetric strains. A multi-mechanism (tensile, shear, pore collapse/compaction, creep) model of the mechanical behavior for highly porous geomaterials is proposed based on the laboratory characterization and constitutive models published in the literature. The proposed model was implemented in FLAC3D and used to simulate laboratory tests in order to verify and validate the implementation.