A Rheological Model of Sandstones considering Response to Thermal Treatment

Abstract

Time-dependentrheologicalresponseofgeomaterialstothermaltreatmentisacrucialissueingeothermalenergyutilizationand deepmineralmining.Thisresponse,however,hasnotyetbeenfullyconsideredintheexistingrheologicalconstitutivemodelsfor sandstones.Inordertoexperimentallyinvestigatesuchresponsesandestablishtheassociatedrheologicalconstitutivemodel,this studyconsidersthesandstonespecimenswhichhavebeenthermallytreatedunderdifferenttemperatures.Thetriaxialrheological test in conjunction with the scanning electron microscope is employed in the investigation to observe the mechanically and macro-/micromorphologically rheological response. Investigation results show that the thermal treatment induces microcracks andmicrodefects,andsubsequently,theypropagateduringthecreep.Asaconsequence,theheterogeneousdeformationoccurs, and macrocracks are present, leading to the irregular fluctuation and mutation in strain over time. A higher temperature contributes to a more severe structure damage and in turn reduces the intactness of sandstones and elevates the rheological response. The investigation allows successful establishment of a three-dimensional constitutive equation considering the instantaneouselasticresponsetothermaltreatment.Basedontheequation,anonlinearvisco-elastoplasticrheologicalconstitutive model is developed for sandstones. Comparison with three existing rheological models shows that the model developed in this study could well represent the rheological process of the thermally treated sandstones.