Strength and damage constitutive model of backfill body after high temperature treatment

Abstract

Constructing mine heat storage reservoirs with water-blocking capabilities using functional filling technology is an innovative approach for underground high-temperature heat storage. However, high-temperature environments can easily cause thermal damage to the backfill body, posing significant risks to the safety of the heat storage reservoir. In this study, we conducted mechanical and microstructural tests on heated backfill body samples to observe changes in their mechanical properties and microstructure at varying temperatures. The test results show that as the temperature goes from room temperature (25 °C) to 350 °C, the backfill body’s compressive strength goes down a lot, with peak stress dropping from about 7 MPa to 3 MPa. At the same time, its ductility and ability to deform go up. Higher temperatures intensify shear failure, leading to the extension of cracks along the shear direction and subsequent surface spalling. The proportion of shear failure increased from 27.86 % to 68.21 %. The microstructure of ettringite, calcium silicate hydrate, and calcium hydroxide breaks down at different temperatures, which makes the pores bigger and the structure less rigid. This study developed a thermal damage constitutive model that incorporates acoustic emission parameters. We can use this model to evaluate and predict the deformation and strength characteristics of backfill after exposure to high-temperature treatment.