Analysis of the process of compaction movements of deposits of crushed salt tailings

Abstract

Abstract In the context of chemical industry production, mining waste from saline materials, mostly consisting of granular rock salt, is stored in tailing piles. During this process, several deformational mechanisms are involved. The crushed salt displays a significant visco-plastic response. Several processes such as “dislocation related deformation mechanisms” or “mechanisms related to presence of humidity”, are activated. The granular saline material consolidates and void ratio reduces. Dissolution and recrystallization phenomena is developed because of confining stresses and the presence of water. Consequently, it produces bonding between salt grains increasing the strength of the material and reductions of porosity. This paper describes the compaction process of waste salt materials due to the tailing pile self-weight. Since then, it undergoes a long-term response which may lead to a material with completely different properties. An experimental program was carried out on salt samples obtained from a tailing pile with the aim of studying the mechanical behavior of the material. This experimental research was divided in three stages. First, the geotechnical profile was determined from a comprehensive laboratory characterization. In this research, the behavior of the salt aggregates was studied by means of oedometer compaction creep tests on granular salt samples. The material used was obtained from two different depths. Samples were saturated during two months using a salt solution under isothermal conditions (23\u202f°C). Vertical stresses applied varied from 0.05 to 1.5\u202fMPa. Permeability measurements were obtained from oedometer tests (initial and final measurements). A relationship between permeability and void ratio was established. In a second stage, a constitutive model proposed by Chumbe, 1996 for aggregate saline material has been calibrated by experimental oedometer results. The model predicts strain rate of the salt aggregates subjected to compaction under constant stress, once calibrated. Moreover, the evolution of permeability can also be estimated by the model. Finally, a model, with a relatively simple geometry, is intended to assess porosity reduction in a crushed salt deposit. In this way, the experimental results can benefit of using the viscoelasticity and viscoplasticity constitutive laws for saline materials implemented in CODE_BRIGHT.