Multiphysics Investigation of the Geotechnical Behaviour of Cemented Paste Backfill with Superplasticizer
Creators: name: Al-Moselly, Zubaida
Publisher: name: Université d'Ottawa | University of Ottawa
Year: 2024
Subjects: Superplasticizer
cemented paste backfill
tailings
pore water pressure
mine
in-situ conditions
THMC

description: The cemented paste backfill (CPB) method finds extensive application in the mining industry as an effective technique to manage mining wastes (tailings) and support underground mine excavations. In this technique, substantial quantities of tailings are repurposed and transformed into a cemented construction material suitable to manage mine wastes, provide structural stability, and diminish the environmental issues associated with the disposal of such waste on the ground surface. CPB comprises of a blend of tailings, a binding agent, water, and, when necessary, additional additives. CPB is usually prepared at a mixing facility (plant) and subsequently, transported into underground mine voids or stopes through pipelines, either via gravity or with the assistance of pumps. To improve the flowability of the freshly mixed CPB through the pipeline system and to prevent the occurrence of pipe blockages, which could lead to unwarranted delays and decreased productivity, high range water-reducing admixtures, commonly referred to as superplasticizers, are often added to the CPB mixture during the mixing process. Once the CPB is transported into the stope as well as throughout its functional service, the CPB structure is subjected to various internal and external factors that affect its engineering behaviour or properties, including thermal (T), hydraulic (H), mechanical (M), and chemical (C) coupled processes. Therefore, multiphysics curing and laboratory testing procedures were conducted to assess the critical engineering design properties (mechanical strength and pore water pressure development) of CPB materials with superplasticizer under several mix components (tailings, dosages of superplasticizer, water chemistry) and various, individually or coupled, THMC field loading conditions close to those encountered in the field using a THMC pressure cell apparatus, specifically modified for the objectives of this study. Several monitoring tests were implemented in this study to comprehensively understand the mechanisms responsible for the observed geotechnical behaviour, such as electrical conductivity, volumetric water content (VWC), suction, and pore water pressure, which were monitored for various curing times using different sensors. Microstructural analyses such as thermal gravity (TG), differential thermal gravity (DTG), X-ray diffraction (XRD), scanning electron microscopy (SEM) observation, and mercury intrusion porosimetry (MIP) tests were conducted on the CPB with polycarboxylate ether-based superplasticizers specimens to provide a rational elucidation regarding the impact of the field THMC factors and their coupling effects. Moreover, the pore structure (e.g., void ratio, porosity, density) of CPB mixtures was examined to assess the impact of the THMC field curing conditions on the CPB structure. The obtained results reveal that the mechanical strength and overall performance of the CPB structure with polycarboxylate ether-based superplasticizers are greatly affected by the THMC factors and their interactions. An accounting for field THMC factors and their coupling effect on the strength development, rate of change of positive pore water pressure and suction within the CPB is vital for the optimal design of safer and more economical CPB structures.