Coupled finite difference and discrete element method for modelling the underground stopes backfilled with the cemented rockfill
Creators: Wei, Chong
Publisher: name: University of Alberta Library
Year: 2023

<p>Backfill columns and the adjacent rock pillars at the underground backfilled stopes are not isolated but mutually supported. Stress transmission and energy alternation occur between them ceaselessly due to the ubiquitous mechanical interactions at the frictional-bonded interfaces between backfill columns and the surrounding rocks when the backfilled stopes are subjected to the disturbance from the sequential mining activities. Consequently, the stress and displacement redistribution takes place in both backfill columns and the surrounding rocks, potentially influencing the stability of the backfilled stopes and the sequential mining activities at the adjacent underground mining area. <br>
Thus, it is an imperative and fundamental task for engineers and researchers to have further study on the principle of the stress and displacement distribution at the backfilled stopes, both in backfill columns and the surrounding rocks, to make optimized designs in both backfill material and rock pillar, to avoid the potential risks in unwanted catastrophic failure and disasters. The main objective of this research is to develop a hybrid modelling approach with higher computation efficiency and precision to study the regime of the mechanical interaction between the CRF columns and the adjacent mining area by using the coupled FD-DE method. Based on a Canadian underground hard rock mine, at which the cemented rockfill (CRF) material was used to backfill the underground mine-out area, five main aspects were covered in this research to analyze the stress and displacement distribution, both in the CRF columns and the surrounding rocks during the entire mining/backfilling sequence at the backfilled stopes, by incorporating the laboratory tests and numerical simulations. <br>
Firstly, the uniaxial and triaxial compression tests were conducted on the large-scale CRF specimens collected from the hard rock mine to study the heterogeneity in the mechanical properties and stress-strain behaviour of the field CRF material in the backfilled stopes. Secondly, the discrete element (DE) method, a discontinuum modelling approach, was used to simulate the CRF specimens according to a simplified particle size distribution to study the stress-strain behaviour, fracture evolution, and failure patterns of the CRF material during the uniaxial and triaxial compression processes. Thirdly, an advanced hybrid numerical modelling approach, the coupled finite difference (FD) and discrete element (DE) method, was applied to study the shear behaviour, stress and displacement distribution at the interface in the combined rock-cemented rockfill (R-CRF) specimen during the direct shear process. Next, the new Johnson-Kendall-Robert (JKR) contact model was employed by the coupled FD-DE method to study the consistency and flowability of the fresh CRF material during the slump test and dumping process at the single backfilled stope. Finally, the stress and displacement distribution and the stability at the multiple backfilled stopes were numerically analyzed with the coupled FD-DE method by considering the shear behaviour at the interfaces between the CRF columns and the surrounding rocks and the primary/secondary manner of the mining/backfilling activities at the hard rock mine. <br>
Four aspects of the main contribution of this research can be highlighted here based on the results from the laboratory tests and numerical simulations. Firstly, this research has some practical laboratory references for assessing the required strength characteristics of backfill columns in the field by considering the heterogeneity in the mechanical properties of the field backfill material. Secondly, this research supplies an effective determination process of the microstructural parameters of the contact model at the interfaces in the coupled FD-DE model which is involved with different geo-materials. Thirdly, this research provides some numerical modelling references for evaluating the flowability and consistency of the fresh backfill material in the backfilled stopes by simulating the coupled FD-DE method and the JKR contact model. Finally, this research provides valuable numerical modelling experience for applying the coupled FD-DE method in investigating the mechanical interaction between different geo-materials involved with frictional, cohesive and bonded interfaces. </p>