Investigation of cemented tailings backfill and wellbore stability for narrow vein mining by drilling

Someehneshin, Javad (2020) Investigation of cemented tailings backfill and wellbore stability for narrow vein mining by drilling. Masters thesis, Memorial University of Newfoundland.

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Abstract

In this thesis, a comprehensive investigation of using tailings in backfilling material and the percentage of Portland cement and binder composition (a combination of Portland cement and fly ash) with the proportion of (80:20) is studied. Curing time and curing strength of the backfilling material after 7 days, 14 days, and 28 days were the main objective of this thesis. The freestanding vertical face of the void space by inclined stope method was calculated. Specimens were made with Portland cement as the first binder, which was composed of 6%, 8%, and 10% of the solid content of the mixture and 20% water content of the backfilling mixture. The Curing time and curing strength of the specimens in this first binder were measured by Geo-mechanical Loading Frame in Drilling Technology Laboratory (DTL). The second series of the specimens were made with binder composed of regular Portland cement 80% type GU and fly ash 20% class C with 6%, 8%, and 10% of the solid content of the mixture and 20% water content of the backfilling mixture. Then the curing time and curing strength of the specimens were measured. Finally, the results were compared and the effect of binder dosage on Unconfined Compressive Strength (UCS), the effect of binder composition on UCS, the effect of curing time on UCS, and the stiffness of backfilling materials for both binders were presented. In addition, an analytical study and Discrete Element Method (DEM) simulation were conducted to evaluate the wellbore stability of steeply mining using various wellbore failure criteria. Mining site data of surface and subsurface in-situ stress and rock mechanics properties was collected to support the study. The dimensions of the studied wellbore were 100m maximum depth, 1.3m maximum diameter, and 45 degrees inclination. The wellbore rock failure was analyzed, and the critical wellbore pressure after drilling in four essential azimuths (i.e. 0˚, 90˚, 180˚, and 270˚) using pure water was calculated. The results of the individual and the analytical-DEM coupled study demonstrated that the wellbore stability. The critical wellbore pressure is negative all along the wellbore; also, all applied stresses around the wellbore are between minimum wellbore pressure and maximum wellbore pressure, which indicates the stability of the well.

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