Tailings composition effects on shear strength behavior of co-mixed mine waste rock and tailings

Abstract

The objective of this study was to evaluate the effect of mine tailings composition on shear behavior and shear strength of co-mixed mine waste rock and tailings (WR&T). Crushed gravel was used as a synthetic waste rock and mixed with four types of tailings: (1) fine-grained garnet, (2) coarse-grained garnet, (3) copper, and (4) soda ash. Co-mixed WR&T specimens were prepared to target mixture ratios of mass of waste rock to mass of tailings (R) such that tailings ''just filled'' interparticle void space of the waste rock (i.e., optimum mixture ratio, R opt ). Triaxial compression tests were conducted on waste rock, tailings, and mixed waste at effective confining stresses (r 0 c ) ranging from 5 to 40 kPa to represent stresses anticipated in final earthen covers for waste containment facilities. Waste rock and co-mixed WR&T specimens were 150 mm in diameter by 300 mm tall, whereas tailings specimens were 38 mm in diameter by 76 mm tall. Shear strength was quantified using effective stress friction angles (/ 0 ) from undrained tests: / 0 for waste rock was 37°, / 0 for tailings ranged from 34°to 41°, and / 0 for WR&T mixtures ranged from 38°to 40°. Thus, shear strength of co-mixed WR&T was comparable to waste rock regardless of tailings composition. Shear behavior of WR&T mixtures was a function of R and tailings composition. Tailings influenced shear behavior for R \ R opt and when tailings predominantly were silt. Shear behavior was influenced by waste rock for R C R opt and when tailings predominantly were sand or included clay particles.

Floor Heave Mechanism of Gob-Side Entry Retaining with Fully-Mechanized Backfilling Mining

“…Sheshpari [11] holds that the gob-backfilled mining method increases the stability of the mined area and decreases land subsidence and rock bursts due to stress pattern changes. Jehring and Bareither [12] analyzed the tailings composition effects on the shear strength behavior of co-mixed mine waste rock and tailings. The study by Huang et al [13] shows that the Under the condition of gob-backfilled mining, the stress and deformation characteristics of the surrounding rocks are radically changed due to the supportive effect of BFA on the roof.…”

Sustainable Reuse of Mine Tailings and Waste Rock as Water-Balance Covers

“…The optimum mixture ratio (R opt ) is defined as a mixture where the finer fraction (tailings) just fills the void space between the coarse particles (waste rock). Co-mixed WR&T prepared at R opt have been reported to have shear strength representative of the waste rock and hydrologic behavior representative of the tailings fraction [18]. An equation for R opt is…”

“…Equation (9) was developed assuming that the specific gravity of tailings and waste rock are the same and density of water = 1 g/cm 3 . Optimum mixture ratios were computed for each mine tailings via determining e t that corresponded to θ s and accounting for an e WR = 0.76, which was reported for a crushed gravel with a PSD representative of hard rock mine waste rock in a loose particle arrangement [18]. Two methods were evaluated in this study to redesign the water storage layer thickness for a co-mixed WR&T cover.…”

“…Mine waste rock has been shown to have shear strength parameters comparable with naturally occurring gravels [13]. The addition of waste rock to mine tailings, known as co-mixed waste rock and tailings (WR&T), has been proposed as an alternative mine waste management approach to enhance impoundment stability, reduce acid rock drainage, reduce storage volume and land required for waste management facilities, and reduce liquefaction potential of tailings [13,17,18]. Waste rock and tailings can be mixed proportionately to develop a material with enhanced strength via waste rock and lower hydraulic conductivity via mine tailings [9,19].…”

Hydraulic Conductivity of Fly Ash-Amended Mine Tailings

“…The fine fraction (i.e., fine-garnet) of the bulk mine tailings was used in this study. A compilation of relevant geotechnical characteristics for the mine tailings is given in Jehring and Bareither (2016), with exception of the compaction parameters.…”