Shear Properties of Cemented Paste Backfill under Low Confining Stress

Abstract

Cemented paste backfill (CPB) plays an important role in the mining industry due to safety, cost efficiency, and environmental benefits. Studies on CPB have improved the design and application of paste backfill in underground mines. Direct shear is one of the most fundamental parameters for assessing backfill strength. This study harnesses direct shear tests to explore the low confining stress behavior of CPB. We perform all the tests in a standard apparatus on the combination of three binder contents of 4.2%, 6.9%, and 9.7% CPB with four curing times of 3, 7, 14, and 28 days, respectively. The applied confining stress levels vary in a range according to the in situ regime. Results are presented by strength envelope, stress-strain property, and shear strength with curing time and binder content. The data suggest that the shear strength follows the Mohr–Coulomb envelope in which the shear strength and behavior are time and binder content dependent. In addition, the results show that shear strength is strongly related to the binder content than the curing time, namely, the higher the degree of binder hydration, the higher the cementation binding force between CPBs.

Cemented paste backfill strength profiles for continuous pouring and liquefaction resistance

“…The strength parameter in Equation 1 is cohesion, c, because the analysis assumes zero effective stress, so only relying on cohesion. The relationship between drained strengths obtained from UCS, direct shear, and direct tension tests was investigated by Pan (2019) and is shown in Figure 8 for a particular binder content and cure time. The results are generally consistent and indicate that cohesion can reasonably be correlated to UCS, which is useful because UCS is the most used type of strength assessment.…”

Hybrid Failure of Cemented Paste Backfill

“…The numerical simulation was performed by RS2 v9.0 FEA software to determine the stress distribution. The CPB strength parameters were based on direct shear, unconfined compression strength (UCS), and direct tensile tests [6,12,23]. The parameters in the finite element simulations are as follows.…”

“…c. The shear modulus (material's resistance to shear deformation) [25] G = τ xy /γ xy . = Fl/A∆x, (6) where G is the shear modulus, τ xy is the shear stress, γ xy is the engineering shear strain, and l is the gauge length of the shear, F is the total applied force, and A is the area of shear, and ∆x is the lateral displacement. d. The Poisson's ratio v (ratio of longitudinal strain to transversal strain) [25]…”

“…Indeed, CPB must remain stable during the extraction of the adjacent stopes to ensure the safety of the mine operations. Significant progress has been made in understanding the mechanical properties of CPB including failure mechanism under direct shear [4][5][6], uniaxial compression [7], triaxial [8][9][10], and tensile failure [11][12][13]. Nevertheless, the shear resistances under tensile stress-particularly those controlling the sprawling and caving-are not well understood due to limited testing techniques.…”