Experimental Study on the Minimum Required Specimen Width to Maximum Particle Size Ratio in Direct Shear Tests

Deiminiat, Akram; Li, Li; Zeng, Feitao

doi:10.3390/civileng3010005

Cited by 5 publications

(1 citation statement)

References 61 publications

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“…In order to handle the coarsest possible sample, most authors that have reported data on coarse materials, such as rockfills and WR, tested samples having low around 6, as recommended by the standard ASTM 7181 (ASTM International 2020;Marsal 1967;Marachi 1969;Linero et al 2007Linero et al , 2020Bard et al 2012;Ovalle et al 2014). However, recent studies have shown that such values of might be too low to ensure a REV (Cerato & Lutenegger 2006;Wu et al 2008;Deiminiat et al 2022).…”

Section: Introductionmentioning

confidence: 99%

Size effects assessment of mine waste-rock shear strength combining numerical, laboratory and in situ approaches

Ovalle,

Girumugisha,

Cantor

et al. 2023

SSIM 2023: Third International Slope Stability in Mining Conference

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With the aim of performing stability analyses of waste-rock (WR) piles, the critical shear strength of loose WR material must be characterised. However, due to the presence of oversized rock clasts, shear tests can only be carried out on small samples prepared using grading scaling techniques. In order to test samples similar to the field material, particle size reduction should be minimised. Considering a testing device able to handle samples of characteristic size , the material should be scaled down to a maximum particle size , given by the minimum sample aspect ratio = / allowing a representative elementary volume (REV). However, worldwide geotechnical standards do not agree on minimum values, and its effects on the mechanical behaviour of coarse samples remain poorly understood. Based on numerical, laboratory and large in situ shear testing approaches, this paper presents a comprehensive study on the effects of sample size and grading on the critical shear strength of WR materials. The main objectives are to analyse the minimum required for a REV in shear testing and to study the suitability of the scalping technique to assess the critical shear strength of mine WR. We study this topic through three methodologies: (1) shearing simulations in the frame of the discrete element method, (2) experimental lab tests using medium to large triaxial devices, and (3) a large in situ direct shear test. We cover a wide range of from 4 to 45. The results show that changes in grading through the scalping technique do not affect the critical shear strength for ≥12, which is higher than some widely applied international standards requirements.

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Section: Introductionmentioning

confidence: 99%

Size effects assessment of mine waste-rock shear strength combining numerical, laboratory and in situ approaches

Ovalle,

Girumugisha,

Cantor

et al. 2023

SSIM 2023: Third International Slope Stability in Mining Conference

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Sample Size Effect on Shear Strength of Mine Waste Rock Using the Scalping Method

Girumugisha,

Ovalle,

Ouellet

2024

Geo-Congress 2024

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Experimental Study on the Reliability of Scaling Down Techniques Used in Direct Shear Tests to Determine the Shear Strength of Rockfill and Waste Rocks

Deiminiat

2022

CivilEng

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The determination of shear strength parameters for coarse granular materials such as rockfill and waste rocks is challenging due to their oversized particles and the minimum required ratio of 10 between the specimen width (W) and the maximum particle size (dmax) of tested samples for direct shear tests. To overcome this problem, a common practice is to prepare test samples by excluding the oversized particles. This method is called the scalping scaling down technique. Making further modifications on scalped samples to achieve a specific particle size distribution curve (PSDC) leads to other scaling down techniques. Until now, the parallel scaling down technique has been the most popular and most commonly applied, generally because it produces a PSDC parallel and similar to that of field material. Recently, a critical literature review performed by the authors revealed that the methodology used by previous researchers to validate or invalidate the scaling down techniques in estimating the shear strength of field materials is inappropriate. The validity of scaling down techniques remains unknown. In addition, the minimum required W/dmax ratio of 10, stipulated in ASTM D3080/D3080M-11 for direct shear tests, is not large enough to eliminate the specimen size effect (SSE). The authors’ recent experimental study showed that a minimum W/dmax ratio of 60 is necessary to avoid any SSE in direct shear tests. In this study, a series of direct shear tests were performed on samples with different dmax values, prepared by applying scalping and parallel scaling down techniques. All tested specimens had a W/dmax ratio equal to or larger than 60. The test results of the scaled down samples with dmax values smaller than those of field samples were used to establish a predictive equation between the effective internal friction angle (hereafter named “friction angle”) and dmax, which was then used to predict the friction angles of the field samples. Comparisons between the measured and predicted friction angles of field samples demonstrated that the equations based on scalping scaling down technique correctly predicted the friction angles of field samples, whereas the equations based on parallel scaling down technique failed to correctly predict the friction angles of field samples. The scalping down technique has been validated, whereas the parallel scaling down technique has been invalidated by the experimental results presented in this study.

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Experimental Study on the Minimum Required Specimen Width to Maximum Particle Size Ratio in Direct Shear Tests

Cited by 5 publications

References 61 publications

Size effects assessment of mine waste-rock shear strength combining numerical, laboratory and in situ approaches

Size effects assessment of mine waste-rock shear strength combining numerical, laboratory and in situ approaches

Sample Size Effect on Shear Strength of Mine Waste Rock Using the Scalping Method

Experimental Study on the Reliability of Scaling Down Techniques Used in Direct Shear Tests to Determine the Shear Strength of Rockfill and Waste Rocks

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