Grading scalping and sample size effects on critical shear strength of mine waste rock through laboratory and in-situ testing

IF 7 1区 工程技术 Q1 ENGINEERING, GEOLOGICAL International Journal of Rock Mechanics and Mining Sciences Pub Date : 2024-09-21 DOI:10.1016/j.ijrmms.2024.105915
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Abstract

Geotechnical stability analyses of mine waste rock (WR) piles require the critical friction angle (ϕcr) of the coarse blasted rock. However, due to the presence of oversized rock clasts, shear strength can only be characterized on small samples prepared using grading scaling techniques, such as scalping. Thus, considering a testing device able to handle samples of characteristic size D, the material should be scaled down to a maximum particle size dmax given by the minimum sample aspect ratio α = D/dmax. However, a practical concern about how far the size scale can be reduced while keeping representative results remains a matter of debate in the geotechnical community. International standards do not agree on the minimum recommended α, and its effects on the mechanical behavior remain poorly understood. This paper aims to investigate the grading effects and sample size effects on ϕcr of WR materials using the scalping technique, to provide insights on the minimum recommended α. Triaxial tests were conducted on loose and dense samples of diameters D = 150 and 300 mm. Samples were scalped from field material having dmax = 75 mm, to allow a range of α from 4 to 30. Additionally, one of the world largest in-situ direct shear boxes (120 × 120 × 38 cm3) was developed to test the same WR material. The results show that scalping is an appropriate technique to assess the critical shear strength of WR. The minimum α for ϕcr assessment in triaxial testing is not sensitive to grading nor sample size, but it is affected by sample density. The aspect ratio was found to be α ≥ 12 and α ≥ 16 for loose and dense samples, respectively. This finding advocates that α values recommended by worldwide standards, such as ASTM D7181-20, might be too low and should be revisited after comprehensive testing.

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通过实验室和原位测试,分级标度和样本大小对矿山废石临界剪切强度的影响
矿山废石(WR)桩的岩土稳定性分析需要粗爆破岩石的临界摩擦角(jcr)。然而,由于存在过大的岩石碎块,只能通过分级缩放技术(如缩放)制备的小样本来确定剪切强度。因此,考虑到测试设备能够处理特征尺寸为 D 的样品,材料应按比例缩小到最大粒度 dmax,该粒度由最小样品长宽比 α = D/dmax 给出。然而,在岩土工程界,如何在保持结果代表性的同时缩小粒度仍是一个值得关注的实际问题。国际标准并未就推荐的最小值 α 达成一致,而且人们对其对力学行为的影响仍知之甚少。本文旨在利用剥离技术研究 WR 材料的级配效应和样本大小对 ϕcr 的影响,从而为推荐的最小 α 提供见解。样品是从 dmax = 75 毫米的现场材料中剥取的,因此 α 的范围在 4 到 30 之间。此外,还开发了世界上最大的原位直接剪切箱(120 × 120 × 38 立方厘米)之一,以测试相同的 WR 材料。结果表明,缩放是评估 WR 临界剪切强度的一种适当技术。在三轴测试中评估ϕcr 的最小 α 对级配和样品大小不敏感,但会受到样品密度的影响。研究发现,松散和致密样品的长宽比分别为 α ≥ 12 和 α ≥ 16。这一发现表明,ASTM D7181-20 等世界标准推荐的 α 值可能过低,应在全面测试后重新考虑。
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来源期刊
CiteScore
14.00
自引率
5.60%
发文量
196
审稿时长
18 weeks
期刊介绍: The International Journal of Rock Mechanics and Mining Sciences focuses on original research, new developments, site measurements, and case studies within the fields of rock mechanics and rock engineering. Serving as an international platform, it showcases high-quality papers addressing rock mechanics and the application of its principles and techniques in mining and civil engineering projects situated on or within rock masses. These projects encompass a wide range, including slopes, open-pit mines, quarries, shafts, tunnels, caverns, underground mines, metro systems, dams, hydro-electric stations, geothermal energy, petroleum engineering, and radioactive waste disposal. The journal welcomes submissions on various topics, with particular interest in theoretical advancements, analytical and numerical methods, rock testing, site investigation, and case studies.
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