Determination of the strength parameters of intact rock samples is an important requirement in rock engineering. On the other hand, proposing a simple method as an index to estimating the strength parameters is one of the tasks of engineering geology. The conventional triaxial test (CTT) is one approach used to determine shear strength parameters (φ and c) that requires standard core cylindrical samples. As it is not possible to prepare standard core samples or collect rock block samples to prepare standard cores under all conditions, the shear strength parameters should be determined using samples having non-standard geometry and dimensions. For this purpose, a miniature triaxial test (MTT) device is introduced and used as an index test to apply triaxial loading on small cubic rock samples in order to estimate their shear strength parameters. The repeatability of the MTT results was determined by performing 27 MTT on 6 × 6 × 6 mm polymethyl methacrylate (PMMA) cubic samples. The results showed that the values measured by the device were repeatable with over 97% similarity. The internal friction angles (φ) of the mortar samples obtained from the CTT on cylindrical samples and MTT on the 6 × 6 × 6 mm samples are similar. However, the cohesion (c) value measured from the MTT test is nearly double the value obtained from the CTT test. The shear strength parameters of 12 different intact limestone samples from the Asmari Formation located in the Siyakouh section were obtained by performing CTT on standard NX core samples and MTT on the 6 × 6 × 6 mm samples. The correlation between the φ and c from the CTT and MTT had coefficients of determination (R) of 0.92 and 0.88, respectively. The precision of the empirical relation for the CTT-MTT correlation was evaluated and showed that shear strength values estimated by the MTT had about 90% similarity with the measured shear strength values from the CTT.

中文翻译：

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利用微型三轴试验估算完整石灰岩的抗剪强度参数

确定完整岩石样品的强度参数是岩石工程的重要要求。另一方面，提出一种简单的方法作为强度参数估算的指标是工程地质学的任务之一。传统的三轴试验 (CTT) 是一种用于确定剪切强度参数（φ 和 c）的方法，需要标准的岩心圆柱形样品。由于不可能在所有条件下制备标准岩心样品或收集岩块样品来制备标准岩心，因此应使用具有非标准几何形状和尺寸的样品来确定抗剪强度参数。为此，引入了微型三轴试验（MTT）装置，并将其用作指标试验，对小型立方岩石样品施加三轴载荷，以估计其抗剪强度参数。 MTT 结果的重复性通过对 6 × 6 × 6 mm 聚甲基丙烯酸甲酯 (PMMA) 立方样品进行 27 次 MTT 来确定。结果表明，该设备测量的数值可重复，相似度超过97%。圆柱形样品的CTT和6×6×6 mm样品的MTT获得的砂浆样品的内摩擦角（φ）相似。然而，MTT测试测得的内聚力(c)值几乎是CTT测试获得的值的两倍。通过对标准NX岩心样品进行CTT和对6×6×6 mm样品进行MTT，获得了位于Siyakouh剖面的Asmari组12个不同完整石灰岩样品的抗剪强度参数。 CTT 和 MTT 的 φ 和 c 之间的相关性决定系数 (R) 分别为 0.92 和 0.88。对 CTT-MTT 相关性经验关系的精度进行了评估，结果表明，MTT 估计的剪切强度值与 CTT 测量的剪切强度值具有约 90% 的相似度。