Predicting the geomechanical behaviour of rockmasses is key to the economic success and safety of rock engineering projects including surface and underground excavations. For these projects, unconfined compressive stress (UCS) laboratory testing provides fundamental geomechanical properties of intact rocks. It is currently standard practice for UCS testing to consider only homogeneous specimens that are free of defects and discard heterogeneous specimens such as those that contain intrablock structures (e.g. veins) or extra-granular defects (e.g. phenocrysts). Understanding the complexities of these heterogeneous rocks and rockmasses is critical for excavation projects such as deep cave mines where extensive tunnel networks, caves, and stopes are regularly excavated through heterogeneous rockmasses. This paper presents the test results and analyses of UCS tests conducted on 29 matrix-type and 21 veined drill core specimens from the Legacy Skarn deposit located in northern New Brunswick, Canada. These specimens are sorted into five lithological units: beige, red, and black varieties of quartz-plagioclase granodiorite, calcareous mudstone, and garnet-pyroxene skarn. Mineralogical compositions of these units are determined using field identification techniques and microscopic laboratory methods including petrographic thin section analysis, powdered X-Ray Diffraction, and micro-X-Ray Fluorescence. Significant effects of hydrothermal veining and phenocrysts on the UCS test results are discussed in this study to highlight the significant influence of mineralogy on the variability of geomechanical properties. For example, vein mineralogy dominated by calcite weakened the granodiorites but strengthened the calcareous mudstone. Vein mineralogy dominated by quartz in the skarn unit had a mixed influence on geomechanical properties. Vein thickness primarily influenced geomechanical properties of specimens with single veins, whereas vein density was more useful to characterize specimens that contained vein networks or stockwork. The effects of vein orientation only partially agree with the established Jaeger model for shear failure through critically oriented foliations. The disseminated alteration in the granodiorites (plagioclase phenocrysts) and skarn (garnet crystals) typically increased stiffness and strength as the large grains arrest crack propagation when under load. Lastly, the effects of sample selection on reported UCS test results using four sample selection methods are presented. The results demonstrate the importance of including heterogeneous veined specimens in UCS sample selection and testing programs to capture rock variability and improve the accuracy of numerical geomechanical design. Recommendations are made to improve geotechnical core logging and sample selection protocols when characterizing heterogeneous complex rockmasses.

预测岩体的岩土力学行为是岩石工程项目（包括地面和地下开挖）的经济成功和安全性的关键。对于这些项目，无边压缩应力（UCS）实验室测试提供了完整岩石的基本地质力学特性。当前，UCS测试的标准做法是仅考虑没有缺陷的均匀样本，并丢弃异质样本，例如那些包含块内结构（例如静脉）或颗粒外缺陷（例如隐晶）的样本。了解这些非均质岩石和岩体的复杂性对于诸如深洞矿等开挖项目至关重要，在该项目中，经常通过非均质岩体开挖大量的隧道网络，溶洞和采场。本文介绍了对来自加拿大新不伦瑞克省北部的Legacy Skarn矿床的29个基质型和21个脉状钻芯标本进行的UCS测试的结果和分析。这些标本分为五个岩性单位：石英斜长石花岗闪长岩的米色，红色和黑色变种，钙质泥岩和石榴石-辉石矽卡岩。这些单元的矿物学成分是使用现场识别技术和微观实验室方法（包括岩相薄片分析，粉末X射线衍射和微X射线荧光法）确定的。在这项研究中，讨论了热液脉管和表晶对UCS测试结果的显着影响，以突出矿物学对地质力学性质变异性的显着影响。例如，方解石为主的脉状矿物学弱化了花岗闪长岩，但强化了钙质泥岩。矽卡岩单元中以石英为主的静脉矿物学对地质力学特性的影响参差不齐。静脉的厚度主要影响单静脉标本的地质力学特性，而静脉密度对于表征包含静脉网或细孔的标本更为有用。静脉取向的影响仅部分与已建立的Jaeger模型有关，该模型通过临界取向的叶面导致剪切破坏。花岗岩中的斜长石和斜长岩（石榴石晶体）中散布的变化通常会增加刚度和强度，因为大颗粒在负载下会阻止裂纹扩展。最后，介绍了使用四种样本选择方法进行的样本选择对报告的UCS测试结果的影响。结果表明，在UCS样品选择和测试程序中包括异类脉状标本的重要性，以捕获岩石的变化性并提高数值岩土力学设计的准确性。在表征非均质复杂岩体时，提出了改善岩土岩心测井和样品选择方案的建议。