The changes in the composition and structure of the rock matrix caused by weathering lead to great alterations in its mechanical and physical properties. When considering this, geologists and engineers should pay special attention to materials from transition zones, namely, between the soil and rock over the weathering profiles. This research aimed to perform a wide characterization of the physical, mineralogical and geomechanical properties of a syenogranite rock in various degrees of weathering developed in a Brazilian tropical climate. Laboratory tests were performed to characterize the rock matrix properties at 5° of weathering. The mineralogical composition, the types and number of microstructures, the main physical and chemical changes, and the micropetrographic and microfracturing indexes of the matrix were obtained from analysing petrographic thin sections. The physical and geomechanical characterization included the determination of physical properties, index properties, strength and strain. The thin sections showed that the tropical climate had a great influence on the mineralogical changes, with the occurrence of mainly chemical processes from the medium to the highest degree of weathering. Among the properties evaluated, porosity was the most sensitive to the weathering, reaching 51 times higher in the highly weathered rock. The microfracturing index did not change much, showing a 42.0% increase from the low value of the fresh rock to the slightly weathered rock. Regarding the mechanical properties, the uniaxial compressive strength was the most sensitive to weathering, as observed by a loss of approximately 99.0% of its initial strength when in highly weathered rock conditions. In agreement with previous studies published on granites worldwide, the larger variations in the syenogranite rock properties were also presented from the medium degree of weathering. An experimental study on the use of Digital Image Correlation produced satisfactory results for determining the axial strain and elasticity modulus for more weathered syenogranite materials. New correlations and a quali-quantitative procedure for its classification have been proposed and tested based on the concepts of applicability, representativeness and significance. From 10 proposed correlations, 50% were considered with high or total applicability, and its use is highly recommended for estimating the parameters for syenogranite. Alternatively, from 31 correlations found in the literature, only 16% have shown high or total applicability for syenogranite.

中文翻译：

---

热带气候风化带花岗岩物理、矿物和地质力学性质的变化

风化作用引起的岩石基质成分和结构的变化，导致其力学和物理性质发生很大变化。考虑到这一点时，地质学家和工程师应特别注意来自过渡带的材料，即风化剖面上的土壤和岩石之间的材料。这项研究旨在对巴西热带气候中不同程度风化作用下正长花岗岩的物理、矿物学和地质力学特性进行广泛的表征。进行了实验室测试以表征在 5° 风化下的岩石基质特性。矿物组成、显微结构的种类和数量、主要的物理化学变化、通过岩相薄片分析得到基质的显微岩相和微压裂指数。物理和地质力学表征包括物理特性、指数特性、强度和应变的测定。薄片显示，热带气候对矿物学变化影响很大，发生的主要是从中等风化到最高风化程度的化学过程。在评估的特性中，孔隙度对风化最敏感，在高度风化的岩石中孔隙度高出 51 倍。微压裂指数变化不大，从新鲜岩石的低值到轻度风化的岩石增加了42.0%。在力学性能方面，单轴抗压强度对风化最敏感，在高度风化的岩石条件下，观察到其初始强度损失约 99.0%。与先前发表的关于全球花岗岩的研究一致，正长花岗岩岩石性质的较大变化也来自中等风化程度。使用数字图像相关的实验研究为确定更多风化正长花岗岩材料的轴向应变和弹性模量产生了令人满意的结果。基于适用性、代表性和重要性的概念，已经提出并测试了新的相关性和用于其分类的定性定量程序。从 10 个提议的相关性中，50% 被认为具有高或完全适用性，强烈建议使用它来估计正长花岗岩的参数。或者，