Mohammad Hosein Ghobadi, Paria Behzadtabar,
Volume 11, Issue 3 (1-2018)
Abstract
Rock anisotropy plays an important role in engineering behavior of rocks. Slates are anisotropic rocks which have long been used for gable roof, floor tiles, borrow materials, and other purposes. The slates studied in this research are calcareous and have a porphyro-lepidoblastic texture. To determine the role of the anisotropy on the tensile strength and fracture pattern, two variables including ψ (the core axis angle to foliation) and β (the angle between the axis of loading and foliation) in the Brazilian tests were used. The angles were selected at 15° intervals. Thus, for both ψ and β, seven angles of 0˚, 15˚, 30˚, 45˚, 60˚, 75˚, and 90˚ were selected (i.e., there are 43 possible modes). In order to name and examine the failure pattern, 11 models were proposed. The average value of the failure strength for the three stations varies from 3.21 MPa to 20.94 MPa. Based on the obtained results, there is a direct relation between the average tensile strength and density. A comparison between Brazilian test data under dry and saturation conditions shows that the saturated Brazilian tensile strength is 30.8% less than the dry Brazilian tensile strength. Moreover, the changes in fracture length with the changes in ψ and β indicate an inverse relation. Eventually, the average of tensile strength (σt) and strength anisotropy index (Ia) demonstrates that the influence of orientation angle (ψ) is much larger than that of foliation-loading angle (β).
, , , ,
Volume 15, Issue 3 (12-2021)
Abstract
In this study, due to the landslide in schist rocks, in the wall of Mouteh gold mines, including of the eastern wall of ChahKhatoon mine, it is important to identify the effective factors. Therefore, due to the diversity of schists in Chah Khatoon and Sanjadeh gold mines (two active mines in Mouteh Complex), to survey the mineralogy of schist rocks in Moteh gold mine has been done by identifying important factors in changes in rock strength. Cosequently, 10 schist samples from walls of these mines were considered for mineralogical, XRD studies. In the next step, these schists were subjected to uniaxial compressive strength (UCS) and Brazilian tests to estimate the mechanical properties and quality of rock mass in different zones of mineral walls. The results showed that the UCS and Brazilian index in these schists are directly and inversely related to the SiO2 and Al2O3 contents of the rocks, respectively, as well as the secondary structures.Some factors such as the presence of secondary structures, continuous surface area, particle size, and mineralogical composition play an important role in the failure modes of these rocks. UCS and Brazilian strength of schists vary from 10 MPa to 72 MPa and 1.9 to 10.2 MPa, respectively. The lowest UCS occurs in strongly weathered rocks with low silica content. However, the type of clay minerals is effective in the stability of the mineral wall. Considering the presence of montmorillonite clay mineral in the eastern wall of Chahkhatoun mine, the rock resistance is moderate despite the high percentage of silica. UCS values of wet and dry rock samples containing muscovite and montmorillonite clay minerals were more different from those of other rocks. In this regard, the rocks with Illite clay minerals are more resistant than Smectite and montmorillonite minerals. In general, the resistance of schists depends on various factors such as mineralogy, which is of great importance because of its involvement in the formation of secondary structures.
./files/site1/files/%D8%AC%D8%B9%D9%81%D8%B1%DB%8C_%D9%82%D8%B1%DB%8C%D9%87.pdf
Reza Mohseni Afkham, Dr Mojtaba Bahaaddini, Dr Abbas Majdi,
Volume 19, Issue 6 (12-2025)
Abstract
Tensile strength is one of the most important mechanical properties of brittle materials and plays a decisive role in the stability of many civil and mining structures. The Brazilian test is the most common indirect method for determining tensile strength and is widely employed. In this test, it is generally assumed that a central tensile crack initiates and propagates along the loading axis. However, the actual fracture process in the Brazilian test remains a controversial issue, and using curved loading platens has been recommended to better concentrate tensile stresses at the center of specimen. This study investigated the influence of platen curvature on the estimated tensile strength and the fracture patterns. To this end, five types of platen with curvature ratios of 0, 0.50, 0.57, 0.67, and 0.80 were prepared. All tests were recorded using a high-speed camera to precisely capture the initiation and propagation of cracks. To minimize the effect of rock heterogeneity and obtain consistent results, synthetic specimens were used, and five samples were tested for each curvature ratio.The results indicated that increasing the platen curvature led to a higher estimated tensile strength. While the increase was negligible for curvature ratios up to 0.67, at the ratio of 0.80 the tensile strength was approximately 48% higher compared to 0.67. Analysis of fracture patterns revealed that at the curvature ratio of 0.80, the fracture mode shifted to an unstable and disturbed pattern, characterized by secondary shear cracks and the irregular propagation of the main crack.
