Argillaceous and anhydritic rocks, along with rocks containing pyrite, are prone to swelling by adsorbing water, leading to an increase in volume or external pressure due to deformation constriction. This swelling behavior can have adverse effects on underground openings, potentially compromising their serviceability, and it can also pose a risk to structural safety. The swelling behavior of pure claystones (rocks without anhydrite) is well understood in the context of tunneling, with the swelling-strain relationship typically determined through oedometer tests conducted in laboratories. However, when dealing with rocks containing anhydrite, the processes associated with the anhydrite-gypsum transformation have only been partially explored. To gain comprehensive insights into these processes and address various related questions, additional types of tests beyond the one-dimensional oedometer tests are necessary. In this paper, we describe the setup of experiments and the corresponding testing procedure used to study the swelling behavior of rocks containing anhydrite. The results from a systematic test series serve as the data foundation for understanding the coupled mechanical and chemical processes responsible for swelling behavior. By better comprehending these mechanisms, we can enhance our understanding of the rock's behavior under various conditions and potentially improve the safety and stability of underground structures.

Crystalline rocks such as granite and gneiss, sedimentary rocks such as mudstone and clay rocks, tuff belonging to volcanic rocks, and rock salt are considered as host rocks for deep geological repository for high-level radioactive waste worldwide. In Korea, all of the above rock types are distributed except rock salt. Considering the distribution of rock types by area, granite took up 30%, metamorphic rock 30%, sedimentary rock 25%, and volcanic rock 6%. In order to evaluate the suitability of the rock types distributed on the Korean Peninsula as the host rocks for deep geological disposal of high-level radioactive waste, the Korean peninsula was divided into four tectonic structures, and then various multidisciplinary analyzes were performed with deep drilling on the four rock types of granite, gneiss, sedimentary rock, and volcanic rock. Based on the literature and information obtained from deep drilling, considering the geological and rock mechanical characteristics, granite among crystalline rocks and Jinju formation and Jindong formation among various sedimentary rocks were derived as proposed candidate rock types. For the derived rock types, multidisciplinary geological information will be obtained through additional multidisciplinary data review, analysis and further detailed investigation. This information is intended to provide basic data that can be used by high-level radioactive waste project agencies when deciding on candidate sites and rock types.

The Rhenodanubian Flysch Zone of Austria comprises cretaceous claystones, siltstones, sandstones and marly limestones. Such rock types are often referred to as weak or soft rocks due to their behaviour when exposed to water or subject to mechanical load. Even though the rock types appear quite uniform on a macroscopic level, they can exhibit a broad variety of geomechanical properties. In this study, the flysch rocks were investigated with respect to their slaking durability, uniaxial compressive strength, abrasivity and mineralogical composition. The influencing factors affecting material behaviour and correlations of different mineralogical-petrographical and rock mechanical parameters are elaborated. It is shown that granulometric and mineralogic properties correlate well, and that the presence of carbonate minerals can favour the slaking resistance. Sheet silicates seem to affect slaking only after many testing cycles. While the rocks exhibit a wide range of slaking durability and low to moderate strength, abrasivity is limited to low values. Unlike in crystalline rocks, quartz imposes less influence on durability, abrasivity and strength. The correlations of engineering rock properties of these soft rocks are weaker compared to those of grain bound crystalline rocks making their characterization and classification challenging.

Stress polygons defined by the Coulomb failure criterion play an integral role in earth sciences and geology for the classification of crustal stress regimes. While the minimum principal stress (σ3), pore pressure, and friction angle of the rock considerably influence rock strength, the intermediate principal stress (σ2) also plays a crucial role. In conventional stress polygons, the boundaries of rock strength are represented by straight lines based on the Coulomb failure criterion. However, when considering σ2, these boundaries should ideally be drawn as curved lines. In our study, we redefined the stress diagram by involving σ2, using true triaxial test results and the Mogi–Coulomb failure criterion. This approach revealed notable visual discrepancies in rock strength boundaries compared to those defined by traditional Coulomb failure criterion. Our findings underscore the importance of incorporating σ2 in failure criteria to accurately draw rock strength in stress diagrams.

A series of laboratory tests have been performed to assess the effects of progressive de-formation on the elasticity and compressive strength of the VQ rock sequence. Specimens of basalts and pyroclastic rocks were obtained from twelve boreholes drilled with depths between 40 and 160 m. UCS tests were performed on a highly stiff and fatigue-rated load frame model MTS 815. Specimens were subjected to increasing-amplitude cyclic loading experiments. Changes in the elastic properties were observed in both sedimentary and vol-canic rock types as the rock approached the rupture. A significant difference in strength was obtained, with UCS values ranging between 13.5 and 23.97 GPa for the basalt, and be-tween 0.96 and 1.27 GPa for the pyroclastic sequence. Our results suggest that the differ-ences in stress failure may explain the debilitating nature of the contacts between basalts and pyroclastic rocks that might explain ground ruptures.

Mode I fracture toughness (K_IC) is one of the most important parameters for predicting and preventing catastrophic failure of cracked structures in brittle material. Several laboratory methods have been suggested to determine the mode I fracture toughness. However, many of them require lengthy sample preparation procedures, premature failure of samples, and difficulties in obtaining the precise value of the fracture toughness property. In this paper, the recently proposed pseudo-compact tension (pCT) method is used to evaluate the crack length effect on mode I fracture toughness in an isotropic homogeneous material, benefiting the advantages of this method including; simplicity of the test, high level of test control and high accuracy of the K_IC value. For this purpose, several disc shaped PPMA samples were loaded in pure tension by performing pCT tests. Digital image correlation (DIC) method was utilized to assess and monitor the distribution of the deformation field during the tests. DIC results were also used to compare the effect of crack length on the deformation field variation in samples. Very good agreement was found between the K_IC values estimated in this study and those reported in the past for the similar material; indicating that the pCT method is convenient for the assessment of K_IC. The experimental results also show that the initial crack length has a net impact on K_IC, although the magnitude of its influence is closely related to material structure and type. According to the obtained results, an increase in the initial crack length leads to increase the ultimate displacement at failure point, decrease the maximum load, and finally decrease the mode I fracture toughness of the material.