The Callovo-Oxfordian claystone (COx) is an anisotropic rock formation that serves as the host for the envisaged deep geological repository for intermediate-level and high-level long-lived radioactive wastes in France. In this context, the construction of several T-shaped gallery intersections is a common technique used for accessing the surrounding cells. In this work, a numerical analysis of a T-shaped gallery intersection excavation at great depth in the COx claystone is presented. A Drucker-Prager elastoplastic constitutive law with shear strength hardening is used to describe the rock matrix and the inherent anisotropy is implemented using the fabric tensor approach. Simulations include galleries with circular cross-sections intersecting at a normal angle. The focus lies on the mechanical characterization of the zone around the intersection. The results highlight the plastic strain distribution around the main gallery walls. Furthermore, the extension of the plastic zone is presented.

This paper proposes an analytical approach for analyzing rock slope stability based on a three-dimensional (3D) Hoek-Brown (HB) criterion to consider the effects of 3D stress and strength. The 3D HB criterion, considering an associate flow rule, is utilized to describe the perfectly-plastic behavior of rock mass under a plane strain condition. To reflect the change of friction angle on the failure surface, the potential failure surface (PFS) is divided into small segments with each segment being assigned a unique friction angle. The upper bound theorem of limit analysis is combined with the strength reduction method to determine the factor of safety (FOS) of a rock slope with a defined PFS. By optimizing the PFS, the minimum FOS and the critical failure surface (CFS) of the rock slope are obtained by the customized genetic algorithm. The proposed approach is validated by comparing it with an HB criterion-based solution and numerical simulations. Parametric studies are also performed to investigate the effects of rock mass properties, slope geometry, and loading conditions on the FOS and CFS. The results indicate that ignoring the 3D stress and strength of rock leads to underestimation of FOS and it is important to consider the various factors when evaluating the stability of a rock slope. For the effortless application of the proposed approach, a Python-based graphical-user-interface application is developed as a stand-alone executable app and is successfully applied to analyze a rock slope.

Dionyssos marble quarry is located 30 km from Athens and it is an important quarrying site in Greece. Apart from standard commercial purposes, it is also used for the restoration of the Parthenon as it is part of the same marble deposit that was used for the construction of Athenian Acropolis monuments in the 5^th century B.C. The Dionyssos marble is a fine-grained metamorphic marble exploited partly open-pit and partly underground. The modern times exploitation started in 1949. The increased demand for ornamental stones has led to intensive exploitation of the existing marble quarry. The gradual depletion of surface deposits is a direct consequence of this increase. For this reason, the company proceeded to exploit part of its deposit using underground methods, which have the added advantage of minimal environmental footprint. By applying the method of room and pillars, openings up to 15 meters wide are achieved, while the maximum height of the rooms is 30 m. In this research the future underground development is considered. It is envisaged at the higher level of the two existing underground openings and will consist of five rooms in the North-North-West direction excavated in six stages and two rooms in the North-North-East direction excavated in twelve stages. Support measures only include resin rockbolts of length adapted to pillar or roof installation. A set of advanced numerical simulations of the room and pillar gradual development and support is performed using a different numerical scheme for the evaluation of the stability; the distinct element method is used so as to include the effects of macro-discontinuities affecting the stability of the pillars during the top-to-bottom development of the marble extraction. Extensive laboratory tests have been performed on rock samples and the effect of scale on the peak compressive strength is also taken into consideration. The results of the analyses have shown that the stability of the exploitation is secured for the specific underground development.

The swelling of anhydritic rocks is responsible for severe damages to numerous tunnels. Alt-hough the first problematic cases were recorded more than a century ago, there are still knowledge gaps concerning the swelling behaviour of anhydrite, which introduce uncertainties in tunnel design. A major uncertainty relates to the magnitude of the developed strains due to the anhydrite to gypsum transformation, which depends inter alia on how gypsum crystals will grow. The latter may be influenced by the porosity, specifically whether the new crystals will grow within the available pore space or push the particles apart causing expansion. This paper investigates this effect by means of experimental tests conducted on artificial specimens of an-hydrite and kaolin powders. It is shown that, ceteris paribus, the strain developing during the anhydrite to gypsum transformation decreases with increasing initial porosity. The presented experimental results are valuable for better understanding of the observed phenomena.

The unloading disturbance during the excavation process in rock masses can significantly affect the safety of deep underground structures, especially when encountering rock frac-tures. In this study, the unloading process of normal stress was conducted using three dif-ferent levels of unloading rates. Simultaneously, the acoustic emission (AE) technique was employed to monitor the growth of microcracks at the interface. The recorded AE count, AE energy and calculated AE b-values were compared with the evolution of stress and displacement to confirm the correlation between AE signals and unloading behaviour. The experimental results revealed that the stress state associated with a low unloading rate is closer to the failure envelope compared to high unloading rates. During the unloading pro-cess, the maximum AE count, the highest AE energy, and the sudden decrease in b-value can serve as indicators that facilitate short-term prediction of failure sliding.

Explosive-free rock breakage methods have been the subject of increasing research in the past three decades as they are considered more environmentally friendly than traditional rock fragmentation with explosive energy. This paper summarizes the results of research findings on rock breakage with expansive cement, also known, soundless chemical demolition agents. Expansive cement is a powdery material that expands upon curing in a borehole causing it to eventually fracture. Expansive cement is a commercially available product that is usually used in the construction industry for the demolition of concrete foundations. Only in recent years that interest in the use of expansive for mining applications has been on the rise. Some of the challenges faced with the use of expansive cement are 1) rock is considerably stronger and stiffer than concrete, 2) rock is subjected to confinement in-situ, and this would inhibit the breakage mechanism by limiting the expansion, and 3) expansive cement does not work well in cold climate conditions, which are frequently encountered in Canadian surface mines. This paper summarizes the results of experimental and numerical studies conducted to estimate the peak expansive pressure and its variation with host medium stiffness. Direct pressure measurement is used to validate the classical analytical method employed for pressure estimate using instrumented thick-walled steel cylinders of different expansive cement borehole diameters and wall thicknesses. A series of rock slabs from Stanstead granite is then tested with a central hole injected with expansive cement and subjected to uniaxial compressive stress of 5 MPa. The results are compared with those obtained from unloaded rock slabs. Expansive cement breakage performance is measured by the time of first fracture (TFC) and the minimum demolition time (MDT). Another series of tests examined the potential benefits in terms of TFC and MDT of a relief hole (empty hole) in the vicinity of the injected hole under uniaxial pressure. Finally, an Extended Finite Element (XFEM) of the granite slab with expansive cement borehole is built with Abaqus software to help estimate the appropriate spacing between EC holes to achieve fragmentation. The results are used as design guidelines for rock fragmentation of boulders and uniaxially loaded pillars in the field.