The Karavanke tunnel connects the highway A2 in the Republic of Slovenia with the highway A11 in the Republic of Austria on European corridor 10. It is a twin-tube, two lane tunnel, with total length 7864 m of which the Slovenian side is 3450 m long. The construction of the first tube was finished in 1990s while the construction of the second tube started in 2020 and is still ongoing. The construction of the tunnel was characterized by demanding and diverse geological conditions, high overburden of up to 900m, and occurrence of methane and high-pressure water ingresses. The subject of the research is the section of the tunnel in the Lower Triassic (Werfen) formation, which consists predominantly of grey limestone and dolomite with lenses and nests of gypsum and anhydrite and red and grey clastic sediments (sandstone and claystone). The formation is tectonically lightly to moderately disturbed, except for a more prominent fault zone, where high water inflow was recorded during the excavation of the first tube and in a smaller amount occurred also during the excavation of the second tube. The rockmass stability was expected to be mainly discontinuity governed, with possible deeper failures along fault zones. Due to the occurrence of gypsum and anhydrite, the occurrence of swelling and squeezing was also expected. The sets of geological parameters for characterization of rock mass (GSI, RMR and BT), which were determined based on geological mapping during the excavation of the first tube, and from geological investigations, were compared with the parameters determined during the tunnel excavation. The latter were obtained based on the observation of the deformation field around tunnel and numerical back calculations, which were carried out to fit the measured deformations. The difference between rock mass parameters determined up-front and those back calculated is studied to derive variation between the two, with an aim to mitigate subjectiveness in the up-front definition of the parameters. Conclusions are developed to present a more objective methodology in determination of realistic parameters to characterize rock mass conditions applicable for tunneling in carbonate rocks.

Knowledge of the in situ stress which affects a rock mass is of great importance for underground excavations and tunnel design. The main method for measuring in situ stress in the laboratory is the determination of the Kaiser effect of a rock, which is a spectrum of acoustic emissions (AE) that can be interpreted as a stress memory effect based on the hypothesis that samples remember the stresses to which they were previously subjected. The present communication describes in situ stress characterization through the determination of the Kaiser effect for the San Marcos tunnel project, which is part of the high-speed railway line in Gipuzkoa, in the Astigarraga-Irún section. For the study of in situ stresses, data from 5 groups of representative samples of the studied materials were compared. For each sample, 4 sub-samples were obtained, 1 vertical and 3 horizontal, arranged at 45º to each other to determine the Kaiser effect for different orientations. Kaiser points were determined when subjected to uniaxial compression with a criterion based on the energy of the AE emitted per unit of time. This criterion allows for a clear separation of noise from the real physical effects that produce AE. In addition, a comprehensive laboratory characterization of the samples was carried out through determination of uniaxial compressive strength for each sample with measurements of the elastic moduli, tensile strength through the Brazilian test, ultrasonic wave transmission velocities, and triaxial test strength, as well as mineralogical, petrographic, and textural characterizations using thin sections. The results show that minimum and maximum stresses are approximately arranged across the horizontal plane, while intermediate stresses are arranged across the vertical plane. The results are reasonably consistent despite some uncertainties, the main one being the orientation of the stress ellipsoid. There are also limitations associated with the homogeneity, lithology, and preparation and testing process of the samples themselves. Based on the results obtained, we conclude that the analysis of the Kaiser effect in laboratory samples is a technique that can provide useful information to determine the stress state of a rock mass.

Understanding the in-situ stress state as a function of depth, is a fundamental concern for optimal underground structures design, minimize geotechnical risks, and foster mining activities, especially in a geologically diverse region like the Canadian Shield. The assessment of stress-depth relationships in the Canadian Shield, predominantly built on statistical methods, revealed that solely relying on these tools might produce misleading interpretations. This research emphasizes the limitations of only depending on statistical tools, highlighting the need for an integrated approach that combines strong geological insights for comprehensive interpretation. Indeed, past relationships divided the in-situ stress data into depth domains were largely driven by statistical techniques, but such domains often overlooked the complex geology of the Canadian Shield. For instance, classifying zones deeper than 500-600m as undisturbed zones might not be universally applicable across the Canadian Shield. Our methodology deliberately disregarded geological influences to only assess the effectiveness of statistical tools in establishing stress-depth relationships in an expanded dataset of 330 stress measurements. The results highlighted the inadequacy of general depth domains. Also, clustering analysis methods such as K-nearest neighbor (KNN), Hierarchical, and the Normal mixture method were utilized to group the stress-depth dataset. While these techniques offered a structured method to identify the optimal number of depth-related clusters, the geological rationale behind these clusters remained unclear. Yet, the developed models for these clusters showed weak predictive accuracy. Moreover, the study assessed the efficacy of multivariable outlier detection methods such as Mahalanobis, Jackknife, T2, and KNN on the determination of in-situ stress-depth relationship. After initially removing identified outliers to refine the dataset, the regression outcomes remained unsatisfactory. This highlighted that some outliers might indeed have geological or tectonic significance. Rather than discarding them, their geological significance needs to be deeply analyzed. In fact, these extreme stress values might be attributed to unique geological or tectonic scenarios. In conclusion, while statistical tools offer valuable insights, a balanced integration of these tools with robust geological insights is essential to capture the complexities of in-situ stress-depth relationships in the Canadian Shield.

In the context of expansion phenomena rock structure refers to the availability of voids or fissures to allow the growth of gypsum crystals. Two case histories illustrate the significance of this concept. In a first case, a building founded on massive anhydrite of Triassic origin, experienced a sustained heave rate of its pillars. Swelling strains concentrate in the damaged upper 3-4 m of the rock. Pillar footings were underpinned by micropiles designed to avoid the upward friction induced by the active layer. The second case describes the heave of deep piled foundations of the pillars of a railway bridge. Continuous extensometers identified a 12m thick active layer below the pile tips. Hydraulic cross-hole test identified a fractured anhydritic claystone, initially unsaturated, that received water inflow from a shallow aquifer because of the construction of piles and reconnaissance borings.

The suitability of a sandstone from Central Italy as armourstone source, was investigated at the specimen and block scale. Once the physical properties were determined, the rock material was subjected to ultrasonic pulse, mechanical and wear/durability tests. The re-sults were linked to the petrographic features observed at the optical and scanning electron microscope. Possible defects in blocks were investigated through drop tests and by com-paring wave velocities measured on specimens and blocks. The rock has good physical, mechanical and durability index properties, whilst its wear resistance addresses the use of blocks in moderately stressing conditions (e.g. internal harbour areas). Blocks can be downgraded if affected by diffuse oxidation, as it is associated to a reduction of physical and mechanical properties.

It is known that some organisms can bore holes in rock formations consisting of such as limestone, sandstone and tuff. The authors investigated some sites in the Ryukyus Islands, Japan and found many examples of rocks bored by organisms. This study is concerned on the role of several organisms on the toe erosion along sea cliffs and their subsequent collapse. The authors carried out some observations on bio-erosion state and causes of rocks along sea-shores with cliffs in several major islands of Ryukyu Archipelago. Rocks are various depending upon the geology of each island surveyed. The erosion state and porous structure of rocks and their effect on their mechanical strength are assessed. Some available mechanical stability assessment methods are utilized to assess the stable and collapsed cliffs surveyed. It is understood that the most likely mechanism would be the dissolution of constituents of rocks by the mechanical excavation or enzym/salvia produced by these organisms and their subsequent discharge of debris from the holes as the UCS of rocks are generally greater than 25MPa. The length of bored holes is generally 5-15 cm with a diameter of 1-25 mm. The bored rock sites are found to be within the tidal and splash zones. Besides, the action of sea waves resulting from high waves caused by hurricanes and typhoons imposing some impact type forces, porous structures resulting from bored holes by organisms cause the strength reduction and cyclic degradation, which can be evaluated from the method utilized in this study. Therefore, the cliff stability can be asssed with the incorporation of the role of bio-erosion. It is anticipated that this study would be quite unique by bringing different disciplines of science and engineering together to this special kind problems and provide some scientific answers to the problems encountered in nature.