Anhydrite and gypsum minerals in claystones are found in different configurations: isolated nodules, filled veins, continuous layers, massive bodies and combinations of these geometrical structures. Continuous or, better, quasi-continuous records of anhydrite and gypsum content measured in boreholes show frequently a marked spatial variability. This heterogeneity may explain to some extent the variability observed in surface heave measurements and swelling pressures measured against structures such as tunnel linings. An additional cause of observed heave and pressure concerns the presence of discontinuities and open pore space required for the precipitation of gypsum crystals. In all cases water should be present. The paper describes two cases that illustrate the relevance of spatial variability of swelling strains and its identification.The first case analyses the origin of the surface heave recorded in a large power station founded on an Eocene anhydritic marl, fairly homogeneous at a large scale. The marl heave was triggered by two modifications of the initial state of the marl: i) a large excavation and its induced vertical tensile strains capable of opening fissures along stratification planes and ii) the establishment of a table water level that wetted the marl through the open discontinuities. The paper describes long term records of heave strains measured by high precision extensometers, the model developed to quantify the surface heave and its comparison with long term records. In a second case, a highly instrumented concrete rigid circular tunnel lining provided data on recorded swelling pressures at the claystone-invert interface and on the measured strains in reinforcing steel bars. This information was processed to derive the histogram of observed stationary boundary swelling pressures. In addition, the strains records measured on the lining reinforcement provided a benchmark for the 3D model built to relate swelling pressures and internal lining stresses. The procedure led to an approximation of the distribution and intensity of swelling forces against the tunnel lining. This analysis, based on long term real data, helped to define new design criteria, more accurate and substantially cheaper, for tunnels excavated in the same geological formation. The paper concludes by suggesting a set of recommendations to limit the risk of damaging swelling of anhydritic rocks and some comforting actions which may be adopted when the swelling phenomenon has initiated.

Since the advent of LiDAR and structure from motion (SfM) techniques, GB-InSAR and thermal imaging, etc. the study of the hazard of failure of the rockfall sources has drastically changed. First, cloud points allow to characterize structures and assess the rockfall source volume distribution by periodic acquisitions, which is fundamental for rockfall hazard assessment. Several studies have shown that volume distributions follow power laws. These distributions are nowadays crucial for real rockfall hazard assessment. However, they have inherent limitations, such as time steps sampling, or fragmentation degree after failure. Such an approach provides for diffuse hazards, i.e., the exact locations of the sources are not known, but also to better characterize the rockfall activity of the different rock source types and structures. When the source is located, the temporal probability of failure must be evaluated. This means that state of stability or rock mass degradation must be assessed. Using remote sensing methods several promising research avenues exist. This can be performed using monitoring rock mass strength degradation via high-resolution 3D tracking of cyclic deformations with hysteresis by 3D point clouds or GB-InSAR. These deformations can result from factors like groundwater circulations, thermal cycles, earthquakes, rainfall, etc. The thermal imaging of shallow rock instability can provide the extend of rock bridges and can be coupled with deformation. Several attempts have been made to extract from 3D point cloud discontinuity set characteristics such as spacing and trace length distributions, but several drawbacks exist such as recognition of traces on point clouds without available surfaces or the true distribution of trace lengths. Nevertheless, more and more solutions are developed. The geological strength index (GSI) can be evaluated using remote sensing such as thermal imaging or discontinuity characterization by 3D data. The GSI can be used to estimate the power-law parameters. One of the key challenges to enhance rockfall sources hazard assessment, it's essential to better understand these processes and their interplay with physical and chemical weathering. Because the erosion of weak rocks, such as marls, may help to understand the thermal and rainfall effects on rock mass degradation. In conclusion, high resolution remote sensing data support the understanding of external forcing on rockfall activity, in particular characterizing volumes distributions and deformations.

Rock engineering activities, such as underground constructions, mining works, and excavation of rock slopes, are responsible of a wide range of changes in the surrounding environment. These effects can significantly alter the rock mass behavior over time, triggering different processes that negatively affect its stability. For this reason, monitoring activities aimed at improving the knowledge of the rock mass response are extremely relevant to ensure safety during construction and operation, check the validity of design hypotheses, and assess the necessity of risk mitigation measures. Overall, the design of effective monitoring systems requires a multidisciplinary approach that considers a range of factors, including geology, engineering, and data science, due to the inherent complexity of the subject. All these expertise play a key role in the development of a procedure able to provide critical information for safe and effective management of rock mass infrastructure. The first challenge involves the selection of the appropriate parameters to monitor. This requires a deep understanding of the observed element and the potential hazards that may arise, as well as the knowledge of the available technology for measuring and recording data. Due to the wide variety of physical quantities to sample, more advanced systems nowadays are designed to integrate multi-parameter devices, able to gather various information at the same time. The second challenge relates to the design of a system that can effectively collect and process the data. This requires careful consideration of factors such as the type and location of sensors, the frequency of data collection, and the method of data transmission and storage. The last key challenge in designing monitoring systems in rock masses involves the selection of the best approach for data integration, elaboration and management. This aspect is especially important when automatic instrumentation is implemented in the monitoring activity. These devices are, in fact, able to reach extremely high sampling frequencies, and the large volumes of data generated by such systems can be difficult to process and interpret. Additionally, it is important to ensure that the data is properly stored and easily available to facilitate its use in decision-making processes. This requirement can be fulfilled with the implementation of appropriate visualization platforms, designed to manage all collected information and to provide a reliable tool for their representation.

All along this lecture we will argue the benefits of integrating structural geology into rock engineering. Despite ISRM’s recommendations, we will also expose the very low percentage of tunnelling or dam projects involving structural geologists and more generally the widespread lack of structural geology expertise in civil and rock engineering projects, its consequences and associated missed opportunities. Standard geological studies are usually not enough to provide adequate level of details and quantitative assessments but this can be done with structural geology which allows us for instance to link fractures’ geometry, stress conditions and hydraulic conductivity no matter the scale, from small (e.g. a tunnel face), to large (e.g. full site). We will provide a suite of concrete examples coming from real-world site investigations, from design to construction, in order to illustrate these major benefits of structural geology in rock engineering. Structural geology is too often reduced to the manual or remote measurement of fractures to elaborate stereonets and distinguish fracture sets, frequently without any overarching assessment of the structure of the site in question. Whilst the use of structural geology is widely accepted and developed in oil & gas industry, especially during investigatory studies, it is not so in civil and rock engineering projects. One explanation is that engineers struggle with geological observations and the establishment of a diagnostic based upon too few or incomplete sets of data. One way to overcome this challenge is to build multi-disciplinary teams with both structural geologists and rock engineers which brings a plurality of perspectives and complementary skillsets. However, hiring both structural geologists and rock engineers will usually increase costs which may explain why it is not often considered. More important, during the last decades there has been a real decline in structural geology university courses around the world, supplanted by “new” disciplines often linked to the environment, so that even when the need for structural geology is understood, geologists with the right training and skillset are not always available. Whilst the ISRM could be more vocal about its recommendation to use structural geology in industrial and research projects, it cannot on its own change our mindsets. Consequently, we argue that individuals also have a responsibility to promote and embed structural geology in all rock engineering projects, from industry to research projects. We show one way forward on how this can be done, on the job or at industry and academic events.

The key role of the shear strength of discontinuities and rock joints in the behavior of rock masses and in the safety of rock engineering projects where stresses are low when compared with the rock intact, such as dam foundations, slopes and surface excavations, or underground tunnels and caverns, is for long acknowledged. Several failure criteria – namely, Coulomb, Patton, Barton and Grasselli – can be used to derive design parameters from results of field investigations, mainly laboratory tests. The keynote will address some particular issues related to the shear behaviour of rock joints that can be found along the path between field investigations and design parameters: in situ versus lab tests and scale effects, joint surface roughness and its influence on the stress distribution along the joints, roughness wear and repeated shear tests on the same joint sample.