The characterization of the thermal properties of crushed rock samples is not experimentally straightforward. In the case of thermal conductivity, some authors estimate this property based on solid rock plugs (e.g. optical thermal scanning, split bar, line heat source) what is not a convenient approach for granular materials with variable grain sizes. On the other hand, the determination of the specific heat of rock samples is typically based on enthalpy balances (e.g. differential scanning calorimetry, DSC) by achieving thermal equilibrium between the hot sample immersed in a reference fluid at a constant temperature. However, such techniques require small-volume comminuted samples if the grain size of the rock forming minerals is significant. All of the previous methods require, in addition, precise information on the physical (grain density, porosity, etc.) and mineralogical properties of the materials tested. To cope with these problems, the preferred approach of some researchers when dealing with granular materials is to assess thermal conductivity by estimating its heat capacity based on cylindrically-packed volumes and then applying to the bulk a radial heat source and simultaneously measuring temperature in selected locations along the diameter of the cylinder. Then, the measured thermal conductivity is an average conductivity of the packed porous sample (i.e. a combination air-filled porosity and the solid grain skeleton). This contribution presents the experimental methodology applied to assess thermal properties in aggregate rock packs as well as the analysis of the results of several tests carried out with basaltic aggregates intended for thermal energy storage.

Understanding the structure of the porous network in chalk is essential for many fields such as unconventional reservoirs, geothermal energy, CO₂ storage, or engineering. First, the study described qualitatively and quantitatively the properties of the porous network of chalk, a major component of the upper crust of Champagne-Ardenne. The chalk studied comes from the Grand Mont quarries (Saint-Germain-la-Ville, France). The study utilized various techniques including water porosity, mercury injection porosity, capillary water uptake tests, P- and S-waves propagation velocities, and scanning electron microscopy. Non-destructive and high-resolution 3D imaging methods such as X-ray microtomography and nuclear magnetic resonance were employed to determine pore geometry. Secondly, chalk was studied to understand its behavior during fluid circulation experiments at contrasting temperatures (cold rock - hot water // hot rock - cold water). A set of 130 samples was tested in 4 devices in order to produce a circulation of fluids: i) 150 cycles of water uptake by capillarity were carried out on chalks heated to 80 °C or at room temperature, with water at 8 °C or at 80 °C; ii) 150 thermal shock damage tests were obtained by quenching the samples at 80 °C in water at 0 °C; iii) a continuous transfer of water (10 L) at 80 °C or at room temperature was carried out by means of a device using the call of air exerted by desiccators placed under vacuum; iv) 10 L in chemical equilibrium with chalk circulated in control samples (without thermal stress) thanks to the design of a constant charge permeameter. The results showed that the water weakening phenomena in the chalk are not irreversible and that the temperature variations did not significantly affect the porous network or cause internal damage. However, the circulation of cold water in chalk preheated to 80 °C led to a reduction in water connectivity, due to the recrystallization of calcium and carbonate ions saturating the fluid and to the thermal expansion of calcite grains during cyclic heating phases. On the other hand, this recrystallization did not necessarily lead to a reduction in the volume of the pores. For experiments involving continuous circulation, the water connectivity has been further reduced. The uninterrupted flow of fluids increased the chances of a grain detaching from its position and entering a pore, thereby rearranging the pore space.

Time-dependent effects play a significant role, accounting for up to 70% of total deformations in tunnels (Sulem et al. 1987) [Int J Rock Mech Min Sci Geomech Abstr 24(3): 145–154]. The focus of this study is to determine whether the information from convergence measurements in a tunnel section can be used to identify specific constitutive law parameters describing both the short-term and long-term behaviour of the ground. Due to scale effect, actual in-situ mechanical parameters may differ from laboratory test results. Thus, the main objective is to directly calibrate constitutive law parameters, such as elasto-plastic or elasto-visco-plastic, from in-situ convergence measurements. A fractional constitutive law, for which an analytical solution is available for the stress and displacement field around the tunnel, has been chosen to model the behaviour of the ground. The use of fractional models is motivated by their ability to capture the time-dependent response of the ground with a good accuracy. Compared to classical constitutive laws, fractional laws enable to better describe the creep behaviour of the rock mass with a number of parameters that is significantly reduced (e.g., Caputo and Mainardi, 1971 [Pure Appl. Geophys. 91: 134–147]; Bagley and Torvik, 1983 [AIAA J, 21: 741–748]). This problem is framed as an optimization search, aiming at minimizing the squared error between convergence data points and the constitutive model predictions. Two approaches are combined to assess tunnel wall deformation: one empirical and one constitutive. The empirical convergence law (Sulem et al. (1987) [Int J Rock Mech Min Sci Geomech Abstr 24(3): 145–154] enables the extrapolation of convergences to long-term scenarios, serving as the basis for the optimization process subsequently applied to a specific constitutive law. The proposed method permits to characterize both the short-and long-term ground behaviour which can ultimately improve tunnel design. The method provides a means of calibrating constitutive parameters for implementation in numerical models and of assessing the long-term ground-lining interaction.

Solar energy installations are a prominent renewable energy source, requiring robust foundation systems to ensure their structural stability, cost-effectiveness, and long-term performance. This study presents a comprehensive assessment of the lateral load resistance of short socket piles for solar plant foundations in Bosnia and Herzegovina through experimental testing and numerical analysis. The experimental investigation was conducted to obtain data on the lateral load performance of the reinforced concrete bored piles. A total of 3 piles with a diameter of 40 cm and a length of 120 and 150 cm were installed for testing purposes. The pile socket depth, reached by the percussion drilling technique in dolomitic limestones, ranged from 20 to 50 cm, with the remaining upper portion of the piles being within clayey debris soil or highly fractured rock mass. Horizontal loading was incrementally applied at a point 20 cm above the ground surface, according to the procedure of the Quick load test outlined in ASTM D3966 – 07. The piles were tested until relatively large displacements were observed, ranging from 2.5% to 10% of the pile diameter, and unloaded to record the irreversible displacements. The test results indicate a notable increase in lateral pile displacement after reaching pile cap displacements ranging from 1% to 2.5% of the pile diameter, providing valuable empirical data for validation and calibration. To complement the experimental findings and gain deeper insights into pile behavior, a 3D numerical back-analysis approach was applied. The analysis included the nonlinear behavior of solid pile and rock mass elements supported by a discrete reinforcement embedded beam model. Good agreement between the model and measured data was obtained, indicating that the pile-rock mass system failed primarily due to reduced pile stiffness related to concrete cracking. Back-analysis results generally helped refine the understanding of pile-soil interaction mechanism, load distribution, and deformation patterns, enhancing the accuracy of predictions and design recommendations.

Coal mining presents several geotechnical challenges around the world. Limitations including data uncertainty and geological anomalies, coupled with risk acceptance in the form of “controlled” bench and inter-ramp scale slope failures in industry guidelines make slope collapsing an unavoidable and foreseeable aspect of economic rock slope designs in the mining industry. Technological advancements, such as three-dimensional slope stability modeling and ground-based interferometric synthetic aperture radar monitoring, in conjunction with traditional site investigation techniques such as drill core logging and face mapping, and remote sensing including photogrammetry and laser scanning, have proven to be successful in improving slope failure risk management. Improvements have included reducing personnel exposure to slope failure risks and earlier detection of emerging hazards which enable better remediation planning. This paper presents two case studies from coal mines in Colombia and Australia involving multi-bench, semi-ductile failures that were successfully managed using slope monitoring and response protocols. The data collected was utilized to improve geotechnical understanding enabling a more reliable forecast of future slope design risks and control measures to mitigate them.

In-situ stress knowledge involves the entire process of enhanced geothermal system (EGS) development, such as borehole stability, hydraulic fracturing propagation patterns, and mitigation of induced seismic risk. To eliminate the influence of high temperature, we employ the Anelastic Strain Recovery (ASR) technique for in-situ stress measurements in geothermal boreholes. ASR is a rock-core-based three-dimensional stress measurement method. Using the ASR method, we successfully measured the magnitude of in-situ stress at depths of 1500-4000m in China's first large-scale EGS site. To evaluate induced seismicity and fracture stimulation during EGS development, we simulated the variations in fracture slip tendency (Ts) near the injection well using the in-situ stress data. The results show that T_s is initially small, but as injection pressure increases to 46 MPa, the fractures reach a critical state (Tsmax=0.6), and further pressurization leads to gradual slipping of the fractures (Ts>0.6).