The knowledge of nanoscale mechanical properties of montmorillonite (MMT) with various compensation cations upon hydration is essential for many environmental engineering-related applications. This paper uses a Molecular Dynamics (MD) method to simulate nanoscale elastic properties of hydrated Na-, Cs-, and Ca-MMT with unconstrained system atoms. The variation of basal spacing of MMT shows step characteristics in the initial crystalline swelling stage followed by an approximately linear change in the subsequent osmotic swelling stage as the increasing of interlayer water content. The water content of MMT in the thermodynamic stable-state conditions during hydration is determined by comparing the immersion energy and hydration energy. Under this stable hydration state, the nanoscale elastic properties are further simulated by the constant strain method. Since the non-bonding strength between MMT lamellae is much lower than the boning strength within the mineral structure, the in-plane and out-of-plane strength of MMT has strong anisotropy. Simulated results including the stiffness tensor and linear elastic constants based on the assumption of orthotropic symmetry are all in good agreement with results from the literature. Furthermore, the out-of-plane stiffness tensor components of C₃₃, C₄₄, and C₅₅ all fluctuate with the increase of interlayer water content, which is related to the formation of interlayer H-bonds and atom-free volume ratio. The in-plane stiffness tensor components C₁₁, C₂₂, and C₁₂ decrease nonlinearly with the increase of water content, and these components are mainly controlled by the bonding strength of mineral atoms and the geometry of the hydrated MMT system. Young’s modulus in all three directions exhibits a nonlinear decrease with increasing water content.

Efficient fracturing is the key issue for the exploitation of geothermal energy in a Hot Dry Rock reservoir. By using the laser irradiation cracking method, this study investigates the changes in uniaxial compressive strength, ultrasonic characteristics and crack distributions of granite specimens by applying a laser beam under various irradiation conditions, including different powers, diameters and moving speeds of the laser beam. The results indicate that the uniaxial compressive strength is considerably dependent on the power, diameter and moving speed of the laser beam. The ultrasonic-wave velocity and amplitude of the first wave both increase with a decreased laser power, increased diameter or moving speed of the laser beam. The wave form of irradiated graphite is flattened by laser irradiation comparing with that of the original specimen without laser irradiation. The crack angle and the ratio of the cracked area at both ends are also related to the irradiation parameters. The interior cracks are observed to be well-developed around the bottom of the grooving kerf generated by the laser beam. The results indicate that laser irradiation is a new economical and practical method that can efficiently fracture graphite.

The behavior of soil–structure interfaces under varying thermal conditions is crucial for the design and stability of geotechnical structures subjected to temperature fluctuations, such as energy piles and underground structures. This study investigates the impact of temperature variation and cycling on the shear strength of the concrete–reconstituted silty clay interface using a custom-designed direct shear apparatus equipped with a temperature control system. Three test series were considered: constant temperatures of 30, 40, 50, and 60 °C; single heating–cooling paths of 25–30–25, 25–40–25, and 25–50–25 °C; and one to three cycles between approximately 25 and 50 °C. Normal stresses of 100–400 kPa were applied, and shearing was conducted at 0.02 mm/min. The interface generally exhibited a strain-hardening response, and its terminal shear stress increased with normal stress but decreased with increasing temperature. In the constant-temperature series, heating from 30 to 60 °C produced a maximum measured reduction of 12.72% in interface shear stress. The apparent interface adhesion decreased from 17.09 to 9.38 kPa, a reduction of 45.11%, while the apparent interface friction angle decreased from 38.66° to 36.50°. Increasing the single-cycle temperature amplitude reduced the fitted apparent interface adhesion and friction angle by 21.65% and 3.05%, respectively. From one to three thermal cycles, these parameters decreased by 18.45% and 9.07%, respectively. The results indicate that temperature level, heating–cooling amplitude, and thermal cycling can modify the measured interface response. The findings highlight the need to consider representative thermal histories when characterizing interfaces for thermally active geotechnical systems.

Classical molecular dynamics (MD) simulations were performed to systematically investigate the swelling behavior, hydration mechanisms, and mobility of interlayer species in Na‐, Cs‐, and Ca‐montmorillonite (MMT) over a wide range of water contents. The results show that hydrated MMT exhibits an initial stepwise crystalline swelling, followed by an approximately linear osmotic swelling phase. Thermodynamic analyses demonstrate that Cs ⁺ ions effectively inhibit MMT swelling—advantageous for nuclear waste disposal—while Na ⁺ and Ca ²⁺ promote swelling to varying extents, with Ca ²⁺ having the most pronounced effect. Structural analyses reveal that interlayer water molecules preferentially form hydrogen bonds with adjacent bridging oxygen atoms; furthermore, the average hydrogen bond number in the interlayer exceeds that of bulk water, indicating stronger aggregation. At thermodynamic equilibrium, the system attains a stable state characterized by local maximum density and minimal atomic free volume, with the density of interlayer water slightly exceeding that of bulk water. The self‐diffusion coefficients of interlayer species are significantly reduced compared to aqueous solution due to confinement by the clay surfaces. Among the investigated cations, the sequence of diffusion coefficients is Cs ⁺ > Na ⁺ > Ca ²⁺ , reflecting differences in their hydration shell structures. These findings provide new atomistic insights into the coupled swelling, hydration, and transport phenomena in clay barriers relevant to nuclear waste disposal and geotechnical engineering.