Liang Cheng

Deep saline aquifers are considered promising sites for large-scale CO2 geological sequestration. However, interactions among supercritical CO2 (ScCO2), pore fluids, and rock minerals may alter shale pore structures and mechanical properties, potentially increasing CO2 leakage risk. In this study, Longmaxi shale was exposed to H2O–ScCO2 and brine–ScCO2 at 90 °C and 12 MPa for 14 days, followed by x-ray diffraction, nuclear magnetic resonance, and uniaxial compressive strength. Both treatments induced mineral dissolution, pore restructuring, and mechanical degradation, with stronger effects under brine–ScCO2 conditions. Dolomite and calcite contents decreased by 42.4%–52.8% and 30.8%–43.1%, respectively, while total porosity increased by 13.2% under H2O–ScCO2 and 18.1% under brine–ScCO2. The increases in the permeation-pore and overall fractal dimensions further indicate enhanced pore-network heterogeneity and geometric complexity, particularly after brine–ScCO2 treatment. Fluid–ScCO2 interactions also altered the pre-failure deformation and crack-evolution processes. Both treatments increased the relative proportions of the crack-closure and stable crack-propagation stages while reducing that of the elastic deformation stage, whereas the unstable crack-growth stage remained nearly unchanged. These changes were more pronounced under brine–ScCO2 conditions. Young's modulus decreased by 7.8% and 11.6%, respectively. Energy analysis revealed a shift from elastic energy storage toward energy dissipation, indicating weakened brittleness and more progressive deformation behavior after treatment. A segmented statistical damage model incorporating porosity related chemical effects and dissipated energy driven mechanical degradation effectively reproduced the initial compaction and pre-peak stress–strain response of chemically altered shale.

During the service life of karst tunnels, groundwater containing Ca²⁺ and CO₃²⁻ can migrate along the shotcrete–surrounding rock interface and induce calcite deposition, thereby changing the interfacial material composition and load transfer path. To clarify the effect of this process on interfacial bonding performance, this study used molecular dynamics simulations to construct CSH–SiO₂, SiO₂–calcite, CSH–calcite, and CSH–calcite–SiO₂ interface models. The interfacial density distribution, radial distribution function, number of hydrogen bonds, interaction energy, and normal tensile failure behavior were analyzed. The results show that all four models reached stable energy plateaus after relaxation, and clear atomic density overlap and short-range RDF peaks appeared in the interfacial regions. These descriptors indicate short-range contact and possible Ca–O electrostatic attraction, hydroxyl-related hydrogen bonding, and carbonate-associated interactions between calcite and both SiO₂ and CSH surfaces. Approximately 80 hydrogen bonds were formed at the SiO₂–calcite interface, approximately 32 at the CSH–calcite interface, and approximately 59 in total for the two hydrogen bond subtypes at the SiO₂–CSH interface, indicating that the hydroxyl state of different substrate surfaces controls the interfacial hydrogen bond network. Interaction energy analysis shows that the single CSH–calcite interface has the strongest interaction (−51,753.6 kcal/mol), approximately 1.90 times that of the SiO₂–CSH interface and 16.43 times that of the SiO₂–calcite interface. However, in the three-layer composite model, the interaction energy on the CSH–calcite side is only approximately 28.0% of that on the SiO₂–calcite side, suggesting that a continuous calcite interlayer introduces asymmetric interfacial constraints. Tensile simulations further show that the SiO₂–calcite model has the highest peak stress (approximately 3.23 GPa) and exhibits brittle failure, whereas failure in CSH-containing systems is more likely to transfer into the CSH layer or weakly connected regions. These results indicate that calcite deposition does not simply strengthen or weaken the interface. Instead, within the two idealized endpoint configurations tested here, its effect depends on deposition continuity, the surface chemistry of the two substrates, and the weak links within the serial interface. This study provides a nanoscale theoretical basis for evaluating relative trends in the long-term service performance of shotcrete–surrounding rock interfaces, and for guiding future multiscale validations of drainage and waterproofing measures in karst tunnels.

Understanding how reactive fluids alter rock-forming minerals at the molecular scale is critical for evaluating the durability of geological CO₂ storage. To address this, we used molecular dynamics (MD) simulations to quantify the structural and mechanical responses of quartz, clinochlore, diopside, and albite under H₂O-ScCO₂ conditions. All four minerals exhibit reductions in elastic modulus: albite 43.9%, diopside 27.6%, clinochlore 22.5%, and quartz 17.6%. These changes were accompanied by unit-cell expansion and structural relaxation. The energy partition shifts from bond-dominated to nonbonded interactions, most pronounced in albite and clinochlore. Radial distribution analyses show that the Si-O coordination remains close to four, preserving the tetrahedral framework, whereas the Al-O coordination in albite and clinochlore increases toward six, indicating a surface structural reorganization driven by the presence of H₂O-ScCO₂ and predefined cation vacancies, which effectively induces structural relaxation of the aluminosilicate framework, introduces structural disorder, and creates pathways for enhanced fluid permeation. In conclusion, these results reveal an atomistic weakening pathway in which hydroxylation and cation release enhance lattice disorder and reduce stiffness. The findings provide a mechanistic link between microstructural degradation and macroscopic weakening and inform long-term stability assessments of basaltic reservoirs for CO₂ storage.

Rockburst is a major safety risk in deep tunnel engineering, closely related to the propagation of fractures and energy release in rock masses. Therefore, a thorough understanding of the laws governing fracture propagation, energy release mechanisms, and their intrinsic relationship with rock failure modes is crucial for the prevention and control of high-energy events. This study, based on the geological characteristics of granite, utilizes PFC2D to establish a numerical model and calibrates the mesoscopic parameters using the trial-and-error method. The mechanical response and energy damage evolution characteristics of fractured granite under different fracture inclinations and lengths are systematically investigated. The results indicate that the inclination and length of fractures significantly affect the failure mode, energy release process, and the extent of crack development in the rock. The failure mechanism is mainly characterized by a shear-dominated, tension-assisted oblique shear-tensile failure mode. When the fracture inclination is 0°, granite is most prone to fracture. As the fracture length increases, the number of macroscopic cracks and the degree of failure reach their maximum when the fracture inclination gradually decreases (60°-30°-15°). A smaller YU value corresponds to greater energy release, an increased number of macroscopic cracks, and a higher degree of failure, which is more conducive to crack formation. A damage constitutive model for granite based on dissipated energy density is established, and the analysis shows good agreement between the theoretical and experimental curves. The results provide a theoretical basis for understanding rock mass failure and safety issues during deep tunnel excavation.

Granite strata is important for the construction of underground water - sealed petroleum storage caverns, and the distribution of fractures in the surrounding rock of the caverns is a crucial factor affecting the water - sealing effect of the caverns. In order to investigate the mechanical properties and energy evolution of the rock body in underground water-sealed petroleum storage caverns, compression test of granite, obtained the macroscopic parameters and damage modes of granite have been carried out; a numerical model is established by using PFC^2D to study the numerical test of the uniaxial compression of granite under the conditions of different slit inclination angles and lengths, and to analysis the mechanical properties and the evolution of the energy damage. The research results show that the inclination angle and length of fractures have a significant impact on the failure mode of rock, the energy release process and the development height of cracks. The failure mechanism is mainly manifested as a shear-dominated and tension-assisted shear-tension failure mode; when the fracture inclination angle is 0°, granite is the easiest to fracture, and with the increase of the fracture length, the macro cracks and the degree of damage of the specimen reach the maximum when the fracture inclination angle gradually decreases (60°-30°-15°). In addition, the smaller the YU value, the greater the released energy, and the number of macro cracks and the degree of damage also increase, which is more conducive to the generation of cracks. The research results can provide a theoretical basis for understanding the rock mass failure and safety problems in excavation of underground water-sealed petroleum storage caverns.

Choosing the reasonable and economical grouting parameters is crucial for controlling the seepage field of surrounding rock and tunnel stability. This paper adopted the fluid–solid coupling theory based on FLAC3D to establish numerous simulations on the stability of surrounding rock and lining structure in karst tunnels under the different grouting conditions. The influences of grouting layer thicknesses and their permeability coefficients on the mechanical behaviors of lining structure, seepage, and stress properties of surrounding rock were investigated. The results show that with the increase of grouting thickness and its ratio of permeability, the maximum flow velocity and flow rate per liner meter in surrounding rock, the bending moments and axial forces, and the horizontal and vertical displacements of the lining structure all exponentially decrease, but safety factors at different positions of the lining structure first rapidly and then slowly increase. The changes in safety factor and uplift displacement at the inverted arch are more significant, and the minimum safety factor occurs at the left arch foot. As the grouting thickness and its ratio of permeability increase, the plastic zone range in surrounding rock decreases and expands, respectively. Through considering the improvement effect and economy of grouting comprehensively, choosing a grouting layer thickness of 7–9 m and a ratio of permeability of 20–50 is an ideal configuration parameter to ensure the stability and safety of karst tunnels under the conditions of this paper. The research results could provide references for choosing the reasonable grouting parameters in karst tunnels.

Underground gas storage is an important technical measure for future natural gas storage. The stability of the surrounding rock during excavation and under ultra-high gas storage pressure is the key to the stable operation of gas storage reservoirs. A numerical calculation model for different surrounding rock conditions, different depth-span ratios, and different buried depth conditions was conducted to study the stability of surrounding rock after large section underground gas storage excavation and under an ultra-high gas storage pressure of 20 MPa. The results show that after construction is completed, the deformation of the rock surrounding the cavern increases with a decrease in the surrounding rock grade, and the deformation of the rock surrounding the cavern increases as the burial depth increases. In addition, the maximum vertical deformation of the surrounding rock decreases with the increase in the depth-span ratio of the cavern, and the maximum horizontal displacement increases with the increase in the depth-to-span ratio. While operating at 20 MPa gas storage pressure, the displacement of the rock surrounding the chamber tends to increase with the decrease in the surrounding rock grade and the deformation of the surrounding rock of the chamber decreases as the burial depth increases. Furthermore, the vertical displacement of the rock surrounding the chamber decreases with the increase in the depth-span ratio, while the horizontal displacement of the surrounding rock increases with the increase in the depth-span ratio. Considering the stability of the surrounding rock during construction and operation, gas storage chambers should be built in areas with better conditions, such as Grade II and Grade III surrounding rocks within a burial depth range of 200 m. Moreover, the stability of the surrounding rocks is better when the chamber depth-span ratio is 2.5~3.0. These research results can provide a theoretical reference for the design of large underground gas storage structures.

Submerged floating tunnels (SFTs) are an innovative traffic structure for transportation in deep and long-distance ocean environments. SFTs have the risk of being subjected to wave action in the complex ocean environment. Therefore, in order to ensure the safety and stability of SFTs during their service, the dynamic behavior of an SFT subjected to the action of waves is experimentally investigated in this study. Based on the wave–current flume, a physical scale-model experiment of an SFT for studying the dynamic behavior of an SFT subjected to regular waves interactions is deeply and thoroughly explored. The results show that the wave outputs from the wave-making system are verified to be reliable. The influence of major load parameters on the dynamic behavior of the SFT are deeply and thoroughly explored. The effects of wave height and wave period on acceleration, wave pressure, anchor cable force and displacement in an SFT are discussed. This experimental study has theoretical and practical significant for SFT design and safety.

Large quasi-elliptical cylinders are extensively used in ocean engineering. To enhance a better understanding of the hydrodynamic wave force on such quasi-elliptical cylinders during extreme events, a series of experiments on extreme wave interaction with a quasi-elliptical cylinder were conducted. A series of waves with various wave heights, wave periods, and wave incident directions were tested to investigate the wave parameter effect and wave directionality effect on the wave forces on the quasi-elliptical structure. The experimental results indicate that the extreme wave-induced forces on the quasi-elliptical cylinder are strongly correlated to the wave period and wave incident direction. The peak forces on the quasi-elliptical model do not vary monotonically with the increasing wave period but show an increase followed by a decrease. Both the longitudinal and transversal forces are significantly increased when the wave incident direction changes from 0° to 45° and the wave directionality effect is enhanced when the wave period is decreased. Additionally, the inertial force equation was applied to the wave force estimation for such quasi-elliptical cylinders, and the inertia coefficient C_M was fitted based on the experimental results of α = 0°.