Accurate prediction of pore pressure evolution during fluid injection is essential for assessing reservoir performance and associated effective stress changes that may promote induced seismicity. Analytical solutions for pressure diffusion commonly assume isotropic permeability, whereas long-term numerical simulations often require large computational domains to reduce boundary effects. We investigate injection-induced pressure evolution over timescales comparable to geothermal project lifespans under hydraulic anisotropy, using analytical and numerical methods with finite and infinite elements. We derive a closed-form three-dimensional analytical solution for continuous point-source injection in a medium with permeability anisotropy. Our closed-form analytical solution shows that the permeability component along a given axis governs the temporal pressure evolution, while the perpendicular components control the pressure amplitude. To identify limitations of numerical modelling for long-term scenarios, we compare analytical and numerical results for isotropic permeability. Boundary effects in conventional finite element models manifest earlier in materials with higher permeability. For an 8 km cubic Berea sandstone model, deviations increase from below 1.4% after 0.1 years to more than 40% after 10 years. Infinite elements reduce the maximum deviation below 0.56% over 10 years while also lowering computational runtime. Finally, we modelled a geothermal doublet to demonstrate how doublet orientation and permeability anisotropy jointly control pore pressure evolution. The combined analytical and numerical framework provides rapid pressure estimates and practical guidance for long-term modelling of geothermal and other subsurface fluid-injection systems.
This study addresses the transient high temperature generated by TBM disc cutter–rock friction and incorporates chemical corrosion and freeze-thaw damage as coupled environmental effects. To investigate the stability of calcareous sandstone-granite composite strata under these multi-damage conditions, a PZ contact model is developed in PFC3D, in which the contact stiffness degrades according to the nonlinear evolution of the elastic modulus observed under cyclic loading. Thermal-mechanical-environmental damage is then mapped onto the microscopic contact parameters through quadratic polynomial fitting, and the model is implemented via secondary code development to enable dynamic stiffness updating during computation. The model achieves relative errors within 3.77%, significantly outperforming the built-in parallel bond model. SPSS multivariate regression establishes inversion equations for microscopic parameters. FLAC3D-PFC3D coupling simulation of the Xiangshan Tunnel reveals that cutter cutting temperature is the primary driver of damage evolution. The worst working window of the single disc cutter occurs at 400°C and pH 7, and freeze-thaw damage peaks at 200°C and 14 cycles. Environmental damage and thermal damage exhibit nonlinear coupling-competition. The parameter optimization logic transforms with cutter number: cutter spacing serves as the leading regulatory factor for single and double cutters, while cutter penetration becomes the most influential factor for triple cutters, with traditional spacing regulation experience invalidating under multi-cutter coupling. This research provides theoretical basis for TBM parameter optimization and support timing determination under complex thermal-environmental damage combinations.
The stabilization of gold tailings (GT) presents both geotechnical and environmental challenges due to their high moisture content, low strength, and heavy-metal content. Recent studies have independently examined the mechanical and leaching behavior of stabilized GT, highlighting the need for more comprehensive research investigating these behaviors in combination, particularly with alternative binders. This study evaluates a one-part alkali-activated binder (AAB) as an alternative to ordinary Portland cement (OPC), focusing on mechanical performance, microstructure, and leaching analysis. The AAB consisted of ground granulated blast furnace slag activated with sodium hydroxide and sodium silicate. GT specimens were stabilized with different binder contents, degrees of compaction, and curing times, and then subjected to unconfined compressive strength (UCS), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX), and leaching tests. AAB-stabilized specimens achieved higher strength at shorter curing times (UCS=8.55 MPa) than OPC-stabilized specimens at longer curing times (UCS=6.92 MPa). Microstructural analysis indicated the formation of a dense matrix of CASH gels, thereby increasing strength and stiffness. Leaching tests showed reductions of several metals, including Mn, Zn, and Cd, with Mn leaching reduced by up to 99.9%. However, AAB stabilization substantially increased arsenic (As) leaching under alkaline conditions, particularly with higher binder contents and longer curing periods. As concentrations increased from 0.014 mg/L in untreated GT to up to 2.1838 mg/L in the most highly cemented AAB treatment, exceeding the toxicity limit. Overall, AABs effectively enhance the geotechnical properties of GT for dry stacking applications. However, their high alkalinity may mobilize oxyanions such as arsenate. These findings highlight the need to integrate mechanical and environmental assessments when designing stabilization strategies for hazardous tailings.
