The seepage action of underground water accelerates the deformation of roadway surrounding rock in deep mines. Therefore, the study of creep characteristics of surrounding rock under seepage action is the basis for the stability control of roadway surrounding rock in deep water-rich areas. In this paper, a seepage-creep coupling test system for complete rock samples was established. Combined with a scanning electron microscopy (SEM) test system, the seepage-creep law of coal measures sandstone and the damage mechanism were revealed. The study results showed that the maximum creep deformation of sandstone under natural and saturation state decreased gradually with the increase of confining pressure, and the maximum creep deformation under saturation state was greater than the corresponding value under natural state when the confining pressure was same. When the confining pressure was constant, the creep deformation, the constant creep deformation rate and the accelerated creep deformation rate of sandstone increased rapidly with the increase of infiltration pressure. With the change of time, the change of permeability parameters went through three cycles; each cycle was divided into two stages, slow change stage and rapid change stage, and the rate of variation increased with the increase of the seepage pressure. Based on the macroscopic and microscopic characteristics of sandstone rupture, the connection between macroscopic and microscopic mechanism on sandstone rupture was established. The results in this paper can provide a theoretical basis for stability control of roadway surrounding rock in water-rich areas.

The equivalent pipe network (EPN) model is an effective way to model fluid flow in large-scale fractured rock masses with a complex fracture network due to its straightforwardness and computational efficiency. This study presents the EPN model for characterizing fluid flow through three-dimensional fracture networks using the Monte-Carlo method. The EPN model is extracted from an original three-dimensional discrete fracture network (DFN) model and is used to simulate the fluid flow processes. The validity of the proposed EPN modeling approach is verified via the comparisons of permeability (k) with analytical solutions and simulation results reported in the literature. The results show that the numerically calculated k using EPN models agrees well with the analytical values of simplified DFN models and the simulation results of complex DFN models. The k increases following an exponential function with the increment of mean length of exponentially distributed fractures (u), which is strongly correlated with fracture density (P₃₂) and average intersection length (L_i). The P₃₂ increases in an exponential way with the increment of u. The L_i increases as u increases, following a power-law function. The increment of u leads to the increment of a number of long fractures in three-dimensional DFN models. A larger u results in a denser fracture network and a stronger conductivity when the number and length distribution range of fractures remain the same. The representative elementary volumes (REVs) of three-dimensional DFN models with u = 9 m and P₃₂ = 0.4 m²/m³ are determined as 2.36 × 10⁴ m³, 9.16 × 10³ m^3, and 1.26 × 10⁴ m³ in 3 flow directions, respectively.

Based on the triaxial test, the elasto‐perfectly plastic strain‐softening damage model (EPSDM) is proposed as a new four‐stage constitutive model. Compared with traditional models, such as the elasto‐brittle‐plastic model (EBM), elasto‐strain‐softening model (ESM), elasto‐perfectly plastic model (EPM), and elasto‐peak plastic‐brittle plastic model (EPBM), this model incorporates both the plastic bearing capacity and strain‐softening characteristics of rock mass. Moreover, a new closed‐form solution of the circular tunnel is presented for the stress and displacement distribution, and a plastic shear strain increment is introduced to define the critical condition where the strain‐softening zone begins to occur. The new analysis solution obtained in this paper is a series of results rather than one specific solution; hence, it is suitable for a wide range of rock masses and engineering structures. The numerical simulation has been used to verify the correctness of the EPSDM. The parametric studies are also conducted to investigate the effects of supporting resistance, residual cohesion, dilation angle, strain‐softening coefficient, plastic shear strain increment, and yield parameter on the result. It is shown that when the supporting resistance is fully released, both the post‐peak failure radii and surface displacement could be summarized as EBM > EPBM > ESM > EPSDM > EPM; the dilation angle in the damage zone had the highest influence on the surface displacement, whereas the dilation angle in the perfectly plastic zone had the lowest influence; the strain‐softening coefficient had the most significant effect on the damage zone radii; the EPSDM is recommended as the optimum model for support design and stability evaluation of the circular tunnel excavated in the perfectly plastic strain‐softening rock mass.

The weakly cemented rock layer is easily damaged under the combined effect of seepage and mining disturbance and creates massive engineering disasters. This paper uses the self-designed weakly cemented remodeling mechanism to prepare weakly cemented rock samples with clay minerals accounting for 20%, 30%, 40%, 50%, and 60% of the total. The MTS816 system, in conjunction with an acoustic emission system and a high-speed camera, completed mechanical and seepage tests on the sample. The results show that when the quantity of clay minerals increases, the uniaxial compressive strength, elastic modulus, and rapid crack propagation stress of the weakly cemented rock samples decrease. Initial stress of crack development increases and then decreases, as well as the sample’s failure mode changes from shear to tensile. The sample’s permeability increases with increasing osmotic and axial pressure differential but decreases with increasing confining pressure under the same amount of clay minerals. The sensitivity of permeability to changes in osmotic pressure differential, axial pressure, and confining pressure increases as the amount of clay minerals increases. The mechanical and seepage characteristics can show significant changes in clay minerals in 20% to 30%.

Determination of the representative elementary volume (REV) of fractured rock masses based on equivalent permeability () is significantly dependent on the geometric characteristics of fractures. In this work, a series of numerical simulations were performed to analyze the relationship between geometric characteristics of fractures and the REV size, in which fracture length follows a power-law distribution. A method to evaluate the of a three-dimensional (3D) discrete fracture network (DFN) by extracting the equivalent pipe network (EPN) model from the DFN model was utilized and verified. The results show that of the 3D DFN model has an exponential relationship with the power exponent () of fracture length distribution and the evaluation of agrees well with that reported in previous studies, confirming the reliability of the EPN model for calculating seepage properties of complex 3D DFN models. When the side length of submodels () is small, the varies significantly due to the influence of random number seeds used to generate fracture length, location, and orientation. The holds a constant value after exceeds some specific value. The critical model scale is determined as the REV size, and the corresponding volume of the 3D DFN model is represented by . The varies within a narrow range when . When , the rapidly increases to more than 3.4 times than that when . The fluid flow becomes more inhomogeneous due to the small nonpersistent fractures that dominate the preferential flow paths when exceeds a certain value (i.e., 4.5). The at the REV size decreases exponentially with the increment of . This tendency can be explained by the decrease of the average intersection length () with the increment of , which is a geometric parameter for reflecting the connectivity of the fracture network.

To address the engineering challenges associated with the high brittleness and poor crack resistance of coal-based solid waste grouting materials, this study systematically investigates the flexural performance and damage evolution characteristics of the material by incorporating various types and amounts of fibers into a matrix composed of coal gangue, fly ash, Portland cement, and sulfoaluminate cement. Macroscopic mechanical testing, digital image correlation (DIC) technology, and scanning electron microscopy (SEM) are employed to reveal the mechanisms by which fibers influence the grouting material. The results demonstrate that fiber type and dosage significantly affect the flexural strength and damage evolution behavior of the material. Among them, basalt fiber exhibits the most pronounced improvement in flexural strength at a dosage of 0.4%, achieving a 28-day flexural strength of 6.33 MPa, which is 73.9% higher than that of the control group. Similarly, glass fiber shows a flexural strength increase of 63.18% at a dosage of 0.8%. The fibers enhance the material’s ductility and promote the uniformity of the failure process through mechanisms such as crack bridging, energy dissipation, and optimized interfacial structure. Furthermore, joint analysis using DIC and acoustic emission (AE) techniques reveals that when the fiber dosage reaches 0.6%, the proportion of shear cracks during material failure significantly increases (12.78–16.13%), indicating that fibers improve the uniformity of strain distribution under loading, delay the propagation of the main crack, and thereby enhance the overall crack resistance of the material. These findings provide theoretical and technical support for the development of high-toughness and high-performance coal-based solid waste grouting materials.