Focusing on red bed soft rock from the Yuanma Basin, uniaxial compression tests, electron microscope scanning tests, and elastic P-wave velocity tests were conducted to study the changes over time in the mechanical properties, microstructure, and elastic P-wave velocity of the soft rock under different water saturation conditions. Digital image processing technology was used to quantify the characteristics of rock microstructure, and the varying characteristics of rock microstructure were quantitatively analyzed. Based on damage mechanics, a failure model for water-saturated red bed soft rock was established. The results show that the strength of red bed soft rock decreases by 14%, 27%, 39%, and 80% respectively after 1, 2, 3, and 5 days of water saturation. As water saturation time increases, the uniaxial compressive strength of red bed soft rock decreases monotonically, and its failure mode gradually transitions from brittle to ductile, with the angle between the rock’s fracture surface and the horizontal plane gradually diminishing. The number of secondary cracks surrounding the main shear fracture initially increases and then decreases. The proportion of defect area in red bed soft rock increases linearly with water saturation time, and the number of pores is negatively correlated with the average pore size, showing a trend of increasing initially and then decreasing. The P-wave velocity of the rock decreases as water saturation time increases, and the expdecl function is suitable for fitting the relationship between P-wave velocity and water saturation time of red bed soft rock. A damage model for water-saturated red bed soft rock was established, and the calculated values from the model were compared with the experimental values, verifying the accuracy of the model. It is concluded that this model can accurately predict the uniaxial compressive strength of rocks after different water saturation times through non-destructive testing and can better describe the damage characteristics of red bed soft rocks after saturation.

The application of static expansion rock fracturing technology has shown that drilling holes with sharp corners significantly enhances the fracturing effect due to the pronounced stress concentration effect. Therefore, it is of great significance to study the directional fracturing mechanism of static rock fracturing using quadrilateral holes with multiple sharp corners and to propose criteria for quantitatively analyzing the fracturing effectiveness. To this end, soft rock specimens with varying fractured rock areas, numbers, and shapes of drill holes were designed to conduct static expansion tests. The fracture processes and dynamic fracture mechanics behaviors of the specimens were monitored and analyzed using particle image velocimetry (PIV) technology and strain rosettes. Secondly, to quantitatively assess the fracturing effectiveness of the specimens, dimensionless parameters such as the average energy utilization rate, fracture time efficiency ratio, stress ratio, and fracture area ratio coefficient were introduced. The fracture coefficient was proposed as a comprehensive evaluation criterion. The results indicate that each specimen developed two main cracks along the angular bisectors of the quadrilateral’s sharp corners. As the cracks propagated, the peak stress and total energy decreased sequentially, while the fracture time lagged. For single-hole fracturing, the stress concentration effect of trapezoidal holes was 13.75% higher than that of rhombic holes, resulting in a better fracturing effect. For dual-hole interaction fracturing, the stress concentration effect of rhombic holes was 16.67% higher than that of trapezoidal holes, and the stress decay was slower. Among the combinations, the square-rhombic hole configuration had the highest average energy utilization rate at 62.66%. The fracturing effectiveness of the rhombic-trapezoidal hole combination was not significantly improved, with a fracture coefficient only 6.67% higher than that of a single trapezoidal hole. The square-trapezoidal hole combination exhibited the best fracturing effect, with a fracture coefficient of 1.15.

Due to the influence of fluctuation of reservoir water level, the joint surface of rock slope is affected by dry-wet cycles. The shear strength of joint surface after dry-wet cycles becomes one of the key factors to control the stability of rock slope. At present, the research on the shear damage constitutive of rock joint surface after dry-wet cycles is not sufficient. Taking the red sandstone in the Three Gorges Reservoir area as an example, we obtain the strength and deformation characteristics of red sandstone under dry-wet cycles by carrying out joint direct shear tests of red sandstone under different dry-wet cycle numbers, and give a modified Iwan joint surface shear damage constitutive model considering the effect of dry-wet cycles. The results show that the shear stress-displacement curve of the joint specimen is characterized by five stages: initial compaction, linear elastic deformation, pre-peak softening, post-peak failure and residual deformation. By introducing the Logistic model, the shear damage constitutive model of the joint surface can reflect the actual damage process of the joint surface and better describe the shear deformation behavior of the regular serrated joint surface in the compaction stage. There is a logarithmic relationship between the number of dry-wet cycles and the parameters of the modified Iwan shear damage constitutive model. Through laboratory tests, the accuracy of the modified Iwan joint surface shear damage constitutive model considering the effect of dry-wet cycles is verified. The model can effectively predict the relationship between shear stress and shear displacement of joint surface after dry-wet cycles. The research results can provide some reference for the study of shear slip failure mechanism and disaster prevention of rock slopes in the Three Gorges Reservoir area.

The method of incorporating tire-derived aggregate (TDA) into ballast not only has the advantages of reducing ballast crushing and vibration but also alleviates the increasing pressure of waste tire disposal. Due to its energy-saving, eco-friendly characteristics, among others, it has increasingly attracted the attention of researchers. However, current research primarily focuses on the effect of TDA content through laboratory tests, with relatively little research on the influence of other parameters. Particle shape is a crucial factor influencing the mechanical properties of granular geomaterials. Studying the dynamic properties and meso-effects of mixtures containing different shapes of TDA is a necessary foundation for enhancing our understanding and promoting the application of these methods. Based on the same TDA content and specimen void ratio, block, elongated, and flat TDA particles were mixed into ballast, and dynamic triaxial tests and discrete element simulations were conducted to compare and analyze the macro-level test results and meso-level effects of the ballast samples. The results show that the cumulative axial strain of ballast mixed with elongated and flat TDA is smaller than that of pure ballast, while the cumulative axial strain of ballast mixed with block TDA is larger than that of pure ballast; the reduction in dynamic elastic modulus caused by elongated and flat TDA is also smaller than that caused by block TDA. The dissipative energy and damping ratio of ballast mixed with elongated TDA are larger and develop stably. The damping ratio of ballast mixed with flat TDA is relatively small and gradually decreases with the number of loadings. Due to their shape characteristics, elongated and flat TDA primarily increase the coordination number between rubber particles, making the aggregate denser. Elongated and flat TDA can significantly inhibit the rotation speed and cumulative rotation angle of the particles, thus reducing the cumulative deformation of the samples

The collision and fragmentation patterns of rockfalls under the influence of joints were studied through physical experiments. Based on indoor collision tests, the discontinuous deformation analysis (DDA) parallel computing method was used to simulate the impact-collision-fragmentation process of rockfalls. The main focus is on discussing the influence of the angle β  between the joint and the slope, the connectivity rate k of the joint, and the impact velocity V of the rockfall on its crushing characteristics. The ratio η  of the surface area of the rockfall to its initial surface area is used as a quantitative measure of the degree of fragmentation, with a larger η  indicating a higher degree of fragmentation. The research findings are as follows: 1) η  increases with k; under high-velocity impact conditions, the η  value at k = 0.75 is 1.2 times that at k = 0.25. 2) When k = 0.25, η  does not vary significantly with β  ; however, when k = 0.50 and 0.75, η  decreases as β  increases. 3) The η  value under high-speed impact (6.8−7.4 m/s) is 1.5 times higher than that under low-speed conditions (3.5−4.5 m/s). 4) As the single-joint connectivity rate k of the rockfall increases from 0 to 0.75, the energy recovery coefficient exhibits a decreasing trend, with its value reduced by 1.6 to 1.9 times. 5) With the increase in impact velocity, the energy recovery coefficient of the rockfall gradually increases with the increase in joint angle β , up to 1.6 times. 6) The fracture characteristics and degree of fragmentation obtained through numerical simulation and indoor collision tests are basically the same. An increase in the single-joint connectivity rate and the angle between the joint and the slope surface affects stress propagation and alters the fracture characteristics of the specimens. 7) When a multi-jointed rockfall is impacted and broken, the cracks do not extend along the outline of the joint setting and do not intersect with joints far from the center of the rock. The velocity of the debris after impact is slightly lower than that before impact. This study has certain reference significance for revealing the collision and fragmentation patterns of rockfalls under the influence of natural joints.

Numerous studies have demonstrated that the strength and deformation characteristics of coarse-grained materials are significantly influenced by the initial particle size distribution (GSD). However, research on constitutive models for coarse-grained materials that consider this influence is still limited. In this study, we introduced an initial GSD index, ϑ, which reflects the ease of particle breakage and links the initial GSD to the ultimate GSD. We systematically investigated and elucidated the mechanism by which ϑ affects the peak shear strength (q_p), peak strain (ε_ap), and the position of the critical state line (CSL) on the e-p plane. The results regarding the effect of ϑ on qp and ε_ap indicate that as ϑ increases, qp decreases, whereas ε_ap increases. Based on these findings and the hump-shaped quadratic curve model proposed by Shen Zhujiang, we established a tangent Young’s modulus that considers the effects of initial GSD and confining pressure. The study on the effect of ϑ on the CSL position reveals that a decrease in ϑ leads to a downward shift and a counterclockwise rotation of the CSL. Subsequently, within the framework of critical state soil mechanics (CSSM), we proposed a state-dependent tangent Poisson’s ratio that considers the effects of initial GSD and confining pressure. For a specific type of coarse-grained material, the model only requires a set of model parameters, and the model’s high accuracy is evidenced by the good agreement between the modeling results and the experimental data.

Piles with non-circular cross-sections are characterized by their non-circular shapes. Due to their complex boundary conditions, their mechanical behavior differs from that of circular piles. Currently, there is a lack of theoretical analysis methods for the lateral dynamic response of such piles. In order to investigate the lateral dynamic response of these piles in homogeneous viscoelastic soil, the soil is approximated as a continuous medium, and the governing equations of the pile-soil system in Cartesian coordinates are derived based on the variational principle and Hamilton’s principle. The displacement function of the soil, considering complex boundary conditions, is solved using the partial differential equation (PDE) interface in COMSOL Multiphysics, while the displacement function of the pile is solved using the BVP4c function in Matlab. An iterative procedure is implemented in Matlab to obtain semi-analytical solutions for both the pile and soil displacement functions. The obtained results are compared with existing theoretical solutions for circular piles, showing good agreement. Analysis of the irregular-shaped piles reveals that, when the cross-sectional area is constant, the shape significantly affects the dynamic response at the pile head, with H-shaped piles exhibiting the highest impedance. When the cross-sectional moment of inertia is constant, X-shaped piles show the highest impedance. Taking X-shaped piles as an example, the impedance at the pile head increases with the pile-soil modulus ratio. As the length-to-diameter ratio increases, the resonance frequency and damping at the pile head decrease, while the stiffness at the pile head increases.

Investigating the strength behavior of rock under the combined effects of bedding plane inclination and confining pressure is fundamental to understanding the strength behavior of gently inclined mine pillars constrained by infill. Numerical simulation was employed instead of inclined loading tests under confining pressure to study the shear failure laws and strength characteristics of rock under the combined effects of inclination and confining pressure. Red sandstone was selected as the research object, and uniaxial and shear tests were conducted to obtain its basic mechanical parameters. Based on the calibrated mechanical parameters of red sandstone, numerical simulations of inclined loading of rock were carried out for 7 dip angles and 6 confining pressure combinations, with the average compressive and shear loads of the specimen in the limit state captured using Fish language. The shear failure laws and strength characteristics of rock under the combined effects of dip angle and confining pressure were obtained. The results show that as the inclination angle increases, the angle between the shear band and the horizontal plane becomes larger, and as the confining pressure increases, the shear band thickens; increasing the confining pressure effectively reduces the influence of the inclination angle on rock strength. Then, an unconventional stress circle was used to characterize the stress state of the rock in the limit state and reveal the changing law of the stress path. Based on the Mohr-Coulomb strength theory, the gradient descent algorithm was used to connect the “points” representing the ultimate stress state on the stress circle for 7 inclination angles and 6 confining pressures, yielding 7 sets of strength envelope equations corresponding to the 7 inclination angles. By employing a polynomial approximation method and introducing the dip angle dimension, the 7 sets of “strength envelopes” were extended to a “strength surface”, realizing the transition from “points” to “lines” to “surfaces” and constructing a rock strength model that includes the dip angle factor. The research results have important scientific significance for revealing the coupling effect of dip angle and confining pressure on the strength of rock mass engineering, such as mine pillars.

Addressing the current issues of poor resource utilization of waste fibers and ineffective vacuum preloading reinforcement for dredger fill, we developed a modified fiber plastic drainage plate based on the modification treatment of waste fibers. Using gradient ratio tests and indoor vacuum preloading model tests, we compared and analyzed the clogging characteristics of various modified fiber filter membranes, as well as the effects and patterns of vacuum preloading using different types of drainage plates on soft soils. The results show that the anti-clogging effect of the modified fiber filter membrane with a pore size of more than 119 µm is better. The modified fiber drainage plate is superior to the ordinary split-type plastic drainage plate in terms of settlement, water output, vacuum degree, pore water pressure, soil moisture content, and vane shear strength. The drainage plate with a filter membrane pore size of 119 µm exhibits the best reinforcement effect. Compared to the ordinary split-type plastic drainage plate, it has a lower cost, reduces moisture content by an average of 6.4%, and increases vane shear strength by an average of 7.8 kPa. This fully demonstrates that the modified fiber drainage plate not only provides excellent reinforcement in engineering applications but also reduces costs, aligning with the national goals for infrastructure construction and economic green sustainable development.

Pressure-driven fracturing technology has been applied to address the challenge of energy replenishment in low-permeability reservoirs. The operating pressure during fracturing-enhanced flooding is a key parameter that influences the water injection capacity of the reservoir. To determine the appropriate operating pressure, a study on the critical pressure for hydraulic fracture extension based on the fracture process zone (FPZ) was conducted. Firstly, a model for assessing the stability of hydraulic fracture extension was established using elastic mechanics and elastic-plastic fracture mechanics, taking into account the influence of the FPZ and wellbore stress concentration on the stress intensity factor at the fracture tip. Secondly, visual experiments on fracturing-enhanced flooding were designed to investigate the evolution of fractures and validate the reliability of the model. Finally, based on the theoretical model and the injection pressure curve, the upper and lower limits of the operating pressure for fracturing-enhanced flooding were determined. The results indicate that there are two modes of fracture extension: steady-state and non-steady-state, which are governed by the driving and resisting forces of fracture extension. Before the breakdown point, the fractures undergo multiple stages of steady-state and non-steady-state extension. The lower limit of the operating pressure is the turning point where the slope of the injection pressure curve decreases, marking the onset of an increase in injection capacity after a period of decline. The upper limit of the operating pressure corresponds to a stress intensity factor at the fracture tip of 0.05 MPa•m^0.5, which is slightly higher than the endpoint of the last stable fracture extension stage before breakdown and represents the maximum injection capacity. This study provides theoretical support for optimizing the operating parameters of fracturing-enhanced flooding.

Vertical cutoff wall is one of the most effective technologies to restrict the migration of contaminants and has been widely used for in-situ management and control of contaminated soil and groundwater. The traditional cutoff wall materials are highly susceptible to performance degradation under dry-wet cycles, leading to a significant reduction in service life. Through a series of macroscopic and microscopic experiments, the influences of sodium bentonite, magnesium oxide, and microcapsules on the evolution of permeability characteristics and microstructure of fly ash-based geopolymer cutoff wall materials under dry-wet cycles were investigated. The results showed that the unconfined compressive strength (UCS) and permeability coefficient of different geopolymer cutoff wall materials all met the anti-seepage design requirements for cement-based cutoff walls, achieving 6.62 MPa and 4.73×10−11 m/s, respectively, after being cured for 28 days. The permeability coefficient of samples without modified materials exceeded 1×10−8 m/s after the first dry-wet cycle, while that of samples with modified materials could still meet the design requirements after five cycles. The three modified materials can effectively influence the proportions of micropores (<0.05 μm), mesopores [0.05 μm, 0.10 μm], and macropores (>0.10 μm), thereby improving the anti-seepage performance of geopolymer cutoff wall materials under dry-wet cycles. This study has significant implications for the performance evaluation and scientific design of cutoff walls.

The directional frictional anisotropy of snake-skin-inspired interfaces has great potential to improve the load-bearing performance of offshore uplift pile foundations and other engineering applications. Such interfaces are designed to withstand cyclic loads, including those induced by waves and earthquakes. To investigate the characteristics of directional frictional anisotropy of soil-structure bio-inspired interfaces under cyclic loading, a series of cyclic direct shear tests were conducted using an advanced interface cyclic shear apparatus. The study examined the effects of initial cyclic position, normal stress, bio-inspired interface morphology, and sand density on cyclic shear anisotropy, along with an initial exploration of shear strength characteristics following cyclic loading. The findings revealed that increasing initial position of the cycle and normal stress enhanced shear anisotropy under the cranial-caudal cyclic loading path, while reducing shear anisotropy under the caudal-cranial cyclic loading path. For interfaces at moderate densities, variations in the ratio of interface scale length to height exhibited negligible effects on shear anisotropy. However, as sand density increased, the influence of this ratio on shear anisotropy became more pronounced under the cranial-caudal cyclic shear path, with a slightly increased effect observed under the caudal-cranial cyclic path. Under constant stress conditions, the peak shear strengths in monotonic shear tests of the bio-inspired interfaces following both types of cyclic shear paths exceeded those observed without prior cyclic shearing, and it was also found that the peak interface friction angle increased significantly. These findings provide valuable insights for the optimization and practical application of bio-inspired interfaces in engineering projects.

The fracture propagation characteristics of weak rock during split grouting reinforcement remain unclear, and empirically designed grouting parameters fail to effectively reinforce the surrounding rock. To investigate these characteristics in in-situ soft rock during split grouting, true triaxial split grouting tests were conducted on soft rock-like specimens. By analyzing acoustic emission parameters, we obtained the influence laws of varying principal stress differences and pre-existing crack angles on fracture propagation. Theoretical analysis and numerical simulation methods were employed to discuss the differences in splitting pressure and the mechanism of fracture propagation turning under triaxial stress conditions in weak rock specimens. The results reveal that as the principal stress difference increases, the angle between the fracture plane and the horizontal direction decreases, and the proportion of shear cracks in the specimen initially decreases and then stabilizes with increasing vertical pressure. As the angle between the pre-existing crack and the vertical principal stress increases, the initial splitting pressure first rises and then falls. When the pre-existing crack angles are 0º and 90º, they have a minimal impact on the direction of fracture propagation. At a 60º angle, the fracture propagates through the pre-existing crack. At a 30º angle, the fracture turns and intersects under high grout pressure. Combining the bare hole splitting theory, the analysis of splitting pressure differences and turning mechanisms under triaxial stress indicates that the higher the ratio of the maximum to minimum principal stresses, the lower the ratio of the tensile strength in bare holes under triaxial stress to the tensile strength measured by the Brazilian test. The initial direction of fracture propagation aligns with the direction of the minimum hoop stress in the bare hole, and it deflects towards areas of stress concentration at both ends of the pre-existing crack during propagation. Changes in the stress distribution within the rock mass are the primary cause of the turning in fracture propagation.

To address the issues of poor acid resistance of cement-stabilized soft soil and the high pollution, energy consumption, and cost associated with cement production, this study proposes using low-cost industrial solid wastes (ground granulated blast furnace slag (GGBFS) and fly ash (FA) in varying ratios) as precursors, with solid sodium hydroxide as the activator, to prepare geopolymer grout through a ‘one-step’ process for stabilizing soft soil. Subsequently, the geopolymer-stabilized soft soil samples were immersed in HNO₃ and H₂SO₄ solutions with different pH values (2, 4, and 6). The acid resistance of the stabilized soil was evaluated at different erosion ages (30, 60, 120, and 240 days) using four indices: mass loss, unconfined compressive strength (UCS), neutralization depth (ND), and pH value. Furthermore, the changes in microstructure and hydration product composition of the samples under different acidic environments were investigated using scanning electron microscope-energy dispersive spectrometer (SEM-EDS) to reveal the degradation mechanisms. The test results indicate that compared to H2SO4 solution, HNO3 solution exerts a milder acid erosion effect on the stabilized soft soil. This is primarily because the Ca²⁺, K⁺, and Na⁺ ions in the stabilized soil form nitrates in water, which can neutralize the erosion of ions, thereby mitigating the degradation of the soil’s properties. When the mass ratio of GGBFS to FA is 80:20, the acid erosion resistance of the geopolymer-stabilized soft soil reaches an optimal level. This suggests that the appropriate incorporation of FA can form a dense microstructure in the samples, effectively impeding the intrusion of H⁺, NO₃^-  and SO₄^2-  ions. The research findings can expand the application scope of low-cost industrial solid wastes and lay a theoretical foundation for the durability assessment of one-step geopolymer-stabilized soft soil.

With the rapid development of the engineering industry, the demand for traditional concrete materials has been steadily increasing, prompting researchers to explore new alternative materials. Industrial by-products such as red mud are believed to have potential in resource conservation, cost reduction, and mitigating environmental impact. However, the hydration mechanism of these solid waste materials in cementitious materials remain unclear. In this study, comprehensive analysis of the hydration kinetics of cementitious materials containing red mud, steel slag, fly ash, and phosphogypsum was conducted using low-field nuclear magnetic resonance and isothermal calorimetry. The study indicates that the hydration process of red mud-based cementitious materials can be divided into three stages: nucleation and crystallization, phase boundary reactions, and diffusion, with the reaction rate being highest during the nucleation and crystallization stage. Steel slag and phosphogypsum accelerate the hydration reaction and improve the material’s pore structure, while fly ash, although reacting more slowly, also contributes to the eventual improvement of the pore structure. Statistical results show that early hydration heat release is strongly correlated with the compressive strength at 7 days, which can effectively predict the material’s early strength.

To investigate the influence of mining rate on the development of fracture structures in water-bearing coal after implementing water injection for rockburst prevention in the working face, uniaxial compression tests at various loading rates were conducted on coal samples with different moisture contents (Dr, Se, Sa). The mechanical properties and acoustic emission characteristics of these water-bearing coal samples were analyzed under different loading rates. Using fractal dimension and scanning electron microscope (SEM), the fracture mechanism of the microstructure of these coal samples was revealed. The results show that an increase in water content weakens the peak strength of coal samples, induces a delay in acoustic emission ringing count and energy signals, and the lubrication effect of water reduces the proportion of tensile cracks in coal samples. Particle hydration is the primary reason for the reduction in brittleness and the alteration of fracture characteristics, with fractures transitioning from brittle to plastic and from transgranular to intergranular. An increase in loading rate inhibits the full propagation of internal cracks in coal samples, enhances their peak strength and elastic modulus, and reduces cumulative damage during the initial loading stage, resulting in acoustic emission ringing counts and energy signals gradually approaching their peak values. The cumulative energy of acoustic emissions shifts from a pattern of long-term slow increase followed by short-term sudden increase to a pattern of short-term slow increase followed by short-term sudden increase. The faster the loading rate, the smaller the slope of the k-value on the lg(M_Leq/M)-lgL_eq curve (where M is the total mass of the fragments, M_Leq is the mass of fragments smaller than the equivalent side length L_eq), the larger the fractal dimension, the less fragmented the coal sample, and the brittleness of the coal sample is enhanced, altering its fracture morphology. The research results can provide a solid experimental basis for rapid, safe, and efficient production in working faces.

Based on strain measurements from distributed fiber-optic sensors (DFOSs), an inversion method for discontinuous buried pipelines is proposed to predict the deflection and gap formation induced by tunnel excavation. The double-layer Winkler foundation beam model, which takes into account the relationship of bending moment-joint rotation, is employed to investigate the pipeline-soil interaction. The inversed pipeline deflection, rotation, and soil settlement are derived by utilizing the finite difference method and the conjugate beam method, respectively. Furthermore, the extent and location of the interface void are also identified. The inversion accuracy is verified in comparison with the numerical solution of the finite element method. Results show that the influence of joint rotational stiffness on the response lies within a certain range, which is seldom influenced by the pipeline flexural stiffness. The void range increases with the pipeline flexural stiffness and soil settlement. The upper void is likely to occur for an overlying subgrade with a large reaction coefficient, while the lower void is likely for an underlying subgrade. The combined boundary conditions of rotation angles at both endpoints and the position of maximum strain result in high inversion accuracy and markedly improve the anti-noise performance.

In order to investigate the hydro-thermal-mechanical process of soft clay under radial freeze-thaw conditions, freeze-thaw tests of soft clay at different temperatures were carried out, and the changes in temperature, water content, soil pressure, water discharge, and power consumption of soil samples were analyzed and compared. The results show that the actual temperature drop rate is positively correlated with the moving rate of the frozen front, and the temperature transfer efficiency is mainly related to the heat transfer distance, heat transfer medium, and energy loss rate. During the freezing of soil samples, the migration of water is closely related to the suction effect of the cold end on water and the relative effect of frost heave on water. The circumferential and radial cryogenic structures produced during the freezing process will accelerate the discharge of water from the soft clay, and the frost heave force will produce a consolidation effect on the soil in the unfrozen area. By comparing the freezing range, water discharge, and power consumption during the test process, it is found that the diameter of the thawing circle generated during the freezing process is the largest when the test temperature is −15 ℃, and the energy consumption ratio is also at its highest at this point. Therefore, −15 ℃ is taken as the optimal freezing temperature for this series of tests.

To prevent structural catastrophic responses induced by the collapse of the roof in goafs, based on field investigations and considering the impact disturbance behavior of roof collapses in goafs on the floor, a structural response model for the impact of goaf collapses on the floor and a dynamic response governing equation are established. The characteristics and attenuation laws of the structural response of the floor in goaf groups are studied, and the effects of factors such as joint density and thickness-to-span ratio on the displacement and stress response of the floor are analyzed, revealing the characteristics of its structural response. The results show that with the increase of the distance, the displacement and stress of the floor attenuation gradually and the attenuation rate decreases under the impact load. The response of floor is affected by the collapse position, distance and surrounding rock. As the collapsed goaf is closer to the center, the displacement and stress attenuation rates of the floor are smaller, and the impact and damage to the surrounding goafs are more extensive. With an increase in joint density, the stiffness, vibration frequency, and energy dissipation rate of the floor decrease, while the peak values of displacement and tensile stress show an increasing trend, leading to a reduction in impact deformation resistance and stability. As the thickness-to-span ratio increases, the peak values of displacement and tensile stress of the floor decrease exponentially. A significant inflection point appears when the thickness-to-span ratio is 0.6, with the attenuation rate differing by more than 10 times. Increasing the thickness-to-span ratio of the floor can shorten the response time, reduce displacement and tensile stress, and improve the stability of the floor. The reliability of the theoretical method is verified by numerical methods. The research results can provide some theoretical support for the safe production and disaster prevention and control in open stope mining method.

The application of a significant additional load induces soil deformation around the pile, generating a downward drag force, commonly referred to as negative skin friction. This phenomenon significantly reduces the pile's ultimate axial load capacity. Therefore, precise estimation of negative skin friction is crucial for pile design. To accurately calculate the negative skin friction acting on the pile, it is essential to determine the stress states at the pile-soil interface under varying soil deformations. However, many existing methodologies solely consider peak or residual stresses on the shear plane, neglecting the process of stress changes in soil deformation. This approach often results in an overestimation of negative skin friction. In this investigation, we propose a novel method for calculating negative skin friction that comprehensively accounts for the whole process of stress state alterations occurring during soil deformation (pre-failure zone and peak stress, post-failure zone and residual stress state) and describes the relationship between soil deformation and stress using a hyperbolic mechanical model. On this basis, soil deformation behavior is classified into three distinct forms. The spatial distribution characteristics for negative skin friction were then explored individually for each form. Additionally, the influence of different soil parameters on the spatial distribution of negative skin friction was also investigated. Finally, the accuracy and applicability of the new negative skin friction calculation method is validated through comparison with field measurement data. It can be used as a reference for practical engineering.

According to the notice issued by the General Office of the State Council on enhancing drinking water safety guarantees, large mountainous cities in southwestern China need to construct numerous water conveyance tunnels to achieve interconnection between backup reservoirs-water supply clusters and water supply clusters. Due to its superior technological and environmental advantages, pipe jacking has been widely used in the construction of these tunnels. In response to the lack of a calculation method for frictional resistance when pipe jacking traverses fault zones with fractured rock, this research relies on the Guanjingkou water control project in Chongqing, one of the 172 major water conservancy projects for water-saving and water supply determined by the State Council. Through on-site monitoring of jacking forces and investigation of sediment accumulation around the pipe sections in deep and extensive fault zones with fractured rock, the extent of sediment filling in the over-excavated gap before and after reinforcement of the fault zones is revealed. Two mechanical models for the contact between the pipe and the surrounding rock are proposed, and based on Janssen’s theory, the elastic-plastic theory of rock, and the multi-layer cylinder model, corresponding calculation methods for the frictional resistance of pipe jacking are derived for the two mechanical models. The applicability of these friction calculation methods for pipe jacking traversing fault zones with fractured rock is verified by comparing on-site friction monitoring data with theoretical calculation values.

Significant floor heave issues arise during the initial mining and roadway retention periods due to the complex stress environments where roof-cutting roadways are situated and their long service periods for retention. The engineering research background drew upon the specific conditions of roof-cutting roadway retaining of 1462(1) track alignment at Dingji Coal Mine in Huainan. A discrete-element numerical calculation model was established to obtain the asymmetric deformation characteristics of the floor and its force state from the primary excavation to the stable stage of roadway retention. Besides, the work constructed the mechanical model of the doubly-clamped twice statically indeterminate floor beam. An equivalent load was introduced to solve the mathematical expression of the floor deflection under each distributed force. The superposition principle was used to derive the deformation expression of the roof-cutting roadway retaining. Roady retaining conditions were utilized to obtain the average floor heave of the roadway (0.74 m) and maximum floor heave (0.77 m). The maximum heaving position was biased to the side of the goaf, 1.15 m from the middle of the roadway. The results were more consistent with the on-site measurements and numerical calculations. Based on the floor deformation expression, the influencing factors of roadway-retaining heave floor were analyzed. The increase in floor heave and floor stiffness exhibited an exponential decrease. When floor stiffness changed at 5−13 MN•m², floor heave in the roadway was more sensitive to its changes. There was a linearly positive correlation between floor heave and the floor load, support load, coal side load, and stress concentration coefficient, with growth rates of 0.082 6, 0.034 9, 0.027 2 m/MPa and 0.007 m/(λ), respectively. The force deformation of roadway-retaining floor and its influencing factors were analyzed to propose the prevention and control countermeasures of “mutual control of roof and floor as well as side and floor reinforcement.” Engineering practice showed that, compared to the initial stage of roadway retention, floor deformation was effectively controlled, with a significant reduction in floor heave. The retained roadway meets the requirements for reuse.

Rainfall-induced instabilities in highly permeable earthen slopes typically originate at the slope toe; however, the triggering mechanism remains unclear. In this study, we captured the initial microscopic deformations and the overall macroscopic progressive damage of slope instability, extracted the stress paths and contact force chains of soil particles in different parts of the slope before and after rainfall, and revealed the triggering mechanism of soil slope instability induced by rainfall by conducting model tests and utilizing CFD-DEM (computational fluid dynamics-discrete element method) fluid-structure coupling numerical simulations. Our findings revealed that the slope toe exhibits stress concentration prior to rainfall and is a sensitive area of the entire slope before rainfall. After rainfall, rainwater infiltrates, and the seepage rate is the highest near the slope toe. The force-chain arch formed by the large particles at the slope toe, which play the role of the skeleton, is gradually weakened. The essence of rainfall-induced soil slope failure lies in the gradual erosion of the stable contact force chains between soil particles at the slope toe by seepage forces, leading to a progressive weakening, fracture, and disappearance from the outside inward in a collective movement. Once the failure of the slope toe is triggered, the damage area of the inter-granular contact force chains is significantly larger than the displacement plastic zone (or shear band), and the stress in the soil near the slope rapidly transitions from high to low. Subsequently, as the soil particles continue to slip and roll, the soil stress fluctuates and gradually increases, forming a stress-concentrated force chain arch at the rear edge of the slip surface highlighting the slope’s certain self-stabilizing capability after failure. Throughout the process, the stress path at the foot of the slope is the longest.

Discrete element simulation of triaxial tests is an important tool for exploring the deformation and failure mechanisms of geotechnical materials such as sands. A crucial aspect of this simulation is the accurate representation of lateral boundaries. Using a coupled finite difference method (FDM)-discrete element method (DEM) approach, numerical simulations of consolidated-drained and consolidated-undrained triaxial tests were conducted under flexible lateral boundary conditions. These results were then compared with those of corresponding triaxial tests using rigid lateral boundaries. The results indicate that, compared to the rigid lateral boundary, the triaxial test using the FDM-DEM coupled flexible lateral boundary better captures both the macroscopic mechanical response and the microscopic particle kinematics of laboratory triaxial specimens. In the consolidated-drained triaxial tests, the strain softening and shear dilatancy of the specimen with the flexible lateral boundary are significantly weaker after reaching peak strength than those of the specimen with the rigid lateral boundary. In the consolidated-undrained triaxial tests, when the axial strain is large, the specimen with the flexible lateral boundary exhibits both a lower deviator stress and a smaller absolute value of negative excess pore pressure. Furthermore, in the consolidated-undrained triaxial tests, as the axial strain increases, the flexible lateral boundary provides weaker lateral constraint and support to the specimen compared to the rigid lateral boundary. Consequently, the stability of the force chains in the specimen with the flexible lateral boundary is lower, leading to more buckling events of force chains within the shear band. As a result, both the anisotropy and the deviator stress are reduced.

With the continuous advancement of highway construction in mountainous regions in China, the stability and disaster-causing mechanisms of waste dump sites have become one of the important factors in project construction evaluation. To achieve a comprehensive analysis of the stability and dynamic processes of instability disasters at waste dump sites, this paper introduces the strength reduction method (SRM) based on the material point method (MPM) in CoSim, a GPU-oriented parallel high-performance computing software. To verify the rationality of the algorithm, the MPM-SRM is compared with the limit equilibrium method (LEM) for a typical uniform slope. The results show that the two methods exhibit good consistency in both the factor of safety F_s and the potential sliding surfaces. Based on this, a case study of a highway waste dump site in Yunnan Province where rainfall-induced instability occurred is analyzed under both natural and heavy rainfall conditions. The results indicate that the slope of the waste dump site is stable under natural conditions, but becomes unstable and experiences large sliding deformation during heavy rainfall. The numerical simulation results correspond well with field investigation findings, demonstrating that the method proposed in this paper has significant advantages in stability analysis and dynamic analysis under large deformation of waste dump site slopes. It can simulate the entire process of slope behavior, from stability to large deformation, flow, and deposition.

Establishing a reasonable rainfall infiltration model is crucial for understanding the mechanisms of rainfall-induced slope failures and for preventing and controlling landslide disasters. Currently, numerical solutions to the Richards equation and the Green-Ampt model are commonly employed to analyze rainfall infiltration in slopes. However, numerical solutions to the Richards equation often encounter convergence issues, while the Green-Ampt model suffers from relatively low accuracy and an inability to account for non-uniform initial soil moisture distribution and pore water redistribution. In this study, we propose a spatiotemporal approximation method based on the Green-Ampt model for analyzing rainfall infiltration in slopes. This method involves discretizing the slope stratum into multiple spatial elements along the depth and dividing the rainfall event into multiple time intervals. Using this method, we investigate the changes in seepage, stability, and reliability of heterogeneous infinite slopes under rainfall infiltration. The results show that, compared to numerical solutions of the Richards equation, the proposed method is a robust and accurate approach for analyzing rainfall infiltration, with no convergence issues. Additionally, ignoring the pore water redistribution process can lead to underestimating the probability of slope failure and misidentifying the location of the critical sliding surface. The research outcome can provide theoretical support for rainfall infiltration analysis of complex slopes and prevention and control of rainfall-induced shallow landslide disasters.

The deformation of surrounding soils and ground surface settlement induced by tunnel construction can have adverse effects on the adjacent underground structures and buildings. In the numerical simulation of soil deformation due to tunnel construction, the selection of constitutive models for soils is crucial. The UH model was developed based on the unified hardening (UH) parameter, which has the advantage of clear conception, fewer parameters and strong practicability, and has served in several major projects. Based on the UH model which accounts for the nonlinear degradation of elastic shear stiffness at the small strain range, a series of coupled hydro-mechanical (HM) finite element analyses has been carried out for simulating the entire construction process of the Crossrail Tunnel at Hyde Park in London. Comparison between the numerical predictions and field monitoring data exhibits excellent agreement. The predicted features of the ground surface settlement and subsurface vertical and horizontal displacements due to the construction of the Crossrail tunnels are analyzed in detail. Finally, by comparing against the predicted results using the modified Cam-clay (MCC) model accounting for the small strain behaviour, the advantages of the UH model in describing the stress-strain response of heavily overconsolidated clays are further verified.

China's underground geotechnical engineering often faces complex geological conditions, such as high in-situ stress, subterranean karst, and extremely soft rock. These conditions can lead to loose and fractured rock structures, making it crucial for underground geotechnical engineering construction to quickly, accurately, and conveniently obtain rock mechanics parameters. We have autonomously developed the XCY-2 rotary cutting and penetrating system, a device for continuous monitoring of the drilling process. Various systems are integrated into this device, such as a power drilling control system, a comprehensive servo system, and an intelligent monitoring system. The installation process is straightforward, and the testing procedures are simple, facilitated by a human-computer interaction interface. To investigate the relationship between drilling parameters and the characteristic responses of different rock types during the rotary drilling process, we conducted comprehensive rotary drilling penetration tests under various conditions, including intact rock layers and layered rock masses, using the device and procedure. The test results showed that: 1) The intelligent monitoring system efficiently controls and monitors drilling parameters in real-time, including drilling speed, rotation speed, drilling torque, water pressure, drilling duration, drilling pressure, and drilling depth. This technology significantly facilitates high-precision drilling operations and continuous monitoring during underground construction. 2) When drilling through rock samples of various strength grades, we observed real-time fluctuations in drilling pressure and torque, while the drilling speed and rotation speed remained stable throughout the testing process. 3) Significant fluctuations in drilling torque and pressure were observed at the interfaces between different rock layers, indicating real-time perception of different rock types and achieving accurate positioning of rock layer interfaces. The XCY-2 rotary cutting and penetrating system provides a new approach for testing the physical and mechanical properties of underground rock masses.