The arching effect is widely observed in geotechnical engineering and is typically studied using trapdoor tests. Traditional trapdoor tests ignore the conditions of passive trapdoors, such as tunnel uplift and anchor plate pullout. To address this gap, a servo-controlled lifting array-type trapdoor test apparatus was developed. A plane strain passive trapdoor test was conducted using dense sand as the backfill material. During the lifting process of trapdoor, the vertical load variations across the entire array and sectional displacements were collected, resulting in load-displacement response curve for the evolution of passive arching effect. The test results show that as the backfill height increases, load redistribution becomes more pronounced. This is evidenced by increases in the maximum arching ratio, ultimate arching ratio, and corresponding normalized displacement. Sectional displacements and sliding surfaces develop towards the backfill surface in a “funnel” shape. Shear strain concentrates on both sides of the trapdoor, forming a significant curved sliding surface. The angle between the sliding surface and the vertical direction is close to 0º at the base and increases with the embankment elevation. When the fill height is greater, new sliding surfaces develop inside the outer sliding surface as the trapdoor continues to rise. A modified limit equilibrium method calculation formula was derived based on the measured angles between the shear band and the vertical direction. The calculated maximum arching ratio closely matches the experimental results.

Sludge particles are fine and have a high water content. The strength of solidified sludge is predominantly provided by cementation strength, with insufficient frictional resistance. Phosphogypsum-based aggregates were synthesized using phosphogypsum, slag, and quicklime as raw materials. These aggregates were combined with cement for sludge solidification, and the physical and mechanical properties of the solidified sludge were assessed. Results show that the phosphogypsum-based aggregates have a water absorption rate of 13.4%, which locally separates free water in the sludge, enhancing cement solidification. After compaction, the leaching concentrations of soluble phosphorus (P) and fluorine (F) in the phosphogypsum are significantly reduced compared to the raw phosphogypsum. Both concentrations are below the discharge standards for class III surface water (the leaching concentration of P is ≤ 0.2 mg/L, the leaching concentration of F is ≤ 1.0 mg/L), meeting environmental protection requirements. When the phosphogypsum aggregates are ≤5 mm, their uniform distribution enhances the skeletal effect, significantly increasing the strength of solidified sludge by 22.3%, exceeding 1 MPa. This occurs because reactions among phosphogypsum, slag powder, and lime generate calcium silicate hydrate (C-S-H) gel and acicular ettringite. These products intertwine to form a spatial network structure, filling the pores inside the phosphogypsum-based aggregates and the transition zone. This immobilizes soluble phosphorus and fluorine and strengthens the bonding capacity of the aggregate-sludge interface transition zone. The research conclusions provide a reference for the comprehensive utilization of phosphogypsum and offer a novel approach to sludge solidification.

The high cost of shale coring limits the application of the Schmidt hardness method based on core samples. This study employs cuttings sieving, sample preparation, and point load testing to reveal variation patterns in the ultimate compressive strength of cuttings with different fragment shapes and sizes, establishing a conversion model between cuttings and core Schmidt hardness. Experimental results show that: (1) Shale cuttings are categorized into four shapes: blocky, wide flaky, elongated, and narrow flaky. (2) The ultimate compressive strength of blocky and wide flaky cuttings decreases with increasing dimensions of the long, intermediate, and short axes, and then stabilizes. No significant pattern is observed for narrow flaky and elongated cuttings. (3) The initial dimensions of the stable stage of ultimate compressive strength are 8.2 mm for the long axis, 5.9 mm for the intermediate axis, and 3.2 mm for the short axis, and results beyond these dimensions exhibit strong stability. (4) The Schmidt hardness of cuttings is lower than that of the core test results. However, a strong correlation exists between the two, with a correlation coefficient exceeding 0.9. The findings provide a low-cost, real-time evaluation method and standard for shale Schmidt hardness, offering a basis for drilling optimization.

To analyze the stress concentration effect at rock joint ends under dynamic disturbance, a modified hyperbolic model of non-uniform joint normal stiffness distribution is introduced, based on the compression closure and elliptical shape characteristics of rock joints. Factors such as in-situ stress, joint inclination angle, and joint length are considered to compare and analyze joint surface stress and end stress concentration effect under P wave and SV wave disturbances. Results indicate that considering joint morphology, the closer to the joint ends, the greater the disturbance amplitude of the stress wave on the joint surface’s normal stress, and the reduction effect of joint on the stress wave diminishes, resembling the propagation effect in intact rock. The stress concentration effect at the joint ends is positively correlated with the compressive stress and shear stress on the joint surface, but the stress concentration effect at the joint end caused by compressive stress is more significant. Considering the characteristics of joint morphology, the fluctuation of stress concentration effect at the end with the incidence of stress wave is more obvious than that of ignoring the joint morphology, increasing the likelihood of damage. Therefore, considering the joint morphology is more conducive to the analysis of engineering safety. Under the same conditions, P wave primarily causes the change of normal stress on the joint surface, while SV wave primarily causes the change of shear stress. Analysis of the joint end extension point shows that as the incident angle of the stress wave increases, the effect of SV wave on the shear stress at the monitoring point weakens, while its effect on normal stress strengthens, opposite to the effect of P wave. The horizontal displacement is positively correlated with the normal stress value, and the vertical displacement increases with the increase of the shear stress. When the joint experiences tensile shear stress, normal stress in most end areas is tensile, whereas it is primarily compressive in the compressive shear state.

The treatment and utilization of substantial quantities of waste dredged silt represent a significant challenge in environmental geotechnical engineering at present. Performance-controlled fluidized solidified backfill (PCFS) is prepared using silt as the soil material and cement as the curing material, with expandable polystyrene (EPS) particles and naphthalene superplasticizer as additives. The variations in density, flowability and strength of PCFS and their regulation method were investigated through a series of tests. The PCFS density decreases with the increase of initial moisture ratio and increases with the increase of cement dosage, but the change is small. The PCFS density changes most obviously with the EPS particles dosage (φ ), and can be reduced to as low as 0.74 g/cm³. The PCFS flowability decreases with the increase of the EPS particles dosage. The ratio of EPS particles volume to PCFS volume increases by 0.3, the PCFS flowability decreases by 15%−20%. The naphthalene superplasticizer admixture significantly enhances the flowability of PCFS, with an improvement rate of nearly 130%. The PCFS strength increases logarithmically with age, increases as a power function with the increase of cement dosage, and decreases linearly with the increase of initial moisture ratio. A power function relationship exists between PCFS strength and EPS particles dosage within the range of 0.3≤φ ≤1.2, with greater sensitivity to EPS particles dosage changes at high cement levels.

To investigate the directional independence of multi-stage stress memory in granite under different loading rates, uniaxial cyclic loading and unloading tests were performed at five loading rates and different deflection angles. Acoustic emission technology was employed to reveal how different loading rates affect the rock’s multi-stage stress memory, including the Kaiser effect (KE) and the incomplete erasion phenomenon (IEP). The results indicate that granite shows directional independence of multi-stage stress memory at different loading rates. The critical angle of directional independence for KE is higher than that for IEP at each loading rate. As the loading rate increases, the KE critical angle of granite gradually increases. When the loading rate is below 10 kN/min, the IEP critical angle also increases, but it decreases to 0º−5º when the loading rate exceeds 10 kN/min. The results offer an experimental foundation for a more systematic and in-depth understanding of the directional independence of multi-stage stress memory in rocks.

The abrupt change area of coal seam dip is one of the complex geological conditions that significantly increase the risk of coal and gas outburst during deep mining. Using a mine in Pingdingshan, Henan Province, as the research subject, we conducted experimental research to simulate coal and gas outburst under various inclination mutation conditions. An interface with a dip mutation was established, positioning raw coal on the upper side and type coal on the lower side to emulate primary and tectonic coal seams, respectively. The initial angle( θ_I) of abrupt change in coal seam dip, the abrupt change angle( θ_M), the critical value of the abrupt change angle( θ_I ), and the gas concentration coefficient(I_θ  ) in the abrupt change area of coal seam dip were defined. The above parameters were used to analyze the effect of abrupt change in coal seam dip on the intensity of coal and gas outburst. The unit outburst intensity(I_U ) was introduced to characterize the strength of coal and gas outburst during the test. Acoustic emission technology was employed to monitor the energy evolution pattern during coal and gas outburst, while temperature changes in each area were recorded using sensors embedded in the sample. The findings of the study indicate that: (1) The abrupt change area of coal seam dip significantly impacts on both the critical gas pressure and the unit outburst intensity during coal and gas outburst. There exists a critical value(θ_T ) of the abrupt change angle in coal seam within the range of 10º<θ_I  ≤20º, 10º≤ θ_M ≤20º. When both θ_I and θ_M  exceed or are equal to θ_T   , a low-index coal and gas outburst becomes more likely to occur. When θ_I  orθ_M is fixed, the unit outburst intensity in the abrupt change area of coal seam dip increases as the gas concentration coefficient( I_θ) increases. (2) A negative correlation exists between θ_I  and both the peak and cumulative AE energy. A similar negative correlation exists between θ_M and both the peak and cumulative AE energy. As bothθ_I  andθ_M  increase, the energy required for the coal body to reach rupture and destabilization progressively diminishes. Under identical geostress conditions, this phenomenon facilitates coal and gas outburst even at lower gas pressures. (3) Notable temperature variations occur within the coal body during the incubation and excitation phases of coal and gas outbursts. Temperature changes in the abrupt change area of coal seam dip are significantly higher than in other zones. Temperature fluctuations in the proximal region of the outburst vent show greater instability than in other regions.

At present, the theoretical research on the uplift capacity method of horizontal anchor plate is limited to sandy soil and saturated soft clay foundations, with challenges in artificially distinguishing shallow and deep buried types. There is no research result on the uplift capacity calculation method applicable to both different buried depths and cohesive soil foundation. This paper employs numerical simulations and theoretical analyses to address issues related to sliding surface characterization, mechanical model, and bearing capacity calculation method for horizontal strip anchor plates in cohesive soil foundations. The main conclusions are summarized as follows: (1) With a constant burial depth ratio, the sliding surface expands outward as soil cohesion increases. Conversely, with a constant cohesion, the sliding surface contracts as the burial depth ratio increases. For each burial depth ratio (or cohesion) value, there is a corresponding cohesion (or burial depth ratio) value where the sliding surface changes morphology. (2) The sliding surface evolution is described by an elliptic arc, with its axial ratio varying with the burial depth ratio and soil mechanical parameters. The ratio k decreases with the increase of buried depth ratio and increases with the increase of cohesion, while the internal friction angle minimally affects it, only determining the initial angle of the sliding surface. According to this law, a formula for calculating the ratio axial k and the initial angle is proposed. (3) Combined with the morphological tendency of the sliding surface, a mechanical model for the ultimate uplift capacity of horizontal anchor plate in cohesive soil foundation was developed. The model considers the relationship between buried depth, ellipse vertex (or the highest point of ellipse position) and anchor plate position under five working conditions. The ultimate uplift capacity calculation method was derived using ultimate equilibrium analysis. This method does not need to introduce the critical depth ratio to distinguish the buried type, and can consider the changes of internal friction angle and cohesion of soil. (4) Compared to four other methods in the calculation of three test cases, the uplift capacity calculation method proposed in this paper achieves the best calculation effect and demonstrates good applicability.

This study introduces a novel linear programming model to address slope stability issues by converting the safety factor calculation into a linear programming problem to determine the horizontal seismic force influence coefficient. In addition to constraints such as normal stress convexity and the Mohr-Coulomb criterion, the model integrates thrust line position constraints into the linear programming framework. This approach further narrows the upper and lower bounds of the limit equilibrium solution and improves computational accuracy. Reasonable assumptions for inter-slice force distribution are established, effectively constraining the range of thrust action points. This enables rapid determination of thrust line positions and informs slope reinforcement measures. Numerical examples show that the obtained upper and lower bounds of the safety factor are relatively narrow. Although the safety factors are close to those from the improved Morgenstern–Price method, the thrust line positions derived here are more reasonable. This method prevents local failure, eliminates stress discontinuities, and ensures the thrust line positions remain within a reasonable range.

Fine particle migration widely exists in two-phase flow processes in both nature and engineering fields, such as pollutant migration, remediation, as well as oil and gas production. However, the effects of particle-induced blockage in porous media on two-phase flow remain unclear. Utilizing a self-developed three-dimensional visualization experimental platform, this study conducted a series of two-phase displacement experiments with different flow rates and pore sizes in a porous medium, and systematically investigated the transport and clogging behavior of fine particles and their subsequent effects on two-phase flow dynamics. The results reveal that particle-induced pore clogging during two-phase flow is governed by the synergistic control of flow rate and pore size. At low flow rates, pore size has minimal impact on clogging. However, at high flow rates, pore size becomes the dominant factor. By analyzing the spatial distribution of residual fluids, the study clarified the relationship between pore clogging and fluid connectivity: more significant clogging leads to a more discrete distribution of the residual wetting phase and reduced fluid connectivity. Additionally, the experiment also revealed the controlling mechanism of blockage on displacement pressure and displacement efficiency during two-phase flow. The findings are expected to provide important theoretical insights and practical guidance for optimizing two-phase flow process and improving energy recovery efficiency.

This study examines the evolution of rockburst in hard surrounding rock of a deep-buried tunnel affected by structural planes. True triaxial rockburst model tests were conducted on cubic sandstone specimens with a circular tunnel, with and without structural surfaces. An acoustic emission system was used in the experiment to monitor the evolution process of rockburst. Results show that the structural planes significantly affect the position and intensity of rockburst, as well as the failure mode of cavern wall. The damaged zone is symmetrical on both sides of specimens without a structural plane. Several rock flakes form a shallow V-shaped notch in the sidewall of the circular tunnel. The failure position on both sides of specimen with a structural plane is asymmetrical. On the side distant from the structural plane, a large number of rock flakes peel off, forming a deep V-shaped notch. Near the structural plane, multiple cracks form, causing the rock mass between the tunnel and the structural face to tend to collapse into the tunnel space. The acoustic emission (AE) events in specimen with structural plane are much more active, with the average energy of a single impact being approximately 2.2 times that of the specimen without a structural pane. According to the evolution of cumulative impact count, the loading process before rockburst can be divided into three stages, including crack closure and linear elastic deformation, crack initiation and stable propagation, and crack unstable development. The crack initiation and stable propagation is earlier in specimen with a structural plane than that in specimen without a structural plane. All cracks generated during the failure process are tension-shear mixed pattern in both tested specimens. The proportion of shear cracks is larger in specimen with a structural plane compared to that without. The presence of structural plane changes the position of initial damage in specimen. The AE location in the experiment generally correspond to the failure pattern of circular tunnel.

The active bioslurry, a urease-active slurry mixture composed of calcium carbonate and embedded urease-producing bacteria, is generated using microbial-induced calcium carbonate precipitation (MICP) technology. This study proposes a method for heritage bricks restoration using active bioslurry. Laboratory experiments and PFC^2D numerical simulations were conducted on notched simulated bricks to examine the mechanical response and microstructure of the repaired bricks and evaluate the feasibility of this method. Additionally, the repair and failure mechanisms under load were analyzed. The results show that active bioslurry effectively repairs notched simulated heritage bricks, with effectiveness influenced by curing time and notch depth. Longer curing time and shallower notch result in higher flexural strength of repaired samples. Analysis of the structure of calcium carbonate in the repaired notches indicates that after immersion curing, active bioslurry forms two layers of calcium carbonate: an outer layer of rhombohedral particles (approximately 10−25 μm), and an inner layer of spherical particles (around 5 μm). This two-layer structure likely results from differences in calcium ion and urea concentrations diffusing into the inner and outer layers of bioslurry. After 1, 3, and 5 days of curing, the thickness of the outer calcium carbonate layer was 2−2.5 mm, 3−4 mm, and 4−5 mm, respectively. PFC^2D numerical simulations indicate that the micromechanical parameters of the inner calcium carbonate layer are approximately 0.1 times those of the outer layer. Experimental and numerical simulation results demonstrate that the increase in flexural strength of the repaired simulated bricks is primarily attributed to the outer calcium carbonate layer. PFC^2D simulations further show that when the repaired bricks are subjected to bending loads, cracks initiate in the inner calcium carbonate layer and gradually propagate through the entire calcium carbonate layer and the undamaged brick body. This study not only expands the application scope of microbial reinforcement technology but also provides new insights for the restoration of heritage bricks.

The unified critical state parameter model (clay and sand model with subloading surface, CASM-S) effectively describes the mechanical behavior of sand and overconsolidated clay. However, the model does not include the nonlinear critical state line of sand. This study investigates the soil’s compression characteristics and its nonlinear critical state line in the e-lnp plane. The CASM-S introduces a power function form of the critical state line and reference compression line (RCC) suitable for sandy soil. With additional parameters ξ  and λ_r, yield surface and subsequent loading surface functions are proposed to describe the shear characteristics of the sand. The linear relationship of the reference compression curve in the e-(p/p)^ξ  plane (where e is the void ratio at the critical state, p is the normal stress, and p_a is the standard atmospheric pressure) is utilized to propose a method for determining the initial consolidation pressure p_c0. All 11 parameters required for this model can be obtained through conventional geotechnical tests or empirical methods. Finally, by comparing the model’s predictions with triaxial drained and undrained shear test results for four types of sand, the refined CASM-S effectively considers the effect of nonlinear critical state line and describes the triaxial shear characteristics of saturated sand under varying void ratios and confining pressures.

To investigate the shear characteristics of limestone joint surfaces with different water-bearing states under normal dynamic loading, the self-made KYZW-50D rock dynamic shear coupling test system was used to conduct dynamic shear tests with different water contents and normal loading frequencies. Additionally, three-dimensional morphology scanning tests were conducted on the sheared joint surfaces to examine the effects of water content and normal dynamic loading frequency on shear strength and morphology parameters. The findings indicate that: (1) The shear strength of the limestone joint surface exhibits a logarithmic decline as normal loading frequency increases. The deterioration of the shear strength gradually decreases and stabilizes when the normal loading frequency exceeds 2 Hz. (2) With constant initial normal stress, an increase in water content results in a gradual decrease in shear strength and morphology parameters of joint surfaces, along with an overall increase in deterioration degree and a reduced difference in deterioration between constant normal stress and dynamic normal stress conditions. (3) Based on Barton's shear strength equation, a shear strength equation considering the effects of normal loading frequency and water content was established. Validation showed it more accurately reflects shear strength deterioration of joint surfaces with different water contents under dynamic normal stress. The relevant methods and conclusions provide a theoretical basis for analyzing the stability of jointed rock bodies under dynamic disturbance conditions.

Strata structure of loess area mostly features a dualistic structure of loess and mudstone. When tunnels traverse mudstone and loess-mudstone composite strata, groundwater tends to redistribute and accumulate at the base of the inverted arch. The interaction between mudstone and water causes tunnel heave, and the lithological differences between the strata significantly affect the deformation and stress characteristics of the tunnel lining. Based on a tunnel project in Tianshui City, Gansu Province, model tests were conducted on tunnel in pure mudstone and loess-mudstone composite strata with the interface at the arch waist. Displacement was applied beneath the inverted arch to simulate the swelling effect of mudstone-water interaction. Differences in internal force, deformation, and failure characteristics of the lining under two loading conditions were investigated, and numerical simulations were conducted for comparison and verification. The differences in internal force, the deformation and failure characteristics of lining under two loading conditions were investigated, and the corresponding conditions numerical simulation was conducted for comparison and verification. The results show that: (1) Expansion deformation due to forced displacement at the model’s base can be divided into two stages: the base soil compaction stage and the equivalent transfer stage of base displacement. (2) With the elastic modulus ratio of mudstone to loess approximately 2:1, the loess stratum exhibits smaller overall stiffness, resulting in larger lining deformation and even larger heave displacement in inverted arch. The arch waist at the interface is more prone to outward expansion, with an expansion deformation of 9.2 mm, about three times that of the pure mudstone stratum. Stress concentration tends to occur at the lining section near the interface. (3) In both strata, the inverted arch and arch foot positions are prone to cracking and damage. Additionally, in the composite strata, the lining arch shoulder shows a high risk of cracking, with cracks at the arch foot tending to expand towards the arch waist. (4) Compared to pure mudstone stratum, the loess near the interface in loess-mudstone strata exerts a load release effect on the heave of inverted arch. The loess at the interface compresses and absorbs some of the heave force, thereby delaying the critical tensile failure time of the filling layer. The results can provide valuable references for theoretical analysis, design and construction of tunnels in similar composite strata.

Due to the high carbon emissions, energy consumption, and environmental pollution associated with cement grout in the construction of post-grouted piles in calcareous sand, this study employed two types of green, low-carbon grouting materials (geopolymer and high polymer) to solidify calcareous sand. The experimental results were compared with those obtained from the traditional cement grouting materials. The study investigated the effects of different grouting materials, curing times, and material ratios on the strength of stabilized soil in calcareous sand using unconfined compressive strength tests. Additionally, techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and nuclear magnetic resonance were combined to analyze the microstructure and mineral composition of the stabilized soil with different grouting materials, revealing the micro solidification mechanism. The results show that increasing the curing time and material ratio enhances the strength of the stabilized soil. High polymer-stabilized soil exhibits the highest strength, with a faster early strength growth. The compressive strength at 7 d is approximately 90% of that at 28 d. The compressive strength of geopolymer-stabilized soil is slightly lower than that of cement-stabilized soil. However, its strength increase rate with curing time gradually surpasses that of cement-stabilized soil, indicating a potential advantage in long-term stability. Additionally, geopolymer and cement-stabilized soil significantly enhance compressive strength by filling gaps between sand grains and binding the sand particles through hydration products. However, the strength improvement of high polymer-stabilized soil is attributed to its inherent properties. The pores in 7 d cured geopolymer and high polymer-stabilized soils are primarily small, accounting for over 95% of total pores. This proportion gradually increases with curing time and is significantly higher than that in cement-stabilized soil. This positively affects strength enhancement. The research findings can serve as a reference for applying green, low-carbon grouting materials in engineering projects involving post-grouted piles in calcareous sand.

For piles above underlying karst caves, the ratio of rock-socketed depth to cave roof thickness (rock-socketed ratio) can be high in certain projects. To study the influence of karst cave roof thickness on the vertical bearing characteristics of piles with high rock-socketed ratio, load tests were conducted on model piles with a rock-socketed ratio of 0.5, while the cave roof thickness was gradually increased from one to five times the pile diameter. Based on the test results, an analysis model for the ultimate bearing capacity of the pile was proposed, and a calculation formula was derived using the limit equilibrium principle. The results show that: (1) The failure mode of karst cave roof is trumpet-shaped punching failure, and the dimensionless fitting function for the fracture surface can reasonably predict the range of roof fracture. (2) The load-displacement curve at the pile top exhibits a steep change type, with an approximately linear relationship before the steep change point. (3) As the roof thickness increases, the ultimate bearing capacity of the pile increases nonlinearly, and the proportion of pile tip resistance supporting the upper load rises from 35.4% to 72.4%. (4) The relative error between the ultimate bearing capacity calculated by the proposed method and the test value ranges from −12.8% to 12.1%, indicating the method’s good rationality.

When the immersion area is small or the self-weight is less than its collapsible pressure, unsaturated loess does not collapse and its large pore structure can be retained. However, long-term hydraulic action significantly reduces the strength of saturated loess, potentially influencing the long-term stability of underground engineering projects. A field immersion test lasting 415 days was conducted to collect undisturbed saturated loess samples under various immersion duration, maintaining original in-situ stress and actual water infiltration conditions. Indoor and in-situ tests were conducted to examine changes in in-situ lateral stress during long-term immersion. The relationship between the softening mechanical behavior of loess and immersion duration was studied in terms of shear characteristics, compressive properties, and in-situ strength and deformation indicators. Results show that: (1) During prolonged immersion, loess transitions from a plastic to a soft or even flow plastic state, forming under-compacted saturated loess with a high void ratio, high water content, medium or high compressibility, and low strength. (2) During prolonged immersion, the in-situ horizontal stress of Q^eol₃ loess and Q^el₃ paleosol significantly increase, while the deep Q^eol₂ loess’s in-situ horizontal stress remains stable due to the strata’s arch effect. (3) Loess softening is time-dependent, and short-term indoor humidification samples are insufficient to show the gradual weakening of soil structure. After 120 days of continuous immersion, various strength and deformation indicators stabilize. (4) As immersion duration increases, the elastic segment of the stress-strain curve gradually shortens. Strength indicators, including unconfined compressive strength, peak shear strength, and in-situ horizontal bearing value, decrease significantly. The compression coefficient shows an exponential trend with increasing load, resulting in a significant increase in value and advancement of the peak interval. Additionally, both in-situ lateral pressure modulus and subgrade coefficient undergo substantial reduction. (5) In the stable stage, formation heterogeneity always exists. The unconfined compressive strength of saturated Q^eol₃ loess and Q^eol₂ loess is approximately 21%−32% of Q^el₃  paleosol, and the bearing capacity is 47% of Q^el₃ paleosol. The horizontal bedding coefficient K_x of saturated  Q^eol₂ loess is 67% of Q^el₃ paleosol, while that for saturated Q^eol₃  loess is 28%.

Sandstone, a widely distributed sedimentary rock, is extensively used in engineering. It is essential to study the macroscale physical and mechanical properties of sandstone from the microscale. A numerical model is proposed to predict the uniaxial compressive strength and longitudinal wave velocity of sandstone from the mineral crystal scale. First, a microscopic rock mechanics test system, consisting of optical microscope, automatic mineral analyzer, and nanoindentation instrument, is established to obtain the mineral composition, microstructure, and mechanical parameters of the major diagenetic and cementing minerals in sandstone. Then, an accurate grain-based model of the sandstone is developed using the obtained results. The stress evolution in the minerals, and the whole process from the initiation of microcracks in the cementing minerals kaolinite and muscovite to their expansion and then to overall shear failure of the model, can be visually shown through the uniaxial compression simulation. Wave velocity simulation intuitively demonstrates that the propagation characteristics of P-waves in sandstone are primarily influenced by micropores. Results show that the simulated uniaxial compressive strength and longitudinal wave velocity of sandstone are similar to the results of laboratory uniaxial compression test and ultrasonic test, which verifies the feasibility of using microscopic rock mechanics test results to establish an accurate grain-based model for predicting these properties. This method provides a new perspective of cross-scale analysis from mineral crystal scale to macroscopic mechanical properties in sandstone research. It also provides a theoretical basis for sandstone engineering application and interpretation of geological evolution history.

Site investigation data are often sparse due to limited project budgets. Using sparse site investigation data to quantify soil parameter inevitably results in significant statistical uncertainties. Meanwhile, the soil parameter database is expanding rapidly due to advancements in geotechnical investigation equipment and information technology. Effectively utilizing the big data in the soil parameter database to quantify soil parameter uncertainties at three-dimensional sparse measurement sites remains a challenging problem. This study proposes a big data assimilation technique to effectively quantify soil parameter uncertainties at three-dimensional sparse measurement sites. The proposed method first constructs a probability distribution model of soil parameters using limited sparse site investigation data. This model considers the autocorrelation of soil data in both horizontal and vertical directions across different soundings. Secondly, a probability distribution model based on the soil parameter database is constructed using Gibbs sampler. Based on the two probability distribution models, the hybrid Bayesian theory is employed to integrate the statistical information of the big data into the site-specific data. A hybrid probability model of soil parameters for the sparse measurement site is derived after assimilating the big data. The incomplete borehole data are simulated to be complete data that satisfy the lattice structure using the hybrid probability density function. The proposed method uses Kronecker product to decompose the large autocorrelation matrix and achieves the efficient reconstruction of the 3D site. Finally, the proposed method is demonstrated using a simulated virtual site and a site in Texas, USA. Results indicate that the proposed method effectively utilizes geotechnical big data. Assimilating geotechnical big data significantly reduces soil parameter uncertainties at three-dimensional sparse measurement sites. The proposed method provides a valuable tool for quantifying soil parameter uncertainties at sparse measurement sites.

The formation of a mixed pile foundation, integrating new and existing piles, is an effective approach for reusing old piles. Based on an elasto-viscoplastic model, this study analyzes the evolution of mechanical properties of the soil surrounding piles during long-term service, and introduces the quasi-overconsolidation ratio to characterize changes in soil shear modulus. By introducing a pile interaction coefficient, we establish an interaction model for old and new pile foundations of different lengths and propose a variable stiffness leveling design method for mixed-pile systems. Furthermore, the effectiveness of this method is verified through comparison with finite element analysis results. Findings indicate that after 30 years of service, the void ratio of soil around old piles reduces by 10.5%, and the shear modulus increases to 3.04 times the initial value due to creep. In addition, increases in the in-situ overconsolidation ratio, decreases in the secondary consolidation index, and prolonged creep time necessitate greater pile lengths during leveling. When the length of new piles increases from 30 m to 37.8 m, the interaction between short piles and long piles decreases, and the settlement difference decreases from 2.07 cm to 0.09 cm.

To mitigate the damage caused by seismic Rayleigh waves to structures, periodic surface wave metabarriers with double resonant cavities are proposed. The vibration isolation performance of the scale model is experimentally studied and verified using finite element simulation result. Consequently, the band structure and vibration transmission characteristics are further examined by using finite element method. The mechanism of bandgap formation is clarified in terms of eigenmodes and displacement field distributions. Simple analytical formulas for the dispersion curves of interactions between Rayleigh waves and vertical and horizontal resonant modes are derived. The results show that in the bandgap frequency range, Rayleigh wave attenuation is effectively validated through dynamic response analysis of surface wave metabarriers under actual ground motion using time history analysis. The peak ground acceleration in the horizontal direction can be reduced by 56.8% because part of the Rayleigh waves is localized to the resonant elements of the periodic surface wave metabarriers, while the rest is converted into bulk waves that propagate away from the ground surface. The study provides a new design idea for the ultra-low frequency vibration reduction and isolation application of periodic surface wave metabarriers.

The morphology of deep rock fractures continuously changes during shear, leading to complex flow characteristics that affect the stability of deep rock engineering. To clarify the shear and flow characteristics of rock fractures under constant normal stiffness (CNS) boundary conditions, three-dimensional self-affine fracture surfaces with different roughness coefficients were constructed using fractal theory. A numerical method accounting for roughness degradation due to shear was employed to analyze the evolution of fracture morphology parameters under different CNS conditions. Subsequently, COMSOL software was utilized to calculate the flow of fractures after shear. The effects of normal stiffness, shear displacement and fractal dimension on nonlinear flow characteristics of fractures were studied. The results show: (1) The mechanical aperture of the fracture increases with the fractal dimension, but the increase in normal stiffness slows down its growth rate. The contact ratio is primarily controlled by normal stiffness and increases as it increases. (2) The relationship between the pressure gradient and flow rate of fracture seepage can be well described by Forchheimer law. The fitting coefficients A and B show a power function decrease trend with the increase of shear displacement, increase with the increase of normal stiffness, and decrease with the increase of fracture fractal dimension. (3) The hydraulic aperture of the fracture increases with the increase of fractal dimension, and decreases with the increase of normal stiffness. A hydraulic aperture model with mechanical aperture and aperture standard deviation as independent variables has been established. (4) The critical Reynolds number for the fracture flow initially decreases and then increases with the increase of shear displacement, and decreases with the increase of fractal dimension and normal stiffness. A formula for calculating the critical Reynolds number of sheared fractures under CNS conditions has been established based on fracture fractal dimension, contact ratio, and hydraulic aperture model.

Seismic waves exhibit strong attenuation and velocity dispersion when they propagate through porous rocks saturated with a fluid. The main cause of such energy dissipation is fluid flow in the pore space, known as squirt flow. A simple and accurate dual crack analytical model is established for the squirt flow caused by the fluid flow in the microcracks with different aspect ratios commonly found in rocks. The effective compliance matrix of the dry dual crack model is constructed using micromechanics. By analyzing the fluid pressure distribution in the dual crack, crack stiffness relaxation in the wet-skeleton dual crack model is calculated using a one-dimensional fluid pressure diffusion equation, with the diameter of the compliant crack serving as the characteristic length for squirt flow in the dual crack model. The attenuation and dispersion characteristics of the frequency-dependent stiffness component of the dual crack model and the torus stiff pore model are compared, and three-dimensional simulations validate the accuracy of the dual crack model. Parameter analysis shows that as the volume of the stiff crack increases, the attenuation of the stiffness component of the dual crack also increases. The application of the dual crack model in velocity prediction is introduced, and its reliability is validated by comparing it with experimental data and the predictions of the torus stiff pore model.

To investigate the performance degradation patterns and thermal damage mechanisms of quartzite, a grain-based model in particle flow code (PFC-GBM) was employed to simulate the uniaxial compression of quartzite under real-time high temperature and after natural cooling. Stress-strain curve, peak stress, elastic modulus, and failure modes under both temperature conditions were analyzed to study the thermal damage mechanisms of quartzite. Further investigation of thermal damage mechanisms was conducted based on thermally induced crack and displacement changes. The following conclusions were drawn: During the natural cooling process, the temperature of quartzite sample generally decreased gradually from the center to the surface. In the 700 ℃ quartzite specimen, crack propagation during cooling caused unstable heat conduction, leading to isotherm displacement. The critical temperature for the brittle-ductile transition of quartzite under real-time high temperature condition ranged from 25 ℃ to 300 ℃, which is lower than the critical temperature from 300 ℃ to 500 ℃ observed in naturally cooled quartzite specimens. Under real-time high temperature, the peak strength and elastic modulus of quartzite samples decreased by approximately 20 MPa and 10 GPa, respectively, compared to those of naturally cooled specimens, with neither parameter showing significant variation with temperature. The elastic modulus was more sensitive to thermal damage within the range of 25 ℃ to 300 ℃ than peak strength. With the increase of temperature, the degree of fragmentation in quartzite under uniaxial compression significantly increases, exhibiting more splitting failure characteristics. The influence of thermally induced microcracks on the failure mode of quartzite becomes progressively stronger. Under both temperature conditions, the macroscopic fracture planes tend to extend along existing thermally induced microcrack paths, with more pronounced macroscopic through-going fractures observed under natural cooling condition.

Currently, industrial and mining enterprises primarily use grouting techniques to modify and reinforce water-bearing sand layers. Accurate grouting at the sand layer level and consolidation of loose water-bearing layers are key challenges in the grouting modification of deep wells with thick loose layers. This study proposes the concept of slurry-water replacement, derives the power-law fluid seepage diffusion equation considering the slurry-water replacement effect, and establishes and verifies the power-law fluid spherical permeation grouting diffusion mechanism under the slurry-water replacement effect through experiments. Using COMSOL, a three-dimensional numerical model of power-law fluid permeation grouting diffusion under the slurry-water replacement effect was established, and the seepage diffusion characteristics of power-law grout in water-bearing sand layers were analyzed. By analyzing the impact of porosity, grout hole spacing, and grouting pressure on the volume of water-bearing sand layers, the key factors affecting the volume of water-bearing sand layers were identified: grouting pressure > grout hole spacing > sand layer porosity. Slurry-water replacement grouting addresses the issues of limited grouting diffusion range and poor grouting effect in water-bearing sand layers under high water pressure.

Like other sensors, ambient temperature changes significantly affect the accuracy of earth pressure cell test data. However, current test methods seldom consider the impact of temperature changes on resistance strain-type earth pressure cell readings. A study was conducted to enhance the reliability of test readings by examining temperature effects on resistance strain-type earth pressure cells. Earth pressure cells with calibration coefficients of 0−100 kN/mV, 100−200 kN/mV, and 200−300 kN/mV were placed in a temperature-controlled chamber. Using the temperature range of Jilin Province as a baseline, the study systematically examined the variations in earth pressure cell readings from −30 ℃ to 40 ℃ and proposed a temperature correction method for the readings of resistance strain-type earth pressure cells. A three-dimensional error correction method for earth pressure cell test readings was developed. The study compared three-dimensional stress values before and after temperature correction in a subgrade frost heave model test, enhancing data accuracy. The results indicate that as the ambient temperature decreases, the earth pressure cell readings increase approximately linearly; as the temperature rises, the readings decrease nonlinearly. Additionally, the hysteresis loop of the stress-temperature curve remains largely unchanged with repeated temperature cycles, though individual earth pressure cells show distinct patterns. Temperature corrections should use incremental formulas for cooling and heating processes, forming a piecewise function. This method is also applicable to three-dimensional stress testing, where temperature-induced errors in normal stress exceed those in shear stress. This study enhances the accuracy of earth pressure cell measurements and provides conditions for accurately revealing stress evolution under variable temperatures.