According to the theory of viscoelasticity and Newton Cotes numerical integration method, a mechanical calculation model of the interaction between the heterogeneous frozen wall, the shaft lining and the surrounding soil considering the creep characteristics is established, and the analytical solutions of the stress, strain and displacement of the heterogeneous frozen wall at different excavation depths (I, II, III) are derived. The calculated results show that taking the excavation depth of 400 m as an example, when considering the heterogeneous characteristics of the frozen wall, the displacements of the inner and outer edges of the frozen wall decreased by 0.976 cm similar to 2.592 cm and 0.384 cm similar to 0.926 cm respectively during the creep time from 1 h to 36 h, while the external load of the frozen wall increased by 0.229 %similar to 0.630 %. When further considering the effect of shaft lining, the displacement of inner and outer edges of the frozen wall decreases by 0.869 cm similar to 17.010 cm and 0.310 cm similar to 6.075 cm, respectively, while the external load on the frozen wall increases by 0.203 %similar to 4.100 %. This study can provide a theoretical basis for the design of the outer shaft lining structure of the multi-refrigerant combined freezing method in water-rich stratum.

Development of functional nanocomposites for bone tissue repair is often hampered by their bioinertness and insufficient antibacterial performance. To overcome the limitation, this study developed a novel ZIF-8@Nar@CS composite nanoparticle system via a ternary co-assembly strategy. The microstructure of the ZIF-8@Nar@CS was explored by SEM, XRD, FTIR, UV-Vis, BET, and the interaction mechanism of the composite was elucidated via XPS and zeta potential analysis. In addition, the drug release behavior, antibacterial activity and osteogenic property of the composite were also evaluated in vitro. The results show that the ZIF-8@Nar@CS achieved a naringin (Nar) drug loading efficiency of 19.22% through the electrostatic interactions and exhibited a distinct pH-dependent drug release profile. Its cumulative release reached 98.89% at pH 5.5, in stark contrast to only 13.6% at pH 7.4, following first-order kinetics. Profiting from the concomitant release of Zn2+, Nar, and chitosan (CS), the ZIF-8@Nar@CS exerted a strong antibacterial activity of 99.99% against both S. aureus and E. coli. Critically, the ZIF-8@Nar@CS also exhibited favorable cytocompatibility and effectively enhanced the osteo-differentiation of MC3T3-E1 cells as compared to the ZIF-8 nanocarrier. This work might provide a new horizon for developing a safe nanoparticle delivery platform for bone repair and regeneration in clinic.

The failure of fractured rock masses under coupled unloading and seepage conditions poses critical threats to underground engineering stability. Conventional fracture mechanics cannot continuously characterize crack evolution from nucleation to coalescence, while existing phase-field models lack systematic treatment of unloading-path dependence and rheological damage. This study develops a thermodynamically consistent phase-field failure model for fractured rock masses under unloading-seepage coupling, grounded in the Clausius-Duhem inequality. Three core innovations are proposed: a stress-path-parameterized damage driving force function capturing unloading-rate-dependent crack initiation asymmetry; a rigorously derived bidirectional seepage-fracture energy coupling mechanism in which pore pressure modifies the critical energy release rate while fracture-induced permeability enhancement feeds back into the seepage field; and an elasto-plastic-rheological damage framework incorporating time-dependent creep-induced microcrack accumulation. Numerical simulations and uniaxial compression experiments on dual-flaw red sandstone specimens confirm that the model accurately reproduces the complete failure sequence, achieving a peak stress deviation of only 6.1%. Parametric studies demonstrate that rapid unloading accelerates damage evolution by 35% and bidirectional coupling reduces strength by 12% compared to one-way models. The proposed framework provides a theoretical foundation for stability evaluation in fractured rock mass engineering.

During coal mining, parallel voids ahead of an advancing working face often trigger intense dynamic loading and structural instability, posing significant risks to operational safety. Using the 43,201 working face of the Shiyangou Coal Mine as a case study, this research investigates the mechanisms of surrounding rock instability and proposes an integrated synergistic control strategy. Based on voussoir beam theory, a mechanical model of the roof structure—incorporating the nonlinear coupling between the gangue and immediate roof—was developed to establish the critical thresholds for the rotational instability of key blocks. Analytical results indicate that the limit breaking distance for “Key Block B” in the main roof is 24.49 m, which defines the primary zone for advanced reinforcement and hazard prevention. Furthermore, applying short-arm beam theory, this study clarifies how pre-split roof cutting disrupts the transmission of advance abutment pressure, identifying 8° as the optimal cutting angle. Building on these insights, a multi-faceted control system was implemented, combining hydraulic fracturing for pressure relief, pumpable backfill pillars, and an artificial false roof (utilizing a suspended I-beam structure 1.2 m above the floor). Field monitoring confirms that this collaborative approach effectively stabilizes the surrounding rock, ensuring the safe and continuous passage of the working face through parallel void areas.

The Huainan-Huaibei mining area is widely covered with calcareous clay layers, characterized by low freezing points, high frost heave, easy disintegration upon water exposure, and low strength. Its mechanical properties are complex and variable, posing significant challenges for the construction of frozen walls. To optimize the design of frozen walls in calcareous clay, this study examined remolded calcareous clay from deep layers in the Huainan-Huaibei area, utilizing equal-stress ratio true triaxial loading tests to systematically analyze the stress-strain behavior of frozen calcareous clay under varying confining pressures and temperatures. The results indicate that variations in confining pressure and the intermediate principal stress ratio significantly affect the mechanical properties of frozen calcareous clay. The stress-strain curves of frozen calcareous clay reveal typical nonlinear characteristics: the material exhibits an elastic response in the small-strain stage and gradually transitions into plastic deformation with increasing strain, showing significant strain hardening during the plastic deformation phase. Based on a hyperbolic model and fractional calculus, a fractional hyperbolic model was developed to suit complex stress conditions, with relevant model parameters derived. The study's findings provide a theoretical basis for rational shaft frozen wall thickness design and serve as valuable references for improving artificial ground freezing construction techniques.

Water-bearing weak red sandstone is commonly encountered in shaft and tunnel projects constructed by the artificial ground freezing method, where moisture and temperature jointly influence its mechanical behavior and failure evolution. To investigate these effects, this study used optical frequency domain reflectometry (OFDR)based distributed fiber optic sensing to monitor the internal horizontal strain field of red sandstone during uniaxial compression tests at moisture contents of 2%, 3%, and 4% and temperatures of -5, -10, and - 15 degrees C.The results show that, within the tested sub-saturated moisture range, rock strength increased with increasing moisture content and decreasing temperature, consistent with the strengthening effect of pore-ice cementation in frozen rock. For example, at -15 degrees C, the compressive strength of specimens with 4% moisture content was 17.8% higher than that of specimens with 2% moisture content. OFDR monitoring further revealed marked spatial heterogeneity in internal horizontal strain, characterized by the migration of localized deformation and damage concentration zones. Based on the coordinated evolution of strain rate, strain variance, and energy release rate, a multi-parameter precursor identification framework was established. Exponential relationships were also obtained between peak stress, peak horizontal strain, precursor stress, and the coupled moisture-temperature conditions. These findings improve the understanding of the deformation and failure evolution of frozen water-bearing red sandstone and highlight the potential of OFDR-based distributed sensing for internal strain monitoring and early warning in geotechnical engineering.

The coupled effects of fissure number and inclination on the mechanical behavior and energy evolution of rock masses are not fully understood, representing a critical gap in stability assessment. This study systematically investigates this interplay in granite under uniaxial compression using AE and DIC monitoring. Our results reveal three key findings: (1) Compressive strength and energy indicators exhibit a distinct “U-shaped” trend with inclination, minimizing at 45°, and decrease monotonically as fissure number increases. (2) The failure mechanism is governed by inclination, transitioning from tension-dominated (0°/90°) to shear-dominated (45°). (3) Rockburst proneness peaks at the 45° inclination and is significantly attenuated by the presence of multiple fissures. These findings clarify the complex relationship between fissure geometry and rock failure mechanisms, offering a quantitative basis for hazard prevention in fissured rock masses.

[Background]The Huanghuai mining area represents an important coal base in eastern China.However,the Cenozoic calcareous clay in the area exhibits high plasticity,low permeability,and potential expansion and deformation during freezing,leading to unstable freezing performance.Consequently,artificial ground freezing(AGF)in the area generally faces a risk of cost surge or out of control due to the excessive thickness or limited strength of frozen walls.[Methods]This study investigated calcareous clay remolded based on soil samples from the Huanghuai mining area.Us-ing a low-field nuclear magnetic resonance(LF-NMR)spectrometer and a high-pressure triaxial system,this study sys-tematically explored the variation patterns of unfrozen water content during freezing under temperatures ranging from 20℃ to-20℃,confining pressures from 1 MPa to 4 MPa,and initial water contents of 17.5％,22.5％,and 31.5％.Ac-cordingly,the impacts of these different factors on the triaxial strength of the frozen calcareous clay were determined.[Results and Conclusions]The results indicate that during the freezing of the remolded calcareous clay,unfrozen water content in the clay evolved through three stages-rapid decline,slow decline,and stabilization,sequentially,with a higher initial water content corresponding to a more distinct rapid decline stage.Accordingly,a modified power func-tion of unfrozen water content(wu)and freezing temperature(t)was developed,with a fitting accuracy(R2)of greater than 0.97.Triaxial test results reveal that the failure stress of the frozen calcareous clay increased significantly with de-creasing freezing temperature.In contrast,the stress increased nonlinearly with initial water content,while the increased amplitude decreased gradually.In the case where the confining pressure exceeded 3 MPa,the strength reversal phe-nomenon occurred due to both pressure-induced ice crystal melting and pore water lubrication at interparticle contacts,with the critical pressure interval determined at 2.5-3.5 MPa.By innovatively introducing the concept of coupling between unfrozen water content and cementation area into the Mohr-Coulomb failure criterion,this study created a mod-el enabling the strength of frozen calcareous clay to be predicted based on merely three parameters:freezing temperature,initial water content,and confining pressure.The correlation coefficient(R2)and average relative error between the mod-el-calculated and measured strength were determined at＞0.95 and＜5％,respectively.From the perspective of thermo-mechanical coupling,the prediction model established in this study allows for the quantitative characterization of the nonlinear and critical evolutionary patterns of calcareous clay strength with temperature,initial water content,and con-fining pressure during freezing.This model provides a theoretical basis and data support for analyzing the mechanical re-sponses of calcareous clay in low-temperature and high-pressure environments.

To cope with the complex and changeable stratum environment,the low-temperature refrigerant in the artificial freezing method construction has gradually developed from a single type to the combined use of multiple refrigerants.The creep characteristics of frozen soil and the shaft lining construction process are important factors affecting the stability of this type of heterogeneous frozen wall.To explore the stress and deformation characteristics of multi-refrigerant hetero-geneous frozen wall considering creep characteristics and the influence of shaft lining construction,the frozen wall formed by the combined freezing of brine and carbon dioxide was taken as the research object.The temperature characteristic cross-section at 1/4 of the pipe spacing away from the main surface of the frozen wall was selected to equivalatively re-place the temperature distribution of the frozen wall,and a temperature field model of the frozen wall was constructed us-ing a three-segment linear function curve.Based on viscoelastic theory and Newton Cotes numerical integration method,a mechanical calculation model for the interaction of heterogeneous frozen wall,shaft lining and peripheral soil with creep characteristics is established,and the analytical solutions of stress,strain and displacement of heterogeneous frozen wall with multiple refrigerants under different tunneling depths(Ⅰ,Ⅱ,Ⅲ)are derived.And the expressions of the external load and freezing pressure acting on the frozen wall and the outer shaft lining.The calculation results show that within 36 hours after the shaft lining pouring,the displacements and strains of both heterogeneous and homogeneous frozen walls show a nonlinear attenuation trend from the inside out.The displacements of the inner and outer edges of the frozen wall first increase and then decrease with the increase of creep time,while the external load of the frozen wall first decreases and then increases.The freezing pressure between the outer shaft lining and the frozen wall increases nonlinearly with the increase of creep time,while the freezing pressure of the heterogeneous frozen wall is always less than that of the homo-geneous frozen wall.Taking the tunneling depth of 600 m as an example,considering the heterogeneous characteristics of the frozen wall,the displacements of the inner and outer edges of the frozen wall decreased by 1.819-4.723 cm and 0.650-1.687 cm respectively during the creep time from 1 h to 36 h,while the external load of the frozen wall increased by 0.285％-0.772％.After further considering the shaft lining effect,the displacements of the inner and outer edges of the frozen wall decreased by 1.967-32.274 cm and 0.702-11.527 cm respectively,while the external load borne by the frozen wall increased by 0.309％-5.246％.The research results of this study can provide a theoretical basis for the design of multi-refrigerant combined freezing construction under complex stratum conditions.

The artificial ground freezing (AGF) method is frequently affected by groundwater seepage. Due to the combined effects of convective heat transfer by water flow and conductive heat transfer from the cold source, the artificial freezing curtain in a seepage field exhibits significant asymmetry. Most existing studies focus on brine freezing, whereas the ultra-low temperature properties of liquid nitrogen make it suitable for freezing projects in high-seepage environments. This study investigates the temperature field of three-pipe liquid nitrogen freezing. An equivalent partitioning and segmentation method is employed to determine the shape of the freezing curtain, an analytical solution for the steady-state temperature field of a three-pipe liquid nitrogen freezing curtain under high seepage-flow is derived. Through model tests and numerical simulations, the evolution of the three-pipe liquid nitrogen freezing temperature field under varying seepage conditions is analyzed, and the validity of the formula is verified. The results indicate that the calculated freezing temperature aligns well with both experimental and numerical results, confirming the validity of the analytical solution through model testing. A high-flow environment enhances heat transfer efficiency at the solid surface. As the flow rate increases, heat transfer efficiency improves, and the asymmetry of the freezing curtain becomes more pronounced. In multi-pipe freezing, the "adjacent pipe effect" occurs. When adjacent freezing fronts contract to the critical threshold (Lc), the freezing front expands more rapidly, shortening the intersection time of the freezing curtain. These findings provide valuable insights for designing liquid nitrogen artificial freezing systems in high seepage-flow.

Vibratory probe compaction is widely used to improve saturated dredged soil foundations; however, the variation of excess pore water pressure induced by the probe motion remains insufficiently understood. This study investigates the spatiotemporal response of excess pore water pressure during vibratory probe compaction through in situ monitoring at multiple depths and horizontal distances. The results reveal a multi-stage pore pressure response characterized by rapid accumulation followed by distance-dependent attenuation and subsequent dissipation. The peak excess pore water pressure exhibits a power-law decay with normalized horizontal distance, reflecting wave spreading and material damping. A unified formulation linking peak pore pressure and liquefaction degree is established, demonstrating that liquefaction potential inherits the same radial attenuation characteristics. Based on a liquefaction threshold of 0.6, the liquefaction influence range at 3 m depth extends to approximately 13 times the probe radius, while deeper layers have more limited zones. The dissipation time follows a generalized power-law scaling with distance, with an exponent smaller than the quadratic value, indicating vibration-induced changes in hydraulic diffusivity. A multivariate regression analysis further quantifies the link between the 80% dissipation time, liquefaction degree and the increase in cone resistance. The findings provide a theoretical basis for evaluating the effectiveness and influence range of vibratory probe compaction in saturated dredged soils.

To address the problem of severe strata pressure behavior and hydraulic support crushing accidents during the uphill mining stage of the 50,211 shallow buried coal seam working face beneath a gully, a directional long borehole hydraulic fracturing pressure relief technology for hard roof strata was investigated through a combination of theoretical analysis, numerical simulation, and field engineering practice. A load model and mechanical relationship model of the main roof cantilever beam in the uphill section beneath the gully were established to reveal the asymmetric roof loading characteristics and the mechanism of abnormal strata pressure behavior under gully terrain conditions. Numerical simulations were conducted to analyze the effects of hydraulic fracturing on roof stress evolution and overburden structural stability, thereby clarifying the pressure-relief mechanism of hydraulic fracturing in hard roof strata. Based on the gully distribution characteristics and borehole lithological data of the 50,211 working face, eight directional long boreholes were drilled perpendicular to the gully direction within the uphill section beneath the gully, and large-flow staged hydraulic fracturing was carried out. Fracture propagation and pressure-relief performance were comprehensively evaluated through pressure-flow monitoring and strata pressure monitoring. The results indicate that the directional long borehole hydraulic fracturing technology can achieve continuous and uniform weakening of the hard roof in the gully-affected area. After fracturing, the average periodic weighting interval of the working face was reduced by approximately 5 m. Safety valves were activated on only 12 hydraulic supports, corresponding to an activation rate of 1.71%. In addition, the coal wall remained intact, and no support crushing accidents or abnormal strata pressure events occurred. The study demonstrates that the proposed technology can effectively control severe strata pressure behavior during the uphill mining stage of shallow-buried coal seam working faces beneath gullies, providing a valuable technical reference for safe extraction under similar complex terrain conditions.

The vibratory probe compaction method has been increasingly applied to improve loess foundations in recent years. However, the underlying improvement mechanisms in structured loess, particularly under dynamic penetration and large deformation conditions, remain insufficiently understood. This study presents a numerical investigation of the vibratory probe compaction process in structured loess using the Geotechnical Particle Finite Element Method. An elasto-plastic constitutive model that accounts for structural evolution under cyclic loading is employed to simulate the dynamic behavior of the soil. The results show that probe penetration induces substantial soil displacement, with horizontal displacements extending up to approximately 5 times the probe radius (R). Vertical oscillations significantly alter both vertical and horizontal stress fields, leading to notable soil improvement. Volumetric plastic strain analysis indicates that the improvement effect is concentrated within a radial distance of 2–3R and a vertical depth of 1–2R below the probe tip. The compaction effectiveness is strongly influenced by vibration frequency, amplitude, and penetration velocity, with optimal values identified as 16 Hz, 3 mm, and 20 mm/s, respectively. These findings provide clear insights into the dynamic improvement behavior of structured loess and offer practical guidance for optimizing vibratory probe compaction in foundation engineering.

Under the influence of a seepage field, the artificial freezing curtain adopts a distinct asymmetrical shape due to the combined effects of convective heat transfer induced by groundwater flow and conductive heat transfer from the freezing pipes. This study investigates the temperature field of a dual-pipe freezing system configured in a linear arrangement. Based on steady-state temperature field theory, a zonal geometric equivalence method is proposed to simplify the complex geometry of the freezing curtain. Using this approach, analytical solutions for the steady-state temperature field of an asymmetric frozen curtain in fractured rock under seepage conditions, along with formulas for calculating its thickness and average temperature, were derived. A coupled seepage-temperature numerical model for artificial freezing in fractured rock was developed using COMSOL Multiphysics to validate the accuracy and applicability of the analytical solution. The results indicated that the isotherms exhibited a distinctive "heart-shaped" pattern at the outer edge of the freezing front. The calculated temperatures along key axes showed strong agreement with the numerical simulation results, confirming the validity of the analytical solution. The time required for the frozen wall to form a closed ring increased with fracture water velocity, and a critical velocity was identified beyond which complete closure could not occur. Overall, the steady-state analytical solution developed in this study accurately captured the temperature distribution of artificial freezing under coupled seepage-thermal conditions and provides a valuable reference for analyzing dual-pipe freezing temperature fields in fractured, highly permeable formations with strong seepage.

To investigate the instability mechanism of interbedded rock strata and remaining coal pillar groups during close-distance coal seam mining, this study takes the 3301 working face of Hanjiawan Coal Mine as the research object. Combining theoretical analysis with numerical simulation, a mechanical model of the "remaining coal pillar group-overburden" system was constructed. Using cusp catastrophe theory, the stability criterion for interbedded rock strata was derived, explicitly proposing that a cusp catastrophe occurs when the ratio of shear stiffness to thickness product between key and non-key strata is <0.206, triggering catastrophic instability. The results indicate that the load on remaining coal pillars is related to the roof flexural rigidity, overlying load, pillar spacing, and the elastic coefficient of concentrated coal pillars. The transfer of advanced abutment pressure and the reduction of k are identified as the primary causes of chain instability in coal pillar groups, leading to shear-sliding failure of interbedded rock strata. Numerical simulations confirm that the maximum vertical stress on coal pillars (8.26 MPa, stress concentration factor 2.95) occurs 4-6 m ahead of the working face when exiting concentrated coal pillars, triggering chain instability and dynamic mine pressure. This research provides a novel theoretical framework for safety control in close-distance coal seam mining.

In response to the urgent demand for efficient and environmentally friendly refrigerants in the artificial freezing technology of ultra-low temperature strata, this study innovatively proposes to use transcritical CO2 as a new type of refrigerant. Based on the self-developed double-pipe freezing physical model test system, by comparing the freezing processes of trancritical CO2 and alcohol in homogeneous sand layers and combining with the COMSOL numerical simulation of heat transfer in porous media, the system reveals the evolution of the temperature field and the development laws of the frozen wall. The results show that the temperature difference between the inlet and outlet of the trancritical CO2 reaches 25°C, which is significantly higher than that of alcohol at 3°C, highlighting its excellent heat exchange capacity. In the regions of the main surface (F5+ F5−), the interface (K+ K5−), and the axial plane (A0 U0), the temperature gradient formed by transcritical CO2 is more than 35

This study explored the feasibility of applying transcritical CO2 in an artificial ground freezing method. By carrying out indoor modeling tests, the temperature field evolution law and the development characteristics of the freezing front during the freezing process of transcritical CO2 in a sand layer were analyzed, and the freezing effect of transcritical CO2 was compared with that of traditional alcohol. The theoretical solution of the freezing temperature field was derived, and the accuracy of the theoretical analytical solution was verified by test results. The results showed that the freezing efficiency of transcritical CO2 was significantly higher than that of alcohol. After 6 h of freezing, the temperature range of the measuring point (C1–C7/C10–C16) can reach −28 °C–3.5 °C, and the freezing front radius exceeded 60 mm. The temperature range of the alcohol measuring point (J1–J7/J10–J16) was only −12.6 °C–8.8 °C, and it took 24 h to achieve the same radius. The test data were in good agreement with the theoretically predicted values, verifying the rationality of the theoretical formula. Freezing temperature Td had a significant influence on the calculation results of freezing front radius. After transcritical CO2 freezing for 24 h, the difference in the freezing front radius R(Td = −2) reached 8.02 mm when the freezing temperature Td was −2 °C and 0 °C. The difference in the freezing front radius caused by the freezing temperature Td was concentrated in the range of 1.5–8.1 mm, and the difference in the effect on different types of refrigerants was small. The research results not only confirm the feasibility of the application of transcritical CO2 in the freezing method but also provide test data and experience for engineering applications, which promotes the innovation and development of freezing method technology.

Calcium clay layers are widely distributed in the Huainan-Huaibei mining area, with the characteristics of low freezing point, strong frost heave, easy disintegration upon contact with water, and low strength, posing a severe challenge to construction using freezing methods. To investigate the mechanical response of frozen calcareous clay under complex stress paths, true triaxial compression tests were performed on the ZSZ-2000 frozen soil true triaxial test platform, varying confining pressures, temperatures, moisture contents, and intermediate principal stress ratios. The strength and deformation characteristics of frozen calcareous clay under these varying conditions were analyzed. The test results indicate that the strength of frozen calcareous clay has a good quadratic relationship with the intermediate principal stress coefficient b and confining pressure, is negatively correlated with temperature, and positively correlated with moisture content. Furthermore, the rate of increase in the failure strength of frozen calcareous clay decreases as the moisture content rises. The failure strength is significantly influenced by the intermediate principal stress and confining pressure, showing both strengthening and weakening effects. A critical intermediate principal stress coefficient of bc=0.75 and a critical confining pressure of sigma(3c)=3 MPa were identified. As the confining pressure rises, the volumetric strain gradually shifts from initial shear contraction followed by shear dilation to pure shear contraction. Moreover, as the b value increases, the peak volumetric strain of the samples also increases. Based on the experimental results, an improved Duncan-Chang model was developed, taking into account the effects of temperature, moisture content, and intermediate principal stress coefficient, and its reliability was verified. The research findings provide a theoretical foundation for optimizing frozen wall design and deep shaft excavation using freezing methods.

Using SFCC measurements obtained via nuclear magnetic resonance, a temperature–pore ice content relationship was established and a numerical simulation method for a thermo-seepage coupling model that accounts for high-seepage effects was developed. The method’s performance was evaluated by comparing results to an analytical solution for a single-pipe liquid nitrogen freezing scenario without seepage and to experimental data from a three-pipe freezing model under high-seepage conditions. Additionally, the approach was compared to the conventional Enthalpy-Porosity Method (EPM). The results show that: under no-seepage conditions, the numerical model predicts temperature distributions and freezing front radii with deviations below 5 %; under high-seepage conditions, the temperature discrepancy between simulation and experiment remains within 2 °C. Compared to EPM, the proposed method significantly reduces errors in closure time and computation time across seepage velocities ranging from 2.5 to 15 m/d; moreover, at high flow rates, the freezing wall maintains a nearly horizontally symmetric closure, avoiding the offset and distortion observed with EPM. This method enhances the accuracy and physical consistency of artificial ground freezing (AGF) simulations under high-seepage conditions, while also improving numerical stability and computational efficiency, thereby providing a more reliable tool for engineering design and safety assessment of liquid nitrogen freezing in high-permeability formations.

The thermal conductivity of soil is a key factor influencing the heat transfer process and temperature distribution, which has significant implications for the design and implementation of freezing methods in geotechnical engineering. To address the challenge of freezing the deeply buried sandy clay layer using the freezing method in the drilling wells of the Huainan-Huaibei mining area, experimental research was conducted on the thermal conductivity of sandy clay and its microstructure. Utilizing the transient plane source method, variations in thermal conductivity with water content, dry density, sand content, and temperature were observed, revealing the patterns and mechanisms underlying these changes. The findings indicate that the thermal conductivity of frozen sandy clay mainly undergoes three stages of temperature variation. During the rapid increase phase (II), the thermal conductivity rises sharply with decreasing temperature, exhibiting a "leap" trend. As the water content increases, the range of the thermal conductivity leap gradually narrows. When the water content increases from 15 % to 22.5 %, the corresponding leap range decreases to 0 similar to -5 degrees C. Microstructural parameters quantitatively reflect the intrinsic reasons for changes in soil thermal conductivity from a microscopic perspective, indicating that these characteristics significantly affect its thermal conductivity. (c) 2025 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).