To investigate the effect of polypropylene fiber doping on the tensile properties of tailings cemented filling materials，Brazilian splitting experiments were conducted on tailings cemented filling materials with different ash-to-sand ratios and polypropylene fiber contents.DIC technology was used to observe and analyze the initiation and propagation evolution of surface cracks on the specimens during the experiment，and scanning electron microscopy （SEM） was used to reveal the mechanism of the reinforcing effect of polypropylene fibers on the internal structure of tailings cemented filling materials.To examine the impact of polypropylene fiber incorporation on the tensile properties of tailings cemented filling materials，Brazilian splitting tests were performed on samples with varying ash-to-sand ratios and polypropylene fiber contents.Digital Image Correlation （DIC） technology was employed to observe and analyze the initiation and propagation of surface cracks on the specimens throughout the experiment.Additionally，scanning electron microscopy （SEM） was utilized to elucidate the mechanism by which polypropylene fibers enhance the internal structure of the tailings cemented filling materials.The findings of the study indicate that incorporating polypropylene fibers significantly enhances the uniaxial tensile strength of the filling material.As the polypropylene fiber content increases，the uniaxial tensile strength initially rises and subsequently declines，with an optimal fiber content identified at 0.6%.For instance，with an ash-to-sand ratio of 1∶4，the maximum uniaxial compressive strength of the filling specimen reaches 0.59 MPa，representing a maximum increase of 37.21%.Furthermore，the inclusion of fibers alters the stress-strain characteristics of the filled specimen.Upon reaching peak tensile strength，the PF-filled specimen did not immediately experience a loss in load-bearing capacity and retained a degree of residual strength.Notably，the residual strength of the specimen filled with 0.6% PF attained its highest value.Observations using Digital Image Correlation （DIC） technology reveal that the strain concentration phenomenon in fiber-reinforced fillers is mitigated during tensile failure，resulting in more tortuous crack patterns.This indicates that the fibers effectively facilitate stress dispersion.Scanning Electron Microscopy （SEM） analysis indicates that an excessive incorporation of fibers results in the enlargement of pores and cracks within the filling body specimen，consequently leading to a gradual reduction in its macro compressive strength.Conversely，an optimal quantity of fibers becomes encapsulated by a substantial amount of hydration product，specifically calcium-silicate-hydrate （C-S-H） gel，within the specimen.This encapsulation facilitates the integration of the fiber-filling body matrix interface into a cohesive unit due to the influence of the C-S-H gel，thereby enhancing the load-bearing capacity of the fiber-reinforced filling body.

Digital Image Correlation （DIC） technology facilitates non-contact，real-time monitoring and analysis of the dynamic mechanical behavior of materials by tracking speckle patterns on the surface of samples.Nevertheless，in the context of Split Hopkinson Pressure Bar （SHPB） testing，characterized by high strain rates and complex loading conditions，DIC technology encounters several challenges，including limited measurement accuracy and inadequate adaptability to environmental variations.In order to fully grasp the application status and optimization methods of DIC technology in SHPB test，based on the principle of SHPB test and DIC technology，the relevant research results on the improvement of large deformation measurement accuracy were summarized from the aspects of incremental correlation，shape function，initial value estimation and deep learning algorithm.Subsequently，based on the specific requirements of SHPB tests， practical optimization strategies for DIC technology were proposed， focusing on speckle fabrication techniques and material mechanical characteristics feedback.These strategies include the utilization of high-speed cameras and the optimization of image processing algorithms to improve the efficacy of the image acquisition and processing system.Additionally，efforts are made to augment the environmental adaptability of DIC technology，ensuring its stable operation in challenging conditions such as high temperature and high pressure.Combined with other testing methodologies，the implementation of multi-parameter measurement and comprehensive analysis facilitates a more thorough understanding of the dynamic mechanical behavior of materials.The application and optimization of DIC technology in SHPB testing are intended to enhance measurement accuracy，broaden the scope of applications，and advance the intelligence of the testing system.This approach is expected to yield more precise evaluations of the dynamic mechanical properties of materials，thereby providing substantial support for advancements in materials science and related engineering disciplines.

In natural settings，rock masses frequently contain various fissures that may exhibit parallel orientations，significantly influencing their mechanical properties.These fractured rock masses are continuously exposed to static loads，such as the weight of overlying rock in subterranean environments，as well as dynamic loads resulting from activities like drilling and blasting.The interaction between these loads and the rock mass is crucial for determining the stability of the rock mass，particularly in underground and mining contexts.This paper seeks to investigate the dynamic characteristics，energy dissipation，and damage mechanisms of parallel-fractured sandstone under cyclic impact testing at varying confining pressures （4，8，12，16，20 MPa），utilizing the Split Hopkinson Pressure Bar （SHPB） for experimentation.The primary aim of this study is to examine how cyclic loading affects the dynamic response and damage evolution of fractured rock masses.The experimental design involves subjecting parallel-fractured sandstone specimens to multiple impact cycles，with confining pressure varied across different levels.The results of the cyclic impact tests indicate that，under a constant confining pressure，the dynamic peak stress of fractured sandstone progressively decreases as the number of cycles increases.The relationship between peak stress and the number of cycles is found to be linearly negative，demonstrating a consistent reduction in the rock’s capacity to endure dynamic loading over time.Furthermore，the study explores the effects of varying confining pressures on the dynamic behavior of fractured sandstone.The findings reveal that as confining pressure increases，the peak stress initially rises and subsequently declines，suggesting that moderate confining pressures enhance resistance to dynamic loading.The maximum number of cycles required to reach failure occurs at a confining pressure of 12 MPa，indicating an optimal confining pressure for the sandstone’s resistance to cyclic impact prior to failure.This observation underscores the critical role of confining pressure in regulating damage accumulation and failure processes in fractured rock masses.Additionally，the study investigates energy dissipation during the cyclic impact process.Throughout the duration of the test，the proportion of reflected energy exhibits a continuous decline，decreasing from 27% to 12%，which constitutes a reduction of approximately 15%.Conversely，the proportion of transmitted energy demonstrates a steady increase，ranging from 41% to 55%，indicating an increase of 14%.The proportion of absorbed energy remains relatively stable，fluctuating between 33% and 35%，with minimal influence from variations in both confining pressure and the number of cycles.This consistent behavior of absorbed energy implies that the intrinsic energy absorption capacity of fractured sandstone remains stable regardless of the loading conditions.The progression of damage in fractured sandstone is also a central focus of this study.Cumulative damage increases progressively with the number of cycles，with the maximum cumulative damage recorded under cyclic impact at confining pressures of 4 to 16 MPa ranging between 0.137 and 0.165.The highest cumulative damage （0.165） is observed at a confining pressure of 4 MPa，whereas the lowest damage （0.092） is noted under a confining pressure of 20 MPa.The findings of this study indicate that lower confining pressures expedite the accumulation of damage，whereas higher confining pressures lead to a more gradual progression of damage.The research concludes that the rate of damage accumulation in fractured sandstone is accelerated during the initial impact phase and as failure approaches.Importantly，the damage incurred during a single impact is relatively substantial，underscoring the necessity of regulating both confining pressure and cyclic impact cycles to mitigate excessive damage and prevent premature failure.These results provide valuable insights into the dynamic behavior of fractured rock masses under cyclic loading，offering practical guidance for assessing the stability of underground rock masses subjected to similar loading conditions，such as those encountered in mining or tunneling operations.

The sulfide minerals present in the tailings of metal mines substantially influence the strength of backfill materials.This study aims to comprehensively investigate the mechanical properties of backfill composed of sulfur-containing and desulfurized tailings.For this purpose，sulfur-containing tailings sourced from a mine and desulfurized tailings processed through industrial trials were utilized as the aggregate in the backfill.Cement served as the binding agent in the preparation of backfill specimens.To evaluate the mechanical performance，uniaxial compression and Brazilian splitting tests were conducted，facilitating a comparative analysis of the desulfurized and sulfur-containing backfill specimens.The research examines the impact of varying cement-sand ratios，solid content concentrations，and curing age on the compressive strength of two types of backfill materials.Furthermore，quantitative relationships among these variables were derived by fitting the experimental data，and the sensitivity of each factor was assessed.The findings reveal that：（1）The com-pressive strength of desulfurized tailings backfill consistently exceeds that of sulfur-containing tailings backfill.The uniaxial compressive strength of desulfurized tailings exhibits an average increase ranging from 2.02% to 14.12% compared to sulfur-containing tailings，while the tensile strength demonstrates an enhan-cement between 7.64% and 58.45%.（2）At a curing age of 28 days and a cement-sand ratio of 1∶8，the uniaxial compressive strength of sulfur-containing tailings remains relatively unchanged with increasing mass concentration.In contrast，the strength of desulfurized tailings backfill displays a distinct upward trend.（3）At a cement-sand ratio of 1∶4，the compressive strength of both sulfur-containing and desulfurized backfill exhibits an increase with higher slurry concentrations after a 60-day curing age；however，this increase is less pronounced compared to the 28-day curing age.Conversely，when the cement-sand ratio is decreased to 1∶8，the strength enhancement of sulfur-containing and desulfurized backfill after 60 days surpasses that observed after 28 days.（4） The reduction in sulfide content enhances the chemical stability of desulfurized tailings，thereby improving the mechanical properties of the backfill.（5） The strength of the backfill is most significantly influenced by curing age，followed by the cement-to-sand ratio，with mass concentration having the least impact.（6） Under constant conditions，the strength of both sulfur-containing and desulfurized backfill exhibits an exponential growth trend with increasing curing age，achieving a goodness of fit value of 0.9 or higher.The study demonstrates a linear growth pattern in relation to the increase in mass concentration，evidenced by a multiple correlation coefficient of 0.94 or higher.This paper aims to offer a practical reference of significance for understanding the developmental behavior of the mechanical properties of sulfur-containing and desulfurization tailings backfill.

To investigate the damage characteristics of the mesoscopic and microscopic pore structures of sandstone subjected to freeze-thaw cycles in cold regions，and to offer theoretical support for construction projects in these areas，the authors selected sandstone with a pronounced freeze-thaw response as the experimental subject.Utilizing nuclear magnetic resonance （NMR） technology，the study obtained porosity data and T₂ distribution curve characteristics of sandstone across varying freeze-thaw cycles.This study examines the alterations in mass of rocks subjected to freezing and thawing cycles，focusing on changes in rock porosity，pore structure，and aperture distribution.Additionally，it investigates the freeze-thaw responses of various pore content types.Utilizing fractal theory and the Coats permeability model，the authors quantitatively characterize the pore structure of rocks affected by freeze-thaw processes.The research establishes the interrelationships among different pore structures，pore fractal dimensions，permeability，and porosity，ultimately identifying the pore types most significantly influencing freeze-thaw damage.The findings indicate that the rock mass exhibits a non-linear increase in response to the number of freeze-thaw cycles，with trends associated with macro disruptions.The T₂ distribution curve reveals that the pore size of the sandstone follows a three-peak distribution.Furthermore，both the porosity and the peak value of the T₂ distribution increase as the number of freeze-thaw cycles rises.However，the inconsistency between the freeze-thaw cycles and the changes in peak area and peak value can be attributed to the imbalance between the rate of pore initiation and the rate of pore expansion within the rock，in which the volume of small pores （T₂<3 ms） exhibited dynamic stability，whereas the volumes of medium pores （3 ms<T₂<33 ms） and macropores （T₂>33 ms） increased linearly.Notably，the expansion rate from small to medium pores exceeded that from medium to large pores.To comprehensively characterize the evolution of freeze-thaw damage，we employed integral fractal dimension，segmental fractal dimension，and permeability in our pore quantification analysis.The fractal dimension exhibits a negative correlation with the number of freeze-thaw cycles，wherein the fractal dimension of macropores （D_b） decreases linearly with increasing porosity.This suggests that rock damage due to freeze-thaw processes is primarily attributable to the behavior of free water within macropores.Conversely，permeability，a parameter employed to characterize freeze-thaw damage in pore throats，demonstrates a positive correlation with the number of freeze-thaw cycles，and it is negatively correlated with the fractal dimension of the macropores due to the expansion of large pores and connected pore throats induced by freeze-thaw effects.This expansion facilitates the migration of free water between the pores and pore throats，thereby enhancing the connectivity of the rock pore structures and subsequently increasing the specimen’s permeability.

This paper examines the issue of asymmetrical pressure at the entrance of a super-large section flat structure mine tunnel.The study employs numerical simulations，utilizing the finite difference software FLAC^3D，to analyze a proposed backfilling scheme.The simulations consider the impact of varying excavation sequences in double-line tunnels on the asymmetrical pressure problem.Consequently，numerical models were developed to examine four distinct excavation strategies：Unbackfilled with the left line excavated first，unbackfilled with the right line excavated first，backfilled with the left line excavated first，and backfilled with the right line excavated first.By analyzing the distribution of plastic zones，as well as the vertical and horizontal displa-cements of the tunnels under these varying excavation strategies，the feasibility of the backfilling approach was assessed and validated.The backfilling scheme effectively addresses the issue of uniform settlement of the surrounding rock under biased conditions，thereby mitigating the horizontal displacement of the tunnel vault and the horizontal convergence of the sidewall，ultimately enhancing the stability of the surrounding rock.The stress distribution within the tunnel’s surrounding rock follows the pattern of “arch foot>sidewall>arch floor>vault” with stress concentrations occurring at the arch foot and the vault being prone to tensile failure，which reflects the stress characteristics of the surrounding rock in super-large section flat structure tunnels.The implementation of a backfilling scheme mitigates issues related to loosening at the vault and asymmetrical stress distribution at the arch footings.Based on an analysis of surrounding rock deformation，the concept of secondary deformation is introduced，allowing for a comparative assessment of the secondary impacts of various excavation sequences on the tunnel.The findings indicate that，for the tunnels under study，the optimal excavation sequence post-backfilling is to first excavate the left line followed by the right line.Conversely，the optimal sequence prior to backfilling involves first excavating the right line and then the left line.The results of the final comprehensive evaluation indicate that initiating excavation on the deeply buried side of the tunnel post-backfilling significantly reduces the deformation of the surrounding rock.Based on numerical simulation outcomes，appropriate reinforcement measures are recommended for practical construction applications.Furthermore，an in-depth analysis of the stress distribution characteristics of the surrounding rocks and supporting structures in super-large section flat structure tunnels is conducted in conjunction with the on-site construction plan.The monitoring data closely align with the numerical simulation results regarding the deformation observed around the periphery of the tunnel’s cross-section.This congruence confirms the accuracy of the numerical model developed in this study and underscores the viability of the proposed optimized construction scheme.The findings presented herein offer theoretical support and serve as a data reference for the design and construction of the entrance bias section in super-large section flat structure tunnels.

Excavation disturbances induce high stress concentrations and stress redistribution within the mine rock body.Additionally，hydraulic factors diminish the rock body’s strength.Mines situated in the southern region of China are particularly susceptible to disasters during the rainy season due to the influence of rainfall.Therefore，investigating the combined effects of these factors on the mechanical properties of mine rock is of significant importance for ensuring the long-term stability of mine side slopes.The study utilized a slope rock body from the Yinshan Mine in Jiangxi Province as a sample and conducted a graded loading creep test based on a triaxial compression test to investigate the mechanical properties of millimeter-scale rock under the combined effects of excavation unloading and pore water pressure.The results indicate that，with increasing excavation unloading and pore water pressure，the short-term peak strength and elastic modulus of the saturated millimeter-scale rock progressively decrease.Under identical excavation unloading conditions，an increase in pore water pressure leads to a reduction in the strength of saturated millimeters due to the influence of the pore water pressure.This results in an increase in transient strain，a decrease in the transient elasticity modulus，and a reduction in resistance to deformation.Additionally，both creep strain and steady-state creep plasticity exhibit exponential growth with the increase in axial stress up to a certain threshold.Under identical pore water pressure conditions，the instantaneous strain and instantaneous elastic modulus of the excavation-disturbed specimen are lower than those of the undisturbed specimen.Additionally，the creep strain and creep rate escalate with the increasing degree of unloading due to excavation.This observation suggests that excavation-induced disturbances diminish the rock strength，rendering the rock body more susceptible to deformation.The findings indicate that the rock strength of phyllite is diminished due to excavation disturbances，rendering the rock mass more susceptible to creep damage.The study further reveals that the combined effects of excavation unloading and pore water pressure exacerbate this reduction in strength.Consequently，the rock mass becomes increasingly prone to creep damage，thereby compromising the stability of slopes.

To investigate the impact of freezing and thawing on the crack evolution characteristics during the fracture instabiligy processes of banded magnetite quartzite，mechanical and acoustic emission tests were conducted on the rock subjected to a temperature range of -20~20 ℃ and a maximum of 280 freeze-thaw cycles.The results indicate that the uniaxial compressive strength and modulus of elasticity decreased from 200.93 MPa and 21.67 GPa in the dry state to 106.64 MPa and 8.24 GPa after 280 freeze-thaw cycles，the reduction in strength and modulus of elasticity exhibited a tendency to stabilize during the later stages of freeze-thaw cycles，resulting in the establishment of a new dynamic equilibrium between the skeletal structure of the rock samples and their internal microcracks.Additionally，under conditions of low freeze-thaw cycles （defined as ≤40 cycles），the evolution of cracks in the rock samples primarily involved the development of tensile and shear cracks，with crack rupture predominantly occurring during the accelerated expansion phase of microfracture. The high freeze-thaw cycle （defined as exceeding 40 cycles） significantly influences the crack evolution process in rock samples，predominantly resulting in tensile cracks，while shear cracks are less prevalent compared to those observed in samples subjected to low freeze-thaw cycles.Notably，as the number of freeze-thaw cycles increases，there is a discernible trend toward a reduction in the overall cracking of the rock samples.Furthermore，during the accelerated expansion phase of microfractures in rock samples exposed to low freeze-thaw cycles，high and medium frequency signals emerge slightly earlier than their medium and low frequency counterparts，the amplitude associated with the high-frequency bands was elevated.During the phase of accelerated microfracture expansion in rock samples subjected to extensive freeze-thaw cycles，there was a simultaneous emergence of middle and high-frequency signals alongside middle and low-frequency signals.Furthermore，as the freeze-thaw cycle period increased，the amplitude corresponding to the ultra-high frequency in the rock samples progressively diminished.Under the influence of a low number of freeze-thaw cycles，high-energy signals predominantly emerge during the accelerated expansion phase of microfractures，characterized by a more concentrated distribution and increased frequency.Conversely，with a higher number of freeze-thaw cycles，the distribution of high-energy signals becomes more dispersed，and their frequency diminishes as the number of cycles increases.These signals are observed throughout the entire loading process. The rock samples subjected to a low number of freeze-thaw cycles exhibit fewer microfractures during the compression stage，the elastic deformation stage，and the microfracture development stage，with no apparent correlation to the location of fracture aggregation at the point of rupture.In contrast，for rock samples exposed to a high number of freeze-thaw cycles，there is a significant relationship between the cracks formed during the initial three stages and the locations where cracks aggregate at the time of rupture.The range of acoustic emission energy and the likelihood of high-energy acoustic emission events in rock samples subjected to a high number of freeze-thaw cycles were reduced compared to those subjected to a low number of freeze-thaw cycles.This observation further suggests that rock samples experiencing fewer freeze-thaw cycles are primarily characterized by the development of large and mesoscale fissures.In contrast，those subjected to more frequent freeze-thaw cycles are predominantly influenced by the expansion，merging，and fusion of localized fissure networks.

The cohesion（c） and internal friction angle（φ） of rock are critical parameters in the design and stability assessment of rock engineering projects.Direct measurement of these parameters necessitates condu-cting numerous rock triaxial or shear tests，which are both time-intensive and expensive.This study proposes the development of intelligent models to predict the values of c and φ based on four readily obtainable parameters：P-wave velocity（V_P），density（ρ），uniaxial compressive strength（UCS），and Brazilian tensile strength（BTS）.A total of 199 datasets containing various rock types were collected and randomly partitioned into a training set（80%） and a test set（2%）.The distribution characteristics and correlations among the data were analyzed using scatter plots for data distribution and correlation plots for variables.To address discrepancies in characteristic attributes，such as magnitude and order of magnitude across different input variables，a normalization function was applied.Subsequently，five ensemble trees were utilized to develop predictive models for rock shear strength parameters.Bayesian optimization was employed to optimize the hyperparameters of the models.Concurrently，five-fold cross-validation was implemented during model training.To evaluate the performance of the models，four widely recognized regression metrics were utilized：The coefficient of determination （R2），root mean square error （RMSE），mean absolute error （MAE），and variance accounted for （VAF）.Additionally，a ranking system was introduced to provide a comprehensive assessment of the five models.The model evaluation demonstrated that the constructed models exhibited robust predictive performance，with the extremely randomized tree model outperforming others.Specifically，for predicting the value of c，the R² was 0.993，the RMSE was 0.45，the MAE was 0.309，and the VAF was 99.306%.For predicting the value of φ，the R² was 0.97，the RMSE was 0.823，the MAE was 0.612，and the VAF was 97.058%.Furthermore，the application of the SHAP interpretation method for sensitivity analysis indicated that V_P，UCS，and BTS significantly influenced on the prediction of c，whereas ρ had a substantial impact on the prediction of φ.Finally，rock blocks were collected and processed into samples for physical-mechanical testing to determine the V_P，ρ，UCS，BTS，c，and φ values of rocks at various locations within the Jinchuan Ⅱ and Ⅳ mining areas in China.The model was effectively utilized to predict the c and φ values for rocks in the Jinchuan mining area，thereby validating its practicability.Furthermore，a graphical user interface was developed to facilitate ease of use for engineers and technicians in the field.

This study investigates the shear strength characteristics of loess under varying water content，with a specific focus on loess from Gansu Province.Through direct shear experiments and nuclear magnetic resonance tests，the research reveals the impact of water content on the shear strength of loess and its underlying microscopic mechanisms.The experimental findings indicate that increasing water content results in elevated internal porosity，an initial increase followed by a decrease in cohesion force，a reduction in the internal friction angle，and enhanced ductility of the soil samples.The mechanism underlying this change involves the alteration in water binding mode，matrix suction，and the degree of cementation between particles due to increased water content.When the initial water content of the soil sample is low，an increase in water content leads to the thickening of the strongly bound water film between particles，thereby enhancing the cementation effect and generating matrix suction，which in turn increases cohesion force.Concurrently，the lubrication of particles by water results in a reduction of the internal friction angle.When the optimal water content is surpassed，the soil sample exhibits a progressive expansion of cracks，an increase in the free water between particles，and a subsequent weakening of the cementation between particles and the matrix suction.This leads to a reduction in cohesion force and an increase in the internal friction angle due to the expansion of soil particles.Finally，when the water content approaches the liquid limit of the soil sample，the soil particles become obstructed by free water，leading to a reduction in the water film force between particles and rendering the cementation effect ineffective.Consequently，the matric suction is reduced to zero，resulting in cohesion approaching zero.Additionally，the occluding force between particles diminishes，causing a further decrease in the internal friction angle.This study also employed nuclear magnetic resonance （NMR） testing to further analyze the microstructural changes and internal water distribution within the loess.The experimental results indicated that an increase in water content led to a significant rise in the main peak of the NMR transverse relaxation time （T₂） spectral distribution.Additionally，the second wave peak exhibited a pronounced rightward shift，suggesting that water infiltrated the smaller pores.Furthermore，the small-sized pores within the soil appeared to expand and merge into medium-sized pores.The proportion of various pore types in soil samples under different water content conditions was also quantified through calculations.The findings indicate that an increase in water content leads to a reduction in the proportion of micropores within the soil，while the proportion of macropores increases，thereby enhancing the overall porosity of the loess soil sample.This phenomenon also contributes to the further diminution of the shear strength of the loess samples.

During the development of high-temperature true triaxial testing， the imposition of high-temperature environments， cyclic loading and unloading， cyclic thermal shocks， and other complex loading conditions necessitates stringent requirements for the thermal insulation performance of the test system. In oder to scientifically and rationally select appropriate thermal insulation materials for the high-temperature true triaxial test machines under such complex conditions， three kinds of high-temperature engineering thermal insulation materials （GX）， glass fiber， and high-temperature resistant resin composite thermal insulation material （BX） and high temperature barrier composite mica material （YM）were prepared. A series of laboratory tests， including cyclic thermal shock， high-temperature exposure， and cyclic loading and unloading， were conducted to simulate the mechanical and thermal conditions representative of operational environments. These tests aimed to evaluate the thermal conductivity， elastic modulus， compressive strength， and microstructural evolution characteristics of the materials under complex working conditions. The results indicate that the thermal conductivity of the three insulation materials initially increases and subsequently decreases with rising temperature under high-temperature conditions， while the elastic modulus exhibits a certain degree of reduction. During cyclic thermal shock experiments， the thermal conductivity of the YM material demonstrated a consistent decline with an increasing number of heating and cooling cycles. In contrast， the thermal conductivity values of the other two materials initially increased and then decreased.The variation in the elastic modulus exhibited a pattern analogous to that observed under high-temperature conditions. Under cyclic loading and unloading conditions， the thermal conductivity of the insulation material initially increases and subsequently decreases as the number of cycles progresses. Notably， the first cycle of loading and unloading exerts the most significant influence on the thermal insulation and physical properties of the material. Scanning Electron Microscopy （SEM） results indicate that the pores within the laminated structure of the YM material remained small following thermal shock， with no significant crack formation observed after high-temperature treatment. The structure was both complete and stable. A comprehensive evaluation of the thermo-mechanical properties revealed that， after exposure to high-temperature environments and cyclic thermal shock， the structural integrity of the YM material was exceptionally stable. Consequently， YM material is deemed the optimal choice for insulation in rock true triaxial testing machines. This study establishes a foundational framework for the selection of thermal insulation materials in true triaxial test equipment and offers significant guidance for both the research and application of thermal insulation material sheets in true triaxial test machines.

In order to examine the influence of hydration conditions on the mechanical properties of skarn，a Split Hopkinson Pressure Bar（SHPB） system was utilized to apply both axial and confining pressure.Cylindrical samples measuring 50 mm×50 mm were subjected to a combined static-dynamic loading method under natural and water-saturated conditions.The axial pressure applied was 3 MPa，with a confining pressure of 1 MPa.Impact tests were carried out at air pressures of 0.8，0.9，1.0，1.1，1.2 MPa，with three replicates con-ducted for each pressure level.The research examined the dynamic compressive strength，energy transfer characteristics，and fracture morphology of rock samples subjected to axial and confining pressures in different states.A comparison was made between the dynamic mechanical properties and fracture patterns of skarn samples in their natural and water-saturated states，with an analysis of the softening effect of water on the rock.Furthermore，the study investigated the dynamic mechanical properties，energy dissipation，and fracture morphology of skarn samples with varying water content.The findings suggest that the dynamic compressive strength of water-saturated skarn samples was，typically lower than that of samples in their natural state，with a reduction ranging from 10.47% to 16.32%.Nevertheless，the impact of water on the dynamic mechanical strength of skarn was found to decrease as the strain rate increased.Additionally，water was observed to decrease the energy absorption rate of skarn samples，although when the energy absorption density reached a certain threshold，the presence of water did not affect the dynamic compressive strength of the skarn.The impact fracture morphology of water-saturated and natural state samples exhibited differences in the strain rate effect due to hydration.Specifically，skarn in the natural state displayed more pronounced characteristics at lower strain rates.

In the extraction of overlying orebodies in complex environments，it is imperative to prioritize safety and efficiency while preserving the stability of rock strata to prevent surface collapse and safeguard structures.To accomplish these objectives，it is essential to develop effective strategies for managing rock strata movement by comprehensively assessing the impact of underground backfill mining.An initial study was conducted on the impact of various mining field structural parameters，including roof thickness，original rock stress，and backfill ratio，on overlying rock movement at the Panlong lead-zinc mine.This analysis utilized a nonlinear elastic foundation beam mechanical model.Subsequent numerical simulations were performed to determine overlying rock movement values under varying backfill ratios.The results were compared to those obtained from the mechanical model，revealing differences ranging from 3% to 9%，thus validating the reliability of the mechanical model’s results.A ground mine backfill mining technology for controlling settlement of overlying rock was proposed and implemented in industrial experiments.Research findings suggest that the primary factors influencing overlying rock movement，in order of significance，are the backfill ratio，structural parameters of the mining field，roof thickness，and original rock stress.Increasing the backfill ratio is crucial for managing overlying rock displacement，while adjusting anchor support spacing and backfill ratio according to the mining field structure are effective methods for controlling overlying rock displacement.

Composite rocks are widely present in underground geotechnical engineering such as tunnel excavation，mining projects，and oil and gas resource extraction.Composite rocks are formed by the layered accumulation of rocks with disparate properties，and are rich in fissures.The intricate features of these fissures，combined with the distribution of stress，collectively influence the stability of composite rocks，making them prone to disasters such as roof collapse，expansion of surrounding rocks，and significant tunnel deformations.Therefore，investigating the mechanical failure mechanisms of composite rocks under different confining pressures and fissure positions is of paramount importance for effectively preventing disasters in underground engineering construction.Based on the above reasons，this study prepared composite rock samples with pre-existing fissures，conducted triaxial compression tests by varying the fissure positions，and analyzed and summarized the influence of fissure positions and confining pressure on the mechanical behavior and failure modes of composite rock.The main conclusions are as follows：（1）Limestone exhibits the highest strength，while sandstone undergoes the greatest deformation under compression.The mechanical deformation of the intact composite rock sample falls between sandstone and limestone，with its strength controlled by the sandstone portion and deformation restricted by the limestone portion.（2） Under lower confining pressures，the intact rock sample and the one with fissures in limestone exhibit brittle failure，while the one with fissures in the contact zone and sandstone exhibits ductile failure.With the increasing of confining pressure，rock samples generally exhibit ductile failure，and the dominant factor in the failure characteristics shifts from the fissure position to the confining pressure.The volumetric contraction of the rock sample increases with the rise in confining pressure，and the volumetric expansion is minimal when fissures are in sandstone.Volumetric contraction is influenced by confining pressure，while volumetric expansion is influenced by fissure position.（3）In uniaxial compression，unstable crack propagation occurs earliest，and at this point，fissures have the greatest impact on the mechanical properties of the rock sample.In triaxial compression，with a constant fissure position，higher confining pressures result in more stable crack propagation when fissures are in limestone.Simultaneously，the strength and elastic modulus of the rock sample show an increasing trend with the change in fissure position from limestone，through the contact zone，to sandstone.With constant confining pressure，crack propagation is most stable when fissures are in sandstone，and the degradation of the sample is minimal when fissures are in limestone.（4）When fissures are in limestone，tensile cracks dominate，whereas in sandstone，shear cracks predominant.With the increasing of confining pressure，the failure mode of the composite rock sample shifts from tensile failure to shear failure，gradually transitioning from fissure-dominated to confining pressure-dominated failure modes.

In order to study the pore structure change and strength deterioration characteristics of marble under different microwave irradiation power and time，the pore structure evolution characteristics of marble under different microwave power and time were analyzed based on nuclear magnetic resonance technology.With the increase of microwave irradiation power or microwave radiation time，the quality，hardness，wave velocity，peak strength and elastic modulus of marble all show different degrees of decline，and the porosity of the rock increases，and the degree of fragmentation is obvious.They are verified by tests such as acoustic waves and rock mechanical strength.At the same time，the damage degradation model of microwave radiation was established based on NMR，and the damage model had good effect.The damage model can further reflect the damage degree of three kinds of damage variables such as porosity under microwave radiation，and can provide reference for the study of damage and deterioration of similar rocks.In addition，the energy evolution process of marble was analyzed based on the energy dissipation theory.With the increase of microwave power or irradiation time，the release amount of elastic energy becomes less and less，and the elastic deformation changes to plastic deformation.With the increase of microwave radiation time from 60 s to 300 s，the total energy and elastic energy both show a linear downward trend，while the dissipated energy showes a linear upward trend，that is the total energy decreased from 350.93 kJ/m³ to 299.07 kJ/m³，with a decrease of 14.78%.The elastic energy decreases from 311.68 kJ/m³ to 240.49 kJ/m³，with a decrease of 22.84%.The dissipated energy increases from 39.25 kJ/m³ to 58.58 kJ/m³，with an increase of 49.25%.When the microwave irradiation power increased from 1 kW to 3 kW，the total energy and elastic energy also show a linear decline trend，and the dissipative energy showes a linear increase trend，that is the total energy decreases from 334.58 kJ /m³ to 289.70 kJ /m³，with a decrease of 13.41%.The elastic energy decreases from 287.39 kJ/m³ to 223.07 kJ/m³，with a decrease of 22.38%.The dissipated energy increases from 47.19 kJ/m³ to 66.70 kJ/m³，with an increase of 41.34%.The results show that the quality，hardness，wave velocity，peak strength and elastic modulus of marble decrease and the porosity increases with the increase of microwave irradiation power and time.With the increase of microwave irradiation power and time，the internal energy of the sample is converted，the proportion of dissipative energy is increased，and the proportion of elastic energy is decreased.The research results reveal the changes of pore structure and energy evolution of marble under microwave irradiation，which also has certain reference significance for the damage evolution mechanism of other types of rock.

Research on damage mechanism of anchor bolt structure under dynamic and static pull-out is very important to the design and construction，the numerical calculation model was established based on elastoplastic damage model of anchorage agent and bond-slip model of anchorage interface，and parameter “static ratio” and sinusoidal dynamic load model with variable amplitudes were also introduced.The numerical model was verified by laboratory test firstly taking deformation curve of anchor bolt as example，then the damage mechanisms of anchor bolt structures with different interface strengths under composite loads were studied，which includes the damage process，mode and characteristics，and the influence of static ratio was also analyzed simultaneously.Results show that three damage modes of anchor bolt structure are included under influence of anchorage interface strength，namely single damage mode（anchorage interface sliding），three phases damage mode（oblique&horizontal cracks of anchorage agent and interface sliding），two phases damage mode（oblique and horizontal cracks of anchorage agent）.Anchor bolt slides with the anchorage interface when the interface strength is small，while the oblique crack of anchorage agent generates with the increase of interface strength，and the dip angle becomes smaller，the oblique crack zone becomes larger，while the oblique crack doesn’t extend to anchorage interface.Bearing capacity of anchor bolt structure increases with the increase of static ratio when it’s less than 70%，while it decreases gradually on the contrary.Ultimate displacement of anchor bolt structure and cycle time of dynamic load decrease with the increase of static ratio.Peak load of anchor bolt structure under composite loads is less than the static condition，and the decrease is apparent of post-peak bearing capacity.In engineering application，strength increases of anchorage interface and agent are suggested，and decrease of static ratio as well，especially the reduction of dynamic impact load.

Rock mass quality classification is the foundation of initial underground engineering design and construction.In order to evaluate rock mass quality more accurately，this study used beluga whale optimization（BWO）to optimize random forest model（RF），a BWO-RF model which can be used for rock mass quality evaluation was proposed.At the same time，the rock mass quality evaluation models of sparrow search al-gorithm optimized random forest（SSA-RF），particle swarm optimization optimized random forest（PSO-RF）and non-optimized random forest（RF） were constructed for comparison.Before the models construction，a data-base containing 131 engineering cases data was established through literature review and field test data collec-tion.After writing the code of models construction，the training and testing of the four models were completed by using the database.Based on the model test results，five model evaluation indexes，accuracy，precision，recall，F1 score and AUC，were used to compare and select the best model of the four kinds of rock mass quality eva-luation models.The results show that the BWO-RF model has the best performance among the four kinds of rock mass quality evaluation models，and each evaluation indexes of model are better than the other three mo-dels，indicating that the BWO-RF model has better practicability in the evaluation of rock mass quality.Through the test set，the prediction accuracy of BWO-RF model proposed in this study is 90%，which can provide a reliable reference for practical engineering construction and has practical engineering application value.

To delve into the size-related effects and directional properties of the roughness on rock fracture surfaces，this paper focus on analyzing the roughness correction coefficient C within the refined formula of the cubic law，as it effectively characterizes the roughness of natural rock fractures. Since Louis first introduced the cubic law，numerous scholars have since proposed numerous modified formulas，including those by Zhang Youtian，Zimmerman，and Xiong et al. Through conversion，we acquire the calculation formula for the roughness correction coefficient and utilize collected natural fractures for related computations.High-precision 3D scanning technology was used to scan natural rock samples and acquire roughness data of fracture surfaces. By combining this data with publicly available high-precision CT scan data of rough rock fractures，we generate spatial coordinates.Both formulaic and numerical methods were used to calculate and analyze the roughness correction coefficient C. Using the formulaic approach，the roughness correction coefficient for sample sizes ranging from 10% to 100% of the fracture surface were calculated and varying results were obtained，which indicates that roughness exhibits a scale effect. According to the numerical method，a well-fitting ellipse was obtained，indicating that the roughness correction coefficient possesses directionality and can be expressed using tensor notation. This conclusion is further supported by calculating the JRC value of rough fractures and their surface and crack width fractal dimensions，revealing that the roughness of fracture surfaces exhibits scale effects and anisotropy. Upon further investigation，it is discovered that the roughness correction coefficient tensor or roughness tensor，when combined with average crack width，can be utilized to form a single crack permeability tensor that quantifies the rough surface in complex rough crack network models

As the demand for transportation increases in China，more and more highway tunnels adopt the form of super-large section.However，there is still a lack of clear guidance for the design and construction of super-large section tunnels with four lanes or more in the current highway tunnel specifications. There is still a need for in-depth research on the section shape，construction methods，and construction mechanics of super-large section tunnels. Existing research indicates that the use of the benching method for excavation construction of super-large section tunnels is feasible. To obtain the optimized schemes for bench length and anchor rod spacing，numerical simulation was performed in this study to investigate seven different scenarios based on the upper and lower bench construction sections of a certain super-large section flat structure tunnel.The scenarios included bench lengths of 30 m，40 m，50 m，and 60 m，as well as anchor rod longitudinal spacings of 1.0 m，1.5 m，and 2.0 m. The distribution patterns of the plastic zone in the surrounding rock mass，the stress of the surrounding rock，and the deformation of the surrounding rock were analyzed.The study results indicate that the overall maximum principal stress around the tunnel shows a trend of “arch foot>arch waist>arch crown”.An increase in bench length or anchor rod spacing leads to a significant increase in the maximum principal stress at the arch crown. Overall，the settlement and horizontal convergence values of the tunnel arch crowns increase with the increase in bench length. An increase in anchor rod spacing requires other support structures in the initial support to exert stronger control over surrounding rock deformation，potentially leading to the destruction of the support structure. Based on the numerical results and on-site monitoring data，considering factors such as construction efficiency and rock stability，the optimized scheme with a bench length of 50 m and an anchor rod spacing of 1 m was applied in the construction site.The results of this research has high reference value for the optimal selection of excavation and support parameters for super-large section flat structure tunnels.

In order to study the load transfer characteristics and the slippage process of anchorage segment of the pressure-type anchor cable in soil strata，the formula of shear stress and axial force distribution of the anchor cable under external load was derived based on theoretical analysis.In addition，the load transfer characteristics was analyzed.The influence degree of soil compressive modulus，anchor diameter，load and Poisson’s ratio on axial force and shear stress were analyzed in detail.The shear stress and axial force in the anchorage segment of the cable has the same distribution function and is all power functions.The shear stress and axial force are the largest near the bearing plate，but far from the bearing plate，the shear stress and axial force gradually decrease to zero.The magnitude and distribution range of the shear stress and axial force in the anchorage segment mainly depend on the anchorage force，and are related to the diameter，elastic modulus and Poisson ratio of anchor body，the compressibility modulus and Poisson ratio of soils，and friction angle of the interface between anchors and soils.In the form of the formula，if the anchorage segment is infinite，the anchoring force P can be infinite in theory.The ultimate anchoring force depends on the strength of the anchors around the bearing plate，the soil and the interface.The position of the maximum shear stress is only related to the soil properties，material parameters and radius of anchorage in anchorage segment of prestressed cable，not related to the magnitude of load.The diameter of anchors also has significant influence on the distribution of shear stress and axial force.With different loads，the distribution form，range and peak position of shear stress is the same，which is independent of load.Under the same conditions，the larger the compressive modulus of soil，the larger of shear stress，and the faster the shear stress decline trendation.The Poisson’s ratio has little effect on the shear stress.When the value of Poisson’s ratio is different，the mechanical property of the whole anchorage system under external load is basically unchanged，and also the value of shear stress.The range of action remains and the axial force is unchanged.In order to verify the correctness of the theoretical analysis results，the load transfer test results of the anchor cable were obtained by in-situ tests of clay and sandy soil.The in-situ test results show that the theoretical analysis results are in good agreement with the engineering results.The research results can provide a basis for analyzing the stress state and optimizing design of soil anchorage engineering.

In order to solve the problem of fuzzy uncertainty of index parameters between adjacent grades of rock quality evaluation， the theory of topology was introduced and the topological rock mass quality grading model based on optimal combination weight was proposed to evaluate the quality of rocks in underground mining of the phosphate mine in Kunyang No.2 mine.According to the geological characteristics of the mine，six influence indexes，namely，uniaxial saturated compressive strength of rock（R_c），rock quality index（RQD），joint spacing（J_d），structural surface condition（J_f），groundwater status（W） and geostress influence coefficient（Z） were selected，and each index was divided into five grades.Then，the subjective and objective weights of the indicators were determined by the improved hierarchical analysis and entropy weight methods，respectively，and the moment estimation method was introduced to optimize the combination of subjective and objective weights.Finally，the modified RMR method and Q-system method were applied to evaluate the quality of the rock mass，and the grading results were compared with the quality classification results of the rock mass based on the optimal combination weights.The results show that，among the five rock masses to be evaluated，the evaluation result for the upper ore body rock is Class Ⅱ，with a characteristic value of 2.57，indicating good rock mass quality and certain self-stabilizing ability.It is determined that the support method of anchor spraying and hanging net should be adopted.For the lower ore body，the characteristic value is 3.68，indicating that the rock mass quality is approaching Class Ⅳ，and the stability of the surrounding rock in the roadway is poor.Immediate initial spraying should be carried out after the excavation of the roadway to control the deformation of the surrounding rock，followed by the use of the anchor spraying and hanging net support method.There are differences in the grading results of the upper ore body N₃，and the grading results of the rest of the rock bodies by the proposed method are the same as those of the modified RMR method.The overall low evaluation results using the Q-system method are caused by the failure to take into account the role of geostress and the discontinuity in the grading between the grades.In addition，the model is able to determine the degree to which the rock mass quality grade leans towards the adjacent grade.The classification results are consistent with the geological exploration report of the Kunyang No.2 mine，and are more accurate than the modified RMR method and Q-system method，validating the reliability of the method proposed in this paper and providing technical support for underground mining.

In engineering operations such as geothermal development and utilization in high-temperature rock formations，underground coal gasification，multiple oil extractions，underground disposal of high-level radioactive waste，and protection and restoration of important buildings after fires，rocks often experience thermal shock due to drastic temperature changes.Thermal shock refers to the phenomenon where an object undergoes a large amount of heat exchange in a short time due to rapid heating or cooling，resulting in the generation of thermal shock stress within the object.To investigate the impact of thermal shock on the dynamic fracture behavior of high-temperature granite，the granite was heated to three different temperature levels of 100，300，600 ℃，followed by cooling using three different methods of furnace cooling，air cooling，and water cooling to provide different cooling rates，resulting in varying degrees of thermal shock within the granite samples.The notched semi-circular bend （NSCB） specimens of the granite samples subjected to thermal shock treatment were tested using a split Hopkinson pressure bar （SHPB） system for dynamic fracture behavior.The fracture pattern of the specimens was recorded using a high-speed camera.The results show that with the increase in specimen temperature and cooling rate，the dry density and longitudinal wave velocity of the specimens decrease significantly，and the porosity increase.Under thermal shock，the dynamic fracture toughness value of the specimens decreased significantly.At the same loading rate level，the dynamic fracture toughness value of the water-cooled specimens is lower than that of the air-cooled specimens，indicating that the crack propagation resistance of rock materials decrease when subjected to dynamic impact.Furthermore，at loading rates higher than 130 GPa·m^0.5/s，the effect of thermal shock on fracture toughness is more pronounced.By analyzing the relationship between dynamic fracture toughness and loading rate，a power law function with a good fitting degree is obtained，revealing the impact of thermal shock on dynamic fracture toughness.Therefore，this study provides valuable reference for the stability of rock formations in cooling treatment projects involving high-temperature rocks，contributing to the design and management of engineering operations such as geothermal development and utilization，underground coal gasification，multiple oil extractions，underground disposal of high-level radioactive waste，and protection and restoration of important buildings after fires.

In the process of tailing cemented filling goaf，the discontinuity of the filling operation causes delamination of the filling body at the interface of the two fillings.In order to study the mechanical properties of the layered tailing cemented backfill and improve the deterioration effect of stratification，three types of delaminated backfill specimens，namely，intact non-delaminated，interface natural delamination，and interface sandblasted delamination，were produced.Each delamination type contains three material ratios of 1∶4，1∶6，and 1∶8 for ash-sand ratio，and uniaxial compression tests were conducted on specimens at curing ages of 3 d，7 d，14 d and 28 d to compare and analyze the deformation and damage characteristics of specimens with different delamination characteristics，different material ratios，and different curing ages.The results show that：（1） The delamination phenomenon significantly affects the mechanical properties of the tailing sand cemented backfill，considerably reducing the uniaxial compressive strength and the elastic modulus.Comparing the intact unstratified，naturally stratified specimens，the strength reduction rate caused by stratification increase ranged from 1.41% to 19.09% and exponentially with the increase of the curing age and ash-sand ratio.It indicates that the more significant the ash-sand proportion and the longer the maintenance age，the more pronounced the weakening effect of delamination of the backfill.Comparing the naturally delaminated and sandblasted delaminated specimens，the strength gain rate due to sandblasted delamination ranges from 1.92% to 16.26%，which increases with the increase of the ash-sand ratio，decreases firstly with the rise of the curing age and then remains flat and stable，and shows a higher strength gain rate in the early curing period.（2） The modulus of elasticity of the three-layered backfill types increases exponentially with the maintenance age.The discount of the modulus of elasticity of the natural layering relative to the complete layering increases with the rise in the maintenance age and decreases with the decrease of the gray sand ratio.The modulus of elasticity of the sandblasted layering relative to the natural layering only has a relatively apparent increase at 3 d，and the rest of the age is basically at the same level.（3） Using the rate of decrease of the post-peak strength curve as the ductility evaluation criterion，the post-peak strength curves of the three-layered types of backfill show better post-peak ductility with the decrease of ash-sand ratio，and it becomes more and more evident with the increase of maintenance age.The post-peak ductility performance of different layered types of backfill is in the order of interface sandblasted layered>interface natural layered>complete non-layered.（4）The damage of the delami-nated backfill is mainly in the form of tensile damage and conjugate shear damage，and the delamination surface makes part of the vertical compressive stress transformed into horizontal tensile stress，and the cracks inside the specimen are concentrated in the soft delamination surface，which makes the compressive strength of the backfill reduced.Sandblasting treatment can improve force transmission on the delamination surface to a certain extent.In order to reduce the degradation of the material’s mechanical properties by delamination，sandblasting，and other roughening treatment can be carried out on the last filling surface at the interval of the second filling.

Bedding structure slate can be always observed in civil and mining engineering in recent years，their physical and mechanical properties are significantly controlled by the existing bedding planes，which are generally considered as weak links that can cause various geological disasters.The fracture behavior of bedding structure slate under dynamic loading is therefore a critical issue for the selection of blasting parameters，stability analysis of rock mass，collapse and burst disaster prevention in tunnel，drift，and other underground structures.In order to investigate the effects of the inclination angle of bedding plane and impact velocity on the dynamic fracture behavior of bedding structure slate，the dynamic impact test and numerical simulation method inserted cohesive element were conducted on the notched semicircular bending（NSCB） specimens by a split-Hopkinson pressure bar（SHPB）system.Tests of NSCB specimens under static loading were conducted for comparison，and the inserted cohesive element method was also used to develop the numerical model of layered NSCB specimens under dynamic loading.The fracture initiation and propagation process of the layered specimen under varied loading conditions were modeled.The results show：（1）Impact velocity and the inclination angle of bedding plane has obvious influence on the crack propagation，and three typical cracking paths can be found for NSCB specimens under both static and dynamic loading.（2）The crack propagates along the bedding plane and then directly propagates to the loading point，the cracking path evidently exhibits dependence on the impact velocity and the inclination angle of bedding plane.For specimens under static loading，the dominated crack is more likely to propagate along the bedding planes while the cracks tend to ignore bedding planes as the impact velocity or the inclination angle of bedding plane increases.At the same time，the crack length along the bedding plane is considerably reduced under dynamic loading than under static loading.（3）It is obvious that the impact velocity and the inclination angle of bedding plane have important influence on fracture toughness，it becomes larger with the increasing impact velocity or the inclination angle of bedding plane.