ObjectivesExisting studies on zonal fracture of surrounding rock mainly focus on single tunnels， whereas the zonal fracture mechanism of surrounding rock in deep-buried multiple tunnels remains unclear in practical engineering. Therefore， the zonal fracture mechanism of surrounding rock during excavation of deep-buried multiple tunnels was investigated.MethodsTaking the diversion tunnels of the Jinping II Hydropower Station as the engineering background， a numerical model based on the strain-softening constitutive model was established. The variation laws of zonal fracture morphology， maximum radial distance of fracture zones， and number of fracture zones with strength parameters， deformation parameters， and dilation angle after excavation unloading were analyzed. In addition， the influences of these parameters on the zonal fracture characteristics of surrounding rock were compared.ResultsThe results show that the fracture patterns around the four tunnels exhibit a certain symmetrical distribution after excavation unloading. More severe zonal fracture phenomena occur in the surrounding rock of Tunnel No. 2， and the zonal fracture on the right side of Tunnel No. 1 is more significant than that on the left side. With decreasing internal friction angle， cohesion， and elastic modulus， or increasing dilation angle， the zonal fracture becomes more pronounced. Poisson's ratio mainly affects the locations of fractured zones. As Poisson's ratio decreases， the fractured zones on both sides of the tunnel gradually migrate deeper into the surrounding rock， whereas the fractured zones near the crown and invert move closer to the tunnel wall. Among all parameters， the strength parameters have the greatest influence on the zonal fracture morphology， followed by the deformation parameters， while the effect of dilation angle is relatively small.ConclusionsThe study reveals the zonal fracture mechanism of surrounding rock after excavation unloading of deep-buried multiple tunnels and provides theoretical support for surrounding rock support design in deep underground multi-cavern excavation engineering.
Objectives To analyze the influence of karst caves on the construction of large-section tunnels,and to investigate the deformation,failure,and water inrush characteristics of tunnel surrounding rock under various occurrence states of karst caves.Methods Based on the Shuangbei Tunnel project,considering the stress-damage-seepage coupling effect of the surrounding rock,numerical simulations were conducted using FLAC3D software.The simulations analyzed the displacement,failure zone,water-conducting fracture channels,and water inflow characteristics of the large-section tunnel surrounding rock under five factors and four levels:the angle between the karst cave and the tunnel center,the clear distance between the karst cave and the tunnel,the diameter of the karst cave,the water pressure in the karst cave,and the initial permeability coefficient of the rock mass surrounding the karst cave.The range analysis method was system-atically used to evaluate the impact of karst caves on the deformation,failure,and water inrush degree of the tunnel surrounding rock.Results The results show that:under conditions without a karst cave,the maximum displacement of the tunnel surrounding rock is 104.1 mm,the failure zone exhibits a"butterfly-shaped"distribution,with failure width and height of 7.0 m and 25.9 m,respectively.When a dry(water-free)karst cavity exists near the tunnel,the plastic zone of the surrounding rock expands and extends toward the karst cave,and the maximum displacement increases by approximately 30%～42%.When a water-rich,high-pressure karst cave exists near the tunnel,one or several water-conducting fracture channels form in the rock mass between the tunnel and the karst cave,and the maximum displacement of the surrounding rock exceeds 1,000 mm.The range values for the influence of the five karst cave occurrence parameters on the maximum displacement of the tunnel surrounding rock are 215.8,443.4,453.1,869.3,and 227.5 mm,respectively.The range values for the influence on the failure area of the tunnel surrounding rock are 351.8,102.1,372.5,243.3,and 166.4 m²,respectively.The range values for the influence on the total water inflow of the tunnel surrounding rock are 1 797.3,2 829.4,1 747.6,2 336.5,and 2 816.0 m³/h,re-spectively.Conclusions When karst caves near the tunnel contain no groundwater,their impact on the sta-bility of the large-section tunnel surrounding rock is relatively small.When groundwater is present,there exists a critical water pressure value that triggers the formation of water-conducting fracture channels between the tunnel and the karst cave,leading to overall sliding instability and water inrush.Among the five karst cave occurrence parameters,the water pressure in the karst cave determines the final displacement magnitude of the tunnel surrounding rock.The diameter of the karst cave and the angle between the karst cave and the tunnel center are key parameters affecting the extent and degree of failure of the tunnel surrounding rock.The clear distance between the karst cave and the tunnel,the initial permeability coefficient of the rock mass surrounding the karst cave,and the water pressure in the karst cave are the most important parameters controlling local and overall water inflow into the tunnel.
ObjectivesTo clarify the mechanical response of fractured sandstone under coupled freeze-thaw cycling and confining pressure conditions， the effects of freeze-thaw cycles and confining pressure on its mechanical properties and failure mechanisms were investigated.MethodsGray sandstone was selected as the research material. Intact， single-fractured， and cross-fractured specimens were prepared and subjected to 0， 30， 60， and 90 freeze-thaw cycles. Uniaxial compression tests and triaxial compression tests under confining pressures of 5 MPa and 10 MPa were conducted.. Stress-strain curves were obtained， and characteristic stresses including crack closure stress， crack initiation stress， and peak stress were extracted. Combined with analyses fracture distribution and failure patterns， the mechanical evolution of different specimens under freeze-thaw and confining pressure coupling was systematically investigated.ResultsWith increasing freeze-thaw cycles， the characteristic stresses of all specimen types decreased， and the overall stiffness was reduced. Intact specimens exhibited significant early-stage damage followed by a gradual stabilization. Single-fractured specimens showed rapid crack propagation in the initial stage and slower development thereafter. Cross-fractured specimens exhibited the most complex damage evolution due to interactions among fractures. Under low confining pressure， multiple crack types and complex failure patterns were observed. Under high confining pressure， the failure mode gradually transitioned from shear-dominated failure to shear-tensile composite failure. Freeze-thaw cycling intensified stress concentration at fracture intersections. Under uniaxial loading， failure tended to be tensile-dominated or disintegrative， while under triaxial conditions with low confining pressure， shear-tensile composite failure was dominant.ConclusionsFreeze-thaw cycling and confining pressure jointly govern the mechanical evolution of fractured sandstone. Freeze-thaw cycling significantly weakens rock strength and promotes crack coalescence， while confining pressure partially suppresses deterioration and inhibits tensile cracking. Compared with intact specimens， cross-fractured specimens exhibit greater reductions in peak strength and characteristic stresses. Their fractures tend to propagate in multiple directions and form interconnected fracture networks， thereby enhancing the sensitivity of fractured sandstone to freez-thaw damage and mechanical loading. These results provide theoretical support for tunnel construction， slope stability evaluation， and disaster prevention in cold-regions engineering.
ObjectivesTo investigate the effects of altitude， gas emission rate， distance between the air supply outlet and the tunnel face， and ventilation velocity on the diffusion and migration of gas in high-altitude gas tunnels during construction， a multi-factor coupled prediction model for gas concentration at the tunnel face was established.MethodsA three-dimensional numerical model was established using computational fluid dynamics （CFD） software. Nineteen working conditions were designed using a single-factor control variable method to analyze the influence of each key factor on gas migration in the tunnel. Based on a four-factor， four-level orthogonal experimental design and multivariate nonlinear regression analysis， a multi-factor coupled prediction model for gas concentration at the tunnel face was constructed. Field measurements and numerical simulation results were used to validate the model accuracy.ResultsThe results show that the gas concentration at the tunnel face increases exponentially with altitude. When altitude increases from 0 km to 5 km， the average gas concentration in the stable flow region rises from 0.072% to 0.128%. A strong positive linear correlation exists between gas concentration and gas emission rate. When the gas emission rate increases from 1 m³/min to 7 m³/min， the average gas concentration at different sections in the stable flow region stabilized within the range of 0.03%-0.23%. The minimum gas concentration at the tunnel face occurs when the distance between the air duct outlet and the face is 10 m. Gas concentration shows a clear inverse power-law relationship with ventilation velocity， and a reduction of up to 44.4% is observed when velocity exceeds 16 m/s. The proposed model achieves a coefficient of determination of 0.903， and the relative prediction error is within 2.79%-4.54%.ConclusionsThe proposed model can effectively predict the gas concentration at the tunnel face under varying altitudes， gas emission rates， ventilation velocities， and air duct positions， providing a scientific basis for ventilation design and gas hazard prevention in high-altitude gas tunnels.
ObjectivesTo safely dispose of the large amount of radioactive waste generated by nuclear energy， the permeability and mechanical properties of barrier materials under optimal proportions were investigated.MethodsThe main properties of bentonite-gravel-sand buffer materials under the optimal proportion were studied， including the relationship between the material proportion and the maximum bulk density. Simulation tests were carried out to explore the bearing capacity and permeability of an artificial simulated foundation.ResultsThe results show that the maximum bulk density of the material is positively correlated with the fine particle content within a certain range. When the fine particle content increases from 5% to 20%， the maximum bulk density increases. The maximum dry density of the material is related to the bentonite content and water content. The lower the bentonite content，the lower the maximum dry density； the higher the water content， the lower the maximum dry density. Under high compaction， the buffer material exhibits high foundation bearing capacity， with no proportional limit in the bearing capacity curve， and a low permeability coefficient. The average permeability coefficient is 1.577 8×10-5 cm/s，indicating a weak permeable layer with good impermeability.ConclusionsThe optimal proportion of the buffer material is related to the content of each component， mainly controlling the maximum dry density by affecting the porosity of the material. The optimal proportion is 10% bentonite + 24.4% manufactured sand + 65.6% gravel. The bearing capacity of the buffer material is related to its compactness. Under the optimal proportion， the buffer material exhibits high bearing capacity and better impermeability， and is classified as a weak permeable layer.
Objectives To address the limited particle size range in studies on the morphology of recycled coarse aggregates and the insufficient research on their effects on concrete properties.Methods 3D laser scanning and image processing techniques were used to analyze the morphology distribution patterns of sphericity,convexity,roughness,and 3D fractal dimension of recycled coarse aggregates in the 4.75～31.5 mm range,and to investigate their effects on the workability and mechanical properties of concrete.Results The results show that:1.The greatest heterogeneity in sphericity and roughness was observed in re-cycled coarse aggregates of 4.75～9.5 mm,whereas convexity heterogeneity peaked in the 9.5～16 mm range.Aggregates of 26.5～31.5 mm exhibited the lowest heterogeneity in sphericity,convexity,and roughness.2.With increasing particle size,the average sphericity remained largely unchanged;convexity first decreased and then increased;roughness first decreased,then increased,and finally decreased again;the 3D fractal dimension gradually decreased.3.Recycled coarse aggregates in all particle size intervals showed strong fractal characteristics,with a 3D fractal dimension of 2.010 for the 4.75～31.5 mm interval.4.A decrease in the proportion of spheroidal and irregular aggregates reduced concrete slump,while compressive and splitting tensile strengths initially increased and then decreased.5.Among the morphological parameters,3D fractal dimension and sphericity had the greatest influence on workability;3D fractal dimension most af-fected compressive strength,and sphericity most affected splitting tensile strength.Conclusions Sphericity is largely independent of particle size,whereas convexity,roughness,and 3D fractal dimension vary with particle size.These morphological parameters have varying degrees of influence on the workability and me-chanical properties of concrete.
Objectives The pipe-roof box culvert jacking method has been widely applied in underground construction in risk-sensitive areas owing to its strong deformation-control capability and limited environ-mental impact.However,research on ground settlement induced by deformation of the pipe-roof structure during the jacking process remains insufficient,and current design practice still relies heavily on engineer-ing experience,lacking systematic theoretical guidance.Therefore,this study investigates the characteris-tics of ground settlement induced by pipe-roof deformation during pipe-roof-supported box culvert jacking.Methods Based on a transfer-passage project at a railway station,a three-dimensional finite-element model considering the interlocking effect of male-female joints was established to systematically analyze the coupled deformation behavior of the pipe-roof structure and surrounding soil during box culvert jacking.According to the mechanical characteristics of the pipe-roof structure and the coupled deformation mechanism between the pipe-roof and soil,the pipe-roof structure was simplified as an elastic thin plate on an elastic foundation.Combined with the two-dimensional soil displacement field theory,a ground-settlement predic-tion model considering both pipe-roof deformation and soil-structure interaction was developed.The pro-posed model was further validated through numerical simulations and field measurements.Results The re-sults indicate that:(1)the pipe-roof structure with male-female interlocking joints exhibits deformation and mechanical behaviors closer to those of an elastic thin plate in both transverse and longitudinal direc-tions;(2)based on the deformation characteristics of the pipe-roof structure during box culvert jacking,the contraction ratio of the pipe-roof-box culvert section was obtained,and a ground-settlement calculation method for pipe-roof-supported box culvert jacking was proposed by incorporating the two-dimensional dis-placement field theory;and(3)the maximum ground settlement predicted by the proposed method differed from the numerical simulation results by approximately 7%,while the maximum errors in the transverse and longitudinal directions compared with field measurements were approximately 16%and 13%,respec-tively.In addition,the transverse and longitudinal settlement trough profiles agreed well with both the numerical simulation and field measurement results.Conclusions The proposed ground-settlement calcula-tion method can effectively characterize the evolution of ground settlement during box culvert jacking under pipe-roof support and can provide a useful reference for settlement analysis and prediction in similar under-ground engineering projects.
ObjectivesTo address the engineering challenge of resource utilization of industrial solid wastes， particularly shield muck， and to optimize a solid waste-based geopolymer grouting material using response surface methodology.MethodsA solid waste-based geopolymer grouting material， with shield muck as the primary component and other industrial wastes as supplementary materials， was developed through D-optimal mixture design and response surface methodology. The D-optimal mixture design was employed to determine the optimal proportions of solid powders， including shield muck， slag， steel slag， and fly ash. Subsequently， response surface methodology was used to investigate the effects of activator modulus， activator concentration， liquid-to-solid ratio， and binder-to-sand ratio on flowability， 28-day compressive strength， and flexural strength of the hardened grout.ResultsResults showed that the grouting material exhibited favorable flowability and mechanical properties when the solid powder proportion consisted of 60% shield muck， 20% slag， 15% steel slag， and 5% fly ash. Analysis of variance showed that activator concentration had the most significant effect on flowability， followed by activator modulus， binder-to-sand ratio， and liquid-to-solid ratio. As activator concentration increased， the flowability of the grouting material decreased， whereas the 28-day compressive and flexural strengths of the hardened grout increased. Activator modulus had the most significant effect on the 28-day compressive and flexural strengths of the hardened grout， followed by activator concentration， binder-to-sand ratio， and liquid-to-solid ratio. As activator modulus increased， flowability improved， whereas the 28-day compressive and flexural strengths decreased. The quadratic prediction models established for flowability， 28-day compressive strength， and flexural strength exhibited coefficients of determination greater than 0.9， and the relative errors between predicted and experimental values were less than 8%， indicating high model reliability.ConclusionsThe developed solid waste-based geopolymer grouting material exhibits excellent flowability and mechanical properties. These findings provide technical guidance for material selection in tunnel grouting projects and offer a feasible approach for the resource utilization of shield muck and other industrial solid wastes.
ObjectivesDuring the tunnel construction， layered rock structures are prone to problems such as vault collapse and initial support cracking. Therefore， it is of great engineering value to deeply analyze the mechanical characteristics of layered rock.Carbonaceous slate， as a typical rock mass of layered metamorphic rock， exhibits poor interlayer cementation and is easily broken， which can lead to serious structural damage when tunneling through it， significantly reducing rock mass strength and altering its mechanical properties. This study aims to analyze the mechanical properties and clarify the disintegration mechanism of carbonaceous slate.MethodsStatic disintegration tests， uniaxial compression tests and triaxial compression tests were carried out on carbonaceous slate. The mechanical properties of slate under different water content states and different bedding plane angles were analyzed， and the deformation failure modes and disintegration mechanisms of rock samples were discussed.ResultsThe results show that： （1） The peak strength of dry samples is higher， the pre-peak stress-strain curve is approximately linear， and plastic failure occurs suddenly. The elastic modulus of the dry samples is higher than that of natural and saturated samples. After the peak strength， dry and natural samples exhibit different degrees of brittle drop， while the post-peak strength of the saturated samples （23.02 MPa） can still be maintained at approximately 21 MPa. （2） After multiple disintegration cycles， the disintegration degree of weakly weathered slate is low. For moderately weathered rock， water molecules entering the rock mass destroy cementation bonds and promote the formation of broken blocks， leading to disintegration. For fully weathered and strongly weathered slate， water absorption and swelling generate uneven stress， driving complete disintegration of the rock samples.ConclusionsThe research results can provide a reference for controlling large deformation and failure in soft rock tunnel construction under similar conditions.
ObjectivesHighway tunnels often suffer from unsymmetrical loading， shallow overburden， and fractured surrounding rock， leading to significant discrepancies between theoretical calculations and field monitoring data. To develop a refined calculation method for shallow-buried tunnels in Class V rock and to analyze the spatial effect， a refined finite element analysis method based on 3D real-scene modeling is proposed.MethodsA shallow-buried portal section of a highway tunnel in Henan Province was selected as the case study. An unmanned aerial vehicle （UAV） oblique photography technique was used to build a high-precision real-scene model. Contour lines were extracted to establish a refined 3D finite element model， which realistically represents the actual overburden load on the tunnel. Using field monitoring data of crown settlement， the mechanical parameters of the Class V rock were back-calculated. The accuracy of the calculated values was then verified using monitoring points from subsequent construction sections. The calculated results from 2D tunnel finite element models with different overburden depths were compared with those from the 3D model to analyze the spatial effect of the shallow-buried tunnel.ResultsWith the Mohr-Coulomb constitutive model and an elastic modulus of E=0.2 GPa， the finite element results matched the field crown settlement data closely， with verification point errors of 3.9% and 8.7%. The settlement deformation during construction of the shallow-buried tunnel exhibits a significant spatial effect. When the ratio of tunnel depth（H） to tunnel width（B） equals 2， the 2D model can predict tunnel settlement deformation reliably. For H/B>2， the 2D model overestimates the settlement compared with the 3D model； for H/B<2， the 2D model underestimates the settlement.ConclusionsUsing a real-scene model generated by UAV oblique photography， a finite element model can be established rapidly. The back-calculation of parameter E based on monitoring data effectively predicts tunnel settlement. Moreover， the crown settlement deformation of shallow-buried tunnels shows a clear spatial effect.
ObjectivesThe influence of servo strut control on the displacement of adjacent existing tunnels during deep excavation was analyzed.MethodsA two-dimensional finite element numerical model， based on a deep excavation project in soft soil in Hangzhou， was established. The small-strain hardening constitutive model was used to simulate soil behavior. The deformation mode of the retaining wall after applying the active deformation control technology using reinforced concrete double-waling servo struts was studied， along with its influence on the displacement and deformation of an adjacent existing shield tunnel. The influence zone of tunnel displacement induced by excavation was delineated and compared with that under the conventional wall deformation mode without servo struts.ResultsThe simulation results show that when the servo strut technology is applied with a relatively large strut force threshold， the retaining wall deforms in an S-shape， which is significantly different from the conventional inward convex deformation mode. Under servo strut control， shallow adjacent tunnels experience horizontal displacement away from the excavation， while tunnels located at greater depths still undergo horizontal displacement toward the excavation along with the wall. The maximum horizontal displacement still occurs near the excavation bottom close to the wall. When the tunnel is shallow， settlement occurs near the wall and slight heave occurs farther away； the tunnel deformation is dominated by horizontal convergence. When the tunnel is deeply buried， the tunnel deformation is mainly characterized by vertical convergence.ConclusionsThe servo strut control technology is significantly effective in controlling the displacement of tunnels located very close to the excavation， but its effectiveness is limited for tunnels that are farther away and shallowly buried.
ObjectivesTo overcome the limitations of high cost and complex data processing in traditional tunnel segment monitoring technologies， as well as the influence of wide-angle lens distortion of panoramic cameras on the reliability of segment feature extraction， this study investigates a metro tunnel segment extraction method based on the Scaramuzza distortion correction model using panoramic cameras to meet the requirements of routine and refined monitoring of metro tunnel segments and ensure tunnel operation safety.MethodsFocusing on high-precision segment monitoring and accurate extraction of geometric features， an imaging geometric mapping relationship is established based on the Scaramuzza model， and homogeneous constraint equations are constructed to estimate the intrinsic and extrinsic camera parameters. The optimal polynomial order is determined using a stepwise order-increasing verification method to optimize calibration performance， with reprojection error adopted as the core evaluation index. After lens distortion correction， a 3D tunnel model is constructed and ring-wise unfolding of tunnel segments is achieved. The effectiveness of the proposed method is validated from three aspects： linear feature restoration， geometric shape recovery， and accuracy evaluation.ResultsExperimental results show that the average reprojection error of calibration based on the Scaramuzza model is reduced to 0.33 pixels， representing an improvement of approximately 37.9% compared with the Fisheye model. After distortion correction， the maximum perimeter deviation and maximum angular deviation of the calibration checkerboard are 1.93 mm and 0.04°， respectively. In addition， the average positional uncertainty of connection points in the 3D model is reduced by 33.24%， indicating improved data quality.ConclusionsThe proposed method features non-contact measurement， full-coverage detection， and strong robustness， while achieving a balance among monitoring accuracy， efficiency， and cost. It provides a feasible approach for refined monitoring of metro tunnel segments and similar application scenarios and demonstrates practical engineering value.
ObjectivesThe horizontal load-bearing mechanism of rock-socketed single piles under different loading paths remains unclear. Therefore， this study investigates the load-bearing behavior of rock-socketed piles subjected to multidirectional horizontal cyclic loading.MethodsBased on a self-developed horizontal cyclic loading test apparatus， field horizontal cyclic loading tests were conducted in four loading directions （0°， 45°， 90°， and 135°） to investigate the horizontal load-bearing behavior of rock-socketed piles under multidirectional cyclic loading.ResultsThe results indicate that the horizontal displacement of the pile decreases with increasing embedded depth. Multidirectional horizontal cyclic loading subjects the surrounding rock mass to cyclic pressures from different directions， resulting in plastic deformation around the pile. The plastic deformation gradually stabilizes with variations in loading direction and the number of loading cycles. The increase in pile bending moment is mainly concentrated within the first 15 loading cycles. After 1 000 cycles， the bending moment no longer increases. The fixity provided by the weathered rock layer is mainly concentrated within the embedded depth range of 0-1.5 m. The peak surrounding rock resistance occurs at an embedded depth of 0.5 m and remains unchanged with the number of loading cycles. As the number of loading cycles increases， the surrounding rock resistance gradually stabilizes. The p-y curves under 0°， 45°， and 90°horizontal cyclic loading are approximately linear， whereas the p-y curve under 135° loading exhibits a nonlinear response. After more than 15 loading cycles， the surrounding rock reaction begins to decrease， accompanied by a reduction in the stiffness of the pile-rock interface.ConclusionsMultidirectional cyclic horizontal loading causes the horizontal load-bearing mechanism of rock-socketed piles to exhibit pronounced path-dependent characteristics， with the shallow strongly weathered rock mass playing a dominant role in controlling the bearing performance. Multidirectional cyclic loading accelerates the degradation of the equivalent stiffness of the pile-rock system and promotes the development of a nonlinear p-y response. In the later loading stages， rock mass failure becomes the key factor limiting the horizontal bearing capacity of rock-socketed piles.
Objectives To solve the problems of poor soil squeezing effect and low side resistance of PHC pipe piles caused by short deposition time and high sensitivity of alluvial strata in the lower reaches of the Yellow River,an experimental study on the compressive bearing capacity of PHC pipe piles after grouting under these stratum conditions was conducted.Methods The post-grouting method and the test pile length were selected as variables,and in-situ tests were carried out based on a project under construction.The post-grouting methods were pile-end post-grouting and combined pile-end and pile-side post-grouting,and a non-grouting control group was set.Piles of 15 m and 19 m in length were installed,with three test piles in each group.The bearing layers were silty clay and silt,respectively.Each group included a combined post-grouting pile,a pile-end post-grouting pile,and non-grouting pile.Strain gauges were attached to the test pile shafts,and load cells were installed at the pile ends.Static load tests were conducted to investigate the variation in pile resistance.Results Compared with the control group,the ultimate bearing capacity of the combined post-grouting test piles increased by 77%(15 m)and 55%(19 m),respectively,while that of the pile-end post-grouting test piles increased by 26%(15 m)and 19%(19 m).After combined post-grouting,the side resistance of the silt layer increased by 96%,and that of the silty clay layer increased by 64%.The pile-soil relative displacement required for the side resistance of the lower soil to reach the limit increased from 5～7 mm to 15～20 mm.When silt was the bearing layer,the improvement in end resis-tance was better than that of the silty clay:combined post-grouting increased end resistance by 84%,and pile-end post-grouting increased by 52%.Conclusions PHC pipe pile post-grouting technology is suitable for alluvial strata in the lower reaches of the Yellow River.It can effectively improve the compressive bear-ing capacity of PHC pipe piles,enhance pile stability,and improve the elastoplastic deformation behavior of the pile-soil system.The results can be directly used to guide engineering practice.
ObjectivesTo investigate the differences in mechanical properties and energy evolution characteristics of precracked granite specimens under unfilled and gypsum-filled conditions， a comparative study on the mechanical behavior and energy evolution of unfilled and gypsum-filled precracked granite was conducted.MethodsGranite specimens containing a central circular hole and prefabricated cracks with different inclination angles were prepared. Considering the influence of gypsum filling， uniaxial compression tests were carried out to investigate the mechanical behavior and energy storage characteristics of the specimens.ResultsThe results show that the peak strength and elastic modulus of both unfilled and gypsum-filled granite increase linearly with increasing crack inclination angle， whereas the peak total input energy and energy storage limit increase exponentially. Gypsum filling does not alter the influence of prefabricated cracks on the peak strength， elastic modulus， or energy evolution characteristics of granite. However， gypsum filling improves specimen integrity and absorbs part of the external input energy， thereby increasing both the energy required for failure and the energy storage capacity of the specimens. This enhancement effect is more pronounced when the crack inclination angle ranges from 0°to 60°， but becomes weaker when the angle ranges from 60° to 90°. In addition， to characterize the energy evolution during specimen failure， an elastic strain energy evolution model based on the energy suppression principle was proposed， and its reliability was verified.ConclusionsThe results can provide theoretical guidance for grouting reinforcement of fractured rock masses.
ObjectivesTo investigate the consistency of intact rock deformation parameters under various loading conditions， a study was conducted based on the generalized Hooke’s Law.MethodsThrough theoretical derivation and laboratory tests，the characteristics of rock elastic modulus and Poisson’s ratio were systematically analyzed under three loading conditions： triaxial compression （three-dimensional stress）， Brazilian disc splitting（two-dimensional stress）， and uniaxial compression （one-dimensional stress）.ResultsThe results indicated that the elastic moduli measured by the three loading methods exhibited high consistency. Compared with the uniaxial compression reference，the relative errors of both triaxial compression and Brazilian disc tests were within 6.1%. It was quantitatively verified that the deformation parameters of intact rock are material constants independent of geometric shape and stress state. In uniaxial compression tests， the method for determining the elastic modulus depended on the calculation approach due to the non-linear characteristics of the stress-strain curve. In contrast， such method-dependent behavior was avoided in triaxial compression and Brazilian disc tests， which yielded more stable results. Furthermore，the consistency of elastic modulus and Poisson's ratio measured by cylindrical and rectangular specimens was demonstrated. This characteristic was attributed not only to the elastic nature of the rock but also to the material geometry and testing theory.ConclusionsThese findings provide a basis for the rational selection of rock mechanics parameter testing methods.
ObjectivesTo address the problems of long testing periods and high costs associated with traditional methods for measuring rock compressive strength， a prediction method for granite uniaxial compressive strength based on ensemble learning was proposed.MethodsAxial compression tests were conducted on granite specimens under different working conditions using an electronic universal testing machine. Based on the experimental results and published data， a dataset for granite the uniaxial compressive strength under multiple working conditions was established. Six different machine learning algorithms were selected to develop prediction models within an ensemble learning framework. The performance of the models was comprehensively evaluated using multiple evaluation metrics， and feature importance analysis was subsequently performed on the input variables.ResultsThe results indicate that the uniaxial compressive strength of granite is significantly affected by different working conditions. All established ensemble learning models exhibited good predictive performance. The overall model performance was ranked as follows： Random Forest， Gradient Boosting， Adaptive Boosting. Feature importance analysis further revealed that the relative importance of the influencing factors followed the order： heating temperature， geological conditions， heating-immersion cycle， immersion temperature， immersion time， cooling method， heat-transfer solution.ConclusionsAmong the ensemble learning models， the RF model achieved the best overall predictive performance. The analysis also showed that high temperature has the most significant influence on granite uniaxial compressive strength. The proposed model provides a new approach for predicting the uniaxial compressive strength of granite under multiple working conditions.
ObjectivesThe current indoor experiments on microwave-assisted mechanical rock breaking typically involve placing the sample directly in the microwave cavity for full exposure. However， this approach does not align with the actual construction scenario where rocks exposed to microwaves only receive single-sided irradiation. Therefore， it is necessary to conduct indoor experiments that simulate the actual engineering condition where the irradiated rock is only exposed on one side.MethodsIn this study， basalt was wrapped in copper foil to modify the traditional experimental method. The study examined the heating characteristics， P-wave velocity，and damage variables of basalt under single-sided irradiation with different irradiation parameters. Additionally， the dynamic properties of basalt after single-sided irradiation were investigated using the SHPB （split Hopkinson pressure bar） system.ResultsThe results showed that after conducting microwave irradiation experiments with the improved method， the thermal images of the samples differed significantly from those obtained using the traditional method. The temperature difference became more pronounced with decreasing sample height. With different irradiation times， the rate of temperature increase on the upper surface of the copper-wrapped rock gradually approached a linear trend as the power increased. The side temperature， from top to bottom，first increased rapidly， then gradually decreased， and finally leveled off. The difference in P-wave velocity increased with increasing power under constant irradiation time. The damage variable increased with the increasing irradiation time and power. When the microwave irradiation energy was the same，the dynamic strength of the rock decreased more with higher irradiation power. The fragmentation size at the unwrapped end of the sample was significantly smaller than that at the wrapped end， with a more obvious size gradation， resembling the rock damage observed in actual construction scenarios.ConclusionsThe results of the improved microwave and dynamic experiments indicate that the improved method is closer to real-world conditions compared to traditional methods
Objectives During the continuous operation of a deep geological repository,groundwater in the surrounding rock continuously erodes the lining concrete,causing it to gradually age and decompose,pro-ducing highly alkaline solutions.Meanwhile,the nuclear waste in the repository continuously decays and generates heat,steadily raising the temperature inside the repository environment.Under these alkali-thermal conditions,the water retention performance of the bentonite buffer layer material will change.To ensure the effectiveness of the buffer barrier performance,an in-depth investigation into its water retention performance was conducted.Methods The saturated salt solution method was employed to determine the wa-ter retention performance curves(degree of saturation Sr vs.suction s)of compacted MX80 bentonite speci-mens under alkali-thermal conditions.The effects of alkali solution concentration(CNaOH=0,0.1,0.3,1.0mol/L)and temperature(T=20,60,90℃)on the water retention performance were investigated.Com-bined with previous XRD and MIP test results from the research group,the mechanisms by which alkali concentration and temperature affect water retention performance were analyzed.Results The results indi-cate that under alkali-thermal conditions,the water retention performance of compacted bentonite speci-mens decreases with increasing alkali concentration and temperature.The higher the alkali concentration and temperature,the more significantly the water retention performance degrades.The change in water re-tention performance of bentonite under alkali-thermal conditions is caused by the alteration of montmorillon-ite content.Temperature accelerates the alkali-induced dissolution of montmorillonite,indirectly leading to a decline in water retention performance.The water retention performance of bentonite decreases with the reduction of montmorillonite content,and there is a clear linear relationship between the two.Conclusions The evolution of water retention performance of bentonite under alkali-thermal conditions was thoroughly discussed.The research results can provide scientific data support for the prediction of hydraulic conductiv-ity and the performance evaluation of engineering barriers.
Objectives To investigate the deformation and failure characteristics of rock mass under the influ-ence of fracture persistence and confining pressure,triaxial compression tests were conducted on rock specimens.Methods The evolution laws of mechanical properties and mechanical behaviors of fractured rock mass were analyzed.The coupled effects of fracture-induced damage and load-induced damage,as well as the resulting macroscopic mechanical responses,were theoretically characterized.Results The re-sults show that as confining pressure increases,the peak point of the stress-strain curve shifts to the right,the post-peak softening segment declines more gently,and the plastic behavior becomes more pro-nounced.Confining pressure promotes rapid activation of defects,inducing microcracks to propagate and co-alesce around pre-existing fractures and specimen ends,ultimately leading to macroscopic rock failure.With increasing fracture persistence,tensile strains gradually transform into compressive strains,and the rock undergoes tension-shear composite failure.The tensile failure observed in stage Ⅱ is essentially the result of the combined coalescence of secondary shear cracks and tensile cracks.An expression relating the total damage of rock mass under loading to the superposition of the two damage components was estab-lished.Using statistical damage theory and the D-P criterion,a damage constitutive model for fractured rock mass was developed to describe the nonlinear effect of fracture persistence on rock damage and failure.The physical meanings of the model parameters were clarified:m represents the brittleness characteristics of the rock mass,and F₀ reflects its average strength.Both m and F₀ show a decreasing trend with increas-ing fracture persistence.The variations in these parameters,reflecting changes in ductility-brittleness and strength characteristics of the rock mass,are consistent with the experimental results,thereby validating the proposed model.Conclusions The findings provide a theoretical basis for evaluating the stability of frac-tured rock mass engineering projects.
