The rock masses in the hydro-fluctuation zone of reservoir banks sustain wettingdrying cycles(WDC),thereby affecting the stability of the reservoir bank slope.In this paper,rock masses with argillaceous siltstone and ...The rock masses in the hydro-fluctuation zone of reservoir banks sustain wettingdrying cycles(WDC),thereby affecting the stability of the reservoir bank slope.In this paper,rock masses with argillaceous siltstone and silty mudstone interbedded in Badong Formation were taken as the research object to investigate the variation of strength parameters of soft and hard interbedded rock masses with WDC and dip angle through laboratory experiments and numerical experiments.Some attempts were made to reveal the mechanical properties deterioration mechanism of interbedded rock masses by quantitatively analyzing the contribution of strength parameters deterioration of hard rocks,soft rocks,and bedding planes to the strength parameters deterioration of rock masses.The results indicate that the logarithmic function could be used to describe the deterioration of each strength parameter of both argillaceous siltstone and silty mudstone and bedding plane with the number of WDC.The strength parameters of interbedded rock masses decrease as the number of WDC increases,with the largest decrease after the first cycle and then slowing down in the later cycles.The strength parameters initially decrease and then increase as the dip angles increase.The impact of deteriorated strength parameters of bedding planes and rocks on the deterioration of strength parameters of interbedded rock masses differs significantly with the dip angle,which can be divided into four typical ranges of different controlling factors.展开更多
In the aggressive marine environment over a long-term service period,coastal bridges inevitably sustain corrosion-induced damage due to high sea salt and humidity.This paper investigates the strength reduction of coas...In the aggressive marine environment over a long-term service period,coastal bridges inevitably sustain corrosion-induced damage due to high sea salt and humidity.This paper investigates the strength reduction of coastal bridges,especially focusing on the effects of non-uniform corrosion along the height of bridge piers.First,the corrosion initiation time and the degradation of reinforcement and concrete are analyzed for bridge piers in marine environments.To investigate the various damage modes of the concrete cover,a discretization method with fiber cells is used for calculating time-dependent interaction diagrams of cross-sections of the bridge piers at the atmospheric zone and the splash and tidal zone under a combination of axial force and bending moment.Second,the shear strength of these aging structures is analyzed.Numerical simulation indicates that the strength of a concrete pier experiences dramatic reduction from corrosion initiation to the spalling of the concrete cover.Strength loss in the splash and tidal zone is more significant than in the atmospheric zone when structures’service time is assumed to be the same.展开更多
The shear strength deterioration of bedding planes between different rock types induced by cyclic loading is vital to reasonably evaluate the stability of soft and hard interbedded bedding rock slopes under earthquake...The shear strength deterioration of bedding planes between different rock types induced by cyclic loading is vital to reasonably evaluate the stability of soft and hard interbedded bedding rock slopes under earthquake;however,rare work has been devoted to this subject due to lack of attention.In this study,experimental investigations on shear strength weakening of discontinuities with different joint wall material(DDJM)under cyclic loading were conducted by taking the interface between siltstone and mudstone in the Shaba slope of Yunnan Province,China as research objects.A total of 99 pairs of similar material samples of DDJM(81 pairs)and discontinuities with identical joint wall material(DIJM)(18 pairs)were fabricated by inserting plates,engraved with typical surface morphology obtained by performing three-dimensional laser scanning on natural DDJMs sampled from field,into mold boxes.Cyclic shear tests were conducted on these samples to study their shear strength changes with the cyclic number considering the effects of normal stress,joint surface morphology,shear displacement amplitude and shear rate.The results indicate that the shear stress vs.shear displacement curves under each shear cycle and the peak shear strength vs.cyclic number curves of the studied DDJMs are between those of DIJMs with siltstone and mudstone,while closer to those of DIJMs with mudstone.The peak shear strengths of DDJMs exhibit an initial rapid decline followed by a gradual decrease with the cyclic number and the decrease rate varies from 6%to 55.9%for samples with varied surface morphology under different testing conditions.The normal stress,joint surface morphology,shear displacement amplitude and shear rate collectively influence the shear strength deterioration of DDJM under cyclic shear loading,with the degree of influence being greater for larger normal stress,rougher surface morphology,larger shear displacement amplitude and faster shear rate.展开更多
This paper aims to present an effective method to partial deteriorated strength columns,and to investigate the mechanical behavior of the defect part. Five groups of 150×150 mm×mm plain square columns are ca...This paper aims to present an effective method to partial deteriorated strength columns,and to investigate the mechanical behavior of the defect part. Five groups of 150×150 mm×mm plain square columns are cast; each specimen has two different strengths,the lower strength in the middle segment and higher strength in both ends. The lower strength is to simulate the status of partial deteriorated region. Different layers of CFRP sheets have been wrapped just on the lower strength part to gain the reinforcement with CFRP sheets,and to verify the practicability of partial confinement. Specimens are subjected to monotonic axial compression until failure. Axial load,axial and transverse strains are measured to compare the different behaviors between the two parts. Experimental results show that partial confinement can significantly enhance the strength and the ductility of the deteriorated strength part,then,the load capacity of the whole column can be increased subsequently. Test data indicate that the ultimate load of the confined column is higher than that of the original column without deterioration; partial confinement on weakness is a feasible approach.展开更多
Understanding the anchorage performance of en-echelon joints under cyclic shear loading is crucial for optimizing support strategies in jointed rock masses.This study examines the anchorage effects on enechelon joints...Understanding the anchorage performance of en-echelon joints under cyclic shear loading is crucial for optimizing support strategies in jointed rock masses.This study examines the anchorage effects on enechelon joints with various orientations using laboratory cyclic shear tests.By comparing unbolted and bolted en-echelon joints,we analyze shear zone damage,shear properties,dilatancy,energy absorption,and acoustic emission characteristics to evaluate anchoring effects across shear cycles and joint orientations.Results reveal that bolted en-echelon joints experience more severe shear zone damage after cycles,with bolt deformation correlating to shear zone width.Bolted en-echelon joints exhibit faster shear strength deterioration and higher cumulative strength loss compared to unbolted ones,with losses ranging from 20.04%to 72.76%.The compressibility of en-echelon joints reduces the anchoring effect during shear cycles,leading to lower shear strength of bolted en-echelon joints in later stages of shear cycles compared to unbolted ones.Bolts reinforce en-echelon joints more effectively at non-positive angles,with the best performance observed at 0°and-60°.Anchorage accelerates the transition from rolling friction to sliding friction in the shear zone,enhancing energy absorption,which is crucial for rock projects under dynamic shear loading.Additionally,rock bolts expedite the transition of the cumulative AE hits and cumulative AE energy curves from rapid to steady growth,indicating that strong bolt-rock interactions accelerate crack initiation,propagation,and energy release.展开更多
This study investigates the compressive and tensile properties of basalt fiber-reinforced concrete (BFRC) after ultra-low-temperature freeze-thaw cycles. Scanning electron microscope (SEM) analysis was conducted to ex...This study investigates the compressive and tensile properties of basalt fiber-reinforced concrete (BFRC) after ultra-low-temperature freeze-thaw cycles. Scanning electron microscope (SEM) analysis was conducted to examine the deterioration mechanisms caused by freeze-thaw cycles and sulfate erosion. The results show that compressive and tensile strengths increase with basalt fiber dosage. The optimal dosage is 0.2%. With longer exposure to sulfate erosion, both strengths decline significantly. Basalt fibers effectively bridge cracks, control expansion, enhance compactness, and improve concrete performance. Ultra-low-temperature freeze-thaw cycles and sulfate erosion cause rapid crack growth. Sulfate erosion produces crystallization products and expansive substances. These fill cracks, create pressure, and damage the internal structure. Freezing and expansion forces further enlarge voids and cracks. This provides space for expansive substances, worsening concrete deterioration and reducing its performance.展开更多
The intrinsic relationships between energy dissipation,energy release,strength and abrupt structural failure are key to understanding the evolution of deformational processes in rocks.Theoretical and experimental stud...The intrinsic relationships between energy dissipation,energy release,strength and abrupt structural failure are key to understanding the evolution of deformational processes in rocks.Theoretical and experimental studies confirm that energy plays an important role in rock deformation and failure.Dissipated energy from external forces produces damage and irreversible deformation within rock and decreases rock strength over time.Structural failure of rocks is caused by an abrupt release of strain energy that manifests as a catastrophic breakdown of the rock under certain conditions.The strain energy released in the rock volume plays a pivotal role in generating this abrupt structural failure in the rocks.In this paper,we propose criteria governing（1） the deterioration of rock strength based on energy dissipation and（2） the abrupt structural failure of rocks based on energy release.The critical stresses at the time of abrupt structural failure under various stress states can be determined by these criteria.As an example,the criteria have been used to analyze the failure conditions of surrounding rock of a circular tunnel.展开更多
The field strengths of cement/lime treated clays were investigated in the Ariake Sea costal lowlands.The deposition environment of the investigation location is reconstructed and compared to the present ground environ...The field strengths of cement/lime treated clays were investigated in the Ariake Sea costal lowlands.The deposition environment of the investigation location is reconstructed and compared to the present ground environment.The mechanism of the ground environment change and its effect on the strength of cement/lime treated soil are discussed.The strength development of improved soil using cement and lime in different curing environments was investigated in the laboratory for studying the effect of environment change on the strength also.It has been found that the strength deterioration of improved soil in deep mixing method is due to 1)the ground environment change due to the secondary oxidation which results in low pH value and high organic content,and 2)the formations of the porous structures result from the elution of the calcium ions.Also,it has been found that the initial strength increase of the improved soil is related to the dissolved silica and that the dissolution of the silica in clay minerals needs long time.When examining the longterm strength for preventing strength degradation,the effect of environmental change has to be considered.The importance of measuring pH and oxidation-reduction potential(ORP)of the ground for cement/lime solidification method is explained.展开更多
基金supported by the Chinese National Key R&D Program(No.2022YFC3080200)the Chinese National Natural Science Foundation(No.42090054)。
文摘The rock masses in the hydro-fluctuation zone of reservoir banks sustain wettingdrying cycles(WDC),thereby affecting the stability of the reservoir bank slope.In this paper,rock masses with argillaceous siltstone and silty mudstone interbedded in Badong Formation were taken as the research object to investigate the variation of strength parameters of soft and hard interbedded rock masses with WDC and dip angle through laboratory experiments and numerical experiments.Some attempts were made to reveal the mechanical properties deterioration mechanism of interbedded rock masses by quantitatively analyzing the contribution of strength parameters deterioration of hard rocks,soft rocks,and bedding planes to the strength parameters deterioration of rock masses.The results indicate that the logarithmic function could be used to describe the deterioration of each strength parameter of both argillaceous siltstone and silty mudstone and bedding plane with the number of WDC.The strength parameters of interbedded rock masses decrease as the number of WDC increases,with the largest decrease after the first cycle and then slowing down in the later cycles.The strength parameters initially decrease and then increase as the dip angles increase.The impact of deteriorated strength parameters of bedding planes and rocks on the deterioration of strength parameters of interbedded rock masses differs significantly with the dip angle,which can be divided into four typical ranges of different controlling factors.
基金National Natural Science Foundation of China under Grant No.51678197the Major State Basic Research Development Program of China(973 Program)under Grant No.2011CB013604Fundamental Research Funds for the Central Universities of China with Grant No.HIT.BRETIV.201320
文摘In the aggressive marine environment over a long-term service period,coastal bridges inevitably sustain corrosion-induced damage due to high sea salt and humidity.This paper investigates the strength reduction of coastal bridges,especially focusing on the effects of non-uniform corrosion along the height of bridge piers.First,the corrosion initiation time and the degradation of reinforcement and concrete are analyzed for bridge piers in marine environments.To investigate the various damage modes of the concrete cover,a discretization method with fiber cells is used for calculating time-dependent interaction diagrams of cross-sections of the bridge piers at the atmospheric zone and the splash and tidal zone under a combination of axial force and bending moment.Second,the shear strength of these aging structures is analyzed.Numerical simulation indicates that the strength of a concrete pier experiences dramatic reduction from corrosion initiation to the spalling of the concrete cover.Strength loss in the splash and tidal zone is more significant than in the atmospheric zone when structures’service time is assumed to be the same.
基金supported by the National Natural Science Foundation of China(Grant Nos.42377182,52079133 and 41931295).
文摘The shear strength deterioration of bedding planes between different rock types induced by cyclic loading is vital to reasonably evaluate the stability of soft and hard interbedded bedding rock slopes under earthquake;however,rare work has been devoted to this subject due to lack of attention.In this study,experimental investigations on shear strength weakening of discontinuities with different joint wall material(DDJM)under cyclic loading were conducted by taking the interface between siltstone and mudstone in the Shaba slope of Yunnan Province,China as research objects.A total of 99 pairs of similar material samples of DDJM(81 pairs)and discontinuities with identical joint wall material(DIJM)(18 pairs)were fabricated by inserting plates,engraved with typical surface morphology obtained by performing three-dimensional laser scanning on natural DDJMs sampled from field,into mold boxes.Cyclic shear tests were conducted on these samples to study their shear strength changes with the cyclic number considering the effects of normal stress,joint surface morphology,shear displacement amplitude and shear rate.The results indicate that the shear stress vs.shear displacement curves under each shear cycle and the peak shear strength vs.cyclic number curves of the studied DDJMs are between those of DIJMs with siltstone and mudstone,while closer to those of DIJMs with mudstone.The peak shear strengths of DDJMs exhibit an initial rapid decline followed by a gradual decrease with the cyclic number and the decrease rate varies from 6%to 55.9%for samples with varied surface morphology under different testing conditions.The normal stress,joint surface morphology,shear displacement amplitude and shear rate collectively influence the shear strength deterioration of DDJM under cyclic shear loading,with the degree of influence being greater for larger normal stress,rougher surface morphology,larger shear displacement amplitude and faster shear rate.
文摘This paper aims to present an effective method to partial deteriorated strength columns,and to investigate the mechanical behavior of the defect part. Five groups of 150×150 mm×mm plain square columns are cast; each specimen has two different strengths,the lower strength in the middle segment and higher strength in both ends. The lower strength is to simulate the status of partial deteriorated region. Different layers of CFRP sheets have been wrapped just on the lower strength part to gain the reinforcement with CFRP sheets,and to verify the practicability of partial confinement. Specimens are subjected to monotonic axial compression until failure. Axial load,axial and transverse strains are measured to compare the different behaviors between the two parts. Experimental results show that partial confinement can significantly enhance the strength and the ductility of the deteriorated strength part,then,the load capacity of the whole column can be increased subsequently. Test data indicate that the ultimate load of the confined column is higher than that of the original column without deterioration; partial confinement on weakness is a feasible approach.
基金financially supported by the National Natural Science Foundation of China (No.42172292)Taishan Scholars Project Special Funding,and Shandong Energy Group (No.SNKJ2022A01-R26)funded by the China Scholarship Council (CSC No.202006220274)。
文摘Understanding the anchorage performance of en-echelon joints under cyclic shear loading is crucial for optimizing support strategies in jointed rock masses.This study examines the anchorage effects on enechelon joints with various orientations using laboratory cyclic shear tests.By comparing unbolted and bolted en-echelon joints,we analyze shear zone damage,shear properties,dilatancy,energy absorption,and acoustic emission characteristics to evaluate anchoring effects across shear cycles and joint orientations.Results reveal that bolted en-echelon joints experience more severe shear zone damage after cycles,with bolt deformation correlating to shear zone width.Bolted en-echelon joints exhibit faster shear strength deterioration and higher cumulative strength loss compared to unbolted ones,with losses ranging from 20.04%to 72.76%.The compressibility of en-echelon joints reduces the anchoring effect during shear cycles,leading to lower shear strength of bolted en-echelon joints in later stages of shear cycles compared to unbolted ones.Bolts reinforce en-echelon joints more effectively at non-positive angles,with the best performance observed at 0°and-60°.Anchorage accelerates the transition from rolling friction to sliding friction in the shear zone,enhancing energy absorption,which is crucial for rock projects under dynamic shear loading.Additionally,rock bolts expedite the transition of the cumulative AE hits and cumulative AE energy curves from rapid to steady growth,indicating that strong bolt-rock interactions accelerate crack initiation,propagation,and energy release.
文摘This study investigates the compressive and tensile properties of basalt fiber-reinforced concrete (BFRC) after ultra-low-temperature freeze-thaw cycles. Scanning electron microscope (SEM) analysis was conducted to examine the deterioration mechanisms caused by freeze-thaw cycles and sulfate erosion. The results show that compressive and tensile strengths increase with basalt fiber dosage. The optimal dosage is 0.2%. With longer exposure to sulfate erosion, both strengths decline significantly. Basalt fibers effectively bridge cracks, control expansion, enhance compactness, and improve concrete performance. Ultra-low-temperature freeze-thaw cycles and sulfate erosion cause rapid crack growth. Sulfate erosion produces crystallization products and expansive substances. These fill cracks, create pressure, and damage the internal structure. Freezing and expansion forces further enlarge voids and cracks. This provides space for expansive substances, worsening concrete deterioration and reducing its performance.
基金Supported by the State Key Basic Research Development Program of China (2002CB412705,2010CB226804) the National Natural Science Foundation of China (50579042,10802092)
文摘The intrinsic relationships between energy dissipation,energy release,strength and abrupt structural failure are key to understanding the evolution of deformational processes in rocks.Theoretical and experimental studies confirm that energy plays an important role in rock deformation and failure.Dissipated energy from external forces produces damage and irreversible deformation within rock and decreases rock strength over time.Structural failure of rocks is caused by an abrupt release of strain energy that manifests as a catastrophic breakdown of the rock under certain conditions.The strain energy released in the rock volume plays a pivotal role in generating this abrupt structural failure in the rocks.In this paper,we propose criteria governing（1） the deterioration of rock strength based on energy dissipation and（2） the abrupt structural failure of rocks based on energy release.The critical stresses at the time of abrupt structural failure under various stress states can be determined by these criteria.As an example,the criteria have been used to analyze the failure conditions of surrounding rock of a circular tunnel.
基金The authors are grateful to the Japan Society for the Promotion of Science for funding the present research work under Grant-in-Aid for Scientific Research$Scientific Research B,23360204(Principal Investigator:Takenori Hino)Grant-in-Aid for Scientific Research·Challenging Exploratory Research,23656300(Principal Investigator:Takenori Hino).
文摘The field strengths of cement/lime treated clays were investigated in the Ariake Sea costal lowlands.The deposition environment of the investigation location is reconstructed and compared to the present ground environment.The mechanism of the ground environment change and its effect on the strength of cement/lime treated soil are discussed.The strength development of improved soil using cement and lime in different curing environments was investigated in the laboratory for studying the effect of environment change on the strength also.It has been found that the strength deterioration of improved soil in deep mixing method is due to 1)the ground environment change due to the secondary oxidation which results in low pH value and high organic content,and 2)the formations of the porous structures result from the elution of the calcium ions.Also,it has been found that the initial strength increase of the improved soil is related to the dissolved silica and that the dissolution of the silica in clay minerals needs long time.When examining the longterm strength for preventing strength degradation,the effect of environmental change has to be considered.The importance of measuring pH and oxidation-reduction potential(ORP)of the ground for cement/lime solidification method is explained.
