Large-scale field shear tests on ten specimens of the red-sandstone embankment at a highway in Hunan,China,were performed to examine mechanical characteristics and parameters of red-sandstone.The curves of thrust-disp...Large-scale field shear tests on ten specimens of the red-sandstone embankment at a highway in Hunan,China,were performed to examine mechanical characteristics and parameters of red-sandstone.The curves of thrust-displacement,failure mode,and shear strength parameters for red-sandstone with different water contents,different compactions,and different grain size distributions were obtained from the tests.A practical procedure of in-situ test for red-sandstone embankment was proposed to normalize the test equipment and test steps.Based on three-dimensional thrust-sliding limit equilibrium method,the formulas for calculating strength parameters of red-sandstone considering three-dimensional sliding surface were inferred.The results show that red-sandstone has typical complete curves of stress-strain,strain softening,which are caused by the special structure of red-sandstone;water content and compaction are important factors for strength and failure mode of red-sandstone;The average value of cohesion and internal friction angle of the specimens calculated by three-dimensional technique are 21.56 kPa and 29.29°,respectively,and those by traditional two-dimensional method are 25.52 kPa and 33.76°,respectively.展开更多
Surface Preparation is very important in adhesive b on ding of spray coatings to the surface of a work piece. The common practice is gr it-blasting of the surface before subjecting it to the spray coating process. In ...Surface Preparation is very important in adhesive b on ding of spray coatings to the surface of a work piece. The common practice is gr it-blasting of the surface before subjecting it to the spray coating process. In this study, grit-blasting of an AISI 4130 steel (of different heat treatmen ts) with Al 2O 3 particles was studied. Various grit-blasting parameters such as blasting particle size, the distance between blasting nozzle and the work pi ece (25, 30 and 40 cm.), blasting pressure (3,4,5,6 and 7 bars), blasting time ( 3, 6 and 10 seconds), and the blasting angle (45° and 90°) were examined in or der to find the optimum roughness. The mean roughness (Ra) of the grit-blasted surfaces were measured and the vari ations of the roughness with respect to the above mentioned variables were studi ed. The results show that by increasing blasting time, surface roughness increas es up to a maximum and then slightly decreases it with further duration of t he process. On the other hand a lengthy blasting causes some undesirable results such as an increase in residual particles between surface irregularities. There fore an optimum blasting time is of great importance. Increasing the blasting pr essure also provides a rougher surface, but in grit blasting of harder specimens the surface roughness decreases when the pressure reaches a certain limit. About the blasting angle, it was noticed that an angle of 45° results in less r esidual particles between the surface irregularities, in comparison to the angle of 90°. After grit-blasting, the specimens were plasma spray coated with 80% ZrO 2-20 % Y 2O 3 powder. The adhesive strength of the coating to the substrate was the n measured according to the DIN 50160 standard. The results show that for a certain base metal, the adhesive strength is directl y related to the surface roughness of the base material. Residual particles afte r grit-blasting the surface of the specimens can also have a strong deteriorati ng effect on adhesive strength. Finally, it was shown that the hardness of the b ase material had a direct effect on the adhesive strength of the sprayed coating s.展开更多
Hoek–Brown(HB)strength criterion can reflect rock’s inherent failure nature,so it is more suitable for analyzing the stability of rock slopes.However,the traditional limit equilibrium methods are at present only sui...Hoek–Brown(HB)strength criterion can reflect rock’s inherent failure nature,so it is more suitable for analyzing the stability of rock slopes.However,the traditional limit equilibrium methods are at present only suitable for analyzing the rock slope stability using the linear equivalent Mohr–Coulomb(EMC)strength parameters instead of the nonlinear HB strength criterion.Therefore,a new method derived to analyze directly the rock slope stability using the nonlinear HB strength criterion for arbitrary curve slip surface was described in the limit equilibrium framework.The current method was established based on certain assumptions concerning the stresses on the slip surface through amending the initial normal stressσ0 obtained without considering the effect of inter-slice forces,and it can satisfy all static equilibrium conditions of the sliding body,so the current method can obtain the reasonable and strict factor of safety(FOS)solutions.Compared with the results of other methods in some examples,the feasibility of the current method was verified.Meanwhile,the parametric analysis shows that the slope angleβhas an important influence on the difference of the results obtained using the nonlinear HB strength criterion and its linear EMC strength parameters.Forβ≤45°,both of the results are similar,showing the traditional limit equilibrium methods using the linear EMC strength parameters and the current method are all suitable to analyze rock slope stability,but forβ>60°,the differences of both the results are obvious,showing the actual slope stability state can not be reflected in the traditional limit equilibrium methods,and then the current method should be used.展开更多
The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant norma...The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant normal loading) shear tests are performed. The influences of the applied normal stress and joint morphology to its shear strength are analyzed. According to the experimental results, the peak dilatancy angle of rock joint decreases with increasing normal stress, but increases with increasing roughness. The shear strength increases with the increasing normal stress and the roughness of rock joint. It is observed that the modes of failure of asperities are tensile, pure shear, or a combination of both. It is suggested that the three-dimensional roughness parameters and the tensile strength are the appropriate parameter for describing the shear strength criterion. A new peak shear criterion is proposed which can be used to predict peak shear strength of rock joints. All the used parameters can be easily obtained by performing tests.展开更多
A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strai...A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strain curves,mechanical properties,AE events,cracking behavior and energy characteristics were analyzed to reveal the macro-mechanical behavior and meso-mechanism of pre-fissured specimens under different loading rates.Investigated results show that:1)When the loading rate is relatively low,the stress-strain curves show a brittle response.When the loading rate is relatively high,the curve shows a more ductile response.Both of the peak strength and elastic mudulus increase with the increase of loading rate,which can be expressed as power functions.2)Four crack types are identified,i.e.,tensile crack,shear crack,far-field crack and surface spalling.Moreover,the tensile crack,far-field crack and surface spalling are under tensile mechanism,while the shear crack is under shear mechanism.3)The drops of the stress-strain curves all correspond to the crack initiation or coalescence,which is also linked to a sudden increasing in the accumulated micro-crack curve.4)Both of the maximum bond force and energy have the similar trend with the increase of loading rate to peak strength,which indicates that the trend of peak strength can be explained by the meso-mechanics and energy.展开更多
基金Project(200612) supported by Hunan Province Transportation Department of China
文摘Large-scale field shear tests on ten specimens of the red-sandstone embankment at a highway in Hunan,China,were performed to examine mechanical characteristics and parameters of red-sandstone.The curves of thrust-displacement,failure mode,and shear strength parameters for red-sandstone with different water contents,different compactions,and different grain size distributions were obtained from the tests.A practical procedure of in-situ test for red-sandstone embankment was proposed to normalize the test equipment and test steps.Based on three-dimensional thrust-sliding limit equilibrium method,the formulas for calculating strength parameters of red-sandstone considering three-dimensional sliding surface were inferred.The results show that red-sandstone has typical complete curves of stress-strain,strain softening,which are caused by the special structure of red-sandstone;water content and compaction are important factors for strength and failure mode of red-sandstone;The average value of cohesion and internal friction angle of the specimens calculated by three-dimensional technique are 21.56 kPa and 29.29°,respectively,and those by traditional two-dimensional method are 25.52 kPa and 33.76°,respectively.
文摘Surface Preparation is very important in adhesive b on ding of spray coatings to the surface of a work piece. The common practice is gr it-blasting of the surface before subjecting it to the spray coating process. In this study, grit-blasting of an AISI 4130 steel (of different heat treatmen ts) with Al 2O 3 particles was studied. Various grit-blasting parameters such as blasting particle size, the distance between blasting nozzle and the work pi ece (25, 30 and 40 cm.), blasting pressure (3,4,5,6 and 7 bars), blasting time ( 3, 6 and 10 seconds), and the blasting angle (45° and 90°) were examined in or der to find the optimum roughness. The mean roughness (Ra) of the grit-blasted surfaces were measured and the vari ations of the roughness with respect to the above mentioned variables were studi ed. The results show that by increasing blasting time, surface roughness increas es up to a maximum and then slightly decreases it with further duration of t he process. On the other hand a lengthy blasting causes some undesirable results such as an increase in residual particles between surface irregularities. There fore an optimum blasting time is of great importance. Increasing the blasting pr essure also provides a rougher surface, but in grit blasting of harder specimens the surface roughness decreases when the pressure reaches a certain limit. About the blasting angle, it was noticed that an angle of 45° results in less r esidual particles between the surface irregularities, in comparison to the angle of 90°. After grit-blasting, the specimens were plasma spray coated with 80% ZrO 2-20 % Y 2O 3 powder. The adhesive strength of the coating to the substrate was the n measured according to the DIN 50160 standard. The results show that for a certain base metal, the adhesive strength is directl y related to the surface roughness of the base material. Residual particles afte r grit-blasting the surface of the specimens can also have a strong deteriorati ng effect on adhesive strength. Finally, it was shown that the hardness of the b ase material had a direct effect on the adhesive strength of the sprayed coating s.
基金Project(2015M580702)supported by China Postdoctoral Science FoundationProject(51608541)supported by the National Natural Science Foundation of ChinaProject(2014122066)supported by the Guizhou Provincial Department of Transportation Foundation,China
文摘Hoek–Brown(HB)strength criterion can reflect rock’s inherent failure nature,so it is more suitable for analyzing the stability of rock slopes.However,the traditional limit equilibrium methods are at present only suitable for analyzing the rock slope stability using the linear equivalent Mohr–Coulomb(EMC)strength parameters instead of the nonlinear HB strength criterion.Therefore,a new method derived to analyze directly the rock slope stability using the nonlinear HB strength criterion for arbitrary curve slip surface was described in the limit equilibrium framework.The current method was established based on certain assumptions concerning the stresses on the slip surface through amending the initial normal stressσ0 obtained without considering the effect of inter-slice forces,and it can satisfy all static equilibrium conditions of the sliding body,so the current method can obtain the reasonable and strict factor of safety(FOS)solutions.Compared with the results of other methods in some examples,the feasibility of the current method was verified.Meanwhile,the parametric analysis shows that the slope angleβhas an important influence on the difference of the results obtained using the nonlinear HB strength criterion and its linear EMC strength parameters.Forβ≤45°,both of the results are similar,showing the traditional limit equilibrium methods using the linear EMC strength parameters and the current method are all suitable to analyze rock slope stability,but forβ>60°,the differences of both the results are obvious,showing the actual slope stability state can not be reflected in the traditional limit equilibrium methods,and then the current method should be used.
基金Project(41130742)supported by the Key Program of National Natural Science Foundation of ChinaProject(2014CB046904)supportedby the National Basic Research Program of China+1 种基金Project(2011CDA119)supported by Natural Science Foundation of Hubei Province,ChinaProject(40972178)supported by the General Program of National Natural Science Foundation of China
文摘The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant normal loading) shear tests are performed. The influences of the applied normal stress and joint morphology to its shear strength are analyzed. According to the experimental results, the peak dilatancy angle of rock joint decreases with increasing normal stress, but increases with increasing roughness. The shear strength increases with the increasing normal stress and the roughness of rock joint. It is observed that the modes of failure of asperities are tensile, pure shear, or a combination of both. It is suggested that the three-dimensional roughness parameters and the tensile strength are the appropriate parameter for describing the shear strength criterion. A new peak shear criterion is proposed which can be used to predict peak shear strength of rock joints. All the used parameters can be easily obtained by performing tests.
基金Project(BK20150005) supported by the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholars,ChinaProject(2014YC10) supported by the Fundamental Research Funds for the Central Universities,China
文摘A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strain curves,mechanical properties,AE events,cracking behavior and energy characteristics were analyzed to reveal the macro-mechanical behavior and meso-mechanism of pre-fissured specimens under different loading rates.Investigated results show that:1)When the loading rate is relatively low,the stress-strain curves show a brittle response.When the loading rate is relatively high,the curve shows a more ductile response.Both of the peak strength and elastic mudulus increase with the increase of loading rate,which can be expressed as power functions.2)Four crack types are identified,i.e.,tensile crack,shear crack,far-field crack and surface spalling.Moreover,the tensile crack,far-field crack and surface spalling are under tensile mechanism,while the shear crack is under shear mechanism.3)The drops of the stress-strain curves all correspond to the crack initiation or coalescence,which is also linked to a sudden increasing in the accumulated micro-crack curve.4)Both of the maximum bond force and energy have the similar trend with the increase of loading rate to peak strength,which indicates that the trend of peak strength can be explained by the meso-mechanics and energy.
