The shear performance of bolts plays a crucial role in controlling rock mass stability,and the roughness of the joint surface is one of the main factors affecting the mechanical properties of anchored joints.The 2nd g...The shear performance of bolts plays a crucial role in controlling rock mass stability,and the roughness of the joint surface is one of the main factors affecting the mechanical properties of anchored joints.The 2nd generation of negative Poisson ratio(2G-NPR)bolt is a new independently developed material characterized by high strength and toughness.However,the influence of joint surface roughness on its anchorage shear performance remains unexplored.This study involves preparing regular saw-tooth jointed rock masses and conducting laboratory shear comparison tests on unbolted samples,2G-NPR bolts,and Q235 steel anchors.A three-dimensional finite element method,developed by the author,was employed for numerical simulations to analyze the influence of saw-tooth angles on the shear resistance of anchored bolts.The findings show that the anchorage of bolts enhances the shear strength and deformation of saw-tooth rock joints.The 2G-NPR bolts demonstrate superior performance in shear strength and deformation enhancement compared to Q235 steel anchors,including improved toughening and crack-arresting effects.Furthermore,the improvement of the shear strength and displacement of the bolt decreases with the increase of the joint saw-tooth angle.These findings provide a valuable test basis for the engineering application of 2G-NPR bolts in rock mass stabilization.展开更多
Rock bolts have been widely used in slopes as a reinforcement measure.Modelling the shear mechanical behaviours of bolted rock joints is very complicated due to the complex factors that affect the axial force and shea...Rock bolts have been widely used in slopes as a reinforcement measure.Modelling the shear mechanical behaviours of bolted rock joints is very complicated due to the complex factors that affect the axial force and shear force on the bolts.Rock bolts under shear action exhibit the guide rail effect;that is,the rock mass slides along the rock bolt as if the rock bolt is a rail.The normal stress can inhibit the guide rail effect and reduce the axial force on bolts.However,this factor is not considered by the existing analysis models.Shear tests of bolted joints under different normal stresses were carried out in the laboratory.During the test,the axial force on each point monitored on the bolt was recorded by a strain gauge,and the attenuation trend of the strain was studied.An analytical model that considers the inhibition of the bolt rail effect due to an increase in the normal stress was proposed to predict the shear mechanical behaviour of rock bolted joints.The new model accommodates the bolt shear behaviours in the elastic stage and plastic stage,and the estimated values agree well with the results of the direct shear tests in the laboratory.The validation shows that the proposed model can effectively describe the deformation characteristics of the bolts in the shear tests.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
Direct shear tests were conducted on the rock joints under constant normal load(CNL), while the acoustic emission(AE) signals generated during shear tests were monitored with PAC Micro-II system. Before and after shea...Direct shear tests were conducted on the rock joints under constant normal load(CNL), while the acoustic emission(AE) signals generated during shear tests were monitored with PAC Micro-II system. Before and after shearing, the surfaces of rock joints were measured by the Talysurf CLI 2000. By correlating the AE events with the shear stress-shear displacement curve, one can observe four periods of the whole course of shearing of rock joints. By the contrast of AE location and actual damage zone, it is elucidated that the AE event is related to the morphology of the joint. With the increase of shearing times, the shear behavior of rock joints gradually presents from the response of brittle behavior to that of ductile behavior. By combining the results of topography measurement, four morphological parameters of joint surface, S p(the maximum height of joint surface), N(number of islands), A(projection area) and V(volume of joint) were introduced, which decrease with shearing. Both the joint roughness coefficient(JRC) and joint matching coefficient(JMC) drop with shearing, and the shear strength of rock joints can be predicted by the JRC-JMC model. It establishes the relationship between micro-topography and macroscopic strength, which have the same change rule with shearing.展开更多
The special columnar jointed structure endows rocks with significant anisotropy,accurately grasping the strength and deformation properties of a columnar jointed rock mass(CJRM)under complex geological conditions is c...The special columnar jointed structure endows rocks with significant anisotropy,accurately grasping the strength and deformation properties of a columnar jointed rock mass(CJRM)under complex geological conditions is crucial for related engineering safety.Combined with the irregular jointed networks observed in the field,artificial irregular CJRM(ICJRM)samples with various inclination angles were prepared for triaxial tests.The results showed that the increase in confining pressure can enhance the ability of the ICJRM to resist deformation and failure,and reduce the deformation and strength anisotropic degrees.Considering the field stress situation,the engineering parts with an inclination angle of 30°−45°need to be taken seriously.Four typical failure modes were identified,and the sample with an inclination angle of 15°showed the same failure behavior as the field CJRM.Traditional and improved joint factor methods were used to establish empirical relationships for predicting the strength and deformation of CJRM under triaxial stress.Since the improved joint factor method can reflect the unique structure of CJRM,the predictive ability of the empirical relationship based on the improved method is better than that based on the traditional joint factor method.展开更多
In the practical slope engineering,the stability of lower sliding mass(region A)with back tensile cracks of the jointed rock slope attracts more attentions,but the upper rock mass(region B)may also be unstable.Therefo...In the practical slope engineering,the stability of lower sliding mass(region A)with back tensile cracks of the jointed rock slope attracts more attentions,but the upper rock mass(region B)may also be unstable.Therefore,in this study,based on the stepped failure mode of bedding jointed rock slopes,considering the influence of the upper rock mass on the lower stepped sliding mass,the improved failure model for analyzing the interaction force(F_(AB))between two regions is constructed,and the safety factors(F_(S))of two regions and whole region are derived.In addition,this paper proposes a method to determine the existence of F_(AB) using their respective acceleration values(a_(A) and a_(B))when regions A and B are unstable.The influences of key parameters on two regions and the whole region are analyzed.The results show that the variation of the F_(AB) and F_(S) of two regions can be obtained accurately based on the improved failure model.The accuracy of the improved failure model is verified by comparative analysis.The research results can explain the interaction mechanism of two regions and the natural phenomenon of slope failure caused by the development of cracks.展开更多
The object of this article is to investigate the energy evolution mechanism and failure criteria of cross-jointed samples containing an opening during deformation and failure based on the uniaxial compression test and...The object of this article is to investigate the energy evolution mechanism and failure criteria of cross-jointed samples containing an opening during deformation and failure based on the uniaxial compression test and rock energy principle.The results show that the energy evolution characteristics of the samples correspond to a typical progressive damage mode.The peak total energy,peak elastic energy,and total input energy of the samples all first decrease and then increase with an increase of half of the included angle,reaching their minimum values when this angle is 45°,while the dissipated energy generally increases with this angle.The existence of the opening and cross joints can obviously weaken the energy storage capacity of the rock,and the change in the included angle of the cross joint has a great influence on the elastic energy ratio of the sample before the peak stress,which leads to some differences in the distribution laws of the input energy.The continuous change and the subsequent sharp change in the rate of change in the energy consumption ratio can be used as the criteria of the crack initiation and propagation and the unstable failure of the sample,respectively.展开更多
Methods that can efficiently model the effects of rock joints on rock mass behavior can be beneficial in rock engineering. The suitability of equivalent rock mass(ERM) technique based upon particle methods is investig...Methods that can efficiently model the effects of rock joints on rock mass behavior can be beneficial in rock engineering. The suitability of equivalent rock mass(ERM) technique based upon particle methods is investigated. The ERM methodology is first validated by comparing calculated and experimental data of lab triaxial compression test on a set of cylindrical rock mass samples, each containing a single joint oriented in various dip angles. The simulated results are then used to study the stress-strain nonlinearity and failure mechanism as a function of the joint dip angle and confining stress. The anisotropy and size effects are also investigated by using multi-scale cubic ERM models subjected to triaxial compression test. The deformation and failure behavior are found to be influenced by joint degradation, the micro-crack formation in the intact rock, the interaction between two joints, and the interactions of micro-cracks and joints.展开更多
A numerical code called RFPA-Dynamics was used to study the rockburst mechanism under dynamic load based on coupled static-dynamic analysis.The results show that dynamic disturbance has a very distinct triggering effe...A numerical code called RFPA-Dynamics was used to study the rockburst mechanism under dynamic load based on coupled static-dynamic analysis.The results show that dynamic disturbance has a very distinct triggering effect on rockburst.Under the dynamic load,rockburst is motivated by tensile stress formed by the overlapping of dynamic waves in the form of instantaneous open and cutting through of cracks in weak planes and pre-damaged areas.Meanwhile,the orientation of joint sets has an obvious leading effect on rockburst locations.Finally,a higher initial static stress state before dynamic loading can cause more pre-damaged area,thus leading to a larger rockburst scope.展开更多
Pre-stressed bolt anchorage is the key technology for jointed rock masses in rock tunnelling,slope treatment and mining engineering.To investigate the mechanical properties and reinforcement effect of jointed rock mas...Pre-stressed bolt anchorage is the key technology for jointed rock masses in rock tunnelling,slope treatment and mining engineering.To investigate the mechanical properties and reinforcement effect of jointed rock masses with pre-stressed bolts,in this study,uniaxial compression tests were conducted on specimens with different anchoring types and flaw inclination angles.ABAQUS software was used to verify and supplement the laboratory tests.The laws of the uniaxial compressive strength(UCS)obtained from the numerical simulations and laboratory tests were consistent.The results showed that under the same flaw angle,both the UCS and elastic modulus of the bolted specimens were improved compared with those of the specimens without bolts and the improvements increased with an increase in the bolt pre-stress.Under the same anchoring type,the UCS and elastic modulus of the jointed specimens increased with an increase in the flaw angle.The pre-stressed bolt could not only restrain the slip of the specimens along the flaw surface but also change the propagation mode of the secondary cracks and limit the initiation of cracks.In addition,the plot contours of the maximum principal strain and the Tresca stress of the numerical models were influenced by the anchoring type,flaw angle,anchoring angle and bolt position.展开更多
The ratio of crack initiation stress to the uniaxial compressive strength(SCI,B/SUC,B) and the ratio of axial strain at the crack initiation stress to the axial strain at the uniaxial compressive strength(B,UCB,CI,A,A...The ratio of crack initiation stress to the uniaxial compressive strength(SCI,B/SUC,B) and the ratio of axial strain at the crack initiation stress to the axial strain at the uniaxial compressive strength(B,UCB,CI,A,A/SSSS) were studied by performing numerical stress analysis on blocks having multi flaws at close spacing's under uniaxial loading using PFC3 D. The following findings are obtained: SCI,B/SUC,B has an average value of about 0.5 with a variability of ± 0.1. This range agrees quite well with the values obtained by former research. For joint inclination angle, β=90°,B,UCB,CI,A,A/SSSS is found to be around 0.48 irrespective of the value of joint continuity factor, k. No particular relation is found betweenB,UCB,CI,A,A/SSSS and β; however, the average B,UCB,CI,A,A/SSSS seems to slightly decrease with increasing k. The variability ofB,UCB,CI,A,A/SSSS is found to increase with k.Based on the cases studied in this work,B,UCB,CI,A,A/SSSS ranges between 0.3 and 0.5. This range is quite close to the range of 0.4to 0.6 obtained for SCI,B/SUC,B. The highest variability of ± 0.12 forB,UCB,CI,A,A/SSSS is obtained for k=0.8. For the remaining k values the variability ofB,UCB,CI,A,A/SSSS can be expressed within ± 0.05. This finding is very similar to the finding obtained for the variability of SCI,B/SUC,B.展开更多
A revised displacement discontinuity method(DDM) program is developed for the simulation of rock joint propagation and dilatancy analysis. The non-linear joint model used in the program adopts Barton-Bandis normal def...A revised displacement discontinuity method(DDM) program is developed for the simulation of rock joint propagation and dilatancy analysis. The non-linear joint model used in the program adopts Barton-Bandis normal deformation model, Kulhaway shear deformation model and Mohr-Coulomb criterion. The joint propagation criterion is based on the equivalent stress intensity factor which can be obtained by regression analysis. The simulated rock joint propagation accords well with the existing knowledge. The closure and opening of joint is investigated by DDM, and it is shown that if the opening volume of propagated joint is larger than closure volume of the old joint, the joint dilatancy occurs. The dilatancy condition is mainly controlled by the normal stiffness of the rock joint. When the normal stiffness is larger than the critical value, joint dilatancy occurs. The critical normal stiffness of rock joint changes with the joint-load angle, and joint dilatancy is most possible to occur at 30°.展开更多
A modified discontinuous deformation analysis (DDA) algorithm was proposed to simulate the failure behavior of jointed rock. In the proposed algorithm, by using the Monte-Carlo technique, random joint network was gene...A modified discontinuous deformation analysis (DDA) algorithm was proposed to simulate the failure behavior of jointed rock. In the proposed algorithm, by using the Monte-Carlo technique, random joint network was generated in the domain of interest. Based on the joint network, the triangular DDA block system was automatically generated by adopting the advanced front method. In the process of generating blocks, numerous artificial joints came into being, and once the stress states at some artificial joints satisfy the failure criterion given beforehand, artificial joints will turn into real joints. In this way, the whole fragmentation process of rock mass can be replicated. The algorithm logic was described in detail, and several numerical examples were carried out to obtain some insight into the failure behavior of rock mass containing random joints. From the numerical results, it can be found that the crack initiates from the crack tip, the growth direction of the crack depends upon the loading and constraint conditions, and the proposed method can reproduce some complicated phenomena in the whole process of rock failure.展开更多
The characteristics of joints are crucial factors which influence the penetration efficiency of tunnel boring machine(TBM).Based on the theoretical study,numerical simulation and experimental research,many researchers...The characteristics of joints are crucial factors which influence the penetration efficiency of tunnel boring machine(TBM).Based on the theoretical study,numerical simulation and experimental research,many researchers have studied the interaction between TBM disc cutters and jointed rock mass.However,in most of these works,the effect of joint on rock fragmentation by double disc cutter has been scarcely investigated.Thus,the effects of joint orientation and joint space on rock fragmentation by double disc cutter are highlighted in this study.During the test,jointed concrete specimens are adopted to simulate jointed rock mass.Improved RYL-600rock shear rheological instrument was employed during the indentation process under disc cutters,and acoustic emission location system was used to analyze the rock damage and physical deterioration.The results show that there are four failure modes and three modes of crack initiation and propagation in jointed rock mass.It is concluded that the existing joint planes have obviously restrained the crack initiation and propagation during the rock fragmentation process.The results also indicate that samples are damaged most seriously when joint orientation equals60°,which is proved to be the optimum joint orientation in TBM penetration.展开更多
In order to obtain the optimal parameters of anchor bolt supporting system for large-span and jointed rock mass in Kaiyang Phosphor Mine, it is expensive and unavailable with the method of in-situ experiments. This pa...In order to obtain the optimal parameters of anchor bolt supporting system for large-span and jointed rock mass in Kaiyang Phosphor Mine, it is expensive and unavailable with the method of in-situ experiments. This paper describes a numerical modeling with discrete element method for the supporting effects of different type of anchor bolts. The anchor bolts with variant length of 0.5m, 0.8m, 1.0m, diameter of 10mm, 15mm, 20mm, setting spacing of 3.0m, 2.5m, 2.0m, and setting angle of 10°, 20°, 30°, are simulated respectively. The results show that there exist optimal parameters of anchor bolt support for large-span and jointed rock mass. For the bolt support of the concerning, the optimal length is 2.53.5m, the diameter is 2535mm, the spacing is 0.50.6m, and the setting angle is 105°.展开更多
Shear band (SB), axial, lateral and volumetric strains as well as Poisson’s ratio of anisotropic jointed rock specimen (JRS) were modeled by Fast Lagrangian Analysis of Continua (FLAC). Failure criterion of rock was ...Shear band (SB), axial, lateral and volumetric strains as well as Poisson’s ratio of anisotropic jointed rock specimen (JRS) were modeled by Fast Lagrangian Analysis of Continua (FLAC). Failure criterion of rock was a composited Mohr-Coulomb criterion with tension cut-off. An inclined joint was treated as square elements of ideal plastic material beyond the peak strength. Several FISH functions were written to automatically find the addresses of elements in the joint and to calculate the entire deformational characteristics of plane strain JRS. The results show that for moderate joint inclination (JI), strain is only concentrated into the joint governing the behavior of JRS, leading to ideal plastic responses in axial and lateral directions. For higher JI, the post-peak stress-axial and lateral strain curves become steeper as JI increases owing to the increase of new SB’s length. Lateral expansion and precursor to the unstable failure are the most apparent, resulting in the highest Poisson’s ratio and even negative volumetric strain. For lower JI, the entire post-peak deformational characteristics are independent of JI. The lowest lateral expansion occurs, leading to the lowest Poisson’s ratio and positive volumetric strain all along. The present prediction on anisotropic strength in plane strain compression qualitatively agrees with the results in triaxial tests of rocks. The JI calculated by Jaeger’s formula overestimates that related to the minimum strength. Advantages of the present numerical model over the Jaeger’s model are pointed out.展开更多
Rock joint shape characteristics,waviness and unevenness play essential but distinct roles in shear mechanism of rock joints.This study presents a novel method to generate virtual rock joint profiles with realistic wa...Rock joint shape characteristics,waviness and unevenness play essential but distinct roles in shear mechanism of rock joints.This study presents a novel method to generate virtual rock joint profiles with realistic waviness and unevenness features.Firstly,joint profiles are obtained by 3D laser scanning device.Secondly,quantification of waviness and unevenness is conducted by traditional method,including digital filtering technique and roughness parameter RL.Thirdly,the discrete Fourier transform(DFT)method is employed to analyze the joint outlines.Two representative Fourier shape descriptors(D3,D8)for characterization of waviness and unevenness are suggested.Then,the inverse discrete Fourier transform(IDFT)is adopted to reconstruct the joint profiles with random values of phase angles but prescribed amplitudes controlled by D3 and D8.The traditional method is then applied to the reconstructed joint profiles to examine statistically the relationships between D3 and D8 and parameters RL of waviness and unevenness,respectively.The results show that larger D8 tends to result in larger waviness while higher D3 tends to increase unevenness.Reference charts for estimation of waviness and unevenness with different pairs of D3 and D8 are also provided to facilitate implementation of random joint reconstruction.展开更多
A new analytical study on stresses around a post-tensioned anchor in rocks with two perpendicular joint sets is presented. The assumptions of orthotropic elastic rock with plane strain conditions are made in derivatio...A new analytical study on stresses around a post-tensioned anchor in rocks with two perpendicular joint sets is presented. The assumptions of orthotropic elastic rock with plane strain conditions are made in derivation of the formulations. A tri-linear bond-slip constitutive law is used for modeling the tendon-grout interface behavior and debonding of this interface. The bearing plate width is also considered in the analysis. The obtained solutions are in the integral forms and numerical techniques that have been used for evaluation. In the illustrative example given, the major principal stress is compressive in the anchor free zone and compressive stress concentrations of 815 k Pa and 727 k Pa(for the anchor load of 300 k N) are observed under the bearing plate and the bond length proximal end, respectively. However, large values of tensile stresses with the maximum of-434 k Pa are formed at the bond length distal end. The results obtained using the proposed solution are compared very those of numerical method(FEM).展开更多
In order to investigate the failure mechanism of rock joint,a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL)conditions were conducted.Morphology parameters of the rock j...In order to investigate the failure mechanism of rock joint,a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL)conditions were conducted.Morphology parameters of the rock joint surface were precisely calculated by means of a three-dimensional laser scanning machine.All test results were analyzed to investigate the shear behavior and normal displacement behavior of rock joints under CNL conditions.Degradation of rock joint surface during cyclic shear tests was also analyzed.The comparison results of the height parameters and the hybrid parameters of the joint surface during cyclic tests show that the degradation of the surface mostly happens in the first shear and the constant normal loads imposed on the joints have significant promotion effects on the morphology degradation.During cyclic shear tests,joints surfaces evolve from rough state to smooth state but keep an overall undulation.Dilatancy of rock joints degrades with the degradation of joint surface and the increase of normal loads.The closure deformation of joint is larger than that of the intact rock,and the normal stiffness increases with the increase of shearing times.展开更多
基金Project(GZB202405561)supported by the Postdoctoral Fellowship Program of China Postdoctoral Science FoundationProject(42377154)supported by the National Natural Science Foundation of China。
文摘The shear performance of bolts plays a crucial role in controlling rock mass stability,and the roughness of the joint surface is one of the main factors affecting the mechanical properties of anchored joints.The 2nd generation of negative Poisson ratio(2G-NPR)bolt is a new independently developed material characterized by high strength and toughness.However,the influence of joint surface roughness on its anchorage shear performance remains unexplored.This study involves preparing regular saw-tooth jointed rock masses and conducting laboratory shear comparison tests on unbolted samples,2G-NPR bolts,and Q235 steel anchors.A three-dimensional finite element method,developed by the author,was employed for numerical simulations to analyze the influence of saw-tooth angles on the shear resistance of anchored bolts.The findings show that the anchorage of bolts enhances the shear strength and deformation of saw-tooth rock joints.The 2G-NPR bolts demonstrate superior performance in shear strength and deformation enhancement compared to Q235 steel anchors,including improved toughening and crack-arresting effects.Furthermore,the improvement of the shear strength and displacement of the bolt decreases with the increase of the joint saw-tooth angle.These findings provide a valuable test basis for the engineering application of 2G-NPR bolts in rock mass stabilization.
基金Projects(41931295,41877258)supported by the National Natural Science Foundation of ChinaProject(2017YFC1501305)supported by the National Key Research and Development Program of China。
文摘Rock bolts have been widely used in slopes as a reinforcement measure.Modelling the shear mechanical behaviours of bolted rock joints is very complicated due to the complex factors that affect the axial force and shear force on the bolts.Rock bolts under shear action exhibit the guide rail effect;that is,the rock mass slides along the rock bolt as if the rock bolt is a rail.The normal stress can inhibit the guide rail effect and reduce the axial force on bolts.However,this factor is not considered by the existing analysis models.Shear tests of bolted joints under different normal stresses were carried out in the laboratory.During the test,the axial force on each point monitored on the bolt was recorded by a strain gauge,and the attenuation trend of the strain was studied.An analytical model that considers the inhibition of the bolt rail effect due to an increase in the normal stress was proposed to predict the shear mechanical behaviour of rock bolted joints.The new model accommodates the bolt shear behaviours in the elastic stage and plastic stage,and the estimated values agree well with the results of the direct shear tests in the laboratory.The validation shows that the proposed model can effectively describe the deformation characteristics of the bolts in the shear tests.
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Projects(51274249,51174228)supported by the National Natural Science Foundation of China
文摘Direct shear tests were conducted on the rock joints under constant normal load(CNL), while the acoustic emission(AE) signals generated during shear tests were monitored with PAC Micro-II system. Before and after shearing, the surfaces of rock joints were measured by the Talysurf CLI 2000. By correlating the AE events with the shear stress-shear displacement curve, one can observe four periods of the whole course of shearing of rock joints. By the contrast of AE location and actual damage zone, it is elucidated that the AE event is related to the morphology of the joint. With the increase of shearing times, the shear behavior of rock joints gradually presents from the response of brittle behavior to that of ductile behavior. By combining the results of topography measurement, four morphological parameters of joint surface, S p(the maximum height of joint surface), N(number of islands), A(projection area) and V(volume of joint) were introduced, which decrease with shearing. Both the joint roughness coefficient(JRC) and joint matching coefficient(JMC) drop with shearing, and the shear strength of rock joints can be predicted by the JRC-JMC model. It establishes the relationship between micro-topography and macroscopic strength, which have the same change rule with shearing.
基金Projects(42307192,41831278)supported by the National Natural Science Foundation of ChinaProject(CKWV20231175/KY)supported by the CRSRI Open Research Program,China。
文摘The special columnar jointed structure endows rocks with significant anisotropy,accurately grasping the strength and deformation properties of a columnar jointed rock mass(CJRM)under complex geological conditions is crucial for related engineering safety.Combined with the irregular jointed networks observed in the field,artificial irregular CJRM(ICJRM)samples with various inclination angles were prepared for triaxial tests.The results showed that the increase in confining pressure can enhance the ability of the ICJRM to resist deformation and failure,and reduce the deformation and strength anisotropic degrees.Considering the field stress situation,the engineering parts with an inclination angle of 30°−45°need to be taken seriously.Four typical failure modes were identified,and the sample with an inclination angle of 15°showed the same failure behavior as the field CJRM.Traditional and improved joint factor methods were used to establish empirical relationships for predicting the strength and deformation of CJRM under triaxial stress.Since the improved joint factor method can reflect the unique structure of CJRM,the predictive ability of the empirical relationship based on the improved method is better than that based on the traditional joint factor method.
基金Projects(52208369,52309138,52108320)supported by the National Natural Science Foundation of ChinaProjects(2023NSFSC0284,2025ZNSFSC0409)supported by the Sichuan Science and Technology Program,ChinaProject(U22468214)supported by the Joint Fund Project for Railway Basic Research by the National Natural Science Foundation of China and China State Railway Group Co.,Ltd.
文摘In the practical slope engineering,the stability of lower sliding mass(region A)with back tensile cracks of the jointed rock slope attracts more attentions,but the upper rock mass(region B)may also be unstable.Therefore,in this study,based on the stepped failure mode of bedding jointed rock slopes,considering the influence of the upper rock mass on the lower stepped sliding mass,the improved failure model for analyzing the interaction force(F_(AB))between two regions is constructed,and the safety factors(F_(S))of two regions and whole region are derived.In addition,this paper proposes a method to determine the existence of F_(AB) using their respective acceleration values(a_(A) and a_(B))when regions A and B are unstable.The influences of key parameters on two regions and the whole region are analyzed.The results show that the variation of the F_(AB) and F_(S) of two regions can be obtained accurately based on the improved failure model.The accuracy of the improved failure model is verified by comparative analysis.The research results can explain the interaction mechanism of two regions and the natural phenomenon of slope failure caused by the development of cracks.
基金Project(FRF-TP-20-041A1)supported by the Fundamental Research Funds for the Central Universities,ChinaProjects(2016YFC0600801,2017YFC0804103)supported by the State Key Research Development Program of ChinaProjects(51774022,52074020)supported by the National Natural Science Foundation of China.
文摘The object of this article is to investigate the energy evolution mechanism and failure criteria of cross-jointed samples containing an opening during deformation and failure based on the uniaxial compression test and rock energy principle.The results show that the energy evolution characteristics of the samples correspond to a typical progressive damage mode.The peak total energy,peak elastic energy,and total input energy of the samples all first decrease and then increase with an increase of half of the included angle,reaching their minimum values when this angle is 45°,while the dissipated energy generally increases with this angle.The existence of the opening and cross joints can obviously weaken the energy storage capacity of the rock,and the change in the included angle of the cross joint has a great influence on the elastic energy ratio of the sample before the peak stress,which leads to some differences in the distribution laws of the input energy.The continuous change and the subsequent sharp change in the rate of change in the energy consumption ratio can be used as the criteria of the crack initiation and propagation and the unstable failure of the sample,respectively.
基金Projects(51074014,51174014) supported by the National Natural Science Foundation of China
文摘Methods that can efficiently model the effects of rock joints on rock mass behavior can be beneficial in rock engineering. The suitability of equivalent rock mass(ERM) technique based upon particle methods is investigated. The ERM methodology is first validated by comparing calculated and experimental data of lab triaxial compression test on a set of cylindrical rock mass samples, each containing a single joint oriented in various dip angles. The simulated results are then used to study the stress-strain nonlinearity and failure mechanism as a function of the joint dip angle and confining stress. The anisotropy and size effects are also investigated by using multi-scale cubic ERM models subjected to triaxial compression test. The deformation and failure behavior are found to be influenced by joint degradation, the micro-crack formation in the intact rock, the interaction between two joints, and the interactions of micro-cracks and joints.
基金Project(90401004)supported by the Fundamental Research Funds for the Central Universities of ChinaProjects(20100471465,201104572)supported by China Postdoctoral Science Foundation+1 种基金Project(20091029)supported by Postdoctoral Science Foundation of Liaoning Province,ChinaProjects(50934006,51111130206)supported by the National Natural Science Foundation of China
文摘A numerical code called RFPA-Dynamics was used to study the rockburst mechanism under dynamic load based on coupled static-dynamic analysis.The results show that dynamic disturbance has a very distinct triggering effect on rockburst.Under the dynamic load,rockburst is motivated by tensile stress formed by the overlapping of dynamic waves in the form of instantaneous open and cutting through of cracks in weak planes and pre-damaged areas.Meanwhile,the orientation of joint sets has an obvious leading effect on rockburst locations.Finally,a higher initial static stress state before dynamic loading can cause more pre-damaged area,thus leading to a larger rockburst scope.
基金Project(51979281)supported by the National Natural Science Foundation of ChinaProject(ZR2018MEE050)supported by the Natural Science Foundation of Shandong Province,ChinaProject(18CX02079A)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Pre-stressed bolt anchorage is the key technology for jointed rock masses in rock tunnelling,slope treatment and mining engineering.To investigate the mechanical properties and reinforcement effect of jointed rock masses with pre-stressed bolts,in this study,uniaxial compression tests were conducted on specimens with different anchoring types and flaw inclination angles.ABAQUS software was used to verify and supplement the laboratory tests.The laws of the uniaxial compressive strength(UCS)obtained from the numerical simulations and laboratory tests were consistent.The results showed that under the same flaw angle,both the UCS and elastic modulus of the bolted specimens were improved compared with those of the specimens without bolts and the improvements increased with an increase in the bolt pre-stress.Under the same anchoring type,the UCS and elastic modulus of the jointed specimens increased with an increase in the flaw angle.The pre-stressed bolt could not only restrain the slip of the specimens along the flaw surface but also change the propagation mode of the secondary cracks and limit the initiation of cracks.In addition,the plot contours of the maximum principal strain and the Tresca stress of the numerical models were influenced by the anchoring type,flaw angle,anchoring angle and bolt position.
基金Project(11102224)supported by the National Natural Science Foundation of ChinaProject(201206370124)supported by the China Scholarship Council,China
文摘The ratio of crack initiation stress to the uniaxial compressive strength(SCI,B/SUC,B) and the ratio of axial strain at the crack initiation stress to the axial strain at the uniaxial compressive strength(B,UCB,CI,A,A/SSSS) were studied by performing numerical stress analysis on blocks having multi flaws at close spacing's under uniaxial loading using PFC3 D. The following findings are obtained: SCI,B/SUC,B has an average value of about 0.5 with a variability of ± 0.1. This range agrees quite well with the values obtained by former research. For joint inclination angle, β=90°,B,UCB,CI,A,A/SSSS is found to be around 0.48 irrespective of the value of joint continuity factor, k. No particular relation is found betweenB,UCB,CI,A,A/SSSS and β; however, the average B,UCB,CI,A,A/SSSS seems to slightly decrease with increasing k. The variability ofB,UCB,CI,A,A/SSSS is found to increase with k.Based on the cases studied in this work,B,UCB,CI,A,A/SSSS ranges between 0.3 and 0.5. This range is quite close to the range of 0.4to 0.6 obtained for SCI,B/SUC,B. The highest variability of ± 0.12 forB,UCB,CI,A,A/SSSS is obtained for k=0.8. For the remaining k values the variability ofB,UCB,CI,A,A/SSSS can be expressed within ± 0.05. This finding is very similar to the finding obtained for the variability of SCI,B/SUC,B.
基金Project(2009318000046) supported by the Western Transport Technical Program of the Ministry of Transport,China
文摘A revised displacement discontinuity method(DDM) program is developed for the simulation of rock joint propagation and dilatancy analysis. The non-linear joint model used in the program adopts Barton-Bandis normal deformation model, Kulhaway shear deformation model and Mohr-Coulomb criterion. The joint propagation criterion is based on the equivalent stress intensity factor which can be obtained by regression analysis. The simulated rock joint propagation accords well with the existing knowledge. The closure and opening of joint is investigated by DDM, and it is shown that if the opening volume of propagated joint is larger than closure volume of the old joint, the joint dilatancy occurs. The dilatancy condition is mainly controlled by the normal stiffness of the rock joint. When the normal stiffness is larger than the critical value, joint dilatancy occurs. The critical normal stiffness of rock joint changes with the joint-load angle, and joint dilatancy is most possible to occur at 30°.
基金Projects(50479071, 40672191) supported by the National Natural Science Foundation of ChinaProject(SKLZ0801) supported by the Independent Research Key Project of State Key Laboratory of Geomechanics and Geotechnical EngineeringProject(SKLQ001) supported by the Independent Research Frontier Exploring Project of State Key Laboratory of Geomechanics and Geotechnical Engineering
文摘A modified discontinuous deformation analysis (DDA) algorithm was proposed to simulate the failure behavior of jointed rock. In the proposed algorithm, by using the Monte-Carlo technique, random joint network was generated in the domain of interest. Based on the joint network, the triangular DDA block system was automatically generated by adopting the advanced front method. In the process of generating blocks, numerous artificial joints came into being, and once the stress states at some artificial joints satisfy the failure criterion given beforehand, artificial joints will turn into real joints. In this way, the whole fragmentation process of rock mass can be replicated. The algorithm logic was described in detail, and several numerical examples were carried out to obtain some insight into the failure behavior of rock mass containing random joints. From the numerical results, it can be found that the crack initiates from the crack tip, the growth direction of the crack depends upon the loading and constraint conditions, and the proposed method can reproduce some complicated phenomena in the whole process of rock failure.
基金Project(11772358) supported by the National Natural Science Foundation of ChinaProject(2013CB035401) supported by the National Basic Research Program of ChinaProject(2015zzts262) supported by the Fundamental Research Funds for the Central Universities,China
文摘The characteristics of joints are crucial factors which influence the penetration efficiency of tunnel boring machine(TBM).Based on the theoretical study,numerical simulation and experimental research,many researchers have studied the interaction between TBM disc cutters and jointed rock mass.However,in most of these works,the effect of joint on rock fragmentation by double disc cutter has been scarcely investigated.Thus,the effects of joint orientation and joint space on rock fragmentation by double disc cutter are highlighted in this study.During the test,jointed concrete specimens are adopted to simulate jointed rock mass.Improved RYL-600rock shear rheological instrument was employed during the indentation process under disc cutters,and acoustic emission location system was used to analyze the rock damage and physical deterioration.The results show that there are four failure modes and three modes of crack initiation and propagation in jointed rock mass.It is concluded that the existing joint planes have obviously restrained the crack initiation and propagation during the rock fragmentation process.The results also indicate that samples are damaged most seriously when joint orientation equals60°,which is proved to be the optimum joint orientation in TBM penetration.
文摘In order to obtain the optimal parameters of anchor bolt supporting system for large-span and jointed rock mass in Kaiyang Phosphor Mine, it is expensive and unavailable with the method of in-situ experiments. This paper describes a numerical modeling with discrete element method for the supporting effects of different type of anchor bolts. The anchor bolts with variant length of 0.5m, 0.8m, 1.0m, diameter of 10mm, 15mm, 20mm, setting spacing of 3.0m, 2.5m, 2.0m, and setting angle of 10°, 20°, 30°, are simulated respectively. The results show that there exist optimal parameters of anchor bolt support for large-span and jointed rock mass. For the bolt support of the concerning, the optimal length is 2.53.5m, the diameter is 2535mm, the spacing is 0.50.6m, and the setting angle is 105°.
基金Project(50309004) supported by the National Natural Science Foundation of China
文摘Shear band (SB), axial, lateral and volumetric strains as well as Poisson’s ratio of anisotropic jointed rock specimen (JRS) were modeled by Fast Lagrangian Analysis of Continua (FLAC). Failure criterion of rock was a composited Mohr-Coulomb criterion with tension cut-off. An inclined joint was treated as square elements of ideal plastic material beyond the peak strength. Several FISH functions were written to automatically find the addresses of elements in the joint and to calculate the entire deformational characteristics of plane strain JRS. The results show that for moderate joint inclination (JI), strain is only concentrated into the joint governing the behavior of JRS, leading to ideal plastic responses in axial and lateral directions. For higher JI, the post-peak stress-axial and lateral strain curves become steeper as JI increases owing to the increase of new SB’s length. Lateral expansion and precursor to the unstable failure are the most apparent, resulting in the highest Poisson’s ratio and even negative volumetric strain. For lower JI, the entire post-peak deformational characteristics are independent of JI. The lowest lateral expansion occurs, leading to the lowest Poisson’s ratio and positive volumetric strain all along. The present prediction on anisotropic strength in plane strain compression qualitatively agrees with the results in triaxial tests of rocks. The JI calculated by Jaeger’s formula overestimates that related to the minimum strength. Advantages of the present numerical model over the Jaeger’s model are pointed out.
基金Projects(51478477,51878668)supported by the National Natural Science Foundation of ChinaProjects(2014122006,2017-123-033)supported by the Guizhou Provincial Department of Transportation Foundation,ChinaProject(201722ts200)supported by the Fundamental Research Funds for the Central Universities,China
文摘Rock joint shape characteristics,waviness and unevenness play essential but distinct roles in shear mechanism of rock joints.This study presents a novel method to generate virtual rock joint profiles with realistic waviness and unevenness features.Firstly,joint profiles are obtained by 3D laser scanning device.Secondly,quantification of waviness and unevenness is conducted by traditional method,including digital filtering technique and roughness parameter RL.Thirdly,the discrete Fourier transform(DFT)method is employed to analyze the joint outlines.Two representative Fourier shape descriptors(D3,D8)for characterization of waviness and unevenness are suggested.Then,the inverse discrete Fourier transform(IDFT)is adopted to reconstruct the joint profiles with random values of phase angles but prescribed amplitudes controlled by D3 and D8.The traditional method is then applied to the reconstructed joint profiles to examine statistically the relationships between D3 and D8 and parameters RL of waviness and unevenness,respectively.The results show that larger D8 tends to result in larger waviness while higher D3 tends to increase unevenness.Reference charts for estimation of waviness and unevenness with different pairs of D3 and D8 are also provided to facilitate implementation of random joint reconstruction.
文摘A new analytical study on stresses around a post-tensioned anchor in rocks with two perpendicular joint sets is presented. The assumptions of orthotropic elastic rock with plane strain conditions are made in derivation of the formulations. A tri-linear bond-slip constitutive law is used for modeling the tendon-grout interface behavior and debonding of this interface. The bearing plate width is also considered in the analysis. The obtained solutions are in the integral forms and numerical techniques that have been used for evaluation. In the illustrative example given, the major principal stress is compressive in the anchor free zone and compressive stress concentrations of 815 k Pa and 727 k Pa(for the anchor load of 300 k N) are observed under the bearing plate and the bond length proximal end, respectively. However, large values of tensile stresses with the maximum of-434 k Pa are formed at the bond length distal end. The results obtained using the proposed solution are compared very those of numerical method(FEM).
基金Project(51274249)supported by the National Natural Science Foundation of ChinaProject(2015zzts076)supported by the Explore Research Fund for Graduate Students of ChinaProject(201406)supported by the Hunan Key Laboratory of Coal Resources and Safe Mining Open-end Funds,China
文摘In order to investigate the failure mechanism of rock joint,a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL)conditions were conducted.Morphology parameters of the rock joint surface were precisely calculated by means of a three-dimensional laser scanning machine.All test results were analyzed to investigate the shear behavior and normal displacement behavior of rock joints under CNL conditions.Degradation of rock joint surface during cyclic shear tests was also analyzed.The comparison results of the height parameters and the hybrid parameters of the joint surface during cyclic tests show that the degradation of the surface mostly happens in the first shear and the constant normal loads imposed on the joints have significant promotion effects on the morphology degradation.During cyclic shear tests,joints surfaces evolve from rough state to smooth state but keep an overall undulation.Dilatancy of rock joints degrades with the degradation of joint surface and the increase of normal loads.The closure deformation of joint is larger than that of the intact rock,and the normal stiffness increases with the increase of shearing times.
