| Rock mass is called dualistic structure body consist of joints and rock blocks,that is,blocks and various joints such as fissures,discontinuity,bedding planes,and faults that all compose the complex structural rock mass.The existence of the rock joints makes the rock mass with anisotropy characteristics,which aggravates the complexity of the research on rock mass mechanical characteristics and stability.Especially for the composite layered rock mass,due to the different rock properties on both sides of the bedding planes,its mechanical characteristics and stability are more complicated.The composite layered rock mass is widely distributed and potentially disastrous in western Hubei,then it has important scientific significance and engineering application value that we are committed to exploring the shear failure evolution characters of the composite layered rock mass joint,and further develop the anchoring mechanism of the anchored composite layered rock mass joint.At present,the research on rock mass joint mainly focuses on the joint with the same rock type in the upper and lower walls,while there are few studies on the joint with different rock type in the upper and lower walls.There are few reports on the research of anchoring mechanism of the the anchored composite layered rock mass joint.The western Hubei region is widely distributed with composite layered rock mass with soft and hard interbed structure.The special rock mass with complex mechanical properties and structural characteristics has led to frequent geological disasters in Badong which belongs to the western Hubei region,so the composite layered rock masses joint in Badong was selected as key objects,revealing the shear failure evolution and anchoring mechanism of typical composite layered rock masses.In view of the importance of the research on the shear properties and anchoring mechanism of the composite layered rock mass joint,and the shortcoming of the current research,using engineering geological analysis,theoretical analysis,indoor test and numerical test methods,the following research was carried out:The spatial distribution and structure characteristics of the composite layered rock mass in the western Hubei region was analyzed,and the joint wall rock properties and three-dimensional morphological characteristics of the joint wall surface was obtained.Considering the different joint wall rock type combinations and the multi-level normal stress factors,taking the compound layered rock mass joint as the research object to carry out the laboratory direct shear test and numerical parallel test,and then the evolution characteristics of macro-and meso-scale indicators such as shear failure area,shear failure depth,crack failure and energy are analyzed from the macro-and meso-scale perspective.Further,based on the similarity ratio theory,a similar model of anchored composite layered rock mass joint was established.The direct shear test was carried out with considering factors about different wall rock type combinations and different normal stresses,and then to analysis the wall rock failure characteristics and anchorage system failure modes,and to discuss bolt deformation relationship with wall rock strength.Analyze the evolution characters of various types of cracks,the number of cracks,energy value,particle rotation angle and particle porosity during the shear process,and discuss the effect of anchoring angle on shear characteristics,from the macro and meso angle to study the anchoring mechanism of anchored composite layered rock mass joint.Next,based on the analysis of the structural characteristics of the composite layered rock mass of the Maya high slope,the long-term creep deformation characteristics of the slope were analyzed using FLAC3D with version 5.0,and compared with the actual engineering monitoring data to verify and analyze the long-term stability of anchored Maya slope.Based on the above research,the following results have been achieved.?1?Based on the laboratory test,the shear failure character of the composite layered rock mass joint is revealed from the macro level.?1?Developed a rock mass joint sample installation device for indoor direct shear test.Based on the portable direct shear instrument,a fixing device for installing irregular specimens with multiple sizes is provided to optimize the installation procedure.After installing the sample through the fixture and placing it in the external shear box,it can make up for the defects of traditional method of sample preparation and sample installation that require a lot of time,materials costs,and the difficulty in ensuring the level of the joint.Achieve the purpose of installing multi-size joint samples,then to carry out test efficient and environmentally friendly.?2?The macro-shear failure character of the composite layered rock mass joint is revealed.Based on 14 sets of natural composite layered rock mass joint samples,indoor direct shear tests were carried out under normal stress of 0.1,0.2,0.3 and 0.4 MPa and three repeated shears under normal stress of 0.4 MPa.Under the four-level normal stress,the shear strength of the composite layered rock mass joint increases with the normal stress increases.The shear failure area of the wall rock surface continues to expand,and the upper wall shear failure area is larger than the lower one.In the three times shear cycles tests,the shear strength gradually decreased and the downward trend slowed down with the number of shear cycles increased.The shear failure area of the wall rock surface still increase,and its increase rate was weaker than the growth rate under the fourth-level normal stress.The wall shear failure area of the upper wall is always greater than that of the lower one.According to comparative analysis,for the typical composite layered rock mass joint samples studied in this paper,the shear failure area is closely related to the strength of the wall rock.The greater the difference between the wall rock properties of the composite layered rock mass,the larger the difference between the shear failure area of the two side wall rocks.Also,the joint shear failure of the composite layered rock mass is affected by the surface morphology.?2?Based on the PFC program,the model building method and shear stress monitoring method are discussed.?1?The PFC microparameters calibration and the model building method of composite layered rock mass joint are discussed.Due to the complicated relationship between macro and meso parameters in PFC,a single factor experiment was conducted to explore the effect of the microparameters of the joint on the macroparameters.The tangential relationship between the microparameters sj?fric with basic friction angle.Microparameters sj?kn and sj?ks are positively correlated with the normal rigidity and tangential rigidity of the rock joint,respectively.The neural network method is used to learn 76 sets parameters and verify the comparison of 5 sets parameters,and then establish 4-5-6 moldel used to calibrate the microparameters of wall rock.In this paper,the rock joint of the natural composite layered rock mass is non-matching and the properties of the two side walls are different.FISH language was used to quickly establish an irregular numerical model,and the numerical model building steps of the natural composite layered rock mass joint was given as building model guideline.?2?A shear stress monitoring method is proposed based on the PFC numerical direct shear test.In the PFC numerical direct shear test,the initial force is usually ignored by the existing methods,resulting in problems with the monitoring results.Therefore,a new method for monitoring shear stress is proposed,and the ratio of the resultant force of the left and right walls to the area of the joint is taken as the shear stress.Numerical tests were carried out on the sawtooth surfaces with angles of 0°,15°and 30°and the Barton standard joints with JRC=5.8,10.8 and 14.5.A comparative study is carried out,which shows that the monitoring results of the new method consistent with the calculation results of the classic model and the laboratory test results,it has advantages especially for direct shear tests with low normal stress or low roughness coefficient.?3?Based on numerical experiments,the shear failure character of the composite layered rock mass joint is revealed from the meso angle.?1?The accuracy of the PFC numerical method is verified based on the comparison between laboratory experiment and numerical experiment.The errors of the peak shear strength of the rock joint of F1#4 group,F2#1 group and F3#4 group obtained by laboratory and numerical experiments are 4.7%,2.3%and-4.2%,respectively.Regarding the comparison of the percentage of shear failure area of the wall rock surface,the shear failure percentage errors of the upper block of F1#4 group,F2#1 group and F3#4 group rock joint obtained from indoor and numerical experiments are-7.5%,-6.9%,6.5%,the shear failure percentage errors of the lower block are-3.8%,-3.7%,3.4%.Therefore,it is considered that the numerical test consistent with the indoor test.?2?The meso-shear failure character of the composite layered rock mass joint was revealed.The following shows the analysis of the numerical test results,in terms of the vertical failure depth characteristics of the wall rock,the upper wall rock damage is earlier than the lower one,and the depth is greater than the lower one.In terms of crack failure type and characteristics,the system crack unmber increase with increasing shear displacement,and the number of shear cracks and the growth rate of the system are much greater than the tensile cracks.The number of cracks in the upper wall rock occupies a larger part of the system cracks.In terms of energy evolution characteristics,the system strain energy in the upper and lower wall rock is nonzero and continues increasing,and the strain energy in the upper wall is greater than that in the lower one.After the shear stress reaches peak,the strain energy of the system,the upper and lower wall rock remains relatively stable.Most of the friction energy is generated at the joint,and a small portion friction energy is generated in the crack of wall rock.?4?Based on indoor experiments,the anchoring mechanism of anchored composite layered rock mass joint is revealed from a macro perspective.According to the characteristics of natural composite layered rock mass and similarity ratio theory,a similar model of anchored composite layered rock mass jont was established.It can be seen that the anchor can increase the shear resistance of the composite layered rock mass joint through indoor direct shear test,the major reson is that the anchor increasing the equivalent cohesion of the joint.As the normal stress increases,the shear strength of the anchored composite layered rock mass joint increases.The stronger the strength of the two side wall rocks,the greater the shear resistance of the anchored joint.Keepping the weaker side wall rock strength unchanged,increasing the strength of the other side wall rock can increase the shear strength,but the increasing strength is limited.The weaker side wall rock has a greater influence on the properties of anchored joint.Taking the joint as the boundary,through theoretical derivation and laboratory test verification,the ratio of the deformation length of the anchor located in the upper and lower wall rock?5?Based on numerical experiments,the anchoring mechanism of anchored composite layered rock mass joint is revealed from a meso perspective.?1?Based on the numerical experiment,the evolution characteristics of the bolt axial force are revealed during the shear test.According to numerical experiments,it can be seen that,as the shear displacement increases,the axial force of the bolt increases,which is equivalent to increasing the normal stress of the direct shear test.The maximum axial force of the bolt is at the joint,and that gradually reduced when away from the joint.The axial force is roughly symmetrically distributed based on the joint,and the axial force in the upper wall is slightly greater than that at the corresponding position of the lower wall.The closer to the joint,the greater the difference,and the smaller the converse.?2?Based on macro and meso evolutionary indicators,the anchoring mechanism of anchored composite layered rock mass joint is revealed.In terms of the type and number of cracks,as the shear displacement increases,the number of tensile cracks in wall rock and mortar increases and is greater than the number of shear cracks,the number of cracks in the upper wall is greater than that of the lower one.The bolt has been in the state of elastic deformation in the early stage,only a few tensile cracks have occurred at the end of the stress-strain curve,and plastic failure has occurred.In terms of energy characteristics,the numerical model stores elastic strain energy during the elastic strain stage.The strain energy stored in the upper wall is greater than that in the lower one and greater than the strain energy in the bolt and mortar.As the shear displacement increases,the elastic strain energy of the system increases but occasionally decreases,while the friction energy gradually increases.During the whole shear test,the wall rock and mortar were destroyed to consume a part of energy and converted into frictional energy consumption.The frictional sliding at the joint occupied most of the system frictional energy.In terms of particle porosity characteristics,in the upper or lower wall,with the bolt as the boundary,the porosity of the particle on the compression side will decrease,while the porosity on the tension side will increase,the scope of influence is getting larger and larger with the shear displacement increasing.Taking the intersection of the joint and the anchor as the reference point,the porosity of the particles on both sides at the symmetrical position is roughly antisymmetric,and the porosity of left side of bolt in the upper wall is higher than that of the right side of bolt in the lower wall,and the porosity of right side of bolt in the upper wall is lower than that of the left side of bolt in the lower wall.The closer to the joint,the greater the difference,and vice versa.Four bolt angles of 45°,60°,75°and 90°were designed for the shear test of the anchored composite layered rock joint.The results show that the anchor system has the largest overall shear strength when the bolt angle is 60°.?3?The evolution stages are divided based on the characteristics of shear stress changes and the characteristics of macro and meso evolution indicators.The relative relationship between wall rock strength and bolt strength is different,and the failure mode of the anchor system is different.In this paper,the strength of the wall rock is relatively lower,and the failure of the anchor system caused by the wall rock broke.The evolution stage is divided into elastic stage,stress drop stage,yield stage,plastic strengthening stage,wall rock failure stage and residual stage.?6?The long-term stability of typical composite layered rock slopes was evaluated.Maya slope is a typical composite layered structure slope.During the long-term creep deformation process,it is affected by the composite layered structure and then the rock slope appear different deformation characteristics of the soft and hard layers,especially in the horizontally weak rock formations have a tendency to extrude,the horizontal deformation is large.Long-term stability analysis shows that the 20-year?240month?creep deformation of Maya high slope is within a controllable range.Through comparative analysis of the numerical simulation and actual monitoring data,it can be seen that the numerical simulation and the actual monitoring results are consistent with each other.The numerical simulation results on the Maya slope from 180 to 240 months show that during this period,the horizontal deformation of TS3 is large,the deformation range is-12.35?-12.03 mm.Deformation analysis shows that the overall deformation of the slope is small,the deformation rate is slow,and the overall stability is good. |
PDF Full Text Request