| The stability of joint rock mass has long been a research hotspot in geotechnical engineering.Relevant scholars have been working hard to find various reinforcement methods for joint rock mass on dam foundations and bank slopes.Reinforcement of joint rock mass has been by one of the numerous reinforced methods.In recent years,more and more experimental researches and engineering applications of fiber reinforced concrete structures have been carried out.The related results show that the fibers have a good effect in controlling or slowing the cracking of concrete,enhancing the relevant mechanical properties of concrete.Based on this,ultrafine cement with carbon fiber is studied in this paper.The joint-reinforced rock specimens and slurry specimens of the composite materials were used as the object,and the optimal carbon fiber content of the composites and the composites were determined by the experimental research method through the reinforcement effect of the composite materials with different carbon fiber contents.Under the condition of optimal carbon fiber content,the durability mechanism of the specimens under long-term water pressure soaking condition was studied,which provided reference for the study of cement-based composite grouting material with carbon fiber reinforcement in the research of reinforced joint rock mass.The main research contents and conclusions of this paper are as follows:1)Six repeated shear tests were performed on joint rock specimens under different normal stress,and the microscopic morphology of the joint surface before each shear test was scanned.It was found that the shear stress-shear deformation occurr under repeated shear stress.The characteristics of curves change are obvious,and the peak shear strength gradually decreases.The degradation of the first two shear test account for more than 65% of the total degradation value.After 2 or 3 times of shearing,there are no obvious peak shear strength appear,and the shear hardening phenomenon is obvious.The shear strength gradually stabilized;the indentations,wear,and filling occurred in the micro-bumps and recesses that meshed with each other on the surface,and the roughness of the joint surface gradually decreases,resulting in its topographic parameters(including Sz,Sq,Sdq,and Sdr)gradually decreases,which in turn led to a gradual deterioration of its shear mechanical properties.Therefore,it is determined that the shear strength at the sixth time of repeated shear test is used as the strength value before strengthening the joint rock specimens.A method for determining the stable shear strength using a repeated shear test is proposed.2)By preparing carbon fiber ultrafine cement-based slurries with carbon fiber contents of 0,0.25%,0.50%,0.75%,and 1.00%(mass fraction)respectively,the physical tests such as the water used for the standard consistency of the composite material slurry,the setting time,water rate and fluidity and showed that with the increase of carbon fiber content,the water extraction rate and fluidity are slightly reduced compared with that of pure cement slurry,the overall change range is small,and the setting time is significantly reduced,indicating that the carbon fiber could short the slurry setting time and initial and final setting time interval,the slurry has a good stability.At the same time,the shear mechanical properties of the slurry sample under different normal stress conditions are studied and found that different dosages of the slurry specimrens had obvious peak and residual strength.With the increase of the carbon fiber content,the shear strength and shear strength parameters are also increased,and the increase of cohesion is greater than the internal friction angle.Slurry specimens with or without carbon fiber had a distinct difference in the failure mode,showing that the upper and lower shear surfaces of the slurry specimen without carbon fiber are cut,completely separated,and the edges of the sheared specimens are peeled off and fell off.However,with the increase of shear displacement in the slurry specimen with carbon fiber added,obvious visible shift occurred between the upper shear surface and the lower shear surface of the slurry specimen,but the contact portion between the two shear surfaces are not sheared,indicating that the incorporation of carbon fiber can exert a toughenitng and crack arresing effect on the slurry material obviously.3)The composite rock specimens of five kinds of carbon fiber contents in 2)were used to reinforce the joint rock specimens,and shear test was performed on the joint rock specimens before and after reinforcement espectively.The results show that the shear forces of the joint rock specimens before and after reinforcement.The shear-displacement curve changes from peak-free intensity to peak-intensity curve,and obvious strain softening stage and residual strength stage appear;With the increase of carbon fiber content,the peak shear strength and residual shear strength of joint rock specimens under five kinds of the normal stress increase by 13.0%~54.1% and 0.61%~44.7%,the shear stiffness increase by 32.4%~216.8%,and the cohesion and friction angle increases by 127.3%~266.5% and 4.3%~20.4% respectively;When the content is 0.75%,the comprehensive reinforcing effect of the shear strength of the joint rock specimens are most obvious,so 0.75% is taken as the optimal carbon fiber content.Combined with the joint surface topography and reinforced shearing,the analysis of the failure surface characteristics shows that the composite material slurry has a good filling and cementation effect on the joint surface.On the one hand,the effect of carbon fiber is similar to the “reinforced” material,and can further increase the strength of the slurry on the basis of the pure cement slurry and limit the development of micro-cracks during the shearing process.On the other hand,carbon fiber provides a better “anchorage” effect on the sheared slurry,further increasing the bondability between the slurry and the joints,making the slurry itself,the slurry and the shear resistance of the cemented surface between the joint surfaces are significantly enhanced,which significantly improve the comprehensive shear resistance of the joint rock mass after reinforcement.4)Joint reinforced specimens and slurry specimens were prepared at the optimum carbon fiber content and impregnated with 0.5 MPa of water pressure.After each phase of soaking,uniaxial compression?splitting and shear tests were performed.It was found that the compressive strength,tensile strength and shear strength gradually decrease with the increase of the soaking period and then become flat.It is because the softening and lubrication of the water-rock physical chemistry interaction,the bond strength between the slurry itself,the joint plane itself,the slurry and the carbon fiber,and the slurry and the rock joint plane are gradually weakened,and at the same time,the rock specimens will also have its own mechanical parameters deterioration under the action of the water-rock interaction.Therefore,macroscopically,it shows the deterioration of the compression resistance,tensile strength and shear strength. |
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