Research On The Mechanism Of Carbon Nanotube Cement-based Grouting Material To Strengthen Broken Rock

In fractured rock reinforcement projects,the macroscopic mechanical properties of carbon nanotube-based cemented bodies have a direct impact on the stability of surrounding rocks and roadway deformation.To study the influence mechanism of consolidation mechanical properties,to explore the nondestructive testing method of consolidation stability,and to understand the evolution law of consolidation fine structure are the fundamental topics of carbon nanotube-cement-based grouting materials for reinforcing fractured rocks.In this paper,the mechanism of reinforcing fractured rocks with carbon nanotubes cement-based grouting materials is systematically studied from the macroscopic point of view using a combination of indoor tests,theoretical analysis and numerical simulation.The main results and conclusions obtained are as follows:（1）The compressive strength of cemented body is enhanced and then deteriorated with the increase of carbon nanotube concentration and fractal dimension of aggregate particle size distribution,and the results show that the appropriate amount of carbon nanotube concentration and reasonable fractal dimension of aggregate particle size distribution can help improve the macroscopic mechanical properties of cemented body.Based on the experimental results,the coupling model of carbon nanotube concentration and fractal dimension of aggregate particle size distribution on the compressive strength of the solidified body was established,through which the carbon nanotube concentration applicable to any aggregate particle size distribution can be solved.（2）The effect of carbon nanotube concentration and fractal dimension of aggregate particle size distribution on the ultrasonic pulse velocity of solidified body of crushed rock was tested and analyzed,and it was found that the ultrasonic pulse velocity of solidified body was quadratically related to both carbon nanotube concentration and fractal dimension of aggregate particle size distribution.The prediction model for the compressive strength of solids was proposed based on genetic algorithm.（3）The mechanism of carbon nanotubes reinforcement of fractured rock consolidation was elucidated by combining the microscopic experiments of mercury pressure,electron microscopy and energy spectrum elemental analysis,and the mechanism of bridging effect of carbon nanotubes on micro-pores and micro-cracks of fractured rocks was revealed.The experiments also revealed that the agglomeration effect of excess carbon nanotubes produced a large number of micropores in the broken rock,induced the formation of hollow cement cement matrix,and finally deteriorated the skeletal structure.（4）Aggregate particles with certain shape parameters were generated by Matlab programming and imported into PFC^2D particle flow software to construct a numerical model of a highly simulated cementitious mass containing different aggregate particles,and the influencing laws of carbon nanotube concentration and fractal dimension of aggregate particle size distribution on particle damage,energy evolution,force chain breakage and crack development were investigated.The results show that the simulation results match with the indoor test results and reveal the damage rupture mechanism of the solidified body under uniaxial compression conditions.