| The paper aims to study a monitoring device for axial force of rock bolt.It is simple in structure,low in cost,easy to install,no damage to anchorage quality,suitable for large-scale installation and convenient monitoring.The bolt supporting technology can be used to reinforce,combine and connect the surrounding rock,improve the strength and stability of the surrounding rock,and is widely used in the fields of coal mine,water power,metallurgy,tunnel and so on.However,as time goes on,the rock bolt axial force is increased as in hostile working environments affected by groundwater corrosion,adjacent mining disturbance and stress change of surrounding rock,and so on.Once the stress of rock bolt reaches or exceeds its strength limit,it will lead to the break of the rock bolt and the failure of the anchor engineering,which will cause serious safety accidents.In order to maintain the stability of the project and ensure the safety of construction,it is necessary to monitor the axial force of the rock bolt.Therefore,the research on the monitoring device of rock bolt axial force has significant social economic benefits and great practical scientific value.However,the recent achievements still have manydisadvantages,such as needing power supply or hydraulic seal,difficult to waterproof and explosion-proof,poor reliability,high manufacturing costs,complex security management and so on,difficult to achieve long-term monitoring accurately and efficiently.In view of the shortcomings of the current monitoring device of rock bolt axial force,a new nondestructive monitoring method is proposed based on the analysis of the existing research results and practical experience.Through analysis and research,it is determined that the monitoring device is mainly composed by the upper cover plate,the elastic cushion,the lower cover plate,the bearing body and the optical film.Under the action of rock bolt axial force,the optical film of monitoring device will generate tiny deformation.According to the linear relationship between the stress and strain of the optical film,the change of the thickness of the optical film under the white light source will cause the change of the color of the interference pattern.Determine the security status of the anchor with the different color of optical film.First of all,the distribution rule of shear stress and axial stress of rock bolt is obtained according to the force analysis of tension-type rock bolt.The model of the anchor bolt is selected,the installation position of the monitoring device is determined and three different stress states are defined.Then material selection,structure design and size selection of each component are discussed and determined according to the analysis of the stress distribution characteristics,practical application scenarios,basis function and workingprinciple of each component monitoring device.The strength of the upper cover,the lower cover and the bearing body are analyzed and validated by ANSYS to ensure the safety and reliability of the monitoring device in the stress measuring ranges.Then the related programs based on MATLAB are written through formula derivation of principle of optical interference and deformation theory of optical film.And then introduces color display method of the interference pattern and simulates the interference pattern of optical film by ANSYS finite element analysis and MATLAB.The analysis and simulation results show that the interference pattern of the optical film changes three colors under three defined stress states in the stress measuring ranges,so can judge the stress state of rock bolt by different colors.The feasibility of the monitoring device is proved. |
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