Research On Nondestructive Detection In Anchorage Quality Of Rock Bolts Based On The Box Dimension

Bolting is more and more important in urban infrastructure constructionand the major projects, such as the subway、 tunneling、 bridges and minebuildings. The work condition of bolting plays a key role in schedule、securityand stability of the whole project. Consequently, it is indispensable and crucialto test the work condition of bolting and repair it on time. Impressive progresshas been made recently in bolt nondestructive monitoring. Nevertheless, themost important question, which keep their research findings from practicalapplication, remain unresolved. That is how to identify the bottom reflectionaccurately and quickly. In addition, the different conditions between laboratoryand engineering project can not be ignored. Whether the existing theory canmeet the practical application is remain controversial.The present study paid attention to bolt nondestructive monitoring.Through a deeper research on the theory, we re-explored the propagation rule ofstress wave in bolt and made the in-depth study in principle and applicablescope of fractal box dimension. Eventually, we put forward an appropriatemathematical computational model for box dimension. We programmed inMATLAB and obtained the curve correlation between box dimension and working load of rock bolt. The feasibility of this method has been demonstrated.The results of the present study are as follows:1) We established the bolt anchoring quality evaluation system andproposed a method to judge the quality of bolt anchoring using seven parameters(attenuation coefficient, amplitude ratio, Effective anchorage length, theconsolidating wave speed, frequency ratio, fundamental frequency and thefundamental point of the dynamic stiffness).2) We re-explored the fractal theory and the specific mathematical model ofbox dimension. Besides, the feasibility of the fractal box dimension applied tothe bolt nondestructive monitoring was demonstrated from the theoretical basisand applicable scope.3) We established the mathematical model of fractal box dimension for boltnondestructive monitoring and programmed in MATLAB. The curve correlationof box dimension and working load of bolting can be got by importing data tospecial software origin.4) We obtained the same trend, increasing first and decreasing after thepeak, in the curve correlation of box dimension and working load amongdifferent specimens. Although the value of box dimension is variant when thespecimens with the same anchorage parameter, the value of working load isconsistent when box dimension reaches the maximum.5) We can directly judge the anchorage quality and the ultimate load by thiscurve. The bolt is approximately in the elastic deformation stage when the value of box dimension located in front of the peak value. The bolt is in anchoragefailure stage when the value of box dimension is equal or close to the peakvalue.