Optimization of the fully grouted rock bolts for load transfer enhancement

The purpose of this study is to investigate the role of bolt profile configuration in load transfer capacity between the bolt and grout.Therefore,five types of rock bolts are used with different profiles.The rock bolts are modeled by ANSYS software.Models show that profile rock bolt T_3 and T_ with load capacity 180 and 195 kN in the jointed rocks,are the optimum profiles.Finally,the performances of the selected profiles are examined in Tabas Coal Mine by FLAC software.There is good subscription between the results of numerical modeling and instrumentation reading such as tells tale,sonic extensometer and strain gauge rock bolt.According to the finding of this study,the proposed pattern of rock bolts,on 7 + 6 patterns per meter with 2 flexi bolt(4 m) for support gate road.

Utilizing a novel fiber optic technology to capture the axial responses of fully grouted rock bolts

Rock bolts are one of the primary support systems utilized in underground excavations within the civil and mining engineering industries. Rock bolts support the weakened rock mass adjacent to the opening of an excavation by fastening to the more stable, undisturbed formations further from the excavation. The overall response of such a support element has been determined under varying loading conditions in the laboratory and in situ experiments in the past four decades; however, due to the limitations with conventional monitoring methods of capturing strain, there still exists a gap in knowledge associated with an understanding of the geomechanical responses of rock bolts at the microscale. In this paper, we try to address this current gap in scientific knowledge by utilizing a newly developed distributed optical strain sensing(DOS) technology that provides an exceptional spatial resolution of 0.65 mm to capture the strain along the rock bolt. This DOS technology utilizes Rayleigh optical frequency domain reflectometry(ROFDR) which provides unprecedented insight into various mechanisms associated with axially loaded rebar specimens of different embedment lengths, grouting materials, borehole annulus conditions, and borehole diameters. The embedment length of the specimens was found to be the factor that significantly affected the loading of the rebar. The critical embedment length for the fully grouted rock bolts(FGRBs) was systematically determined to be430 mm. The results herein highlight the effects of the variation of these individual parameters on the geomechanical responses FGRBs.

Analysis profile of the fully grouted rock bolt in jointed rock using analytical and numerical methods

The purpose of this study was to investigate the effect of bolt profile on load transfer mechanism of fully grouted bolts in jointed rocks using analytical and numerical methods. Based on the analytical method with development of methods, a new model is presented. To validate the analytical model, five different profiles modeled by ANSYS software. The profile of rock bolts T3 and T4with load transfer capacity,respectively 180 and 195 kN in the jointed rocks was selected as the optimum profiles. Finally, the selected profiles were examined in Tabas Coal Mine. FLAC analysis indicates that patterns 6+7 with2 NO flexi bolt 4 m better than other patterns within the faulted zone.

Finite difference numerical simulation of guided wave propagation in the full grouted rock bolt

Based on guided wave theory and considering the grouted rock bolt as waveguide medium, we have constructed a three dimensional model of grouted rock bolt with the dynamics of finite difference numerical simulation software FLAC3D4.0, and simulated the propagation behavior of the guided wave in the full grouted rock bolt. The simulated waveform and wave velocity matched well with the experimental results. We have made a more in-depth and comprehensive study of the wave velocity, wave component and attenuation characteristics of the guided wave propagating in rock bolt, and found some new characteristics and phenomena. In addition, some phenomena that haven’t been explained in the previous researches have also been discussed in this paper. The result showed that when guided wave propagates in grouted rock bolt, after the body wave decays, there is still the interface wave-Stoneley wave that does not decay in the axial direction of the bolt. The findings can provide some reference for rock bolt testing and the selection of the optimal excitation wave of testing.