Studies On Shear Stress Distribution Of Fully Grouted Rock Bolt

The present thesis has investigated both numerically and experimentally the behavior of shear stress distribution along the grouted displacement of full grouted rock bolt subject to pull out axial force.It was found in the literature through extensive studies that failure of full grouted rock bolts occurred most probably due to the de bonding phenomenon between grout and bolt interface which is under extreme axial load.Keeping in view the importance of aforementioned topic,the study has been carried out in Laboratory and through Abaqus software.The main research contents are as follows:(1)To conduct numerical study,Abaqus software has been opted to carry out simulation and to make comparison with theoretical and experimental results which is basically based on Finite Element Analysis.Four different diameter of rock bolts have been simulated having diameter of 12.5,16,20 and 15mm respectively.Two breeds of rock bolt were taken into consideration during simulation that is with ribs and without ribs.For each type of rock bolt four different ratios of Elastic Modulus of concrete to Elastic Modulus of rebar Ec/Ebhave been used.Ec/Eb ratios are 0.2,0.1,0.05 and 0.025.The effect of changing material properties(Ec/Eb)and geometry(diameter)of rock bolt on the behavior of distribution of shear stress has been deeply investigated.Firstly,it was found that for lower ratio of Ec/Eb,the peak shear stress value is higher which shows inverse relation between peak shear stress and Ec/Eb.Secondly,the shear stresses are more dominant at the open end of the grout which is near to the position of applying pull out force.Thirdly,with increasing the diameter of rock bolt,the peak normalized shear stresses were also increased.In addition,results show good agreement between numerical and theoretical study.(2)In experimental part,rock bolt of 20mm diameter with and without rib was chosen.In order to get the excellent results,10 strain gauges was mounted at opposite face of each rock bolt.For the grouting material,water to cement ratio was taken to be 0.4.The curing time of concrete was seven days.The pull-out test was performed with the sophisticated machinery i.e.pre stressed electric oil pump and hydraulic jack.The data was than simulated with the latest model of data acquisition device that belongs to Ganten Instrument brand.It was found that the axial force required to de bond the grouted material of ribbed rock bolt is about two third time higher than plain rock bolt.The results achieved from experiment also confirm the results obtained from both theory and simulation.