Experimental Study On Mechanical Shear Properties Of Irregular Rock Fractures

Fractures,joints and faults which cause discontinuity,nonuniformity and anisotropy and widely distribute in engineering rock mass greatly influence the strength and stability of rock mass.Shear properities of rock fractures are the main factor to dominate the stability of engineering rock mass.In this thesis,rock fracture is treated as the main object to study the shear deformation properity,acoustic emission properity,shear dislocation mechanism and the prediction of peak shear strength by means of AE technology and laser scanning method.Single-fractures of sandstone and marble were induced in the thesis by Brazilian splitting method.3D morphology of rock fractures were obtained and analyzed by using laser scanner.Direct shear tests were conducted under different constant normal load(CNL)by using RDS-200 apparatus and austic emission(AE)signals were monitored and recorded as while as AE location.By fitting analysis about direct shear test results,it was considered that normal load was the main factor to influence shear behaviors including peak shear strength,peak shear displacement,pre-peak shear stiffness,peak dilatancy angle,drop gradient and residual shear coefficient.Shear process was devided into several phases according to the shear properities of different rock type or grain size.The normal deformation properities were also analyzed and concluded.AE parameters such as energy,total energy and counts that happened during the test were analyzed and AE properities of different rock type were concluded.Frequeccy spectrum of different shear stage was found out through analyzing their waveforms.Shear deformation model for regular rock fracture was proposed for regular fracture.The exact occurrence of shear dislocation(the start point of the shear movement)happens at the drop point of peak shear stress was proved from different angles(AE location at different shear displacement,comparison between AE location and 3D scanning model,density distribution of AE location and the migration of main resistant area).A new method to describe rock fracture roughness,which was average ailatancy angle(i_a),was proposed in the thesis.A new empirical formula of shear strength of rock fractures based on the new roughness parameter(i_a)was proposed in the thesis.The empirical formula could be commonly used for different types(sandstone and marble)and grain sizes(powder-grained,fine-grained,medium-grained and coarse-grained)of rock fractures.