Pull experiment to validate photogrammetrically predicted friction angle of rock discontinuities

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Insinööritieteiden korkeakoulu | Master's thesis
European Mining Course
Degree programme
European Mining, Minerals and Environmental Programme
116 + 6
The accurate estimation of the mechanical properties of a rock joints is crucial in terms of safety when it comes to design of slopes in open pit mines or caverns used for the storage of hazardous materials, for instance – nuclear waste. Photogrammetry provides a simple and objective method of joints roughness assessment, without the need for expensive and time consuming laboratory tests or imprecise empirical methods. In this thesis photogrammetric method developed in KARMO II project was used to estimate the roughness, shear strength and friction angle of a discontinuity of big scale sample. That estimation was done by analyzing the profiles of digital models of joint surface. Surface length and slope measurement methods were used to calculate the values of joint roughness coefficient of analyzed surfaces. Alternatively, JRC was also estimated empirically, with hand profiling method, and the same calculations were done for JRC values obtained this way. Next, Barton – Bandis criterion was used to calculate the shear strength and friction angle of the joint. Additionally, the shear strength and friction angle of the rock discontinuity were obtained experimentally with multistage pull testing. The results obtained with all methods were analyzed and compared. JRC values from photogrammetrically created digital models of the joint surface were overestimated due to the models not being dense enough which resulted in high noise to signal ratio. High JRC values combined with low normal load used during the pull test constrained the applicability of Barton – Bandis criterion and the linear interpolation was used to determine the shear strength and friction angle of tested rock surfaces. Values of shear strength obtained with photogrammetrically created models were overestimates in relation to the results of the pull test by approximately 45%. The errors made during this research are analyzed in the thesis and recommendations on how to improve reliability of the results are made. Main error in photogrammetric prediction was too low density of the point clouds and in laboratory test too low stiffness of the test arrangement. The alternative methodology for photogrammetric studies used in previous stage of the KARMO I project was tested in this thesis and was proven to give significantly higher accuracy of generated digital models. The stiffness of the testing machine and proper positioning of the sample halves on top of each other were identified as the most sensitive aspects of methodology of big scale pull test when it comes to reliability of the results.
Rinne, Mikael
Thesis advisor
Uotinen, Lauri
Sirkiä, Joni
photogrammetry, pull test, friction angle, rock joints
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