Evaluation of Oriented Rock Cores for Determination of Weakness Zones within a Rock Mass
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
This thesis covers the question if oriented rock cores can be of benefit, compared with non-oriented rock cores when determining the orientation of a weakness zone within a rock mass. The aim is to suggest when oriented rock cores is preferable to use and to make concluding remarks on the advantage and disadvantage of oriented rock cores compared to non-oriented rock cores for weakness zone prediction. In mining and civil engineering and especially in areas with low stresses (i.e. often shallow or distressed constructions), the discontinuities in the rock mass are of great importance for the stability. The discontinuities consists of beddings, joints and weakness zones that reduce the strength of the rock mass and therefore the structures are investigated in an early stage to prevent cause of structural dependent failures. In this work the definition of a weakness zone is a zone of very poor rock (Rock Quality Designation (RQD) less than 10%) that is greater than 20 cm in width. The hypothesis used in this work is that the weakness zone has a high joint frequency and that this frequency is decreasing further away from the zone.The data provided and analyzed in this work has been from rock cores in seven boreholes, each with different amount of orientation data available. The procedure has been developed in a stepwise manner, where each step was of equal importance for the preceding step. Each detected weakness zone in the studied rock cores was summarized and the orientation data was utilized in a stereographic projection. To cover all the potential important structures, the orientations of joints at a distance of two meters before and two meters after the observed weakness zone were added in the projection. Based on the stereographic projection a mean value of the major orientation was determined for each major joint set with a deviation of 15 degrees. The orientations and the width of the observed weakness zones in the seven boreholes were extrapolated in a 3D software to predict the intersection of the zones in the surrounding boreholes. Photos of the rock core at the predicted depths were studied and compare with the visual characteristics of the analyzed weakness zone that was the starting point (reference zone) to find the propagation of the weakness zone within the rock mass. The orientation of the weakness zones those could be connected to the reference zone were studied and compared in order to verify the interpolation of the reference zone. When verifying the connection from the reference zone to the weakness zones in the surrounding boreholes this weakness planes are further called large scale weakness zone in this thesis. Based on the evaluation 14 large scale weakness zones could be summarized and based on the comparison with photos of the rock cores these zones is assumed to be predicted with high certainty.The conclusion from this study was that oriented rock core can be of large benefit when determining the orientation and location of a weakness zone. This study has shown that with the stepwise procedure, used to evaluate major weakness zones by orientation data and through comparison with rock core photos, the location and orientation could be predicted. Hence, one oriented rock core can be used to study the geology, rock mechanic properties as well as prediction of location and orientation of structures. The stepwise procedure to study weakness zones in this work can be of use in the design of rock constructions where structures are likely to control the stability or i.e. when it is important to know the location and orientation of ore contacts. By determining the orientations of weakness zones within the rock mass the constructions can be designed with respect to these and reduce potential structural dependent failures. If this is fully performed with good precision and accuracy the amount of boreholes can most likely be reduced, compared with using non-oriented rock cores, which might lead to lower costs.
Place, publisher, year, edition, pages
2014. , 76 p.
IdentifiersURN: urn:nbn:se:ltu:diva-55999Local ID: ccb5e3af-a7c8-40dc-9d55-1858f0a3da9cOAI: oai:DiVA.org:ltu-55999DiVA: diva2:1029385
Subject / course
Student thesis, at least 30 credits
Civil Engineering, master's level
Validerat; 20140514 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved