Rock mass characterization of the Underground Research Laboratory of Aalto University (URLA)
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Insinööritieteiden korkeakoulu |
Master's thesis
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Authors
Date
2024-08-19
Department
Major/Subject
Rock Engineering
Mcode
Degree programme
Master's Programme in Geoengineering (GEO)
Language
en
Pages
96+6
Series
Abstract
Rock mass characterization is vital for assessing the geotechnical and geomechanical sta-bility of a rock mass which ensures safe tunnel designs and ultimately a sufficient reinforce-ment design. The validity and reliability of different rating systems is based on the accurate characterization of fracture parameters like orientation, joint set number, spacing etc. A comprehensive study of such fracture parameters will only ensure the correctness of nu-merical models. In this thesis, a combination of non-invasive techniques for mapping frac-ture properties is studied. Photogrammetry uses 3-D digitization technique to generate high resolution models of the rock mass while ground penetrating radar can image the sub-surface for fractures in a tunneling environment. The research location is one of the tunnels at the Underground Research Laboratory of Aalto University (URLA). This thesis was sup-ported by the FinGeo-project and the motivation was the collection of tunnel data to obtain new digital models for educational purposes. The research questions are: What are the limitations imposed by ground penetrating radar in tunnels? How can GPR be used for characterization of fractures within the rock mass namely aperture and filling? How can photogrammetry be used to evaluate geometrical properties of fractures and digitization of roughness profiles? This thesis deals with the characterization of fracture properties such as orientation, joint set number, aperture, filling, roughness, and spacing using photogrammetry and GPR. Photogrammetry is carried to reconstruct a 3-D point cloud which is analyzed in a point cloud editing software and discontinuity set extractor for the extraction of joint properties. The test site is divided into two mapping windows. GPR (800 MHz) is used to survey four vertical profiles on the rock mass where photogrammetry is conducted. The four profiles are processed and interpreted showing two to maximum of four fractures. The analysis sug-gest that the fractures observed with GPR in the test site are all thin bed fractures whose aperture is smaller than the radar range resolution. The floor survey profile by 250 MHz and 500 MHz in the same tunnel shows three wide fractures with a mean aperture of 10.3 cm in one of the fractures. Sensitivity analysis resulted in three joint sets for mapping window one and four joint sets for mapping window two. The surface analysis concluded in moderate spacing of joint sets ranging between 0.2-0.6 m with undulating rough fracture surfaces as indicated by the manual and digitized joint roughness profiles. GPR studies concluded the wall surveys to have thin-bed, subvertical fractures in the subsurface with moderate spacing of 0.2-0.6 m between the individual fractures.Description
Supervisor
Leveinen, JussiThesis advisor
Janiszewski, MateuszHokkanen, Tero
Keywords
photogrammetry, ground penetrating radar, fracture properties, thin bed fractures, joint roughness