Browsing by Author "Valtonen, Riikka"

A 370 meter deep drill hole was drilled on the Kumpula Campus of the Univerity of Helsinki for teaching purposes at the end of the year 2015. This work deals with fragile structures in the borehole, which have been compared with existing research data from the Helsinki area and nearby outcrop data. Natural breaks were observed and measured from the drill core and that data was compared to the acoustic and optical images of the drill hole in the Wellcad software. The drill core was not oriented, so the dip direction and dip of the breaks were measured in the Wellcad software and the final correction was made in Excel. depth, possible filling, surface roughness, and slickenside feature of the breaks were recorded. A preliminary RQD value was also measured, which was excellent (94%). Five filling samples, which differed in color and texture, were subjected to XRD analysis. Approximately 700 natural breaks plus two crushed zones, with hearth loss were found found in the drill core. About 11% of the breaks were classified as slickensides. Most of the other break points were filled with minerals. a fracture group in which the gap was not open in the core was observed on the basis of the acoustic image. These kinds of fractures were about 11% of the natural breaks. Comparative field work was carried out on Kumpula campus and surroundings. There were altogether ten outcrops, three of them were road cuts. In addition to the location and direction and dipping, the visible length of the fracture, possible filling of surfaces, surface roughness, and density of the parallel fractures were observed. Observations were greatly affected by the quality and freshness of the outcrops. The main processing of the results was carried out in software Move in 3D, in which the fractures of the drill hole and the collected outcrop fracture data were compared, and the locations of the crushed zones were examined more closely. Both drill hole fractures and the fractures from the outcrops have one main dip direction to the northeast (ie the strike towards the NW), which is in line with previous studies in the Helsinki area. The study also revealed that the strikes of the fractures differ in the northern and southern sides on the hill: the main direction on the south side was in NW-SE, while on the north side it was in E-W direction. To further reinforce this finding, more data is needed, e.g. a comparative borehole on the north side of the hill would provide extra exposure for this possible direction. Another interesting research topic would be the more accurate classification of the drill hole fractures with the help of fillings. The preliminary studies show that slickensides differ from other filled fractures in both the orientation and filling and there are at least four different fillings as well. Such studies could help in estimating the relative ages of the brittle structures.