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Uppsala, Sweden

Stepinski T.,AGH University of Science and Technology | Mattson K.-J.,Geosigma AB
2015 IEEE International Ultrasonics Symposium, IUS 2015

In this paper we present a new digital ultrasonic instrument for nondestructive inspection of rock bolts using guided waves. The Rock Bolt Tester (RBT) instrument applies long-range ultrasound to investigate bolt's status, especially its grouting condition. RBT features an application tailored ultrasound probe that transmits high-energy, low frequency (below 100kHz) guided waves. It is also capable of receiving weak echoes reflected from the discontinuities at the bolt surface as well its end-echo, which have propagated back and forth in the range of up to 4 meters. The RBT is a portable instrument that consists of a specially designed analog electronics for generation and reception of guided waves and an embedded digital computer that performs for signal processing, operator communication and data storage. In the paper we will focus on advanced processing techniques applied to enhance tiny echo signals received by the probe. © 2015 IEEE. Source

Hakami E.,Geosigma AB | Christiansson R.,Swedish Nuclear Fuel and Waste Management Company
Harmonising Rock Engineering and the Environment - Proceedings of the 12th ISRM International Congress on Rock Mechanics

In the design of a future underground storage for nuclear waste there is a need for good determination of in situ stress orientation. The aim of this project was to try to induce spalling in boreholes by heating, and then using the spalls to interpret the orientation of the in-situ stress. The heating was performed with electrical heating elements in the centre of empty boreholes. The change in borehole geometry due to the heating was detected by making optical and acoustic televiewer loggings before and after heating periods. This methodology was tested in two boreholes, one at Äspö hard rock laboratory in Sweden at 450m depth and one at ONKALO site in Finland at 390m depth. The results indicate that the amount of spalling was less than expected at both locations, but the interpreted orientation of principal stress orientation was the same as observed from other measurements. © 2012 Taylor & Francis Group, London. Source

Ask M.V.S.,Lulea University of Technology | Ask D.,Geosigma AB | Elvebakk H.,Geological Survey of Norway | Olesen O.,Geological Survey of Norway
Rock Mechanics and Rock Engineering

Nordland in northern Norway is characterized by enhanced seismicity and uplift that makes it the most tectonically active area in Norway. This study is part of a project entitled Neotectonics in Norway—Implications for Petroleum Exploration, which aims at enhancing the understanding of regional-scale stress and strain dynamics in Nordland, and to impact risk and hazard assessment and petroleum exploration. This paper attempts to constrain the orientation of in situ horizontal stress using high-resolution acoustic televiewer logging data. The Geological Survey of Norway has drilled two 0.8 km deep near-vertical boreholes on opposite sides of the Vestfjord in Nordland, the open bight of sea that separates the Lofoten archipelago from the Norwegian mainland. Both boreholes are drilled just North of 68°N, with borehole Leknes Bh located near the geographic center of the Lofoten archipelago, and borehole Drag Bh located on approximate equal distance from the shore, on the Norwegian mainland. The results of this study are in most practical aspects inconclusive, mainly due to poor data quality. The data analysis has revealed erroneously high-borehole diameter, and several artifacts such as eccentric logging tool, rugose borehole wall, spiral hole, tool sticking and missing data. Four intervals with passive in situ stress indicators (borehole breakout and drilling-induced fractures) were found in travel time and amplitude images of the Drag Bh, suggesting approximately N–S orientation of maximum horizontal stress. However, these intervals are not found in cross-plots. Either result yields the lowest World Stress Map ranking quality (E). © 2014, Springer-Verlag Wien. Source

Nordqvist R.,Geosigma AB | Hjerne C.,Geosigma AB | Andersson P.,Geosigma AB
Hydrogeology Journal

As part of the Swedish site investigations and research associated with the disposal of spent nuclear fuel, tracer experiments in deep boreholes have been employed in order to characterize solute transport and hydraulic connectivity in the fractured bedrock at two sites-Forsmark and Laxemar-Simpevarp. Performance and analytical results are presented from a suite of tracer experiments in varying scales, from single-hole injection-withdrawal tests, intermediate-scale tests with sorbing tracers, to large-scale connectivity tests over distances up to several hundred meters in major fracture zones or networks of zones. In addition to demonstrating transport connectivity over large distances, a general result is that the single-hole tests, as well as the cross-hole tests with sorbing tracers, have clearly demonstrated the process of solute retention of water-conductive features in the rock at different scales. © 2011 Springer-Verlag. Source

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