Semiautomatic characterization of rock masses using photogrammetry, 3D printing technology and ground penetrating radar

Lauri Uotinen, Zhen Song, Otto Hedström, Eeva Huuskonen-Snicker, Tiina-Liisa Toivanen, Jorma Palmén, Tero Hokkanen

PROBLEM: Rock mass characterization is the classification of rock mass for scientific, ore prospecting or construction purposes. Currently, it is mainly done using traditional empirical methods. This is slow, subjective and dangerous, due to long exposure times in freshly made unreinforced underground spaces. In the last years, new methods have been developed to make partial automatization possible.

FACILITIES: 20 m beneath Otaniemi the Geoengineering has an Underground Research Tunnel and supporting facilities. The tunnel is used for research projects and for practical exercises and there is a conference niche and a small workshop for maintenance. The Test Tunnel is also used to teach rock mass characterization.

Mobile X-Ray Fluorescence Laboratory was tested in the tunnel during spring 2013. XRFL is a part of SOREX (Service oriented automation for efficient rock and ore exploration) TEKES Green Mining program. In 2012, the Department of Signal Processing and Acoustics did a series of acoustical experiments in the test tunnel using a log-sweep locating. Recently, a series of 48 geophones were installed in a parallel tunnel and drilling induced vibrations were recorded to discover drill bit position.

PHOTOGRAMMETRY: One problem is how to acquire a 3D point cloud affordably, quickly and safely. Two solutions exist: Traditional Photogrammetry and Laser Scanning Approach. Photogrammetry is slow, requires heavy image processing and expensive hardware, and has limited accuracy. LADIMO (pat. pend.) was invented to combinethe benefits of both methods. A known diffraction patternis projected and two photographs are taken: one with the pattern (geometry) and one clean exposure with flash illumination (texture). LADIMO is cheaper, faster, safer, smaller and easier to use.

3D PRINTING: 3D printing constructs objects layer by layer from bottom up. It enables the easy production of surface replica molds, which may be used to study the mechanical parameters of a joint in non-destructive way. Another use for the 3D printing is the production of scale models, which are used in verification of calculation methods in complex geometry of coupled physics problems. Compared to traditional replication or scale modelling, 3D printing is cheaper, more accurate and faster (despite the slowprinting process). It eliminates previous problems arising from complex or intricate geometries. Currently replicas are being casted into 3D printed molds and further research is needed to enable 3D mineral printers for direct replication. Aalto has several 3D printers available for research projects ranging from rapid prototyping machines at FabLab to professional grade 3D printers at ADD.

GROUND PENETRATING RADAR can be used in semiautomated rock mass characterization: emitted electromagnetic pulses reflect from discontinuities(bedrock surface, rock joints, ground water level orobjects). The travelling time determines the depth of the reflecting surface. GPR is a completely non-destructive imaging method and the studied rock mass remains intact. Rock joints can be detected and located and information about the aperture and filling materials gathered.

IMPACT: Photogrammetry, 3D printing and GPR are great examples of tools available in solving the larger problem. Semiautomatic characterization will revolutionize site investigations and shift the balance from manual labor to automated data processing. In time, fully automated site investigation will be possible and operators will mainly do quality assurance and maintenance. Automated methodsare faster, more precise and considerably safer.