From documentation to prediction - a computer-based method for discontinuity analysis and block stability assessment in tunnelling

Tunnel face documentation done by a geologist is a well-established task during tunnel excavation. It mainly serves for the establishment of a geotechnical model and for the “conservation of evidence” for later contractual claims. This contribution describes a method for the documentation of the rock mass conditions, the establishment of a geotechnical model and the prediction of stability of keyblocks. This method is based on a hierarchical procedure which digitally processes discontinuity data from the acquisition to the analysis. The acquisition is performed using a remote sensing system, JointMetriX3D, a three-dimensional
imaging system based on photogrammetry. It uses a pair of high-resolution digital panoramic images to establish a metric 3D image of the tunnel face. Geometrical properties are measured from these 3D images serving as the basis for the determination of the discontinuity system of the rock mass. Subsequently a geometrical model is determined which relates the thoroughly determined discontinuity system to the excavation. This geometrical model is analysed with respect to the identification of keyblocks which may result with proceeding excavation. Finally, the stability of keyblocks is calculated. The result serves for decision aids on site and
for the final design of excavation and support as well