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Abstract: In some projects the selection of TBM is straight forward, but in others all boundary conditions have to be carefully evaluated in order to make the most suitable choice. For underground projects the actual ground conditions remain to certain degree always unknown, regardless of the performed ground investigations. This means specific parameters, which may have significant impact on the project success, might be over‐ or underestimated. Such parameters could be different rock mass properties as well as water ingress. This paper discusses some relevant parameters for TBM selection in hard rock environment, mainly based on the experience gained in the Follo Line Project in Norway. Four double shield TBMs with excavation diameter of 9.96 m are drilling through various kinds of gneisses with banding and lenses of amphibolite and pegmatite. More than 75 % of a total of 36 km have already been excavated with several kilometres of pre‐excavation grouting for reduction of water ingress. Furthermore, potential improvements for TBMs will be proposed in order to make TBMs even more successful. [ABSTRACT FROM AUTHOR]

ABSTRACT Hard rock seismic exploration normally has to deal with rather complex geological environments. These types of environments are usually characterized by a large number of local heterogeneity (e.g., faults, fracture zones, and steeply dipping interfaces). The seismic data from such environments often have a poor signal-to-noise ratio because of the complexity of hard rock geology. To be able to obtain reliable images of subsurface structures in such geological conditions, processing algorithms that are capable of handling seismic data with a low signal-to-noise ratio are required for a reflection seismic exploration. In this paper, we describe a modification of the 3D Kirchhoff post-stack migration algorithm that utilizes coherency attributes obtained by the diffraction imaging algorithm in 3D to steer the main Kirchhoff summation. The application to a 3D synthetic model shows the stability of the presented steered migration to the presence of high level of the random noise. A test on the 3D seismic volume, acquired on a mine site located in Western Australia, reveals the capability of the approach to image steep and sharp objects such as fracture and fault zones and lateral heterogeneity. [ABSTRACT FROM AUTHOR]

One of the main hazards during tunnel boring machine (TBM) excavation in hard rock is related to the occurrence of unforeseen adverse conditions, leading to unfavourable rock mass behaviour during tunnel boring. In this respect, the continuous analyses of TBM excavation parameters may represent an interesting tool for a continuous monitoring of geotechnical conditions at the tunnel face and for early detection of changing ground conditions in the rock mass. This work provides a back‐analysis of TBM data recorded during the excavation of the Frejus Safety Tunnel, bored across the French‐Italian border in the Western Alps. It is a 13 km‐long tunnel excavated by a 9.4 m diameter, single‐shield TBM through strongly anisotropic calcareous schist, with cover up to 1800 m. Main problems faced during TBM excavation were related to the local occurrence of buckling‐related convergence and consequent asymmetrical loading on the precast segment rings. Correlating TBM performance parameters to the encountered geological and geomechanical conditions provides the possibility to identify which parameters are most affected by geomechanical properties of the rock mass at the tunnel face and by rock mass behaviour. Conversely, the analysis indicates which parameters can be adopted as monitoring tool of ground conditions during TBM advance. In addition, this work highlights how buckling phenomena can be distinguished, in terms of TBM operation and performance, from other adverse conditions as, e.g., blocky ground or squeezing. [ABSTRACT FROM AUTHOR]

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Assisted ultrasonic vibration technique can significantly improve the efficiency of hard rock drilling in petroleum and mineral engineering. In this study, to determine the fragmentation mechanism of rocks under ultrasonic vibration, numerical simulations using the discrete element method (DEM) were performed. A novel flat‐joint model (FJM), combined with an ultra‐high‐frequency loading boundary condition, was used to model the damage process of the hard rock under ultrasonic vibration loading. The numerical results demonstrated that the evolution of local strain and fragmentation were in good agreement with the experimental results. Based on the established model, the influence of loading parameters was investigated. Furthermore, by analyzing the development of the full strain field, crack orientations, and crack distribution, the fragmentation mechanism was revealed for the rock under ultrasonic vibration. Under ultra‐high‐frequency loading, the rock deformed in a heterogeneous manner and produced both compressive and tensile strain zones. The compressive zones were mainly distributed in the fringe and tensile zones in the top center. The generated tensile cracks caused by compression and tension in these two strain zones led to the rock failure. [ABSTRACT FROM AUTHOR]

Abstract: The effect of pore fluids on acoustic wave dispersion in rocks with low aspect ratio crack porosity is important for the interpretation of laboratory and field observations in hard rock mineral exploration environments. Here we make laboratory measurements of shear modulus dispersion at frequencies 0.01–1 Hz and at 1 MHz with different saturating fluids (dry, argon, and water saturated) in two thermally cracked quartzite samples with ~2% total porosity. Measurements are made across a range of effective pressures (10–150 MPa), with the resulting very low permeabilities of the samples varying from 1–300 × 10−21 m2. Moduli across the 0.01–1 Hz band were typically independent of frequency. The shear moduli measured at sub‐Hz frequencies are unaffected by fluid saturation, as expected for the saturated isobaric (Gassmann) regime. In marked contrast, water saturation of the cracked rocks results in very large increases in the shear moduli measured at 1 MHz and low effective pressures, indicative of saturated isolated conditions. Thus, at an effective pressure of 20 MPa, the shear moduli for the two water‐saturated quartzites increase by 74% and 98% from 1 Hz to 1 MHz. The contrast in elastic moduli between dry and water‐saturated conditions is well represented by the theoretical model developed by Walsh and others. The observed dispersion highlights the need for care in seismological application of results obtained at MHz frequencies from laboratory ultrasonic measurements. [ABSTRACT FROM AUTHOR]

Abstract: Cutter consumption and parameters such as cutter ring wear has a great relevance in the overall excavation time and cost in hard rock tunnel boring machines (TBMs), especially in hard rock conditions. Cutter wear involves a complex tribological system that interacts also with the geologicy of the rock mass. Understanding the processes and failure mechanisms during cutter wear (e.g. modes of contact, wear, load effects) and assessing the influence of temperature on cutter ring wear processes enables new knowledge to be applied to get better cutter consumption predictions and future improvements in cutter ring development. In addition, it might be used to evaluate the suitability of the new rock abrasivity test method (Rolling Indentation Abrasion Test, RIAT) for assessing cutter ring wear. [ABSTRACT FROM AUTHOR]