Excavations in rock masses determine the creation of temporary or final exposed surfaces. Features of these surfaces are depending on both geostructural pattern of the rock mass and adopted excavation method: among the others, roughness, quality of the contour and induced damage inside the rock left in place. These aspects are important as they are requirements expected during the excavation and construction procedures, such those involving dam sidewalls, quarry benches, tunnel profile, slope scaling.
This methodological paper describes a list of the possible cases, with a particular emphasis on quarrying and tunneling. By following current modes for profile surveying, the damages are reported, in order to obtain suitable indices for induced damage. Finally the proper techniques for excavation are commented on the basis of real case histories of tunnels and quarries in order to reach the primary objectives of damage reduction and stability/productivity goals.
Excavations in rock masses for civil or mining purposes involve the creation and development of new exposed surfaces, either temporary or final. Rock mass properties and geostructural features are driving the adopted excavation techniques, namely blasting, mechanized (punctual or full face), scaling, profiling, sawing and cutting. The local stress state and the extension of the contour (free surfaces) are then completing the pattern that determines the final behaviour of the rock mass. The combination of such a consistent number of conditions claims for the assessment of key factors that can induce a damage in the rock mass: this is a particularly relevant aspect as it is linked with geomechanical properties, such as in situ strength and deformability, convergence and displacements, mode of detachment of rock elements, changing the local conditions for hydraulic conductivity and for support selection, if any. The paper focuses on the possible cases, referring to quarrying, tunnelling and slope stabilization. Then, description of current modes for surveying the induced damages and the corresponding suitable indices to determining the contour profile quality are reported. Damage in rock mass around the excavation is accompanied by a strength reduction, caused by the opening or shearing of new or extended cracks and joints as a consequence of lack of confinement and it can affect both underground and open pit excavations. Poor profiling or off-profile directly affect construction costs: in tunnelling more supports are required to avoid that some rock falls and more concrete is necessary to fill up empty spaces in order to help covering layer installation; in quarrying there are consequences of poor blast control in terms of higher consumption and undesired effects (projections, inaccurate grain size distribution); in dimension stone quarrying block recovery and safety during exploitation are directly dependant on proper profiling techniques and careful local geostructural pattern assessment can lead to proper solutions.