Glossary
Abrasivity the property of a soil or rock to cause abrasion and wear of metallic elements. Accuracy the closeness of the measurements/predictions to the real value. Adhesion (of clay) the phenomenon that occurs when the steel surfaces of the machine are completely covered by the excavated material (see stickiness). Advancement ratio (of a TBM) the excavated length divided by the operating time during a continuous boring phase. Analytical solution a closed-form expression derived from the exact integration of the differential equation system governing a hydro-thermo-chemo-mechanical problem. Anisotropy the characteristic of a mechanical or physical property to be different in different directions. Aperture see opening. Aquiclude a solid, impermeable area underlying or overlying an aquifer, the pressure of which could create a confined aquifer. Aquifer an underground layer of water-bearing permeable rocks, rock fractures or soils. Aquitard a bed of low permeability along an aquifer arching transfer of stress from a part of a soil/rock mass subject to excavation to adjoining parts of the mass. Arching effect the stress redistribution occurring near the tunnel face from unsupported to supported zones. Asbestos the silicate minerals with a fibrous morphology, belonging to the mineralogical group of serpentine and amphibole, whose health risk is linked to the inhalation of airborne fibres (asbestos respirable fibre: elongated asbestos with length L ≥ 5 μm, diameter ϕ≤ 3 μm and elongation ratio L/ϕ ≥ 3). As-built model the report of the monitoring data and the notes recorded during the excavation and construction of a tunnel. Associated flow rule the condition for which the plastic strain flow occurs in a direction normal to the yielding surface (i.e. the plastic potential corresponds to the yielding surface and the dilatancy angle is equal to the friction angle). Annulus (annulus gap or void) the space, gap or void left around the body of a full-face Tunnel Boring Machine (TBM) by the slightly larger cut diameter of the TBM cutterhead and around the rings of the segmental lining, which are smaller again in outside diameter.
