Table 2.

Mechanical effects of anthropogenic subsurface modification

TypeMagnitude of effect (m)Mechanical alteration processes and effectsNatural analogueReferences
Earthworks10−3–102Mechanical compaction of sediment or weak rock.
Induced seismicity and consolidation through loading, e.g. dam construction.
Glacial/sediment loadingGupta (1985)
Boreholes and wells10−3–10−2 (mechanical fractures)
10−3–103
(hydraulic fractures)
Production and partial or complete infill of discontinuities adjacent to boreholes and wells from mechanical disturbance and/or hydraulic fracture to increase permeability (Fig. 3).
Fault reactivation, subsidence during pore-fluid extraction and induced seismicity.
Consolidation from pore-fluid extraction; can be countered by swelling from injection of drilling fluids.
Fracture enhancement through acidulation in carbonate aquifers.
Natural hydraulic fractures, sand-filled injectites and fracture pipesBanks et al. (1993), Cox et al. (1996), Cuss et al. (2015), Davidson et al. (1995), Davies et al. (2012, 2013), Doornhof et al. (2006), Gale et al. (2007, 2014), Kelsall et al. (1983), Simon (2005)
Tunnels and caverns10−3–103Excavation Damage Zone (EDZ) resulting in opening or closing of fractures and rock-crystal realignment (e.g. salt mining). Extent of EDZ from cavity excavation is typically 0.3–0.7 excavation radius.
Ground subsidence.
Natural dissolution collapse structuresBlümling et al. (2007), Kelsall et al. (1983)
Geological Disposal Facility10−3–100EDZ extent influenced by presence of natural fractures, initial stress field, bulk materials properties and geometry of excavation.
EDZ resulting in opening of natural sub-vertical fractures; fractures may self-seal if excavated material deforms plastically with increasing stress.
Creation of shear zones.
Natural nuclear fission reactors, e.g. Oklo (Gabon)Blümling et al. (2007), Cai & Kaiser (2005), De Windt et al. (1999), Martino & Chandler (2004), Mertens et al. (2004)
Solid mineral workings10−3–104Subsidence whose magnitude and style depends on rock physical properties, seam/ore thickness, overburden thickness, groundwater conditions and excavation style (Figs 5 and 6).
Partial or complete fill of mining-induced voids with artificial cement (grout).
Fault reactivation and induced seismicity through roof collapse/floor heave.
Opening of discontinuities including fractures.
Natural dissolution collapse structuresBell (1978), Bowell et al. (1999), Commission on Energy and the Environment (1981), Li et al. (2007), Waters et al. (1996)
Munition detonation10−3–103Induced seismicity resulting in rock fracture and crushing (Fig. 7). Zones of rock crushing rock cracking and zone of irreversible strain.
Creation of voids (radii 4–12 m/kton1/3) and debris chimneys (Fig. 7).
Temperature effects include partial or complete rock melting; magnitude decreases from detonation zone.
Inverted bedrock stratigraphy in deep subsurface detonation (Fig. 8).
Consolidation and subsidence (deep subsurface detonation).
Meteorite impact, e.g. Meteor Crater (Arizona)Adushkin & Spivak (1994), Hawkins & Wohletz (1996), McEwan (1988), Shoemaker (1959), US Congress (1989)

The magnitude, style and extent of the example effects is in part dependent on the properties of the excavated material, including its consolidation characteristics, stiffness and drained and/or undrained shear strength behaviour, which is in turn influenced by its past, present and future stress condition.