Evaluation of excavation-induced changes in rock permeability

Kelsall, P.C.; Case, John B.; Chabannes, C.R.

doi:10.1016/0148-9062(84)91530-4

Cited by 96 publications

(35 citation statements)

References 14 publications

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“…Regarding the effect of redistributed stresses, a number of studies have been conducted about the permeability alterations around the excavated openings [6,7]. They considered blast damage and fracture closures/openings from stress-relief as the main sources of permeability alteration, without considering shear dilations of fractures.…”

Section: Introductionmentioning

confidence: 99%

Stress-dependent permeability of fractured rock masses: a numerical study

Min

Rutqvist

Tsang

et al. 2004

International Journal of Rock Mechanics and Mining Sciences

447

233

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We investigate the stress-dependent permeability issue in fractured rock masses considering the effects of nonlinear normal deformation and shear dilation of fractures using a two-dimensional distinct element method program, UDEC, based on a realistic discrete fracture network realization.A series of "numerical" experiments were conducted to calculate changes in the permeability of simulated fractured rock masses under various loading conditions. Numerical experiments were conducted in two ways: (1) increasing the overall stresses with a fixed ratio of horizontal to vertical stresses components; and (2) increasing the differential stresses (i.e., the difference between the horizontal and vertical stresses) while keeping the magnitude of vertical stress constant.These numerical experiments show that the permeability of fractured rocks decreases with increased stress magnitudes when the stress ratio is not large enough to cause shear dilation of fractures, whereas permeability increases with increased stress when the stress ratio is large enough.Permeability changes at low stress levels are more sensitive than at high stress levels due to the nonlinear fracture normal stress-displacement relation. Significant stress-induced channeling is observed as the shear dilation causes the concentration of fluid flow along connected shear fractures.Anisotropy of permeability emerges with the increase of differential stresses, and this anisotropy can become more prominent with the influence of shear dilation and localized flow paths. A set of empirical equations in closed-form, accounting for both normal closure and shear dilation of the fractures, is proposed to model the stress-dependent permeability. These equations prove to be in good agreement with the results obtained from our numerical experiments.2

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Section: Introductionmentioning

confidence: 99%

Stress-dependent permeability of fractured rock masses: a numerical study

Min

Rutqvist

Tsang

et al. 2004

International Journal of Rock Mechanics and Mining Sciences

447

233

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“…The coupling between these processes and the hydraulic processes is also taking place at the scale of the rock mass as well as in the fractures. Makurat et al, 1990) Figure 2.4 : L'effet des changements de contraintes sur la conductivité hydraulique 15 du massif rocheux autour d'une excavation (comportement élastique) (tiré de Kelsall et al, 1984) Figure 2.5 : L'effet des changements de contraintes sur la conductivité hydraulique 15 du massif rocheux autour d'une excavation (comportement élasto-plastique) (tiré de Kelsall et al, 1984) Figure 2.6 : Essai de macroperméabilité à Stripa (tiré de Nelson et Wilson, 1980) 17 Figure 2.7 : L'effet de la température sur le profil radial de la charge hydraulique 17 du tunnel (tiré de Wilson et al, 1983) Figure 2.8 : Analogie rhéologique de roches fracturées dans le concept multilaminaire 19 (tiré de Vargas et al, 1995) Figure 2.9 : Définition des domaines par UDEC (tiré de Lemos et Lorig, 1990) 21 Tableau 13.1 : Estimation de la superficie de la fracture recouverte 223 par la calcite pour les échantillons testés. Tableau 13.2 : Résumé des résultats du taux de dissolution de la calcite 286 par unité de surface pour les essais à pH 2 Tableau 13.3 : Résumé des résultats du taux de dissolution de la calcite 318 par unité de surface pour les essais à pH 2,5 Tableau 13.4 : Résumé des résultats du taux de dissolution de la calcite 334 par unité de surface pour les essais à pH 4 Tableau 13.5 : Résumé des résultats du taux de dissolution de la calcite 348 par unité de surface pour les essais à pH 7…”

Section: Résuméunclassified

Étude des processus chimio-hydro-mécaniques dans un massif rocheux fracturé perturbé par une exploitation minière :

Benlahcen¹

2003

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This study on the chemical, hydraulic and mechanical processes and their coupling, was conducted at the Bouchard-Hébert Mine, located in the Abitibi Mining District in Québec, Canada. In this mine environment, the acidic water migrating from the old mine workings to the new ones, in combination with the perturbed geomechanical stress field caused by the excavations, affect the rock mass permeability. Both field work and laboratory experiments were conducted in order to investigate these processes, particularly in the rock mass portion located between the two mine workings (drift at level 6A).Results of discontinuity mapping show that at the western part of the drift at level 6A (from 10600E to 10900E), the rock mass contains two sets of fractures: one set is subhorizontal (dip between 0° and 30°) with a trace length between 1 and 1.5 m, and the other set is subvertical (dip between 75° and 90°). This subvertical set is divided into two groups depending on their trace length: one group includes fractures with a trace length between 0.5 and 2 m, and the second group comprises fractures with a trace length between 3 and 3.5 m. The fracture density of these two sets of fractures varies from 1 to 6 m" 1 and their veins are 2 mm in width. At the eastern part of the drift at level 6A (from 10900E to 11200E), the rock mass contains the same two sets of fractures observed at the western part, plus a set of fractures with a moderate dip (between 15° and 45°) with NE trend. This later set of fractures is less frequent and has a variable trace length between 0.5 and 2.5 m; their veins have a width of 2 mm. The fracture density of all the fracture set is between 1 and 4 m' 1 . Although the rock mass at the eastern part of the drift at the level 6A contains three sets of fractures, it is less permeable than the one located at the western part considering its lower fracture density. Consequently, grounwater flow would be more intense in the rock mass at the western part of the drift at the level 6 A of the mine.The results of hydraulic testing in boreholes in the rock mass located immediately under the drift 6A and over a lengh of 48 m, have shown that in the eastern part of this excavation, the hydraulic conductivity of the rock mass is low and constant, between 1 xlO" 10 and 1 xlO " n ms"1 . In the central part of this drift, located just under the old excavations, the rock mass hydraulic conductivity is higher and increases with depth from 1 xlO" 11 and 1 xlO ' 6 ms" 1 , which is in accordance with the higher fracture density in this part of the drift.Hydrogeochemical results show that waters sampled from boreholes at the mine are of neutral pH and contain high concentrations in ions, such as Ca, SO4 and metals. Calcium originates from the dissolution of calcite which is in abundance in fractures. Sulfate and metals originate from sulfide mineral oxidation present in fractures as well as in the rock matrix. Waters at a bulkhead at the base of the old excavations and the mixing waters at the surface, pumped from all ...

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“…La création de cavités souterraines affecte le champ de contraintes et par le fait même la conductivité hydraulique du massif rocheux au pourtour de ces excavations (Kelsall et al, 1984;Hudson, 1988;Pusch, 1989). Le dénoyage du massif rocheux engendré par le pompage est beaucoup plus important près de la surface et diminue au fur et à mesure qu'on se rapproche de la base de l'exploitation.…”

Section: Lithologies Rencontrées Dans Les Forages F-l à F-3 20unclassified

“…Trois processus contribuent à la formation de zone perturbée autour des excavations souterraines: la redistribution des contraintes (Kelsall et al, 1984), les dommages causés par le sautage de la roche en place dû au dynamitage (Montazer et al, 1982, Pusch, 1989 et finalement l'altération de la roche dû à l'interaction eau-roche. La redistribution des contraintes au pourtour des ouvertures affecte la conductivité hydraulique du massif rocheux.…”

Section: Création D'ouverture Dans Le Massif Rocheuxunclassified

Caracterisation hydrogeologique du massif rocheux a la Mine Niobec St-Honore Quebec

Tremblay¹

1993

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Evaluation of excavation-induced changes in rock permeability

Cited by 96 publications

References 14 publications

Stress-dependent permeability of fractured rock masses: a numerical study

Stress-dependent permeability of fractured rock masses: a numerical study

Étude des processus chimio-hydro-mécaniques dans un massif rocheux fracturé perturbé par une exploitation minière :

Caracterisation hydrogeologique du massif rocheux a la Mine Niobec St-Honore Quebec

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