A variable aperture fracture network model for flow and transport in fractured rocks

Nordqvist, Anneli; Tsang, Yvonne; Tsang, C.F.; Dverstorp, Björn; Andersson, Johan

doi:10.1029/92wr00216

Cited by 137 publications

(62 citation statements)

References 19 publications

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“…The variable crack aperture is a widely studied problem. (Tsang & Tsang, 1989;Hakami, 1995;Nordqvist et al, 1992; Larsson, 1997 among others). A proposal to relationship between the hydraulic aperture and the physical aperture was made by Zimmerman et al (1991) and Cheng et al (2000).…”

Section: Rock Structurementioning

confidence: 99%

Penetrability due to filtration tendency of cement-based grouts

Eklund

Stille

2008

Tunnelling and Underground Space Technology

105

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ii iii SummaryGrouting as a method of strengthening and sealing rock, soil and concrete is widely used. The possibilities of sealing structures are of great importance from both an economical and environmental point of view. The cost of grouting has in certain projects been as high as the cost for the blasting and excavation of the tunnel. To improve the technique of grouting with cement based material, it is necessary to focus on the properties of the used grout mixture. The ability of a grout to penetrate cavities, channels and porous material, the penetrability, depends on two things, the theology and the filtration tendency. Extensive laboratory tests on stable, low w/cratio, injection grouts show that the most significant limitation to their penetrability is the tendency of cement grains to agglomerate into an impermeable filter cake. The properties of a grout that may prevent passing obstructions in the flow path without the cement grains clogging and preventing further penetration is in this work called filtration tendency. An inert material mixture and a cement-based mixture are used for the investigations in this work. The inert material, which is crushed dolomite stone, does not react with the added water in the mixture. The used cement grouts are based upon three types of commercial available Portland cements and four Portland cements with modified grain size distribution curves.Performed tests show that the grain size and grain size distribution is of great importance for the filtration tendency. According to performed experiments with inert and cement material, it seems to be advantageous for the penetrability to have a grain size distribution that contains neither too many fine or coarse grains. It is reasonable to believe that the grain size distribution should be relatively steep (narrow grain size range) between minimum and maximum grain size. The maximum grain size is of importance in terms of for example d 95 . Too large maximum grain size will prevent penetration of the mixture through obstructions in the flow path. According to performed tests, the value of d 95 , should be between 4-10 times smaller than the aperture to be penetrated by the cement based mixture. The small grain sizes are also of importance in order to achieve a low filtration tendency of the grout. This is because of the increased tendency for the small grains to flocculation into larger agglomerates, compared to larger grain sizes.The filtration experiments with cement based grouts show that influences of parameters like surface chemistry (use of superplastisisers) and cement chemistry (hydration of cement grains) will strongly affect the filtration tendency of the mixture.To visualize the phenomenon of filtration tendency it can be investigated on a larger scale than usually takes place. Filtration experiments in the scale of approximately 100:1 have been performed in order to see influences of grain concentration, grain shape and the penetrated slot aperture. It can be seen that used grain sizes (monodisperse and inert m...

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Section: Rock Structurementioning

confidence: 99%

Penetrability due to filtration tendency of cement-based grouts

Eklund

Stille

2008

Tunnelling and Underground Space Technology

105

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“…In case of no correlation, however, the tendency of t m /t m based on values of λ/L was slightly different from that in correlated condition, and the calculated CR value was 0.80, thus resulting in a slightly lower compatibility compared to that in correlation condition. The empirical formula of σ and t m /t m suggested in this study was expected to be applicable for providing solute particle transport characteristics for individual fracture factors constituting fracture networks generated within a three-dimensional space, as in the study conducted by Nordqvist et al [25].…”

Section: Discussionmentioning

confidence: 96%

Numerical Study of Spatial Behavior of Solute Particle Transport in Single Fracture with Variable Apertures

Jeong

2018

Water

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Abstract:The aim of this study is to numerically analyze spatial behaviors of solute particle transport in a single fracture with spatially correlated variable apertures under application of effective normal stress conditions. The numerical results show that solute particle transport in a single fracture is strongly affected by spatial correlation length of variable apertures and applied effective normal stress. As spatial correlation length increases, mean residence time of solute particles decreases and tortuosity and Peclet number (a dimensionless number representing the relationship between the rate of advection of solute particles by the flow and the rate of diffusion of solute particles) also decreases. These results indicate that the geometry of the aperture distribution is favorable to solute particle transport when the spatial correlation length is increased. However, as effective normal stress increases, the mean residence time and tortuosity tend to increase but the Peclet number decreases. The main reason for a decreasing Peclet number is that the solute particle is transported by one or two channels with relatively higher localized flow rates owing to increase in contact areas resulting from increasing effective normal stress. Based on the numerical results of the solute particle transport produced in this study, an exponential-type correlation formula between the mean residence time and the effective normal stress is proposed.

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“…The fracture aperture is generally assumed to follow a log-normal distribution [15,16]. The probability density function (PDF) for the log-normal distribution of fracture apertures (h) can be written, in a general form, as where µ and σ are the mean and standard deviation of the natural logarithm of the fracture aperture, respectively.…”

Section: Hydraulic and Geometric Characteristics Of Fracturesmentioning

confidence: 99%