Repair, Evaluation, Maintenance and Rehabilitation Research Program: Evaluating the Stability of Existing Massive Concrete Gravity Structures Founded on Rock

Assessment of Geology as it Pertains to Modeling Uplift in Jointed Rock: A Basis for Inclusion of Uncertainty in Flow Models

“…For a discontinuum approach, the parameter for hydraulic conductivity in Darcy's equation (Equation 2.11) is replaced by parameters describing the equivalent parallel plate aperture, e, and the number of joints intersecting the test section (Equations 2.12 and 2.13), as discussed earlier in this chapter. Finite element models have also been developed to simulate and analyze flow in jointed media (for example, Ebeling, Pace, and Morrison 1997). Bennett and Anderson (1982) state that most references to rock mass analysis emphasize the homogeneous, isotropic case of hydraulic property distribution and treat anisotropy as a special condition.…”

“…Morrison 1997, after Bandis 1980). c" = effective normal stress, AV y = joint closure, V m = maximum joint closure Ebeling, Pace, and Morrison (1997) observed several relationships from Bandis' (1980) joint closure model. The maximum closure (the asymptote, V m ) is generally 0.3 to 0.9 times the average initial joint aperture.…”

“…International Society for Rock Mechanics (ISRM) (1978), proposing discontinuity descriptors for rock mass classification, defined open joints as those with mechanical apertures of 500 urn (0.5 mm) or greater. Ebeling, Pace, and Morrison (1997) adopted a mechanical aperture of 250 urn (0.25 mm) as the lower limit of open joints from work reported in Lee and Fanner (1993), who used data from Barton (1973). Headquarters, U.S. Army Corps of Engineers (1994), applied a similar classification scheme to discontinuities in his discussion of rock mass characterization for rock foundations.…”

“…Headquarters, U.S. Army Corps of Engineers (1994), applied a similar classification scheme to discontinuities in his discussion of rock mass characterization for rock foundations. Table 2.1 shows the aperture classification used by Lee and Farmer (1993) (and Ebeling, Pace, and Morrison 1997) and by Nicholson. The relative importance of mechanical and conducting apertures to flow modeling and prediction is discussed further in this chapter and in Chapter 5.…”

“…Stone and Webster Engineering Corporation (1992) provide an excellent evaluation of the effects of geologic conditions on uplift pressure distributions for several existing large concrete gravity dams. Ebeling, Pace, and Morrison (1997) discussed the relationship between uplift pressures developed beneath a dam and the stresses imposed on the foundation by the dam and reservoir. Changes in loading imposed on the rock joints change the joint apertures, which change the hydraulic conductivity of the joints and ultimately the uplift pressures developed in the foundation.…”