Inverse and predictive modeling of seepage into underground openings Page: 4 of 35
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To study drift seepage, a series of air-injection and liquid-release tests were conducted in
boreholes drilled above excavated openings. We first describe these experiments and the
preliminary processing of the data, before we discuss the development of a numerical model that
is calibrated against the observed data to estimate seepage-relevant parameters.
2. Air-Injection and Seepage Experiments
2.1 Objectives
The overall test objective was to collect data that allow for the determination of effective,
seepage-relevant parameters for subsequent use in seepage prediction models. Besides the
geometry of the drift, capillarity and permeability are the key factors affecting seepage. Seepage
is mainly governed by the capability of individual fractures to hold water by capillary forces, and
by the permeability and connectivity of the fracture network, which enables water to be diverted
around the drift. Both properties determine the effectiveness of the capillary barrier, which is the
process that diverts flow and thus reduces seepage rates below the prevailing percolation flux.
If inversely determined from seepage data alone, permeability and capillarity would be
strongly correlated, i.e., they cannot be estimated simultaneously with acceptably low estimation
uncertainties. Two different sets of experiments were performed to independently obtain
permeability (and its spatial variability) and an appropriate parameter describing the capillary
strength of the fracture network. Air-injection tests were aimed at determining permeability (see
Section 2.3), whereas liquid-release tests were conducted to infer seepage-relevant capillary
strength parameters (see Section 2.4).2.2 Test Locations and Borehole Layout
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Finsterle, S.; Ahlers, C. F.; Trautz, R. C. & Cook, P. J. Inverse and predictive modeling of seepage into underground openings, article, August 13, 2001; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc735197/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.