Fundamentals 1: Hydraulic forces in permeable media|
K.U. Weyer Ph.D., P.Geol., P.HG.
WDA Consultants Inc., 4827 Vienna Drive NW, Calgary, Alberta, Canada
© 1978 Copyright K.U.Weyer
In groundwater flow a multitude of flow equations exists, all claiming to be a valid expression of DARCY's law.
In one way of another, all of them use gradients as forces that cause flow. Thus, it appears there is a variety
of different force fields available.
During the 60s and 70s, however, new scientific and practical develpments (J. TOTH, 1962, 1963; A.R. FREEZE and
P.A. WITHERSPOON, 1966, 1967, 1968; P. MEYBOOM, 1967; I.C. BROWN, 1967; K.U. WEYER, 1972) have shown, that only
one of the many so-called DARCY equations describes the physics of groundwater flow and the mechanical force
fields involved satisfactorily, namely HUBBERT's force- potential theory (M.K. HUBBERT, 1940, 1957).
HUBBERT'S forces, however, cannot be tied dimensionally and physically into some of the engineering concepts
used in connection with force fields. One of those concepts is the effective and neutral stress concept of
K. TERZAGHI (1925, 1948) that attempts to couple forces within fluids with those in solids. Because of this
discrepancy and because the physical and practical meaningfulness of HUBBERT's concept is proven, the question
arises whether there exists for certain problems as, for example, in geodynamics, the need to adapt the force
system theory in solids to HUBBERT's force potential theory and whether a different coupling mechanism should
be developed. This proposal should not be seen as disputing the proven usefulness of the application of the
principles of continuum mechanics within engineering sciences.
The physical background to these questions will be discussed briefly as far as space limitations allow. To
clarify the difference in approach, it will be shown that, under certain hydrodynamic conditions of downward
flow, the principle of ARCHIMEDES (buoyancy) can be shown as non-existent. This is of considerable consequence
to practical problems of engineering science and to several theories in geodynamics, as for example, those
dealing with orogenesis, plate tectonics, subsidence, uplift and isostasy.