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Unsaturated Hydraulic Characterization of
Carbonatic Rock in the Laboratory
M.C. Caputo, Water Research Institute IRSACNR,
Bari, Italy J.R. Nimmo, US Geological Survey,
Menlo Park, CA, USA A. Basile, ISAFOMCNR,
Napoli, Italy N. Walsh , Department of Geology
and Geophysics - University of Bari, Italy
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Objective

• We measured in the laboratory the unsaturated
  hydraulic conductivity K(q) and water retention
  q(h) of several lithotypes of calcarenite using
  two methods
• a modification of Winds (1968) evaporation
  method for soils
• a new quasi-steady centrifuge (QSC) method

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Materials

• Calcarenite
• Sedimentary rock
• Marine origin
• Widely found in the Mediterranean basin
• Often constitutes a thick layer of the vadose
  zone

Lithotypes tested

• From Apulia in Southern Italy
• Lithotypes A and B from same quarry, different
  depths
• Lithotype M from a quarry in another area

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Materials
The lithotypes tested vary in their proportions
of lithoclasts, bioclasts, matrix, and cement.
Thin sections photographed using an optical
microscope
() Dunham, 1962
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Methods
Winds evaporation method allows the simultaneous
determination of q(h) and K(q).
Required Assumptions

• Homogeneous with respect to the property measured
• Water flow obeys Darcys law q -K(h)dh/dz
• Potentials other than matric are neglegible
• Sample is conceptually divided into compartments
• Water content varies linearly within each
  compartment

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Methods

• Winds method
• The measured data include
• matric potential with depth and time, h(z,t)
• average water content of the whole sample,
  qavg(t)

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Methods
Winds method Convert matric potential values to
water content using estimated water retention
curve. Compare with the measured qavg(t). If
differences are significant, estimate a new
retention curve, iterate until discrepancies are
tolerable. Use measured h(z,t) and calculated
qe(z,t) to calculate the hydraulic conductivity,
K(q).

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Methods
The quasi-steady centrifuge (QSC) method is based
on the steady-state centrifuge (SSC) method,
which has a steady flow of water within a sample
in a centrifuge, applied by either a constant
head (Nimmo et al., 1987) or a metering pump
(Conca and Wright, 1998). If suitable conditions
develop within the sample, hydraulic conductivity
can be computed using the centrifugal form of
Darcys law. The QSC method somewhat relaxes
the criterion for steadiness. This entails a
slight increase in measurement uncertainty, but
affords advantages including simpler apparatus,
larger sample capacity, and adaptability to
various machines and operating conditions.

The quasi-steady centrifuge (QSC) method The
steady-state centrifuge (SSC) method, which the
QSC method derives from has a steady flow of
water within a sample in a centrifuge, applied by
either a constant head (Nimmo et al., 1987) or a
metering pump (Conca and Wright, 1998). If
suitable conditions develop within the sample,
K(q) can be computed using the centrifugal form
of Darcys law. The QSC method somewhat relaxes
the criterion for steadiness. This entails a
slight increase in measurement uncertainty, but
affords advantages including simpler apparatus,
larger sample capacity, and adaptability to
various machines and operating conditions.
The quasi-steady centrifuge (QSC) method The
steady-state centrifuge (SSC) method, which the
QSC method derives from has a steady flow of
water within a sample in a centrifuge, applied by
either a constant head (Nimmo et al., 1987) or a
metering pump (Conca and Wright, 1998). If
suitable conditions develop within the sample,
K(q) can be computed using the centrifugal form
of Darcys law. The QSC method somewhat relaxes
the criterion for steadiness. This entails a
slight increase in measurement uncertainty, but
affords advantages including simpler apparatus,
larger sample capacity, and adaptability to
various machines and operating conditions.