Unsaturated Hydraulic Characterization of Carbonatic Rock in the Laboratory of Carbonatic Rock in the Laboratory November 2-5 Geoscience Horizons M.C. Caputo, Water Research Institute – IRSA–CNR, Bari, Italy J.R. Nimmo, US Geological Survey, Menlo Park, CA, USA A. Basile, ISAFOM–CNR, Napoli, Italy N. Walsh, Department of Geology and Geophysics - University of Bari, Italy

We measured in the laboratory the unsaturated hydraulic conductivity K(  ) and water retention  (h) of several lithotypes of calcarenite using two methods:   a modification of Wind’s (1968) evaporation method for soils   a new quasi-steady centrifuge (QSC) method November 2-5 Geoscience Horizons Objective

  Calcarenite   Sedimentary rock   Marine origin   Widely found in the Mediterranean basin   Often constitutes a thick layer of the vadose zone November 2-5 Geoscience Horizons Materials   From Apulia in Southern Italy   Lithotypes A and B from same quarry, different depths   Lithotype M from a quarry in another area Lithotypes tested

November 2-5 Geoscience Horizons Materials Lithotype A   medium-fine grains   “ grainstone ” type   “ grain-sustained ” texture (*) Lithotype M   fine grains   “ wackestone ” type   “ mud-sustained ” texture (*) Lithotype B   biocalcarenite   medium-coarse grains   “packestone ” type   “ grain-sustained ” texture (*) The lithotypes tested vary in their proportions of lithoclasts, bioclasts, matrix, and cement. Thin sections photographed using an optical microscope (*) Dunham, 1962

November 2-5 Geoscience Horizons Methods Required Assumptions   Homogeneous with respect to the property measured   Water flow obeys Darcy’s 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 Wind’s evaporation method Wind’s evaporation method allows the simultaneous determination of  (h) and K(  ).

November 2-5 Geoscience Horizons Methods Wind’s method The measured data include:   matric potential with depth and time, h(z,t)   average water content of the whole sample,  avg (t) fan load cell sample tensiometers

November 2-5 Geoscience Horizons Methods Wind’s method Convert matric potential values to water content using estimated water retention curve. Compare with the measured  avg (t). If differences are significant, estimate a new retention curve, iterate until discrepancies are tolerable. Use measured h(z,t) and calculated  e (z,t) to calculate the hydraulic conductivity, K(  ).

November 2-5 Geoscience Horizons Methods 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(  ) can be computed using the centrifugal form of Darcy’s 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. quasi-steady centrifuge (QSC) method 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 Darcy’s 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.