Hydro-Mechanical Properties of an Unsaturated Frictional Material

5.3. SPECIMEN PREPARATION AND TESTING PROCEDURE 99
- Water pluviation technique
Water pluviation technique, where the soil is pluviated into water, is commonly used
to provide an initially saturated specimen. Similarly to the air pluviation technique
specimens prepared by water pluviation tend to be uniform (Vaid & Negussy 1988).
Frost & Park (2003) performed image analysis on moist tamped sand specimen and air-
pluviated as well as water-pluviated sand specimen. The sand specimens were preserved
using epoxy resin (Jang et al. 1999) and vertically cut for R-ray analysis. Their results show
significant discontinuities in density in the moist tamped specimen. Discontinuities in density
were especially observed between the contact area of the layers. The X-ray images of the
air-pluviated and also the water-pluviated sand specimens show uniform density along the
specimens. Variations in density were only found on the bottom and on the top of the speci-
men. Thus specimens prepared by pluviating the sand into water or air tend to be uniform,
whereas specimens prepared using compaction methods are less uniform. Finn et al. (1971),
Vaid & Negussy (1988) used water-pluviation method for reconstituting initially saturated
sand specimen. Schanz & Vermeer (1996), Desrues et al. (1996), Gennaro et al. (2004) used
pluviation technique for preparation of sand samples to ensure homogeneity and reproducibil-
ity.
Because the air-pluviated and water-pluviated specimens show homogeneous distribution
of density the pluviation method was selected for preparation technique. To provide a fully sat-
urated specimen, sand was directly pluviated into the equipment, that was filled with deaired
water. The sand used in this study is an poorly graded medium sand with insignificant amount
of finer particles, where segregation is not influencing homogeneity. Thus water pluviation
technique is used to produce homogeneous initially saturated sand specimen. Preferably in
this investigation the water-pluviation method was used because nearly all experiments were
conducted on initially saturated sand specimen (column testing device I, column testing device
II). Due to limitations of equipment, specimens in the modified pressure plate apparatus and
in the controlled-suction oedometer cell were prepared using the air-pluviated method, which
includes the pluviation of dry sand into the equipment. The specimens were saturated in an
additional step. Special care was taken to produce homogeneous and reproducible specimen.
For instance during large scale experiments in the sand column device I (SC I) in each layer
the mass of dry sand filled into the cell and thus the void ratio was checked. The mass of dry
sand filled into the bearing capacity box (BCB) was controlled every fifth centimeter. Some
results of dry density and void ratio for each layer are given for these tests in Tab. 5.3.
To analyze the homogeneity (distribution of density, distribution of water) in the pluviated
sand specimen computer tomography (CT) was used additionally (Dewitz 1996). Computer
tomography is an adequate non-destructive method for the investigation of the internal struc-
ture of samples. This method has been successfully used not only in medical science but
also in soil science, rock mechanics or hydrology (Duliu 1999). Based on the attenuation of