Hydro-Mechanical Properties of an Unsaturated Frictional Material

96 CHAPTER 5. MATERIAL USED AND EXPERIMENTAL PROGRAM
5.2 Hostun Sand
The experimental program for this study was conducted on Hostun Sand, a reference sand
well studied in the research literature (Biarez et al. 1989, Flavigny et al. 1990, Hammad 1991,
Schanz & Vermeer 1996, Schanz 1998, Gennaro et al. 2004). Hostun Sand is a quartz sand
with grain sizes ranging from 0.1 mm to 1.0 mm in diameter. According to the USCS classi-
fication the material is a poorly-graded medium sand SP (Fig. 5.1). The main classification
properties as the density of the soil particles ϱs, the coefficient of uniformity Cu, the coeffi-
cient of curvature Cc, the values of maximum and minimum void ratio e max/min, as well as the
corresponding values of maximum and minimum specific weight γ max/min are summarized in
Table 5.1. The saturated hydraulic conductivity of the sand is required when computing the
unsaturated hydraulic conductivity from the soil-water characteristic curve using the indirect
method. The saturated hydraulic conductivity of the sand for several initial void ratios was
measured using constant head permeability test (Lins et al. 2002, Lins & Schanz 2005). The
results are given in Table 5.1. Experimental results of the saturated hydraulic conductiv-
ity are presented in Fig. 5.2. In further calculations and predictions for loose Hostun sand
specimen (e = 0.89) saturated hydraulic conductivity of ks = 2.75 · 10 −4 m/s and for dense
Hostun sand specimen (e = 0.66) ks = 2.03 · 10 −4 m/s were used. Shear strength parameters
obtained by Hammad (1991) and Schanz & Vermeer (1996) under plain strain and triaxial
condition on saturated sample tests are given in Table 5.2. These parameters are necessary
for prediction of unsaturated shear strength using indirect method and also for prediction of
unsaturated bearing capacity.
Percent passing by weight (%)
100 80
20 40 60
0
Silt medium Gravel Sand fine coarse Clay
Reihe2
Reihe3
Grain size (mm)
Hostun Sand (Flavigny et al. 1990) Hostun Sand (Lins & Schanz 2005) 100 10 1 0.1 0.01 0.001
Figure 5.1: Grain-size distribution of Hostun Sand