Hydro-Mechanical Properties of an Unsaturated Frictional Material

64 CHAPTER 2. STATE OF THE ART
a)
Sand grain
Silt grain
b)
Clay particles
Figure 2.30: Several cases of bonding
c)
Clay particles
Fluid
Barden et al. (1973) suggested several cases of bonding. This cases are shown in Fig. 2.30.
Four types of bond are presented: a fine silt bond (Fig. 2.30 a)), a clay bond (Fig. 2.30 b))
and flocculated clay buttress (Fig. 2.30 c)) and a bonding due to fluid (Fig. 2.30 d)). An
Environmental Scanning Electron Microscope (ESEM) photo (Schanz et al. 2001) of bonding
between sand grains due to capillary meniscus and cementing agent is given in Fig. 2.31.
Metastable structure was investigated by Barden et al. (1973). The authors found that due
to matric suction the decrease in strength will be immediate and due to clay bonding or
cementing agent the collapse might be retarded. In general the collapse process in unsaturated
soils is considered in terms of two separate components of stress, namely the applied vertical
Drainage Imbibition
Figure 2.31: Capillary meniscus during drainage (left) and imbibition (right) as well as cementing
in partially saturated sand
d)