Hydro-Mechanical Properties of an Unsaturated Frictional Material

Chapter 5
Material used and Experimental
Program
5.1 General
In this chapter the investigated material is introduced and classified. For the present in-
vestigations Hostun sand (Flavigny et al. 1990, Mokni & Desrue 1999, Desrues & Viggiani
2004) was chosen, that is a well known reference sand in the literature. The main classifica-
tion properties are presented. To ensure the investigation on reproducible, homogenous sand
specimens a study on preparation of Hostun sand specimen is carried out, that includes com-
puter tomography (CT) on saturated (S=0) and unsaturated sand specimens and an electron
microscopy study.
It follows a detailed description of the experimental program including initial conditions,
loading history, the specimen preparation and also the testing procedure in the different test-
ing devices. In the tests the hydro-mechancial behavior of unsaturated Hostun sand was
investigated. Therefore flow experiments in different columns are performed (modified pres-
sure plate apparatus, sand column testing device I and II). The influence of initial condition
(i.e. void ratio), the hydraulic loading path (i.e. drainage or imbibition paths) and the
test boundary condition (i.e. steady state and transient state tests) were considered in the
derivation of the soil-water characteristic curve and the unsaturated hydraulic conductivity
function. Special attention was paid to the significance of hysteresis with regard to both the
hydraulic relations. Additionally the effect of suction rate on the flow process was quantified
in the sand column device I and II under different boundary conditions.
The volumetric mechanical behavior of unsaturated sand is investigated. Therefore the
stiffness behavior as well as the collapse potential is determined by conducting one-dimensional
compression and rebound tests in a controlled suction oedometer cell. The influence of initial
conditions (i.e. void ratio, suction), the mechanical loading path (i.e. loading or unloading
paths) and the hydraulic loading path (i.e. saturation procedure) were considered in the
derivation of the stiffness behavior.
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