Hydro-Mechanical Properties of an Unsaturated Frictional Material

76 CHAPTER 4. EXPERIMENTAL SETUPS
stress on the shape of the soil-water characteristic curve. Volume measurements are
performed by the attached dial gauge.
- Column testing device I
In the column testing device I large scale (boundary condition problem) sand specimen
are examined. Special feature of the cell are pairs of tensiometer and TDR sensors
in several depth, that directly measure suction and water content while withdrawing
and injecting water from the specimen. The measurements of volumetric water con-
tent and matric suction enable to apply steady state flow (multistep method) and also
transient state flow (continuous flow method) to the specimens. Therefore the relation
between suction and water content obtained under equilibrium and dynamic condition
can be compared. The unsaturated hydraulic conductivity can be either directly (e.g.
via instantaneous profile method) or indirectly determined (e.g. by use of statistical
models).
- Column testing device II
Further drainage transient state tests (boundary condition problem) are conducted in
column testing device II, where suction is applied to the specimen using axis-translation
technique. Pairs of tensiometer and TDR sensors in several depths directly measure soil-
water characteristic curve. Due to the ceramic disc on the bottom of the column the
cell allows to apply certain suction to the specimen (hanging water column technique,
axis translation technique). Also the cell has a piston for application of mechanical
stress at top of the specimen. Volume measurements are performed by the attached
dial gauge. The influence of the net stress on the hydro-mechancial behavior of Hostun
sand specimens using column testing device II is not discussed in this work.
Hydraulic functions are measured and/ or estimated under different flow conditions (steady
state and transient state flow condition) and loading path directions (initial drainage, main
drainage and main imbibition, scanning drainage and scanning imbibition processes) using
hanging water column as well as axis-translation technique and/ or tensiometer and TDR
sensor measurements and/ or measurements of cumulative water flow.
For determination of mechanical behavior of unsaturated Hostun sand suction-controlled
oedometer cell is used. The suction-controlled oedometer cell developed by Romero (1999) for
the purpose of testing clay samples is upgraded with a burette for applying and controlling
small suctions in the cell using hanging water column technique. The mechanical behavior of
unsaturated sand was investigated by performing one dimensional compression and rebound
tests at different constant suctions as well as collapse tests.