Hydro-Mechanical Properties of an Unsaturated Frictional Material
Hydro-Mechanical Properties of an Unsaturated Frictional Material
Hydro-Mechanical Properties of an Unsaturated Frictional Material
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Chapter 4<br />
Experimental Setups<br />
4.1 General<br />
The investigation <strong>of</strong> unsaturated soils dem<strong>an</strong>ds for particular requirements <strong>of</strong> the testing<br />
equipment. Depending on the type <strong>of</strong> soil, if it is a clay, silt or s<strong>an</strong>d, equipment has to<br />
be carefully chosen to be able to study the entire r<strong>an</strong>ge <strong>of</strong> suction (where the soil-water<br />
characteristic curve takes place), to measure either suction, matric suction or osmotic suction<br />
(i.e. unsaturated soil behavior <strong>of</strong> clay is influenced by osmotic as well as matric suction <strong>an</strong>d<br />
unsaturated soil behavior <strong>of</strong> s<strong>an</strong>d is influenced by the matric suction) or to be able to carry<br />
out proper measurements with suitable accuracy (i.e. volume ch<strong>an</strong>ges during vertical loading<br />
<strong>of</strong> a clay are larger th<strong>an</strong> the volume ch<strong>an</strong>ges <strong>of</strong> a s<strong>an</strong>d). Among others the investigation <strong>of</strong><br />
unsaturated soils requires the measurement <strong>of</strong> either the suction <strong>an</strong>d/ or the water content.<br />
During the present work several devices for testing unsaturated s<strong>an</strong>d are developed <strong>an</strong>d<br />
modified. The aim <strong>of</strong> the newly developed equipments is to design testing devices <strong>an</strong>d to<br />
propose special experimental setups for investigation <strong>of</strong> hydraulic <strong>an</strong>d mech<strong>an</strong>ical behavior <strong>of</strong><br />
s<strong>an</strong>d. For application <strong>of</strong> suction, that is for s<strong>an</strong>d experiments varying between ψ = 0.1 <strong>an</strong>d<br />
50 kPa, h<strong>an</strong>ging water column <strong>an</strong>d axis-tr<strong>an</strong>slation technique are used. Other cells (column<br />
testing device I <strong>an</strong>d II) are equipped with tensiometers <strong>an</strong>d TDR sensors.<br />
For determination <strong>of</strong> hydraulic functions <strong>of</strong> unsaturated Hostun s<strong>an</strong>d different testing<br />
devices are developed in the present investigation:<br />
- Modified pressure plate apparatus<br />
The main feature <strong>of</strong> the modified pressure plate apparatus is a ceramic disk, which<br />
enables to use h<strong>an</strong>ging water column technique <strong>an</strong>d axis-tr<strong>an</strong>slation technique for de-<br />
termination <strong>of</strong> soil-water characteristic curve under equilibrium condition (multistep<br />
flow method). Thus suction is controlled in the cell. Precise cumulative water outflow<br />
<strong>an</strong>d inflow measurements are carried out by me<strong>an</strong>s <strong>of</strong> the attached burette, that has<br />
a high accuracy. The apparatus additionally allows to investigate the influence <strong>of</strong> net<br />
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