The one-dimensional consolidation test, called the oedometer test, is used to fi nd Cc, Cr, Ca, Cv, mv, and s9zc. The hydraulic conductivity, kz, can also be calculated from the test data. The experimental arrangement we used in Section 9.3 is similar to an oedometer test setup. The details of the test apparatus and the testing procedures are described in ASTM D 2435. A disk of soil is enclosed in a stiff metal ring and placed between two porous stones in a cylindrical container fi lled with water, as shown in Figure .
A metal load platen mounted on top of the upper porous stone transmits the applied vertical stress (vertical total stress) to the soil sample. Both the metal platen and the upper porous stone can move vertically inside the ring as the soil settles under the applied vertical stress. The ring containing the soil sample can be fi xed to the container by a collar (fixed ring cell, Figure or is unrestrained (fl oating ring cell, Figure ).
Incremental loads, including unloading sequences, are applied to the platen, and the settlement of the soil at various fi xed times under each load increment is measured by a displacement gage. Each load increment is allowed to remain on the soil until the change in settlement is negligible and the excess porewater pressure developed under the current load increment has dissipated. For many soils, this usually occurs within 24 hours, but longer monitoring times may be required for exceptional soil types, for example, montmorillonite. Each load increment is doubled. The ratio of the load increment to the previous load is called the load increment ratio (LIR); conventionally, LIR 5 1. To determine Cr, the soil sample is unloaded using a load decrement ratio—load decrement divided by current load—of 2.
At the end of the oedometer test, the apparatus is dismantled and the water content of the sample is determined. It is best to unload the soil sample to a small pressure before dismantling the apparatus, because if you remove the fi nal consolidation load completely, a negative excess porewater pressure.
that equals the fi nal consolidation pressure will develop. This negative excess porewater pressure cancause water to fl ow into the soil and increase the soil’s water content. Consequently, the fi nal void ratio calculated from the fi nal water content will be erroneous.
The data obtained from the one-dimensional consolidation test are as follows:
1. Initial height of the soil, Ho, which is fi xed by the height of the ring.
2. Current height of the soil at various time intervals under each load (time–settlement data).
3. Water content at the beginning and at the end of the test, and the dry weight of the soil at the end of the test.
You now have to use these data to determine Cc, Cr, Ca, Cv, mv, and s9zc. We will start with fi nding Cv.