To determine the settlements due to primary consolidation of soil by conducting one dimensional test.
The test is conducted to determine the settlement due to primary
consolidation. To determine :
i. Rate of consolidation under normal load.
ii. Degree of consolidation at any time.
iii. Pressure-void ratio relationship.
iv. Coefficient of consolidation at various pressures.
v. Compression index.
From the above information it will be possible for us to predict the time rate and extent of settlement of structures founded on fine-grained soils. It is also helpful in analyzing the stress history of soil. Since the settlement analysis of the foundation depends mainly on the values determined by the test, this test is very important for foundation design.
When a compressive load is applied to soil mass, a decrease in its
volume takes place, the decease in volume of soil mass under stress is
known as compression and the property of soil mass pertaining to its
tendency to decrease in volume under pressure is known as
compressibility. In a saturated soil mass having its void filled with
incompressible water, decrease in volume or compression can take place
when water is expelled out of the voids. Such a compression resulting
from a long time static load and the consequent escape of pore water is
termed as consolidation.
Then the load is applied on the saturated soil mass, the entire load is
carried by pore water in the beginning. As the water starts escaping
from the voids, the hydrostatic pressure in water gets gradually
dissipated and the load is shifted to the soil solids which increases
effective on them, as a result the soil mass decrease in volume. The
rate of escape of water depends on the permeability of the soil.
1) From the sample tube, eject the sample into the consolidation ring.
The sample should project about one cm from outer ring. Trim the sample
smooth and flush with top and bottom of the ring by using a knife. Clean
the ring from outside and keep it ready from weighing.
2) Remoulded sample :
a) Choose the density and water content at which samples has to be
compacted from the moisture density relationship.
b) Calculate the quantity of soil and water required to mix and compact.
c) Compact the specimen in compaction mould in three layers using the
standard rammers.
d) Eject the specimen from the mould using the sample extractor.