Unconfined (uniaxial) compression strength

The test for determing the unconfined compression strenght of the soil gives approximative values of the angle of internal friction I,for the cohesion C and for the modulus of compression MC­.
There are a number of ways for determing the unconfined compression strenght.
The soil sample is placed in the aparatus under the piston compressor.
The sample is stressed with downward acting forces in specified time intervals.
After each loading the value on the comparameter is read.
When the loading reaches the value of 25-30% of the ultimate bearing capacity,which is determed by a prevoius test,the sample is relieved in the same way.
When the soil sample is relieved,it is once again stressed as before,but this time we load it to its ultimate bearing capacity.
As the breaking point of the soil we take the moment when a rupture apears visible to the naked eye,or if the soil is verry soft,when a sudden lateral expansion occures.
The results of the experiment we draw on the diagram.
The values of stressing the sample show us the diagram of settlement or subsidence,and the values of relieveing the sample show us the diagram of swelling.
If we stress the sample again we will get the diagram of secondary settlement.