Behaviour of Stress-Strain of different type of Sands
River sands are generally sheared under same conditions as they have comparatively higher value of permeability. This nature of sands can be investigated by direct shear or triaxial tests procedure. The important parameters governing their nature of behaviour are known as relative density (ID)and other one is magnitude of effective stress (s¢). The relative density is generally are defined in percentage as
where emax = Maximum void ratio and
emin = Minimum void ratio
e = Present void ratio
that can be determined from standard tests in the laboratory method. This expression of dry densities can be written as follows
where gdmax =Maximum dry densities,
gdmin =Minimum dry densities and
gd =Permanent dry densities
Sand is generally termed as dense if ID> 65% and loose if < 35%.
The influence or effect of relative density on the nature of behaviour of saturated sand can be observed from the diagram of laboratory tests performed at the same effective confining stress. There are no induced pore water pressures existing in the collected soil samples.
All the sands samples approach the same ultimate conditions of shear stress value and void ratio, irrespective of the primary density value.
For the highly dense sand sample, the deviator stress attain at maximum level peak at a low value of axial strain and then fall down, whereas due to loose sand sample, the deviator stress value builds up gradually and consistantly with axial strain. The nature of behaviour of the medium sands sample is exists in between. The following observations can be noted:
The denser sands sample attains maximum peak angle of shearing resistance in between.
• Primary dense soil samples expand or dilate when sheared, and primary loose sands samples compress.