Compressibility characteristics of soils

Compressibility characteristics of soils forms one of the important soil parameters required in design considerations. Compression index, C<SUB>c</SUB>, which is the slope of the linear portion of void ratio, e vs. logaritham of effective pressure p(log p) relationship, is extensively used for settlement determination. The e-log p is most often assumed to be linear at higher pressure range and hence C<SUB>c</SUB> is taken as a constant. Both published experimental results as well as results obtained in this investigation reveal that the e vs. log p could be curved, concave upwards or concave downwards depending upon the soil plasticity characteristics and initial water content. Thus, assuming C<SUB>c</SUB> to be constant may not be valid for many cases. In this paper, an alternate procedure is given to characterise the compressibility of a soil. Experimental results show that the deformation expressed as a percent of thickness of the soil, (strain) vs. effective pressure could be treated as a rectangular hyperbola and the behaviour could be characterised by two parameters, a and b. Characterising the compressibility behaviour with effective pressure by two parameters is better than a single parameter, C<SUB>c