Figure 7: Correlation of UCS to Isp(50)
of slightly weathered shale
Uniaxial Compressive Strength to Elastic Modulus and Stiffness
The correlation between the uniaxial compressive strength with elastic
modulus, E50 , and intact properties,
Ii are plotted in the same graph as shown in Fig
8. The graphical plot produced two empirical correlations. The
correlation of elastic modulus of the shale with respect to compressive
strength can be predicted using Eqn. 9,
with R 2 = 1.0 (9)
and similarly the strength index of weathered shale is predicted by
using eqn (10) below,
with R 2 = 0.99 (10)
It was found that the elastic modulus decreases linearly with the
decrease in uniaxial compressive strength, meanwhile the stiffness of
material exponential increases with a decrease in uniaxial compressive
strength . The intersection of the two lines indicated the boundary
between soil-like weathered shale on the left and rock-like weathered
shale on the right hand side.