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.