Strength Index, Is of
R2 = 0.9305
Weathered Sandstone
Strength index, Is, is defined as the ratio of
uniaxial compressive strength to point load strength and is a
dimensionless parameter. It represents the ratio of compressive strength
to the tensile strength properties of a rock material. Based on the
plotted data as shown in Fig 5 and Fig 6, the strength index of
sandstone correlated exponentially to σ2 (Eqn. 6)
and Isp50 (Eqn. 7) as follows:
with R 2 = 0.9 (6)
with R 2 = 0.98 (7)
Based on the above correlations, it is observed that at
σ2 > 60 MPa ,
Is < 125, the strength index reduction
rate is not significant probably due to the high brittleness of
weathered sandstone. On the contrarily the weathered sandstone having
σ2 < 60 MPa and
Is >125, can be due to reduction in
the brittleness indicated by a large increment of strength index at low
compressive strength. The profile revealed the boundary between
rock-like weathered sandstone and soil-like highly weathered sandstone.
The similar behaviour was also observed at the boundary of point loads
strength of 1 MPa. The sandstone behaved as a brittle material when the
point load strength is more than 1 MPa, otherwise it can be considered
as a ductile material.