GEOMECHANICAL STRENGTH
A series of strength test was carried out according to ISRM 1981,
suggested method of testing. Some blocks of sandstone and shale have
been sampled from the site according to the weathering grade and later
prepared for uniaxial compressive strength and point load strength
tests. The objective is to determine the material strength as it varies
from slightly weathered to highly weathered i.e from rock to soil like
state. The strength and stiffness of the weathered composite materials
i.e a matrix of weathered sandstone and weathered shale are then
formulated.
Uniaxial Compressive Strength
The test was carried out according to the suggested method with some
modification to the procedure of testing .The non-homogeneity of
weathered sandstone from Kenny Hill formation constitute of a wide range
in uniaxial compressive strength values. The broad varieties are due to
the aggressive tropical rock weathering and the unique weathering
pattern of the sedimentary rock. The removal of inherited physical
properties of weathered sandstone and shale materials due to sample
preparation process resulted to the mechanical properties obtained was a
representative of tropical weathering characteristics of the tested
samples. However by repeating the test on as many samples with the same
quality of weathering has enabled the comparison of the strength
deterioration of sandstone and shale being concluded. Table 2 summarized
the uniaxial compressive strength (σc) of weathered sandstone and shale
which has been physically characterized and clustered accordingly. The
data obtained in the first column was statistically analyzed and has
been reclassified to reflect the true uniaxial compressive strength of
the weathered rock by its quality of weathering grade.
Point Load Strength
A point load strength test is not popular as a method for geotechnical
assessment among civil engineer in Malaysia however result shows that by
using a lower scale of load cell and higher sensitivity of strain
measurement, the point load strength (Isp50) of slightly
to highly weathered sandstone and shale has been successfully measured.
Table 3 summarized the result of the point load strength index tested
perpendicular to the sample lamination.
Table 2: Summary of σc2 for weathered sandstone
and shale samples from Kenny Hill rock mass