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