Comparison study on the strength index of tropical shale and sandstone influenced by moisture content

Abstract

The effects of variation of moisture content on the strength index are different depending on the type of rocks. Hence this paper compares effect of moisture content to the strength and anisotropy index of moderately weathered shale and sandstone of Jurong Formation. Both field and laboratory works had been carried out to in order to gain useful data such as the physical description, the strength index and also the anisotropy index of the rocks. Twenty-four samples of moderately weathered for each shale and sandstone (total 48 samples) were tested at a wide range of moisture content varying from original moisture content to saturated condition. The results revealed that the presence of water has affected the strength index of shale more than sandstone. The strength index of shale decreased up to 80% with just 7.4% increment of moisture content while the strength index of sandstone only decreased up to 46% by 6.94% increase in moisture content. The presence of water also affected the anisotropy index of the material. The results discovered that the presence of moisture content has affected the anisotropy index of shale more than sandstone. With original moisture content of 1.06% to moisture content of 8.45%, the shale is shifting from fairly-moderately anisotropic to highly anisotropic while sandstone that had not been affected much in term of anisotropy index still remain as fairly-moderately anisotropic material with 6.94% increase of moisture content. Field and experimental results shown the increment of moisture content has affected the strength and anisotropy index of shale more than sandstone of the same weathering grade. The impact of moisture content on tropical shale and sandstone strength index is required for the design and construction of foundations, tunneling and slope stability studies in rock mass.