Prediction of Long-Term Strength of Some Weak Rocks

Abstract

A series of slake durability tests, point load strength index tests, tilt tests and x-ray diffraction analyses were carried out on thirteen rock types, in an attempt to correlating the rock  durability with their strengths and mineral compositions.  A concept was proposed to describe the rock degradation characteristics under the slake durability test cycles.  A new classification system was also introduced for rock durability, which allowed predicting the rock strength as affected by weathering process.  Results indicated that Pichit pumice breccia, Phra Wihan siltstone, Phu Kradung sandstone, Khok Kruat sandstone and Chonburi schist are classified as low to very low durability rocks, primarily due to the kaolinite content.  Nam Duk slaty-shale is considered high durability, not sensitive to water, but is easily disintegrated by rapid change of surrounding temperatures.  The point load strength index decreases with an increasing difference in slake durability indices obtained from adjacent cycles (DSDI).  Basic friction angles of the smooth (saw-cut) surfaces of the rocks decrease as the rapid heating-cooling cycles increase.