Water saturation effects on the tensile strength of rocks

• Main Author: Li, Zhihuan.
• Other Authors: School of Civil and Environmental Engineering
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Civil engineering::Geotechnical
• Online Access: http://hdl.handle.net/10356/53906
• Institution: Nanyang Technological University

For the design of underground structures within a rock mass, the two most important parts are to find out the design stresses that the structure will withstand, as well as the design strength of the rock mass. As the tensile strength of rocks is known to be much lower than its compressive strength, it is likely that an underground structure will undergo tensile failure. However, the effects of water saturation on the tensile strength of rocks are not well researched. This study aims to determine the effects of water saturation on the tensile strength of rocks. Specimens were made from molded Hydrocal B-11 gypsum. The prepared specimens were then soaked in tap water as well as solutions of differing pH levels for different amounts of time. Brazilian tensile tests were then performed on these specimens with differing moisture contents to determine their tensile strength. The test result showed that the tensile strength of the specimens dropped to around 50% of its dry tensile strength after soaking for a period of time as little as 1 day. The tensile strength of the specimens soaked in the acidic and the alkaline solutions were found to be consistently lower than the ones soaked in tap water. Furthermore, there was a sharp decline in tensile strength after 8 weeks for the specimens soaked in the acidic and alkaline solutions. Inspection of the tested specimens as well as the high speed camera footage validated most of the tests by showing that most cracks initiated from the middle of the specimens. This study showed that there is a negative effect of water saturation on the tensile strength of rocks, and that the pH level of the water plays a part in determining the tensile strength of rocks as well. The saturated tensile strength of rocks should be used while designing an underground structure, and the pH level of the groundwater saturating the rocks should be monitored as well.