STUDY OF ROCK VOLUMETRIC STRAIN IN TRIAXIAL TESTING

• Main Author: TRIDES (NIM : 22109011), TOMMY
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/20582
• Institution: Institut Teknologi Bandung

Triaxial test is one method to determine the rock strength in three directions stress condition. The test results can be described by the stress-strain curve. One method to determine the lateral strain from the triaxial test is measuring the volumetric strain. Volumetric strain can be measured from the changing of oil volume in the triaxial cell by stabilizing the confining pressure during the triaxial test. Axial strain and particularly volumetric strain can be directly used to determine the lateral strain of rock sample from triaxial test. <br /> <br /> <br /> Rock samples used in this study is the sandstone and claystone which each of them are consist of two blocks of rock. Sandstone and claystone blocks are drilled to obtain 13 samples of sandstone and 13 samples of claystone with cylindrical shape with 45 mm and 54 mm diameters. Every rock samples are prepared with terms 2 L/D and the unprepared rock is used for physical properties test. In addition, dynamic property is also measured on each rock samples. To determine the value of confining pressure of sandstone and claystone, the uniaxial compressive strength test has been done and the value of confining pressure is not more than 50% of the uniaxial compressive strength. To measure the volumetric strain, triaxial cell is connected directly to the linear displacement pump and electric hydraulic pump. Rock sample is placed inside the triaxial cell and connect directly with linear displacement filled by oil from oil reservoir. Beside measuring the volumetric strain, linear displacement pump is also purposed as a confining pressure generator during triaxial test process. <br /> <br /> <br /> Based on the triaxial test which has been done on the sandstone and claystone, it can be clearly seen that the triaxial compressive strength of rock samples (sandstone and claystone) with 45 mm diameter tend to be lower than the triaxial compressive strength of rock samples (sandstone and claystone) with 54 mm diameter. Based on that results, there are no scale effects on the rock samples. This phenomenom is caused by the uniaxial compressive strength, modulus of elasticity, natural density, and ultrasonic velocity of rock samples (sandstone and claystone) of which 45 mm diameter is lower than 54 mm diameter. In addition to the Poisson ratio of sandstone and claystone has a very clear distinction. Sandstone has a Poisson ratio range from 0.26 to 0.30 while the claystone has a range from 0.33 to 0.37. It can be clearly seen that Poisson ratio of sandstone is lower than claystone which has the plastic behaviour.