Development and application of an oedometer with negligible side-wall friction for rockfill materials

The oedometer is one of the most commonly used apparatuses to investigate the long-term deformation behaviors of rockfill materials. However, the side-wall friction restrains its application. To overcome this limitation, an oedometer that can provide long-term and stable loading and measure the side-wall friction is developed. The main features of the apparatus are presented. To minimize the side-wall friction, the linings that consist of spaced and greased Polyamide plates are used to cover the oedometer wall. The consolidation tests are carried out to evaluate the performance of the anti-friction linings with layers in the range of 1~3 and with layer thickness of 0.3 and 0.5 mm, respectively. The best test results are obtained by using 3 layers of 0.5 mm-thick linings. At the same vertical stress, the side-wall friction is 91% smaller on average while the vertical strain is 20%~80% larger with 3 layers of 0.5 mm-thick anti-friction linings than that without linings. Therefore, the proposed method is chosen to reduce the side-wall friction, and the creep tests are carried out on air-dried rockfill materials. The test results show that the vertical strain at the end of the tests and the coefficient of the secondary consolidation are about 1.0 and 1.2 times larger with 3 layers of 0.5 mm-thick linings than those without linings. The apparatus substantially reduces the side-wall friction and improves the accuracy of creep test results.