Biaxial apparatus testing for dike stability assessment

Abstract

Stability assessment for dikes and dike reinforcement requires insight in soil strength behaviour. The required parameters for this assessment are typically obtained from conventional laboratory tests. These conventional tests are not performed under conditions found in the field. For example, a dike section resembles to plane strain conditions. Limited research is available for laboratory test under plane strain conditions, especially for organic clays. The plane strain biaxial apparatus presented by Allersma (1993) is used to perform tests on organic clay. The apparatus has not been used for several decades and it is described how the machine is refurbished. Preliminary tests and further improvements lead to familiarization with the apparatus. After this stage, laboratory tests on organic clay are performed and presented. The soil sample is loaded, leading to stress and pore pressure measurement. The measurements from laboratory tests are presented in chronological order. Several test set ups, most notably varying in their method to control the drainage conditions and to measure the pore pressure, are used. Assessment of the standard of these results in terms of accuracy, reliability and reproductivity is given. A notable challenge arising in the tests, is the uncontrolled drainage boundaries at the boundary between soil sample and soil sample enclosure: the biaxial cell. Conclusions are drawn from individual tests and consequentially improvements are made on the test set up. The test is re-created and numerically analysed in finite element programmes PLAXIS2D and PLAXIS3D. The numerical analysis and laboratory are compared and help to understand and predict the stress conditions found during tests in the laboratory. Remaining challenges are discussed on technical specifications and laboratory test set up. Concluded is that tests with this biaxial apparatus do not lead to results of a sufficiently high standard for further soil testing.