Measurement of Lateral Stress and Friction in Rockfill Oedometer Tests Enabling the Analysis of the Experimental Results in the p′-q Space

Abstract

Abstract The oedometer is one of the simplest and most reliable laboratory tests. Its main drawback is that stress state is not fully known. Over the years, a number of enhancements were intended to overcome this limitation. This work presents the development of a large size oedometer for testing gravels made of crushed rock under varying moisture conditions. Load application is done by air pressure acting on the upper end of the specimen (Rowe type oedometer), and the lateral stress is measured using a strain-gage-instrumented oedometer ring. Special features were included in the ring geometry for enhancing the lateral stress measurement signal, while keeping the deformation of the ring to acceptably low levels. The lateral friction between specimen and oedometer wall is computed as the difference between the applied load and the reaction force at the specimen base, measured by means of three load cells. The performance of the oedometer is studied by means of a finite element model of the oedometer ring. The deformability of the ring and the production of spurious readings of lateral stress due to varying operation conditions are evaluated and found to be satisfactorily low. Some experimental results on a rockfill type material are presented. The lateral stress and friction data are analysed in terms of the lateral stress ratio and in the p′-q space. The observed behavior is found to be stress– and suction–dependent. The results are consistent with triaxial tests of the same material published elsewhere.