Behaviour of Clay Subjecting to Vacuum and Surcharge Loading in an Oedometer

Abstract

The deformation of clayey soil subjected to the combination of a vacuum pressure and a surcharge load in an oedometer apparatus, with either vertical or inward radial drainage, has been investigated experimentally. A parameter Kw, defined as the horizontal effective stress exerted on the wall of the consolidation ring (s’hw) divided by the vertical effective stress (s’v) in the soil specimen is suggested as an indicator of the tendency for lateral deformation under field conditions. It is observed that if the value of Kw is close to the value of K0 of the soil (the ‘at-rest’ earth pressure coefficient), there should be very limited lateral displacement in field situations. The laboratory test results show that during the loading process, the value of Kw is mainly influenced by the ratio of the magnitude of the surcharge pressure to the vacuum pressure (RL) and the rate of surcharge loading (SLR). At the end of consolidation the value of Kw increases with increasing RL, but it is almost independent of SLR for the conditions investigated. In the presence of a vacuum pressure, at the end of consolidation the value of Kw is usually less than the original value of K0 of the soil. The test results also indicate that Kw has a strong correlation with the synthetic non-dimensional loading parameter, RLS, as defined by Chai et al. (2013), which includes the effects of both RL and SLR as well as the consolidation properties of the soil. It is suggested that the parameter RLS can be used to predict lateral displacements under field conditions that involve combined surcharge and vacuum pressure loading.