Assessment of the strength and swelling potential of soft soils before and after electrokinetic biocementation

This paper presents results of a laboratory investigation to instruct the setting up of a field electrokinetic biocementation pilot trial in East England, enabled by UK railway owners and operators. The geological setting of the field trial area is highly heterogeneous, comprising a succession of soft marine fine-grained soil deposits, including swelling and organic soils. The unfavourable ground conditions cause serviceability problems and track deterioration due to the underlying soil volume changes/deformation incurring high annual maintenance costs. Although the water table is generally high, seasonal effects and extensive pumping are linked to a large part to the engineering problems. Ramboll UK and London South Bank University were commissioned to investigate the feasibility of electrokinetic biocementation as a method of mitigating these problems of the problematic soil site. In this paper, the proposed ground improvement methods are evaluated based on the effects of biostimulation/biocementation laboratory treatments on a soft soil undrained shear strength, as well as the plasticity characteristics and soil water retention curves of the soil before and after treatment, that can be used to interpret their swelling/shrinking potential under changing water table levels and saturation conditions.