Electrokinetic biocementation of an organic soil

Abstract

Organic soils are a continuing challenge to civil engineers, as they are subject to settlements, negatively impacting on civil engineering infrastructure. To improve the in situ properties of these, chemical soil stabilisers (e.g. cement or lime) can be commonly used. Although successful in minimising severe damage, these stabilisers may have environmental side-effects (e.g. cement and lime production is linked to 7%–8% of overall CO2 emissions). Therefore, the development of innovative, superior, cost-effective and overall more sustainable soil improvement techniques is a field of ongoing research effort. In this context, this paper studies the electrokinetic (EK) biocementation of a problematic soft organic soil of the UK railway network using indigenous ureolytic bacteria. The paper focuses on aspects relevant for the effective implementation of treatments, namely the effect of degree of saturation of the soil and different ways of treatment implementation. The results in terms of unconfined compressive strength and CaCO3 content, proved the feasibility of EK biocementation using an indigenous microorganism, either premixed with the soil or injected electrokinetically. Higher strength gains were recorded for degrees of saturation in the region of 85%–95%. Strength gains and increased CaCO3 contents compared to the control samples were also noted when treatment duration was halved to one week although strengths increased further by 13–17% after a two-week treatment. Overall, the study gives promise for the applicability of the EK-biocementation technique under existing infrastructure. Further optimisation of the treatment variables and refinement of the implementation details could enhance the efficiency of the process.