Towards the Development of Sustainable Ground Improvement Techniques —Biocementation Study of an Organic Soil

Ongoing research effort is dedicated to the development of innovative, superior and cost-effective ground improvement techniques to mitigate natural and man-made hazards while minimising waste and other environmental impacts. In this context, the nature-based process of biocementation of soils has been proposed as a potentially more sustainable technique than conventional chemical ground improvement practices. This paper focuses on the biocementation of an organic soil of the UK railway network. Having recently proven the feasibility of biocementing this soil using indigenous ureolytic bacteria, in this paper, the authors perform a parametric study to identify treatments successful in increasing the strength of the soil. Selected treatments are then applied to the soil to assess its volume change during consolidation, secondary compression and shrinkage upon drying. The results show that, depending on the treatments used, biocementation has increased the unconfined compressive strength by up to 81% compared to that of the control samples. For selected treatments and the range of water contents tested (55–33%), shrinkage upon drying reduced by 16%, while the volumetric strains of the soil upon 1-D compression reduced by 32–47%. This was reflected in the values of the coefficient of volume compressibility and the coefficient of secondary compression (the latter either reduced by up to an order of magnitude or secondary compression was not observed altogether in the testing period). Overall, the results proved that biocementation improved considerably the mechanical properties of the organic soil, which gives promise for addressing the settlement problems of this soil

Electrokinetic biocementation of an organic soil

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