Innovative methods of ground improvement for railway embankment peat fens foundation soil

Abstract

This paper presents research initiated with the aim of assessing the feasibility of biocementing peat fens soil, a problematic soil underlying many of the embankments of the East Anglia railway network (UK). Biocementation of soil is an emerging, novel, ground improvement technique. It has recently attracted the interest of researchers worldwide because it has been proposed as potentially environmentally superior to chemical grouts and other common soil stabilisers – for example, cement or lime (linked to high carbon dioxide emissions). In this study, the authors screened and isolated non-pathogenic indigenous ureolytic microbial candidates with potential for biocementation from samples originating from peat fens in East Anglia, UK. Four strains were selected as the most suitable candidates, based on their growth rate and their viability in a wide range of temperatures, pH and soil moisture contents corresponding to typical seasonal field conditions. After a number of unconfined compressive strength (UCS) tests, one strain (Bacillus licheniformis) was selected as the most promising for this soil treatment and used for further study. Two different methods of implementation of the treatments were considered: namely, pressure flow soil column and electrokinetic injection. The UCS results supported by calcium carbonate measurements proved that biocementation did occur for both implementation methods and for a number of treatment combinations. Ongoing work on optimisation of treatments and implementation methods is being carried out towards the upscaling of the techniques for in situ implementation, which is planned for the next stage of the research.