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Ground source heat pumps (GSHPs) in urban environments can take advantage of surplus ground heat energy generated by subterranean infrastructures such as underground railways (URs). This paper describes seminal work in this area and a novel 3D numerical investigation into the heat energy recovery from URs with nearby vertical ground heat exchangers (GHEs). The investigation uses the London Underground (LU) as a case study but its results are generic worldwide. The investigation included a number of studies considering different geometrical configurations of the railway tunnels and the nearby GHE array, and the impact of that variation on the GHEs heat extraction rates. The results showed that heat extraction rates of GSHPs installed near UR tunnels can be significantly improved by up to ~ 43%. This will enhance overall GSHP system efficiencies, resulting in substantial savings in both operational costs and carbon emissions. In addition, the outcomes were used to develop a relationship which allows approximating the GHEs heat extraction improvements due to the nearby tunnel(s) heat load(s). This could give guidance to engineers working in fields where thermal interactions between URs and nearby GHEs arise.

This paper refers to biocementation of a problematic soil of the UK railway network as a potential stabilisation technique of this soil using indigenous ureolytic bacteria. The soil is peat, a soft foundation soil also subject to oxidation wastage. As the peat is under existing embankments, electrokinetics (EK) is proposed as a promising technique to implement treatments. In the context of unsaturated soils the paper thus focuses on two particular aspects relevant for the implementation of treatments and the stability of this soil, namely: a) the effect of degree of saturation of the peat on the bio-electrokinetic treatment ; b) the soil water retention curve of the soil affecting flow and transport; these are relevant as we focus on understanding and modelling the implementation of treatments through electrokinetics; moreover for the peat it is of importance to understand moisture exchange in the vadose zone and control groundwater table levels (e.g. during electrokinetics) in order to prevent further oxidation. After isolation and screening of indigenous microorgansisms Bacillus licheniformis was selected for further testing. The results in terms of unconfined compressive strength, CaCO3 content, swelling and compression behaviour and water retention proved the feasibility of biocementation using this indigenous microorganism. Ongoing work is assessing the required treated soil characteristics and related required biocementation degree to solve UK rail's peat foundation problems. Upscaling of the techniques towards in situ implementation is also planned in the next stage of the research.

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.

Ground source heat pumps (GSHPs) can provide an efficient way of heating and cooling buildings due to their high operating efficiencies. The implementation of these systems in urban environments could have further benefits. In such locations the ground source heat is potentially more accessible through alternative sources such as through underground railways (URs). The heat from the ground surrounding an UR tunnel could be exploited to enhance the operation of GSHPs operating in heating mode. To achieve this, the interactions of GSHPs with neighbouring URs must be fully understood but there is little exploration of these in current literature. This paper focuses on the potential benefit of understanding such interactions. It starts with a summary of typical and alternative heat sources for heat pumps and then it highlights the reasons why URs can be regarded as one of the most attractive ones. Then the paper reviews the current approaches used to model GSHPs and URs. Based on that review the paper suggests a method for the combined analysis of GSHPs and URs. The reasons why London is a sensible choice for a case study are also described. Summary of results from a preliminary investigation are also presented.

This paper assesses comparatively the performance of a number of innovative soil stabilisers for the treatment of a highly swelling-shrinking soil, against that of commercial calcium lime. The production of lime, a most common soil stabiliser, involves high energy consumption, carbon dioxide emissions and the depletion of natural raw materials. Alternatives are actively sought, in particular industrial wastes and by-product materials or lower energy demand cements e.g. reactive magnesia (MgO) cements. In this paper calcium lime, reactive magnesia, industrial wastes and mixes of these with lime are comparatively assessed, based on a number of conventional measures of the propensity of a soil to swell, i.e. plasticity characteristics and swelling characteristics (swelling strains, swelling pressures, swelling indices). Furthermore, as expansive soils are typically in an unsaturated state hence sensitive to both changes in water content and suction, filter paper testing was performed to provide additional evidence of the effect of the treatments on the swelling/shrinking soil. According to the main findings, for the treatment of swelling shrinking soils, binders coming from the paper recycling industry show most promise as alternatives to lime; reactive magnesia cement had a smaller effect than calcium based stabilisers in improving the swelling-shrinking of the soil, yet it also suppressed swelling and shrinkage considerably; it thus shows potential for use as an alternative to common soil stabilisers (Portland cement and calcium lime) to alleviate the environmental impact of the latter.

This paper investigates the drying and wetting soil water retention curves (SWRCs) of statically compacted lime-stabilised London Clay specimens. A series of tests were performed using the contact filter paper method, pressure plate apparatus and a suction-controlled triaxial system incorporating the axis translation technique. These investigated the water retention of the soil under different boundary and stress-state conditions and simultaneously determined the volume change in the soil during drying and wetting. Factors relevant to the lime treatment of soils, such as curing period and method (air vs. water curing), were also considered. Finally, the hysteresis of the SWRC of the chemically treated soil (for which there appears to be a lack of information in the international literature) was investigated. The results showed that the treatment with lime increased the volumetric stability but reduced the water retention ability due to a more open structure enabled by the flocculation and chemical bonding effects. Curing period and method effect appears to be small. Hysteresis was noted to some degree in all instances.