Lime stabilisation is a versatile technique applied during earthworks operations. Modern soil recycling units are much more efficient at pulverising fill material and intermixing the added binder/water than machinery available 20 years ago. While supplier innovation adds flexibility to the site working method, specifications have not been sufficiently updated to permit optimal application. This review paper details the physico-chemical changes instigated through the lime-clay soil reaction, updating previous reviews. It aims to assist scientific debate, current practitioners and future specification changes. For example, the application of the minimum 24 h mellowing periods (mandatory to UK specifications) with high reactivity, quicklime powders is concluded to cause increased air voids in the compacted fill.Increased air voids are associated with reduced long-term strength and potential volume change from water ingress, which is of particular concern for sulfate swelling. Shorter mellowing periods and/or use of hydrated lime may lesson this issue; however, a 'one size fits all' approach is discouraged in preference to site-specific methodologies refined to suit the fill material and project requirements. The discussion also summarises working methods which may lower the risk of sulfate swell and defines areas requiring further practical research.

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Railway transitions from cut to fill are locations across which significant differential settlements may develop. Compounded by similar abrupt changes to subgrade stiffness, accelerated track movement during high speed (HS) train passage may cause tracksubstructure deterioration and instability. This paper considers a foreseeable scenario in UK rail engineering with transition from unweathered Mercia Mudstone (MMG) to MMG cohesive fill. Separate analysis of (1) differential settlement using one-dimensional oedometer consolidation methods and (2) track bed movements using a three-dimensional Finite Element Analysis (FEA) with moving load were undertaken. This included comparison of untreated and lime treated embankment fill material with parameters for each taken from laboratory and field test data. Results showed a difference in settlement of 26.6mm across the modelled cut to 8metre fill transition giving differential settlement for untreated fill that was too high to meet literature criteria of <20mm over 20m. However, 1.5% lime treatment of the fill causes significant reduction to both consolidation settlement and track movement under dynamic loading to meet the serviceability criteria. Consideration of the full settlement profile across the transition has identified that the Rate of Change (ROC) of settlement is maximum at the start of the fill zone and the ROC in settlement could be a more relevant measure of what a moving train would experience with a sudden unloading/loading action. It is concluded that future work including a coupled FEA analysis, including consolidation and then subsequent stages modelling the resulting amplification of moving loads across the settled profile would give stronger understanding of how differential settlement causes rail level movement from HS traffic. This would help confirm how best to apply differential settlement criteria in geotechnical design of transitions and whether ROC in settlement (e.g. 1mm per 1m) is more informative than a settlement range across a longer fixed distance.

Innovative non-contact sensing and monitoring systems based on Vision-Based (VB) technology are becoming a viable method to remotely capture railway track vibrations and quality. This paper describes the use of VB system for the measurement of track vertical displacements and the estimation of track stiffness. The dynamic response of the track under a moving vehicle load was investigated through experimental and numerical modelling using a series of large-scale trails and finite element (FE) simulations. The accuracy of the VB system was examined with a conventional sensor used to measure the rail deflection. The viability of VB system in detecting voids between rail and sleeper due to faults in fastening were discussed. Results obtained from the VB monitoring was then used to calibrate FE models used to estimate the subsoil stiffness. The paper concludes with a discussion of how this methodology can be utilised in the railway industry for assessing the track performance with less complicated and more cost-effective hardware compared to conventional monitoring systems.

Working platforms are temporary geotechnical structures that provide stability to heavy plant on construction sites. Traditionally made from granular unbound material of sufficient thickness, platforms are implemented where the natural ground is not strong enough to support imposed loads. To reduce the depth of minimum required fill, hydraulically bound materials (HBM) can be used. However, there is no design guidance on HBM working platforms as any available methods were developed for purely granular material. This paper considers the case of HBM platforms of varied thicknesses made from lime treated Mercia Mudstone (MMG). The platforms were designed under the industry approved methods and the outputs were analysed using Discontinuity Layout Optimization software. The analysis included comparison between the bearing capacity of granular platforms and HBM of different strength parameters. Results showed that the industry design methods are heavily reliant on the frictional angle of platform material, and they could not properly account for strength of HBM which mobilise substantial strength through cohesion. Although the granular platform design obtained through these methods aligned well with the DLO analysis, they were found to underestimate bearing capacity of HBM platforms when compared to the software. Further DLO analysis showed that the granular platforms had much lower bearing capacity than that of HBM. In the scenarios considered, even adding 0.75% of lime had the potential to decrease the required platform depth to 0.1m (although such a large reduction is not recommended with the design guidance limit advised as 0.3m), compared to 0.7m which would be required if a granular platform was used. It is concluded that future work into the subject with the use of additional analytical software method, while considering the strength of the subgrade as another variable, would give stronger understanding of how HBM platforms could be designed to the greatest benefit.