Hydro-mechanical properties of lime-stabilised shrinkable UK clays

Some clay soils of high plasticity show large volumetric changes in response to seasonal cycles of wetting and drying. Such clays are called shrinkable or expansive clays. In the UK, a range of shrinkable clays can be found in South and East England. Due to their presence, seasonal variations in moisture content can cause annual surface movements as high as 50mm. This can cause significant distress and damage to civil engineering structures (in particular light buildings and pavements). Previous research has estimated that the damage caused by shrinkable soils may be higher than damage due to any other natural hazard, including earthquakes and floods. This can result in millions of pounds of damage to homes every year, as several millions of homes are affected, and has also led to a rapid increase in insurance claims for 'subsidence damage' to low-rise buildings, principally housing, in the UK. Maintenance and repair cost of the affected infrastructure (pavement, railway tracks etc) can also be very high and may incur severe traffic delays.One method to improve the engineering properties of the shrinkable soil and prevent damage to structures is to stabilise the soil using chemical additives and in particular lime. The technique is particularly attractive, as it allows the improvement and use of the soil in-situ. For this reason, it is often a more economic (in terms of both time and money) and environmentally-friendly alternative to the conventional methods, which involve removal and disposal of the unsuitable soil to landfills and its replacement with imported quarried aggregate material. When the lime-treated material is in place it is subject to environmental effects, including seasonal cycles of wetting and drying. This implies that during its design life, the lime-treated soil will be at different states, from being fully saturated with water, to almost completely dry. When the soil is in a partially saturated state, its behaviour and properties are fundamentally different from those when it is fully saturated. It is therefore important to know its properties and behaviour in both states. Such a complete picture of the lime-treated soils is currently lacking.With the scope of an increased use of the technique in a wider range of projects and applications, the need has emerged for predictive numerical tools able to describe the behaviour of lime-treated soils for a variety of problems and conditions (including partially saturated soil conditions). Such tools are not available at the moment for this type of soil. The aim of this research is to develop computer software which will allow predictions to be made. This will be based on new experimental data on lime-treated UK clay soils, which will allow to create an appropriate model for the behaviour of the lime-treated soil. An additional novelty of the research is that both fully saturated and partially saturated soil conditions will be considered. The predictive tool will enable engineers to perform sophisticated analyses and to make better informed decisions on the behaviour of lime-treated materials in a variety of applications. The research is timely as with extreme weather conditions becoming more common due to climate change, engineering problems due to cyclic shrinkage/expansion of soils are expected to rise in the years to come. Moreover there is currently an increased environmental and economic pressure to upgrade material by stabilisation of in situ soil, as an alternative to its export to landfill and replacement by imported granular fill. In particular, the EU Landfill Directive on the Landfilling of Waste (Council Directive 1999/31/EC) which has also been transposed to Britain, is based on the policy objective to manage resources in a more sustainable manner. Improving the in-situ soil with lime is a sustainable solution, as it saves construction time and money (including landfill taxes) and reduces emissions from vehicles.