Biopolymer treatment for stabilisation of transport infrastructure slopes

Slope failures (landslides) cause significant disruption to our transport network. In 2015 143 failures like these were recorded on the rail network alone. In addition to causing frustrating delays these failures also cost a significant amount to repair. Failures usually occur during winter months as a result of high rainfall but this is just the end point of a process which may have been occurring for several years. Long exposure to the UK's changing weather causes the compacted clay soil which forms the embankments that our highways and railways are built upon to weaken over time. Very fine cracks develop as the soil is repeatedly dried out and then re-wetted by periods of dry and then wet weather. This effects the way water moves through the soil, the cracks allow water to get deep into the slope very quickly and large pressures can build up, pushing soil particles apart. Ordinarily, during hot dry weather the opposite happens. Water is taken out of the soil by the action of evaporation and transpiration of plants, this induces negative pressures which force soil particles together, strengthening the slope. These negative pressures build up during the summer and help keep the slopes stable during the winter. The capability of soils to generate these negative pressures is reduced by the formation of cracks. A combination of these factors can weaken the soil to such a point where one large rainfall event can cause a slope to de-stabilise.

This project will develop a new way of strengthening soil slopes and preventing these types of failure from occurring. Biopolymers, naturally occurring polymers formed by the action of microorganisms, can be added to soil to improve its strength and reduce the potential for cracking. The biopolymers mix with water in the soil to form gels which bind with soil particles giving the soil greater strength and reducing permeability. Biopolymers are already utilised in cosmetics and food as thickening agents so they are relatively cheap. They also do not require significant amounts of energy to produce and therefore they are not associated with high carbon dioxide emissions like other potential soil binders (e.g. cement and lime). Whilst the potential of biopolymers has previously been identified they have not been applied to slope stability problems and the way they form bonds and fill soil pores has not been studied fully. This project will carry out a detailed investigation of how biopolymers interact with compacted soils and use the information gathered to develop a new binder suitable for use in the repair and maintenance of highway and railway embankments.

The research described in this proposal will provide a proof of concept for a new method of stabilising engineered slopes at risk of failure.

Academic benefits
The study will produce a greatly improved understanding of the mechanisms that cause deterioration of engineered soils and how to prevent this deterioration from occurring. The study will collect a detailed data set of soil property interrelationships during weather cycling. This data is vital for the proposed project and will also be valuable to geotechnical researchers developing new tools and techniques for predicting future engineered slope behaviour. A further academic benefit will be an improved understanding of how biopolymer binders influence soil properties and the mechanisms through which this occurs. This knowledge could be applied to other areas of ground improvement research such as the treatment of contaminated land and in wider civil engineering research in the production of structural elements such as rammed earth blocks.
The post-doctoral research associate working on the project will benefit through having the opportunity to interact with a range of stakeholders whilst conducting research in a rapidly developing topic. At the end of the project the geotechnical academic community will have gained an experienced researcher, conformable interacting with stakeholders and with detailed knowledge new binder technologies.

Economic Benefits
The study aims to prove the concept of using biopolymer stabilisers for slope stabilisation works and as such aims to introduce a new type of binder to the market place. Production, marketing and sales of a new product such this will generate considerable economic activity and provide new opportunities for businesses. It is hoped that using biopolymer will prove cheaper than existing types of slope stabilisation works and hence there will be a financial saving to infrastructure asset owners on the costs of repair and maintenance activities. Ultimately it is expected that utilising biopolymers will improve the long term stability of slopes reducing the number of disruptive failures and consequent loss of productivity.

Societal Benefits
The principal societal benefit from the research outlined in the proposal will be a reduction in transport delays due to earthworks failures. Improved slope stability also means less likelihood of dangerous slope failures with the potential to derail trains or injure motorists.

Environmental Benefits
Biopolymers require less energy to produce than standard cementitious materials such as Portland cement or lime. Consequently there is a potential Carbon Dioxide emission saving to be made by their use.