Report 305 Review of lime piles and lime-stabilised soil columns

Publication Year

1997

Document Status

Current

Abstract

There is a requirement for cheap, simple and effective methods of improving stability for ageing earthworks slopes on the national motorway network. To be acceptable, methods should be long lasting and not give rise to maintenance problems in the future; they also should not require excessive lorry movements during installation or much disposal of spoil. Lime piles (small-diameter boreholes filled with quicklime) have been proposed as a method of improving slope stability, and this Report reviews their possible use for this purpose. Lime-stabilised soil columns (larger-diameter holes filled with lime-stabilised soil mixed in place) have been used for many years to improve bearing capacity and reduce settlement and, because of their similarity to lime piles, are included in this review. The proprietary Colmix process, which is a method of producing in-situ stabilised soil columns using a mixture of lime and cement as the binder, is also reviewed. It offers the advantage of a proven technique that has already been used to improve the stability of in-service embankment slopes. Lime and the effects of lime on clay soils are also reviewed, and the clays most at risk from slope instability are compared with the clays most suitable for treatment with lime. It is concluded that all the clays most at risk would respond to lime treatment. Some of the considerations that need to be borne in mind when designing a lime pile or lime-stabilised soil column are outlined. The importance of obtaining reliable values for the pile-to-soil shear strength ratio is stressed. The review concludes that both lime piles and lime-stabilised soil columns could be used to improve earthworks slope stability, because the shear strength of the pile or column is likely to be greater than the shear strength of the soil in which the installation is made. Reinforced lime piles (ones having a central, steel reinforcing bar) would be more effective than ordinary, non-reinforced, lime piles. Lime piles give rise to spoil that may have to be transported off site and disposed of Lime-stabilised soil columns, including Colmix columns, are said not to produce spoil but this needs to be verified for British clays. This may be an important operational consideration on motorways.

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