Stabilization of Shallow Slope Failures with Lime Piles

Lime piles essentially consist of boreholes filled with lime. They have been used to stabilize slopes in many countries worldwide but have not been adopted as a standard means of stabilization in any country. The literature on the subject makes several claims about the way lime piles stabilize the soil. However, the reported results of experimental work are in some cases contradictory and are too few to facilitate appropriate engineering judgment of the stabilizing mechanisms. Research at Loughborough University, United Kingdom, has investigated the use of quicklime piles in the context of stabilization of shallow slope failures in clay slopes. The stabilizing mechanisms observed in a series of laboratory and field investigations are ( a) increased strength of an annular zone of clay surrounding the pile caused by lime-clay reaction, ( b) clay dehydration, ( c) generation of negative pore-water pressure, ( d) over-consolidation of the soil in the shear plane, and ( e) pile strength. The idea of lateral consolidation of the clay surrounding the pile as a result of physical pile expansion has been shown not to occur in the case of augured quicklime piles sealed with a clay plug at the surface. Data are presented to quantify each of the stabilization mechanisms and advice is given on how to use the data in design. It is concluded that lime piles provide a potentially valuable addition to the techniques available for shallow slope stabilization and are particularly suitable for sites with access problems.