Why is sleeving applied in piles constructed on slopes?

For high-rise buildings constructed on steep cut slopes, these buildings are usually supported by large diameter piles. Though the piles are founded at some depth below the slopes, lateral load arising from wind on buildings may induce loads on the slop and causes slope failures. For shallow depths of slope which is marginally stable, it is more vulnerable to slope failure.

Hence, an annulus of compressible material called sleeving is introduced in piles so as to reduce the transfer of lateral loads from buildings to slopes.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.