Pier thrust in extremely reactive soils

[MrJB]

Hi all, interested to know what approach people use for the design of reinforced concrete piers in extremely reactive soils ie ys>75mm. Depth of suction is about 3500mm. Have always tried to have piers that found through to the stable soils with some slipery mechanism (black plastic etc) yet for some house designs on posts this results in numerous piers and large volumes of concrete. Thanks