Geotechnical design and analysis Subject:
I am designing drilled piers and driven piles foundation system for a bridge. There are some thin strata (less than 300mm thick) of gypsum within the sound bedrock. Though the pier will be penetrated at least 3m into the sound bedrock, should I be concerned with gypsum layers on the sides and any layers below the bearing surface.
Gypsum lenses is 300mm thickness only, for pile foudnation, it appears to have little impacts on bearing capacity and side friction of piles.
However, geochemistry has to be included as part of geotechnical assessment. There are two cases: (1) Gypsum layer is higher than groundwater level, water chemistry will be controlled by Gypsum; please check water corrosion, especially SO4;
(2) If Gysum layer is higher than groundwatre level, problem maybe less, but don't forget rainfall effects.
In either case, groundwater sampling and chemistry analysis has to be carried out to determine the necesseity of use anti-sulphate cement for pile and steel (reinforcement).