As a ribbed raft slab has no trenching, what holds it in place?

The only ground penetrations in the Palace Pod ribbed raft waffle slab system are 300mm diameter holes dug at a number of rib intersections to form seismic piles called shear keys. Poly Palace also supply polystyrene shear key supports, circles of 100mm thick polystyrene that are often required at the bottom of pile holes. 

The depth and number of seismic piles are specified by the consulting engineer, to match the structural performance of the building with the earthquake requirements of the site.