When wet, the soil volume can increase by 10% or more, creating massive upward pressure.

Chen is a pragmatist. He does not advocate one solution but matches the foundation to the degree of expansion. His PDF covers four main approaches:

High-density polyethylene (HDPE) geomembranes placed 2–3 feet below grade can isolate the foundation from moisture changes. Chen’s era used clay caps; we now use engineered liners.