Chen proposes that the magnitude of heave is directly proportional to the thickness of the active zone. If your foundation bears on soil within the active zone, it is floating on a moving platform. If you anchor below it, you are safe from heave (though you must consider the friction of the surrounding soil pulling down on the pile—a concept known as "negative skin friction" or downdrag in other contexts, but "uplift friction" here).
Typical calculations and design checks
: Designing rigid systems that can withstand differential movement [17, 20]. foundations on expansive soils chen pdf
I hope this guide helps! Let me know if you have any questions or need further clarification. Chen proposes that the magnitude of heave is