Have you heard piles are sometimes heaved? Is this not strange that pile can lift out without any action of uplift generated by structural members? Structural member can produce uplift due to foundation settlement of one end and uplifting another end or earthquake generated pull out force or same by the action of wind. These causes are found in regular structural distress and we used to face such phenomenon and engineers provide safety factors to neutralize these uplift forces.
Yes friends, this can happen in construction of pile foundation when a site has plastic clay in saturated condition. During driving piles into plastic clay it displace an amount of soil. The amount of soil may be as large as the volume of pile itself. Mentioning again the soil should be:
a. Plastic clay
b. Soil in saturated condition.
This displacement phenomenon results another occurrence-this is heaving action. This heaving action not only lifts out structures adjacent to this driving site but also results coming out of piles, driven previously.
Normally Foundation engineers calculate pile capacity considering both skin resistance and end bearing. This capacity is calculated summing a skin resistance in each stratum and also end resistance in the end bearing stratum. If a pile heaved out then it lifted up from its desired depth and pile capacity becomes less.
Embedment length reduction during lifting also results less skin resistance. Friends these piles that heaved out resulting less bearing resistance is called heaved pile. Dear reader please stay with this blog we are providing every answerer of what, why, how in foundation and concrete engineering.