Outstanding Issues in Understanding the Behaviour of Thermally-Activated Pile Foundations-PPT Presentation

PPT Presentation

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Thermally activated (TA) piles experience a complementary interaction between thermal stresses and movements, both as single piles and within groups. Their monotonic thermal response is well understood and can be reproduced by appropriately formulated numerical models. However, small-scale tests and analyses show that cyclic thermal loading can cause progressive settlement, or “thermal ratcheting,” though this does not occur in every case.<br /><br />Finite-element analyses examined cyclic loading based on Milan’s climate, varying shaft-resistance factor of safety and pile spacing. The results indicate that the initial mechanical load is critical: ratcheting generally begins when more than about 80–90% of the available shaft resistance is mobilised. Below this range, behaviour is largely thermo-elastic. In an isolated pile, the first settlement increment occurs during cooling, as confining stress on the shaft decreases. Further increments occur during heating, accompanied by increased base reaction.<br /><br />Pile spacing also affects group behaviour. At sufficiently close spacing, the ground between piles can reach a steady thermal state, reducing settlement and increasing tensile thermal stresses.<br /><br />The causes and practical significance of ratcheting remain uncertain. High mobilisation or reduced shaft resistance in numerical models may help explain it, while thermal soil compaction or degradation of friction resistance may also contribute. Further investigation is needed to quantify these effects and reconcile analytical findings with experimental observations.

Keywords

thermally activated piles

thermal ratcheting

cyclic thermal loading

finite-element analysis

shaft resistance

pile spacing

monotonic thermal response

settlement

thermal stresses

soil-pile interaction