Pile group behavior under unsymmetrical cyclic thermal loading in dry silty sand: 1g Physical modeling

Abstract

The effect of unsymmetrical thermal loading on the behavior of 2×2 pile groups is studied using 1g physical modeling. Three tests were conducted with 1, 2 and 3 energy piles in each pile group to apply the cyclic unsymmetrical thermal load. Model piles were closed-end aluminum pipes and the model ground was fine-grained dry silty sand, placed in the container with dry tamping technique. 10 successive heating-cooling cycles with amplitude of ±6°C were applied to the energy piles. Displacements and rotations of the cap, axial forces and bending moments along the piles, changes in soil pressure under the pile tip and temperature distribution around the group are monitored and discussed in detail. A new parameter, named as "pile tip behavior index" (I pt ) is introduced to determine the elastic/plastic state of the soil under the pile tip during each test. Results suggest that build-up of plastic zones in the soil under the energy pile during first stages of the unsymmetrical thermal cycling along with redistribution of the mechanical surcharge among different piles of each group may contribute to cause unallowable rotations of the pile cap.