P>The behaviour of energy piled-raft is different from single energy piles because of the thermal interaction between piles as well as the presence of the raft and its restraint on the piles. The non-symmetric thermal loading of an energy piled raft can trigger unfavourable serviceability conditions of the group in terms of differential settlement and tilting. These unfavourable conditions do not exist in the case of symmetrical thermal loading. Moreover, in soft soils, Operating energy piled-raft non-symmetrically can stimulate more critical scenarios due to the thermal sensitivity of these soils. Previous studies show the critical performance of energy piles in clay due to its plastic contractive behaviour leading to thermally induced excess pore water pressure and hence changing confin...[ Read more ]

The behaviour of energy piled-raft is different from single energy piles because of the thermal interaction between piles as well as the presence of the raft and its restraint on the piles. The non-symmetric thermal loading of an energy piled raft can trigger unfavourable serviceability conditions of the group in terms of differential settlement and tilting. These unfavourable conditions do not exist in the case of symmetrical thermal loading. Moreover, in soft soils, Operating energy piled-raft non-symmetrically can stimulate more critical scenarios due to the thermal sensitivity of these soils. Previous studies show the critical performance of energy piles in clay due to its plastic contractive behaviour leading to thermally induced excess pore water pressure and hence changing confining stress on the pile.

This research aims to study the performance of non-symmetric thermally loaded energy piled-raft in clay. In this study, a series of centrifuge model tests were conducted on piled-raft in kaolin clay with an overconsolidation ratio (OCR) of 1.7 at the pile toe. The serviceability state of floating 2x2 energy piled raft with 3D as well as 5D (D denotes pile diameter) pile spacing was investigated subjected to different non-symmetrical thermal loading patterns. One, two and three piles out of four piles within the group were subjected to 15 thermal cycles of ±14˚C. Thereafter, one more series of centrifuge tests was performed to investigate the effect of applying different thermal load levels on the thermo-mechanical response of non-symmetric thermally loaded energy piled-raft (ΔT = ±14 °C versus ΔT = ± 20 °C ).

The results show that the group settlement gradually accumulated at a reducing rate, and this irreversible settlement increases by operating more energy piles within the group. Unlike thermally induced irreversible settlement, tilting is more critical in the case of operating two energy piles. However, all tests, with ΔT = ±14 °C, showed that irreversible settlement and tilting are within the permissible limit proposed by EN 1997-1 serviceability criterion. The main reason for these results is the presence of soil-raft interaction which helps to reduce the group tilting as the contact pressure provides an additional restoring moment. Due to non-symmetrical thermal loading, an extra bending moment is induced, and it reaches 25% of the cap yield moment. This should be properly accounted for in practice. Additionally, it is found that piled-raft with more number of operated energy piles experienced larger apparent loss of group capacity and hence more reduction of the initial FoS. The initial FoS decrease by 60%, 80% and 90% by operating one, two and three piles out of four piles within the group, respectively. In the case of using 5D pile spacing, the differential settlement between piles decreases significantly and hence tilting decreases leading to a noticeable improvement in serviceability of the group. Tilting of 5D piled-rafts decreased by almost 50% from that of 3D ones. It is recommended for practice to use energy piled-rafts with 5D spacing, especially in clay. This will reduce the expected thermal interaction between operated and non-operated energy piles within the group significantly and hence increase the serviceability of the entire group. Moreover, it is recommended not to use temperature change ΔT = ±20˚C for energy piled-rafts in soft soils. Increasing the applied thermal load by less than 50% results in an increase in the thermally induced settlement of more than double.