Pile foundations of buildings have been studied as “heat exchangers” (so-called “energy-piles”) in the way that fluid circulates in a pile foundation as well as inside building to save energy usage [Laloui et al., 2003; Hamada et al., 2007]. The application ascertains the potential of the building foundation to be part of a comprehensive renewable energy system. We can also utilize building foundations in different way of energy storage in which air is compressed using an excess energy generated from solar panels and then it is stored in a hollow steel pipe pile so that the stored compressed air can be used later (the idea was initially proposed by Zhang et al. [2012]; concept is shown in the figure below): CAES (Compressed Air Energy Storage) pile.

 

For the successful operation of CAES pile, comprehensive study is needed to confirm mechanical integrity of the whole system that is subjected to repetitive cyclic pressure loadings during the long period. Repeated loading is known to cause progressive shear stress degradation due to gradual densification of soil layer adjacent to structural surface as well as reduction in normal stress [Poulos, 1989; Fakharian and Evgin, 1997; Mortara et al., 2007]. In this group, we are attempting to explore in detail the mechanical behavior of a pile when internal pressure is increased and then decreased back to an original value as a result of compressed air energy storage (i.e., pressure cycle). We then will extend our investigation to the long-term behavior of a CAES pile, such as strain-ratcheting and plastic deformation around a pile.