In this paper, the method of numerical analysis to estimate the frost heaving pressure and the amount of frost heaving caused by the freezing phenomenon of the circumferential ground of LNG inground tank is described. Using the developed program based on the analytical method, in which the non-linear mechanical properties of frozen and unfrozen soils and the characteristics of frost heaving of soil materials are taken into account, the mechanical behaviours of the real LNG inground tank (which has the capacities of 60,000 kI) and the circumferential ground due to the freezing phenomenon of the ground have been taken hold of quantitatively. Furthermore, the comparison of the results due to the theoretical equation proposed by Takashi to estimate the frost heaving pressure with the results obtained by the numerical analysis are performed and the problems of the case that estimate it in the former are pointed out.
In recent years, inground-type tank constructed as the storage facilities of Liquefied Natural Gas (hereinafter referred to as LNG) consumed for fuel of thermal power plant in Japan. However, for the reason that LNG being stored into the tank has the extreme low temperature (i.e., -162°C), there are many problems such as follow. Namely,
Some technical problems when construct a large caliber tank in the ground.
Some problems regarding with the characteristic of materials that compose the inground tank.
Some problems caused by freezing phenomenon of the ground around inground tank.
Therefore, on the design and the execution of the construction for the tank, it is a passing need to make clear the behaviours of the tank and the circumferential ground under the temperature fall. Especially, because the frost heaving pressure (that is, earth pressure) and the amount of frost heaving (that is, an amount of deformation) caused by freezing phenomenon of the ground act on the tank and the circumferential attached facilities, it is important to predict those influences quantitatively. Accordingly, the authors have been attempting to take hold of analytically the behaviours of the case that the tank and the ground freeze (Ito, 1979a, 1979b). This paper is intended to describe the results estimated the mechanical behaviour of LNG inground tank and the circumferential ground using the developed program based on axi-symmetrical FEM.
LNG inground-type tank make a general classification into the outside bucket and the inside bucket structurally. The outside bucket is composed of the side wall and the bottom plate and is built in reinforce concrete. The contact part between the bottom plate and side wall is the hinged structure. The structure of the outside bucket is decided'' by estimating to the earth pressure, lift of ground water, frost heaving pressure and an amount of frost heaving. On the other hand, the inside one is the membranous structure built in stainless steel and the structure is decided by estimating to the thermal shrinkage and the degree of airtight and liquid-tight.
