Anti-freezing method and apparatus for ground surrounding liquified gas storing underground tank
DETAILED DESCRIPTION OF THE INVENTION 
     This invention relates to a method and an apparatus for anti-freezing of the ground surrounding a liquified gas storing underground tank. 
     In general, the ground surrounding a liquified gas storing underground is necessarily frozen because of an extremely low (sub-zero) temperature of liquified gas, with the result that a pressure is produced due to freezing and resulting expansion of water, and the pressure thus produced acts on a body proper and the peripheral construction of the tank, thus impairing the safety of the tank. 
     For this reason, there has been proposed an attempt such as to provide a protective wall around the tank or to pump out underground water in the peripheral ground of the tank for reducing a pressure caused by the freezing of water. However, the former attempt poses a problem that there is required an expenditure of much time and efforts for the construction of a protective wall, and in addition, the construction of the tank itself should be high in strength, thus increasing the cost of construction of an underground tank. The latter attempt suffers from disadvantages in that pumping of underground water for a long period of time, and the operation is attended with difficulties, and the safety of the underground tank can not be necessarily be insured, in the event of a trouble of a pump device. 
     It is accordingly a principal object of the present invention to provide a method and an apparatus for anti-freezing of the ground around the tank, by warming same with water being circulated. 
     It is another object of the present invention to provide a method and an apparatus for anti-freezing of the ground surrounding an underground tank, which are simple in operation and control, and may warm the ground in an efficient manner. 
     It is a still another object of the present invention to provide a method and an apparatus for anti-freezing of the ground surrounding a tank, which allows a simple construction with less expensive materials and equipments. 
     It is a yet another object of the present invention to provide a method and an apparatus for anti-freezing of the ground surrounding a tank, which permits the stable and safe use of the tank for a long period of time. 
     According to the present invention, there is provided a method for anti-freezing of the ground surrounding a liquified gas storing underground tank, in which the ground is excavated into a columnar or wall-shaped cavity and then a water impermeable envelope is placed therein, after which granular materials such as sand and/or gravel is filled therein, thereby providing a columnar or wall-shaped water permeable body. In addition, water at a given temperature is fed into the water permeable body for warming the ground surrounding the tank to prevent the freezing thereof. 
     In addition, according to the present invention, there is provided an apparatus for use in the aforesaid method, which includes water feeding and discharging devices are provided for feeding and discharging water into or from the aforesaid water permeable body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-sectional view of an anti-freezing apparatus according to the present invention; 
     FIGS. 2A and 2B are longitudinal cross-sectional, detailed views of the anti-freezing apparatus according to the present invention; and 
     FIGS. 3, 4, 5 and 6 are longitudinal cross-sectional views of the anti-freezing apparatus according to the present invention, which are given in the order of its construction. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, water permeable bodies 3 of the number required are buried in the ground 2 surrounding a liquified gas storing underground tank 1, and then water at a given temperature is continuously introduced into the water permeable bodies to fill up the water permeable bodies from their bottoms to their tips, and then water is discharged from the tops, respectively. The ground around the water permeable bodies 3 may be warmed with the above water, so that the freezing of ground may be prevented. 
     The water permeable body 3 may be prepared by excavating the peripheral ground 2 into a vertical hole 4 and then charging granular materials 5 such as sand or gravel therein. Thus, water permeable body 3 of columnar or wall-shape may be formed, with its periphery enclosed with a water impermeable envelope or bag 6. In FIG. 2A, a water feeding pipe 7 is inserted into the water permeable body 3, so that water at a given temperature may be fed into the water permeable body 3 from its bottom continuously. Water injected into the water permeable body 3 fills the body 3 from its bottom to its top, progressively, through the granular materials filled therein, after which water is discharged into a water discharge channel 9 which is provided close to the top of the body 3 and leads to a river or the like, or water is warmed again to a given temperature and then supplied to the water permeable body 3 through the water feeding pipe 7. 
     As another embodiment, as shown in FIG. 2B, water having a given temperature may be continuously injected into the water permeable body 3 from its top portion through the pump 8. The water injected into the water permeable body 3 permeates through the granular materials down to the bottom of the water permeable body 3, and then the water may be pumped up by a pump 8&#39; through a drain pipe 7&#39; and collected into the water discharge channel 9. 
     The temperature and amount of water to be injected into the water permeable body 3 depends on the temperature of the peripheral ground of the water permeable body 3, the volume and number of the bodies 3. 
     FIGS. 3 to 6 show the steps of the method for constructing the anti-freezing apparatus according to the present invention. 
     As shown in FIG. 3, the ground is excavated by means of an excavator 10 by using a bentonite solution 11, thereby forming a vertical hole 4. Then, as shown in FIG. 4, an envelope or bag 6 made of water impermeable sheet such as a synthetic resin sheet and having a weight 12 at its lower end is inserted into the vertical hole 4. Then, the water feeding pipe 7 is inserted into the vertical hole 4. Then, the water feeding pipe 7 is inserted into the envelope 6 and thereafter, as shown in FIG. 5, gravel is first filled therein, followed by sand, and finally gravel again, thereby forming the water permeable body 3 consisting of granular materials. Meanwhile, the bentonite solution 11 which has overflown from the top of the hole 4 due to the charging of granular materials 5 therein is discharged as required. Finally, a water discharge channel 9 is provided close to the top of the water permeable body 3, as shown in FIG. 6, and then the water feeding pipe 7 is connected to a pump 8. 
     Meanwhile, the water permeable body 3 may consist of a steel pipe inserted into the ground, with the interior thereof filled with granular materials 5. In addition, water may be introduced into the water permeable body from its top and then pumped from its bottom through a water discharge pipe.