JP2009257048A - Low temperature base rock storage tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane system low temperature base rock storage tank capable of sufficiently improving structural stability and reliability, by eliminating adverse influence by the freezing expansion. <P>SOLUTION: A lining composed of spraying concrete 2, skeleton concrete 3, a cold insulator 4 and a membrane material 5, is arranged on a surface of a cavity 1 formed by excavating base rock, and its inside space is formed as a storage tank for storing a low temperature fluid. An underground water flow (f) flowing toward a drainage channel network is generated in the surrounding base rock of the cavity by arranging the drainage channel network 6 for collecting and draining underground water from the surrounding base rock into the spraying concrete, and an unfreezing area can be formed around the cavity by maintaining the temperature of the surrounding base rock of the cavity at the freezing temperature or above by its underground water flow. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a low-temperature rock storage tank that uses a cavity excavated in the rock as a storage tank (tank) for storing a low-temperature fluid.

  This kind of low temperature rock storage tank excavates a large-scale cavity in a stable rock mass, and makes the cavity function as a tank to make low temperature liquefied gas such as LPG, LNG, DME (dimethyl ether) or other low temperature liquid or low temperature A gas is stored, and a so-called “freezing type” as shown in Patent Document 1 and a so-called “Patent Document 2” as shown in Patent Document 1 depending on a lining structure provided on the inner surface of the cavity. It is roughly classified into “membrane type”.

In the cryogenic low temperature rock storage tank, the stored water is at a temperature below freezing point, so the groundwater around the storage tank naturally freezes to form a freezing area around the storage tank.Therefore, there are some cracks and gaps in the rock mass. However, it can be expected that the air tightness and liquid tightness of the storage tank are naturally secured. Therefore, it is possible to omit a special lining material and large-scale lining just by providing a simple support such as sprayed concrete and rock bolts on the inner surface of the cavity, and the construction is relatively simple and the construction cost is suppressed. This is advantageous in that
However, since such a freezing type is concerned that temperature cracks may occur in the rock if the storage temperature is extremely low, the storage temperature is limited to about −60 ° C. to −80 ° C. Therefore, the DME (boiling point) -25 ° C) and LPG (boiling point -42 ° C), which can be suitably used for fuels with relatively high storage temperatures, but is not suitable for cryogenic fluids such as LNG (boiling point -162 ° C). It is said that.

On the other hand, the membrane-type cryogenic rock storage tank was proposed to be applied to the storage of cryogenic particles such as LNG, and the membrane material ensures the airtightness and liquid-tightness required for the storage tank. It is. In this case, concretely, a lining with sprayed concrete and framed concrete is provided inside the cavity, and a lining with a multilayer structure is provided in which a membrane material is attached to the surface after a cold insulation material is provided on the inside. Therefore, although the structure is more complicated than that of the freezing type, it is difficult to be affected by the rock, and as with the freezing type, a freezing region is formed outside the storage tank. Since it can be considered as a next barrier, it is considered more advantageous in terms of reliability and stability.
JP-A-2005-195110 Japanese Unexamined Patent Publication No. 7-54366

By the way, a freezing low-temperature rock mass storage tank must have a good freezing area around the storage tank after operation, so even when excavating a cavity as a storage tank, the surrounding rock mass is always saturated. It needs to exist. In other words, when excavating a cavity, if the groundwater level of the surrounding rocks declines and becomes temporarily unsaturated, even if the groundwater level is subsequently recovered, it is difficult to recover to a fully saturated state. For this reason, it is assumed that a good freezing area is not formed around the storage tank even after operation, and there is a concern that the problem may remain in terms of reliability and safety required for this type of facility.
Therefore, when constructing a cryogenic low-temperature rock storage tank, prior to excavating the cavity as a storage tank, a large-scale water injection tunnel or water injection boring hole is pre-constructed above it, and from there to the surrounding rock mass in the cavity excavation area It is said that it is necessary to excavate the cavity while maintaining the surrounding rock mass in a saturated state by continuously performing a large amount of water injection as artificial groundwater recharge, which requires a lot of labor and cost. It was.

On the other hand, in the membrane-type low-temperature rock storage tank, it is advantageous to perform excavation by reducing the groundwater level around the cavity and making the surroundings dry during construction. In other words, in the case of the membrane type, a skeleton body is constructed in a cavity excavated in the ground, but if such construction is performed in a bedrock deeper than the groundwater level, a large amount of groundwater inflow occurs. In addition, large groundwater pressure acts as an external pressure on lining materials during construction, especially concrete and membrane materials, so it is extremely difficult to ensure construction accuracy and construction accuracy. is there.
Therefore, when constructing a membrane-type low-temperature bedrock storage tank, the groundwater level is lowered by draining the groundwater from the surrounding rocks in the same way as in ordinary subsurface construction, so that the construction area is dry and the cavity is excavated and covered. It is necessary to construct. For this purpose, a large drainage tunnel and drainage borehole for collecting and draining water are pre-constructed below the area where the cavity should be excavated, and a large amount of groundwater is pumped from there to lower the groundwater level. It is necessary to keep the surroundings dry, and much labor and cost are required to implement such a large-scale drainage method. In addition, even with such construction methods, it is assumed that it cannot always be sufficiently dry depending on the condition of the bedrock, in which case the groundwater pressure acts on the lining and the workability is not good, and the construction quality may be adversely affected. There is.

  Also in the case of the membrane type, the groundwater level will eventually recover by stopping drainage from the surrounding rock mass after the start of low-temperature storage after completion of the storage tank, so that after operation, a frozen area will be formed around the storage tank. Although it is thought that it functions as a secondary barrier, as described above, the surrounding rock mass is desaturated during construction, so there is no guarantee that a good frozen area will be formed. Since it is assumed that a sufficient function as a barrier cannot be expected, it is necessary to design the lining in anticipation of this.

  In addition, after the storage tank is completed, it cools down in a short time and starts low-temperature storage, but if the area around the storage tank is not sufficiently dry, large groundwater pressure acts locally, or freezing expansion causes the surrounding rock mass Concerns about the occurrence of abnormal cracks cannot be completely denied, and it is necessary to eliminate the adverse effects of groundwater pressure and freezing expansion as much as possible in order to ensure structural stability and reliability. It is considered.

In Patent Document 1, water is circulated in a water-sealed boring provided in a bedrock above the storage tank for the purpose of preventing the frozen region formed around the storage tank from reaching the surface area. It is disclosed that the surrounding ground is maintained above the freezing temperature. Patent Document 2 discloses that a surrounding pipe rock is prevented from being frozen by a heating pipe as a well-known technique in a general underground tank for LNG.
If such anti-freezing method is applied to the surrounding rock mass of membrane type low-temperature rock mass storage tank, it is thought that the adverse effect on the lining due to freezing and expansion can be prevented. No method has been proposed.

  In view of the above circumstances, the present invention can effectively eliminate the adverse effects of receiving groundwater pressure from the surrounding rock mass and the freezing and expansion of the surrounding rock mass, and sufficiently improve the structural stability and reliability. An object of the present invention is to provide a membrane-type low-temperature rock mass storage tank having an effective and suitable structure.

  The present invention is a membrane type in which a cover made of sprayed concrete, reinforced concrete, cold insulation material, membrane material is provided on the surface of a cavity formed by excavating a rock, and the internal space is used as a storage tank for storing a cryogenic fluid A low temperature rock storage tank of the above-mentioned, in which the drainage channel network for collecting and draining groundwater from the surrounding rock mass is provided in the sprayed concrete, and flows toward the drainage channel network in the surrounding rock mass of the cavity A groundwater flow is generated, and the temperature of the surrounding rock mass of the cavity is maintained at a freezing temperature or more by the groundwater flow, so that a non-freezing region can be formed around the cavity.

In the present invention, it is conceivable to provide a water injection well for recharging groundwater by pouring water from the ground surface to the surrounding rock mass of the cavity above the cavity.
In addition, it is conceivable to provide a draining boring hole that leads to the drainage channel network in the surrounding rock mass of the cavity, and in that case, a highly permeable crushing region is formed in the surrounding rock mass of the draining boring hole It is preferable to do.

In this type of conventional low-temperature rock storage tank, since groundwater is retained in the surrounding rock mass of the cavity, the groundwater is frozen and a frozen region is formed around the cavity. In the rock storage tank, groundwater in the surrounding rock is actively collected by the drainage network and drained, so that a groundwater flow that flows toward the cavity naturally occurs, and such a groundwater flow is always secured. This keeps the temperature of the surrounding rock mass above the freezing temperature. Therefore, in the low-temperature rock storage tank of the present invention, a non-freezing region is naturally formed around the cavity, thereby eliminating the adverse effects caused by freezing and expansion, which has been a concern in the past, and the structural mechanical reliability and safety of the lining Can be secured sufficiently.
In addition, since groundwater in the surrounding rock mass is always collected by the drainage network and drained quickly, excessive groundwater pressure does not act as external pressure on the lining after the storage tank is completed. Also, the structural mechanical reliability of the lining can be improved.
In addition, it is possible to drain from the surrounding rock mass through the drainage network at the construction stage, thereby providing a large drainage tunnel and drainage boring hole as in the case of constructing a conventional membrane-type storage tank. It is not necessary to dry the entire surrounding rock mass, so that the workability can be sufficiently improved and the construction period can be greatly reduced and the construction cost can be reduced.

If sufficient groundwater flow cannot be expected due to the low groundwater level of the surrounding rock mass, a groundwater flow can be maintained by maintaining a high groundwater level by installing a well for groundwater recharge above the cavity. It can be ensured.
In addition, if the surrounding rock mass is low in permeability and sufficient groundwater flow does not occur, drain boring holes leading to the drainage channel network can be formed in the surrounding rock mass, and a crushing area can be formed around it. In this way, the permeability of the surrounding rock mass can be increased so that the groundwater flow can be generated more reliably, and thereby the non-frozen area can be reliably formed.

1 to 3 show a schematic configuration of a low temperature rock storage tank according to an embodiment of the present invention.
The low-temperature bedrock storage tank of this embodiment is formed by sequentially stacking sprayed concrete 2, concrete frame 3, cold insulation material 4, and membrane material 5 on the inner surface of a tunnel-shaped cavity 1 having a substantially horseshoe-shaped cross section formed in the bedrock. By forming a membrane type lining, it functions as a storage tank (tank) for low-temperature fluids such as LNG, LPG, DME, etc. In the shotcrete 2, there is a drainage channel network 6 for always collecting and draining groundwater from the surrounding rock mass.

In other words, this kind of conventional low temperature rock storage tank is based on the fact that the freezing area that naturally occurs in the surrounding rock mass due to the storage of the low temperature fluid as described above is also used as a secondary barrier. Since various adverse effects due to expansion may be a problem, the cryogenic rock storage tank of this embodiment does not intentionally generate such a frozen region.
For this purpose, in this embodiment, a drainage channel network 6 is buried in the shotcrete 2, and groundwater in the surrounding rock mass is actively collected by the drainage channel network 6 to flow into the cavity 1. The groundwater flow f that flows toward the drainage network 6 is naturally generated in the rock around the cavity.

As the drainage network 6, for example, a resin molded product, a porous material, a perforated pipe, or the like that is used as a material for slope drainage in the field of civil engineering work can be used. As shown in Fig. 2, a long strip plate-like drainage material having a flat rectangular cross section is used, and it is installed along both the axial direction and the circumferential direction of the cavity 1. Yes.
That is, on the bottom surface and the peripheral surface of the cavity 1, plate-shaped drainage materials that become the vertical drainage channel 6 a along the axial direction of the cavity 1 and the horizontal drainage channel 6 b along the circumferential direction are arranged in a state where they intersect each other at a predetermined interval. As a result, the drainage channel network 6 is formed as a vertical and horizontal grid network. The drainage network 6 is connected to a main drainage groove 7 provided at the center of the bottom of the cavity 1, and a main drainage pipe 8 such as a perforated fume pipe is laid in the inside. These main drain grooves 7 and main drain pipes 8 are preferably inclined downward toward the wellhead and drained by natural flow.

  In the present embodiment, by providing the drainage network 6 as described above, a groundwater flow f that always flows toward the cavity 1 side is generated in the surrounding rock mass of the cavity 1 as shown in FIG. By f, the temperature of the surrounding rock mass is prevented from dropping below the freezing temperature, whereby a non-freezing region can be naturally formed around the cavity 1.

  That is, in the conventional general low temperature rock storage tank, the rock surrounding the cavity is cooled by the cryogenic storage fluid and becomes below the freezing temperature, so that the groundwater staying there freezes. As described above, if the groundwater flow f always flows with a sufficient amount of water and a sufficient flow velocity so that the groundwater does not stay, the stored heat amount of the groundwater is always transferred to the surrounding rock mass (that is, Therefore, the surrounding rock mass that is being cooled below the freezing temperature is always warmed by groundwater having a water temperature of about room temperature), and thus the temperature of the surrounding rock mass can be maintained above the freezing temperature. Of course, since running water is generally more difficult to freeze than static water, if the groundwater flow f flows at a sufficient flow rate and flow velocity, it will not freeze immediately even if the bedrock temperature is below freezing point. The water is quickly drained through the drain network 6 without any gap.

This will be further described with reference to FIG. “Heat” as a physical quantity flows from the high temperature side toward the low temperature side (heat is transferred), so that the low temperature side is heated (heated), but here the high temperature flows from the low temperature side toward the high temperature side. A hypothetical concept of “cooling heat” for cooling the side is assumed.
As shown in FIG. 3, it is assumed that the cold heat quantity Q1 is transferred from the cavity 1 side to the surrounding rock mass through the membrane material 5, the cold insulating material 4, the frame concrete 3 and the shotcrete 2, and conversely, from the surrounding rock mass to the cavity 1 side. Assuming that the amount of heat (original amount of heat) Q3 is transferred, if the groundwater is retained as usual, the amount of cold Q1> the amount of heat Q3, and the temperature of the bedrock gradually decreases. Eventually it will freeze.
However, when the groundwater flow f is positively generated by collecting and draining the groundwater through the drainage channel network 6 as in the present embodiment, a part Q2 of the cold heat quantity Q1 is caused by the groundwater flow f. The heat is dissipated outside the system, and the amount of cold heat transferred to the rock is reduced accordingly. And if the thermal equilibrium which becomes Q1-Q2 = Q3 arises, it will be possible to maintain the rock mass temperature at a constant temperature and prevent it from becoming below the freezing temperature.

  As described above, according to the low temperature rock storage tank of the present embodiment, the surrounding rock mass is prevented from freezing by generating the groundwater flow f in the surrounding rock mass by the drainage channel network 6 embedded in the shotcrete 2. Thus, adverse effects caused by freezing and expansion, which has been a concern in the past, can be eliminated, and the structural mechanical reliability and safety of the lining can be sufficiently secured.

In addition, groundwater in the surrounding rock mass is always collected by the drainage network 6 and quickly drained through the main drainage pipe 8, so that excessive groundwater pressure acts on the lining as an external pressure after the storage tank is completed. In this respect, the structural mechanical reliability of the lining can be improved.
In addition, it is possible to drain from the surrounding rock mass through the drainage network 6 even at the construction stage, so that large drainage tunnels and drainage boreholes can be formed as in the case of constructing conventional membrane-type storage tanks. It is not necessary to provide the entire surrounding bedrock to be dry, so that the workability can be sufficiently improved and the construction period can be greatly reduced and the construction cost can be greatly reduced.

Although one embodiment of the present invention has been described above, the above embodiment is merely a preferred example, and the present invention is not limited to the above embodiment, and appropriate design changes and applications are possible.
For example, in the above-described embodiment, the drainage channel network 6 is formed in a vertical and horizontal grid pattern with the vertical drainage channels 6a and the horizontal drainage channels 6b having a flat rectangular cross section. If water and drainage are possible, only the vertical drainage channel 6a or only the horizontal drainage channel 6b may be provided, or conversely, a mat-like drainage channel network may be provided almost entirely.

In the low-temperature rock storage tank of the present invention, it is necessary to ensure that a stable groundwater flow f is always generated around the cavity 1. Therefore, in planning the low-temperature rock storage tank of the present invention, Fully grasp data such as groundwater level and groundwater recharge, and properly predict temperature changes of surrounding rock mass during facility operation, such as coupled analysis simulation technology that simultaneously predicts heat flow and groundwater flow in the rock mass There is a need.
In any case, the location conditions require a high groundwater level and a large amount of rock permeability, but coastal areas where soft rocks such as the Tokyo metropolitan area and Osaka area are distributed fall under such location conditions. Therefore, it can be said that the low-temperature bedrock storage tank of the present invention is optimal as an LNG storage facility installed in those metropolitan areas.

However, even if the groundwater level is low and sufficient groundwater recharge is not expected, or if the surrounding rock mass is not sufficiently permeable, the present invention can be applied by measures such as shown in FIGS. It is.
In FIG. 4, a well 10 for water injection is provided above the cavity 1 to artificially recharge groundwater from the surface, so that a sufficient groundwater flow f can be generated while maintaining a high groundwater level. It is a thing.
FIG. 5 shows that a large number of draining boring holes 11 are provided in the surrounding rock mass of the cavity 1 so as to communicate with the drainage channel network 6. As a result, a water-permeable path that is guided to the drainage network 6 through the borehole 11 is secured, and the groundwater flow f is reliably generated in the surrounding rock mass.
In this case, it is more preferable to crush the surrounding rock mass during construction of the drainage boring hole 11 to form a crushing region 12 having high water permeability. Such a crushing region 12 can be efficiently constructed by a hydraulic crushing method (hydrofracturing) in which a high water pressure is loaded in the drainage boring hole 11.
6 includes the water injection well 10 shown in FIG. 4 and the drainage boring hole 11 and the crushing region 12 shown in FIG. 5, so that a reliable groundwater flow can be generated by them as a whole. Can do.

It is the cross-sectional view which shows schematic structure of the low-temperature bedrock storage tank which is one Embodiment of this invention, and an expanded sectional view of lining. It is a figure which shows a drainage channel network. It is explanatory drawing about the groundwater flow collected and drained by a drainage channel network, and heat transfer by it. It is a figure which shows embodiment at the time of providing the well for water injection similarly. It is a figure which shows embodiment at the time of providing the boring hole for drainage, and the crushing area | region similarly. It is a figure which shows embodiment at the time of providing the well for water injection, the boring hole for drainage, and the crushing area | region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cavity 2 Shotcrete 3 Frame concrete 4 Coolant 5 Membrane material 6 Drainage channel network 6a Vertical drainage channel 6b Horizontal drainage channel 7 Main drainage channel 8 Main drainage pipe 10 Water injection well 11 Drainage borehole 12 Crushing area

Claims (4)

Membrane-type low-temperature bedrock storage tank that has a lining made of sprayed concrete, reinforced concrete, cold insulation, and membrane material on the surface of the cavity formed by excavating the bedrock, and uses the internal space as a storage tank for storing low-temperature fluid Because
In the sprayed concrete, by providing a drainage channel network for collecting and draining groundwater from the surrounding rock mass, a groundwater flow flowing toward the drainage channel network is generated in the surrounding rock mass of the cavity, A low-temperature rock storage tank characterized in that a non-freezing region can be formed around the cavity by maintaining the temperature of the rock surrounding the cavity above the freezing temperature by a groundwater flow. The low-temperature bedrock storage tank according to claim 1,
A low-temperature bedrock storage tank provided with a water injection well for recharging groundwater by pouring water from the surface to the surrounding rock mass of the cavity above the cavity. The low-temperature bedrock storage tank according to claim 1 or 2,
A low-temperature bedrock storage tank characterized in that a draining borehole leading to the drainage channel network is provided in the surrounding rock mass of the cavity. A low temperature rock storage tank according to claim 3,
A low temperature rock mass storage tank, wherein a crushing region having high water permeability is formed in a rock mass surrounding the boring hole for drainage.

Images