JP2534080B2 - Cooling method in concrete gravity dam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to solve the following problems.

(Field of Industrial Application) The present invention relates to a method for cooling a concrete gravity dam to radiate heat of hydration of cement accumulated inside.

(Prior Art) Conventionally, a gravity dam has a cross-sectional structure (a cross section perpendicular to the dam axis) as shown in FIG. That is, on the outer surface of the concrete gravity dam 1, 2 is a dam surface, and 3 is a downstream surface. Further, inside the gravity dam 1, 4 is an inspection passage hole provided at a lower position, which is formed at a height of, for example, 8 to 10 m from the bottom of the dam along the direction of the dam axis. In such a gravity dam 1, the concrete that constitutes the gravity dam 1 accumulates the heat of hydration of cement and becomes high temperature,
The dam surface 2 is deprived of heat by the water 5 or the outside air, and the downstream surface 3
Are deprived of heat by the air (outside air) and are cooled to lower temperatures. Further, in the state where water is blocked by the dam surface 2, the dam surface 2 also loses heat by the water and becomes low in temperature. That is, the temperature distribution in the horizontal direction inside the gravity dam is taken as an example, A,
The positions shown by B and C are as shown in FIGS. 6A, 6B and 6C, respectively.
In each figure of FIG. 6, 7 is an area affected by the temperature decrease by the water 5, 8 is an area affected by the temperature decrease by the outside air, and 9 is not affected by the temperature decrease by any means. Regions, which are shown in FIG. 5 when they are represented in FIG. 5, respectively. Of these, one end of the region 7 is the dam surface 2 that is cooled by the water 5, so that the temperature gradient in the region 7 is large. Water blocked again 5
As shown by the water temperature curve 6, the water temperature decreases as the water depth increases, and becomes a low value of about 4 ° C. below a certain water depth. Therefore, the temperature gradient becomes large accordingly. When the temperature gradient increases in this way, the tensile stress generated in the concrete increases corresponding to the temperature gradient, and the area 7
The tensile stress generated in the concrete at 30 k
g / cm ² ) is the tensile strength of concrete (eg 10 to 15 kg / c)
There is a region that exceeds m ² ). In such an area, the concrete that constitutes the gravity dam will crack. The occurrence of such cracks increases the lift force due to water intrusion into the cracks, which adversely affects the stability of the dam. In the present specification, the above-mentioned area is called a crack generation risk area, and an example thereof is shown by reference numeral 7a in FIG.

Therefore, conventionally, in order to prevent the above-mentioned cracks from being generated, as shown in FIG. 7, an extremely large number of cooling water is passed when pouring concrete when constructing a dam. By embedding the water pipes 10 in a horizontal state and passing cooling water through the water pipes 10 to remove the heat of hydration and to moderate the temperature gradient, it is possible to prevent a large tensile stress from occurring in the concrete. Has been.

However, in such a method, a large amount of cost is required for the equipment, and there is an uneconomical need of a large amount of operating cost even in the cooling operation.

(Problems to be Solved by the Invention) Except for the above-mentioned conventional problems, the present invention is a concrete gravity dam capable of economically preventing cracks from occurring with a small facility cost and a low operating cost. It is intended to provide a cooling method in.

 The configuration of the present invention is as follows.

(Means for Solving Problems) The invention of the present application employs means as described in the claims, and its operation is as follows.

(Operation) When constructing a dam, a passage hole for inspection, a ventilation hole, and a cooling hole are formed inside the dam. Air is passed from the passage hole to the ventilation hole through the cooling hole. The heat of the concrete around the cooling holes is taken away by the circulation of the air,
The temperature gradient in the region affected by the temperature decrease due to the dam surface becomes gentle, and the stress generated in the concrete due to the temperature gradient in that region is suppressed to be equal to or lower than the strength of the concrete.

(Embodiment) The drawings showing the embodiment of the present application are shown in FIGS.
The figure will be described. It is to be noted that the same reference numerals as those in FIGS. 5 and 6 in the same figure represent the portions having functionally equivalent configurations, and the duplicated description of the portions will be omitted. In FIG. 1, reference numeral 11 denotes a vent hole (also called an upper inspection hole) provided above the inside of the gravity dam, which is formed long along the direction of the dam axis. The ventilation hole 11 extends from the dam surface 2 to the downstream surface 3
It is provided when the thickness dimension up to is about 20 to 30 m or more. A large number of cooling holes 12 are provided inside the gravity dam 1 at a position close to the dam surface 2 and at a portion where the heat of hydration of cement is accumulated and the temperature is raised. The limit of such a portion close to the dam surface 2 is a portion which is cooled by the water 5 in contact with the dam surface 2 through the dam surface 2 and has the same temperature as the outside air temperature (for example, the first temperature). It is a portion indicated by reference numeral D in FIG. 6). Further, the limit far from the dam surface 2 is a temperature gradient in a region affected by the low temperature water due to the water in contact with the dam surface 2 even if outside air is passed through the cooling holes 12 provided therein and heat is taken from the surrounding concrete. This has no effect on the mitigation of. In addition, the area of such a range is also called an air cooling effective area in this specification. The air cooling effective area is several meters (5 to 6 m) from the dam surface 2
It is an area within the range of about 20 m. The lower part of each cooling hole 12 is in communication with the passage hole 4, and the upper part is in communication with the ventilation hole 11. Each cooling hole 12 is formed to have an inner diameter of 15 to 30 cm, for example. Further, the mutual intervals are determined according to the inner diameter of the cooling holes 12 and the amount of heat released by ventilation through the cooling holes 12 so that the intermediate portions between the adjacent cooling holes 12 can be appropriately cooled. For example, if the inner diameter of the cooling hole 12 is about 15 cm, about 4 m,
If it is about 30 cm, it is about 8 m. Reference numerals 13 and 13 indicate joints of well-known blocks at the time of dam construction, and the mutual intervals are about 15 m, for example.

In the gravity dam 1 as described above, cooling holes are being constructed during construction.
Ventilate through 12, and after the construction is completed, install an exhaust fan at the end of the vent 11 and operate it. Then, the outside air is drawn into the passage hole 4, and the drawn air passes through the passage hole 4 to reach each cooling hole 12 and flows there. The heat of the concrete in the portion where each cooling hole 12 is arranged and the portion around the cooling hole 12 is taken away by the circulating air due to the circulation of the air. The air whose temperature has been raised by removing the heat is released to the outside through the ventilation hole 11. Since the heat around the cooling holes 12 is taken away as described above, the temperature distribution inside the gravity dam 1 becomes as shown in FIG. 2 (a) (before flooding). Even if the dam surface 2 is cooled by the water 5 by flooding in this state, the temperature distribution inside the gravity dam 1 is as shown in FIG. 2 by the cooling action as described above due to the circulation of air through the cooling holes 12. B). That is, the temperature gradient in the region that is in contact with the dam surface 2 and is affected by the temperature decrease by the outside air or water 5 becomes gentler than in the conventional case,
The tensile stress generated in the concrete due to the temperature gradient becomes less than the tensile strength of the concrete. As a result, the risk of cracking is eliminated. The flow rate of the above air is
The amount may be increased or decreased so that the tensile stress becomes equal to or less than the tensile strength as described above.

The temperature distribution after several years of flooding is shown in Figure 2 (c).
As shown in Figure 2, the temperature of the concrete in the region that is not affected by the temperature reduction by water or the outside air gradually decreases. Due to this decrease in temperature, the temperature gradient in the region affected by the temperature decrease due to the water 5 contacting the dam surface 2 becomes gentle, and the tensile stress generated in the concrete due to the temperature gradient becomes less than the tensile strength of the concrete. When it becomes (for example, after 5 to 10 years), the circulation of the air by the operation of the fan may be terminated.

Next, the formation of the cooling holes 12 at the time of constructing the dam may be performed as follows. That is, as shown in FIG. 4, when placing the concrete of the lower part 1a of the gravity dam,
The pipe 14 for forming the cooling hole is provided so that its lower portion communicates with the passage hole 4. Then, as the gravity dam 1 is gradually completed toward the upper part, the above-mentioned pipes 14 are sequentially added. By repeating this, the cooling hole 12
Is formed with the inside of the pipe 14. Alternatively, after the concrete is poured and when it is initially hardened (for example, after about 3 days), the pipe 14 is moved upward by a pulling device such as an oil jack. Then, the next concrete is placed. By repeating this, the portion after the pipe 14 is sequentially pulled up becomes the cooling hole 12. During the construction of the dam, an exhaust fan 15 is attached to the upper end of the pipe 14, and by operating it, air is circulated through the cooling holes to cool the concrete during the construction of the dam.

(Effect of the invention) As described above, in the present invention, when the gravity dam 1 made of concrete is constructed, when the concrete is in a high temperature state by storing heat of hydration, the dam surface 2 is Even in a situation in which the temperature gradient in the region near the dam surface may increase due to the temperature being lowered by the outside air or the water being dammed by the dam surface 2 causing the temperature to be lowered by cold water. The flow of air to the cooling holes 12 can moderate the temperature gradient in the above region so that the tensile stress generated in the concrete there can be made equal to or lower than the tensile strength of the concrete, and cracks can be prevented from occurring.

Moreover, even if it has the above-mentioned effects, when the equipment is installed, the inspection passage hole 4 that is essentially provided in the gravity dam is used, and the ventilation hole 11 and the cooling hole are also used.
Since only 12 is provided, it is economical to install equipment at a lower cost than before, and furthermore, during cooling, air is circulated through the cooling holes 12 using the passage holes 4 and the ventilation holes 11. However, there is also the economical efficiency that cooling can be performed with an extremely low operating cost.

[Brief description of drawings]

The drawings show the embodiments of the present application. FIG. 1 is a vertical cross-sectional view of a gravity dam, FIG. 2 is a view showing temperature distribution in the gravity dam of FIG. 1, and FIG. 3 is III-III in FIG. Line cross section,
FIG. 4 is a vertical cross-sectional view for explaining the procedure for forming the cooling holes, FIG. 5 is a vertical cross-sectional view of a gravity dam showing a conventional example, and FIG.
The figure which shows the temperature distribution in the gravity dam of the figure, FIG. 7 is a longitudinal cross-sectional view of the gravity dam which shows another prior art example. 1 ... Gravity dam, 2 ... Dam surface, 4 ... Passage hole, 11 ...
Vents, 12 ... Cooling holes.

Claims (1)

(57) [Claims] 1. A gravity dam made of concrete in which a passage hole for inspection along the direction of the dam axis is provided below the inside of the gravity dam, and above the inside of the gravity dam in the direction of the dam axis. In addition, a ventilation hole is provided along the inside of the gravity dam, and at a position close to the dam surface and where the heat of hydration of semmet is accumulated to raise the temperature, the lower part of itself is placed in the passage hole and Providing a large number of cooling holes, the upper part of which is communicated with the ventilation holes, respectively, by circulating air from the passage holes through the plurality of cooling holes to the ventilation holes, the portion where the cooling holes are arranged and the portion thereof. The heat of the concrete in the surrounding area is taken away to moderate the temperature gradient in the area that is in contact with the dam surface and is affected by the temperature decrease due to water or the outside air. Cooling method in concrete gravity dams, characterized in that as a tensile strength below.