JPH0132337B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to pile foundations among structure foundations in cold regions, and more specifically to frost damage prevention piles. When constructing pipeline frames and other types of structures in cold regions such as permafrost or seasonal frozen zones, protect the structures from frost damage such as frost heave and thaw subsidence of active and seasonal frozen layers. It is necessary and imperative to do so. Various countermeasure construction methods are used for this purpose, but the most common is pile foundations. Here, the permafrost zone is, for example, Alaska,
This refers to areas such as Canada and Siberia, where there is a geological layer (hereinafter referred to as permafrost) that is frozen throughout the year regardless of the season, and the average annual temperature is below 0°C. The active layer is the area from the earth's surface to the permafrost layer, which is greatly affected by annual temperature changes, freezing and heaving in the winter, and thawing and sinking in the summer. Furthermore, the seasonal frozen layer refers to a geological layer that freezes in the winter and thaws in the summer in areas where there is no permafrost and the average temperature is below 0°C. In the following explanation, the seasonal frozen layer may be included in the active layer. By the way, pile foundations in cold regions are rooted deep into the permafrost, and use the strength of freezing between the permafrost and the pile surface to counteract the superstructure's own weight, frost heave force, and negative friction. For this purpose, it is necessary to have reliable freezing strength between the permafrost and the piles and a sufficient depth of penetration of the piles into the permafrost. However, the permafrost layer does not necessarily have uniform properties, and the freezing strength varies greatly depending on the soil quality and temperature. Even if the structure is embedded, the structure often suffers from frost damage, and the embedment length must be determined based on a design that takes into account the safety factor, which poses a major problem in terms of workability and economy. Due to these prerequisites, several methods have been considered to reduce the frozen soil force acting on pile foundations as a countermeasure. Figures 1 to 3 show the conventional methods of reducing frost heaving force of pile foundations in permafrost and seasonally frozen land. Figure 1 is the thermal pile method, and Figure 2 is frost heave prevention. Figure 3 shows the pile method with increased freezing strength. Figure 1 is a vertical cross-sectional view showing an example of a thermal pile system, in which 1 is a pile body made of steel pipe piles, concrete piles, etc., 2 is corrugation provided on the outer periphery of the pile body 1 to increase freezing strength, and 3 is a vertical cross-sectional view showing an example of a thermal pile system. A heat pipe 4 is inserted into the pile body 1 and a radiator. 5 is permafrost, 6
is an active layer, and the pile body 1 is embedded in an excavated hole 7 provided in an active layer 6 and a permafrost layer 5, and is backfilled with sand slurry 8. In addition, H indicates the rooting length of the pile body 1, and h indicates the thickness of the active layer 6. In such a thermal pile method, the temperature of the permafrost 5 at the rooted part is forcibly cooled during the winter by the heat pipe 3, and cold energy is stored, thereby controlling the freeze-thaw thickness (the active layer 6). The objective is to reduce the thickness h) and thereby increase the anti-freezing ability. Furthermore, this thermal pile can prevent the permafrost on the circumferential surface of the pile body 1 from melting due to heat input from the upper structure in the summer. In other words, according to the thermal pile method, negative friction acts on the pile as the permafrost around the pile thaws and sinks, and when this thawing part freezes in winter, extra frost heave force acts on the pile. This can be prevented. However, although the thermal pile can reduce the layer thickness h of the active layer 6 to some extent, it cannot reduce the freezing heave force and negative friction to a large extent, and it still cannot prevent frost damage to the structure. For example, in the winter of the first year of use,
Due to the decrease in the deep temperature of the ground, the amount of frost heave increases compared to when thermal piles are not used, and large frost heave forces may occur. Also, 2
It is thought that a decrease in the temperature of the active layer will tend to increase the freezing heave force even after the first year. In conventional usage, the penetration length H of the thermal pile into the permafrost has been considerably increased to prevent frost damage, which poses problems from the viewpoint of workability and economy. The frost heaving prevention pile method uses a
The pile is filled with a material that breaks the adhesion between the pile and the frozen soil.The one shown in Figure 2a is a double pipe system in which a casing 9 is placed concentrically with the outside of the pile body 1. The space between the body 1 and the casing 9 is filled with a mixture 10 of highly concentrated oil and wax, and the outer periphery of the casing 9 is backfilled with sand slurry 8 to isolate the freezing heave force. . Note that 9a is a flange provided at the lower end of the casing. Further, in the case shown in FIG. 2b, a material 10a containing a mixture of soil, oil and wax is used as a backfilling material for the active layer 6 of the construction hole 7. This type of frost heaving prevention pile method involves filling or backfilling the surrounding surface of the pile with a mixture of oil and wax, but this must be done on-site and requires machinery and equipment for this purpose. Not only that, but also the workability is not very good. In addition, since mixtures such as oil and wax have enough fluidity to allow backfilling on site, the backfilling material permeates and disperses into the surrounding ground during the summer, resulting in the need for refilling. It also causes environmental damage by melting permafrost due to freezing point depression. In addition, in the double-pipe system, the casing may lift and sink as the active layer freezes and thaws, which can adversely affect the superstructure. Figure 3 shows the freezing strength increasing pile method.
By providing notches and corrugations 2 at the root of the pile body 1 into the permafrost 5, the permafrost 5 and the pile body 1 are
This increases the freezing strength between the active layer 6 and the active layer 6 to counteract the freezing heaving force of the active layer 6. In this method, the properties of the permafrost at the root of the pile body 1 are not necessarily uniform, resulting in variations in the freezing strength, and the frost heaving force changes depending on the shape and spacing of the notches and corrugations. In order to obtain a large freezing strength by this, there are problems such as the need for manufacturing and processing with considerable precision in processing the end portion into a deformed steel bar. In addition, frost damage prevention piles must have a length L that corresponds to the thickness h of the active layer 6 at the pile installation location, but the thickness h of the active layer 6 varies significantly depending on the region, location, etc. Because of the difference, piles of various lengths corresponding to the thickness of the active layer 6 must be prepared. For this reason, when installing a pile foundation over a long distance using frost damage prevention piles, for example, as a stand for a pipeline, conventionally, piles of various lengths were manufactured in advance at a factory and transported to the site. Piles corresponding to the thickness of active layer 6 were selected and installed. For this reason, not only is it troublesome to pack, but the cargo becomes large, making transportation troublesome, and since it is not suitable for mass production, costs rise, leading to problems such as an increase in labor costs. The present invention was made to solve the above-mentioned conventional problems, and reduces the frost heaving force that acts on piles due to freezing of the active layer and the seasonal frozen layer, and the negative friction that occurs in the summer. By adding a material to the pile body, it prevents frost damage to the superstructure, and the length of the pile can be adjusted arbitrarily according to the thickness of the active layer, making it possible to mass produce and pack.
The object of the present invention is to provide a frost damage prevention pile that is easy to transport and can reduce costs. In order to achieve the above-mentioned object, the frost damage prevention pile according to the present invention is a pile installed in a cold region where freezing heaving force acts, and is provided with an expandable member attached to a pile body having a length obtained by cutting a regular pile into multiple pieces. The pile member is constructed by fitting the pile body and fixing its upper and lower ends watertightly inside the upper and lower ends of the pile body, and filling the space formed by the pile body and the expandable member with a fluid substance. , the pile members are connected as appropriate depending on the thickness of the active layer. The present invention will be explained below with reference to the drawings. FIG. 4 is a longitudinal sectional view of an embodiment of the present invention. Note that the same parts as in FIGS. 1 to 3 are denoted by the same reference numerals, and explanations thereof will be omitted. In the figure, reference numeral 10 denotes a frost damage prevention pile according to the present invention, which is constructed by connecting a plurality of pile members 11, 11a, . . . of appropriate length.
An example of the structure of the pile members 11, 11a, . . . is shown in FIG. 6. Reference numeral 12 denotes a pile body (a steel pipe pile is shown in the figure), and its length l is selected to be the length of a normal pile cut into multiple pieces (for example, about 0.5 m).
Reference numeral 13 denotes a bellows-shaped extensible member, whose upper and lower ends are watertightly fixed to the pile body 12 by fixing members 14 and 15 via l ₁ and l ₂ from the end of the pile body 12, respectively. 16 is a fluid substance filled in the space formed by the pile body 12 and the expandable member 13. Although there are differences depending on the region, the expandable member 13 used in the present invention generally does not cause brittle wave breakage from room temperature to low temperatures of about -50°C, and the recoverable displacement is the amount of frost heave in the active layer 6 ( h ₁ -h) and not be deteriorated or corroded by fluid substances, and representative examples are shown in Table 1 as those satisfying these conditions. In addition, although there are differences depending on the region, the fluid substance 16 is generally a substance that exhibits fluid behavior from room temperature to low temperatures of about -50°C, and does not deteriorate or corrode the pile body 1 and the expandable member 13. Table 2 shows representative examples of those satisfying these conditions.

【table】

〔Example〕

(1) Steel pipe pile (conventional type) Outer diameter: 34 mm, length: 4000 mm, embedded length: 250 mm (2) Freeze damage prevention pile (corresponding to the example shown in Figure 4) (a) Pile dimensions Outer diameter: 27.5mm, length: 400mm, embedded length: 250
mm, length of pile member: 50mm (b) Material and dimensions of expandable member Material: low density polyethylene, thickness: 1.5mm,
Pitch of peak: 9.0 mm, difference between peak and valley: 6.0 mm (c) Fluid substance isoparaffin (C ₁₃ - C ₁₈ ) A conventional steel pipe pile as described above and a frost damage prevention pile according to the present invention, After setting up the experimental equipment shown in Figure 10, the experimental equipment was placed in a freezing room, cooled from room temperature to -20°C, and after about 24 hours, the temperature was changed to -40°C, and the condition was kept at about -20°C. Cooling was discontinued after 48 hours. Soil 35 in the soil tank 35 during this time
Fig. 11 shows the results of measuring changes over time in the amount of frost heaving using the displacement meter 39, and Fig. 12 shows the results of measuring changes over time in the frost heaving force using the load cell 38 (A in the figure shows the conventional Steel pipe pile, B is the experimental result of the frost damage prevention pile of the present invention.) As is clear from the figure,
Even though the amount of frost heave is almost the same in both cases,
The freezing heaving force of steel pipe pile A at -40℃ is 3.5 kg/
cm ² , whereas the frost damage prevention pile B according to the present invention had almost 0, and it was confirmed that the frost damage was significantly reduced. In the above embodiments, the present invention was applied to steel pipe piles, but the present invention can also be applied to concrete piles, and it is also possible to apply the present invention to expanded-bottomed piles with concrete poured inside. In that case, plastic pipes can also be used instead of steel pipes. Furthermore, it can also be used in conjunction with conventional frost damage prevention piles (for example, the frost damage increasing pile shown in FIG. 3). The materials, shapes, dimensions, etc. of other parts are not limited to the above embodiments, and can be changed as appropriate without departing from the gist of the present invention. As is clear from the above description, according to the present invention, the following remarkable effects can be achieved. (1) Since the freezing heave force of the active layer against the pile body can be reduced to almost zero, structures in cold regions can be sufficiently protected from frost damage. (2) Since the frost heave force acting on the pile body can be reduced, the pile penetration length can be significantly shortened. (3) The length of the pile can be adjusted arbitrarily according to the thickness of the active layer. (4) It can be produced in large quantities and is easy to pack and transport, reducing costs.

[Brief explanation of drawings]

Figures 1 to 3 show conventional methods for reducing frost heaving force. Figure 1 is the thermal pile method, Figures 2 a and b are the frost heaving prevention pile method, and Figure 3 is the frost heaving prevention pile method. FIG. 2 is an explanatory diagram of the method. FIG. 4 is a longitudinal sectional view of an embodiment of the present invention, FIG. 5 is an explanatory diagram of its operation, and FIG.
Fig. 7 is an enlarged sectional view of the main part showing an embodiment of the pile member which constitutes the main part of the present invention, and Fig. 8 a, b and Fig. 9 a to f show another embodiment of the main part of the present invention. Enlarged cross-sectional view,
FIG. 10 is a conceptual diagram of an apparatus for testing the frost damage prevention pile according to the present invention, and FIG. 11 is a diagram showing the change over time in the amount of frost heave of the conventional steel pipe pile and the frost damage prevention pile according to the present invention. FIG. 12 is a diagram showing the change in frost heaving force over time. 5: permafrost layer, 6: active layer, 8: sand slurry, 10: frost damage prevention pile, 11, 11a: pile member,
12: Pile body, 13: Expandable member, 16: Fluid substance.

Claims (1)

[Claims] 1. For piles to be installed in cold regions where freezing heaving forces act, a regular pile is cut into multiple lengths, each of which is fitted with an expandable member, and the upper and lower ends of each of the piles are Watertightly fixed inward from the upper and lower ends,
Freeze damage characterized in that the space formed by each of the pile bodies and the expandable member is filled with a fluid substance to form a pile member, and the pile members are connected as appropriate depending on the thickness of the active layer. Prevention pile.