JPS61261524A - Frost-damage preventor pile - Google Patents

Abstract

PURPOSE:To reduce the setting depth of a pile as well as protect structures in cold areas from frost damage by smoothly forming a plastic covering layer of more than a specific glass transition temperature over a specific length on the outer surface of a pile. CONSTITUTION:A plastic covering layer 11 of more than a specific glass transition temperature above 0 deg.C is smoothly formed over 0.5-5m lengths above the thickness (h) of the active layer 6 on the surface of a pile 1. The active layer 6 and the permanent frozen ground 5 are excavated by the setting depth h+H of a pile 10, the pile 10 is erected into the pit 7, and the surrounding of the pile 10 is embedded back with sand slurry 8. The frost-heaving forces of the active layer 6 against the pile body 1 can be reduced by the plastic covering layer 11, and structures in the cold areas can be protected from frost damage. The setting depth of the pile body 1 can also be reduced, and the corrosion resistance effect of the pile body 1 can be raised.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to pile foundations among the foundations of structures in cold regions, and more specifically to prevention of frost damage to piles due to freezing heave, thawing and subsidence of soil. This relates to frost damage prevention piles.

[Prior art]

In cold regions such as permafrost or seasonally frozen land,
When constructing pipeline frames and other types of structures, it is essential to protect the structures from frost damage such as frost heave, thawing, and subsidence in active and seasonal frozen layers.
The most common of these is the pile foundation.

Here, the permafrost zone refers to an area where a stratum that is frozen throughout the year (hereinafter referred to as permafrost) is distributed, such as Alaska, Canada, Siberia, etc., and the annual average The 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.

Additionally, the seasonal frost 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 attempt to counteract the superstructure's own weight, frost heave force, and negative friction through the strength of freezing between the permafrost and the pile surface. This requires reliable freezing strength between the permafrost and the piles and sufficient depth of the piles to penetrate 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. However, in reality, structures often suffer from frost damage, and the penetration length must be determined based on a design that takes into account a safety factor, which poses major problems in terms of workability and economic efficiency.

Due to these prerequisites, several methods have been considered to reduce the frost heaving force acting on pile foundations as a countermeasure.

As shown in Figures 4 to 6, the conventional method of reducing frost heave force on pile foundations involves inserting antibodies into permafrost and seasonal frozen zones. There are the thermal pile method as shown in Figure 4, the frost heaving prevention pile method as shown in Figure 5, and the frost heaving strength increasing pile method as shown in Figure 6.

Figure 4 is a longitudinal cross-sectional view showing an example of the thermal pile method.
1 is an antibody made of a steel pipe pile, a concrete pile, etc.; 2 is a corrugation provided on the outer periphery of the pile body 1 to increase the freezing strength; 3 is a heat pipe inserted into the antibody 1; and 4 is a radiator.

5 is the permafrost layer, 6 is the active layer, and antibody 1 is the active layer 6.
and are rooted in a borehole 7 made in the permafrost layer 5,
It is backfilled with sand slurry 8.

In addition, H indicates the root length of the pile body 1, and h indicates the thickness of the active pile body 6.

In such a thermal pile method, the temperature of the permafrost 5 in the joists is forcibly cooled during the winter by the heat pipe 3, and cold energy is stored, thereby increasing the freeze-thaw thickness and the thickness of the active layer 6 (h). The aim is to reduce this and thereby increase the effect of preventing frost heave.

Furthermore, this thermal pile can prevent the permafrost on the surface of the pile body 1 from melting due to heat input from the superstructure in summer.

In other words, according to the thermal pile method, negative friction acts on the pile due to the thawing and subsidence of permafrost around the entrance of the pile, and when this thawing part freezes in winter, extra frost heave force is applied to the pile. It can be prevented.

The frost heaving prevention pile method of GG is filled with a material that breaks the adhesion between the pile and the frozen soil between the active layer and the surrounding surface of the pile. A casing 9 is placed concentrically on the outside of the casing 9 to form a double back system, and the space between the pile 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 filled with sand. Slurry
By backfilling with 8.8 ml, the freezing heaving force is isolated.

Note that 9a is a flange provided at the lower end of the casing.

Moreover, what is shown in FIG. 5(b) is a material 10Aie which is a mixture of soil, oil and wax and is used as a backfilling material in the active layer 6 of the hole 7.

In addition, the freezing strength increasing pile method shown in FIG. The freezing strength of the active layer 6 is increased to counteract the freezing heaving force of the active layer 6.

[Problem that the invention seeks to solve]

However, although the thermal pile can reduce the thickness 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 a drop in the deep ground temperature, the amount of frost heave increases compared to the case without thermal piles, and a large frost heave force may occur.

In addition, from the second year onwards, it is thought that the decrease in temperature of the active layer will tend to increase the freezing heave force.

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.

In addition, the frost heaving prevention pile method shown in Figure 5 involves filling or backfilling the surrounding surface of the pile with a mixture of oil, wax, etc., but this must be done on-site. Not only does it require several machines and equipment, but it is also not very easy to construct.

In addition, since mixtures such as oil and wax have enough fluidity to allow backfilling at the horse site, the backfilling material penetrates and disperses into the surrounding ground during the summer, making refilling unnecessary. This causes environmental damage such as melting of 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 have a negative impact on the superstructure.

Furthermore, with the increased freezing strength pile method, the properties of the permafrost at the root of the pile body 1 are not necessarily uniform, causing variations in the freezing strength, and the frost heaving force varies depending on the shape and spacing of the notches and corrugations. Therefore, in order to obtain a large freezing strength, there is a problem that manufacturing processing with considerable precision is required for processing the end portion into a deformed steel bar.

In addition, the length of the frost damage prevention pile must correspond to the thickness h of the active layer 6 at the installation location, but since the thickness h of the active layer 6 varies significantly depending on the region, location, etc. Piles of each pole length 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 each pole length were manufactured in advance at a factory and transported to the site. Therefore, 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 it is not suitable for mass production, resulting in increased costs and labor costs.

[Means for solving problems]

The present invention was developed as a result of studies to solve the above-mentioned conventional problems, and is aimed at reducing freezing heave force and negative friction acting on piles for use in cold regions. This type of pile is a type of pile that is made of steel pipe or the like and is coated smoothly with plastic having a glass transition temperature of 0°C or higher over a length of 0.5 to 5 m on the outer surface of the antibody, and is brought into close contact with the antibody to prevent frost damage. It concerns piles.

[For production]

This will be explained below based on the drawings.

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention.

In addition, the same parts as in Figs. 4 to 6 are given the same reference numerals.
The explanation will be omitted.

In the figure, 1 is an antibody, and the feature of the present invention is that a plastic coating layer 11 having a glass transition temperature of 0° C. or higher is smoothly formed on the surface of the antibody over a length that is equal to or more than the thickness h) of the active layer 6.

The plastic coating layer 11 is configured such that the lower end 11g is located near or below the bottom of the active VH layer or the seasonal frozen layer, and the upper end 11b is located above the ground surface, in order to further reduce the freezing heave force. Coating is preferred.

The plastic mentioned here has a glass transition temperature of 0.
Targets those that can be coated on the surface of antibodies at temperatures above ℃.

Specifically, polyolefin plastics such as polypropylene, propylene/ethylene copolymer, poly4-methyl-1-pentene, thermoplastic polyesters such as polyethylene terephthalate and polybutylene ethylene phthalate, polystyrene, hard polyvinyl chloride, Polyhaloolefin plastics such as polychloro-3-fluoroethylene, polyacrylates such as polyacrylic acid and polymethacrylic acid, polyacrylonitrile, polyphenylene oxide, polyphenylene sulfide, 6-
Polyamides such as nylon, 6.6-nylon, polycarbonates, aromatic polyesters, epoxy resins, melamine resins, urea resins, phenol JFM resins, thermosetting plastics such as polyurethane, and one or more of the above-mentioned materials. Contains plastics whose main components are composite materials.

When using a material with a glass transition temperature below 0°C, such as low-density polyethylene, repeated freezing and thawing of the soil may cause scratches on the coating surface or encroachment of earth and sand, increasing the actual surface area. However, since the number of physical connections increases, the effect of reducing frost heave cannot be sufficiently exerted, and therefore, such a product cannot be used.

The same reason applies to smoothing the surface of the coated plastic.

Freeze damage prevention piles are constructed according to the various requirements listed above.
Construction will be carried out using a construction method similar to that used in regular construction.

(1) The active layer 6 and permafrost layer 5 are excavated by the burial depth of the piles 10 (h+H), the piles 10 are built into the excavated holes 7, and the sand slurry 8 is backfilled around the piles 10.

(2) If the strength of the permafrost layer 5 is relatively low, or if it takes root in unfrozen soil, the active layer 5
After drilling the piles 10 into the excavated holes 7, they are driven into permafrost or unfrozen soil using a pile driver, and finally, sand slurry 8 is applied around the piles 10 in the active layer 6. Backfill.

This process is used to construct frost damage prevention piles.

As is clear from the above explanation, the original purpose of the present invention is related to frost damage prevention piles, but by utilizing some of the requirements described herein, in addition to piles, for example, It goes without saying that it is possible to prevent frost damage to steel pipe columns, fire hydrants, water pipes, etc.

〔Example〕

In a cold region, a comparison was made between the case where conventional steel pipe piles were used as they were and the case where the frost damage prevention pile according to the present invention was used.

In the experiment, a device as shown in FIG. 2 was used, which consisted of a frame 13 set up on a base 12.
．． The reaction force frame 14 is applied between the base 12 and the base 12.
Surrounded by insulation material 15 with a thickness of 100 mm on top and ±1 inside.
A model pile 18 is placed in the top 17, and a load cell 19 installed between the pile 18 and the reaction frame 14 is used to control the voltage of ±1 within the soil tank 17.
8 is measured and the amount of displacement is determined using a displacement meter 20.

Materials used (1) Steel pipe pile (conventional) Outer diameter 34mm, length 400III111 embedment length 50
mm (2) Freeze damage prevention pile (shown in Figure 1) Pile body: (
Same as 1) Covering material: A Polypropylene 2mm (Acid anhydride grafted polypropylene 0.2mm as adhesive)
mm was used. ) Tg = 20°C, covering length 300 m B Bo IJ ethylene terephthalate 2 g (no adhesive) Tg = 80°C, covering length 30〇- (3) Comparative example pile body: same as (1) above, but with ethylene propylene and Polymer (2m 1T g = -20℃) Covering length 300m
m After installing the conventional steel pipe pile as described above and the frost damage prevention pile according to the present invention into an experimental apparatus as shown in Fig. 2, the experimental apparatus was placed in a freezing apparatus and the test was started at room temperature. The mixture was then cooled to -40°C, and this state was maintained for about 24 hours, after which cooling was discontinued.

Figure 3 shows the results of measuring the change over time in the freezing heave force during this period using the load cell 19. In the figure, (1) is the result of a conventional steel pipe pile, (21A and B are the results of the present invention, and (3) is the result of a comparative example.

As is clear from this figure, the freezing heaving force at -40°C is around 2,400 kg for the steel pipe pile (1), while the frost heaving force for the piles (2) A and B according to the present invention is 400 to 500 kg. On the other hand, in Comparative Example (3) in which a glass transition temperature of less than 0°C was used, it was confirmed that the effect of reducing frost heave was small at around 1500°C.

In the above experimental example, the present invention was applied to ordinary steel pipe piles, but it can also be applied to conventional frost damage prevention piles (for example, piles with increased freezing strength as shown in Figure 6). I can do it.

In the case of coating thermoplastic plastics, the method for manufacturing frost damage prevention piles of the present invention is to extrude the molten plastic from a rad die into a cloth having a cylindrical discharge opening and coat it in the longitudinal direction of a steel pipe, or to coat a steel pipe in the longitudinal direction. If necessary, coating the preheated steel pipe with the preheated plastic by fluid dipping or electrostatic coating can be adopted, and when coating thermosetting plastic, the latter method or spray coating method can be adopted. You can also do it.

In addition, in the present invention, the outermost coating is made of plastic with a glass transition temperature of 0°C or higher, but in order to prevent scratches from forming on the surface during transportation and construction, a protective coating layer is further provided on the outside. Needless to say, it is okay.

〔Effect of the invention〕

By using the frost damage prevention pile obtained according to the present invention, the following effects can be expected.

(1) Since the freezing heave force of the active layer against antibodies can be significantly reduced, structures in cold regions can be sufficiently protected from frost damage.

(2) Since the freezing heave force acting on the antibodies can be reduced, it is possible to significantly shorten the length of pile penetration, and furthermore, when maintenance is taken into account, it is possible to significantly reduce the overall cost.

(3) Easy to manufacture because the antibody structure is simple
□ Moreover, the solid film formed on the surface of the antibody has an anticorrosive effect and can withstand long-term use.

(4) Mass production is possible, and packaging and transportation are easy, so costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a frost damage prevention pile formed according to the present invention;
FIG. 2 is a sectional view of the experimental apparatus, FIG. 3 is a graph showing the behavior of frost heaving force over time, and FIGS. 4 to 6 are sectional views illustrating conventional pile foundations. 1... Pile, 2... Corrugated, 3... Heat pipe,
4...Radiator, 5...Permafrost layer, 6...Active layer, 7...Moat 111J hole, 8...Sand slurry, 9...
・Casing, 10... mixture of oil and wax,
11... Plastic coating layer, 12... Base, 13
...Frame, 14...Reaction force frame, 15...
Insulation material, 16... Soil tank, 17... Soil, 18... Model pile, 19... Load cell, 20... Displacement meter.

Claims (2)

[Claims] (1) For piles used in cold regions, the piles are of a type that reduces the freezing heave force and negative friction that act on the pile, and the outer surface of the body made of steel pipe etc. is coated with plastic with a glass transition temperature of 0°C or higher. A frost damage prevention pile characterized by being coated smoothly over a length of 5 to 5 m and brought into close contact with antibodies. (2) According to claim 1, the lower end of the plastic covering layer is built near or below the bottom of the active layer or seasonally frozen layer, and the upper end is located above the ground surface. Freeze damage prevention piles listed.