JPS61282520A - Pile for permanently frozen ground - Google Patents

Abstract

PURPOSE:To stably support a superstructure by a method in which a pile is connected with the superstructure through a heat-insulating pad, the surface of a support pile of a given length is covered with a continuous heat insulator, and the outside of the heat insulator is covered with a continuous protective material. CONSTITUTION:A pile 11 is welded with an upper pile 13, and the upper part of the periphery of a pile 15 is covered with a heat-insulating pad 17 for preventing the conduction of heat. The pile 15 is welded with the pile 13 through a receiving base 18, and a load is transmitted through the base 18 to the pile 11, and the joint position of the base 18 is positioned within the active layer below the ground's surface. The surface of the heat insulator 16 is covered with a protective material 21 of polyethylene, polyvinyl chloride, etc., and the inner surface of the pile 13 is bonded to the outer surface of the material 21 within the active layer. The effect of frost heave of the ground on the pile in the winter season can thus be reduced, whereas in the summer season, negative friction to be occurred when the thawing and settlement of the ground take place can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application] The present invention relates to pile foundations among the foundations of structures in cold regions, and more specifically, to the prevention of freezing and frost heaving of soil in winter,
Prevents piles from being affected by ground melting and subsidence in the summer, and prevents permafrost from melting due to heat conduction from the superstructure, atmospheric temperature, or solar radiation, and provides great support at the root site within the permafrost. This invention relates to piles for permafrost areas that can maintain strength.

[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 freezing heave, thawing and subsidence of active and seasonal frozen layers, and the countermeasures used for this purpose are: The most common of these is the pile foundation.

In addition, the permafrost zone to be described in the present invention is, for example,
This refers to areas such as Alaska, Canada, and Sipella where there is a stratum that remains frozen throughout the year regardless of the season (hereinafter referred to as permafrost), in which case the annual average temperature is below 0°C.

In addition, the active layer is the part from the ground surface to the permafrost layer.
A geological formation that is greatly affected by annual temperature changes, freezing and heaving in the winter, and thawing and sinking in the summer.

Seasonal frozen layer is an average temperature of 0 degrees Celsius where no permafrost layer exists.
In the following regions, it refers to strata that freeze in the winter and thaw in the summer. 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 root length 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 it is installed, the structure often suffers from frost damage, and the penetration 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 freezing heaving force acting on pile foundations as a countermeasure.

In the permafrost zone and the seasonal frozen zone, concrete examples of conventional methods for reducing the freezing heave force of pile foundations are shown in FIGS. 9 to 11, for example.

Among these, the one shown in FIG. 9 is the thermal pile method, the one shown in FIG. 10 is the frost heaving prevention pile method, and the one shown in FIG. 11 is the frost heaving strength increasing pile method.

Figure 9 is a longitudinal cross-sectional view showing an example of the thermal pile method.
1 is an antibody made of a steel pipe pile, 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 pile body 1, 4 is a radiator, and 5 is a The permafrost layer, 6 is the active layer, and the antibody 1 was installed in the active layer 6 and the permafrost layer 5.
)-3. Note that H indicates the root 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 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 as the permafrost around the pile thaws and sinks, and when this thawing area freezes in winter, extra frost heave force acts on the pile. This prevents

In addition, the frost heaving prevention method is to fill the space between the active layer and the surrounding surface of the pile with a material that breaks the adhesion between the pile and the frozen soil. A casing 9 is placed concentrically on the outside of the body 1 to form a double pipe 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 By backfilling with sand slurry 8, the freezing heaving force due to freezing is separated.

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

Moreover, what is shown in FIG. 10(b) is a material 10ae made of a mixture of soil, oil and wax, and an active layer 6 in hole 7.
It was used as a backfilling material in the area.

Furthermore, what is shown in FIG. 11 is an example of a pile system that increases the freezing strength, and by providing notches and corrugations 2 at the part of the pile body 1 that is embedded into the permafrost 5, the permafrost 5 is strengthened. Pile body 1
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.

[Problem that the invention seeks to solve]

However, although the thermal pile can reduce the layer thickness of the 'fls dynamic layer 6 to some extent, it cannot significantly reduce the freezing heave force and negative friction, 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.

Furthermore, in the ground where thermal piles are built, the surface temperature of the thermal piles becomes uniform in the depth direction in winter, resulting in a predominant temperature gradient in the radial direction of the piles, and an antifreeze water flow is generated in this direction. It is possible that ice lenses may form on the container.

In this case, the bearing capacity of the pile is determined by the freezing strength between the pile and the ice, and since the freezing strength of the ice is smaller than that of the frozen soil, the pile bearing capacity becomes smaller. It turns out.

Therefore, even though the use of thermal piles can prevent the decline in pile bearing capacity due to thawing of permafrost, the overall effect will be limited due to the increase in frost heave force and decrease in bearing capacity due to the reasons mentioned above. You can't expect much.

In conventional usage, the penetration length H of thermal piles into permafrost is made longer than necessary to prevent frost damage.
There are problems from the viewpoint of workability and economy.

On the other hand, the frost heaving prevention pile method involves filling or backfilling the surrounding surface of the pile with a mixture of oil, wax, etc., but this must be constructed on site and requires machinery and equipment for this purpose. Not only that, but also the workability is not very good.

Additionally, since mixtures such as oil and wax have enough fluidity to allow backfilling on site, the backfilling material penetrates and disperses into the surrounding ground during the summer, resulting in the need for refilling. It also 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, the frost heaving prevention pile method does not take into account insulation measures, and cannot prevent heat from the superstructure or solar radiation from transmitting through the pile and melting the permafrost in the pile circumference.

In the freezing strength increasing capture method, the properties of the permafrost in the root part 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. Therefore, in order to obtain a large freezing strength, there are problems such as processing the end portion into a deformed steel bar, etc., and requiring a high degree of precision in pre-manufacturing.

Also, in this case, as with the frost heaving prevention pile method, no insulation measures have been considered.

[Means for solving problems]

The present invention was arrived at as a result of intensive studies to solve the above-mentioned conventional problems, and is a type of pile that reduces the freezing heave force and negative friction that act on piles in cold regions. Connected to the superstructure via a pad, the support pile surface of a predetermined length on the ground surface and from the ground surface to the bottom of the active RJ layer is continuously covered with a heat insulating material, and the outside of the heat insulating material is covered with a protective material. Continuously cover with ■
Protrusions with a predetermined width and height are continuously provided at predetermined intervals on the outer surface of a pile embedded in the permafrost layer below the active layer, or ■ Continuous to the surface of the protection member and the protection member A covering member or a solid covering having a length equal to or greater than the thickness of the active layer is continuously formed on the surface of the lower support pile, and the lower end thereof is fixed near the bottom of the active layer, or according to [1] to [3] above. The present invention relates to piles for permafrost areas, which are characterized by having all of the following.

[For production]

In order to achieve the above-mentioned object, the permafrost zone pile according to the present invention is characterized in that the outer surface of the antibody made of steel pipe or the like is subjected to the above-described specific treatment.

A more specific explanation will be given below based on the drawings.

FIG. 1 is a longitudinal sectional view of the embodiment according to the present invention, and the same functional parts as in FIGS. 9 to 11 are denoted by the same reference numerals, and their explanations are omitted.

In FIG. 1, reference numeral 11 denotes a pile that shares the bearing capacity within the permafrost, and projections 12 having a predetermined width and a predetermined height are continuously rolled on the outer surface of the pile at predetermined intervals.

The pile 11 is connected to the upper resistor 13 by welding, and the pile 11 is activated! Fi! The welded portion 14 is located below the bottom of the active layer so as not to be located within the IN.

The pile 15 is surrounded by a heat insulating material 16 and its upper part is covered with a heat insulating pad 17 to prevent solar radiation, atmospheric temperature, heat from the superstructure, etc. from being transmitted to the pile on the ground surface. For this purpose, the support has a smaller diameter than the pile 13 and is connected to the pile 13 by welding or the like, and transmits the load of the upper structure to the pile 11 via the stand 18.

The joint position of this support stand 18 is within the active layer below the ground surface from the viewpoint of heat insulation, and the upper end position of the pile 13 is above the position where the support stand 18 is attached and within the active layer.

Similarly, the supports attached to the pegs 15 transfer the loads of the superstructure to the lower resistors 13.12 by means of the platforms 19.

Further, 20 is a connecting tool such as an anchor bolt embedded in the heat insulating pad 17 to connect the upper structure and the pile.

The pile 15 and the heat insulating pad 17 are connected to each other by the support plate 19.
Alternatively, the adhesive force between the protrusion provided on the inner surface of the pile 15 and the heat insulating pad may be used.

21 is a member made of polyethylene, polyvinyl chloride, etc. that covers the surface of the heat insulator 16 to protect the heat insulator 16, and adheres the inner surface of the pile 13 and the outer surface of the member 21 within the active layer.

Furthermore, 22 is a coating formed on the outer surface of the resistor 13 and the member 21 via an adhesive layer as necessary, and the lower end is placed above the welding part 14 near the active layer, and the upper end is placed above the ground surface. It is fixed to a length equal to or up to 1.5 times the maximum frost heave of the installation ground.

Although the heat insulating material 16 used in the present invention varies depending on the region, it is generally necessary that the heat insulating material 16 does not cause brittle fracture from room temperature to a low temperature of about -50°C.

Clinker,
Foamed slag, sintered powder ash, foamed clay, foamed slay 1-1 foamed perlite, asphalt, glass wool, rock wool, wood, sawdust, rice husk, diatomaceous earth, polystyrene foam, extrusion 1) Foamed polystyrene, rigid polyurethane foam , flexible polyurethane foam, phenolic resin foam, foamed urea resin, acrylic resin foam, polyvinyl chloride foam, polyethylene foam,
There is a material whose main component is 1W or 2 or more selected from closed-cell foam rubber and the like.

Although the insulation pad 17 varies depending on the region, it generally (1) does not cause brittle fracture at temperatures ranging from room temperature to about -50°C, and (2) has sufficient compressive strength to withstand the load of the superstructure. It is desirable that the following conditions be satisfied.

Things that are considered to meet this condition include, for example, foams made of various types of glass W4 fiber reinforced plastics, various types of concrete, and general FRP.

Furthermore, in addition to the conditions described in (1) above, the member 21 must have a strength and thickness that will not cause the member 21 to be destroyed by the pressure exerted by the tightening applied in the radial direction when the active layer freezes; (4) It is desired to have the following characteristics: to have a thermal diffusivity comparable to or lower than that of the surrounding area.

Examples of materials that meet this condition include polyolefin plastics such as low to high density polyethylene, polybutylene/-1, polypropylene, ethylene/propylene co-M combination, Ho!J-4 methyl-1 pentene, polyethylene terephthalate, and polybutylene. Thermoplastic polyesters such as terephthalate, rigid polyvinyl chloride, polyhaloolefins such as polychlorotrifluoroethylene, poly(meth)acrylic acid or its salts, poly(meth)acrylates, etc.
Acrylic compounds such as esters of acrylic acid, 6-
Thermosetting plastics such as nylon, polyamides such as 6,6-nylon, polystyrene, polyacrylon, polyphenylene oxide, polyphenylene sulfide, polycarbonate, aromatic polyester, epoxy resin, melamine resin, urea resin, phenol resin, polyurethane, etc. One or more selected from among these may be used as is or, if necessary, a composite system containing these as main components may be used.

The coating 22 counteracts the freezing heave force of the active layer, and its action can be divided into the following types:

In addition to the conditions described in (1) above, Type A of the coatings requires that: (5) the coefficient of friction of the coating is smaller than the coefficient of friction of the surfaces of the piles 13 and members 21; (7) It must have a thermal diffusivity equal to or lower than that of the surrounding soil.

Materials that meet this condition include the above-mentioned plastic materials, as well as materials containing these above-mentioned plastic materials as main components and mixed with 3- or 4-fluoride ethylene powder, polyvinylidene fluoride, and polyvinylidene fluoride. Materials mainly composed of polyhaloolefins such as fluorinated ethylene and poly-4 can also be used.

Type B coating generally only needs to meet the conditions (11 and (7) above), and materials that can be used for this include natural rubber, isoprene rubber, styrene rubber, etc.
Butadiene rubber, butadiene rubber, chloroprene rubber,
Butyl rubber, ethylene propylene rubber, ethylene propylene diene rubber, chlorosulfonated polyethylene, nitrile butadiene rubber, fluororubber, nitroso rubber, polyester urethane rubber, polyether urethane rubber, fluorinated silicone rubber, phenyl methyl silicone rubber, chill silicone Rubber, vinyl silicone rubber, polysulfide rubber, polyolefin thermoplastic elastomer, urethane thermoplastic elastomer, polyester thermoplastic elastomer, polyamide thermoplastic elastomer, ethylene/acetic acid, vinyl copolymer, ethylene/ethylene acrylate copolymer There are composite materials with one or more composites (blends, copolymers, or laminates) selected from the group of polymers, or inorganic fillers.

Pile for permafrost zone configured as above! t1 is usually installed by the following process.

That is, first, the active layer 6 and the permafrost layer 5 are
A pile 23 is erected in the excavated hole 7, and a sand slurry 8 is backfilled around the pile 23.

FIG. 1 shows the state in summer when the permafrost zone pile 23 is installed in the excavated hole 7 in the active layer 6 and the permafrost layer 5.

In summer, the thickness h of the active layer is the longest, and the temperature of the permafrost layer is the highest throughout the year.

For this reason, the freezing strength between the surface of the pile 11 in the permafrost layer and the permafrost becomes smaller in winter, but in the present invention, since the projections 12 are formed on the surface of the pile 11 in the permafrost, The freezing strength is significantly increased compared to ordinary piles.

Therefore, in the present invention, the length of penetration into the permafrost required to support the load of the superstructure can be made shorter than that of school piles.

In addition, for piles installed in permafrost zones, the superstructure,
Heat due to solar radiation or heat transfer based on atmospheric temperature may melt the permafrost in the rooted area, but in the present invention,
Heat from the upper structure is prevented from being transmitted to the piles 15 by the heat insulating pad 17, and solar radiation and atmospheric temperature are prevented from being transmitted to the piles 15 by the heat insulating material 16, so that the permafrost does not thaw.

In addition, the member 21 and the covering 22 have a thermal diffusivity that is the same as or lower than that of the surrounding soil, and the heat input from these parts is almost the same as the heat input from the ground where no piles are built. or smaller.

FIG. 2 shows the state in winter, and when the active layer 6 freezes, the sand slurry 8 also freezes and is frozen to the surface of the covering member 22 of the pile 23.

When the covering member on the pile surface is of type A, the friction coefficient of the covering is smaller than that of the pile body 13 and the member 21, so the freezing strength between the permafrost and the pile surface is the value that can be obtained on a normal pile surface. become smaller.

Therefore, due to the frost heaving of the active layer 6, the frost heaving force acting on the antibodies is also smaller than that of ordinary piles.

On the other hand, in the case of type B, the frost heave deformation is absorbed by the elastic elongation of the cover, and the frost heave is absorbed by the elastic recovery force of the cover which is compressed above ground and under tension in the unfrozen soil area in the active layer. For two reasons: resistance to deformation. The freezing heaving force acting on antibodies is smaller than that of normal piles.

Therefore, no matter which type of AlB coating is used,
The piles float due to the heaving force of freezing, which prevents the structure from suffering frost damage.

Furthermore, in summer, the negative friction that occurs as the active layer 6 melts and sinks is reduced for exactly the same reason as the freezing heave force, and has almost no effect on antibodies.

An experiment was conducted to compare the difference between using conventional steel pipe piles as they are in permafrost zones and using the permafrost piles of the present invention.

This experimental device is installed vertically on a base 24 as shown in Figure 3.
In addition to bridging the reaction frame 26 to the i-frame 25.25111J, a heat insulating material 2 with a thickness of 100 mm is placed on the base 24.
A soil tank 28 surrounded by 7 and filled with soil 29 is installed, and a model pile 30 is built in the top 29.
A load cell 31 is interposed between the and the reaction force frame 26,
A displacement meter 32 is provided for measuring the displacement of the surface of the soil 29 in the soil tank 28.

As mentioned above, the present invention relates to frost damage prevention piles, and by utilizing some of the functions and configurations described herein, it can be applied to pillars, fire hydrants, gas pipes, and water pipes in cold regions. It can be applied to prevent frost damage.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in further detail by specifically showing examples.

(1) Steel pipe pile (conventional) Outer diameter = 3411II11 Length 400mm, Embedded length = 2
50 (2) Pile for permafrost zone (corresponds to the one shown in Figure 1) Antibody = Same as (1) Covering member: Material: 47 fluoride ethylene (modified silicone elastomer is used as the adhesive layer) Thickness After installing the conventional steel pipe pile prepared as described above and the permafrost zone pile according to the present invention into the experimental apparatus shown in Figure 3, the entire apparatus was assembled. It was placed in a constant temperature bath and cooled from room temperature to -40°C, and cooling was continued until the entire layer of soil 29 was frozen and frost heaving deformation was completed.

Next, the temperature of the constant temperature bath was raised to +30°C to thaw the entire layer of frozen soil and return it to the condition before the experiment, and then cooled again under the same conditions to freeze the entire layer.

This repeated freezing and thawing operation was performed for 6 cycles, and the behavior of the pile during the experiment was investigated.

Figure 4 shows the change over time in the freezing heave force of the steel pipe pile obtained from the experiment, and Figure 5 shows the change over time in the freezing heave force of the pile for permafrost areas according to the present invention. .

As can be clearly seen from the behavior of both, the frost heave force of permafrost piles is reduced to about 178 compared to steel pipe piles, and exhibits an extremely large effect. I can understand that it is a thing.

In the case of the above experimental example, the covering was done with Type A, but when we repeated the above method using piles for permafrost areas with Type B covering, we obtained results that had similar trends. .

FIG. 6 shows a test device used to confirm how much the freezing strength between the permafrost and the pile surface increases due to the surface protrusion 12 of the pile 11 in the permafrost. A reaction frame 35 is bridged over the frame 34, and a test specimen 36 is placed on the test bed 33, and a 500-ton hydraulic jack 37 is used to push through the specimen to investigate the adhesion strength between the concrete and the inner surface of the steel pipe. be.

The adhesion strength is measured by a load cell 38 placed between the hydraulic jack and the test specimen, and in actual testing, a steel pipe with an outer diameter of 400 mm and a wall thickness of 9 m+a and a steel pipe of the same size are used to measure the adhesion strength on the inner surface. Projection height 2.511II
11 protrusion width 3. Using two types of steel pipes with protrusions of OL 11m continuously formed at intervals of 40 mm or less,
Concrete with a 28-day compressive strength of 180 kg/cj was poured onto each of these.

As a result of experiments, the bond strength between a normal steel pipe pile and concrete is 10 kg/-, while the bond strength between a steel pipe with projections and concrete is 80 kg/d, and the bond strength of steel pipes with projections is 8 times that of normal steel pipes. I found out something.

Of course, it is not possible to directly apply the results of this experiment to the freezing strength of frozen soil and pile surfaces, but the effectiveness of external protrusions can be fully understood from this experiment.

〔Effect of the invention〕

The following effects can be expected from the permafrost zone pile obtained according to the present invention.

In other words, (1) it reduces the freezing heave force that acts on piles as the ground freezes and heaves in the winter; (2) it reduces the negative friction that acts on the piles when the ground thaws and sinks in the summer; , (3) Based on heat from the superstructure, atmospheric temperature or solar radiation (
(4) It prevents heat from conducting through the pile and melting the permafrost, and (4) it maintains a large bearing capacity at the part where it is embedded in the permafrost. These effects work together to prevent the pile from floating. This is a permafrost pile that can prevent rising or subsidence and stably support the superstructure for a long period of time.

[Brief explanation of drawings]

gg1 and 2 are cross-sectional views of a permafrost zone mine formed according to the present invention, FIG. 3 is a cross-sectional view of the experimental equipment, and FIG.
Figures 7 and 5 are graphs showing the behavior of frost heaving force over time, Figure 6 is a cross-sectional view of another experimental device, and Figures 7 and 8 are graphs showing the behavior of the freezing heave force over time. A plan view, a partial sectional view, and FIGS. 9 to 11 are sectional views for explaining a conventional pile foundation. 1... Pile, 2... Corrugated, 3... Heat pipe, 4
...radiator, 5.. permafrost, 6.. active layer,
7. Drilling hole, 8... Sand slurry, 9... Casing,
10°...Mixture of oil and wax, 11...Pile,
12 protrusion, 13... wire, 14... welded part, 15.
...Pile, 16...Insulation material, 17...Insulation pad, 18
．． 19... Support is a stand, 20... Joint part, 21... Protection member, 22... Covering, 23... Pile for permafrost zone,
24...Base, 25...Frame, 26...Reaction force frame, 27..., 28...Earth tank, 29
...Soil, 30...Model pile, 31...Load cell,
32...Displacement meter, 33...Test bed, 34...
Frame, 35--reaction frame, 36--L [body, 37--hydraulic jack, 38 load cell.

Claims (1)

[Claims] (1) A type of pile that reduces the freezing heave force and negative friction that act on piles in cold regions: The surface of the support pile of a predetermined length in between is continuously covered with a heat insulating material, and the outside of the heat insulating material is continuously covered with a protective material, and [2] the pile is embedded in the permafrost layer below the active layer. Protrusions with a predetermined width and height are continuously provided on the outer surface of the pile at predetermined intervals, or [3] The thickness of an active layer is provided on the surface of the protection member and the surface of the lower support pile connected to the protection member. A permanent coating characterized by continuously forming a coating member or a solid coating having a length of at least 100 mm or more, and fixing the lower end thereof near the bottom of the active layer, or having all of the above [1] to [3]. Piles for frozen land areas.