JPH0555657B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to pile foundations among the foundations of structures in cold regions, and more specifically to frost damage prevention piles for preventing frost damage to piles due to freezing and heaving of soil, thawing and subsidence. be. [Prior art] When constructing pipeline frames and various other structures in cold regions such as permafrost or seasonal frozen land, frost damage such as frozen ground, thawing, and subsidence in the active layer and seasonal frozen layer must be avoided. It is essential to protect structures from damage, the most common of which is pile foundations. The permafrost zone mentioned here 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.
The annual average temperature is below 0℃. 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 addition, in the following explanation,
The active layer may include the seasonal frozen 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. To achieve this, 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 you take root,
In reality, structures often suffer from frost damage, and the depth of penetration must be determined based on a design that takes into account a 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 frost heaving force acting on pile foundations as a countermeasure. The conventional method for reducing frost heave force of pile foundations is to insert pile bodies into permafrost and seasonally frozen land zones, as shown in Figures 4 to 6. There are three types of pile systems: the thermal pile system as shown in Figure 4, the frozen ground prevention pile system as shown in Figure 5, and the freezing strength increasing pile system as shown in Figure 6. Figure 4 is a longitudinal cross-sectional view showing an example of a thermal pile system, in which 1 is made of steel pipe piles, concrete piles, etc., pile body 2 is corrugated on the outer periphery of 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,
Reference numeral 6 indicates an active layer, and the pile body 1 is embedded in an excavated hole 7 provided in the active layer 6 and the 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 this type of thermal pile method, the temperature of the permafrost 5 in the rooted part is forcibly cooled down during the winter using a heat pipe 3, and cold energy is stored. The objective is to reduce the thickness h), thereby increasing the effect of preventing frozen soil. 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 area freezes in winter, extra frost heave force acts on the pile. can be prevented. The following frost heaving prevention pile method is one in which a material is filled between the active layer and the surrounding surface of the pile to break the adhesion between the pile and the frozen soil. A casing 9 is arranged concentrically on the outside to form a double pipe system, and a mixture 1 of highly concentrated oil and wax is installed between the pile body 1 and the casing 9.
0 and fill the outside of the casing 9 with sand slurry 8.
By backfilling with water, the frozen soil force is separated. Note that 9a is a flange provided at the lower end of the casing. In the case shown in FIG. 5b, a material 10a made of a mixture of soil, oil and wax is used as a backfilling material in the active layer 6 of the built-in hole 7. Furthermore, the freezing strength increasing pile system shown in FIG. The freezing strength between the layers is increased to counteract the frozen ground force of the active layer 6. [Problems to be Solved by the Invention] However, although thermal piles can reduce the layer thickness h of the active layer 6 to a certain extent, they cannot significantly reduce the freezing heave force and negative friction, and are still It is not possible to prevent structures from freezing. For example, in the winter of the first year of use, due to a drop in the deep ground temperature, the amount of frozen soil may increase even more than if thermal piles were not installed, and a large frost heave force may occur. It is also conceivable that from the second year onwards, the temperature drop in the active layer tends 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 in terms 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 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. Furthermore, in the pile method with increased freezing strength, the properties of the permafrost at the root of the pile body 1 are not necessarily uniform, and the freezing strength may vary, and the shape and spacing of the notches and corrugations may cause freezing heave. Since the force changes, in order to obtain a large freezing strength, 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 that corresponds to the thickness h of the active layer 6 at the installation location, but the thickness h of the active layer 6 varies significantly depending on the region, location, etc. Therefore, 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 pedestal for a pipeline, conventionally, piles of various lengths are manufactured in advance at a factory, transported to the site, and removed from the active layer. The piles corresponding to the thickness of 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 the Problems] The present invention was arrived at as a result of studies to solve the above-mentioned conventional problems, and includes forming a layer on the surface to reduce negative friction. The negative friction that forms on the surface of a frost damage prevention pile that is driven or buried in permafrost or fixed ground through an active layer that freezes up in the winter and thaws and sinks in the summer in cold regions. The reducing layer is an elastic covering with a length of 0.5 to 5 m that covers the pile at least over the active layer, and the elastic covering has an adhesion force greater than the shear stress generated during frost heaving on the outer surface of the pile. The present invention relates to a frost damage prevention pile characterized in that it is formed through a strong adhesive layer. [Operation] The following will be explained based on the drawings. FIG. 1 is a longitudinal cross-sectional view showing one embodiment of the present invention. Note that the same parts as in FIGS. 4 to 6 are designated by the same reference numerals, and explanations thereof will be omitted. In the figure, 1 is a pile body with an active layer 6 on its surface.
A covering layer of an elastic body 12 is formed over a length equal to or more than the thickness (h) of the elastic body 12 with an adhesive material 11 interposed therebetween as necessary. In addition, in order to further reduce the freezing heave force, the coating layer 12 should be coated so that its lower end 12a is located near or below the bottom of the active layer, and its upper end 12b is located above the ground surface. is preferred. The elastic coating layer 12 in the present invention refers to a material whose main component is an elastic body whose molecular chains have a network structure or a polymeric elastic body whose molecular main chain is composed of soft segments and hard segments. Specifically, natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, chloroprene rubber, butyl rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, chlorosulfonated rubber, nitrile-butadiene rubber,
Fluorine rubber, nitroso rubber, polyester urethane rubber, polyether urethane rubber, fluoride silicone rubber, phenyl methyl silicone rubber, methyl silicone rubber, vinyl silicone rubber, polysulfide rubber, polyolefin elastomer, urethane thermoplastic elastomer, polyamide type One or more composites (which may be blends, copolymers, or laminates) selected from thermoplastic elastomers, ethylene/vinyl acetate copolymers, and ethylene/ethylene acrylate copolymers Alternatively, there are composite materials obtained by mixing this with an inorganic filler. The elastic covering layer 12 formed by selecting from among these is capable of adhesion to the pile body that is greater than the shear stress generated within the elastic body due to frozen heaving or thawing of the soil, or the frictional force generated between the soil and the elastic body. Power is required. For this purpose, the adhesive layer 11 must be provided as necessary. The elastic coating layer 12 firmly adhered to the pile body absorbs the shear stress on the pile body due to freezing and frost heaving of the soil through its elastic deformation, and also has a comparatively high stress relaxation property and elastic recovery property at low temperatures. It returns to its original state with a small amount of force. Therefore, it can withstand large deformations in the soil and can be used for a long period of time. In addition, the elastic coating layer 12 has a shear stress (τ) generated between the soil and the pile body due to the vertical movement of the soil, which is τ∝E/t (E: elastic modulus of the elastic coating layer, t: coating membrane layer). ), it is preferable that the film has a low elastic modulus and is thick. The frost damage prevention pile of the present invention has the configuration shown in FIG. 1, and the outermost layer is the elastic coating layer 12. Therefore, in order to prevent damage during transportation or on-site construction, the frost damage prevention pile has the structure shown in FIG. A protective coating layer may be provided. In this case, the protective coating layer does not necessarily need to be adhered to the elastic coating layer 12, nor does it need to be removed at the time of installation. Freeze damage prevention piles constructed according to the various requirements mentioned above are usually constructed using the following construction methods. (1) The active layer 6 and the permafrost layer 5 are excavated by the burial depth of the pile 10 (h+H), the pile 10 is built into the excavated hole 7, and the area around the pile 10 is filled with sand slurry 8.
fill it back up. (2) If the strength of the permafrost layer 5 is relatively low, or if the soil is to be embedded in unfrozen soil, only the active layer 6 is excavated and the piles 10 are installed in the excavated hole 7.
After erecting the pile, use a pile driver to drive it into permafrost or unfrozen soil.
Finally, the area around the piles 10 in the active layer 6 is backfilled with sand slurry 8. This process is used to construct frost damage prevention piles. Incidentally, the original purpose of the present invention is related to frost damage prevention piles, as is clear from the above explanation.
It goes without saying that by using some of the requirements described here, it is possible to prevent frost damage not only to piles but also to steel pipe columns, fire hydrants, water pipes, etc. in cold regions. [Example] The results of an outdoor experiment in a cold region using conventional steel pipe piles as they are and using frost damage prevention piles according to the present invention will be described. For the experiment, we used the equipment shown in Figure 2, which is a schematic diagram of the frost heaving force of a model pile with a covering layer fixed to it, measured outdoors in Hokkaido. In the figure, 13 is 5000mm wide, 5000mm long, and 2000mm deep.
mm concrete earthen tank, and this earthen tank 13
A gravel layer 14 with a thickness of 200 mm is laid as a base layer at the bottom of the bed, and the top layer is filled with silty soil 15 with a thickness of 1700 mm, which is highly susceptible to frost heaving. Note that the earth tank 13 is buried by excavating the native ground, and the end surface of the earth tank 13 matches the ground surface height of the native ground. Reference numeral 16 indicates a frame of H-beam steel that is erected by being embedded in a concrete mass.
9, a load cell 20 is provided between the model pile 18 and the reaction frame 19, and at the same time a displacement gauge 21 for measuring ground surface displacement and a freezing depth gauge for measuring the freezing depth from the ground surface. 22 is set. Materials used (1) Steel pipe piles (conventional) External diameter 60.5 mm, length 2500 mm, embedded depth 1800 mm (2) Freeze damage prevention piles (as shown in Figure 1) Pile body: Same as (1) above Elastic sheathing tank: A Chloroprene rubber film thickness 30mm, covering length 2000mm, urethane adhesive used B Polyolefin thermoplastic elastomer film thickness 20mm, covering length 2000mm, modified polyolefin used as adhesive Conventional steel pipe piles as mentioned above (1) and frost damage prevention piles (2) A and B of the present invention were set in the device shown in Fig. 2, and soil displacement and freezing heave force were measured over time. As a result, soil freezing started. After two months had passed, the amount of frost heave on the soil was approximately 200 mm, and the frost heave force was as shown in the table below.

〔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 tank against the pile body can be significantly reduced, structures in cold regions can be sufficiently protected from frost damage. (2) Since the freezing heave force acting on the pile body can be reduced, it is possible to significantly shorten the pile penetration length, and furthermore, when considering maintenance, it is possible to significantly reduce the overall cost. . (3) The structure of the pile is simple, so it can be manufactured easily, and the solid coating formed on the surface of the pile has an anticorrosion effect, so it can withstand long-term use. (4) Mass production is possible, and costs can be reduced because packaging and transportation are easy.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a frost damage prevention pile formed according to the present invention, Fig. 2 is a plan view of the experimental equipment, Fig. 3 is a side view of the experimental equipment, and Figs. 4 to 6 are conventional piles. It is a sectional view explaining a foundation. 1...Pile, 2...Corrugation, 3...Heat pipe, 4...Radiator, 5...Permafrost layer, 6...
...Active layer, 7...Drilling hole, 8...Sand slurry, 9...
...Casing, 10...Mixture of oil and wax, 11...Adhesive material, 12...Elastic body, 13
...earth tank, 14...gravel layer, 15...silty soil,
16... H-shaped steel frame, 18... Model pile, 1
9...Reaction force frame, 20...Load cell, 21
... Displacement meter, 22 ... Freezing depth meter.

Claims (1)

[Scope of Claims] 1. A layer that reduces negative friction is formed on the surface, and is cast or buried in permafrost or fixed ground through an active layer that freezes up in the winter and thaws and sinks in the summer in cold regions. In a frost damage prevention pile, the layer for reducing negative friction formed on the surface of the pile is an elastic covering with a length of 0.5 to 5 m that covers the pile at least over the active layer, and A frost damage prevention pile characterized in that the elastic covering is formed on the outer surface of the pile via an adhesive layer having an adhesive force greater than the shear stress generated during frost heaving. 2. A patent characterized in that the elastic covering is made of a material whose main component is an elastic body whose molecular chains have a mesh structure or a polymeric elastic body whose main chain is composed of hard segments and soft segments. A frost damage prevention pile according to claim 1.