Screw pile for installation in permafrost soil

Abstract

This utility model relates to construction and is intended, in particular, for the construction of building and structure foundations, temporary and permanent supports, especially during installation in permafrost soils (PMS). The technical result of this utility model is to reduce the impact of frost heave forces on the pile, increase the load-bearing capacity of the screw pile, and enhance the structural reliability of the screw pile. This technical result is achieved by the screw pile being constructed from a hollow tube containing a tip and having two flanges of a smaller diameter and a flange of a larger diameter. The flange of the larger diameter is positioned above the two flanges of the smaller diameter, and the tip is provided with cutouts.

Description

[0001] The utility model relates to the field of construction and is intended, in particular, for the construction of foundations for buildings and structures, temporary and permanent supports, especially during installation in conditions of permafrost soils (PMS).

[0002] Hole piles are commonly used in the Far North, where soils are plastically frozen. However, existing pile designs are not suitable for all engineering and geocryological conditions in frozen zones. In winter, soil temperatures in frozen zones drop to 15 degrees Celsius and below. At such low temperatures, soil strength increases to such an extent that pile flanges may experience significant deformations during installation and fail to provide the required bearing capacity after installation. The situation is exacerbated by the presence of unpopulated sands in the soil, which can result in the entire soil mass being frozen solid during winter.

[0003] When installing piles in MMG, it is necessary to take into account the high resistance to screwing due to the hardness of the soil, which entails the risk of deformation of the flanges, their insufficient fixation in the cryogenic structure of the soil, followed by deformation of the foundation and a decrease in stability under vertical pull-out loads.

[0004] A pile for constructing a pile foundation is known under Russian Federation Patent No. 2660692 for an invention (IPC: E02D 27 / 12; publication date: 07 / 09 / 2018), consisting of a tubular metal shaft and a flange with two blades at the end of the pile, wherein the pile shaft is made sealed, at the upper end the pile is equipped with a swivel for feeding hardening mortar under pressure into the cavity of the pile shaft, and at the lower end of the pile under the flange blade a one-way valve for the release of hardening mortar and impregnation of the soil with the formation of a load-bearing shell made of soil concrete around the flange.

[0005] Common features of the declared and known solutions are the presence of a pipe (barrel) and flanges.

[0006] However, the known solution has low bearing capacity under MMG conditions.

[0007] Also known is a multi-blade pile according to the Russian Federation patent No. 2816722 for a utility model (IPC: E02D5 / 56; publication date: 04 / 03 / 2024), designed for work in non-rocky soils, consisting of a shaft, extension elements connected to the shaft, screw blades of the same size located along the length of the shaft, and a conical tip, while the screw blades are located within the bearing soil layer with a thickness of H н.сл. At a certain distance from each other, a multiple of the pitch of the screw blade "a".

[0008] Common features of the declared and known solutions are the presence of a barrel, flanges and the location of the flanges at a certain distance from each other.

[0009] However, the pile according to the well-known patent has a different design, in particular, a conical tip, and flanges of the same size, which complicates the process of installing a screw pile and does not allow for such an increase in the bearing capacity of the screw pile and a reduction in the impact of frost heaving forces on it.

[0010] Also known is a screw pile according to the Russian Federation patent No. 80690 for a utility model (IPC: E02D5 / 56; publication date: 02 / 20 / 2009), adopted as a prototype, which includes a hollow cylindrical barrel and a screw blade, the lower turn of which is made with a diameter reduction of (0.6÷0.8) from the value of its maximum diameter (D нвах ), while the diameter of the upper turn of the blade (D вв ) is (3-4) of the outer diameter d нар barrel, maximum diameter of the lower turn of the blade (D нвmax ) is equal to (0.8÷0.9) the diameter of the upper turn of the blade (D BB ), blade pitch (N Л ) is (1.0÷1.2) of the outer diameter (d нар) of the pile shaft, the number of turns of the blade is (1.2÷1.25), while on the working part of the pile shaft there are two diametrically located cutouts, and the beginning of the blade is located from the cutout at a distance equal to (0.9÷1.0) of the outer diameter (d нар ) trunk.

[0011] Common features of the declared and known solutions are the presence of a pipe (shaft) and cutouts on the bottom of the pile (tip), as well as the implementation of flanges (blade turns) of various diameters, with the flange (turn) of a larger diameter located higher than the flange (turn) of a smaller diameter.

[0012] However, the design of the known solution does not include separate flanges spaced along the length of the pipe, which impacts the pile's load-bearing capacity and structural reliability. This design results in unstable engagement of smaller-diameter flanges with the formed thread, causing deformations, and significantly complicates the installation of the screw pile due to the excessively large diameter of the final thread.

[0013] The technical problem that this utility model is aimed at solving is the creation of a pile design that would increase the load-bearing capacity of the pile in conditions of the spread of MMG and facilitate the installation of the pile.

[0014] The technical result of this utility model is to reduce the impact of frost heaving forces on the pile, increase the bearing capacity of the screw pile, and improve the reliability of the screw pile design.

[0015] The technical result is achieved due to the fact that the screw pile is made from a hollow pipe containing a tip, and on which two flanges of a smaller diameter are located, a flange of a larger diameter, while the flange of a larger diameter is located above the two flanges of a smaller diameter, and the tip is made with cutouts.

[0016] That is, the pile tip, made with notches, and two flanges of smaller diameter facilitate effective pile penetration into the frozen ground and increase its bearing capacity. The notches in the pile tip ensure better penetration and securement (robust fixation) in the frozen ground. The location of the flange of larger diameter above the two flanges of smaller diameter, at a distance equal to the pitch of the lower flanges, ensures that the flange of larger diameter is screwed into the thread created by the two flanges of smaller diameter in the soil mass, simplifying pile penetration into frozen soil and preventing soil collapse and loosening. The two flanges of smaller diameter, located lower (closer to the pile tip) than the flange of larger diameter, stabilize the lower part of the pile, reducing lateral displacement and enhancing fixation in dense soil layers.

[0017] In one embodiment, the hollow pipe may be made of steel.

[0018] In one embodiment, the fastening of the flanges to the pile pipe is carried out using cold welding, which ensures high strength of the connection without thermal exposure, which is especially important in MMG conditions; this design additionally minimizes the risk of deformation and maintains the corrosion resistance of the pipe shaft, for example, in contrast to arc welding.

[0019] In one embodiment, the flanges are attached to the pile pipe using semi-automatic welding in a protective gas environment, which allows for the formation of a uniform, strong seam, ensuring a connection without pores and cracks due to a stable arc and gas flow, which further increases the reliability of the pile structure during installation in MMG.

[0020] In one embodiment, an anti-corrosion coating is applied to the pipe, which protects the pipe from corrosion, maintaining the load-bearing capacity of the pile and minimizing weakening of its shaft (pipe).

[0021] In one embodiment, the pile tip notches are feather-shaped, ensuring reliable penetration into the MMGP, reducing torque and preventing jamming. The notches direct the removal of frozen soil and ice up the pipe shaft, minimizing the resistance of cutting into the ground, which is critical for dense cryogenic rocks. The feather-shaped notches enhance the cutting effect, loosening the MMGP around the tip's periphery, reducing the risk of pipe shaft deformation when screwing into layers with temperatures down to -15 degrees Celsius. The number of notches depends on the pipe diameter.

[0022] In one embodiment, the pile tube is designed with a circular cross-section, which minimizes lateral friction during insertion into the MMG, reducing torque and ensuring stable anchorage without stress anisotropy. The circular cross-section of the pile increases its reliability due to ease of reproducibility and eliminates deformation due to uniform resistance to freezing and thawing temperature cycles.

[0023] In one embodiment, the pile tube is designed with an elliptical cross-section, which increases resistance to lateral loads and frost heave in the active layer of the MMG. The increased contact perimeter of the pile with the ground enhances friction and stability in plastically frozen soils. The elliptical cross-section of the steel pile tube facilitates meltwater drainage along the long axis, reducing corrosion and extending the service life, which in turn increases the reliability of the pile structure.

[0024] In one embodiment, the screw pile, after its installation, is filled with cement-sand mortar, cement-sand mixture, polyurethane foam or any other filler.

[0025] In one embodiment, the smaller-diameter flanges are designed with a constant pitch, ensuring uniform distribution of forces along the height of the pile, creating a stable helical trajectory, and increasing the pile's bearing capacity through consistent soil compaction without peak loads. A constant pitch between the smaller-diameter flanges minimizes soil compaction, reducing torque compared to a variable pitch, where the larger flange captures a greater volume of soil in the upper layers, stabilizing the structure in loose and frozen layers. This eliminates the risk of trajectory deviation, ensuring vertical penetration with a deviation of less than 1-2% and uniform fixation of all flanges without shaft deformation. In the MMG, a constant pitch enhances the freezing of the flanges with the soil throughout the contact zone, increasing resistance to pullout due to the anchoring effect of the larger-diameter flange and the smaller-diameter flanges.That is, the design increases durability by increasing the reliability of the structure, which directly affects the load-bearing capacity of the pile structure.

[0026] In this case, the larger-diameter flange can be positioned at a distance from the smaller-diameter flange, which differs from the pitch between the smaller-diameter flanges. This optimizes the pile's interaction with heterogeneous soil, adapting the compaction profile to layers of varying density and increasing overall load-bearing capacity. This reduces peak torque in the MMG transition zones, preventing jamming and ensuring a smooth transition from the cutting effect of the smaller-diameter flange to the grip of the larger-diameter flange. This improves alignment accuracy and minimizes compaction by eliminating pipe eccentricity. This solution increases structural reliability by reducing stress and adapting to complex geological sections. The distance from the smaller-diameter flange to the larger-diameter flange should ensure that the larger-diameter flange fits into the already formed groove in the form of a cylindrical cavity (thread) in the soil mass.

[0027] The flange diameters depend on the width of the flanges themselves.

[0028] The essence of the utility model is explained by drawings:

[0029] Fig. 1 - general diagram of the execution of a screw pile,

[0030] Fig. 2 - a specific example of the implementation of a screw pile.

[0031] The following notations are used on the figures:

[0032] 1 - hollow pipe,

[0033] 2 - larger diameter flange,

[0034] 3 - smaller diameter flange,

[0035] 4 - tip,

[0036] 5 - tip cutouts,

[0037] H - step between flanges of smaller diameter,

[0038] P - the distance between the flange of larger diameter and the flange of smaller diameter.

[0039] The utility model is implemented as follows.

[0040] A screw pile made of a hollow pipe 1 containing a tip 4 (the lower end of the pipe 1) and on which two flanges of smaller diameter 3 and a flange of larger diameter 2 are located. In this example of implementation, the pipe 1 is made of steel, and two flanges of smaller diameter 3 are located on the pipe 1, wherein flanges 2 and 3 are attached to the pipe by cold welding. Moreover, the flange of larger diameter 2 is located higher on the pipe 1 than the flanges of smaller diameter 3. The flanges of smaller diameter 3 are made with a constant pitch H. The flange of larger diameter is located at a distance P from the flanges of smaller diameter. The tip 4 has two cutouts 5. The cutouts 5 of the tip 4 are made in the form of a feather.

[0041] Let us consider an example of the implementation of the utility model in more detail (see Fig. 2). A screw pile made of a hollow pipe 1, length L. The pipe diameter is 159 mm. Pipe 1 is made of steel grade 09G2S. Pipe 1 contains a tip 4 (the lower end of pipe 1) and on which (on pipe 1) two flanges of smaller diameter 3 are located at a distance of 400 m from the lower edge of the pipe, as well as a flange of larger diameter 2. Flanges 2 and 3 are attached to the pipe by cold welding. The thickness of flanges 2 and 3 is 6 mm. The diameter of the flange of larger diameter is 280 mm, the diameter of the flanges of smaller diameter is 240 mm. Flanges of smaller diameter 3 are made with a constant pitch H, which is equal to 150±5 mm. In this case, the flange of larger diameter 2 is located on the pipe 1 higher than the flanges of smaller diameter 3, the distance between the flange of larger diameter 3 and the flanges of smaller diameter 2 is 1500±5 mm.The distance from the smaller-diameter flange 3 to the larger-diameter flange 2 ensures that the larger-diameter flange 2 fits into the already formed groove in the form of a cylindrical cavity (thread) in the soil mass. The cutouts 5 of the tip 4 are feather-shaped. The tip 4 has two cutouts 5, the dimensions of which are shown in Figure 2.

[0042] To prove the technical result, tests were carried out on a pile made similar to the declared pile in Figure 2. It was determined that this version of the design has a higher resistance to pull-out load due to the selected step between flanges of a smaller diameter and the distance between flanges 2 and 3. It was also proven that this version of the pile is optimal for work on sandy and clayey frozen soils, which is confirmed by the calculation of the stress-strain state of the soil and the pile, for example, the maximum displacement of soil (sand) is 17 mm, the maximum stress in the pile is 46 mm, the maximum stress in the soil (sand) is 0.37 MPa, the maximum plastic deformations in the pile are 1.51 mm, which indicates the provision of the bearing capacity of the pile.

[0043] The proposed technical solution in any of the embodiments ensures a reduction in the impact of frost heaving forces on the pile, an increase in the load-bearing capacity of the pile, and also contributes to an increase in the reliability of the structure, including through the use of a flange of a larger diameter and two flanges of a smaller diameter, as well as cutouts located on the tip of the pile.

Claims

1. A screw pile made from a hollow pipe containing a tip and on which are located two flanges of a smaller diameter, a flange of a larger diameter, wherein the flange of a larger diameter is located above the two flanges of a smaller diameter, and the tip is made with cutouts.

2. A screw pile according to item 1, in which the hollow pipe is made of steel.

3. A screw pile according to item 1, in which the flanges are attached to the pipe by cold welding.

4. A screw pile according to item 1, in which the flanges are attached to the pipe by a method of semi-automatic welding in a protective gas environment.

5. A screw pile according to item 1, in which the pipe is fully or partially covered with an anti-corrosion coating.

6. A screw pile according to item 1, in which the tip cutouts are made in a feather-shaped form.

7. A screw pile according to item 1, in which the flanges of smaller diameter are made with a constant pitch.

8. A screw pile according to claim 1, in which the pipe has a circular cross-section.

9. A screw pile according to claim 1, wherein the pipe has an elliptical cross-section.

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