Frost-heaving-resistant pile system and construction method

Abstract

A frost-heaving-resistant pile system and a construction method. The frost-heaving-resistant pile system comprises a variable-cross-section pile body (1), an upright pile body (2) connected to the bottom of the variable-cross-section pile body (1), and a geothermal pipe (3) pre-buried in the variable-cross-section pile body (1) and the upright pile body (2). At least one variable-cross-section pile body (1) is arranged above the upright pile body (2); the variable-cross-section pile body (1) comprises a truncated cone portion (11) and an inverted truncated cone portion (12); the inverted truncated cone portion (12) is connected to the bottom of the truncated cone portion (11); and the geothermal pipe (3) is connected to a ground source heat pump set. The truncated cone portion (11) is combined with the inverted truncated cone portion (12) to form the variable-cross-section pile body (1), thereby achieving an effect of actively weakening a frost-heaving force, facilitating decomposition and conversion of the force, effectively reducing the frost-heaving effect of frost-heaving shear stress on a pile foundation, and improving the heaving resistance stability of the pile foundation; and the geothermal pipe (3) can effectively heat the variable-cross-section pile body (1) and the upright pile body (2), improving the frost-heaving resistance of the pile body. Such a frost-heaving-resistant pile structure can effectively improve the reliability of a pile foundation in a frozen area and facilitate reduction of economic costs of pile foundation manufacturing and construction.

Description

Antifreeze pile extraction system and construction method

[0001] This patent application claims priority to Chinese Patent Application No. CN202410020684.5, filed on January 5, 2024, entitled "Anti-freeze pile extraction system and construction method." The disclosure of that prior application is incorporated herein by reference in its entirety. Technical Field

[0002] The present application belongs to the technical field of antifreeze pile extraction, and more specifically, relates to an antifreeze pile extraction system and a construction method. Background Art

[0003] In seasonally frozen areas, pile foundations (pile foundations, or simply piles) often experience frost heave. This frost heave is primarily caused by the seasonal freeze-thaw process and is closely related to the frost heave properties of the soil. During the freeze-thaw process, when the temperature drops below the soil's freezing point, the frost heave phase begins. During this period, the frozen soil layer in the foundation expands upward in volume and thickness, creating an upward frost heave force on the pile foundation.

[0004] During the above-mentioned freeze-thaw process, the horizontal frost heave force around the existing pile foundation increases, the friction resistance at the contact surface between the pile foundation and the active layer of frozen soil increases, and the frost shear stress formed at the contact surface between the pile foundation and the frozen soil causes the pile body to displace upward, forming the pile foundation frost shear phenomenon. The above phenomenon can easily lead to uneven deformation of the building foundation, causing damage to the building, affecting the normal use of the building, and posing a major safety hazard. Technical issues

[0005] The purpose of this application is to provide an anti-freeze pile pulling system and construction method, which can effectively reduce the freeze-pull effect of freeze-pull shear stress on the pile foundation, improve the anti-freeze and pull stability of the pile foundation, and solve the technical problem that the pile foundation freezing phenomenon causes uneven deformation of the building foundation, thereby affecting the normal use of the building and causing major safety hazards to the building. Technical Solutions

[0006] To achieve the above objectives, the technical solution adopted in this application is:

[0007] In the first aspect, the present application provides an anti-freeze pull-out pile, comprising a variable-section pile body, a straight pile body connected to the bottom of the variable-section pile body, and a geothermal pipe pre-buried in the variable-section pile body and the straight pile body. The variable-section pile body is provided with at least one above the straight pile body. The variable-section pile body comprises a positive cone portion and an inverted cone portion, the inverted cone portion is connected to the bottom of the positive cone portion, and the geothermal pipe is connected to a ground source heat pump unit.

[0008] In a possible implementation, the cone angle of the inverted cone is α, 0°≤α≤45°, and the ratio of the height of the positive cone to the height of the inverted cone is 2:1≤h i1 :hi2 ≤3:1, where h i1 is the height of the positive cone of the i-th variable cross-section pile, h i2 is the height of the inverted cone of the i-th variable-section pile.

[0009] In some embodiments, the height h3 of the straight pile body is greater than h i1 +h i2 , where h3 is the height of the straight pile.

[0010] In a possible implementation, the minimum diameter of the positive tapered portion and the minimum diameter of the inverted tapered portion are respectively equal to the diameter of the straight pile body.

[0011] In a possible implementation, two variable-section pile bodies are provided, and the two variable-section pile bodies are arranged in an up-down direction, and the lower end of the variable-section pile body located at the lower end is connected to the upper end of the straight pile body.

[0012] In one possible implementation, one end of the geothermal pipe is connected to the outlet of the ground source heat pump unit, and the other end of the geothermal pipe is connected to the inlet of the ground source heat pump unit. The geothermal pipe is used to heat the variable-section pile and the straight pile.

[0013] In a possible implementation, the forward tapered portion and the inverted tapered portion are integrally formed, and the variable-section pile body and the straight pile body are integrally formed.

[0014] In a second aspect, the present application further provides a method for constructing frost-resistant piles, which comprises the following steps:

[0015] S100: placing a geothermal pipe in the antifreeze pile template, connecting the geothermal pipe to the ground source heat pump unit, pouring concrete between the geothermal pipe and the antifreeze pile template, and after curing, removing the antifreeze pile template to obtain the antifreeze pile;

[0016] S200: Apply asphalt water repellent to the surface of the antifreeze pile to form a coating layer;

[0017] S300: Drilling a pile hole on the ground, placing an antifreeze pile into the pile hole, and aligning the antifreeze pile so that its axis is perpendicular to the ground;

[0018] S400: Fill the natural soil between the anti-freeze pile and the inner wall of the pile hole, and vibrate the natural soil to make it dense.

[0019] In some embodiments, before step S200, the concrete on the surface of the antifreeze pile is cleaned, and after step S200, vaseline is applied to the periphery of the coating layer.

[0020] In some embodiments, the asphalt hydrophobic material includes a ferroferric oxide solution, asphalt, and asphalt oil residue mixture coated sequentially from the inside out, the density of the asphalt is greater than 95%, and the thickness of the asphalt layer is 5 mm to 6 mm. Beneficial effects

[0021] Compared with the prior art, the solution shown in the embodiment of the present application is a frost-proof pile pulling system provided by the embodiment of the present application, which utilizes a combination of a positive cone and an inverted cone to form a variable-section pile body, thereby actively reducing the frost-proof pullout force, facilitating the decomposition and conversion of force, effectively reducing the frost-proof pullout effect of frost-proof pullout shear stress on the pile foundation, and improving the pull-out stability of the pile foundation. The geothermal pipe can effectively heat the variable-section pile body and the straight pile body, thereby improving the frost-proof pullout performance of the pile body. The above-mentioned frost-proof pile pulling system is convenient for engineering production and mechanized construction, can effectively shorten the construction period, improve the reliability of the pile foundation in the frozen area, and facilitate reducing the economic cost of pile foundation production and construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0023] FIG1 is a schematic structural diagram of an antifreeze pile extraction method according to an embodiment of the present application;

[0024] FIG2 is a schematic diagram of a front cross-sectional structure of an antifreeze pile provided in an embodiment of the present application;

[0025] FIG3 is a force analysis diagram of the positive cone portion and the soil in FIG1 of the embodiment of the present application;

[0026] FIG4 is a force analysis diagram of the inverted cone and the soil in FIG1 of the embodiment of the present application;

[0027] FIG5 is a force analysis diagram of the antifreeze pile in FIG1 of the embodiment of the present application;

[0028] FIG6 is a schematic diagram of a front cross-sectional structure of the inverted cone portion in FIG1 according to an embodiment of the present application;

[0029] FIG7 is a top view of the inverted cone and the soil in FIG1 according to an embodiment of the present application;

[0030] FIG8 is a schematic diagram of parameter selection of a bamboo cone pile according to an embodiment of the present application;

[0031] FIG9 is a schematic diagram of the structure of bamboo cone piles at different height ratios when N=3 and α=7° according to an embodiment of the present application;

[0032] FIG10 is a schematic diagram of the structure of bamboo cone piles at different height ratios when N=2 and α=7° according to an embodiment of the present application;

[0033] FIG11( a ) is a perspective schematic diagram of the bamboo-jointed cone pile according to an embodiment of the present application, and FIG11( b ) is a perspective schematic diagram of the bamboo-jointed cone pile according to an embodiment of the present application after being damaged by frozen soil.

[0034] Figures 12(1) to 12(5) (a)-(j) are two-dimensional schematic diagrams comparing the frozen pullout displacement of bamboo cone piles under different factors;

[0035] Figures 13(a) and 13(b) are both three-dimensional schematic diagrams comparing the frozen-pullout displacement of bamboo cone piles under different factors.

[0036] Among them, the reference numerals in the figures are: 1, variable-section pile body; 11, positive cone portion; 12, inverted cone portion; 2, straight pile body; 3, geothermal pipe. Modes for Carrying Out the Invention

[0037] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0038] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or indirectly on the other element. It should be understood that the terms "length", "width", "upper", "lower", "front", "back", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. The terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, "several" means two or more, unless otherwise clearly and specifically defined.

[0039] Please refer to Figures 1 to 7 together, and the antifreeze pile system and construction method provided by this application will now be described. The antifreeze pile system includes a variable-section pile body 1, a straight pile body 2 connected to the bottom of the variable-section pile body 1, and a geothermal pipe 3 pre-buried in the variable-section pile body 1 and the straight pile body 2. The variable-section pile body 1 is provided with at least one above the straight pile body 2. The variable-section pile body 1 includes a positive cone portion 11 and an inverted cone portion 12. The inverted cone portion 12 is connected to the bottom of the positive cone portion 11. The geothermal pipe 3 is connected to the ground source heat pump unit. Among them, the variable-section pile body 1 and the straight pile body 2 together constitute an antifreeze pile. The shape of the antifreeze pile is named a bamboo cone pile, and one variable-section pile body 1 is called a bamboo node.

[0040] Compared with the prior art, the anti-freeze pile pulling system provided in this embodiment uses a variable-section pile body 1 structure formed by combining a positive cone 11 and an inverted cone 12, which can achieve the effect of actively weakening the frost pull force, facilitate the decomposition and transformation of force, effectively reduce the frost pull effect of frost pull shear stress on the pile foundation, and improve the anti-freeze pull stability of the pile foundation. The geothermal pipe 3 can effectively heat the variable-section pile body 1 and the straight pile body 2, thereby improving the anti-freeze pull performance of the pile body. The above-mentioned anti-freeze pile pulling system is convenient for engineering production and mechanized construction, can effectively shorten the construction period, improve the reliability of the pile foundation in frozen areas, and facilitate reducing the economic cost of pile foundation production and construction.

[0041] For ease of description, the combined structure of the variable-section body 1 and the straight pile body 2 is defined as the pile body, which is cast using concrete. A geothermal pipe 3 is pre-buried within the pile body to heat the pile body using geothermal energy. Specifically, the geothermal pipe 3 comprises two interconnected stainless steel pipes within the pile body, allowing ground-source heat to flow in and out of the pipes, ensuring orderly heat transfer.

[0042] Furthermore, the stainless steel pipe is arranged into a bent structure in its extension direction, which can increase the contact area between the geothermal pipe 3 and the pile body, improve the heat exchange capacity between the stainless steel pipe and the pile body, and enhance the heating effect on the pile body.

[0043] In this embodiment, when the ground freezing depth is within the height range of the positive cone portion 11, due to the existence of the cone angle of the positive cone portion 11, the shape of the pile body in the corresponding area can weaken the frost pull effect of the surrounding soil on the pile foundation. The above is the advantage of the cone angle of the positive cone portion 11.

[0044] When the depth of ground freezing increases gradually to within the height range of the inverted cone portion 12, the pile shape of the inverted cone portion 12 not only cannot reduce the frozen-out effect of the pile foundation, but instead increases the risk of the pile foundation being frozen-out. But at this moment, the interaction force between the pile body and the soil layer in the inverted cone portion 12 regions progressively increases as the degree of soil freezing deepens, and stress concentration occurs in the soil body near this position. In addition, because cold energy is transmitted downward by the surface, the ground temperature near the inverted cone portion 12 positions is still in a higher state just after freezing, and the frozen soil strength is lower. Under the larger pressure of the inverted cone portion 12 pile bodies, the frozen soil at this position very easily enters a plastic state, and even occurs destructive situations such as cracking damage when serious. Therefore, the degree of destruction of the peripheral soil bodies of the inverted cone portion 12 increases relatively, weakens the force on the inverted cone portion pile body, and then reaches the effect of reducing the pile foundation frozen-out.

[0045] The advantageous cone angle of the positive cone 11 and the plastic failure of the high-temperature frozen soil at the inverted cone 12 effectively reduce the frost pullout effect of the pile body, making the frost pullout displacement of the anti-freeze pile much smaller than that of a traditional straight pile. Compared to ordinary integrally tapered piles of equal height, the structure of the variable-section pile body 1 is such that when the taper of the integrally tapered pile is the same as that of the positive cone 11, the bottom cross-sectional area of ​​the integrally tapered pile is much larger than the cross-sectional area of ​​the variable-section pile body 1 at any height. The structure of the variable-section pile body 1 can effectively reduce the amount of construction materials, thereby reducing the project cost.

[0046] Thus, it can be seen that the essence of frost-uplift-resistant piles is to reduce the frost-up force acting on the pile body by changing the pile shape, taking advantage of the cone angle advantage of the positive cone 11 and the stress concentration and plastic failure of the surrounding soil caused by the inverted cone 12. This pile shape not only reduces the frost-up force acting on the positive cone 11 of the pile body, but also takes advantage of the pile body's inherent strength being higher than that of the frozen soil. During the cold transfer process, when the compressive stress of the inverted cone 12 on the surrounding frozen soil reaches the plastic failure strength of the frozen soil, the frost-up effect of the pile body is reduced.

[0047] Changes in ambient temperature affect the physical and mechanical properties of frozen soil. Negative temperature is a prerequisite for soil freezing and is also a key factor in determining the mechanical properties of the pile-soil interface during the freezing process.

[0048] Referring to Figures 3 and 4, taking a single variable-section pile 1 as an example, considering only the stress state of the positive tapered portion 11 under soil frost heave deformation (i.e., when the anti-freeze pile is above the freezing depth line), Figure 3 shows the stress state of the positive tapered portion 11, while Figure 4 shows the stress state of the inverted tapered portion 12. The stress state of the portion of the anti-freeze pile above the freezing depth line is opposite to that of the corresponding portion below the freezing depth line.

[0049] In Figure 4, V is the vertical frost heave force generated by frozen soil; H is the horizontal frost heave force generated by frozen soil; V' is the vertical resistance generated by the pile; and H' is the horizontal resistance generated by the pile. The frost-resistant pullout piles are primarily subject to the vertical frost heave force V and the horizontal frost heave force H generated by the frozen soil; the soil is primarily subject to the vertical resistance V' and the horizontal resistance H' generated by the pile.

[0050] From the force analysis diagram we can see that:

[0051] Frozen shear stress of positive cone 11:

[0052] Normal compressive stress of the positive cone 11:

[0053] Frozen shear stress of the inverted cone 12:

[0054] Normal compressive stress of the inverted cone 12:

[0055] Where: τ1 is the frost shear stress on the positive cone 11 of the anti-freeze pile; τ2 is the frost shear stress on the inverted cone 12 of the anti-freeze pile; N1 is the normal compressive stress on the positive cone 11 of the anti-freeze pile; N2 is the normal compressive stress on the inverted cone 12 of the anti-freeze pile. It represents the tangential component of the vertical frost heave force exerted by the frozen soil on the positive cone 11, It represents the tangential component of the horizontal frost heave force generated by the frozen soil on the positive cone 11, It represents the normal component of the horizontal frost heave force generated by the frozen soil on the cone 11, It represents the normal component of the vertical frost heave force generated by the frozen soil on the cone 11, It represents the tangential component of the vertical frost heave force generated by the frozen soil on the inverted cone 12, It represents the tangential component of the horizontal frost heave force generated by the frozen soil on the inverted cone 12, It represents the normal component of the horizontal frost heave force generated by the frozen soil on the inverted cone 12, It represents the normal component of the vertical frost heave force generated by the frozen soil on the inverted cone 12. The above parameters are obtained by combining the components of the vertical resistance V′ and the horizontal resistance H′ of the pile body.

[0056] It should be noted that the above stress conditions of the positive cone portion 11 and the inverted cone portion 12 are only for the stress conditions of the positive cone portion 11 and the inverted cone portion 12 when the bamboo node is located above the freezing depth line.

[0057] Under the conditions of negative temperature and no overlying load (i.e., at sub-zero temperature, there is no other force above the pile body, and it is only subject to gravity and pile-soil forces), the overall force analysis of the anti-freeze pull-out pile is shown in Figure 5.

[0058] The equilibrium condition of the vertical force is:

[0059] Where: P is the resultant force of frost pullout; G is the weight of the pile foundation (i.e., the weight of the entire frost pullout pile); F is the reaction force at the bottom of the frost pullout pile; α is the cone angle of the positive cone 11; β is the angle between the positive cone 11 and the inverted cone 12, τ k is the shear freezing stress on the pile-soil interface of the vertical pile body; τ is the freezing shear stress of the corresponding part of the anti-freeze pull-out pile; N is the normal compressive stress of the corresponding part of the anti-freeze pull-out pile, τ 1i (i=1, 2, 3) represents the tangential stress of the first section positive cone 11, the tangential stress above the freezing depth line of the second section positive cone 12, and the tangential stress below the freezing depth line of the second section positive cone 11, τ 2j (j=1, 2) represents the tangential stress of the first section of the inverted cone 12 and the tangential stress of the second section of the inverted cone 12, N 1i (i=1, 2, 3) represents the normal stress of the first section of the positive cone 11, the normal stress above the freezing depth line in the second section of the positive cone 11, and the normal stress below the freezing depth line in the second section of the positive cone 11, N 2j (j=1, 2) represents the normal stress of the first section of the inverted cone 12 and the normal stress of the second section of the inverted cone 12, L i Indicates the height of the positive tapered portion 11, L j Indicates the height of the inverted tapered portion 12, L k represents the height of the cylinder (the height of the straight pile body 2), D1 represents the top diameter of the positive tapered portion 11, and D2 represents the bottom diameter of the positive tapered portion 11.

[0060] Refer to Figure 5. It shows that the normal compressive stresses above and below the frost depth line are in the same direction, while the frost shear stresses are in opposite directions. The frost pullout resistance of the pile is primarily reflected in the area above the frost depth line.

[0061] In Figure 5, the part of the variable-section pile body 1 located above the frost depth line, due to the existence of the cone angle of the positive cone 11, the normal compressive stress of the surrounding soil on the positive cone 11 is directed toward the lower side of the axis of the positive cone 11. The positive cone 11 can form an outward and upward reaction force on the soil, which can reduce the frost pull effect of the surrounding soil on the pile foundation. The above effects form the cone angle advantage of the positive cone 11.

[0062] At the same time, the normal compressive stress of the surrounding soil on the inverted cone 12 is directed toward the upper axial side of the positive cone 11. The inverted cone 12 can form an outward and downward reaction force on the soil, which can cause the frozen soil at this position to enter a plastic state. In severe cases, it may even cause cracking damage and other damage. Therefore, the degree of damage to the soil outside the inverted cone 12 is relatively increased.

[0063] The advantageous cone angle of the positive cone 11 and the plastic failure of the inverted cone 12 on frozen soil effectively reduce the frost pullout effect of the pile, making the frost pullout displacement of the anti-freeze pile much smaller than that of a traditional straight pile. Compared to ordinary tapered piles of the same height, the volume of the tapered pile 1 is much larger when the cone angle of the tapered pile is the same as that of the positive cone 11. The structure of the variable-section pile 1 can effectively reduce the amount of construction materials, thereby reducing the project cost.

[0064] In summary, the variable-section pile body 1 structure formed by combining the positive cone 11 and the inverted cone 12 can achieve the effect of actively weakening the frost-drawing force, facilitate the decomposition and transformation of the force, effectively reduce the frost-drawing effect of the frost-drawing shear stress on the pile foundation, and improve the anti-freeze-drawing stability of the pile foundation.

[0065] In order to verify whether the frozen soil near the inverted cone 12 of the antifreeze pile can achieve plastic failure, the plastic state of the antifreeze pile was analyzed based on the failure theory at the pile-soil interface. During the freezing process of the soil, the soil on the side of the pile in the range near the inverted cone 12 will be subjected to pressure. Under the action of compression, the soil on the side of the pile gradually deforms and enters a plastic state. The area outside the plastic zone is the elastic deformation zone, as shown in Figures 6 and 7. Due to the effect of force, the antifreeze pile will produce slight deformation, forming a cross-sectional shape that is approximately elliptical. Similarly, the plastic zone and elastic zone also have a cross-sectional shape that is approximately elliptical.

[0066] Assume that the minimum radius of the inverted cone 12 of the antifreeze pile is R, the cone angle of the inverted cone 12 is γ, and the radius of the plastic zone is R P The plastic failure condition complies with the Mohr-Coulomb model criterion. The structural type of the anti-freeze pull-out pile shows that the inverted cone 12 generates compressive stress on the pile-soil interface under the combined action of the pile side normal pressure N and the tangential force τ.

[0067] According to the elastic theory of soil under compression:

[0068] Where: σ r , σ θ are the radial and tangential stresses at a point in the soil around the pile (kPa); σ ru is the compressive stress of the horizontal stress at the pile-soil interface (kPa).

[0069] Horizontal stress σ at a point on the pile-soil contact surface ru is: ru =(Νcosγ-τsinγ) (2-3)

[0070] Wherein: γ is half of the cone top angle of the inverted cone portion 12 of the antifreeze pile.

[0071] The Mohr-Coulmb failure condition can be used to determine whether the soil material has reached the yield state:

[0072] Where: is the internal friction angle of the soil; c is the cohesion of the soil (kPa).

[0073] Substituting formula (2-2) into formula (2-4) yields:

[0074] This formula still holds true at the boundary between the elastic zone and the plastic zone; if a plastic zone appears in the soil, then the plastic zone will inevitably appear first at the pile-soil interface.

[0075] Therefore, we can make:

[0076] Then σ ru The value indicates that the material is at the end of the elastic stage and is about to enter the plastic flow stage;

[0077] That is to say: when the compressive stress on the pile-soil surface meets When the pile is in the vertical direction, plastic deformation occurs in the soil around the pile.

[0078] In one possible implementation, referring to FIG2 , the antifreeze pile pulling system further includes a geothermal pipe 3 pre-buried in the variable-section pile body 1 and the straight pile body 2 , wherein a geothermal pipe 3 is provided in the geothermal pipe 3 , and the geothermal pipe 3 is connected to the ground source heat pump unit for heating the variable-section pile body 1 and the straight pile body 2 .

[0079] In this embodiment, the antifreeze pile and ground source heat pump technology are combined to utilize the ground source heat pump unit to extract the low-level heat energy in the soil, which is then transferred through the ground source heat pump unit to the antifreeze pile to heat the fill in the antifreeze pile, thereby achieving the purpose of preventing the antifreeze pile from being damaged by frost. The above method can not only solve the problem of frost damage to the antifreeze pile, but also make full use of renewable energy, thereby achieving the purpose of energy saving and reducing energy consumption.

[0080] In a possible implementation, the above-mentioned characteristic inverted cone portion 12 may adopt a structure as shown in FIG2 . Referring to FIG2 , the cone angle of the inverted cone portion 12 is α, 0°≤α≤45°, and the height ratio of the positive cone portion 11 to the inverted cone portion 12 is 2:1≤h i1 :h i2 ≤3:1, where h i1 is the height of the positive cone 11 of the i-th variable-section pile 1, h i2 is the height of the inverted cone 12 of the i-th variable-section pile body 1.

[0081] When selecting the angles of the inverted cone 12 and the normal cone 11, the angle α of the inverted cone 12 should be within a certain range to ensure the pile's frost pullout resistance. The angle α of the normal cone 11 should be within a range of 0°≤α≤45°. For example, it can be 5°, 10°, 15°, 20°, 22.5°, 25°, 30°, 35°, 40°, 45°, etc., to avoid excessively large or small angles that make it difficult to achieve a cone angle advantage. The above-mentioned angle range can cause the high-temperature frozen soil around the inverted cone 12 to undergo plastic failure, thereby achieving the effect of reducing the frost pullout of the pile.

[0082] Specifically, the ratio of the height of the positive tapered portion 11 to the height of the inverted tapered portion 12 is 2:1≤h i1 :h i2 ≤3:1, for example, it can be 2:1, 12:5, 3:1, etc. The above height ratio satisfies a certain range of values, so that the relative ratio of the positive tapered portion 11 and the inverted tapered portion 12 is within a certain range, achieving a cone angle advantage.

[0083] On the basis of the above structure, the height ratio of the positive cone portion 11 and the inverted cone portion 12 is limited, and then, on the premise that the maximum outer diameters of the two are equal and the minimum outer diameters are equal (the minimum outer diameters of the two are equal to the outer diameter of the straight pile body 2), the length of the positive cone portion 11 is made greater than the length of the inverted cone portion 12. Under the premise of ensuring the cone angle advantage of the positive cone portion 11, the inverted cone portion 12 is used to form plastic destruction on the frozen soil, thereby reducing the frost pullout force acting on the pile body and improving the frost pullout resistance of the pile body.

[0084] The height h3 of the straight pile body 2>h i1 +h i2 , where h3 is the height of the straight pile body 2. The minimum diameters of the positive tapered portion 11 and the inverted tapered portion 12 are respectively equal to the diameter of the straight pile body 2. This arrangement maintains the length of the straight pile body 2 below the frost depth line within a certain height range, allowing the straight pile body 2 to have a certain extended length, increasing its deadweight and ensuring the frost-proof performance of the anti-freeze-pull pile.

[0085] In one possible implementation, the characteristic variable-section pile body 1 can adopt a structure as shown in Figure 2. Referring to Figure 2, two variable-section pile bodies 1 are provided, and the two variable-section pile bodies 1 are arranged in the vertical direction, with the lower end of the variable-section pile body 1 located at the bottom connected to the upper end of the straight pile body 2.

[0086] In this embodiment, the number of variable-section pile bodies 1 is determined based on the height of the frost depth line, with two variable-section pile bodies 1 arranged in a vertically connected arrangement. During construction, the frost depth line should be located within the region of the tapered portion 11 of the lower variable-section pile body 1. This improves the frost-proof pile's frost-proof performance and enhances the pile foundation's frost-proof stability.

[0087] In one possible implementation, the geothermal pipe 3 characterized above can be installed as follows. One end of the geothermal pipe 3 is connected to the outlet of a geothermal heat pump unit, and the other end is connected to the inlet of the geothermal heat pump unit. The geothermal pipe 3 is used to heat the variable-section pile 1 and the straight pile 2. During installation, the ends of the geothermal pipe 3 are connected to the inlet and outlet of the geothermal heat pump unit, respectively, so that the heat exchange medium can smoothly enter the geothermal pipe 3 for heat exchange, thereby heating the pile body and preventing freeze-pull.

[0088] In one possible implementation, the positive tapered portion 11 and the inverted tapered portion 12 are integrally formed, and the variable-section pile body 1 and the straight pile body 2 are integrally formed. The positive tapered portion 11 and the inverted tapered portion 12 are cast by concrete, and the variable-section pile body 1 and the straight pile body 2 are integrally formed. This molding method ensures the structural strength of the entire frost-resistant pull-out pile, improves the bearing capacity of the pile body, and enhances the pull-out stability of the pile foundation.

[0089] Based on the same inventive concept, the present application also provides an antifreeze pile pulling construction method, which includes the following steps:

[0090] S100: Place the geothermal pipe 3 in the antifreeze pile template, connect the geothermal pipe 3 to the ground source heat pump unit, pour concrete between the geothermal pipe 3 and the antifreeze pile template, and after curing, remove the antifreeze pile template to obtain the antifreeze pile.

[0091] When the temperature drops in winter, the ground source heat pump unit hydraulically delivers a certain amount of water-based antifreeze liquid into a highly sealed tank at a certain pressure, and then performs heat exchange between different heat sources, so that the outlet end of the ground source heat pump unit can deliver a higher temperature water-based antifreeze liquid, and deliver the water-based antifreeze liquid to the geothermal pipe 3 (the geothermal pipe 3 is a highly sealed stainless steel pipe structure). The geothermal pipe 3 is used to transfer the heat carried inside to the inside of the pile body, so that the temperature inside the pile body increases, effectively avoiding the occurrence of pile foundation freeze-out.

[0092] In order to ensure the structural performance of the antifreeze piles, they need to be cured for a certain period of time after pouring. After the curing is completed, the antifreeze pile templates are removed to obtain the formed antifreeze piles.

[0093] S200: Clean the concrete and other impurities on the surface of the antifreeze pile to ensure the cleanliness of the antifreeze pile. Then, apply asphalt water repellent to the surface of the antifreeze pile to form a coating layer, and finally apply vaseline to the periphery of the coating layer.

[0094] First, apply a ferroferric oxide solution evenly to the surface of the antifreeze piles and let it dry. Next, heat and melt the asphalt, dehydrate it, and apply the molten asphalt to a thickness of 5-6 mm around the ferroferric oxide solution. Allow it to solidify. The density of the asphalt should be maintained above 95%.

[0095] Afterwards, prepare an asphalt oil residue mixture, which has good frost heave resistance. Apply the asphalt oil residue mixture to the surface of the asphalt layer, check the uniformity of the application, and reapply any defects in a timely manner.

[0096] Finally, apply Vaseline on the outside of the asphalt oil residue mixture to prevent the antifreeze piles from combining with the soil due to unpredictable factors, such as moisture entering the gaps between the antifreeze piles and the soil. The use of Vaseline can prevent the antifreeze piles from freezing into one with the soil, thereby preventing the two from being pulled up as a whole.

[0097] S300: Drill a pile hole into the ground, place the frost-resistant pile into the hole, and align the pile axis so that it is perpendicular to the ground. Drill the hole at the designated location on the ground to a depth consistent with the height of the frost-resistant pile. Place the frost-resistant pile into the hole. The inner diameter of the pile hole should be larger than the maximum outer diameter of the frost-resistant pile to ensure smooth placement of the frost-resistant pile. Then, align the pile in the hole so that its axis is perpendicular to the ground.

[0098] S400: Fill the gap between the frost-resistant pile and the inner wall of the pile hole with natural soil, and vibrate and compact the soil. When burying the frost-resistant pile, the frost depth should be within the height range of the normal tapered portion 11 of the lowest variable-section pile body 1, ensuring the frost-resistant pile has optimal frost resistance. Furthermore, the gap between the outer perimeter of the frost-resistant pile and the inner wall of the pile hole is filled with natural soil, which needs to be vibrated and compacted to ensure the service stability of the frost-resistant pile.

[0099] The anti-freeze-pulling pile construction method provided in this embodiment utilizes a variable-section pile body 1 structure formed by combining a positive cone 11 and an inverted cone 12, which can achieve the effect of actively weakening the frost-pulling force, facilitate the decomposition and transformation of force, effectively reduce the frost-pulling effect of frost-pulling shear stress on the pile foundation, and improve the anti-pulling stability of the pile foundation. The geothermal pipe 3 can effectively heat the variable-section pile body 1 and the straight pile body 2, thereby improving the anti-freeze-pulling performance of the pile body. The above-mentioned anti-freeze-pulling pile is convenient for engineering production and mechanized construction, can effectively shorten the construction period, improve the reliability of the pile foundation in frozen areas, and facilitate reducing the economic cost of pile foundation production and construction.

[0100] In order to further explore the selection of the preferred bamboo cone pile parameters for the above-mentioned anti-freeze piles, a detailed description is given below.

[0101] The inventors discovered that when the ground freezing depth falls within the positive cone 11 of the antifreeze pile, its mechanical behavior is similar to that of tapered piles previously studied. Due to the cone angle, the pile shape can mitigate the freeze-up effect of the surrounding soil on the pile. However, as the ground freezing depth gradually increases to within the inverted cone 12 of the antifreeze pile, the shape of the inverted cone 12 fails to mitigate the freeze-up effect and instead increases the risk of freeze-up. However, the frozen soil in the inverted cone 12 is weaker and, under high pressure, is prone to entering a plastic state and even cracking and damage. Under the compression of the high pile-soil interaction, the overall freeze-up force acting on the antifreeze pile is weakened compared to traditional straight piles due to the destruction of the soil surrounding the inverted cone 12. Therefore, to better utilize the freeze-up resistance of the positive cone 11 and the freeze-up force-reducing effect of the inverted cone 12, it is necessary to analyze and calculate different height ratios of the positive cone 11 to the inverted cone 12 to find the height ratio with the best freeze-up resistance.

[0102] As described above, the essence of the bamboo cone pile in reducing the effect of frost pullout is to reduce the frost pullout force acting on the pile body by changing the pile type and taking advantage of the cone angle advantage of the positive cone 11 and the characteristics of stress concentration and plastic failure of the soil around the inverted cone 12. If the height of the positive cone 11 is too small, it will not be possible to play the advantage of the cone angle of the positive cone 11. If the height of the inverted cone 12 is too small, it will not be possible to achieve the purpose of causing plastic failure of the surrounding soil and thus reducing the vertical frost pullout force on the pile body. Taking comprehensive consideration, the height ratio range of the two is selected between 1:0 and 1:1, as shown in the gray trapezoidal part in Figure 8. Figures 9 and 10 are schematic diagrams of different height ratios when the number of bamboo nodes is 3 and 2, respectively. When the number of bamboo nodes remains unchanged, the angle α is 3°, 5°, 7° and 9°, and the height ratio of the positive cone 11 to the inverted cone 12 is 1:1, 2:1, 4:1 and 1:0, which are combined into 16 working conditions. Together with the case where α is 0° (straight pile), there are a total of 17 working conditions.

[0103] Based on the thermal-mechanical sequential coupling, the ABAQUS simulation software was used to analyze the frost-pullout characteristics of bamboo-jointed cone piles for different cone angles α, different height ratios h of the positive cone 11 to the inverted cone 12, and different numbers of bamboo nodes N. The analysis yielded pile parameters with optimal frost-pullout resistance. The cone angles include α = 3°, 5°, 7°, and 9°; the height ratios h of the positive cone 11 to the inverted cone 12 include 1:1, 2:1, 4:1, and 1:0; a bamboo node consists of a positive cone 11 and an inverted cone 12; and the number of bamboo nodes N = 2 or 3. Each bamboo node number has 16 calculation conditions, plus 33 calculation conditions when α is 0° (straight pile). The bamboo-jointed cone pile is a variable-section pile foundation structure whose geometric shape primarily consists of a true truncated cone, an inverted truncated cone, and a cylinder. The overall structure is shown in Figure 11(a). The morphology of the bamboo-jointed cone pile after frozen soil damage is shown in Figure 11(b).

[0104] In Figure 11, α is the cone angle of the bamboo cone pile (°); h i1 is the height of the positive cone 11 of the i-th bamboo node, (m); h i2 is the height of the inverted cone 12 of the i-th bamboo node, (m); height ratio h=h i1 / h i2 ; h3 is the height of the straight pile body, (m); h4 is the total height of the bamboo cone pile, (m).

[0105] The comparison diagrams of the frozen pullout of bamboo cone piles under different parameters can be seen in Figures 12 and 13. It can be seen that:

[0106] 1. Under the same number of bamboo nodes and height ratio, the frozen pull-out displacement of the pile body is inversely proportional to the cone angle of the pile body. The larger the cone angle, the smaller the frozen pull-out displacement of the pile body and the more stable the pile body. The frozen pull-out displacement of pile foundations with different cone angles is ranked from large to small as follows: 3° bamboo cone pile > 5° bamboo cone pile > 7° bamboo cone pile > 9° bamboo cone pile.

[0107] 2. For a bamboo-jointed cone pile with the same number of bamboo nodes and cone angle, the height ratio of the positive cone 11 to the inverted cone 12 is inversely proportional to the pile's frozen-out shear. As the height ratio of the positive cone 11 increases, the cumulative frozen-out shear of the pile gradually decreases. Because the pile displacement is similar when h = 4:1 and h = 1:0, and to fully utilize the characteristic that the soil around the inverted cone 12 is prone to plastic failure, a height ratio of 4:1 was selected.

[0108] 3. Under the same height ratio and cone angle, the frozen-up displacement of piles with different numbers of bamboo nodes is different. As the number of bamboo nodes increases, the cumulative frozen-up displacement tends to increase. When the number of bamboo nodes is 2, the frozen-up displacement of the pile is the smallest.

[0109] In summary, the frost pullout of the pile body is closely related to the cone angle, the number of bamboo nodes, the number of freeze-thaw cycles, the height ratio of the positive cone part 11 to the inverted cone part 12, etc. When the cone angle α = 9°, the number of bamboo nodes N = 2, and the height ratio h = 4:1 of the positive cone part 11 to the inverted cone part 12, the frost pullout of the pile body is the smallest, and the bamboo-node cone pile has the best frost pullout resistance.

[0110] As shown in Figure 13, it can be seen that the frozen-pull displacement of the pile body is closely related to the number of bamboo nodes, the height ratio of the positive cone 11 to the inverted cone 12, and the size of the cone angle. Among them, the influence of the cone angle on the frozen-pull displacement is much greater than the influence of the height ratio of the positive cone 11 to the inverted cone 12 on the frozen-pull displacement. When the cone angle changes, the frozen-pull displacement changes significantly. When the height ratio of the positive cone 11 to the inverted cone 12 changes, the frozen-pull displacement changes less. Therefore, in the actual design and construction process, the influence of the frozen pull-out displacement is affected by factors such as the depth of frozen soil, the volume of the pile body, the structural strength of the pile body, the difficulty of construction, the cost, and the height ratio of the positive cone 11 to the inverted cone 12. The height ratio of the positive cone 11 to the inverted cone 12 can be preferably selected within the range of 2:1≤h≤3:1. Compared with the height ratio h of the positive cone 11 to the inverted cone 12 being 4:1, the influence on the frozen pull-out displacement is not obvious, but the volume of the pile body can be further reduced, the structural strength of the pile body at the bamboo joint connection can be increased, the difficulty of construction can be reduced, and the cost of the project can be reduced.

[0111] In addition, as shown in Figure 13, it can be seen that the frozen pullout displacement of the pile body is closely related to the size of the cone angle. The larger the cone angle, the smaller the frozen pullout displacement. Although the cone angle can be designed to be larger, considering factors such as the larger the cone angle, the larger the volume of the entire pile body, the higher the project cost, and the greater the construction difficulty, combined with the actual finding that the frozen soil expansion rate is around 9%, it is found that when the cone angle is designed to be 9°, it is possible to achieve the best project cost-effectiveness while achieving a good anti-freeze pullout effect.

[0112] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. Anti-freezing and anti-pulling pile system, characterized in that, It includes a variable cross-section pile body, a straight pile body connected below the variable cross-section pile body, and a geothermal pipe embedded in the variable cross-section pile body and the straight pile body. There are two variable cross-section pile bodies above the straight pile body. The variable cross-section pile body includes a positive cone part and an inverted cone part. The inverted cone part is connected below the positive cone part. The variable cross-section pile body and the straight pile body form an anti-freezing and anti-pulling pile. The geothermal pipe is connected to a ground source heat pump unit; the cone angle of the inverted cone part is α, 0° ≤ α ≤ 45°, and the ratio of the height of the positive cone part to the height of the inverted cone part is 2:1 ≤ h i1 : h i2 ≤ 3:1, where h i1 is the height of the positive cone part of the i-th variable cross-section pile body, and h i2 is the height of the inverted cone part of the i-th variable cross-section pile body; the height h3 of the straight pile body is greater than h i1 + h i2 , where h3 is the height of the straight pile body; the positive cone part above the frost depth line is used to form an upward and outward reaction force on the soil to weaken the frost heaving effect of the soil; the inverted cone part above the frost depth line is used to form a downward and outward reaction force on the soil, so that the frozen soil enters the plastic state and weakens the frost heaving effect; the minimum diameter of the positive cone part and the minimum diameter of the inverted cone part are respectively equal to the diameter of the straight pile body; the two variable cross-section pile bodies are arranged in the up and down direction, and the lower end of the variable cross-section pile body below is connected to the upper end of the straight pile body; one end of the geothermal pipe is connected to the outlet end of the ground source heat pump unit, and the other end of the geothermal pipe is connected to the inlet end of the ground source heat pump unit. The geothermal pipe is used to heat the variable cross-section pile body and the straight pile body; Define V as the vertical frost heaving force generated by frozen soil; H as the horizontal frost heaving force generated by frozen soil; V′ as the vertical resistance force generated by the pile; H′ as the horizontal resistance force generated by the pile; The freezing and pulling shear stress of the positive cone part: The normal compressive stress of the positive cone part: The freezing and pulling shear stress of the inverted cone part: The normal compressive stress of the inverted cone part: Where: τ1 is the frost heaving shear stress received by the positive cone part of the anti-frost heaving pile; τ2 is the frost heaving shear stress received by the inverted cone part of the anti-frost heaving pile; N1 is the normal compressive stress received by the positive cone part of the anti-frost heaving pile; N2 is the normal compressive stress received by the inverted cone part of the anti-frost heaving pile. The above parameters are all obtained through the vertical resistance force V′ and the horizontal resistance force H′ generated by the pile; Under the condition of negative temperature and no load on the overlay, the force balance condition in the vertical direction of the pile body is: Where: P is the combined uplift force due to frost heaving; G is the gravity of the pile foundation of the anti-frost heaving pile; F is the reaction force at the bottom of the anti-frost heaving pile; α is the cone angle of the positive cone part; β is the angle between the positive cone part and the inverted cone part, τ k is the shear freezing stress at the pile-soil interface of the straight pile body; τ is the frost heaving shear stress at the corresponding part of the anti-frost heaving pile; N is the normal compressive stress at the corresponding part of the anti-frost heaving pile, L i is the height of the positive cone part; The directions of the normal compressive stresses on both sides of the frost depth line are the same, and the directions of the frost heaving shear stresses on both sides of the frost depth line are opposite. The anti-frost heaving effect of the pile body is mainly reflected in the part of the anti-frost heaving pile above the frost depth line. The construction method of the anti-frost heaving pile system includes the following steps: S100: Place the geothermal pipe in the anti-frost heaving pile formwork, connect the geothermal pipe to the ground source heat pump, pour concrete between the geothermal pipe and the anti-frost heaving pile formwork. After curing is completed, remove the anti-frost heaving pile formwork to obtain the anti-frost heaving pile; S200: Apply asphalt hydrophobic material to the surface of the anti-frost heaving pile to form a coating layer; S300: Drill a pile hole on the ground, place the anti-frost heaving pile into the pile hole, and correct the anti-frost heaving pile so that its axis is perpendicular to the ground; S400: Fill natural soil between the anti-frost heaving pile and the inner wall of the pile hole, and vibrate the natural soil densely.

2. The anti-pulling pile system according to claim 1, wherein The positive cone part and the inverted cone part are integrally formed, and the variable cross-section pile body and the straight pile body are integrally formed.

3. The anti-pulling pile system according to claim 1, wherein Before step S200, clean the concrete on the surface of the anti-frost heaving pile. After step S200, apply vaseline to the outer periphery of the coating layer.

4. The anti-pulling pile system according to claim 3, wherein The asphalt hydrophobic material includes a ferric tetroxide salt solution, asphalt, and an asphalt oil residue mixture coated in sequence from the inside to the outside. The density of the asphalt is greater than 95%, and the thickness of the layer formed by the asphalt is 5 mm - 6 mm.

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