Highway foundation variable-stiffness pile arrangement method suitable for permafrost canal-shaped degradation

Abstract

The invention discloses a highway foundation variable-stiffness pile arrangement method suitable for permafrost canal-shaped degradation. The method comprises the steps that spatial distribution of foundation stiffness is determined; designing the number of prefabricated pipe piles and pile arrangement; drilling and cleaning holes; the prefabricated pipe pile is pressed in and grouted for reinforcement; and pile cap pouring and reinforcement treatment. The corresponding number of long piles and dense piles are arranged in the severe permafrost degradation area for strong reinforcement, the short piles and sparse piles are arranged in the slow permafrost degradation area for weak reinforcement, the foundation rigidity is leveled by adjusting and controlling the strength, the space balance of the foundation bearing capacity is achieved, roadbed deformation caused by uneven settlement of the foundation is eliminated, and the foundation quality is improved. Wherein the long piles and the short piles extend into 2 m below the upper limit of frozen soil, and the foundation bearing capacity is improved; the dense piles can effectively disperse loads and reduce foundation settlement and displacement.

Description

Technical Field

[0001] The invention belongs to the technical field of frozen soil highway engineering construction, and in particular relates to a variable-rigidity pile arrangement method for highway foundation adapting to permafrost channel-shaped degradation. Background Art

[0002] my country has a wide distribution of frozen soil, ranking third in the world in terms of area. The area of ​​permafrost and seasonally frozen soil accounts for two-thirds of the country's total land area. Permafrost refers to a soil and rock layer that has been frozen for many years. The rock and soil near the surface usually freeze and melt seasonally, and the temperature changes dramatically. It is also called the active layer. Below the active layer is the rock and soil that has been frozen for many years, which is called the permafrost layer. The temperature is stable and maintained below 0℃. In the permafrost area of ​​the Qinghai-Tibet Plateau, the roadbed structure of "protecting frozen soil" is currently widely used, such as heat rods, block stones, ventilation pipes, and insulation layers. However, with the warming and humidification trend of the Qinghai-Tibet Plateau and the strong heat absorption effect of the asphalt pavement of the highway, the permafrost under the highway roadbed has seriously degraded into a channel-like shape, and the melting interlayer has a significant thickening trend, resulting in the difference in the bearing capacity of the foundation in the cross-sectional direction, inducing a series of diseases such as uneven settlement. To this end, we provide a variable stiffness pile layout method for highway foundations that is adapted to the channel-like degradation of permafrost to solve the above problems. Summary of the invention

[0003] The purpose of the present invention is to make up for the deficiencies of the prior art and to provide a variable stiffness pile arrangement method for highway foundations adapted to permafrost channel-like degradation, which solves the problems of insufficient bearing capacity of highway foundations in frozen soil areas and difficulty in controlling road settlement and deformation.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] A method for distributing piles with variable stiffness for highway foundation adapted to channel-shaped degradation of permafrost soil comprises the following steps:

[0006] Step 1: Determine the spatial distribution of foundation stiffness: Conduct ground penetrating radar and electrical geophysical surveys on the road surface and roadside of existing highways, and determine the spatial distribution of groundwater and frozen soil layers in combination with observation data from temperature and humidity observation holes; determine the channelization degradation morphology of the upper limit of permafrost and the spatial distribution of foundation bearing capacity based on borehole profiles, static and dynamic penetration, and load test data, and delineate areas with severe degradation and areas with slow degradation;

[0007] Step 2: Design of the number and arrangement of prefabricated pipe piles: Calculate the length, diameter, pile spacing, and pile cap size parameters of the prefabricated pipe piles according to the area demarcated in step 1; Determine the horizontal and vertical arrangement spacing of the prefabricated pipe piles according to the number of corresponding prefabricated pipe piles in the demarcated area, and mark the positions of the prefabricated pipe piles in the area;

[0008] Step 3, drilling and hole cleaning: after excavating the existing roadbed to the surface elevation, according to the pile position marked in step 2, use rotary drilling to the designed depth to break the permafrost layer;

[0009] Step 4: Pressing in and grouting the prefabricated pipe piles: Use a pile driver to press the prefabricated pipe piles into the hole. After the prefabricated pipe piles sink to a stable state, check and correct the pile position, pile top elevation and pile body verticality, and grout the gap between the hole wall and the prefabricated pipe piles and the inside of the prefabricated pipe piles for reinforcement.

[0010] Step 5: Pile cap casting and reinforcement: Form the pile cap by casting on the top of the prefabricated pipe pile. After the strength of the pile cap is stable, continue to lay the gravel cushion layer and geogrid reinforcement on the pile cap. Fix the geogrid reinforcement after compacting the gravel cushion layer.

[0011] As a further illustration of the present invention, in step 1, the severely degraded area and the slowly degraded area are delineated by the following conditions: 0.8>q 差 / q ult ≥0.5 is defined as a severely degraded area, 0 差 / q ult <0.5 is defined as the slow degradation area, where q ult is the ultimate bearing capacity of the foundation in the cross-sectional direction, q 差 =Ultimate bearing capacity of standard foundation in cross-sectional direction - Ultimate bearing capacity of current foundation in cross-sectional direction.

[0012] Furthermore, the ultimate bearing capacity q of the foundation in the cross-sectional direction is ult The calculation formula is:

[0013] q ult =cN c +qN q +0.5BN γ ;

[0014] Where: c is the cohesion of the soil, q is the effective stress of the soil, γ is the unit weight of the soil, B is the width of the area, N c 、N q 、N γ Both are bearing capacity coefficients, which are related to the internal friction angle of the soil and the foundation type.

[0015] As a further illustration of the present invention, in step 2, the number of the prefabricated pipe piles is calculated based on the ultimate bearing capacity of the foundation in the cross-sectional direction, and the calculation formula is:

[0016]

[0017] Among them, N 总 is the total number of prefabricated pipe piles in the area, F s ​is the area of ​​the region calculated based on the length and width of the region, Q s It is the vertical bearing capacity of a single precast pipe pile.

[0018] Furthermore, the vertical bearing capacity Q of the single prefabricated pipe pile is s The calculation formula is:

[0019] Q s =Q u +Q p ;

[0020] Where: Q u is the friction bearing capacity of the soil around the precast piles, Q p is the pile tip bearing capacity;

[0021] in:

[0022] Q u =∑(f s ·π·d·L);

[0023] Where: f s The unit friction force of the soil around the precast pile, d is the diameter of the precast pile, and L is the effective burial depth of the precast pile;

[0024]

[0025] In the formula, q p Unit bearing capacity of soil at the end of precast pipe pile.

[0026] As a further illustration of the present invention, in step three, the specified depth of the drilling hole is 2 m below the upper limit of the frozen soil when the pile bottom reaches.

[0027] As a further illustration of the present invention, in step 4, any one of silicate cement binder with low hydration heat, silicate mineral cement or calcium sulfate cement is used for grouting.

[0028] The present invention further illustrates that in step 2, the design parameters of the length, diameter, pile spacing, pile cap size, etc. of the prefabricated pipe piles can be determined by the following methods:

[0029] ① Melting depth calculation

[0030] The melting depth of the prefabricated pipe pile frozen soil composite foundation can be calculated as follows:

[0031]

[0032] Where: H max ——Melting depth of prefabricated pipe pile composite foundation (m); ψ j ——Comprehensive influence coefficient, the value shall be taken according to specification B.0.1-1; λ u——weighted average thermal conductivity of foundation soil in molten state [W / (m·C)]; f ——weighted average thermal conductivity of frozen foundation soil [W / (m·C)]; T B ——Average road surface temperature (℃), preferably based on the actual measured value of the local road surface; T cp ——Annual average ground temperature (℃); B——Road width (m); ψ c ——Soil coefficient of coarse-grained soil, the value shall be taken according to specification B.0.1-2; h c ——Soil coefficient of coarse-grained soil (m); ψ Δ ——Influence coefficient of roadbed height difference, the value shall be taken according to specification B.0.1-3; Δh——roadbed height (m).

[0033] The depth of frozen soil thawing can also be calculated by numerical calculation. The annual average temperature of the test section is -4.2℃; the extreme maximum temperature is 24.7℃, and the extreme minimum temperature is -45.2℃; the temperature in this area rises by 0.3-0.6℃ every ten years. This calculation assumes that the temperature rises by 0.5℃ every ten years, and 0.05℃ every year. The temperature fitting function used is as follows:

[0034] f(t)=34.95sin(2π / 365t-1.89255)-4.2+0.05[t / 365];

[0035] In the formula: t is the number of days; [] is the integer symbol.

[0036] The values ​​of the thermophysical parameters of each soil layer refer to the relevant contents of "Concrete Structure Design Code" and "Frozen Soil Physics". The thermophysical performance parameters are shown in the following table. f , C f Respectively represent the thermal conductivity and specific heat capacity of each soil layer in the frozen state, l u , C u They respectively represent the thermal conductivity and specific heat capacity of each soil layer in the melted state.

[0037] Thermophysical parameters of each layer

[0038] Physical quantity <![CDATA[l f [W / (m·K)]]]> <h2 style=";text-align:left;direction:ltr"><![CDATA[C <h2 style=";text-align:left;direction:ltr"> f <h2 style=";text-align:left;direction:ltr"> [J / (kg·K)]]]><h2 style=";text-align:left;direction:ltr"> <![CDATA[l u [W / (m·K)]]]> <h2 style=";text-align:left;direction:ltr"><![CDATA[C <h2 style=";text-align:left;direction:ltr"> u <h2 style=";text-align:left;direction:ltr"> [J / (kg·K)]]]><h2 style=";text-align:left;direction:ltr"> Roadbed soil 2.02 882 1.68 1102 Crushed stone cushion 1.56 791 1.51 920 Cement Concrete 1.65 861 1.51 970 Foundation soil 1.18 1268 0.95 1440

[0039] Unsaturated frozen soil is an inhomogeneous porous medium composed of solid, liquid and gas phases. Its heat transfer process is very complex, including heat transfer of soil particles, water evaporation and ice-water phase transition. In order to simplify the model, the temperature field simulation calculation of frozen soil mainly considers the heat transfer of soil, without considering water evaporation and ice-water phase transition. The heat conduction control equation of frozen soil is expressed as follows:

[0040]

[0041] Where: T is the transient temperature of the soil, °C; k is the thermal conductivity of the soil, kg / (m 3 ·℃); ρ——soil density, kg / m 3 ; c——specific heat capacity of soil, J / (kg·℃).

[0042] ② Calculation of single pile bearing capacity

[0043] The bearing capacity of a single pile foundation in permafrost soil is calculated as follows:

[0044]

[0045] Where: R a ——Eigenvalue of vertical bearing capacity of single pile (kN); q pa ——Characteristic value of pile end resistance (kPa). If there is no local experience, the value can be obtained according to Table 5.3.3-2 of the Code for Design of Building Foundations in Frozen Soil Areas JGJ 118; q sja ——The characteristic value of the lateral resistance of the soil around the jth layer of pile (kPa). If there is no local experience, the value can be obtained according to Table 5.3.3-1 of the Code for Design of Building Foundations in Frozen Soil Areas JGJ 118; when the permafrost around the pile is thaw-settled or strongly thaw-settled soil, the lateral friction of the soil layer above the lower limit of permafrost is ignored, and the downward pull load caused by negative friction should be considered during the calculation. When there is no measured data, the negative friction can be calculated according to Article 5.4.4 of the current code "Code for Design of Building Foundations in Frozen Soil Areas" JGJ 118; j ——Length of each pile section divided by soil layer (m); A p ——Cross-sectional area of ​​pile bottom (m 2 );U p ——Pile body peripheral length (m); m——Number of melted soil layers.

[0046] ③ Calculation of bearing capacity of composite foundation

[0047] The bearing capacity of composite foundation is calculated as follows:

[0048]

[0049] Where: f spk ——Embodiment value of composite foundation bearing capacity (kPa); f sk ——The characteristic value of the bearing capacity of the soil between piles after treatment (kPa), which can be determined according to regional experience; λ——The bearing capacity of a single pile, which can be determined according to regional experience (kPa); m——Area replacement rate, d is the average diameter of the pile (m), e The equivalent circle diameter (m) of the treated foundation area shared by one pile; d e =1.05s, square pile d e=1.13s, rectangular pile s, s 1 、s 2 are the pile spacing, longitudinal pile spacing and transverse pile spacing respectively. a ——Eigenvalue of vertical bearing capacity of single pile (kN); A p ——Cross-sectional area of ​​pile (m 2 );β——bearing capacity factor of soil between piles, which can be determined according to regional experience.

[0050] ④ Pile foundation freeze-draw calculation

[0051] Under the action of tangential frost heave force, the stability verification of pile foundation shall comply with the following provisions:

[0052] ∑τ dik A τi ≤0.9G K +R ta ;

[0053] Where: τ dik ——standard value of unit tangential frost heave force in the i-th layer of soil (kPa); A τi ——Surface area of ​​pile side frozen together with the i-th layer of soil (m 2 );G K ——standard value of permanent load acting on the foundation (kN); R ta ——The characteristic value (kN) of the anchoring force generated by the foundation soil when the pile foundation extends below the frost-heaving soil layer.

[0054] The anchoring force R between the side surface of the permafrost foundation and the frozen soil ta (Freezing force) can be calculated as follows:

[0055] R ta =∑(f cia G JZ fi );

[0056] Where: f cia ——the characteristic value of the freezing strength between the frozen soil in the i-th layer and the foundation surface (kPa); A fi ——Surface area of ​​the base side of the i-th layer of frozen soil below the maximum melting depth (m 2 ).

[0057] ⑤ Arrangement of prefabricated pipe pile frozen soil composite foundation

[0058] Precast concrete pipe piles are used as reinforcements, together with the soil between piles and the cushion layer on the top of the piles to form a rigid pile composite foundation. The composite foundation transfers the load borne by the precast concrete pipe piles to the deeper soil layer through displacement and correspondingly reduces the load borne by the soil between piles, thereby increasing the bearing capacity of the composite foundation and reducing deformation.

[0059] After calculation, the main technical parameters of the prefabricated pile frozen soil composite foundation initially adopted are as follows:

[0060] (1) Piles: Pile spacing 2.5 m, pile length L (determined according to ground conditions), outer diameter 0.4 m, inner diameter 0.21 m;

[0061] (2) Pile cap: 1.4m long, 1.4m wide, 0.35m high;

[0062] (3) Geogrid: mesh size 30 mm × 40 mm;

[0063] (4) Cushion: thickness 50 cm;

[0064] (5) Insulation layer: XPS 60mm.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] 1. The present invention arranges a corresponding number of long piles and dense piles for strong reinforcement in areas with serious permafrost degradation, and arranges short piles and sparse piles for weak reinforcement in areas with slow permafrost degradation. The foundation stiffness is leveled through strong and weak regulation to achieve spatial balance of foundation bearing capacity and eliminate roadbed deformation caused by uneven foundation settlement. The long piles and short piles are both inserted 2m below the upper limit of the frozen soil to improve the foundation bearing capacity. The dense piles can effectively disperse the load and reduce the foundation settlement and displacement. The sparse piles can reduce the mutual influence between the piles and reduce the disturbance to the foundation.

[0067] 2. The present invention can effectively disperse and transfer the load of the superstructure by arranging prefabricated pipe piles in the degraded area, significantly improve the bearing capacity of the foundation, and prevent settlement and damage caused by insufficient foundation bearing capacity. The deep burial and grouting reinforcement of the prefabricated pipe piles can improve the pull-out resistance of the foundation, and prevent the pile body from being pulled out or becoming unstable during freeze-thaw cycles and water level changes. At the same time, through reasonable pile layout design, the settlement difference caused by temperature changes and moisture effects can be reduced, ensuring the flatness and safety of the highway. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 It is a schematic diagram of the structure after the prefabricated pipe piles in the present invention are arranged.

[0069] In the figure: 1- prefabricated pipe pile; 2- pile cap; 3- gravel cushion layer; 4- geogrid reinforcement. DETAILED DESCRIPTION

[0070] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0071] Example: See Figure 1 A variable stiffness pile arrangement method for highway foundation adapted to permafrost channel-shaped degradation comprises the following steps:

[0072] Step 1: Determine the spatial distribution of foundation stiffness: Conduct ground penetrating radar and electrical geophysical surveys on the road surface and roadside of existing highways, and determine the spatial distribution of groundwater and frozen soil layers in combination with observation data from temperature and humidity observation holes; determine the channelization degradation morphology of the upper limit of permafrost and the spatial distribution of foundation bearing capacity based on borehole profiles, static and dynamic penetration, and load test data, and delineate areas with severe degradation and areas with slow degradation;

[0073] Specific:

[0074] The severe degradation area and slow degradation area can be delineated by the following conditions: 0.8>q 差 / q ult ≥0.5 is defined as a severely degraded area, 0 差 / q ult <0.5 is defined as the slow degradation area, where q ult is the ultimate bearing capacity of the foundation in the cross-sectional direction, q 差 = Ultimate bearing capacity of standard foundation in cross section direction - Ultimate bearing capacity of current foundation in cross section direction;

[0075] The ultimate bearing capacity of the foundation in the cross-sectional direction is q ult The calculation formula is:

[0076] q ult =cN c +qN q +0.5BN γ ;

[0077] Where: c is the cohesion of the soil, q is the effective stress of the soil, γ is the unit weight of the soil, B is the width of the area, N c 、N q 、N γ Both are bearing capacity coefficients, which are related to the internal friction angle of the soil and the foundation type.

[0078] ​Step 2: Design the number and arrangement of prefabricated pipe piles: Calculate the length, diameter, pile spacing, and pile cap size parameters of the prefabricated pipe piles 1 according to the area demarcated in step 1; Determine the horizontal and vertical arrangement spacings of the prefabricated pipe piles 1 according to the number of prefabricated pipe piles 1 corresponding to the demarcated area, and mark the positions of the prefabricated pipe piles 1 in the area;

[0079] Specific:

[0080] The number of prefabricated pipe piles is calculated based on the ultimate bearing capacity of the foundation in the cross-sectional direction, and the calculation formula is:

[0081]

[0082] Among them, N 总 is the total number of prefabricated pipe piles in the area, F s is the area of ​​the region calculated based on the length and width of the region, Q s is the vertical bearing capacity of a single precast pipe pile;

[0083] The vertical bearing capacity Q of a single prefabricated pipe pile s The calculation formula is:

[0084] Q s =Q u +Q p ;

[0085] Where: Q u is the friction bearing capacity of the soil around the precast piles, Q p is the pile tip bearing capacity;

[0086] in:

[0087] Q u =∑(f s ·π·d·L);

[0088] Where: f s The unit friction force of the soil around the precast pile, d is the diameter of the precast pile, and L is the effective burial depth of the precast pile;

[0089]

[0090] In the formula, q p Unit bearing capacity of soil at the end of precast pipe pile.

[0091] Step 3, drilling and hole cleaning: after excavating the existing roadbed to the surface elevation, according to the pile position marked in step 2, use rotary drilling to the designed depth to break the permafrost layer;

[0092] Specifically, the specified depth of the drilling is that the bottom of the pile reaches 2m below the upper limit of the frozen soil.

[0093] Step 4, prefabricated pipe piles are pressed in and reinforced by grouting: the prefabricated pipe pile 1 is pressed into the hole by a pile driver. After the prefabricated pipe pile sinks to a stable state, the pile position, pile top elevation and pile body verticality are inspected and corrected, and grouting is injected into the gap between the hole wall and the prefabricated pipe pile and the inside of the prefabricated pipe pile for reinforcement; grouting can preferably use any one of low hydration heat silicate cement binder, silicate mineral cement or calcium sulfate cement.

[0094] Step 5: Pile cap casting and reinforcement: Form the pile cap 2 by casting on the top of the prefabricated pipe pile 1. After the strength of the pile cap is stable, continue to lay the gravel cushion layer 3 and geogrid reinforcement 4 on the pile cap. After the gravel cushion layer 3 is compacted, the geogrid reinforcement 4 is fixed.

[0095] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for laying piles with variable stiffness for highway foundations adapted to channel-shaped degradation of permafrost soil, characterized by: The following steps are involved: Step 1: Determine the spatial distribution of foundation stiffness: Conduct ground penetrating radar and electrical geophysical surveys on the road surface and roadside of existing highways, and determine the spatial distribution of groundwater and frozen soil layers in combination with observation data from temperature and humidity observation holes; determine the channelization degradation morphology of the upper limit of permafrost and the spatial distribution of foundation bearing capacity based on borehole profiles, static and dynamic penetration, and load test data, and delineate areas with severe degradation and areas with slow degradation; Step 2, designing the number and arrangement of prefabricated pipe piles: according to the area demarcated in step 1, calculating the length, diameter, pile spacing, and pile cap size parameters of the prefabricated pipe piles (1); according to the number of corresponding prefabricated pipe piles (1) in the demarcated area, determining the transverse arrangement spacing and longitudinal arrangement spacing of the prefabricated pipe piles (1), and marking the position of the prefabricated pipe piles (1) in the area; Step 3, drilling and hole cleaning: after excavating the existing roadbed to the surface elevation, according to the pile position marked in step 2, use rotary drilling to the designed depth to break the permafrost layer; Step 4: Pressing in and grouting the prefabricated pipe piles: Use a pile driver to press the prefabricated pipe pile (1) into the hole. After the prefabricated pipe pile (1) sinks to a stable state, the pile position, pile top elevation and pile body verticality are inspected and corrected, and grouting is performed to reinforce the gap between the hole wall and the prefabricated pipe pile (1) and the inside of the prefabricated pipe pile (1); Step 5: Pile cap casting and reinforcement treatment: Forming and casting the pile cap (2) on the top of the prefabricated pipe pile (1). After the strength of the pile cap (2) is stabilized, a gravel cushion layer (3) and geogrid reinforcement (4) are laid on the pile cap (2). The gravel cushion layer (3) is compacted and then fixed with the geogrid reinforcement (4).

2. The method for laying piles with variable stiffness for highway foundation adapted to permafrost channel-shaped degradation according to claim 1 is characterized by: In step 1, the severely degraded area and the slowly degraded area are delineated by the following conditions: 0.8>q 差 / q ult ≥0.5 is defined as a severely degraded area, 0 差 / q ult <0.5 is defined as the slow degradation area, where q ult is the ultimate bearing capacity of the foundation in the cross-sectional direction, q 差 =Ultimate bearing capacity of standard foundation in cross-sectional direction - Ultimate bearing capacity of current foundation in cross-sectional direction.​ 3. The method for laying piles with variable stiffness for highway foundation adapted to permafrost channel-shaped degradation according to claim 2 is characterized by: The ultimate bearing capacity of the foundation in the cross-sectional direction is q ult The calculation formula is: what ult =cN c +qN q +0.5BN γ ; Where: c is the cohesion of the soil, q is the effective stress of the soil, γ is the unit weight of the soil, B is the width of the area, N c 、N q 、N γ Both are bearing capacity coefficients, which are related to the internal friction angle of the soil and the foundation type.

4. The method for laying piles with variable stiffness for highway foundation adapting to permafrost channel-shaped degradation according to claim 2 is characterized by: In step 2, the number of the prefabricated pipe piles (1) is calculated based on the ultimate bearing capacity of the foundation in the cross-sectional direction, and the calculation formula is: Among them, N 总 is the total number of precast pipe piles (1) in the area, F s is the area of ​​the region calculated based on the length and width of the region, Q s is the vertical bearing capacity of a single prefabricated pipe pile (1).

5. The method for laying piles with variable stiffness for highway foundation adapted to permafrost channel-shaped degradation according to claim 4 is characterized by: The calculation formula of the vertical bearing capacity of the single prefabricated pipe pile (1) is: Q s =Q u +Q p ; Where: Q s is the vertical bearing capacity of a single prefabricated pipe pile (1), Q u is the friction bearing capacity of the soil around the precast pile (1), Q p is the pile tip bearing capacity; in: Q u =∑(f s ·π·d·L); Where: f s The unit friction force of the soil around the prefabricated pipe pile (1), d is the diameter of the prefabricated pipe pile (1), and L is the effective burial depth of the prefabricated pipe pile (1); In the formula, q p Unit bearing capacity of the soil at the end of the precast pipe pile (1).

6. The variable stiffness pile arrangement method for highway foundation adapting to permafrost channel-shaped degradation according to claim 1 is characterized by: In step 3, the specified depth of the drilling is 2 m below the upper limit of frozen soil when the pile bottom reaches 2 m.

7. The method for laying piles with variable stiffness for highway foundation adapting to permafrost channel-shaped degradation according to claim 1 is characterized by: In step 4, grouting uses any one of low hydration heat silicate cement binder, silicate mineral cement or calcium sulfate cement.

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