Variable-section anti-seismic screw pile foundation and construction method

Abstract

The invention relates to the technical field of pile foundations, in particular to a variable-section anti-seismic spiral pile foundation and a construction method.The variable-section anti-seismic spiral pile foundation comprises a pile body, a spiral blade set, a seismic isolation layer and an anti-seismic ring, and the spiral blade set and the pile body form the spiral pile foundation through pouring in a construction soil layer; the shock insulation layer is installed on the top of the pile body and integrated with the pile body through pouring, the anti-seismic ring is arranged outside the shock insulation layer in a surrounding mode and connected with the shock insulation layer, the spiral blade set is composed of a plurality of sets of spiral blades of different specifications, and the spiral blades are arranged upwards from the lower portion of the pile body from small to large. And compared with the scheme that the outer diameter of the blade is increased in the prior art, the economic construction cost is reduced, and the anti-seismic performance and the bearing capacity are synchronously improved.

Description

Technical Field

[0001] This invention relates to the field of pile foundation technology, specifically to a variable cross-section seismic-resistant helical pile foundation and its construction method. Background Technology

[0002] As the most widely used building foundation, the seismic design of pile foundations is crucial in areas with high earthquake intensity. The study of their dynamic response has become a key topic in the field of civil engineering. In areas with strong earthquakes, pile foundations often bear higher vertical compressive loads, leading to damage or excessive settlement of the pile foundations. Therefore, in earthquake-prone zones, helical pile foundations are often used as the supporting structure.

[0003] Traditional bored cast-in-place helical pile foundations often use helical blade assemblies with equal spacing and cross-sections. However, in practice, helical pile foundations mainly rely on the benefits of the helical blade assembly on the upper part of the pile to resist the influence of horizontal loads. This leads to an increase in the outer diameter of the blades, resulting in higher economic construction costs, while the improvement in seismic performance and bearing capacity fails to achieve the expected benefits. Therefore, a variable cross-section seismic-resistant helical pile foundation and its construction method are proposed. Summary of the Invention

[0004] To address the technical problems existing in the prior art, the present invention provides a variable cross-section seismic-resistant helical pile foundation and its construction method.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a variable cross-section seismic-resistant helical pile foundation, comprising a pile body, a helical blade assembly, a seismic isolation layer, and a seismic-resistant ring;

[0006] The spiral blade assembly and the pile body are cast into the construction soil layer to form a spiral pile foundation. The seismic isolation layer is installed on the top of the pile body and is cast into a whole with the pile body. The seismic ring is set around the outside of the seismic isolation layer and connected to the seismic isolation layer.

[0007] Preferably, the spiral blade group includes several groups of spiral blades of different specifications, and the several groups of spiral blades are arranged upward along the lower part of the pile body in order of increasing diameter.

[0008] Preferably, the diameter of the helical blade is less than five times the diameter of the pile body, and the number of helical blades in the helical blade group is at least three levels.

[0009] Preferably, the seismic isolation layer includes an upper steel pad, a lower steel pad, several sets of elastic elements, and several sets of vertical magnetorheological dampers. There is a space between the upper and lower steel pads for placing the elastic elements and the vertical magnetorheological dampers. The several sets of elastic elements and vertical magnetorheological dampers are arranged alternately in a ring along the space. The two ends of the elastic elements are fixedly connected to the upper and lower steel pads, respectively. The two ends of the vertical magnetorheological dampers are fixedly connected to the upper and lower steel pads, respectively.

[0010] Preferably, the seismic ring includes double-ended hinged rods, a ring beam assembly, a connecting part, and a transverse magnetorheological damper assembly. The double-ended hinged rods include two separate ends and one merged end, forming a V-shaped structure. Several sets of the double-ended hinged rods are installed at equal intervals within the seismic isolation layer. The ring beam assembly and the connecting part are integrally cast on the outside of the seismic isolation layer. The number of connecting parts matches the number of double-ended hinged rods. The transverse magnetorheological damper assembly is disposed inside each set of connecting parts. The fixed end of the transverse magnetorheological damper assembly is connected to the connecting part. A synchronization pad is provided between the movable ends of the transverse magnetorheological damper assembly. The merged end of the double-ended hinged rod is hinged to the middle of the synchronization pad.

[0011] Preferably, the ring beam assembly is composed of at least two stacked ring beams.

[0012] A construction method for a variable cross-section seismic-resistant helical pile foundation includes the following steps:

[0013] Step S1, set the length of the pile body as The diameter of the pile is The helical blade assembly consists of three stages of helical blades, each located at 0.3 meters of the pile shaft. 0.5 and 0.9 Location;

[0014] Step S2: Calculate the blade spacing between adjacent helical blades based on the position of the three-stage helical blades on the pile body. The blade spacing between the first-stage and second-stage helical blades for:

[0015] ;

[0016] The blade spacing between the second-stage and third-stage helical blades for:

[0017] ;

[0018] Step S3, set the diameter of each stage of the helical blades to be First-stage helical blades outer diameter of the second-stage helical blade for:

[0019] ;

[0020] Third-stage helical blade outer diameter for:

[0021] ;

[0022] Step S4, based on the outer diameter of the second-stage helical blade and the outer diameter of the third-stage helical blade Calculate the blade spacing of the second-stage and third-stage helical blades. Corresponding control pitch :

[0023]

[0024] In the formula, The inclination angle of the helical blade. Let α be the internal friction angle of the soil layer, and α be the angle between the slip surface and the horizontal direction. It is a natural constant;

[0025] The formula for calculating α is:

[0026] ;

[0027] blade spacing The calculated control pitch Comparison:

[0028] When the blade spacing Greater than the control pitch At that time, the forces on adjacent helical blades are calculated according to the blade bearing mode;

[0029] When the blade spacing Less than the control pitch At that time, the adjacent helical blades are subjected to force calculations according to the cylindrical bearing mode;

[0030] Step S5: Combine the load design of the variable cross-section seismic-resistant helical pile foundation with seismic load, and calculate the characteristic value of the bearing capacity of a single pile. :

[0031]

[0032] In the formula, This represents the average vertical force acting on the helical pile foundation pile. For safety factor, take , This refers to the cylindrical shear load-bearing capacity between the first-stage and second-stage helical blades. For the load-bearing capacity of the blade bearing mode, This refers to the skin friction of the pile.

[0033] Step S6, when That is, when the second-stage helical blade and the third-stage helical blade are in blade-loaded mode:

[0034] ;

[0035] when That is, when the second-stage and third-stage helical blades are in a cylindrical bearing mode:

[0036] ;

[0037] In the formula, This is the bearing capacity coefficient of the second-stage helical blade. This refers to the bearing capacity coefficient of the third-stage helical blade.

[0038] The The formula for calculation is:

[0039] ;

[0040] In the formula, The length of the pile body, Where β is the diameter of the pile body, β is the inclination angle of the helical blade, φ is the internal friction angle of the soil layer, and α is the angle between the slip surface and the horizontal direction. The cohesion of the soil layer;

[0041] The pile embedment depth is 0~0.1m. The cohesion of the soil layer at that location, The pile embedment depth is 0.9~1. The cohesion of the soil layer at that location, This refers to the cohesion of the soil layer between the first-stage and second-stage helical blades. This refers to the cohesion of the soil layer between the second-stage and third-stage helical blades. The effective length of the external pile side friction resistance of the slip surface in the blade bearing mode involves the cohesion of the soil layer.

[0042] This refers to the normal pressure on the slip surface of the first-stage and second-stage helical blades. This refers to the normal pressure on the slip surface of the second-stage and third-stage helical blades. The normal pressure on the slip surface under the effective length of the external pile side friction resistance in the blade bearing mode is the slip surface normal pressure. The pile embedment depth is 0~0.1m. The lateral pressure of the soil layer on the pile body, The pile embedment depth is 0.9~1. The lateral pressure of the soil layer on the pile body;

[0043] The internal friction angle of the soil layer between the first-stage and second-stage helical blades. This refers to the internal friction angle of the soil layer between the second-stage and third-stage helical blades. The internal friction angle of the soil layer under the effective length of the external pile side friction resistance of the slip surface in the blade bearing mode. The pile embedment depth is 0~0.1m. The internal friction angle of the soil layer, For a burial depth of 0.9~1 The internal friction angle of the soil layer;

[0044] The effective length of the external pile side friction of the slip surface in the blade bearing mode. The calculation formula is:

[0045] ;

[0046] Combining the two groups The length of the pile can be obtained by solving the relational formula. and the diameter of the pile body Through the length of the pile body Calculate the blade spacing between adjacent helical blades and the diameter of each level of helical blade ;

[0047] Step S7, based on the length of the pile body and the diameter of the pile body Excavate pile holes, increase the burial depth of the third-stage spiral blade to the outer diameter of the third-stage spiral blade, and install the third-stage spiral blade;

[0048] Step S8: Backfill soil on the upper surface of the third-stage spiral blade to the depth of the second-stage spiral blade, compact the soil, and bury the second-stage spiral blade. Backfill soil on the upper surface of the second-stage spiral blade to the depth of the first-stage spiral blade, bury the first-stage spiral blade, and compact the soil.

[0049] Step S9: Backfill the soil on the upper surface of the first-stage spiral blade to the elevation of the pile body and compact the soil.

[0050] Step S10: Hoist the pile reinforcement cage into the pile hole. The reinforcement cage is welded with protruding steel bars that cooperate with the first-stage spiral blade, the second-stage spiral blade and the third-stage spiral blade. Pour concrete into the reinforcement cage. After the concrete solidifies, the pile body is formed. The first-stage spiral blade, the second-stage spiral blade and the third-stage spiral blade are integrated with the pile body to form a whole. Install the seismic isolation layer on the top of the pile body.

[0051] Step S11: Install an anti-seismic ring outside the seismic isolation layer and connect the anti-seismic ring to the seismic isolation layer through a double-ended hinged rod.

[0052] Preferably, the cylindrical shear mode bearing capacity in step S5 The formula for calculation is:

[0053]

[0054] In the formula, For the load-bearing capacity of the second-stage helical blades, The soil column shear resistance between the first-stage and second-stage helical blades;

[0055] The calculation formula is:

[0056]

[0057] In the formula, The outer diameter of the second-stage helical blade. The inclination angle of the helical blade. The diameter of the pile body. The internal friction angle of the soil layer. Let α be a natural constant, and α be the angle between the slip surface and the horizontal direction. The cohesion of the soil layer;

[0058] The formula for calculation is:

[0059]

[0060] In the formula, This is the normal force on the shear surface. The outer diameter of the second-stage helical blade. The inclination angle of the helical blade. The blade spacing between the first-stage and second-stage helical blades. For the cohesion of the soil layer, The internal friction angle of the soil layer.

[0061] Preferably, the blade mode bearing capacity in step S5 The formula for calculation is:

[0062]

[0063] In the formula, For the load-bearing capacity of the third-stage helical blade, Shear resistance at the slip surface of the soil column between the second and third stage helical blades;

[0064] The calculation formula is:

[0065]

[0066] In the formula, The outer diameter of the third-stage helical blade. The inclination angle of the helical blade. The diameter of the pile body. It is a natural constant. The internal friction angle of the soil layer. The angle between the slip surface and the horizontal direction. The cohesion of the soil layer;

[0067] The calculation formula is:

[0068]

[0069] In the formula, The effective length of the external pile side friction resistance of the slip surface in the blade bearing mode.

[0070] Preferably, in step S5, the pile side friction resistance The formula for calculation is:

[0071]

[0072] In the formula, L b This refers to the pile length involved in load-bearing modes other than cylindrical and blade-type load-bearing modes. For the cohesion of the soil layer, The internal friction angle of the soil layer. This is the normal force on the shear surface. The diameter of the pile body.

[0073] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0074] 1. In this invention, a spiral blade group is set up, which is composed of several groups of spiral blades of different specifications. The several groups of spiral blades are arranged from the bottom of the pile body upward in order of increasing size, thereby forming different bearing modes and realizing overall stress. Compared with the original technology that relies on increasing the outer diameter of the blades, the economic construction cost is reduced, and the seismic performance and bearing capacity are improved at the same time.

[0075] 2. In this invention, a data calculation method for variable cross-section seismic-resistant helical pile foundations is established to ensure that the variable cross-section seismic-resistant helical pile foundations can achieve the expected purpose. Attached Figure Description

[0076] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0077] Figure 2 This is a schematic diagram of the three-dimensional structure of the vibration isolation layer of the present invention;

[0078] Figure 3 This is a schematic diagram of the three-dimensional structure of the anti-seismic ring of the present invention.

[0079] Figure 4 This is a force diagram of the present invention.

[0080] The numbers in the diagram represent:

[0081] 1. Pile body; 2. Helical blade assembly; 3. Seismic isolation layer; 31. Upper steel pad; 32. Lower steel pad; 33. Elastic element; 34. Vertical magnetorheological damper; 4. Seismic ring; 41. Double-end hinged rod; 42. Ring beam assembly; 43. Connection part; 44. Lateral magnetorheological damper assembly. Detailed Implementation

[0082] The present invention will be further described below with reference to the accompanying drawings and embodiments, which illustrate the above and other technical features and advantages of the present invention. However, the following embodiments are merely preferred embodiments of the present invention and are not exhaustive.

[0083] Example 1:

[0084] like Figures 1-4 As shown, the present invention provides a variable cross-section seismic-resistant helical pile foundation, including a pile body 1, a helical blade assembly 2, a seismic isolation layer 3, and a seismic-resistant ring 4;

[0085] The spiral blade assembly 2 and the pile body 1 are poured into the construction soil layer to form a spiral pile foundation. The seismic isolation layer 3 is installed on the top of the pile body 1 and is poured into the pile body 1 to become an integral part. The seismic ring 4 is surrounded on the outside of the seismic isolation layer 3 and connected to the seismic isolation layer 3.

[0086] The spiral blade group 2 includes several groups of spiral blades of different specifications. The spiral blades are arranged upward along the lower part of the pile body 1 in order of increasing diameter. The diameter of the spiral blades is less than five times the diameter of the pile body 1. The number of spiral blades in the spiral blade group 2 is at least three levels.

[0087] The seismic isolation layer 3 includes an upper steel pad 31, a lower steel pad 32, an elastic element 33, and a vertical magnetorheological damper 34;

[0088] There is a space between the upper steel pad 31 and the lower steel pad 32 for placing the elastic element 33 and the vertical magnetorheological damper 34. Several sets of elastic elements 33 and vertical magnetorheological dampers 34 are arranged alternately in a ring along the space. The two ends of the elastic element 33 are fixedly connected to the upper steel pad 31 and the lower steel pad 32 respectively, and the two ends of the vertical magnetorheological damper 34 are fixedly connected to the upper steel pad 31 and the lower steel pad 32 respectively.

[0089] When the top of the pile body 1 undergoes vertical displacement, the size of the helical blades in the helical blade assembly 2 near the top of the pile body 1 is increased to perform primary damping, thereby reducing the lateral and vertical displacements at the top of the pile body 1. At the same time, the kinetic energy of the pile body 1 is consumed by the vertical magnetorheological damper 34 in the isolation layer 3 to perform secondary damping.

[0090] The seismic ring 4 includes a double-ended hinged rod 41, a ring beam assembly 42, a connecting part 43, and a transverse magnetorheological damper assembly 44;

[0091] The double-ended hinge member 41 includes two separate ends and one merged end, which form a V-shaped structure. Several sets of double-ended hinge members 41 are installed at equal intervals inside the seismic isolation layer 3. The ring beam group 42 and the connecting part 43 are cast together on the outside of the seismic isolation layer 3. The number of connecting parts 43 is the same as the number of double-ended hinge members 41. The transverse magnetorheological damper group 44 is set inside each connecting part 43. The fixed end of the transverse magnetorheological damper group 44 is connected to the connecting part 43. A synchronous pad is provided between the movable ends of the transverse magnetorheological damper group 44. The merged end of the double-ended hinge member 41 is hinged to the middle of the synchronous pad.

[0092] The ring beam group 42 is composed of no less than two stacked ring beams. The ring beam group 42 can convert the vertical displacement of the isolation layer 3 into the horizontal displacement of the transverse magnetorheological damper group 44. The pile body 1 drives the double-end hinge rod 41 to move. The double-end hinge rod 41 transmits the motion to the ring beam group 42, so that the motion is transmitted to the transverse magnetorheological damper group 44, and energy is consumed three times.

[0093] When the top of the pile body 1 undergoes horizontal displacement, the lateral displacement of the top of the pile body 1 is reduced by the upper helical blades to perform primary vibration reduction. Since the top of the pile body 1 is circumferentially surrounded by the anti-seismic ring 4, the horizontal movement of the pile body 1 is transmitted to the transverse magnetorheological damper group 44 through the double-end hinge rod 41. The transverse magnetorheological damper group 44 performs secondary vibration reduction to reduce the deformation of the upper structure.

[0094] The construction method for variable cross-section seismic-resistant helical pile foundations includes the following steps:

[0095] Step S1, set the length of pile body 1 as The diameter of pile body 1 is The helical blade assembly 2 includes three stages of helical blades, each located at 0.3 meters of the pile body 1. 0.5 and 0.9 Location;

[0096] Step S2: Calculate the blade spacing between adjacent helical blades based on the position of the three-stage helical blades on the pile body 1. The blade spacing between the first-stage and second-stage helical blades for:

[0097] ;

[0098] The blade spacing between the second-stage and third-stage helical blades for:

[0099] ;

[0100] Step S3, set the diameter of each stage of the helical blades to be First-stage helical blades outer diameter of the second-stage helical blade for:

[0101] ;

[0102] Third-stage helical blade outer diameter for:

[0103] ;

[0104] Step S4, based on the outer diameter of the second-stage helical blade and the outer diameter of the third-stage helical blade Calculate the blade spacing H between the second-stage and third-stage helical blades. 23 Corresponding control pitch :

[0105]

[0106] In the formula, The inclination angle of the helical blade. Let α be the internal friction angle of the soil layer, and α be the angle between the slip surface and the horizontal direction. It is a natural constant;

[0107] The formula for calculating α is:

[0108] ;

[0109] blade spacing The calculated control pitch Comparison:

[0110] When the blade spacing Greater than the control pitch At that time, the forces on adjacent helical blades are calculated according to the blade bearing mode;

[0111] When the blade spacing Less than the control pitch At that time, the adjacent helical blades are subjected to force calculations according to the cylindrical bearing mode;

[0112] Step S5: Combine the load design of the variable cross-section seismic-resistant helical pile foundation with seismic load, and calculate the characteristic value of the bearing capacity of a single pile. :

[0113] ;

[0114] In the formula, This represents the average vertical force acting on the helical pile foundation pile. For safety factor, take , This refers to the cylindrical shear load-bearing capacity between the first-stage and second-stage helical blades. For the load-bearing capacity of the blade bearing mode, This refers to the skin friction of the pile.

[0115] Cylindrical shear mode bearing capacity The formula for calculation is:

[0116]

[0117] In the formula For the load-bearing capacity of the second-stage helical blades, The soil column shear resistance between the first-stage and second-stage helical blades;

[0118] The calculation formula is:

[0119]

[0120] In the formula The outer diameter of the second-stage helical blade. The inclination angle of the helical blade. The diameter of pile body 1, The internal friction angle of the soil layer. Let α be a natural constant, and α be the angle between the slip surface and the horizontal direction. The cohesion of the soil layer;

[0121] The formula for calculation is:

[0122]

[0123] In the formula, This is the normal force on the shear surface. The outer diameter of the second-stage helical blade. The inclination angle of the helical blade. The blade spacing between the first-stage and second-stage helical blades. For the cohesion of the soil layer, The internal friction angle of the soil layer;

[0124] Blade mode bearing capacity The formula for calculation is:

[0125]

[0126] In the formula For the load-bearing capacity of the third-stage helical blade, Shear resistance at the slip surface of the soil column between the second and third stage helical blades;

[0127] The calculation formula is:

[0128]

[0129] In the formula, The outer diameter of the third-stage helical blade. The inclination angle of the helical blade. The diameter of pile body 1, It is a natural constant. Let α be the internal friction angle of the soil layer, and α be the angle between the slip surface and the horizontal direction. The cohesion of the soil layer;

[0130] The calculation formula is:

[0131]

[0132] In the formula, The effective length of the external pile side friction resistance of the slip surface in the blade bearing mode;

[0133] Pile side friction The formula for calculation is:

[0134]

[0135] In the formula, This refers to the pile length involved in load-bearing modes other than cylindrical and blade-type load-bearing modes. For the cohesion of the soil layer, The internal friction angle of the soil layer. This is the normal force on the shear surface. The diameter of pile body 1;

[0136] Step S6, when That is, when the second-stage helical blade and the third-stage helical blade are in blade-loaded mode:

[0137] ;

[0138] when That is, when the second-stage and third-stage helical blades are in a cylindrical bearing mode:

[0139] ;

[0140] In the formula This is the bearing capacity coefficient of the second-stage helical blade. This refers to the bearing capacity coefficient of the third-stage helical blade. The formula for calculation is:

[0141] ;

[0142] The length of pile body 1, Where β is the diameter of pile body 1, β is the inclination angle of the helical blade, φ is the internal friction angle of the soil layer, and α is the angle between the slip surface and the horizontal direction. The cohesion of the soil layer;

[0143] The pile embedment depth is 0~0.1m. The cohesion of the soil layer at that location, The pile embedment depth is 0.9~1. The cohesion of the soil layer at that location, This refers to the cohesion of the soil layer between the first-stage and second-stage helical blades. This refers to the cohesion of the soil layer between the second-stage and third-stage helical blades. The effective length of the external pile side friction resistance of the slip surface in the blade bearing mode involves the cohesion of the soil layer.

[0144] This refers to the normal pressure on the slip surface of the first-stage and second-stage helical blades. This refers to the normal pressure on the slip surface of the second-stage and third-stage helical blades. The normal pressure on the slip surface under the effective length of the external pile side friction resistance in the blade bearing mode is the slip surface normal pressure. The pile embedment depth is 0~0.1m. The lateral pressure of the soil layer on pile 1, The pile embedment depth is 0.9~1. The lateral pressure of the soil layer on pile 1;

[0145] The internal friction angle of the soil layer between the first-stage and second-stage helical blades. The internal friction angle of the soil layer under the effective length of the external pile side friction resistance of the slip surface in the blade bearing mode. The pile embedment depth is 0~0.1m. The internal friction angle of the soil layer, For a burial depth of 0.9~1 The internal friction angle of the soil layer;

[0146] The effective length of the external pile side friction of the slip surface in the blade bearing mode. The calculation formula is:

[0147] ;

[0148] Combining the two groups The length of pile 1 is obtained by solving the relational expression. and the diameter of pile body 1 Through the length of pile body 1 Calculate the blade spacing between adjacent helical blades and the diameter of each level of helical blade ;

[0149] Step S7, based on the length of pile body 1 and the diameter of pile body 1 Excavate pile holes, increase the burial depth of the third-stage spiral blade to the outer diameter of the third-stage spiral blade, and install the third-stage spiral blade;

[0150] Step S8: Backfill soil on the upper surface of the third-stage spiral blade to the depth of the second-stage spiral blade, bury the second-stage spiral blade, backfill soil on the upper surface of the second-stage spiral blade to the depth of the first-stage spiral blade, bury the first-stage spiral blade, apply mud slurry to protect the pile hole or apply steel barriers to prevent the pile hole from collapsing, and then compact the soil.

[0151] Step S9: Backfill the soil on the upper surface of the second-stage spiral blade to the designed elevation of the pile body 1 and compact the soil.

[0152] Step S10: Hoist the pile reinforcement cage into the pile hole. At different heights outside the reinforcement cage, protruding steel bars that cooperate with the first-stage spiral blade, the second-stage spiral blade and the third-stage spiral blade are welded. Pour concrete into the reinforcement cage. After the concrete solidifies, the pile body 1 is formed. The first-stage spiral blade, the second-stage spiral blade and the third-stage spiral blade are integrated with the pile body 1 to form a whole. Install the seismic isolation layer 3 on the top of the pile body 1.

[0153] Step S11: Install an anti-seismic ring 4 outside the seismic isolation layer 3 and connect the anti-seismic ring 4 to the seismic isolation layer 3 through a double-ended hinged rod 41.

[0154] Example 2:

[0155] When subjected to a standard combination of earthquake and load, the load acting on the helical pile foundation piles is... For 500 The soil layer is homogeneous cohesive soil. 40 , It is 10°. 18 .

[0156] Step S1: Determine the diameter of pile body 1 as d, take the number of helical blades as 3, the inclination angle β of the third-stage helical blades as 15°, and let the length of pile body 1 be L, then its pitch H 12 and H 23 Approximately 0.2L and 0.4L respectively;

[0157] Step S2: The outer diameters of the first helical blade group, the second helical blade group, and the third helical blade group are respectively:

[0158]

[0159] ;

[0160] ;

[0161] Step S3: Calculate the control pitch based on the diameter of the helical blades, and obtain... =0.31 ,but < , > That is, the first-stage helical blade and the second-stage helical blade are subjected to force in a cylindrical bearing mode, while the second-stage helical blade and the third-stage helical blade are subjected to force in a blade bearing mode.

[0162] Step S4: Based on the combination of earthquake and load standards, If it is 1000kN, then It should be greater than 1600kN;

[0163] Step S5: Calculate the distance between the first-stage and second-stage helical blades. :

[0164] ;

[0165] Calculate the relationship between the second-stage and third-stage helical blades :

[0166] ;

[0167] The external pile side friction resistance under cylindrical bearing mode and blade bearing mode is:

[0168] ;

[0169] but for:

[0170] ;

[0171] After calculation, the diameter of pile body 1 is selected. The length of pile body 1 is 0.5m. Taking 13.5m as an example, the outer diameter of the first-stage helical blade is... and the outer diameter of the second-stage helical blade Take 1.35m as the outer diameter of the third-stage helical blade. Take 0.9m, pitch Take 2.7m, pitch When the height is 5.4m, the bearing capacity meets the requirements;

[0172] Step S6: Excavate the pile hole with a diameter of 0.5m and a depth of 13.5m. Expand the pile hole diameter by 0.9m to the burial depth of the third-stage helical blade, i.e., 12.15m, and bury the steel blade shell of the third-stage helical blade.

[0173] Step S7: Backfill the third-stage spiral blade with soil to a depth of 6.75m above the blade, and use mud slurry to protect the pile hole or apply steel barriers to prevent the pile hole from collapsing. Then, compact the backfill soil.

[0174] Step S8: Enlarge the pile hole diameter to 1.35m and the depth to the second-stage helical blade embedment depth of 6.75m. Embed the steel blade shell of the second-stage helical blade and backfill the soil to the first-stage helical blade embedment depth of 4.05m. Directly embed the first-stage helical blade steel helical blade and backfill the soil to the surface elevation of the pile body 1 foundation.

[0175] Step S9: Pour concrete, lay steel pad 32 in the poured concrete, and after curing, the pile body 1 and the spiral blade assembly 2 are completed. Install elastic element 33 and vertical magnetorheological damper 34, install steel pad 31, and install double-end hinge rod 41. Then the seismic isolation layer 3 is completed.

[0176] Step S10: Construct the ring beam assembly 42 and the connecting part 43 with an appropriate diameter. After curing, install the transverse magnetorheological damper assembly 44 in the connecting part 43 and connect the double-end hinged rod 41. The construction of the seismic ring 4 is then completed.

[0177] The above are merely preferred embodiments of the present invention and are illustrative in nature, not restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A variable cross-section seismic-resistant helical pile foundation, characterized in that, It includes the pile body (1), the spiral blade assembly (2), the seismic isolation layer (3), and the seismic ring (4); The spiral blade assembly (2) and the pile body (1) are poured into the construction soil layer to form a spiral pile foundation. The seismic isolation layer (3) is installed on the top of the pile body (1) and is poured into the pile body (1) to become an integral part. The seismic ring (4) is arranged around the outside of the seismic isolation layer (3) and connected to the seismic isolation layer (3).

2. The variable cross-section seismic-resistant helical pile foundation as described in claim 1, characterized in that, The spiral blade group (2) includes several groups of spiral blades of different specifications. The several groups of spiral blades are arranged upward along the lower part of the pile body (1) in order of increasing diameter.

3. The variable cross-section seismic-resistant helical pile foundation as described in claim 2, characterized in that: The diameter of the spiral blade is less than five times the diameter of the pile body (1), and the number of spiral blades in the spiral blade group (2) is at least three levels.

4. The variable cross-section seismic-resistant helical pile foundation as described in claim 1, characterized in that, The isolation layer (3) includes an upper steel pad (31), a lower steel pad (32), several sets of elastic elements (33) and several sets of vertical magnetorheological dampers (34). There is a space between the upper steel pad (31) and the lower steel pad (32) for placing the elastic elements (33) and the vertical magnetorheological dampers (34). Several sets of elastic elements (33) and vertical magnetorheological dampers (34) are arranged alternately in a ring along the space. The two ends of the elastic elements (33) are fixedly connected to the upper steel pad (31) and the lower steel pad (32) respectively. The two ends of the vertical magnetorheological dampers (34) are fixedly connected to the upper steel pad (31) and the lower steel pad (32) respectively.

5. A variable cross-section seismic-resistant helical pile foundation as described in claim 4, characterized in that, The seismic ring (4) includes a double-ended hinge rod (41), a ring beam assembly (42), a connecting part (43), and a transverse magnetorheological damper assembly (44). The double-ended hinge rod (41) includes two separate ends and one merged end, which form a V-shaped structure. Several sets of the double-ended hinge rods (41) are installed at equal intervals in the seismic isolation layer (3). The ring beam assembly (42) and the connecting part (43) are integrally cast on the outside of the seismic isolation layer (3). The number of the connecting parts (43) matches the number of the double-ended hinge rods (41). The transverse magnetorheological damper assembly (44) is set inside each set of the connecting parts (43). The fixed end of the transverse magnetorheological damper assembly (44) is connected to the connecting part (43). A synchronous pad is provided between the movable ends of the transverse magnetorheological damper assembly (44). The merged end of the double-ended hinge rod (41) is hinged to the middle of the synchronous pad.

6. A variable cross-section seismic-resistant helical pile foundation as described in claim 5, characterized in that, The ring beam group (42) is composed of at least two sets of ring beams stacked together.

7. A construction method for a variable cross-section seismic-resistant helical pile foundation as described in any one of claims 1-6, characterized in that, Includes the following steps: Step S1, set the length of the pile body (1) as The diameter of the pile body (1) is The helical blade assembly (2) includes three stages of helical blades, each located at 0.3 meters of the pile body (1). 0.5 and 0.9 Location; Step S2: Calculate the blade spacing between adjacent helical blades based on the position of the three-stage helical blades on the pile body (1). The blade spacing between the first-stage and second-stage helical blades for: ； The blade spacing between the second-stage and third-stage helical blades for: ； Step S3, set the diameter of each stage of the helical blades to be First-stage helical blades outer diameter of the second-stage helical blade for: ； Third-stage helical blade outer diameter for: ； Step S4, based on the outer diameter of the second-stage helical blade and the outer diameter of the third-stage helical blade Calculate the blade spacing of the second-stage and third-stage helical blades. Corresponding control pitch : In the formula, The inclination angle of the helical blade. Let α be the internal friction angle of the soil layer, and α be the angle between the slip surface and the horizontal direction. It is a natural constant; The formula for calculating α is: ； blade spacing The calculated control pitch Comparison: When the blade spacing Greater than the control pitch At that time, the forces on adjacent helical blades are calculated according to the blade bearing mode; When the blade spacing Less than the control pitch At that time, the adjacent helical blades are subjected to force calculations according to the cylindrical bearing mode; Step S5: Combine the load design of the variable cross-section seismic-resistant helical pile foundation with seismic load, and calculate the characteristic value of the bearing capacity of a single pile. : In the formula, This represents the average vertical force acting on the helical pile foundation pile. For safety factor, take , This refers to the cylindrical shear load-bearing capacity between the first-stage and second-stage helical blades. For the load-bearing capacity of the blade bearing mode, This refers to the skin friction of the pile. Step S6, when That is, when the second-stage helical blade and the third-stage helical blade are in blade-loaded mode: ； when That is, when the second-stage and third-stage helical blades are in a cylindrical bearing mode: ； In the formula, This is the bearing capacity coefficient of the second-stage helical blade. The bearing capacity coefficient of the third-stage helical blade, the The formula for calculation is: ； The length of the pile body (1) is... Let β be the diameter of the pile body (1), β be the inclination angle of the helical blade, φ be the internal friction angle of the soil layer, and α be the angle between the slip surface and the horizontal direction. The cohesion of the soil layer; The pile embedment depth is 0~0.1m. The cohesion of the soil layer at that location, The pile embedment depth is 0.9~1. The cohesion of the soil layer at that location, This refers to the cohesion of the soil layer between the first-stage and second-stage helical blades. This refers to the cohesion of the soil layer between the second-stage and third-stage helical blades. The effective length of the external pile side friction resistance of the slip surface in the blade bearing mode involves the cohesion of the soil layer. This refers to the normal pressure on the slip surface of the first-stage and second-stage helical blades. This refers to the normal pressure on the slip surface of the second-stage and third-stage helical blades. The normal pressure on the slip surface under the effective length of the external pile side friction resistance in the blade bearing mode is the slip surface normal pressure. The pile embedment depth is 0~0.1m. The lateral pressure of the soil layer on the pile body (1), The pile embedment depth is 0.9~1. The lateral pressure of the soil layer on the pile body (1); The internal friction angle of the soil layer between the first-stage and second-stage helical blades. This refers to the internal friction angle of the soil layer between the second-stage and third-stage helical blades. The internal friction angle of the soil layer under the effective length of the external pile side friction resistance of the slip surface in the blade bearing mode. The pile embedment depth is 0~0.1m. The internal friction angle of the soil layer, For a burial depth of 0.9~1 The internal friction angle of the soil layer; The effective length of the external pile side friction of the slip surface in the blade bearing mode. The calculation formula is: ； Combining the two groups The length of the pile body (1) is obtained by solving the relational expression. and the diameter of the pile body (1) The length of the pile body (1) Calculate the blade spacing between adjacent helical blades and the diameter of each level of helical blade ; Step S7, based on the length of the pile body (1) and the diameter of the pile body (1) Excavate pile holes, increase the burial depth of the third-stage spiral blade to the outer diameter of the third-stage spiral blade, and install the third-stage spiral blade; Step S8: Backfill soil on the upper surface of the third-stage spiral blade to the depth of the second-stage spiral blade, compact the soil, and bury the second-stage spiral blade. Backfill soil on the upper surface of the second-stage spiral blade to the depth of the first-stage spiral blade, bury the first-stage spiral blade, and compact the soil. Step S9: Backfill the soil on the upper surface of the first-stage spiral blade to the elevation of the pile body (1) and compact the soil. Step S10: Hoist the pile reinforcement cage into the pile hole. The reinforcement cage is welded with protruding steel bars that cooperate with the first-stage spiral blade, the second-stage spiral blade and the third-stage spiral blade. Pour concrete into the reinforcement cage. After the concrete solidifies, the pile body (1) is formed. The first-stage spiral blade, the second-stage spiral blade and the third-stage spiral blade are integrated with the pile body (1) to form a whole. Install the vibration isolation layer (3) on the top of the pile body (1). Step S11: Set an anti-seismic ring (4) outside the seismic isolation layer (3) and connect the anti-seismic ring (4) to the seismic isolation layer (3) through a double-ended hinge rod (41).

8. The construction method of a variable cross-section seismic-resistant helical pile foundation as described in claim 7, characterized in that: Cylindrical shear mode bearing capacity in step S5 The formula for calculation is: In the formula, For the load-bearing capacity of the second-stage helical blades, The soil column shear resistance between the first-stage and second-stage helical blades; The calculation formula is: In the formula, The outer diameter of the second-stage helical blade. The inclination angle of the helical blade. The diameter of the pile body (1) is The internal friction angle of the soil layer. Let α be a natural constant, and α be the angle between the slip surface and the horizontal direction. The cohesion of the soil layer; The formula for calculation is: In the formula, This is the normal force on the shear surface. The outer diameter of the second-stage helical blade. The inclination angle of the helical blade. The blade spacing between the first-stage and second-stage helical blades. For the cohesion of the soil layer, The internal friction angle of the soil layer.

9. The construction method of a variable cross-section seismic-resistant helical pile foundation as described in claim 7, characterized in that: Blade mode bearing capacity in step S5 The formula for calculation is: In the formula, For the load-bearing capacity of the third-stage helical blade, Shear resistance at the slip surface of the soil column between the second and third stage helical blades; The calculation formula is: In the formula, The outer diameter of the third-stage helical blade. The inclination angle of the helical blade. The diameter of the pile body (1) is It is a natural constant. The internal friction angle of the soil layer. The angle between the slip surface and the horizontal direction. The cohesion of the soil layer; The calculation formula is: In the formula, The effective length of the external pile side friction resistance of the slip surface in the blade bearing mode.

10. The construction method of a variable cross-section seismic-resistant helical pile foundation as described in claim 7, characterized in that: Pile side friction resistance in step S5 The formula for calculation is: In the formula, L b This refers to the pile length involved in load-bearing modes other than cylindrical and blade-type load-bearing modes. For the cohesion of the soil layer, The internal friction angle of the soil layer. This is the normal force on the shear surface. The diameter of the pile body (1) is given.

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