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

Abstract

The present application relates to the technical field of pile foundation, in particular to a variable cross-section anti-seismic spiral pile foundation and a construction method, comprising a pile body, a spiral blade group, a shock insulation layer and an anti-seismic ring, the spiral blade group and the pile body form a spiral pile foundation by pouring in the construction soil layer, the shock insulation layer is installed on the top of the pile body and becomes an integral whole with the pile body by pouring, the anti-seismic ring is arranged outside the shock insulation layer and is connected with the shock insulation layer, the spiral blade group is composed of several groups of spiral blades with different specifications, and the several groups of spiral blades are arranged in order from small to large from the lower part of the pile body upwards, so that different bearing modes are formed, overall stress is realized, compared with the original technology relying on the scheme of increasing the outer diameter of the blade, the economic construction cost is reduced, and the anti-seismic performance and the bearing capacity are simultaneously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pile foundation, in particular to a variable cross-section anti-seismic spiral pile foundation and a construction method. BACKGROUND

[0002] As the most widely used building foundation, the anti-seismic design of pile foundation is very critical in high-intensity earthquake areas, and the dynamic response research has become a key topic in the field of civil engineering. Under the action of strong earthquakes, pile foundations often bear higher vertical compression loads, resulting in damage or excessive settlement of pile foundations. Therefore, spiral pile foundations are often used as support structures in earthquake-prone areas.

[0003] The traditional drill hole filling spiral pile foundation is often an equal distance equal cross-section spiral blade group. In actual process, the spiral pile foundation mainly relies on the benefits of the spiral blade group in the upper part of the pile to resist the influence of horizontal load, which causes the increase of blade outer diameter to cause the rise of economic construction cost, and the improvement of anti-seismic performance and bearing capacity fails to achieve the expected benefits. Therefore, a variable cross-section anti-seismic spiral pile foundation and a construction method are proposed. SUMMARY

[0004] In order to solve the above technical problems in the prior art, the present application provides a variable cross-section anti-seismic spiral pile foundation and a construction method.

[0005] In order to solve the above technical problems, the present application provides the following technical scheme: a variable cross-section anti-seismic spiral pile foundation, comprising a pile body, a spiral blade group, a shock isolation layer and an anti-seismic ring.

[0006] The spiral blade group and the pile body form a spiral pile foundation by pouring in the construction soil layer, the shock isolation layer is installed at the top of the pile body and becomes an integral whole with the pile body by pouring, and the anti-seismic ring is arranged around the outside of the shock isolation layer and connected with the shock isolation layer.

[0007] Preferably, the spiral blade group comprises several groups of spiral blades with different specifications, and the several groups of spiral blades are arranged in order from small to large in diameter along the lower part of the pile body upwards.

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

[0009] Preferably, the shock insulation layer comprises an upper steel base plate, a lower steel base plate, a plurality of groups of elastic members and a plurality of groups of vertical magnetorheological dampers, the upper steel base plate and the lower steel base plate have a placement space for placing the elastic members and the vertical magnetorheological dampers, the plurality of groups of the elastic members and the vertical magnetorheological dampers are alternately arranged in a ring shape along the placement space, two ends of the elastic members are fixedly connected with the upper steel base plate and the lower steel base plate respectively, and two ends of the vertical magnetorheological dampers are fixedly connected with the upper steel base plate and the lower steel base plate respectively.

[0010] Preferably, the anti-seismic ring comprises a double-end hinge rod, a ring beam group, a connecting part and a transverse magnetorheological damper group, the double-end hinge rod comprises two separated ends and one combined end, the two separated ends and the one combined end form a V-shaped structure, a plurality of groups of the double-end hinge rods are installed in the shock insulation layer at equal intervals, the ring beam group and the connecting part are integrally cast and formed outside the shock insulation layer, the number of the connecting parts matches the number of the double-end hinge rods, the transverse magnetorheological damper group is arranged inside each of the connecting parts, fixed ends of the transverse magnetorheological damper group are connected with the connecting part, and a synchronous base plate is arranged between movable ends of the transverse magnetorheological damper group, and the combined end of the double-end hinge rod is hingedly connected with the middle part of the synchronous base plate.

[0011] Preferably, the ring beam group is stacked by at least two groups of ring beams.

[0012] A construction method of a variable cross-section anti-seismic spiral pile foundation, comprising the following steps:

[0013] Step S1, setting the length of the pile body as , the diameter of the pile body as , and the spiral blade group comprising three levels of spiral blades, the three levels of spiral blades being respectively located at positions of 0.3 , 0.5 and 0.9 of the pile body;

[0014] Step S2, calculating the blade spacing of adjacent spiral blades according to the positions of the three levels of spiral blades on the pile body, the blade spacing of the first level of spiral blades and the second level of spiral blades being:

[0015] ;

[0016] the blade spacing of the second level of spiral blades and the third level of spiral blades being:

[0017] ;

[0018] Step S3, setting the diameter of each level of spiral blades as , the first level of spiral blades and the outer diameter of the second-stage helical blade is:

[0019] ;

[0020] the outer diameter of the third-stage helical blade is:

[0021] ;

[0022] Step S4, the outer diameter of the second-stage helical blade and the outer diameter of the third-stage helical blade are used to calculate the blade spacing of the second-stage helical blade and the third-stage helical blade corresponding control pitch :

[0023]

[0024] wherein, is the helical blade inclination angle, is the internal friction angle of the soil layer, and is a natural constant;

[0025] The calculation formula of the is:

[0026] ;

[0027] The blade spacing is compared with the calculated control pitch :

[0028] When the blade spacing is greater than the control pitch , the adjacent helical blades are calculated according to the blade bearing mode;

[0029] When the blade spacing is less than the control pitch , the adjacent helical blades are calculated according to the cylindrical bearing mode;

[0030] Step S5, the load of the variable cross-section seismic spiral pile foundation is designed in combination with the seismic load, and the characteristic value of the single pile bearing capacity is calculated :

[0031]

[0032] wherein, is the average vertical force acting on the spiral pile foundation pile, is a safety factor, and is taken as , is the cylindrical shear mode bearing capacity between the first-stage helical blade and the second-stage helical blade, 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 depth is 0.9~1 meters. 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 depth is 0.9~1 meters. The side pressure of the soil layer on the pile body;

[0043] The internal friction angle of the soil layer between the first-stage spiral blade and the second-stage spiral blade, The internal friction angle of the soil layer between the second-stage spiral blade and the third-stage spiral blade, The internal friction angle of the soil layer under the effective length of the outer pile side friction of the slip surface of the blade bearing mode, The internal friction angle of the soil layer when the pile depth is 0~0.1 The internal friction angle of the soil layer, The internal friction angle of the soil layer when the depth is 0.9~1 The internal friction angle of the soil layer;

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

[0045] ;

[0046] The relationship formula of the two groups The length of the pile body and the diameter of the pile body are obtained by solving the relationship formula of the two groups The blade spacing between adjacent spiral blades and the diameter of each spiral blade are calculated by the length of the pile body

[0047] Step S7, according to the length of the pile body and the diameter of the pile body , excavate the pile hole, enlarge the soil layer at the depth of the third-stage spiral blade to the outer diameter of the third-stage spiral blade, and bury the third-stage spiral blade;

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

[0049] Step S9, backfill the soil to the elevation of the pile body on the upper surface of the first-stage spiral blade and compact the soil;

[0050] Step S10, hoist the pile reinforcement cage into the pile hole, and the reinforcement cage is respectively welded with the outer reinforcement which cooperates with the first-stage spiral blade, the second-stage spiral blade and the third-stage spiral blade, pour concrete into the reinforcement cage, form the pile body after the concrete solidifies, the first-stage spiral blade, the second-stage spiral blade and the third-stage spiral blade are fused with the pile body to form a whole, and install the shock isolation layer at the top of the pile body;

[0051] Step S11, setting an anti-seismic ring outside the isolation layer and connecting the anti-seismic ring with the isolation layer through a double-end hinged bar.

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

[0053]

[0054] In the formula, is the bearing capacity of the second-stage spiral blade, is the soil column shear resistance between the first-stage spiral blade and the second-stage spiral blade;

[0055] The calculation formula is:

[0056]

[0057] In the formula, is the outer diameter of the second-stage spiral blade, is the spiral blade inclination angle, is the diameter of the pile body, is the internal friction angle of the soil layer, is a natural constant, and α is the angle between the sliding surface and the horizontal direction, is the cohesion of the soil layer;

[0058] The calculation formula is:

[0059]

[0060] In the formula, is the normal pressure of the shear surface, is the outer diameter of the second-stage spiral blade, is the spiral blade inclination angle, is the blade spacing between the first-stage spiral blade and the second-stage spiral blade, is the cohesion of the soil layer, is the internal friction angle of the soil layer.

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

[0062]

[0063] In the formula, is the bearing capacity of the third-stage spiral blade, is the soil column sliding surface shear resistance between the second-stage spiral blade and the third-stage spiral blade;

[0064] The calculation formula is: ​​

[0065]

[0066] In the formula, is the third spiral blade outer diameter, is the spiral blade angle, is the diameter of the pile body, is a natural constant, is the internal friction angle of the soil layer, is the angle between the sliding surface and the horizontal direction, is the cohesion of the soil layer;

[0067] The calculation formula is:

[0068]

[0069] In the formula, is the effective length of the outer pile side friction of the blade bearing mode sliding surface.

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

[0071]

[0072] In the formula, L b is the length of the pile involved in the cylindrical bearing mode and the blade bearing mode, is the cohesion of the soil layer, is the internal friction angle of the soil layer, is the normal pressure of the shear surface, is the diameter of the pile body.

[0073] The beneficial effects of the present application compared with the prior art are:

[0074] 1. In the present application, the spiral blade group is provided, and the spiral blade group is composed of a plurality of groups of spiral blades with different specifications, and the plurality of groups of spiral blades are arranged from small to large from the lower part of the pile body upwards, thereby forming different bearing modes and realizing overall stress. Compared with the original technology relying on the scheme of increasing the outer diameter of the blade, the economic construction cost is reduced, and the anti-seismic performance and bearing capacity are simultaneously improved.

[0075] 2. In the present application, the data calculation method of the variable cross-section anti-seismic spiral pile foundation is established, so that the variable cross-section anti-seismic spiral pile foundation can achieve the expected purpose. BRIEF DESCRIPTION OF DRAWINGS

[0076] Figure 1 is a schematic diagram of the three-dimensional structure of the present application;

[0077] Figure 2 is a schematic diagram of the three-dimensional structure of the shock isolation layer of the present application;

[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 image 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 vertically displaces, the size of the spiral blade near the top of the pile body 1 in the spiral blade group 2 is increased, and once damping is performed, so that the lateral displacement and vertical displacement of the top of the pile body 1 are reduced, at the same time, the kinetic energy of the movement of the pile body 1 is consumed by the vertical magnetorheological damper 34 in the isolation layer 3, and secondary damping is performed;

[0090] The anti-seismic ring 4 comprises double-end hinge bar members 41, ring beam groups 42, connecting parts 43 and a transverse magnetorheological damper group 44;

[0091] The double-end hinge bar member 41 comprises two separated ends and one combined end, and the two separated ends and the combined end form a V-shaped structure. A plurality of groups of double-end hinge bar members 41 are installed at intervals in the isolation layer 3. The ring beam group 42 and the connecting part 43 are integrally formed outside the isolation layer 3. The number of the connecting parts 43 is consistent with the number of the double-end hinge bar members 41. The transverse magnetorheological damper group 44 is arranged inside each group of connecting parts 43. The fixed end of the transverse magnetorheological damper group 44 is connected with the connecting part 43. The movable ends of the transverse magnetorheological damper group 44 are provided with a synchronous pad. The combined end of the double-end hinge bar member 41 is hingedly connected with the middle part of the synchronous pad.

[0092] The ring beam group 42 is composed of a plurality of 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 movement of the double-end hinge bar member 41. The double-end hinge bar member 41 transmits the movement to the ring beam group 42, so that the movement is transmitted to the transverse magnetorheological damper group 44 for three times of energy dissipation.

[0093] When the top of the pile body 1 horizontally displaces, the upper spiral blade reduces the lateral displacement of the top of the pile body 1, and once damping is performed. Since the top of the pile body 1 is 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 bar member 41, and the transverse magnetorheological damper group 44 performs secondary damping to reduce the deformation of the superstructure.

[0094] The construction method of the variable cross-section anti-seismic spiral pile foundation comprises the following steps:

[0095] Step S1, the length of the pile body 1 is set to , the diameter of the pile body 1 is , the spiral blade group 2 comprises three levels of spiral blades, and the three levels of spiral blades are respectively located at the positions of 0.3 , 0.5 and 0.9 of the pile body 1;

[0096] Step S2, the blade spacing of adjacent spiral blades is calculated according to the positions of the three levels of spiral blades on the pile body 1. The blade spacing of the first level of spiral blades and the second level of spiral blades is 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, load of variable cross-section seismic spiral pile foundation designed in combination with seismic load is combined to calculate the characteristic value of single pile bearing capacity :

[0113] ;

[0114] In the formula, is the average vertical force acting on the spiral pile foundation pile, is the safety factor, taken as , is the cylindrical shear mode bearing capacity between the first and second spiral blades, is the blade bearing mode bearing capacity, is the pile side friction;

[0115] The calculation formula of the cylindrical shear mode bearing capacity is:

[0116]

[0117] In the formula is the second spiral blade bearing capacity, is the soil column shear resistance between the first and second spiral blades;

[0118] The calculation formula is:

[0119]

[0120] In the formula is the outer diameter of the second spiral blade, is the spiral blade inclination angle, is the diameter of the pile body 1, is the internal friction angle of the soil layer, is a natural constant, and α is the angle between the sliding surface and the horizontal direction, is the cohesion of the soil layer;

[0121] The calculation formula is:

[0122]

[0123] In the formula, is the normal pressure of the shear surface, is the outer diameter of the second spiral blade, is the spiral blade inclination angle, is the blade spacing between the first and second spiral blades, is the cohesion of the soil layer, is the internal friction angle of the soil layer;

[0124] The 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] The relationship formula of the two groups The length of the pile body 1 is obtained by solving the relationship formula and the diameter of the pile body 1 The length of the pile body 1 The blade spacing of adjacent spiral blades is calculated and the diameter of each level of spiral blades ;

[0149] Step S7, according to the length of the pile body 1 and the diameter of the pile body 1 Excavate the pile hole, expand the soil layer at the third level of spiral blade burial depth to the outer diameter of the third level of spiral blade, and bury the third level of spiral blade;

[0150] Step S8, backfill the soil to the second level of spiral blade burial depth on the upper surface of the third level of spiral blade, bury the second level of spiral blade, backfill the soil to the first level of spiral blade burial depth on the upper surface of the second level of spiral blade, bury the first level of spiral blade, mud wall protection or steel fence is applied to prevent the pile hole from collapsing, and the soil is rammed;

[0151] Step S9, backfill the soil to the design elevation of the pile body 1 on the upper surface of the second level of spiral blade and perform soil compaction;

[0152] Step S10, hoist the pile reinforcement cage into the pile hole, and the reinforcement cage is respectively welded with the outer extending steel of the first level of spiral blade, the second level of spiral blade and the third level of spiral blade at different heights outside the reinforcement cage. Pour concrete into the reinforcement cage, and form the pile body 1 after the concrete solidifies. The first level of spiral blade, the second level of spiral blade and the third level of spiral blade are fused with the pile body 1 to form a whole. Install the shock isolation layer 3 at the top of the pile body 1;

[0153] Step S11, set the anti-seismic ring 4 outside the shock isolation layer 3 and connect the anti-seismic ring 4 with the shock isolation layer 3 through the double-end hinge link 41.

[0154] Example two:

[0155] When the standard combination of the acting earthquake and load acts on the spiral pile foundation pile, the is 500 , the soil layer is uniform cohesive soil, is 40 , is 10°, is 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. Take 13.5m, the first stage spiral blade outer diameter And the second stage spiral blade outer diameter Take 1.35m, the third stage spiral blade outer diameter Take 0.9m, the pitch Take 2.7m, the pitch Take 5.4m, the bearing capacity meets the requirements;

[0172] Step S6: excavate the pile hole, the pile hole diameter is 0.5m, the depth is 13.5m, the pile hole diameter is expanded to 0.9m to the depth of the third stage spiral blade, that is, the depth of the buried soil layer is 12.15m, and the third stage spiral blade steel blade shell is buried;

[0173] Step S7: backfill the soil to the depth of the upper blade, that is, 6.75m, mud wall protection or steel fence is applied to the pile hole to prevent the pile hole from collapsing, and the soil is tamped;

[0174] Step S8: the pile hole diameter is expanded to 1.35m, the depth is expanded to the depth of the second stage spiral blade, that is, 6.75m, the second stage spiral blade steel blade shell is buried, the soil is backfilled to the depth of the first stage spiral blade, that is, 4.05m, the first stage spiral blade steel spiral blade is directly buried, and the soil is backfilled to the upper surface elevation of the pile body 1;

[0175] Step S9: pour concrete, lay the lower steel pad plate 32 in the poured concrete, after curing, the pile body 1 and the spiral blade group 2 are completed, the elastic member 33 and the vertical magnetorheological damper 34 are installed, the upper steel pad plate 31 is installed, and the double-end hinge rod 41 is constructed, so that the shock insulation layer 3 is completed;

[0176] Step S10: the ring beam group 42 and the connecting part 43 are constructed according to the appropriate diameter, after curing, the transverse magnetorheological damper group 44 is installed in the connecting part 43, and the double-end hinge rod 41 is connected, so that the anti-seismic ring 4 is completed.

[0177] The above is only a preferred embodiment of the present application, which is only illustrative but not limiting. Those skilled in the art understand that many changes, modifications and even equivalents can be made to the present application within the spirit and scope defined by the claims of the present application, but all will fall within the protection scope of the present application.

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 cast 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 cast into a whole with the pile body (1). The seismic ring (4) is arranged around the outside of the seismic isolation layer (3) and connected to the seismic isolation layer (3). 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. 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). The 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. 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.

2. The variable cross-section seismic-resistant helical pile foundation as described in claim 1, 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.

3. The variable cross-section seismic-resistant helical pile foundation as described in claim 1, characterized in that, The ring beam group (42) is composed of at least two sets of ring beams stacked together.

4. A construction method for a variable cross-section seismic-resistant helical pile foundation as described in any one of claims 1-3, 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 helical blade and the third-stage helical blade 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).

5. The construction method of a variable cross-section seismic-resistant helical pile foundation as described in claim 4, 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.

6. The construction method of a variable cross-section seismic-resistant helical pile foundation as described in claim 4, 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.

7. The construction method of a variable cross-section seismic-resistant helical pile foundation as described in claim 4, 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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