Anti-pulling and anti-compression prestressed jet expansion frustum press-grouting pile

Abstract

The utility model discloses an anti-pulling and anti-compression prestressed jet expansion frustum press-grouting pile. The press-grouting pile is composed of a pile body and a prestressed rod body combined component located in the pile body. The pile body comprises a pile cap and a pile body which are of an integrated structure, at least three rib plates are arranged on the peripheral face of the pile body, and at least one double-frustum expanding body is arranged below the pile body. The prestressed rod body combined component comprises a rod body tensioning end component, a rod body steel pull rod component and a rod body anchoring end component which are sequentially connected from top to bottom. The pile type can be used for an uplift pile and an uplift and compression resistant pile, and is high in bearing capacity, small in deformation and low in manufacturing cost; the prestress is applied at the top of the pile, so that cross construction of raft plates is avoided, and the construction period is shortened; a pile cap is arranged at the top of the pile to prevent local compression damage of pile end concrete during prestress tensioning; the pile end is of a bottom anchor type structure, and stress is reasonable; the steel pull rod in the double-frustum expanding body is sleeved with the external thread anchoring steel pipe and filled with the high-strength grouting material, corrosion resistance is good, and anchoring is stable and reliable.

Description

Technical Field

[0001] The utility model relates to the technical field of civil engineering pile foundation, in particular to a pull-out and compression-resistant prestressed spray-expanded cone-shaped pressurized pile. Background Art

[0002] With the adjustment and development of the construction industry, construction projects have increasingly higher requirements for foundation design and construction, and concrete piles are being used more and more widely in high-rise buildings, bridges, high-speed railways, ports and other construction projects.

[0003] At present, cast-in-place concrete piles are generally used as compression piles. When used as pull-out piles, the longitudinal steel bars in the piles are subjected to tensile force, and the steel bars extend and deform, which will cause cracks in the concrete of the pile body. In order to ensure the durability of the tensile steel bars in the pile body, the crack width of the concrete needs to be controlled. The pile body reinforcement ratio calculated according to the current specifications is very high, which is bound to cause a large waste of steel bars.

[0004] To address these problems, the improved method is to remove the steel cage and set an unbonded prestressed tie rod in the center of the pile, which reduces the amount of steel bars used, forms prestress on the concrete of the pile body, and avoids cracks in the free section of the pile body. However, there are still cracks in the pile body of the anchor section, and the durability of the steel tie rod in the anchor section cannot be ensured, and this type of pile is often only tensile and not compressive. When prestress is applied to the pile end of conventional small-diameter prestressed piles, local compressive failure may occur. Conventional prestressed pull-out piles generally apply prestress on the top of the raft slab, and a prestressed rod channel needs to be reserved. The construction is cross-constructed with the raft slab, which takes a long time and often causes the common problem of water leakage in the basement raft slab. Conventional prestressed pull-out piles have no enlarged head at the pile end, low pull-out bearing capacity, and large deformation. Therefore, to date, no type of pile has been able to systematically and comprehensively solve the above technical problems.

[0005] The applicant disclosed a spray-expanded extrusion composite pile and its construction method and a spiral spray-expanded extrusion drill used in the method in CN108330959B. The pile body of the composite pile (renamed as spray-expanded cone pressure-cast pile when the standard was compiled) consists of a pile body, an expansion body and a pile end. The utility model has high bearing capacity for a single pile, high construction efficiency and economic savings. However, when used as a pull-out pile, in order to control the cracks in the concrete of the pile body and ensure the durability of the steel bars in the pile body, a large amount of longitudinal reinforcement needs to be configured to solve the problem of crack width. The reinforcement ratio is high and the material cost is high, which limits the large-scale application of the composite pile as a pull-out pile.

[0006] Therefore, in order to solve the problems of concrete cracks in the pile body and the durability of steel bars, reduce the amount of steel bars used, and at the same time achieve the purpose of making the pile both pull-out and compressive, thereby achieving greater economic and social benefits, it is urgent to design a new and efficient cast-in-place pile. Utility Model Content

[0007] The utility model aims to provide a prestressed spray expansion cone grouting pile with tensile and compression resistance.

[0008] In order to achieve the above purpose, the technical solution adopted by the utility model is as follows:

[0009] A pull-out and compression-resistant prestressed spray-expanded cone-shaped grouted pile, comprising a pile body and a prestressed rod body composite component located in the pile body; the pile body comprises a pile cap, a pile body, a rib plate and a double cone-shaped expansion body of an integrated structure, at least three rib plates are arranged on the outer circumference of the pile body, and at least one double cone-shaped expansion body is arranged below the pile body; the prestressed rod body composite component comprises a rod body tensioning end component, a rod body steel tie rod component and a rod body anchoring end component which are sequentially connected from top to bottom;

[0010] The pile cap is in a cone shape, and the rod tensioning end member is located at the top of the pile cap and together with the pile cap constitutes a pile tensioning end structure; the pile cap is arranged at the pile tensioning end to prevent the concrete at the pile end from being locally compressed and damaged during prestressing;

[0011] The rod body steel tie rod component includes an isolation tube located in the center of the steel cage, a steel tie rod is inserted into the isolation tube, the lower end of the isolation tube extends to the top center of the double-cone expansion body, the lower end of the steel tie rod passes through the isolation tube and passes through the externally threaded anchoring steel pipe located inside the double-cone expansion body, and is fixed together with the prestressed anchoring steel plate located in the bottom center of the double-cone expansion body through a second locking nut.

[0012] The rod body tensioning end member comprises a prestressed support steel plate located on the top of the pile cap, and a first locking nut is arranged above the prestressed support steel plate.

[0013] Furthermore, the interior of the pile cap and the pile body is a concrete structure with a steel cage, and the outer layer is a cement-soil transition layer; a rod body steel tie rod component is provided on the central axis of the pile body; the interior of the rib plate is concrete, and its outer layer is a cement-soil transition layer, and the purpose of providing the rib plate is to increase the side friction resistance of the pile; the pile body, rib plate and rod body steel tie rod component together constitute the pile free section structure, and the free section structure is to realize the pile bottom anchor type structure.

[0014] Furthermore, the outer surface of the steel tie rod is provided with an anti-corrosion coating; the upper end of the steel tie rod passes through the prestressed support steel plate and passes through the spiral reinforcement to be connected to the anchor plate located above the spiral reinforcement; the first locking nut fixes the steel tie rod and the prestressed support steel plate together.

[0015] Furthermore, the interior of the double-cone expansion body is concrete, the outer layer is a cement-soil transition layer, and a rod body anchoring end member is also provided inside the double-cone expansion body. The double-cone expansion body and the rod body anchoring end member together constitute a pile bottom anchor type structure. Above the upper end surface of the double-cone expansion body is the pile free section, the double-cone expansion body is the anchoring section, and is located in the deep dense soil layer at the bottom of the pile, forming a pull-out resistant pile bottom anchor type structure.

[0016] Furthermore, high-strength grouting material is injected into the externally threaded anchoring steel pipe; a guide ring is respectively provided on the upper and lower parts of the externally threaded anchoring steel pipe; the externally threaded anchoring steel pipe, the prestressed anchoring steel plate, the second locking nut, the high-strength grouting material and the guide ring together constitute the rod body anchoring end component.

[0017] Furthermore, a compacted soil layer is formed on the outside of the pile body, and the compacted soil layer wraps the lower part of the pile cap, the pile body and the double-cone expansion body; a cushion layer is arranged around the upper part of the pile cap, and the upper part of the cushion layer is a foundation raft.

[0018] The position where the prestress is applied to this type of pile is the pile cap at the top of the pile. There is no need to reserve a prestressed rod channel in the raft slab. The steel tie rod above the pile top is anchored in the concrete raft slab to avoid cross-construction with the raft slab, and also to avoid the common problem of water leakage in the basement raft slab.

[0019] The design method of the pull-out and compression-resistant prestressed spray-expanded cone-shaped pressure-cast pile described in the utility model is based on the following principles:

[0020] When the pull-out and compression-resistant prestressed spray-expanded cone-type pressure-cast pile is pulled out, the pile type is a bottom anchor type structure. The pulling force is applied to the top of the double cone expansion body, and the upper pile body concrete is compressed. Due to the Poisson's ratio effect, the pile side friction resistance is higher than that of ordinary pull-out piles. Based on the above reasons and field tests, the pile side friction resistance pull-out coefficient λ i It was adjusted from 0.5~0.8 in the "Technical Standard for Spray-Expanded Conical Grouting Piles" T / CECS657-2020 to between 0.8 and 0.95.

[0021] Due to the cement-soil transition layer and ribs, the pile side friction resistance is higher than that of ordinary pull-out piles, and the pile side friction resistance increase coefficient β si It is 1.2 to 2.1.

[0022] The pull-out force is directly applied to the top of the double-cone expansion body. Compared with the conventional pull-out resistant expanded bottom pile, the double-cone expansion body can be subjected to force in advance, and the role of the expansion body can be fully exerted. The conventional pull-out resistant expanded bottom pile has no free section, and the pull-out force is applied to the top of the pile. The side resistance of the pile body is exerted first, and the force on the expansion head is delayed, so the expansion head cannot fully play its role.

[0023] The upper surface of the double-cone expansion body is provided with a conical inclined surface, and the angle between the soil rupture sliding surface and the vertical surface is increased, which can enable more deep dense soil to participate in the pull-out work, and the pull-out resistance of the double-cone expansion body is greatly improved. The top surface of the expansion head of the conventional pull-out expanded pile is a horizontal plane, and the angle between the soil rupture sliding surface and the vertical surface is reduced, so that less soil participates in the pull-out work and the pull-out resistance is small; the upper pile body of the double-cone expansion body is provided with ribs along the entire length, and the ribs extend to the distant soil layer around the pile body, so that the range of soil layers around the pile body that participate in the pull-out work is increased. Based on the above reasons and field tests, the standard value of the deadweight of the foundation pile and the deadweight of the soil above the expansion body that participates in the pull-out work in the formula of this patent is 1.2 times the current standard.

[0024] According to the above principle, the anti-pullout design method of the anti-pullout and anti-compression prestressed spray expansion cone pressure-cast pile has the following specific steps:

[0025] The first step is to determine the geometric parameters of the pile according to the compression and pull-out resistance of the pile and the ground conditions. The geometric parameters of the pile include the pile diameter, pile length, ribs, expansion body, pile cap structural geometric dimensions, position and other parameters, and refer to the Technical Standard for Spray-Expanded Cone Grouting Piles T / CECS 657-2020;

[0026] The second step is to arrange the pile positions according to the upper load and water buoyancy;

[0027] The third step is to verify the vertical pull-out bearing capacity of a single pile:

[0028] When the pile group is not in overall failure, the pull-out resistance of the prestressed spray-expanded cone-type cast-in-place pile is calculated according to formula (1): First determine the pull-out coefficient λ i , calculate T according to formula (2) uk ; Then calculate G according to the Technical Standard for Spray-Expanded Cone Grouting Piles T / CECS 657-2020 p , respectively, into formula (1) for verification;

[0029]

[0030] T uk =Σλ i q sik u i l i β si (2)

[0031] N k ——vertical pullout force acting on the pile corresponding to the standard combination of actions (kN);

[0032] T uk ——When the pile group is not in overall failure, the standard value of the total pull-out limit lateral resistance of the pile foundation (kN);

[0033] Gp ——The standard value of the deadweight of the pile and the deadweight of the soil above the expanded diameter that participates in the pull-out work (kN). When calculating the deadweight of the pile below the groundwater level, the water buoyancy should be deducted. When estimating, the value should be 1.2 times the deadweight of the pile soil in the Technical Standard for Spray-Expanded Cone-Grought Piles T / CECS657-2020;

[0034] λ i ——Pull-out coefficient, ranging from 0.8 to 0.95;

[0035] q sik ——The standard value of the ultimate lateral resistance of the i-th layer of soil on the pile side (kPa) should be determined based on test data and local engineering experience. When test data is lacking, the value can be taken according to Appendix C of the Technical Standard for Spray-Expanded Cone Grouting Piles T / CECS 657-2020;

[0036] u1——the circumference of the pile body at the upper part of the expansion body (m);

[0037] l i ——thickness of the i-th layer of soil around the pile above the expanded diameter body (m);

[0038] β si ——The side resistance enhancement coefficient of spray-expanded cone grouted piles shall be taken in accordance with the Technical Standard for Spray-Expanded Cone Grouted Piles T / CECS 657-2020.

[0039] When the pile group is in overall failure, the calculation formula for the pull-out resistance of the prestressed spray-expanded cone-type pressure-cast piles is the same as that of Formula 4.3.1-2 and 4.3.2-2 in the Technical Standard for Spray-Expanded Cone-Type Pressure-Casing Piles T / CECS 657-2020;

[0040] The fourth step is to verify the local compression of the pile cap concrete, the compressive bearing capacity of the pile body, the tensile bearing capacity of the prestressed steel tie rod, and the anchorage force of the steel tie rod at the bottom expansion body. The above verification formulas are implemented in accordance with the "Concrete Structure Design Code" (2015 Edition) GB 50010-2010.

[0041] The compressive design method of tensile and compressive resistant prestressed spray-expanded cone grouted piles shall be implemented in accordance with the "Technical Standard for Spray-Expanded Cone grouted Piles" T / CECS 657-2020.

[0042] Compared with conventional bottom-enlarged anti-pullout piles, the pull-out coefficient λi of the prestressed spray-expanded cone-shaped pressure-cast piles is increased, and the pile side resistance enhancement coefficient βsi is increased. As the soil involved in the pull-out work increases, the self-weight Gp of the foundation pile and the soil increases. Compared with the pull-out spray-expanded cone-shaped pressure-cast piles, the pull-out coefficient λi of the prestressed spray-expanded cone-shaped pressure-cast piles is increased. As the double cone expansion body is stressed in advance, the role of the deep dense soil layer is fully utilized. When the prestressed spray-expanded cone-shaped pressure-cast piles are compressed, the principle calculation is the same as that of the spray-expanded cone-shaped pressure-cast piles. Compared with conventional bottom-enlarged piles, the compressive bearing capacity is greatly improved.

[0043] Analysis of the pull-out and compression resistance mechanism of the pull-out and compression resistance prestressed spray expansion cone pressure-cast pile of the utility model:

[0044] (1) The stress mechanism of the pull-out and compression-resistant prestressed spray-expanded cone-shaped pressure-cast pile in the soil during pull-out: a prestressed rod body composite component is added to the concrete pile body, and the steel tie rod is provided with an external threaded anchor steel pipe in the bottom double cone expansion body. The external threaded anchor steel pipe forms a bonding anchor and a mechanical anchor. The steel tie rod is sleeved with an isolation pipe above the upper end surface of the double cone expansion body to form a free section, and the pile end forms a bottom anchor type structure. When the pile is pulled out, the pull-out force is first transmitted to the double cone expansion body and the surrounding deep compacted soil layer through the steel tie rod. The double cone expansion body has a large anchoring force in the deep compacted soil layer. The double cone expansion body of the pile body is like "welded" in the compacted soil layer, connecting the pile and the soil into a whole. When the expansion body is slightly deformed, the pile body and the rib plate above generate friction resistance to jointly resist the pull-out force of the free section steel tie rod. Due to the existence of the cone slope on the double cone expansion body, the angle between the soil rupture sliding surface and the vertical plane is increased, which can enable more deep dense soil to participate in the pull-out resistance work. Part of the vertical pull-out force on the slope will be converted into horizontal force and transmitted to a distance, and the total pull-out resistance can be increased by more than 2 times.

[0045] (2) Load-bearing mechanism of pile cross section: When the pile cross section is subjected to load, the load is first transferred to the double-cone expanded concrete core pile, which is then transferred to the cement soil through the bonding force between the cement soil and the core pile. Then, the cement soil is transferred to the outer compacted soil layer through the bonding force between the cement soil and the compacted soil layer, and the compacted soil layer is transferred to the outer soil layer. In this way, a gradual strength change process of strong, medium and weak is formed from the core pile, cement soil, compacted soil and outer soil layer, forming a reasonable load transfer structure with high strength of the intermediate material and low strength of the outer material. The side friction resistance of the pile is controlled by the shear strength of the pile-soil interface of the ordinary pile, which is converted into the shear strength control of the outer soil layer, pulling the soil around the pile to move together, improving the side bearing capacity of the pile and reducing deformation.

[0046] (3) The working mechanism of the tensile and compressive prestressed spray expansion cone cast-in-place pile when prestress is applied at the pile top: After the prestress is applied to the pile top and locked, the pile concrete and the steel cage are in a compressive state. When there is water buoyancy on the raft, the force conversion can be achieved through the steel tie rods and the anchor plates in the raft. The prestress in the steel tie rods is converted into a downward pulling force on the raft, reducing the deformation of the raft. The steel cage is always under compression under the action of the prestress.

[0047] (4) The stress mechanism of the tensile and compressive resistant prestressed spray-expanded cone-type pressure-grouted piles under compression: the same as the spray-expanded cone-type pressure-grouted piles, which can be referred to the relevant mechanism in CN108330959B.

[0048] Compared with the prior art, the outstanding effects of the utility model are:

[0049] (1) The pull-out and compression-resistant prestressed spray-expanded cone-shaped pressurized piles of the utility model can be used for pull-out piles as well as pull-out and compression-resistant piles, have high bearing capacity, small deformation, fast construction speed, reliable quality, are green and environmentally friendly, and have good comprehensive benefits.

[0050] (2) The pull-out and compression resistant prestressed spray-expanded cone-shaped cast-in pile of the utility model has a prestressed rod body composite component arranged in the concrete pile body, and can be used as a pull-out pile. When a steel cage is arranged at the same time, it can be used as a pull-out and compression resistant pile.

[0051] (3) Prestress is applied to the pile body, and there is no crack in the pile body, which can save more than 80% of steel and save construction costs.

[0052] (4) The tensile and compressive resistant prestressed spray-expanded cone-type grouted piles of the utility model, when prestress is applied, the concrete of the free section of the pile body above the double cone expansion body is compressed, the pile body has high rigidity, no cracks, and a cement soil layer and a compacted soil layer are arranged on the periphery of the pile body, so the anti-corrosion and waterproof effects are good, and the durability of the free section of the pile body is good, and it is particularly suitable for underground environments that are corrosive to steel bars.

[0053] (5) The tensile and compressive prestressed spray expansion cone grouting pile of the utility model applies prestress at the top of the pile, avoiding cross construction with the raft slab, saving construction time, and no prestressed rod channel is required in the raft slab, thus avoiding the common problem of water leakage in the basement raft slab.

[0054] (6) The pull-out and compression-resistant prestressed spray-expanded cone-shaped pressurized pile of the utility model has a much higher pull-out bearing capacity than conventional pull-out piles, and the prestress value of the steel tension rod is much higher than that of conventional pull-out piles. A local compression cone pile cap is arranged on the pile top, which together with the tension end member of the rod body forms a pile tension end structure, thereby avoiding local compression damage on the pile top when prestressing a small diameter pile.

[0055] (7) The pull-out and compression-resistant prestressed spray-expanded cone-shaped grouting pile of the utility model has a double cone-shaped expansion body at the pile end, and a rod anchoring end member is arranged in the double cone-shaped expansion body to form a pile bottom anchor structure. It has high pull-out bearing capacity and small deformation.

[0056] (8) The utility model is a prestressed spray-expanded cone-type grouted pile that is tensile and compressive resistant. The steel tie rod in the double cone expansion body is covered with an externally threaded anchor steel pipe and filled with high-strength grouting material, thereby forming a bonding anchor and a mechanical anchor with a large anchoring force. The externally threaded anchor steel pipe and the high-strength grouting material filled inside have a double layer of anti-corrosion protection, which effectively avoids the influence of concrete cracks in the anchoring section, and the steel tie rod at the anchoring end has good durability.

[0057] (9) The tensile and compressive resistant prestressed spray expansion cone grouted pile of the utility model has an external threaded anchor steel pipe outer sleeve guide ring, which can ensure that the prestressed rod body composite component is installed in the center of the pile body.

[0058] The pull-out and compression-resistant prestressed spray-expanded cone-type pressure-cast pile of the utility model will be further described below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is a structural schematic diagram of the prestressed, tension-resistant and compression-resistant spray-expanded cone-type cast-in-place piles.

[0060] Figure 2 Schematic diagram of prestressed rod composite member.

[0061] Figure 3 Schematic diagram of the pile stress structure.

[0062] Figure 4-Figure 11 This is a schematic diagram of the construction steps of the prestressed spray expansion cone grouting piles, which are tensile and compressive. Figure 4 For drilling; Figure 5 For the rotary spraying cement slurry, a double cone expansion body is made; Figure 6 It is to pressurize the double cone expansion body concrete; Figure 7 It is a double cone enlarged body concrete with extrusion, vibration and compression; Figure 8 It is fixed shotcrete rib plate, extrusion vibration pressure cast pile body and rib plate concrete; Fig. 9 The concrete pouring is completed; Fig.10 To install prestressed rod components and steel cages; Fig.11 To tension and lock the pile top and form the pile.

[0063] Among them, 1-pile tensioning end structure, 2-pile free section structure, 3-pile bottom anchor structure, 4-pile cap, 5-pile body, 6-rib plate, 7-double cone expansion body, 8-rod tensioning end member, 9-rod steel tie rod member, 10-rod anchoring end member, 11-first locking nut, 12-prestressed support steel plate, 13-steel tie rod, 14-anti-corrosion coating, 15-isolation pipe, 16-externally threaded anchor steel pipe, 17-prestressed anchor steel plate, 18-second locking nut, 19-high-strength grouting material, 20-guide ring, 21-concrete, 22-cement soil transition layer, 23-reinforcement cage, 24-compacted soil layer, 25-anchor plate, 26-spiral reinforcement, 27-foundation raft, 28-cushion, 29-cement soil. DETAILED DESCRIPTION

[0064] Example 1: Pull-out design method for pull-out and compression-resistant prestressed spray-expanded cone-type pressure-cast piles

[0065] Based on the following principles:

[0066] When the pull-out and compression-resistant prestressed spray-expanded cone-type pressure-cast pile is pulled out, the pile type is a bottom anchor type structure. The pulling force is applied to the top of the double cone expansion body, and the upper pile body concrete is compressed. Due to the Poisson's ratio effect, the pile side friction resistance is higher than that of ordinary pull-out piles. Based on the above reasons and field tests, the pile side friction resistance pull-out coefficient λ i Adjusted from the current standard of 0.5~0.8 to between 0.8~0.95.

[0067] Due to the cement-soil transition layer and ribs, the pile side friction resistance is higher than that of ordinary pull-out piles, and the pile side friction resistance increase coefficient β si It is 1.2 to 2.1.

[0068] The pull-out force is directly applied to the top of the double-cone expansion body. Compared with the conventional pull-out resistant expanded bottom pile, the double-cone expansion body can be subjected to force in advance, and the role of the expansion body can be fully exerted. The conventional pull-out resistant expanded bottom pile has no free section, and the pull-out force is applied to the top of the pile. The side resistance of the pile body is exerted first, and the force on the expansion head is delayed, so the expansion head cannot fully play its role.

[0069] The upper surface of the double-cone expansion body is provided with a conical inclined surface, and the angle between the soil rupture sliding surface and the vertical surface is increased, which can enable more deep dense soil to participate in the pull-out work, and the pull-out resistance of the double-cone expansion body is greatly improved. The top surface of the expansion head of the conventional pull-out expanded pile is a horizontal plane, and the angle between the soil rupture sliding surface and the vertical surface is reduced, so that less soil participates in the pull-out work and the pull-out resistance is small; the upper pile body of the double-cone expansion body is provided with ribs along the entire length, and the ribs extend to the distant soil layer around the pile body, so that the range of soil layers around the pile body that participate in the pull-out work is increased. Based on the above reasons and field tests, the standard value of the deadweight of the foundation pile and the deadweight of the soil above the expansion body that participates in the pull-out work in the formula of this patent is 1.2 times the current standard.

[0070] According to the above principle, the anti-pullout design method of the anti-pullout and anti-compression prestressed spray expansion cone pressure-cast pile has the following specific steps:

[0071] The first step is to determine the geometric parameters of the pile according to the compression resistance, pull-out resistance and formation conditions of the pile. The geometric parameters of the pile include pile diameter, pile length, ribs, expansion body, structural geometric dimensions of the pile cap, position and other parameters, and refer to the "Technical Standard for Spray-Expanded Cone Grouting Piles" T / CECS 657-2020 for implementation.

[0072] The second step is to arrange the pile positions according to the upper load and water buoyancy.

[0073] The third step is to verify the vertical pull-out bearing capacity of a single pile. When the pile group is not in overall failure, the pull-out resistance of the pull-out and compression-resistant prestressed spray-expanded cone-type cast-in-place pile is calculated according to the following formula (1): First determine the pull-out coefficient λi, and calculate Tuk according to formula (2); then calculate

[0074] Gp is ​​calculated according to the Technical Standard for Spray-Expanded Cone Grouting Piles T / CECS 657-2020 and is substituted into formula (1) for verification;

[0075]

[0076] T uk =Σλ i q sik u i l i β si (2)

[0077] N k ——vertical pullout force acting on the pile corresponding to the standard combination of actions (kN);

[0078] T uk ——When the pile group is not in overall failure, the standard value of the total pull-out limit lateral resistance of the pile foundation (kN);

[0079] G p ——The standard value of the deadweight of the pile and the deadweight of the soil above the expanded diameter that participates in the pull-out work (kN). When calculating the deadweight of the pile below the groundwater level, the water buoyancy should be deducted. When estimating, the value should be 1.2 times the deadweight of the pile soil in the Technical Standard for Spray-Expanded Cone-Grought Piles T / CECS657-2020;

[0080] λ i ——Pull-out coefficient, ranging from 0.8 to 0.95;

[0081] q sik——The standard value of the ultimate lateral resistance of the i-th layer of soil on the pile side (kPa) should be determined based on test data and local engineering experience. When test data is lacking, the value can be taken according to Appendix C of the Technical Standard for Spray-Expanded Cone Grouting Piles T / CECS 657-2020;

[0082] u1——the circumference of the pile body at the upper part of the expansion body (m);

[0083] l i ——thickness of the i-th layer of soil around the pile above the expanded diameter body (m);

[0084] β si ——The side resistance enhancement coefficient of spray-expanded cone grouted piles shall be taken in accordance with the Technical Standard for Spray-Expanded Cone Grouted Piles T / CECS 657-2020.

[0085] When the pile group is in overall failure, the calculation formula for the pull-out resistance of the prestressed spray-expanded cone-type pressure-cast pile is the same as that of Formula 4.3.1-2 and 4.3.2-2 in the Technical Standard for Spray-Expanded Cone-Type Pressure-Casing Piles T / CECS 657-2020:

[0086] The fourth step is to verify the local compression of the pile cap concrete, the compressive bearing capacity of the pile body, the tensile bearing capacity of the prestressed steel tie rod, and the anchorage of the steel tie rod at the bottom expansion body. The above verification formulas refer to the relevant national standards in force.

[0087] The compression design method of prestressed spray-expanded cone-type pressure-cast piles is based on the "Technical Standards for Spray-Expanded Cone-Type Pressure-Casing Piles"

[0088] T / CECS 657-2020 implemented.

[0089] The pull-out coefficient λ of the prestressed spray-expanded cone-shaped piles is relatively high compared with the conventional expanded bottom pull-out piles. i Improve, increase the pile side resistance improvement coefficient β si As the soil mass involved in the pull-out work increases, the self-weight of the pile and soil G p Increase.

[0090] Compared with the pull-out and compression-resistant prestressed spray-expanded cone-type pressure-casting pile, the pull-out coefficient λ i Improved, because the double cone expansion body is stressed in advance, the role of deep dense soil layer is fully played.

[0091] When the tensile and compression resistant prestressed spray-expanded cone-type pressure-casting piles are subjected to pressure, the principle calculation is the same as that of the spray-expanded cone-type pressure-casting piles. Compared with the conventional expanded base piles, the compressive bearing capacity is greatly improved.

[0092] Example 2: Tensile and compression resistant prestressed spray expansion cone pressure-cast pile

[0093] The tensile and compressive resistant prestressed spray expansion cone grouted pile designed by the design method of Example 1 has a structure as follows: Figure 1-3 shown.

[0094] The tensile and compression resistant prestressed spray expansion cone grouted pile consists of a pile body and a prestressed rod body composite component located in the pile body; the pile body includes an integrated pile cap 4, a pile body 5, ribs 6 and a double cone expansion body 7, three ribs 6 are provided on the outer peripheral surface of the pile body 5, and a double cone expansion body 7 is provided below the pile body 5; the prestressed rod body composite component includes a rod body tensioning end component 8, a rod body steel tension rod component 9 and a rod body anchoring end component 10 which are sequentially connected from top to bottom.

[0095] The pile cap 4 is in a frustum shape. The rod tension end member 8 is located at the top of the pile cap 4 and together with the pile cap 4 forms a pile tension end structure 1 .

[0096] The rod tension end member 8 includes a prestressed support steel plate 12 located on the top of the pile cap 4 , and a first locking nut 11 is provided above the prestressed support steel plate 12 .

[0097] The interior of the pile cap 4 and the pile body 5 is a concrete structure with a steel cage 23, and the outer layer is a cement-soil transition layer 22; a rod body steel tie rod component 9 is provided on the central axis of the pile body 5; the interior of the rib plate 6 is concrete, and its outer layer is a cement-soil transition layer 22; the pile body 5, the rib plate 6 and the rod body steel tie rod component 9 together constitute the pile free section structure 2.

[0098] The rod body steel tie rod component 9 includes an isolation tube 15 located in the center of the steel cage 23, a steel tie rod 13 is passed through the isolation tube 15, and the outer surface of the steel tie rod 13 is provided with an anti-corrosion coating 14; the upper end of the steel tie rod 13 passes through the prestressed support steel plate 12, and passes through the spiral rib 26 to be connected to the anchor plate 25 located above the spiral rib 26; the first locking nut 11 fixes the steel tie rod 13 and the prestressed support steel plate 12 together.

[0099] The interior of the double-cone enlarged body 7 is concrete, and the outer layer is a cement-soil transition layer 22 . A rod anchoring end member 10 is also provided inside the double-cone enlarged body 7 . The double-cone enlarged body 7 and the rod anchoring end member 10 together constitute a pile bottom anchor structure 3 .

[0100] The lower end of the isolation tube 15 extends to the top center of the double-cone expansion body 7, and the lower end of the steel pull rod 13 passes through the isolation tube 15 and passes through the externally threaded anchoring steel tube 16 located inside the double-cone expansion body 7, and is fixed together with the prestressed anchoring steel plate 17 located at the bottom center of the double-cone expansion body 7 through the second locking nut 18; the externally threaded anchoring steel tube 16 is filled with high-strength grouting material 19; the upper and lower parts of the externally threaded anchoring steel tube 16 are each provided with a guide ring 20; the externally threaded anchoring steel tube 16, the prestressed anchoring steel plate 17, the second locking nut 18, the high-strength grouting material 19 and the guide ring 20 together constitute the rod body anchoring end member 10.

[0101] High-strength grouting material 19 is a non-shrinkage high-strength grouting material with a strength grade ≥ C40.

[0102] A compacted soil layer 24 is formed on the outside of the pile body, and the compacted soil layer 24 wraps the lower part of the pile cap 4, the pile body 5 and the double-cone expansion body 7; a cushion layer 28 is arranged around the upper part of the pile cap 4, and a foundation raft 27 is arranged above the cushion layer 28.

[0103] like Figure 4-Figure 11 As shown, the construction method of the pull-out and compression-resistant prestressed spray-expanded cone-shaped pressure-cast pile has the following specific steps:

[0104] (1) According to the design requirements, the rod body steel tie rod components 9 (steel tie rods 13, anti-corrosion coatings 14, isolation tubes 15) and the rod body anchor end components 10 (externally threaded anchor steel pipes 16, high-strength grouting materials 19, guide rings 20, prestressed anchor steel plates 17, locking nuts 18) are assembled on site to form prestressed rod body composite components, which are then transported to the hoisting location.

[0105] (2) According to the designed position of the pile hole, use a spiral multifunctional drilling rig with a drill bit with a variable cross section on the top to drill the hole to the designed depth, stop the drilling rotation, and the pile hole construction with the cone pile cap cavity is completed. Figure 4 .

[0106] (3) Adjust the nozzle cement slurry pressure to 15-20 MPa and the drill rod lifting speed to 10-20 cm / min. While lifting the drill rod, spray cement slurry to make a double cone expansion cavity, such as Figure 5 At the same time, concrete is poured until it is 1.0 to 3.0 m above the upper end surface of the double cone expansion body 7. Figure 6 , use the drill rod to vibrate and squeeze the double cone expansion body concrete, compact the soil layer around the double cone expansion body 7 to the set position, such as Figure 7 .

[0107] (4) Stop the rotary spraying of cement slurry, adjust the lifting speed of the drill rod, and spray the ribs and pressurize the pile body concrete at the same time. Use the drill rod to squeeze the pile body and rib concrete in sections to compact the soil layer around the pile body. Figure 8, the concrete of the pile body and rib plate is poured to the designed elevation of the pile top, and the concrete pouring of the pile body 5, rib plate 6 and pile cap 4 is completed. Fig. 9 .

[0108] (5) Insert the prestressed rod composite component (reinforcement cage) into the pile hole concrete to the designed elevation, and the construction of the tensile and compressive prestressed spray expansion cone grouted pile with pile cap is completed. Fig.10 .

[0109] (6) After the concrete strength of the pile body reaches the design requirements, the rod body tensioning end member 8 is installed at the design elevation position of the pile top, and the steel tie rod 13 is tensioned according to the design requirements. The tensioning force is transmitted to the anchor structure 3 at the bottom of the pile through the free section of the steel tie rod to form the prestress of the pile body. The construction of the tensile and compressive prestressed spray expansion cone pressure-grouted pile is completed. Fig.11 .

[0110] Example 3 Engineering Example Comparison

[0111] The social and economic benefits of the new type of tensile and compression resistant prestressed spray-expanded cone-shaped pressure-grouted piles are compared with those of the existing common expanded bottom piles and spray-expanded cone-shaped pressure-grouted piles through the following engineering examples.

[0112] In a pile foundation project in Jining, Shandong, the original design used ordinary expanded base piles with a pile diameter of 300mm, an expanded base diameter of 800mm, a pile length of 20m, four main reinforcement bars of the reinforcement cage made of 40mm diameter grade 3 steel, and a single pile pull-out bearing capacity characteristic value of 560kN; spray-expanded cone grouted piles with a pile diameter of 300mm, an expanded body diameter of 800mm, a pile length of 16m, four main reinforcement bars of the reinforcement cage made of 40mm diameter grade 3 steel, and a single pile pull-out bearing capacity characteristic value of 560kN.

[0113] The design adopts the prestressed spray expansion cone grouting pile with tensile and compressive strength. The design parameters calculated by formula (1), (2) and relevant standards are: pile diameter 300mm, expansion body diameter 800mm, pile length 13m, main reinforcement 1 piece of 40mm diameter fine rolled threaded steel bar, and single pile tensile bearing capacity characteristic value 560kN. The economic comparison is shown in the following table:

[0114]

[0115]

[0116] From the above comparison, it can be seen that the tensile and compression-resistant prestressed spray-expanded cone-shaped grouted piles of the utility model have low cost, save costs, and have high application value compared with the existing ordinary expanded base piles and spray-expanded cone-shaped grouted piles. With large-scale application, it will produce great economic, social and environmental benefits.

[0117] The embodiments described above are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A prestressed, tension-resistant and compression-resistant spray-expanded cone-shaped grouting pile, characterized in that: The invention is composed of a pile body and a prestressed rod body composite component located in the pile body; the pile body comprises a pile cap (4), a pile body (5), a rib plate (6) and a double frustum diameter expansion body (7) of an integrated structure; at least three rib plates (6) are arranged on the outer peripheral surface of the pile body (5); and at least one double frustum diameter expansion body (7) is arranged below the pile body (5); the prestressed rod body composite component comprises a rod body tensioning end component (8), a rod body steel tension rod component (9) and a rod body anchoring end component (10) which are sequentially connected from top to bottom; The pile cap (4) is in a frustum shape, the rod tension end member (8) is located at the top of the pile cap (4), and together with the pile cap (4) forms a pile tension end structure (1); The rod body tensioning end member (8) comprises a prestressed support steel plate (12) located on the top of the pile cap (4), and a first locking nut (11) is provided above the prestressed support steel plate (12); The rod body steel tie rod component (9) includes an isolation tube (15) located in the center of the steel cage (23), a steel tie rod (13) is inserted into the isolation tube (15), the lower end of the isolation tube (15) extends to the top center of the double-cone expansion body (7), the lower end of the steel tie rod (13) passes through the isolation tube (15) and passes through the external threaded anchoring steel tube (16) located inside the double-cone expansion body (7), and is fixed together with the prestressed anchoring steel plate (17) located in the bottom center of the double-cone expansion body (7) through a second locking nut (18).

2. The tensile and compressive resistant prestressed spray expansion cone grouting pile according to claim 1 is characterized by: The interior of the pile cap (4) and the pile body (5) is a concrete structure with a steel cage (23), and the outer layer is a cement-soil transition layer (22); a rod body steel tie rod component (9) is provided on the central axis of the pile body (5); the interior of the rib plate (6) is concrete, and the outer layer is a cement-soil transition layer (22); the pile body (5), the rib plate (6) and the rod body steel tie rod component (9) together constitute a pile free section structure (2).

3. The tensile and compressive resistant prestressed spray expansion cone grouting pile according to claim 1 is characterized by: The outer surface of the steel tie rod (13) is provided with an anti-corrosion coating (14); the upper end of the steel tie rod (13) passes through the prestressed support steel plate (12), and passes through the spiral rib (26) to be connected to the anchor plate (25) located above the spiral rib (26); the first locking nut (11) fixes the steel tie rod (13) and the prestressed support steel plate (12) together, and together with the pile cap, forms a pile tensioning end structure (1).

4. The tensile and compressive resistant prestressed spray expansion cone grouting pile according to claim 1, characterized in that: The interior of the double-cone enlarged diameter body (7) is concrete, the outer layer is a cement-soil transition layer (22), and a rod body anchoring end member (10) is also provided inside the double-cone enlarged diameter body (7), and the double-cone enlarged diameter body (7) and the rod body anchoring end member (10) together constitute a pile bottom anchor type structure (3).

5. The pull-out and compression-resistant prestressed spray-expanded cone-shaped pressurized pile according to claim 1, characterized in that: The externally threaded anchoring steel pipe (16) is filled with high-strength grouting material (19); the upper and lower parts of the externally threaded anchoring steel pipe (16) are each provided with a guide ring (20); the externally threaded anchoring steel pipe (16), the prestressed anchoring steel plate (17), the second locking nut (18), the high-strength grouting material (19) and the guide ring (20) together constitute a rod body anchoring end member (10).

6. The tensile and compressive resistant prestressed spray expansion cone grouting pile according to claim 1, characterized in that: A compacted soil layer (24) is formed on the outside of the pile body, and the compacted soil layer (24) wraps the lower part of the pile cap (4), the pile body (5) and the double-cone expansion body (7).

7. The tensile and compressive resistant prestressed spray expansion cone grouting pile according to claim 1, characterized in that: A cushion layer (28) is arranged around the upper part of the pile cap (4), and a foundation raft (27) is arranged above the cushion layer (28).

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