Vibrating-free pouring method for small-diameter super-long steel pipe pile

Abstract

The invention relates to the field of steel pipe pile construction, and aims to provide a small-diameter super-long steel pipe pile vibration-free pouring method which comprises the following steps: S1, according to stress calculation and construction requirements, performing on-site blending on a grouting material, gravel aggregate and water, and mixing to prepare a mixture; s2, the steel pipe pile frame is installed on the designed ground position; s3, the mixture is conveyed to the pipe opening position of the small-diameter steel pipe pile at the uppermost end in a pumping mode, and the mixture naturally falls through the gravity effect and fills pipe cavities of all the small-diameter steel pipe piles; and S4, after the mixture reaches the design age, a compressive strength test and a single-pile bearing capacity static load test are conducted on the small-diameter steel pipe pile, and the pile foundation quality is verified. The grouting material doped with the gravel aggregate is creatively adopted to replace concrete, and the method has the advantages of high-fall pouring, no vibration, convenience in construction and the like.

Description

Technical Field

[0001] The present invention relates to the field of steel pipe pile construction, and particularly to a method for pouring small-diameter super-long steel pipe piles without vibration Background Technique

[0002] Steel pipe piles are a relatively common and mature type of pile foundation, which consists of steel pipes and the core concrete filled inside. By utilizing the confinement effect of the steel pipes on the core concrete, the strength and anti-deformation ability of the pile body are improved. During actual construction, the precast steel pipes are first sunk into the soil by means of hammering, vibration or static pressure, and then the core concrete is poured. It has the advantages of simple operation, reliable construction quality, strong formation adaptability, low cost, etc.

[0003] Steel pipe piles can be divided into small-diameter piles, medium-diameter piles and large-diameter piles according to the pile diameter. Among them, small-diameter piles are mainly used in the fields of adding floors to existing buildings, foundation underpinning, rectifying and displacing existing buildings due to their layout flexibility and construction convenience, while large-diameter piles are more used in various new construction projects due to their higher bearing capacity. Conventional-length small-diameter piles have good applicability to general soft soil foundations, but in areas with particularly deep soft soil layers such as Fuzhou, Shanghai, Ningbo, Guangzhou, etc., the pile length of small-diameter piles still needs to be particularly lengthened so that the pile tip can penetrate the soft soil layer and enter a certain depth into a better bearing layer. When the diameter is too small and the pile length is too long, during the concrete pouring process, it is extremely easy for the coarse aggregate and the cement mortar to be separated from each other due to the excessive falling height, resulting in the deposition of the coarse aggregate at the bottom of the mixture and the suspension of the cement mortar at the upper part of the mixture. Coupled with the fact that the steel pipe is slender and the vibrating rod cannot extend into the bottom of the steel pipe for effective vibration, segregation finally occurs. On the one hand, this will make the distribution of the concrete structure extremely uneven, especially in the upper region of the mixture. The concrete strength in this region is significantly reduced and stress concentration is likely to occur. Under the action of external loads, the stress in this region is extremely easy to reach the concrete strength limit, thereby increasing the possibility of strength failure of the structure. On the other hand, after segregation, the concrete often undergoes uneven shrinkage deformation during hardening. Under the continuous action of non-uniform strain, tiny pores and cracks are extremely easy to form inside the concrete, and once they penetrate to the outside, they will become the infiltration channels for corrosive media, which will accelerate the deterioration process of the concrete and cause the reduction of the structural durability.

[0004] Conventional segregation prevention methods include adding conduits or changing to self-compacting concrete, but there are certain problems with both. Adding conduits and installing baffles at regular heights inside the conduits can effectively slow down the falling speed of the concrete and avoid segregation. However, for ultra-long small-diameter steel pipe piles, it is not feasible. On the one hand, the diameter of the conduit should be correspondingly reduced to ensure that the conduit can smoothly extend into the steel pipe. However, if the diameter of the conduit is too small, the baffles cannot be installed, and the overly narrow pouring space will also increase the sidewall resistance, resulting in the inability of the concrete to flow smoothly and increasing the possibility of pipe blockage. On the other hand, the length of the conduit will also increase to ensure that the conduit can reach the bottom of the steel pipe. However, if the length of the conduit is too long, the weight and flexibility of the conduit will both increase significantly, which makes the conduit extremely prone to bending or deformation during the pouring process, affecting the pouring quality. At the same time, the overly long conduit also faces the problem of being difficult to lower and install in a low-clearance environment. As for self-compacting concrete, through special mix design, it improves the fluidity and workability of the concrete, enabling it to achieve a high degree of compaction without relying on external vibration. However, this only applies to low-drop conditions. If the drop is too high, it may still experience local segregation due to the too-fast falling speed. In addition, ultra-long small-diameter steel pipes do not have vibration conditions. Therefore, the segregated self-compacting concrete can only rely on its self-leveling characteristics to complete compaction, which will damage the uniformity of the internal structure of the concrete and seriously affect the pile body performance. In addition, during actual construction, self-compacting concrete often uses commercial concrete, that is, it is pre-mixed at the mixing station and then transported to the site. However, if the construction environment is fully enclosed (such as the basement of an existing building, an underground utility tunnel), after the self-compacting concrete arrives at the site, forklifts, cranes, etc. are still needed to transfer it from the ground to the underground space, greatly extending the logistics path and increasing the construction cost and difficulty.

[0005] The grouting material has characteristics such as quick hardening, early strength, no shrinkage, and slight expansion, and its self-flowability and self-compactness are both good. It is not prone to segregation even under high-drop and vibration-free conditions, meeting the pouring requirements of ultra-long small-diameter steel pipe piles. At the same time, it can be mixed on-site and used immediately without repeated turnover, saving logistics costs and having good applicability for construction projects in fully enclosed environments. The grouting material has been widely used in the field of existing structure reinforcement, but it is still relatively rare in the field of pile foundations. How to innovatively use the grouting material to replace concrete according to the characteristics of pile foundations is of great significance for promoting the good development of the construction field. Summary of the Invention

[0006] The purpose of the present invention is to provide a vibration-free pouring method for ultra-long small-diameter steel pipe piles. The present invention innovatively uses grouting material mixed with crushed aggregate to replace concrete, having the advantages of high-drop pouring, vibration-free, segregation prevention, and convenient construction.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for pouring small-diameter super-long steel pipe piles without vibration compaction, comprising the following steps:

[0009] S1. According to the force calculation and structural requirements, the grouting material, crushed stone aggregate and water are proportioned on-site and mixed to form a mixture, wherein the mass ratio of the grouting material, crushed stone aggregate and water is (0.8 - 1.2):(1.8 - 2.2):(1.8 - 2.2);

[0010] S2. Install the steel pipe pile frame at the designed ground position, and sink several small-diameter steel pipe piles into the soil one by one. The small-diameter steel pipe piles are butt-jointed to form a super-long steel pipe pile. The pile tip of the super-long steel pipe pile penetrates through the soft soil layer and enters a certain depth into a better bearing layer;

[0011] S3. The mixture is pumped to the pipe orifice position of the uppermost small-diameter steel pipe pile, and the mixture naturally falls by gravity and fills the cavities of all the small-diameter steel pipe piles. During the filling process, it is not necessary to vibrate the mixture in the piles;

[0012] S4. After the mixture reaches the designed age, conduct a compressive strength test and a static load test for the single-pile bearing capacity of the small-diameter steel pipe piles to verify the quality of the pile foundation.

[0013] Compared with the prior art, the advantages of the present invention are as follows:

[0014] Innovatively, the grouting material admixed with crushed stone aggregate is used to replace concrete, avoiding the phenomenon of core concrete segregation during the construction pouring of traditional small-diameter super-long steel pipe piles, and avoiding the phenomenon that the strength of the core concrete area decreases significantly due to the traditional pouring method, resulting in stress concentration in the pipe piles;

[0015] The mixture prepared by the present invention can be directly pumped at the orifice, having the advantages of high-drop pouring, vibration-free, anti-segregation, convenient construction, etc., and is especially suitable for projects in enclosed underground spaces, with good popularization. Description of the Drawings

[0016] Figure 1 is the strength test result diagram of the standard test block of the mixture of the present invention;

[0017] Figure 2 is the single-pile vertical compressive static load test result diagram of the steel pipe pile of the present invention. Detailed Embodiments

[0018] The content of the present invention will be described in detail below with reference to the drawings of the specification and embodiments:

[0019] As Figure 1-2 shown, it is a schematic diagram of an embodiment of a method for pouring small-diameter super-long steel pipe piles without vibration compaction provided by the present invention:

[0020] A method for pouring small-diameter ultra-long steel pipe piles without vibration compaction, comprising the following steps:

[0021] S1. According to the force calculation and structural requirements, the grouting material, crushed stone aggregate and water are proportioned on-site and mixed to form a mixture, wherein the mass ratio of the grouting material, crushed stone aggregate and water is (0.8 - 1.2):(1.8 - 2.2):(1.8 - 2.2);

[0022] Preferably, the mass ratio of the grouting material, crushed stone aggregate and water is 1:2:2.

[0023] Preferably, the grouting material is a high-strength non-shrinking grouting material with a grade not lower than H-40; the maximum particle size of the crushed stone aggregate is not greater than 40 mm.

[0024] Preferably, the initial fluidity of the grouting material ≥ 300 mm, the retention value after 30 minutes ≥ 260 mm; the expansion rate after 24 hours ≥ 0.02%.

[0025] S2. Install the steel pipe pile frame at the designed ground position, and sink several small-diameter steel pipe piles into the soil layer one by one. The small-diameter steel pipe piles are butt-jointed to form an ultra-long steel pipe pile. The pile tip of the ultra-long steel pipe pile penetrates through the soft soil layer and enters a certain depth into a better bearing layer;

[0026] The inner diameter of the small-diameter steel pipe pile is not greater than 300 mm, and the total length after splicing is not less than 30 m.

[0027] In this embodiment, the inner diameter of the small-diameter steel pipe pile is 288 mm, and the total length after splicing is 36 m.

[0028] S3. Pump the mixture to the pipe orifice position of the uppermost small-diameter steel pipe pile, and let the mixture fall naturally by gravity to fill the cavities of all small-diameter steel pipe piles. During the filling process, there is no need to vibrate the mixture in the piles.

[0029] S4. After the mixture reaches the designed age, conduct a compressive strength test and a static load test for the single-pile bearing capacity on the small-diameter steel pipe piles to verify the quality of the pile foundation.

[0030] To further illustrate the construction effect of the present invention, a specific engineering example is now described in detail:

[0031] There is a renovation project at the junction of Building A and Building B of a certain project. It is planned to add a 2-story basement connecting body between Building A and Building B, with a north-south width of 8.80 m, an east-west length of 74.80 m, and a height of 8.80 m. On the side of the original Building A adjacent to Building B, the upper load of the 6-story old building is borne by the cantilever of the ground beam (section width 1600 mm × height 1800 mm). Now it is planned to add 4 floors on top of Building A, which will cause excessive concentrated force at the end of the cantilever beam. To avoid strength failure or large deformation of the cantilever beam, a steel reinforced concrete column will be added below the beam end during the renovation project, and steel pipe static pressure piles will be used as the foundation for the added column;

[0032] The strata of this site from top to bottom are miscellaneous fill, silt, silty clay, silty soil, medium-coarse sand, silty soil, silty clay, completely weathered granite, and strongly weathered granite. Among them, the total thickness of the silt and silty soil layers reaches 30 m, belonging to a deep soft soil stratum.

[0033] The steel pipe piles of this project are about 36 m long, with a steel pipe inner diameter of 288 mm, belonging to super-long small-diameter steel pipes; the engineering design requires that the pile tip uses the strongly weathered granite layer as the bearing stratum, the pile tip enters the bearing stratum by no less than 1.0 m, and the characteristic value of the single-pile vertical bearing capacity is 1400 kN. The outer diameter of the steel pipe is 320 mm, and the wall thickness is 16 mm. The original design was to use C30 self-compacting micro-expansion concrete to fill the core of the pipe. However, due to the super-long small-diameter steel pipe of the pile body, the conduit method cannot be used for pouring and it cannot be vibrated, so the concrete is extremely prone to segregation. After indoor test verification and design review, it can be changed to use grouting material mixed with crushed stone aggregate to fill the core. This mixture is difficult to segregate under the condition of high-drop pouring without vibration, and at the same time, it has a relatively high compressive strength after hardening, meeting the design requirements.

[0034] If the design requirements cannot be achieved by using the traditional concrete mix ratio and conduit pumping construction technology, after comprehensive consideration, it is decided to use the mixture described in this invention patent technology. The mixture is prepared on-site by mixing grouting material: crushed stone aggregate: water = 1:2:2 by mass ratio. Among them, the grouting material uses H-40 high-strength non-shrinking grouting material (preferably a grouting material with a class higher than class III, that is, the initial fluidity of the grouting material ≥ 300 mm, the 30-minute retention value ≥ 260 mm; the 24-hour expansion rate ≥ 0.02%), and the maximum particle size of the crushed stone aggregate does not exceed 40 mm; and the mixture is transported to the pipe orifice position of the upper steel pipe pile by pumping, and the mixture relies on its own weight to fall naturally, filling all the steel pipe piles at one time without vibration throughout the process.

[0035] After the steel pipe piles reach the design age (28 days in this project), as Figure 1 shown, the strength test of the reserved test blocks of the mixture is carried out. It can be seen that the representative value of the compressive strength of the mixture at 28 days of age is 37.2 MPa, which is about 124% of the standard value of the cube compressive strength of the original designed C30 concrete, far meeting the design requirements;

[0036] And, as Figure 2 shown, a single-pile vertical compressive static load test was carried out on the steel pipe piles. It can be seen that under the action of the maximum test load, the pile top settlements of the two test piles (i.e., pile No. 20 and pile No. 22) are both less than 40 mm (i.e., the specification requirements for the static load test of pipe piles), and there is no obvious phenomenon of increasing settlement, indicating that neither of the two test piles has reached the ultimate bearing capacity state, and the true characteristic value of the bearing capacity should be greater than 1400 kN, far meeting the design requirements.

[0037] In summary, after the core filling construction with the mixture described in the present invention, the cross-sectional strength and pile body bearing capacity of the ultra-long small-diameter steel pipe piles both meet the design requirements, which verifies the feasibility, reliability and excellent mechanical properties of the present invention.

[0038] The above is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, should be covered by the protection scope of the present invention.

Claims

1. A vibration-free casting method for small-diameter ultra-long steel pipe piles, characterized in that: The following steps are involved: S1. According to the force calculation and the structural requirements, the grouting material, the crushed stone aggregate and the water are mixed on site and mixed to form a mixture, wherein the mass ratio of the grouting material, the crushed stone aggregate and the water is (0.8-1.2): (1.8-2.2): (1.8-2.2); S2. Install the steel pipe pile frame at the designed ground position, and sink several sections of small-diameter steel pipe piles into the soil one by one. The small-diameter steel pipe piles are connected to form an extra-long steel pipe pile. The pile end of the extra-long steel pipe pile penetrates the soft soil layer and enters a certain depth into the better bearing layer. S3, pumping the mixture to the pipe opening of the uppermost small-diameter steel pipe pile, allowing the mixture to fall naturally by gravity and fill the cavities of all the small-diameter steel pipe piles, without vibrating the mixture in the piles during the filling process; S4. After the mixture reaches the design age, the small-diameter steel pipe piles are subjected to compressive strength tests and single pile bearing capacity static load tests to verify the quality of the pile foundation.

2. The vibration-free pouring method for small-diameter super-long steel pipe piles according to claim 1 is characterized in that: The mass ratio of the grouting material, crushed stone aggregate and water is 1:2:

2.

3. The vibration-free pouring method for small-diameter and extra-long steel pipe piles according to claim 1 is characterized in that: The grouting material is a high-strength non-shrinkage grouting material with a grade not lower than H-40; the maximum particle size of the crushed stone aggregate is not greater than 40mm.

4. The vibration-free pouring method for small-diameter super-long steel pipe piles according to claim 3 is characterized in that: The initial fluidity of the grouting material is ≥300mm, the 30-minute retention value is ≥260mm, and the 24-hour expansion rate is ≥0.02%.

5. The vibration-free casting method for small-diameter super-long steel pipe piles according to any one of claims 1 to 4, characterized in that: The inner diameter of the small-diameter steel pipe pile is not greater than 300 mm, and the total length after splicing is not less than 30 m.

6. The vibration-free pouring method for small-diameter super-long steel pipe piles according to claim 5 is characterized in that: The inner diameter of the small-diameter steel pipe pile is 288 mm, and the total length after splicing is 36 m.

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