A method for reinforcing the early bond performance between a pile and the soil surrounding the pile

Abstract

The present application belongs to the technical field of pile foundation, and discloses a method for reinforcing early bonding performance between a pile and soil around the pile, in order to solve the problem that the pile foundation is prone to negative skin friction due to low early bonding strength between the pile foundation and the soil around the pile, and provide a method for reinforcing early bonding performance between a pile and soil around the pile.The present application (1) measures a line to determine the position of a pile hole; (2) forms a pile hole by mechanical hole forming; (3) implants a steel reinforcement cage into the pile hole; (4) places a spacer sleeve; (5) grouts; (6) pulls out the spacer sleeve; (7) cuts off the pile head.The present application can improve the early bonding performance between the pile foundation and the soil around the pile, thereby reducing the negative skin friction of the pile foundation, and further improving the bearing capacity of the pile foundation.

Description

Technical Field

[0001] This invention belongs to the field of pile foundation technology, specifically relating to a method for strengthening the early bond performance between piles and the surrounding soil, which is particularly suitable for the construction of pile foundations in soft soil strata. Background Technology

[0002] The grouting materials used for reinforced piles (pile foundations) are usually ordinary silicate cement grouting materials and chemical grouting materials. Chemical grouting materials have a certain degree of toxicity and cause serious environmental pollution; therefore, reinforced piles (pile foundations) are generally grouted with ordinary silicate cement.

[0003] The skin friction between a pile foundation and the surrounding soil includes positive and negative skin friction. Positive skin friction occurs when the pile moves downwards relative to the surrounding soil, causing an upward frictional force on the pile. This frictional force constitutes part of the bearing capacity of the bearing pile. Negative skin friction occurs when the pile foundation moves upwards relative to the surrounding soil, causing a downward frictional force on the pile. This frictional force constitutes part of the load on the bearing pile, reducing its bearing capacity and potentially causing significant settlement. Generally, negative skin friction occurs primarily when the settlement of the surrounding soil exceeds the settlement of the pile foundation (i.e., the pile foundation moves upwards relative to the surrounding soil). Especially in areas with soft soil strata, due to their high water content, low permeability, high compressibility, large deformation, and long duration, negative skin friction is prone to occur in pile foundations in soft soil, thus reducing their bearing capacity. The main reason for poor bearing capacity of pile foundations is that ordinary cement mortar is generally used for pouring during the pile foundation construction process. Because ordinary cement mortar has a long setting time, the bonding effect between the slow-setting soil and the weak stratum is prolonged, resulting in poor bond performance between the pile foundation and the weak stratum. Ultimately, this leads to negative skin friction in the later stages of pile foundation construction, affecting its bearing capacity. Therefore, improving the early bond strength between the pile foundation and the surrounding soil is an effective way to reduce negative skin friction in pile foundations. Summary of the Invention

[0004] To address the problem of negative skin friction in pile foundations due to low early-age bond strength, this invention provides a method for strengthening the early-age bond performance between piles and surrounding soil. This method improves the early-age bond performance between the pile foundation and surrounding soil, thereby reducing negative skin friction and ultimately increasing the bearing capacity of the pile foundation.

[0005] To solve the technical problem, the technical solution adopted by this invention is as follows:

[0006] A method for improving the early bond performance between a pile and the surrounding soil, characterized by comprising:

[0007] (1) Measure and set out to determine the location of the pile hole;

[0008] (2) Mechanical drilling forms pile holes;

[0009] (3) Insert a steel cage into the pile hole. The steel cage includes multiple vertical bars. The vertical bars are connected together by several stirrups to form a cylindrical steel cage. Several horizontal bars are also connected to the vertical bars. The horizontal bars are distributed along the diameter of the steel cage and the two ends of the horizontal bars are respectively connected to two opposite vertical bars. The horizontal bars are connected to the vertical bars at intervals and interlaced with each other, and each horizontal bar forms a "+" shape.

[0010] (4) A cylindrical isolation cylinder is placed inside the reinforcing cage, the axis of the isolation cylinder being coincident with the axis of the reinforcing cage; a support frame for supporting and positioning the isolation cylinder is fitted around the upper end of the isolation cylinder, the lower end of the isolation cylinder extends downward to the bearing layer of the pile hole, and the upper end of the isolation cylinder extends above the ground; there is a gap between the outer wall of the isolation cylinder and the inner wall of the reinforcing cage.

[0011] (5) Grouting: The grouting includes a first stage grouting and a second stage grouting. The first stage grouting involves injecting a first grouting material into the isolation cylinder, which fills the bearing layer corresponding to the pile hole. The second stage grouting involves continuously injecting the first grouting material into the isolation cylinder until a set elevation is reached. The second stage grouting also includes injecting a second grouting material into the periphery of the isolation cylinder until a set elevation is reached. The second grouting material is used to cover the reinforcing cage and fill the space around the reinforcing cage. In the second stage grouting, the grouting into the isolation cylinder and the grouting into the periphery of the isolation cylinder are carried out simultaneously. The setting time of the first grouting material is longer than that of the second grouting material.

[0012] (6) After the first grouting material injected in the second grouting reaches the design strength, the isolation cylinder is pulled out, and the third grouting material is used to grout into the gap formed after the isolation cylinder is pulled out.

[0013] (7) After the third grouting material reaches the design strength, the pile head of the pile foundation is excavated and cut off, thereby completing the construction of the pile foundation.

[0014] In some embodiments, when the first grouting material is poured into the upper section of the isolation cylinder, pre-embedded vertically arranged pre-embedded steel bars are inserted into the isolation cylinder, and each pre-embedded steel bar is evenly arranged inside the isolation cylinder; when the pile head is cut off in step (7) and the steel cage and pre-embedded steel bars are exposed, the pre-embedded steel bars and the steel cage are connected by connecting steel bars to form a whole.

[0015] In some embodiments, when the pile head of the pile foundation is cut off in step (7), the length of the cut-off pile head is greater than the design required cut-off length; at the same time, the lower end of the pre-embedded steel bar is located at least 1m below the pile head cut-off position.

[0016] In some embodiments, the isolation cylinder has vertical strip grooves formed according to the position of the horizontal ribs, and sealing strips are provided on both sides of the vertical strip grooves. The sealing strips have receiving grooves formed at the height positions of the horizontal ribs to facilitate the covering of the horizontal ribs through the receiving grooves.

[0017] In some embodiments, the inner and outer walls of the isolation cylinder are provided with a plurality of protrusions.

[0018] In some embodiments, in step (6), grouting the gap formed after the isolation cylinder is pulled out using a third grouting material includes:

[0019] If the gap formed after the isolation cylinder is pulled out is smaller than the outer diameter of the grouting pipe, then the third grouting material is epoxy resin adhesive.

[0020] If the gap formed after the isolation cylinder is pulled out is larger than the outer diameter of the grouting pipe, it includes the following:

[0021] (1) First, cement grout is sprayed onto the inner wall of the gap (i.e., the outer wall of the concrete formed by the first grouting material, the inner wall of the concrete formed by the second grouting material, and the inner bottom surface of the concrete formed by the second grouting material), thereby filling the gap on the concrete surface with the sprayed cement grout.

[0022] (2) Then, the gap is filled with the second grouting material.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The method of the present invention for strengthening the early bond performance between piles and surrounding soil firstly involves integrally casting the bearing layer corresponding to the pile hole using the first grouting material of the first grouting stage, thereby making the bearing section of the pile foundation a whole as the main bearing capacity foundation of the pile foundation; then, integrally casting the first grouting material of the second grouting stage with the bearing section of the pile foundation, and simultaneously grouting the periphery of the isolation cylinder using the second grouting material of the second grouting stage. Since the setting time of the second grouting material is shorter than that of the first grouting material, it can quickly bond with the surrounding soil, improve the early bond strength between the pile foundation and the surrounding soil, thereby reducing the negative skin friction caused by the settlement of the surrounding soil being greater than that of the pile foundation, and ultimately achieving the purpose of improving the bearing capacity of the pile foundation.

[0025] Meanwhile, since the pile foundation described in this invention is a bearing pile (also known as a compression pile in construction engineering), its main function is to bear vertical loads. The vertical load primarily depends on the poured concrete (because the compressive strength of concrete is much greater than that of the reinforcing cage). In actual use, the pile foundation inevitably also experiences bending moments, and the bending strength of the reinforcing cage is much greater than that of the concrete. Therefore, the bending strength mainly depends on the reinforcing cage. Thus, this invention utilizes a second grouting material to cover and pre-embed the reinforcing cage, ensuring that the overall bending strength of the pile foundation is not affected by layered grouting (i.e., layered grouting achieved by the first grouting material inside the isolation cylinder and the second grouting material outside the isolation cylinder). After the isolation cylinder is pulled out, the reserved holes are grouted and bonded using a third grouting material. Through the structural design of the third grouting material and the transverse reinforcement, the concrete inside and outside the isolation cylinder can be connected together to form a whole. In fact, due to the structural design of the horizontal reinforcement bars, when one side of the pile foundation is subjected to bending moment, the horizontal reinforcement bars are directly connected to the two vertical reinforcement bars in the diameter direction of the steel cage. Therefore, the bending moment can be quickly and directly transferred to the vertical reinforcement bars on the other side through the horizontal reinforcement bars (that is, the force transfer effect of the horizontal reinforcement bars is faster and more direct than that of the stirrups). This allows the bending moment to be quickly and directly transferred to the other side of the steel cage when one side is subjected to bending moment, thereby making the stress on both sides of the steel cage more uniform when it is subjected to bending moment, and ultimately achieving the purpose of improving the bending resistance of the pile foundation.

[0026] This invention is particularly applicable to the construction of pile foundations in soft soil strata. Attached Figure Description

[0027] Figure 1 This is a structural schematic diagram of the steel reinforcement cage. Figure 1 Includes 1A and 1B, where 1A is a structural schematic diagram of the steel cage of an existing cast-in-place pile, and 1B is a structural schematic diagram of the steel cage of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of the present invention when the isolation cylinder is inserted into the steel cage;

[0029] Figure 3 This is a schematic diagram of the structure of the present invention when grouting is injected into the interior of the isolation cylinder and when grouting is injected into the exterior of the isolation cylinder using a first grouting material.

[0030] Figure 4 This is a schematic diagram of the structure of the present invention when pre-embedded steel bars are inserted into the isolation cylinder;

[0031] Figure 5 This is a schematic diagram of the structure of the present invention after the isolation cylinder is removed;

[0032] Figure 6This is a schematic diagram of the structure after the isolation cylinder is pulled out and grouting is performed using a third grouting material according to the present invention;

[0033] Figure 7 This is a schematic diagram of the structure of an embodiment of the isolation cylinder of the present invention;

[0034] The markings in the diagram are: 1. Reinforcing cage, 11. Vertical bar, 12. Stirrup, 13. Horizontal bar, 2. Pile hole, 3. Isolation cylinder, 31. Vertical strip groove, 32. Sealing strip, 33. Protrusion, 4. Support frame, 5. Embedded steel bar. Detailed Implementation

[0035] The present invention will be further described below with reference to embodiments. These embodiments are merely some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the protection scope of the present invention.

[0036] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description; they do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "joined" should be interpreted broadly, for example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0037] Referring to the accompanying drawings, the method of the present invention for improving the early bond performance between a pile and the surrounding soil includes:

[0038] (1) Measure and set out to determine the location of the pile hole.

[0039] (2) Mechanical drilling to form pile hole 2; among which, mechanical drilling to form pile hole 2 is existing technology, which can be understood by those skilled in the art. For cast-in-place piles, drilling methods include: dry drilling (dry drilling piles are formed after casting), mud wall drilling (mud wall drilling piles are formed after casting), driven pipe drilling (driven pipe piles are formed after casting), etc. Among them, mud wall drilling piles are the most common method of cast-in-place piles. Mud wall drilling is a mechanical drilling method that uses mud to protect and stabilize the hole wall. It suspends the cut mud and rock debris and discharges it outside the hole through circulating mud. It is suitable for soil layers with and without groundwater. For mud wall drilling, drilling machinery includes submersible drilling rigs, impact drilling rigs, and percussion cones. The construction process for slurry-walled bored piles is as follows: determining the pile location, installing steel casing (excavating the surface soil of the pile hole according to the pile location and installing the casing), positioning the pile driver, preparing slurry, mechanical drilling, slurry circulation and slag removal, cleaning the hole, installing the reinforcing steel cage, and pouring concrete, thereby forming a slurry-walled bored pile.

[0040] The steel casing is a cylinder made of 4-15mm thick steel plate, and its inner diameter should be 200mm larger than the drill bit diameter. The casing's function is to fix the position of the pile hole, protect the borehole opening, prevent surface water from flowing in, increase the water pressure inside the hole to prevent collapse, and guide the drill bit's direction during drilling. The steel casing is generally installed 0.3m above the ground surface.

[0041] Therefore, the technology for forming pile holes 2 by mechanical drilling is existing technology, which can be understood by those skilled in the art, and will not be elaborated here.

[0042] (3) A reinforcing cage 1 is inserted into the pile hole 2. The reinforcing cage 1 includes multiple vertical bars 11, which are interconnected by several stirrups 22 to form a cylindrical reinforcing cage 1. Several horizontal bars 13 are also connected to the vertical bars 1. The horizontal bars 13 are distributed along the diameter of the reinforcing cage 1, and the two ends of each horizontal bar 13 are respectively connected to two opposite vertical bars 11. The horizontal bars 13 are connected to the vertical bars 11 at intervals and interlaced, and each horizontal bar forms a cross shape. However, the reinforcing cages in the prior art are only composed of vertical bars 11 and stirrups 12, and do not have the several horizontal bars 13 of this invention. This invention improves the rigidity of the reinforcing cage by installing transverse reinforcement bars 13 inside the reinforcing cage 1. This prevents the cage from bending under gravity during the process of being lowered into the pile hole using a crane or other lifting equipment, thus ensuring the straightness of the cage and ultimately improving the tensile strength of the pile foundation. On the other hand, and more importantly, the transverse reinforcement bars strengthen the connection between the concrete inside the isolation cylinder (i.e., the concrete formed by the first grouting material) and the concrete outside the isolation cylinder (i.e., the concrete formed by the second grouting material) during the second grouting process. This prevents the connection between the concrete inside and outside the isolation cylinder from being affected by the isolation effect of the isolation cylinder, thereby ensuring that the integrity of the pile foundation is not affected by the isolation cylinder and that the bearing capacity of the pile foundation meets the design requirements.

[0043] (4) A cylindrical isolation cylinder 3 is placed inside the reinforcing cage 1, with the axis of the isolation cylinder 3 coinciding with the axis of the reinforcing cage 1. A support frame 4 for supporting and positioning the isolation cylinder 3 is fitted around the upper periphery of the isolation cylinder 3. The lower end of the isolation cylinder 3 extends downward to the bearing layer of the pile hole 2, and the upper end of the isolation cylinder 3 extends above the ground. There is a gap between the outer wall of the isolation cylinder 3 and the inner wall of the reinforcing cage 1. In specific implementation, the gap between the outer wall of the isolation cylinder 3 and the inner wall of the reinforcing cage 1 is 40-65mm, thereby ensuring that the grouting material poured can cover the reinforcing cage 1.

[0044] In the specific implementation process, the isolation cylinder 3 and the support frame 4 can be an integral structure, and the isolation cylinder 3 can be supported and hoisted by the support frame 4.

[0045] (5) Grouting; the grouting includes a first grouting stage and a second grouting stage. The first grouting stage involves injecting a first grouting material into the isolation cylinder, which fills the bearing layer corresponding to the pile hole. The second grouting stage involves continuously injecting the first grouting material into the isolation cylinder until a set elevation is reached. The second grouting stage also involves injecting a second grouting material into the periphery of the isolation cylinder until a set elevation is reached. The second grouting material is used to cover the reinforcing cage and fill the space around the reinforcing cage (i.e., the area between the outer wall of the isolation cylinder and the pile hole is filled by the second grouting material, which covers the reinforcing cage during filling). In the second grouting stage, the grouting into the isolation cylinder and the grouting into the outside of the isolation cylinder are performed simultaneously. The setting time of the first grouting material is longer than that of the second grouting material. In the specific implementation process, the cement added to the first grouting material is ordinary Portland cement, and the cement added to the second grouting material is early-strength cement. By utilizing the characteristics of early-strength cement, which has rapid solidification and high early strength, the second grouting material quickly bonds and solidifies with the soil around the pile, thus forming a whole with the soil around the pile. This prevents the settlement rate of the soft strata from exceeding the settlement rate of the pile foundation, which would cause negative skin friction in the pile foundation, thereby improving the bearing capacity of the pile foundation after it is formed.

[0046] (6) After the first grouting material injected in the second grouting stage reaches the design strength, the isolation cylinder 3 is pulled out, and the third grouting material is used to grout the gap formed after the isolation cylinder 3 is pulled out. In the specific implementation process, the inner and outer walls of the isolation cylinder are coated with release oil or formwork paint to facilitate separation from the concrete after pouring.

[0047] In practice, the required demolding time varies depending on the grade of the grouting material and the span of the structure, but this is generally understood by those skilled in the art. For example, the removal of concrete side formwork typically takes about 2 to 3 days, while the removal of concrete bottom formwork depends on the span. When the concrete span is between 2 and 8 meters, the bottom formwork can only be removed after the concrete has reached at least 75% strength, which takes about 7 days. When the concrete span is greater than 8 meters, the bottom formwork can only be removed after the concrete has reached 100% strength, which typically takes about 28 days.

[0048] The isolation cylinder of the present invention is a side mold. Therefore, the isolation cylinder can be pulled out by referring to the demolding time of the concrete side mold. Those skilled in the art will understand this, and it will not be elaborated here.

[0049] (7) After the third grouting material reaches the design strength, the pile head of the pile foundation is excavated and cut off, thereby completing the construction of the pile foundation.

[0050] This invention first utilizes the first grouting material of the first grouting stage to integrally cast the bearing layer corresponding to the pile hole, thus making the bearing section of the pile foundation a single unit serving as the main bearing capacity foundation. Then, the first grouting material of the second grouting stage is integrally cast with the bearing section of the pile foundation, and the second grouting material of the second grouting stage is used to simultaneously grout the periphery of the isolation cylinder. Because the setting time of the second grouting material is shorter than that of the first grouting material, it can quickly bond with the surrounding soil, improving the early bond strength between the pile foundation and the surrounding soil. This reduces the negative skin friction caused by the soil settling more than the pile foundation settlement, ultimately achieving the goal of improving the bearing capacity of the pile foundation. This invention is particularly suitable for the construction of pile foundations in soft soil strata.

[0051] Meanwhile, since the pile foundation described in this invention is a bearing pile (also known as a compression pile in construction engineering), its main function is to bear vertical loads. The vertical load primarily depends on the poured concrete (because the compressive strength of concrete is much greater than that of the reinforcing cage). In actual use, the pile foundation inevitably also experiences bending moments, and the bending strength of the reinforcing cage is much greater than that of the concrete. Therefore, the bending strength mainly depends on the reinforcing cage. Thus, this invention utilizes a second grouting material to cover and pre-embed the reinforcing cage, ensuring that the overall bending strength of the pile foundation is not affected by layered grouting (i.e., layered grouting achieved by the first grouting material inside the isolation cylinder and the second grouting material outside the isolation cylinder). After the isolation cylinder is pulled out, the reserved holes are grouted and bonded using a third grouting material. Through the structural design of the third grouting material and the transverse reinforcement, the concrete inside and outside the isolation cylinder can be connected together to form a whole. In fact, due to the structural design of the horizontal reinforcement bars, when one side of the pile foundation is subjected to bending moment, the horizontal reinforcement bars are directly connected to the two vertical reinforcement bars in the diameter direction of the steel cage. Therefore, the bending moment can be quickly and directly transferred to the vertical reinforcement bars on the other side through the horizontal reinforcement bars (that is, the force transfer effect of the horizontal reinforcement bars is faster and more direct than that of the stirrups). This allows the bending moment to be quickly and directly transferred to the other side of the steel cage when one side is subjected to bending moment, thereby making the stress on both sides of the steel cage more uniform when it is subjected to bending moment, and ultimately achieving the purpose of improving the bending resistance of the pile foundation.

[0052] In some embodiments, when the first grouting material is poured into the upper section of the isolation cylinder 3, pre-embedded vertically arranged pre-embedded steel bars 5 are inserted into the isolation cylinder 3, and each pre-embedded steel bar 5 is evenly arranged inside the isolation cylinder 3; after the pile head is cut off in step (7), the steel cage and the pre-embedded steel bars 5 are exposed, and the pre-embedded steel bars and the steel cage are connected by connecting steel bars to form a whole. When the pile head is cut off and the foundation is poured, the poured concrete is used to cover the steel cage and the pre-embedded steel bars again, thereby further improving the integrity of the concrete inside the isolation cylinder 3 (i.e., the concrete poured inside the isolation cylinder using the first grouting material) and the concrete outside the isolation cylinder (i.e., the concrete poured outside the isolation cylinder using the second grouting material), so that the load borne by the top of the pile foundation is evenly transferred to the pile body, further ensuring that the pile head will not crack due to layered pouring, and ensuring that the bearing capacity of the pile foundation meets the design requirements.

[0053] In some embodiments, when the pile head is cut off in step (7), the length of the cut-off pile head is greater than the design required length; at the same time, the lower end of the pre-embedded steel bar 5 is located at least 1m below the pile head cutting position. Naturally, before cutting off the pile head, the depth of excavation of the soil around the pile foundation is also increased accordingly to expose a longer pile head. This is clear and understandable to those skilled in the art, and will not be elaborated further here.

[0054] The cut-off length of the pile head for cast-in-place piles is generally 500-1000mm (i.e., the design requirement for the cut-off length is generally 500-1000mm). This is primarily because during the casting process, the aggregate (i.e., the aggregate in the first and second grouting materials) sinks while the grout rises, causing the pile head strength to fail to meet design requirements. Therefore, cast-in-place piles generally have their pile heads cut off to ensure that the strength of the top of the pile foundation after the cut-off pile head meets design requirements. The design requirements for the cut-off length of the pile head for cast-in-place pile foundations are well understood by those skilled in the art, for example, by referring to the "Code for Construction of Pile Foundations," and will not be elaborated upon here.

[0055] In the specific implementation process, the length of the pile head cut by the present invention is 300-600mm larger than the design requirement. While ensuring that the strength of the pile head meets the design requirements, the connection between the pre-embedded steel bar 5 and the steel cage 1 makes the concrete inside and outside the isolation cylinder 3 form a whole with greater strength.

[0056] In some embodiments, the isolation cylinder 3 has vertical strip grooves 31 formed according to the position of the transverse ribs. Sealing strips 32 are provided on both side walls of the vertical strip grooves 31. Receiving grooves are formed on the sealing strips 32 at positions corresponding to the height of the transverse ribs 5, so as to cover the transverse ribs through the receiving grooves. The isolation cylinder of the present invention has strip grooves, sealing strips in the strip grooves, and receiving grooves on the sealing strips, so that the isolation cylinder can extend downwards normally without being obstructed by the transverse ribs. At the same time, the sealing strips prevent the grouting materials inside and outside the isolation cylinder from mixing. In specific implementations, since the grouting materials inside and outside the isolation cylinder are different (i.e., the first grouting material and the second grouting material are different), the sealing strips ensure that the first and second grouting materials do not interfere with each other. Since the inner and outer sides of the isolation cylinder are poured simultaneously, the pressure on both sides of the sealing strip is actually balanced. Therefore, the injection of the first and second grouting materials will not damage the sealing performance of the sealing strip.

[0057] In order to prevent the grouting materials (first grouting material and second grouting material) from adhering to the sealing strip, the outer wall of the sealing strip is coated with release oil.

[0058] In the specific implementation process, the isolation cylinder 3 can be made of aluminum alloy so that the isolation cylinder has the characteristics of being lightweight and high strength, and can be reused in the project.

[0059] In some embodiments, the inner and outer walls of the isolation cylinder 3 are provided with a plurality of protrusions 33. The protrusions 33 serve to roughen the concrete surface when the isolation cylinder 3 is pulled out, so as to improve the connection strength of the concrete inside and outside the isolation cylinder after the third grouting material is injected.

[0060] In a preferred embodiment of the invention, the isolation cylinder 3 is shaped like a frustum with a smaller top and a larger bottom. This results in the concrete inside the isolation cylinder 3, which is poured with the first grouting material, also being shaped like a frustum with a smaller top and a larger bottom. When the isolation cylinder 3 is pulled out, the concrete poured with the third grouting material is shaped like a frustum with a larger top and a smaller bottom, thereby further improving the integrity of the pile foundation and facilitating the removal of the isolation cylinder 3.

[0061] In this invention, after the isolation cylinder is poured (i.e., the first grouting material and the second grouting material), the isolation cylinder can be rotated slightly intermittently to loosen it and facilitate its subsequent removal.

[0062] In some embodiments, in step (6), grouting the gap formed after the isolation cylinder is pulled out using a third grouting material includes:

[0063] If the gap formed after the isolation cylinder is pulled out is smaller than the outer diameter of the grouting pipe, then the third grouting material is epoxy resin adhesive. That is to say, when the thickness of the isolation cylinder is small, that is, when the reduction between the concrete formed after the first grouting material solidifies and the concrete formed after the second grouting material solidifies is small, annular resin adhesive can be directly injected to connect them, thereby connecting the concrete on the inside and outside of the isolation cylinder together.

[0064] If the gap formed after the isolation cylinder is pulled out is larger than the outer diameter of the grouting pipe, it includes the following:

[0065] (1) First, cement grout is sprayed onto the inner wall of the gap (i.e., the outer wall of the concrete formed by the first grouting material, the inner wall of the concrete formed by the second grouting material, and the inner bottom surface of the concrete formed by the second grouting material), thereby filling the gap on the concrete surface with the sprayed cement grout.

[0066] (2) Then, the gap is filled with the second grouting material.

[0067] The third grouting material of this invention can be configured according to actual conditions. When the gap is small after the isolation cylinder is pulled out, epoxy resin adhesive can be used for bonding directly. When the gap is large after the isolation cylinder is pulled out, cement grout can be sprayed onto the surface first, so that the cement grout can penetrate into the gap of the concrete surface. In particular, the first grouting material of the bearing layer corresponding to the pile hole and the second grouting material on the outside of the isolation cylinder are prone to cracks at the junction due to the different curing times of the first and second grouting materials. Therefore, cement grout is used for bonding. Then, the second grouting material is filled to fill the gap and finally make the pile foundation a whole, thereby ensuring that the overall strength of the pile foundation is not affected.

[0068] In some embodiments, the cement slurry used in the "spraying the inner wall of the gap with cement slurry" described in this invention can be prepared in the following manner:

[0069] The cement slurry consists of: silicate cement: 90-97 parts, fly ash: 1-5 parts, nano-alumina: 1-5 parts, alkaline initiator NaOH: 0.5-3 parts, and water-reducing agent: 0.5-2 parts. Specific preparation steps:

[0070] Step 1: Add water and ordinary Portland cement to a mixer and mix well;

[0071] Step 2: Add fly ash to the mixture from Step 1, and then stir well.

[0072] Step 3: Dissolve the water-reducing agent in water to prepare a solution, and add the solution to the mixture in step 2 and stir until well mixed;

[0073] Step 4: Add nano-alumina to the mixture from step 3 and stir until homogeneous;

[0074] Step 5: Add NaOH alkaline initiator to the mixture in step 4, stir evenly to obtain the grouting material of the present invention, wherein the water-cement ratio in the grouting material is 0.6.

[0075] The cement slurry of this invention, on the one hand, benefits from the large specific surface area of ​​nano-alumina and fly ash, resulting in good water binding. Their addition reduces the slurry's fluidity and pumpability. On the other hand, the nano-alumina of this invention, under the action of an alkaline activator, exhibits better solubility, accelerating the consumption of gypsum in silicate cement and thus promoting the hydrolysis of tricalcium aluminate to form hydrated calcium aluminate crystals. The hydrolysis reaction of tricalcium aluminate is extremely rapid, and is usually controlled by gypsum added to cement. However, the dissolution of nano-alumina accelerates the consumption of gypsum, thereby shortening the setting time and promoting early setting.

[0076] In this invention, the cement grout utilizes nano-alumina and fly ash as fine particles to fill the gaps between cement particles, reducing the porosity of the grouting material and achieving a uniform and dense state, thereby improving the strength of the grout. Furthermore, the alkaline activator of this invention promotes the hydration reaction of nano-alumina. The solution action of nano-alumina accelerates the consumption of gypsum in silicate cement, thereby promoting the hydration of tricalcium aluminate, generating CSH gel and Ca(OH)2, reducing the porosity between cement particles, and thus improving the strength of the cement grout after solidification.

[0077] Furthermore, in a preferred embodiment of the present invention, the following components are used: 92-97 parts of silicate cement (i.e., ordinary silicate cement), 1-4 parts of fly ash, 1-3 parts of nano-alumina, 0.5-1 part of alkaline activator, and 0.5-1 part of FDN water-reducing agent.

[0078] Furthermore, in a preferred embodiment of the present invention, the alkaline activator includes potassium hydroxide, sodium hydroxide, or barium hydroxide. Preferably, the alkaline activator is sodium hydroxide.

[0079] Furthermore, in a preferred embodiment of the present invention, the average particle size of the silicate cement is 20μm-30μm; the average particle size of the nano-alumina is 25nm-35nm; and the average particle size of the silica fume is 0.1μm-0.5μm.

[0080] This invention uses fly ash with a smaller particle size to fully fill the gaps between cement particles and between cement particles and nano-alumina, so as to achieve a high density and ensure the strength of cement paste.

[0081] Example 1

[0082] The weight ratio of the cement slurry in this embodiment is:

[0083] Ordinary silicate cement: 97 parts; fly ash: 1 part; nano alumina: 1 part; water-reducing agent: 0.5 parts; alkaline initiator: 0.5 parts.

[0084] Example 2

[0085] The weight ratio of the cement slurry in this embodiment is:

[0086] Ordinary silicate cement: 92 parts; fly ash: 4 parts; nano alumina: 2 parts; water-reducing agent: 1 part; alkaline initiator: 1 part.

[0087] Example 3

[0088] The weight ratio of the cement slurry in this embodiment is:

[0089] Ordinary silicate cement: 92 parts; fly ash: 4 parts; nano alumina: 3 parts; water-reducing agent: 0.5 parts; alkaline initiator: 0.5 parts.

[0090] Example 4

[0091] The weight ratio of the cement slurry in this embodiment is:

[0092] Ordinary silicate cement: 90 parts; fly ash: 3 parts; nano alumina: 4 parts; water-reducing agent: 1 part; alkaline initiator: 2 parts.

[0093] Example 5

[0094] The weight ratio of the cement slurry in this embodiment is:

[0095] Ordinary silicate cement: 91.5 parts; fly ash: 4 parts; nano alumina: 3 parts; water-reducing agent: 0.5 parts; alkaline initiator: 1 part.

[0096] Example 6

[0097] The weight ratio of the cement slurry in this embodiment is:

[0098] Ordinary silicate cement: 90.5 parts; fly ash: 4 parts; nano alumina: 3 parts; water-reducing agent: 0.5 parts; alkaline initiator: 2 parts.

[0099] Compare with Example 1

[0100] The cement slurry in this comparative example did not contain an alkaline activator and consisted of, by weight, 92.5 parts of silicate cement (i.e., ordinary silicate cement), 4 parts of fly ash, 3 parts of nano-alumina, and 0.5 parts of water-reducing agent. Its preparation method was consistent with that of Example 1.

[0101] Compare with Example 2

[0102] The cement slurry in this comparative example did not contain silica fume. It consisted of 96 parts silicate cement, 3 parts nano-alumina, 0.5 parts alkaline activator, and 0.5 parts FDN water-reducing agent. Its preparation method was consistent with that of Example 1.

[0103] Compare with Example 3

[0104] The cement grout used in the control example was ordinary silicate cement grout available on the market.

[0105] The parameter tables for the cement slurry of the above embodiments and comparative examples are as follows:

[0106]

[0107] As can be seen from the table above, the fluidity of the cement slurry in Examples 1-4 of this invention decreases with increasing nano-alumina content, and the pumpable time decreases accordingly. While the setting time of the cement slurry shortens slightly with increasing nano-alumina content, it has little effect on the initial and final setting time interval, indicating that nano-alumina can promote early setting of the cement slurry. Furthermore, the table also shows that the addition of nano-alumina can improve the compressive strength at different ages.

[0108] The fluidity and pumpability of the cement grouts in Examples 3, 4, 6 and Comparative Example 1 decreased with the increase of alkaline activator dosage, while the early strength of the cement grouts was greatly improved by the addition of alkaline activator, and the setting time was shortened with the increase of alkaline activator dosage. When the alkaline activator dosage was 2 parts, the setting time changed significantly, and the setting time of the grout was shortened by about 60% compared with the setting time of the grout in Comparative Example 1, showing a significant effect in promoting early setting.

[0109] The fluidity and pumpability of the grouting materials in Example 3 and Comparative Example 2 decreased due to the addition of silica fume, while the early strength of the grouting materials increased and the setting time was shortened. The 1-day compressive strength of the grouting material in Example 3 was 148% higher than that of the 1-day compressive strength of Comparative Example 3, the 3-day compressive strength was 133% higher, and the 7-day compressive strength was 40% higher.

[0110] Therefore, the cement grout used in this invention can shorten the setting time and increase the strength of the cement grout after setting, thereby quickly repairing and connecting the cracks generated on the concrete surface of the first and second grouting stages.

Claims

1. A method for improving the early bond performance between a pile and the surrounding soil, characterized in that, include: (1) Measure and set out to determine the location of the pile hole; (2) Mechanical drilling forms pile holes; (3) Insert a steel cage into the pile hole. The steel cage includes multiple vertical bars. The vertical bars are connected together by several stirrups to form a cylindrical steel cage. Several horizontal bars are also connected to the vertical bars. The horizontal bars are distributed along the diameter of the steel cage and the two ends of the horizontal bars are respectively connected to two opposite vertical bars. The horizontal bars are connected to the vertical bars at intervals and interlaced with each other, and each horizontal bar forms a "+" shape. (4) A cylindrical isolation cylinder is placed inside the reinforcing cage, the axis of the isolation cylinder being coincident with the axis of the reinforcing cage; a support frame for supporting and positioning the isolation cylinder is fitted around the upper end of the isolation cylinder, the lower end of the isolation cylinder extends downward to the bearing layer of the pile hole, and the upper end of the isolation cylinder extends above the ground; there is a gap between the outer wall of the isolation cylinder and the inner wall of the reinforcing cage. (5) Grouting: The grouting includes a first grouting stage and a second grouting stage. The first grouting stage involves injecting a first grouting material into the isolation cylinder, which fills the bearing layer corresponding to the pile hole. The second grouting stage involves continuously injecting the first grouting material into the isolation cylinder until a set elevation is reached. The second grouting stage also involves injecting a second grouting material into the periphery of the isolation cylinder until a set elevation is reached. The second grouting material is used to cover the reinforcing cage and fill the space around the reinforcing cage. In the second grouting stage, the grouting into the isolation cylinder and the grouting into the periphery of the isolation cylinder are carried out simultaneously. The setting time of the first grouting material is longer than that of the second grouting material. (6) After the first grouting material injected in the second grouting reaches the design strength, the isolation cylinder is pulled out, and the third grouting material is used to grout into the gap formed after the isolation cylinder is pulled out. (7) After the third grouting material reaches the design strength, the pile head of the pile foundation is excavated and the pile head is cut off, thereby completing the construction of the pile foundation.

2. The method for improving the early bond performance between a pile and the surrounding soil according to claim 1, characterized in that, When the first grouting material is poured into the upper section of the isolation cylinder, pre-embedded vertically arranged pre-embedded steel bars are inserted into the isolation cylinder, and each pre-embedded steel bar is evenly arranged inside the isolation cylinder; after the pile head is cut off in step (7), the steel cage and pre-embedded steel bars are exposed, and the pre-embedded steel bars are connected to the steel cage with the connecting steel bars to form a whole.

3. The method for improving the early bond performance between a pile and the surrounding soil according to claim 2, characterized in that, When cutting the pile head in step (7), the length of the cut pile head is greater than the design required length; at the same time, the lower end of the pre-embedded steel bar is located at least 1m below the pile head cutting position.

4. The method for strengthening the early bond performance between a pile and the surrounding soil according to any one of claims 1-3, characterized in that, The isolation cylinder has vertical strip grooves formed according to the position of the horizontal ribs. Sealing strips are provided on both sides of the vertical strip grooves. Receiving grooves are formed on the sealing strips at the height position of the horizontal ribs so as to cover the horizontal ribs through the receiving grooves.

5. The method for improving the early bond performance between a pile and the surrounding soil according to claim 4, characterized in that, The inner and outer walls of the isolation cylinder are provided with several protrusions.

6. The method for improving the early bond performance between a pile and the surrounding soil according to claim 1, characterized in that, In step (6), the grouting of the gap formed after the isolation cylinder is pulled out using a third grouting material includes: If the gap formed after the isolation cylinder is pulled out is smaller than the outer diameter of the grouting pipe, then the third grouting material is epoxy resin adhesive. If the gap formed after the isolation cylinder is pulled out is larger than the outer diameter of the grouting pipe, it includes the following: (1) First, the inner wall of the gap is sprayed with cement grout, and then the gap on the concrete surface is filled with the sprayed cement grout. (2) Then the gap is filled with the second grouting material.

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