Precast pile construction method for specific geology

Abstract

The invention provides a specific geological precast pile construction method which comprises the following steps: S1, acquiring design parameters, and determining parameters of a precast pile and parameters of a stirring hole according to the design parameters; s2, taking the parameters of the stirring hole as a construction target, drilling the stirring hole downwards by taking the pile pressing point as a stirring center, and performing wet operation through a stirrer to obtain a stirring pile; and S3, before initial setting of the cement paste in the stirring pile, the selected precast pile is pressed into the stirring pile until design parameters are achieved. By means of the reasonable design and construction method, the precast pile can quickly reach the designed elevation, the soil squeezing effect of a traditional precast pile in a sand layer is greatly weakened, and the phenomenon that the follow-up precast pile is difficult to construct to reach the designed elevation and needs to be cut due to the pile group soil squeezing effect is avoided; and meanwhile, the phenomenon that pile splicing is needed when the re-pressed precast pile is controlled by pile pressing force is avoided, the pain caused by traditional precast pile construction is solved, and the design and construction principle is simple.

Description

Technical Field

[0001] The invention relates to the field of building structure foundation design, and more specifically, to a prefabricated pile construction method for a specific geology. Background Art

[0003] In the field of building structure foundation, there are two commonly used pile types: one is the cast-in-place pile with concrete poured on site, and the other is the prefabricated pile produced on site in the factory. Concrete cast-in-place piles are drilled on site. When using the mud wall drilling process, a mud pool needs to be made. The steel cage is tied on site, sunk into the pre-drilled hole, and then commercial concrete is poured to form a concrete cast-in-place pile. The problem is that the workload of on-site construction is large, the quality of the pile body concrete is not easy to guarantee, and the highest concrete strength grade is C60. Prefabricated piles are piles of various concrete forms produced in batches in the factory. They are constructed on site by static pressure or hammering. The on-site work is small, the operation is simple, and it is environmentally friendly. The strength grade of the pile body concrete can be C80 and above, which can give full play to the compressive performance of concrete. Compared with concrete cast-in-place piles, prefabricated piles do not need to make mud pools on site, and the amount of wet work is small, which is conducive to reducing pollution and carbon emissions; factory batch production improves construction efficiency and helps save construction time.

[0004] Due to the particularity of its construction process, the interaction between precast piles and the surrounding soil is mainly friction. In the case of dense soil, such as dense sand layer or old clay, the deeper the pile enters the soil layer, the more obvious the soil extrusion is, resulting in the pile bursting before the pile reaches the design elevation during the pile pressing process. For precast piles constructed later, sometimes the pile pressing force specified in the design is reached, but the pile elevation does not meet the design requirements, so the precast piles need to be cut to ensure that the pile top elevation meets the design requirements. Since the density of the dense sand layer has a time effect, when the pile cannot be pressed to the design elevation and is re-pressed, the sand layer around the pile becomes loose again, and the precast pile can enter a certain depth again. In this case, the design elevation has been reached, but the pile pressing force has not yet reached the design requirements. At this time, the piles need to be connected to ensure that the pile pressing force meets the design requirements. In the case of specific geological soil layers, the construction process leads to pile connection and pile cutting, which makes it difficult to assemble precast piles, while increasing the cost and reducing construction efficiency.

[0005] Therefore, it is necessary to study a solution that can solve the problems of pile cutting and pile connection during precast pile construction under specific geological conditions, so as to efficiently meet the design requirements of precast piles, reduce construction costs and improve construction efficiency. Summary of the invention

[0006] The present invention aims at the technical problems existing in the prior art and provides a precast pile construction method for specific geological conditions, so as to solve the problems of low construction efficiency and high construction cost caused by pile cutting and pile connection during the precast pile construction process in specific geological conditions.

[0007] In order to solve the problems existing in the prior art, the present invention provides a prefabricated pile construction method for a specific geological condition, comprising: S1, obtaining design parameters, and determining parameters of the precast pile and the mixing hole according to the design parameters; S2, with the parameters of the mixing hole as the construction target, the mixing hole is drilled downward with the pile pressing point as the mixing center, and the mixing pile is obtained by wet operation of the mixer; S3, before the cement slurry in the mixing pile initially sets, the selected prefabricated pile is pressed into the mixing pile until the design parameters are reached.

[0008] Based on the above technical solution, the present invention can also make the following improvements.

[0009] Optionally, in step S1, obtaining design parameters includes: S101, determine the characteristic design value of the single pile bearing capacity based on the designed column / wall bottom internal force; S102, calculating the effective pile length of a single precast pile according to the characteristic design value of the single pile bearing capacity and the pile foundation parameters of the current geological exploration hole in the geological exploration report, and calculating the characteristic values ​​of the single pile bearing capacity in three cases A, B, and C respectively according to the effective pile length: A. Treat the cement soil and precast pile in the mixing hole as an integral pile, and consider the side resistance and end resistance of the integral pile; B. Consider the side resistance of the cement soil and precast piles in the mixing hole, as well as the end resistance of the precast piles; C. Only consider the compressive bearing capacity of the concrete of the precast pile body; The minimum value of the single pile bearing capacity characteristic value under the three conditions is taken to obtain the single pile bearing capacity characteristic estimation value; S103, comparing the estimated value of the single pile bearing capacity characteristic with the designed value of the single pile bearing capacity characteristic, and if the error is within the allowable range, substituting the estimated value of the single pile bearing capacity characteristic into the calculation formula of situation A to back-calculate the pile length, and obtaining an alternative value of the pile length of the current single pile; S104, obtaining pile foundation parameters of all geological exploration holes according to geological exploration data, each geological exploration hole corresponds to a pile driving point, calculating the pile length candidate values ​​corresponding to all pile driving points, and taking the maximum value of all pile length candidate values ​​as the final prefabricated pile length.

[0010] Optionally, in step S102, according to the effective pile length, the characteristic value of the single pile bearing capacity in case A is calculated using formula (1): ………………………………(1), in, is the characteristic value of the vertical compressive bearing capacity of a single pile, in kN; is the circumference of the pile after mixing treatment, in m; For the The coefficient of increase of characteristic value of side resistance of soil mixing pile, The value of is set based on experience for different soil types. For example, when the soil layer to be treated is silty soil, it can be 1.3, and for other soil layers, it can be 1.5. It is the sequence number of soil layers arranged from the ground surface downward within the pile length range; For the Soil layer thickness, in m; For the The characteristic value of the side resistance of the soil mixing pile, in kPa; is the coefficient of soil resistance increase at the pile end, which can be taken as 2.0; is the characteristic value of the soil bearing capacity at the pile end, in kPa; It is the cross-sectional area of ​​the treated pile body of the mixing pile, in kPa.

[0011] Optionally, in step S102, according to the effective pile length, the characteristic value of the single pile bearing capacity in case B is calculated using formula (2): ……………………………… (2), in, is the characteristic value of the vertical compressive bearing capacity of a single pile, in kN; is the length of precast pile, in m; is the perimeter of the precast pile, in m; is the characteristic value of the side resistance of the precast pile after mixing treatment, in kPa; The value of is set based on experience for different soil types. For example, when the soil layer to be treated is silty soil, the value can be 135 kPa; for other soil layers, the value can be 270 kPa. is the characteristic value of the end resistance of the soil at the end of the precast pile, in kPa; is the cross-sectional area of ​​the precast pile body, in m 2 , calculate the area according to the outer diameter of the pile.

[0012] Optionally, in step S102, the characteristic value of the single pile bearing capacity in case C is calculated using formula (3): / K………………………… (3), in, is the characteristic value of the vertical compressive bearing capacity of a single pile, in kN; is the working condition coefficient, which is determined according to the degree of damage that the pile construction process may cause to the pile body and can be taken as 0.80; The design value of the axial compressive strength of concrete, in MPa, is taken according to the standard, for example, according to the provisions of the current national standard "Code for Design of Concrete Structures" GB 50010; It is the conversion coefficient between design value and characteristic value, which is taken based on experience and can be 1.35.

[0013] Optionally, in step S1, determining the parameters of the precast pile and the mixing hole according to the design parameters includes: S105, determining the design elevation, radial dimensions and pile bottom bearing layer of the precast pile to be constructed at the current pile pressing point according to the precast pile length and foundation burial depth requirements, wherein the design elevation of the precast pile includes the pile bottom elevation and pile top elevation of the precast pile; The drilling depth of the mixing hole is set to be consistent with the design elevation of the precast pile, and the drilling diameter of the mixing hole is larger than the radial dimension of the precast pile.

[0014] Optionally, step S2 includes: The mixer uses the pile pressing point as the rotating mixing center, rotates downward to drill mixing holes, and pours cement slurry into the mixing holes while mixing to form mixing piles; The drilling time does not exceed the initial setting time of the cement slurry, the height of the obtained mixing pile is compatible with the design elevation of the precast pile, and the diameter of the mixing pile is larger than the radial dimension of the precast pile.

[0015] Optionally, in step S3, before the cement slurry in the mixing pile initially sets, the selected prefabricated pile is pressed into the mixing pile until the design parameters are reached, including: S301, selecting a precast pile according to the parameters of the precast pile; S302, before the cement slurry in the mixing pile initially sets, align the center of the selected precast pile with the center of the mixing pile, apply a vertical pile-pressing force to the precast pile, and press the precast pile into the mixing pile until the position of the precast pile reaches the designed elevation of the precast pile.

[0016] Optionally, in step S302: If the selected precast pile is a solid square pile, before the cement slurry in the mixing pile initially sets, align the center of the solid square pile with the center of the mixing pile, apply a vertical pile-pressing force to the solid square pile, and press the solid square pile into the mixing pile until the position of the solid square pile reaches the design elevation of the precast pile; If the selected precast pile is a hollow round pile, before the cement slurry in the mixing pile initially sets, a closed steel pile tip is welded to the bottom end of the hollow round pile, the center of the hollow round pile is aligned with the center of the mixing pile, a vertical pile pressing force is applied to the hollow round pile, and the hollow round pile is pressed into the mixing pile 1 until the position of the hollow round pile reaches the design elevation of the precast pile.

[0017] Optionally, in step S302, if the selected precast pile is a hollow round pile, after the position of the hollow round pile reaches the design elevation of the precast pile, the following steps are further included: Pour core-fill concrete at the bottom and top of the hollow circular pile.

[0018] The present invention provides a precast pile construction method for specific geology. Under specific geological conditions, for example, there is a sand layer with a thickness of more than 10m in the soil layer below the base, the density of the sand layer is medium to dense, the characteristic value of the bearing capacity of the sand layer under the standard penetration test is not less than 200kPa, and the sand layer is partially sandwiched with gravel. Through reasonable design and construction methods, the mixing pile process is combined with the precast pile pressing construction, so that the precast pile construction can quickly reach the design elevation, which greatly weakens the soil squeezing effect of traditional precast piles in the sand layer, and there will be no phenomenon that the subsequent precast piles are difficult to construct to the design elevation due to the soil squeezing effect of the pile group, and the pile cutting is required. At the same time, due to the reinforcement effect of the mixing pile on the soil body, the side resistance of the pile body is increased, and the phenomenon that the precast piles need to be connected when the pile pressure force is controlled by the repeated pressing of the precast piles will not occur, which solves the pain points of traditional precast pile construction, simplifies the construction process, improves the construction quality and efficiency, and reduces the project cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A flow chart of a prefabricated pile construction method for a specific geological condition provided by the present invention; Figure 2 A schematic cross-sectional diagram of a stirring hole forming process provided in a certain embodiment; Figure 3 A schematic cross-sectional view of a prefabricated solid square pile after being formed provided by a certain embodiment; Figure 4 A schematic cross-sectional view of a prefabricated hollow circular pile after being formed provided in a certain embodiment; Figure 5 for Figure 3 AA section view; Figure 6 for Figure 3 BB cross-section diagram.

[0020] In the accompanying drawings, the components represented by the reference numerals are listed as follows: 1. Mixed piles, 2. Surface soil layer, 3. Thick to medium-dense sand layer, 4. Solid square piles, 5. Hollow round piles, 6. Core-filled concrete at the bottom of the pile, 7. Core-filled concrete at the top of the pile, 8. Closed steel pile tip. DETAILED DESCRIPTION

[0021] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0022] The specific geological conditions referred to in the present invention mainly refer to the existence of a sand layer with a thickness of more than 10m below the base (surface soil layer 2), the density of the sand layer is medium to dense, the characteristic value of the bearing capacity of the sand layer under the standard penetration test is not less than 200kPa, and the sand layer is partially interspersed with gravel. In this case, the bearing layer at the bottom of the precast pile is a medium to dense fine sand layer, referred to as a deep medium to dense sand layer 3, and the depth of the bottom of the pile entering the bearing layer is not less than 10.0m.

[0023] Based on the above-mentioned specific geological conditions, the embodiments of the present invention provide Figure 1 A prefabricated pile construction method for a specific geological condition is shown, the method comprising steps S1 to S3: S1, obtain design parameters, and determine the parameters of the precast pile and the parameters of the mixing hole according to the design parameters; the design parameters are determined in the precast pile design stage, and the parameters of the mixing hole are adapted to the precast pile parameters. After the precast pile parameters are obtained, the adapted parameters of the mixing hole can be obtained.

[0024] S2, with the parameters of the mixing hole as the construction target, the mixing hole is drilled downward with the pile pressing point as the mixing center, and the mixing pile 1 is obtained by wet operation of the mixer; the mixing pile 1 is located in the mixing hole, and is mainly formed by mixing the soil around the hole and the cement slurry poured during the wet operation, for example Figure 2 The structure of the mixing pile 1 obtained in a certain implementation scenario is shown; S3, before the cement slurry in the mixing pile 1 initially sets, the selected precast pile is pressed into the mixing pile 1 until the design parameters are reached, such as the design elevation of the precast pile. Figure 3 and Figure 4 The finished structure obtained after pressing the precast piles into the cast-in-place piles in two implementation scenarios is shown respectively.

[0025] It is understandable that, based on the defects in the background technology, for example, for certain specific geological conditions, such as dense sand layers or old clay, the soil squeezing effect during the construction of precast piles is obvious, and there are difficulties in cutting or connecting piles. The embodiment of the present invention proposes a precast pile construction method for specific geology. The method of this embodiment combines the mixing pile 1 process with the precast pile pressing construction process through reasonable design and construction methods. Before pressing the precast pile, the soil layer is stirred by a mixing pile 1 machine to make it loose, the dense soil layer is stirred to form a hole, and cement slurry is poured to form a mixing pile 1. The cement slurry is flexible before initial setting, and the hole diameter of the mixing hole is larger than the diameter of the precast pile. The subsequent precast pile can be quickly and easily reached during the press-in construction, which greatly weakens the soil squeezing effect of the traditional precast pile in the sand layer when it is pressed in, and there will be no phenomenon that the subsequent precast piles are difficult to construct to the design elevation due to the soil squeezing effect of the pile group, resulting in the need to cut the pile. At the same time, since the mixing pile 1 is obtained by wet operation in advance, the mixing pile 1 is pressed into the lateral soil body during the precast pile pressing process. After the cement of the mixing pile 1 is solidified, the soil body is reinforced, which increases the friction resistance of the soil layer around the precast pile, greatly improves the side friction resistance of the precast pile, and does not need to be controlled by the pile pressing force when pressing the pile, only the pile length needs to be controlled, which simplifies the difficulty of construction and pile matching. Since the pile length control is mainly used and the pile pressing force control is auxiliary, there will be no phenomenon of pile connection when the precast pile is repeatedly pressed with the pile pressing force control, which solves the pain points of traditional precast pile construction, simplifies the construction process, and improves the construction quality and efficiency. For relatively loose sand layers and silty clay, the same treatment method can also solve the problem of pile connection. This method eliminates the steps of pile connection and pile cutting, and reduces the overall cost of the project.

[0026] Based on the above embodiment, this embodiment can also be improved as follows.

[0027] In a possible implementation manner, in step S1, obtaining the design parameters includes S101-S104: S101, determine the characteristic design value of the single pile bearing capacity based on the internal forces at the bottom of the column / wall designed for the building structure; S102, calculating the effective pile length of a single precast pile according to the design value of the single pile bearing capacity characteristic and the pile foundation parameters of the current geological exploration hole in the geological exploration report; It can be understood that the effective pile length is an assumed pile length, which can be optimized through subsequent steps. When calculating the effective pile length, the following situation A needs to be considered, and the subsequent formula (1) is further used for calculation, which will not be repeated here.

[0028] According to the effective pile length, the characteristic values ​​of the single pile bearing capacity in the three cases of A, B and C are calculated respectively: A. Treat the cement soil and precast pile in the mixing hole as an integral pile, and consider the side resistance and end resistance of the integral pile; B. Consider the side resistance of the cement soil and precast piles in the mixing hole, as well as the end resistance of the precast piles; C. Only consider the compressive bearing capacity of the concrete of the precast pile body; The minimum value of the single pile bearing capacity characteristic value under the three conditions is taken to obtain the single pile bearing capacity characteristic estimation value; It can be understood that in step S102, the calculation of the estimated value of the single pile bearing capacity characteristic needs to consider multiple situations for calculation and comparison, and the smaller value of the bearing capacity characteristic values ​​calculated considering the three situations A, B, and C is taken as the estimated value of the single pile bearing capacity characteristic. Such a precast pile design method is safer and reduces the risks of cutting and connecting precast piles. There is no need for re-pressing in the subsequent precast pile pressing process, which simplifies the subsequent construction process and reduces the construction cost.

[0029] S103, compare the estimated value of the single pile bearing capacity characteristic with the designed value of the single pile bearing capacity characteristic. If the error is within the allowable range, substitute the estimated value of the single pile bearing capacity characteristic into the calculation formula of situation A to back-calculate the pile length, and obtain the candidate value of the pile length of the current single pile; this step optimizes the effective pile length (assumed pile length) in step S102 by back-calculating the pile length according to the estimated value of the single pile bearing capacity characteristic; and repeatedly calculate through steps S102 and S103 until a reasonable candidate value of the pile length is calculated.

[0030] S104, obtaining pile foundation parameters of all geological exploration holes according to geological exploration data, each geological exploration hole corresponds to a pile driving point, calculating the pile length candidate values ​​corresponding to all pile driving points, taking the maximum value of all pile length candidate values, and preferably taking the integer number of meters as the final prefabricated pile length.

[0031] It can be understood that the alternative pile lengths are calculated for each precast pile in the geological survey hole, and then the alternative pile lengths corresponding to all the geological survey holes are combined to select a pile length that can take into account the construction requirements of all pile driving points to make precast piles, eliminating the pile connection and cutting processes during subsequent construction.

[0032] In a possible implementation manner, in step S102, according to the effective pile length, the characteristic value of the single pile bearing capacity in case A is calculated using formula (1): ………………………………(1), in, is the characteristic value of the vertical compressive bearing capacity of a single pile, in kN; is the circumference of the pile after mixing treatment, in m; For the The coefficient of increase of characteristic value of side resistance of soil mixing pile, The value of is set based on experience for different soil types. For example, when the soil layer to be treated is silty soil, it can be 1.3; for other soil layers, it can be 1.5; It is the sequence number of soil layers arranged from the ground surface downward within the pile length range; For the Soil layer thickness, in m; For the The characteristic value of the side resistance of the soil mixing pile, in kPa; is the coefficient of soil resistance increase at the pile end, which can be taken as 2.0; is the characteristic value of the soil bearing capacity at the pile end, in kPa; It is the cross-sectional area of ​​the treated pile body of the mixing pile, in kPa.

[0033] It can be understood that in this embodiment, formula (1) is used to calculate the characteristic value of the single pile bearing capacity in case A. The calculation principle is mainly based on the consideration that the mixing pile 1 reinforces the surrounding soil layer. The mixing pile 1 and the precast pile are combined into one and subjected to force together. Therefore, when calculating the side resistance, the diameter of the mixing pile 1 is used, and the increase coefficient is taken into account. When calculating the bottom resistance, since the soil layer at the bottom of the pile is in its original state or is loosened by mixing, the bottom resistance cannot be taken according to the compaction state of the traditional precast pile, and the characteristic value of the soil layer should be taken. In addition, due to the cement reinforcement effect, the increase coefficient is taken into account, and the calculated area of ​​the pile bottom is also calculated according to the diameter of the mixing pile 1.

[0034] In a possible implementation manner, in step S102, according to the effective pile length, the characteristic value of the single pile bearing capacity in case B is calculated using formula (2): ……………………………… (2), in, is the characteristic value of the vertical compressive bearing capacity of a single pile, in kN; is the length of precast pile, in m; is the perimeter of the precast pile, in m; is the characteristic value of the side resistance of the precast pile after mixing treatment, in kPa; The value of is set based on experience for different soil types. For example, when the soil layer to be treated is silty soil, the value can be 135 kPa; for other soil layers, the value can be 270 kPa. is the characteristic value of the end resistance of the soil at the end of the precast pile, in kPa; is the cross-sectional area of ​​the precast pile body, in m 2 , calculate the area according to the outer diameter of the pile.

[0035] It can be understood that in this embodiment, formula (2) is used to calculate the characteristic value of the single pile bearing capacity in case B. The calculation principle is that the side resistance of the pile is calculated based on the precast pile and the mixed cement soil, and the bottom resistance of the pile is considered based on the precast pile end resistance.

[0036] In a possible implementation manner, in step S102, the characteristic value of the single pile bearing capacity in case C is calculated using formula (3): / K………………………… (3), in, is the characteristic value of the vertical compressive bearing capacity of a single pile, in kN; is the working condition coefficient, which is determined according to the degree of damage that the pile construction process may cause to the pile body and can be taken as 0.80; The design value of the axial compressive strength of concrete, in MPa, is taken according to the standard, for example, according to the provisions of the current national standard "Code for Design of Concrete Structures" GB 50010; It is the conversion coefficient between design value and characteristic value, which is taken based on experience and can be 1.35.

[0037] It can be understood that in this embodiment, formula (3) is used to calculate the characteristic value of the single pile bearing capacity in case C, and the calculation principle is based on the concrete material of the precast pile body.

[0038] In a possible embodiment, in step S1, determining the parameters of the precast pile and the parameters of the mixing hole according to the design parameters includes: S105, determining the design elevation, radial dimensions and pile bottom bearing layer of the precast pile to be constructed at the current pile pressing point according to the precast pile length and foundation burial depth requirements, wherein the design elevation of the precast pile includes the pile bottom elevation and pile top elevation of the precast pile; The drilling depth of the mixing hole is set to be consistent with the design elevation of the precast pile, and the drilling diameter of the mixing hole is larger than the radial dimension d of the precast pile.

[0039] It is understandable that when calculating the design elevation of precast piles, such as the elevation of the bottom end and the elevation of the top of the precast pile, the foundation depth thickness should be added to the length of the precast pile. Therefore, the elevation of the bottom end of the precast pile is longer than the length of the precast pile. Figure 3 For example, a certain burial depth should be reserved from the ground to the top of the precast pile. After the subsequent precast pile pressing process is completed, the soil layer or soil-cement mixture from the top of the precast pile to the ground can be excavated for the next construction step.

[0040] In a possible embodiment, Figure 2 The figure shows a cross-sectional view of the structure of the mixing pile 1 obtained in a certain implementation scenario. Step S2 includes: Prepare a cement mortar pool for use in the construction of mixing pile 1, with the cement content in the cement mortar not less than 15%; The mixer uses the pile pressing point as the rotating mixing center, rotates downward to drill the mixing hole, and pours cement slurry into the mixing hole while mixing to form a mixing pile 1; Among them, the drilling time does not exceed the initial setting time of the cement slurry, so as to prevent the precast piles from being difficult to press into the hole in the subsequent process after the cement has initially set, thereby increasing the difficulty of construction; the height of the obtained mixing pile 1 is compatible with the design elevation of the precast pile, for example, the bottom position of the mixing pile 1 is consistent with the elevation of the bottom end of the precast pile, and the diameter D of the mixing pile 1 is larger than the radial dimension d of the precast pile, so that only a smaller pressure control force is required to press the precast pile to the designed position, thereby reducing the difficulty of construction.

[0041] For example, the pile pressing point determined by the exploration hole is used as the rotating mixing center, and a three-axis mixer is used to wetly mix downward to form a hole. When the mixing hole is relatively small, a three-axis mixer is used, and a single drill rod is used. The bottom elevation of the hole formed by mixing must reach the design bottom elevation of the precast pile. When the precast pile is a round pile, the hole diameter D is 200mm larger than the design pile diameter of the precast pile; when the precast pile is a square pile, the hole diameter D is 150mm larger than the diagonal length of the square pile.

[0042] In a possible embodiment, Figure 3 and Figure 4 The figure shows a schematic cross-sectional structure diagram of a precast pile after being pressed into the bottom of a mixing pile 1 in two implementation scenarios. In step S3, before the cement slurry in the mixing pile 1 initially sets, the selected precast pile is pressed into the mixing pile 1 until the design parameters are reached, including steps S301 to S302: S301, selecting a precast pile according to the parameters of the precast pile, mainly selecting the precast pile according to the length of the precast pile. The cross-sectional shape and cross-sectional size of the precast pile can be set in advance according to the architectural design data and the geological survey data, and can be defaulted to known data; the precast pile may be a solid square pile 4 or a hollow round pile 5, Figure 3 The prefabricated piles shown are solid square piles 4. Figure 4 The prefabricated pile shown is a hollow circular pile 5; S302, before the cement slurry in the mixing pile 1 initially sets, align the center of the selected precast pile with the center of the mixing pile 1, apply a vertical pile-pressing force to the precast pile, and press the precast pile into the mixing pile 1 until the position of the precast pile reaches the designed elevation of the precast pile.

[0043] In step S302, the center of the precast pile should coincide with the center of the mixing pile 1, and a verticality guarantee mechanism, such as a precast pile clip, is required to control the verticality of the precast pile. The main reason is that the soil layer is mixed and loose, and the precast pile is easy to deviate when pressed in, so a verticality guarantee mechanism needs to be set to control the verticality of the precast pile to ensure the construction quality.

[0044] The operation is completed when the precast pile is driven to the designed elevation. The driving process is mainly controlled by pile length and supplemented by pile driving force control. The pile driving force does not need to be twice the design characteristic value as in traditional processes. This avoids the pain of cutting or connecting piles when the traditional precast pile driving force control is the main method, and also reduces the difficulty of the pile driving operation.

[0045] In a possible implementation manner, in step S302: like Figure 3 The figure shows the case where the precast pile is a solid square pile 4. Figure 5 for Figure 3 AA cross-sectional view, if the selected precast pile is a solid square pile 4, before the cement slurry in the mixing pile 1 initially sets, align the center of the solid square pile 4 with the center of the mixing pile 1, and use a static press or hammer to apply a vertical pile pressing force to the solid square pile 4, and press the solid square pile 4 into the mixing pile 1 until the position of the solid square pile 4 reaches the design elevation of the precast pile.

[0046] like Figure 4 The example shown is a case where the prefabricated pile is a hollow circular pile 5. Figure 6 for Figure 4 BB cross-sectional view, if the selected precast pile is a hollow round pile 5, before the cement slurry in the mixing pile 1 initially sets, a closed steel pile tip 8 is welded to the bottom end of the hollow round pile 5, the center of the hollow round pile 5 is aligned with the center of the mixing pile 1, a static press or hammer is used to apply a vertical pile pressing force to the hollow round pile 5, and the hollow round pile 5 is pressed into the mixing pile 1 until the position of the hollow round pile 5 reaches the design elevation of the precast pile, and then the pile bottom core filling concrete 6 and the pile top core filling concrete 7 are poured into the hollow round pile 5.

[0047] The present invention is now described by way of example using a specific implementation scenario.

[0048] like Figures 2~6 As shown, the specific geology includes a surface soil layer 2 and a thick medium-dense sand layer 3 from top to bottom, wherein the thick medium-dense sand layer 3 is the bearing layer of the precast pile, and the bottom end of the precast pile enters the bearing layer to a depth of not less than 10.0 m.

[0049] First: In the precast pile design stage, determine the characteristic design value of the single pile bearing capacity based on the internal force at the bottom of the wall column. Then select the precast pile type, which may be a solid square pile 4 or a hollow round pile 5, and obtain the cross-sectional dimensions of the selected type of precast pile (such as the radial dimension d in the figure). According to the minimum gap between the outer wall of the mixing hole and the precast pile of not less than 100mm, determine the mixing hole diameter D, that is, the mixing pile 1 diameter D. According to the pile foundation parameters, precast pile parameters and mixing (hole) pile parameters in the geological survey report, the above three formulas are used to calculate and determine the final precast pile length L, and then determine the pile bottom elevation, pile top elevation and pile end bearing layer depth according to the foundation burial depth requirements. Prepare a sufficient number of precast piles according to the precast pile parameters.

[0050] Second: Use a three-axis mixer for wet operation, stir the hole diameter D, the bottom elevation of the hole is consistent with the design elevation of the precast pile (the elevation of the bottom end of the pile), the top elevation of the construction hole can start from the natural ground, or a certain burial depth can be reserved. The cement content of the hole corresponding to the length of the precast pile is not less than 15%, and the cement content from the top of the pile to the natural ground elevation is not less than 6%. The time from the beginning of mixing to the end should not exceed 3 hours, and it should not exceed the initial setting time of cement. If it exceeds the above time, a retarder should be added.

[0051] Third: After the mixing pile 1 is bored, the three-axis mixing pile machine is immediately removed and a prefabricated pile static press is set up.

[0052] Fourth: The static press machine is corrected and positioned so that the center of the precast pile coincides with the center of the mixing pile 1, and the precast pile solid square pile 4 or hollow round pile 5 is pressed in. If the precast pile is a hollow round pile 5, before pressing in the hollow round pile 5, a closed steel pile tip 8 needs to be welded at the bottom of the pile to seal the bottom, and the elevation of the pile bottom needs to be pressed to the bottom elevation of the pre-mixed hole.

[0053] Fifth: After the current single pile driving construction is completed, the next pile construction can be carried out. When the prefabricated pile is a hollow round pile 5, the subsequent excavation to the pile top design elevation, it is necessary to pour the pile bottom core filling concrete 6, the depth is not less than 1.5m, and then pour the pile top core filling concrete 7, the depth of the pressure bearing is not less than 1.5m, and the pull-out resistance is not less than 3.0m.

[0054] The precast pile construction method for a specific geological condition provided by the embodiment of the present invention is different from the traditional method mainly in the precast pile design stage and the precast pile construction stage: 1. Design stage: Precast piles use thick sand layers as bearing layers, which are dense in the middle and deep into the bearing layers, and the depth of the bearing layers is not less than 10.0m. In traditional design methods, the characteristic value of the bearing capacity of a single pile is obtained by directly calculating the side resistance and end resistance of the precast pile according to the standard formula. Due to the soil squeezing effect of precast piles, it is difficult for the post-pressed precast piles to reach the design elevation for the first time, and re-pressing is required. Sometimes, even if the pile pressure meets the design requirements, it is difficult to reach the design elevation. In this case, it is necessary to cut the piles; sometimes, when the pile pressure reaches the design elevation, the pile pressure does not meet the requirements, and in this case, the piles need to be connected. The novel design method of the volume of the present invention introduces a mixing pile 1 process. The calculation of the characteristic value of the bearing capacity of a single pile requires multiple calculations and comparisons. The first is to form an integral pile according to cement soil and precast piles, and calculate the side resistance and end resistance according to the diameter of the integral pile; the second is to calculate the side resistance and end resistance between the precast pile and the cement soil pile; the third is to calculate the bearing capacity of the precast pile body. The bearing capacities calculated by the three methods are taken as the characteristic value of the bearing capacity of the single pile. This design method is safer and reduces the risks of cutting and connecting precast piles, and does not require re-pressing.

[0055] 2. Construction phase: A three-axis mixer is used to wet-work the mixing hole in advance. The diameter of the hole is 200mm larger than the precast pile, and the depth of the hole is the same as the design elevation of the precast pile. The amount of cement added during mixing is not less than 15%. After obtaining the mixing pile 1, the three-axis mixer is removed. Before the cement soil is initially set, the precast pile is pressed into the precast pile with a static press. The precast pile is mainly controlled by the design elevation and supplemented by the pile pressing force. The pile pressing force does not need to reach 2.4 times the characteristic value of the single pile bearing capacity of the traditional precast pile, but only needs to reach 1.0~1.6 times the characteristic value. Since the soil layer is mixed and softened in advance, the precast pile can be easily pressed to the design elevation, so there will be no problem of pile cutting, which reduces the construction difficulty and improves the construction efficiency. Since the design elevation is mainly controlled, the pile pressing force requirement is not high, and there is no need to re-press to cause the pile connection problem.

[0056] In summary, the method of the present invention solves the problems of pile connection and pile cutting in traditional prefabricated pile construction, simplifies the construction process, improves construction quality and efficiency, and reduces engineering cost.

[0057] It should be noted that in the above embodiments, the description of each embodiment has its own emphasis, and for parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0058] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0059] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for constructing prefabricated piles in a specific geological situation, characterized in that: include: S1, obtaining design parameters, and determining parameters of the precast pile and the mixing hole according to the design parameters; S2, with the goal of achieving the parameters of the mixing hole, the mixing hole is drilled downward with the pile pressing point as the mixing center, and the mixing pile is obtained through wet operation of the mixer; S3, before the cement slurry in the mixing pile initially sets, the selected prefabricated pile is pressed into the mixing pile until the design parameters are reached.

2. The method for constructing prefabricated piles for specific geological conditions according to claim 1, characterized in that: In step S1, obtaining design parameters includes: S101, determine the characteristic design value of the single pile bearing capacity based on the designed column / wall bottom internal force; S102, calculating the effective pile length of a single precast pile according to the characteristic design value of the single pile bearing capacity and the pile foundation parameters of the current geological exploration hole in the geological exploration report, and calculating the characteristic values ​​of the single pile bearing capacity in three cases A, B, and C respectively according to the effective pile length: A. Treat the cement soil and precast pile in the mixing hole as an integral pile, and consider the side resistance and end resistance of the integral pile; B. Consider the side resistance of the cement soil and precast piles in the mixing hole, as well as the end resistance of the precast piles; C. Only consider the compressive bearing capacity of the concrete of the precast pile body; The minimum value of the single pile bearing capacity characteristic value under the three conditions is taken to obtain the single pile bearing capacity characteristic estimation value; S103, comparing the estimated value of the single pile bearing capacity characteristic with the designed value of the single pile bearing capacity characteristic, and if the error is within the allowable range, substituting the estimated value of the single pile bearing capacity characteristic into the calculation formula of situation A to back-calculate the pile length, and obtaining an alternative value of the pile length of the current single pile; S104, obtaining pile foundation parameters of all geological exploration holes according to geological exploration data, each geological exploration hole corresponds to a pile driving point, calculating the pile length candidate values ​​corresponding to all pile driving points, and taking the maximum value of all pile length candidate values ​​as the final prefabricated pile length.

3. The method for constructing prefabricated piles for specific geological conditions according to claim 2, characterized in that: In step S102, according to the effective pile length, the characteristic value of the single pile bearing capacity in case A is calculated using formula (1): ………………………………(1)， in, is the characteristic value of the vertical compressive bearing capacity of a single pile, in kN; is the circumference of the pile after mixing treatment, in m; For the The coefficient of increase of characteristic value of side resistance of soil mixing pile, The value of is set based on experience for different soil types; It is the sequence number of soil layers arranged from the ground surface downward within the pile length range; For the Soil layer thickness, in m; For the The characteristic value of the side resistance of the soil mixing pile, in kPa; is the pile end soil resistance increase coefficient, which is taken as 2.0; is the characteristic value of the soil bearing capacity at the pile end, in kPa; It is the cross-sectional area of ​​the treated pile body of the mixing pile, in kPa.

4. The method for constructing prefabricated piles for specific geological conditions according to claim 3, characterized in that: In step S102, according to the effective pile length, the characteristic value of the single pile bearing capacity in case B is calculated using formula (2): …………………………… (2)， in, is the characteristic value of the vertical compressive bearing capacity of a single pile, in kN; is the length of precast pile, in m; is the perimeter of the precast pile, in m; is the characteristic value of the side resistance of the precast pile after mixing treatment, in kPa; The value of is set based on experience for different soil types; is the characteristic value of the end resistance of the soil at the end of the precast pile, in kPa; is the cross-sectional area of ​​the precast pile body, in m 2 , calculate the area according to the outer diameter of the pile.

5. The method for constructing prefabricated piles for specific geological conditions according to claim 4, characterized in that: In step S102, the characteristic value of the single pile bearing capacity in case C is calculated using formula (3): / K…………………………… (3)， in, is the characteristic value of the vertical compressive bearing capacity of a single pile, in kN; is the working condition coefficient, which is determined according to the degree of damage that the pile construction process may cause to the pile body; is the design value of concrete axial compressive strength, in MPa, and is taken according to the standard; It is the conversion coefficient between design value and characteristic value, which is determined based on experience.

6. A method for constructing prefabricated piles for specific geological conditions according to any one of claims 2 to 5, characterized in that: In step S1, the parameters of the precast pile and the mixing hole are determined according to the design parameters, including: S105, determining the design elevation, radial dimensions and pile bottom bearing layer of the precast pile to be constructed at the current pile pressing point according to the precast pile length and foundation burial depth requirements, wherein the design elevation of the precast pile includes the pile bottom elevation and pile top elevation of the precast pile; The drilling depth of the mixing hole is set to be consistent with the design elevation of the precast pile, and the drilling diameter of the mixing hole is larger than the radial dimension of the precast pile.

7. The method for constructing prefabricated piles for specific geological conditions according to claim 6, characterized in that: Step S2 comprises: The mixer uses the pile pressing point as the rotating mixing center, rotates downward to drill mixing holes, and pours cement slurry into the mixing holes while mixing to form mixing piles; The drilling time does not exceed the initial setting time of the cement slurry, the height of the obtained mixing pile is compatible with the design elevation of the precast pile, and the diameter of the mixing pile is larger than the radial dimension of the precast pile.

8. The method for constructing prefabricated piles for specific geological conditions according to claim 7, characterized in that: In step S3, before the cement slurry in the mixing pile initially sets, the selected prefabricated pile is pressed into the mixing pile until the design parameters are reached, including: S301, selecting a precast pile according to the parameters of the precast pile; S302, before the cement slurry in the mixing pile initially sets, align the center of the selected precast pile with the center of the mixing pile, apply a vertical pile-pressing force to the precast pile, and press the precast pile into the mixing pile until the position of the precast pile reaches the designed elevation of the precast pile.

9. The method for constructing prefabricated piles for specific geological conditions according to claim 8, characterized in that: In step S302: If the selected precast pile is a solid square pile, before the cement slurry in the mixing pile initially sets, align the center of the solid square pile with the center of the mixing pile, apply a vertical pile-pressing force to the solid square pile, and press the solid square pile into the mixing pile until the position of the solid square pile reaches the design elevation of the precast pile; If the selected precast pile is a hollow round pile, before the cement slurry in the mixing pile initially sets, a closed steel pile tip is welded to the bottom end of the hollow round pile, the center of the hollow round pile is aligned with the center of the mixing pile, a vertical pile pressing force is applied to the hollow round pile, and the hollow round pile is pressed into the mixing pile until the position of the hollow round pile reaches the design elevation of the precast pile.

10. The method for constructing prefabricated piles for specific geological conditions according to claim 9, characterized in that: In step S302, if the selected precast pile is a hollow round pile, after the position of the hollow round pile reaches the design elevation of the precast pile, the following steps are further included: Pour core-fill concrete at the bottom and top of the hollow circular pile.

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