A design method of a combined retaining structure of a non-excavation pile group and a common pile

Abstract

The application discloses a design method of a non-excavation pile group and ordinary pile combined supporting structure and belongs to the technical field of landslide area anti-slide pile treatment. The anti-slide pile is excavated to the bottom elevation of the pile, micro-pile drilling is performed, a steel pipe is positioned and lowered, the steel pipe is grouted, an anti-slide pile steel reinforcement cage is bound, and the anti-slide pile is poured. The micro-pile hole must be dry drilled without water, and high-pressure air must be used to clean the hole after the hole is formed; the steel pipe and the steel reinforcement should be installed immediately after the drilling is completed, and grouting is performed, the grouting material is cement mortar, the water-cement ratio is 0.40-0.45, the cement-sand ratio is 1:1, the mortar body strength is not less than 35MPa, and after the construction of each group of micro-pile groups is completed, the anti-slide pile project should be constructed immediately to ensure a certain bearing capacity.

Description

Technical Field

[0001] This invention belongs to the field of pile foundation support technology, specifically relating to a design method for non-excavation pile groups and ordinary pile combination support structures. Background Technology

[0002] Slope reinforcement is a frequent problem encountered during highway construction. Improper handling can lead to slope instability and landslides, affecting project progress, causing accidents, and even casualties. Anti-slide piles, as an effective landslide control measure, possess strong anti-slide capabilities, are less likely to disrupt the original landslide structure, and can further verify geological conditions, making them widely used in slope reinforcement projects.

[0003] The mechanism of anti-slide piles is to transfer the remaining sliding force of the landslide to the stable rock layers below or on the sides, thereby achieving the balance and stability of the landslide body. However, due to the complex stress conditions and numerous influencing factors of anti-slide piles, current stress calculation methods still have some discrepancy with actual stress. The design value in engineering is often an upper limit; if the design value differs too much from the maximum stress, it will cause unnecessary waste of resources. In practical engineering applications, the appropriate pile type should be selected based on factors such as landslide type, scale, geological conditions, properties of the sliding bed rock and soil, construction conditions, and schedule requirements.

[0004] For slopes with a surface of limestone fragments mixed with clay and a bedrock of thick limestone layers, ordinary rectangular anti-slide piles with strong anti-slide capacity can be used. However, because they require manual excavation, they have disadvantages such as low construction efficiency and high cost. If micro anti-slide pile groups are used, the construction efficiency will be greatly improved, but their hollow internal structure is easily broken up by the loose clay body of the landslide, thereby weakening their bearing capacity and posing certain safety hazards.

[0005] Regarding the aforementioned types of anti-slide piles, we have found that existing construction technologies for anti-slide piles do not effectively address multiple issues simultaneously, including construction difficulty, cost, and stability. Therefore, a novel anti-slide pile structure is needed to solve these problems. The design of this new structure must fully consider geological environment and topography to ensure it is scientifically sound, safe, and reliable, thereby guaranteeing its sustainable application and promotion in highway construction. Summary of the Invention

[0006] This invention provides a design method for trenchless pile groups and ordinary pile combination retaining structures. The purpose is to fully consider geological environment, topography and other factors to provide a brand-new retaining structure that is scientific, reasonable and safe, so as to ensure its sustainable application and promotion in the field of highway construction.

[0007] Therefore, the present invention adopts the following technical solution: A design method for trenchless pile groups and ordinary pile combined retaining structures includes the following steps: 1) Conduct geological surveys of the landslide area to be constructed, and calculate the landslide thrust based on the shear strength index of the soil and rock mass at the landslide geological section and sliding surface; 2) Based on the magnitude of the landslide thrust and the geological structure, it is proposed that the entire pile be constructed using ordinary anti-slide piles as the retaining structure. The parameters of the ordinary anti-slide piles are proposed, including the planar position, cross-sectional dimensions and pile length parameters. 3) Reference Figure 9 The proposed length parameters for ordinary anti-slide piles are divided into two parts, H1 and H2, where H1 is the upper part of the ordinary anti-slide pile and H2 is the lower part; H' is the length of the embedded section of the ordinary pile. The portion of length H2 will be subsequently replaced by a trenchless pile group. Considering the geological properties and economic benefits, the value of H2 follows the following principles: 1 / 5(H1+H2)≤H2≤1 / 3(H1+H2), H2≤1 / 2H' 4) Determine the calculated width of the piles based on the proposed ordinary anti-slide pile structure, and select the foundation reaction coefficient; 5) Determine the deformation nature of ordinary anti-slide piles, whether they are rigid piles or elastic piles; 6) Calculate the internal forces and deformations of the pile based on its deformation properties; where [M] is the bearing bending moment of the ordinary anti-slide pile, and [V] is the bearing shear force of the ordinary anti-slide pile. Take M as the design bending moment and V as the design shear force. Determine whether the ordinary anti-slide piles meet the requirements, i.e., whether M≤[M] and V≤[V] are satisfied; if not, return to step 2) to redefine the parameters of the ordinary anti-slide piles; if the requirements are met, proceed to the next step. 7) Design reinforcement for the H1 section of the ordinary anti-slide pile; replace the H2 section of the ordinary anti-slide pile with a trenchless pile group composed of micropiles; 8) Calculate the internal forces of each section of the ordinary anti-slide pile with a length of H2 based on the boundary conditions at the bottom of the pile, so as to determine the maximum bending moment and maximum shear force values, which are respectively used as the design bending moment M' and design shear force V' of the trenchless pile group; 9) Based on the above calculation results, using the formula M'≤f y A s (ha) s -a s The bearing bending moment of the trenchless pile group is determined by the formula V'≤f. y 'A s Determine the bearing shear force of the trenchless pile group; Where M' is the design bending moment, V' is the design shear force, and f y f represents the compressive strength of the steel structure. y 'A' represents the shear strength of the steel structure. sThe area of ​​the steel structure on the compression side is given by , h is the height of the concrete section, and a is the area of ​​the steel structure on the compression side. s a is the distance from the resultant point of all longitudinal reinforcement in the tension zone to the tension edge. s 'The distance from the resultant point of all longitudinal reinforcement in the compression zone to the compression edge;' 10) Before setting up a trenchless pile group consisting of micropiles, the anti-slide piles must be excavated to the pile bottom elevation, and then the micropiles must be drilled. The micropiles must be drilled dry without water. Grouting pipes are installed in the boreholes, steel pipes and reinforcing bars are installed, and grouting is performed.

[0008] Furthermore, in step 10), in order to ensure that the grouting fluid inside the micropile borehole is fully saturated, two cuts are reserved at the lower end of the steel pipe pile.

[0009] Furthermore, in step 10), the grouting material is cement mortar with a water-cement ratio of 0.40 to 0.45 and a mortar strength of not less than 35 MPa. The micropile grouting is performed using a return-type low-pressure grouting method.

[0010] Furthermore, the upper part of the micropile group is embedded in the ordinary anti-slide pile body for no less than 3m, and the lower part is buried in the bottom of the pile pit for no less than 6m. After the construction of each group of micropile groups is completed, the anti-slide pile project is immediately constructed to ensure that it has a certain bearing capacity.

[0011] The beneficial effects of this invention are as follows: 1. The retaining structure of this application uses micro-pile groups embedded in ordinary piles, thereby shortening the pile length, reducing the excavation depth, lowering labor costs, and improving construction efficiency. Furthermore, it significantly reduces concrete usage, lowers project costs, and has significant economic benefits. 2. The upper part of the anti-slide pile structure in this application still adopts the ordinary anti-slide pile design. Compared with micro pile groups, it can effectively prevent the gravel and clay in the slope from eroding the hollow part inside, ensuring the bearing capacity of the pile body while reducing the construction cost of the anti-slide pile. Attached Figure Description

[0012] Figure 1 A schematic diagram of the structure of a conventional anti-slide pile of this invention; Figure 2 Schematic diagram of the anti-slip structure of this invention; Figure 3 Schematic diagram of the micropile structure of this invention; Figure 4 Schematic diagram of the grouting pipe structure of this invention; Figure 5 Schematic diagram of the reinforcement structure of the micropile of this invention; Figure 6 Schematic diagram of the cross-section of the micropile structure of this invention; Figure 7 Schematic diagram of the construction location of this invention; Figure 8 Flowchart of this invention; Figure 9 This is a schematic diagram of the pile length of the present invention; In the figure: 1-Anti-slide pile body; 2-Miniature pile group; 3-Main reinforcement; 4-Structural reinforcement; 5-Stirrups; 6-Borehole wall; 7-Steel pipe; 8-Grouting pipe; 9-Cutout; 10-Reinforcing bar; 11-Centering support; 12-Cement mortar; 13-Crushed stone mixed with clay; 14-Thick layer of limestone. Detailed Implementation

[0013] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The present invention provides a design method for trenchless pile groups and ordinary pile combination retaining structures, specifically including the following steps: like Figure 1 and Figure 7 As shown, the anti-slide structure used to treat the slope includes anti-slide piles 1 and a group of micropiles 2. The upper part of the micropiles 2 extends 3m into the interior of the anti-slide piles 1, and the lower part is embedded 6m into the bedrock. Figure 2 As shown, the anti-slide pile body 1 is equipped with two rows of 32mm HRB400 main reinforcement bars 3, 22mm HRB400 structural reinforcement bars 4, and 10mm HRB400 stirrups 5. Two rows of micropiles 2 are set on the compressive and tensile sides respectively. The bearing bending moment of the micropiles is determined by the formula M'=f y A s (ha) s -a s The bearing shear force is determined by V'=f y 'A s Confirmed; such as Figure 3 As shown, the micropile is placed in the 150mm borehole wall 6, with a 32mm grouting pipe 8 at the center. A 28mm HRB400 steel bar 10 is installed outside the grouting pipe 8, and then a 108mm steel pipe 7 is fitted on top. To ensure that the borehole is filled with grouting fluid, two micro-cuts 9 are reserved at the lower end of the steel pipe pile; Figure 4 As shown, the grouting pipe 8 is externally equipped with 6mm HPB300 steel reinforcement centering supports 11, with a spacing of 3m between supports, and 3 supports are set at each cross-section. Each micropile has 3 support cross-sections; as shown Figure 5 and Figure 6 As shown, the micropile is constructed by first fixing a 32mm grouting pipe 8, a 6mm HPB300 steel rebar centering bracket 11, and a 28mm HRB400 steel rebar 10, and then fitting a 108mm steel pipe 7 onto it; as shown Figure 7 As shown, the anti-slide structure, which is composed of the anti-slide pile body 1 and the micro anti-slide pile group 2, is placed in a slope where the bedrock is a thick layer of limestone 14 and the surface is gravel mixed with clay 13.

[0014] The construction sequence of the design method in this application is as follows: excavation of anti-slide piles to the pile bottom elevation → drilling of micropiles → positioning and lowering of steel pipes → grouting of steel pipes → binding of anti-slide pile reinforcement cages → pouring of anti-slide piles. Micropiles must be drilled dry without water, and high-pressure air cleaning must be used after drilling. After drilling, steel pipes and reinforcement should be installed immediately, and grouting should be performed. The grouting material should be cement mortar with a water-cement ratio of 0.40–0.45 and a cement-sand ratio of 1:1. The mortar strength should not be less than 35 MPa. After the completion of each group of micropiles, the anti-slide pile project should be constructed immediately to ensure a certain bearing capacity.

[0015] Example: This embodiment illustrates the application of the design method for a combined trenchless pile group and ordinary pile retaining structure of the present invention at a test site. The original square pile design at this site was changed to a combined structure of ordinary anti-slide piles on top and trenchless pile group below. The specific implementation is shown in the figure below: 1) Conduct geological surveys of the landslide area to be constructed, and calculate the landslide thrust based on the shear strength index of the soil and rock mass at the landslide geological section and sliding surface; When designing the aforementioned combined retaining structure, an engineering geological survey of the landslide site is first required. The deposited mass is of relatively early age, with the surface consisting of limestone fragments interbedded with clay and gravelly silty clay. Near the steep slope, the surface is composed of rocky soil, and the underlying bedrock is limestone, with large isolated limestone boulders visible in some areas. No signs of deformation were observed in the deposited mass on the slope. The calculation parameters are selected as shown in the table below: Recommended values ​​of geotechnical design parameters The landslide thrust is calculated based on the parameters obtained from the geological survey.

[0016] 2) A preliminary design scheme for ordinary anti-slide piles is proposed. The pile length H0 is the sum of the stratum thicknesses, and the pile cross-section dimensions are 2m × 3m. Specific parameters are shown in the table below: 3) The above-mentioned ordinary anti-slide pile design divides the ordinary anti-slide pile into two parts with pile lengths of H1=24m and H2=4m respectively. The bottom part of the ordinary anti-slide pile with H2=4m is the part that will be replaced by a non-excavation pile group later. Taking into account economic benefits and stratum properties, it is recommended to take 1 / 5(H1+H2)≤H2≤1 / 3(H1+H2), H2≤1 / 2H', where H' is the length of the embedded section of the anti-slide pile.

[0017] 4) The subgrade coefficients for each layer are shown in the table below: 5) Based on the foundation coefficient and the cross-sectional form and dimensions of the anti-slide pile, calculate the calculated width and depth of the pile, and determine that the deformation nature of the pile is a rigid pile.

[0018] 6) Using the corresponding calculation method for rigid piles, the internal forces and deformations of ordinary anti-slide piles were calculated. The specific results are shown in the table below: Based on the above calculation results, determine whether the bearing moment [M] of the ordinary anti-slide pile is greater than the design moment M and whether the bearing shear force [V] is greater than the design shear force V, so as to ensure that the bending moment and shear force of the part of the ordinary anti-slide pile replaced by the trenchless pile group can meet the design requirements.

[0019] 7) Design reinforcement for the unreplaced portion of the ordinary anti-slide piles, and design stirrups according to the design bending moment and design shear force: e.g. Figure 2 As shown, two rows of 32mm HRB400 main bars 3, 22mm HRB400 structural bars 4, and 10mm HRB400 stirrups 5 are installed inside the pile body.

[0020] 8) Replace the bottom H2=4m portion of the above-mentioned anti-slide piles with a non-excavation pile group with a pile length of 9m. The upper part of the non-excavation pile group extends 3m into the ordinary pile body, and the lower part is embedded 6m into the bedrock. The non-excavation pile group structure reduces the excavation depth and the amount of concrete used. The original ordinary anti-slide pile concrete pile body is replaced with limestone with better lithology, which improves the stability of the anti-slide pile structure.

[0021] like Figure 2 As shown, the trenchless pile group consists of multiple micropiles, distributed on both the compressive and tensile sides of the anti-slide piles. Figure 5 and Figure 6 As shown, the micropile is assembled by first fixing a 32mm grouting pipe, a 6mm HPB300 steel rebar centering bracket and a 28mm HRB400 steel rebar, and then fitting a 108mm steel pipe on top.

[0022] 9) The maximum bending moment of the bottom section of the ordinary anti-slide pile (H2=4m), 4869 kN·m, and the maximum shear force of 2557 kN, are taken as the design bending moment M' and design shear force V' of the trenchless pile group. Whether the trenchless pile group meets the design requirements is determined using the formulas M'≤fyAs(h-as-as') and V'≤fy'As, where f... y f represents the compressive strength of the steel structure. y 'For shear strength, A s The area of ​​the steel structure on the compression side is given by , h is the height of the concrete section, and a is the area of ​​the steel structure on the compression side. s a is the distance from the resultant point of all longitudinal reinforcement in the tension zone to the tension edge. s 'This represents the distance from the resultant force point of all longitudinal reinforcement in the compression zone to the compression edge.' The calculation results are shown in the table below: 10) Before setting up a trenchless pile group consisting of micropiles, the anti-slide piles must be excavated to the pile bottom elevation, and then the micropiles must be drilled. The micropiles must be drilled dry without water. Grouting pipes are installed in the boreholes, steel pipes and reinforcing bars are installed, and grouting is performed.

Claims

1. A design method for trenchless pile groups and ordinary pile combination retaining structures, characterized in that, Includes the following steps: 1) Conduct geological surveys of the landslide area to be constructed, and calculate the landslide thrust based on the shear strength index of the soil and rock mass at the landslide geological section and sliding surface; 2) Based on the magnitude of the landslide thrust and the geological structure, it is proposed that the entire pile be constructed using ordinary anti-slide piles as the retaining structure. The parameters of the ordinary anti-slide piles are proposed, including the planar position, cross-sectional dimensions and pile length parameters. 3) The proposed length parameters of the ordinary anti-slide piles are divided into two parts, H1 and H2, where H1 is the upper part of the ordinary anti-slide pile and H2 is the lower part; H' is the length of the embedded section of the ordinary pile. The portion of length H2 will be subsequently replaced by a trenchless pile group. Considering the geological properties and economic benefits, the value of H2 follows the following principles: 1 / 5(H1+H2)≤H2≤1 / 3(H1+H2), H2≤1 / 2H' 4) Determine the calculated width of the piles based on the proposed ordinary anti-slide pile structure, and select the foundation reaction coefficient; 5) Determine the deformation nature of ordinary anti-slide piles, whether they are rigid piles or elastic piles; 6) Calculate the internal forces and deformations of the pile based on its deformation properties; where [M] is the bearing bending moment of the ordinary anti-slide pile, and [V] is the bearing shear force of the ordinary anti-slide pile. Take M as the design bending moment and V as the design shear force. Determine whether the ordinary anti-slide piles meet the requirements, i.e., whether M≤[M] and V≤[V] are satisfied; if not, return to step 2) to redefine the parameters of the ordinary anti-slide piles; if the requirements are met, proceed to the next step. 7) Design reinforcement for the H1 section of the ordinary anti-slide pile; replace the H2 section of the ordinary anti-slide pile with a trenchless pile group composed of micropiles; 8) Calculate the internal forces of each section of the ordinary anti-slide pile with a length of H2 based on the boundary conditions at the bottom of the pile, so as to determine the maximum bending moment and maximum shear force values, which are respectively used as the design bending moment M' and design shear force V' of the trenchless pile group; 9) Based on the above calculation results, using the formula M'≤f y A s (ha) s -a s The bearing bending moment of the trenchless pile group is determined by the formula V'≤f. y 'A s Determine the bearing shear force of the trenchless pile group; Where M' is the design bending moment, V' is the design shear force, and f y f represents the compressive strength of the steel structure. y 'A' represents the shear strength of the steel structure. s The area of ​​the steel structure on the compression side is given by , h is the height of the concrete section, and a is the area of ​​the steel structure on the compression side. s a is the distance from the resultant point of all longitudinal reinforcement in the tension zone to the tension edge. s 'The distance from the resultant point of all longitudinal reinforcement in the compression zone to the compression edge;' 10) Before setting up a trenchless pile group consisting of micropiles, the anti-slide piles must be excavated to the pile bottom elevation, and then the micropiles must be drilled. The micropiles must be drilled dry without water. Grouting pipes are installed in the boreholes, steel pipes and reinforcing bars are installed, and grouting is performed.

2. The design method for trenchless pile groups and ordinary pile combination retaining structures according to claim 1, characterized in that, In step 10), in order to ensure that the grouting fluid inside the micropile borehole is full, two cuts are reserved at the lower end of the steel pipe pile.

3. The design method for trenchless pile groups and ordinary pile combination retaining structures according to claim 2, characterized in that, In step 10), the grouting material is cement mortar with a water-cement ratio of 0.40 to 0.45 and a mortar strength of not less than 35 MPa. The micropile grouting is performed using a return-type low-pressure grouting method.

4. The design method for trenchless pile groups and ordinary pile combination retaining structures according to claim 3, characterized in that, The micropile group is embedded at least 3m into the upper part of the ordinary anti-slide pile body and buried at least 6m into the bottom of the pile pit. After the construction of each micropile group is completed, the anti-slide pile project is immediately constructed to ensure that it has a certain bearing capacity.

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