Sand soil pile foundation cement mixing pile reinforcing structure and construction method

Abstract

The application discloses a sandy soil pile foundation cement mixing pile reinforcing structure and a construction method, a closed ring-shaped mixing pile curtain is first constructed, the sandy soil around the pile is solidified before hole forming, a rigid ring-shaped retaining wall is formed, hole collapse, piping and quicksand in hole forming of the sandy soil pile foundation are completely eliminated, and hole forming quality is stable and reliable. Adjacent mixing piles are mutually engaged to form a continuous closed water stop curtain, groundwater seepage is effectively blocked, and slurry leakage in the hole and sand leakage between the piles are prevented. A pile top corbel beam connects the cement mixing piles into a whole and is rigidly connected with a center bored pile through a cross beam, so that the retaining wall structure and the center bored pile are in cooperative stress, and the overall bearing capacity and stability are improved.

Description

Technical Field

[0001] This invention relates to the field of building foundation construction technology, and in particular to a cement mixing pile reinforcement structure and construction method for sandy soil foundations. Background Technology

[0002] Sandy soils, including silt, fine sand, medium sand, and sandy loam, are characterized by loose particles, lack of cohesion, high permeability, and poor self-stabilizing ability. When constructing bored piles in sandy soil strata using techniques such as rotary drilling, percussion drilling, and rotary shaft drilling, the following problems are highly likely to occur during the hole formation process: 1. Borehole collapse: Sandy soil has no self-stabilizing ability. The borehole wall collapses under the action of lateral earth pressure and water head difference. In mild cases, the borehole diameter may be enlarged; in severe cases, the drill bit may be buried. 2. Piping and quicksand: Under the action of groundwater seepage, sand particles are carried into the hole by the water flow, causing continuous loss of the hole wall and excessive sediment at the bottom of the pile; 3. Excessive concrete volume: Collapse and expansion of the borehole led to the amount of concrete poured far exceeding the design volume, resulting in uncontrolled costs; 4. Defects in pile quality: Collapse of the hole, sediment leading to pile breakage, mud inclusion, and diameter reduction are among the quality accidents.

[0003] The existing processing method has the following drawbacks: 1. Slurry wall protection: It increases the specific gravity and viscosity of bentonite slurry for wall protection, but its effect on pure sandy soil is limited. The slurry is prone to leakage and requires a large-scale slurry circulation system. The discharge of slurry pollutes the environment. 2. Steel casing follow-up: Steel casing sinks to protect the wall, but in sandy soil, the casing sinks with high frictional resistance and is easy to get stuck, and it cannot follow up to the deep part, so the deep hole wall still cannot be protected. 3. Cement-soil mixing pile wall protection, such as the national construction method "Construction Method for Strengthening Weak Hole Walls of Rotary Drilling Piles with Cement-Soil Mixing Piles": Some construction methods and equipment exist, but most are single-point technologies, either for grout loss in water-rich sand layers or for soft soil foundation reinforcement. There is still a lack of methods specifically for the "construction of sandy soil pile foundations".

[0004] Therefore, it is necessary to develop a cement mixing pile reinforcement structure and construction method for sandy soil pile foundations to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to design a cement mixing pile reinforcement structure and construction method for sandy soil pile foundation in order to solve the above problems.

[0006] The present invention achieves the above objectives through the following technical solutions: A cement-mixing pile reinforcement structure for sandy soil foundations includes: Circular cement mixing pile curtain; Central bored pile; The central bored pile is placed at the center of the annular cement mixing pile curtain. The lower ends of both the annular cement mixing pile curtain and the central bored pile pass through the sandy soil layer and are placed in the stable bearing layer. The pile top capping beam is cast at the top of the annular cement mixing pile curtain. Multiple crossbeams; the first end of the crossbeam is anchored to the top cap beam of the pile, and the second end of the crossbeam is anchored to the central bored pile.

[0007] Specifically, the annular cement mixing pile curtain includes multiple cement mixing piles forming a ring, with adjacent cement mixing piles connected by interlocking sections.

[0008] Preferably, the occlusal width of the occlusal segment is 100-200mm.

[0009] Preferably, the inner diameter of the annular cement mixing pile curtain is 200-400 mm larger than the diameter of the central bored pile.

[0010] Preferably, the bottom of the cement mixing pile extends at least 1m below the stable bearing layer.

[0011] Preferably, the diameter of the cement mixing pile is 500-600mm, and the number is 12-20.

[0012] Preferably, there are four crossbeams, evenly distributed around the central bored pile.

[0013] A construction method for cement-mixed pile reinforcement structure for sandy soil foundation includes the following steps: S1. Site leveling and surveying: Mark the center of the central bored pile to be constructed and the ring line of the annular cement mixing pile curtain on the sandy soil foundation. S2. Construction of curtain mixing piles: Multiple cement mixing piles are arranged along the ring line and constructed using the skip-driving technique. Adjacent cement mixing piles interlock with each other to form a ring-shaped cement mixing pile curtain. The lower end of the ring-shaped cement mixing pile curtain passes through the sandy soil layer and is placed in the stable bearing layer. S3. Curtain pile maintenance: Once the annular cement mixing pile curtain has solidified and reached a certain strength, maintenance shall be carried out. S4. Hole Formation Inside the Ring: Hole formation is carried out at the center of the closed annular cement mixing pile curtain to the designed pile bottom elevation; S5. Lower the reinforcing cage; reserve an anchorage section at the top of the main reinforcement bars of the reinforcing cage that extends into the crossbeam; S6. Pour concrete for the central bored pile; S7. Remove the pile heads of cement mixing piles and central drilled cast-in-place piles, and tie the reinforcing bars of the pile top cap beam to the top of multiple cement mixing piles, and tie the reinforcing bars of multiple cross beams between the reinforcing bars of the central drilled cast-in-place piles and the pile top cap beam. S8. Pour concrete for the pile top cap beam and multiple crossbeams.

[0014] Preferably, the hole forming in step S4 is completed by rotary drilling or rotary excavation.

[0015] Specifically, the sandy soil layer consists of silt, fine sand, medium sand, or sandy silt.

[0016] The beneficial effects of this invention are as follows: (1) Eliminate hole collapse from the source: First, construct a closed ring-shaped mixing pile curtain. Before drilling, solidify the sandy soil around the pile to form a rigid ring wall, which completely eliminates hole collapse, piping and sand flow in the drilling of sandy soil pile foundation, and the drilling quality is stable and reliable.

[0017] (2) Interlocking and sealing, water stop and leakage prevention: Adjacent mixing piles interlock with each other (interlocking width 100-200mm) to form a continuous and closed water stop curtain, effectively blocking groundwater seepage and preventing grout leakage in the hole and sand leakage between piles.

[0018] (3) Integration of curtain wall and engineering piles: The top cap beam connects each cement mixing pile into a whole and is rigidly connected to the central drilled cast-in-place pile through the cross beam, so that the wall structure and the central drilled cast-in-place pile are stressed together, thereby improving the overall bearing capacity and stability.

[0019] (4) No mud wall protection and green environmental protection: The hole forming inside the ring does not need to rely on a large mud circulation system, which reduces the amount of mud used and the discharge, and meets the requirements of green construction.

[0020] (5) Mature technology and easy to promote: It can be constructed using conventional deep mixing pile machinery and grouting pile machinery, without the need for special equipment. The overall cost is low and it is suitable for the promotion of pile foundation projects in various sandy soil areas. Attached Figure Description

[0021] Figure 1 This is a top view of the cement mixing pile reinforcement structure for sandy soil pile foundation in this invention; Figure 2 This is a front view of the cement mixing pile reinforcement structure for sandy soil pile foundation in this invention; Figure 3 This is a schematic diagram of the connection structure of two adjacent cement mixing piles in this invention; Figure 4 This is a schematic diagram of the layout of multiple cement mixing piles in this invention; Figure 5 This is a schematic diagram of the construction method for cement mixing pile reinforcement structure for sandy soil pile foundation.

[0022] In the diagram: 1. Circular cement mixing pile curtain; 11. Cement mixing pile; 12. Interlocking section; 2. Central drilled cast-in-place pile; 21. Reinforcing cage; 3. Pile top cap beam; 4. Sandy soil layer; 5. Stable bearing layer; 6. Crossbeam. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0026] In the description of this invention, it should be understood that the terms "upper," "lower," "inner," "outer," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0027] Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0028] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, terms such as "set" and "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0029] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0030] like Figure 1-3 As shown, a cement mixing pile reinforcement structure for sandy soil pile foundation includes: Annular Cement Mixing Pile Curtain 1; The annular cement mixing pile curtain 1 comprises multiple cement mixing piles 11 arranged in a circular ring, with adjacent cement mixing piles 11 connected by interlocking sections 12. The interlocking width of the interlocking sections 12 is 100-200mm. The bottom of the cement mixing piles 11 penetrates at least 1m below the stable bearing layer 5. The diameter of the cement mixing piles 11 is 500-600mm, and the number is 12-20. 2. The central borehole pile 2 is placed at the center of the annular cement mixing pile curtain 1. The lower ends of the annular cement mixing pile curtain 1 and the central borehole pile 2 pass through the sandy soil layer 4 and are placed in the stable bearing layer 5. The inner diameter of the annular cement mixing pile curtain 1 is 200-400mm larger than the pile diameter of the central borehole pile 2. Pile top capping beam 3; Pile top capping beam 3 is cast on the top of the annular cement mixing pile curtain 1; Four horizontal beams 6; the first end of the horizontal beams 6 is anchored to the top cap beam 3 of the pile, and the second end of the horizontal beams 6 is anchored to the central bored pile 2. The four horizontal beams 6 are evenly distributed around the central bored pile 2.

[0031] like Figure 5 As shown, a construction method for a cement mixing pile reinforcement structure for sandy soil pile foundation includes the following steps: S1. Site leveling and surveying: On the sandy soil foundation, mark the center of the central bored pile 2 to be constructed and the ring line of the annular cement mixing pile curtain 1. S2. Construction of curtain-type mixing piles: Multiple cement mixing piles 11 are arranged along the ring road, and the skip-driving technique (driving one pile every other day) is adopted for construction (e.g., Figure 4 As shown), two adjacent cement mixing piles 11 interlock with each other to form an annular cement mixing pile curtain 1. The lower end of the annular cement mixing pile curtain 1 passes through the sandy soil layer 4 and is placed in the stable bearing layer 5. The sandy soil layer 4 is a layer of silt, fine sand, medium sand or sandy silt. S3. Curtain Pile Maintenance: Curing is carried out after the annular cement mixing pile curtain 1 has solidified and reached a certain strength. After solidification, the annular cement mixing pile curtain 1 forms a rigid annular protective wall with good water stability, preventing sandy soil from flowing into the hole from the source, thus preventing hole collapse and piping. S4. Hole Formation within the Ring: Hole formation (using rotary drilling or rotary excavation) is carried out at the center of the closed annular cement mixing pile curtain 1 to the designed pile bottom elevation. Since the hole wall of the hole formed within the ring is already supported by the solidified curtain, there is no need to rely on mud wall protection or steel casing during the hole formation process, and the hole formation quality is stable. S5. Lower the reinforcing cage; reserve an anchorage section at the top of the main reinforcement bars of the reinforcing cage that extends into the crossbeam; S6. Pour concrete for the central bored pile 2; S7. Remove the pile head of the cement mixing pile 11, and tie the reinforcing bars of the pile top cap beam 3 to the top of the multiple cement mixing piles 11. Tie the reinforcing bars of multiple cross beams 6 between the reinforcing bars of the central drilled cast-in-place pile 2 and the pile top cap beam 3. S8. Pour concrete for the pile top capping beam 3 and the four crossbeams 6. The pile top capping beam 3 and the four crossbeams 6 connect the cement mixing pile 11 and the central bored pile 2 into a whole, and are rigidly connected to the pile top of the central bored pile. The capping beam makes the annular curtain and the engineering piles form an integral load-bearing system, improving the overall rigidity and sealing of the curtain, and bearing the transmission and distribution of the pile top load.

[0032] In some embodiments, the cement mixing pile uses a bentonite-cement dual grout. The bentonite forms a mud cake on the borehole wall to prevent the cement grout from flowing out, and the cement content is appropriately increased to 12%-15% to ensure the pile strength in sandy soil.

[0033] Example 1 Construction according to this method: (1) Survey and set out the center of the central bored pile 2 to be constructed and the ring line of the annular cement mixing pile curtain 1 on the sandy soil foundation (the center line radius of the ring is 1200mm). (2) Construction of curtain mixing piles - 16 φ600mm cement mixing piles are arranged along the ring line, with a center distance of 450mm between adjacent piles and an interlocking distance of 150mm; the process of driving one pile every other time is adopted, first driving piles No. 1, 3, 5... 15, and after initial setting, piles No. 2, 4, 6... 16 are added, and the piles are driven first and then interlocked; the cement mixing piles use bentonite-cement slurry with a water-cement ratio of 0.9, the bentonite content is 4% of the cement mass, and the cement content is 14% of the reinforced sand mass; the cement mixing pile is 9m long and penetrates 1m below the stable bearing layer. (3) Curing and shaping of curtain piles. (4) Drilling holes in the curtain ring to a pile bottom elevation of 12m. (5) Lower the reinforcing cage, with the top of the main reinforcing bars of the cage reserved for anchorage sections extending into the capping beam. (6) Pour underwater concrete for the central bored pile. (7) Remove the pile head to the design elevation. (8) Pour the ring-shaped capping beam (900mm wide and 600mm high), with ring-shaped longitudinal reinforcing bars and stirrups inside the capping beam. The main reinforcing bars of the central bored pile are anchored into the crossbeam with an anchorage length of not less than 35 times the diameter of the reinforcing bars.

[0034] Example 2 The difference between this embodiment and Embodiment 1 is that in step (4), when drilling inside the ring, low-density mud is still used to protect the wall, keeping the mud level inside the hole at least 1m above the groundwater level outside the hole, and the mud density is controlled at 1.15-1.25. This method further improves the stability of the deep hole wall and is suitable for working conditions with high groundwater levels and particularly loose sand layers.

[0035] Example 3 The difference between this embodiment and Embodiment 1 is that the interlocking parameters are adjusted according to the particle size distribution and permeability coefficient of the sandy soil. For silty fine sand strata, the center-to-center distance between adjacent mixing piles is 400mm and the interlocking distance is 200mm; for medium-coarse sand strata, the center-to-center distance between adjacent mixing piles is 480mm and the interlocking distance is 120mm. By adjusting the interlocking width, the number of mixing piles is optimized and the cost is reduced while ensuring the curtain's sealing performance.

[0036] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A cement mixing pile reinforcement structure for sandy soil pile foundations, characterized in that, include: Circular cement mixing pile curtain (1); The central borehole cast-in-place pile (2) is placed at the center of the annular cement mixing pile curtain (1). The lower ends of the annular cement mixing pile curtain (1) and the central borehole cast-in-place pile (2) pass through the sandy soil layer (4) and are placed in the stable bearing layer (5). The pile top capping beam (3) is cast on the top of the annular cement mixing pile curtain (1); Multiple crossbeams (6); the first end of the crossbeam (6) is anchored to the top cap beam (3) of the pile, and the second end of the crossbeam (6) is anchored to the central bored pile (2).

2. The cement mixing pile reinforcement structure for sandy soil pile foundation according to claim 1, characterized in that, The annular cement mixing pile curtain (1) includes multiple cement mixing piles (11) forming a circular ring, with adjacent cement mixing piles (11) connected by interlocking sections (12).

3. The cement mixing pile reinforcement structure for sandy soil pile foundation according to claim 2, characterized in that, The occlusal width of the occlusal segment (12) is 100-200mm.

4. The cement mixing pile reinforcement structure for sandy soil pile foundation according to claim 1, characterized in that, The inner diameter of the annular cement mixing pile curtain (1) is 200-400 mm larger than the diameter of the central borehole cast-in-place pile (2).

5. The cement mixing pile reinforcement structure for sandy soil pile foundation according to claim 2, characterized in that, The bottom of the cement mixing pile (11) should be at least 1m below the stable bearing layer (5).

6. The cement mixing pile reinforcement structure for sandy soil pile foundation according to claim 2, characterized in that, The diameter of the cement mixing piles (11) is 500-600mm, and the number is 12-20.

7. The cement mixing pile reinforcement structure for sandy soil pile foundation according to claim 1, characterized in that, There are four crossbeams (6), which are evenly distributed around the central bored pile (2).

8. A construction method for a cement-mixing pile reinforcement structure for sandy soil pile foundation according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Site leveling and surveying: On the sandy soil foundation, mark the center of the central bored pile (2) to be constructed and the ring line of the annular cement mixing pile curtain (1); S2. Construction of curtain mixing piles: Multiple cement mixing piles (11) are arranged along the ring line and the skip-driving process is adopted. Two adjacent cement mixing piles (11) interlock with each other to form a ring-shaped cement mixing pile curtain (1). The lower end of the ring-shaped cement mixing pile curtain (1) passes through the sandy soil layer (4) and is placed in the stable bearing layer (5). S3. Curtain pile maintenance: Once the annular cement mixing pile curtain (1) has solidified and reached a certain strength, maintenance shall be carried out. S4. Hole forming inside the ring: Hole forming is carried out at the center of the closed annular cement mixing pile curtain (1) to the designed pile bottom elevation; S5. Lower the steel cage (21); the top of the main reinforcement of the steel cage (21) is reserved for the anchorage section extending into the crossbeam (6); S6. Pour concrete for the central bored pile (2); S7. Remove the pile heads of cement mixing piles (11) and central drilled cast-in-place piles (2), and tie the reinforcing bars of the pile top cap beam (3) to the top of multiple cement mixing piles (11), and tie the reinforcing bars of multiple cross beams (6) between the reinforcing bars of the central drilled cast-in-place piles (2) and the pile top cap beam (3). S8. Pour concrete for the pile top cap beam (3) and multiple crossbeams (6).

9. The construction method of a cement mixing pile reinforcement structure for sandy soil pile foundation according to claim 8, characterized in that, The hole formation in step S4 is completed by rotary drilling or rotary excavation.

10. The construction method of a cement mixing pile reinforcement structure for sandy soil pile foundation according to claim 8, characterized in that, The sandy soil layer (4) is a layer of silt, fine sand, medium sand or sandy silt.

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