Construction device and method for soft foundation replacement sand pile sleeve punching cement mixing pile

Abstract

The application discloses a construction device and a construction method for replacing sand pile with cement mixing pile in soft foundation, and belongs to the technical field of foundation treatment equipment. Technical scheme points of the application include a pile machine chassis, a pile machine frame, a power head trolley sliding along the pile machine frame, a lifting driving module, a rotary driving unit arranged on the power head trolley, a composite drilling tool assembly suspended below the rotary driving unit and a material supply system. The composite drilling tool assembly comprises coaxially arranged outer mixing drill pipes and central sand discharge pipes which can move relatively. The application integrates sand pile construction and cement mixing pile construction, and through one-time drilling and lifting operation, composite processes of drilling and soil discharge, sand replacement and jet grouting mixing can be completed synchronously, thereby greatly improving construction efficiency, reducing equipment transfer cost and construction period, and ensuring the pile forming quality and concentricity of the sand pile core and the cement soil pile body. The formed composite pile body structure is stable and has excellent bearing performance.

Description

Technical Field

[0001] This invention relates to the field of foundation treatment equipment technology, and in particular to a construction device and method for driving cement mixing piles with sand piles for soft soil replacement. Background Technology

[0002] In civil engineering construction, soft soil foundations such as silt, silty soil, and fill soil are frequently encountered. These foundations are characterized by high water content, high compressibility, low shear strength, and poor bearing capacity. If used directly as the foundation for buildings without treatment, excessive settlement may occur, potentially leading to structural instability and failure. Therefore, reinforcing soft soil foundations is an indispensable and crucial step in engineering construction. Currently, commonly used methods for soft soil foundation treatment include sand pile methods and cement-soil mixing pile methods.

[0003] The sand pile method involves drilling holes in soft soil foundations using methods such as vibration, impact, or water jetting, then filling the holes with coarse-grained materials such as sand or gravel, and compacting them to form large-diameter sand piles. The main function of sand piles is to form vertical drainage channels, accelerating the consolidation and drainage of the soft soil layer under load, thereby improving the strength and stability of the foundation. The cement-soil mixing pile method, also known as the deep cement mixing method (DCM), uses specialized deep mixing machinery to forcibly mix cement or lime and other solidifying agents with soft soil deep within the foundation. Through a series of physicochemical reactions, the soft soil hardens, forming cement-soil piles with integrity, water stability, and a certain strength, thereby improving the bearing capacity of the foundation and reducing settlement.

[0004] In current engineering practice, when it is necessary to simultaneously utilize the drainage consolidation effect of sand piles and the load-bearing reinforcement effect of cement-soil piles to form a composite foundation, operators often face a series of difficulties. Traditional construction techniques completely separate the construction of these two types of piles. Specifically, the construction team first needs to deploy a set of sand pile construction equipment, such as a tracked vibratory compactor or a casing drilling rig, to construct sand piles at designated locations. After completing the construction of all sand piles in an area, this equipment needs to be removed from the site. Subsequently, another completely different cement mixing pile machine, such as a dual-axis or triple-axis cement mixing pile machine, is deployed to construct cement-soil mixing piles around or at the locations of the already constructed sand piles. This series of operations has at least two significant drawbacks and shortcomings.

[0005] First, the construction is inefficient, has a long construction period, and is costly. Because it requires two independent construction machinery systems, involving two separate processes of equipment entry, installation, commissioning, construction, and final removal, the entire process not only consumes a significant amount of time but also significantly increases equipment rental, transportation, and labor costs. The coordination between the two processes can also be delayed due to weather, equipment scheduling, and other factors, further extending the overall construction period. Furthermore, with two sets of equipment operating on the same small construction site, they are prone to mutual interference, making site planning and management difficult and consequently reducing overall operational efficiency.

[0006] Secondly, the quality of pile formation is difficult to guarantee, and the synergistic performance of the composite pile body is poor. Because sand piles and cement-soil mixing piles are constructed in two separate stages, the alignment accuracy of the pile positions is difficult to control. The later-constructed cement-soil mixing piles may deviate from their pre-set relative positions with the sand piles, resulting in irregular cross-sections and uneven stress distribution in the composite pile, failing to achieve the ideal synergistic working state designed for the project. During the drilling process of the cement-soil mixing piles, the mixing blades may disturb or even damage the already formed sand pile structure, affecting its compaction and drainage performance. Conversely, if the cement-soil mixing piles are constructed first, and then sand piles are constructed inside or beside them, the same disturbance problem exists. This non-integrated construction method results in a weak interface between the sand pile core and the surrounding cement-soil pile body, affecting both the integrity and bearing capacity, making it difficult to form a structurally complete and reliable composite pile body, ultimately affecting the overall effect and long-term stability of the foundation reinforcement. Current technology lacks an integrated and efficient specialized equipment that can organically combine the sand pile replacement and cement-soil mixing processes, completing the composite pile construction in a single operation. Summary of the Invention

[0007] To address the aforementioned problems, this invention proposes a construction device for driving cement mixing piles with sand piles for soft soil replacement, thereby more accurately solving the problems mentioned in the background art.

[0008] This invention is achieved through the following technical solution: This invention proposes a construction device for driving cement mixing piles using sand piles for soft soil replacement, comprising a pile driver chassis, a pile driver frame mounted on the chassis, a power head trolley that slides vertically along a guide structure of the pile driver frame, and a lifting drive module for driving the power head trolley to rise and fall. It also includes: a rotary drive unit mounted on the power head trolley, the rotary drive unit having a vertical through-hole at its center and a rotatable hollow output flange at its bottom; and a composite drilling assembly suspended below the rotary drive unit, the composite drilling assembly comprising: a coaxial... The system includes an outer mixing drill rod and a central sand discharge pipe; the upper end of the outer mixing drill rod is fixedly connected to a hollow output flange for rotation by a rotary drive unit; the central sand discharge pipe passes through the vertical through hole of the rotary drive unit and the interior of the outer mixing drill rod, and is fixed to the power head trolley to prevent rotation; and a material supply system, including a sand storage hopper connected to the upper end of the central sand discharge pipe, and a cement slurry input pipe fluidly connected to the annular cavity between the outer mixing drill rod and the central sand discharge pipe, the sand storage hopper being fixed to the top of the power head trolley by a bracket.

[0009] Preferably, the piling machine frame includes two main columns that are parallel to each other and vertically fixed to the piling machine chassis, and guide rails are provided on the opposite side walls of the main columns; the power head trolley slides in cooperation with the guide rails through guide rollers set on it.

[0010] Preferably, the rotary drive unit includes a drive motor and a hollow reducer that is connected to the drive motor for transmission; the hollow reducer is fixedly installed on the mounting platform of the power head trolley, and the hollow output flange is the output end of the hollow reducer.

[0011] Preferably, a composite drill bit is provided at the bottom of the composite drill assembly, and the composite drill bit is fixedly welded to the end of the outer mixing drill rod; the composite drill bit is provided with several cement slurry spray outlets, and the cement slurry spray outlets are connected to the annular cavity between the outer mixing drill rod and the central sand discharge pipe.

[0012] Preferably, a sand discharge valve is hinged at the bottom outlet of the central sand discharge pipe. The sand discharge valve is used to open outward under the gravity of the sand inside the central sand discharge pipe.

[0013] Preferably, the lifting drive module includes a winch, a traction rope, a directional wheel, and a traction head. The traction rope is wound around the outer wall of the winch, slides on the surface of the directional wheel, and its end is connected to the traction head. The traction head is connected to the power head pulley, and the directional wheel is installed above the pile driver frame.

[0014] Preferably, it also includes a rotary sealing joint disposed on the rotary drive unit; the rotary sealing joint has a stationary end connected to the cement slurry input pipe and a rotary end communicating with the annular cavity between the outer mixing drill rod and the central sand discharge pipe.

[0015] Preferably, a thrust bearing assembly is provided between the housing of the rotary drive unit and the central sand discharge pipe. The thrust bearing assembly is used to support the central sand discharge pipe and allow the rotary drive unit to rotate relative to the central sand discharge pipe.

[0016] Preferred, the outer wall of the outer mixing drill rod is spirally welded with mixing blades for cutting and mixing the soil. When the rotary drive unit is working, the hollow output flange drives the outer mixing drill rod to rotate around its own axis, while the central sand discharge pipe remains axially stationary under the constraint of the power head trolley.

[0017] The construction method of the construction device for driving cement mixing piles with sand piles for soft soil replacement includes the following steps: Start the lifting drive module: The winch works, sliding on the surface of the directional wheel via the traction rope, and the traction head drives the power head trolley to descend vertically along the guide structure of the pile driver frame.

[0018] Start the rotary drive unit: The drive motor rotates, which drives the hollow reducer through the transmission connection. The hollow output flange of the hollow reducer drives the outer stirring drill rod to rotate around its own axis. Since the central sand discharge pipe is fixed to the power head trolley, it remains axially stationary under the constraint of the power head trolley.

[0019] Drilling and mixing of the composite drill bit assembly: As the power head trolley descends, the rotating outer mixing drill rod drives the spirally welded mixing blades on its outer wall to cut and mix the soil. Simultaneously, the composite drill bit also penetrates the soil for mixing. During this process, cement slurry flows through the cement slurry inlet pipe into the annular cavity between the outer mixing drill rod and the central sand discharge pipe, and then exits from the cement slurry outlet on the composite drill bit, fully mixing with the soil to form a cement mixing pile.

[0020] Opening the sand discharge valve: When the composite drill assembly is drilled to the designed depth, the sand in the central sand discharge pipe exerts downward pressure on the sand discharge valve under its own gravity, causing the sand discharge valve to open outward.

[0021] Sand material discharge forms sand piles: Sand material is discharged from the bottom outlet of the central sand discharge pipe through the opened sand discharge valve and enters the central part of the already formed cement mixing pile. As the sand material is continuously discharged, a structure of soft foundation replacement sand piles and cement mixing piles is gradually formed.

[0022] Compared with the prior art, the present invention provides a construction device and method for driving cement mixing piles with sand piles for soft soil replacement, which has the following beneficial effects: 1. This invention achieves simultaneous integrated operation of multiple processes such as drilling, soil removal, replacement and sand filling, and shotcrete mixing by setting up an outer mixing drill rod and a central sand discharge pipe that are coaxially arranged and rotate relative to each other, and setting up independent supply channels for cement slurry and sand for each of them. This integrates the composite pile construction task that traditionally requires two machines and two processes into one operation cycle of a single machine, thereby achieving the effect of significantly shortening the construction period, reducing equipment relocation, and reducing construction costs.

[0023] 2. By fixing the central sand discharge pipe and driving only the outer mixing drill rod to rotate and mix, this invention achieves precise and stable delivery of sand to the center of the pile hole while simultaneously cutting and mixing the surrounding soil with cement slurry. This ensures the concentricity of the sand pile core and the cement-soil pile body and the quality of the pile formation, resulting in a complete composite pile structure with high bearing capacity. It completely solves the problems of pile position deviation and structural defects caused by step-by-step construction.

[0024] 3. This invention integrates core operating components such as the sand storage hopper and the rotary drive unit onto a power head trolley that can slide vertically along the piling machine frame, and controls its lifting and lowering by an independent lifting drive module. This achieves precise feeding and lifting control of the drilling tool. The overall structure is compact, the transmission chain is clear, and the degree of automation is high, thus achieving the effects of simple operation, precise construction control, and strong adaptability to different geological conditions and pile diameter and length designs. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall three-dimensional structure of the present invention.

[0026] Figure 2 This is a schematic diagram of the overall three-dimensional structure of the present invention from another perspective.

[0027] Figure 3 This is a schematic diagram of the main structure of the present invention.

[0028] Figure 4 This is a side view of the structure of the present invention.

[0029] Figure 5 This is a top view of the structure of the present invention.

[0030] Figure 6 This is a partially enlarged schematic diagram showing the connection between the lifting drive module and the power head trolley of the present invention.

[0031] Figure 7 This is a schematic cross-sectional view of the composite drill bit portion of the present invention.

[0032] Figure 8 This is a partially enlarged schematic diagram of the connection between the rotary drive unit and the composite drill assembly of the present invention.

[0033] Figure 9 This is a partial structural diagram of the outer stirring drill rod of the present invention.

[0034] Component numbering list in the diagram: 1. Pile driver chassis; 2. Pile driver frame; 3. Lifting drive module; 4. Power head trolley; 5. Rotary drive unit; 6. Material supply system; 7. Composite drilling tool assembly; 21. Main column; 31. Winch; 32. Traction rope; 33. Directional wheel; 34. Traction head; 42. Installation platform; 51. Drive motor; 52. Hollow reducer; 53. Hollow output flange; 61. Sand storage hopper; 62. Cement slurry input pipe; 71. Outer mixing drill rod; 72. Central sand discharge pipe; 73. Mixing blades; 74. Composite drill bit; 75. Cement slurry spray outlet; 76. Sand discharge valve; 81. Rotary sealing joint; 82. Thrust bearing assembly. Detailed Implementation

[0035] A pile driver frame 2 is securely installed on the pile driver chassis 1 using high-strength bolts or integral welding. The pile driver frame 2 is the main load-bearing structure of the entire device, and its form is a tall gantry or mast structure. Specifically, as... Figure 2 and Figure 3 As shown, the piling machine frame 2 includes two parallel main columns 21 extending vertically. These two main columns 21 are welded from large-section rectangular steel pipes or H-beams and connected by a top crossbeam and a bottom base, forming a highly rigid frame structure to ensure sufficient stability and anti-overturning capacity during the lowering and raising of the drilling tool. Precision guide rails, serving as guiding structures, are machined or installed on the opposing inner walls of the two main columns 21. The surfaces of these guide rails are hardened and ground, exhibiting high hardness and high straightness, providing a precise reference for the smooth vertical movement of the power head trolley 4.

[0036] The power head trolley 4 is a mobile platform carrying the core working unit, and its structure is a robust steel frame or box. On the side of the power head trolley 4 facing away from the main column 21, multiple sets of guide rollers are symmetrically installed. The rim shape of these guide rollers matches the cross-section of the guide rail on the main column 21, and they fit tightly with the guide rail through rolling contact. Compared with sliding guides, this rolling guide pair design has the advantages of low friction, smooth movement, low wear, and high guiding accuracy, ensuring that the power head trolley 4 can still slide precisely and vertically along the guide structure of the pile driver frame 2 without swaying even when subjected to huge axial and torsional loads.

[0037] The core drilling and material conveying functions are accomplished collaboratively by the rotary drive unit 5, the composite drill assembly 7, and the material supply system 6, all integrated on the power head trolley 4.

[0038] Please refer to this carefully. Figure 8A horizontal mounting platform 42 is installed on the power head trolley 4. The rotary drive unit 5 is securely fixed to this mounting platform 42. The core internal components of the rotary drive unit 5 include a drive motor 51 and a hollow reducer 52 connected to it. The drive motor 51 can be a variable hydraulic motor or a high-power variable frequency motor, capable of providing powerful, speed-adjustable torque output. The output shaft of the drive motor 51 is connected to the input end of the hollow reducer 52 via a coupling or gear. The hollow reducer 52 is one of the key components of this device, characterized by a through vertical hole in both the output shaft and the center of the entire reducer housing. This reducer typically employs a planetary gear system or a cycloidal pinwheel structure to achieve a large reduction ratio and torque amplification within a compact space. The housing of the hollow reducer 52 is securely fixed to the mounting platform 42 with bolts, and its output end is a rotatable hollow output flange 53.

[0039] The composite drill assembly 7 is suspended below the rotary drive unit 5; its structure is ingenious and its functions are multifaceted. For example... Figure 7 and Figure 8 As shown, the assembly includes an outer stirring drill rod 71 and a central sand discharge pipe 72 coaxially disposed inside it. The upper flange of the outer stirring drill rod 71 is fastened to the hollow output flange 53 of the rotary drive unit 5 by multiple high-strength bolts. Therefore, when the drive motor 51 is working, its power is transmitted to the hollow output flange 53 via the hollow reducer 52, thereby driving the entire outer stirring drill rod 71 to rotate around its own central axis. The outer stirring drill rod 71 is made of high-strength wear-resistant alloy steel pipe, and its outer wall, as shown... Figure 9 As shown, continuous or intermittent mixing blades 73 are spirally welded along the entire or partial length. The pitch, angle, and width of these mixing blades 73 are carefully designed to achieve powerful cutting, crushing, and agitation of the soft soil foundation as the drill rod rotates, and to fully mix with the subsequently injected cement slurry.

[0040] The central sand discharge pipe 72 passes through the vertical through-hole of the hollow reducer 52 and further through the entire internal space of the outer stirring drill rod 71, remaining coaxial with it. Unlike the outer stirring drill rod 71, the upper end of the central sand discharge pipe 72 is securely connected to a non-rotating component of the power head trolley 4, such as the mounting platform 42 or the trolley frame itself, via a specially designed fixed bracket or flange. This connection method ensures that the central sand discharge pipe 72 remains axially stationary throughout the entire operation and does not rotate with the outer stirring drill rod 71. To support the weight of the central sand discharge pipe 72 and the gravity of the sand inside the pipe, and to isolate the torque transmission of the rotating components, a precision thrust bearing assembly 82 is installed between the upper part of the housing of the hollow reducer 52 of the rotary drive unit 5 and the outer wall of the central sand discharge pipe 72. The inner ring of this thrust bearing assembly 82 is fixed to a collar on the central sand discharge pipe 72, and the outer ring is fixed to the reducer housing. It bears a huge axial load from the central sand discharge pipe 72, while its rolling element structure allows the gearbox housing (i.e., the rotary drive unit 5) to rotate freely and with low friction relative to the fixed central sand discharge pipe 72.

[0041] Material supply system 6 is responsible for supplying two different materials to the composite drill assembly 7. For example... Figure 4 and Figure 8 As shown, the system includes a sand storage hopper 61 and a cement slurry input pipe 62. A large-capacity sand storage hopper 61 is fixed to the top of the power head trolley 4 by a special bracket, positioned higher than the rotary drive unit 5. The lower outlet of the sand storage hopper 61 is connected to the upper opening of the stationary central sand discharge pipe 72 via a flexible connecting pipe or sealing sleeve, forming an unobstructed gravity discharge channel. Cement slurry is delivered to the power head trolley 4 from a slurry preparation station on the ground via a high-pressure pump and hose. On the trolley, the hose is connected to the cement slurry input pipe 62. The other end of the cement slurry input pipe 62 is connected to a key fluid conversion component—a rotary sealing joint 81. The rotary sealing joint 81 is installed on the side or top of the rotary drive unit 5 and has a complex internal structure, including dynamic and static ring seals. Its stationary end is connected to the cement slurry input pipe 62, while its rotating end is fluidly connected to the annular cavity formed between the outer mixing drill rod 71 and the central sand discharge pipe 72 through an internal channel. In this way, even if the outer mixing drill rod 71 is rotating at high speed, the cement slurry on the ground can still be continuously and leak-free injected into this rotating annular channel.

[0042] At the very bottom of the composite drill assembly 7, such as Figure 7As shown, a specially designed composite drill bit 74 is fixedly welded. This drill bit 74 is integrated with the outer mixing drill rod 71 and rotates with it. The drill bit 74 is equipped with carbide cutting edges or teeth for breaking up the soil and overcoming hard interlayers. The internal structure of the drill bit 74 is hollow, with several cement slurry injection ports 75. The positions and angles of these injection ports 75 are optimized, and they are directly connected to the annular cavity between the outer mixing drill rod 71 and the central sand discharge pipe 72. Therefore, the cement slurry injected via the rotary sealing joint 81 flows downwards along this annular cavity and is finally ejected at high pressure from these injection ports 75, achieving the most efficient mixing with the soil cut and agitated by the drill bit and mixing blades 73 in the area at the bottom of the pile that most needs reinforcement.

[0043] The bottom outlet of the central sand discharge pipe 72 is located in the central area of ​​the composite drill bit 74. At this outlet, a sand discharge valve 76 is movably connected via a hinge. This valve is typically one or two semi-circular metal plates that, under normal conditions, close naturally due to the pressure of the external soil and slurry, sealing the sand discharge port. When the central sand discharge pipe 72 is filled with sand, the weight of the sand column itself exerts downward pressure on the valve 76. This pressure is sufficient to overcome external resistance, pushing the valve 76 to open outward and downward, allowing the sand to be discharged smoothly and forming a sand core in the center of the pile hole. When the sand supply stops or the drill is pulled back, the valve 76 automatically closes, effectively preventing external mud or soil from flowing back into the central sand discharge pipe 72, ensuring the cleanliness of the sand transport channel.

[0044] 1. Positioning and Alignment: The operator drives the construction device and moves it to the designed pile position through the walking mechanism of the pile driver chassis 1, and aligns it precisely.

[0045] 2. Drilling and Grouting: The lifting drive module 3 is activated, and the winch 31 slowly releases the traction rope 32. The power head trolley 4 drives the entire rotary drive unit 5 and the composite drill assembly 7 to begin vertical descent under its own weight and additional pressure. Simultaneously, the drive motor 51 of the rotary drive unit 5 is activated, driving the outer mixing drill rod 71 and the composite drill bit 74 to rotate at high speed. The drill bit 74 and the mixing blades 73 begin cutting, breaking, and mixing the in-situ soft soil. The surface cement slurry pumping system is activated, pumping cement slurry through the cement slurry input pipe 62, the rotary sealing joint 81, and the annular cavity, finally injecting it into the soil through the cement slurry nozzle 75 on the composite drill bit 74. The slurry mixes thoroughly with the stirred soft soil, forming a fluid cement-soil mixture. During this process, the central sand discharge pipe 72 remains stationary, sinking with the drill, while its bottom sand discharge valve 76 remains closed due to external soil pressure.

[0046] 3. Drill to the design elevation: Continue to sink and spray grout until the composite drill bit 74 reaches the designed pile bottom elevation.

[0047] 4. Lifting and Sand Replacement: Stop the sinking and start the lifting drive module 3 to lift the power head trolley 4. During the lifting process, the rotary drive unit 5 continues to work, keeping the outer mixing drill rod 71 rotating to perform secondary mixing on the formed cement-soil column, ensuring uniform mixing and improving the strength of the pile body. At the same time, the sand filling equipment on the ground begins to fill sand into the sand storage hopper 61 at the top of the power head trolley 4. Under the action of gravity, the sand enters the stationary central sand discharge pipe 72 through the sand storage hopper 61, forming a continuous sand column. The weight of the sand column acts on the sand discharge valve 76, pushing it outward. As the composite drill assembly 7 is slowly and uniformly lifted, a cavity gradually forms below it, and the sand is smoothly discharged from the opened valve 76, filling the central area of ​​the pile hole to form a dense sand pile core.

[0048] 5. Pile Completion: When the composite drilling assembly 7 is completely lifted out of the ground, the supply of cement slurry and sand also stops. At this point, a composite pile with a sand core and a cement-soil body is completed in one operation. The device can then be moved to the next pile location, and the above cycle can be repeated.

[0049] The drive motor 51 in the rotary drive unit 5 can employ a multi-motor combined drive scheme. For example, two or four smaller motors can be symmetrically arranged and jointly drive the input end of the hollow reducer 52 through a parallel gear transmission box. This design helps to balance the load, reduce the size and weight of a single motor, and ensures that the remaining motors can still provide some power in the event of a failure of one motor, thereby improving the redundancy and reliability of the system.

[0050] The construction of the mixing blades 73 in the composite drilling assembly 7 can be more diversified. In addition to continuous helical blades, segmented, angle-adjustable paddle-type mixing blades can also be used. By adjusting the installation angle of the blades, their lifting or pressing effect on the soil can be changed, thereby better controlling the intensity and range of mixing and adapting to soils with different cohesion and water content.

[0051] In the material supply system 6, the sand storage hopper 61 can be equipped with an auxiliary feeding device, such as installing a vibrating motor on the hopper wall or setting a screw conveyor on the upper part of the sand discharge pipe 72, to prevent sand with high moisture content from arching or blocking in the hopper or pipe, and to ensure the continuity and stability of sand supply.

[0052] Furthermore, this device can integrate an advanced automated control system. This system includes a PLC controller, a touchscreen human-machine interface, and various sensors (such as depth sensors, rotational torque sensors, slurry flow meters, and sand level gauges). Operators can preset construction parameters such as pile length, drilling speed, lifting speed, rotation speed, and cement slurry injection volume via the touchscreen in the cab. During operation, the PLC controller automatically adjusts the winch speed, drive motor power, and cement slurry pump flow rate based on real-time data feedback from the sensors, achieving closed-loop precise control of the construction process. This ensures that the quality of each pile strictly meets design requirements and records and stores detailed construction data for future verification.

Claims

1. A construction device for driving cement mixing piles with sand piles for soft soil replacement, comprising a pile driver chassis (1), a pile driver frame (2) mounted on the pile driver chassis (1), a power head trolley (4) that slides vertically along the guide structure of the pile driver frame (2), and a lifting drive module (3) for driving the power head trolley (4) to rise and fall, characterized in that, Also includes: The rotary drive unit (5) is mounted on the power head trolley (4). The rotary drive unit (5) has a vertical through hole through its center and a rotatable hollow output flange (53) at its bottom. A composite drill assembly (7), suspended below the rotary drive unit (5), the composite drill assembly (7) comprising: The outer stirring drill rod (71) and the central sand discharge pipe (72) are coaxially arranged; the upper end of the outer stirring drill rod (71) is fixedly connected to the hollow output flange (53) so as to be driven to rotate by the rotary drive unit (5); the central sand discharge pipe (72) passes through the vertical through hole of the rotary drive unit (5) and the interior of the outer stirring drill rod (71), and the central sand discharge pipe (72) is fixed to the power head trolley (4) to keep it from rotating; The material supply system (6) includes a sand storage hopper (61) connected to the upper end of the central sand discharge pipe (72) and a cement slurry input pipe (62) in fluid communication with the annular cavity between the outer stirring drill rod (71) and the central sand discharge pipe (72). The sand storage hopper (61) is fixed to the top of the power head trolley (4) by a bracket.

2. The construction device for driving cement mixing piles with sand piles for soft soil replacement according to claim 1, characterized in that, The pile driver frame (2) includes two main columns (21) that are parallel to each other and vertically fixed on the pile driver chassis (1). The opposing side walls of the main columns (21) are provided with guide rails. The power head trolley (4) slides with the guide rails through guide rollers set on it.

3. The construction device for driving cement mixing piles with sand piles for soft soil replacement according to claim 1, characterized in that, The rotary drive unit (5) includes a drive motor (51) and a hollow reducer (52) that is connected to the drive motor (51) in a transmission manner; the hollow reducer (52) is fixedly installed on the mounting platform (42) of the power head trolley (4), and the hollow output flange (53) is the output end of the hollow reducer (52).

4. The construction device for driving cement mixing piles with sand piles for soft soil replacement according to claim 1, characterized in that, The bottom end of the composite drill assembly (7) is provided with a composite drill bit (74), which is fixedly welded to the end of the outer stirring drill rod (71); the composite drill bit (74) is provided with a plurality of cement slurry spray outlets (75), which are connected to the annular cavity between the outer stirring drill rod (71) and the central sand discharge pipe (72).

5. The construction device for driving cement mixing piles with sand piles for soft soil replacement according to claim 4, characterized in that, A sand discharge valve (76) is hinged at the bottom outlet of the central sand discharge pipe (72). The sand discharge valve (76) is used to open outward under the gravity of the sand material in the central sand discharge pipe (72).

6. The construction device for driving cement mixing piles with sand piles for soft soil replacement according to claim 1, characterized in that, The lifting drive module (3) includes a winch (31), a traction rope (32), a directional wheel (33), and a traction head (34). The traction rope (32) is wound around the outer wall of the winch. The traction rope (32) slides on the surface of the directional wheel (33) and its end is connected to the traction head (34). The traction head (34) is connected to the power head trolley (4). The directional wheel (33) is installed above the pile driver frame (2).

7. The construction device for driving cement mixing piles with sand piles for soft soil replacement according to claim 1, characterized in that, It also includes a rotary sealing joint (81) disposed on the rotary drive unit (5); the rotary sealing joint (81) has a stationary end connected to the cement slurry input pipe (62) and a rotary end communicating with the annular cavity between the outer stirring drill rod (71) and the central sand discharge pipe (72).

8. The construction device for driving cement mixing piles with sand piles for soft soil replacement according to claim 1, characterized in that, A thrust bearing assembly (82) is provided between the housing of the rotary drive unit (5) and the central sand discharge pipe (72). The thrust bearing assembly (82) is used to support the central sand discharge pipe (72) and allow the rotary drive unit (5) to rotate relative to the central sand discharge pipe (72). The outer wall of the outer mixing drill rod (71) is spirally welded with mixing blades (73) for cutting and mixing the soil.

9. The construction device for driving cement mixing piles with sand piles for soft soil replacement according to claim 1, characterized in that, When the rotary drive unit (5) is working, the hollow output flange (53) drives the outer stirring drill rod (71) to rotate around its own axis, while the central sand discharge pipe (72) remains axially stationary under the constraint of the power head trolley (4).

10. The construction method of the construction device for driving cement mixing piles with soft soil replacement sand piles according to claims 1-9, characterized in that, Includes the following steps: Start the lifting drive module (3): the winch (31) works and slides on the surface of the directional wheel (33) through the traction rope (32), and the traction head (34) drives the power head trolley (4) to descend vertically along the guide structure of the pile driver frame (2); Start the rotary drive unit (5): The drive motor (51) runs, driving the hollow reducer (52) through the transmission connection. The hollow output flange (53) of the hollow reducer (52) drives the outer stirring drill rod (71) to rotate around its own axis. Since the central sand discharge pipe (72) is fixed to the power head trolley (4), it remains axially stationary under the constraint of the power head trolley (4). Drilling and mixing of the composite drill assembly (7): As the power head trolley (4) descends, the rotating outer mixing drill rod (71) drives the spirally welded mixing blades (73) on its outer wall to cut and mix the soil. At the same time, the composite drill bit (74) also penetrates into the soil for mixing. During this process, cement slurry flows into the annular cavity between the outer mixing drill rod (71) and the central sand discharge pipe (72) through the cement slurry input pipe (62), and then sprays out from the cement slurry spray outlet (75) on the composite drill bit (74), fully mixing with the soil being mixed to form a cement mixing pile; Open the sand discharge valve (76): When the composite drill assembly (7) is drilled to the designed depth, the sand in the central sand discharge pipe (72) exerts downward pressure on the sand discharge valve (76) under its own gravity, causing the sand discharge valve (76) to open outward. Sand material is discharged to form sand piles: Sand material is discharged from the bottom outlet of the central sand discharge pipe (72) through the opened sand discharge valve (76) and enters the central part of the already formed cement mixing pile. As the sand material is continuously discharged, a structure of soft foundation replacement sand pile and cement mixing pile is gradually formed.

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