Preparation method of cement-soil composite pile body based on ectopic stirring

Abstract

The invention relates to the technical field of building foundation construction, in particular to a preparation method of a cement-soil composite pile body based on ectopic stirring, which comprises the following steps: S1, mixing cement, water, a water reducing agent and a retarder to prepare slurry; and S2, positioning and punching are conducted on the construction site. And S3, underground soil is drilled through a drilling machine, and the underground soil is fished to the ground. And S4, stirring and mixing the slurry and underground soil on the ground to obtain a mixed solution. And S5, the mixed liquid is conveyed back into the piling hole. And S6, the precast pile is inserted into the pasty mixed liquid in the piling hole to form a composite pile body. Cement slurry is prepared into slurry with a gelling agent function, and a process method of a cement mixing pile is completely changed, namely underground soil is firstly taken out to the ground and then is mixed and stirred with the slurry from the ground to complete ectopic stirring, so that close combination of a cement soil material and a precast pile on a microstructure level is realized, and the construction efficiency is improved. And the integrity, the bearing capacity and the durability of the composite pile are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of building foundation construction technology, specifically a method for preparing cement-soil composite piles based on off-site mixing. Background Technology

[0002] Currently, high-rise buildings, industrial plants, and bridges bear extremely heavy loads. Correspondingly, the piling technology for these structures has also improved. As urban underground space development moves towards deeper and higher load-bearing requirements, current piling methods are insufficient to provide adequate support. Specifically, piling mainly includes precast piles and on-site mixing piles. While precast piles offer advantages such as high strength and stable quality, they lack effective synergy with the undisturbed soil, making it difficult to fully utilize side friction and end bearing capacity. On-site mixing piles (such as cement-soil mixing piles), while able to integrate well with the soil, generally suffer from low strength and poor uniformity of underground mixing, making it difficult to meet high load and stringent deformation control requirements.

[0003] Therefore, in order to improve the high bearing capacity of piles while ensuring the integration effect with the original soil, precast pipe piles are generally inserted into cement mixing piles to form a composite. Existing technologies attempt to enhance the bonding with cement and soil by setting grooves or special shapes on the surface of precast piles, but such methods are still "post-coupling" and cannot fundamentally solve the problems of interface weakening and discontinuous stress transmission between cement and soil and the core of precast pipe piles at the microstructural level. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing cement-soil composite piles based on in-situ mixing, which can effectively solve the problems in the background art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing cement-soil composite piles based on ex-situ mixing includes the following specific steps: S1: Mix cement, water, water-reducing agent and retarder to prepare a slurry with cementitious properties; S2. Locate and drill holes at the construction site to determine the pile driving position; S3. Using a drilling rig, the underground soil at the piling location in S2 is drilled out and brought to the surface so that the piling location extends downward to form a piling hole. S4. Mix the slurry in S1 with the underground soil in S3 on the ground to form a slurry-like mixture. S5. The slurry mixture formed in S4 is transported back to the pile hole in S3 through the drilling rig. S6. Insert the precast pile into the slurry mixture in the pile hole to form a composite pile.

[0006] Preferably, step S1 includes the following steps: The following are recommended: ordinary Portland cement of strength grade 42.5 with a water-cement ratio of 0.7 to 0.9, clean tap water or drinking water free of impurities, polycarboxylate superplasticizer, and sodium hexametaphosphate retarder added at a rate of 0.1% to 0.3% of the cement mass.

[0007] Preferably, it also includes adding bentonite, accounting for 0.5% to 2.0% of the total weight of the cementitious material, when preparing the slurry in S1.

[0008] Preferably, the slurry in S1 and the underground soil extracted in S3 are mixed in a mixing device.

[0009] Preferably, the mixing device includes a front mixing cover, a rear mixing cover, a mixing body, and a cleaning mechanism; The front stirring cover is hinged to one side of the rear stirring cover, and the other side of the front stirring cover is fastened to the rear stirring cover. The front stirring cover has an inlet that communicates with the stirring chamber. One end face of the front stirring cover extends towards the side of the rear stirring cover to form a mixing cylinder. The mixing cylinder abuts against the end face of the rear stirring cover to form the stirring chamber. The stirring body is provided on one end face of the rear stirring cover. The stirring body has stirring blades. The cleaning mechanism is provided inside the rear stirring cover. The cleaning mechanism has a high-pressure nozzle that can spray water into the stirring chamber.

[0010] Preferably, the stirring blade is a multi-section hinged stirring blade, and each stirring blade is spindle-shaped.

[0011] Preferably, the bentonite added to the slurry is dry powder, which is first mixed with the slurry and then water is added.

[0012] Preferably, the precast pile has a hollow cavity in its pipe wall, and the bottom end of the outer wall of the precast pile has an opening that communicates with the hollow cavity.

[0013] Compared with the prior art, the beneficial effects achieved by the present invention are: By preparing cement slurry with a gelling agent function and completely changing the process of cement mixing piles, the underground soil is first extracted to the surface and then mixed with the slurry to complete the off-site mixing. This achieves a tight bond between cement-soil materials and precast piles at the microstructural level, significantly improving the integrity, bearing capacity, and durability of composite piles. It effectively overcomes the technical bottlenecks of weak interfacial bonding and poor mixing uniformity in traditional processes, providing a reliable and efficient solution for deep high bearing capacity pile foundation engineering. Attached Figure Description

[0014] Figure 1This is a flowchart of a method for preparing cement-soil composite piles based on in-situ mixing according to the present invention. Figure 2 for Figure 1 A schematic diagram of the mixing equipment in S4; Figure 3 for Figure 2 A cross-sectional schematic diagram; Figure 4 for Figure 3 A magnified view showing the details of the circled "A".

[0015] In the picture: 1. Front mixing cover; 11. Feed inlet; 12. Mixing cylinder; 101. Mixing chamber; 2. Rear mixing cover; 3. Mixing body; 31. Mixing blade; 311. Mixing plate; 4. Cleaning mechanism. Detailed Implementation

[0016] This invention provides a method for preparing cement-soil composite piles based on in-situ mixing, the specific implementation of which is as follows.

[0017] Example 1 To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0018] Currently, with the continuous evolution of urban underground space development towards deeper and higher bearing capacity, pile foundation engineering places higher demands on structural strength, deformation control, and soil synergy. While traditional precast concrete piles possess advantages such as high strength and stable quality, they lack effective integration with the surrounding undisturbed soil, resulting in insufficient utilization of lateral friction and end bearing capacity. On the other hand, while on-site cement-soil mixing piles can bond well with the foundation soil, they are limited by inherent defects such as poor mixing uniformity and low solidification strength, making it difficult to meet the engineering requirements of high loads and strict settlement control. To address the aforementioned technical problems, this invention proposes a method for preparing cement-soil composite piles based on ex-situ mixing. This method involves transforming cement slurry into a slurry with a gelling agent function, and completely altering the traditional cement mixing pile process. Specifically, the underground soil is first extracted to the surface, and then mixed with the slurry from the surface to complete the ex-situ mixing. This achieves a tight bond between the cement-soil material and the precast pile at the microstructural level, significantly improving the integrity, bearing capacity, and durability of the composite pile. It effectively overcomes the technical bottlenecks of weak interfacial bonding and poor mixing uniformity in traditional processes, providing a reliable and efficient solution for deep, high-bearing-capacity pile foundation engineering. This method is applied to the preparation of cement-soil composite piles based on ex-situ mixing.

[0019] Reference Appendix Figure 1 This invention proposes a method for preparing cement-soil composite piles based on in-situ mixing, the method comprising the following steps: S1: Mix cement, water, water-reducing agent and retarder to prepare a slurry with cementitious properties; S2. Locate and drill holes at the construction site to determine the pile driving position; S3. Using a drilling rig, the underground soil at the piling location in S2 is drilled out and brought to the surface so that the piling location extends downward to form a piling hole. S4. Mix the slurry in S1 with the underground soil in S3 on the ground to form a slurry-like mixture. S5. The slurry mixture formed in S4 is transported back to the pile hole in S3 through the drilling rig. S6. Insert the precast pile into the slurry mixture in the pile hole to form a composite pile.

[0020] In the above-mentioned method for preparing cement-soil composite precast piles based on in-situ mixing, the outer surface of the precast pile can be sandblasted before S1 to form a uniformly rough surface. The arithmetic mean deviation of the roughness profile is controlled within the range of 6.3 micrometers to 12.5 micrometers. An epoxy resin-based interface agent with a thickness of 0.2 mm to 0.5 mm is then coated onto the treated surface. During the sandblasting process, diamond particles impact the surface of the precast pile at high speed, forming a random concave-convex structure with a depth of 30 to 80 micrometers on the concrete surface through micro-cutting and micro-fragmentation. The peak-valley spacing of this structure is controlled between 100 and 300 micrometers, thus providing sufficient anchoring space for the subsequent interface agent. The sandblasting equipment adopts a closed-loop circulation system and is equipped with a dust recovery device to ensure that the working environment meets occupational health standards. After sandblasting, dry compressed air at 0.4 MPa to 0.6 MPa is immediately used to blow along the pile axis three times to thoroughly remove abrasive particles and dust embedded in the grooves, preventing impurities from interfering with interface bonding.

[0021] Furthermore, the epoxy resin-based interface agent is composed of a two-component epoxy resin and a curing agent mixed at a weight ratio of 2:1. Its viscosity at 25°C is 1500 mPa·s to 2500 mPa·s. After application, it needs to be allowed to stand at room temperature for 30 to 45 minutes to complete surface drying, forming a transition layer with high bonding strength to the precast pile surface and subsequent cement-soil slurry. The interface agent is applied using an airless spraying device with a nozzle orifice diameter of 0.3 mm to 0.5 mm and a spraying pressure of 10 MPa to 15 MPa, ensuring a uniform coating thickness distribution within the range of 0.2 mm to 0.5 mm. The epoxy resin components include bisphenol A type epoxy resin, reactive diluent, and coupling agent. The curing agent is a modified aliphatic amine. The initial setting time after mixing is 60 to 90 minutes, and the final setting time is 4 to 6 hours. The silane coupling agent in the interface agent undergoes a condensation reaction with the silanol groups on the concrete surface at one end and crosslinks with the epoxy resin network at the other end. Simultaneously, its polar groups can form hydrogen bonds with cement hydration products, thus constructing a chemical-physical dual bonding mechanism between the precast pile and the cement-soil coating layer. After coating, the pile is placed in a clean environment to avoid dust contamination, and can only proceed to the next step after it is surface dry.

[0022] In the above-mentioned method for preparing cement-soil composite piles based on in-situ mixing, in step S1, ordinary Portland cement of strength grade 42.5 with a water-cement ratio of 0.7 to 0.9 is mixed with clean tap water or drinking water free of impurities, as well as polycarboxylate superplasticizer and retarder (such as sodium tripolyphosphate and sodium hexametaphosphate, with an addition amount of 0.1% to 0.3% of the cement mass) in a forced mixer. The mixing speed is controlled at 50 revolutions per minute, and the mixing time is maintained for 15 minutes to obtain a slurry with a fluidity of 180 mm to 220 mm and a gelling agent function.

[0023] In addition, it also includes adding 0.5% to 1.0% polypropylene fiber by weight of the total cementitious material when preparing the slurry in S1. After adding the fiber, the cohesiveness of the slurry is significantly improved, which can effectively inhibit the generation of plastic shrinkage cracks and improve the fracture energy and impact resistance of the material after hardening.

[0024] In the above-mentioned method for preparing cement-soil composite piles based on in-situ mixing, step S2 involves positioning and drilling holes at the construction site to determine the pile driving location. Specifically, this involves first measuring and laying out the lines, and then marking the drilling locations on the ground with a diameter of 0.6m and a spacing of 1.3m between adjacent pile driving holes.

[0025] Furthermore, in step S3, the underground soil at the piling location in S2 is drilled using a drilling rig and brought to the surface, so that the piling location extends downwards to form a piling hole. The drill rod is continuously driven into the ground to continuously transport the underground soil to the surface.

[0026] S4. Mix the slurry in S1 with the underground soil in S3 on the ground to form a slurry-like mixture.

[0027] It should be noted that the underground soil is dredged to the surface and then mixed with the gelling slurry in a surface mixer. Compared to existing underground mixing methods, this embodiment uses a dedicated mixing mixer with spiral-shaped blades 31, which allows for more thorough mixing of the slurry and the underground soil.

[0028] In the above-mentioned method for preparing cement-soil composite piles based on in-situ mixing, in step S5, the slurry mixture formed in step S4 is transported back to the pile hole in step S3 through a drilling rig.

[0029] Furthermore, it also includes adding bentonite, accounting for 0.5% to 2.0% of the total weight of the cementitious materials, when preparing the slurry in S1.

[0030] Furthermore, the slurry in S1 and the underground soil extracted in S3 are mixed in a mixing device.

[0031] Furthermore, the mixing equipment includes a front mixing cover 1, a rear mixing cover 2, a mixing body 3, and a cleaning mechanism 4. The front mixing cover 1 and the rear mixing cover 2 are hinged on one side and fastened to each other on the other side. The front mixing cover 1 has an inlet 11 communicating with the mixing chamber 101. One end face of the front mixing cover 1 extends towards the rear mixing cover 2 to form a mixing cylinder 12, which abuts against the end face of the rear mixing cover 2 to form the mixing chamber 101. The mixing body 3 is located on one end face of the rear mixing cover 2, and has mixing blades 31. The cleaning mechanism 4 is located inside the rear mixing cover 2 and has a high-pressure nozzle that can spray water into the mixing chamber 101. It should be noted that this mixing equipment provides a relatively sealed mixing chamber 101, and the mixing of the slurry and underground soil occurs entirely within the mixing chamber 101, limiting the mixing range and allowing the mixing effect of the mixing body 3 to be more thorough. In addition, the mixing body 3 also includes a mixing motor that drives the mixing shaft. Driven by the stirring motor, the stirring shaft can rotate to drive the stirring blades 31 for stirring. The stirring chamber 101 separates the connection between the front stirring cover 1 and the rear stirring cover 2, facilitating cleaning and material unloading at the connection point, making operation convenient. Additionally, water is sprayed into the stirring chamber 101 through the high-pressure nozzle 4 for easy cleaning after stirring.

[0032] Furthermore, the stirring blade 31 is a multi-section hinged stirring plate 311, each stirring plate 311 being shuttle-shaped. Due to the certain viscosity of the slurry, it interacts with the stirring plate 311, causing the stirring plate to rotate while stirring, further enhancing the stirring effect.

[0033] Furthermore, the bentonite added to the slurry is in the form of dry powder. It is first mixed with the slurry before water is added. This ensures better mixing and prevents clumping.

[0034] Furthermore, the precast pile has a hollow cavity in its pipe wall, and an opening communicating with the hollow cavity is provided at the bottom end of the outer wall of the precast pile.

[0035] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing cement-soil composite piles based on in-situ mixing, characterized in that: The specific steps include the following: S1: Mix cement, water, water-reducing agent and retarder to prepare a slurry with cementitious properties; S2. Locate and drill holes at the construction site to determine the pile driving position; S3. Using a drilling rig, the underground soil at the piling location in S2 is drilled out and brought to the surface so that the piling location extends downward to form a piling hole. S4. Mix the slurry in S1 with the underground soil in S3 on the ground to form a slurry-like mixture. S5. The slurry mixture formed in S4 is transported back to the pile hole in S3 through the drilling rig. S6. Insert the precast pile into the slurry mixture in the pile hole to form a composite pile.

2. The method for preparing a cement-soil composite pile based on in-situ mixing according to claim 1, characterized in that: S1 includes the following steps: The following are recommended: ordinary Portland cement of strength grade 42.5 with a water-cement ratio of 0.7 to 0.9, clean tap water or drinking water free of impurities, polycarboxylate superplasticizer, and sodium hexametaphosphate retarder added at a rate of 0.1% to 0.3% of the cement mass.

3. The method for preparing a cement-soil composite pile based on in-situ mixing according to claim 1, characterized in that: It also includes adding bentonite, accounting for 0.5% to 2.0% of the total weight of cementitious materials, when preparing the slurry in S1.

4. The method for preparing a cement-soil composite pile based on in-situ mixing according to claim 1, characterized in that: in, The slurry in S1 and the underground soil extracted in S3 are mixed in a mixing device.

5. The method for preparing a cement-soil composite pile based on in-situ mixing according to claim 4, characterized in that: The mixing device includes a front mixing cover (1), a rear mixing cover (2), a mixing body (3), and a cleaning mechanism (4). The front stirring cover (1) is hinged to one side of the rear stirring cover (2), and the front stirring cover (1) is fastened to the other side of the rear stirring cover (2). The front stirring cover (1) has an inlet (11) that communicates with the stirring chamber (101). One end face of the front stirring cover (1) extends toward the side of the rear stirring cover (2) to form a mixing cylinder (12). The mixing cylinder (12) abuts against the end face of the rear stirring cover (2) to form the stirring chamber (101). The stirring body (3) is provided on one end face of the rear stirring cover (2). The stirring body (3) has stirring blades (31). The cleaning mechanism (4) is provided inside the rear stirring cover (2). The cleaning mechanism (4) has a high-pressure nozzle that can spray water toward the stirring chamber (101).

6. The method for preparing a cement-soil composite pile based on in-situ mixing according to claim 5, characterized in that: The stirring blade (31) is a multi-section hinged stirring plate (311), and each stirring plate (311) is spindle-shaped.

7. The method for preparing a cement-soil composite pile based on in-situ mixing according to claim 3, characterized in that: The bentonite added to the slurry is a dry powder. It is first mixed with the slurry and then water is added.

8. The method for preparing a cement-soil composite pile based on in-situ mixing according to claim 1, characterized in that: The precast pile has a hollow cavity in its pipe wall, and an opening communicating with the hollow cavity is provided at the bottom of the outer wall of the precast pile.

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