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E-mail: [email protected] Whatsapp: +8613647327093 Tel: +86-731-8403-0163
In modern foundation reinforcement and deep foundation construction, CFA piles and FDP piles are two common and widely used pile foundation forms. They each have different construction processes, applicable conditions and technical advantages. This article will systematically compare CFA piles and FDP piles to provide you with reference:
CFA pile, or continuous flight augment pile, is a pile-forming technology that pours concrete while drilling. During the construction process, the drill rig drills into the ground with a drill bit with continuous spiral blades to form a pile hole. After the drill bit reaches the designed depth, concrete is pumped through the hollow pipe of the drill rod, and concrete is continuously poured while the drill rod is lifted, and then a steel cage is inserted to complete the pile.
FDP pile, or full displacement pile, uses a non-excavation hole-forming method. The soil is squeezed horizontally to the periphery through a large-diameter displacement drill bit to form a hole. At the same time, concrete is pumped in during the process of lifting the drill bit, and then a steel cage is inserted to form the pile body.
1. Hole-making principle and construction method
This is the most essential difference between CFA and FDP.
CFA piles use a spiral drill bit to drill, breaking the soil and bringing it out of the ground. The drill rod is a hollow structure. When drilling to the designed depth, concrete is poured through the drill rod, and the drill rod is lifted while pouring to keep the hole wall stable. After the concrete pouring is completed, the steel cage is inserted.
FDP piles use solid or special expanded diameter drill bits. Instead of taking soil, the soil is squeezed horizontally to the periphery of the hole through displacement to achieve "soil squeezing" type hole-making. During the process of lifting the drill bit, concrete is also poured through the hollow pipe to form a pile structure.
The core difference is:
CFA is a soil-breaking hole-making, and FDP is a soil-squeezing hole-making.
CFA takes soil out of the hole, and FDP leaves the soil at the edge of the hole.
This difference determines the construction logic, equipment requirements and geological adaptability of the two pile types.
2. The degree of disturbance to the stratum
The degree of stratum disturbance is directly related to the stability of the foundation, the safety of adjacent buildings, and the probability of risks such as hole collapse and slurry leakage during construction.
Since CFA piles need to break the ground for drilling, they are prone to hole collapse, hole wall collapse, and hole diameter expansion when constructed in soft or saturated soil layers. Especially in fluid plastic clay or saturated sand layers, if concrete is not poured in time, it is very easy to form hole deformation, affecting the quality of the pile body.
FDP piles compact the surrounding soil by extrusion, which can improve the density and bearing capacity of the surrounding foundation. During the construction process, the stratum disturbance is minimal, the hole formation is highly stable, and it is not easy to collapse. Therefore, it is very suitable for strata that are sensitive to disturbance or projects adjacent to existing buildings.
In short:
CFA disturbance is relatively large, and the risk of hole collapse needs to be paid attention to.
FDP disturbance is small, and construction is more stable and safe.
3. Excavation volume and environmental performance
Currently, many projects have put forward higher requirements for environmental protection. The amount of excavation directly affects the cleanliness of the construction site, the cost of soil treatment and the pressure of transportation.
During the drilling process of CFA piles, a large amount of drilling slag and mud will be brought out. These need to be centrally stacked, transported and treated off-site, which increases the construction cost and may also cause environmental pollution problems.
FDP piles are zero excavation processes. The pile holes are formed by in-situ displacement of the soil body without any excess soil. This means that the construction process is more environmentally friendly, saves transportation and treatment costs, and reduces interference with surrounding roads and the environment during urban construction.
Especially in large and medium-sized cities with limited construction space and strict environmental supervision, the advantage of FDP piles without excavation is more obvious.
4. Bearing capacity and pile performance
Bearing capacity is a key factor in determining the safety of pile foundations, and the two also have different force mechanisms.
The lateral resistance and end bearing capacity of CFA piles mainly come from the bonding force between concrete and the original soil body. Because the original state of the surrounding soil body is destroyed during the hole forming process, some lateral friction resistance is weak. Therefore, its bearing capacity depends on multiple factors such as concrete quality, pile diameter control and verticality of the hole.
Because FDP piles use compaction hole forming technology, the surrounding soil is compacted during the drilling process, forming a strong "soil squeezing effect", which can significantly improve the strength and density of the soil around the pile, thereby increasing the side friction resistance of the pile. Many experiments have shown that under the same pile diameter and burial depth conditions, the bearing capacity of FDP piles is usually about 15~30% higher than that of CFA piles.
In addition, the pile diameter control of FDP piles is more precise, and the hole quality is uniform, which is conducive to later inspection and acceptance.
5. Construction equipment and technical requirements
CFA and FDP are also different in terms of construction equipment:
CFA pile construction equipment technology is mature, the market supply is wide, and the threshold for operator training is low. Most rotary drilling rigs can be modified to meet CFA construction requirements.
FDP piles have higher requirements for equipment, and need to be equipped with special displacement drills and control systems. At the same time, they have higher requirements for the control of construction parameters such as pouring rhythm, drill speed, and displacement depth. Construction personnel need to have strong technical capabilities and experience, and the construction organization needs to be more rigorous.
In addition, FDP equipment is expensive, and small contractors may face financial pressure. It is suitable for large projects or large construction units that attach importance to quality and environmental protection.
6. Noise and vibration control
In urban projects, construction noise and vibration are important regulatory indicators:
During the construction process, the main noise of CFA piles comes from the drilling motor and concrete pumping, but the overall vibration is small, which is suitable for construction in the city.
FDP piles have less noise and vibration due to the lack of impact, and are especially suitable for areas with high requirements for quiet construction such as hospitals, schools, and cultural relics protection units.
In this dimension, FDP piles have more prominent environmental protection and social coordination advantages.
7. Cost difference and economic analysis
From the perspective of single pile cost:
CFA piles have popular equipment, conventional materials, rich construction experience, low overall cost, and high cost performance, which is suitable for projects that are sensitive to cost control.
Although FDP piles have high equipment costs and high requirements for construction personnel, due to their excellent bearing performance, they can reduce the length or number of piles, and overall may achieve better total cost control.
| Item | CFA pile | FDP pile |
| Construction efficiency | High | Medium |
| Environmental protection | Drilling residues to be treated | Almost no excavation, environmental protection |
| Geological adaptability | Soft soil, saturated strata | Medium-dense to dense soil layers |
| Noise/vibration | Low | Very low |
| Bearing capacity | Good | Superior |
| Cost | Moderate | High but good overall benefits |
The following factors should be considered when choosing which type of pile to use:
Geological conditions: If the soil is loose and the water level is high, CFA piles are recommended; if the soil is dense, FDP piles can be given priority.
Environmental protection and disturbance requirements: FDP piles are suitable for sensitive areas or sites with high environmental protection requirements.
Construction site restrictions: FDP piles are recommended for projects with small sites and inconvenient transportation.
Project budget: CFA piles can be used first if the budget is tight; FDP is better if long-term stability and environmental protection are sought.
For example:
When building high-rise residential buildings in the city center, if the underground space is compact and the environmental protection requirements are high, FDP piles are often a better choice; while in industrial parks and areas with soft geology, CFA piles are more cost-effective.
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