James Harrington’s team installed 340 continuous flight auger piles to the residential structure in inner city London and finished the foundation in the course of 14 actual work days. Any noise complaints filed by residents were not received. It is necessary to mention that the construction site was situated between equipped dwellings as well as a school. As an example, bored piles would have needed six weeks to complete the work. Driven piles on the other hand, caused public outcry, and would have been no better.
The benefits of the tripods in relation to community complaints are not the only positive things that can be derived from the use of a continuous flight auger. The use of CFA piles in comparison to other foundation types helps in getting more jobs and winning more finishing on site even better and cost reduction. This handbook focuses on the special characteristics that make CFA the most practical and efficient method for city construction, certain medium-load applications as well as any eco-sensitive locations, in chronological order.
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What Makes Continuous Flight Auger Piles Different
Drilling a continuous casing auger pile involves a process in which a hollow-stem auger first bores to the final depth within one elongated drilling stage. While depressing the auger, the requisite concrete mix is pumped into the hollow tube. You can then include the framework in the wet concrete just before it turns hard. All of these steps are done within a single round of action, from in situ casting concrete backfill to side demolition of formwork.
This type of work carried out in one go has its merits that cannot be exceeded with any other form of construction. It is necessary to perform operations step by step when using boring equipment, that is to say: drilling, dumping soil, cleaning process and augmenting, and finally, pouring. Each additional procedure increases the time required, equipment expenses and cost price. Driven piles remain limited due to vibration induced by pounding. There is no such concern in the construction of CFA piles.
The major difference lies in the requisite simultaneity. As a single procedure, drilling and cement pouring are combined. In most geological settings, even without employing a mud or a temporary tube, horizontal movements are restricted because the drilling auger keeps the hole from caving in. This single-pass approach is what makes CFA a rational choice for all the explained benefits.
Want to understand how the CFA method works in detail? Read our complete guide to auger drill methods and equipment for a full technical breakdown.
Speed and Productivity Advantages
When it comes to construction, time is money, construction professionals understand this well. Utilization of continuous flight auger (CFA) piles offers a strategic speed advantage that results in direct cost and time savings.
Production Rate Benchmarks
Provided that conditions on site are conducive to the CFA drilling, the crew can drill between 25 and 40 piles a day. The number of piles they are able to drill per day may deviate from this average due to several factors, for example the diameter of the pile, the depth of the bore, the type of soil, as well as the capacity of the rig. In comparison, where bored piles are concerned, the team digs up about 4 to 8 bored piles on average. This is due to the thorough bore cleaning and the means of augmentation that each bore pile unit requires.
CFA drilling does not involve the installation and removal of the casings at all. There is also no need to come up with slurry, circulate, dispose of it, and/or quench well to free the construction. After completion of the drilling, it is not required to remove rubble and then re-drill the pile, swiveling inside it. There are no interruptions in the course of work, as every pile only needs the drilling completed prior to coming to the next process.
During the construction of a warehouse near Lisbon by the Portuguese contractor, when they changed from bored piles to CFA, the time of construction of the bases decreased from six weeks to four. The workers got rid of the delays connected with the mixture of bentonite, cases and spoil removal. The project was completed 12 days before the deadline.
Reduced Weather Dependency
Cost Efficiency Advantages
It is generally known that the strategy of saving time automatically leads to saving money. For example, when the foundation work is completed earlier than planned, the costs in terms of labor hours, equipment rent, site overhead, etc., are likely to be less. Yet, the other cost benefits of construction by CFA piles are not dependent on finishing on time only.
Direct Cost Savings
Some people believe that the U.S. Department of Transportation’s Federal Highway Administration indicates that the use of cast-in-place concrete piles in foundation construction can reduce the overall project cost in certain conditions by 30 to 50% compared to the technique of utilizing conventional bored piles. It is reported from historical construction quotations that the CFA piles for U. S. highway projects are designated at a $15-$40 range per linear foot while the bored pile costs are three to fifteen times higher at the $100-$300 range per linear foot, dependent on the diameter and the nature of the soil conditions.
These are savings that result from doing without some specific line items. There is no temporary steel casing that the contractor has to pay to hire, transport and bring back. There are no costs associated with the procurement of bentonite or polymer slurry, where it is obtained then mixed, followed by the anticipated disposal of it. Spoil minimization process is employed because the soil is only, in simple terms, removed by the spiral conveyor flights to the surface and does not involve creating overly large soil volumes for off-site disposal transport.
Indirect Cost Savings
The fewer the number of movements from one place to another, the better it is as there is no movement and setting of items costs. If the expanse within the construction is less than, so will the costs for preparing an access and platform. There is no need to apply several labor hours, as the wages and supervision are also minimized. The presence of less machinery at the site reduces fuel consumption and maintenance frequencies.
According to Hans Weber’s German contracting team, who quoted on a commercial office building project in Hamburg, a bored pile assessment came with options for either base bored piles or CFA piles. The bored pile projection also included other activities, such as the use of casings, the cleaning of the slurry, and more people. All these aspects had been omitted from the CFA projections. Over 280 piles, the difference in the entire foundation cost exceeded 180,000 euros.
Material Efficiency
Environmental and Site Advantages
Noise, vibration, and environmental issues are areas of concern for construction sites. More especially, installing CFA piles without a doubt helps in eliminating these three worries better compared to any driven or conventional bored methods.
Minimal Noise and Vibration
The installation of the CFA pile gives off noise that is almost the same as the standard equipment. The process is quiet and involves no hammer strikes. Noise comes from the rotation of the bits, but subsides fast thanks to the size of both boreholes. This operation does not produce any vibrations. The vibrations are almost at zero.
This factor becomes particularly important in case of executing works in urban areas, on an existing hospital plant or a school construction site, or on an occupied site with any other functional buildings or in the vicinity of protective transport infrastructures. Currently, and in some of the major cities in Europe in particular, the control of vibrations is a prerequisite for carrying out any work on driven piles. CFA piles, on the other hand, need no such compliance.
The medical clinic which was extended by Yuki Tanaka’s team in Osaka, will have to deal with the problem of vibration size since the first thing to consider when using driven piles – adjacent operating hospital has its vibration size limits. The bored piles required the use of slurry to avoid spillages even in the urban territories with restricted space. The use of CFA piles on the project made it possible to carry on with foundation work without interrupting the pressing hospital activities. In fact, the city engineer of the town even gave his certificate of appreciation for the little construction activities interrupting the hospital enclosure.
Reduced Spoil and Waste
The standard methodology for the installation of CFA piles is that they produce less excavated material than bore holes since a continuous transport of the soil is always maintained. Such auger arrangements as displacement augers are used to the elimination of spoil from the bore by shifting the soil to the later phases of the construction. This helps to some extent to prevent long trucking and disposal costs in addition to limiting the risks of contaminating the site.
Smaller Site Footprint
While carrying out in CFA operations, the drilling rig requires a meager amount of support equipment, as opposed to a bore rig setup. No extending slurry mixing facilities. No storing of casings in large boxes. No big heap of used spoil. This avails the much-needed space in highly urban locations and ensures that all the operations are smooth.
Quality and Performance Advantages
When the quality of a pile is compromised, the benefits of the high speed and the low costs are never achieved. Today, modern construction methods of the CFA piles provide the user with the same level of insurance as the previous well known methods or even more.
Structural Performance
CFA pile, once cast, provides a continuous mass of concrete shaft without joints or cold joints. The CFA method creates a rough soil-concrete interface when extracting the tool, and this helps in increasing the shaft friction and the safety of the load transfer. Such piles are very effective in carrying axial, uplift, and horizontal forces.
The load bearing capacities per pile are usually in the ranges of 1,000 to 2,500 kilonewtons, depending on the diameter, length and bearing conditions of the soil. Drilling diameters of 300 to 1200 millimeters and Depths of 36 meters are required for most of the commercial and residential foundation requirements.
Real-Time Quality Monitoring
Current CFA installers have simple devices that enable them to monitor all the crucial data required for proper placement. These are the system’s depth, the speed that the auger is turning at, the ability of the auger to penetrate the soil, the amount of concrete being pushed, the rate that auger is being withdrawn and the volume of concrete being poured with that temperature at that particular location. All piles have their own individual digital settings provided.
It is also advisable for conventional bored piles to use traceable voided CFA piles. Anomalies are immediately spotted thanks to the real-time monitoring. The operator can change the concrete pressure or the extraction speed to prevent the formation of any defects. The system recorded data also provides a trail the user can use to resolve any claim that may be made concerning the work done.
Consistent Concrete Placement
Such a system of delivering concrete through the hollow auger, with control over the pressure during the withdrawal, allows for continuous filling in the borehole. The filled-up ends out soil inclusions and piling shaft is fully compacted. This is unlike the tremie cast technique which uses a vertical pipe, where the distance of a free fall is observed, in which the possibility of concrete segregation is very high.
Soil and Groundwater Advantages
CFA piling offers dependable performance across a myriad of ground conditions. This trait is beneficial, especially for contactors who are not sure of the nature of the job at hand.
Broad Soil Suitability
The works with CFA are very effective in clay, silt, sand, and gravel and soft rocks. The selection of auger cutting heads to carry out the works in different soils may be adjusted through selection or rotation of the teeth. With cohesive soils, bullet teeth are adequate. If the rock under treatment has been weathered, carbide-tipped teeth can also be effective.
High Groundwater Performance
A hollow-stem auger is used as a temporary liner during the drilling process. This benefits those drilling in zones where water enters the borehole. At the end of the day, concrete is poured immediately to prevent the retention system from being exposed to groundwater for any length of time.
This is unlike with the bored piles placed in similar conditions, which require the application of expensive temporary casing or bentonite slurry to facilitate the drilling holes. In most cases, the CFA piles take care of such situations as a matter of course without adding any other remedies.
No Slurry Required
Moving heavy bentonite and polymer slurries and their disposal often proves harder than their use on a jobsite. Waste slurry is a non-issue since it is not generated in the first place. There is even less boring machinery needed since there is no disposal site necessary after completion
When Continuous Flight Auger Piles Deliver Maximum Advantage
Not every project suits CFA piles. But when conditions align, the advantages compound into decisive project benefits.
Urban and Restricted Sites
Lower noise levels, vibration control, and a congested urban environment are some of the factors that make Continuous Flight Auger the most appropriate method for city center structures. This technique is among the least energy-intensive options, and it can work in minimal space with low vertical space.
Medium-Load Foundations
These are the types of vertical construction facilities – multistoried buildings, office complexes, parking buildings, light industrial facilities – which typically require the performance of working stresses borne but also unpredictable and on inaccessible places, which usually drives larger diameter bored pile installation. The full use of CFA is appropriate for such projects.
Accelerated Schedules
Very critical projects with limited time available have the advantage of using this particular technique since the application is completed faster, between 20% and 30% faster than bored pile casing. The saving of time for drying or curing of materials is one of the time savings that CFA brings.
Environmentally Sensitive Locations
There is little ground for doubt the best way to place it is work associated with the building or repair of the hospital, school, art object or residential buildings, as the properties of CFA has low vibration and noise characteristics. Where spatial restrictions with regard to muck away are imminent, benefits such as controlled excavation strategies that produce very little soil are presented.
When to Consider Alternatives
Rocky surfaces can also halt standard CFA augers. In areas where very heavy loadings are to be placed, large-diameter bored piles with rock sockets may be necessary. Areas densely packed with boulders, or with weathered structures which will necessarily have to be demolished, present particular problems to CFA operations, primarily due to the stoppage and starting problem.
CFA Piles vs Bored Piles vs Driven Piles
| Factor | CFA Piles | Bored Piles | Driven Piles |
|---|---|---|---|
| Installation Speed | Fast (continuous) | Slower (sequential) | Moderate |
| Noise Level | Low | Moderate | High |
| Vibration | Virtually none | Low to moderate | High |
| Temporary Casing | Not required | Often required | Not applicable |
| Slurry Required | No | Often yes | No |
| Spoil Generation | Minimal | Significant | None |
| Typical Depth | Up to 36 m | 60 m+ | Variable |
| Typical Diameter | 300–1,200 mm | Up to 2,000+ mm | Variable |
| Cost (per LF) | 15–40 | 100–300 | Variable |
| Urban Suitability | Excellent | Good | Poor |
| Hard Rock Ability | Limited | Excellent | Moderate |
Apart from that, this contrast helps to understand why CFA is at the peak of demand in the foundation of urban buildings. These structures make the most of constructions from the standpoint of building conditions as well as their coordination in terms of speed, impact, and economy.
Conclusion
Contractors who handle this technology on projects of the right complexity fully grasp the merits of using continuous flight auger (CFA) piles which are easy to install. The design of continuous flight auger piles allows them to achieve productivity benefits throughout the entire project duration, contracting the program to the foundations by 20 to 30%. The inability to install a casing and, in some situations, slurry and the limitations of removal, allows for significant design-to-cost savings in the foundation. Continuous flight auger construction projects can be undertaken without noise and vibration restrictions being imposed in environmentally sensitive areas.
Here are the key takeaways:
- Speed wins projects. CFA crews install 25 to 40 piles per day, far exceeding bored pile production rates.
- Cost savings are real. Eliminating casing, slurry, and spoil handling cuts foundation costs by 30 to 50 percent in suitable ground.
- Urban sites favor CFA. Low noise and vibration keep regulators and neighbors satisfied.
- Quality is verifiable. Real-time instrumentation on modern rigs produces individual logs for every pile.
- Soil versatility extends usefulness. CFA handles clays, sands, silts, and water-bearing strata without special measures.
Changsha Mingyi Machinery Equipment Co., Ltd. is a Chinese manufacturer of CFA machines, drilling buckets, core barrels and all the equipment used in drilling holes in the ground. Our machines create a boring motion by pushing the flight of the auger downward. The company makes CFA machines, drilling buckets, core barrels of various diameters and foundation drilling tools.
Contact us today for a free CFA auger specification and tooling recommendation based on your project requirements.
