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Geotechnical Engineering Circular (GEC) No. 8
Design And Construction Of Continuous Flight Auger Piles
Final
April 2007

Chapter 3: Applications For Transportation Projects

3.1 Introduction

This chapter presents several advantages and limitations of using CFA piles, and provides information on project and geotechnical conditions that may be favorable or problematic for this type of pile. This chapter also illustrates applications of CFA piles on transportation projects, including bridge piers and abutments, soundwalls, earth retaining structures, and pile-supported embankments. At the end of this chapter, several examples of typical costs for CFA piles in U.S. construction are provided, which can be beneficial when considering CFA as an alternative foundation to more traditional methods.

3.2 Advantages and Limitations of CFA Piles

3.2.1 Background

CFA piles have been more widely used in private, commercial work in the United States and abroad than in transportation work. Several factors appear to contribute to this trend; some factors are inherently associated with CFA pile technology and some are institutional perceptions. The factors that might have contributed to a wider acceptance of CFA piles in commercial applications than in transportation projects are:

  • Simple foundation requirements: a large number of piles are commonly used in a compact area (Figure 3.1) primarily to support large concentrated dead loads.
  • Speed of installation of CFA piles over other pile types.
  • Increased use of design-build contracting in private work, in which contractors are highly motivated toward speed, economy, and innovations to those means.
  • Increased requirements to minimize noise and vibrations from pile installation in heavily populated areas.
  • A reluctance by many owners to utilize CFA piles because of concerns about quality control and structural integrity.
  • The typical demand on bridges for uplift and lateral load capacity, scour considerations, and/or seismic considerations, require pile diameters and possibly lengths up to a range not commonly used with CFA piles in private commercial work in U.S. markets.

The following sections describe advantages and limitations of CFA piles and present geotechnical and project conditions that affect the selection and use of these piles.

Figure 3.1: Use of CFA Piles for Commercial Building Projects

Photo showing the use of CFA piles for commercial building projects

3.2.2 Geotechnical Conditions Affecting the Selection and Use of CFA Piles
3.2.2.1 Favorable Geotechnical Conditions

CFA piles generally work well in the following types of soil conditions:

  • Medium to very stiff clay soils. In these soils, the side-shear resistance can provide the needed capacity within a depth of approximately 25 m (80 ft) below the ground surface. The major advantage of cohesive soils for CFA pile construction is that clays are generally stable during drilling and less subject to concerns about soil mining during drilling.
  • Cemented sands or weak limestone. These soils are favorable if the materials do not contain layers that are too strong to be drilled using continuous flight augers. In cemented materials, it is not so critical that the cuttings on the auger maintain stability of the hole. In addition, CFA piles can often produce excellent side-shear resistance in cemented materials because of the high side resistance created by the rough sidewall and good bond achieved using cast-in-place grout or concrete.
  • Residual soils. Residual soils, particularly silty or clayey soils that have a small amount of cohesion, are favorable for CFA pile installation because installation can be particularly fast and economical.
  • Medium dense to dense silty sands and well-graded sands. These sands, even when containing some gravel, are commonly favorable. This is especially true if the groundwater table is deeper than the pile length.
  • Rock overlain by stiff or cemented deposits. CFA piles can achieve significant end-bearing capacity on rock, provided that the overlying soil deposits are sufficiently competent to allow installation to the rock without excessive flighting. Flighting is the lifting of soil on the auger as the auger turns, in the manner of an Archimedes pump. Rock that is directly overlain by strong material or a transitional zone is well suited.
3.2.2.2 Unfavorable Geotechnical Conditions

The installation of CFA piles can be problematic in the following types of soil conditions:

  • Very soft soils. In these soils, the installation of CFA piles can present problems concerning ground stability due to soft-ground conditions, which can produce necks or structural defects in the pile. Even with oversupply of concrete or grout (which is a costly measure and the piles become less economical), the result is a bulge in the very soft zones that can cause an increase in downdrag loads. Under these conditions, it is difficult to reliably control the volume per unit length of the pile during withdrawal of the auger.
  • Loose sands or very clean uniformly graded sands under groundwater. Clean, loose sands with shallow groundwater are unfavorable because the potential for soil mining is high. Therefore, under these conditions, the control of the penetration rate during drilling and grout placement is extremely critical. For these soil conditions, DD piles are likely to be more reliable because this type of pile tends to densify the surrounding loose soil.
  • Geologic formations containing voids, pockets of water, lenses of very soft soils, and/or flowing water. These subsurface conditions may cause the hole to collapse, initiate problems during drilling and grouting, and make the penetration and grouting rates hard to control. For example, solution cavities in limestone are a common source of such difficulties.
  • Hard soil or rock overlain by soft soil or loose, granular soil. The installation of CFA piles is typically difficult in a soil profile in which it is necessary to drill into a hard bearing stratum overlain by soft soil or loose granular soil (Figure 3.2a). The problem occurs when the hard stratum is encountered and the rate of penetration is slowed because of the difficult drilling; the overburden soils are then flighted by side loading of the auger above the hard stratum. Decompression of the ground above the hard stratum and ground subsidence can result in the case of a stiff clay layer underlying a water-bearing sand deposit, even if the stiff clay can be drilled without great difficulty. The rate of penetration required for the stiff clay is lower than that for the sand, and the sand will tend to flight during drilling of the clay.

    In addition, a hard rock layer overlain by soft material presents a quality assurance concern in that there is difficulty ensuring that the pile has sound bearing on the rock formation. Piles are typically driven to a resistance that ensures sound bearing, and drilled shafts are typically socketed a short depth into the rock.

    The potential for difficult drilling conditions also exists when a sand stratum is sandwiched between an upper and a deeper clay deposit; in this case, the sand also tends to be flighted and a cone of sand tends to collapse and displace toward the hole. This cone of depression in the sand deposit is caused by over-removal of the sand, which may not be visible at the surface, but could result in: (1) a void beneath the upper clay; (2) loosening of the sand; and (3) over consumption of concrete or grout.

    In comparison, these soil conditions are more favorable for the use of driven piles or drilled shafts, for which cases drilling through sands can be controlled using casing or slurry.

    Figure 3.2: Examples of Difficult Conditions for Augured Piles

    Illustration showing examples of difficult conditions for augured piles

  • Sand-bearing stratum underlying stiff clay. When the bearing stratum is composed of clean, dense, water-bearing sand and is overlain by a stiff clay deposit, pile installation may be difficult (Figure 3.2b). In this case, the slower rate of penetration (relative to the rate of turning of the auger) used in the clay can cause loosening of the sand stratum below when this stratum is encountered, and this results in excessive flighting of the sand from the stratum intended as the primary bearing formation. Excessive flighting occurs when the auger is rotated too much in proportion to the penetration into the soil, such that too much soil is flighted towards the surface and the auger flights do not maintain adequate soil to provide lateral support for the hole. The water pressure in a confined aquifer may contribute to this problem. The result is that the pile does not support the load at the tip in the deeper sand as intended, but almost solely relies on side-shear resistance in the clay. Under these conditions, it is better that the pile either terminate in the clay (assuming an appropriate design capacity is achieved) or the pile be drilled into the sand.
  • Highly variable ground conditions. When highly variable ground conditions exist, in which one of the cases noted above may be encountered at some locations across the site, it is more difficult to provide a relatively uniform drilling criteria for the site. Having varying drilling criteria across the site can lead to problems with quality control and quality assurance, particularly if the wrong criteria are applied to individual piles. Highly variable ground conditions also create additional problems with respect to reliability of capacity predictions.
  • Conditions requiring penetration of very hard strata. When a stratum is very hard to penetrate (e.g., rock), drilling of CFA piles would be very difficult. This condition requires a modification to the CFA pile design so that penetration in the rock is avoided or the use of drilled shafts socketed into the material or driven piles driven to refusal on the material are employed. CFA piles designed to bear on hard rock that cannot be penetrated with an auger must be designed for a smaller bearing value than the rock may be capable of sustaining in other conditions because of the difficulty in achieving sound contact at the pile/rock bearing surface.
  • Ground conditions requiring uncommonly long piles. CFA piles longer than 30 m (100 ft) require unusual equipment for this technique; however, there have been isolated circumstances in which CFA piles longer than 30 m (100 ft) have been used. CFA piles of such length are uncommon, and may require equipment with unusually high torque, high lifting capacity, and tall leads
  • Ground conditions with deep scour or liquefiable sand layers. In these circumstances, where a total or near-total loss of lateral support may occur at significant depths, the piles may be subject to high bending stresses at great depths. CFA piles are most efficient in relatively smaller diameters, and placement of a rebar cage to great depths can be difficult. CFA piles also are not typically designed with reinforcement to achieve high bending resistance. If ground conditions exist where deep loss of support may occur, this condition tends to favor the use of larger diameter drilled shafts or large driven piles. CFA piles may require structural steel inserts, such as steel pipe or H sections, to achieve adequate bending resistance through a zone where loss of support may occur.

Design applications requiring significant shear, bending, or uplift resistance may not be suitable for CFA piles, regardless the type of soil conditions at the site. The limitations associated with reinforcement installation typically restrict the use of CFA piles in these applications. In some cases, groups of CFA piles can provide adequate shear, bending, or uplift resistance; however, another deep foundation system may be more economical.

3.2.3 Project Conditions Affecting the Selection and Use of CFA Piles

CFA piles may be a viable alternative for projects with the following conditions:

  • Projects where speed of installation is important. CFA piles can be installed very quickly, provided the rig has a good working platform on which to move around the site and the geotechnical conditions are otherwise favorable (Figure 3.3). For projects requiring a large number of piles and on projects where high production rates are important, CFA piles can have advantages over drilled shafts or some types of driven piles. Typical production rates on private projects for piles having diameters of 300 to 450 mm (12 to 18 in.) and lengths of less than 20 m (65 ft) are about 300 to 450 m (1,000 to 1,500 ft) per day. These rates are achievable on private projects, such as large buildings, where most of the piles on the project are relatively close together, reducing the amount of movement of the rig between piles. Lower production rates, such as 60 to 150 m (200 to 500 ft) per day, should be expected for transportation projects where pile groups supporting bridge bents are spread across a large project area, or a significant number of battered piles are installed.

    Figure 3.3: CFA Piles at Bridge Interchange

    Photo showing CFA piles at bridge interchange

  • Batter Piles Required. Although not commonly a viable alternative, it is also possible to install CFA piles on a batter, but the speed of installation decreases and these piles are more difficult to construct in other ways. For example, the drill rig capability is diminished when working on a batter and the reinforcing cage is more difficult to install with proper cover. Pile batter should generally be limited to 1 (horizontal):4 (vertical) or steeper for bearing piles. Greater batter angles ranging to even horizontal can be used to install anchor piles in competent, non-caving soil, but these are typically not designed to support large axial compression loads.
  • Projects where large numbers of piles are required. The costs for CFA piles reflect the high productivity for projects where large numbers of piles are required. Prices for CFA piles are often a few dollars per foot less than prestressed concrete or steel piles of similar size and axial capacity, assuming both pile types meet the project performance criteria.
  • Low headroom conditions. Low headroom equipment can be used effectively with CFA piles and is often more cost effective than high strength micropiles if the ground conditions are favorable for CFA pile installation (Figure 3.4). Note that continuous placement of grout is not possible when the auger string must be broken during withdrawal. Therefore, this technique should only be used in favorable ground conditions and with close control to maintain grout pressure and volume during extraction.

    Figure 3.4: Low Headroom CFA Pile Application

    Photo showing low headroom CFA pile application

  • Secant or tangent pile walls up to 10 m (33 ft) of exposed wall height. When CFA piles of less than 1.2 m (4 ft) in diameter can be used for a retaining wall, and when geotechnical conditions are otherwise favorable, CFA piles can be a viable alternative to drilled shafts or slurry walls (Figure 3.5). For this application, it is important to utilize heavy drilling equipment, which can maintain good vertical alignment. A structural steel section may be used for pile reinforcement rather than a reinforcing cage. The CFA drilling technique has been used successfully on many such projects with both anchored earth retention and cantilever walls. Higher walls are possible with the use of tiebacks.
  • Soundwalls in favorable soil conditions. Because soundwalls tend to have large numbers of relatively short piles, CFA piles can be quite fast and economical. Figure 3.6 illustrates an example of a long row of CFA piles for a soundwall along a highway.
  • Pile-supported embankments. Although this type of construction commonly takes place in relatively soft soils, the loading demands on a per pile basis are not particularly very large. The speed and economy of CFA piles especially DD piles, make them a potentially effective alternative to ground modification (Figure 3.7). CFA piles have been utilized for embankment support to limit excessive settlement from soft or compressible foundation soils. This is a special application of CFA piles that requires consideration of edge stability, design of the individual pile caps (if any) and reinforced embankment overlying the piles, as well as the magnitude and time rate of settlement. The reader is referred to Collin (2004) and Han and Akins (2004) for further details.

    Figure 3.5: Secant Pile Wall with CFA Pile Construction

    Photo showing secant pile wall with CFA pile construction

    Figure 3.6: CFA Piles for Soundwall (at right) along Highway (out of view to left)

    Photo of CFA piles for soundwall (at right) along highway (out of view to left)

3.3 Advantages and Limitations of Drilled Displacement Piles

Drilled displacement (DD) piles have many of the same features, advantages, and limitations as CFA piles. Some of the factors that may differ for DD piles compared to CFA piles are outlined below.

  • Better performance in loose sandy soils. DD piles increase the horizontal stress in the ground and densify sandy soils around the pile during installation (Figure 3.8).

    Figure 3.7: Pilecaps on CFA Piles for a Pile-Supported Embankment

    Photo showing pile caps on CFA piles for a pile-supported embankment

    Therefore, this technique achieves some ground improvement around the pile. This improvement leads to higher values of side-shear resistance in granular soils, especially in loose to medium dense sands. DD piles are less subject to the problems of soil flighting, described previously for CFA piles. Hence, mixed soil profiles having loose granular soils interbedded with clays are less of a concern. In general, DD piles will achieve a given load carrying capacity at a shorter length than for a CFA pile of similar diameter.

  • Little or no spoil removed from site. In areas where contaminated ground exists or it is desirable to limit the spoil removed from the site, DD piles are more advantageous than CFA piles or drilled shafts because little or no spoil is generated.
  • Difficult to penetrate dense or hard soils and more limited depth range. Because of the much greater torque required for DD piles relative to CFA piles, it may be impossible or impractical to penetrate deeply into soils with strong resistance. In general, DD piles are not installed as deep as CFA piles and lengths greater than about 20 to 25 m (65 to 80 ft) are not very common. DD piles are not used in rock (a condition favoring drilled shafts), or even weak rock or hard cemented soils (where CFA piles may be used).
  • Effect of displacement. In confined areas or areas in close proximity to utilities or sensitive structures, the use of DD piles can pose potential problems for affecting these structures. Closely spaced DD piles can also cause large pore pressures in loose fine grained soils. Partial displacement piles may work better in this application.

    Figure 3.8: Drilled Displacement Piles Limit Spoil Removal

    Photo of drilled displacement piles limiting spoil removal

3.4 Applications

In this section, several typical applications of CFA piles for transportation projects are described.

3.4.1 Soundwalls

The use of CFA pile foundations for soundwalls represents an easy-to-implement application. Soundwall foundations are commonly characterized by single piles at each column location and by the use of reinforcement or anchor bolts designed to make a moment connection to the column. Figure 3.9 provides an illustration of the standard design detail used by the Florida Department of Transportation (FDOT). These piles are relatively lightly loaded, with the foundation design controlled by overturning from wind loads. A typical foundation has a diameter of 450 to 900 mm (18 to 36 in.) and a depth of 4 to 8 m (13 to 26 ft). CFA piles are an alternative to drilled shafts for these foundations.

Figure 3.9: CFA Pile Foundation for Soundwall
Click on image for full sized version.

Illustration showing CFA pile foundation for soundwall

3.4.2 Bridge Piers and Abutments

Where conditions are favorable, the use of CFA pile foundations is a feasible alternative to other types of deep foundations for bridges. Most often, the type of bridge most suited for the use of CFA foundations are interchange structures (where scour is not a major issue), approach structures, or those involving bridge widening. CFA piles may be favored in areas where pile driving vibrations or noise requirements cannot be met or simply for situations where cost or speed advantages can be achieved.

As of this writing, there have been relatively few cases of bridge structures supported on CFA pile foundations in the United States. An example is provided by Vipulanandan et al. (2004) for a bridge at the Krenek Road site in Crosby, Texas, constructed in the Pleistocene soils of the Gulf coast region. The Texas Department of Transportation (TXDOT) constructed this bridge entirely using CFA piles as an implementation project to provide a comparison of the CFA alternative to driven piles. The project included load tests up to failure on instrumented piles as well as instrumentation on production piles to monitor pile performance in service. The CFA bridge project is located a short distance [about 1 km (0.6 mile)] from the Runneburg Road Bridge site, where a bridge was constructed using driven piles in very similar soil conditions. An examination of the two projects provides a comparison of CFA and driven pile alternates on two very similar projects.

The Krenek Road site for the CFA pile-supported bridge was underlain predominantly by stiff clays with two thin layers of sand and the groundwater table located about 1.5 m (5 ft) below the ground surface. The bridge was founded on 64 CFA piles, 17 to 19 m (56 to 62 ft) long and 450 mm (18 in.) in diameter. A schematic diagram is presented in Figure 3.10. The abutment piles were installed on a batter of 1:4. Intermediate bent columns were founded on 4-pile groups of vertical piles. The piles were designed to terminate in a dense sand stratum (Figure 3.11). Side-shear and end-bearing resistance provide a design axial capacity of 810 kN (90 tons). There was no significant design uplift or lateral load requirements for these piles.

Figure 3.10: Schematic Diagram of the Foundation on CFA Piles for the Krenek Road Bridge

Illustration showing a schematic diagram of the foundation on CFA piles for the Krenek Road Bridge

Vipulanandan et al. (2004)

The foundation for the Runneburg Road Bridge was almost identical to the Krenek Road Bridge, except that the Runneburg Road Bridge was founded on 400 mm (16 in.) square prestressed concrete piles driven to a depth of 14 m (46 ft). The piles of the Runneburg Road Bridge were terminated entirely within the stiff clay formation and designed to support the design axial load of 810 kN (90 tons) primarily using side friction.

Figure 3.11: CFA Piles at the Krenek Road Bridge Site

Photo of CFA piles at the Krenek Road Bridge site

Source:University of Houston

Each vertical CFA pile of the Krenek Road Bridge was installed relatively fast, within about 15 minutes. For this project, the time needed to move the rig was a significant factor to the schedule, especially for the driven piles, which experienced equipment delays during installation of the central bent piles. The cycle time for the battered abutment piles was about 45 minutes for each type. For the driven piles, about one third of this time was due to the required pre-boring.

Vipulanandan et al. (2004) noted some construction issues for the installation of CFA piles. In several cases, the contractor had difficulty installing the full-length cages due to excessive grout viscosity and/or lack of timely work to install the cages immediately after completion of the grouting. On numerous occasions, the contractor was observed slowly turning the auger with the auger in the borehole and without either excavating or pumping grout. This operation was performed because grout was not available in a timely fashion and the operator could not stop rotation and risked seizing the auger in the ground. This practice increased soil mining, particularly in the sand strata.

Load tests were conducted on test piles at both sites, and the CFA piles were instrumented to determine the distribution of side-shear and end-bearing resistance. Although the designers had anticipated higher side-shear strength values for the driven piles, the CFA piles actually mobilized higher side friction than the driven prestressed piles. Note that this conclusion is based on an estimated distribution of side-shear and end-bearing in the driven piles, because the driven piles were not fully instrumented. The base resistance for CFA piles was virtually zero, probably reflecting the effect of decompression of the dense sand-bearing stratum during installation of the pile through the stiff clay. The CFA piles actually provided the needed axial capacity, but through higher than anticipated side-shear resistance and much lower than anticipated end-bearing resistance.

Twelve production piles were instrumented and monitored during construction and load testing using trucks. The results from the pile instrumentation suggest that the piles supported the fully loaded bridge entirely by mobilizing side friction alone and with very small [around 3 mm (0.1 in.)] movements (Figure 3.12). A lesson learned from this project is that CFA piles would have been better designed to terminate in the clay rather than attempting to mobilize end-bearing in a water-bearing sand stratum below the stiff clay.

Figure 3.12: Comparison of Measured Settlements and Test Pile, Krenek Road Bridge Site

Photo and illustration showing the comparison of measured settlements and test pile at the Krenek Road Bridge site

Photo and illustration showing the comparison of measured settlements and test pile at the Krenek Road Bridge site

Vipulanandan et al., (2004)

The unit cost of CFA piles was approximately $65 per linear meter ($20 per linear foot). The instrumentation and full-length cage, required for the instrumentation, affected the unit cost, which was estimated to be about $7 higher per linear meter ($2 per linear foot) than would normally be anticipated for production piles. Cost per pile for CFA piles at the central bent was $1,140 per pile. The cost for the driven piles at the central bent of the Runneburg Road Bridge was less than the CFA pile cost at the Krenek Road Bridge; however, the load tests indicated that a higher factor of safety was achieved for the CFA piles than for the driven piles and, if the lengths were adjusted to provide a similar factor of safety for axial loading, the unit cost of the CFA piles would have been about 8% less.

The comparison study between these two bridges suggests that CFA piles can provide a viable alternative to conventional driven pile foundations. As a result of these experiences, TXDOT plans to utilize CFA piles on other future bridge projects where conditions appear favorable.

3.4.3 Retaining Structures

CFA piles can be used to construct secant or tangent pile walls in a manner very similar to that of drilled shaft walls, which can be designed as cantilever or anchored walls. The most significant distinction relating to CFA piles, as opposed to other types of vertical elements, is the construction method for the vertical element. The CFA piles are intended to provide a reinforced vertical wall member having a similar function as that of a drilled shaft, slurry wall section, or sheet pile. In almost all such cases, the contractor provides designs of CFA piles for retaining structures as a design-build option. Figure 3.13 illustrates a typical CFA secant pile wall.

Figure 3.13: Secant CFA Pile Wall for a Light Rail System in Germany

Photo showing a secant CFA pile wall for a light rail system in Germany

The major differences for CFA pile wall systems as compared to other pile types are discussed below.

  • Diameters of CFA piles are generally limited to about 1 m (40 in.).
  • Maximum depths for CFA piles are generally no more than 10 to 18 m (33 to 60 ft) with wall heights generally around 12 m (40 ft) or less. This limitation is not only related to machine capability, but also due to the fact that the reinforcement must be placed into the fluid concrete and verticality of the piles can be difficult to maintain for long piles.
  • Control of verticality is critical to keep the piles aligned, especially if a watertight structure is needed; some of the hydraulic rigs equipped with inclinometers are well-suited for this construction.
  • For secant pile systems, the sequencing of pile installation and set time and initial strength characteristics of the concrete is critical so that the excavation equipment can cut into previously drilled piles. Some contractors install primary piles using a weaker concrete mix and utilize a stronger mix for the secondary piles, which provide the main structural strength of the wall (see Figures 3.14 and 3.15). Large, high torque-capacity rigs are necessary, especially when cutting into existing concrete piles.
  • Placement of reinforcement can be more difficult in a CFA pile than in a conventional drilled shaft or slurry wall, in which the reinforcement is placed ahead of the concrete.

    Figure 3.14: Schematic Plan View of a Secant Pile Wall

    Illustration showing schematic plan view of a secant pile wall

    Figure 3.15: Drilling CFA Piles through Guide for Secant Wall

    Photo showing the drilling of CFA piles through guide for secant wall

3.4.4 Pile-Supported Embankments

The use of CFA piles for a pile-supported embankment may represent a cost-effective alternative to ground modification or embankment support using driven piles. The use of pile support for embankments is likely to be considered only when the foundation strata consist of weak and compressible subsoils, which would take a long time to consolidate. Furthermore, there is an interest in minimizing post-construction settlements of the embankment or accelerating construction. Examples include, widening of existing embankments (where the additional fill may result in costly or disruptive damage to the existing structure); a fill supporting a transportation facility that is particularly sensitive to settlements (such as a high-speed rail); or the fill approach to a pile-supported structure (where differential settlements may be a problem). Accelerated construction is required for projects where additional cost due to traffic shifts, geotechnical instrumentation, and related time delays present an unacceptable situation to project owners.

CFA piles offer the advantages of installation speed and economy (cycle times of 15 minutes or less per pile are not uncommon), and costs on the order of $40 per linear meter ($12 per linear foot) are feasible on a large volume project using many small diameter [i.e., 300 to 350 mm (12 to 14 in.)] CFA piles.

A diagram of a pile-supported embankment for a railway project in Italy is illustrated in Figure 3.16. This embankment was designed as part of a widening project to increase traffic capacity. The pile support was used to limit settlements produced by the new fill on the existing railway structure and the new rail line. The piles were capped using precast cylinder sections filled with concrete (shown previously in Figure 3.7), and the fill overlying the pile caps was reinforced using geotextiles.

3.5 Construction Cost Evaluation

Because the use of CFA piles in U.S. transportation facilities has been very limited, there are few records of cost data for transportation projects. Costs of CFA piles on private projects often range from approximately $40 to $60 per linear meter ($12 to $20 per linear foot) for 300- to 450-mm (12- to 18- in.) diameter piles. However, these projects typically include much greater quantities of piling and fewer moves across the site than is typical for a bridge or soundwall; prices on transportation projects are likely to be higher. In addition, costs relating to performance and integrity testing are likely to be higher on transportation projects. A major factor on transportation projects is the impact of site constraints on productivity. Many variables affect pile costs, including length, diameter, reinforcement, and grout strength. Costs will also vary according to region of the country, as well as the size of the project.

The aforementioned project in Texas has been followed by another bridge project on State Highway 7 in Houston County, which was awarded in early 2005. This project includes 24 760-mm (30-in.) diameter piles. The bid price was $200 per linear meter ($60 per linear foot) for 237 linear meters (778 linear feet) of piling, along with a mobilization cost of $25,000 and a cost of $25,000 each for two static load tests.

The Kansas DOT has used CFA piles on only a few projects, including two bridges and a secant pile wall. These projects utilized 400- to 450-mm (16- to 18-in.) diameter piles, with typical costs in the range of $72 to $85 per linear meter ($22 to $26 per linear foot). Some low headroom work was bid at $320 per linear meter ($98 per linear foot). According to Jim Brennan, Kansas State Geotechnical Engineer, the prices are quite sensitive to mobilization costs and the numbers of piles on the project, with fewer piles resulting in higher unit costs.

Figure 3.16: Diagram of Pile-Supported Embankment for Italian Railway Project

Illustration showing diagram of pile-supported embankment for Italian railway project

The Florida DOT has used CFA piles for soundwalls, usually in the 760- to 900-mm (30- to 36-in.) diameter range and for depths typically less than 9 m (30 ft). Bid prices on these projects are typically in the range of $200 to $260 per linear meter ($60 to $80 per linear foot). Production ranges from 6 to 15 piles per day. Frizzi and Vedula (2004) identify relative costs of CFA piles vs. driven precast concrete piles for a project in south Florida. Details of their cost comparison can be found in their paper.

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Updated: 04/07/2011
 

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