3.5 Driven Piles

3.5.1 Prestressed Concrete Piles [5.13.4.4] (01/06) Jan 2006 Per Tom Andres: Combined sections 3.5.2 and 3.5.15

A. For prestressed piling not subjected to significant flexure under service or impact loading, design strand development in accordance with LRFD [5.11.4] and [5.8.2.3].  Bending that produces cracking in the pile, such as that resulting from ship impact loading, is considered significant.

B. A 1-foot embedment is considered a pinned head condition. For the pinned pile head condition the strand development must be in accordance with LRFD [5.11.4] and [5.8.2.3].

C. For the standard, square, FDOT prestressed concrete piles (12-inch through 30-inch), a pile embedment of 48-inches into a reinforced concrete footing is considered adequate to develop the full bending capacity of the pile. The pile must be solid, (or the pile void filled with structural concrete) for a length of no less than 8 feet (4 feet of embedment length plus 4 feet below the bottom of the pile cap).

D. Grouting a pipe or reinforcing bar cage into the void can strengthen a voided pile. With this detail, the full composite section capacity of the pile and pipe/cage can be developed. The required length of this composite pile section is a function of the loading but must be no less than 8 feet (4 feet below the bottom of the pile cap).

E. Bending capacity versus pile cap embedment length relationship for prestressed piles of widths or diameters larger than 30-inches will require custom designs based upon LRFD specifications, Department approval, and may require strand development/pile embedment tests.

Commentary:

The FDOT Structures Research Center conducted full scale testing of two 30-inch square concrete piles reinforced with prestressing steel and an embedded steel pipe.  The piles, which were embedded 4 feet into a reinforced pile cap, developed the calculated theoretical bending strength of the section without strand slip.  See FDOT Report No 98-9 Testing of Pile-to-Pile Cap Moment Connection for 30 Prestressed Concrete Pipe-Pile.  It was concluded that the confinement effects of the pile cap serve to improve the bond characteristics of the strand.

F. Minimum Sizes

1.) Fender Systems: 14-inch square piling.

2.) Bridges: 18-inch square piling.

3.) Bridges (Extremely Aggressive Environment due to chlorides): 24-inch square piling.

4.) Specify minimum 24-inch piles for "Extremely Aggressive" salt-water sites. Smaller piles may be acceptable with the approval of the District Maintenance Engineer or his designated representative. This decision is dependent upon site-specific conditions and the history of piles in the vicinity. If pile bents will be exposed to wet/dry cycles that could necessitate future jacketing, a minimum 24-inch pile must be used. The District Maintenance Engineer may grant exemptions for pedestrian bridges and fishing piers.

3.5.2 Concrete Cylinder Piles (01/06) Jan 2006 - Per Tom Andres: was 3.5.17
July 2004 - Minor revision for ducts v. strands.

A. Plant produced, post-tensioned segmented cylinder piles (horizontally assembled, stressed and grouted) or pretensioned wet cast cylinder piles are allowed by the Department. Internal redundancy of segmented cylinder piles is provided by the number of strands (maximum of 3 strands per duct.) If cylinder piles are included in the final design at a water location, provide alternate designs utilizing 54-inch and 60-inch cylinder pile sizes. If cylinder piles are used in the final design on a land project and the anticipated lengths are too long for transport by truck, provide alternate designs; one for field assembled, segmented cylinder piles and another for drilled shafts or square precast piles.

B. For concrete cover on cylinder pile reinforcement, see Table 1.2 Minimum Concrete Cover Requirements.

C. For cylinder piles in water and designed for vessel impact, fill the void with concrete to prevent puncture; see 3.11.H for required plug lengths.

D. For cylinder piles on land and within the clear zone, fill the void with concrete plug to prevent puncture from vehicular impact; see 3.11.I for required plug lengths.

E. Segmented cylinder piles in water (within the splash zone) require a redundant load path for durability.  For segmented cylinder piles in water, design an independent plug that develops the full capacity of the pile from 2 feet below MLW to the bottom of the bent cap.

F. Segmented cylinder piles with water line footings do not require a redundant load path for durability.

3.5.3 Steel Piles and Wall Anchor Bars (07/07) July 2007 - 3.5.3.A. Revised coating requirements. 3.5.3.B. (Table) - Revised sacrificial thickness. (Commentary) - Added corrosion rates for completely buried piles and Design Life. 3.5.3.C. Added requirement to include sacrificial thickness in Section Properties on plans and expanded commentary. Jan 2006 - Added new sections A through C. Added requirement for domestic suppliers to C.1

A.  Protective Coatings and Corrosion Mitigation Measures

1.)  Permanent Steel Sheet Piles: Use a three coat shop applied system comprised of an inorganic zinc primer and two coats of coal tar-epoxy in accordance with Specification Section 560-14. Include a plan note requiring the  exposed side of sheet piles be coated from the top of the sheet piles to a depth of five feet below  the lower of the design ground surface or the design scour depth. Depict design ground surface or the design scour depth on Wall Control Drawings. Coat weathering steel piles in the same manner as non-weathering steel piles.

2.)  Wall anchor bars: Use an epoxy-mastic heat shrink wrap or ducting and grouting. At the connection to wall, use a coal tar-epoxy mastic coating.

3.) Pipe and H-Piles with corrosion protection measures as noted in table below: Use a three coat system comprised of an inorganic zinc primer and two coats of coal tar-epoxy in accordance with Specification Section 560-14. Include a plan note requiring all exposed outside surfaces of piles be coated from the top of the piles to a depth of five feet below the lower of the design ground surface or the design scour depth. Depict design ground surface or the design scour depth in plans.

B.  Additional Steel Thickness

To account for future corrosion, add an additional sacrificial steel thickness to all permanent steel substructure and wall components as shown in the table below.

Commentary:

The following criteria  were used to determine the additional steel thickness required:

Environmental Classification versus Corrosion Rate per side for partially buried piles and wall anchor bars:

Slightly Aggressive: 0.001 inches/year

Moderately Aggressive: 0.002 inches/year

Extremely Aggressive: 0.003 inches/year

Environmental Classification versus Corrosion Rate per side for completely buried piles:

Slightly Aggressive: 0.0005 inches/year

Moderately Aggressive: 0.001 inches/year

Extremely Aggressive: 0.0015 inches/year

Design Life:

Pipe and H-Piles without corrosion protection measures:

75 years (additional sacrificial thickness required)

Pipe and H-Piles, Sheet Piles and Wall Anchor Bars with corrosion protection measures:

75 years ( coating system 30 years and sacrificial thickness 45 years),

(Corrosion rates for anchored sheet pile walls beyond the coating system life are neglected due to structural redundancy).

Application:

Partially buried Pipe Piles and H-Piles : Two Sided Attack at soil and/or water line.

Completely buried Pipe Piles and H-Piles: Two Sided Attack below ground line as shown in table above; single sided attack if Pipe Piles are concrete filled.

Sheet Piles: Single Sided Attack at soil and/or water line.

C.  Sheet Piles

1.) Design and detail the sheet pile properties for both cold-rolled and hot-rolled sections where possible. Include the required additional sacrificial steel thickness in the section properties shown in the plans. Design the cold-rolled section using flexural section properties that are 120% of the hot-rolled section values. Assure that standard shapes meeting the required properties are readily available from domestic suppliers.

2.) Detail wall components such as caps and tie-backs to work with both the hot-rolled and cold-rolled sections where possible.

3.) Indicate on the plans:

a.) minimum tip elevations (ft).

b.) minimum section modulus (in3/ft).

c.) minimum moment of inertia (in4/ft).

Commentary:

Tests have shown that cold-rolled sheet pile sections fail in bending at about 85% of their full-section capacity, while hot-rolled sections develop full capacity.  There is also some question on the availability of hot-rolled sheet piles; so, by showing the required properties for both types, the Contractor can furnish whichever is available.

The corrosion rate of weathering steel in contact with soil and water is the same as for ordinary carbon steel. The benefits, if any, associated with the use of weathering steel are questionable in partial burial applications like sheet pile walls.  Therefore, weathering steel sheet piles are to be coated in the same manner as carbon steel sheet piles in accordance with Specification Section 560-14.

Anchored steel sheet pile walls should be considered for use in extremely aggressive environments due to the additional sacrificial steel thickness required for steel sheet piles used in cantilevered walls.

3.5.4 Spacing and Clearances [10.7.1.5]

Delete the first sentence of LRFD 10.7.1.5 and substitute the following:

"Minimum pile spacing (center-to-center) must be at least three times the least width of the pile measured at the ground line."

3.5.5 Downdrag [10.7.14]

A. Show the downdrag load on the plans.

B. For pile foundations, downdrag is the ultimate skin friction above the neutral point (the loading added to the pile due to settlement of the surrounding soils) plus the dynamic resistance above the neutral point (the resistance that must be overcome during the driving of the pile) minus the live load. The dynamic resistance typically equals 0.50 to 1.0 times the ultimate skin friction.

C. Scour may or may not occur as predicted; however, do not discount scourable soil layers to reduce the predicted downdrag.

3.5.6 Resistance Factors [10.5.5]

Delete LRFD Table 10.5.5-2 and substitute SDG Table 3.1 for piles.

3.5.7 Battered Piles [10.7.1.6]

A. Plumb piles are preferred; however, if the design requires battered piles, a single batter, either parallel or perpendicular to the centerline of the cap or footing, is preferred.

B. If the design requires a compound batter, orient the pile so that the direction of batter will be perpendicular to the face of the pile.

C. With input from the Geotechnical Engineer, the Structures Engineer must evaluate the effects of length and batter on the selected pile size. Do not exceed the following maximum batters, measured as the horizontal-to-vertical ratio, h:v:

Commentary: When driven on a batter, the tips of long, slender piles tend to deflect downward due to gravity. This creates undesirable flexure stresses and may lead to pile failure, especially when driving through deep water and in very soft/loose soil.  Hard subsoil layers can also deflect piles outward in the direction of batter resulting in pile breakage due to flexure. The feasibility of battered piles must be determined during the design phase.

3.5.8 Minimum Tip Elevation [10.7.1.11]

The minimum pile or drilled shaft tip elevation must be the deepest of the minimum elevations that satisfy lateral stability requirements for the three limit states. The minimum tip elevation may be set lower to satisfy any unique soil conditions provided the requirements in the FDOT Soil and Foundation Handbook are met. The minimum tip must be established by the Structures Engineer with the concurrence of the Geotechnical Engineer.

Use the following procedure to establish the Minimum Tip Elevation:

A. Establish a high end bearing resistance such that the pile or shaft tip will not settle due to axial forces;

B. Apply the controlling lateral load cases, raising the pile/shaft tips until the foundation becomes unstable;

C. Add 5 feet or 20% of the penetration, whichever is less, to the penetration at which the foundation becomes unstable to establish the Minimum Tip Elevation.

Commentary:

The assumed soil-pile/shaft ultimate skin friction is not modified using this procedure. It is assumed that the difference in axial capacity predicted during this portion of the design phase versus what is established during construction is due to end bearing only.

3.5.9 Anticipated Pile Lengths [10.7.1.10]

The anticipated pile lengths are used only to estimate quantities and set test pile lengths. These lengths are determined by using the lower of the minimum tip elevations specified on the plans or the axial capacity elevations predicted by the pile capacity curves (SPT 97 Davisson Capacity Curves.)

3.5.10 Test Piles [10.7.9] (01/07) Jan 2007 - Per TDB C06-10, added D. requiring embedded data collectors.

A. Test piles include both static and dynamic load test piles, which are driven to determine soil capacity, pile-driving system, pile drivability, production pile lengths, and driving criteria. Test piles are required for all projects unless, in the opinion of the District Geotechnical Engineer, pile-driving records for the existing structure include enough information (i.e., stroke length, hammer type, cushion type, etc.) to adequately determine the authorized pile lengths and driving criteria.

B. At least one test pile must be located approximately every 200 feet of bridge length with a minimum of two test piles per bridge structure. These requirements apply for each size and pile type in the bridge except at end bents. For bascule piers and high-level crossings that require large footings or cofferdam-type foundations, specify at least one test pile at each pier. Consider maintenance of traffic requirements, required sequence of construction, geological conditions, and pile spacing when determining the location of test piles. For phased construction, test piles should be located in the first phase of construction. The Geotechnical Engineer must verify the suitability of the test pile locations.

C. Test piles should be at least 15 feet longer than the estimated length of production piles. Additional length may be required by the load frame geometry when static load tests are used. The Structural Engineer must coordinate his recommended test pile lengths and locations with the District Geotechnical Engineer and Geotechnical Consultant, before finalization of the plans.

D. Specify one Embedded Data Collector (EDC) per test pile on all projects with bridges containing 18-inch, 20-inch, 24-inch or 30-inch prestressed concrete test piles. Include Pay Item No. 455-146 (Embedded Data Collector, each) on the Summary of Pay Items. Coordinate with the District Specifications Office to ensure that special provision SP4550512 is included in the specifications package.

Commentary:  Test piles are exploratory in nature and may be driven harder, deeper, and to a greater bearing value than required for permanent piling or may be used to establish soil freeze parameters.  (See FDOT Specifications Section 455). The Structures Engineer must consider these facts when establishing test pile lengths.

3.5.11 Load Tests [10.7.3.8][10.8.3.5.6]

A. Load test options include static load tests, dynamic load tests, Osterberg load tests, and Statnamic load tests. Both design phase and construction phase load testing should be investigated. When evaluating the benefits and costs of load tests, consider soil stratigraphy, design loads, foundation type and number, type of loading, testing equipment, and mobilization.

 Commentary: In general, the more variable the subsurface profile, the less cost-effective static load tests are. When soil variability is an issue, other options include additional field exploration, more laboratory samples, in-situ testing, and pullout tests.

B. Static Load Test [10.7.3.8]: When static load tests are required, show on the plans: the number of required tests, the pile or shaft type and size, and test loads. Piles must be dynamically load tested before static load testing. Static load tests should test the pile or drilled shaft to failure as required in Section 455-2 of the Specifications. The maximum loading of the static load test must exceed the nominal capacity of the pile or twice the factored design load, whichever is greater.

 Commentary: Test piles or drilled shafts can be subjected to static compression, tension, or lateral test loads.  Static load tests may be desirable when foundation investigations reveal sites where the soils cause concern regarding the development of the required pile capacity at the desired depths, and/or the possibility that considerable cost savings will result if higher soil capacities can be obtained.  Furthermore, static load tests will reduce the driving effort since a higher Performance Factor is applied to the Ultimate Bearing Capacity formula.

C. Dynamic Load Test [10.7.3.8.3]: All test piles must have dynamic load tests. Indicate this requirement with a note on the foundation layout sheet.

 Commentary: Dynamic load testing of piles employs strain transducers and accelerometers to measure pile force and acceleration during driving operations.  A Pile Driving Analyzer (PDA) unit (or similar) is used for this purpose.

D. Statnamic Load Test: When Statnamic load tests are required, show on the plans: the number of required tests, the size and type of pile or shaft, and test loads. Piles must be dynamically load tested before Statnamic load testing. Equivalent static load tests derived from Statnamic load tests should test the pile or drilled shaft to failure as required in Section 455-2 of the Specifications. The maximum derived static loading must exceed the nominal capacity of the pile or twice the factored design load, whichever is greater.

E. Special Considerations: Load testing of foundations that will be subjected to subsequent scour activity requires special attention. The necessity of isolating the resistance of the scourable material from the load test results must be considered.

3.5.12 Pile Driving Resistance [10.7.1.3]

A. The Geotechnical Engineer calculates the required Nominal Bearing Resistance (Qn) as:

B. Typically, Qn will be the required driving resistance. Nominal Bearing Resistance values given in the Pile Data Table must not exceed the following values unless specific justification is provided and accepted by the Departments District Geotechnical Engineer for Category I structures or the State Geotechnical Engineer for Category II structures:

Table 3.2 Maximum Pile Driving Resistance

C. When the minimum tip requirements govern over bearing requirements, construction methods may need to be modified so that pile-driving resistance never exceeds the values given above. Construction methods such as preforming or jetting may be required at these locations. See the Pile Data Table in the Structures Detailing Manual Examples.

D. The values listed above are based on upper bound driving resistance of typical driving equipment. The maximum driving resistance values listed above should not be considered default values for design. These values may not be achievable in certain areas of Florida based on subsoil conditions. Local experience may dictate designs utilizing substantially reduced ultimate bearing loads. Contact the District Geotechnical Engineer for guidance in the project area.

3.5.13 Pile Jetting and Preforming

A. When jetting or preforming is allowed, the depth of jetting or preforming must comply with all the design criteria. For projects with scour, jetting or preforming will not normally be permitted below the 100-year scour elevation (EL100).If jetting or preforming elevations are deeper than EL100, the lateral confinement around the pile must be restored to EL100.  If jetting or preforming is utilized, the Net Scour Resistance to that depth is assumed to be equal to 0.0 kips (provided the hole remains open or continuous jetting is being done).

B. Verify that jetting will not violate environmental permits before specifying it in the contract documents.

3.5.14 Pile Data Table

A. Include in the plans, a Pile Data Table and notes as shown on SDME EX-9.

B. For items that do not apply, place "N/A" in the column but do not revise or modify the table.  

C. Round loads to the nearest ton. Round elevations and pile lengths to the nearest foot.

D. The Pile Data Table is not required in the Geotechnical Report; however, the Geotechnical Engineer of Record must review the information shown on the plans for these tables.

3.5.15 Plan Notes

A. Use Equation 3.1 to determine the Required Driving Resistance value (Qn) for the Pile Data Table.

B. Additional Plan Notes:

1.) Minimum Tip Elevation is required _________________________ (reason must be completed by designer, for example: for lateral stability, to minimize post-construction settlements or "for required tension capacity").

2.) When a required jetting or preformed elevation is not shown on the table, do not jet or preform pile locations without prior written approval of the District Geotechnical Engineer. Do not advance jets or preformed pile holes deeper than the jetting or preformed elevations shown on the table without the prior approval of the District Geotechnical Engineer.  If actual jetting or preforming elevations differ from those shown on the table, the District Geotechnical Engineer will determine the required driving resistance.

3.5.16 Fender Piles....See SDG 3.14 Fender Systems

3.5.17 Concrete Piling Spliced with Steel Devices (07/07) July 2007 - Added Section 3.5.17

Concrete piling spliced with steel devices (e.g. welded connection or locking devices) shall only be used where the splices will be at least 4 feet below the lower of the design ground surface or the design scour depth.