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Transportation Curriculum Coordination Council |
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You have verified that the Contractor's equipment matches what was submitted and approved in the Pile Installation Plan, that they have complied with Protection of Existing Structures requirements and they are now getting ready to place the first pile in position.
It is important that the pile be located in the proper plan position and be plumb or if battered, at the correct batter. Piles driven at the wrong locations, not plumb or at incorrect batters are a waste of everyone's time. Though not your responsibility you need to verify that tolerances are adhered to. Let's review tolerances.
It is imperative that the pile be located where it is supposed to be. If not, the remainder of the structure may not match up and that's not good. The plans provide the pile locations and the specifications provide the degree of accuracy the Contractor must meet.
How close is the pile to the planned location? The center of the pile is to be within three inches of the planned position.
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Ensure that the final position of the pile head at cut-off elevation is no more than 3 inches [75 mm] from the plan position indicated in the plans.If the pile is to be plumb or battered it is important that it be within a certain axial alignment as specified in.
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Ensure that the axial alignment of the driven piles does not deviate by more than ¼ in/ft [20 mm/m] from the vertical or batter line indicated in the plans.
The pile cut-off elevation is specified in the plans. This is the elevation at which the designers want the top of the pile to be. In some cases, the Contractor may need to build-up the pile or cut it off to achieve the elevation. Regardless of how the pile top gets to the planned elevation, it must be within the tolerances specified in.
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Ensure that the final elevation of the pile head is no more than 1½ inches [38 mm] above, or more than 4 inches [100 mm] below, the elevation shown in the plans. Do not embed the pile less than 6 inches [150 mm] below the elevation shown in the plans unless a minimum penetration requirement is shown.
Perhaps this pile is to be driven through an embankment and predrilled holes are required or the plans call for preformed holes due to below grade conditions. One is a pay item; one isn't, so let's review Predrilled and Preformed Holes.
There are situations presented by geologic conditions or other conditions requiring the use of a predrilled hole or a preformed hole.
Notice that these terms are not interchangeable. They are totally separate and distinct terms, with a significant difference.
Predrilled holes are not paid for. Preformed holes are paid for.
Therefore, it is important that you know the difference in these two types of holes.
Predrilled holes are either "starter holes", holes that have a maximum depth of 4 feet, or holes drilled through an embankment or compacted fill. They are also used for getting through rock material that may damage the pile during driving.
It is important to note that displacement piles, for example square concrete prestressed piles, are not to be driven through an embankment. When predrilling through an embankment, the hole is to be drilled to "natural ground" surface. This is the elevation of the existing grade prior to placement of the embankment fill. Often times this is estimated, if not specifically identified in the plans. The Contractor's estimate and the Inspector's estimate of "natural ground" should be fairly close.
These are holes determined to be necessary by the designer or engineer to penetrate a strata that would prevent the driving or jetting of the piles to the desired penetration. They serve as a penetration aid when the piles cannot be advanced with driving, jetting or a combination of these. Generally, preformed holes are identified in the project plans.
It is important to note that the Contractor cannot just preform a hole to the pile tip elevation required and stick in the pile. They must drive the pile to determine that the driving criteria has been met.
Does the Contractor plan on jetting? Is he going to use external jets or center hole jets? There are times when jetting isn't permitted. Let's review jetting.
Jetting is simply the process of using water under pressure to erode the soil, thereby allowing for the advancement of the pile. The Engineer must approve all jetting.
Jetting is typically performed with either a center-hole jet, where a jet is inserted into a hole down the center of the pile or performed by external water jets attached outside the pile.
Note- Jetting through an embankment is not permitted.
The Inspector needs to set-up the Pile Driving Record Book and some information can be entered prior to driving, so let's prepare the Pile Driving Record.
Prior to the Contractor commencing pile driving, the Inspector can fill in a vast majority of the Pile Driving Record book for that pile and should make it a habit to do this before driving begins on any pile.
As covered earlier, much of the requested information is already known, either from the plans, the Pile Installation Plan, the Driving Criteria Letter or the Authorized Lengths Letter. However, following are two extremely helpful items that can be entered prior to driving commencing and will make your job so much easier.
Minimum Tip Target (MT) - MT, This is the specified Minimum Tip Elevation Target. If a Minimum Tip is specified, this is the elevation the tip of the pile must achieve before driving can be stopped, unless approved by the Engineer. This is an elevation that you can mark ahead of time. To have to constantly be calculating where the pile tip is in relation to Minimum Tip Elevation can be a hassle. By making a mark ahead, the Inspector has one less thing to worry about. So, what is it and how does the Inspector calculate it?
Stop for Set-Check (CO) - CO, The "Stop for Set-Check" mark is also a mark the Inspector can make ahead of time. During the heat of battle, to have to constantly be calculating where Cutoff is in relation to the amount of pile remaining can just be another thing to worry about. Remember, the specification states we should stop driving, if the pile is within 12" of the Cutoff elevation and the required resistance has not been achieved, for a 15 minute Set-Check. This interruption in driving will allow us to perform a set-check to see if the pile gains capacity. By making a mark ahead, the Inspector eliminates one more thing to worry about. So, what is it and how does the Inspector calculate it?
Minimum Tip Target is a mark in the Pile Log Book, prior to driving, that assists the Inspector in easily identifying when the pile tip has reached "Minimum Tip".
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MT = Reference Elev. - Min. Tip Elev.
EXAMPLE 1:
Assume Reference Elevation = +10.00 ft.
Assume Specified Min. Tip Elev. = -53.00 ft.
Therefore;
+10.00 - (-53.00) (Remember- A plus minus a minus equals a plus
+10.00 + 53.00 (So our equation looks like this now)
= 63.00 feet
Therefore at the 63-foot mark in the logbook you would make your MT mark and when the 63 foot mark on the pile reaches the reference point you have reached Minimum Tip.
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Assume Reference Elevation = +80.00 ft.
Assume Specified Min. Tip Elev. = +20.00 ft.
Assume batter is 10:3
Therefore;
(+80.00 - +20.00)/.958
60/.958
= 62.63 feet
Therefore at the 62-foot mark in the logbook you would make your MT mark.
| Batter Ratio (V:H) | Correction Factor (R) |
|---|---|
| 12:1 | 0.997 |
| 10:1 | 0.995 |
| 12:2 (6:1) | 0.986 |
| 10:2 (5:1) | 0.981 |
| 12:3 (4:1) | 0.971 |
| 10:3 | 0.958 |
| 12:4 (3:1) | 0.949 |
| 10:4 (5:2) | 0.928 |
| 12:5 | 0.923 |
"Stop for Set-Check Target" is a mark in the Pile Log Book, prior to driving, that assists the Inspector in easily identifying when the specified pile "Cutoff Elevation" is within 2 feet of the elevation. We suggest 2 feet prior to cutoff for this mark, even though the specification states 12". A little extra time is the Inspector's friend.
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CO = Pile Length - 2' - (Cut-off Elev. - Ref. Elev.)
EXAMPLE 1:
Assume pile length (L) is 90 ft.
Assume Cut-off Elev. = + 12.00 ft.
Assume Reference Elevation = +10.00 ft.
Therefore;
90'- 2' - (+12.00 - +10.00)- Remember, always do the function in brackets first
90'- 2' - (2)88' - 2' = 86'
= 86.00 feet
Therefore at the 86 foot mark in the logbook you would make your CO mark and as the 86 foot mark on the pile reaches the reference point, you will know you are at that critical Set-Check decision making point.
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CO = Pile Length - 2' - [(Cut-off Elev. - Ref. Elev.)/Corr. Factor]
(See correction factors in above table)
EXAMPLE 1:
Assume pile length (L) is 90 ft.
Assume Cut-off Elev. = + 12.00 ft.
Assume Reference Elevation = +10.00 ft.
Assume batter is 10:3
Therefore;
90'- 2' - [(+12.00 - +10.00)/.958] t
90'- 2' - [2/.958]
90'-2'- 2.08
88-2.08 = 85.9'
= 85.92 feet
Therefore at the 85.9 foot mark in the logbook you would make your CO mark and watch for the 85.9 pile mark passing reference point.
In some instances, the authorized pile length may not be long enough. In those instances, the Contractor needs to splice on additional length, so let's review Splicing of Piles.
There are several situations which would necessitate the splicing of piles to achieve additional length, such as:
In the event splicing is needed, ask yourself these questions:
Once the type of splice is determined, the following items should be checked to ensure that the splice is properly performed:
Spliced prestressed concrete piles are highly susceptible to damage from high tension stresses due to the lack of prestressing in the splice. The Inspector should pay particular attention to the splicing operation and the driving of the spliced pile. Alignment is probably the major cause of failure of spliced piles. Incorrect use of the epoxy procedure is the second leading cause of splice failure. Also remember that spliced piles cannot withstand the same tension stresses as an unspliced pile. Therefore, driving in high tension needs to be avoided if at all possible. If any cracking appears, the driving operation should be stopped and the Engineer notified.
The Specification uses a variety of terms, interchangeably, to describe these splices- Extension, Build-Up and Splice. These terms are based upon the length of the "splice". To keep this simple, remember:
Build-up- less than 2 feet below cutoff with dowels drilled in place. Concrete and steel are placed as part of the cap.
Splice- less than 21 feet as a nondriven or nondrivable.
Splice- greater than 21 feet must be made as a drivable splice.
Therefore- A Buildup is anything 2 feet or less in length, everything else is a splice.
Splices are use to bring piles driven below the pile cut-off elevation to the proper elevation. For steel piles, a length of pile is welded on as shown in the plans. This is a relatively simple process. As a pile driving inspector, you are responsible for ensuring the following.
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