Difference between revisions of "705 - Foundation Piling"

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<center><span STYLE="font: 60pt arial;">'''705'''</span></center>
 
<center><span STYLE="font: 60pt arial;">'''705'''</span></center>
  
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==[[#GENERAL|GENERAL]]==
 
==[[#GENERAL|GENERAL]]==
  
Foundation piles are usually steel H sections or cast-in-place (CIP) concrete in steel shells.
+
Foundation piles are typically steel H sections or cast-in-place (CIP) concrete in steel shells. Occasionally the plans specify treated timber piles.  Foundation piles provide support for the bridge or structure when the existing soils do not provide adequate bearing capacity to support a spread footing. 
  
Fluted shells are usually an allowable alternate but rarely used. Occasionally the plans specify treated timber piles.
+
Foundation piles may be straight or battered.  Generally, piles are battered no flatter than 3V:1H.  This can be increased to 2.5V:1H or even 2V:1H where soil conditions are not good enough to provide sufficient lateral pile resistance and this will be noted on the plans.  It can be difficult to maintain driving accuracy when the batter is flatter than 3V:1H.
  
{{top}}
+
The most common steel section used for piles is the HP section.  For example, for a HP 12X53 section, H stands for the “section shape”, P stands for “pile”, the 12 represents the height, h, in inches, and the 53 represents the unit weight per foot of material.  Figure 1 shows the typical HP section configuration.
  
==[[#MATERIALS|MATERIALS]]==
+
[[File:Fig 705-1.png|thumb|center|600px|Figure 1. Typical HP shape]]
  
 +
Steel pipe piles for CIP piles are typically designated by the outer radius, and the pipe wall thickness.  All pipe pile used on MDOT projects shall be seamless, meaning the welds shall be done from the electric resistance, or fusion welding processes.
  
===[[#Bearing Capacity|Bearing Capacity]]===
+
It should be noted that static analysis is performed during the design phase of the project to determine the appropriate design pile section, design pile lengths, design pile tip elevations.  These values are shown on the plans, and are used to determine the estimated pile lengths, and estimated pile tip elevations.
  
 +
Steel piles brought to the site can be new or used, however, used piles must be in good condition, and the Contractor must provide mill test reports, and required Buy America certification.  Contact the Geotechnical Services, or the Bridge Field Services areas for any questions regarding acceptable condition.
  
====[[#Dynamic Formula|Dynamic Formula]]====
+
Piles are to be stored off the ground on cribbing when on site.  The following should be checked prior to incorporation into the project:
  
Bearing capacity of foundation piling will be determined either by the static or dynamic formula. The dynamic formula is generally used.
+
*  Check for bending or distortion of steel piles
 +
*  Ensure steel piles do not have any section loss, drilled holes, or stray weld strikes
 +
*  Ensure dirt, water or other deleterious materials do not enter steel shells for CIP piles
 +
*  Timber piles are to be closely stacked together to prevent sagging
  
Using the dynamic formula, test piles are driven with pile lengths determined from these results. When using the dynamic formula first solve for the coefficient (C) and then solve for (S) using the following equations.  A worked example is included.
 
  
[[File:Figure 705.08-1.jpg|center]]
+
{{top}}
  
The following information is necessary so bearing charts can be made up prior to the start of work.  The bearing charts are obtained by providing the Lansing Construction & Technology, Bridge Construction Section with the hammer information along with the minimum and maximum estimated pile lengths to be used. Charts can also be developed in the field using the formula.
+
==[[#MATERIALS|MATERIALS]]==
  
{| class="wikitable"
+
===[[#Timber Piles|Timber Piles]]===
|-
+
Ensure timber piles are structural timber or lumber of the material grade as called for on the plans, and per subsection [http://mdotcf.state.mi.us/public/specbook/files/2012/912%20Timber%20and%20Lumber.pdf 912.05 of the Standard Specifications for Construction].
!
+
 
<center>'''Formula Item'''</center>
+
Ensure piles are treated with preservative per subsection [http://mdotcf.state.mi.us/public/specbook/files/2012/912%20Timber%20and%20Lumber.pdf 912.06 of the Standard Specifications for Construction].
!
 
<center>'''Description'''</center>
 
|-
 
|
 
<center>E</center>
 
|
 
manufacturer's maximum rated energy in foot (joules).
 
|-
 
|
 
<center>Wr</center>
 
|
 
weight of striking parts of the hammer (ram) in pounds (kilograms).
 
|-
 
|
 
<center>Wp</center>
 
|
 
weight of the parts being driven and including the anvil (if any), driving helmet, driving cap, mandrel, pile weight, etc., in pounds (kilograms).
 
|-
 
|
 
<center>k</center>
 
|
 
coefficient of restitution of the impact areas.
 
|-
 
|
 
<center>P</center>
 
|
 
bearing resistance value in pounds (kiloNewtons).
 
|-
 
|
 
<center>S</center>
 
|
 
pile set, the average penetration in inches (mm) per blow for the last 10 blows of the hammer.
 
|}
 
  
 
{{top}}
 
{{top}}
 +
===[[#Steel Piles and CIP Pile Shells|Steel Piles and CIP Pile Shells]]===
 +
Ensure steel piles, steel pile shells for CIP piles, and pile points are of the material grade and yield strength as called for on the plans, and per [http://mdotcf.state.mi.us/public/dessssp/spss_source/12SP906(A)v1.pdf 12SP906(A).]
 +
Check the plans and specifications for galvanizing requirements.  If required, ensure the Contractor provides proper documentation of galvanizing
  
====[[#Ordering Pile Driving Charts|Ordering Pile Driving Charts]]====
+
{{top}}
 
+
===[[#Concrete|Concrete]]===
When the chart is needed immediately, complete Form 1157A (see '''''Figure 705-4''''') on-site and phone the information in to the C&T Bridge Construction Section.
+
Ensure concrete for CIP piles is Concrete, Grade S1, per subsection [http://mdotcf.state.mi.us/public/specbook/files/2012/701%20PCC%20for%20Structures.pdf 701 of the Standard Specifications for Construction].
  
 
{{top}}
 
{{top}}
  
====[[#Static Formula|Static Formula]]====
+
==[[#CONSTRUCTION|CONSTRUCTION]]==
  
When the static formula is used, Design Division will compute the length necessary and the piling will be driven to the penetration shown on the plans unless practical refusal is obtained at a higher elevation.
+
===[[#EQUIPMENT|Equipment]]===
  
{| class="wikitable"
+
Ensure the contractor is using appropriate equipment to drive production piles and test piles without damaging them.  The following pile driving equipment is subject to the approval of the MDOT [http://www.michigan.gov/mdot/0,4616,7-151-9623_26663_27303-269622--,00.html Geotechnical Services Section] area based on the pile driveability analysis:
|-
 
!
 
<center>'''Refusal'''</center>
 
!
 
<center>'''Description'''</center>
 
|-
 
|
 
<center>Practical</center>
 
|
 
a bearing of 1-1/2 times the required pile bearing as determined by using the dynamic formula.
 
|-
 
|
 
<center>Absolute</center>
 
|
 
a bearing of 2 times the required pile bearing as determined by using the dynamic formula.
 
|}
 
  
 +
*Pile Driving Hammer
 +
*Hammer cushion
 +
*Pile helmet
 +
*Pile cushion
 +
*Any other pertinent equipment
  
[[File:Figure 705.08-2.jpg|thumb|center|600px|Figure 705–4 - Form 1157A – Pile Driving Table]]
+
Submit [http://mdotcf.state.mi.us/public/webforms/public/1956.pdf MDOT form 1956 LRFD Pile Driving and Equipment Data] to the [http://www.michigan.gov/mdot/0,4616,7-151-9623_26663_27303-269622--,00.html Geotechnical Services Section] and [http://www.michigan.gov/mdot/0,4616,7-151-9623_26663_56139_56173---,00.html Bridge Field Services] for review and creation of pile driving charts.
  
{{top}}
+
See Figure 2 for typical pile driving equipment set up with the hammer supported in swinging leads:
  
====[[#Determination of Bearing Value Using Dynamic Formula|Determination of Bearing Value Using Dynamic Formula]]====
+
[[File:Fig 705-2.png|thumb|center|600px|Figure 2. Typical pile driving equipment set up]]
  
'''Example:'''
+
Pile driving equipment is to be selected such that the piles are installed at a rate of 2 blows per inch to 10 blows per inch.
  
{| class="wikitable"
+
Pile stresses shall not exceed the values shown in [http://mdotcf.state.mi.us/public/specbook/files/2012/705%20Foundation%20Piling.pdf Table 705-1 of the Standard Specifications for Construction].
|-
 
!
 
<center>'''Variables'''</center>
 
!
 
<center>'''Measurement'''</center>
 
!
 
<center>'''Description'''</center>
 
|-
 
|
 
<center>Wr</center>
 
|
 
<center>3371 lbs</center>
 
|
 
weight of striking parts of hammer
 
|-
 
|
 
<center>Wp</center>
 
|
 
<center>5368 lbs</center>
 
|
 
<nowiki>weight of parts being driven including pile weight [(1718) + (50 ft)(73 lbs/ft)]</nowiki>
 
|-
 
|
 
<center>E</center>
 
|
 
<center>30412 ft. lbs</center>
 
|
 
energy of hammer
 
|-
 
|
 
<center>k</center>
 
|
 
<center>0.65</center>
 
|
 
coefficient of restitution for laminated Micarta blocks
 
|-
 
|
 
<center>P</center>
 
|
 
<center>60 tons = 120,000 lbs</center>
 
|
 
bearing resistance
 
|-
 
|
 
<center>S</center>
 
|
 
<center>Unknown to be solved for</center>
 
|
 
pile set, average penetration in inches/blow for the last ten hammer blows
 
|}
 
  
 +
The [http://www.michigan.gov/mdot/0,4616,7-151-9623_26663_27303-269622--,00.html Geotechnical Services Section] will predict pile stresses using the wave equation analysis, based on hammer efficiencies shown in [http://mdotcf.state.mi.us/public/specbook/files/2012/705%20Foundation%20Piling.pdf Table 705-2 of the Standard Specifications for Construction].
  
[[File:Figure 705.08-3.jpg|center]]
+
The pile driving system proposed by the Contractor is subject to approval from the Geotechnical Services Section.
  
 +
Air (steam), diesel or hydraulic hammers can be used.
  
'''Metric Example:'''
+
{{top}}
 
 
{| class="wikitable"
 
|-
 
!
 
<center>'''Variables'''</center>
 
!
 
<center>'''Measurement'''</center>
 
!
 
<center>'''Description'''</center>
 
|-
 
|
 
<center>Wr</center>
 
|
 
<center>1723.65 kg</center>
 
|
 
weight of striking parts of hammer
 
|-
 
|
 
<center>Wp</center>
 
|
 
<center>4535.92 kg</center>
 
|
 
weight of parts being driven including pile weight
 
|-
 
|
 
<center>E</center>
 
|
 
<center>20337.26 Nm</center>
 
|
 
energy of hammer
 
|-
 
|
 
<center>k</center>
 
|
 
<center>0.64</center>
 
|
 
coefficient of restitution for laminated Micarta blocks
 
|-
 
|
 
<center>P</center>
 
|
 
<center>484 kN</center>
 
|
 
bearing resistance
 
|-
 
|
 
<center>S</center>
 
|
 
<center>Unknown to be solved for</center>
 
|
 
pile set, average penetration in mm/blow for the last ten hammer blows
 
|}
 
  
 +
====[[#Drop Impact Hammers|Drop Impact Hammers]]====
 +
Drop impact hammers are gravity type hammers, where a weight is simply lifted and released.  Drop hammers may be prohibited on timber piles, check the plans and specifications for any restrictions.
  
[[File:Figure 705.08-4.jpg|center]]
+
Drop Impact hammers are not to be used for piles where the required nominal pile driving resistance exceeds 200 kips.
  
 
{{top}}
 
{{top}}
  
==[[#CONSTRUCTION|CONSTRUCTION]]==
+
====[[#Single Acting (Air) Hammers|Single Acting (Air) Hammers]]====
  
===[[#Equipment|Equipment]]===
+
These hammers are powered by compressed air or steam provided from an air compressor or steam boiler.
  
 +
The hammer is generally assumed to be developing its rated energy when it is striking the number of blows per minute as shown in the manufacturer's catalog.  If a hammer will not develop its rated number of blows at bearing, the inspector should suspend driving operations.  In most cases, the problem is caused by insufficient pressure at the hammer because of line losses caused by leaky connections, excessive line length, etc.
  
====[[#Pile Hammers|Pile Hammers]]====
+
{{top}}
  
Vibratory equipment may be used for sticking piles, but not for advancing piles.
+
====[[#Closed-Top Type Diesel Hammers|Closed-Top Type Diesel Hammers]]====
 +
Closed ended hammers are closed at the top, and contain a bounce chamber to throw the ram back down upon rebound.
  
Drop hammers are not permitted for driving permanent piling.
+
The maximum rated energy should be used in calculating bearing only when the hammer is on the verge of floating on top of the pile.  If this floating action is unattainable, the Contractor should furnish an instrument to measure the bounce chamber pressure and resulting hammer output, and use the manufacturers chart to correlate pressure reading with the energy being delivered by the hammer.
  
Hammers used for pile driving will be:
+
{{top}}
  
* single acting steam (air),
+
====[[#Open-Type Diesel Hammers|Open-Type Diesel Hammers]]====
 +
These are the most common.  Open ended hammers are open at the top, allowing observation of the ram going up and down.  Diesel fuel is ignited, which thrusts the ram upward, followed by the ram falling and striking the pile top.
  
* double acting steam (air), or
+
{{top}}
  
* diesel-powered.
+
====[[#Hydraulic Impact Hammers|Hydraulic Impact Hammers]]====
 +
Hydraulic hammers are fueled by a hydraulic unit, with the hammer energy correlated through pressure readings.
  
In leads which do not bind or restrain free vertical movement, and equipped with a suitable bonnet or cap which will accurately hold the pile top in correct position with reference to the ram, in order to distribute the ram blow over the entire top of the pile.
+
A wave equation analysis must be performed by the Contractor, and check by the Geotechnical Services area to determine the nominal driven bearing of the pile
  
 
{{top}}
 
{{top}}
  
====[[#Leads|Leads]]====
+
====[[#Non-Impact Hammers|Non-Impact Hammers]]====
  
Leads used for pile driving are either swing or fixed-type.
+
Vibratory equipment may be used for sticking piles, but not for advancing piles.  Do not use vibratory hammers, driving aids, followers or prebored holes unless approved by the Geotechnical Services area.
  
The Contractor should be encouraged to use the fixed-type wherever possible as they do a better job of holding the pile in position.
+
{{top}}
  
{{top}}
+
====[[#Hammer Cushion|Hammer Cushion]]====
  
====[[#Single Acting (Air) Hammers|Single Acting (Air) Hammers]]====
+
Hammer cushions are to be used to prevent damage to the pile during driving by dampening reflected forces, and ensuring a uniform strike at the top of the pile.  Certain hammer types are designed for use without a cushion.
  
The hammer is generally assumed to be developing its rated energy when it is striking the number of blows per minute as shown in the manufacturer's catalogIf a hammer will not develop its rated number of blows at bearing, the inspector should suspend driving operationsIn most cases, the problem is caused by insufficient pressure at the hammer because of line losses caused by leaky connections, excessive line length, etc.
+
Wood, elastomerics, wire rope or asbestos cannot be used, as these materials tend to deform during driving.  Ensure a striker plate is used on top of the cushion to ensure uniform compression of the materialModern hammer cushions use phenolic laminates (synthetic resin), or special alloyed nylon blocks with aluminum layersSee Figure 3 for typical nylon hammer cushions:
  
{{top}}
+
[[File:Fig 705-3.png|thumb|center|600px|Figure 3. Typical nylon hammer cushions]]
  
====[[#Closed-Top Type Hammer|Closed-Top Type Hammer]]====
+
Inspect the cushion before production pile driving commences, and inspect after 100 hours of operation, or prior to driving at each subsequent structure.  The striker plate portion of the helmet needs to be remove to gain access to the cushion.  See Figure 4 for a typical helmet and cushion configuration.  Ensure the contractor replaces the cushion once the thickness is reduced more than 25% of the original thickness.
  
The maximum rated energy should be used in calculating bearing only when the hammer is on the verge of ''floating'' on top of the pile. If this floating action is unattainable, the Contractor should furnish an instrument to measure the bounce chamber pressure and resulting hammer output.
+
[[File:Fig 705-4.png|thumb|center|600px|Figure 4. Typical helmet and cushion configuration]]
  
 
{{top}}
 
{{top}}
  
====[[#Open-Type Diesel Hammer|Open-Type Diesel Hammer]]====
+
====[[#Helmet|Helmet]]====
 +
Hammer helmets distribute the hammer blow uniformly and concentrically to the pile top.  Ensure the helmet surface in contact with the pile is smooth, and aligned with the hammer base and the pile top.
 +
 +
Ensure the helmet is guided with the leads, and not allowed to swing freely.
  
When using an open-type diesel hammer, the manufacturer's rated energy should be used, providing the hammer appears to be functioning properly.
+
For timber piles, ensure the helmet does not exceed the pile top by more than 2 inches.  The Contractor shall trim the pile top to fit into the helmet.
  
 
{{top}}
 
{{top}}
  
===[[#Construction Inspection|Construction Inspection]]===
+
====[[#Pile Cushion|Pile Cushion]]====
 +
Pile cushions are only required when CIP concrete piles require redriving after the concrete placement and curing.
  
Prior to the start of driving and during the operation, check all of the following:
+
{{top}}
  
* Excavation - The excavation will be complete.
+
====[[#Leads|Leads]]====
 +
Leads are typically box shaped frames used align the pile and hammer in the appropriate position throughout the driving operation, and maintain hammer and pile alignment to ensure concentric impact on the top of the pile during striking.
  
* Embankment Areas - Embankment will be completed to the bottom of substructure concrete elevation.
+
Leads used for pile driving are either swing or fixed-type.  Ensure swing type leads contain a pile gate at the bottom.  Ensure leads of appropriate length to eliminate the need for followers.
  
* Battered Piles - Proper elevation of fill or cut. Check to ensure that battered piles will clear the toe of any cofferdam sheet piling.
+
The Contractor should be encouraged to use the fixed-type wherever possible as they do a better job of holding the pile in position.
  
* Wall-type Abutments - On certain types of abutments, an error in grade could easily result in the piling being too close to or possibly outside the wall forms.
+
{{top}}
  
* Pile Layout - The Contractor will do the actual pile layoutThe layout should then be checked by the inspector.
+
====[[#Followers|Followers]]====
 
+
Pile followers are essentially extensions of the piles being driven allowing the piles to be driven at a higher elevationFollowers are only to be used with approval from the [http://www.michigan.gov/mdot/0,4616,7-151-9623_26663_27303-269622--,00.html Geotechnical Services Section], as there is uncertainty as to how much hammer energy is transferred across the joint between the follower and the production pile.
* Soil Borings and Blow Count Data - Prior to driving, the inspector should become familiar with the soil borings in the footing area.  The problem of leaving the piling hung up on a thin, hard layer underlain by unsuitable material can be avoided.
 
 
 
* Embankment Areas - When specified, holes will be pre-bored to the elevation shown on the plans.  The diameter of the pre-bored hole shall be equal or slightly greater than the piling diameter.
 
 
 
* Refusal - The specifications allow stopping at absolute refusal if minimum pile penetration has been achieved. If an underlying soft material layer exists, the region soils Engineer or representative or the C&T Lansing office should be contacted to determine if penetration is necessary, requiring extra work.
 
  
 
{{top}}
 
{{top}}
  
 
===[[#Test Piles|Test Piles]]===
 
===[[#Test Piles|Test Piles]]===
 +
When test piles are shown in the plans and specifications, the pile lengths shown on the plans are for estimating purposes only.  There are typically two test piles per substructure unit.
  
Will be driven prior to the regular piling so the results can be used as a guide in ordering piles and driving all the regular piling.
+
Test piles should be driven prior to the production piling so the results can be used as a guide in ordering piles and driving all production piling. Contractors typically place test and production piling orders simultaneously due to mill and fabricator schedules.
  
Will be driven to practical refusal with bearing observations taken at 1 foot (300 mm) intervals.
+
Ensure test piles are driven to the minimum pile length shown on the plans, practical refusal (110% of nominal), whichever is greater.
 +
 
 +
To track test pile driving information, use [http://mdotcf.state.mi.us/public/webforms/public/1157L.pdf MDOT form 1157L – TEST PILE RECORD, LRFD].
  
 
{{top}}
 
{{top}}
  
====[[#Pile Penetration Observations|Pile Penetration Observations]]====
+
====[[#Test Pile Penetration Observations|Test Pile Penetration Observations]]====
 
 
 
It is important at the start of the blow count to reference the pile to some fixed object, preferably the leads, providing they are not reset during the observation period.
 
It is important at the start of the blow count to reference the pile to some fixed object, preferably the leads, providing they are not reset during the observation period.
  
Line 309: Line 179:
  
 
====[[#Reference Stake|Reference Stake]]====
 
====[[#Reference Stake|Reference Stake]]====
 
 
Driving a reference stake adjacent to the pile should be avoided because clay soil has the tendency to heave and sandy soil has the tendency to consolidate.
 
Driving a reference stake adjacent to the pile should be avoided because clay soil has the tendency to heave and sandy soil has the tendency to consolidate.
  
 
Soil heaving and consolidating soil would raise or lower the reference stake causing erroneous penetration readings affecting the recorded bearing.
 
Soil heaving and consolidating soil would raise or lower the reference stake causing erroneous penetration readings affecting the recorded bearing.
  
Besides the penetration readings, the inspector will simultaneously record the distance the pile point is below cutoff.  This is accomplished by having the piling marked off in 1 foot (300 mm) intervals starting from the point and referencing the piling marks to a grade stake set at cutoff elevation.
+
Besides the penetration readings, the inspector will simultaneously record the distance the pile point is below cutoff.  This is accomplished by having the piling marked off in 1 foot intervals starting from the point and referencing the piling marks to a grade stake set at cutoff elevation.
  
 
{{top}}
 
{{top}}
  
===[[#Splicing|Splicing]]===
+
====[[#Restrike|Restrike]]====
 +
Restriking is allowed for test piles only.  If practical refusal cannot be achieved after driving 10 feet below the estimated pile tip elevation, and the resistance is at least 85% of the required nominal pile driving resistance, the Contractor may leave the piles to set up for 48 hours.
  
Steel piles and steel pile shells may be furnished in full length sections or the pile shells may be spliced according to the splicing method as shown on the plans or as approved by the Engineer.
+
After the 48 hours waiting period, The Contractor may restrike the piles.  Contact the [http://www.michigan.gov/mdot/0,4616,7-151-9623_26663_27303-269622--,00.html Geotechnical Services] area to determine the nominal pile driving resistance based on the number of blows necessary to advance the pile an additional 3 inches.
  
Splices will be made according to subsection [http://mdotcf.state.mi.us/public/specbook/files/2012/707%20Str%20Steel%20Construction.pdf 707.03.D.10 b,c,d] of the Standard Specifications for Construction with the welding done by a certified welder qualified in the 2G position for welding the pile in the vertical position.  If the piling is spliced while lying on the ground, the welder will also be qualified in the 3G position.  There is no limit to the number of splices made on any one pile.
+
Ensure the hammer is warmed up with 25 blows.
  
{{top}}
+
Ensure the appropriate records for test piles are kept, including:
  
====[[#Welded|Welded]]====
+
*Number of blows per inch for the driven length, and stroke height.
 +
*As-driven length of test pile
 +
*Cutoff elevation
 +
*Penetration into the ground
 +
*Number of splices
  
Welded splices for piles will be made only by qualified welders using E6010, E7015, E7016 or E7018 electrodes.
+
Ensure test piles not included in production pile locations are cutoff or pulled.
  
 
{{top}}
 
{{top}}
  
====[[#CIP Concrete Piles|CIP Concrete Piles]]====
+
====[[#Pile Points|Pile Points]]====
 +
Check the plans and specifications to see if pile points are to be used.  Pile points are welded to the driving end of HP, and CIP piles to aid in tough driving conditions and/or end bearing in rock.  A typical HP pile point is shown in Figure 5 below.  Typical pile points for CIP piles are shown in Figure 6 below:
  
Shells for CIP concrete piles will be spliced using a chill ring or other type backing detail as shown on the plans.
+
[[File:Fig 705-5.png|thumb|center|600px|Figure 5. Typical HP section pile points]]
 +
 
 +
[[File:Fig 705-6.png|thumb|center|600px|Figure 6. Typical conical pile pile points]]
  
 
{{top}}
 
{{top}}
  
====[[#Steel Piles|Steel Piles]]====
+
====[[#Equipment Changes|Equipment Changes]]====
 
+
All piles for a given foundation unit will be driven with the same hammer operated under the same conditions with the same cushion material as used to drive test piles.  Changing hammers requires additional test pile driving at the Contractor’s expense.
Steel piles will be spliced as shown on the plans using preformed-preassembled bent plates or flat splice plates.
 
  
 
{{top}}
 
{{top}}
  
====[[#Full Penetration, Butt Welded|Full Penetration, Butt Welded]]====
+
===[[#Driving of Production Piles & Construction Inspection|Driving of Production Piles & Construction Inspection]]===
 
+
To track pile driving operations, use [http://mdotcf.state.mi.us/public/webforms/public/1990.pdf MDOT form 1990 – COFFERDAM INSTALLATION, PILING PLACEMENT, AND TREMIE POUR INSPECTOR’S CHECKLIST], and [http://mdotcf.state.mi.us/public/webforms/public/1161L.pdf MDOT form 1161L - FOUNDATION PILING RECORD, LRFD]
Full penetration butt welding of piles will be performed as outlined herein, with emphasis placed on burning, alignment and welding.
 
  
 
{{top}}
 
{{top}}
  
====[[#Scarfing|Scarfing]]====
+
====[[#Prior to Pile Driving|Prior to Pile Driving]]====
 +
Prior to the start of driving and during the operation, check the plans and specifications, and pay close attention to all of the following:
  
Scarfing the upper splice length of the piles preparatory to butt welding will be done by a cutting torch using a guide to assure a smoother chamberA maximum of 1/8 inch (3 mm) land (shoulder) will be retained. If the end of the driven length of pile is damaged during the driving operation, it must be trimmed.
+
*Ensure the proper orientation and layout of the pileThe contractor will do the actual layout. For example, on integral abutments with a single row of piles, the web of the pile is oriented perpendicular to the construction centerline of the bridge.  This is also referred to orienting the pile about the weak axis of bending.
  
All splices require welding. Splicing devices which do not develop the full plan weld are not permitted.
+
*Ensure all piles meet the material grade requirements as specified in the plans, and [http://mdotcf.state.mi.us/public/dessssp/spss_source/12SP906(A)v1.pdf 12SP906(A).]
 +
*Review the Soil Borings and SPT Blow Count Data shown on the plans.  Become familiar with the soil borings in the footing area.  Be aware of potential hard layers above the estimated pile tip elevations that can give false bearing.  These areas are typically underlain by unsuitable material.
  
{{top}}
+
*Review the plans and specifications for preboring requirements.  If required, ensure holes are prebored to the elevations shown on the plans, and the hole diameter is 6 inches greater than the pile dimensions.  Preboring also includes the following:
 +
**Boring pile holes
 +
**Disposal of excavated material
 +
**Backfilling voids
 +
**Installing and removing temporary casings
 +
**Providing and disposing of drilling slurry
 +
**Restriking completed piles within a radius of 20 feet
 +
**Equipment operating costs, unless including in the Pile Driving Equipment, Furn pay item
  
====[[#Offhand Burning|Offhand Burning]]====
+
*Ensure all excavation and embankment is complete to the bottom of substructure concrete elevation.
  
Offhand burning will be permitted if trimming is minor.  When it is necessary to cut a small section off the end of the driven pile length to square the end, burning must be done using a guide either clamped or tack welded in place.  All adhering slag will be removed and the joint surfaces will be thoroughly cleaned by wire brushing before welding.  A root opening of the butt joint will provide a 1/8 inch (3 mm) clear opening at the nearest point.  When the 1/8 inch (3 mm) opening at the nearest point allows more than a ¼ inch (6 mm) opening at other points, correction will be made to provide the correct opening before welding.  Beveling by cutting will be required for correcting openings wider than ¼ inch (6 mm).
+
*If the Contractor is using a template, check the template dimension against the plan dimensions.
  
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+
*Check to ensure that battered piles will clear the toe of any cofferdam sheet piling.
  
====[[#Root Opening|Root Opening]]====
+
*On certain types of abutments an error in grade could easily result in the piling being too close to or possibly outside the wall forms.
  
The root opening may be held by two wedges before tacking.  The members to be welded will be brought into correct alignment along the pile length and held rigidly by clamps or by dogging.  Clamps or dogs may be removed after tack welding sufficiently to hold the member in place.  Where the parts are restrained against bending due to eccentricity in alignment, an offset not exceeding 10 percent thickness of the thinner part joint, but no more than 1/8 inch (3&nbsp;mm), may be permitted as a departure from the theoretical alignment.  In correcting misalignment, the parts will not be drawn into a greater slope than ½ inch per foot (12 mm in 300&nbsp;mm).  Offset measurement will be based upon the centerline of parts unless otherwise shown on the drawing.  The root pass will be a stringer bead, placed with sufficient amperage to fully penetrate through the joint.  Passes will be made symmetrically and will alternate on both flanges to minimize distortion.  After the face side of both flanges and web have been welded completely, a backing bead will be made on the opposite side.
+
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+
====[[#During Pile Driving|During Pile Driving]]====
 +
*During construction, the nominal pile driving resistance is measured and verified during pile driving with the dynamic formula or dynamic testing methods
  
==[[#MEASUREMENT AND PAYMENT|MEASUREMENT AND PAYMENT]]==
+
*Ensure the pile tops are square with the axis of the pile.
  
 +
*If impenetrable obstructions are encountered during driving, direct the Contractor to remove and reuse the pile, or cut off and drive a new pile.  Ensure the pile is cut to the lowest possible elevation, and drive another pile, adjusted laterally.
  
===[[#Production Piles|Production Piles]]===
+
*Check the plans for design pile lengths (pile lengths shown on the plans), or estimated pile lengths (pile lengths shown on plans used as guide if the nominal pile driving resistance is shown on the plans.
 +
**If the plans show design pile lengths, ensure piles are driven to the design pile tip elevations shown on the plans, unless driving operations attain absolute refusal (150% of the nominal pile driving resistance shown on the plans).
 +
**If the plans show estimated pile lengths, install piles to a the following penetration:
 +
***The nominal pile driving resistance equals at least the required nominal pile driving resistance; and
 +
***The bottom of the pile is at or below the minimum pile penetration elevation shown on the plans.
  
 +
*Ensure piles are not driven past absolute refusal unless Dynamic Testing is required. Any unnecessary production piling overdriving is to be avoided as it adds unnecessary project cost.
  
====[[#Recording Production Piles|Recording Production Piles]]====
+
*Ensure completed piles are driven according to the following accuracy criteria:
 +
**1/4 inch per foot from vertical or batter line
 +
**Pile cutoff location is within 6 inches from plan position unless noted on plans
 +
**9 inches between the edges of piles and the outline of the concrete forms
 +
**Pile bents are to meet the tolerances as shown on the plans
 +
**Pile cut off within 1”
  
Only the original length, splice lengths, final penetration bearing and cutoff lengths are recorded.
+
*Do not allow the Contractor to laterally pull piles to correct misalignment, or splice subsequent piles to correct misalignment.
  
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+
*Take level readings to measure pile heave after driving.  If piles heave up during driving of adjacent piles, direct the Contractor to re-drive to the required bearing capacity or penetration elevation.  For heaved CIP piles, ensure the concrete obtains its 28 day compressive strength prior to re-drive.
  
====[[#Required Bearing|Required Bearing]]====
+
*For battered piles, ensure the piles are driven to the angle shown on the plans.  Note that the hammer energy will need to be reduced to account for losses due to the inclination of the hammer.  Check the batter with a carpenter’s level attached to the vertical side of the Contractor’s template.
  
Production piles are driven to the required bearing and the driving is stopped provided the pile has been driven to the minimum penetration as shown on the plans.
+
If at any time, the nominal pile driving resistance cannot met, but minimum pile penetration is achieved, contact the [http://www.michigan.gov/mdot/0,4616,7-151-9623_26663_27303-269622--,00.html Geotechnical Services] area for guidance.
  
 
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====[[#Overdriving|Overdriving]]====
+
====[[#After Pile Driving|After Pile Driving]]====
 +
*Ensure battered piles are cut perpendicular to the axis of the pile, not parallel with finished grade. 
  
Any unnecessary production piling overdriving is to be avoided as it adds unnecessary project cost.
+
*After driving CIP shell piling inspection will be done by using a mirror or light provided by the Contractor, suitable for illuminating the shell interiors.  The shells will be free of bends, kinks or other deformations that would impair the completed pile strength.
  
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+
*After driving the piling, piling tops will be immediately covered to keep out rain, sand, etc.  The piling should be cut off within 1 inch of the specified elevation and filled with grade S1 concrete as soon as possible.
  
====[[#Equipment Changes|Equipment Changes]]====
+
*Ensure any subsequent pile driving within a radius of 25 feet from concrete element pours are done after concrete has attained 75 percent of its design strength.
  
All piles for a given foundation unit will be driven with the same hammer operated under the same conditions with the same cushion material as used to drive test pilesChanging hammers requires additional test pile driving at the Contractor’s expense.
+
*Concrete should be cast in slowly so that an air pocket is not formed in the pile.  An inspector should be present at all times during placementNo concrete will be placed in any pile until all piles within a 20 foot radius have been driven and accepted.
  
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+
*For CIP piles, ensure concrete is placed per [http://mdotcf.state.mi.us/public/specbook/files/2012/706%20Str%20Conc%20Construction.pdf subsection 706.03.H of the Standard Specifications for Construction].  Concrete in the pile shell’s upper third (not to exceed 25 feet) is to be vibrated by an approved method.
  
====[[#Variation|Variation]]====
+
*Ensure the Contractor cleans the shells of CIP concrete piles where embedded 1 foot or more in structural concrete.
  
Piling will be driven with a variation of not more than ¼ inch per foot (20&nbsp;mm/m) from vertical or the batter line shown on the plans.
+
*Check for any heaved piles.  Heaved piles are to be redriven, and will be paid for as extra work.
  
 
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====[[#Batter|Batter]]====
+
====[[#Defective Piles|Defective Piles]]====
 +
Methods to correct piles damaged by internal defects, improper driving, driven below cutoff elevation, or driven outside of plan locations are as follows:
  
The batter is checked by making a template to the shape shown on the plans. With a carpenter's level attached to the vertical side of the template, it should show when the template is held against the pile in its battered position.
+
*Withdraw the pile and replace with a new, longer stick (if feasible).
 +
*Drive a second pile adjacent to the defective pile (verify with Bridge Design, and the [http://www.michigan.gov/mdot/0,4616,7-151-9623_26663_27303-269622--,00.html Geotechnical Services] area).
 +
*Splice or build up the pile, or extend a portion of the footing to properly embed the pile
  
 
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====[[#Pile Position|Pile Position]]====
+
====[[#Obstructions|Obstructions]]====
 +
Removal of obstructions that require special equipment or tools will be measured and paid for as extra work per [http://mdotcf.state.mi.us/public/specbook/files/2012/109%20Measurement%20&%20Payment.pdf subsection 109.05.D of the Standard Specifications or Construction].  A budget amount will be established to pay for removing obstructions.  If the Contractor and the Engineer cannot agree on a lump sum price, the Engineer will direct the work to be done on a force account basis.
  
After driving, each pile position at the cutoff elevation will be within 6&nbsp;inches (150 mm) of plan position, with a minimum 9 inches (225 mm) concrete cover in all directions.  Piles used as pier columns will meet the plan accuracy requirements.
+
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+
===[[#Splicing|Splicing]]===
 +
Steel piles and steel pile shells may be furnished in full length sections or the pile shells may be spliced according to the splicing method as shown on the plans.  Note when pile splicers are not permitted in the plans.
  
====[[#Inspection|Inspection]]====
+
Splices will be made according to [http://mdotcf.state.mi.us/public/dessssp/spss_source/12SP705(A)V1.pdf 12SP705(A)] – Pile Splicing and the Contractor shall submit a QA/QC plan in accordance with special provision [http://mdotcf.state.mi.us/public/dessssp/spss_source/12SP705(B)v1.pdf 12SP705(B)] – Quality Control Plan for Welding Foundation Splices.  Welding is to be done by a certified welder qualified in the 2G position for welding the pile in the vertical position.  If the piling is spliced while lying on the ground, the welder will also be qualified in the 3G position.  Furnished pile less than 40 shall contain no more than 3 splices, and furnished pile greater than 40 feet shall contain no more than 4 splices.
  
After driving CIP shell piling inspection will be done by using a mirror or light provided by the Contractor, suitable for illuminating the shell interiorsThe shells will be free of bends, kinks or other deformations that would impair the completed pile strength.
+
All welded splices shall be done in accordance with the [http://www.michigan.gov/documents/mdot/Field_Manual_for_Pile_Welding_407880_7.pdf MDOT Field Manual for Pile Welding] –See this manual for more details
  
 
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====[[#Pile Tops|Pile Tops]]====
+
====[[#Welded|Welded]]====
 
+
Welded splices for piles will be made only by qualified welders using E7015, E7016 or E7018 electrodes.
After driving the piling, piling tops will be immediately covered to keep out rain, sand, etc.  The piling should be cut off within 1 inch (25 mm) of the specified elevation and filled with grade S1 concrete as soon as possible.
 
  
 
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====[[#Driving|Driving]]====
+
====[[#CIP Concrete Piles|CIP Concrete Piles]]====
 
+
Shells for CIP concrete piles will be spliced using a chill ring or other type backing detail as shown on the plans.
Driving within a radius of 25 feet (7.5 m) will not be permitted until the concrete has attained 75 percent of its design strength.
 
  
 
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====[[#Concrete|Concrete]]====
+
====[[#Steel Piles|Steel Piles]]====
 +
Steel piles will be spliced as shown on the plans using preformed-preassembled bent plates or flat splice plates for pier piles, and other piles that are not considered primary members as called for on the plans.  Pile acceptance is based on the Contractor’s conformance to their QA/QC plan, and can be visual.
  
Concrete should be cast in slowly so that an air pocket is not formed in the pileAn inspector should be present at all times during placement.  No concrete will be placed in any pile until all piles within a 20 foot (6 m) radius have been driven and accepted.
+
Full penetration butt weld, or Complete Joint Penetration (CJP) welds are required for piles in integral abutments, and when otherwise defined as primary members on the plansPile acceptance for these members is based on 100% ultrasonic thickness testing (UT).
 +
 
 +
All splices require welding. Splicing devices which do not develop the full plan weld are not permitted.
  
 
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====[[#Piles 60 feet (20 m) or more in Length|Piles 60 feet (20 m) or more in Length]]====
+
====[[#Scarfing|Scarfing]]====
 
+
Scarfing the upper splice length of the piles preparatory to butt welding will be done by a cutting torch using a guide to assure a smoother chamber.  A maximum of 1/8 inch land (shoulder) will be retained.  If the end of the driven length of pile is damaged during the driving operation, it must be trimmed.
Approximately 2 cubic feet (0.05 m3) of Type R-2 mortar will be placed in the bottom of the steel shell before placing the grade S1 concrete.
 
  
 
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====[[#Upper 1/3 Pile Shell|Upper 1/3 Pile Shell]]====
+
====[[#Offhand Burning|Offhand Burning]]====
 
+
Offhand burning will be permitted if trimming is minor.  When it is necessary to cut a small section off the end of the driven pile length to square the end, burning must be done using a guide either clamped or tack welded in place.  All adhering slag will be removed and the joint surfaces will be thoroughly cleaned by wire brushing before welding.  A root opening of the butt joint will provide a 1/8 inch clear opening at the nearest point. When the 1/8 inch opening at the nearest point allows more than a ¼ inch opening at other points, correction will be made to provide the correct opening before welding.  Beveling by cutting will be required for correcting openings wider than ¼ inch.
Concrete in the pile shell’s upper third [not to exceed 25 feet (7.5 m)], will be vibrated by an approved method.
 
  
 
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===[[#Record-Keeping|Record-Keeping]]===
+
====[[#Root Opening|Root Opening]]====
 +
The root opening may be held by two wedges before tacking.  The members to be welded will be brought into correct alignment along the pile length and held rigidly by clamps or by dogging.  Clamps or dogs may be removed after tack welding sufficiently to hold the member in place. 
  
 +
Where the parts are restrained against bending due to eccentricity in alignment, an offset not exceeding 10 percent thickness of the thinner part joint, but no more than 1/8 inch may be permitted as a departure from the theoretical alignment.  In correcting misalignment, the parts will not be drawn into a greater slope than ½ inch per foot.  Offset measurement will be based upon the centerline of parts unless otherwise shown on the drawing.
  
====[[#Test Pile Records|Test Pile Records]]====
+
The root pass will be a stringer bead, placed with sufficient amperage to fully penetrate through the joint.  Passes will be made symmetrically and will alternate on both flanges to minimize distortion. After the face side of both flanges and web has been welded completely, a backing bead will be made on the opposite side.
 
 
Test pile records will be kept on Form 1157.
 
 
 
[[File:Figure 705.07-1.jpg|thumb|center|600px|Figure 705-1 - "H" Pile Splices]]
 
  
 
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====[[#Timber or Treated Timber Piling|Timber or Treated Timber Piling]]====
+
===[[#DETERMINATION OF NOMINAL PILE RESISTANCE|DETERMINATION OF NOMINAL PILE RESISTANCE]]===
 +
The capacity of foundation piles is achieved through skin friction between the soil and the surfaces of the pile, tip capacity of the pile tip embedding into bedrock, or a combination of the two.  The following methods are used to attain required nominal pile driving resistance:
  
Where timber or treated timber piling is called for on the plans, the Engineer will furnish the Contractor with the lengths to be ordered.
+
*Piles are driven to the minimum pile penetration elevation, and nominal resistance, or
 +
*Static load tests for piles with a nominal pile driving resistance greater than 600 kips, or
 +
*Using the Dynamic Formula for production piles less than 600 kips nominal pile driving resistance, or
 +
*Dynamic testing and analysis
  
Treated timber piles (furnished) will be paid for by the length determined by the Engineer.
 
  
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+
A saximeter is to be used to verify blow counts, and the results compared to the dynamic analysis results.  The saximeter works for several hammer types as follows:
  
====[[#CIP Concrete and Steel Pile|CIP Concrete and Steel Pile]]====
+
*For open ended diesel hammers, the saximeter computes stroke and potential energy from the measured blows per minute.  This information is then multiplied by the hammer weight to obtain the hammer energy.
  
The Contractor will be responsible for ordering pile lengths for CIP concrete and steel piling based on test pile results.
+
*For other types of hammers, the Contractor is required to provide an electronic measuring device.
  
 
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====[[#Pile Sketch|Pile Sketch]]====
+
====[[#Static Load Test|Static Load Test]]====
 
+
For high capacity piles, < 600 kip nominal pile resistance, static load tests may be required.  Load testing details will be in the plans and specifications.  This generally involves the placement of large amounts of weight on a group of piles, and recording measurements on vertical displacements and deflections.  The Geotechnical Services Section will approve the load test methods.  
A pile sketch will be made if the pilings are not numbered on the plans or if the final driven position changes.
 
  
 
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====[[#Form 1161 - Foundation Piling Record|Form 1161 - Foundation Piling Record]]====
 
  
Regular piling information is kept on this formMeasurements for driven lengths and cutoffs will be made in feet (m) and inches (mm).
+
====[[#Dynamic Formula|Dynamic Formula]]====
 +
The Dynamic Formula (FHWA Modified Gates Formula) is not to be used on piles with a required nominal pile driving resistance greater than 600 kipsCheck the plans and specifications for dynamic testing with signal matching.
  
The information should be recorded onto the form directly and not on separate sheets of paper that are easily misplaced.  To ensure against loss, a copy of each day's driving should be made, or a permanent record can be made in a bound field book.
+
For battered piles, use a hammer energy reduction coefficient.
 +
 +
These formulas are applicable under the following conditions – Notice if these conditions are not met:
  
Note: See examples of Form 1157 - Test Pile Record and Form 1161 - Foundation Piling Record - shown in '''''Figures 705-2''''' and '''''705-3'''''.
+
*Hammers and unrestricted free fall
 +
*Pile tops are not broomed, crushed, or splintered
 +
*The hammer exhibits no appreciable bounce after striking the pile
 +
*Penetration is at a uniform or uniformly decreasing weight
  
 +
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[[File:Figure 705.07-2.jpg|thumb|center|600px|Figure 705-2 - Form 1157 – Test Pile Record]]
+
====[[#Ordering Pile Driving Charts|Ordering Pile Driving Charts]]====
 +
When pile charts are needed immediately, submit MDOT [http://mdotcf.state.mi.us/public/webforms/public/1956.pdf form 1956 – LRFD Pile Driving and Equipment Data] to the [http://www.michigan.gov/mdot/0,4616,7-151-9623_26663_27303-269622--,00.html Geotechnical Services Section] and [http://www.michigan.gov/mdot/0,4616,7-151-9623_26663_56139_56173---,00.html Bridge Field Services] for review and creation of pile driving charts.
  
 +
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[[File:Figure 705.07-3.jpg|thumb|center|600px|Figure 705-3 - Form 1161 – Foundation Piling Record]]
+
==[[#MEASUREMENT AND PAYMENT|MEASUREMENT AND PAYMENT]]==
  
 
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[[Category:Construction Manual]]
 
[[Category:Construction Manual]]

Revision as of 10:00, 19 March 2014

705
Foundation Piling
2012 STANDARD SPECIFICATIONS FOR CONSTRUCTION - SECTION 705


GENERAL

Foundation piles are typically steel H sections or cast-in-place (CIP) concrete in steel shells. Occasionally the plans specify treated timber piles. Foundation piles provide support for the bridge or structure when the existing soils do not provide adequate bearing capacity to support a spread footing.

Foundation piles may be straight or battered. Generally, piles are battered no flatter than 3V:1H. This can be increased to 2.5V:1H or even 2V:1H where soil conditions are not good enough to provide sufficient lateral pile resistance and this will be noted on the plans. It can be difficult to maintain driving accuracy when the batter is flatter than 3V:1H.

The most common steel section used for piles is the HP section. For example, for a HP 12X53 section, H stands for the “section shape”, P stands for “pile”, the 12 represents the height, h, in inches, and the 53 represents the unit weight per foot of material. Figure 1 shows the typical HP section configuration.

Figure 1. Typical HP shape

Steel pipe piles for CIP piles are typically designated by the outer radius, and the pipe wall thickness. All pipe pile used on MDOT projects shall be seamless, meaning the welds shall be done from the electric resistance, or fusion welding processes.

It should be noted that static analysis is performed during the design phase of the project to determine the appropriate design pile section, design pile lengths, design pile tip elevations. These values are shown on the plans, and are used to determine the estimated pile lengths, and estimated pile tip elevations.

Steel piles brought to the site can be new or used, however, used piles must be in good condition, and the Contractor must provide mill test reports, and required Buy America certification. Contact the Geotechnical Services, or the Bridge Field Services areas for any questions regarding acceptable condition.

Piles are to be stored off the ground on cribbing when on site. The following should be checked prior to incorporation into the project:

  • Check for bending or distortion of steel piles
  • Ensure steel piles do not have any section loss, drilled holes, or stray weld strikes
  • Ensure dirt, water or other deleterious materials do not enter steel shells for CIP piles
  • Timber piles are to be closely stacked together to prevent sagging


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MATERIALS

Timber Piles

Ensure timber piles are structural timber or lumber of the material grade as called for on the plans, and per subsection 912.05 of the Standard Specifications for Construction.

Ensure piles are treated with preservative per subsection 912.06 of the Standard Specifications for Construction.

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Steel Piles and CIP Pile Shells

Ensure steel piles, steel pile shells for CIP piles, and pile points are of the material grade and yield strength as called for on the plans, and per 12SP906(A). Check the plans and specifications for galvanizing requirements. If required, ensure the Contractor provides proper documentation of galvanizing

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Concrete

Ensure concrete for CIP piles is Concrete, Grade S1, per subsection 701 of the Standard Specifications for Construction.

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CONSTRUCTION

Equipment

Ensure the contractor is using appropriate equipment to drive production piles and test piles without damaging them. The following pile driving equipment is subject to the approval of the MDOT Geotechnical Services Section area based on the pile driveability analysis:

  • Pile Driving Hammer
  • Hammer cushion
  • Pile helmet
  • Pile cushion
  • Any other pertinent equipment

Submit MDOT form 1956 – LRFD Pile Driving and Equipment Data to the Geotechnical Services Section and Bridge Field Services for review and creation of pile driving charts.

See Figure 2 for typical pile driving equipment set up with the hammer supported in swinging leads:

Figure 2. Typical pile driving equipment set up

Pile driving equipment is to be selected such that the piles are installed at a rate of 2 blows per inch to 10 blows per inch.

Pile stresses shall not exceed the values shown in Table 705-1 of the Standard Specifications for Construction.

The Geotechnical Services Section will predict pile stresses using the wave equation analysis, based on hammer efficiencies shown in Table 705-2 of the Standard Specifications for Construction.

The pile driving system proposed by the Contractor is subject to approval from the Geotechnical Services Section.

Air (steam), diesel or hydraulic hammers can be used.

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Drop Impact Hammers

Drop impact hammers are gravity type hammers, where a weight is simply lifted and released. Drop hammers may be prohibited on timber piles, check the plans and specifications for any restrictions.

Drop Impact hammers are not to be used for piles where the required nominal pile driving resistance exceeds 200 kips.

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Single Acting (Air) Hammers

These hammers are powered by compressed air or steam provided from an air compressor or steam boiler.

The hammer is generally assumed to be developing its rated energy when it is striking the number of blows per minute as shown in the manufacturer's catalog. If a hammer will not develop its rated number of blows at bearing, the inspector should suspend driving operations. In most cases, the problem is caused by insufficient pressure at the hammer because of line losses caused by leaky connections, excessive line length, etc.

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Closed-Top Type Diesel Hammers

Closed ended hammers are closed at the top, and contain a bounce chamber to throw the ram back down upon rebound.

The maximum rated energy should be used in calculating bearing only when the hammer is on the verge of floating on top of the pile. If this floating action is unattainable, the Contractor should furnish an instrument to measure the bounce chamber pressure and resulting hammer output, and use the manufacturers chart to correlate pressure reading with the energy being delivered by the hammer.

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Open-Type Diesel Hammers

These are the most common. Open ended hammers are open at the top, allowing observation of the ram going up and down. Diesel fuel is ignited, which thrusts the ram upward, followed by the ram falling and striking the pile top.

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Hydraulic Impact Hammers

Hydraulic hammers are fueled by a hydraulic unit, with the hammer energy correlated through pressure readings.

A wave equation analysis must be performed by the Contractor, and check by the Geotechnical Services area to determine the nominal driven bearing of the pile

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Non-Impact Hammers

Vibratory equipment may be used for sticking piles, but not for advancing piles. Do not use vibratory hammers, driving aids, followers or prebored holes unless approved by the Geotechnical Services area.

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Hammer Cushion

Hammer cushions are to be used to prevent damage to the pile during driving by dampening reflected forces, and ensuring a uniform strike at the top of the pile. Certain hammer types are designed for use without a cushion.

Wood, elastomerics, wire rope or asbestos cannot be used, as these materials tend to deform during driving. Ensure a striker plate is used on top of the cushion to ensure uniform compression of the material. Modern hammer cushions use phenolic laminates (synthetic resin), or special alloyed nylon blocks with aluminum layers. See Figure 3 for typical nylon hammer cushions:

Figure 3. Typical nylon hammer cushions

Inspect the cushion before production pile driving commences, and inspect after 100 hours of operation, or prior to driving at each subsequent structure. The striker plate portion of the helmet needs to be remove to gain access to the cushion. See Figure 4 for a typical helmet and cushion configuration. Ensure the contractor replaces the cushion once the thickness is reduced more than 25% of the original thickness.

Figure 4. Typical helmet and cushion configuration

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Helmet

Hammer helmets distribute the hammer blow uniformly and concentrically to the pile top. Ensure the helmet surface in contact with the pile is smooth, and aligned with the hammer base and the pile top.

Ensure the helmet is guided with the leads, and not allowed to swing freely.

For timber piles, ensure the helmet does not exceed the pile top by more than 2 inches. The Contractor shall trim the pile top to fit into the helmet.

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Pile Cushion

Pile cushions are only required when CIP concrete piles require redriving after the concrete placement and curing.

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Leads

Leads are typically box shaped frames used align the pile and hammer in the appropriate position throughout the driving operation, and maintain hammer and pile alignment to ensure concentric impact on the top of the pile during striking.

Leads used for pile driving are either swing or fixed-type. Ensure swing type leads contain a pile gate at the bottom. Ensure leads of appropriate length to eliminate the need for followers.

The Contractor should be encouraged to use the fixed-type wherever possible as they do a better job of holding the pile in position.

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Followers

Pile followers are essentially extensions of the piles being driven allowing the piles to be driven at a higher elevation. Followers are only to be used with approval from the Geotechnical Services Section, as there is uncertainty as to how much hammer energy is transferred across the joint between the follower and the production pile.

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Test Piles

When test piles are shown in the plans and specifications, the pile lengths shown on the plans are for estimating purposes only. There are typically two test piles per substructure unit.

Test piles should be driven prior to the production piling so the results can be used as a guide in ordering piles and driving all production piling. Contractors typically place test and production piling orders simultaneously due to mill and fabricator schedules.

Ensure test piles are driven to the minimum pile length shown on the plans, practical refusal (110% of nominal), whichever is greater.

To track test pile driving information, use MDOT form 1157L – TEST PILE RECORD, LRFD.

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Test Pile Penetration Observations

It is important at the start of the blow count to reference the pile to some fixed object, preferably the leads, providing they are not reset during the observation period.

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Reference Stake

Driving a reference stake adjacent to the pile should be avoided because clay soil has the tendency to heave and sandy soil has the tendency to consolidate.

Soil heaving and consolidating soil would raise or lower the reference stake causing erroneous penetration readings affecting the recorded bearing.

Besides the penetration readings, the inspector will simultaneously record the distance the pile point is below cutoff. This is accomplished by having the piling marked off in 1 foot intervals starting from the point and referencing the piling marks to a grade stake set at cutoff elevation.

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Restrike

Restriking is allowed for test piles only. If practical refusal cannot be achieved after driving 10 feet below the estimated pile tip elevation, and the resistance is at least 85% of the required nominal pile driving resistance, the Contractor may leave the piles to set up for 48 hours.

After the 48 hours waiting period, The Contractor may restrike the piles. Contact the Geotechnical Services area to determine the nominal pile driving resistance based on the number of blows necessary to advance the pile an additional 3 inches.

Ensure the hammer is warmed up with 25 blows.

Ensure the appropriate records for test piles are kept, including:

  • Number of blows per inch for the driven length, and stroke height.
  • As-driven length of test pile
  • Cutoff elevation
  • Penetration into the ground
  • Number of splices

Ensure test piles not included in production pile locations are cutoff or pulled.

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Pile Points

Check the plans and specifications to see if pile points are to be used. Pile points are welded to the driving end of HP, and CIP piles to aid in tough driving conditions and/or end bearing in rock. A typical HP pile point is shown in Figure 5 below. Typical pile points for CIP piles are shown in Figure 6 below:

Figure 5. Typical HP section pile points
Figure 6. Typical conical pile pile points

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Equipment Changes

All piles for a given foundation unit will be driven with the same hammer operated under the same conditions with the same cushion material as used to drive test piles. Changing hammers requires additional test pile driving at the Contractor’s expense.

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Driving of Production Piles & Construction Inspection

To track pile driving operations, use MDOT form 1990 – COFFERDAM INSTALLATION, PILING PLACEMENT, AND TREMIE POUR INSPECTOR’S CHECKLIST, and MDOT form 1161L - FOUNDATION PILING RECORD, LRFD

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Prior to Pile Driving

Prior to the start of driving and during the operation, check the plans and specifications, and pay close attention to all of the following:

  • Ensure the proper orientation and layout of the pile. The contractor will do the actual layout. For example, on integral abutments with a single row of piles, the web of the pile is oriented perpendicular to the construction centerline of the bridge. This is also referred to orienting the pile about the weak axis of bending.
  • Ensure all piles meet the material grade requirements as specified in the plans, and 12SP906(A).
  • Review the Soil Borings and SPT Blow Count Data shown on the plans. Become familiar with the soil borings in the footing area. Be aware of potential hard layers above the estimated pile tip elevations that can give false bearing. These areas are typically underlain by unsuitable material.
  • Review the plans and specifications for preboring requirements. If required, ensure holes are prebored to the elevations shown on the plans, and the hole diameter is 6 inches greater than the pile dimensions. Preboring also includes the following:
    • Boring pile holes
    • Disposal of excavated material
    • Backfilling voids
    • Installing and removing temporary casings
    • Providing and disposing of drilling slurry
    • Restriking completed piles within a radius of 20 feet
    • Equipment operating costs, unless including in the Pile Driving Equipment, Furn pay item
  • Ensure all excavation and embankment is complete to the bottom of substructure concrete elevation.
  • If the Contractor is using a template, check the template dimension against the plan dimensions.
  • Check to ensure that battered piles will clear the toe of any cofferdam sheet piling.
  • On certain types of abutments an error in grade could easily result in the piling being too close to or possibly outside the wall forms.

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During Pile Driving

  • During construction, the nominal pile driving resistance is measured and verified during pile driving with the dynamic formula or dynamic testing methods
  • Ensure the pile tops are square with the axis of the pile.
  • If impenetrable obstructions are encountered during driving, direct the Contractor to remove and reuse the pile, or cut off and drive a new pile. Ensure the pile is cut to the lowest possible elevation, and drive another pile, adjusted laterally.
  • Check the plans for design pile lengths (pile lengths shown on the plans), or estimated pile lengths (pile lengths shown on plans used as guide if the nominal pile driving resistance is shown on the plans.
    • If the plans show design pile lengths, ensure piles are driven to the design pile tip elevations shown on the plans, unless driving operations attain absolute refusal (150% of the nominal pile driving resistance shown on the plans).
    • If the plans show estimated pile lengths, install piles to a the following penetration:
      • The nominal pile driving resistance equals at least the required nominal pile driving resistance; and
      • The bottom of the pile is at or below the minimum pile penetration elevation shown on the plans.
  • Ensure piles are not driven past absolute refusal unless Dynamic Testing is required. Any unnecessary production piling overdriving is to be avoided as it adds unnecessary project cost.
  • Ensure completed piles are driven according to the following accuracy criteria:
    • 1/4 inch per foot from vertical or batter line
    • Pile cutoff location is within 6 inches from plan position unless noted on plans
    • 9 inches between the edges of piles and the outline of the concrete forms
    • Pile bents are to meet the tolerances as shown on the plans
    • Pile cut off within 1”
  • Do not allow the Contractor to laterally pull piles to correct misalignment, or splice subsequent piles to correct misalignment.
  • Take level readings to measure pile heave after driving. If piles heave up during driving of adjacent piles, direct the Contractor to re-drive to the required bearing capacity or penetration elevation. For heaved CIP piles, ensure the concrete obtains its 28 day compressive strength prior to re-drive.
  • For battered piles, ensure the piles are driven to the angle shown on the plans. Note that the hammer energy will need to be reduced to account for losses due to the inclination of the hammer. Check the batter with a carpenter’s level attached to the vertical side of the Contractor’s template.

If at any time, the nominal pile driving resistance cannot met, but minimum pile penetration is achieved, contact the Geotechnical Services area for guidance.

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After Pile Driving

  • Ensure battered piles are cut perpendicular to the axis of the pile, not parallel with finished grade.
  • After driving CIP shell piling inspection will be done by using a mirror or light provided by the Contractor, suitable for illuminating the shell interiors. The shells will be free of bends, kinks or other deformations that would impair the completed pile strength.
  • After driving the piling, piling tops will be immediately covered to keep out rain, sand, etc. The piling should be cut off within 1 inch of the specified elevation and filled with grade S1 concrete as soon as possible.
  • Ensure any subsequent pile driving within a radius of 25 feet from concrete element pours are done after concrete has attained 75 percent of its design strength.
  • Concrete should be cast in slowly so that an air pocket is not formed in the pile. An inspector should be present at all times during placement. No concrete will be placed in any pile until all piles within a 20 foot radius have been driven and accepted.
  • Ensure the Contractor cleans the shells of CIP concrete piles where embedded 1 foot or more in structural concrete.
  • Check for any heaved piles. Heaved piles are to be redriven, and will be paid for as extra work.

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Defective Piles

Methods to correct piles damaged by internal defects, improper driving, driven below cutoff elevation, or driven outside of plan locations are as follows:

  • Withdraw the pile and replace with a new, longer stick (if feasible).
  • Drive a second pile adjacent to the defective pile (verify with Bridge Design, and the Geotechnical Services area).
  • Splice or build up the pile, or extend a portion of the footing to properly embed the pile

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Obstructions

Removal of obstructions that require special equipment or tools will be measured and paid for as extra work per subsection 109.05.D of the Standard Specifications or Construction. A budget amount will be established to pay for removing obstructions. If the Contractor and the Engineer cannot agree on a lump sum price, the Engineer will direct the work to be done on a force account basis.

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Splicing

Steel piles and steel pile shells may be furnished in full length sections or the pile shells may be spliced according to the splicing method as shown on the plans. Note when pile splicers are not permitted in the plans.

Splices will be made according to 12SP705(A) – Pile Splicing and the Contractor shall submit a QA/QC plan in accordance with special provision 12SP705(B) – Quality Control Plan for Welding Foundation Splices. Welding is to be done by a certified welder qualified in the 2G position for welding the pile in the vertical position. If the piling is spliced while lying on the ground, the welder will also be qualified in the 3G position. Furnished pile less than 40 shall contain no more than 3 splices, and furnished pile greater than 40 feet shall contain no more than 4 splices.

All welded splices shall be done in accordance with the MDOT Field Manual for Pile Welding –. See this manual for more details

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Welded

Welded splices for piles will be made only by qualified welders using E7015, E7016 or E7018 electrodes.

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CIP Concrete Piles

Shells for CIP concrete piles will be spliced using a chill ring or other type backing detail as shown on the plans.

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Steel Piles

Steel piles will be spliced as shown on the plans using preformed-preassembled bent plates or flat splice plates for pier piles, and other piles that are not considered primary members as called for on the plans. Pile acceptance is based on the Contractor’s conformance to their QA/QC plan, and can be visual.

Full penetration butt weld, or Complete Joint Penetration (CJP) welds are required for piles in integral abutments, and when otherwise defined as primary members on the plans. Pile acceptance for these members is based on 100% ultrasonic thickness testing (UT).

All splices require welding. Splicing devices which do not develop the full plan weld are not permitted.

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Scarfing

Scarfing the upper splice length of the piles preparatory to butt welding will be done by a cutting torch using a guide to assure a smoother chamber. A maximum of 1/8 inch land (shoulder) will be retained. If the end of the driven length of pile is damaged during the driving operation, it must be trimmed.

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Offhand Burning

Offhand burning will be permitted if trimming is minor. When it is necessary to cut a small section off the end of the driven pile length to square the end, burning must be done using a guide either clamped or tack welded in place. All adhering slag will be removed and the joint surfaces will be thoroughly cleaned by wire brushing before welding. A root opening of the butt joint will provide a 1/8 inch clear opening at the nearest point. When the 1/8 inch opening at the nearest point allows more than a ¼ inch opening at other points, correction will be made to provide the correct opening before welding. Beveling by cutting will be required for correcting openings wider than ¼ inch.

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Root Opening

The root opening may be held by two wedges before tacking. The members to be welded will be brought into correct alignment along the pile length and held rigidly by clamps or by dogging. Clamps or dogs may be removed after tack welding sufficiently to hold the member in place.

Where the parts are restrained against bending due to eccentricity in alignment, an offset not exceeding 10 percent thickness of the thinner part joint, but no more than 1/8 inch may be permitted as a departure from the theoretical alignment. In correcting misalignment, the parts will not be drawn into a greater slope than ½ inch per foot. Offset measurement will be based upon the centerline of parts unless otherwise shown on the drawing.

The root pass will be a stringer bead, placed with sufficient amperage to fully penetrate through the joint. Passes will be made symmetrically and will alternate on both flanges to minimize distortion. After the face side of both flanges and web has been welded completely, a backing bead will be made on the opposite side.

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DETERMINATION OF NOMINAL PILE RESISTANCE

The capacity of foundation piles is achieved through skin friction between the soil and the surfaces of the pile, tip capacity of the pile tip embedding into bedrock, or a combination of the two. The following methods are used to attain required nominal pile driving resistance:

  • Piles are driven to the minimum pile penetration elevation, and nominal resistance, or
  • Static load tests for piles with a nominal pile driving resistance greater than 600 kips, or
  • Using the Dynamic Formula for production piles less than 600 kips nominal pile driving resistance, or
  • Dynamic testing and analysis


A saximeter is to be used to verify blow counts, and the results compared to the dynamic analysis results. The saximeter works for several hammer types as follows:

  • For open ended diesel hammers, the saximeter computes stroke and potential energy from the measured blows per minute. This information is then multiplied by the hammer weight to obtain the hammer energy.
  • For other types of hammers, the Contractor is required to provide an electronic measuring device.

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Static Load Test

For high capacity piles, < 600 kip nominal pile resistance, static load tests may be required. Load testing details will be in the plans and specifications. This generally involves the placement of large amounts of weight on a group of piles, and recording measurements on vertical displacements and deflections. The Geotechnical Services Section will approve the load test methods.

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Dynamic Formula

The Dynamic Formula (FHWA Modified Gates Formula) is not to be used on piles with a required nominal pile driving resistance greater than 600 kips. Check the plans and specifications for dynamic testing with signal matching.

For battered piles, use a hammer energy reduction coefficient.

These formulas are applicable under the following conditions – Notice if these conditions are not met:

  • Hammers and unrestricted free fall
  • Pile tops are not broomed, crushed, or splintered
  • The hammer exhibits no appreciable bounce after striking the pile
  • Penetration is at a uniform or uniformly decreasing weight

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Ordering Pile Driving Charts

When pile charts are needed immediately, submit MDOT form 1956 – LRFD Pile Driving and Equipment Data to the Geotechnical Services Section and Bridge Field Services for review and creation of pile driving charts.

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MEASUREMENT AND PAYMENT

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