00520.20 443 Section 00520 - Driven Piles
Description
00520.00Scope - This Work consists of furnishing and driving piles of the type and dimensions
shown or specified, including cutting off or building up piles when required.
Materials
00520.10Materials - Furnish Materials meeting the following requirements:
Reinforced Pile Tip ................................................................................ 02520.10 Steel Piles ............................................................................................. 02520.10
00520.11Engineer's Estimated Length List - Furnish steel piles of sufficient length to attain the
penetration and bearing resistance specified, and to extend into the cap or footing as shown. The Contractor may, at no additional cost to the Agency, drive test piles, make borings, and perform other investigations the Contractor considers necessary. The "E ngineer's Estimated Length" of steel piles will be listed in the Special Provisions.
00520.13Test Piles - Furnish test piles according to the test pile length list in the Special Provisions
When test piles are required, the production pile lengths sh own or specified in the Special Provisions are estimated lengths only. The actual lengths to be furnished for production piles will be determined by the Engineer after the test piles have been driven. This applies for all pile types.
00520.14Unused Piles - Acceptable full length piles furnished according to the estimated length list,
order list, or revised pile order list, but not incorporated in the Work , will be handled according to one of the following:
• Mark and identify piles f or the Contractor's own use. • Return piles to the Supplier with the Agency paying transportation and restocking charges. • The Agency will purchase from the Contractor piles that are stockpiled at a location on the Project selected by the Engineer according t o 00195.80.
Equipment
00520.20Equipment for Driving Piles - Provide pile driving Equipment meeting the following
requirements:
weight of the helmet and pile being driven, but never less than 2,750 pounds.
sufficient capacity under working conditions to maintain the volume and pressure at the ham mer specified by the manufacturer and with accurate pressure gauges easily accessible to the Engineer.
with a device which allows the Engineer to visually determine ha mmer stroke at all times during pile driving operations. Provide the Engineer with the hammer manufacturer's chart equating stroke and blows per minute.
00520.20 444 (3) Closed -End Diesel Hammers - Provide closed- end (double-acting) diesel hammers equipped with a bounce chamber pressure gauge, mounted near ground level so the Engineer can easily read it. Before driving, provide the Engineer a chart calibrated within 6 months before first use on the Project to actual hammer performance, equating bounce chamber pressure to either equivalent energy or stroke.
2,000 pounds and 5,000 pounds and a drop height of not more than 10 feet. The weight of gravity hammers shall not be less than the c ombined weight of helmet and pile.
with monitoring systems to measure impact velocity and determine equivalent energy and stroke. Locate monitoring systems for easy access by the Engineer.
to the power consumption, rate of penetration, specified tip elevation, or other acceptable means which assure the pile resistance equals or exceeds the required nominal pile bearing resistance. After driving piles with a vibratory hammer, verify pile resistance (see 00520.42) by driving them with an impact hammer of suitable energy. Do not use vibratory hammers to drive test piles or when preboring or jetting.
helmet shall:
• Fit around the pile top. • Be axially aligned with the hammer and pile. • Distribute the hammer ener gy to the total Cross Section of the pile head. • Be guided by leads.
hammer cushion material to prevent damage to the hammer or pile and to ensure uniform driving perfor mance. Provide hammer cushions of durable manufactured materials according to the hammer manufacturer's guidelines. Do not use wood, wire rope, or asbestos hammer cushions. Place a striker plate, as recommended by the hammer manufacturer, on the hammer cushion to ensure uniform compression of the cushion material . Inspect the hammer cushion in the presence of the Engineer at the beginning of pile driving at each Structure or after each 100 hours of use during pile driving, whichever is less. Replace the hammer cushion when its thickness becomes less than 75 percent of its original thickness.
the pile head is below the reach of the hammer, if allowed by the Special Provisions or approved in writing. If a follower is allowed, drive the first pile in each bent, and every tenth pile driven after that, full length without a follower. Before additional piles are installed, verify that the first two piles installed with followers in each Substructure unit meet the position and alignment criteria of 00520.41(f).
the hammer freedom of movement while maintaining alignment of the hammer and the pile to ensure concentric impact for each blow. Leads shall be fixed unless the Engineer approves the use of swinging leads. Fit swinging leads, when u sed, with a pile gate at the bottom of the leads. 00520.20 445 To maintain alignment of batter piles, use horizontally braced swinging leads, adequately embedded in the ground, or rigidly attached to prevent movement during pile driving.
pile driving Equipment .
To obtain approval, complete and submit the Agency's "Pile and Driving Equipment Data" form at least 14 Calendar Days before pile driving begins. This form is available from the Engineer. Within 14 Calendar Days of receiving the form, the Engineer will notify the Contractor of approval or rejection of the pile-driving Equipment .
During pile- driving operations, no changes to the approved Equipment will be allowed without the Engineer's written permission. Submit a request for change on a "Pile and Driving Equipment Data" form. The Engineer will give notification of approval or rejection within 7 Calendar Days of receiving the form. Time required for resubmission and review of a Contractor's Equipment change request is not a basis for a Contract Time extension request unless the Engineer does not respond in 7 Calendar Days.
requires that the field-measured hammer energy be within the range of energy levels given in Table 00520-1 corresponding to the nominal pile bearing resistance shown.
Table 00520-1 Pile Hammer Requi rements 1 Nominal Pile Bearing Resistance Minimum Field Energy
≤ 180 6,500 > 180 and ≤ 300 13,000 > 300 and ≤ 400 20,000 > 400 and ≤ 500 30,000 > 500 and ≤ 600 40,000 over 600 Wave Equation required
1 Requirements are based on the FHWA Gates equation (see 00520.42(b)), except all driving criteria for double acting and differential hammers both air/steam and diesel will be by the wave equation analysis.
If during the pile- driving operation, the Engineer determines the hammer is not operating properly and is unable to drive the piles to the required resistance, do not use the hammer until repaired to the Engineer's satisfaction.
The required number of hammer blows indicated by the FHWA Gates equation at the nominal pile bearing resistance shall be at a rate between 2 and 10 blows per inch.
equation analyses. Use the latest version of the Wave Equation Analysis Program (WEAP). Conduct the wave equation analyses using personnel qualified by training and experience to perform this type of Work .
Submit the WEAP analysis concurrent with the Pile and Driving Equipment Data Form . The Engineer will approve or reject the pile driving Equipment submittal after a review of the wave equation analysis conducted by the Contractor.
00520.20 446 Provide pile hammers meeting the following requirements based on wave equation analysis:
• The energy of t he submitted hammer shall produce a wave equation predicted blow count between 2 and 10 blows per inch for the nominal resistances, pile lengths and other conditions specified. • The pile stresses indicated by the wave equation at the nominal resistance shal l not be greater than the stress at the point of impending damage to the pile as follows:
• Steel Piles - Tensile and compressive stresses in the pile of 90 percent of the pile material 's yield strength for the grade of steel specified at any time during the pile installation. • Prestressed Concrete Piles:
• A tensile stress of (.095cf') + effective prestress • A compressive stress of (0.85cf') - effective prestress Where: cf' = concrete compressive strength (ksi) • Timber Piles - A compressive driving stress of three times the allowable static design stress.
Hammers not meeting these requirements will be rejected. Replace rejected hammers with suitable hammers.
Use input values for the wave equation analyses provided in the Special Provisions and according to the following:
Use the following settings and default values as input to the wave equation analysis program:
• Output option (IOUT) zero (normal option). • R N is the nominal pile bearing resistance. • Smith damping. • Do not use residual stress option. • Default hammer efficiency values. Do not adjust the hammer's efficiency outside of the wave equation program recommended (default) values without prior concurrence of both the pile hammer m anufacturer and the Engineer. • % skin is the percent skin friction. A Pile Driving Analyzer (PDA) test may be required prior to approval of non-default wave equation input values.
At a minimum, provide the following information and documentation:
• A written summary of how the proposed hammer and associated Equipment meets the Specifications regarding blow count criteria and allowable pile stresses. • Electronic and paper copies of the wave equation input and output files. Output files shall be in the standard WEAP output format. 00520.41 447 • WEAP analysis demonstrating that for the required nominal bearing resistances and conditions provided, the hammer will produce pile stresses less than those described above for the range of hammer strokes expected in the field. • The Pile and Driving Equipment Data form. • WEAP hammer input files for hammers not in the wave equation default hammer files.
For Agency reviewing and approving of the wave equation analysis submittals, the following will be taken into consideration:
• The pile length for use in the WEAP analysis will be the total pile length at the end of driving, including all pile length above the ground surface. This length may be longer than the Engineers Estimated length depending on the site conditions, Equipment used, pile hammer access limitations and other factors. • The properties and thicknesses of the hammer and pile cushion materials. • Various hammer types such as direct -drive diesel, standard diesel, air/steam or hydraulic hammers have major effects on predicted stresses and blow counts. • Changes in pile type or size will affect the blow count rate and pile stresses. • Battered piles may effect hammer energy transfer and blow counts.
Failure to address these issues may be cause for rejection of the proposed pile hammer.
The size of the pile hammer selected according to the above specification may have significant impacts on the size and capacity of associated Equi pment including the leads and crane. This Equipment , in turn, may have significant impacts on the size and capacity of work Bridges, shoring required for existing Structures or other aspects and elements of construction.
Failure of a previously approved hammer to operate properly during construction will be cause for rejection.
Construction
00520.40Preparation for Driving :
is complete. Remove to the correct elevation any material forced up by pile driving before concrete for the foundation is placed, at no additional cost to the Agency.
embankment at bridge ends is in place according to 00330.42. Drive piles completely through roadway embankments to the required penetration and bearing in the underlying material.
00520.41Driving :
penetration depth and to the required nominal pile bearing resistance as shown or specified.
groups starting from the center of the group and proceeding outward in either direction, or as approved.
below the footing or pile cap, 12 feet below the groundline at trestl e pile locations, and completely through embankments at bridge ends. When shown or specified drive piles to a greater minimum 00520.41 448 penetration. If the required penetration cannot be attained with a hammer complying with 00520.20(d), provide a larger hammer, p rebore or jet holes, or use other approved methods as necessary to attain the required penetration.
specified or with written approval. When allowed, prebore holes at pile locations and to the depths shown or directed. Make prebored holes smaller than the diameter or diagonal of the pile Cross Section, but sufficient to allow penetration of the pile to the specified depth. If subsurface obstructions, such as Cobbles, Boulders or Rock layers are encountered, the hole diameter may be increased to the least dimension which is adequate for pile installati on. The use of a reinforced section (spud) to loosen the subsurface material at pile locations is not allowed unless otherwise approved. Perform preboring in a manner that will not impair the bearing or lateral capacity of the piles already in place or t he safety of existing adjacent Structures. When it is determined that preboring has disturbed the load bearing resistances of previously installed piles, restore those piles that have been disturbed to conditions meeting the requirements of this Specification by redriving or by other acceptable methods. The Contractor shall be responsible for the costs of any necessary remedial measures unless the preboring method was specifically included in the Contract Documents and properly executed by the Contractor.
carried to the surface of the end-bearing foundation material. Following that, drive pile with an approved impact pile hammer to the specified blow count.
then drive pile with an approved impact pile hammer to the specified blow count.
After completion of driving, fill any void space remaining around the pile with Sand or other approved Material .
writing. When jetting is not required in the Contract Documents, but approved at the Contractor's request, determine and submit for review the number of jets and the volume and pressure of water at the jet nozzles necessary to freely erode the material adjacent to the pile with out affecting the lateral stability of the final in -place pile. The Contractor shall be responsible for all damage caused by unapproved or improper jetting operations, unless the jetting method was specifically included in the Contract Documents and properly executed by the Contractor. Control, treat if necessary, and dispose of all jet water in a satisfactory manner. Drive all jetted pile with an approved impact hammer.
horizontally within 6 inches of plan locations. No pile shall be nearer than 4 inches from any edge of the cap. Any increase in cap size to meet this edge distance requirement will be at no addi tional cost to the Agency. Install piles so the axial alignment of the top 10 feet of the pile is within 5 inches of the specified alignment. For piles that cannot be inspected after installation, make an alignment check before installing the last 5 feet of pile. The Engineer may require that driving be stopped to check the pile alignment. Pulling laterally on piles to correct misalignment or splicing a properly aligned section onto a misaligned section is not allowed.
If the specified location or alig nment tolerances are exceeded, the effect of the pile misalignment on the Substructure design will be investigated. If the Engineer determines corrective measures 00520.42 449 are necessary, implement suitable measures and pay all costs and delays associated with the corrective action.
heave. Take elevation readings after each pile has been driven and again after piles within a radius of 15 feet have been driven. Redrive to the required penetration and resistance all piles that have risen more than 1/2 inch, at no additional cost to the Agency. Continue readings until the Engineer determines that such checking is no longer required. If pipe piles which have been fil led with concrete subsequently heave, redrive them to original position, after the concrete has attained specified strength, with an approved hammer -pile cushion system.
directed. All test piles shall be of the kind and size specified for the permanent foundation piles unless otherwise directed. Drive all test piles with approved pile driving Equipment . The specified length of test piles will be greater th an the estimated length of production piles to provide for variation in Soil conditions. Drive test piles using driving Equipment identical to that which the Contractor proposes to use on the production piling. Excavate to the elevation of the bottom of the footing before driving test piles. ( See Section 00510 .)
Drive test piles to or below the required minimum tip elevation and to a hammer blow count established by the Engineer. Allow test piles which do not attain the hammer blow count specified at the minimum tip elevation shown to "set up" for 24 hours, or less if directed, before being redriven. ( See 00520.42(d) .) If the tops of test piles reach plan grade without attaining the required pile bearing resistance, splice them and drive until the required bearing resistance is attained. Remove test piles that are not to be incorporated in the completed Structure to at least 2 feet below the surface of the ground and backfill the remaining hole with acceptable M aterial .
Do not order pili ng to be used in the permanent Structure until test pile data has been reviewed and the production pile order lengths are determined. The Engineer will provide the Engineer's estimated length list or pile order list within 7 Calendar Days after completion of all test pile driving specified in the Contract.
00520.42Nominal Pile Bearing Resistance:
the required penetration and nominal pile bearing resistance. Adequate pile penetration will be considered reached when the piles are driven to or below the minimum penetration depth and the specified bearing resistance is achieved. If piles do not achieve the specified resistance when driven to order length or estimated length, splice and drive them to penetrations established by the Engineer. The pile blow count shall be at a rate of between 2 and 10 blows per inch at the required nominal pile bearing resistance. The required number of hammer blows per inch at final penetration shall be maintained for 3 consecutive inches unless "refusal" driving is first obtained. "Refusal" driving is defined as 20 blows per 1 inch or as determined by the Engineer.
If water jets are used with the driving, the bearing value shall be determined by the specified equation from the results of driving after the jetting has been completed according to 00520.42(e).
bearing resistance of the driven pile by the FHWA Gates equation:
00520.42 450 Rn = 1.75 ( E) log 10(10N) - 100
where: Rn = Nominal Pile Bearing Resistance (kips) E = W x H (Hammer energy (foot -pounds) at the ram stroke observed in the field) W = Weight (pounds) of striking parts of hammer H = Height of fall (feet) of the ram measured during pile driving in the field Log 10(10N) = Logari thm to the base 10 of the quantity 10 multiplied by N N = Number of hammer blows per inch at final penetration to be sustained for 3 consecutive inches
−+ =1 E75.1100 Rn 10N
or N = 10 to the power in brackets
The FHWA Gates equation is applicable only if:
• The hammer is in good condition and operating in a satisfactory manner • The hammer has a free fall • A follower is not used • The head of the pile is not broomed or crushed
If the Engineer determines that the hammer being used may not be attaining the specified bearing resistance when the above equation is applied, the Engineer may order the Contractor, at no additional cost to the Agency, to verify the bearing resistance values obtained by the use of a different hammer.
resistance based on wave equation analysis.
driven to the specified length, and if allowed or required, allow the piles to stand for a "set period" without driving. The "set period" shall be a minimum of 24 hours. After the set period, perform check driving on either two piles in each bent or on one pile in every 10 piles, whichever is more. The Engineer will designate the piles on which check driving is to be performed. Do not use a cold hammer for redriving. Warm up the hammer before redriving begins by applying at least 20 blows to another pile. Redriving shall consist of dri ving the pile to the required bearing resistance with a maximum of 15 blows. If the specified hammer blow count is not attained on redriving, the Engineer may direct the Contractor to drive all of the remaining pile length and repeat the set period and redriving procedure. Splice those piles driven to plan grade that do not attain the hammer blow count required, and drive until the required bearing resistance is attained. If the required bearing resistance is attained for each pile that is redriven, then the remaining piles in that bent will be considered satisfactory when driven to at least the same penetration and resistance as the redriven piles.
blow count after jetting has been completed. Jet pipes may be removed when the pile tip is at the required minimum pile tip elevation and before the pile is driven to the required bearing resistance. For piles that are jetted at the Contractor's request and do not attain the required nominal bearing resistance at the ordered length, splice, as required, and drive with a specified impact pile hammer until the required nominal bearing resistance is achieved according to appropriate criteria 00520.43 451 in 00520.42. Regardless of Agency approval, the Contractor shall pay all costs of splicing and driving piles beyond the order length if jetting is requested by the Contractor.
be considered acceptable when the follower -driven piles attain the same tip elevation as piles driven without followers. ( See 00520.20(c)( 3).)
will be based on impact driving blow count after the vibratory Equipment has been removed. When vibratory installation of the piles is approved by the Engineer and the vibrated piles do not attain the required nominal bearing resistance at the specified length, spl ice them as required, at no additional cost to the Agency, and drive with a specified impact pile hammer until the required nominal bearing resistance is achieved, according to 00520.42.
required. Conduct static load tests according to ASTM D1143 using the quick load test method to plunging failure or the capaci ty of the loading system. Use testing Equipment and measuring systems capable of applying 150 percent of the nominal pile bearing resistance or 1,000 Tons, whichever is less.
designated as dynamic load test piles as specified. Perform dynamic testing according to ASTM D4945.
Drive the pile to such depth that the dynamic load test Equipment indicates that the n ominal pile bearing resistance shown has been achieved, unless otherwise directed. Monitor the stresses in the piles during driving with the dynamic test Equipment to ensure the values do not exceed the values in 00520.20(d)(3). If necessary, reduce the driving energy by using additional cushions or reduce the energy output of the hammer to stay below the values in 00520.20(d)( 3). If non -axial driving is indicated by dynamic test Equipment measurements, immediately realign the driving system.
00520.43Steel Piles:
lengths.
Bent or kinked piles will be rejected.
manufacturer's recommendations and Section 02520.
details.
with the welding procedures of AWS D1.1.
00520.43 452 (2) Mechanical Splices - Mechanical splices may be used if the splice transfers the full pile strength in compression, tension, and bending, according to unstamped Working Drawings submitted according to 00150.35 and approved by the Engineer.
according to AWS D1.1.
Groove Weld) in D1.1. Weld back -up rings with a full penetration groove weld. Pipe pile splices that include a steel plate for Soil plug formation shall conform to Joint TC -U4a or TC -U4a -GF.
Splice joints for H -piles shall conform to Joint B -U3b or B -U3-GF (Double V -Groove Weld) in D1.1 for both the web and flange sections. Joint B -U4a or B -U4a-GF may be substituted on the flange weld. Provide access holes at the ends of the web acc ording to D1.1.
• A Welding Procedure Specification (WPS) for all pile welds, conforming to the limitations of D1.1. Both ASTM A36 and ASTM A252 Grade 1 and 2 may be treated as prequalified base metals under Group 1. ASTM A252 Grade 3 will not be considered a prequalified base metal unless the steel has a Carbon Equivalent (CE) of 0.30 percent or less. Develop a Procedure Qualification Record (PQR) for all welding using Grade 3 steel or present proof that the chemistry of the steel meets the CE requirements. • Qualification documents for each welder. Use welders qualified according to D1.1 Section 4 for the position, process and pile diameter used on the job.
Do not begin welding without approval.
Following completion of all welding, submit the following:
• An inspection r eport stating that the welding under the Contract was performed according to D1.1. The report shall include a review of the WPS, a review of welder qualifications and a report on visual inspection of the welds on the Project Site . The inspection shall be signed by a Certified Welding Inspector (CWI) holding QC1 certification as defined in D1.1. • If the Plans or Specifications call for additional inspection other than visual, include reports in the submittal.
such as radiography or ultrasonic testing of any or all welds. If the additional testing identifies defects warranting rejection, perform repair and additional inspection at no additional cost to the Agency. I f the additional NDT does not identify defects warranting rejection, the Agency will pay the cost of the additional testing. Radiographic and ultrasonic defect indications will be evaluated according to the statically loaded criteria of D1.1.
shown or as directed. All cut -off pile becomes the property of the Contractor. Dispose of according to 00290.20. With approval, undamaged c utoffs may be used as pile extensions or welded together to form full length piles. Steel pile cutoffs welded together, whether pile extensions or full length piles, shall not vary from a straight line more than 1/4 inch in 20 feet measured along any edge of the pile.
All acceptable cutoffs and unused pile lengths remaining at completion of pile driving will be marked for identification by the Engineer as acceptable for use on other or future Agency projects if requested by the Contractor. 00520.80 453
shown. Connect this cap to the pile according to the details shown.
and to the elevations specified in 00520.11.
00520.46Damaged or Defective Piles - In addition to other specified requirements:
• Approval of a pile hammer shall not relieve the Contractor of responsibility for piles damaged from misalignment of the leads, failure of capblock or cushion materials, failure of splices, malfunctioning of the pile hammer or other improper construction methods. • Piles damaged during installation will be considered unsatisfactory unless the nominal bearing resistance is proved by load tests performed by the Contractor. If such tests indicate inadequate resistance, take corrective measures, such as the use of damaged piles at reduced resistance, installation of additional piles, strengthening of damaged piles, or replacem ent of damaged piles. • A concrete pile will be considered defective if a visible crack appears around the entire periphery of the pile, or any other crack or defect is observed which is determined to affect the strength or performance of the pile. • Do not pl ace footing concrete until all piles within a footing are inspected by the Engineer.
Measurement
00520.80Measurement - The quantities of Work performed under this Section will be measured
according to the following:
Equipment for driving piles.
length basis, as follows:
from the pile tip to the cutoff plane.
measured according to 00520.80(b)(1). No allowance will be made for th e length of pieces furnished by the Contractor to replace piles previously accepted by the Engineer that are damaged before completion of the Project .
basis. Driving test piles includes test piles remaining in the completed Work .
Preboring will be measured on the length basis.
Jetting will be measured on the unit basis, for each pile driven with the aid of jetting.
tests completed and accepted. Load tests made at the option of the Contractor will not be measured.
00520.90 454 (f) Pile Splices - Pile splices will be determined as follows:
length of the pile 5 feet or more for estimated pile lengths of 60 feet or less and 10 feet or more for estimated pile lengths of over 60 feet beyond the estimated pile length will be measured on the unit basis. Only one splice will be measured per pile.
No measurement will be made for splices to steel piles withi n the estimated lengths listed in 00520.11 of the Special Provisions .
protective coatings. The estimated quantities of steel pile protective coatings is listed in the Special Provisions.
Payment
00520.90Payment - The accepted quantities of Work performed under this Section will be paid for
at the Contract unit price, per unit of measurement, for the following items:
Pay Item Unit of Measurement
Partial payments for Item (a) will be made as follows:
• When Equipment for driving piles is furnished and is satisfactorily dr iving piles ....75% • When driving piles is complete and Equipment has been removed from site ........25%
Item (a) includes:
• furnishing all Materials, Equipment , and labor necessary for transporting, erecting, maintaining, replacing any ordered Equipment , dismantling and removing the entire pile driving Equipment • resubmittal of wave equation analysis data if original data is rejected • replacing previously approved hammers if hammer operates improperly • all considerations when selecting the pile hammer size
The cost of all Materials and labor, including the manipulation of the pile driving Equipment in connection with driving piles will be included in the unit price each for driven piles. Furnishing Equipment for driving sheet piling is not included in this Work .
In items (b), (c), (d) and (k) the type and size of pile will be inserted in the blank.
00520.90 455 Item (d) includes cutting off piles, treating and capping pile heads, attaching anchor brackets, and lugs or other attachments.
Items (d) and (e) include all e xpenses involved in driving piles which have not attained the required bearing resistance and are required to stand for a "set period".
Item (j) includes attaching the tips to the piles. Item (k) includes steel pile splices required to increase pile length beyond the estimated length listed in 00520.11 of the Special Provisions . No payment will be made for splices to steel piles that are within the estimated lengths listed in 00520.11 of the Special Provisions .
Payment will be payment in full for furnis hing and placing all Materials, and for furnishing all Equipment , labor, and Incidentals necessary to complete the Work as specified.
No separate or additional payment will be made for:
• Work needed to drive piles to minimum tip elevation as shown or spec ified • welding inspection performed according to 00520.43(g)(2) • preboring and jetting of piles if not included in the Contract Schedule of Items but requested by the Contractor Preboring and jetting, if not included in the Contract Schedule of Items, larger hammers, and construction of concrete pile extensions, build -ups, and splices ordered by the Engineer, as a result of differing site conditions (see 00140.40) will be made according to 00195.30.