GS_2a_Piling.doc

General SpecificationSection 2a-

Piling

SECTION 2a1 - PILING GENERALLY

2a1.01 Contractor's Responsibility

the Contractor shall be entirely responsible for the safety of the work and for taking all necessary precautions to prevent settlement or damage to adjacent buildings, roads and surrounding ground. He shall inspect the adjacent buildings and surrounding area at regular frequent intervals and shall immediately report to the Engineer any signs of damage or distress which may become evident.

If directed by the Engineer the Contractor shall provide shoring to the adjacent buildings and shall move and reposition any shores as may be necessary to get the rigs into position for driving the piles adjacent to the buildings.

All such work shall be carried out and any damage rectified at the Contractor's own expense.

Piling works shall be carried out in accordance with the Code of Practice for Foundations 2004.

2a1.02 Damage to Existing Services

Care shall be taken not to disturb existing drains, gas or water mains, cables or other underground work. Should any damage occur the Utility Authority and the Engineer are to be notified immediately and all damage made good at the Contractor's expense.

The Engineer is to be informed as soon as possible if it is found that any of the existing services shown on the drawings are significantly out of position and if any additional services are found.

2a1.03 Site Investigation Report

Where a site investigation report and/or borehole logs are made available by the Engineer they are given in good faith as to the ground condition likely to be met. The Contractor is to make his own interpretation of the report and/or borehole logs and of the applicability of the conditions shown in the boreholes over the site as a whole and of the possible and probable variation in conditions which may occur between boreholes.

document.doc - S2a/1 - Dec 2011


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2a1.04 Contractor to Visit Site

Contractors tendering are advised to visit the site of the works and make themselves thoroughly acquainted with the location, general site conditions, accessibility, storage space, restrictions for loading and off loading materials etc. and any other conditions which may affect their tender.

2a1.05 Size and Capacity of Piles

The piles shall be of the size or sizes shown on the drawings. They shall be capable of carrying the loads shown on the loading schedule without undue settlement and of withstanding the loading test required by the Building Authority.

2a1.06 Materials

Unless otherwise stated, materials for concrete piles shall be of the quality described in Section 2e Concrete Specification.

2a1.07 Setting Out

The Contractor shall provide all necessary instruments, lines and pegs and shall set out the pile positions in accordance with the piling plan and any further details provided by the Engineer.

Although the setting out of piles may be checked by the Engineer, it is the Contractor's responsibility to ensure that the piles are installed in correct position and to the required levels and rake.

If any discrepancy should be found between the dimensions shown on the drawings and the dimensions found on site the Contractor shall inform the Engineer who shall give instructions to resolve the discrepancy.

The position of any pile shall not be adjusted by the Contractor without the prior approval of the Engineer or his representative.

The Engineer may require additional piles to supplement any pile which deviates from the acceptable tolerances or is incorrectly located to such an extent that the eccentricity cannot reasonably be provided for by a simple amendment of the pile cap.

Such additional piles shall be provided at the Contractor's expense and no claim for extension of time will be entertained.



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2a1.08 Tolerances for Piles

Piles shall be driven as accurately as possible to the vertical or to the specified rake. Unless other tolerances are shown on the drawings, piles shall not deviate more than 1 in 75 from the specified alignment and in no cases the pile shall be more than 75mm from the true centre on plan.

No part of any piles shall be allowed outside site boundaries, unless the Engineer specifies otherwise on the drawings.

2a1.09 Driving Test for Piles

The Contractor shall, when required, carry out driving tests on piles selected by the Buildings Department or by the Engineer. Such tests shall be performed in the presence of the Engineer or his representative and the Buildings Department. A full record of hammer drop, number of blows and penetration shall be kept for the full length of penetration and a number of temporary compression diagrams shall be taken as directed by the Engineer.

2a1.10 Notification to Commence Piling

The Contractor shall give at least 48 hours advance notice to the Engineer prior to commencing the first pile to enable the Buildings Department and the Engineer of his representative to be present.

2a1.11 Load Tests on Working Piles

Load tests on working piles selected by the Building Authority or by the Engineer will be required. The number will usually be about one test for every hundred piles.

Tests required by the Building Authority shall be done in the manner prescribed by the Building Regulations and as required by the Buildings Department. Tests required by the Engineer shall be by the maintained load method usually with eight increments. One unloading cycle may be required upon reaching the working load. The test load will usually be twice the maximum capacity of the pile.

If a pile fails under test, any additional piles and testing to compensate for the failure shall be at the contractor's expense.

Full records shall be kept of time, load settlement and recovery during the test and the test and the test report shall include plots of load and settlement against time and load against settlement.



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2a1.12 Pile Load Test Procedure

(A). Loading

The kentledge shall be set up over the pile and supported in such a manner as will avoid any dangerous tilting before, during or after the tests.

The load shall be transferred to the pile head by means of a hydraulic jack and loading frame. If a dynamometer is not incorporated in the loading equipment the jack shall be calibrated immediately before the test by an approved independent laboratory.

(B) Records

Settlement readings shall be taken from a datum which will not be affected by any movement of the ground due to the test load. Measurements shall be taken to an accuracy of 0.01 mm.

Records shall be kept of time, load and settlement. Graphs of these records shall be plotted showing:-

(i) load plotted above and settlement plotted below a common base line of time and

(ii) (for constant rate of penetration test) settlement plotted below a base line of load, or

(iii) (for sustained load tests) final settlement under each increment plotted below a base line of applied load.

The recovery of the pile on removal of the test load should be recorded in a similar manner.

(C) Constant Rate of Penetration (Type A Tests)

The constant rate of penetration test is carried out by controlling the increase in loads on the pile in such a way as will cause the pile to penetrate into the ground at a constant rate. The load is increased in this manner until the rate of penetration increase without application of further load. The load is then released to zero.

Three such tests are to be carried out consecutively on each pile. The rate of penetration for the first test should be about 0.5 mm per minute, for the second test 0.75 mm per minute and for the third test 1.0 mm per minute.

A plot of settlement against time shall be kept during the test both as a guide for controlling the rate of settlement



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and as a record of the actual rate obtained and any variation from a constant rate.

(D) Sustained Load (Type B Tests)

Sustained load tests shall be carried out by loading the pile in equal increments and observing the settlement for each increment until it has substantially ceased. The next increment then applied & the procedure repeated.

Unless otherwise specified or ordered, the full test load shall be twice the estimate working load of the pile and it shall be applied in four increments.

Settlement readings shall be taken immediately before, and immediately after applying the increment. They should then be taken at short intervals which can be increased as the rate of settlement decreases. Settlement can be considered to have substantially ceased when the slope of the settlement curve plotted below a base line of time decreases and approaches the horizontal (incremental settlement less than 0.05 mm per 10 minutes).

(E) Failure

For the constant rate of penetration test, failure shall be taken as the point at which the rate of settlement increases without the application of further load or alternatively the point at which it is no longer necessary to increase the load to maintain the constant rate of settlement.

For the substained load test failure shall be taken as the point at which the rate of settlement continues undiminished or increases without the application of further increments or alternatively the point at which the load/settlement graph approaches the vertical.

(F) Acceptance Criteria

The acceptance criteria for tests on working piles shall be the criteria specified by the Building Authority.

2a1.13 Trimming Pile Heads

Concrete piles shall be carefully trimmed to cut off level in a manner which will not damage the shaft. Reinforcement where provided shall be stripped of concrete ready for bonding into the pile cap.



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2a1.14 Records

An accurate and comprehensive record shall be kept of each pile and the following data and daily record sheets signed by the Contractor's representative and the Engineer's representative shall be submitted to the Engineer each week in duplicate:-

(a) pile reference number(b) date and time of commencement and completion of installation(c) ground level at pile position(d) depth driven or bored(e) depth concreted and quantity of concrete used(f1) final set for last ten blows (if applicable)(f2) `N' value below tip of pile (if applicable)(f3) the torque at each metre of penetration (if applicable)(g) details of obstructions or delays(h) details of inclination or displacement of the pile during driving

For each caisson the following additional information is required:

(i) daily progress(j) type of ground encountered(k) date of approval of base(l) tables and charts showing the data for proving the bases

Test pile driving records and copies of the results of any load tests shall be submitted to the Engineer in triplicate.

A copy of the daily records shall be kept on site together with a marked up copy of the piling plan showing the depths of the piles and date of installation.

2a1.15 Foundation Record Plans and Report

The Contractor shall prepare a piling record plan in the form of a tracing or sepia of the piling plan showing the following information:

(a) The final positions of the piles (i.e. any deviation greater than the tolerance).

(b) The toe level of each pile referred to P.D.(c) A number of spot levels to show the general ground level

of the site.



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This plan shall be brought up to date at intervals during the work so that prints can be taken for submission to the Building Authority as each section of the work is completed. Six copies of the completed record plan shall be submitted to the Engineer without delay after the last pile has been installed.

The Contractor shall also prepare a piling report containing all the information required by the Building Authority. This report shall be brought up to date at intervals so that it will be ready for submission section by section. Four copies will be required.

2a1.16 Site Clearance

On completion of the work the Contractor shall leave the site clean and tidy, and free from all debris, surplus materials, etc. resulting from his operations.

2a1.17 Obstructions and Delays

The Contractor is deemed to have included in his rates for installing the piles through any type of strata encountered.

Prior to any pile installation, the Contractor shall submit his proposal on the method of overcoming underground obstructions for the Engineer's approval. If a method is already specified by the Engineer, the Contractor shall follow without deviation.

Any delays caused by the overcoming of underground obstructions shall not constitute a claim for extension of time.

2a1.18 Pile Length

The piles shall be capable of carrying without distress to the superstructure the working loads shown on the drawings and shall satisfy the requirements in respect of settlement under test load. The contractor shall determine the length of the piles based on the pile tests, and/or available site investigation reports and/or the results of such other tests and investigations as he may carry out, and the lengths of pile already driven.

Before fabricating any pile the contractor shall submit for the Engineer's approval the length of pile he proposes to drive and details of the number and position of splices he proposes to use to make up the pile. The Engineer's agreement shall not relieve the Contractor from his responsibility for providing piles of adequate length capable of carrying the working loads indicated on the drawings and schedules, but shall be mainly for the purpose of agreeing the measurement as the work proceeds.



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The minimum net length below cut-off level shall be 4.5m for driven piles. The contractor shall use appropriate methods, including preboring, to achieve installing the minimum length.

2a1.19 Defective Piles

If, in the opinion of the Engineer, any pile is incapable of permanently carrying its design load because of the pile having been installed outside the specified tolerances or damaged by over-driving or by the construction of another pile nearby or otherwise failing to conform to the Specification, the Contractor shall submit remedial works proposal for the Engineer's approval. The remedial works may consist of re-installation of the defective pile at another location, additional piles or revisions to pile cap and tie beam details.

The Engineer may instruct that the approved remedial works be carried out by the Contractor or by the Superstructure Contractor with the cost recovered from the Contractor if, in the opinion of the Engineer, it is more beneficial for the execution of the project to do so. Normally, if the remedial works fall within the scope of the Superstructure Contract, the Engineer will instruct the Superstructure Contractor to carry out the remedial works. The decision of the Engineer in this respect is final.

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SUBSECTION 2a2 - AUGERED PILES

2a2.01 Additional Ground Investigation

Carry out additional ground investigation borings immediately after commencement in order to supplement the original ground investigation for the purpose of confirming the lengths required for augered piles. The number, location and depth of the additional boreholes shall be agreed with the Engineer before starting.

2a2.02 Length of Augered Piles

The length of augered piles shall be based on friction on a shaft of the specified diameter. For the purpose of estimating the pile length, the allowable unit friction shall be taken as 1.6N kPa up to a maximum of 64 kPa where N is the standard penetration test blow count.

The load transmitted to the ground by the length of shaft above any level is taken as the lesser of the total shaft friction above that level or the safe bearing capacity of the stratum at that level.

2a2.03 Construction of Augered Piles

The piles shall be constructed by boring to the required depth with a continuous flight auger of the required size and forming the shaft by pumping in a Portland cement/sand grout/mortar as the auger is withdrawn. The grout/mortar shall be pumped under pressure to ensure that the shaft is the full specified size and in tight contact with the ground.

The grout/mortar shall be cast to such a height above cut off level as will ensure that the whole length of the shaft is sound and not contaminated by soil falling in above cut off level.

The reinforcement cage shall be installed immediately after completion of grouting and before the grout/mortar reaches the initial set. The cage shall be free from soil or other deleterious material and shall fall under its own weight to the specified level within the shaft.

Adjacent piles closer than 6 pile diameters shall not be grouted within 24 hours of each other.



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2a2.04 Underground Obstructions

If underground obstructions are encountered at depths greater than a few metres that cause auger refusal, the following steps shall be taken:

(a) Grout the augered hole and relocate the pile when the pile is closer than 6 pile diameters from any completed pile.

(b) Remove the obstruction by a method approved by the Engineer, backfill the hole with sand and reinstall the pile when the pile is 6 pile diameters or more away from any completed pile. However, the shaft friction resistance above the obstruction shall be ignored in the design of the pile length.

2a2.05 Grout/mortar for Augered Piles

The grout/mortar used shall not be inferior to Grade 25D.

Fluidity of the grout/mortar shall be checked on a sample taken from the chute of each truckload of grout using a 19mm diameter flow cone in accordance with ASTM C939-10. The flow rate shall be within the range of 10 to 25 seconds.

The maximum grout/mortar temperature shall not exceed 380

C.

2a2.06 Reinforcement for Augered Piles

Augered piles shall be reinforced for at least the top 10m of the pile. Longitudinal bars shall be deformed high tensile bars and binders shall be mild steel.

The reinforcement shall be made up into cages and provided with suitable means of maintaining the specified cover. The cages shall be lowered into the fluid grout and held at the correct level until it sets.

The cover to the reinforcement shall not be less than 75mm. Any tolerance required must be applied to the cages of reinforcement to ensure that the cover is not less than this minimum value.

2a2.07 Sampling and Testing of Materials

One sample per pile of the grout/mortar shall be taken. Two 150mm cubes, which may be replaced with 100mm cubes if accepted by the Engineer, shall be made from each sample and



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tested at 28 days in accordance with CS1:2010.

Reinforcing bars shall be sampled and tested in accordance with CS2:1995.

2a2.08 Integrity Testing of Piles

When instructed by the Engineer, pile integrity testing with Sonic Echo Test or Vibration Test shall be carried out on 15% of the augered piles selected by the Engineer.

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SUB - SECTION 2a3 - DRIVEN CAST-IN-PLACE CONCRETE PILES

2a3.01 Construction of Driven Cast-in-place Piles

Piles shall be constructed by driving a steel tube to the required depth of set, pouring concrete to form the shaft and extracting the tube. The tubes may be driven either from the top or from the bottom.

Care must be taken when driving tubes near newly concreted piles. No tube shall be driven closer than 5 diameters from any pile cast less than one day earlier.

The Contractor shall submit particulars of the tube and hammer he proposes to use and the driving criteria he proposes to adopt for the agreement of the Engineer. The adequacy of the piles to carry the working load shall remain the responsibility of the Contractor.

2a3.02 Reinforcement for Piles

Piles shall be reinforced with at least dowel bars at the top. Longitudinal bars shall be deformed high tensile bars and binders shall be mild steel.

The reinforcement shall be made up in cages and provided with suitable spacers securely fixed to the cage to maintain the specified cover. Care shall be taken to set the cages at the correct level in the pile.

The cover to the reinforcement shall not be less than 75mm. Any tolerance required must be applied to the cages of reinforcement to ensure that the cover is not less than this minimum value.

2a3.03 Concreting Piles

The concrete shall be Grade 20D or a special concrete of equivalent strength suitable for the particular piling method used. Particulars of the mix proportions shall be submitted to the Engineer.

Unless the concrete is compacted by ramming it shall be designed with a high workability so that it will flow to fill the shaft completely as the tube is extracted. For reinforced piles the concrete must be able to flow around and embed the reinforcement.

Before placing concrete the pile must be checked for cleanliness and any soil or debris which may have entered the



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tube must be removed. The concrete shall be placed continuously and as quickly as possible so that it is still workable when the tube is extracted. The tube shall be extracted with care to allow the concrete to flow out and prevent necking. If it is necessary to extract the tube in stages an ample head of concrete must be maintained to overcome ground water pressure.

The shaft shall be concreted to a height above cut off level sufficient to ensure a sound shaft and to prevent contamination by soil falling into the hole.


One sample per 25 cu m or 25 batches, whichever is the smaller volume, of the concrete used in the piles shall be taken. Two 150mm cubes, which may be replaced with 100mm cubes if accepted by the Engineer, shall be made from each sample and tested at 28 days in accordance with CS1:2010.


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SUB - SECTION 2a4 - LARGE DIAMETER BORED PILES

2a4.01 Boring

A temporary steel casing shall be used for bored piles unless the Engineer approves another method for supporting the sides of the hole.

In soils liable to "flow" the bottom of the casing must be kept far enough in advance of the boring tool to prevent the entry of soil into the casing, so preventing the formation of cavities and settlement in the adjoining ground. The Contractor shall take all possible precautions to prevent this and shall allow in his tender for any such action necessary.

Care shall be taken when excavating within the casing to avoid excessive pumping action caused by the grab.

2a4.02 Bell-out

An enlarged base or bell-out may be formed where piles are founded on rock. Such bell-out shall have a gradient not exceeding 30 degrees from the vertical, and the size shall not exceed 1.5 times the shaft diameter.

2a4.03 Founding Stratum Determination / Pre-drilling

Where piles are founded on soil standard penetration tests shall be taken at each pile at 1.5m maximum intervals from the tentative pile founding level down to a distance of at least 3 times the diameter of the pile shaft, or 5m whichever is greater.

Where piles are founded on rock pre-drilling using NX size drill shall be carried out for each pile to a depth of at least 5m into the category of rock specified for founding.

The cost of all proving shall be borne by the Contractor unless otherwise provided for in the Contract.

2a4.04 Reinforcement

Steel reinforcement shall comply in every respect with the requirements of the Concrete Specification (Section 2e).

The reinforcement shall be made up into cages well tied and braced to withstand handling without damage.

The cover between the main bars and the inside of the casing shall be 75 mm and shall be maintained by mild steel spacer



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rods tack welded to the binders.

2a4.05 Concrete

Materials for concrete, proportions for concrete, mixing, transporting and testing concrete shall comply in every respect with the requirements of the Concrete Specification (Section 2e).

In general concrete for piles will not be vibrated and the mix should therefore be designed with a higher workability than concrete for normal structural work.

2a4.06 Placing Concrete in Piles

No concrete shall be placed until the reinforcement has been inspected and approved.

Immediately before starting to place concrete the bottom of the pile shall be thoroughly cleaned out.

Each pile shall be concreted in a continuous operation. The Contractor shall arrange for an adequate and continuous supply of concrete in order to avoid interruption of the work.

For concrete placed in the dry a hopper or funnel shall be used with a length of pipe sufficient to direct the flow of concrete and prevent it falling against the reinforcement or the sides of the shaft. Concrete placed in the wet shall be placed by tremie.

2a4.07 Tremie Concrete

Concrete mixes designed for placing by tremie shall contain not less than 400 kg of cement per cu m and will generally require a higher percentage of fines than ordinary concrete.

The tremie pipe shall not be less than 150 mm dia for concrete with 20 mm max. aggregate nor less than 250 mm dia for concrete with 40 mm aggregate. The pipe shall extend to the bottom of the bored pile. Length of pipe shall be connected with a quick-acting coupling so that sections can be removed as required without delay. The joints shall be made watertight by a gasket or other effective method.

The top of the pipe shall be connected to a hopper of suitable size for the length of pipe used and for the rate at which the concrete is to be supplied. A means of raising and lowering the hopper and pipe under full control at all times must be provided.



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A sliding plug (e.g. an inflated rubber ball of suitable size) which will be pushed down the pipe by the weight of concrete shall be placed in the pipe ahead of the first charge to prevent the concrete mixing with the water in the pipe. Once the pipe is charged the bottom end shall be kept buried in the concrete to a depth of 1 m to 1.5 m. A means of sounding shall be provided to check the level of the concrete surface and ensure that the pipe is buried to a sufficient depth to maintain a seal and control the flow of concrete.

The hopper must be continually recharged without delay in order to maintain the flow and prevent the pipe from becoming clogged. With proper control the concrete should flow as the pipe is gradually raised. If it should be necessary to surge the pipe to discharge the concrete great care must be taken to prevent accidental withdrawal of the bottom of the pipe with consequent loss of seal.

In the event of accidental loss of seal, a record shall be kept of the level at which it occurred and the pipe must be recharged using the sliding plug and taking care to avoid a sudden out surge of water from the pipe.

Tremie concrete shall be placed until the top of the pour is 0.3 to 0.7 m above cut off level so that sound concrete is within 75mm of the specified level after cutting away the weak surface layer.

2a4.08 Pressure Grouting

Pressure grouting below the tips of the piles, if stated on the drawings or required by the Engineer, shall be carried out by the Contractor as described hereunder.

Method A - An NX size hole shall be drilled to 5.00 m below the base and two grout pipes of 25 mm minimum diameter shall be installed (one to bottom of the drilled hole and the other to pile base level). The Contractor shall submit details of the grout mix he proposes to use, for the Engineer's approval, prior to commencing. Mixers must be able to provide a continuous supply of grout to the pump and the pump able to deliver the required grouting pressure. Immediately before grouting the system shall be flushed with clean water. Grout shall be pumped into the pipe extending to the bottom of the drill hole until it appears through the return pipe (extending to pile base level). The return pipe shall then be plugged off and grout pumped until the required pressure is reached.



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Method B - If directed by the Engineer four 25 mm diameter PVC grout tubes shall be installed in the pile prior to pouring of concrete.

These grout tubes shall extend from base level to 1 metre above existing ground level and shall be equally spaced around the perimeter of the pile.

Details of the proposed grout mix shall be submitted for approval prior to commencement of grouting.

Grout shall be pumped into each tube in turn until a pressure of 3 MPa is reached and this pressure shall be held for a period of 5 minutes or as directed by the Engineer.

For both Methods A & B the Contractor shall keep full records of grouting including the date each tube was grouted, the proportions of the grout and any admixtures used, pressure records and details of any interruptions and details of the volume of grout used. Copies of these records shall be supplied to the Engineer within 3 days of grouting.




2a4.10 Post Construction Proof Drilling

For piles founded on rock, core-drilling shall be carried out, through a closed-end tube cast in the pile, for each pile to verify the soundness of the concrete/rock interface. At least 1m length above and below the interface shall be covered by such core-drilling.

2a4.11 Test Coring

The Contractor is to take one NX size drill coring through the full depth of the piles selected by the Engineer or the Building Authority.

For piles founded on rock the core shall be taken 600mm or half a diameter of the pile base, whichever is the greater, into the base material.



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For piles founded on soil the core shall be stopped when it has broken through the base and standard penetration tests shall be made at 1.5m maximum intervals from the pile founding level down to a distance of at least 3 times the diameter of the pile base, or 5m whichever is greater.

The cores are to be properly arranged in core boxes and marked with the pile number and depths. The Engineer or the Building Authority may require a number of samples from each core to be sent to an approved laboratory for crushing tests.

Should the appearance of the core or the test results raise doubt as to the quality of the concrete the contractor shall carry out at his own expense such additional coring, tests or remedial work as the Engineer may require.

2a4.12 Pile Integrity Testing

Sonic logging tubes shall be cast in each pile, the number of tubes determined in the following manner:

Pile Shaft Diameter Number of Tubes900mm or below 3Above 900mm 4

When instructed by the Engineer, sonic logging shall be carried out on piles selected by the Engineer up to a maximum of all the piles.

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SUB - SECTION 2a5 - HAND-DUG CAISSONS

2a5.01 Use of Hand-dug Caissons

Hand-dug caissons shall not be used unless expressly permitted by the Engineer.

2a5.02 Construction Methods

The methods of excavation, equipment and temporary works used in the construction of the caisson foundations shall be those which have been successfully employed on previous occasions where the ground and substrata conditions have been similar. They shall be such as will minimise the risk of loss of ground or settlement of adjacent structures and services.

If in the opinion of the Engineer modifications or amendments to the methods of construction are required during the course of the work in order to ensure that the caissons are constructed in accordance with these contract documents, the contractor shall carry out such modifications and amendments without additional payment.

2a5.03 Dewatering

The Contractor shall submit with his method for caisson excavation full details of the dewatering system he proposes to use for the approval of the Engineer. Such approval shall in no way relieve the Contractor of his obligations under clause.

If the Building Authority should require modifications or additional precautions to the proposed method of dewatering, the Contractor shall carry out such modifications and/or precautions without additional payment.

2a5.04 Safety

The Contractor's attention is drawn to the relevant construction safety regulations and to BS 8008: 1996 " Safety Precautions and Procedures for the Construction and Descent of Machine-bored Shafts for Piling and Other Purposes."

The Contractor shall give special attention to:

(a) preventing surface water, spoil or other objects running or falling into the caisson excavations,

(b) adequate ventilation of the excavations whenever men are in them,

(c) guarding unattended holes by means of railings or covers



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of ample strength properly secured in position,(d providing alternative means of access in case of

breakdown of mechanical lifting appliances and for rescue,

(e) preventing exhaust fumes from engine driven plant from entering the excavation,

(f) the provision of such equipment for rescue and first aid as may be appropriate to the nature and extent of the works.

2a5.05 Blasting

Blasting is prohibited.

2a5.06 Casing

All caisson excavations are to be properly cased down to foundation level or rock level to prevent the entry of ground water and to support the sides of the excavation.

The clear internal diameter of the casing shall be not less than the nominal diameter of the caisson.

The top section of casing to a depth of 2 m below ground level shall be constructed of Grade 20P concrete not less than 150 mm or 1/20 of the nominal diameter of the caisson in thickness.

A heavier top section may be required where mechanical equipment is to be used close to the excavation. The remainder of the casing may be of steel or of precast or insitu concrete.

The contractor shall submit for the approval of the Engineer his proposals for the method of construction and materials to be used for the casing.

2a5.07 Caisson Bottoms

Caisson shall be taken down to a compact soil stratum or rock which can safely support the bearing pressures shown on the drawings to the satisfaction of the Engineer.

In caissons founded on soil the main excavation shall stop about 300 mm above final base level. The last 300 mm to 500 mm shall be excavated and the bottom cleaned out immediately before placing concrete.

Caissons founded on rock directly under colluvium, alluvium or marine deposits shall be socketed about 300mm into the rock.



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Where the surface of the rock is reasonably level (i.e. slopes at not more than 1 in 10 from the horizontal) the Engineer may accept 40 mm dia dowel bars drilled and grouted into the rock in place of a socket. The aggregate cross sectional area of such dowels shall be not less than 1% of the nominal area of the caisson shaft.

Caissons which have penetrated a sufficient thickness of completely weathered, highly weathered or moderately weathered rock before reaching a stratum of adequate bearing capacity will not be normally require sockets. The depth of penetration through the more weathered rock will depend on the degree of weathering and the slope and joint pattern of the foundation rock. Where the surface of the foundation rock slopes at more than 1 in 6 it shall be cut back or stepped so that the bearing surface is at not more than 1 in 6 from the horizontal.

Where the bearing stratum comprises fractured or closely jointed rock a socket or belling out of the base may be required.

2a5.08 Proving the Base

In caissons founded on soil when the agreed bottom level has been reached a series of standard penetration tests shall be taken at the centre of the caisson to a depth of 1.5 times the diameter below the final bottom level.

In caissons founded on rock, the rock at the bottom of each caisson shall be proved for a depth of 5.00 m under the general supervision of the Engineer or his representative. Proving shall be done by drilling holes with a rock drill weighing not less than 32 kg timing each 300 mm of penetration and plotting the results on a graph. Alternatively proving may be done by taking NX cores 5.00 m long. The proving holes will usually be vertical but the Engineer may require some or all of them to be inclined in order to check the location of weathered joints or the horizontal extent of boulders. Prior to the Engineer's final inspection the contractor shall place a 20 mm dia mild steel rod 5.5 m long in the proving holes ready for inspection.

The cost of all proving tests shall be borne by the Contractor.

2a5.09 Additional Excavation or Belling Out

The Engineer may order any additional excavation or belling out which he considers necessary.

Where extra excavation is required proving tests shall be



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carried out or repeated from the new bottom level.

Where belling out is required the angle of dispersion of the load from the shaft shall be taken at 60 degrees from the horizontal and all parts of the excavation for the bell shall be taken clear of the core of dispersion of load.

2a5.10 Approval of Caisson Base

No reinforcement or concrete shall be placed in caisson until the base has been inspected and approved by the Engineer or his representative.

The Contractor shall provide safe and convenient access for such inspection and shall clean out all loose material and pump the caisson dry ready for inspection.

2a5.11 Reinforcement

Steel reinforcement shall comply in every respect with the requirements of the Concrete Construction Specification.

The reinforcement shall be made up into cages well tied and braced to withstand handling without damage.

The cover between the main bars and the inside of the casing shall be 75 mm and shall be maintained by mild steel spacer rods tack welded to the binders.

2a5.12 Dowel Bars and Anchor Bars

Where dowel or anchor bars are required they shall be of the lengths shown on the drawing or approved by the Engineer.

The holes in the rock shall be flushed out with clean water and filled with 1:1 cement sand grout by means of a pipe extending to the bottom of the hole immediately before inserting the dowel or anchor bars.

2a5.13 Concrete

Materials for concrete, proportions for concrete, mixing, transporting and testing concrete shall comply in every respect with the requirements of the Concrete Construction Specifications.

In general concrete for caissons will not be vibrated and the mix should therefore be designed with a higher workability than concrete for normal structural work.



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2a5.14 Placing Concrete in Caissons - General

No concrete shall be placed until the reinforcement has been inspected and approved.

Immediately before starting to place concrete the bottom of the caisson shall be thoroughly cleaned out.

Whenever possible each caisson shall be concreted in a continuous operation. The contractor shall arrange for an adequate and continuous supply of concrete in order to avoid interruption of the work.

Where breaks in construction cannot be avoided the concrete shall be allowed to set. The surface shall then be cut or chipped back to sound concrete to the approval of the Engineer and thoroughly cleaned out before concreting recommences.

Whenever possible any seepage through the casing shall be sealed off and the caissons are to be concreted dry.

For concrete placed in the dry, a hopper or funnel shall be used with a length of pipe sufficient to direct the flow of concrete and prevent it falling against the reinforcement or the sides of the shaft.

Concrete placed in the wet shall be placed by tremie.

2a5.15 Placing Concrete in Caissons Founded on Soil

Caissons founded on soil are to be concreted 'dry' unless the special approval of the Engineer is obtained for the contractors alternative proposals.

Immediately after excavating and cleaning out the final 0.3 m to 0.5 m soil, a layer of concrete at least 0.5 m thick shall be placed on the bottom. This concrete shall be lowered down the shaft in skips in order to avoid disturbing the prepared bottom surface.

When this concrete has set concreting of the shaft may continue in the manner specified.

2a5.16 Placing Concrete with Seepage at Base

When a minor seepage at the base cannot be entirely prevented the Engineer may approve the use of a richer mix with a lower w/c ratio for the first few batches which are to be placed immediately after removing the pumps to form a plug about 2 m deep before continuing with the concrete mix



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approved for the shaft.

Where major seepage occurs at the base the Engineer may approve casting a plug of tremie concrete of sufficient depth to form an effective seal. The surface of the plug must be cut back as specified in clause 13 before the remainder of the shaft is cast in the dry.

2a5.17 Tremie Concrete

Concrete mixes designed for placing by tremie shall contain not less than 400 kg of cement per cubic metre and will generally require a higher percentage of fines than ordinary concrete.

The tremie pipe shall not be less than 150 mm dia for concrete with 20 mm maximum aggregate nor less than 250 mm dia for concrete with 40 mm aggregate. The length shall extend to the bottom of the caisson. Lengths of pipe shall be connected with a quick-acting coupling so that sections can be removed as required without delay. The joints shall be made watertight by a gasket or other effective method.

The top of the pipe shall be connected to a hopper of suitable size for the length of pipe used and for the rate at which the concrete is to be supplied. A means of raising and lowering the hopper and pipe under full control at all times must be provided.

A sliding plug (e.g. an inflated rubber ball of suitable size) which will be pushed down the pipe by the weight of concrete shall be placed in the pipe ahead of the first charge to prevent the concrete mixing with the water in the pipe. Once the pipe is charged the bottom end shall be kept buried in the concrete to a depth of 1 m to 1.5 m. A means of sounding shall be provided to check the level of the concrete surface and ensure that the pipe is buried to a sufficient depth to maintain a seal and control the flow of concrete.

The hopper must be continually recharged without delay in order to maintain the flow and prevent the pipe from becoming clogged. With proper control the concrete should flow as the pipe is gradually raised. If it should be necessary to surge the pipe to discharge the concrete great care must be taken to prevent accidental withdrawal of the bottom of the pipe with consequent loss of seal.

In the event of accidental loss of seal, a record shall be kept of the level at which it occurred and the pipe must be recharged using the sliding plug and taking care to avoid a sudden out surge of water from the pipe.



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Tremie concrete shall be placed until the top of the pour is 0.3 m to 0.7 m above cut off level so that sound concrete is within 75 mm of the specified level after cutting away the weak surface layer.

2a5.18 Pressure Grouting

Pressure grouting below the tips of the caisson, if stated on the drawings or required by the Engineer, shall be carried out by the Contractor as described hereunder.

Method A - An NX size hole shall be drilled to 5.00 m below the caisson base and two grout pipes of 25 mm minimum diameter shall be installed (one to bottom of the drilled hole and the other to pile base level). The Contractor shall submit details of the grout mix he proposes to use, for the Engineer's approval prior to commencing.

Mixers must be able to provide a continuous supply of grout to the pump and the pump able to deliver the required grouting pressure. Immediately before grouting the system shall be flushed with clean water. Grout shall be pumped into the pipe extending to the bottom of the drill hole until it appears through the return pipe (extending to pile base level). The return pipe shall then be plugged off and grout pumped until the required pressure is reached.

Method B - If directed by the Engineer four 25 mm diameter PVC grout tubes shall be installed in the pile prior to pouring of concrete.

These grout tubes shall extend from base level to 1 metre above existing ground level and shall be equally spaced around the perimeter of the pile.

Grout tubes shall be fitted with nozzles which can be locked off without loss of pressure.

Details of the proposed grout mix shall be submitted for approval prior to commencement of grouting.

Grout shall be pumped into each tube in turn until a pressure of 3 MPa is reached and this pressure shall be held for a period of 5 minutes or as directed by the Engineer.



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For both Methods A & B the Contractor shall keep full records of grouting including the date each tube was grouted, the proportions of the grout and any admixtures used, pressure records and details of any interruptions and details of the volume of grout used. Copies of these records shall be supplied to the Engineer within 3 days of grouting.




2a5.20 Test Coring

The Contractor is to take one NX size drill coring through the full depth of the caissons selected by the Engineer or the Building Authority. For caissons founded on rock the core shall be taken 600 mm into the base material. For caissons founded on soil the core shall be stopped when it has broken through the base and a standard penetration test shall be made in the soil immediately below the base.

The cores are to be properly arranged in core boxes and marked with the pile number and depths. The Engineer of the Building Authority may require a number of samples from each core to be sent to an approved laboratory for crushing tests.

Should the appearance of the core or the test results raise doubt as to the quality of the concrete the Contractor shall carry out at his own expense such additional coring, tests or remedial work as the Engineer may require.

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SUB - SECTION 2a6 - STEEL H - PILES

2a6.01 High Yield Steel

The steel for pile section shall be weldable structural steel conforming to:

BS EN 10025:2004 Grade S355JR, BS EN 10025:2004 Grade S450J0

or to such other specification of equivalent quality as may be approved by the Engineer.

The steel for reinforcing the piles and for the cap plates may be mild steel to BS EN 10025:2004 Grade S275JR.

2a6.02 Test Certificates

As soon as the material is delivered to the site, the Contractor shall provide the Engineer with the manufacturer's test certificates to show that the material fully complies with the specification.

2a6.03 Pile Marking

After fabrication and before driving the head, each pile shall be marked with a serial reference number. The pile shall also be marked off at half meter intervals, measured from the toe, to facilitate record keeping during driving.

2a6.04 Stacking and Handling

Piles should be stacked in such a way that no part of the pile is over stressed. The Contractor shall submit his proposal for stacking the piles to the Engineer for his approval. The Contractor shall exercise care in the lifting and handling of piles. Piles shall be straight before commencement of driving.

2a6.05 Driving

The Contractor shall obtain the prior approval of the Engineer for his rig, weight of hammer and driving procedure before commencing to drive any piles.

As the piles are expected to be driven to a hard stratum, care shall be taken to avoid damage to the piles by over-driving or by causing excessive driving stresses. Calculated driving stresses shall not exceed 0.9 yield stress unless approved otherwise by the Engineer.



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The drop or stroke used shall be such that the piles are not damaged. Each pile shall be fitted with a well-fitting helmet of a pattern suitable for the pile head and properly packed before being driven. If necessary, the head of the pile shall be reinforced to resist high driving stresses.

The piles shall be driven to a set proposed by the Contractor, agreed by the Engineer and based on the test pile results. The Engineer's agreement shall not relieve the Contractor of his responsibility for the load carrying capacity of the piles.

2a6.06 Offcuts

Offcuts which show no signs of damage may be used in the most economical manner to make up or extend piles. Such piles shall be arranged with the minimum number of splices, and the Contractor shall obtain the Engineer's approval before such pile are driven.

The bottom section of each pile shall be a full 12.00 m (or longer) section without splices. For the intermediate part of a pile made up from offcuts, each offcut used shall not be less than 4.00 m and two or more offcuts shall be welded together and checked that they are straight and true before being welded to the section already driven.

Shorter offcuts may be used at the top part of the pile to make up the required length.

2a6.07 Lengthening of Pile

Where found necessary, the Engineer may order a driven pile to be lengthened. The lengthening piece shall be of similar section to the driven section. Care shall be taken to ensure that the extension is truly in line with the driven section.

2a6.08 Cutting off Piles

After a pile has been driven to required set and to the satisfaction of the Engineer, the section of the pile above the cut off level shall be cut away as instructed by the Engineer.

2a6.09 Pile Heads

After the pile has been cut off to the level shown on the drawings, the head shall be ground to give a true and level surface onto which shall be welded a steel bearing plate.



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2a6.10 Pile Protection

Prior to driving, all piles shall be coated to a depth specified on the drawings with two coats of bituminous solution complying to BS 3416, Type 1 for protection against corrosion. All paint shall be supplied to the painters ready for application, and the addition of thinners or of any other material shall be thereafter prohibited. Any instructions given by the paint manufacturer shall be strictly followed.

Paint shall be applied to dry surfaces which have been prepared and cleaned as specified by the paint manufacturer. The interval between the preparation of the surface and the application of the first priming coat shall be as specified. Where not specifically stated, the priming coat shall be applied on the same day that the preparation is carried out.

Any coat that has become damaged or defective in any way shall be made good before application of the subsequent coat. If the final coat is damaged during handling, the affected area shall be rubbed down and additional coatings shall be applied to the approval of the Engineer.

2a6.11 Re - Driving

The Engineer may order that the operation be ceased at any stage of driving, to be resumed after a lapse of 24 hours or any other period. Redriving is to be carried out in a manner similar to the initial driving and continued until the required ultimate resistance is achieved. Piles which have risen for any reason shall be re-driven to the original level (or to such others as the Engineer may determine) unless otherwise directed by the Engineer.

2a6.12 General Requirements for Welding

Welding shall be carried out in accordance with the requirements of BS EN 1011-1:1998 and BS EN 1011-2:2001 or other accepted standards. Unless otherwise specified, manual metal-arc welding shall be used.

All welding shall be carried out by skilled and competent welders. If required, welders shall have passed approval tests to BS EN 287-1: 2004, BS 4871-3:1985 or BS 4872-1:1982 as applicable.

An experienced and competent operator shall be assigned to supervise welding and a record shall be kept on site to identify welders responsible for major welds.



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Welding shall not be carried out under adverse weather conditions unless under adequate cover.

Electrodes for welding shall be covered electrodes complying with BS EN ISO 2560:2005. Welding consumables, including electrodes, shall be kept in a controlled manner. Any drying or baking of electrodes shall be carried out in strict compliance with the manufacturer’s recommendations.

Low hydrogen electrodes shall be used for the welding of high tensile steel.

2a6.13 Details of Welds

Fusion Fa ces

Fusion faces shall be free from irregularities and properly prepared such that the accuracy of the specified size of welds can be maintained.

Fusion faces and the surrounding surface shall be free from heavy scale and oil, paint or other substances which may affect the quality of the weld.

If the initial preparation is by gas cutting, the faces shall be ground, filed or dressed to remove irregularities and to maintain the tolerances specified.

Fillet W elds

Parts to be fillet welded shall be brought into close contact and the gap due to incorrect fit up shall not exceed 1.5 mm.

The minimum leg length of a fillet weld as deposited shall be not less than the specified size, and the throat thickness as deposited not less than 0.7 of the leg size where the fusion faces are at right angles to each other.

Butt W elds

Butt welds shall be single V or double V with the following tolerances:

Included angle of V 60 degrees minimumRoot face 3 mm maximumGap 1.5 mm minimumMisalignment of parts 3 mm maximum

The face of butt welds shall be at all places proud of the surfaces of parent metal. Where a flush surface is required, the



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surplus metal may be dressed off. In all complete penetration butt welds, where these are to be welded from both sides, the back of the first run shall be gouged out to clean metal before welding is started on that side.

Butt welds for thickness of more than 12 mm shall be welded from both sides.

Where butt welds are to be welded from one side only, these shall be completed with the aid of a backing strip of mild steel or by the adoption of a special method of welding approved by the Engineer. In all cases, it must be ensured that complete fusion of the parts to be joined is readily obtained.

2a6.14 Non - Destructive Tests on Welds

Prior to driving in the spliced sections of the piles, the fillet and butt welds of not less than 10% of the total number of welded joints shall be tested by means of non-destructive tests (ultrasonic and/or magnetic particle inspection). The test reports shall form part of the piling records.

2a6.15 Dynamic Pile Testing

When instructed by the Engineer, Dynamic Pile Test shall be carried out on up to 15% of the piles or 30 numbers, whichever is greater, selected by the Engineer. Computer Pile Wave Analysis shall be carried out on up to 5% of the piles selected by the Engineer.

2a6.16 Additional Requirements for Piles Driven to Bedrock

Driving Test for Piles

At least 2 driving tests shall be required to demonstrate that this type of piles can be successfully installed at the site.

Pre-drilling

Pre-drilling using NX size drill shall be carried out to a depth of at least 5m into the category of rock specified for forming the rock socket, or the designed rock socket length of the pile, whichever is the greater.

The extent of the pre-drilling shall be such that the position of every pile lies within 5m of the position of a pre-drilling hole.

Verticality Checking

The verticality of the piles shall be checked during installation



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by a method acceptable to the Engineer.

Additional Proof Testing

Dynamic Pile Tests shall be carried out on at least 10% of the piles as a more stringent proof test requirement.

Post Construction Proof Drilling

After the completion of the piles, additional proof drilling shall be carried out to verify the rockhead profile. The proof drill holes shall be sunk at least 5m into the category of rock specified for founding. The number of proof drill holes shall be at least 2 for sites with 100 piles or less; or 1% of the number of piles for sites with more than 100 piles.

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SUB - SECTION 2a7 - PRECAST REINFORCED CONCRETE PILES

2a7.01 Piles

The piles shall be precast reinforced concrete piles. Materials and workmanship for casting the piles shall comply with Section 2e Concrete Specification unless otherwise stated in this section.

2a7.02 Pile Shoes

Pile shoes shall be made of "chilled-hardened" cast iron with straps of mild steel cast into the base and running continuously through it. The cast iron shall be clean grey tough metal, free from sand, honeycombing, porous places, air holes or other defects.

2a7.03 Reinforcement for Piles

The reinforcement for piles shall be mild steel. The longitudinal bars shall be butt welded in accordance with BS 7123:1989. No bar shall have more than four welds in its length and every bar shall be straight after welding. The top ends of the longitudinal bars shall be cut, filed or ground square and set flush with the top surface of the pile. The corner bars shall be held apart by pairs of purpose made spacer forks.

Binders shall be accurately bent to size and shape. The tolerance limits on the bending dimensions shown on the drawings are +1 mm or -2 mm. Tie the binders securely to the longitudinal bars with iron binding wire to form a strong cage of reinforcement so that the bars will not be displaced when the concrete is placed and compacted around them. Tuck the ends of the wire ties towards the centre of the pile.

2a7.04 Concrete for Piles

The concrete for the piles shall have a minimum cement content of 400 kg per cubic metre of concrete and a maximum water/cement ratio of 0.5. The water contained in damp aggregate shall be determined and the water added to the mixer shall be adjusted to ensure that this water/cement ratio is not exceeded.

Before making the trial mixes required by the Specification, submit to the Engineer grading curves of the coarse and fine aggregates and of the combined aggregates proposed for the trial mixes. From each trial mix make six test cubes and arrange for two cubes to be tested at 3 days, two at 7 days and two at 28 days. Also test the workability of the trial mixes by



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means of the slump cone or the compacting factor method. Casting of the piles may proceed when satisfactory 7 day cube tests are obtained.

2a7.05 Casting the Piles

The Contractor may choose to cast the piles on site or in his own casting yard. In the latter case, the Contractor shall allow the Engineer and his representative access to the casting yard for inspection at any time during working hours.

Piles shall be cast on level platforms in strong, well braced moulds. The moulds shall be straight and true to shape with a tolerance of -0 and +5 mm on the dimensions of the cross section. The heads of the piles shall be truly perpendicular to the axis of the pile.

The cages of reinforcement shall be suspended in the moulds and braced in position by wire loops and ties which shall be removed after compacting the concrete and before finishing the surface. Spacer blocks will not be permitted.

Cast each pile in a continuous operation. If any interruptions occur the affected piles may be rejected. Take two samples of the concrete for each pile at approximately the quarter and three quarter stages of the concreting. From one sample make eight cubes and make four from the other, and cure the set of four cubes by immersion in a tank of water. Cure the set of eight cubes under wet sacking in the same manner as is used for curing the piles. Send two cubes from each sample for testing at 3 days and send two from each for testing at 7 days. Send two cubes for testing at 28 days. The last of the 12 cubes from each pile may be tested at any age at the contractor's discretion e.g. to confirm the strength before lifting or before driving the pile.

Side forms may be stripped after two days but the piles shall not be lifted or stacked until the concrete reaches a strength of 17 MPa. Such stripping of forms or lifting and stacking must not adversely affect the curing of the concrete.

Take good care to cure the piles by keeping them continuously damp with a covering of wet sacking or by other means approved by the Engineer. The surface of the concrete (and the sacking) must not be allowed to become dry for a period of at least 10 days. Curing by means of impervious membranes will not be accepted unless they have wet sacking underneath. Curing compounds will not be accepted for the initial curing but may be used after seven days of wet curing.



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2a7.06 Lifting and Stacking

Piles shall be handled and stacked in such a way as will avoid overstressing any part of the pile. The Contractor shall submit his proposals for lifting, stacking and pitching the piles to the Engineer for his approval. Take care in lifting the piles to avoid shock particularly when lifting them off the casting beds.

Piles may be stacked horizontally one above the other for curing and storage. The base on which the piles are stacked must be firm, level and capable of supporting the weight of the piles without differential settlement. The piles must be supported on wooden blocks of uniform thickness and at least 300 mm wide, arranged in the same vertical line in each stack and at spacings which will not overstress the pile nor be likely to cause permanent deflections due to creep of the concrete.

2a7.07 Pitching

Piles shall not be pitched until 21 days after casting or until the strength of the cubes is at least 25 MPa whichever is the later. Place the piles accurately as to position and rake and guide them in their movements by the leaders of the driving rig or by other approved means. If damage occurs due to heavy driving of piles of this minimum age, the period between casting and driving shall be extended to allow further gain in strength.

2a7.08 Driving

Piles shall be driven by a drop hammer of not less than 8 tonnes in weight. Driving shall be through a helmet of steel plate with a 75 mm thick hardwood cushion set with the grain vertical between the helmet and the pile and a short hardwood dolly above to receive the blow of the hammer. The packing and the dolly shall be renewed as necessary to ensure they are in good condition when driving to the final set.

Take all reasonable precautions to ensure that each pile is driven continuously to the required level or set. The final set shall be such as will give a resistance to penetration, calculated by the Hiley formula using the measured temporary compressions, of at least twice the designed working load.

A short drop shall be used at the start and it shall be increased as the resistance to penetration increases to a maximum drop of 1.4 m. Take care to ensure that the hammer blow is coaxial with the pile in order to avoid transverse vibrations in the unsupported length of the pile.

2a7.09 Redriving



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The first two piles to be driven shall be redriven after a period of rest of at least 24 hours, in order to confirm that the resistance to penetration increase after the period of rest. If the resistance on redriving is less than the resistance on the first driving, the piles shall be driven to final resistance of 2.5 times the designed working load. Two additional piles in another part of works as directed by the Engineer shall be redriven for further confirmation.

If the resistance to penetration has been confirmed to increase after a period of rest, the Engineer may order any pile which does not attain the required set to be redriven a further 300 mm after a period of rest of not less than 24 hours. If the final set on redriving indicates a driving resistance which in the opinion of the Engineer provides an adequate factor of safety the pile may be accepted.

2a7.10 Lengthening

If a pile has not reached the required set during the initial driving or upon redriving after a period of rest, it shall be lengthened and redriven to the required set.

Lengthening shall be carried out by striping the concrete for a length of 1 m and removing the lateral ties. New bars of the same size with the ends cut filed or ground square shall be butted to the longitudinal bars and the joint covered by 2 m long splice bars securely wired to the old and the new bars. Binders of type A and type B alternately shall be added at 75 mm centres for the length of the splice. Between the splice and the head of the extension binders shall be provided to the same detail as in the original pile.

Strongly constructed shuttering shall be constructed around the pile and held firmly and accurately in alignment. The bottom of the shutters shall overlap the top of the existing concrete and shall be sealed with a rubber gasket or by caulking to prevent loss of mortar from the concrete. The extension shall then be concreted with the same mix of concrete as was used in the piles and the head shall be accurately finished perpendicular to the axis.

The shuttering shall not be striped for 4 days. The head of the extension and the sides, after the shuttering has been stripped, shall be covered with sacking which shall be kept continuously wet for a period of 10 days.

The lengthened pile shall not be redriven until the extension has reached a strength or age approved by the Engineer.



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2a7.11 Bracing

As soon as two or three piles have been driven erect substantial bracing to the piles and to each subsequent pile as soon as it has been driven. Timber bracing shall be not less than 300 mm x 200 mm in cross section.

2a7.12 Jetting

Where piles are required to pass through a stratum of sand to reach a bearing in a lower stratum and the sand is so compact as to cause high driving stresses which may damage the pile, jetting may be used to loosen the sand.

Jet pipes may either be attached to the sides of the pile or be independent pipes surged down at the sides of the pile. The arrangement of jets shall be balanced to ensure that the pile does not lead off out of alignment.

Jetting shall be stopped if there is any tendency for the tips of the piles to be drawn out of alignment, or when the pile reaches the decomposed granite stratum. In every case jetting shall be stopped before the completion of driving which must always be finished by ordinary methods.

The Contractor shall notify the Engineer in advance if he intends to use jetting.

2a7.13 Inspection

The Contractor shall appoint a responsible member of his site staff to inspect each pile during driving, to keep the records required by this Specification and to notify the Engineer as soon as possible of any cracks, damage or irregularities observed during the driving.

Where serious transverse vibrations or other irregularities have been observed during driving or where cracking has been seen or suspected, the piles affected shall be inspected immediately after driving or, if ordered by the Engineer or his representative, before the completion of driving. Piles with normal driving records may be inspected at any convenient time.

Inform the Engineer when such inspections are to be carried out and keep proper records of the dates and results of the inspections of the piles.



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2a7.14 Dynamic Pile Testing


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SUB-SECTION 2a8 - PRECAST PRESTRESSED SPUN CONCRETE PILES

2a8.01 Pile Types

The piles must be of a proprietary type manufactured and handled in accordance with the manufacturer's compliance standards approved by the Building Authority.

2a8.02 Manufacturer's Certificates

Manufacturer's certificates for each batch of piles delivered to the site shall be submitted to the Engineer. Such certificates shall state

(a) that the piles have been manufactured in accordance with the manufacturer's compliance standard approved by the Building Authority;

(b) that the piles are satisfactory for the purpose intended;

(c) the mix proportions and admixtures used in the concrete; and

(d) the results of all cube and core tests.

2a8.03 Storage and Handling

Piles shall be delivered, handled and lifted with due care and in accordance with the manufacturer's recommendations.

Piles shall be stacked neatly off the ground.

2a8.04 Driving

During the final set, hammers of weight less than 70% of the weight of the pile shall not be used. If a drop hammer is adopted, its stroke shall be limited to not more than 1.2m.

2a8.05 Splicing

Splicing to increase the pile length shall be carried out by welding the jointing plates of the lower and upper segments in accordance with the manufacturer's approved details.

During the progress of the works, the Engineer may require certain of the welded joints to be examined by radiograph and/or ultrasonic tests. These test shall be carried out to the satisfaction of the Engineer and the results shall be submitted for approval.



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2a8.06 Pile Integrity Tests

Depending on the ground conditions giving rise to the possibility of cracking of piles, the Engineer may specify a certain proportion of the piles for non-destructive pile integrity tests such as Pile Driving Analyser tests and Vibration tests. Any defects detected by these tests shall be rectified to the satisfaction of the Engineer and at the Contractor's own cost.

2a8.07 Pile Heads

After the pile has been cut off to the specified level, concrete plugs shall be placed and dowel bars provided as shown on the drawings.

2a8.08 Pile Dynamic Testing


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SUB - SECTION 2a9 - MINI-PILES

2a9.01 Grouting Material

Grout for piling shall consist of ordinary Portland cement and water with approved non-shrinkage additive.

Water for grout shall be clean, fresh and potable having a temperature not exceeding 300C nor less than 50C.

Any approved admixtures shall be chloride-free and comply with BS EN 934-3:2009.

The maximum total chloride content, expressed as a percentage relationship between the chloride ion and the cementitious content by mass in the grout shall be 0.1%.

The maximum amount of bleeding of grout shall not exceed 2% in the first 3 hours and not exceed 4% in total. In addition, the water must be reabsorbed by the grout within 24 hours after mixing.

Free expansion of the grout measured 24 hours after mixing shall lie between 0% and 5%. A negative percentage shall not be accepted.

2a9.02 Grouting Design

The grout shall be non-shrink and have a minimum characteristic strength of 30 MPa at 28 days.

The grout mix shall be designed by the Contractor to conform to the strength requirement specified and to have a consistency suitable for pumping.

A trial grout mix shall be carried out to demonstrate the suitability of the grout with respect to strength and consistency for the Engineer's approval.

2a9.03 Sampling and Testing of Grout

Test for Crushing Strength

One sample of the grout shall be taken for each pile not more than 30 minutes after mixing and protected from change in moisture content before making test cubes. Two 150mm grout cubes, which may be replaced with 100mm cubes if accepted by the Engineer, shall be made from each sample and tested at 28 days in accordance with CS1:2010.



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Test for Bleeding and Free Expansion

One sample from the trial grout mix shall be provided not more than 30 minutes after mixing and protected from changes in moisture content before tests are carried out.

The sample shall be divided into 3 specimens. Each specimen is to be placed in a covered cylinder with a diameter of 100± 10mm to a depth of 100± 5mm and the amount of bleeding and free expansion is measured by a scale fixed to the outside of the cylinder.

F low Cone Efflux Test-

One sample from the trial grout mix shall be taken and tested in accordance with ASTM C939-10 to determine the Flow Cone Efflux time.

Except with engineer's prior agreement for grout mixes containing additives, grout having an efflux time of less than 15 seconds will be rejected.

2a9.04 Reinforcing Bars

Reinforcing bars shall be 50 mm diameter hot rolled deformed high yield steel bars of Grade 460 conforming to Construction Standard CS2:1995 "Carbon Steel Bars for the reinforcement of Concrete", free from rolling defects, loose rust, scale , oil or grease.

The Contractor shall submit the manufacturer's mill certificates for the bars for the Engineer's approval. Samples of bars shall be tested in accordance with the Building (Construction) Regulations as augmented by Practice Notes to Authorized Persons and the Registered Structural Engineers.

2a9.05 Mechanical Couplers

Mechanical couplers shall be of the specified proprietary type or an approved equivalent tension type coupler.

Reinforcing bars shall be prepared and couplers installed strictly in accordance with the manufacturer's recommendations.

2a9.06 Pre-drilling

Pre-drilling using NX size drill shall be carried out to a depth of at least 5m into the category of rock specified for forming the rock socket, or the designed rock socket length of the pile,



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whichever is the greater.


2a9.07 Mini - pile Excavation

Drilling for minipiles shall be carried out using a 219 x 6.3 mm CHS casing to form a 235 mm minimum diameter hole. When the casing reaches rock of the required quality, a 190 mm minimum diameter rock socket shall be formed for a minimum depth of 4.5 m. The casing shall remain in position during the formation of the rock socket.

Where water flushing is used, care shall be taken to prevent erosion of the existing ground. Water shall pass through a sedimentation tank before being discharged outside the site.

When drilling is completed, the hole shall be thoroughly cleaned to get rid of loose soils before receiving reinforcing bars and grout.

2a9.08 Mini - pile Installation

If necessary, reinforcing bars shall be spliced by mechanical couplers arranged in a staggered pattern. Spacers shall be fixed to the bars at regular intervals to maintain the bars in the desired positions and to provide adequate grout cover. The couplers in the pile head shall be adequately protected from the ingress of grout into the unoccupied end.

Grout shall be placed via a suitable tremie pipe which extends to the bottom of the hole, in less than 30 minutes after the grout is mixed. The casing shall not be withdrawn during the grouting operation.

Grout shall be allowed to fill the hole up to the ground level to ensure that the pile is completely grouted.

2a9.09 Verticality Check

Verticality, inclination and alignment of the mini-piles shall be checked during installation by a method acceptable to the Engineer.





Piling


After the completion of the piles, additional proof drilling shall be carried out to verify the rockhead profile. The proof drill holes shall be sunk at least 5m below the as-built top level of the rock socket of the nearest pile or to the as-built bottom level of the rock socket of the nearest pile, whichever is the deeper. The number of proof drill holes shall be at least 2 for sites with 100 piles or less; or 1% of the number of piles for sites with more than 100 piles.

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Piling

SUB - SECTION 2a10 - SOCKETED STEEL H-PILES

2a10.01 Grouting Material

Grout for piling shall consist of ordinary Portland cement and water with approved non-shrinkage additive.

Water for grout shall be clean, fresh and potable having a temperature not exceeding 300C nor less than 50C.

Any approved admixtures shall be chloride-free and comply with BS EN 934-3:2009.

The maximum total chloride content, expressed as a percentage relationship between the chloride ion and the cementitious content by mass in the grout shall be 0.1%.

The maximum amount of bleeding of grout shall not exceed 2% in the first 3 hours and not exceed 4% in total. In addition, the water must be reabsorbed by the grout within 24 hours after mixing.

Free expansion of the grout measured 24 hours after mixing shall lie between 0% and 5%. A negative percentage shall not be accepted.

2a10.02 Grouting Design

The grout shall be non-shrink and have a minimum characteristic strength of 30 MPa at 28 days.

The grout mix shall be designed by the Contractor to conform to the strength requirement specified and to have a consistency suitable for pumping.

A trial grout mix shall be carried out to demonstrate the suitability of the grout with respect to strength and consistency for the Engineer's approval.

2a10.03 Sampling and Testing of Grout

Test for Crushing Strength

One sample of the grout shall be taken for each pile not more than 30 minutes after mixing and protected from change in moisture content before making test cubes. Two 150mm grout cubes, which may be replaced with 100mm cubes if accepted by the Engineer, shall be made from each sample and tested at 28 days in accordance with CS1:2010.



Piling

Test for Bleeding and Free Expansion

One sample from the trial grout mix shall be provided not more than 30 minutes after mixing and protected from changes in moisture content before tests are carried out.

The sample shall be divided into 3 specimens. Each specimen is to be placed in a covered cylinder with a diameter of 100± 10mm to a depth of 100± 5mm and the amount of bleeding and free expansion is measured by a scale fixed to the outside of the cylinder.

Flow Cone Efflux Test

One sample from the trial grout mix shall be taken and tested in accordance with ASTM C939-10 to determine the Flow Cone Efflux time.

Except with engineer's prior agreement for grout mixes containing additives, grout having an efflux time of less than 15 seconds will be rejected.

2a10.04 Steel for Pile

The steel for pile section shall be weldable structural steel conforming to:

BS EN 10025:2004 Grade S355JR, BS EN 10025:2004 Grade S450J0

or to such other specification of equivalent quality as may be approved by the Engineer.

The steel for reinforcing the piles and for the cap plates may be mild steel to BS EN 10025:2004 Grade S275JR.

2a10.05 Test Certificates of Steel

As soon as the material is delivered to the site, the Contractor shall provide the Engineer with the manufacturer's test certificates to show that the material fully complies with the specification.

2a10.06 Stacking and Handling

H-Piles shall be stacked in such a way that no part of the pile is over stressed. The Contractor shall submit his proposal for stacking the piles to the Engineer for his approval. The Contractor shall exercise care in the lifting and handling of piles. Piles shall be straight before commencement of



Piling

installation.

2a10.07 Offcuts

Offcuts which show no signs of damage may be used in the most economical manner to make up or extend piles. Such piles shall be arranged with the minimum number of splices, and the Contractor shall obtain the Engineer's approval before such pile are driven.

The bottom section of each pile shall be a full 12.00 m (or longer) section without splices. For the intermediate part of a pile made up from offcuts, each offcut used shall not be less than 4.00 m and two or more offcuts shall be welded together and checked that they are straight and true before being welded to the section already driven.

Shorter offcuts may be used at the top part of the pile to make up the required length.

2a10.08 Cutting off Piles

After a pile has been installed to required level and to the satisfaction of the Engineer, the section of the pile above the cut off level shall be cut away as instructed by the Engineer.

2a10.09 Pile Heads

After the pile has been cut off to the level shown on the drawings, the head shall be ground to give a true and level surface onto which shall be welded a steel bearing plate.

2a10.10 General Requirements for Welding

Welding shall be carried out in accordance with the requirements of BS EN 1011-1:1998 and BS EN 1011-2:2001 or other accepted standards. Unless otherwise specified, manual metal-arc welding shall be used.

All welding shall be carried out by skilled and competent welders. If required, welders shall have passed approval tests to BS EN 287-1: 2004, BS 4871-3:1985 or BS 4872-1:1982 as applicable.

An experienced and competent operator shall be assigned to supervise welding and a record shall be kept on site to identify welders responsible for major welds.

Welding shall not be carried out under adverse weather conditions unless under adequate cover.



Piling



Piling

Electrodes for welding shall be covered electrodes complying with BS EN ISO 2560:2005. Welding consumables, including electrodes, shall be kept in a controlled manner. Any drying or baking of electrodes shall be carried out in strict compliance with the manufacturer’s recommendations.

Low hydrogen electrodes shall be used for the welding of high tensile steel.

2a10.11 Details of Welds

Fusion F aces

Fusion faces shall be free from irregularities and properly prepared such that the accuracy of the specified size of welds can be maintained.

Fusion faces and the surrounding surface shall be free from heavy scale and oil, paint or other substances which may affect the quality of the weld.

If the initial preparation is by gas cutting, the faces shall be ground, filed or dressed to remove irregularities and to maintain the tolerances specified.

Fillet W elds

Parts to be fillet welded shall be brought into close contact and the gap due to incorrect fit up shall not exceed 1.5 mm.

The minimum leg length of a fillet weld as deposited shall be not less than the specified size, and the throat thickness as deposited not less than 0.7 of the leg size where the fusion faces are at right angles to each other.

Butt W elds

Butt welds shall be single V or double V with the following tolerances:

Included angle of V 60 degrees minimumRoot face 3 mm maximumGap 1.5 mm minimumMisalignment of parts 3 mm maximum

The face of butt welds shall be at all places proud of the surfaces of parent metal. Where a flush surface is required, the surplus metal may be dressed off. In all complete penetration butt welds, where these are to be welded from both sides, the back of the first run shall be gouged out to clean metal before



Piling

welding is started on that side.

Butt welds for thickness of more than 12 mm shall be welded from both sides.

Where butt welds are to be welded from one side only, these shall be completed with the aid of a backing strip of mild steel or by the adoption of a special method of welding approved by the Engineer. In all cases, it must be ensured that complete fusion of the parts to be joined is readily obtained.

2a10.12 Non - Destructive Tests on Welds

Prior to grouting the spliced sections of the piles, the fillet and butt welds of not less than 10% of the total number of welded joints shall be tested by means of non-destructive tests (ultrasonic and/or magnetic particle inspection). The test reports shall form part of the piling records.

2a9.13 Pre-drilling

Pre-drilling using NX size drill shall be carried out to a depth of at least 5m into the category of rock specified for forming the rock socket, or the designed rock socket length of the pile, whichever is the greater.


2a10.14 Pre-boring

A temporary steel casing shall be used for pre-bored H-piles for supporting the sides of the hole. The casing shall be seating on rockhead or top of rock socket before the rock socket hole is formed.

In soils liable to "flow" the bottom of the casing must be kept far enough in advance of the boring tool to prevent the entry of soil into the casing, so preventing the formation of cavities and settlement in the adjoining ground. The Contractor shall take all possible precautions to prevent this and shall allow in his tender for any such action necessary.

The temporary casing shall be free from any distortion, internal projections and hardened grout.

Extraction of temporary casing shall be carried out while the grout is sufficiently workable to ensure that it is not lifted.

The use of an approved vibratory extractor will be permitted.



Piling

Bentonite slurry or other drilling muds shall not be used.

When boring is completed, the hole shall be thoroughly cleaned to get rid of loose soils before receiving steel H-pile and grout.

Where water flushing is used, care shall be taken to prevent erosion of the existing ground. Water shall pass through a sedimentation tank before being discharged outside the site.

2a10.15 Pile Installation

Spacers shall be fixed to the H-piles at regular intervals to maintain the H-piles in the desired positions and to provide adequate grout cover. A minimum cover of 40mm shall be provided to the H-piles. The Contractors shall submit the proposed spacer details for the Engineer's approval before commencement of work.

Grout shall be placed via a suitable tremie pipe which extends to the bottom of the hole, in less than 30 minutes after the grout is mixed.

Each pile shall be cast in one continuous operation and in any circumstances shall not be left partially grouted.

Grout shall be allowed to fill the hole up to the ground level to ensure that the pile is completely grouted.


After the completion of the piles, additional proof drilling shall be carried out to verify the rockhead profile. The proof drill holes shall be sunk at least 5m below the as-built top level of the rock socket of the nearest pile or to the as-built bottom level of the rock socket of the nearest pile, whichever is the deeper. The number of proof drill holes shall be at least 2 for sites with 100 piles or less; or 1% of the number of piles for sites with more than 100 piles.

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Documents

GS_2a_Piling.doc