3. MATERIALS
3.1
Source of Materials
Do not change sources of supply until it has been demonstrated that the materials
from the new source can meet all the specified requirements.
Remove from site any material
that fails to comply with the specification.
3.2
Drilling Fluid
3.2.1 General Requirement
Where drilling fluid is used it
is to be such as to:
a. Provide continuous support of the excavation b. Be easily displaced
during concreting
c. Not pollute
the ground at any stage
d. Not coat the reinforcement such as to impair
the steel/concrete bond
Drilling fluid including Bentonite supplied to the site and prior to mixing is to be in accordance with API Specification 13A 5th Edition (1993) Drilling
Fluid.
3.3
Water
Water used for the construction
is to be clean and free from harmful matter in solution or
suspension.
If taken from a source other than the Public Utilities Board,
water is to be tested in
accordance with BS EN 1008.
3.4
Concrete
Refer to section C3-10, clause
3.0 for general
requirement of concrete.
3.5
Grout
Grout containing fine aggregate may be
used in place of concrete. Constituents are to be water,
ordinary Portland cement, fine aggregate where permitted and admixtures subject to agreement.
3.5.1 Minimum Cement Content
Minimum cement content
is to be 390kg/m3 for concrete to be placed under water or drilling fluid by tremie method.
3.5.2 Fine
Aggregate
Fine aggregate is to be in accordance with grading C or M of
SS 31 (1998) Table 6.
3.6
Reinforcement
Refer to section C3-20, clause
3.0 for general requirements of reinforcement.
3.7
Temporary Casings
Unless otherwise agreed with the SO, temporary casings of accepted quality or an
accepted alternative method is to be used to maintain the stability
of pile excavation.
Propose to SO’s acceptance, the depth, size and thickness of casing to be provided.
Temporary casings are to be free from significant
distortion. They are to be of uniform cross-section throughout each continuous length. During concreting they are to be free from
internal projections and encrusted concrete, which might prevent proper formation
of the piles.
NPQS
C4-10 Bored Piling Piles
3.8 Permanent Steel Casings
EN 10210.
NPQS
C4-10 Bored Piling Piles
4. WORKMANSHIP
4.1 General Workmanship Requirements
Ensure the equipment set up and installation procedures are in conformance with SS CP
4: 2003.
4.1.1 Depth of
Penetration
Install each pile to
the designated penetration
as indicated
in the
drawings or as adjusted
as a
result of the design verification check.
4.1.2 Socketing of End Bearing Piles
For all piles indicated as end bearing in the drawings or schedules, form a socket of depth at least 1m or 1 times diameter, whichever is larger, into the material that meets
the founding conditions, unless indicated in the drawings or modified as a result of the verification check in clause 1.4.1,
as approved by the SO.
4.1.3 Pile Toe
Adopt a construction method, which ensures that the soil below the pile is not softened.
Ensure that no drilling fluid or slurry remains at
the base of the pile.
4.1.4 Continuity of Construction
4.1.4.1 Time for Excavation and Concreting
Each pile is to be excavated and concreted within twenty-four hours from the start of excavation below any temporary casing.
Where this time restraint cannot reasonably be met, set out an alternative in the method
statement together with an estimate of the likely effect on the performance and capacity of the pile.
4.1.4.2 Construction without temporary casing
A pile constructed
in
a stable cohesive soil without the use of temporary casing or other
form of support is to be bored and concreted without prolonged delay and in any case soon enough to ensure that the performance of the pile is not impaired.
4.2 Trial Bores
Conduct trial bores to confirm the ground conditions and the feasibility of the proposed
method of installation.
Agree with the SO on the location,
depth and size of the trial bores.
4.3 Boring
Excavation
4.3.1 General
Submit a detailed method statement clarifying the procedure for installing the bored piles including the method of overcoming any obstructions encountered and drilling through
hard
rock for SO’s acceptance. The method of excavation is to ensure no soil collapse in the bored holes. Do not
commence working pile excavation before method of excavation
is
accepted.
Carry out boring excavation generally using boring or reversed circulation drilling
equipment operating at the existing ground level.
Provide temporary steel
casing and drilling fluid if necessary to support the excavation.
Ensure the extreme dimensions (teeth
to
teeth) of the boring bucket or auger is not smaller than the specified pile diameter.
Do not dewater
within the excavated bored holes.
4.3.2 Boring Proximity
NPQS
C4-10 Bored Piling Piles
Do not bore so close to
piles that have been recently cast which contain workable or partially set concrete that a flow of concrete or instability could be induced or damage
sustained by any previously formed piles.
Boring is to be kept clear from a minimum distance of 5 times pile diameter from a newly cast
pile within 24 hours after casting.
4.3.3 Ground Conditions
Report to the SO immediately any apparent variance in the ground conditions from those
reported or might have been inferred from
reports.
4.3.4 Rock Socketing and Obstructions
When socketing through rock had been
called for or in the event of encountering obstructions below ground level during boring, use reverse circulation drilling method,
chiseling or propose other means for SO’s acceptance to bore through the obstruction or
rock.
Should the
reverse circulation
drilling
method fail to
clear the
obstruction or rock, propose and employ
other methods including predrilling with coring to assist in the clearing of the obstructions.
4.3.5 Temporary Casing
Unless otherwise agreed, provide a temporary casing of appropriate
size and length to
support the excavation. Use low vibration equipment to install and extract casing for
bores in built-up areas. Refer
to
design drawings for vibration limits.
4.3.6 Pumping from Pile Excavation
Do not pump from a pile excavation unless a casing has been placed into a stable stratum, which prevents the flow of water from other strata in significant quantities into
the
boring, or unless it can be shown that pumping will not have detrimental
effect on the
surrounding soil or property.
4.3.7 Determining Penetration Depth
Verify soil extracted as consistent with design assumptions in accordance with clause
1.4.1 above. Terminate
boring at the level indicated in the drawings, subject to
modifications as a result of verification check in clause 1.4.1. and to SO’s approval.
Keep soil samples drilled at strata change
and at 2m intervals for
records,
unless otherwise indicated in PSD. The
samples shall be stored in
a safe place which
is
sheltered from
sunlight and rain.
NPQS
C4-10 Bored Piling Piles
4.4 Use of Drilling Fluid
4.4.1 Proposal for
Use
Propose to the SO’s acceptance on
the
need to use drilling fluid. If acceptable, propose suitable type and method of drilling fluid to be used.
4.4.2 Storage
Store solid additives in
separate waterproof stores or containers, which
will prevent the
materials from
becoming contaminated.
4.4.3 Use
Use in accordance with the manufacturer’s instructions unless there is a demonstrable
reason to do otherwise.
4.4.4 Mixing
Mix drilling fluid thoroughly
with clean
fresh water to make a suspension, which will
maintain the stability of the pile excavation for the period necessary to place concrete and complete construction.
Where saline or chemically contaminated groundwater occurs, take special precautions to modify the drilling fluid suspension or prehydrate the drilling fluid in fresh water so as to render
it
suitable in all respects for the construction of piles.
4.4.5 Stability of Pile Excavation Using Drilling Fluid
Where the use of drilling fluid is accepted for maintaining the stability of
a boring, maintain the level of the
fluid in the excavation so that the fluid pressure
always exceeds
the
pressures exerted by the soils and groundwater. Use an adequate temporary casing
in
conjunction with the method to ensure
stability of the strata
near ground level until concrete has been placed.
Maintain the fluid level at a level not less than 2m above the level of the groundwater unless otherwise agreed.
In the event of a rapid loss of drilling fluid from the pile excavation, backfill the excavation
without delay
and inform the SO immediately. Obtain directions
from
the SO before excavation at that
location is resumed.
4.4.6 Spillage and Disposal
Take all reasonable steps to prevent the spillage
of
drilling fluid suspension on the site in areas outside the immediate vicinity of boring. Remove discarded drilling fluid from the
site without delay. Disposal of drilling
fluid is to comply with the regulations of the appropriate authority.
4.5 Cleanliness of Pile Bases
On completion of boring
and immediately prior to casting, remove all loose, disturbed or
remoulded soil or rock from the base of the pile while avoiding disturbance to the
ground
below
the
base. Maintain the stability of the
bore at all times, using appropriate levels of support fluid as required.
4.6 Reinforcement
4.6.1 General
Refer to section C3-20, clause 4.0.
4.6.2 Fixing
NPQS
C4-10 Bored Piling Piles
Keep the number of joints in the longitudinal bars to a
minimum. Arrange the joints such
that the full strength of each bar
is
effective.
Ensure the reinforcement cages are sufficiently rigid to enable them to be handled, placed and concreted without damage.
Welding is to be in accordance with BS 7123.
4.6.3 Placing
Lower the steel reinforcement accurately
into position with sufficient spacer blocks to ensure
the
correct cover is maintained at all times. Spacer blocks are to
be of suitable
durability. Allow a vertical tolerance of +150/-50mm on the level of the
reinforcement projecting above the cut-off level.
4.6.4 Cover to Reinforcement
Ensure cover provided comply with SS CP 65 and SS CP 4, unless otherwise indicated in the drawings.
4.7 Pile Casting
Read these clauses in conjunction with section C3-10,
clause 4.1 to 4.3.
4.7.1 General
Adopt a method of placing, and a suitable workability
of the concrete, so as to
form a continuous
monolithic concrete shaft
of
the full cross-section.
Place the concrete without such interruption as would allow
the
workability of the
previously
placed batch to have deteriorated significantly. The method of placing is to be
accepted by the SO. If necessary, incorporate an accepted set retarding additive into the
mix in order to ensure extended workability of the concrete after
placement.
Take all precautions in the design of the mix and placing of the
concrete to avoid arching
of
the concrete in a casing.
Prevent contamination of the concrete by spoil, liquid or other foreign matter.
4.7.2 Workability of Concrete
Use slump testing for mixes with workability type A as in Table 4.7.2 below. Use flow testing as
alternative workability test for higher workability mixes if practical, submit
proposals for SO’s acceptance.
Slump measured at the time of discharge into the pile shaft or at the time of discharge
into the concrete pump hopper
is to be in accordance with the standards shown in the
table below, unless otherwise agreed.
Do not use a concrete pump to place tremie concrete directly into the pile shaft.
Table 4.7.2
Class
of
Workability
|
Target flow
|
Slump
|
Typical condition of use
|
|
mm
|
Min
(mm)
|
Max
(mm)
|
||
A
|
Not applicable
|
75
|
125
|
Placed into water-free or
permanently lined shaft;
reinforcement spaced at
not
less than 100mm centres
|
B
|
500+/-50
|
100
|
175*
|
Where reinforcement is spaced at less than 600mm, or pile
bore I water free and less than 600mm diameter
|
C
|
550+/-50
|
175
|
225*
|
Where concrete is to be placed by tremie under drilling fluid
|
NPQS
C4-10 Bored Piling Piles
4.7.5.3 Delay in Concreting Operation
Should a delay
or breakdown occur during the concreting operation, which in the opinion
of
the SO could cause a cold joint, entrapment of laitance in the tremie concrete, or
otherwise lead to defective concrete, abandon the concrete placing.
Ensure that an adequate supply of concrete
to
the tremie is available at all times so that placement is continuous.
4.7.6 Monitoring of Concrete Level During Pile Casting
For each truckload of concrete discharged, counter-check the
rise
in concrete level
against the expected increase. A
graph showing the theoretical and
placed concrete volumes is to be plotted against depth during concreting and submitted to SO
for confirmation. If the rise in concrete level is found to be higher than it is physically
possible with the amount of concrete
discharged, demonstrate the integrity
of the
pile to the satisfaction of
the
SO.
4.7.7 Pile Head Casting Level Tolerances
4.7.7.1 Piles cast in dry bores with temporary casing
Cast pile heads
to a level above the
specified cut-off so
that a
sound concrete connection can be made
after trimming. The casting level is to be 0.75m to 1.0m above the cut-off level.
In the event of the
ground water level being higher than the required
pile head casting level shown on the Drawings, submit proposals for acceptance prior to placing concrete. Do not leave the pile head below the ground water level unless acceptable precautions are taken.
4.7.7.2 Piles Cast in Dry Bores with Permanent Lining Tubes or Casings
Where permanent lining tubes or casings are used to where the cut-off is in stable
ground below
the
base of any casing used, cast pile heads to a level above the specified cut-off so that a sound concrete connection can be made after trimming. The casting
level is to be 0.75 to 1.0m above the cut-off level.
Where Cut-off levels are specified below the standing groundwater level, do not reduce
the
borehole fluid level below the standing groundwater level until the concrete has set.
4.7.8 Extraction of Casing
4.7.8.1 General
Remove the casing in such a manner that no defect or damage
will be sustained by the
newly cast piles.
4.7.8.2 Workability of Concrete
Extract temporary casings before the initial setting time of the concrete expires and when
the
concrete remains sufficiently workable to ensure that
it is not lifted. Should a semi-dry mix have been accepted for formed piles, submit the means of ensuring that the semi-dry
concrete does not lift
during extraction of
the
casing.
During extraction maintain the motion of the casing in the axial direction of
the
pile.
4.7.8.3 Concrete Level
When the casing is being extracted, maintain a sufficient quantity of concrete within it to
ensure that pressure from external water, drilling fluid or soil is exceeded and that the
pile is neither reduced in section nor contaminated.
Do not place concrete in the boring once
the bottom of the casing has been lifted above the
top
of the concrete; place it continuously
as the casing is extracted until the desired head
of concrete is obtained.
NPQS
C4-10 Bored Piling Piles
Take adequate precautions in all cases where excess heads of water or drilling fluid
could be caused as the casing is withdrawn because
of the displacement of water or
fluid by the concrete as it flows into its final position against the walls of the shaft.
Where two
or more discontinuous lengths of casing (double
casing) are used in the construction, the
proposed method of working is to be acceptable to the SO.
4.7.9 Overbreak
Ensure that the method of construction does not cause an overbreak of larger than100% of the nominal pile concrete volume. Where the overbreak is larger than 100%,the pile is deemed
to
be
defective. Propose suitable
remedial measures includingload
tests justifying the capacity of the piles for
SO’s acceptance.
4.8 Backfilling Empty Boring
After each pile has been cast, backfill any empty bore
remaining carefully as soon
aspossible with acceptable materials. Ensure the method of discharging is accepted bythe SO and in a manner that
will not affect
the
integrity of
the
completed pile.
4.9 Grouting of Piles
4.9.1 Specific Requirement
for
Pile Base Grouting
( Not in use )
4.9.2 Grout
4.9.2.1 Batching
Maintain weighing and water dispensing mechanisms to the levels of accuracy stipulated
in
BS 1305. Measure the moisture contents of aggregates immediately before mixing.
4.9.2.2 Mixing
Mix all ingredients thoroughly to produce a homogeneous mix. After mixing, pass mix
through a 5mm
aperture sieve and use within 30 minutes.
4.9.2.3 Transporting
Transport so as to avoid segregation of
the
mix.
4.9.3 Method of
Grouting
The method adopted is to be such that all requirements of the specification in regard to
load-settlement behaviour and pile uplift during grouting are met.
4.9.4 Grout
Tubes
Test the tubes to ensure that leakage at the joints does not occur under pressure. Protect the tops of
the
tubes during and after
grouting.
Clean the
tubes by flushing with
water
after
grouting is
complete.
Re-grout if
the specified uplift
or target pressures are not achieved.
Monitor the grout pressure during all operations.
4.9.5 Pile Uplift
Monitor the uplift of piles during grouting using an appropriate monitoring device and
reference frame. During base grouting the pile uplift is to be within the range 0.2 to
2.0mm.
4.10 Tolerances
4.10.1 Setting Out
NPQS
C4-10 Bored Piling Piles
Establish all lines, levels and be responsible
for the
correct positions of all piles. Carryout
setting out from the
main grid lines of the proposed structure. Immediately beforeinstallation of the pile, mark the pile position with suitable identifiable pins or markers.
4.10.1.1 Casing position
Check the casing position during and after
placing the casing.
4.10.2 Position
The maximum permitted
deviation at cut off level of the pile centre
from the centre point shown on the setting out drawing is to be 75
mm in any direction. A survey of the
eccentricity of each pile and the pile group is to be carried out by a Licensed Surveyor, with the
results submitted
to the
SO
within 14 days or as
directed after the pile
has been trimmed to its cut-off level.
4.10.3 Verticality
For vertical piles, the maximum permitted deviation of the finished pile from the vertical is
1 in 75.
4.10.4 Rake
For raked piles, the piling rig is to be set and maintained to attain the required rake. The maximum permitted deviation of the finished pile from the specified rake is 1 in25.
4.10.5 Pile Diameter
The cross-sectional dimension
of the
pile is
not
to be less
than
specified. Check theauger width as required and
record for each pile to ensure the
specified diameter isachieved.
Allow a tolerance of 5% on the auger
width.
4.10.5.1 Enlarged Pile Bases
Enlarged bases formed
mechanically is to be not less than the specified dimensions and
concentric with the pile shaft
within a tolerance of
10% of
the
shaft diameter.
The angle between
the sloping (upper) surface of the base and the axis
of the
pile is not to exceed 35° and at the specified diameter of the base at the perimeter the thickness of
the
base is not
to
be less than 150mm.
4.11 Protection to Piles
Ensure that, during the course of the
work, no damage or displacement, which could
impair performance or durability, occurs to the completed piles.
Do not bore nor drive pile casing nearer than
five times its diameter (measured centre to centre) from an unfilled
pile excavation or from an uncased concrete
pile where the concrete has been in place less than 24 hours.
4.11.1 Undesirable Imposed Forces
Do not subject installed piles to any
forces
(direct or indirect) prior to their incorporation into the superstructure unless accepted by the SO.
Cracks, tilting or bending of piles are sufficient evidence that undesirable forces had
been imposed on the piles.
4.12 Replacement
of Piles
4.12.1 Rejection of Piles
Any piles cracked, deformed, twisted or suspected to be damaged in
anyway or not installed within the specified tolerance is to be rejected at the discretion of the SO.
NPQS
C4-10 Bored Piling Piles
4.12.2 Remedial
Proposals
In the event of pile rejected, propose remedial measures including replacing the rejected
piles or supplement
by substitute piles for
SO’s acceptance.
Propose the details of modification of design
to the pile caps, any required
compensating
piles, and other
measures as necessary. All proposals are to be endorsed by a PE.
4.13 Cleaning Up
Remove from the site
periodically
during the works and on completion all unnecessary
plant, rubbish and debris resulting from the activities.
4.14 Non-Performance of Working Piles
Notify the SO if the performance of any
pile is expected to be less than that of a similar pile whose test behaviour has been accepted.
4.15 Cutting Off Pile Heads
On completion of installation of piles, cut off the piles to the required level as shown on the Drawings and to a tolerance of ±20 mm unless otherwise agreed.
Where a pile has been formed below
the
required cut-off level, build up the deficient
portion and ensure the reinforcement is to project for a minimum length as stipulated
below. Submit the method of cutting the pile heads for SO’s acceptance.
Take care to avoid shattering or otherwise damaging the rest of the pile. Cut away
any cracked or defective concrete and
make
good
with new concrete properly bonded to the
old.
Table 4.15 Minimum Bond Length
Grade of Pile Cap Concrete
|
30
|
40 or
more
|
High Tensile Steel
(fy= 460 N//mm2)
|
37D
|
32D
|
Mild Steel
(fy= 250 N/mm2)
|
30D
|
25D
|
D = nominal diameter
of bar.
4.16 Noise and Disturbance
Carry out the work in such a manner as to minimize noise, vibration and other disturbance. Comply with all current regulations and environmental controls.
4.17 Final
Survey and As-Built Drawing
On completion of the trimming to
cut-off-levels of the piles, engage a registered land surveyor to survey and prepare a survey plan and as-built drawing showing the position,
cut off level, founding levels and eccentricity of the piles.
Allow for the survey plans to be taken in batches and to carry out the survey work on several visits. Submit
within timing and format as directed by the SO.
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