4.
WORKMANSHIP
12
4.1
Schedule of Tests
12
4.2
Construction of Preliminary Test Pile
12
4.3
Load Testing: General
13
4.4
Load Test: Static Load Test Procedures
16
4.5
Load Test: Osterberg Load Test
20
4.6
Load Test: Lateral Load Test
21
4.7
Load Test: Dynamic Test
21
4.8
Integrity Tests: Proof Coring
22
4.9
Integrity Test: Non Destructive Tests (NDT)
23
4.10
Protection of Testing Equipment
24
4.11
Noise and Disturbance
25
5.
VERIFICATION AND SUBMISSIONS
26
5.1
General Submissions
26
5.2
Preliminary Test Piles
26
5.3
Results of Static Gravity and Lateral Load Tests
27
5.4
Results of Dynamic Load Tests
30
5.5
Results of Osterberg Cell Load Tests
32
5.6
Results of Pile Integrity Tests
33
4. WORKMANSHIP
4.1 Schedule of
Tests
Refer to drawings
For the purpose of establishing the number of tests required, the percentages given in the schedule relate
to the total number of working piles on a contract. Round up part
number of tests calculated based on the total number of piles.
4.2 Construction of Preliminary Test Pile
4.2.1 Method of
Construction
Construct each preliminary
test
pile in a manner similar to that for the working piles, and by the use of similar equipment and materials. Install preliminary test piles in ground
similar to that where the working piles are to be installed.
Provide extra reinforcement and concrete of increased strength
as directed by the SO to
ensure no premature structural failure during load tests.
4.2.2 Instrumentation for Preliminary Piles
Instrument the preliminary piles with 2 or 4 nos. of extensometers
through
the
pile depth and a minimum of 2 nos. of vibrating wire strain gauges per level at various levels as shown in the drawings.
Fix the vibrating wire strain gauges and extensometer securely to the reinforcement cages
of
the piles, and maintain orientation in the direction of the movement to
be measured, and protect
from damage at all stages of pile construction.
4.2.3 Cut-off Level
Terminate the pile shaft slightly above the normal cut-off level or at a level required by the SO.
Extend the pile shaft above the cut-off level of working piles so that gauges and other
apparatus to be used in the testing process will not be damaged by water or falling
debris.
Where the pile shaft is extended above the
cut-off level of a
working pile
in soil which
would influence the
load
bearing capacity of the
pile, install
a
sleeve
to eliminate additional friction which would not arise in the working pile. Alternatively, if the friction above
the designed cut-off level can be calculated with reasonable accuracy, a sleeve
need not be used, take the calculated friction into account in assessing the load applied
to
the pile.
4.2.4 Pile Head Construction
4.2.4.1 Compression Test
For a pile that is tested in compression, form the pile head in a plane surface normal to
the
axis of the pile, sufficiently
large to
accommodate the loading and settlement
measuring equipment and adequately reinforced or protected to prevent damage from
the
concentrated application of load from
the
loading equipment.
Ensure the pile head and/or cap is concentric with the test pile; check that the
joint
between the cap and the pile is not
weaker
than
the pile.
Make sufficient clear space under any part of the cap projecting beyond the section of the pile so that, at the maximum expected settlement, load is not transmitted to the
ground except
through the pile.
4.2.4.2 Tension Test
For a pile that is tested in tension, provide means for transmitting the test load axially to
the
pile. Construct the connection between the pile and the loading equipment with strength equal to the maximum load which is to be applied to the pile during the test with an appropriate factor of safety on the structural design.
4.2.5 Uniformity of Pile Shaft
For bored test piles, ensure the pile is uniform
in
diameter along its entire shaft with
overbreaks not exceeding 10% of its nominal diameter at any section.
Compute the percentage overbreak in
the
pile as the
percentage excess between the
concrete volume discharged per truck as indicated by the concrete delivery docket and
the
resulting concrete displacement in the bored pile based on the nominal size of the piles. Take the overbreak into account in the interpretation of test results
or reject at the
SO’s direction.
4.3 Load Testing: General
In addition to
the methods
and procedures prescribed
below, ensure that the
load testing
is
in general conformance with the requirements of SS CP 4.
4.3.1 Testing Equipment
4.3.1.1 Stability
Ensure that when
the hydraulic jack and
load measuring device are
mounted
on the pile head, the whole system is stable up to the maximum load to be applied. Provide the means to enable dial gauges to be read
from
a position clear of the kentledge stack or test
frame in conditions where failure in any part of the system due to overloading,
buckling,
loss of hydraulic pressure etc. will not constitute a hazard to personnel.
4.3.1.2 Test Pressure
Ensure that the hydraulic jack, pump, hoses, pipes, couplings and other apparatus to be
operated under hydraulic pressure are capable of withstanding a test pressure of one
and a half times the maximum working pressure without leaking.
4.3.1.3 Maximum
Test
Load
Check that the maximum test load or test pressure expressed as a reading on the
gauge in use is displayed and all operators are aware of this limit.
4.3.2 Verification of datum
Prior to carrying out a pile load test and
setting up of the load test equipment, survey to
establish a datum for the pile head level relative to a permanent bench mark. Verify the pile level
each time before a loading cycle to
ensure
that
the pile is not loaded prior to being subjected to the test loads.
4.3.3 Reaction Systems
4.3.3.1 Compression Tests
Carry out compression tests using kentledge, tension
piles or specially constructed
anchorage. Do not use kentledge for tests on raking piles.
Where kentledge is
to be used, support it on
cribwork disposed around the pile head so
that
its centre of gravity
is on the axis of the pile. The bearing pressure under supporting
cribs is to be such as to ensure stability of the kentledge stack, and if necessary, provide
a pile support system to the kentledge.
Do not rest the kentledge directly on the pile head.
4.3.3.2 Tension Tests
Carry out tension tests using compression piles or rafts constructed on the ground. The
use of inclined reaction piles, or rafts is
not precluded, subject to the
acceptance of the
SO.
In
all cases, ensure that
the
resultant force of
the
reaction system is co-axial with the
test pile.
4.3.3.3 Use of Working Piles
Do not use working piles as reaction piles without acceptance from the SO.
Where used
as reaction piles, measure their
movement
to
within accuracy of 0.5 mm.
4.3.3.4 Use of Kentledge
Where kentledge is used for loading vertical piles in compression, the
distance
from theedge of the test pile to the nearest part of the
crib supporting the
kentledge stack in
contact with
the ground is to be not
less than 3 times
the diameter of the test pile
and a minimum of 2m whichever is greater.
4.3.3.5 Tension Pile and Ground Anchors
Where tension piles or ground anchors are used,
ensure that
the load is correctly transmitted to all the tie rods or bolts. Do not extend the rods by welding unless it can be ensured that the steel will not reduce in strength by welding. Ensure that the bond stresses of the rods in tension do not exceed normal permissible bond
stresses
for the type of steel and grade of concrete used.
4.3.3.6 Spacing of Vertical Reaction Piles
The centre to centre spacing of vertical
reaction piles, including working piles used as
reaction piles, from a test pile, is to be not less than 3 times the diameter of the test pile or the reaction piles or 2 m, whichever is the greatest. Where a pile to be tested has an
enlarged base, apply
the
same criterion with regard to the pile shafts, with the additional requirement that the
surface of the
reaction piles is to
be no closer to the base of the test pile than half of the enlarged base diameter.
4.3.3.7 Spacing of
Ground Anchors
Where ground anchors are used to provide a test reaction for loading in compression, no part of the section of the anchor
transferring load to the ground is to be closer to the test
pile than 3 times the diameter of the test pile. Where the pile to be tested has an
enlarged base, apply
the same criterion with regard to the pile shaft, with the additional
requirement that no section of the anchor transferring load to the ground is to be closer
to
the pile base than a distance equal to the base diameter.
4.3.3.8 Care of Piles
Ensure that the method employed in the installation of any reaction piles, anchors orrafts do not
damage any test pile or working pile.
4.3.4 Measurement of Load
Measure the load by
a load measuring device and by a calibrated pressure gauge included in the hydraulic system. Record readings of both the load measuring device and
the
pressure gauges. In
interpreting the test data, regard the readings from the load measuring device as normal and use the pressure gauge readings as a check for
gross
error.
4.3.4.1 Calibration of Load Measuring Devices
Calibrate the
load measuring devices before and
after each series of tests, whenever adjustments are
made to the device or at intervals appropriate to
the type of equipment.
Calibrate the pressure gauge and hydraulic jack together.
4.3.4.2 Adjustability of Loading Equipment
Check that the loading equipment is capable of adjustment throughout the test to obtain a smooth increase of load
or to maintain
each load constant at the required
stages
of
a maintained loading test.
4.3.5 Measuring Movement of Pile Heads
4.3.5.1 Maintained Load Test
In a maintained load test measure the movement of the pile head by two of the methods in Clauses 4.3.5.3 to 4.3.5.5 using methods appropriate to vertical piles or raking piles, as
required.
4.3.5.2 Constant
Rate of Penetration (CRP)
or Constant Rate of Uplift (CRU) Test
In a CRP or CRU test, use the method in Clause 4.3.5.4 or 4.3.5.5 below.
4.3.5.3 Levelling Method
An optical or any
other levelling method by reference to an external datum may be used. Where a level and a staff are used, choose
the level and scale of the staff to enable
readings to be made to within an accuracy of 0.5 mm. A scale attached to the pile or pile
cap may be used instead of a levelling staff. Establish at least two datum points on permanent objects or other well-founded structures or install deep datum points. Site each
datum point so that
only one setting up of
the level is needed.
Ensure that Datum points are not affected by the test loading or other operations on the
Site.
4.3.5.4 Independent Reference Frame
An independent reference frame may be set up
to permit measurement of the movement of the pile. The supports
for
the frame is to be founded in such a manner and at such a distance from the test pile, kentledge support cribs, reaction piles, anchorages and rafts
that
movements of the
ground in vicinity
of the
equipment do not cause movement of the
reference frame during the test which will affect the required accuracy of the test.
Check observations of any movement of the reference frame and check the movement
of
the pile head relative to an external datum during the progress of the
test. In no case the supports are not to
be less than three test pile diameters or 2
m,
whichever is the greater, from
the
centre of the test pile.
Measure the pile movement by
at least two dial gauges
rigidly mounted on the reference
frame that bear on
surfaces normal to the pile
axis, fixed to the pile
cap or head. Alternatively, fix the gauges to the pile and bear on surfaces on
the
reference frame.
Place the dial gauges in diametrically opposed positions and equidistant from the pile axis. The dial gauges are to enable readings to be made up to within an accuracy of
0.1mm. Use a scale ruler and levelling device to provide an independent measurement
of
the pile head movement.
Protect the reference frame from the weather.
4.3.5.5 Other Methods
Details of any other
method for measuring the movement of pile heads may be submitted
for acceptance.
4.3.5.6 Calibration of Dial Gauges
Calibrate the dial gauge used for the
measurement of load by
a SINGLAS accredited
laboratory to the accuracy as required.
4.3.6 Continuous Testing
Once commenced, carry
out any test to completion without stoppage unless otherwise agreed by the SO.
4.3.7 Completion of a Load Test
4.3.7.1 Measuring Equipment
On completion of a test dismantle and check all equipment and measuring devices and either store so that they are available for use in further
tests or remove from
the
site.
4.3.7.2 Kentledge
Remove Kentledge and its supporting structure
from
the test pile and store so that they are available for use in further
tests or remove from
the
site.
4.3.7.3 Ground
Anchors and Temporary Piles
On completion of a preliminary test, cut off temporary piles 2 m below
ground level, and
make good the ground with accepted material.
Remove all ground anchors unless otherwise directed.
4.3.7.4 Preliminary Test Pile Cap
Break off the pile cap, if formed in concrete, dispose the resulting material off the site. If
the
pile cap is made of steel, cut it off and store
so that it is available for use in further
tests, or remove from the site.
Break down preliminary test piles to 2 m below
original
ground level or as required and
backfill to the original ground level with suitable material.
4.3.7.5 Working Load Test Pile Cap
On completion
of a working load test,
strip the test
pile
cap if in concrete
unless otherwise agreed. Leave the pile in a state ready for incorporation in the permanent works and dispose
the resulting material off
the
site.
If the pile cap is made of steel, cut it off and store so that it is available for use in further tests, or
remove from
the
site as directed.
4.4 Load Test: Static Load Test Procedures
4.4.1 Ultimate Load Test by Maintained Load
Unless otherwise specified
the maximum load which is
to be applied in an ultimate
load test is 3
times the specified working load. This test is only applicable to preliminary piles.
The
loading and unloading is to be carried out
in
stages as shown in the table below.
Ultimate Load Test Cycles
Load, Percentage of
Working Load
|
Minimum Time of Holding
(Minutes)
|
Load Cycle Number
|
0
|
-
|
1
|
25
|
60
|
|
50
|
60
|
|
75
|
60
|
|
100
|
24hrs
|
|
70
|
60
|
|
35
|
60
|
0
|
60
|
|
0
|
-
|
2
|
50
|
60
|
|
100
|
60
|
|
125
|
60
|
|
150
|
60
|
|
175
|
60
|
|
200
|
24hrs
|
|
150
|
60
|
|
100
|
60
|
|
50
|
60
|
|
0
|
60
|
|
0
|
-
|
3
|
50
|
60
|
|
100
|
60
|
|
150
|
60
|
|
200
|
60
|
|
225
|
60
|
|
250
|
60
|
|
275
|
60
|
|
300
|
24hrs
|
|
200
|
60
|
|
100
|
60
|
|
0
|
60
|
Following each application of load, hold the load for not less than the period shown or
until the rate of settlement is less than 0.1 mm/hr and slowing down. Calculate the rate of
settlement from the slope of the curve obtained by plotting values of settlement versus
time and drawing a smooth curve through the points.
Proceed unloading for
each stage after
the
expiry of the period shown in the table.
For any period when the load is constant, record time and settlement immediately on reaching the load and at approximately
15 min intervals for the 1st hr, at 30 min intervals between the 1st and 4th
hr and at 1 hr intervals between the 4th and
12th hr after the
application of the increment of the load.
Continue testing until the maximum test load has been reached or when the settlement exceeds 10% of the pile diameter.
4.4.2 Working Load Test by Maintained Load
Unless otherwise specified the maximum load to be applied in a working load test on a working pile is 2 times
the specified working load. Carry out
the loading and unloading in stages as shown in the table below.
NPQS
C4-30 Bored Piling Piles
Working Load Test Cycles
Load, Percentage of
Working Load
|
Minimum Time of Holding
(Minutes)
|
Load Cycle Number
|
0
|
-
|
1
|
25
|
60
|
|
50
|
60
|
|
75
|
60
|
|
100
|
24hrs
|
|
70
|
60
|
|
35
|
60
|
|
0
|
60
|
|
0
|
-
|
2
|
50
|
60
|
|
100
|
60
|
|
125
|
60
|
|
150
|
60
|
|
175
|
60
|
|
200
|
24hrs
|
|
150
|
60
|
|
100
|
60
|
|
50
|
60
|
|
0
|
60
|
Following each application of an increment of load, hold the load for not less than the
period shown or until the rate of settlement is less than 0.1 mm/hr and slowing down. Calculate the rate of settlement from
the
slope of the curve obtained by plotting values of
settlement
versus time and drawing a smooth curve through the points.
Proceed unloading for each stage
after the expiry
of the period shown in the
table. For any
period when
the load
is constant, record time
and
settlement
immediately
on reaching the load and at approximately 15 min intervals for the
1st hr, at 30 min intervals between the 1st and 4th hr and at 1 hr intervals between the 4th and 12th hr after the
application of the increment of the load.
4.4.3 Constant Rate of Penetration (CRP) or Constant Rate of
Uplift
(CRU)Test
The rate of loading is to be such that a CRP/CRU is maintained throughout the test
as far as practicable.
Propose the rate of
movement of each pile to be tested for
SO’s acceptance prior to the start of
the
test.
Take readings of load, penetration or
uplift and time simultaneously at
regular intervals; choose the intervals such that a curve of load versus penetration or
uplift can be plotted without ambiguity.
Continue loading until one of the following results is obtained.
a. the maximum
specified test load is reached.
b. a constant or reducing load has been recorded for an interval of penetration or
uplift of 10 mm.
c. a total movement
of
the pile base equal to 10%
of the base diameter,
or any other greater value of movement required has been reached.
Reduce the load in five approximately equal stages to zero load; record penetration or
uplift and load at
each stage and at zero load.
4.4.4 Combined
Working Load
Test and Constant Rate of Uplift
(CRU) or
Constant Rate of Penetration (CRP)
Test
When required, carry out a Working Load Test by maintained loading prior to a CRU or
CRP Test.
4.4.5 Quick Load Test
Method
The testing procedure is to be in accordance with ASTM D1143.
Apply the load in increment of 10% to 15% of the proposed design load with a constant
time interval between increments of 2.5 min
unless otherwise agreed. Add load
increments until continuous jacking is required to maintain the test load or until the specified capacity of the loading apparatus is reached, whichever occurs first, at which
time stop the jacking. After a 5-min or otherwise agreed interval, remove the full load
from
the
pile.
4.4.6 Abandoning of Tests
Abandon a static load test if any of the following occurs:
The specified material and workmanship requirements for loading and testing are not
met
for any reason.
If any test had to be discontinued due to:
i. faulty jack on the gauge,
ii. unstable support
of
the kentledge,
iii. cracking in or damage to the pile cap, iv.
incorrect or disturbed datum,
v. prejacking or
preloading before commencement of
test.
vi. Any other causes deemed to affect the validity of the test
results.
Disregard the results of abandoned
tests. In the event of an abandoned test, carry out another
test as directed by the SO.
4.4.7 Failure of
Static Load Test
A static pile load test is deemed to have failed if the load-deflection performance criteria specified in the piling specification are not satisfied. Carry
out remedial measures as stipulated in the piling specifications.
4.5 Load Test: Osterberg Load Test
4.5.1 Preparation of Pile
For bored piles, prior to
concreting, clean the toe of pile and install O-cell. Attach the
O- cell assembly, including O-cells, bearing plates, related hydraulically supply, tremmie pipes and instrumentation to reinforcing steel
cage and lower them into the bored hole. Initially, position the bottom of the O-cell assembly about 600mm above the pile base.
Use
concrete with retarder to fill sufficiently high (at least 2m) above the O-cell assembly. Lower the pile re-bars cage and O-cell assembly slowly into the underlying concrete.
Carry out the concreting as per
standard/approved procedure.
For driven piles, cast the O-cell assembly, including O-cells, bearing plates, related
hydraulically supply and instrumentation together with the pile. After the concrete have gained sufficient strength, drive the
pile into the ground as per standard/approved
driving procedure.
4.5.2 Maximum
Test Loads
Unless otherwise agreed, the maximum test load
in
an Osterberg Cell Load is to be the ultimate
capacity of a pile in either end bearing or side shear, or the
maximum stroke of
the
O-cell.
4.5.3 Abandoning of Osterberg Load Tests
Abandon load test if any of the following occurs:
-
The specified material and workmanship requirements for loading and testing are not
met
for any reason.
If any test has to be discontinued due to:
i. faulty O-cells,
ii. cracking in or damage to the pile,
iii. incorrect or disturbed datum,
iv. prejacking or preloading before commencement
of test.
v. Any other causes deemed to affect the validity of the test
results.
Disregard the results of abandoned tests.
4.5.4 Failure of Osterberg Cell
Load Test
An Osterberg Cell load test is deemed to have
failed if the load-deflection performance
criteria specified in the piling specification are not satisfied. Carry
out remedial measures
as stipulated in the piling specifications.
4.6 Load
Test: Lateral Load Test
4.6.1 Lateral Load
Test on Preliminary Piles
Design the reaction and testing system to apply
a horizontal load on the preliminary
pile. Check that the horizontal lateral load on the pile head is parallel to a pair of strain
gauges already
installed in the pile. Identify
piles into which the inclinometer tube is
required and submit to the SO for acceptance not less than 72 hours before the pile is
concreted.
The testing procedures are to be the same as that for static load tests
except that only
one load cycle is required with each load increment to be held for 1 hour
(mm) until the
ultimate lateral load capacity or 300mm
pile top deflection, whichever occurs first.
Monitor the strain gauges in the pile at
every load step.
4.6.2 Lateral Load
Tests on Working Piles
Undertake lateral load tests on an adjacent pair
of
bored cast insitu piles. Test by either jacking the piles apart
or pulling them
together.
Apply the test load at or within 0.5 metres of the pile cap soffit level. The test load is to be equal to the lateral
working load of the pile. Measure pile deflections parallel to the direction of
the applied
load such that
the movement of
each
pile is
measured in
absolute terms and not as a relative movement between piles. Check that dial gauges
and load cells used are accurate to 0.1mm and 10kN
for deflection and load
measurements respectively.
4.6.3 Recording Deflection
Record deflection
for every 12.5% of the test load during both
loading and unloading.
Where specified on the Drawings, record
the
rotation of the pile at the same increments. Carry out loading sequence in 2 cycles. At the first cycle, test the pile to
75% of the test load and then reduce to zero. At the second cycle, test to 100% of the test load and then
reduce to zero.
4.6.4 Increase of Load
For both loading cycles, increase the load only if the rate of movement is less than
0.2mm in 20 minutes and subject to a minimum holding period of 20 minutes at the end
of each incremental
increase.
The
minimum holding
period
may
be reduced
to 10 minutes if
the rate of movement
is less than 0.1mm
in
10 minutes for
every load
increment previously
applied on the first cycle during the second
loading cycle. The
minimum holding period
is
3 hours at the maximum load
for both the
first and second loading cycle. The
minimum holding period during unloading is 20 minutes at the
end of each incremental decrease for both load cycles.
4.6.5 Failure of
Lateral Load
Tests on Working Piles
A pile or pile group under lateral load test is deemed to have failed if the lateral deflection
or rotation at the pile cap soffit level exceeds the Serviceability Limit State (SLS) criteria at the test
load. Carry out
remedial measures as stipulated in the piling specifications.
4.7 Load
Test: Dynamic Test
Carry out dynamic tests by companies accredited by
SAC-SINGLAS only.
4.7.1 Preparation of Pile Heads
Prepare and level the pile head for fixing the
testing instruments, such
that
consistent results are obtained. Ensure
that
the pile head is free of debris and other deleterious
smaterial. Remove any loose material
from the pile head to expose sound concrete, and
ensure the head is horizontal over its complete cross-section.
4.7.2 Dynamic Load Testing Requirement
Piles may be tested during the entire
driving process, at the end of driving or during restrike. Carry out computer analysis of the
field measurements to obtain the pile
resistance distribution and vertical load against
displacement relationship.
Unless otherwise directed, conduct
dynamic tests on all preliminary test piles which are
to
be statically load tested, to provide the basis and calibration for other dynamic load
test results.
Provide a suitable hammer system able
to mobilise
the piles to a minimum of 2.5 times
the specified working load
for driven
piles, and a minimum of 1.5
times the specified
working load
for bored piles. Check that the hammer system consists of an adequately heavy hammer with a controlled drop to limit the
driving stresses in the pile. In general, the energy provided on to the pile during restrike tests is not to be less than that used to drive the pile initially.
4.7.3 Failure Criteria for
Working Piles
Piles which are dynamically tested are deemed
to
have failed if the measured resistance of the pile is less than 2.0 times the specified working load or if any part of the test piles
is
damaged during driving or testing. Carry
out remedial measures as stipulated in the piling specifications.
4.7.4 Damage Caused
Be responsible for any
damage caused to
the
pile or dynamic test equipment, including
transducers and cables, due to handling of the pile, objects falling from the pile
frame or
the
pile hammer.
NPQS
C4-30 Bored Piling Piles
4.8 Integrity Tests: Proof Coring
Check the quality of concrete in bored piles by vertical coring to at least 0.5 metre below
the
pile toe using a diamond coring barrel at an agreed location of the pile. Ensure that the core so
produced is not affected by
drilling disturbance and reflect the condition
of concrete in
the
pile. The core is not to be less than 100 mm in diameter and is placed in
suitable core boxes in the order of core recovery.
Complete coring work before the concrete in the pile has reached an age of 28 days to allow the cores to be tested at 28 days. Arrange
for transport to the testing laboratory.
Deliver the remainder of cores to a core store.
On completion of proof coring, grout the core cavity within and below a pile. The grout is to be of the same grade as the pile concrete, of a non-shrinkage type. Submit details o
fthe
proposed grouting method and mixes for acceptance 14 days prior to undertaking any
such operation.
4.8.1 Acceptance of Proof Coring
Check the quality
of cores produced against criteria as set out below. Piles, from which
cores do not satisfy the given requirements,
may
be rejected at the discretion of the SO.
4.8.1.1 In Concrete
For this purpose, concrete is considered as being rock. Requirements for cores are as
follows:
a. Visually free from defects, such as contaminants and honeycombing. b. 100% Total Core Recovery (TCR)
c. 100% of Rock Quality Designation (RQD)
4.8.1.2 In Soil/Rock
Requirements for cores are:
a. 100% Total Core Recovery.
4.9 Integrity Test: Non Destructive Tests (NDT)
4.9.1 Sonic Logging Tests
4.9.1.1 Sonic Logging Tubes
Provide sonic logging tubes cast into piles selected for sonic logging tests.
The tubes are to be manufactured
from steel and extend 0.2 m to 0.5 m above the pile
head and 0.2 to 0.5
m above the pile toe. The tubes are to have an internal diameter not exceeding 50 mm, except
for
one tube
in each
pile, which is
to be of
internal
diameter100 mm
in
order to allow for coring of
the concrete at
the
base of the pile.
Provide three tubes for piles up to 800 mm in diameter and four tubes for piles above800 mm
in
diameter.
4.9.1.2 Coring
At least 7 days after the pile has been cast, but before carrying out any sonic logging
test,
take a core of concrete and soil or rock from
the
founding material.
Take the core from the base of the 100 mm diameter sonic logging tube using a triple
tube
core barrel. The core is to have a minimum diameter of 50 mm.
Keep the core in a suitable wooden box with depths clearly recorded on rigid markers,
and photograph it along with a scale and colour chart. Thereafter, deliver these
to a designated core store.
Scan the pile toe for its integrity by measuring the propagation time of transmitted waves
between the vertical tubes and the pile toe/ founding strata.
4.9.1.3 Sonic Logging Test
Procedure
Carry out the following operations in sequence:
a. Fill the tubes with water.
b. Insert the probes into an adjacent pair of tubes and mount the drum over the pile.
Lower the probes to the bottom of the pile. Adjust their depths such that the delay
time is minimised, i.e.
they are at the same level.
c. Slowly raise the probes so that successive traces of the time between signal
emission and receipt are displayed on the screen of the oscilloscope. Each time
the
screen is filled, take
a "Polaroid" photograph
in
order to provide a permanent record.
d. Repeat the process for each pair of tubes, i.e. three runs for a pile with three
tubes and six runs for a pile with four
tubes.
e. Lower one probe to the base of a 50 mm diameter tube while lower the other to the same depth in the 100 mm diameter tube. While the
former probe is held in
position, lower the latter probe into the cored hole to its lower limit. Obtain a record of the received signal delay
time as a function of the depth of the
second probe. Repeat this process with the first probe in all available tubes.
4.9.2 Low Strain Impact Tests
4.9.2.1 Preparation of Pile Heads
Refer to the requirements of Clause 4.7.1.
4.9.2.2 Procedures for vibration testing
a. Connect
the
electrodynamics vibrator
unit firmly to the centre of the pile.
b. Connect
the
velocity transducer
to
the head of the pile near to its circumference.
c. Drive the vibrator at constant force output through two cycles up to 500 Hz and
1000Hz.
d. Process the signal from the velocity transducer to provide a measurement of the
mechanical admittance of the pile as a
function
of
frequency or both
frequency ranges.
Obtain a permanent record of the mechanical admittance.
4.9.2.3 Procedures for Modified Shock
Test
a. Connect a velocity transducer to the pile head.
b. Strike the head of the pile a sharp blow with a hammer of mass approximately 2
kg, to
which is attached
a triggering device connected to the
signal processing equipment.
c. Process the signal from the velocity transducer to provide a permanent record of
the
seismic response.
d. Transfer this response either in analogue or digital
form as appropriate to a
microprocessor which is to perform a fast Fourier transform on the output signal from which the relationship between mechanical admittance and frequency can
be determined.
4.9.2.4 Procedures for simple shock tests
a. Connect
the
velocity transducer
to
the pile head.
b. Strike the head of the pile in a sharp blow with the hammer.
c. Process the signal from the velocity transducer
to provide a permanent record of
the
seismic response.
4.9.3 Non-Destructive Testing - Anomalous Test Results
Any piles with
anomalous
results from
typical non-destructive tests
such as sonic
logging, vibration test and modified shock tests
may be rejected at the discretion of the
SO, unless it can be demonstrated
that
the pile integrity is acceptable through proof coring.
4.10 Protection of Testing Equipment
4.10.1.1 Protection from Weather
Throughout the test period, protect all equipment
for measuring load and movement from
the
weather.
4.10.1.2 Prevention of Disturbance
Keep construction equipment and persons who are involved in the testing process at a sufficient
distance from the test
to
avoid disturbance to the measurement apparatus.
4.11 Noise and Disturbance
Carry out the work in
such
a
manner
as
to minimise
noise, vibration
and
other
disturbance.
Comply with all current
regulations and environmental controls.
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