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Design and installation of steel open end piles in weathered
basalt
Luc Maertens* * Manager Engineering Department Besix, Belgium,
[email protected] Associate Professor Catholic University Leuven,
[email protected] Abstract The Dabhol Power Company
(DPC) is constructing Indias first Liquefied Natural Gas (LNG)
Terminal on a remote strip of the western coast along the Arabian
Sea about 160-km south of Mumbai. Designed to handle the largest
LNG carriers, the Terminals marine facilities includes a Jetty that
extends 1750-m into open sea to reach adequate depth, a jetty head
supporting the unloading arms and the control tower, four berthing
dolphins, four mooring dolphins, walkway support dolphins, three
navigation dolphins and one tug berth. 473 steel open-end piles
(dia.762-mm) support all these structures and are driven into
weathered basalt to support working compression loads up to 4000
kN. Tensile loads up to 2000 kN are supported by 610-mm diameter
sockets that are bored beneath the pile tip in the underlying
basalt. The subsoil consist of three subsequent layers: 1. Soft
clay layer with a thickness varying between 0 and 6-m. 2. Weathered
Basalt with a thickness of 1 to 5-ms, and a RQD value varying
between
0 to 90%. 3. Sound Basalt with unconfined compression strength
varying between 29 and 115
MPa. A significant problem consists of defining a installation
procedure for the piles, which reconcile the requirement to
guarantee an adequate bearing capacity with a risk of damaging the
pile tip, and the requirement of limiting the deformation of the
pile tip in such way that the installation of the socket through
the steel open end pile remains possible without damaging the bore
hammer. An onshore test program was performed to solve this
problem. To confirm the findings of the test program, Dynamic Pile
Tests were carried out on offshore piles. In this way the bearing
capacity of the installed piles was controlled. This paper
discusses the test program which was carried out to define the
installation conditions (Hammer Energy and Penetration per blow) in
order to guarantee the bearing capacity in compression and tensile
together. For compression piles, a penetration of 1 mm per blow is
required and for tension piles 5 mm per blow for 16 m piles and 2,5
m per blow for 19 m piles is not to exceed
1
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Description of the project.
Dabhol LNG Project.
The Marine Works of the Dabhol LNG project were awarded by Enron
Engineering and Construction Company to the Belgian Contractor
BESIX as a design and built contract in December 1997. The jetty
consists of a concrete deck that is supported by prestressed beams.
The beams are supported by bents 30-m apart. Vertical and raked
steel open-end piles support the bents. Every 120-m is a
construction joint and in the centre of each section of 120-m is a
strong point bent. Berthing, mooring, navigation and walkway
support dolphins as well as the jetty head are slab-structures
supported by the same piles. Two types of piles are used: piles
dia.762, th.16-mm and piles dia.762, th.19-mm. All piles are
provided with toe reinforcement consisting of a 12-mm thick steel
plate welded inside the pile tip. The height of this reinforcement
is 380-mm. The length of the piles varies from 20 to 35 meters and
the steel grade is X60 (413 N/mm). The marine structures are
protected from the sea attack by a breakwater of 2300-m parallel to
the shoreline. However, during the first monsoon, the progress of
the breakwater will not be sufficient to give an adequate
protection. For this reason all structures are designed to resist
to wave loads with a significant height of 9-m. Other loads to
consider are: a current of 1 m/sec, live loads on the decks and
last but not least an earthquake load with a ground acceleration of
0.16-g. Mooring and berthing dolphins have to resist to horizontal
forces of 6000 kN.
2
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Pile hammer and boring equipment. 1. Pile Hammer: The driving
hammer used for the installation of the piles is an IHC Hydrohammer
S90. The hammer is hydraulically operated and the weight of the
hammer is 92 MN, the weight of the ram is 45 MN. The hammer has an
operating impact energy operation rate of 2 to 90 kJ. 2. Boring
equipment:
RCDS-3 Drilling Equipment.
The drilling equipment used in Dabhol is specially designed and
build for the site by Geotec International (Belgium) and consists
of a Numa Reversh Circulation Hammer (Massachusetts, USA) combined
by a RCD rotary head (NCB, Italy). It allows for boring a 610-m
socket in the weathered and sound basalt trough the 762-m piles.
The RCDS-3 drilling equipment consists in (see figure): 1. Casing
clamp 2. Working platform 3. Raking cylinder 4. Mast
inclination
cylinder 5. Rotary head 6. Mast 7. Pull-down hydraulic
gear motor 8. Suction pipe 9. Drill rod 10. Casing 11.
Stabiliser 12. Down-the-hole hammer
3
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Soil conditions at onshore test location.
Typical boring at test location.
Boring at test location
0
5
10
15
0 10 20 30 40 50 60 70 80 90 100
TCR RQD (%)
DEP
TH (m
)
TCR
RQD
To perform the onshore trial pile test, a series of onshore
borings were carried out in order to find a location with a
geological profile which was as similar as possible as the
available offshore borings. The aim was to find a location with a
sufficient thick layer of weathered basalt. A typical boring at the
test location is given here beside. Nine unconfined rock core tests
were performed, giving an UCS of respectively: 72,5 43,1 61,6 50,8
113,3 52,6 65,1 30.0 and 42,8 MPa
Definition of the Static Resistance from Hammer Records. IHC
carried out wave equation runs made with the TNOWAVE software of
TNO Delft (Netherlands), taking into account the following
parameters: 1. The soil conditions as given in chapter 3. 2. The
geometry of the piles, including the 12-mm toe reinforcement. 3.
Hammer characteristics (IHC S-90) The calculations include runs for
100, 75 and 50% hammer energy and for different depths, resulting
in a matrix of Energy, Penetration per blow, Stress during driving,
and SRD (Static Resistance to Driving). These calculations were
performed for the 19-mm piles as well as for the 16-mm piles.
4
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A mathematical treatment of all this results allowed
Besixengineers to define specifically for the site a general
equation for the SRD in function of the number of blows for 100-mm
of penetration (N) and the applied hammer energy (E). This gives
the following dimensional formulas: SRD = (21.70*E + 564.22)*ln(N)
- 24.03*E - 809 for the 762x16-mm piles [1] SRD = (28.39*E +
392.35)*ln(N) - 48.49*E + 114 for the 762x19-mm piles [2] SRD in
kN, E in kJ, N = number of blows for a penetration of 100-mm. In
the figure here below, one can see the mathematical approach
(lines) against the calculated by IHC applying TNOWAVE (dots).
TNOWAVE calculations against Dimensional Formula for 19 mm
piles
2000
3000
4000
5000
6000
7000
8000
0 10 20 30 40 50 60 70 80 90
Blows per 100 mm penetration
SRD
(kN
)
SRD = (28.39 E + 392.35) ln(N) - 48.49 E + 114
90 kJ
67,5 kJ
45 kJ
TNOWAVE
TNOWAVE calculations against Dimensional Formula for 16 mm
piles
2000
3000
4000
5000
6000
7000
8000
0 20 40 60 80 100 120 140Blows per 100 mm penetration
SRD
(kN
)
SRD = (21.70 E + 564.22) ln(N) - 24.03 E - 809
90 kJ 67,5 kJ
45 kJ
TNOWAVE
5
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Static Compression Test.
Static Compression Test
A pile test up to 8000 kN was performed on pile C2. The pile
characteristics are as follows: The pile with an external diameter
of 762-m and a wall thickness of 19-mm was embedded over a length
of 3,28-m. The total length of the pile was 4,40-m. The ultimate
bearing capacity can be calculated from the formula: Qub = * qub *
Ab with: = installation coefficient = 0,5 for driven open end piles
[1] qub = ultimate bearing pressure Ab = section of the pile basis
= 0,456 m qub = c * Nc with: c = cohesion = * quc quc = unconfined
compression test of the rock ( 30 MPa) = 0,1 for RQD = 0 70% [2]
Nc= bearing factor = 15 for = 35 (= internal angle of friction
for
basalt) [3] Qub = 0,5 * 0,1 * 30 * 15 * 0,456 = 10,26 MN The
results of the compression test are given in the figures below.
Ultimate bearing capacity was not reached for a load of 8000 kN. By
extrapolating the settlement curves it was found that a bearing
capacity of 10.000 kN was found for a penetration of 7,65-m which
is only 1% of the pile diameter and still far below the 10% for the
conventional ultimate bearing capacity.
6
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Pile test C2 (23-24/09/1999) : Average settlement
0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
1500
Time (min)
Load
(ton
)
0
1
2
3
4
5
6
7
8
9
10
Ave
rage
set
tlem
ent (
mm
)
Load
Settlement
Pile load test C2 (23-24/09/1999) - Loading and unloading
curves
0
1
2
3
4
5
6
7
0 1000 2000 3000 4000 5000 6000 7000 8000
Load (kN)
Ave
rage
Set
tlem
ent (
mm
) loading
loading 2
unloading 2
WORKING LOAD
unloading 1
The bearing capacity was also measured by a local subcontractor,
using a dynamic test procedure together with the well-known CAP-WAP
program but unfortunately, the results were not trustable. Below
gives the driving records for pile C2 together with the
interpretation for the bearing capacity using formula [2] and the
not trustable dynamic test results are given.
7
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Ultimate Bearing Capacity - Pile C2 (19 mm)Comparison of values
calculated with the
dimensional formula [2] and from Dynamic Test.0,0
1,0
2,0
3,0
4,0
5,00 2000 4000 6000 8000 10000
Ultimate Bearing Capacity (kN)
Penetration (m)
Ultimate Bearing Capacity:* from dimensional formula and
hammer records : 9200 kN* from dynamic test : 6600 kN
9200
6600
8
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Static Tensile Tests.
Tensile pile test arrangement
Testpiles 762x16mm
Sockets 61mm9,59 9,60
8,54 8,59
5,95
4,35
1,35
-0,05
T1 T2
Two static tensile pile tests were performed on pile T1 with a
socket of 6-m and on pile T2 with a socket of 3-m. A tensile test
up to 4000 kN was performed on pile T1 and a tensile test up to
2000 kN on pile T2. As the result of the tensile test on both piles
T2 and T1 was totally satisfactory, it was decided to carry out a
pull out test on pile T2 up to 5000 kN (limit due to the strength
of the testing frame). The pile characteristics are given in Figure
12. The results of the T2-test and the pullout test are given here
below.
9
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Pile load test T2 (15-16/09/99) - Interpretation of socket
load
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0 250 500 750 1000 1250 1500 1750 2000
Tensile Load (kN)
Ave
rage
upl
ift (m
m)
First Loading Slope
Second Loading Slope
Load supported by friction on steel pile
Unloading
T2 - superposition of loading and unloading curves to 2000 kN
and 5000 kN
0
0,5
1
1,5
2
2,5
3
3,5
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Tensile Load (kN)
Ave
rage
upl
ift (m
m)
Wor
king
load
10
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As the tensile capacity of the pile is not only generated by the
friction on the socket, but also by the friction on the steel pile,
and since the uplift design is neglecting the last, it was
advisable to split up both. In Figure 17 one can distinguish two
slopes in the loading curve. We assumed that the change in slope
corresponds to the start of mobilisation of the friction on the
socket. One can see that it was found that the friction on the
steel pile was 1250 kN or 123 kN/m (= 0,123 MPa). Results of the
tensile test:
Pile Socket length
(m)
Working load (kN)
Deflection at working load (mm)
Test load (kN)
Deflection at test load
(mm) T1 6.0 2000 1.5 4000 2.8 T2 3.0 1000 0.5 2000 0.7 T3 3.0
1000 5000 3.4
Table 1 Evaluation of the Uplift Capacity. The uplift capacity
is defined by: (1) bond between the concrete socket & rock (2)
mass of mobilised soil (3) bond between the steel pile and the rock
(4) bond between steel and concrete (inside the pile). (2): The
mass of mobilised soil can easily be calculated. It is not measured
since the
foundations of the reaction supports of the tensile test are
inside the influence core.
(1) (3): Only the sum of both is measured. The split of both is
done according to pile
load test T2 figure. (4): The length of the socket plug inside
the pile was 2,3-m. The bonded surface is
thus : * 0,73 * 2,3 = 5,3 m According to BS 5400, the bond
stress between the steel pile and the infill
concrete is 0,4 MPa for ULS. During pull-out test, the bond
stress was 0,71 MPa
(1): The bond stress between the concrete socket and the rock
was: 3750 /( * 0,61 * 3) = 0,65 MPa According to Tomlinson [4] the
bond stress is 0,36 MPa in ULS. Under working load, a bond stress
equal to 0,12 MPa was assumed in the design.
Bond stress (MPa) ULS Test Test/ULS Steel pile concrete 0,4 (*)
0,75 1,8 Concrete socket - rock 0,36 0,65 1,8
(*) according to BS 5400 Part 5 art 11.1.3
11
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Installation procedure for piles.
Damaged pile tip
Damage of pile tip as shown above can not be accepted since
excessive damage of pile tip prevents the installation of the
sockets through the piles. The TNOWAVE analyses as documented in
chapter 4 also gives the stress during driving. The combination of
the SRD, Stress during driving, Hammer Energy and penetration per
blow leads to graphs as given in below for a 16-mm compression
pile. It shows that the stresses during driving, for a same SRD,
decrease significantly with the hammer energy, and increase
slightly with the number of blows for a penetration of 100-mm.
12
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Definition of refusal for compression pile 16 mm
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Blows per 100 mm penetration
SRD
(kN
)Maximum SRD = 2 Maximum Working Load
= 2 * 2620 kN = 5250 kN
67,5 kJ
45 kJ
150
200
250
300
350
400
450
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Blows per 100 mm penetration
Max
imum
Driv
ing
Stre
ss (M
Pa)
Yield stress = 415 MPa
Allowable stress = 332 MPa
90 kJ
On another hand, analysis of the pile toe damage during driving
(using the IHC Hammer at full Energy = 90 KJ), leads to the
following conclusions:
Pile Thickness
(mm) Max blows for
100-mm penetration (at 90 kJ)
Maximum Driving Stress (from output of TNO-
wave model) (MPa)
Damage at toe (m)
T1 16 51 380 0.1 T2 16 50 380 0.5 T3 19 57 360 0.5
13
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As one can see, the maximum stresses during driving were close
to the yield stress (415 MPa). In fact these maximum driving
stresses are computed by the IHC model with the assumption that the
stresses are uniformly distributed over the entire cross section.
This is of course never true in reality, and an appropriate safety
factor has to be used in the definition of the refusal criteria.
Considering the stress analysis in view to guarantee the SRD,
together with the damage analyses leads to the final installation
criteria. It was decided to allow 80% of the yield stress (=332
MPa) for compression piles and 55% (= 225 MPa) for tension piles,
since tension piles need a socket. Finally the installation
procedure was as follows:
Refusal criteria for permanent works Hammer Energy Blows per
100-
mm penetration Pile
(kj) (% of full energy) Compression 16-mm
19-mm 45
67.5 50 75
100 100
Tension 16-mm (*) 19-mm (*)
45 45
50 50
20 40
(*) This criterion was checked by installing two additional
raking piles on the test
location onshore. After inspection, no damage at pile tip was
observed as shown below.
Pile tip after driving
14
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Dynamic offshore test. Since dynamic onshore test was not
trustable, dynamic offshore test was carried out by another
Al-Futtain Tarmac from Dubai. Parameters used for PDA analysis are:
1. Parameters concerning the driving hammer: 2. Parameters
concerning the piles:
Characteristic impedance = 4.107 kg.m-2 . sec-1 Wave velocity =
5172 m/sec
3. Parameters concerning calculation of the bearing capacity
with the CASE-
model. As damping coefficient, Jc = 0,1 have been used.
4. Overview of the results :
Structure Bent Rake Loading Type Thickn. (mm)
Ultimate Resistance
SRD (hammer records)
SRD (dynamic
test)
1 Jetty Approach 16 V Compression 19 7650 8626 15700
2 Jetty Approach 7 1/3 Compression 19 7650 7693 7935
3 Jetty Approach 15 1/3 Tension 19 3825 4767 7140
4 Jetty Approach 8 V Tension 19 3825 4654 15950
5 Jetty Approach 7 1/3 Tension 19 3825 4720 8700
6 Jetty Head - 1/3 Tension 19 3825 3780 8970
7 Jetty Head - 1/3 Tension 16 2620 3006 6245
8 Jetty Head - 1/3 Tension 16 2620 3998 6109
9 Jetty Head - 1/3 Tension 16 2620 3147 5650
10 Jetty Head - V Tension 16 2620 3398 6085
An overview of these results is also given in the figure
below.
15
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1 2 3 4 5 6 7 89 10
0
2000
4000
6000
8000
10000
12000
14000
16000
Res
ista
nce
(kN
)
Dynamic offshore tests
Req
uire
d U
ltim
ate
Res
ista
nce
Dyn
amic
Offs
hore
Tes
t
SRD
(di
men
sion
al fo
rmul
a)
Conclusions Installation of open end piles in rock (weathered
basalt) can be controlled efficiently under the condition that a
continuous controlled hammer is used together with an adequate pile
recorder. In the case of Dabhol, all hydraulic functions of the
IHC-S90-Hammer are electronically regulated. This ensures optimum
control of the energy blow rate and an optimum control of the
penetration of the pile to the required depth without damaging the
pile toe. This is essential in the case that sockets have to be
drilled through the pile toes after driving. Onshore tests and
preliminary calculations allowed for a prediction of the Ultimate
Bearing Capacity in function of the applied Hammer Energy and the
penetration per blow. Offshore dynamic tests confirmed the presumed
bearing capacity. References [1] Ministre de lEquipement, du
Logement et des Transports (1993). Rgles
techniques de conception et de calcul des fondations des
ouvrages de gnie civil.. Fascicule 62, Titre V. Paris.
[2] Kulhawy F. and Goodman R.E. (1987). Foundations in rock,
chapter 15 of Ground Engineering Reference Book, ed. F.G. Bell,
Butterworth, London.
[3] Wyllie D.C. (1991). Foundations on rock. E & FN Spon,
London. [4] Tomlinson M.J. (1995). Pile design and construction
practice. E & FN Spon,
London.
16
Luc Maertens*AbstractRCDS-3 Drilling Equipment.Static
Compression TestTensile pile test arrangementTest loadPileRefusal
criteria for permanent worksPileWave velocity = 5172 m/secAs
damping coefficient, Jc = 0,1 have been
used.ConclusionsReferences
