PERTAMINA HULU ENERGI WEST MADURA OFFSHORE, MADURA STRAIT – EAST JAVA – INDONESIA METHOD STATEMENT PRE-TRENCHING WORK FOR PIPELINE RELOCATION DOCUMENT NUMBER: PHEWMO-PPP-N-PRC-0004 REV ISSUE PREPARED BY REVIEWED BY APPROVED BY ISSUE DATE 0 For Method Statement FMA NS 27-08-2014
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Pre Trenching for 16" Pipeline Relocation PHE WMO Project Method Statement
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PERTAMINA HULU ENERGI WEST MADURA OFFSHORE, MADURA STRAIT – EAST JAVA – INDONESIA
METHOD STATEMENT
PRE-TRENCHING WORK FOR PIPELINE RELOCATION
DOCUMENT NUMBER: PHEWMO-PPP-N-PRC-0004
REV ISSUE PREPARED BY REVIEWED BY APPROVED BY ISSUE DATE
0 For Method Statement
FMA NS 27-08-2014
EAST MARINE PTE. LTD
PERTAMINA HULU ENERGI – WEST MADURA OFFSHORE
METHOD STATEMENT
TITLE DOCUMENT NUMBER REV DATE PAGE
PRE-TRENCHING WORK FOR PIPELINE RELOCATION
PHEWMO-PPP-N-PRC-0004
0 27 Aug 14 1 of 29
PHEWMO-PPP-N-PRC-0004
1. Introduction
1.1. Project Title
The Project is called “16 inch Pipeline Relocation PHE WMO Project”, and the Project
Owner is Pertamina PHE WMO (Pertamina Hulu Energi West Madura Offshore).
1.2. Indicative Location of Dredging Works for Access
The working area is located in offshore, west side of Karang Jamuang Island – Bangkalan –
East Java - Indonesia. Indicative location of working area is shown in Figure 1 below.
Figure 1. Indicative location of working area (source : google earth)
SURABAYA , CAPITAL OF EAST JAVA PROVINCE
MADURA ISLAND
PRE TRENCHING FOR PIPELINE RELOCATION ILLUSTRATIVE
LOCATION
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1.3. Document Purpose
The main purpose of this document is to define the method statement to be performed by
East Marine Pte. Ltd. as the sub-contractor, under PT. Rekayasa Industri as main contractor, for pre-trenching work (dredging) at the west side of Karang Jamuang Island – Bangkalan –
Madura - East Java - Indonesia. The objective is to achieve the required work quality within the project specification and the time frame.
2. Quantity, Equipment, and Manpower
2.1. Quantity of Dredging
Pursuant to client request and refer to drawing number PHEWMO-PPP-W-PLD-5003-
REV.B, seabed lengths required to be dredged are 1000m (1km) which start from KP 36.11 to KP 37.09. Seabed contour is various, but trench thickness is determined with the same
thickness with minimum is 4.5m from original seabed level along the pipe route. Actually, refer
to the requirement, the gas pipe need to be buried minimum 4m from original seabed. The pipe itself has 16” OD, so total minimum trench thickness is 4.5m from existing seabed. After
considering the siltation effect, we will dredge extra 0.5m as precaution, so total thickness plan for this pre-trenching work at PHE WO Project is 5m. Design of slope based on drawing no
PHEWMO-PPP-W-PLD-5003-REV.0 is 1:1, so estimate dredging quantity for trench at PHE
Figure 14. Heavy Duty Clam Shell Bucket 4m3 (40Ton)
Figure 15. 25 Ton Chisel Breaker.
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2.4.2. Survey Equipment
To obtain and to evaluate the dredging result, bathymetric survey required. To carry out the bathymetric survey, East Marine Pte Ltd as subcontractor will use survey equipment as follows:
Figure 16. 1 Set PC or Laptop
Figure 17. LCD Monitor
Figure 18. GPS Trimble SPS 232
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Figure 19. Echo Sounder Knudsen 320 M
Figure 20. Transducer Knudsen 320 M
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Function of each survey equipment described as follow:
Personal Computer : To run the survey software (Hydro-Pro), to record electrical
data of bathymetric survey result, and to display the general information of bathymetric
survey such as: survey line, tide, boat speed, boat position (latitude & longitude), etc.
LCD Monitor : As display for survey boats operator to follow the survey line
GPS Trimbe SPS 232 : As the receiver of information from the satellites using radio
waves to calculate the survey boat exact location.
Echo Sounder Knudsen 320M : Used to determine the depth of water by transmitting
sound pulses into water by Transducer Knudsen 320M. The time interval between
emission and return of a pulse is recorded, which is used to determine the depth of water along with the speed of sound in water at the time. Distance is measured by multiplying
half the time from the signal's outgoing pulse to its return by the speed of sound in the water, which is approximately 1.5 kilometres per second. Illustration how echo sounder
works could be seen in Figure 21 below.
Figure 21. Basic principle of echo sounding
3. Work Schedule
3.1. Work Schedule
Tentative schedule of pre-trenching works for pipeline relocation at PHE WMO project is
shown in Table 2 below. It is subject to condition of current project schedule and preparation prior to mobilization.
Table 2. Pre-Trenching tentative works schedule by 10m3 GD Greip
Description Quantity Unit 2014
August September October W1 W2 W3 W4 W1 W2 W3 W4 W1 W2 W3 W4
Preparation - -
Mobilization of Dredger and Anchor Boat
1 Trip
Pre Trenching 45,000 m3
Mobilization of Split Barge 1 Trip
Demobilization 1 Trip
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3.2. Work Flow Chart
Illustration about the dredging works sequence shown in Figure 22 below.
Figure 22. Pre-trenching for hard and soft material work sequences.
Shifting to working area
towed by tug boat
Arrive at designated working area then
deploy 4 anchors by anchor boat
4 anchors deployed, shifting
to pre-trench location
Material
Type
Hard Material (UCS>5.0
MPa)
Soft Material
(UCS<5.0MPa)
Direct dredging with light duty
clam shell bucket 10m3
Install 25T chisel
breaker
Chiseling 1st layer (seabed to
-2.5m from seabed)
Complete chiseling 1st layer then change
bucket to heavy duty clam shell bucket 4m3
Dredging 1st layer hard material by 4m
3 clam shell
bucket, load material to split barge or side casting
Complete dredging 1st layer, Install 25T chisel
breaker, shifting for chiseling 2nd
layer
Chiseling 2nd
layer (-2.5 from
seabed to -5.0m from seabed)
Complete chiseling 2nd
layer then change
bucket to heavy duty clam shell bucket 4m3
Dredging 2nd
layer hard material by 4m3 clam shell
bucket, load material to split barge or side casting
Dredging soft material by 10m3 clam shell bucket,
placement material by side casting method
Complete pre-trenching
scope
Material flowing
back to trench
No
Yes
Load the material to split
barge then dredger carry out
anchor positioning to the
designated dumping location
Bathymetric Survey
Yes
Bathymetric survey result indicate that
bottom trench design level achieved
No
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4. Work Methodology
4.1. Preparation Works
4.1.1. Installation of Base Station
Base station for correction of Greip and survey boat GPS will install at Karang Jamuang
Island. Universal Transverse Mercator (UTM) coordinate of our base station at Karang Jamuang Island is mentioned below:
Easting 690919.631
Northing 9233703.524
4.1.2. Pre-Survey for Dredging Works
Bathymetric pre-survey data for this works shall be prepared and conducted before project started. Bathymetric survey shall be performed at all working locations where
associated with this works, include also access route from temporary anchoring location to
designated working location to avoid grounding and provide general view for movement of our pusher boat, anchor boat and for dredger itself.
4.2. Main Works
4.2.1. Positioning System
10m3 grab dredger “Greip” will be utilized for dredging and chiseling works for this pre-trenching scope. Four (4) points mooring system shall be utilized with anchor wire rope.
Anchors will be deployed by anchor boat Takamaru-2.
Pre-trenching work will start from KP 36.5 to KP 36.0, then later will go to KP 37 and
continue pre-trenching works until KP 36.5.
For horizontal control (Positioning), Differential Global Positioning System (DGPS) shall be installed onboard crane barge with full accessories such as Gyro Compass etc., which is
able to achieve 0.3 to 1.0 m accuracy. For vertical control, to determine the dredging level and to avoid over dredge or under dredge, Dredger will use lead sounding method and
also check the marking line which is painted to hoisting wire of clam shell bucket. Base
station for horizontal positioning and tide gauge for vertical control shall be set and installed on land before dredging started.
Since dredging work around Karang jamuang Island will have interface with ship traffic on Alur Pelayaran Barat Surabaya (APBS), Contractor consider to provide 2 personnel pilot
(pandu) from port authority to assist barge movement during pre-trenching work if any interference with other vessel .
4.2.2. Dredging Soft Material
Refer to drawing PHEWMO-PPP-W-PLR-5004, in pre-trenching section, between KP 37 to KP 36, there are 2 soil investigation test had been conducted. From those soil
investigation results, we have got the conclusion that there are 2 general types of soil. Mostly is soft material which contains silty sand, and hard material which contains coral reef. These
data are based on our references in BH (borehole) OSBH-02 for soft material, and BH OSBH-
01 for hard material. Detail data attached in Appendix I. Summary of soil investigation result is presented in the following table:
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Table 3. Soil investigation result at pre-trenching section (OSBH-01 and OSBH-02)
Reference: Document 007-PTC-PTRI-13-R0
For soft material, Greip 10m3 GD will directly use 10m3 clam shell light duty bucket. At
the time when project commence, for shallow area (-5 to -8), contractor will use side-casting method for disposal of dredging material and for deep area (-8 to -12), dredger will load the
material to the split barge then later will be transported to designated dumping location. Detail procedure of material dumping transportation using split barge could be read in the next
chapter (4.2.5 material dumping transportation). For side casting method, dredger should ensure that material will be placed far enough from top slope of trenching area (around 8 to
15m depends on boom angle) to avoid the dredging material from flowing back to the trench.
Illustration of pre-trenching work and side-casting method can be seen in Figure 24, Figure 25, and Figure 28 below.
4.2.3. Dredging Hard Material
If we encounter material which couldn’t grab by clam shell bucket, first of all, we
would like to conduct pre-bathymetric survey to calculate volume and area. For this hard
material (coral reef, UCS>5MPa), we shall need to give additional treatment with chiseling work. Chiseling or breaking the hard material will use 25T chisel breaker. Photo of Greip’s
chisel breaker could be seen in Figure 15 above.
As explained at the work sequences, for chiseling work, we will divide trench into 2
layers. 1st layer is the thickness from original seabed to -2.5m from seabed level. And 2nd layer
is layer between -2.5m from original seabed to bottom of trench (-5.0m from seabed). For hard material, we will follow the original trench design with the slope 1:1. Illustration of hard
material cross section which divided into 2 layers is shown in Figure 23 below.
Figure 23. Hard material cross section
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At first, Greip will dismantle her clam shell bucket and then install the chisel breaker.
She will carry out chiseling work of 1st layer hard material until complete and then dismantle the chisel breaker to install 4m3 heavy duty bucket. After heavy duty bucket installed, she will
dredge all hard material on 1st layer along the hard material route before shift back to
commence point and carry out the chiseling work for the 2nd layer. Next sequence is repeat the chiseling and dredging work for 1st layer hard material.
Illustration of chiseling and dredging work for hard material 1st layer can be seen in Figure 29 and Figure 30. And Illustration of chiseling and dredging work for hard material 2nd
layer can be seen in Figure 31 and Figure 32.
For method of disposal dredging material, Greip will use exactly same method with soft material, which is side casting method for shallow area and load the material to the split barge
for deep area. During side casting, she also should ensure that material will be placed far enough from top slope of trenching area (around 8 to 15m depends on the boom angle) to
avoid the dredging material from flowing back to the trench.
4.2.4. Dredging Production and Monitoring
Productivity of Grab Dredger is always based on the type of dredging material. As we
know before, there are 2 types of material, soft material and hard material. Based on our record, average productivity of Greip for dredging soft material using 10m3 clam shell bucket is
6,000-8,000m3 per day. Whereas average productivity of Greip for dredging hard material using 4m3 clam shell bucket is 3,000-4,000m3 per day. Need to be considered, productivity for
dredging hard material is not include the chiseling work. For chiseling, productivity is almost
same with dredging, which is 3,000m3 per day. So with those value, if combine, dredging and chiseling, Greip’s productivity for hard material (for UCS >5.0 MPa) is 1,500-2,000m3.
For monitoring work, every 100m progress, east marine will perform the progress survey using survey boat. This progress survey will be conducted with 10m interval and 1 long
line for long section. Purpose of bathymetric progress survey is to obtain the actual level of the
trench. With that information, we could do the evaluation to improve quality of dredging result.
4.2.5. Material Dumping Transportation
To anticipate material flowing back to trench, contractor will provide 1 split barge named MT-18 which has 1000m3 cargo hold capacity. Dredger will load dredging material to
split barge and then after fully loaded, dredger will carry out by anchor positioning to the
designated dumping location. Dredger captain shall ensure that anchors deployed far enough to accommodate this movement. Illustration of material dumping transportation using this
method could be seen in Figure 26 and Figure 27.
Detail arrangement for disposal of dredging material explained at “Appendix-3
Disposal material sequence with or without split barge”. Illustration of disposal material result could be seen at “Appendix-3 Dumping simulation at KP 36 - KP 36.5 and dumping simulation
at KP 37 - KP 36.5”.
For arrangement of dumping location at this PHE WMO project, the material shall not be dumped to waterways or channel, also could not be dumped along the pipeline route.
Materials shall be dumped with the distance minimum 50m from the pipeline. East Marine has to ensure the material placed in accordance with the proper arrangement to avoid any hazard
in future. For this PHE WMO project, because west side of the trench is outer channel of
shipping line, so proposed dumping location is 50m from trench to east direction or to Karang Jamuang Island direction.
In case dumping area at the east side of the trench is shallow area, especially at KP 37.0 until KP 36.90, Greip will choose new designated dumping area at the north or north-west
side of trench. This arrangement based on pre-survey data that in the north or north-west side of Karang Jamuang Island is deep area which has elevation more than -10m.
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Prior to carry out this special dumping job, contractor will always make coordination
with pilotage who stay onboard Greip and certainly has to get approval from them as well. This arrangement also valid for side casting method.
4.3. Closing Works
4.3.1. Post-Survey
Bathymetric post-survey for this work shall be conducted after pre-trenching work
complete. Bathymetric post-survey shall be performed to all area along the pre-trenching section, which is start from KP 36 to KP 37. Bathymetric data at the boundary or intersection
between pre-trenching area and post trenching area shall be obtained as well. Furthermore,
post trenching survey shall be conducted to all area of dumping location, to provide general view of bathymetric information for pipe laying installation (PLB) or other purpose in future.
Purpose of bathymetric survey is to obtain the actual level of the trench. Bathymetric post-survey will be performed per 20m grid for cross section and 1 long line at the center of
trench for long section. The design level of bottom trench shall be fulfilled by East Marine as
sub-contractor, which minimum level after dredged is -4.5m from the original seabed or -4.0m from top of pipe. This requirement is refer to drawing no PHEWMO-PPP-W-PLD-5003-
REV.0. If there are still have several high spot, dredger should shift back to those high spot area and carry out the dredging work one more time until the design level achieved.
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Figure 24. Illustration of pre-trenching work by Greip 10m3 Grab Dredger (soft material)
50T HOOKAUX; HOST
B.L
UPP. DK.C.LUPP. DK.C.L
2 4 6 8 10 12 14 16 18 20 22 24 26 28AP 1 3
STBD VIEW
GREIP
Existing Seabed (Soft Material)
Final Pre-Trenching Target Elevation
-5.0 m from Original Seabed
Final Pre-Trenching Target Elevation
-5.0 m from Original Seabed
Seabed Level
Various -6 to -11
10 M LIGHT DUTY BUCKET3
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Figure 25. Illustration of dredging using side casting method using Greip 10m3 GD for PHE WMO Project
Slope (1:3) for soft material
Slope (1:3) for soft material
Slope (1:3) for soft material
Slope (1:3) for soft material
Bottom Trench (4m Width)
15 m
4 m
Placing Material by Side Casting Method
Bottom Trench (4m Width)
GREIP
15 m
15 m
4 m
15 m
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Figure 26. Illustration of dumping dredging material by anchor positioning
Slope 1:3
Slope 1:3Slope 1:3
Slope 1:3
Minimum 50m
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Figure 27. Illustration of dumping dredging material by anchor positioning (cross section)
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Figure 28. Illustration of dumping dredging material by side casting (cross section)
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Figure 29. Illustration of chiseling using chisel breaker for 1st layer of hard material
Existing Seabed (Hard Material)
50T HOOKAUX; HOST
B.L
UPP. DK.C.LUPP. DK.C.L
2 4 6 8 10 12 14 16 18 20 22 24 26 28AP 1 3
STBD VIEW
25 TON CHISEL BREAKER
1st Layer
Hard Material
Final Pre-Trenching Target Elevation
-5.0 m from Original Seabed
Final Pre-Trenching Target Elevation
-5.0 m from Original Seabed
Seabed Level
Various -6 to -111st Layer
Hard Material
GREIP
-2.5 m from Existing Seabed -2.5 m from Existing Seabed2nd Layer -2.5 m Thickness
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Figure 30. Illustration of dredging hard material 1st layer using 4m3 heavy duty bucket
Existing Seabed
(Hard Material)
Final Pre-Trenching Target Elevation
-5.0 m from Original Seabed
Seabed Level
Various -6 to -11
Final Pre-Trenching Target Elevation
-5.0 m from Original Seabed
50T HOOKAUX; HOST
4 M HEAVY DUTY BUCKET3
B.L
UPP. DK.C.LUPP. DK.C.L
2 4 6 8 10 12 14 16 18 20 22 24 26 28AP 1 3
STBD VIEW
Existing Seabed
(Hard Material)
1st Layer
Hard Material
1st Layer
Hard Material
GREIP
-2.5 m from Existing Seabed -2.5 m from Existing Seabed2nd Layer -2.5 m Thickness
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Figure 31. Illustration of chiseling using chisel breaker for 2nd layer of hard material
Existing Seabed (Hard Material)
50T HOOKAUX; HOST
B.L
UPP. DK.C.LUPP. DK.C.L
2 4 6 8 10 12 14 16 18 20 22 24 26 28AP 1 3
STBD VIEW
25 TON CHISEL HAMMER
2nd Layer
Hard Material
Final Pre-Trenching Target Elevation
-5.0 m from Original Seabed
1st Layer Completely Dredged2nd Layer
Hard Material
GREIP
Final Pre-Trenching Target Elevation
-5.0 m from Original Seabed
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Figure 32. Illustration of dredging hard material 2nd layer using 4m3 heavy duty bucket
(Hard Material)
50T HOOKAUX; HOST
B.L
UPP. DK.C.LUPP. DK.C.L
2 4 6 8 10 12 14 16 18 20 22 24 26 28AP 1 3
STBD VIEW
(Hard Material)
2nd Layer
Hard Material 2nd Layer
Hard Material
Final Pre-Trenching Target Elevation
-5.0 m from Original Seabed
Final Pre-Trenching Target Elevation
-5.0 m from Original Seabed
4 M HEAVY DUTY BUCKET3
GREIP
1st Layer Completely Dredged
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4.4. Contingency Plan
4.4.1. Non-Working Condition
For this pre-trenching work PHE WMO project, there is non-working condition which require all pre-trenching activity to be stopped, the table could be seen in Table 4 below.
Table 4. Non-working condition
Kind Standard
Wind Velocity More than 10 m/s (in average 10 minutes)
Precipitation More than 10 mm/h
Lightning When see the lightning
Wave height More than 1.5 m
Visibility Less than 1 km
Beside non-working condition, there is also an extreme condition which needs to carry out the
evacuation, explained in Table 5 below:
Table 5. Evacuation condition
Kind Extreme
Wind Velocity More than 20 m/s (in average 5 minutes)
Wave height More than 2.5 m
Current Velocity More than 5 knots (in average 5 minutes)
4.4.2. Shelter Area
Shelter area of Greip group when the extreme weather occurred is Karang Jamuang Island. Fortunately, Karang Jamuang Island is located very near with the pre-trenching area
which is between KP 37 to KP 36. During extreme weather condition, Greip group will go to
calm water nearby the island. Greip and Toak-7 will deploy their emergency anchor and 2 (two) spuds as well after arrive at the shelter point. Illustration of shelter point for East Marine
spread when inclement weather occurred could be seen in the Figure 33 below.
Figure 33. Illustration of shelter area for dredging equipment during extreme weather condition