banyu urip project trenching work method statement

East Marine Pte. Ltd. Address: No. 1 Benoi Road Singapore 629875 Tel: (65) 6778 1400 Fax: (65) 6778 6689

BANYU URIP PROJECT, TUBAN - INDONESIA

METHOD STATEMENT

PRE-TRENCHING FOR PIPELINE FOUNDATION

DOCUMENT NUMBER: EM-BU-MS-002-13

REV ISSUE PREPARED BY REVIEWED BY APPROVED BY ISSUE DATE

4 For Method Statement

FMA NS 4-Dec-2013

EAST MARINE PTE. LTD

BANYU URIP PROJECT, TUBAN - INDONESIA METHOD STATEMENT

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NUMBER REV DATE PAGE

PRE-TRENCHING FOR PIPELINE FOUNDATION EM-BU-MS-003-13 4 13 Dec 13 1 of 14

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1. Introduction

1.1. Project Title

The Project is called “Banyu Urip Project, Tuban - Indonesia”

1.2. Indicative Location of Dredging Works for Access

The working area is located in shore of Tuban – East Java– Indonesia. Indicative Location of

working area is as shown on Figure 1 below.

Figure 1. Indicative location of working area.

TUBAN

TRENCHING FOR PIPELINE FOUNDATION BANYU URIP PROJECT



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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. (Sub-Contractor) for dredging works at Banyu Urip Project, located at Tuban –

East Java - Indonesia. The objective is to achieve the required work quality within the project specification and within the time frame.

2. Quantity and Equipment

2.1. Quantity of Dredging

Refer to drawing number IDBE-HF-YDZZZ-EF0114 (attached in Appendix I), within 3m

range of seabed thickness, normal trenching volume for pipeline foundation is 34.5m3/m. Seabed length needs to be excavated is 650m in which started from KP 0.100 to KP 0.750.

Regarding the various thickness of existing seabed per unit length, as shown in drawing

number IDBE-HF-YDZZZ-EF0114, trench volume based on various thicknesses which have been calculated per 100 linear meter. Estimated quantity of dredging volume shown in Table 1

below.

Table 1. Dredging Volume

Trenching for Pipeline Foundation

KP Minimum Trench

Thickness Area per Section

(m2) Length Total Quantity

0.100 – 0.200 3.0 m 45.5 m3/m 100m 4,550 m3

0.200 – 0.300 3.0 m 34.5 m3/m 100m 3,450 m3

0.300 – 0.400 3.0 m 34.5 m3/m 100m 3,450 m3

0.400 – 0.500 3.0 m 34.5 m3/m 100m 3,450 m3

0.500 – 0.600 3.0 m 34.5 m3/m 50 m 3,450 m3

0.500 – 0.600 2.25 m 21.09 m3/m 50 m 2,109 m3

0.700 – 0.750 1.0 m 5.83 m3/m 50 m 292 m3

Total Estimation Volume 20,751 m3

2.2. Equipment

To accomplish above tasks, East Marine will use these marine equipment:

1. 5,0 m3 Excavator Dredger “Rhea” shown on Figure 2 2. 1500 ps Pusher Boat “Tolak-1” shown on Figure 3

3. 10 tons Anchor Boat “Sardine” shown on Figure 4



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Figure 2. 5.0 m3 Excavator Dredger “RHEA”

Figure 3. 1200 ps Pusher Boat “Tolak 1”.



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Figure 4. 10 tons Anchor Boat “Sardine”.

3. Work Schedule

3.1. Work Schedule

Tentative schedule of dredging works for pipeline foundation at Banyu Urip Project shown in

Table 2 below. It is subject to condition of current project schedule.

Table 2. Trenching for pipeline foundation by Rhea 5m3 ED tentative works schedule

Description Quantity Unit 2013 2014

December January Week 1 Week 2 Week 3 Week 4 Week 1 Week 2 Week 3 Week 4

Preparation for Agency - -

Mobilization 1 Trip

Trenching for Pipeline Foundation

20,751 m3

Demobilization 1 Trip



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3.2. Work Flow Chart

Illustration about the dredging works sequence shown in Figure 5 below.

Figure 5. Trench excavation for pipeline foundation works sequence.

4. Work Methodology

4.1. Preparation Works

4.1.1. Pre-Survey for Dredging Works

Bathymetric pre-survey data for this works shall be prepared or provided by client. 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 give general view for movement of our pusher boat and dredger.

4.2. Main Works

4.2.1. Dredging

5m3 Excavator dredger “Rhea” will be used for dredging works for creating the pipeline foundations at Banyu Urip Project. Four (4) points mooring system shall be utilized with anchor

wire rope. Anchors will be deployed by anchor boat “Sardine”. For safety matter, client should provide us the complete data of project area and surrounding area to avoid that our anchors

placed at prohibited location which could creating any damage to the other party.

For restrain the huge force when excavator grabbing the trench material, three (3) spuds will

be released to seabed. Illustration when Rhea 5m3 performs the trenching works for Banyu Urip

Project can be seen in figure 6.

Anchor Shifting

or

Positioning

Dredging by

5m3 Excavator Dredger

“Rhea”

Continue Dredging to Next Area

Survey for Approval of Accomplishment

(Geotindo)



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Figure 6. Illustration of trenching works by Rhea 5m3 Excavator Dredger

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 for avoid over dredge or under dredge, Dredger will use lead sounding method and also

checking the marking line which is painted in the excavator’s arm. Base station for

horizontal positioning and tide gauge for vertical control shall be provided by client. Illustration of GPS which installed in our dredger is shown in Figure 7.

Figure 7. Positioning of dredger to working location at the previous project.

Due to no arrangement for material dumping transportation, this project will use side-casting

method. Refer to drawing number IDBE-HF-YDZZZ-EF0114, depth of some existing seabed

is too shallow for Rhea’s draft (1.5m). After analyzing, this trenching works from KP 0.300

Hyd; Cylinder (Stroke :3000mm)RAIL BASE

25~

25~

25~

W.L

Foundation of Pipeline

Existing Seabed



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going to south (KP 0.100). KP 0.300 is selected because at that point Rhea can get sufficient

depth for works even in extremely low tide condition. From KP 0.300 to KP 0.100, we dredge the trench at the same time with creating access channel to reach more shallow area. In this

case (case 1), Rhea will be positioned exactly in the center line of pipeline foundation trench. After considering the current direction (data provided by client), Rhea will throw the dredging

material to the same way of the current direction. Illustration of this case is shown in Figure 8 below.

Figure 8. Illustration of dredging using side casting method by Rhea 5m3 ED (at shallow area KP 0.100 –

KP 0.300) For KP 0.300 to KP 0.750, because we have sufficient depth for Rhea’s draft, she will use

different method for positioning and placing the trench material. For this case, trench will divide into 2 (two) sections, east side and west side, and dredger has to the positioning

following those 2 sections. Dredger should ensure that material will be placed far enough from

top slope of trenching area (around 12 to 20m depends on arms angle) to avoid the dredging material from flowing back to the trench. Illustration of trenching for pipeline foundation at KP

0.300 to KP 0.750 by Rhea 5m3 ED can be seen Figure 9 below.

W.L

14

32

ARM EXTENSION 1.1m

ARM EXTENSION 1.1m

AR

M E

XT

EN

SIO

N 1

.1m

14 m

18°1

8°

20 m

2 m

3 m

Trench

4 - 12 m

KP 0.100 - KP 0.300

Center Line

Current

Direction

Current

Direction Designated Place for

Trenching Material



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Figure 9. Illustration of dredging using side casting method by Rhea 5m3 ED (at deep area KP 0.300 –

KP 0.750)

4.2.2. Working Sequences

This sub-chapter explains the working sequences since Rhea arrive at project site until the pre-

trenching works accomplished.

W.L

1432

ARM EXTENSION 1.1m

ARM E

XTENSION 1.1m

AR

M E

XT

EN

SIO

N 1

.1m

14 m

18°1

8°

20 m

2 m

3 m

TrenchDesignated Place for

Trenching Material

12 - 20 m

KP 0.300 - KP 0.550

Center Line

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ARM EXTENSION 1.1m

ARM EXTENSION 1.1m

AR

M E

XT

EN

SIO

N 1.1m

14 m

Designated Place for

Trenching Material

12 - 20 m

West Side East Side



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1. From Tanjung Priok, Tolak-1 shall arrive at temporary anchoring point location, this

point will be used for vessel agency matter before start the project.

2. After get the working permit, Tolak-1 will bring Rhea to KP 0.300, and then sardine will

deploy 4 of her anchors to designated points. KP 0.300 was selected because in that area, Rhea can get sufficient depth for working or go in.

3. Deployment of anchors will be assisted by survey boat “Hercules” (Geotindo), so it will minimalize the risk of accidents. This assistance only available during daytime.

4. After 4 anchors deployed, Rhea will positioning to the designated trench area. Rhea

will use 2 types of positioning template, based on east side and west side. Illustration of this action shown in Figure 10 and Figure 11.

5. After Rhea in position, 3 spuds shall be released to seabed to ensure that rhea’s position stable during dredging (Anticipate the huge force when excavators grabbing

the material)

6. Start from KP 0.300, rhea will dredging to rearward, this movement method proves that the dredging result will be clearer and better than if Rhea go forward. This

trenching works will be finish at KP 0.750. Anchor setup need to re-arrange per minimum 100m trenching accomplishment.

7. From KP 0.300 to KP 0.600, Rhea will dredge with 3m thickness from existing seabed.

But from KP 0.600 to KP 0.750, she will dredge variously following the designated elevation due to the transition zone of pipeline. Trench cross section for KP 0.200 to KP

0.750 is shown in Figure 14.

8. Every 50m of the trenching accomplishment, survey boat “Hercules” will do the

progress survey to find out that trench has been formed in accordance with the design or not.

9. After KP 0.300 to KP 0.750 accomplished, Rhea will go forward to KP 0.300. Purpose of

this shifting is in order to dredging KP 0.100 to KP 0.300. Anchors setup will use also Sardine for anchor boat and Hercules for positioning boat.

10. For this section (KP 0.100 to KP 0.300), due to insufficient depth to accommodate Rhea’s draft, she has to always move forward (north to south). It means she will make

the trench at the same time with creating the access for herself. Illustration of the

anchoring arrangement for dredging at this area is shown in Figure 12.

11. Especially for KP (0.100 to KP 0.200), although Rhea creating the access following

trench design, the slope design still can’t accommodate her draft. In consequences, the trench design needs to be revised. Revised trench cross section for KP 0.100 to KP

0.200 is shown in Figure 14. For this section, due to shallowness of seabed level, anchor boat “Sardine” also can’t go in. To anticipate this matter, Rhea will pull all of

front anchors and will use only excavator’s arm and spuds for the movement.

Illustration of this arrangement is shown in Figure 13.



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Figure 10. Illustration of Rhea’s anchoring arrangement when dredging from KP 0.300 to KP 0.750

ARM E XT ENSION 1 .1m

ARM

EXT

ENSIO

N 1

.1m

AR

M E

XT

EN

SIO

N 1

.1m

W.L



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W.L


AR

M E

XT

EN

SION

1.1m



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W.L


ARM

EXT

ENSION

1 .1m

AR

M E

XT

EN

SION

1.1m



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Figure 14. Trench Cross Section for Pre-trenching at Banyu Urip Project

banyu urip project trenching work method statement

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