On-bottom Stability Analysis

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REVISION CONTROL SHEET

REV.NO DATE SECTION NO. SUMMARY OF CHANGES

A 4/12/13 4.1 Table Revised A 4/12/13 5.2 Formulas Added A 4/12/13 5.8 Text Added A 4/12/13 6.1 Text Added A 4/12/13 6.3 Text Added A 4/12/13 7 References Added

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TABLE OF CONTENTS

1.0 INTRODUCTION ... 4

1.1 General ... 4

1.2 Scope ... 5

2.0 UNITS AND ABBREVIATIONS ... 6

2.1 System of Units ... 6

2.2 Abbreviations ... 6

3.0 SUMMARY AND CONCLUSION ... 7

3.1 Summary ... 7 3.2 Conclusions ... 8 4.0 DESIGN DATA ... 9 4.1 Pipeline Properties ... 9 4.2 Pipeline Route ... 10 4.3 Environmental Data ... 11

4.3.1 Water Depth and Water Level ... 11

4.3.2 Seawater Properties ... 13

4.3.3 Wave and Current Data - Offshore ... 13

4.3.4 Wave and Current Data – Nearshore ... 14

4.4 Soil Properties ... 15

5.0 DESIGN METHODOLOGY ... 17

5.1 General ... 17

5.2 Lateral Stability ... 17

5.2.1 Generalized Lateral Stability Method... 18

5.3 Vertical Stability in Water ... 18

5.4 Vertical Stability of the pipeline in soil at liquefied phase ... 19

5.5 Design Loads and Assumptions ... 19

5.6 Nearshore Waves Transformation ... 21

5.7 Trenched section at onshore ... 22

5.8 Trenched Sections at Shore Approach ... 23

6.0 RESULTS AND CONCLUSIONS ... 24

6.1 Results ... 24

6.2 Trenching at Onshore Section ... 26

6.3 Trenching at Shore Approach ... 26

7.0 REFERENCES ... 27

APPENDIX A – TRENCH DEPTH AT ONSHORE SECTION ... 28

APPENDIX B – NEARSHORE WAVE CALCULATIONS ... 29

APPENDIX C- VERTICAL STABILITY CHECK IN LIQUIEFIED SOIL ... 36

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1.0

INTRODUCTION

1.1 General

Shell Gabon is operating and producing oil from numerous fields located in the western part of Gabon. Crude is treated and exported from the Gamba Terminal to tankers through a 30 inch offshore export line connected to a SBM via a PLEM and 2 x 16 inch floating hose strings (risers).

The total length of the existing export line is about 10.7km from the export pump in Gamba terminal to a PLEM (1.3km located onshore and 9.4km located offshore).

Figure 1-1 Project Location

Shell Gabon intends to replace the existing export pipeline. Zeetech B.V. has been awarded by Shell to perform a concept replacement study and Front End Engineering Design (FEED) for the selected concept.

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This report presents the results of the on-bottom stability analysis performed for the 22 inch Gamba Export Dual pipelines, in accordance with Shell DEP 31.40.00.10 (Ref. 1) and DNV RP F-109 (Ref. 2) using DNV STABLELINES software for the proposed pipeline layout.

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2.0

UNITS AND ABBREVIATIONS

2.1 System of Units

In accordance with Shell DEP 00.00.20.10. (Ref. 1), the International System (SI) of units is adopted as the main system of units unless noted otherwise.

2.2 Abbreviations

CWC Concrete Weight Coating DEP Design Engineering Practices DNV Det Norsk Veritas

FEED Front End Engineering Design KP Kilometer Point

LAT MSL

Lowest Astronomical Tide Mean Sea level

PLEM Pipeline End Manifold

RP Recommended Practice

WD Water Depth w.r.t. With Relative To

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3.0

SUMMARY AND CONCLUSION

3.1 Summary

The required concrete weight coating thickness to ensure on-bottom stability of the pipeline (vertical and lateral) against environmental loading, due to waves and currents, has been calculated for one individual 22” Gamba pipeline in accordance with the applicable codes and subsequent defined load cases. The stability analysis has been considered for both installation and operation phases.

Analysis has been performed by using DNV StableLine Software and allowing a lateral displacement up to half of the pipe diameter.

The on- bottom stability of the pipeline under following cases has been assessed:

- Installation empty – 1 year wave + 10 year current or 10 year wave + 1 year current

- Operation – 100 year wave + 10 year current or 10 year wave + 100 year current.

The critical loading condition to define the required concrete thickness is during installation phase and in empty condition.

Refraction theory has been applied for the shore approach sections to determine the appropriate wave height and approach angle to the pipeline.

Since the two export pipelines will be routed parallel in close distance, the environmental data will be quite similar. Therefore stability results of one pipeline shall be applicable also for the other line.

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3.2 Conclusions

Selected concrete weight coating thickness along the pipeline route are shown in Table 3-1, based on the results of Section 6.0. The selected thicknesses are based on the installation case which is the critical load case to assess the stability of the pipeline for 25 years design life.

Table 3-1, Selected Concrete Coating Thickness along the Route

Inst 0 1.07 1.175 40 1 1.175 1.194 41 2 1.194 1.207 50 3 1.207 1.220 61 4 1.220 1.236 71 5 1.236 1.275 65 6 1.275 1.700 54 8 1.700 2.280 47 10 2.280 5.600 44 15 5.600 8.500 40 20 8.500 10.600 63 23 10.600 63 Remarks Pre trenched/ cofferdam Exposed 65 CWC required

from Stablelines selected concrete thickness (mm) min WD (m) Approximate Starting Point (KP) Approximate End Point (KP)

A concrete coating thickness of 50mm has been selected for the onshore section based on floatation prevention in case of liquefaction of the surrounding soil.

The pipeline route is to be pre-trenched from the starting point at Gamba Terminal to the water depth of 5m and will be backfilled.

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All design data to be considered in the on-bottom stability calculations for both 22in Gamba export lines, as presented in the following subsections, have been obtained from the Pipeline Design Basis (Ref. 9).

4.1 Pipeline Properties

The pipeline properties to be used in the design are presented in Table 4-1 as below

Table 4-1, Pipeline Properties

Descriptions Units 22in Gamba Export Lines

Outside Diameter inch 22

Selected Pipeline Wall thickness mm 9.5 Material Grade of Linepipe - API 5L X65 Internal Corrosion Allowance mm 3 Density of Steel Pipe kg/m3 7850 Minimum Density of Product* kg/m3 850 Concrete Coating Density kg/m3 3040 Anti-Corrosion Coating Material 3 layers Polyethylene Anti-Corrosion Coating Thickness mm 3.2 Anti-Corrosion Coating Density kg/m3 950

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4.2 Pipeline Route

The export pipeline length is approximately 10.7km; with an onshore length of approximately 1.3 km.

The pipeline starts from the export pump at onshore Gumba terminal and then heading towards south-west to a subsea PLEM.

In accordance with Ref. 5, the proposed dual pipelines will be routed toward South-West with the approximate angle of heading of 225 deg from North. Figure 4-1 shows the layout of the dual pipeline concept and the route data are presented in Table 4-2

Table 4-2, Pipeline Route Data

Item Remark

Initial Point Export Pump at Onshore

Terminal

Final Point Subsea PLEM

Approximate onshore Length (km) 1.3

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Figure 4-1, Dual Pipeline Concept Layout

4.3 Environmental Data

4.3.1 Water Depth and Water Level

The selected pipeline route has been divided into two sections for on-bottom stability analysis i.e. offshore and shore approach sections. Table 4-3 shows maximum and minimum water depth (relative to LAT) along the route used in the analysis.

The seabed profile along the existing 30”pipeline is shown in Figure 4-2 . (Ref 9)

The 22inch dual pipeline system is in close proximity to the existing 30 inch pipeline route; hence bathymetry data can be assumed to be identical for the purpose of the on- bottom stability analysis.

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Figure 4-2, Seabed profile along the Existing Pipeline Route

Table 4-3, Water Depth relative to LAT

Item

Depth (m)

Approximate

Location

(kp)

Minimum Water Depth 0 1.07

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4.3.2 Seawater Properties

The seawater density of 1026 kg/m3 is used in the analysis.

4.3.3 Wave and Current Data - Offshore

Wave and current data are considered in the on-bottom stability analysis have been extracted from Ref. 6 and are given in Table 4-4 and Table 4-5.

Table 4-4: Wave Data – Offshore (25m WD)

Parameter Unit

Return Period

1 10 100

Significant Wave Height (Hs) m 2.01 2.46 2.91

3-hourly Maximum Wave Height (Hmax)

m 4.0 4.8 5.7

Spectral Peak Period (Tp) s 13.0 13.9 14.3

Associated Maximum Period (Tm) s 10.8 11.6 11.9

Mean Wave Direction (from North) deg 187-215

Based on Reference 6, the waves are swell dominated therefore the highest value of spectral spreading factor has been applied in the Stablelines input (Ref.7)

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Table 4-5: Current Data – Offshore (20-25m WD)

Current Velocity Unit

Return Period

1 10 100

Mean current speed at 24m above seabed (m/s) 1.13 1.41 1.73 Mean current speed at 20m above seabed (m/s) 1.03 1.29 1.58 Mean current speed at 15m above seabed (m/s) 0.89 1.12 1.36 Mean current speed at 10m above seabed (m/s) 0.73 0.91 1.11 Mean current speed at 5m above seabed (m/s) 0.52 0.65 0.79 Mean current speed at 1m above seabed (m/s) 0.23 0.29 0.35

Current Direction deg Perpendicular to the pipe

4.3.4 Wave and Current Data – Nearshore

The significant wave height being a prime parameter to define a seastate has been used in the analysis.

As waves propagate from the open ocean over the continental shelf towards shore, they are affected by the seabed bathymetry and experience shoaling, refraction and breaking phenomena. The wave’s transformation towards shore is determined in accordance with Coastal Engineering Manual (Ref. 4) and is explained in Section 5.6 Table 4-6 shows the wave data to be used in the analysis considering near shore effects.

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Table 4-6, Wave and Current Data, From Reference Depth to the Shore Approach

1-yr 10-yr 100-yr 1-yr 10-yr 100-yr 1-yr 10-yr 100-yr 0 1 0.78 0.78 0.78 13 13.9 14.3 0.23 0.29 0.35 214 208.2 214.2 2 1.56 1.56 1.56 13 13.9 14.3 0.23 0.29 0.35 214 205.9 214.3 3 2.34 2.34 2.34 13 13.9 14.3 0.23 0.29 0.35 214 204.1 214.4 4 2.62 3.12 3.12 13 13.9 14.3 0.23 0.29 0.35 214 202.6 214.4 5 2.49 3.14 3.77 13 13.9 14.3 0.23 0.29 0.35 214 201.2 214.5 6 2.40 3.02 3.62 13 13.9 14.3 0.23 0.29 0.35 209 200.0 214.5 8 2.26 2.84 3.40 13 13.9 14.3 0.23 0.29 0.35 209 198.0 214.6 10 2.16 2.71 3.25 13 13.9 14.3 0.23 0.29 0.35 209 196.2 214.7 15 2.01 2.52 3.01 13 13.9 14.3 0.23 0.29 0.35 209 192.5 214.8 20 1.93 2.41 2.87 13 13.9 14.3 0.23 0.29 0.35 254 189.0 214.9 Current Speed, Uc (m/s) Pipe angle wrt North (deg) Wave Angle wrt North (deg) Min WD (m)

Wave Height, Hs (m) Peak Period, Tp (s)

4.4 Soil Properties

Based on the Reference 5, the majority of the seabed along the pipeline route consists of sandy parts. Since no detailed soil properties have been provided, the top layer of the soil has been assumed as fine sand with the minimum roughness as a conservative assumption (Ref.2). The assumed soil data is summarized in Table 4-10. (Ref.8)

A more detailed evaluation of the soil parameters is to be performed during detailed design stage.

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Table 4-1: Soil Properties

Soil Description Unit

Value

Submerged Unit Weight of Soil (γ’s) kN/m3 9 Dry Unit Weight of Soil (γs ) kN/m3 19 Presumed unit weight of the liquefied

soil

kN/m3 17

Bottom Roughness (z0) m 1E-05 Grain Size (d50) mm 0.25

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5.0

DESIGN METHODOLOGY

5.1 General

The details of on-bottom stability design methodology for both lateral and vertical stability is presented in the following sections.

5.2 Lateral Stability

The pipeline lateral stability analysis is performed using the Generalized Lateral Stability Method (half a pipe diameter displacement) as stated in Section 3.5 of DNV RP F109 (Ref. 2). However, if any of the following conditions are met, then the Absolute Lateral Static Stability Method as per Section 3.6 of DNV RP F109 (Ref. 2) shall be used:

 Cases dominated by current.  sg < 1.05, sg > 3

 At deep waters, where the K value is very small and the M value is very large.  N > 0.024 for clay and N > 0.048 for sand

 Stiff clay soils, GC > 2.78

Where:

sg = Pipe specific density, as defined in Section 1.5.1 of DNV RP F109

K = Significant Keulegan-Carpenter number = Us. Tu/ D , as defined in Section 1.5.1 of DNV RP F109

M = Steady to oscillatory velocity ratio for design spectrum V/Us , as defined in Section

1.5.1of DNV RP F109

N = Spectral acceleration factor, as defined in Section 1.5.1 of DNV RP F109 GC = Soil (clay) strength parameter, as defined in Section 1.5.1 of DNV RP F109

A design based on absolute stability criteria will lead to high concrete coating thicknesses and consequently a very heavy pipe. Therefore the generalized lateral

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(Half a pipe diameter displacement) has been applied in this analysis as the governing criterion of on-bottom stability of the pipe.

5.2.1 Generalized Lateral Stability Method

The minimum required concrete weight coating thickness for allowing the pipe to half of its diameter lateral displacement, is calculated in accordance with the following formulas:

Where:

LY = Significant weight parameter, as defined in Section 1.5.1 of DNV RP F109

Lstable = Minimum pipe weight required to obtain a virtually stable pipe, as defined in

Appendix A of DNV RP F109

L0.5 = Minimum pipe weight required to limit the lateral displacement to half of the pipe

diameter, as defined in Appendix A of DNV RP F109

τ

= Number of oscillations in the design bottom velocity spectrum, as defined in Section 1.5.2 of DNV RP F109

5.3 Vertical Stability in Water

In order to avoid floatation in water, the submerged weight of the pipeline shall meet the following criterion. (Ref 2)

Where:

γ

w = Safety factor 1.1 if a sufficiently low probability of negative buoyancy is not

documented

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5.4 Vertical Stability of the pipeline in soil at liquefied phase

Buried sections of the pipeline are to be checked for the possible floatation in case of liquefaction of the surrounding soil mass.

Upward floatation of a pipe is prevented if the following criterion is satisfied:

Wpipe Where:

Wpipe = weight of the pipe (including contents) (N/m) B = Buoyancy Force (N/m)

ρsoil = Density of the liquefied soil (kg/m3)

Dtot = Outside diameter of the pipe including coatings (m) g = Gravitational acceleration (m/s2)

The vertical stability of the pipe in soil at liquefied phase has been checked based on the selected CWC thickness for the onshore and offshore sections. For details of the analysis reference is made to Appendix C.

5.5 Design Loads and Assumptions

The load combinations to be considered in the pipeline on-bottom stability analysis for both lateral and vertical stability are summarized as follows. The load combination which result in a higher CWC thickness should be selected.

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Table 5-1: Design Loads for Lateral on-bottom stability analysis Design Load Design Condition Installation Operation Environmental Load Return Period

10-yr Wave + 1-yr Current & 1-yr Wave + 10-yr Current

100-yr Wave + 10-yr Current & 10-yr Wave + 100-yr Current Internal Product Empty Min. Product Density

The required design data have been provided in Section 4.3.

The pipeline route has been divided in different sections and the minimum water depth at each section has been considered to calculate the required concrete weight coating thickness.

Table 5-2 shows the minimum water depth at these sections with the corresponding approximate KP.

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Table 5-2, Minimum Water Depth along the Pipeline Route Approximate Starting Point (KP) Approximate End Point (KP) Min WD (m) 1.07 1.175 0 1.175 1.194 1 1.194 1.207 2 1.207 1.220 3 1.220 1.236 4 1.236 1.275 5 1.275 1.700 6 1.700 2.280 8 2.280 5.600 10 5.600 8.500 15 8.500 10.600 20 10.600 23

5.6 Nearshore Waves Transformation

When waves propagate from deep to shallow waters the underlying bathymetry causes the wave crest to turn to follow the seabed contours (i.e. parallel to the contours) a process known as “refraction”. As the pipelines are routed almost perpendicular to the shoreline the angle of incidence between the wave and pipelines reduces, until it reaches approximately zero at the shore.

The reduction in angle of incidence reduces the wave induced hydrodynamic forces acting on the pipe and subsequent the required concrete coating thickness.

In addition, the change in water depth produces a corresponding change in wave speed and wave group celerity leading to a change in the wave’s energy and height (a process known as “shoaling”). The wave speed and wave length decrease in shallow

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water, therefore the energy per unit area of the wave increases, and hence the wave height. The wave period remains the same during shoaling process.

The waves increase in steepness until they reach a limit after which the waves begin to “break”. The refracted/shoaled wave height in a specific water depth can only reach a maximum height equivalent to the breaking wave height for that water depth.

The approach used to determine the near shore wave parameters (through the transformation of a wave approaching from deep water to shore) is outlined in the Coastal Engineering Manual (Reference 4).

By taking into account shoaling and refraction effect, the wave height has been calculated from a depth of 25m (as the deep water reference wave) towards the shore line. The results are presented in Section 4.3.4 . A sample of the calculations is presented in Appendix B for the 1 year significant wave height and wave direction of 187 degree.

Table 5-3, Deep Water Reference Wave Characteristics (WD=25m)

Parameter Unit

Return Period

1 10 100

Significant Wave Height (Hs) m 2.01 2.46 2.91

Spectral Peak Period (Tp) sec 13.0 13.9 14.3

Mean Wave Direction (from North) deg 187-215

5.7 Trenched section at onshore

The pipeline route is pre-trenched from the starting point at Gamba Terminal and should be continued to the breaker zone. As the new pipelines will be installed at the vicinity of the existing 30” pipeline, the approximate required cover on top of the pipe

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can be assumed to be similar to the one of the existing pipelines i.e. a cover depth of 0.9 meters. Based on Reference 10, the burial depth of the 22” pipelines has been presented in Appendix A.

5.8 Trenched Sections at Shore Approach

Due to high hydrodynamic loads at the shore approaches, the required concrete weight coating thickness to ensure a stable pipeline are high.

By installing the pipeline in a pre-dredged trench and decrease the exposure of the pipe, the required CWC thickness will reduce. The pre-dredged trench should extend up to the breaker zone.

The depth at which a single wave (maximum wave) breaks is shown in the Table 5-4. For the installation phase, the breaker zone has been considered up to the depth of 5m. More explanation is provided in Section 6.1

A sample of calculating the breaker zone has been provided in Appendix B.

Table 5-4, Depth of Breaking Wave Depth of

Breaking Wave (m)

Return Period

1 Year 10 Year 100 Year

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6.0

RESULTS AND CONCLUSIONS

6.1 Results

Based on the provided design data (Section 4.0) and environmental data which are summarized in Table 6-1 , on bottom stability of the 22”pipeline has been analyzed in accordance with the applicable codes and standards.

Table 6-1, Environmental Load Cases during Operation and Installation Phase

1-yr 10-yr 1-yr 10-yr 10-yr 100-yr

1 1.175 1.194 0.78 0.78 13 13.9 0.29 0.35 214 208.2 214.2 2 1.194 1.207 1.56 1.56 13 13.9 0.29 0.35 214 205.9 214.3 3 1.207 1.220 2.34 2.34 13 13.9 0.29 0.35 214 204.1 214.4 4 1.220 1.236 2.62 3.12 13 13.9 0.29 0.35 214 202.6 214.4 5 1.236 1.275 2.49 3.14 13 13.9 0.29 0.35 214 201.2 214.5 6 1.275 1.700 2.40 3.02 13 13.9 0.29 0.35 209 200.0 214.5 8 1.700 2.280 2.26 2.84 13 13.9 0.29 0.35 209 198.0 214.6 10 2.280 5.600 2.16 2.71 13 13.9 0.29 0.35 209 196.2 214.7 15 5.600 8.500 2.01 2.52 13 13.9 0.29 0.35 209 192.5 214.8 20 8.500 10.600 1.93 2.41 13 13.9 0.29 0.35 254 189.0 214.9 Peak Period, Tp (s) Installation Operation Current Speed, Uc (m/s) Pipe angle wrt North (deg) Wave Angle wrt North (deg) Wave Height, Hs (m) Approximate End Point (KP) Approximate Starting Point (KP) Min WD (m)

Table 6-2 represents the required and selected CWC thickness along the route for installation and operation cases. As shown, the empty pipe during the installation phase is more unstable. Therefore the installation case is the governing case from a pipeline stability point of view.

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Table 6-2, Required and Selected CWC Thickness along the Route Inst Ops 0 1.07 1.175 40 40 1 1.175 1.194 41 0 2 1.194 1.207 50 0 3 1.207 1.220 61 7 4 1.220 1.236 71 18 5 1.236 1.275 65 25 6 1.275 1.700 54 9 8 1.700 2.280 47 0 10 2.280 5.600 44 0 15 5.600 8.500 40 0 20 8.500 10.600 63 16 25 10.600 63 15 Remarks 0.5 x D disp. Pre trenched/ cofferdam Exposed 65 CWC required selected concrete thickness (mm) min WD (m) Approximate Starting Point (KP) Approximate End Point (KP)

A concrete coating thickness of 50mm has been selected from KP 0.0 to KP 1.07, based on the floatation prevention in case of liquefaction of the surrounding soil. (Appendix C)

The concrete weight coating thickness has been selected based on the results of the stability analysis and by considering the constructability and logistic point of view. Therefore the thickness of 65mm has been taken along the pipeline at the offshore section.

The breaker zone has been regarded up to the depth of 5m.

Considering a pre-dredged trench from the Gamba Terminal up to the breaker zone, and also constructing a cofferdam from the shoreline along the trench, will result to less exposure of the pipeline to hydrodynamic loads during installation. Consequently the thickness of 65mm will be adequate for stability of the shore approach sections up to the depth of 5m. Moreover the selected thickness will be sufficient to provide the stability of the pipeline up to the calculated breaker zone at water depth of 5.8 meter (Table 5-4). Therefore considering the breaker zone up to the water depth of 5m will result to less extension of the trench and cofferdam.

Table 6-3 shows the pipeline submerged weight with different contents.

The results of the program for the considered sections and load conditions can be found in Appendix D.

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Table 6-3, Pipe weight with selected CWC thickness

Empty Water Filled Product Filled

65 1313 3618 3223

Submerged Weight of the Pipe (N/m) Selected CWC

thickness (mm)

6.2 Trenching at Onshore Section

The pipeline route should be pre- trenched from the Gamba Terminal to the breaker zone as it was discussed in Section 5.7. The approximate cover depth of 0.9meters should be provided on top of the pipe. (Appendix A)

6.3 Trenching at Shore Approach

At the shore approach the pipeline will be pulled into a pre-dredged trench. The trench must be extended from Gamba Terminal up to the depth of 5m, as was explained in Section 5.8 and 6.1, to protect the pipeline against breaking waves. In order to prevent the backfilling of the pre-dredged trench, a sheet piled cofferdam is to be constructed from the shore line to the depth of 5m.

The length of the cofferdam is approximately 170 m. Based on the existing 30“ pipeline and also Ref 11. the minimum required cover depth on top of the pipe in the offshore section can be considered about 0.9 meters. (Appendix A).

According to Ref. 12, along the cofferdam the trench width will be kept 5m from a constructability point of view.

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7.0

REFERENCES

1- Shell DEP 31.40.00.10, Pipeline Engineering (amendments/ supplement to ISO 13623), 2010.

2- DNV-RP-F109, “On-Bottom Stability Design of Submarine Pipelines.” Oct. 2010.Shell DEP 00.00.20.10, The Use of SI Quantities and Units, 2005Design basis

3- Concept Evaluation - Gamba Export Loading Line, Doc.No: Z.100.1. 4- EM 1110-2-1100, “Coastal Engineering Manual (CEM).” U.S Army Corps of

Engineers. 30/04/2002.

5- Pipeline Route, 8207-PR-01, 8207-PR-02, 8207-PR-03, 8207-PR-04 6- Gabon Metocean Geophysical and Environmental data collection, Doc. No:

GSL-08207-GPH-003.

7- DNV-RP- C205, Environmental Conditions and Environmental loads, October 2010

8- DNV RP F105, Free Spanning Pipelines, 2006. 9- Design Basis Doc. No:13027-ER-001

10- Pipe Cover, DW.PL.M.218029.013

11- ABS Subsea Pipeline Guideline, May 2006 12- Routing Report Doc. No: 13027-ER-004

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APPENDIX A – Trench Depth at Onshore Section

Based on Reference 10, the ground level, top of pipe, sheet pile level and bottom of the sheet pile have been extracted.

The breaker zone has been considered up to the depth of 5m to which the cofferdam requires to be extended. KP soil level (w.r.t.m.s.l) top of pipe (w.r.t.m.s.l) cover depth on T.O.P. (m) sheet pile level (m) (w.r.t.m.s.l ) 1.200 2.5 1.6 0.9 1.226 3.6 2.7 0.9 4 -5.8 1.276 -0.2 -1.1 0.9 4 -5.8 1.327 -0.6 -1.5 0.9 4 -7.6 1.366 -1.0 -1.9 0.9 4 -7.6 1.386 -2.0 -2.9 0.9 4 -10.5 1.412 -4.5 -5.4 0.9 4 -10.5 1.428 -4.8 -5.7 0.9 4 -10.5 1.467 -6.0 -6.9 0.9 bottom of the sheet pile (m) (w.r.t.m.s.l) -12 -10 -8 -6 -4 -2 0 2 4 6 1200.0 1250.0 1300.0 1350.0 1400.0 1450.0 1500.0 1550.0 1600.0 Lev el w .r.t m.s .l (m ) KP

soil profile sea level at HAT sheet pile level

Series4 Series5 Series6

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APPENDIX B – Nearshore Wave Calculations

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APPENDIX C- VERTICAL STABILITY CHECK IN LIQUIEFIED SOIL

Wpipe

Buoyancy

Wpipe= Mpipe* g

where:

ρsoil : density of the liquified soil (kg/m3) g : gravitational acceleration (m/s2) Mpipe : mass of the pipe including contents

- for the offshore sections with the CWC of 65mm and content density of 850 kg/m3

Mpipe: 720 kg/m Dtotal: 0.695 m

Unit weight of the liquefied soil: 17000N/m3 Wpipe= 720 * 9.81= 7063.2 N/m

B= 17000 x 1/4x π x 0.695 2 = 6445 N/m Wpipe > B No Floatation Pipe is vertically stable in liquefied soil

- Onshore sections

For the onshore section, the CWC of 50mm has been assumed and checked to meet the floatation criterion in case of soil liquefaction:

Mpipe: 622.6 kg/m Dtotal: 0.665 m

unit weight of the liquefied soil: 17000N/m3 Wpipe= 622.6 * 9.81= 6108 N/m

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