Coastal Management Coastal Management Progr Program En - PowerPoint PPT Presentation

Dr Dr. . S. NEELAMANI NEELAMANI & & Dr Dr. . K. K. Al-Banaa Al-Banaa Senior R Senior Research Scientist search Scientist Asso Asso. . Research search Scientist Scientist Coastal Management Coastal Management Progr Program En Environment & Life Sciences R vironment & Life Sciences Research Centre search Centre Kuwait Institute for Scientific R it Institute for Scientific Research search KUW KUWAIT IT Email: Email: nsubr nsubram@kisr m@kisr.edu.kw .edu.kw

L H i Sea Water Level d Sea Bed Engineering & e D Hydraulic Properties of the soil Challenging Question: What is the Minimum safe Burial Depth of submarine pipelines?

Typical view of pipeline entering from land to sea

Coastal pipelines during laying

Offshore effluent pipeline deployed and ready for sinking into position (See the concrete collars for stability)

Collar installation onto new offshore effluent outfall pipeline

Typical cross section of a submarine pipeline with different forces acting on it

F B F B F L F L F D F I F D F I e e  s  c  s  c F P F W F W F S F O F C F C F C ELEVATED PIPE LINE 8

F B F B F B F L F L F L F D F I F D F I F D F I  s  c  s  c  s  c F p F p B F W B F s F s F W F s F W F C F C SURFACE or PARTIALLY BURIED PIPELINE 9

SWL SWL F B Sea Bed F V  s  c  s  c F B F V F H F H F W F W F C BURIED PIPELINE F C 10

Armor rock Beam Sea bed Sea bed Pile Ballasted pipe Pile supported pipe Hold down strap Concrete saddle Sea bed Sea bed Screw or Explosive Anchor Pipe Saddle Pipe Anchor Stabilization methods for Exposed submarine pipeline 11

Sea bed Trench wall Natural fill Buried pipe- Natural Fill Jetted in pipe Tremie concrete Armor rock Back fill Bedding Bedding Buried pipe- Armor Cover Buried pipe- Concrete Cover Stabilization Methods for buried Submarine pipeline 12

MINIMUM SAFE BURIAL DEPTH OF SUBMARINE PIPELINE DEPENDS ON  DESIGN WAVE CONDITION  TYPE OF SEA BED MATERIAL  ENVIRONMENTAL IMPACT OF FAILURE  INITIAL COST  MAINTENANCE COST  ZONE  CARGO  RISK

ARABIAN GULF KUWAIT

Sabiya Coastal Soil, (k=0.412 mm/s)

Al-Koot Coastal Soil, (k=0.286 mm/s)

Shuaiba Coastal Soil, (k=1.84 mm/s)

Al-Khiran Coastal Soil, (k=0.652 mm/s)

The Range of input and normalized hydrodynamic parameters Hydrodynamic parameter Range Unit Wave period, T 1.0 – 3.0 with 0.2 s increment s Wave height, H i 0.05 – 0.3m with 0.05 m increment m Water depth at the test section, d 0.45 m m Pipeline burial depth, e 0.0, 0.1, 0.2, 0.3 and 0.4 m Pipe dia, D 0.2 m Wave length at the test section, L 1.491 – 6.089 m Relative depth of burial, e/D 0.0, 0.5, 1.0, 1.5 and 2.0 Unitless H i /d 0.111 – 0.666 Unitless H i /L 0.008 – 0.125 Unitless d/L 0.074 – 0.302 Unitless kd 0.465 – 1.897 Unitless D/L 0.033 – 0.134 Unitless ka 0.103 – 0.422 Unitless Ur 1.22 – 122.07 Unitless U max . SWL 0.121 – 0.828 m/s U max . Bed 0.048 – 0.653 m/s KC 0.241 – 9.798 Unitless R e 9652.54 – 130642.0 Unitless

Soil location Soil Property Unit Sabiya Al-Koot Shuaiba Al-Khiran D 10 mm 0.250 0.410 0.250 0.380 D 30 mm 0.570 0.275 0.570 0.275 D 50 mm 1.450 0.295 0.950 0.310 D 60 mm 1.700 0.310 1.500 0.330 C u Unitless 4.470 1.240 3.660 1.320 C c Unitless 0.500 0.976 0.528 0.917 Bulk density t/m 3 1.560 1.550 1.621 1.792 Saturated density t/m 3 1.850 1.855 1.948 2.130 Submerged density t/m 3 0.811 0.815 0.815 1.090 Porosity Unitless 0.290 0.360 0.908 0.339 Hydraulic Conductivity, k mm/s 0.412 0.286 1.840 0.652 Angle of shearing resistance, Degree 31.460 32.110 32.110 27.010 Φ Coefficient of friction, tan Φ Unitless 0.612 0.628 0.628 0.510 Passive earth pressure Unitless 3.183 3.269 3.269 2.664 coefficient of the soil, K p Remarks - Well Uniformly Almost well Uniformly graded graded graded soil graded

Incident wave Horizontal wave forces on the submarine pipe for e/D = 0.0, 0.5, 1.0, 1.5 and 2.0 respectively (H i = 0.2 m, and T = 2.0 s, Hydraulic conductivity, k=0.652 mm/s).

Vertical wave forces on the submarine pipe for e/D = 0.0, 0.5, 1.0, 1.5 and 2.0 (H i = 0.2 m, and T = 2.0 s, Hydraulic conductivity, k=0.652 mm/s).

The locus of the resultant wave force on the submarine pipeline for different e/D, H i =0.15 m and T=3.0 s in a soil with high hydraulic conductivity of 1.84 mm/s

k=1.84 mm/s k=0.29 mm/s Effect of relative burial depth of submarine pipeline on shoreward force coefficients for four different soil types (Hi/d=0.666, d/L=0.074)

k=0.29 mm/s k=1.84 mm/s Effect of relative burial depth of submarine pipeline on seaward force coefficients for four different soil types (Hi/d=0.666, d/L=0.074).

k=0.29 mm/s k=1.84 mm/s Effect of relative burial depth of submarine pipeline on downward force coefficients for four different soil types (Hi/d=0.666, d/L=0.074).

k=1.84 mm/s k=0.29 mm/s Effect of relative burial depth of submarine pipeline on uplift force coefficients for four different soil types (Hi/d=0.666, d/L=0.074).

Workout Example Input conditions: Steel Pipe; OD: 1.0 m; Wall Thickness:15 mm Water depth: 2.25 m; Wave period: 6.7 s; Design wave height: 1.6 m. Soil Type: Four different marine soils discussed in this paper Pipe line purpose: Crude oil transport Find: a. Minimum safe burial depth b. Surcharge required for stability for any selected depth of burial

Minimum Minimum Safe e/D W as for Location e/D FS Uplift Minimum FS Horizontal Minimum W as for W as for Value Satisfying Safe e/D Safe e/D FS Uplift of FS Horizontal Sliding Consideri Both Value to Value to 1.5 (t/m) of Sliding ng Both FS Uplift Prevent Prevent 1.5 (t/m) Vertical and Vertical Horizonta and FS Horizontal Pop-up l Sliding Horizonta of Sliding l Stability 1.5 (t/m) 1.10 0 1.04 0.02 0.42 1.10 e/D 0.68 0.5 e/D in e/D 0.87 1.13 0.68 0.09 Sabiya between 0.62 between 1.0 between 0.94 10.96 0.62 0.0 (k=0.41 1.5 and 0.5 and 0.17 1.5 1.5 and 1.34 26.02 0.17 0.0 2.0 mm/s) 1.0 0.0 2.0 2.0 1.97 101.80 0.0 0.0 1.10 0 1.04 0.02 0.42 1.10 0.87 0.5 e/D bit e/D in 0.78 0.71 0.87 0.17 Al-Koot 0.54 more between 1.0 e/D bit 0.98 19.82 0.54 0.0 (k=0.29 than 1.5 0.5 and 0.06 1.5 more 1.44 85.08 0.06 0.0 mm/s) 1.0 0.0 2.0 than 1.5 2.05 230.83 0.0 0.0 1.10 0 1.04 0.02 0.42 1.10 e/D 0.46 0.5 e/D 1.01 1.64 0.46 0.0 Shuaiba between 0.58 1.0 between 0.96 13.12 0.58 0.0 e/D=0.5 (k=1.84 1.5 and 0.08 1.5 1.5 and 1.42 31.87 0.08 0.0 2.0 mm/s) 0.0 2.0 2.0 2.07 78.25 0.0 0.0 1.10 0 1.04 0.02 0.42 1.10 0.60 0.5 0.92 1.54 0.60 0.0 Al-Khiran 0.51 e/D = 1.5 1.0 1.01 13.77 0.51 0.0 (k=0.65 0.0 1.5 1.53 40.96 0.0 0.0 mm/s) 0.0 2.0 e/D=0.5 e/D = 1.5 2.33 85.14 0.0 0.0

Conclusions  An attempt is made to solve the question “What is the optimum burial depth of submarine pipeline?”  Solution is derived for Four different soil types with hydraulic conductivity in the range of 0.286 to 1.84 mm/s and for wide input wave conditions.  The results can be used to estimate the optimum depth of burial of submarine pipelines for future projects in Kuwait and other countries.  For Kuwaiti marine condition and for a crude oil steel pipe of 1.0 m dia and 15 mm wall thickness, the optimum depth of burial is 1.5 m to 2.0 m.

Acknowledgements  Kuwait Foundation for Advancement of Science and Kuwait Pipe Industries and Oil Services Company (K.S.C) for sponsoring this R&D work.  Kuwait Institute for Scientific Research for the infrastructure and logistic support.