From prediction to reality

From prediction to reality Gas transmission pipeline protected with a surface slab [email protected] 25 Novembre 2005 Introducti...
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From prediction to reality Gas transmission pipeline protected with a surface slab

[email protected]

25 Novembre 2005

Introduction Gaz de France transmission pipeline • Operated by GRTgaz (subsidiary of Gaz de France) • 32 000 km • Diameter from 80 mm to 1100 mm • Operating pressure 67.7 bar • Depth > 0.8 m

Introduction Gaz de France Research & Development centre Transmission technologies section • Pipe diagnosis • Defect assessment and repair • Risk management • New materials and technologies

Issue It is necessary to protect buried pipeline against heavy load traffic

Common protective measure : concrete slab or steel plate

Issue How does the system (pipe + soil + slab) reacts to heavy loadings ? What is the maximum stress in the pipe ? What are the minimum dimensions of the slab ? • Small enough to be laid in semi-urban area • Large enough to be fully efficient

Equipment Experimental tank • dimension : 3m×3m×3m

Equipment Hydraulic jack • Maximum load = 100 tons

Equipment Instrumented pipe Strain gauges

• External Diameter = 323.9 mm

S1

• Wall thickness = 7.7 mm S4

Tube

S2

S3 Soil pressure cells on the pipe PT1 PT4

Tube PT3

PT2

Equipment Soil pressure cells

Est

Ouest 120 cm 2

1

20cm 4

3 65 cm

10 cm

40 cm

45cm

65cm

Soils Sandy soil • Purchased from a construction material shop

Clayey soil • Taken from a construction site (south suburb of Paris)



Triaxial tests



Grains size



Atterberg limits

Tank filling The soil is put in place layer by layer (5 cm thick) Compaction of the layers with a manual dam • Control of the density at 9 points • Control of the water content at 9 points • Control of the strength with a scissometer at 9 points

Tank filling with sandy soil Putting in a layer of sandy material

Tank filling with sandy soil Putting in the pipe in the sandy soil

Tank filling with sandy soil Putting in the slab and the hydraulic jack

Tank filling with clayey soil Trench effect in the clayey soil

Tank filling with clayey soil Laying down the pipe in the clayey soil

Tank filling with clayey soil Filling in of the trench with loose clayey soil (no compaction)

Numerical modelling 2D model Geometry and boundaries conditions Ld

Lb

tôle

F

ed 1

4 lois de contact glissement avec frottement de Coulomb

d 2

3

sol encaissant

Substratum rigide (nœuds encastrés)

ht

4

h Lt

Numerical modelling Non linear soil behavior • Drucker Prager with a cap • Taking into account compaction • Calibrated with triaxial tests Steel property (slab and pipe) • Elastic linear

Shear stress (τ) Slipping

τmax

Contact law • Coulomb friction

Sticking

ϕ Contact pressure (σn)

Numerical modelling Sandy soil plastic strain

Numerical modelling Clayey soil plastic strain

Results – Sandy soil Vertical displacement vs loading (sandy soil)

Force exercée sur la dalle (kN) 0

50

100

150

200

250

Enfoncement de la dalle (mm)

0 Essai Eléments finis -5

-10

-15

300

Results – Clayey soil Vertical displacement vs loading (clayey soil) • Elastic return close to experimental results

Force exercée sur la dalle (kN) 0

100

200

300

Enfoncement de la dalle (mm)

0 Essai -50

-100

-150

-200

Eléments finis

400

Results – sandy soil

S1

Hoop stress vs loading (sandy soil)

S4

canalisation

S2

S3

S3 20 0 Contrainte (MPa)

0

50

100

150

200

-20 -40 -60 -80

Essai Eléments finis

-100 Force exercée sur la dalle (kN)

250

300

Results – clayey soil

S1

Hoop stress vs loading (clayey soil)

S4

canalisation

S3

S3 20

Contrainte (MPa)

0 -20

0

100

200

300

-40 -60 -80 -100

Essai Eléments finis

-120 Force exercée sur la dalle (kN)

400

S2

Results Importance of the pipe / soil interaction model

Soft area PT3

PT3

Bedding Full scale tests

Finite Element models

Results – sandy soil Soil pressure on the pipe vs loading (sandy soil) PT4

PT1 canalisation

PT2

PT3 PT3

PT1

700

700

600

Eléments finis

400 300 200

300 200 100

0

0 0

50

100

Eléments finis

400

100

-100

Essai

500 Pression (kPa)

500 Pression (kPa)

600

Essai

150

200

Force exercée sur la dalle (kN)

250

300

-100

0

50

100

150

200

Force exercée sur la dalle (kN)

250

300

Results – clayey soil PT1

Soil pressure vs loading (clayey soil)

canalisation

PT4

PT2

PT3

PT3

PT1

900

300

800 Eléments finis

600

Eléments finis

200 Pression (kPa)

Pression (kPa)

700

Essai

250

Essai

500 400 300 200 100

150 100 50 0

0 0

100

200

300

Force exercée sur la dalle (kN)

400

-50

0

100

200

300

Force exercée sur la dalle (kN)

400

Conclusion The stress in the pipe stay reasonable • Less than 110 MPa in both tests

The vertical displacement of the slab can be important in presence of trench effect • 170 mm

Numerical modelling can reproduce the tests • Importance of the soil behavior law and the value of its parameters • Importance of an accurate modelling of the pipe/soil interaction

Conclusion Field applications • Minimum pipe / slab distance = 300 mm • Minimum width of slabs in function of the pipe diameter Pipe

Slab width

DN 100

1.1 m

DN 200

1.15 m

DN 300

1.25 m

DN 600

1.6 m

DN 900

1.9 m

DN 1200

2.25 m

Results used in a GESIP guide book (GESIP : Groupe d’Étude de Sécurité des Industries Pétrolières et Chimiques)

Perspective Accurate modelling of the pipe / soil interaction Comparison with classic analytical Marston models Simulations for field applications