Design of Buried Pipelines against Permanent Ground

Design of Buried Pipelines

against Permanent Ground Displacements

Dr Dimitris KaramitrosLecturer in Civil Engineering

Dr Dimitris Karamitros - Lecturer in Civil Engineering

E-mail: d.karamitros@bristol.ac.uk

Society for

Earthquake and

Civil Engineering

Dynamics

National

Technical

University of

Athens

Problem DescriptionSeismic Fault Crossings

Kocaeli, Turkey (1999) Chi-Chi, Taiwan (1999)

Problem DescriptionTypes of Permanent Ground Displacements

Underground works (e.g. tunneling)

Wang et al (2011)

Slope failures

O’Rourke et al (1989)

Lateral-spreading (liquefaction)

O’Rourke et al (1989)

…and others…

Differential settlement / heave

ALA-ASCE (2005)

Presentation Outline

E-mail: d.karamitros@bristol.ac.uk bristol.ac.uk

Problem Description

Current Design Practice

Simplified Analytical Methodologies

Strike-Slip Fault Crossings

Normal Fault Crossings

Oblique Fault Crossings

Pipelines with Bends

Practical Design Considerations

Limitations & Future Research

Current Design Practice3-D Finite Element Analyses

American Lifelines Alliance

ASCE (2005)

pipeline

transverse horizontal soil springs

axial soil springs

vertical soil springs

applied fault displacement

Shell elements

Rigid element

Beam elements

Axial soil springs

Horizontal soil springs

Vertical soil springs

Current Design Practice3-D Finite Element Analyses

American Lifelines Alliance

ASCE (2005)

Non-linear behavior of pipeline steel

Elasto-plastic soil springs

Second-order effects

Current Design PracticeNon-linear Winkler-type Springs

pipeline

axial soil springs

…after Trautman & O’Rourke (1983)

AXIALTRANSVERSE

HORIZONTALVERTICAL

pipeline

axial soil springs

AXIALTRANSVERSE

HORIZONTALVERTICAL

pipeline

axial soil springs

AXIALTRANSVERSE

HORIZONTALVERTICAL

pipeline

axial soil springs

AXIALTRANSVERSE

HORIZONTALVERTICAL

Current Design PracticeTypical Example

PLAN VIEW

Natural Gas Supply Pipeline for the Alexandroupolis Hospital, Greece

t=6.35mm

ANSI/API5L Grade B

Normal Fault

ψ = 70° (dip angle)

Δf = 0.45m

Typical mitigation measures:

Increased pipeline thickness

Higher grade pipeline steel

Use of different backfill material

Protective casing

Flexible joints

Alteration of pipeline route

Allowable longitudinal strains:

Tensile strain: e.g. 4% (0.5% for welded pipelines)

Compressive strain: e.g. 1.76 t/D (to avoid buckling)

need for Simplified Design Methodologies

Preliminary design

Determine critical areas

Quick checking of numerical results

Evaluation of mitigation measures

Problem Description

Existing Analytical MethodologiesStrike-slip fault crossings

initial route

deformed pipeline

ΔyPLAN

Newmark & Hall (1975)

Kennedy et al. (1977) adopted by the ASCE (1984) Guidelines

✔ Non-linear behavior of pipeline steel

✔ Soil-pipeline interaction in both longitudinal & transverse directions

✖ Large fault movement ➭ pipeline section under yield ➭ ignore bending stiffness

➭ overestimate curvature ➭ (over) conservative

Wang & Yeh (1985)

✔ Bending stiffness taken into account

✖ Ignore the effect of axial tension on bending stiffness

➭ underestimate curvature ➭ under conservative

0 0.5 1 1.5 2

Fault movement (Δf) /Pipeline diameter (D)

0 0.5 1 1.5 2

Kennedy et al.

Wang & Yeh

Num. Analyses

Crossing angle: β=30° β=45° β=60°β=30° β=45° β=65°

Typical HPTS

Natural Gas Pipe

Diameter D=0.9144 m

Thickenss t=0.0119 m

API5L-X65 steel

(σy=490MPa)

Medium dense sand

(γ=18KN/m3 , φ=36°)

Embedment H=1.30m

q(x) = - k w(x)

pipeline

New Analytical MethodologyKaramitros et al (2007) – Strike-Slip Fault Crossings

Basic Principle: Partitioning of the pipeline into 4 segments

q(x) = - k w(x)

pipeline

q(x) = - k w(x)

Segment Α´Α (and CC´):

Elastic Beam on Elastic Foundation

Boundary conditions for segments ΑΒ and BC

q(x) = - k w(x)

pipeline

Segments ΑB (and BC)

Maximum Bending Moment

→ Maximum Bending Strain

Compatibility of displacements:

(pipeline elongation = fault displacement)

Obtain axial force Fa

ΔL 2 ε L dL Δx

Simplified computation of axial strains (similar to existing methodologies)

Compatibility of displacements:

(pipeline elongation = fault displacement)

Obtain axial force Fa

ΔL 2 ε L dL Δx

Simplified computation of axial strains (similar to existing methodologies)

Equivalent linear solution (iterative), using secant modulus:

π-φ2

εmax=εa+εb

εmin=εa-εb

Τμήματα της διατομής σε διαρροή

ΑνηγμένεςΠαραμορφώσεις

Τάσεις

Steel Under Yield

stressesstrains

Obtain maximum bending strain εb and maximum axial force Fa

from elastic solution

➭ Calculate axial strains εa, so that 𝜎 ∙ 𝑑𝐴 = 𝐹𝑎

➭ Readjust secant Young’s modulus 𝐄′ =Mmax∙𝐷

2∙I∙𝜀𝑏

0 0.5 1 1.5 2

Kennedy et al.

Wang & Yeh

Prop. Methodology

Num. Analyses

Crossing angle: β=30° β=45° β=60°β=30° β=45° β=65°

Typical HPTS

Natural Gas Pipe

Diameter D=0.9144 m

API5L-X65 steel

(σy=490MPa)

Medium dense sand

(γ=18KN/m3 , φ=36°)

Embedment H=1.30m

New Analytical MethodologyKaramitros et al (2011) – Normal Fault Crossings

ΔfΔz

initial route

deformed pipeline

LAB LBC

q(x) = - k w(x)

ρήγμ

αγωγός

pipeline

Pipeline discretized in 3 segments:

Numerical

Analytical

0 0.5 1 1.5 2

Δf / D

0 0.5 1 1.5 2

Δf / D0 0.5 1 1.5 2

Δf / D

ψ=55° ψ=70° ψ=85°

Typical HPTS

Natural Gas Pipe

Diameter D=0.9144 m

API5L-X65 steel

(σy=490MPa)

Medium dense sand

(γ=18KN/m3 , φ=36°)

Embedment H=1.30m

= max { , }

Oblique

Crossing

Δx, Δy, Δz

Normal Fault

Crossing

Δx, Δz (Δy=0)

Strike-Slip

Fault Crossing

Δx, Δy (Δz=0)

Maximum strains occur at:

• different locations along the pipeline

• different positions on the cross-section

z εmax,normal

εmax,strike-slip

0 0.5 1 1.5 2

Δf / D

Numerical

Analytical(normal)

Analytical(strike-slip)

0 0.5 1 1.5 2

Δf / D0 0.5 1 1.5 2

Δf / D

ψ=30° - β=30° ψ=45° - β=45° ψ=60° - β=60°

Application to Practical Cases

Range of Parameters

Pipelines

✔ D = 4÷36 in

✔ t/D = 1.3÷4.2 %

✔ Grade B, X52, X65

Faults

✔ Δf = 0.08÷1.06 m

✔ β = 20÷90˚

✔ ψ = 60÷70˚

εmax (%)

Aναλυτική μεθοδολογία

ιθμ

ητι

κές

ανα

λύσ

εις

Analytical Methodology

erical A

Typical Pipeline Layout in Practice

Problem Description

Limitations & Ongoing Research

pipeline

fault trace

Step 1: Analyze the pipeline close to the bend

Step 2: Fault – bend interaction

Step 3: Analyze the pipe at the fault crossing

LA fault trace

New Analytical MethodologyKaramitros et al (2016) – Pipelines with Bends

Step 1: Analysis of the Bend

Analysis using the Direct Stiffness Method:

𝑷 − 𝑷𝑳 = 𝑲 + 𝑲𝒔𝒑𝒓 𝒖

Lateral and Rotational Springs

Elastic beam on elastic foundation

➭ Obtain relations between Μ(0), Q(0) and w΄(0), w(0)

Axial Spring at end Β

Axial force (and strain) distribution along the pipeline

➭ Obtain relation between FB and uB

Step 2: Fault-Bend Interaction

Axial component of

Fault movement

Axial displacement

at bend uΑ

Integral of strains

along the pipeline= +

Step 3: Verification at Fault Crossing

Analytical Methodology

for normal fault crossings

Karamitros et al (2011)

Analytical Methodology for

strike-slip fault crossings

Karamitros et al (2007)

ρήγμα

αγωγός

q(x) = - k w(x)

LAB LBC

q(x) = - k w(x)

ρήγμ

αγωγός

Calculate axial force Ffault at the position of the fault

and employ one of the existing analytical methodologies:

…or their newer versions, e.g. Trifonov & Cherniy (2010)

New Analytical MethodologyKaramitros et al (2016) – Pipelines with Bends

Problem Description

Practical design considerations

Numerical simulations & analytical methodologies should take into

account material (pipeline steel, soil) & geometric non-linearities.

When the axial force exceeds the yielding limit, pipeline strains

become very sensitive to the applied movement.

The existence of bends along the pipeline route needs to be taken into

account.

The assumption of 90° bending angles is not always conservative.

Pipeline behavior at bends is significantly affected by the radius of

curvature.

Analytical methodologies should only be employed within their defined

range of application.

Limitations & Ongoing Research

Both numerical & analytical solutions are affected by the p-y curves

considered for the (Winkler-type) soil springs.

pipeline

axial soil springs

Limitations & Ongoing ResearchTrench Effects

Bouckovalas, G.D., Chaloulos, Y.K., Karamitros, D.K. (2016): “Trench effects on lateral p-y

relations for embedded pipelines”, Computers & Geotechnics (under review)

x+ymax

Ultimate soil resistance may increase up to one order of magnitude!

Limitations & Ongoing ResearchCoupling-effects

Winkler-type

representation:

Dr Dimitris Karamitros – Lecturer in Civil Engineering

E-mail: d.karamitros@bristol.ac.uk

Thank you for your attention!

Karamitros D.K., Bouckovalas G.D., Kouretzis G.P. (2007): “Stress Analysis of Buried Steel Pipelines at

Strike-slip Fault Crossings”, Soil Dynamics and Earthquake Engineering, vol. 27, pp. 200–211.

Karamitros D.K., Bouckovalas G.D., Kouretzis G.P., Gkesouli V. (2011): “An Analytical Method for Strength

Verification of Buried Steel Pipelines at Normal Fault Crossings”, Soil Dynamics and Earthquake

Engineering, vol. 31(11), pp. 1452-1464.

Kouretzis G.P., Karamitros D.K., Sloan S.W. (2015): “Analysis of buried pipelines subjected to ground

surface settlement and heave”, Canadian Geotechnical Journal, vol. 52(8), pp. 1058-1071.

Karamitros D.K., Bouckovalas G.D., Zoupantis C. (2016): “Buried Pipelines with bends: Analytical

verification against permanent ground displacements”, Canadian Geotechnical Journal (under review)

Bouckovalas G.D., Chaloulos Y.K., Karamitros D.K. (2016): “Trench effects on lateral p-y relations for

embedded pipelines”, Computers & Geotechnics (under review)

Calculation spreadsheets available at: www.dimitriskaramitros.com

National

Technical

University of

Athens

Society for

Earthquake and

Civil Engineering

Dynamics

Design of Buried Pipelines against Permanent Ground

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