Assessment of earthquake-related geohazards and seismic ... · Assessment of earthquake-related geohazards and seismic design ... Assessment of earthquake-related geohazards ... design

Assessment of earthquake-related geohazards

and seismic design of onshore and offshore pipelines

by

Prodromos PSARROPOULOS

Andreas ANTONIOU

31 March 2016

Geneva, Switzerland

IPLOCA

Novel Construction Spring Plenary Session

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiM7vHI5NnLAhXD0hoKHRnnAiYQjRwIBw&url=http://www.pipelinebrush.com/IPLOCA.46.0.html?&L=3&psig=AFQjCNFQ3EoznLuHDpeifJxKgSCz-Hd0_g&ust=1458924800077315

Prodromos PSARROPOULOS Geotechnical Earthquake Engineer, M.Sc., Ph.D.

Andreas ANTONIOU Geotechnical Engineer, Ph.D.

Assessment of earthquake-related geohazards

and seismic design of onshore and offshore pipelines

More than 20 years of professional experience

in geotechnical and earthquake engineering

Our main onshore pipeline projects that required seismic design :

a) FEED of the Italy-Greece Interconnector – Poseidon,

b) FEED of the Trans Adriatic Pipeline ( TAP )

Presentation Contents

1. Introduction

2. Quantitative assessment and treatment of geohazards

• Strong ground motion

• Active-fault rupture

• Soil liquefaction

• Slope instability

3. Proposals and general conclusions


1. Introduction







Geohazard:

Any geological, hydro-geological or geomorphological

event or process

that poses an immediate or potential risk

that may lead to damage or uncontrolled risk

Earthquake-related geohazard:

Any geohazard

that is related directly or indirectly

to the seismic activity

Definition of the

terms “geohazard” and “earthquake-related geohazard”

To assess global oil and gas deposits,

major onshore ( and/or offshore ) pipelines

will traverse remote regions with extreme terrains

( and/or seabeds ).

Many pipeline projects, constructed or planned,

are in tropical jungles, mountains and deserts, in permafrost

and wetlands ( or deep waters ).

Each of these natural environments is associated

with a range of geohazards,

which may include landslides, soil erosion, karst,

river migration, and seismic or volcanic activity.

At the same time, society demands

increasing availability and reliability of supply,

together with improved environmental standards,

all making for substantial challenges.

Motivation of the presentation (1/3)

According to the Road to Success ( RtS ) of IPLOCA:

a) Terrain, soil types, and geohazards

traversed by an onshore pipeline are key factors to consider

in the design, construction, operation and maintenance

of a pipeline project.

b) Earthquakes and fault lines are included

in the list of geohazard types for onshore pipelines.

Nevertheless, since in many areas

characterized by moderate or high seismicity

the avoidance of a “problematic area” is not feasible,

the quantitative assessment and effective treatment

of an earthquake-related geohazard

is a demanding and challenging issue

directly related to the pipeline integrity.


On the other hand,

the simplistic provisions of the seismic standards / norms

( e.g. ISO, PRCI, EN )

are rather incapable to cover sufficiently all the issues

of the seismic design of onshore pipelines.

Important note:

For the time being,

there exists no standard / norm worldwide

that covers the seismic design of offshore pipelines !


Pipelines vs. seismic hazard in Europe

European Seismological Commission Pipeline Technology Journal

levels of seismic hazard

in Europe

north : low

central : moderate

south : high

low

moderate

high

Global seismic hazard map

in terms of peak ground acceleration at the rock outcrop

Note that local site conditions may alter the picture…

hard rock

Typical layout

of a buried or above-ground pipeline

How an earthquake may distress the pipeline ?

( types of seismic loading )

stiff soil layers

lake

or sea

soft soil layers

pipeline

Types of seismic loading

1. Strong ground motion ( dynamic loading ) due to seismic waves and local site conditions

2. Permanent ground deformations ( quasi - static loading ) due to fault rupture, soil liquefaction, and/or slope instabilities

focus

hard rock

active - fault

rupture

stiff soil layers

lake

or sea

soft soil layers

slope

instability soil

liquefaction

seismic waves

hard rock

Earthquake-related geohazards

direct : ∙ strong ground motion ( along the pipeline )

∙ active – fault rupture ( locally )

active - fault

rupture

stiff soil layers

lake

or sea

soft soil layers

slope

instability soil

liquefaction

focus

seismic waves

hard rock


direct : ∙ strong ground motion ( along the pipeline )

∙ active – fault rupture ( locally )

indirect : ∙ soil liquefaction ( locally )

∙ slope instability ( locally )

active - fault

rupture

stiff soil layers

lake

or sea

soft soil layers

slope

instability soil

liquefaction

focus

seismic waves

causing

permanent

ground

deformations

Case histories of damaged pipelines

Observed damages of pipelines in the past have shown that

pipelines ( especially the buried ones ) are sensitive to permanent ground deformations (PGDs)

Reminder:

Strong ground motion is an indirect cause of PGDs as it causes ground failures

( i.e. soil liquefaction, slope instability )

Case histories of damaged pipelines Buried pipelines

during the 1971 San Fernando earthquake in USA


Fault‐induced damage of a buried pipeline

during the Manjil earthquake 1990, Iran


Large deformation of steel pipe section

crossing an active fault ( 1999 Chi‐Chi earthquake )

Failure of steel pipes crossing faults

(a) 1999 Kocaeli eq., Turkey, (b) 1999 Chi‐Chi eq., Taiwan

Liquefaction-induced failures to concrete pipelines

during the 1993 Nansei-Oki Earthquake ( Japan )



1. Introduction







Structural distress and mitigation measures

Αny structure may be distressed by:

a) external loading, and/or

b) induced permanent ground deformations ( PGDs )

A D C

B A D C B

external

loading p

induced PGD

u

Structural distress and mitigation measures

( Capacity )

( Safety ) =

( Geohazard )

S can be increased by :

a) decreasing G ( by geotechnical mitigation measures ), or

b) increasing C ( by structural mitigation measures ), or

c) decreasing G and increasing C in parallel

( by a combination of geotechnical and structural measures )

Main steps of the pipeline seismic design

( and our suggested contribution to the RtS of IPLOCA )

1. Quantitative assessment of the earthquake – related

geohazards

( various difficulties due to many uncertainties )

2. Verification of the pipeline against geohazards

( after the quantification of the geohazards in the previous

step, it is a quite straightforward procedure,

based on dynamic and static SSI analyses )

3. Design of mitigation / protection measures

( required only in the case

that the corresponding verifications are not satisfied )

Need for a geotechnical earthquake engineering study !

Why geotechnical earthquake engineering study is

necessary for the Seismic Design ?

1. Seismic norms are based on seismic zonation maps

and simplistic soil and topography factors

( that are not capable to capture all local site effects )

2. Seismological studies estimate the ground shaking levels,

but at the rock outcrop ( or at the bedrock )

( impact of local site conditions is not taken into account )

3. Tectonic ( or seismotectonic ) surveys / studies

estimate the potential offset at the bedrock

( ignoring the potential impact of soft soil layers )

4. Geological surveys rarely include quantitative identification

of slope instabilities

( especially under seismic conditions )

Prerequisites of the

geotechnical earthquake engineering study

Topographic ( or bathymetric ) survey

( topographic features of the area under examination )

Geological mapping / survey

( qualitative identification of the potential geohazards )

Tectonic ( or seismotectonic ) survey / study

( active-fault identification and potential offset at bedrock )

Seismological study

( estimation of the acceleration levels at rock outcrop )

Geotechnical ( and geophysical ) study / investigation

( identification of the soil properties / local site conditions )


1. Introduction







Strong ground motion

Local site conditions and local site effects

are basic issues in

geotechnical earthquake engineering

Local site effects modify the :

• amplitude,

• frequency content,

• duration, and

• spatial variability

of the strong ground motion ( at the ground surface )

rock

soil layer

soil layer

rock

soil


Categorization of local site conditions

rock

stratigraphy (1-D)

geomorphology of

the bedrock (2D or 3D) surface topography

(2D or 3D)

note: all of them coexist in nature !


Effect of topography

diffraction and refraction phenomena on the crest

area of wave confluence

literature:

records & analyses

show

aggravation of motion

and

damage concentration

< 300 m


area 2 area 3

30ο 40 m

heavily damaged

area

1999 Athens eq.

-0.4

-0.2

0

0.2

0.4

0 0.4 0.8 1.2

-0.4

-0.2

0

0.2

0.4

0 0.4 0.8 1.2

-0.4

-0.2

0

0.2

0.4

0 0.4 0.8 1.2

0.10 g

Α

0.29 g 0.37 g

2. Strong ground motion Response to pulse excitation

Α

t

Α

t

0.4

0.2

0

-0.2

-0.4

0.4

0.2

0

-0.2

-0.4

0.2

0.1

0

-0.1

-0.2

0 0.4 0.8 1.2 t

0 0.4 0.8 1.2 0 0.4 0.8 1.2

Ricker

pulse

x

x (m)

H

H

2 - D

1 - D

a

a


Spatial variability of topographic aggravation

horizontal motion at the ground surface

1.5

1.0

0.5

0

300 200 100 0

0

0.5

1.0

1.5

0100200300

x : m

x : m

y : m

a m

ax :

g amax : g

Assessment of local site effects ( topography and soil )

( prerequisite for the slope stability assessment )

Acceleration distribution along a slope of IGI-Poseidon

cross – section and location of

boreholes / accelerometers


records in a valley on Cephalonia island ( Greece )

100 m

30 m marl

B3 B1 B2

: accelerometer

2 3 4

1

?

? ? soft soils

4E

1E

3E2E

100 m30 m

Vs = 250 m/s

Vs = 320 m/s

Vs = 150 m/s

MARLVs = 500 m/s

Vs = 1000-1500 m/s

LIMESTONE


records in a valley on Cephalonia island ( Greece )

EF4E

-240

-160

-80

0

80

160

240

0 2 4 6 8 10t : seca

: c

m/s

/s

EF1E

-240

-160

-80

0

80

160

240

0 2 4 6 8 10t : sec

a :

cm

/s/s

1

4

EF3E

-240

-160

-80

0

80

160

240

0 2 4 6 8 10t : sec

a :

cm

/s/s

EF2E

-240

-160

-80

0

80

160

240

0 2 4 6 8 10t : sec

a :

cm

/s/s

2 3 0.24 g

0.04 g

0.06 g

substantial amplification: AF ≈ 4

( PGSA : 0.24g vs. PGBA : 0.06g )

spatial variability on the surface

( 0.24g vs. 0.04g )

0.24 g


Main danger of valley amplification

small earthquake ( linear soil behavior ) :

PGBA ≈ 0.06g & AF ≈ 4 → PGSA ≈ 0.24g

moderate earthquake ( non-linear soil behavior ) :

PGBA ≈ 0.12g & AF ≈ 2 → PGSA ≈ 0.24g

strong earthquake ( very non-linear soil behavior ) :

PGBA ≈ 0.24g & AF ≈ 1 → PGSA ≈ 0.24g

Note: due to local site conditions a moderate ( or even a small earthquake ) may lead to surface acceleration levels comparable to them of a strong earthquake


In areas characterized

by moderate seismicity the seismic risk may be high

( depending on the circumstances )

low

moderate

high

Verification against strong ground motion

Should be based on the

estimation of the maximum developed strains for both the

pipeline straight sections and the pipeline bends.

According to the current state of practice,

the strains induced due to seismic wave propagation

on the pipeline

could be calculated utilizing the analytical methods

described in the corresponding design guidelines / provisions,

as well as in the relative literature.


1. Introduction







Active-fault rupture

Categorization of active faults

depending on the tectonic movement

normal

( tension )

reverse

( compression )

strike-slip

( shear )

http://www.google.gr/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&docid=uOJU7oNHtSLbaM&tbnid=uvTbEdOKuDoLVM:&ved=0CAUQjRw&url=http://dip9.aaschool.ac.uk/xl-seams-scores/&ei=DY9zU-zqM-Ko4gT6sIDwBw&bvm=bv.66699033,d.bGE&psig=AFQjCNHTgpTnr0Nn2g_NvprsqjkefX0qyA&ust=1400168564896362

Categorization of active faults

depending on their location and the geological conditions:

a) outcropped

b) covered ( blind )

Note:

The rupture of an outcropped fault is

a direct threat to a crossing pipeline,

while in a covered fault the ground ( or seabed ) conditions

may alter the fault rupture propagation and the PGD

pattern at the ground surface ( or seafloor ).

Assessment of PGDs due to fault rupture

Collapse of a concrete dam and a bridge

due to an outcrop fault rupture

( 1999 Chi-Chi earthquake in Taiwan )

fault rupture

of the order

of 7 m

bridge

dam

bedrock

( hard rock )

soft soil layers

stiff soil ? stiff soil layers

buried or above-ground pipeline

?

fault rupture

?

?

Assessment of PGDs due to fault rupture Sketch of the rupture propagation through soil at a covered fault

Assessment of PGDs due to fault rupture Numerical simulation of the rupture propagation path

a) Covered normal fault

( offset ≈ 2m ) soft

soil layers

bedrock

H=50m

surface

soft soil layers

bedrock

surface


soft

soil layers

b) Covered reverse fault

( offset ≈ 2m )

a) Covered normal fault

( offset ≈ 2m ) soft

soil layers

bedrock

bedrock

H=80 m

H=50m

surface

soft soil layers

bedrock

bedrock

surface surface

surface

The pattern of PGDs at the surface depends on:

a) the geometrical and mechanical properties of geomaterials,

b) the fault type, and

c) the induced offset at the bedrock

Note:

The PGDs will be the imposed displacements to the pipeline

( as a quasi – static loading )


Verification of a pipeline

crossing an active outcrop fault

FEED phase of Italy-Greece Interconnector (IGI) – Poseidon

excessive strains &

need for mitigation measures

Mitigation measures for active-fault rupture

In case of excessive pipeline strains due PGDs,

the following mitigation measures should be adopted :

a) an increase in pipe wall thickness

b) reduction of the angle of interface friction between the

pipeline and the soil. The reduction of the angle of interface

friction may be achieved through various techniques

c) backfilling the surrounding of the pipeline with a loose to

medium granular soil without cobbles or boulders.

The backfill could be either soil or a synthetic smooth

material with similar mechanical behavior

d) construction of a soft embankment above the fault

The final solution(s) should be verified in order the pipeline

to comply with the strain limits imposed by the norms


If a slight relocation of the pipeline is possible,

then the pipeline crossing a fault should be oriented in such

a way as to place the pipeline in tension

( and not in compression )

Additionally,

in fault zones the depth at which the pipeline is buried

should be minimized

in order to reduce soil restraint on the pipeline

during fault movement


Important note:

If the final solution proposes exclusively modifications of the

pipeline mechanical and/or geometrical properties,

the pipeline should be re-verified to comply with the strain

limits imposed by the norms and standards

Otherwise, in the case of new backfill,

a re-assessment of the fault rupture propagation

should have preceded of any pipeline re-verification

in order to estimate the impact of the backfill material

properties on the PGDs at the ground surface

Reduction of the angle of interface friction

axial friction forces are expected to be reduced by

(a) polyethylene coating and/or

(b) one or multiple layers of geotextile fabric

after

Monroy et al.

(2012)

Mitigation measures

soft embankment above the trace of an outcrop fault

in the cases of a normal and a reverse active fault

normal fault 45ο

reverse fault 45ο

wide fault zone

narrow fault zone

Mitigation measures applied for IGI-Poseidon pipeline that crosses an active fault

( oversized trench )

fau

lt t

race

normal trench

oversized trench

normal trench

pipe

15 m 15 m

normal

trench

oversized trench

ground level

pipe

4 m

5 m

plan view

cross section

a loose to medium granular

soil (e.g. fine sand) without

cobbles or boulders in an

L =

S =

D = rock

Note: the width of fault zone W

(trace) has to be defined

A famous example of an innovative

( and successful ) pipeline seismic design

2002 Denali – Alaska earthquake :

seismic isolation of the Trans-Alaska pipeline against

the rupture of a pre-existing active strike – slip fault

The special footings allow the pipe to move

6m laterally and 1.5m vertically

//upload.wikimedia.org/wikipedia/commons/7/7d/800px-Trans_Alaska_Pipeline_Denali_fault_shift.JPG


1. Introduction







Soil liquefaction phenomena

Soil liquefaction is

an extreme consequence of strong ground motion

which leads to

practically total loss of shear strength

in relatively loose cohesionless soil formations

below the water table

Soil liquefaction phenomena

a) Uplifting and liquefaction-induced settlements

( i.e. almost vertical PGDs )

b) Lateral spreading

( i.e. almost horizontal PGDs )

1999 Izmit earthquake

( Turkey )

2011 Christchurch earthquake

( N. Zealand )

Assessment of PGDs

of soil liquefaction phenomena

In the literature

there exist various analytical and empirical methods

for the realistic estimation

of vertical and horizontal PGDs

Mitigation measures for lateral spreading

In the case of excessive lateral spreading,

the “isolation” of the pipeline

from the damaging horizontal PGDs can be achieved by:

re-routing or HDD method

In case of lateral spreading being developed

in a relatively small ( spatially ) area,

an alternative solution is to apply retaining structures,

such as bored-pile walls or sheet-pile walls.

Mitigation measures for uplifting

Concrete coating, rings or other anchoring systems

should be installed

in order to avoid the pipeline uplifting

due to pore-pressure built-up

Mitigation measures for vertical PGDs

In areas where the distress of the pipeline

due to vertical PGDs is excessive,

there are three commonly-used methodologies

to protect the pipeline:

a) reduce PGDs by various means,

b) increase the pipe wall thickness,

c) “isolate” the pipeline from the damaging PGDs


The reduction of the liquefaction-induced PGDs

may be achieved by

a) dynamic compaction or preloading,

b) increasing the dissipation of pore-water pressure,

c) grouting and deep soil mixing, and/or

d) lowering the ground water level

Note that (d) may be applied only at a local scale

An alternative is to reduce the liquefaction risk

by replacing liquefiable soils in the vicinity of the pipeline

with non-liquefiable materials ( such as gravels )


In the cases where the aforementioned methods

are considered as inappropriate,

the placement of the pipeline below the hazardous area

( achieved by horizontal directional drilling – HDD )

is a more practical methodology

( apart from rerouting )

Note that, if the final solution proposes the isolation of the

pipeline, there is no need for re-verification of the pipeline

for liquefaction.

In any other case a re-assessment of the improved

mechanical soil properties should have preceded of any

pipeline re-verification.


1. Introduction







Slope instabilities under static and seismic conditions

and pipeline distress - failures

Many static ( as well as seismic ) slope instabilities

have been observed worldwide in the past.

Nevertheless, few pipeline failures have been recorded

during only static slope instabilities.

This is attributed to the fact that up to date very

limited pipelines have been constructed

in mountainous areas characterized by high seismicity.

The pipeline construction

on a high slope subjected to seismic loading may lead to

pipeline failure due to earthquake-triggered slope instabilities

( i.e. pre-existing landslides or first-time slope failures )

( unless appropriate seismic design has been adopted ).

Examples of static slope instability


Trans-Ecuador pipeline, Ecuador

from American Geophysical Union



Camisea pipeline, Peru

after Lee et al. 2009

http://www.google.gr/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=http://qjegh.lyellcollection.org/content/42/2/251/F4.expansion.html&ei=Z-5iVdCjM8OrsAHhvoPQAg&bvm=bv.93990622,d.bGg&psig=AFQjCNFrM-yPhxW8N1wdpu3McwFleeoJ8A&ust=1432633247411929



water pipeline in central Albania

Examples of seismic slope instability

Huge landslide at Aratozawa

during the 2008 lwate-Miyagi Nairiku earthquake

( M = 7.2 )


Great mountainous landslides

caused by the 2008 Wenchuan earthquake in southwest China

( Mw = 7.9 )


two landslides during the 2014 earthquake on Cefalonia island, Greece

( Μ = 6 )

http://www.paleoseismicity.org/wp-content/uploads/2014/02/cephalonia_report.bmp

Slope instability and pipeline distress:

a soil – structure interaction problem

If pipeline routing is parallel to the induced PGD,

the pipeline is subjected to tension and compression

If the pipeline is transverse to the induced PGD,

the pipeline is subjected to bending

Assessment of slope (in)stability

a) Static slope instability If FSST are below the acceptable levels,

stabilization measures should be adopted.

b) Seismic slope instability

If FSPS are below the acceptable levels, there are two

options:

• to apply conservatively stabilization measures, or

• to estimate PGDs and to verify the pipeline

( if the verification is not satisfied, mitigation

measures should be analyzed – under static and

seismic conditions – and designed, and optionally

the pipeline has to be re-verified for the new PGDs )

FS = “resistance”

“cause”

Modern philosophy of seismic design

(a) earthquakes are accidental phenomena

with an estimated possibility of occurrence

(b) most of the steel pipelines may accommodate

certain levels of strain without failure ( i.e. rupture )

Therefore, a balance between safety and economy

may be achieved by applying

the concept of “strain – based design” and

the “modern philosophy of seismic design”,

according to which repairable damages to a structure

( i.e. exceedance of yield strain ) may be allowed or

accepted in the case of the design earthquake,

provided that the non-failure requirement has been

fulfilled ( i.e. non exceedance of failure strain ).

1200 m

35

0 m

clay – silt clayey sand

limestone

Assessment of FS and PGDs

Case study of a slope stability assessment

FEED phase of Italy-Greece Interconnector (IGI) – Poseidon

limestone

clayey silt clayey sand

Note that pipeline is parallel to the slope

Assessment of FSst

Static slope stability assessment

FSst = 1.33 ( > 1 )

Assessment of FSps

Pseudo – static slope stability assessment

ULS ( TR = 2475 yr )

Ah = 0.30g & Av = + 0.15g FSps = 0.80

Ah = 0.30g & Av = - 0.15g FSps = 0.65

DLS ( TR = 475 yr )

Ah = 0.20g & Av = + 0.10g FSps = 0.96

Ah = 0.20g & Av = - 0.10g FSps = 0.86

Since FSPS < 1 in all cases, slope may be regarded as

unstable and stabilization measures may be applied

Assessment of slope instability

seismic ( dynamic ) slope stability assessment

estimation of AC ( A that corresponds to FSPS = 1 )

AC = 0.16g

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0 1 2 3 4 5 6 7 8 9 10

1985 Kalamata eq.,

Greece

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0 2 4 6 8 10 12 14 16 18 20

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0 5 10 15 20 25


selected excitations ( recorded time histories )

1973 Lefkada eq.,

Greece

1999 Duzce eq.,

Turkey

( all scaled to 0.25g )

kala

mata

lefk

ad

ad

uzce

model S3 – DLS – circular deep

kala

mata

lefk

ad

ad

uzce

model S3 – DLS – circular deep


Seismic slope stability assessment

ULS: PGD = 27 cm DLS: PGD = 9 cm

At the verification phase it was examined ( with SSI analyses )

whether the pipeline under design

is capable to withstand these deformations.

Finally, no stabilization measures are required.

kala

mata

lefk

ad

ad

uzce

model S3 – ULS – circular deep

kala

mata

lefk

ad

ad

uzce

model S3 – ULS – circular deep


According to the

guidelines of California Geological Survey ( CGS, 2008 )

for evaluating and mitigating seismic hazards,

referring to slope movements:

PGDs < 15 cm

no serious slope movement, slope is regarded stable

PGDs > 100 cm

slope is regarded unstable

15 cm < PGDs < 100 cm

requires good engineering judgment

( in the case of a pipeline, verification is required )

Seismic design of pipelines in mountainous areas major issue: slope instability assessment and treatment

( steep slopes, poor geotechnical conditions, high PGA )

Seismic design of pipelines in mountainous areas

seismic slope stability analysis

if instability is located on the ground surface

topography effects are important

( light stabilization measures )

Seismic design of pipelines in mountainous areas

seismic slope stability analysis

if failure surface is deep seated

topography effects are not important

( heavy stabilization measures )

Given the special characteristics of the problematic area,

the selection of the optimum mitigation measure

should take into consideration various parameters

( e.g. environmental impact, constructability, accessibility,

cost, etc. )

The very final geometrical and mechanical properties

of any adopted measure,

along with its impact on the pipeline distress,

should be verified by detailed geotechnical investigation

and simulations on a case-by-case basis

Potential mitigation measures

Typical slope stabilization measures

FS = “resistance”

“cause”

decrease of “cause”

lowering GWT inclination

embankment piles or diaphragm retaining structure

increase of “resistance”

Slope stabilization measures at crest application of two sheet-pile walls

( optionally anchored or connected with tie rods )

Slope stabilization measures at crest application of passive anchors,

optionally with piles underneath the pipe

Modern philosophy of seismic design

Repairable damages to any structure are allowed,

provided that the non-collapse requirement

has been fulfilled.

Nevertheless, since the mainshock may have caused

serious damages to the pipeline, the pipeline may be

vulnerable even to an aftershock of smaller magnitude

Therefore, field monitoring would help to identify

immediately the pipeline damages due to a strong

earthquake in order to repair it as fast as possible.

Field monitoring scheme at critical areas

a) Accelerometers

recording of the ground motion at the ground surface

b) Inclinometers, topographical instrumentation, etc.

measuring permanent ground deformations

( slope instabilities, soil liquefaction, fault rupture )

c) Early warning systems

connected with strain gauges, fibre optics, etc.

measuring the pipeline strain levels

Note:

In remote areas with limited accessibility,

remote real-time field monitoring is required not only for (c)

in order to react asap...


1. Introduction







Traditional practice against geohazards

1. Avoidance of the problematic area(s)

by pipeline re-routing ( horizontally or vertically )

Note that it is not always feasible

due to various technical and/or environmental constraints

( or even time limitations )

2. Various geotechnical mitigation measures

aiming to minimize the expected PGDs

Usually geotechnical mitigation measures have a substantial

cost, depending on the geohazard type and extent

no OK

yes no

gas transmission infrastructure

pipeline or facility (CS ) ?

potentially problematic area ?

OK qualitative and/or rough quantitative

geohazard assessment

yes potentially problematic area ?

pipeline facility (CS)

OPTIONS

avoidance of the problematic area

crossing through / constructing in ( with mitigation measures )

OK design of mitigation measures

1 2

LEGEND

CS: Compressor Station PGD: Permanent Ground Deformation SSI: Soil – Structure Interaction

Designing gas transmission infrastructures projects against ground movements

Modern practice against geohazards

A third option

may be the most cost-effective in many cases:

3. Crossing through the problematic area(s)

without mitigation measures

( provided that pipeline has been checked that it is capable

to accommodate the expected PGDs )


In the case of the third option

the design should include:

a) Detailed PGD assessment, and

b) Soil – structure interaction analyses,

in order to assess the structural capability of the structure

under examination to accommodate the expected PGDs

( “strain-based design” )

Basic prerequisites:

a) Specifications and supervision

in order to achieve in practice the high-strain capacity

b) Monitoring of the geohazard and the structure (i.e. pipeline)

simultaneously

no

yes

no OK

yes no


pipeline or facility (CS) ?


OK rough PGD assessment and

preliminary SSI analyses



OPTIONS


crossing through / constructing in ( without mitigation measures )



advanced SSI analyses

acceptable strain ? ( strain -based design )

detailed PGD assessment

OK (with monitoring)

no

1

3

2

LEGEND


Designing of gas transmission infrastructures projects against ground movements


Note that usually the application

of geotechnical mitigation measures

under seismic conditions

cannot eliminate the PGDs

In other words, the elimination of PGDs

means very expensive mitigation measures

Therefore,

in some cases there is need for

a realistic re-estimation of PGDs and pipeline verification

after the application of mitigation measures.

If re-verification is not satisfied,

structural mitigation measures may be the solution.

no

yes

no OK

yes no


pipeline or facility (CS) ?


OK rough PGD assessment and

preliminary SSI analyses



OPTIONS


crossing through / constructing in ( without mitigation measures )



advanced SSI analyses

acceptable strain ? ( strain -based design )


PGD ≈ 0 ?


OK (with monitoring)

yes

OK

no

1

3

2

no no

LEGEND


Optimum design of gas transmission infrastructures projects against ground movements

General conclusions ( 1 / 2 )


are potentially serious threats to

all new or existing onshore and offshore pipelines

( and the related infrastructures )

The simplistic provisions

of the seismic standards / norms

are rather incapable to cover sufficiently

all the issues of the seismic design of pipelines

The realistic estimation of

(a) strong ground motion, and

(b) permanent ground deformations

is a prerequisite for reliable pipeline seismic design

The seismic design of pipelines

( and the design of mitigation measures )

is a demanding step of engineering design

( especially when cost-effectiveness is desired )

It requires reliable data and realistic modeling of

the pipeline, the soil, and the soil-pipeline interaction

General conclusions ( 2 / 2 )

Thank you very much

for your attention

Prodromos PSARROPOULOS Geotechnical Earthquake Engineer, M.Sc., Ph.D.

[email protected]

[email protected]

Documents

Assessment of earthquake-related geohazards and seismic ... · Assessment of earthquake-related geohazards and seismic design ... Assessment of earthquake-related geohazards ... design