geohazard tutorial geoddo

7/31/2019 Geohazard Tutorial GeoDDO

1/70


2/70

GeoDDO- Geological Analysis for Offshore Engineering

31 July 2012

slide 2

Geohazards : objectives of this seminar

Clarification of what comprises or does not comprise ageohazard

Introduction to a wide range of common and not-so-

common geohazards

Correlation of geohazards with specific geologicalenvironments

Evaluation of geohazard-related risks for subsea

installations

How to mitigate geohazard-related risk


3/70


31 July 2012

slide 3

Geohazards : what is a geohazard?

Most geohazards are initially identified from geophysical data.

Geohazards comprise naturally occurring seabed featuresor sub-surface conditions that may pose a risk to the installationor operational life of subsea structures and pipelines.

The identification of potential geohazards should be one

of the primary goals of any site or pipeline route survey.


4/70


31 July 2012

slide 4

When is a Hazard not a Geohazard?


5/70


31 July 2012

slide 5

Hazards that are not Geohazards


6/70


31 July 2012

slide 6



7/70


31 July 2012

slide 7



8/70


31 July 2012

slide 8


http://tv-antenna.com/heavy-seas


9/70


31 July 2012

slide 9



10/70


31 July 2012

slide 10

Geohazard Evaluation : Assess the quality of theavailable information and identify the environment

What type and quality of data are available?

What type of geological environment?


11/70


31 July 2012

slide 11

Geohazard Evaluation : Assess the quality

Are the data site specific?

Are the geophysical interpretations confirmed by geotechnicaldata?

Are the different data sets consistent with each other?

Is the equipment used fit for purpose?

Have the data been processed and presented in a sensiblemanner?


12/70


31 July 2012

slide 12

Geohazards : Identify the environment

areas of current and wave action

polar latitudes

tropical latitudes

glaciated terrains

areas affected by sea level changes

zones of gas escape ultra deep water

near shore areas

zones of structural weakness

Individual geohazardsmay be associatedwith more than onetype of environment


13/70


31 July 2012

slide 13

Geohazards Generated by Current or Wave Action

ripples

megaripples

sand waves

flutes scour

lag deposits

slope failures

steep gradients

often connected withnearshore environments,but exceptions to therule exist


14/70


15/70


31 July 2012

slide 15


Megaripples

Height between trough andcrest from 0.1 m to 1.0 m,

wavelengths greater than 1m (AGI)

These are the ones towatch...


16/70


31 July 2012

slide 16


Sand Waves:> 1 m amplitudes


17/70


31 July 2012

slide 17

Sand Waves


18/70


19/70


31 July 2012

slide 19

Comparison of DTM imagery Bathymetry (m)

m

ITT DTM Rock dumper DTMKP 8.300KP 8.300

KP 7.650KP 7.650



20/70


31 July 2012

slide 20

Comparison of DTM imagery : Slope angles (in degrees)

ITT DTM Rockdumper DTM

KP 7.650 KP 7.650

KP 8.300 KP 8.300



21/70


31 July 2012

slide 21

Comparison of survey data :

X

X

X

X



22/70


31 July 2012

slide 22


Flutes and Megaflutes


23/70


31 July 2012

slide 23


Scour


24/70


31 July 2012

slide 24


Lag

Deposits


25/70


31 July 2012

slide 25

Geohazards Associated with High Latitudes

iceberg impacts

iceberg scarring

ice pits

sea ice scour

gas hydrates


26/70


31 July 2012

slide 26


Iceberg impact


27/70


31 July 2012

slide 27


Iceberg Scours


28/70


31 July 2012

slide 28


Ice pits


29/70


31 July 2012

slide 29


Sea Ice

Scour


30/70


31 July 2012

slide 30

Gas Hydrates



31/70


31 July 2012

slide 31

Geohazards Associated with Low Latitudes

coral reefs

carbonate sediments


32/70


31 July 2012

slide 32


Coral Reefs


33/70


31 July 2012

slide 33


Carbonate Sediments

a soil (or rock) which

requires geotechnical

testing for identification


34/70


35/70


31 July 2012

slide 35

Geohazards Associated with Glaciated Terrains

GlacialTopography

scars

pits kettles

drumlins

eskers

end moraines

rock glaciers


36/70


31 July 2012

slide 36


Dropstones


37/70


38/70


31 July 2012

slide 38

BuriedBoulders



39/70


31 July 2012

slide 39


Steep Gradients


40/70


31 July 2012

slide 40


Bedrock Highs


41/70


31 July 2012

slide 41

UnstableSlopes



42/70


31 July 2012

slide 42


43/70


31 July 2012

slide 43


44/70


31 July 2012

slide 44


45/70


31 July 2012

slide 45

Geohazards: Features Generated during Changesin Sea Level

hardpan

peat

gyttja

shallow gas

submerged terraces

lag deposits


46/70


31 July 2012

slide 46


Hardpan

a soil, which requires geotechnical testing

for identification


47/70


31 July 2012

slide 47


Peat deposits

a soil, which requires

geotechnical testing

for identification


48/70


31 July 2012

slide 48


Gyttja

a soil, which requires

geotechnical testing

for identification


49/70


31 July 2012

slide 49


Submerged Terraces


50/70


31 July 2012slide 50

Geohazards: Gas Features

pockmarks

cemented ground

cold water corals

shallow gas

mud volcanoes

gas hydrates


51/70




Pockmarks


52/70




53/70




54/70




CementedGround


55/70



Geohazards: Gas Features : Cold Water Corals


56/70



Shallow Gas



57/70



Geohazards: Gas Features: Mud Volcanoes


58/70





59/70





60/70



Geohazards: Gas Features:

Gas Hydrates


61/70



Geohazards associalted with ultra-deep water

soft clay

gas hydrates

slope failure

gas release features shallow faulting

deep water corals


62/70




A soil, which requiresidentification (or

confirmation) bygeotechnical testing

Soft Clay


63/70



Soft Clay

foundations


64/70



Soft Clay

backfill

(not strictly a geohazard,but a soils issue)

G h d i lt d ith lt d t


65/70



Shallow faulting



66/70

G h d i f j t l k


67/70



Earthquakes

destroy stuff

Geohazards in zones of major crustal weakness


68/70




Liquefaction


69/70




Volcanism


70/70



Tsunamis

geohazard tutorial geoddo

Documents