geophysical investigations 4 eng'g

8/3/2019 Geophysical Investigations 4 Eng'g

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Geophysical Exploration forGeophysical Exploration forEngineering InvestigationsEngineering Investigations

Dr. Adly AlDr. Adly Al--SaafinSaafin

20112011


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OUTLINEOUTLINE

GEOLOGY OF ARABIAGEOLOGY OF ARABIA PHASES OF SITE INVETIGATIONPHASES OF SITE INVETIGATION EXPLORATIONEXPLORATION ROLE OF GEOPHYSICAL TECHNIQUES ONROLE OF GEOPHYSICAL TECHNIQUES ONENGINEERING WORKSENGINEERING WORKS FACTRORS INFLUENCING GEOPHYSICALFACTRORS INFLUENCING GEOPHYSICALINVESTIGATIONINVESTIGATION

GEOPHYSICAL METHODSGEOPHYSICAL METHODS


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GEOLOGY OF ARABIAGEOLOGY OF ARABIA


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For Detailed Information

Read Attachment # 1


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PHASES OF SITE INVESTIGATIONPHASES OF SITE INVESTIGATION

DESK STUDY

RECONNAISSANCE FIELD TRIP

PRLEMINARY SITE INVESTIGATION SITE EXPLORATION

Surface Exploration

Sub-surface Exploration

LAB / IN-SITU TESTING

ENGINEERING GEOLGICAL ASPECTSENGINEERING GEOLGICAL ASPECTS


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EXPLORATIONEXPLORATION

SURFACE EXPLORATION

UBUB-SURFACE EXPLORATIONURFACE EXPLORATION

Destructive Techniques

Trenching Drilling

Non-destructive Techniques:Geophysical InvestigationGeophysical Investigation


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FACTRORS INFLUENCINGFACTRORS INFLUENCING

GEOPHYSICAL INVESTIGATIONGEOPHYSICAL INVESTIGATION

Geophysical exploration methods provide an indirect source ofinformation about subsurface setting.

Geophysical techniques depend on the variations of physical /

chemical properties of soil and rock:

Mineralogical composition

Water content

Clay content

Porosity / fractures

Salinity

Magnetic susceptibility

Density

Elastic moduli

Velocity

Resistivity

xxxx


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ROLE OF GEOPHYSICAL TECHNIQUESROLE OF GEOPHYSICAL TECHNIQUES

ON ENGINEERING WORKSON ENGINEERING WORKS

StratificationStratification Depth to water tableDepth to water table Groundwater qualityGroundwater quality Depth to bedrock,Depth to bedrock,

Thickness of weathering zoneThickness of weathering zone

Underground cavities detectionUnderground cavities detection Faults, Shear zones allocationFaults, Shear zones allocation

Corrosion susceptibilityCorrosion susceptibility

Rock Quality determinationRock Quality determination Rock RippabilityRock Rippability Physical characteristicsPhysical characteristics xxxxxxxx


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GEOPHYSICAL METHODSGEOPHYSICAL METHODS

Passive MethodsPassive Methods::

Gravity field Magnetic field

Seismic arrival

(EQs) Active MethodsActive Methods::

Seismic

Electric Resistivity Electromagnetic

GPR

EM

Surface MethodsSurface Methods::GravityMagnetic

Seismic

Electric ResistivityElectromagnetic

Borehole MethodsBorehole Methods::

Crosshole Test (CHT)

Downhole Test (DHT)

Logging

xxx


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Contrasts in physical properties from different geological targets give rise to

geophysical target.

Wet rock Wet rock

Which MethodWhich Method.?.?


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Usefulness of engineering geophysical methods


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Usefulness of engineering geophysical methods (continued)


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SEISMIC METHODSSEISMIC METHODS


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SEISMIC METHODS

1.1. IntroductionIntroduction

2.2. Seismic wavesSeismic waves

3.3. Seismic methodsSeismic methods

4.4. SEISMIC REFRACTION METHODSEISMIC REFRACTION METHODi.i. Seismic waves propagation in theSeismic waves propagation in the

groundgroundii.ii. Data acquisition & InstrumentsData acquisition & Instruments

iii.iii. Data processing & InterpretationData processing & Interpretation


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Seismic methods developed based on

the fact that the elastic properties of soiland rock determine the velocities ofwave propagation through them.

Vp and Vs are the P and S wavevelocities of the medium is a

function of , and k.Whereas

is the density of the medium,and

and k are referred to as the shear

and bulkmodules of the media.


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2.2. Seismic WavesSeismic Waves Seismic waves; transfer of energy by

way of particle motion. Seismic wavefront


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Elastic WavesElastic Waves

.

.


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Seismic WavesBody wavesBody waves - These are elastic waves that propagate through

the Earth's interior. In reflection and refraction prospecting, bodywaves are the source of information used to image the Earth's

interior.P Waves

- P waves are also called primary waves, because they

propagate through the medium faster than the other wavetypes.

S Waves

- S waves are sometimes called secondary waves,

because they propagate through the medium slower than Pwaves.

Surface WavesSurface Waves - that propagate along the Earth's surface.Their amplitude at the surface of the Earth can be very large, butthis amplitude decays exponentially with depth. Surface wavespropagate at speeds that are slower than S waves.


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Types of WavesTypes of Waves


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Types of Body WavesTypes of Body Waves

Compressional waves (P), which travelin any medium (solid, water and airsolid, water and air).

Shear waves (S), which travels only in

solidsolid.


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Compressional (P) Wave

Identical to sound wave particle

motion is parallel to wave propagation

direction.

Animation courtesy Larry Braile, Purdue University


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Shear (S) Wave

Particle motion is perpendicular

to propagation direction.

Animation courtesy Larry Braile, Purdue University


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Mechanical of Body Waves

SourceReceiver (Geophone)

Oscilloscope

P

S R

Time

AmplitudeAmplitude

R S P


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Vp values forSelected Earths

Materials


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Seismic WavesSeismic Waves

Body waves

Surface waves


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3.3. SEISMIC METHODSSEISMIC METHODS

1.1. Reflection methodReflection method2.2. Refraction MethodRefraction Method


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44 -- SEISMIC REFRACTION METHODSEISMIC REFRACTION METHODi.i. Seismic waves propagation in theSeismic waves propagation in the

groundground

ii.ii.Data acquisition & InstrumentsData acquisition & Instruments

iii.iii.Data processing & InterpretationData processing & Interpretation


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4.i4.i-- Seismic Refraction Waves PropagationSeismic Refraction Waves Propagation

in the Groundin the Ground Refraction Seismology-A program to map geologic structure by using head

waves.

Head waves involve energy that enters a high-velocity medium (refractor)near the critical angle and travels in the high-velocity medium nearly parallel

to the refractor surface.

The change in curvature of the wave front as the wave passes through theinterface implies that the ray-paths describing the direction of propagationof the wave change direction through the boundary. This change in direction

of the ray-path as it crosses a boundary is described by a well-known lawknown as Snell's Law.


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Wave PropagationWave Propagation


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Wave propagation (Two Layers)Wave propagation (Two Layers)


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Wave Propagation (Multiple Layers)Wave Propagation (Multiple Layers)


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What causes refraction?

Notice.


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layer Model-Waves propagation in a two


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Travel TimeTravel Time

ii4 ii D A i i i ID A i i i & I


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4.ii4.ii-- Data Acquisition & InstrumentData Acquisition & Instrument

Seismic Source, Geophones, Recording System


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Field Survey

Data Acquisition:

Geophones

Connection cable

Other connections

Generate sufficient energy

Seismic record

See Movie # 1See Movie # 1
http://seismic%20training%201-0%20%28field%20setup%29.flv/http://seismic%20training%201-0%20%28field%20setup%29.flv/http://seismic%20training%201-0%20%28field%20setup%29.flv/http://seismic%20training%201-0%20%28field%20setup%29.flv/http://seismic%20training%201-0%20%28field%20setup%29.flv/http://seismic%20training%201-0%20%28field%20setup%29.flv/http://seismic%20training%201-0%20%28field%20setup%29.flv/http://seismic%20training%201-0%20%28field%20setup%29.flv/http://seismic%20training%201-0%20%28field%20setup%29.flv/http://seismic%20training%201-0%20%28field%20setup%29.flv/http://seismic%20training%201-0%20%28field%20setup%29.flv/http://seismic%20training%201-0%20%28field%20setup%29.flv/


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Seismic Waves Record

Oscilloscope


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Seismic Refraction

Vertical GeophonesSource

(Plate)

Rock: Vp2

ASTM D 5777

Soil: Vp1

x1x2x3x4

t1 t2t3t4

Note: Vp1

< Vp2

zR

Determine depthto rock layer, zR?


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4.iii4.iii-- Data InterpretationData InterpretationDetermination of X ThicknessDetermination of X Thickness

1

2

1. Intercept time

value.

2. Critical distance

value.


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Example.


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Multiple LayersMultiple Layers


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Hidden Layer CaseHidden Layer Case!......!......

Comments & Suggestions?..omments & Suggestions?..


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Dipping Layer CaseDipping Layer Case!......!......

By acquiring refraction seismic observations in two directions, we can immediately determine

whether or not subsurface layers are dipping.If dipping layers are present, the travel-time curves obtained in the two directions are no longermirror images of each other.


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Using Seismic Refraction to

Map the Subsurface

Depth{

For layer parallel tosurface

12

12

2 VV

VVXcDepth

)cos(sin22

11

1

VV

VTi

V2 > V1


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Seismic Refraction and Fault Detection

D P & I i


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Data Process & Interpretation

Using Computer.

Rippability of In-place Rock by Caterpillar Dozer Evaluate by P-Wave Velocity.


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pp y p y p y y(After Franklin and Dusseault, 1989)


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ELECTRIC RESISTIVITYELECTRIC RESISTIVITY

METHODSMETHODS


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Electric Resistivity MethodElectric Resistivity Method


2.2. Current flow in the groundCurrent flow in the ground

3.3. Electrode configurationElectrode configuration

4.4. Field method and instrumentationField method and instrumentation

5.5. Data interpretationData interpretation

6.6. Case studiesCase studies

11 I t d tiI t d ti


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Electric Resistivity Methods developed based on somefactors that effect the resistance of earth material to electriccurrent flow.

Seismic techniques depend on the physical properties ofearth materials.

Electric resistivity methods depend on combination of (i)

conductivity of the fluid present in porosity and (ii) earthmaterial itself as:

Variations in mineralogy,Variations in mineralogy,

Porosity / fractures,Porosity / fractures,

Water contentWater content

Clay contentClay content

Salt contentSalt content


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Introducing current to the earth through two

electrodes that are pushed into the ground surface.The Resistance of earth material to current flow is

obtained from (Ohms law) by measuring the

potential drop between two electrodes that arepositioned with the field of the current electrodes.

V = I. R

Depth of investigation is proportional to the currentelectrode separation.

Introducing current to the earth through twoelectrodes that are pushed into the ground surface.

The Resistance of earth material to current flow is

obtained from (Ohms law) by measuring the

potential drop between two electrodes that arepositioned with the field of the current electrodes.

V = I. R

Depth of investigation is proportional to the currentelectrode separation.

Basic ConceptsBasic Concepts

)) and Resistivity (RResistance (


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)) and Resistivity (RResistance (

El i l R i i i MEl t i l R i ti it M t


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Electrical Resistivity MeasurementsElectrical Resistivity Measurements

1 10 100 1000 10000

Bulk Resistivity,

(ohm-meters)

Clay

Loam

Loose Sands

Sands & Gravels

Glacial Till

Weathered Rocks

Resistivity Values (ConeTec & GeoProbe, 1997)


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C d ti it (1/C d ti it (1/ ) f diff t il) f diff t il


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Conductivity (1/Conductivity (1/) for different soils) for different soils

2 C fl i h d


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2.2. Current flow in the groundCurrent flow in the ground


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Current flow in the ground



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Apparent Resistivity (a)

El d C fi i


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Electrodes Configuration

33 El t d C fi tiEl t d C fi ti


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3.3. Electrodes ConfigurationElectrodes Configuration


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4 D t A i iti (Fi ld A ti it )

44 Data Acquisition (Field Activity)Data Acquisition (Field Activity)


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4. Data Acquisition (Field Activity)

Instrumentation: Current Source, Ammeter, Voltmeter, Electrodes, Cables.

4.4. Data Acquisition (Field Activity)Data Acquisition (Field Activity)

InstrumentationInstrumentation: Current Source, Ammeter, Voltmeter, Electrodes, Cables.

VES-1AB/2=1 5 MN/2=0 5

Schlumberger SoundingVES-1

Wenner Sounding


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AB/2=1.5, MN/2=0.5

AB/2=2, MN/2=0.5

AB/2=3, MN/2=0.5

AB/2=4, MN/2=0.5

AB/2=5, MN/2=0.5

AB/2=5, MN/2=1

AB/2 R a1.5

2

3

4a

AB/2

a=1m

a=2m

a=3m

a=4m

a=5m

a,m R a

1

2

3

4

a

a,m

Data Table

Field Curve

Data Table

Field Curve


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Electrode spacing & current penetration

Arrangement for the Wenner Test


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Arrangement for the Wenner Test

Recommended probe spacing/depths for soil


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Recommended probe spacing/depths for soilresistivity tests


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Data Acquisition:

1.

2.

3.4.

5.

6.

http://www.fluke.eu/comx/products/demos/geox2_en.swf
http://www.fluke.eu/comx/products/demos/geox2_en.swfhttp://www.fluke.eu/comx/products/demos/geox2_en.swf


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Gulf Consult Vertical Electric sounding

Normal profiling

Environmental applications

Others

5.5. Data processing & InterpretationData processing & Interpretation

VES-1

a 1m

Wenner Sounding


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a=1m

a=2m

a=3m

a=4m

a=5m

a,m R a

1

2

3

4

a

a,m

Data Table

Field Curve

s Expertises Expertise

Gulf ConsultGulf Consult

Gulf Consult RequirementsGulf Consult Requirements


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Gulf Consult RequirementsGulf Consult Requirements

Apparent resistivity

(a) = 2aR (ohm-m)Resistance (R)

[V/I] (ohm)Spacing (a)

(m)SN

11/121/2

41/361/4

81/5101/6

1/n

Typical Soil Resistivity Plot


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Typical Soil Resistivity Plot

VES & Normal ProfilingVES & Normal Profiling


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VES & Normal ProfilingVES & Normal Profiling

Vertical Electric Soundings (VES): theresistivity method carried out to detect

vertical variations in resistivity thatoccur solely with depth.

Resistivity Profiles: the resistivity

survey employed to detect lateralvariations in resistivity (NormalProfiling).

Vertical Electric Soundings (VES): theresistivity method carried out to detect

vertical variations in resistivity thatoccur solely with depth.

Resistivity Profiles: the resistivity

survey employed to detect lateralvariations in resistivity (NormalProfiling).

S


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Vertical Electric Sounding(VES)

Vertical Electric Sounding(VES)

Electrode Spacing and Apparent Resistivity Plots


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p g pp y

AB/2, of 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0, 2.25, 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, 20.0, 22.5,

50.0, 75.0, 100.0, 125.0, 150.0, 175.0, 200.0, and 250.0 meters were taken.

Apparent Resistivity Curves for


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Apparent Resistivity Curves forSoundings Over One-Layered Media

Apparent Resistivity Curves in


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Apparent Resistivity Curves in

Two-Layered Media

P ibl I t t ti f ERPossible Interpretation of ER survey


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Possible Interpretation of ER surveyPossible Interpretation of ER survey


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VES & GeoVES & Geo--electrical Profileelectrical Profile


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VES & GeoS & Geo electrical Profilee ect ca o e

geophysical investigations 4 eng'g

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