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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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1.1. IntroductionIntroduction
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/8/3/2019 Geophysical Investigations 4 Eng'g
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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
1.1. IntroductionIntroduction
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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1.1. IntroductionIntroduction
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
Current 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.swf8/3/2019 Geophysical Investigations 4 Eng'g
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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 & GeoVES & Geo--electrical Profileelectrical Profile
VES & GeoVES & Geo--electrical Profileelectrical Profile
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VES & GeoS & Geo electrical Profilee ect ca o e