Ground Ground Penetrating Penetrating

RadarRadarfor for

Utilities mapping Utilities mapping and Detectionand Detection ์์

Warawutti Loh Warawutti Lohawijarnawijarn

ObjectiveObjective• To determine locations

of buried utilities and a rchaeological structure

s at some underground train stations in Krung

Rattanakosin area

Map of Bangkok with study area

STUDY AREA

Ground Ground Penetrating Radar Penetrating Radar

(GPR)(GPR)•nondestructive method

•gives continuous pictures of underground features /structures without drilling

Applications of Applications of GPRGPR

(http://www.malags.se/ramac/applications.shtml)

• Utilities location• UST detection• Bedrock mapping• Bathymetry

studies• Archeological

investigation• Forensics• Road bed

investigations

• Concrete/Asphalt thickness

• Hydrological investigations

• Fracture mapping• Karst and void detection• Hazardous waste

detection• Landfill delineation• Earth dam studies• sedimentological

studies

Principle of GPRPrinciple of GPR• Transmitter (Tx)

transmits electromagnetic pulses into the ground

• Scattering of signals from buried objects or interfaces

• Scattering signals r eceived and record

ed by receiver (Rx)

Pulse signal of Pulse signal of GPRGPR• (a) pulse signal

of GPR• (b) ideal pulse of

GPR• (c) power

spectrum of pulse (b)

• central frequency

GPR surveyGPR survey• GPR antennae are

moved in a profile• spacing between mea

suring points is given ( spacing between trace

s)• pictures of ground int

erfaces and buried obj ects showed up by alig

nments of trace signa ls on computer monito

r

radargramradargram• Reflection point

appears as hyperbola

• reflection planes appear as planes

• horizontal and vertical resolutions are about 0.01-0.20 m depended on antenna frequency and depth of investigation

GPRGPR•Antennae•Receiver

unit •Transmitte

r unit•Control

Unit•Notebook

computer

Speed of radar p Speed of radar pulsesulsesMedium Relative Permittiv

ityVelocity

(x106 m/s)

Air 1 300Fresh water

81 33

Concrete

4-10 95-150

Asphalt 2 212Clay 4-6 74-150Silt 9-23 63-100

Sand 4-30 55-150

Depth penetration and Depth penetration and Resolution of GPRResolution of GPR

(Parasnis, 1997)(Parasnis, 1997)•Penetration depth ( )

•Vertical resolution : smallest layer thickness detectable is

•Lateral resolution : shape of reflector accurately mapped if its lateral extent greater than a, but diffraction pattern will dominate if its extent less than a

2/11222

2/1

2

1

f2/v

ft

a2v

GPR test line / GPR test line / drainage pipes drainage pipes

GPR tested GPR tested line / electric line / electric

cablecable

GPR tested line GPR tested line /water pipe (iron)/water pipe (iron)

GPR tested line / GPR tested line / water pipe (rubber)water pipe (rubber)

GPR surveyGPR survey

station

Number of lines

Length (meters)

planned

surveyed

planned

surveyed

1( ) Phan Fa 15 16 225 298.5(2) Royal

Palace 13 13 204 184.6

(3) Wang Buraaa 21 21 337 319.4

total 49 50 766 802.5

Phan Fa station Phan Fa station

EquipmentEquipment•Model : 21-0010•S/N : 96 50 01•Antenna : 200

MHz•Sampling

frequency : 2049 MHz

•Recording window : 249.86 ns

•Stacking : 64

AcquisitionsAcquisitions•Antenna separation : 0.6 m

•Survey line spacing : 15 m

•Tracing spacing : 0.10 m

LevelingLeveling

Data ProcessingData Processing• GRADIX v. 1.11• Butterworth

Band Pass Filter : 100-400 MHz with slope of 24 dB

• Elevation statics

• Depth conversion with constant velocity of 10

0m/s

0 .0 4 .0 8 .0 1 2 .0 1 6 .0 2 0 .0D ista n ce a lo n g su rv ey lin e (m )

1

3

5

7

9

1 1

1 3

1 5

Surv

ey lin

e num

ber

Su

rvey

lin

e

nu

mb

er

Survey results at Pha Survey results at Pha n Fa station n Fa station

ภาพสั�ญญาณภาพสั�ญญาณ

23

2018167513119

3

222119171514121086

4

21

Electric

Cable

Water

Pipe

Telephone

Cable

Drainage

Pipe

Water

Pipe

W T WD

Unknown

anomaly

BH18

BH17

Drainage

Pipe

D E

Radargram on line 12, Prasumen Road, Bangkok

0.00-0.20m.: Asphalt

0.20-0.60m.: Road suc-beded, limestone fragments

0.60-4.00m.: SILTY CLAY,brownish grey, medium softto soft.

Bottom of Hole 4.00m.

0.0

1.0

2.0

3.0

4.0

5.0

BORING NO. : BH-18

0.00-0.50m.: Refilled sand

0.50-1.50m.: Stiff CLAY withbrick Fragments

1.50-3.50m.: Ancient wall,trace of soft clay at 1.70-1.80m and 3.20-3.30m.

3.50-4.00m.: SANDY CLAY,grey to dark grey, softBottom of Hole 4.00m.

0.0

1.0

2.0

3.0

4.0

5.0

BORING NO. : BH-17

Boring Logs on line 12, Prasumen Road, Bangkok

Boring No.17Boring No.18

ConclusionsConclusions•Present locations of buried utilities were picked up

•Radar reflections from unknown causative bodies were later identified by drilling as parts of ancient walls

AcknowledgemeAcknowledgementnt

• Geotechnical & Foundation Engineeri ng Co., Ltd.

• Mr Somchai Payongpan and GFE team• Department of Physics, Faculty of Sci

ence, Prince of Songkla University•International Programme in the Physical Sciences (IPPS), Uppsala University, Sweden