enviromental geological application of ground penetrating radar

8/12/2019 Enviromental Geological Application of Ground Penetrating Radar

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Enviromental geological application of ground penetrating radar

Abstract – this paper introduce the combining application of GPR and high density

method, that achieved good detecting effect of engineering geophysical exploration on

island frozen soil, karst cave, subgrade collapsing, Lndslide hazard and so on. The two

differences of dielectric constant and the resistivity geology, but also has high correlation.

The ambiguity can be effectivety eliminated from two ways describing the underground

target. GPR can describe the shallow characterization whit details and features, the high

density resistivity methoa can describe the deep macroscopic characteristics for the

underground target, so easy to form conceptual geological model and to convenient for

data analysis and data interpretation. The combining is effective that have

complementarity, validation and validity for each other. The detecting parameters of GPR

is more important than the data processing, which determines the quality of original data,

it is necessary to do a certain amount of field test for determine the detection parameters

before you start work especially in a strange area.

Keywords- GPR; dielectric constant; environmental geology high density resistivity

method.

I. INTRODUCTION

Ground penetrating radar GPR is a kind of electromagnetic wave technology for

underground interface positioning. Its working principle is high frequency

electromagnetic wave with broadband pulse into the underground through a transmiting

antenna, the electromagnetic wave is reflection to the ground through the subsurface

strata or reflection of objects with electrical differences and is received by the receiving

antenna. The intensity of electromagbetic field and waveform is changing on the

propagating og high frequency alectromagnetic wave with the medium properties and

geometry in the medium and other interference. There will be strong reflection wih

electromagnetic wave from air into the layer of rock and soil, which due to the

propagation speed of electromagnetic wave is greater in the air than in the rock and in



soil. That the negative phase of electromagnetic wave is produced at the groand, the

image of specific reflection wave group is produced when the electromagnetic wave from

one medium interface to another, which the phase and amplitude of radar wave is

changing similarity and the basus characteristics of geological target can be detreminned.

It is low loss medium to the displacement current usually that encountered in engineering

exploration and detectin with high frequency electromagnetic pulse relatively, the

reflection coefficient and the wave velocity of radar wave depends on the dielectric

constant. In this medium. In which,c

The reflection coefficient of Radar wave:

(cong thuc)

The speed of adar wave:

(cong thuc)

It is more important that the detection parameters ic selected than the data processing for

GPR, which determines the quality of original data. It is necessary especially to

determine detection parameters of GPR in the strange area before strart work, which needto do a amount of field test, and can be reduce the quantity of field test through the

experience accumulation. The data processing of GPR is generally to use a high-pass

filter. Mean, average, gain adjustment of automatic compensation, complex signal

analysic method and so on, that can improve the quality of GPR profile and iobtain the

best interpretation. The processing of actual data is closely related to the field situation. It

is important that determine the concept geological moadel and have exploration

experience. GPR mainly characterized in high resolution, no-destructive, work efficiency,

strong anti-interference ability and as a captivating methods of ground feophysical

exploration, and due to the high attenuation of GPR wave in medium, the GPR

application is limited, which is mainly manifested in probing depth, the high penetrability

with absorbing medium and the stability of the instrument on the oter hand, GPR wave is



jamemed by multiple wave and lateral reflection wave that will cause the detection

accuracy of GPR and the difficulties of image interpretation. Still not to be able to use a

single geophysical exploration method to provides a ve accurate answer of detection

target , it is an important issue that this paper discusses the application pf GPR inenvironment geology.

II. MEDIUM PHYSICS PROPERTIES AND JOINT DETECETION

it is to certain restriction that to solve geological problems with a single GPR method,

because of environmental geological exploration field and detect targets of the

divetrsity and complexity. Practice proves that is very pratical that combined GPR

and high density resistivity method to solve the problem of environmental geology, both of which belong to the high precision ground geophysical methods whit the

dielectric constant difference and resistivity diference as the physical basic of

detection target respectivity. The two diference of the dielectric constant and the

resistivity are prevalent in environmental feology, but also has high correlation. The

ambiguity can be effectively eliminated fromtwo ways of the dielectric constant and

the resistivity to describing the underground target. GPR has high longitudinal

resolution that transmit electromagnetic waves which of broadband short pulse and

high frewuency electromagnetic wave, it is based on the time domain reflection

waveform acquisition, processing and analysis that can identify the spatial location

and structure of underground interface or geological. But the detection capability of

GPR is restricted by the high dielectric constant medium and probing depth limited.

The high density resistivity method is of highest resolution in the DC resistivy method

and has volume effect significantly fot detecting target, which reflect the rich

macroscopical feature of detection target from the medium conductivity, and the

probing depth greater than the GPR. GPR and high density resistivity method

combination is both belong to the method combination of deep and shallow, GPR can

describe the shallow characterization whit details and features, the high density

resistivity method can descreibe the deep macroscopic characteristics for the



underground target, so easy to form conceptual geological model, which is convenient

for data analysis and interpretation, it is effective to solve geological problems.

Exploration practice has proved that combining have obvious complementarity,

validation and validity for each other.

III. PRACTICAL ENFINEERING APPLICATION

A. Subgrade collapsing range detection

Two collapse in the construction of a runway happened at a highway tunnel axis part

beneath the runway subgrade in Fujian Province xia Pu area, the collapsing range are

respectively the 190m..60m…180m..55m, and made a preliminary backfill. Requires

to identify the collasing hole distribution and disturbance range and groundwaterenrichment situation in the geophysical methods. The original physiognomy is the

hilly terrain and relatively fat in the site. Quaternary cover layer is eluvial and

slopewash whit reddish brown, yellow and purple clay, sandy silt and gravel clay,

visible strong weathered stone. The underlying rock is the uff and andesite of

Mesozoic. The roadbed backfills is graded poor blasting gravel soil. The gravel

lithology is volcano sedimentary rocks and instrusive rocks. Highway tunnel is

construction in weathered rock section. The GPR type to use is Canadian EKKO-

100A, the antenna center frequency is 50MHZ, measuring point space is 1 meter, the

antenna space is 1.6 meter. The instrument of high density electrical method is

WGMD-3 type of Chongqing geological instrument factory made, using wenna

quadrupole arrangement device, channel spaceis 1.5 meter, isolation coefficient is 11,

the power supply time of 4 seconds. Resistivity image accurately reflects the deep

features about rock collapse position and the loose zone of surrounding rock.

Detection effect is very deal, the shadow particulars is clear about roadbed collapse

and disturbed zone in GPR image, which illustrate mainly strong waves breaking and

messy- shaped wave reflection froup (fig.2)

B. ISLAND PERMAFROST DETECTION



The instrument of high density electrical is WGMD-6 instrument made in

Chongqing geological instrument factory, using wenna quadrupole arrangement

device, channel space is 3.0 meter, isolation coefficient is 18, the time to supply

power is 5 seconds. The karst cave illustrate the characteristics of strong wavegroup (fig.5) of weak wave group after grouting treatment in resistivity image

(fig.7), detection results is accurate after excavation confirmed(fig.8)

D. landslide mass detection

a road engineering Tibet boni conty tongmai countryside In 1997, which is located

thr intersecting whit the fault zone of yigong- palongzangbu, where landslide is

serious, require close geological investigation. First detecting using high density

resistivity method on landslide. Thr resistivity profile display the fault zone of

Yigong-palongzangbu underneath the sliding body (fig.9) groundwater

enrichment. However, the displaying of landslide slip surface is not clear. It is

follow-up to using the GPR of EKKO-IV to probing, antenna space is 1.2 meter,

sampling point is 400, time window recording is 450ns. Using GPR to investing

the gliding mass at the foreslope, the landslideslip surface is cleare as a strong

phase of reflection wave in GPR image (fig.10), which is appromimate to the

depth position of resistivity pofile interpretation, that make the sliding body

outline more clearly, and provides a strong basis for the landslide governance

IV. COCLUSION

1. It is very pratical that combined GPR and high density resistivity method to solve

the problems of environmental geology, but the detection capability of GPR is

restrited bay high dielectric constant medium and probing depth limited. The high

density resisticity method can reflect the rich macroscopical feature of detection

target from the medium conductivity and the probing depth greater than GPR;

GPR and high density resistivity method is both belong to the method combination

of deep and shallow. Gpr can describe the shallow characterization whit details

and features, the high density resistivity method can describe the deep

macroscopic characteristics for underground target



2. . the two diference of the dielectric constant and the resistivity are prevalent in

environmental geology and engineering geology, but also has high correlation,.

The ambiguity can be effectivity eliminated from two ways of the underground

target, so easy to form conceptual geological model and to convenient for dataanalysis and data interpretation. The combining is effectivive that have

compementarity, validation and validity for each other.

3. The detection parameter of GPR is more important than the data processing, it

determines the quality of original data. It is ne to do a necessary to do a certain

amount of field test for determine the detection parameters before you strat work

especially in a strange area, the accumulation of detecting experience can reduce

the workload. Data processing can improve the quality of GPR profile and get the

best interpretation

enviromental geological application of ground penetrating radar

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