CRACK DETECTION ON RETAINING WALL BY USING THERMAL

CAMERA AND IMAGE PROCESSING TECHNIQUE

AFIQAH BINTI ISMAIL

A project report submitted in fulfilment of the

requirement for the award of the degree of

Master of Engineering (Geotechnics)

School of Civil Engineering

Faculty of Engineering

Universiti Teknologi Malaysia

JANUARY 2019

iii

DEDICATION

This thesis is dedicated to my father, who taught me that the best kind of

knowledge to have is that which is learned for its own sake. It is also dedicated to my

mother, who taught me that even the largest task can be accomplished if it is done

one step at a time.

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ACKNOWLEDGEMENT

In preparing this thesis, I was in contact with many people, researchers and

academicians. They have contributed towards my understanding and thoughts. In

particular, I wish to express my sincere appreciation to my main thesis supervisor,

Associate Professor Dr. Ahmad Safuan bin A. Rashid for encouragement, guidance,

critics and friendship.

I am also very thankful to my lecturers, Associate prof Dr Mushairry bin

Mustaffar and Dr Radzuan Sa’ari for their guidance and advices in analysing the data.

Without their continued support and interest, this thesis would not have been the same

as presented here. I am also indebted to Survey unit department of Universiti

Teknologi Malaysia (UTM) for allowing me to borrow their equipment and tools for

my project.

My fellow postgraduate student should also be recognised for their support.

My sincere appreciation also extends to all my colleagues and others who have

provided assistance at various occasions. Their views and tips are useful indeed.

Unfortunately, it is not possible to list all of them in this limited space. I am grateful

to all my family member and my fiancé for the support they gave to me. I am more

than blessed. Alhamdulillah.

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ABSTRACT

Monitoring on geotechnical structure such as retaining wall, beams and dams

is an essential task to retain its serviceability. One of the necessary component to be

monitored is the presence of crack. In this paper, the potential of infrared

thermography (IRT) as an operational tool for detecting cracks was tested and

demonstrated on retaining wall. Two main work phase is employed in this study. First

phase is focused on fieldwork which involve capturing the image by using infrared

thermal (IRT) camera and digital single lens camera (DSLR). Second phase is focused

on image processing technique by using a MATLAB numerical software. Targeted

crack sample from the retaining wall have been scratched to observe the deformation

of the crack before and after scratching. Analysis of the infrared thermal (IRT) image

show that crack stand as cold area (low temperature) with respect to surrounding area.

Disturbance of the heat flow allow the thermal camera to detect the presence of crack

on retaining wall. Processing of the image extracted allows geometric characterization

and direction of propagation of the crack through the wall to be determine. Within

limited testing, detection and analysis of cracks is better with the proposed method

because it is economical, can reduce time and involve no contacts. This paper presents

a preliminary study for further inspection development on retaining wall.

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ABSTRAK

Pemantauan terhadap struktur geoteknik seperti dinding penahan tanah,

empangan dan juga tiang pengukuh struktur adalah penting bagi memastikan

fungsinya untuk mengekalkan kestabilan dapat berjalan lancar. Antara komponen

yang perlu diperhatikan pada struktur geoteknik adalah kehadiran retakan.

Penggunaan kamera berdasarkan sinar haba inframerah digunakan dan diuji bagi

mengesan retakan pada dinding penahan. Terdapat dua fasa kerja dalam kajian ini.

Fasa pertama tertumpu pada kajian lapangan di mana gambar struktur dinding penahan

akan diambil menggunakan kamera sinar inframerah dan juga kamera digital.

Kawasan retakan yang terdapat pada dinding penahan ditoreh bagi menguji dan

melihat perbezaan sebelum dan selepas retakan itu dibesarkan. Fasa kedua tertumpu

kepada kaedah memproses data dan maklumat yang dikumpulkan. Gambar yang telah

ditangkap akan diproses menggunakan perisian MATLab. Keputusan sinar haba

inframerah terhadap retakan yang terdapat pada dinding penahan menujukkan

kawasan retakan mempunyai suhu yang rendah dan dikategori sebagai kawasan yang

sejuk manakala permukaan dinding penahan yang lain menunjukkan suhu yang lebih

tinggi dan dikategori sebagai kawasan yang panas. Gangguan terhadap pengaliran

haba menyebabkan retakan dapat dikenalpasti. Selain itu, hasi analisis gambar

menunjukkan arah retakan dan perubahan yang berlaku pada dinding penahan. Hasil

kajian ini membuktikan kaedah berdasarkan sinar haba inframerah dan teknik

memproses gambar memudahkan proses mengenalpasti retakan dan mengetahui

perubahan yang berlaku pada retakan.Kaedah ini lebih menjimat masa, tidak

memerlukan sentuhan dengan subjek yang diuji dan juga lebih ekonomi. Kertas kerja

ini merupakan kajian permulaan dalam melakukan pemantauan terhadap dinding

penahan.

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TABLE OF CONTENTS

TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES ix

LIST OF FIGURES x

LIST OF ABBREVIATIONS xii

LIST OF APPENDICES xiii

CHAPTER 1 INTRODUCTION 1

1.1 Problem Background 1

1.2 Problem Statement 1

1.3 Research Goal 1

1.3.1 Research Objectives 3

1.4 Scope of project 4

1.5 Limitation 4

1.6 Significance of project 4

1.7 Thesis outline 5

CHAPTER 2 LITERATURE REVIEW 7

2.1 Introduction 7

2.2 Type of crack 7

2.3 Causes of the crack occurence 8

2.4 Image Processing Technique 8

2.5 Existing method on detection of crack 9

2.5.1 Ultrasonic Image 10

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2.5.2 UAV camera image 10

2.5.3 Camera based image 11

2.5.4 Laser Image 11

2.6 Concept of thermography 12

2.6.1 Infrared thermography method 12

2.6.2 IR Thermal Imaging Camera 13

2.7 Particle Image Velocimetry (PIV) 15

CHAPTER 3 RESEARCH METHODOLOGY 19

3.1 Introduction 19

3.2 Data Collection 20

3.2.1 Thermal Imaging 21

3.2.2 Digital Single Lens Camera 22

3.2.3 Camera Calibration 23

3.2.4 Data Acquisition 25

3.3 Data Processing 28

3.3.1 Infrared Thermography image 29

3.3.2 Particle Image Velocimetry (PIV) 29

CHAPTER 4 RESULT AND DISCUSSION 30

4.1 Infrared Thermography Image 30

4.1.1 Retaining Wall A 32

4.1.2 Retaining Wall B 34

4.2 Particle Image Velocimetry 36

4.3 Chapter Summary 44

CHAPTER 5 CONCLUSION AND RECOMMENDATIONS 45

5.1 Research Outcomes 45

5.2 Contributions to Knowledge 46

5.3 Future Works 46

REFERENCES 47

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LIST OF TABLES

TABLE NO. TITLE PAGE

Table 2.1 Classification of crack based on crack width 8

Table 2.2 Regression analysis for the results of preliminary feature

screening 13

Table 2.3 Thermal Imaging Surveillance System Model (Wong et al.,

2009). 14

Table 3.1 Thermal camera specifications 22

Table 3.2 XY coordinate of target marker 24

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

Figure 2.1 Preprocessing of crack (Lee et al., 2007) 9

Figure 2.2 Procedure on calculating crack width 10

Figure 2.3 Thermal Imaging Surveillance System Model (Wong et al.,

2009) 14

Figure 2.4 Thermal images with temperature range(Wong et al., 2009)

14

Figure 2.5 Schematic view of the setup 15

Figure 2.6 Schematic diagram of image set up of PIV (J Westerweel) 17

Figure 2.7 PIV analyses workflow in MATLAB 17

Figure 3.1 Flowchart of methodology 19

Figure 3.2 Location of retaining wall 20

Figure 3.3 Equipment used in collecting data 20

Figure 3.4 Digital Single Lens Camera 22

Figure 3.5 Target Marker 23

Figure 3.6 Process in capturing the image of crack 25

Figure 3.7 Diagram illustrating position of camera at site 25

Figure 3.8 Image of crack 26

Figure 3.9 Image of crack on retaining wall B 27

Figure 3.10 Surface temperature taken on retaining wall 27

Figure 3.11 Measuring crack width using Vernier calliper 28

Figure 3.12 FLIR Tools Software 29

Figure 3.13 Steps in analysing the crack using MATLAB Software Particle 30

Figure 3.14 Processing of the crack image 31

Figure 4.1 Raw thermography image 32

Figure 4.2 Raw thermography image 33

Figure 4.3 Distribution of temperature on the wall by infrared thermography and

temperature recorded at site 34

Figure 4.4 Temperature at specific location of the image 34

Figure 4.5 Thermal image of retaining wall B 35

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Figure 4.6 Thermal image of uppert part on retaining Wall B. 36

Figure 4.7 Contour along horizontal direction of the crack 38

Figure 4.8 Contour along horizontal direction of the crack 39

Figure 4.9 Contour with temperature distribution 40

Figure 4.10 Contour with temperature distribution 40

Figure 4.12 Image Analysis by Vector Flow 41

Figure 4.13 Image analysis by vector flow (base and enlarge image) 43

xii

LIST OF ABBREVIATIONS

IR - Infrared Thermography

DSLR - Digital Single Lens Camera

PIV - Particle Image Velocimetry

NDT - Non Destructive Testing

xiii

LIST OF APPENDICES

APPENDIX TITLE PAGE

Appendix A Schematic Diagram of Retaining Wall B 50

Appendix B Schematic Diagram of Retaining Wall A 51

Appendix C Thermal Image of Retaining Wall A 52

Appendix D Thermal Image of Retaining Wall B 53

Appendix E GeoPIV Software Usage (White et al., 2002) 54

Appendix F Vector around scratched area 56

Appendix G Contour along vertical direction 57

Appendix H Contout along horizontal direction 58

Appendix I Testing the PIV method on wall before and after crack occur 59

1

CHAPTER 1

INTRODUCTION

1.1 Problem Background

This chapter outline the objectives, methodology and arranged plan for a

research project that will be carried out as a partial fulfilment for the Master of Civil

Engineering (Geotechnics), University Technology Malaysia. This project will be

conducted during second and third semester of 2018/2019 session. The title of the

proposed project is “Evaluation of Cracks on Retaining Wall by using Thermal Camera

and Image Processing Technique”.

Monitoring and maintenance of geotechnical structure such as retaining wall,

earth-fill dams and beams is an essential task to retain its serviceability. Mageswari,

Divakar & Aravind (2016) stated that it is effective to monitor the structural health of

a building, so that the life cycle cost of a building can be reduce from construction to

maintenance. One of the necessary component to be monitored is the presence of

cracks. This is because a structure will develop cracks whenever the stress in the

components exceeds its strength. Traditionally, visual inspection has been done to

monitor the cracks on building. However, this method need specialist knowledge and

experience, lacks objective and time consuming. Automation of this process was

suggested by researchers to increase the productivity, efficiency and also the

inspection cycles.

1.2 Problem Statement

Concrete retaining walls are the most common type of geotechnical structures

that function to control lateral pressure and resist the back soil or other materials when

there is a change in elevation. It is used for stabilizing the slope and provide space at

2

highway, structures below the ground level and around the building. However in

Malaysia, there are quite numbers of issues related to the failure of retaining wall such

as on 2017 at Tanjung Bungah, Penang and same year occur at Bangsar, Kuala

Lumpur. There are also 8 failures in rapid rail transit works that were related to

retaining walls and strutting works and the failures resulted in economic loses and

collapsed building (Moh & Hwang, 2007). When concrete retaining wall fail, it will

not only cause an extensive damage of the landscape but the price to repair is also

costly. Thus, preventive measures or regular inspection need to be taken to prevent

this kind of problem to be happen.

To prevent subsequent damage, early detection of growing cracks is one of the

major concerns in engineering. Crack usually initiate at the microscopic level on the

structure surface. When cracks in these structures are created, the stability may be

enforced and causes to defeat. Cracking can be result of one or a combination factors,

all of which involve some form of restraint. The factors include drying and shrinkage,

thermal contraction or expansion, settlement, differential bearing capacity and stresses

from applied force or load. Due to some limitations in manual inspection, automatic

crack detection have been suggested to give better analysis. Recently, non-destructive

testing (NDT) techniques is proposed as a method in detecting crack such as ultrasonic

testing, infrared and thermal testing, laser testing and radiographic testing (Mohan and

Poobal, 2017).

Among these technologies, thermography testing is seen as a possible approach

in provide an easy visualisation data for crack studies. Thus, the scientific interest of

this paper is to apply the infrared (IR) thermography camera in detecting the crack on

retaining wall. A thermal camera detects radiation in the infrared range of the

electromagnetic spectrum and produces images of that radiation. According to the

black body radiation law, all objects emit the infrared radiation with intensity related

to their temperatures. The amount of radiation emitted by an object increases with

temperature. Therefore, the thermography allows to see the area as variations in

temperature of the target objects.

3

In 2008, thermographic testing has been applied by STARMANS electronic

s.r.o in determine crack on square steel bars used in automotive industry. Starman (

2008) mentioned that the system show faster inspection times, excellent detection

sensitivity and it has ability to detect hidden, subsurface cracks. Besides, Martin et al.,

(2016) also used thermal images to predict different depth of cracks on steel and the

results demonstrate good precision of the method in predict depth values of crack with

15% of maximum deviation. Since thermal camera can be used to inspect the heat loss,

it may suitable to be apply in detecting the location of the cracks on the geotechnical

engineering structure.

1.3 Research Goal

The aim of this study is to apply the thermal testing method to detect and

analyse crack on geotechnical structure.

1.3.1 Research Objectives

The objectives of the research are:

(a) To detect cracks on retaining wall by using infrared thermography method.

(b) To determine displacement and orientation of the cracks on retaining wall by

using image processing technique

(c) To establish a thermal model representing temperature distribution of retaining

wall with propagation of the cracks.

4

1.4 Scope of Project

This study was undertaken to capture the retaining wall image by using thermal

camera and subsequently processing them using computer to detect and analyse the

characterization of crack. Therefore, the scope of this thesis can be summarized as:

(a) Capture the image of retaining wall by using thermal camera and transfer it

into the computer to identify the cracks.

(b) Develop suitable image processing technique in classifying and quantifying

different type of cracking based on width, length or other properties.

(c) Establish a thermal model of the structure with the surface temperature.

(d) Assessing the performance of the proposed method against existing methods

in term of accuracy and practicality.

1.5 Limitations

The research will be limited to :

(a) The distance between the sensor (thermal camera) and the crack.

(b) Weather conditions (light, wind and surrounding temperature).

(c) Time for the data collection.

(d) The location of the structure of study.

1.6 Significance of the project

(a) Propose a two dimensional analysis with both quantitative and qualitative data

extraction.

5

(b) Provide an alternative method in crack detection system, which is viable to be

apply in maintenance the geotechnical structure.

Replace the existing manual inspection due to several limitations.

1.7 Thesis Outline

This paper will be consist of five chapters. Presentation of the findings of the

present investigation begins in chapter two with a literature review describing the

background of study. The type and causes of cracks, the non-destructive methods,

existing image processing techniques for crack detection are reviewed. Besides, the

theory involved in thermography are also discussed.

Chapter three explains the processes to be followed using the thermal testing

technique. In addition, this chapter will describes the image processing developed

including, how to detect the cracks and cracking classification. Simple manual method

assessments are discussed.

Chapter four present the result obtained from the proposed method. The results

are compared and validated using a visual inspection.

Chapter five discusses and concludes the findings of the project. Future work

of this topic is also suggested.

47

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