Testing of Structural Integrity of U-Shaped Sheet Pile in Canal Engineering Using Ground Penetrating Radar

Round 1

Reviewer 1 Report

To-date, there is a growing interest for novel applications of no-invasive electromagnetic sensing technologies for civil infrastructures monitoring. Then, papers about the use of the GPR technology for monitoring the U-shaped piles for engineering infrastructures are welcomed and must be encouraged. 

However, I have to point out many critical aspects in the manuscript.

- The more relevant aspect is the following, there is the absence of a critical approach. All the results are described without critical discussion and analyses. In many parts the manuscript is quite similar to a technical report.

- The introduction is a list of previous papers, a more organized description of the current state-of-the-art is mandatory.

- The choice of the value of the dieletric constant (5.5) is very important and plays an important role in the GPR data interpretation. It is not acceptable that authors assumed this value (5.5) without any comments.

- The wavelet method is a powerful tool for GPR image processing, but it cannot be used without a rigorous analysis of the GPR section. 

- The comparison between the GPR images (after the wavelet processing) and the cause of the cracks in the piles is generic and purely qualitative. A sample list of considerations is presented. It is not acceptable in a scientific paper! Furthermore, this is the key goal of the paper!

- The figure captions are no informative. It is mandatory to well describe the figures of the manuscript. 

- The paragraph "Conclusions" is a purely list of sentences quite generic and without any critical considerations on the results respect to the current state-of-the-art. 

Taking into account all these comments, I suggest the publication of the paper only after an accurate major revision.

Author Response

Response to Reviewer 1 Comments:

Point 1: The more relevant aspect is the following, there is the absence of a critical approach. All the results are described without critical discussion and analyses. In many parts the manuscript is quite similar to a technical report.

Response 1: The discussions and analysis are supplemented to all the results are described. The specific can be seen in revised manuscript.

 

Point 2: The introduction is a list of previous papers, a more organized description of the current state-of-the-art is mandatory.

Response 2: The introduction was reorganized and the latest reference has been added. The specific can be seen in revised manuscript.

 

Point 3: The choice of the value of the dieletric constant (5.5) is very important and plays an important role in the GPR data interpretation. It is not acceptable that authors assumed this value (5.5) without any comments.

Response 3: The value (5.5) of relative permittivity is explained. Through the radar measurement of undriven piles on the ground, the average value (5.5) can be obtained.

 

Point 4: The wavelet method is a powerful tool for GPR image processing, but it cannot be used without a rigorous analysis of the GPR section.

Response 4: The problem of using wavelet transform to deal with radar signals has been discussed in detail in literature [24] and marked in the paper, so it is not discussed too much in this paper.

 

Point 5: The comparison between the GPR images (after the wavelet processing) and the cause of the cracks in the piles is generic and purely qualitative. A sample list of considerations is presented. It is not acceptable in a scientific paper! Furthermore, this is the key goal of the paper!

Response 5: The failure mechanism of U-shaped-sheet-pile is analyzed from soil mechanics between line233 and line236. Expansive soil generally has high strength and low compressibility in the natural state. In the process of driving U-shaped-sheet-pile, it is subjected to great resistance and requires many times (up to hundreds of times) of hammerings to drive, which inevitably has a great impact on the pile structure.

 

Point 6: The figure captions are no informative. It is mandatory to well describe the figures of the manuscript.

Response 6: The information of all figures are completed. The specific can be seen in revised manuscript.

 

Point 7: The paragraph "Conclusions" is a purely list of sentences quite generic and without any critical considerations on the results respect to the current state-of-the-art.

Response 7: The conclusion was rewritten.

The U-shaped-sheet-pile wall is used for the protection of the vertical slope of the river canal. Most of the pile body after driving is hidden below the construction surface. The structural integrity of pile body is an important index that controls the bearing capacity and durability of pile foundation. The method of adopting U-shaped sheet pile wall to protect expansive soil vertical slope includes the mechanism of protection and the method of testing the effectiveness of protection measures. Under the condition of natural expansive soil deposit, the U-shaped-sheet-pile must be strong enough to overcome the high stresses from the natural expansive soil layer. The degree of damage to the pile structure is the key basis for determining the pile driving process.

The method of filtering reflected radar wave of U-shaped-sheet-pile in expansive soil is studied. The effective reflection information of abnormal parts of U-shaped plate pile is obtained, and the method of discrimination of defective radar wave is established. The integrality testing of U-shaped-sheet-pile wall in expansive soil presented in this paper can also be applied to other types of pile foundation, which has strong practicability.

 

Reviewer 2 Report

Dear Authors,

The manuscript is presenting a principally interesting approach for non-destructive testing of concrete piles in canal engineering. The paper needs a thorough workover of the English language. Furteron, I have a few detailed comments to the paper:

 

1. Abstract line 13 ff: This statement is not well describing the paper. „Method and theorie of using U-shaped piles“ are not dicussed. What you discuss here is the non-destructive testing of U-shaped piles. The abstract text is suggesting that you perform geomechanical investigations, including modelling in order to assess stability of pile constructions in the presence of underwater expansive soil. But this is not discussed in the paper at all.

2. Better say „non-destructive testing“ rather than detection. „Detection“ as a term rather refers to finding particular elements affecting the stability of a structure, in this context. Non-destructive testing is the general procedure of investigating a structure, in order to (poetentially) detect fractures or other issues.

3. Line 25: receive → reception

4. Chapter title data recognition is unclear → identification of data format. The schematic diagram needs more details. „Left“ and „Right“ shold be rather West and East.

5. Ch. 2.1, Lines 67 ff: The site description is a bit unclear. What do the two „length“ indications mean? This is a canal construction. Is the east west length rather the canal's width?

6. Chapter 2.2: This chapter needs language editing, as it is hard to understand. It is dealing with the issue of data format. To my knowledge, GPR systems typically generate data in SEG-Y format, which is the industry standard for seismic (and GPR) trace data. There are quite a number of commercial and also freely available open source software codes available for reading and converting such data. Please clarify a bit especially the text of the flines 79 to 89 if you think this issue is really so important. Alternatively, you can just say a few words in one or two sentences that you use previously developed own code to convert GPR data for further processing in your own environment.

7. Automatic gain control is widely used in seismic data processing, it is a standard procedure available in any processing software for seismic (and gpr) data for decades already, I do not see the new development here. At least reference to (open source) AGC tools included in the Seismic Unix package would be appropriate. The novelty in this paper is rather the application in canal engineering, rather than the implementation of long-time existing processing methods.

8. Lines 147 – 152 contain incomplete phrases, please check and modify to complete the sentences.

9. Line 168: You mean here the relative permittivity (dimensionless), not the dielectric constant which has a unit (SI: As/Vm) and a defined value for vacuum.

10. Figures 9 and 10 show the same data comparison as figures 11 and 12, just using another tool (Matlab). These figures do not add information to the whole paper and can be skipped.

11. For Figures 7, 8, and 11, 12 I suggest to plot them in the same horizontal spatial scale in order to make comparison of the results easier. I am aware that the 100 MHz data have fewer traces but still the point-to-point comparison would be easier with both sections having the same width.

12. Line 245: detection should rather be named non-destructive testing. This is what you basically do when doing GPR measurements on such piles.

 

Author Response

Response to Reviewer 2 Comments:

Point 1: Abstract line 13 ff: This statement is not well describing the paper. „Method and theories of using U-shaped piles“ are not discussed. What you discuss here is the non-destructive testing of U-shaped piles. The abstract text is suggesting that you perform geomechanical investigations, including modelling in order to assess stability of pile constructions in the presence of underwater expansive soil. But this is not discussed in the paper at all.

Response 1: “Method and theories of using U-shaped piles” is revised to “non-destructive testing of U-shaped-sheet-pile”. ……In this paper, the non-destructive testing of U-shaped-sheet-pile wall to protect the vertical slope of underwater expansive soil in the canal project is studied, which is of great significance in reducing the construction area and minimizing the cost of construction. It is necessary to test the structural integrity of the U-shaped-sheet-pile, which is also vital in ensuring the quality of the whole project. Ground penetrating radar (GPR) is used to detect the structural integrity of the U-shaped-sheet-pile in expansive soil. On the basis of identification and conversion of the original GPR data format, the processing methods based on the time-varying automatic gain and wavelet analysis are implemented. A case study proves GPR testing method is effective to estimate the quality of the U-shaped-sheet-pile.

 

Point 2: Better say „non-destructive testing“ rather than detection. „Detection“ as a term rather refers to finding particular elements affecting the stability of a structure, in this context. Non-destructive testing is the general procedure of investigating a structure, in order to (potentially) detect fractures or other issues.

Response 2: The relevant “detection” are replaced by “non-destructive testing”.

 

Point 3: Line 25: receive → reception

Response 3: Line25: receive  →  reception

 

Point 4: Chapter title data recognition is unclear → identification of data format. The schematic diagram needs more details. „Left“ and „Right“ shold be rather West and East.

Response 4: Schematic diagram (Figure 2) has been completed. Chapter 2.2 has been revised as “Identification and conversion of original GPR data format”. The new Figure 2 can be seen in revised manuscript.

 

Point 5: Ch. 2.1, Lines 67 ff: The site description is a bit unclear. What do the two „length“ indications mean? This is a canal construction. Is the east west length rather the canal's width?

Response 5: This is a test section project. The east-west length of the bottom of canal deep excavation is 13.75 meters and the south-north length of the bottom of canal deep excavation is 11 meters. Therefore, the two lengths refer to the bottom length of the canal deep excavation. It is not the canal’s width.

 

Point 6: Chapter 2.2: This chapter needs language editing, as it is hard to understand. It is dealing with the issue of data format. To my knowledge, GPR systems typically generate data in SEG-Y format, which is the industry standard for seismic (and GPR) trace data. There are quite a number of commercial and also freely available open source software codes available for reading and converting such data. Please clarify a bit especially the text of the flines 79 to 89 if you think this issue is really so important. Alternatively, you can just say a few words in one or two sentences that you use previously developed own code to convert GPR data for further processing in your own environment.

Response 6: Language editing is done in Chapter 2.2. The developed own program is more convenient to the processing and analysis of the GPR original data. GPR users can freely add some latest processing methods and modify it. The program also provides a basic platform for the secondary development of GPR interpretation system.

 

Point 7: Automatic gain control is widely used in seismic data processing, it is a standard procedure available in any processing software for seismic (and gpr) data for decades already, I do not see the new development here. At least reference to (open source) AGC tools included in the Seismic Unix package would be appropriate. The novelty in this paper is rather the application in canal engineering, rather than the implementation of long-time existing processing methods.

Response 7: Time-varying AGC is different from the conventional AGC. The deep radar information is obtained by adjusting the time window. With the change of time window, different gain effects are acquired.

 

Point 8: Lines 147 – 152 contain incomplete phrases, please check and modify to complete the sentences.

Response 8: It has been modified as required from line 147 to line 152. The wavelet transform is a time-frequency analysis method that the time-frequency window has a fixed size but its shape can be changed. The main characteristics of the wavelet transform are a high frequency-resolution and a low time-resolution in the low frequency range, and a high time-resolution and a low frequency-resolution in the high frequency range. So it’s highly adaptive, also known as a mathematical microscope.

 

Point 9: Line 168: You mean here the relative permittivity (dimensionless), not the dielectric constant which has a unit (SI: As/Vm) and a defined value for vacuum.

Response 9: Line168: it is a relative permittivity (dimensionless).

 

Point 10: Figures 9 and 10 show the same data comparison as figures 11 and 12, just using another tool (Matlab). These figures do not add information to the whole paper and can be skipped.

Response 10: Figure 9 and Figure 10 have been skipped.

 

Point 11: For Figures 7, 8, and 11, 12 I suggest to plot them in the same horizontal spatial scale in order to make comparison of the results easier. I am aware that the 100 MHz data have fewer traces but still the point-to-point comparison would be easier with both sections having the same width.

Response 11: The horizontal spatial scales of these figures were adjusted and the analysis of these figures were added.

 

Point 12: Line 245: detection should rather be named non-destructive testing. This is what you basically do when doing GPR measurements on such piles.

Response 12: It is revised in comment 2.

 

Round 2

Reviewer 1 Report

Dear authors,

I greatly appreciated your work to improve the overall quality of the manuscript. However, I have to point out that many critical aspects still remain.

The reply about the wavelet and the dielectric constant  was too generic.  No effort was made to introduce a more critical analysis of the results. The quality of the figure captions was not improved. 

A new round with a minor revision is mandatory.

Author Response

Response to Reviewer 1 Comments:

Point 1: The reply about the wavelet and the dielectric constant was too generic. No effort was made to introduce a more critical analysis of the results. The quality of the figure captions was not improved.

Response 1: In the radar signal, the useful signal is usually manifested as low frequency signal or some relatively stable signal, and the noise signal is usually shown as high frequency signal. Therefore, after wavelet decomposition, the noise part is usually included in the high frequency, and the amplitude of the high frequency coefficient of the noise is rapidly attenuated with the increase of scale and decomposition levels. In addition, the performance of noise on different scales is also unrelated. Thus, the high frequency wavelet coefficients are processed in the form of threshold values and then the processed signals are reconstructed to achieve the purpose of denoising. (Line 156-163)

In order to determine the relative dielectric constant value, two undriven piles are selected on the ground surface, and 100MHz antennas are used for radar test respectively. Since the test pile length is known (11.5m), the top-bottom interface is determined according to the reflection characteristics of radar images at the top and bottom of sheet pile, and the depth h(m) corresponding to the bottom interface is set as 11.5m. The electromagnetic wave propagation time t(ns) can be directly read by the ordinate of the radar image, the electromagnetic wave propagation speed v(m/ns) can be obtained by the formula v=2h/t, and then the relative dielectric constant can be obtained by the formula v=C/. Where C is the velocity of light (C=0.3m/ns). The average relative permittivity ()/2 can be acquired from the two piles. Where  and  are the relative dielectric constant values of the two piles respectively. (Line 169-179)

The quality of the figure captions was improved in Figure 2, 7, 9, 10.

 

Reviewer 2 Report

Thank you for the revised version of the manuscript. The paper has improved but there are still some formal/language issues which make the paper difficult to read at some places. This should be fixed before the final version will be ready for publication. Here are my detailed comments:

 

1. Line 26: „geophysical method“ instead of „equipment“

2. Line 27: „As the difference...“ Phrase needs workover, incomplete.

3. Line 31 – 33: This phrase is also unclear. Needs re-writing: „For the pile foundation, which is doubt in the low strain detection and analysis, the GPR method can be used for retargeting, so as to give an accurate interpretation and ensure the quality of engineering of the pile foundation.“ I think you mean something like: „It is difficult to detect low strain in pile foundations as potential damage is hidden in the subsurface. The GPR method can detect such targets in the subsurface and helps to ensure the engineering quality of pile foundations.“

4. Chapter 2.2: I still cannot see the relevance of this chapter. I suggest to mention the format identification and conversion issue briefly within the chapter „acquisition and processing“ instead of having this in one short chapter.

5. Line 220 and following: What is the relation between the GPR measurements and the pictures shown in Fig. 11? Have the piles been retrieved after the investigations and photos been taken? Please explain a bit more what can be seen on Fig. 11 before discussing the crack distribution.

6. Written english needs corrections in general. Please try to have someone (if possible English native speaker) revise the language.

Author Response

Response to Reviewer 2 Comments:

Point 1: Line 26: “„geophysical method” instead of “„equipment”.

Response 1: Line26: “...geophysical method” instead of “…geophysical detection equipment”.

 

Point 2: Line 27: “„As the difference...” Phrase needs workover, incomplete.

Response 2: Line27: “…As the difference…” instead of “…Because of the difference…”.

 

Point 3: Line 31 – 33: This phrase is also unclear. Needs re-writing: “ „For the pile foundation, which is doubt in the low strain detection and analysis, the GPR method can be used for retargeting, so as to give an accurate interpretation and ensure the quality of engineering of the pile foundation.” I think you mean something like: “It is difficult to detect low strain in pile foundations as potential damage is hidden in the subsurface. The GPR method can detect such targets in the subsurface and helps to ensure the engineering quality of pile foundations.”

Response 3: Line 31-33: “For the pile foundation, which is doubt in the low strain detection and analysis, the GPR method can be used for retargeting, so as to give an accurate interpretation and ensure the quality of engineering of the pile foundation.” instead of “It is difficult to detect some potential damages are hidden in the pile foundation using low strain testing method. The GPR can be used to retest and give an accurate explanation to ensure the engineering quality of pile foundation.”

 

Point 4: Chapter 2.2: I still cannot see the relevance of this chapter. I suggest to mention the format identification and conversion issue briefly within the chapter “…acquisition and processing” instead of having this in one short chapter.

Response 4: It has been modified as required from Line 101 to Line 105. GPR data storage format is binary or hexadecimal in domestic and international systems. In addition, each GPR data file has a file header. In this paper, we adopted Yang’s method to process the GPR data because of the flexibility [18]. In the meanwhile, the converted data can be reconverted to the original data format, and the build-in processing software can be used for display and processing.

 

Point 5: Line 220 and following: What is the relation between the GPR measurements and the pictures shown in Fig. 11? Have the piles been retrieved after the investigations and photos been taken? Please explain a bit more what can be seen on Fig. 11 before discussing the crack distribution.

Response 5: Line 236-240: The water injection test was carried out by excavating the bottom of foundation ditch to the elevation of riverbed to evaluate the water injection effect of sheet pile wall. The results of excavation can be used to further check the effect of radar test before water injection. The surface of U-shaped-sheet-pile after excavation is shown in Figure 11. The damages of U-shaped-sheet-pile also verify the correctness of the radar test results.

Since the test results did not meet the requirements, the U-shaped-sheet-piles were not retrieved after the investigations and photos been taken, and the construction measures of cutting off piles were directly adopted to ensure the smooth flow of the river.

 

Point 6: Written english needs corrections in general. Please try to have someone (if possible English native speaker) revise the language.

Response 6: The paper has been submitted to the English majors for review.