Active Bearing Technology of Foot Steel Pipe Applied in Controlling the Large Deformation of Tunnels: A Case Study

Round 1

Reviewer 1 Report

The reviewed manuscript is a case study that reports on active bearing technology of foot steel pipe, which can be applied to control the deformation of tunnels. The paper describes the concept of the active bearing technology and both the FEM analyzes and the technological process with the effects of the application. All sections of the manuscript relate logically to the study's statement of purpose. The outcome is interesting for readers. However, there are several aspects that could be improved.

Below are my questions and comments to the manuscript:

Do the FEM analyzes presented in the paper relate directly to the research conducted in the field?

Whether the material parameters given in Table 1 relate directly to ground conditions during in situ testing? How the values of these parameters were determined?

What was the length and the steel grade of the steel pipes used in the research?

Figure 20 - can the authors refer to the differences in arch vault settlement obtained for two arcs with nonnative load bearing?

Did the authors of the article consider the influence of pipe length on the obtained results?

Is the described technology is applicable only in loess tunnels, can it be used or should it be tested in other ground conditions?

Some of the figures (Figure 2, 3, 5, 17) are hardly legible - font color and/or height.

Author Response

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Reviewer 2 Report

The background references describe the complexity of the problem that the authors are dealing with. This background gives an appropriate idea of the problem. The description of the project also gives a correct idea of the problem.

The justification of the introduction of a vertical load to active bearing of pre-deformed FSP is supported in the context of a quicker control of deformation in the tunnel section.

On pages 5-7, the model used should be better explained and a justification of the selected mesh and de parameters used should be done. A sensibility analysis could help to understand if the variation on the model results is due just to the different FSP solutions proposed or it also could be dependant on the soil conditions. The presence and variation of water conditions also could be considered in terms of solution analysis. Why are material parameters or table 1 used, no reference of any geotechnical study or laboratory analysis is given?

In figure 12 the difference of results explained in the text is not clear according to the information given results are very close to each other. Also figure 13 says that there is a settlement reduction of 17.3 mm that is not clear the two curves are the same until day 3. From this point to day 11 the settlement difference of 15.4 mm of the curves can be differentiated clearly. This should be corrected or better explained to be well understood.

In section 5.3, it is identified what happens when introducing the proposed technique into the real field construction by measuring settlement under different conditions. In figure 20 into this section results from active load bearing and no active load bearing are compared, but no reference is given to the properties of the FSPs used. It is supposed that 50 mm FSPs are used, and a 10 cm preloading displacement is used, but not clear reference is used in the actual section, it could be confusing if results whit the model want to be compared. Also, a comparation with model results could improve the work. The model could be validated with the measured results.

Conclusions are according to the developed work although they could be improved if some of the considerations proposed are worked.

Author Response

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Reviewer 3 Report

The overall quality of the presentation should be improved. Starting with the abstract and continuing with the other sections, the English writing should be reconsidered. 

The conclusion 2, presented in the abstract seems miss-leading. 
"The active bearing mode of exerting its 18 bearing capacity in advance by pre pressing the foot steel pipe can effectively reduce the settlement 19 of the vault. The settlement rate of the vault can be reduced by about 70% in 1-2 days, and more 20 than 50% in 1-3 days." 

The numerical model presented in Ch. 3.1 must be explained in more detail (e.g. element type, constraints, loads, supports, assumptions, etc.). Figure 7 does not provide sufficient detail!

Ch. 4.1 states that for the steel pile only vertical load is considered (see line 200). This approach does not align with Ch. 3.1, which explain the FSP and its action mechanism (refer to Figure 7 and Figure 8) and contradicts the pile real behaviour.

Tables 2 through 5 presents several cases of analysis (two vs. four piles). The content is not clearly explained (What does two vs four piles refers to? How are they installed? What is the model setup for the two cases?). 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

All major points have been addressed and the paper quality was significantly increased.