Experiment and Numerical Simulation on Grouting Reinforcement Parameters of Ultra-Shallow Buried Double-Arch Tunnel

Round 1

Reviewer 1 Report

• The English level is to be improved.
• A nomenclature is to be added.
• What is the relation between the experimental and numerical analysis.
• The numerical method is to be detailed.
• The solved governing equations are to be presented.
• The title of Fig.10 is to be changed. 
• A figure presenting the boundary conditions is to be added.
• A mesh sensitivity test is to be performed.
• Is the studied configuration 3D or 2D? 
• Higher quality resolution figures are to be provided for: Figs 2, 10, 11, 12-21.
• The abstract is to be shortened.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Review on Experiment and numerical simulation on grouting reinforcement parameters of ultra-shallow buried double-arch tunnel

Summary:

Building urban highway tunnels can be difficult due to geological constraints and the surrounding environment. Poor geological conditions, shallow burial depths, tight engineering land, a complex surrounding environment, and strict control standards are some of the challenges. Several methods and measures are frequently used to reinforce the surrounding rock, according to modern tunnel theory, to maximize the self-supporting capacity of the surrounding rock, including grouting reinforcement, advance support, small pipe reinforcement, and other measures. This research aims to fill the gap between laboratory tests, literature analysis, and numerical simulation to determine the grouting parameters of the Haicang double-arch tunnel’s surrounding rock.

Haicang Tunnel is a 240m long double arch tunnel in Xiamen, China, that runs beneath a six-lane urban expressway. It passes through several power cables, water supply and drainage lines. The two-way, six-lane tunnel has a cross-sectional area of 119.27 m², a headroom width of 14.60 m, and a headroom height of 10.15 m. Three sections of the tunnel were dug using the three-heading excavation method.  A total of 152 tests were conducted with a single liquid cement slurry grouting ratio of 0.4, 0.6, 0.8, and 1.

The relationship between w/c ratio and initial setting time of cement slurry was found to be well-fitting with a good correlation coefficient (R² = 0.9997) in this study.  For the slurry water cement ratio values of η=0.75 and η=1.0 using the cubic polynomial, the fitting correlation coefficients R² were found to be 0.9738 and 0.8349, respectively, indicating that the model fit well.

Positive Points of this study:

• The ground settlement, deformation of the vault and adjacent pipeline under different grouting parameters were studied to determine the suitable grouting thickness and w/c ratio of the surrounding rock of the double arch tunnel in Haicang Tunnel.
• When determining the proper grouting parameters, the methodology includes laboratory experiments and numerical simulations based on extensive literature reviews.
• The results show that grouting reinforcement reduces surface settlement and horizontal convergence effectively.
• Using h=1.0 m and h=1.5 m for the grouting reinforcement layer thickness, the reinforcement effect obtained was better, and the benefit was greater. Similarly, the maximum ground settlement caused by excavation was smaller and the reduction range was larger.
• When the w/c ratio was increased from 0.4 to 1.0, the bleeding rate increased from 0.1% to 22.5% since the viscosity of cement slurry decreased with the increase of w/c ratio.
• The w/c ratio of the slurry and the unconfined compressive strength of the rock mass before grouting can be used to calculate the frictional angle (φ) and cohesive force (C).

Area of Improvement:

• For the purposes of this research, a two-dimensional model was created using FLAC3D software. As a result, the effect of excavation disruption along the tunnel axis direction was overlooked.

• As seen above, the water-to-cement ratio has unique effects on viscosity, bleeding rate, and initial setting time of cement slurry. To come up with an adequate water cement ratio for the project, more research was necessary.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

In the paper entitled “Experiment and numerical simulation on grouting reinforcement parameters of ultra-shallow buried double-arch tunnel”, the land part of Haicang undersea tunnel was selected as background; laboratory test, theoretical analysis and numerical simulation were performed to determine the grouting solid strength and grouting reinforcement parameters. Firstly, the effects of different water cement ratio on slurry fluidity, setting time, bleeding rate and sample strength were studied by laboratory test. Then, a method was proposed to determine the shear strength parameters of grouted surrounding rock through the grout water-cement ratio and the unconfined compressive strength of the rock mass before grouting by analyzing the experimental data and literatures. Finally, a numerical model was established, and multiple sets of working conditions were designed with the grouting reinforcement layer thickness h and the water-cement ratio η as independent variables.

COMMENTS

- The Abstract is too long. It should be rewritten to be more concise and comprehensive.

- In the caption of Figure 2, units should be given at the end:

Figure 2. Cross-section of the double-arch tunnel (units in …).

- In the vertical axis of Figure 4: Viscosity (s)    [and NOT Viscosit !].

- Some editing of the English language and style is required, e.g.:

LINE 184: …. η refers …

etc.

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

The paper presents the results of test and numerical simulation for shallow buried tunnels. The detailed comments are as follows:

1. The validation of FDM simulation must be given by comparing the computed settlement and deformations with the field measurement or reported data in literature.
2. The method procedures and/or standard of experiments should be added. Also, curing method and periods of test samples should be given in test program.
3. The units of empirical equations (eg. eq. 1 - sec) and tables (table 2 – degree) should be added and given properly.
4. Make the sample identification and mixture components shown in Table 1 concise and clear. Current table is presented in report style.
5. It seen in in Figs. 8-9 that the fitting curves shown does not have engineering meaning. Revise or delete the prediction equations.

Author Response

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Round 2

Reviewer 1 Report

Reviewer 4 Report

The reviewer has examined the revision made by the authors. It is shown that most comments are reflected in the anuscript. However, in Fig. 12, the obtained values from the present simulation should be plotted with the measured data for direction comparison.