A Technic for Ground Anchor Force Determination from Distributied Strain Using Fiber Optic OFDR Sensor with the Rejection of a Temperature Effect
Round 1
Reviewer 1 Report
The manuscript focuses a strain sensing technique for ground force determination using OFDR. This kind of method is broadly used in geotechnical instrumentation and it is not considered a novelty within the optical fiber sensor community. The authors should highlight the novelty and contribution to the field in a clearer way. It should also be clear what is the novelty when comparing to the previous work (ref 12).
In "In this study, we devise a way to exclude the temperature effect in the measured strain and propose a way to get a representative strain value in the varying strain field. We also experimentally demonstrate that the strain measured and processed with the proposed method well correlated with the applied anchor force.", the authors stated that the novelty of the work relates to the temperature compensation. However, simultaneous measurement of strain/temperature are a common practice when using OFDR for sensing purposes. What is the achievement using the proposed method in comparison with the well-known OFDR temperature/strain simultaneous measurement? Is there a neglected effect of the component of the thermal-induced strain within the community? If so, references must be added.
In the introduction, the authors must better describe or add references on what are the difficulties on “the wireless sensor unit maintenance” and the “optical fiber fabrication for embedding in the tensile strands to measure tensile forces”, comparing the latter with the proposed method.
In light of the above, the title must be reconsidered to highlight the thermal expansion (not temperature) compensation. The current title acknowledges the temperature compensation method as a mere extra feature where it should be considered the main focus.
The experimental data should be compared to that obtained from the numerical simulations and presented as a validation of the method.
In Figure 6, the statement that the 140 mm and 180 mm circle values are identical should be confirmed by showing the mean values for both cases. A table should be added for this.
The first half of the conclusion should be placed on the introduction:
“The anchor forces must be managed in order to secure the safety of the soil slope reinforced with ground anchors. The tensile force of a ground anchor can be indirectly determined by measuring the strain of a bearing plate because the anchor force is applied to the bearing plate as a compressive load by the anchor head. However, the bearing plate experiences not only non-uniform strain distribution, and but also temperature variation. Thus it was difficult to directly correlate the strain with the tensile force of the anchor. In this study, we propose a reliable method to correlate the bearing strain with the anchor force by excluding the effects of temperature and spatial variation of the strain field. For the experimental demonstration, we use a fiber optic OFDR sensor system to measure the strain field on the bearing plate.”
Moreover, the conclusion must be extended and account for whether the temperature compensation was successful and whether the experimental data corroborates with the numerical simulation.
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
Dear Authors,
This seems to be a short paper describing a method to remove thermal expansion effects from the strain readings with verification. The manuscript has been prepared to a high standard. Here are some suggestions:
1. Could the authors include in Figure 8 values of both mechanical strains before subtraction, plotted against the amount of force (ton)?
2. Comment on its general applicability to other strain sensing systems (non-OFDR)
3. Quantify the improvement seen on using this correction.
4. Comment on its potential ease of installation with respect to existing methods.
Thanks.
Best wishes,
Reviewer
Author Response
Please see the attachment.
Author Response File: Author Response.docx
