Strengthening Strategies for Existing Rammed Earth Walls Subjected to Out-of-Plane Loading

Round 1

Reviewer 1 Report

The manuscript presents two techniques for the retrofitting and strengthening of "rammed earth walls" in Bhutan. In view of the experimental results, such strengthening systems seems to increase the out-of-plane behaviour of the tested structures. The experimental program involved just one specimen per series so that ho statistical analysis could be carried out. The experimental part is interesting, but the numerical part is not clear and does not show its interest in the manuscript.

- For each type of wall, only 1 specimen was tested, so the repeatability of the results was not checked.
- L. 283, p. 11: "These rigid bodies are drawn based on the failure mechanism of each test specimen." As mentioned above, for each type of wall, only 1 specimen was tested, so these mechanisms may be different. It is not easy to generate here the mechanisms for the walls?

Following the precedent comments and following the general content of the manuscript, I think the experimental part is interesting and the authors should concentrate on that part by providing more details. For the theoretical formulation section, according the reviewer´s opinion, the analyses carried out in this section are poor. Moreover, some assumptions appear, in my opinion, questionable like, for example, the extension of the part of the masonry involved in the collapse mechanism. The authors should better clarify that section, overwise, the authors should delete that section. I do not really see the interest of section 3.3 in this manuscript.

Author Response

RESPONSE TO REVIEWER 1

The authors would like to express our sincere appreciation to the referee. The authors hope that the revisions made are appropriate as response to the comments and questions posed by the reviewer.

The manuscript presents two techniques for the retrofitting and strengthening of "rammed earth walls" in Bhutan. In view of the experimental results, such strengthening systems seems to increase the out-of-plane behavior of the tested structures. The experimental program involved just one specimen per series so that no statistical analysis could be carried out. The experimental part is interesting, but the numerical part is not clear and does not show its interest in the manuscript.

1. For each type of wall, only 1 specimen was tested, so the repeatability of the results was not checked.

Although the presents study reports on just one specimen per series, the authors would like to check the repeatability of the test results particularly for the unreinforced and mesh-wrap retrofitting technique in future.

2. L. 283, p. 11: "These rigid bodies are drawn based on the failure mechanism of each test specimen." As mentioned above, for each type of wall, only 1 specimen was tested, so these mechanisms may be different. It is not easy to generate here the mechanisms for the walls?

Following the precedent comments and following the general content of the manuscript, I think the experimental part is interesting and the authors should concentrate on that part by providing more details. For the theoretical formulation section, according the reviewer´s opinion, the analyses carried out in this section are poor. Moreover, some assumptions appear, in my opinion, questionable like, for example, the extension of the part of the masonry involved in the collapse mechanism. The authors should better clarify that section, otherwise, the authors should delete that section. I do not really see the interest of section 3.3 in this manuscript.

Following the reviewer’s comments, the authors omitted Section 3.3 since this section does not contribute to betterment of the paper. Furthermore, the authors added more details on the experimental part where necessary.

Reviewer 2 Report

Page 2:

Do you have a reference in literature to support the sentence “The final finished block looked smooth and shiny, indicating the sufficient hardness achieved”?

 

Page 3:

Did you consider the mechanical, physical and chemical compatibility between mesh and mortar? This aspect affects the durability and effectiveness of the strengthening.

 

Page 4:

How were the horizontal timber elements fixed to the rammed earth wall?

Regarding the spraying of dry cement powder, what is the goal of this treatment? Is it compatible with the substrate and the matrix?

Please use "earth-based" instead of "mud".

Actually, the cement can change the aspect of the earth mortar making the latter not aesthetically compatible with the rammed earth finishing. In addition, the cement stabilized mortar can be not compatible with the rammed earth with the consequent detachment of the coating. Please elaborate on these aspects.

Although one month curing can be enough for cement stabilized earth mortar, the curing of the entire specimen lasted at maximum 2 months, which cannot be enough for the rammed earth. How did you control the drying of the rammed earth?

You stated “It is possible to have weaker joints at the intersection points and lapping region; therefore, extra attention had to be paid to avoid such weak points”. Please clarify how.

 

Page 5:

How did you consider the likely damage of the specimens due to the drilling? The characterization of these cylinders might be affected by the presence of the interface between 2 layers of rammed earth. In addition, the compressive strength of rammed earth can be different according to which direction of the wall is considered during the test (see the paper “Assessing the anisotropy of rammed earth”, Construction and Building Material, 2009).

The range 146-200 mm seems quite large. How did you consider the size effect (ratio D/H) in the mechanical characterization of the cylinders?

 

Page 6:

Did you check the water content of the specimens after the compressive test to guarantee that they were dried?

Regarding the sentence “The samples extracted from 147 location favoring the wall drying has higher strength than the samples extracted from the least 148 favoured drying place”, the difference could be due to the position in the wall from where the cylinders were extracted. There could be a gradient of density from the bottom section to the top section of the wall due to the construction process (“Compression behaviour of non-industrial materials in civil engineering by three scale experiments: the case of rammed earth”, Materials and Structures, 42, 2009), this might affect the strength of the specimens.

Table 1, please clarify how you calculated the elastic modulus.

Table 1, please report the coefficient of variation (CoV) instead of the standard variation to better understand the scattering of results.

 

Page 7:

In the statement “top level of transverse walls (mean of sensor 7 and 9)”, why did you not consider also the sensors 8 and 10?

The displacements at the base of the wall was not measured; how can you guarantee that the wall is not sliding?

In any case, the maximum displacement of the top of the buttressess is 1 mm, which is quite small. I believe it may not be representative. Please elaborate. In addition, did you consider the sensitivity of the sensor?

 How did you define the ultimate load? Apparently, the maximum load is highlighted in Figure 9.

How did you define the ultimate displacement?

 

Page 8:

You are referring to the mortar only, but the increment of strength should be attributed to the mesh or timber. As written in the text sounds like the mortar improves the out-of-plane capacity, if so, why should you use mesh or timber?

Regarding the sentence “This larger deformation capacity after the peak can be attributed to the effect of strengthening measures adopted”. This is because of the strengthening, but why? How?

 

Page 9:

Table 2, what is the "Theoretical Value T"? Please report the content of the table in the text.

The sentence “The overturning behavior characterized by the separation of the top blocks with the first block shows a lack of connection between the blocks in the vertical direction” is not clear. Please clarify.

Please provide support to the statement “there was effective load transfer over the wall's section through the mesh–wrap strengthening”.

Although Figure 9d is not really clear, it seems that the mortar is already separating from the substrate. Please clarify.

 

Page 10:

Regarding the last paragraph, the timber frame is clearly not compatible with a rammed earth building, therefore its aim must be reconsidered, perhaps it is useful as a first intervention in case of emergency, such to secure and prevent the collapse of an unsafe structure. Please elaborate.

 

Page 11:

Regarding the sentence “For, Mesh-RE, the failure in the rammed earth wall was inspected after removal of the mesh”, what does it mean? What did you observe?

 

Page 12:

You are basing on limit analysis and assuming the yielding of the mesh, but are you sure? You might have the detachment of the mortar, while the mesh is still in elastic stage. Please elaborate.

 

Page 13:

The sentence “The use of mesh-wrapped strengthening technique and confined timber-framed system helped to unite the front facade and transverse walls, and also showed improved performance with a controlled failure mechanism” is not completely true for Timber-RE. Please clarify it in the paper.  

 

Author Response

RESPONSE TO REVIEWER 2

The authors would like to express our sincere appreciation to the referee. The authors hope that the revisions made are appropriate as response to the comments and questions posed by the reviewer.

1. Page 2: Do you have a reference in literature to support the sentence “The final finished block looked smooth and shiny, indicating the sufficient hardness achieved”?

Based on the reviewer’s comments, the sentence was revised and two photos are added to Figure 3, showing the earth before and after compaction.

2. Page 3: Did you consider the mechanical, physical and chemical compatibility between mesh and mortar? This aspect affects the durability and effectiveness of the strengthening.

The authors understand that the mechanical, physical and chemical compatibility between mesh and mortar requires a more detailed study. We have already reported some works on this in Wangmo et al. 2020 [20]. Nevertheless, the authors also plan to do detailed study on the compatibility test between the mesh and the stabilized earth-based mortar in future. The following reference has been added to the revised manuscript:

Page 1, Line 35: reinforcement [19], mesh composite [20] and canvas and tarpaulin as externally bonded fibers [3].

Page 14, Line 412:

20. Wangmo, P.; Shrestha, K.C.; Aoki, T. Exploratory study of rammed earth walls under

      static element test. Constr. Build. Mater. 2020, 266, 121035,  

      doi:10.1016/j.conbuildmat.2020.121035.

3. Page 4: How were the horizontal timber elements fixed to the rammed earth wall?

Firstly, vertical members were installed on both face of the wall, and over them the horizontal timber elements were fixed through the joineries made on both vertical and horizontal members. And finally, these members at both faces of the wall were connected together by transverse members with help of timber wedge. Following the reviewer’s comment, following sentence is added to the revised manuscript:

Page 4, Line 129: The chronology of installing the timber members involved fixing the vertical members on both faces, followed by fixing horizontal members over them at interval of 600 mm, connecting all vertical members together (Figure 5(b)). Finally these members were connected through timber wedges forming a confined frame.

4. Regarding the spraying of dry cement powder, what is the goal of this treatment? Is it compatible with the substrate and the matrix?

Following sentence is added to the revised manuscript to elaborate on the purpose of spraying of dry cement powder:

Page 3, Line 107: The rammed earth wall was moistened before application of plaster to avoid excessive water absorption from the plaster by the dry wall. However, the water sprayed to wall was not quantified which sometimes leads to dampen the wall and thereby, affecting the wall’s strength. Spraying dry cement helped to absorb the excessive water on the wall surface. Further, moistening wall surface and spraying dry cement powder also helped for proper bonding between the wall and the plaster.

5. Please use "earth-based" instead of "mud".

Following the reviewer’s comments, the word “mud” is replaced by “earth-based” throughout the manuscript.

6. Actually, the cement can change the aspect of the earth mortar making the latter not aesthetically compatible with the rammed earth finishing. In addition, the cement stabilized mortar can be not compatible with the rammed earth with the consequent detachment of the coating. Please elaborate on these aspects.

Regarding the comment on the aesthetic compatibility, the color of earth-based plaster (1 cement: 4 earth) adopted is actually aesthetically compatible with the actual rammed earth finishing as illustrated in Figure 4 (d) and (e). Change in current cement and earth proportion, with increment in percentage of cement, would result in an appearance different to the actual rammed earth. The following sentences are added to the revised manuscript to reflect the reviewer’s comment:

Page 4, Line 113: The idea of using earth-based plaster was to maintain the aesthetic view of the rammed earth wall while protecting the mesh against the weather. Figure 4(e) presents the view of Mesh-RE after completion of plastering work, where the plaster is seen aesthetically compatible to its substrate rammed earth wall. Changes in current cement and earth proportion, with increment in percentage of cement, can result in an appearance different to the actual rammed earth.

Further, based on the reviewer’s comment on detachment of coating, the authors have added following statement:

Page 4, Line 118: It should be noted that durability issues and detachment of stabilized mortar provided as the covering to the mesh in the present study requires further detailed study. The present work proposes clamping of the meshes at two faces of the wall through the jugshing holes that will enable to retain its effectiveness despite losing the mortar over the time.

 

Further, the authors have explicitly mentioned in the conclusion the importance of connecting the meshes together as following:

Page 12, Line 345:  However, it is important to connect the meshes at both faces of the wall to avoid the detachment of mesh while adopting the proposed technique.

 

7. Although one month curing can be enough for cement stabilized earth mortar, the curing of the entire specimen lasted at maximum 2 months, which cannot be enough for the rammed earth. How did you control the drying of the rammed earth?

The specimen was left for natural drying in an open area to realize the actual drying scenario of the real building. The drying period of 2-3 months is normally practiced for rammed earth construction in Bhutan as reported in authors’ previous works [5,12–14,20,24].

8. You stated “It is possible to have weaker joints at the intersection points and lapping region; therefore, extra attention had to be paid to avoid such weak points”. Please clarify how.

Based on the above comment, the sentence has been modified as following:

Page 4, Line 136: Poor workmanship leads to weaker joints at the intersection points and lapping region, therefore, extra attention was taken at such regions.

9. Page 5: How did you consider the likely damage of the specimens due to the drilling? The characterization of these cylinders might be affected by the presence of the interface between 2 layers of rammed earth. In addition, the compressive strength of rammed earth can be different according to which direction of the wall is considered during the test (see the paper “Assessing the anisotropy of rammed earth”, Construction and Building Material, 2009).

The drilling for core extraction for each specimen was done after the pull-down tests from the undamaged transverse walls, therefore, there was no question of damage to the specimen. To address other comments from the reviewer, following sentences were added to the revised manuscript:

Page 6, Line 169: It should be noted that the core drilling was done within a single layer avoiding the interface between the layers. Further, the core drill samples were extracted in horizontal direction perpendicular to the direction of ramming. The anisotropy of rammed earth [30] affecting the material characterization tests is not within the scope of this paper.

The following new reference is added to the revised manuscript:

Page 14, Line 434:

30. Bui, Q.B.; Morel, J.C. Assessing the anisotropy of rammed earth. Constr. Build. Mater. 2009, 23, 3005–3011, doi:10.1016/j.conbuildmat.2009.04.011.
31. The range 146-200 mm seems quite large. How did you consider the size effect (ratio D/H) in the mechanical characterization of the cylinders?

Due to difficulty in core drilling of rammed earth, the length of the extracted cylinders varied from one another and this has been mentioned in the revised manuscript, Page 5, Line 150. The authors have added Figure 8 showing the size effect in the revised manuscript. The following sentences are also added:

Page 6, Line 178: Figure 8 shows the effect of ratio of height (H) and diameter (D) of the extracted samples on compressive and tensile strengths. Clearly, there is minimal effect of H/D ratio on the strength characteristics of the tested core samples.

11. Page 6: Did you check the water content of the specimens after the compressive test to guarantee that they were dried?

The water content of the specimens was not checked during this study. However, the authors would like to check in the future studies.

12. Regarding the sentence “The samples extracted from location favoring the wall drying has higher strength than the samples extracted from the least favoured drying place”, the difference could be due to the position in the wall from where the cylinders were extracted. There could be a gradient of density from the bottom section to the top section of the wall due to the construction process (“Compression behaviour of non-industrial materials in civil engineering by three scale experiments: the case of rammed earth”, Materials and Structures, 42, 2009), this might affect the strength of the specimens.

As per the reviewer’s comment, the reason for having different mechanical characteristics has been justified as following and additional reference has been added.

Page 6, Line 174: Furthermore, it is also influenced by the gradient of density from the bottom section to the top section of the wall due to construction process involving manual ramming [29].

The following reference has been added to the revised manuscript:

Page 14, Line 431:

29. Bui, Q.B.; Morel, J.C.; Hans, S.; Meunier, N. Compression behaviour of non-industrial materials in civil engineering by three scale experiments: The case of rammed earth. Mater. Struct. Constr. 2009, 42, 1101–1116, doi:10.1617/s11527-008-9446-y.
30. Table 1, please clarify how you calculated the elastic modulus.

The elastic modulus is calculated from the elastic-linear range of the compressive stress-strain curve, and is mentioned in the revised manuscript as follows:

Page 6, Line 176: The elastic modulus reported in Table 1 is calculated from the elastic-linear range of the compressive stress-strain curve, between around zero and 40% of the maximum compressive strength

14. Table 1, please report the coefficient of variation (CoV) instead of the standard variation to better understand the scattering of results.

As per the comment, the coefficient of variation (CoV) is mentioned in the Table 1 in revised manuscript.

15. Page 7: In the statement “top level of transverse walls (mean of sensor 7 and 9)”, why did you not consider also the sensors 8 and 10?

The authors chose only sensors 7 and 9 to present the displacement of top level of transverse walls, and did not choose sensors 8 and 10 since they are 800 mm below (at mid-level of transverse walls) the sensors 7 and 9. Following reviewer’s comment, the authors have put the results of sensors 8 and 10 in the Figure 10(e) of the revised manuscript.

16. The displacements at the base of the wall was not measured; how can you guarantee that the wall is not sliding?

The authors did not keep instrumentation to measure the actual sliding of the wall. However, it was clear through the video recordings and visual observations that sliding failure mode was not observed. The authors thank the reviewer for pointing out and in the future study, we will take note on this. The following sentences were added to the revised manuscript to reflect reviewer’s comment:

Page 11, Line 321: It should be noted that no instrumentation was placed to measure the actual sliding of the walls during the pull-down tests. However, it was clear through the video recordings and visual observations that sliding failure mode was not observed.

17. In any case, the maximum displacement of the top of the buttressess is 1 mm, which is quite small. I believe it may not be representative. Please elaborate. In addition, did you consider the sensitivity of the sensor?

The participation of the transverse walls was limited since the test was predominantly done on the front facade. A maximum displacement of the top of transverse wall of around 1 mm in Timber-RE and Mesh-RE is relatively small compared to the movement of the facade (exceeding 50 mm). It should be noted that no deformation of the transverse walls was observed for U-RE. Small deformations of transverse walls in Timber-RE and Mesh-RE, however, shows that the strengthening interventions do help to transfer the load to some extent to the transverse walls as well.  

The sensitivity of the displacement sensors (SDP-100C) used is
(50x10^-6 strain/mm) with rated output of 2.5 mV/V (5000x10^-6 strain)±0.2%. The sensors are well calibrated.

Details on displacement sensor may be found here:

https://www.tml.jp/e/product/transducers/displacement.html

18. How did you define the ultimate load? Apparently, the maximum load is highlighted in Figure 9.

As per the reviewer’s comment, the word “ultimate load” is replaced with “peak load” throughout the revised manuscript.

19. How did you define the ultimate displacement?

As per the reviewer’s comments, the authors have corrected the statement to corresponding displacement at peak load as following:

Page 8, Line 228: Further, the corresponding displacement at peak load at the top level of facade wall for Mesh-RE and Timber-RE was 46.17 mm and 78.95 mm, respectively, which is 7.76 times and 13.27 times the U-RE.

20. Page 8: You are referring to the mortar only, but the increment of strength should be attributed to the mesh or timber. As written in the text sounds like the mortar improves the out-of-plane capacity, if so, why should you use mesh or timber?

As per the reviewer’s comment, the sentence has been modified from “In this stage, the existing cracks in mesh plaster widened and propagated further for Mesh-RE” to “At this stage, the existing cracks in mesh plaster widened due to mesh elongation for Mesh-RE.” in Page 8, Line 241.

21. Regarding the sentence “This larger deformation capacity after the peak can be attributed to the effect of strengthening measures adopted”. This is because of the strengthening, but why? How?

Based on the reviewer’s comment, the sentence has been modified giving the reason as following:

Page 8, Line 245: This larger deformation capacity after the peak shows that the strengthening measures adopted are effective in delaying the out-of-plane collapse of the facade and distributing the load over the larger section of the wall.

22. Page 9: Table 2, what is the "Theoretical Value T"? Please report the content of the table in the text.

The authors omitted Section 3.3, therefore, the theoretical value in table 2 is also been removed in the revised manuscript.

23. The sentence “The overturning behavior characterized by the separation of the top blocks with the first block shows a lack of connection between the blocks in the vertical direction” is not clear. Please clarify.

The separation of top blocks (block 2, 3, 4 and 5) with the first block (block 1) is resulted due to lack of vertical connections between the blocks. The sentence is revised in the manuscript as following for better understanding:

Page 10, Line 271: The overturning behavior characterized by the separation of the top blocks with the first block shows a lack of vertical connection between the blocks. 

24. Please provide support to the statement “there was effective load transfer over the wall's section through the mesh–wrap strengthening”.

The load transfer from facade wall to transvers walls are characterized by the deformation of transverse wall. However, in case of unreinforced wall specimen, the load transfer to transverse wall is not observed due to lack of strengthening measures. The sentence has been modified in the revised manuscript as following:

Page 10, Line 286: The final failure mode was local with sliding of the top RE block; however, before that, there was effective load transfer over the wall's section through the mesh–wrap strengthening characterized by deformation of transverse walls.  

25. Although Figure 9d is not really clear, it seems that the mortar is already separating from the substrate. Please clarify.

It should be noted that the photo in Figure 13(d) is taken at a moment before the collapse. At this stage, the top block of the wall was deformed and therefore, a mortar is observed separating from the wall.

26. Page 10: Regarding the last paragraph, the timber frame is clearly not compatible with a rammed earth building, therefore its aim must be reconsidered, perhaps it is useful as a first intervention in case of emergency, such to secure and prevent the collapse of an unsafe structure. Please elaborate.

Based on the reviewer’s comment, the authors have added the following sentence in the revised manuscript:

Page 11, Line 319: Nevertheless, timber frame can be useful as a first intervention in case of emergency to secure and prevent the collapse of an unsafe wall sections.

27. Page 11: Regarding the sentence “For, Mesh-RE, the failure in the rammed earth wall was inspected after removal of the mesh”, what does it mean? What did you observe?

The authors omitted the Section 3.3.

28. Page 12: You are basing on limit analysis and assuming the yielding of the mesh, but are you sure? You might have the detachment of the mortar, while the mesh is still in elastic stage. Please elaborate.

The authors omitted the Section 3.3.

29. Page 13: The sentence “The use of mesh-wrapped strengthening technique and confined timber-framed system helped to unite the front facade and transverse walls, and also showed improved performance with a controlled failure mechanism” is not completely true for Timber-RE. Please clarify it in the paper.  

As per the reviewer’s comment, the sentence has been modified as following:

Page 12, Line 333: The use of mesh-wrapped strengthening technique and confined timber-framed system helped to unite the front facade and transverse walls, and particularly the mesh-wrapped technique showed improved performance with a controlled failure mechanism.

Reviewer 3 Report

The authors are to be congratulated for an interesting and novel study. However, before acceptance they should complete the following changes:

1. The abstract is fine, but would be improved by including comment on what they feel is best solution.
2. Include explicit aim(s) and objectives at the end of the Introduction
3. Include brief background/literature review on past work
4. Include more explanation on background to experimental work, rather than straight into details about specimens. Why did they adopt their approach?
5. Report on Optimum Moisture Content and Maximum Dry Density of materials
6. Table 1: it is rather unfortunate that weakest soil was used in unreinforced wall, providing a low base line to compare on enhancement. Discuss significance of this further in paper.
7. The Coefficient of Variation for compressive strength of U-RE was nearly 80%. This is very high. Why? Does this affect significance/reliability of test data?
8. In discussion 'could have been..' is used rather a lot. Some more definitive explanations on performance would be welcome. What really happened rather than what could have?

Author Response

RESPONSE TO REVIEWER 3

The authors would like to express our sincere appreciation to the referee. The authors hope that the revisions made are appropriate as response to the comments and questions posed by the reviewer.

The authors are to be congratulated for an interesting and novel study. However, before acceptance they should complete the following changes:

1. The abstract is fine, but would be improved by including comment on what they feel is best solution.

Following the reviewer’s comment, the authors added following sentences to the revised manuscript.

Page 1, Line 19: Mesh-wrapped strengthening technique was found more effective over the timber-framing which was disrupting the visual aspects of the wall’s facade and needed proper anchoring to the foundation. 

 

2. Include explicit aim(s) and objectives at the end of the Introduction

As per the reviewer’s comment, the aim of the study is explicitly mentioned in the introduction section as following.

Page 2, Line 60: The present study aims to evaluate the feasibility and effectiveness of the two proposed strengthening technique that can be adopted in retrofitting the rammed earth buildings in Bhutan.

 

3. Include brief background/literature review on past work

Based on the reviewer’s comment, a brief review on the authors’ previous work has been mentioned in the revised manuscript as following:

Page 2, Line 57: This work is an extension of authors’ previous works [5,12–14,20,24] which were largely focused on numerical modelling, reinforced RE with reinforced dowels and wedges, floor anchorage system and mesh-wrapped strengthening on reduced scale walls.

A new reference has been added as following:

Page 14, Line 412:

20. Wangmo, P.; Shrestha, K.C.; Aoki, T. Exploratory study of rammed earth walls under

      static element test. Constr. Build. Mater. 2020, 266, 121035,  

      doi:10.1016/j.conbuildmat.2020.121035.

 

4. Include more explanation on background to experimental work, rather than straight into details about specimens. Why did they adopt their approach?

Based on the above comment, following sentence has been added to the revised manuscript:

Page 2, Line 65: The experimental program includes pull-down test of U-shaped wall to understand the out-of-plane behavior of rammed earth wall while assessing the feasibility and effectiveness of the proposed strengthening techniques. The test specimen prototype represents a real-scale wall facade and transverse walls.

 

5. Report on Optimum Moisture Content and Maximum Dry Density of materials

The water content was checked through traditional field test as reported in Page 2, Line 85 to realize the actual traditional construction method, and not measured in terms of actual quantity. The authors will consider measuring the optimum moisture content in future works. The maximum dry density of material is mentioned in the revised manuscript.

Page 6, Line 166: The maximum average dry density observed is 2045 kg/m³ for Mesh-RE and the least is observed 1926 kg/m³ for Timber-RE.

 

6. Table 1: it is rather unfortunate that weakest soil was used in unreinforced wall, providing a low base line to compare on enhancement. Discuss significance of this further in paper.

The lower strength in unreinforced wall despite being constructed of the same material composition is highlighted in the revised manuscript as following:

Page 6, Line 167: The difference in strength characteristics of rammed earth samples is observed, although they are constructed from the same soil composition. Such variability is influenced by the place where the samples were extracted [13]. It should be noted that the core drilling was done within a single layer avoiding the interface between the layers. Further, the core drill samples were extracted in horizontal direction perpendicular to the direction of ramming. The anisotropy of rammed earth [30] affecting the material characterization tests is not within the scope of this paper.  The samples extracted from location favoring the wall drying has higher strength than the samples extracted from the least favored drying place. Furthermore, it is also influenced by the gradient of density from the bottom section to the top section of the wall due to construction process involving manual ramming [29].

 

7. The Coefficient of Variation for compressive strength of U-RE was nearly 80%. This is very high. Why? Does this affect significance/reliability of test data?

The coefficient of variation is mentioned in the Table 1 in the revised manuscript. The deviations for some of the test data are clearly high. Such variability is common for rammed earth samples since it is based on several factors as detailed in response to Comment 6.

 

8. In discussion 'could have been..' is used rather a lot. Some more definitive explanations on performance would be welcome. What really happened rather than what could have?

As per the reviewer’s comment, definitive sentences are used where applicable.

Reviewer 4 Report

The out-of-plane loading of rammed earth wall is an important subject and worth to be investigated. This study contributes the important experimental results for the researchers in this domain. In particular, the strengthening techniques (mesh-wrapped and timber-framed) here proposed and discussed. The paper is well written and worth to be published. The authors should take into account the following suggestions/comments to clarify some aspects of their research:

-Normally, for this case of U-Shape wall with the presence of two return walls, the out-of-plane loading will give the different results in two directions of loading (pull outside such as in this paper, or pull in the other side). Please explain why the authors chose this direction to pull and not the other side.

-In figure 9, please add one more figure which zoom more on the elastic and initial crack phase. More precisely, the authors can take the similar figure 9a, but stop at 20mm (or 15mm).

-The rigidity in the elastic phase before getting the first crack is really important, especially for the case of out-of-loading. This value of bending rigidity (k=load/out-of-plane displacement) which is determined by the boundary conditions and the elastic module of wall can help to validate the numerical model. Therefore, please provide this “value k” of three walls by using the curve in figure 9a. Even that, the similar linear phase was found for three walls, but the value k will be a little different.

-Beside the reference [10], the authors could add one more recent study of strengthening rammed earth by post-tensioned vertical rebar: Q.B. Bui, T.T.Bui, R. El-Nabouch, D.K.Thai, 2019: «Vertical rods as a seismic reinforcement technique for rammed earth walls: an assessment». Advances in Civil Engineering, Volume 2019, 12 pages, DOI:10.1155/2019/1285937.

Author Response

RESPONSE TO REVIEWER 4

The authors would like to express our sincere appreciation to the referee. The authors hope that the revisions made are appropriate as response to the comments and questions posed by the reviewer.

The out-of-plane loading of rammed earth wall is an important subject and worth to be investigated. This study contributes the important experimental results for the researchers in this domain. In particular, the strengthening techniques (mesh-wrapped and timber-framed) here proposed and discussed. The paper is well written and worth to be published. The authors should take into account the following suggestions/comments to clarify some aspects of their research:

1. Normally, for this case of U-Shape wall with the presence of two return walls, the out-of-plane loading will give the different results in two directions of loading (pull outside such as in this paper, or pull in the other side). Please explain why the authors chose this direction to pull and not the other side.

The reason for outside pulling of the front facade is to grasp the out-of-plane failure mechanism with separation of facade wall from the transverse wall from the front direction. This direction was chosen since the majority of post-earthquake observation of such rammed earth buildings (DCHS 2011 [1]) showed out-of-plane failure mechanism with outer separation of facade.

2. In figure 9, please add one more figure which zoom more on the elastic and initial crack phase. More precisely, the authors can take the similar figure 9a, but stop at 20mm (or 15mm).

As per the reviewer’s comment, the authors have added Figure 10(b) in the revised manuscript to show the details of elastic and initial crack phase.

3. The rigidity in the elastic phase before getting the first crack is really important, especially for the case of out-of-loading. This value of bending rigidity (k=load/out-of-plane displacement) which is determined by the boundary conditions and the elastic module of wall can help to validate the numerical model. Therefore, please provide this “value k” of three walls by using the curve in figure 9a. Even that, the similar linear phase was found for three walls, but the value k will be a little different.

As per the reviewer’s comments, following sentences have been added to the revised manuscript:

Page 8, Line 216: Figure 10(b) shows zoomed-in curve of Figure 10(a) with displacement up to 10 mm showing the elastic and initial crack phase of the wall. The initial stiffness, reported in Table 2 is calculated as the ratio of pull-down load to the corresponding out-of-plane displacement up to the linear range of the load-displacement curve. Clearly, a slight improvement in the stiffness is observed in Mesh-RE and Timber-RE specimens as an effect of mesh-wrapped and timber framed strengthening technique.

4. Beside the reference [10], the authors could add one more recent study of strengthening rammed earth by post-tensioned vertical rebar: Q.B. Bui, T.T.Bui, R. El-Nabouch, D.K.Thai, 2019: «Vertical rods as a seismic reinforcement technique for rammed earth walls: an assessment». Advances in Civil Engineering, Volume 2019, 12 pages, DOI:10.1155/2019/1285937.

Based on the reviewer’s comment, above reference has been added to the revised manuscript.

Page 14, Line 406:

17. Bui, Q.B.; Bui, T.T.; El-Nabouch, R.; Thai, D.K. Vertical Rods as a Seismic Reinforcement Technique for Rammed Earth Walls: An Assessment. Adv. Civ. Eng. 2019, doi:10.1155/2019/1285937.

Round 2

Reviewer 1 Report

The authors revised the manuscript according the reviewer's suggestions. The manuscript can be accepted for publication. 

Reviewer 2 Report

Thes sentence "Spraying dry cement helped to absorb the excessive water on the wall surface" is not totally clear to me as controlling the spraying of water on a rammed earth surface is not so difficult. From the sentence, it seems like you were "washing" the wall.