Excavation Method Determination of Earth-Retaining Wall for Sustainable Environment and Economy: Life Cycle Assessment Based on Construction Cases in Korea

Round 1

Reviewer 1 Report

In the Reviewer opinion the research paper entitled “Construction method determination of earth retaining wall considering excavation conditions for sustainable environment: Life cycle assessment based on construction cases in Korea” is good.

This study described the life cycle assessment (LCA) results based on the excavation depth and ground condition in medium-sized excavation ground, in order to examine the effect of construction method on environmental economic feasibility for an earth retaining wall. In addition, the environmental cost of construction method for the earth retaining wall was calculated, and its selection criteria were analyzed based on the calculation results. The evaluation result of the environmental cost of construction methods for the earth retaining wall showed that the environmental cost increased as the excavation depth increased, and the sandy soil conditions have higher environmental cost than complex soil conditions.

Some comments which greatly enhance the understanding of the paper and its value are presented below. Specific issues that require further consideration are:

1. The title of the manuscript is matched to its content, but it is too long.
2. The Introduction generally covers the cases.
3. In the Reviewer’s opinion, the current state of knowledge relating to the manuscript topic has been presented, but the author's contribution and novelty are not enough emphasized.
4. Experimental program and results looks interesting and was clearly presented.
5. In the Reviewer’s opinion, the bibliography, comprising 32 references, is rather representative.
6. An analysis of the manuscript content and the References shows that the manuscript under review constitutes a summary of the Author(s) achievements in the field.
7. In the Reviewer’s opinion the manuscript is well written, and it should be published in the journal after minor revision.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have made attempts to undertake Life Cycle Assessment (LCA) for excavating conditions for sustainable earth retaining wall construction method. While acknowledging the importance of the work the following comments needs to be critically before accepting manuscript for publication.

In the introduction section, the authors state that LCA is "method of deriving the optimal available technology 35 after determining the degree of contribution of industrial technology to reductions in greenhouse gas emissions”, This is not the correct definition of LCA! Please refer to ISO14040, ISO14044 and the following works to define the correct LCA definition.

• Sandanayake, M., G. Zhang, and S. Setunge, A comparative method of air emission impact assessment for building construction activities. Environmental Impact Assessment Review, 2018. 68: p. 1-9.
• Guggemos, A.A., Environmental impacts of on-site construction processes: Focus on structural frames. 2003, University of California, Berkeley.
• Sandanayake, M., G. Zhang, and S. Setunge, Environmental emissions at foundation construction stage of buildings – Two case studies. Building and Environment, 2016. 95: p. 189-198.
• Guggemos, A.A. and A. Horvath, Comparison of environmental effects of steel-and concrete-framed buildings. Journal of Infrastructure Systems, 2005. 11(2): p. 93-101.
• Guggemos, A.A. and A. Horvath, Decision-support tool for assessing the environmental effects of constructing commercial buildings. Journal of Architectural Engineering, 2006. 12(4): p. 187-195.

The meaning of the following sentence in 2^nd Paragraph of introduction is very confusing. What is meaning of any effect will be magnified if LCA is applied? What effects?

“… energy consumption of the materials used during construction are 41 high, any effect will be magnified if LCA is applied to the construction industry”.

There are numerous similar previous studies that are not acknowledged in the literature review section. Please reference them in the revised manuscript and acknowledge the contributions.

• Zhang, G., et al., Selection of emission factor standards for estimating emissions from diesel construction equipment in building construction in the Australian context. Journal of Environmental Management, 2016.
• Junnila, S., A. Horvath, and A. Guggemos, Life-Cycle Assessment of Office Buildings in Europe and the United States. Journal of Infrastructure Systems, 2006. 12(1): p. 10-17.
• Mao, C., et al., Comparative study of greenhouse gas emissions between off-site prefabrication and conventional construction methods: Two case studies of residential projects. Energy and Buildings, 2013. 66(0): p. 165-176.
• Hong, J., et al., Greenhouse gas emissions during the construction phase of a building: a case study in China. Journal of Cleaner Production, 2015. 103: p. 249-259.
• Sandanayake, M., et al., Estimation and comparison of environmental emissions and impacts at foundation and structure construction stages of a building – A case study. Journal of Cleaner Production, 2017. 151: p. 319-329.
• Luo, W., M. Sandanayake, and G. Zhang, Direct and indirect carbon emissions in foundation construction–Two case studies of driven precast and cast-in-situ piles. Journal of cleaner production, 2019. 211: p. 1517-1526.
• Sandanayake, M., G. Zhang, and S. Setunge, Environmental emissions at foundation construction stage of buildings – Two case studies. Building and Environment, 2016. 95: p. 189-198.
• Frey, H.C., W. Rasdorf, and P. Lewis, Comprehensive field study of fuel use and emissions of nonroad diesel construction equipment. Transportation Research Record: Journal of the Transportation Research Board, 2010. 2158(1): p. 69-76.
• Lewis, M.P., Estimating fuel use and emission rates of nonroad diesel construction equipment performing representative duty cycles. 2009: ProQuest.
• Lewis, P., H.C. Frey, and W. Rasdorf, Development and use of emissions inventories for construction vehicles. Transportation Research Record: Journal of the Transportation Research Board, 2009. 2123(1): p. 46-53.

LCA is not only assessing greenhouse gas emissions. The authors need to justify why only greenhouse gas emissions are mentioned in literature review section. Also sustainability is not only environmental sustainability but also include economic and social sustainability aspects as well, therefore the title should reflect only environmental and economic sustainability.

In section 2, authors mention LCC? What is LCC? Is it Life Cycle Cost or Carbon? Not clear. Similarly there so many abbreviations used in the manuscript that needs explanation

A typical LCA study requires systematic definition of four phases as follows. Please refer to ISO 14040 and ISO14044 for more details.

1. Goal and scope definition
2. Inventory analysis
3. Impact assessment
4. Interpretation 

Currently, the study doesn’t explain goal and scope (system boundary) of the study, models and methods used in the inventory analysis and the interpretation process. Only impact assessment is provided in detail. Also, authors need to define what functional unit is used for comparative basis? This si one of the most important factors in LCA study.

How do you compare different construction method when the equipment used, construction management techniques are different? Authors need to define the comparative basis is used in study.

Why only environmental cost is considered? What about the other costs? Don’t they contribute to the sustainability? Needs justification

What is the innovation and findings of the research apart from a comparative study? Different retaining wall systems and construction methods are used based on factors such as the soil type and surrounding construction conditions. How do authors generalise the findings and apply them in practical conditions?

Please review the whole manuscript for grammar and formatting errors. Recommend using a professional proof-reading service to improve the quality of writing and presentation.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The Revised manuscript has addressed all the requirements. IT is now suitable for publication.