Life cycle analysis and specialist geotechnical works: development of an operational calculation tool

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1 Life cycle analysis and specialist geotechnical works: development of an operational calculation tool Antoine Requin (1), Marine Lasne (1) (1) Soletanche Bachy, France Antoine Requin, Marine Lasne Abstract The use of Life Cycle Analysis (LCA) by construction companies is a sound approach yet with multiple issues. A variety of methodologies, indicators and databases exist all over the world. Companies must therefore make choices and assumptions in order to adapt LCA to their operational requirements, to different geographical contexts, and above all to users and customers, while keeping a consistent and reliable methodological approach. The appropriation of LCA by construction companies requires adapted and optimized tools, even capable of incorporating business aspects. LCA will help the construction industry to evolve if its language is recognized by that industry. Communication and internal training are also key factors in the success of the approach. Soletanche Bachy developed an LCA tool named PRISM in International, easy to use and understandable by all, PRISM can provide project environmental analysis at tender stage or during the works, and allows comparison of design alternatives. Keywords: Life Cycle Assessment (LCA), special geotechnical works 1. INTRODUCTION LCA applied to specialist geotechnical works faces generic issues, intrinsic to the production of environmental assessments as well as issues specific to the type of techniques considered. Developing an LCA tool is therefore a relatively challenging exercise for a geotechnical works contractor. The approach becomes more complex when an international company has to develop a common environmental assessment methodology capable of delivering results that are still relevant on the regional or local scale, compatible with both local conditions and general guidelines. Moreover, a variety of LCA methodologies already exist all over the world, with multiple indicators used to characterize environmental assessments, as well as numerous databases to calculate emission factors in different ways. The problem for LCA is therefore to integrate such issues while remaining pragmatic in order to match the operational needs of specialist geotechnical works, and easily 179

2 understandable to users and customers (not necessarily experts in construction techniques or in environmental assessments). In this context, the objective pursued by Soletanche Bachy was to develop a tool capable of meeting the above requirements, based on a consistent methodological approach including the selection of the most relevant databases and indicators. This led in 2010 to the development of PRISM, LCA tool aiming at providing project environmental analysis at tender stage or during the works, and allowing comparison of design alternatives. 2. METHODOLOGY 2.1 LCA references and indicators The methodology adopted by PRISM follows the recommendations of ISO and standards [1] [2], universal references for environmental management and LCA. Yet these references remain relatively generic while no specific rules exist to complete an environmental assessment and to choose appropriate indicators in the context detailed earlier. In order to establish the most relevant indicators to be adopted, a 3-step approach was followed [3]: 1 Identification and categorization of applicable LCA references including, but not limited to, standards, guidelines, etc; and 2 Identification of corresponding indicators; and 3 Selection of the most appropriate (relevant) indicators among this list on the basis of specific criteria. Global LCA references were therefore initially studied in the main regions of activity of Soletanche Bachy and/or regions with a recognized LCA approach: Europe, the United States, Canada, Australia and Japan. The following graph includes the various references listed and their interactions: Figure 1: Identification of LCA references 31 environmental indicators were identified among these references [3] and collected in the graph below. The following criteria were used to note and select only the most appropriate indicators, rated from 1 to 10 in order of importance (1 being the lowest level of importance, 180

3 10 being the highest): relevance to the business of the company, normative significance, comprehension, and geographical significance. Only indicators whose mark exceeded 20 were selected in that process. The final ranking obtained is provided hereafter, in Figure 2, showing three categories of indicators specific indicators NFP indicators not included in PRISM 30 ratings Figure 2: Indicators ranking and selection Specific indicators and NFP indicators were chosen to be included in PRISM. Specific indicators were collected from international standards but may not be part of the same reference. They were selected as being the most relevant and understandable indicators illustrating the environmental impact of specialist geotechnical works. NFP indicators arise from the French standard [4] and have been integrated in the tool in order to allow the presentation of results, if required, as per a single reference standard (Figure 3). Other indicators were considered as less relevant, or difficult to incorporate into this type of tool. For instance, the "noise" indicator, that is particularly appropriate to the construction activity, cannot be evaluated at the stage of the tender with a tool like PRISM that is mainly quantity based, and would require additional and site specific inputs (arrangement of equipment, configuration of the site, etc.). Such an indicator would require the use of different types of acoustic tools that are also available on the market, including among Soletanche Bachy subsidiaries. 181

4 Table 1: Selected indicators Specific indicators Unit NFP indicators Unit Site energy consumption Liters of fuel Resources energy consumption GJ Materials consumption tons Resources depletion tons eq antimony Water consumption m 3 Water consumption m 3 Waste tons Solid waste tons Climate change tons eq CO 2 Climate change tons eq CO 2 Global freight tons.km Air acidification kg eq SO 2 Local freight # of trucks/day Air pollution m 3 Land occupation m 2.day Water pollution m 3 Ozone layer destruction kg eq CFC Photochemical ozone formation kg eq C 2 H Life cycle stages PRISM environmental assessments include life cycle stages that are normally under the control of geotechnical works companies (figure 3): - production, that corresponds to the manufacturing of materials and encompasses all stages upstream of the manufacture of the final product; and - transportation, corresponding to the freight of materials and equipment to the construction site; and - final implementation on site : water and energy consumption, etc The environmental evaluation ends with the project delivery, considering that: - the contribution of the utilization stage to the selected indicators is in general very limited compared with the first three stages, and falls generally outside of the construction company s sphere of influence; - the end life stage has so far been excluded from the perimeter. Indeed, this stage corresponds to the demolition of the works constructed, which varies greatly from one project to the other, falls outside of the contractor s sphere of influence, and is most of the time unknown at the time of the invitation to tender Figure 3: Life cycle stages 2.3 Databases The approach adopted for databases selection was similar to the choice of indicators [3]. After identifying various databases already existing in the regions mentioned earlier, the 182

5 following selection criteria were used as rated from 1 to 20 in order of importance (1 corresponding to the lowest level, 20 to the highest): completeness, relevance to the company, and geographical significance. The final ranking is provided in figure 4: ratings Figure 4: Database selection Ecoinvent was clearly identified as the most comprehensive and relevant database for special geotechnical works and geographical representation, and was therefore chosen to build the environmental assessment tool. NFP standard indicators, in particular, are entirely derived from Ecoinvent. However, Ecoinvent is not specific to special geotechnical works, and a small number of emission factors required a more specific analysis. For instance, only one emission factor is available in Ecoinvent for the production of concrete, whatever its formula. Therefore, the database was completed by external values based on research performed respectively by VINCI Group, the ADEME (French Environment and Energy Management Agency) emission factors guide [5], and Soletanche Bachy for all technical ratios and equipment characteristics. 2.4 Example of the climate change indicator Greenhouse Gas (GHG) emissions are calculated in accordance with the ISO standard methodology. The perimeter studied corresponds to the ISO scope 3, applied to the first three stages of life cycle. Several methodological choices were made, in particular: - integration of the energy mix for each country in order to calculate the impact of the electricity consumption on the construction site and during the manufacturing of materials; - incorporation of equipment depreciation, considering the steel mass in equipment converted into operating hours, as a function of the service life of the apparatus; - refining, when deemed appropriate, of a small number of Ecoinvent emission factors using specific reference documentation. For example, the emission factor of steel recycling was calculated using a study from the French RECORD association (Research Network on Waste) [6] which takes into account avoided emissions; the emission factors of types of 183

6 concrete come from OmegaTP tool, created by the FNTP (National Federation of Public Works); the emission factors of cement are calculated from the ATILH (Technical Association of Hydraulic Binders Industry) emission factor of clinker, and Ecoinvent emission factors of slag and fly ash. 2.5 Environmental assessment normalization When PRISM environmental assessment is performed, a normalization of results is proposed: impacts of the project are compared individually with impacts of an average European during one year [7] [8] [9], providing a better understanding of results. Such normalization is also a prerequisite to the comparison of the overall environmental footprints of two solutions that are characterized by indicators expressed in different units (GHG emissions in teqco 2, water consumption in m 3, waste in tons, etc ), and that cannot be summarized otherwise. For example, a solution may generate more CO 2 emissions than the other, but produce less waste: which one would be the most environmentally friendly? Normalization of results provides, for each indicator, dimensionless figures that can be aggregated into a total value showing what solution can be considered as more efficient, in a particular context, and depending on the indicators and normalization method chosen. The following table shows results obtained from the environmental assessment of 3 solutions: diaphragm wall, secant piles and Geomix. For example, CO 2 emissions of secant piles would represent the emissions of 92 average Europeans during one year. In this study, choosing Geomix instead of diaphragm wall as a technical option for the project would mean reducing the corresponding environmental footprint by 56%. Table 2: Comparison and normalization Indicator Unit Unit per Average European / year Diaphragm Wall Secant Piles Geomix (soil mixing) Greenhouse Gas emissions teq CO Site energy consumption liters eq fuel Global freight tkm Site water consumption m Total materials consumption t Total solid waste production t The results for each indicator are divided by the coefficient of normation, then summed to define the global note % -56% 3 RESULTS AND PERSPECTIVES 3.1 Tool usage and deployment PRISM is now considered within the company as a valuable tool for decision support, adapted to the issues of special geotechnical works. The choice of specific indicators, pragmatic and understandable by all, has been essential for appropriation of the tool by users and customers. Since it was launched in early 2011, 50 people have been trained internally. PRISM has been used for about twenty bids (simple environmental assessments or comparison of several alternatives), 25 environmental assessments of construction sites (including a report handed over to the customer at the end of construction), and 5 environmental comparisons required by R&D purpose in order to compare new technologies with more traditional techniques. 184

7 Reference brochures that include site characteristics and key figures in the environmental assessment have been created and provide an «environmental picture» of those specialist geotechnical works, revealing their respective advantages/disadvantages through a simplified LCA, and enabling to build up environmental ratios for each technique. 3.2 General observation and trends The extensive usage of PRISM on projects has revealed a certain number of trends. First of all, it appears that materials manufacturing contributes to more than 80% of the project total CO 2 emissions, followed by freight and by site energy consumption (around 10% each), while on-site accommodation and employee transportation remain generally insignificant. Cement and steel are responsible for the majority of emissions from materials manufacturing. Out of these two, cement accounts for the greater part, even though its emissions factor is lower than the one of steel. This is due to the fact that it is used in larger quantities on site. Site energy consumption varies from one project to another, depending on the type of machines used on site. 3.3 Environmental mapping of specific geotechnical works General trends have also been found in the more specific analysis of techniques. The above mentioned environmental assessments performed on the main techniques used by Soletanche Bachy (SB) have been collected into a specific database, from which an extract is shown below: Table 3: Extract from SB techniques environmental assessments # of construction sites studied Description DIAPHRAGM WALL REINFORCED SLURRY WALL GEOMIX + profiled steel TRENCHMIX A diaphragm wall is a reinforced concrete wall in the ground. Trench stability during excavation, reinforcing and concreting is obtained with a bentonite mud Reinforced slurry wall is a bentonite-cement wall combined with metal reinforcement of appropriate form in order to resist the bending moments and shear force. Geomix is a soil mixing process which consists of using the in-situ soil as a construction material. The soil is destructured during excavation and mixed with cement grout. The technique involves the construction, below ground, of trenches comprising soil mixed with binder. The binder may be introduced as powder (dry method) or in the form of a previously mixed grout (wet method). GHG Emissions 0,5 <teqco2 / m3 wall<1,0 0,31<teqCO2 / m3 wall<0,42 0,38<teqCO2 / m3 wall<0,56 0,11<teqCO2 / m3 wall<0,22 Average 0,68 teqco2 / m3 wall 0,36 teqco2 / m3 wall 0,45 teqco2 / m3 wall 0,16 teqco2 / m3 wall Site energy consumption 5,5 <liters eq fuel / m3 wall<10 10<liters eq fuel / m3 wall<22 10<liters eq fuel / m3 wall<26 3,1 <liters eq fuel / m3 wall< 5 Average 7,2 liters eq fuel / m3 wall 15 liters eq fuel / m3 wall 20 liters eq fuel / m3 wall 4,3 liters eq fuel / m3 wall Materials consumption 2,6 <t / m3 wall<3,2 0,40<t / m3 wall<0,78 0,3<t / m3 wall<0,42 0,2<t / m3 wall<0,4 Average 2,8 t / m3 wall 0,5 t / m3 wall 0,38 t / m3 wall 0,3 t / m3 wall Waste production 1,21 <t / m3 wall<1,65 1,7<t / m3 wall<2,6 0,1<t / m3 wall<0,28 0 <t / m3 wall< 0,3 Average 1,5 t / m3 wall 1,9 t / m3 wall 0,2 t / m3 wall 0,1 t / m3 wall Advantages The advantages of Diaphragm wall are mainly technical. The environmental footprint is higher than the other techniques (slurry wall or Geomix) Lower environmental footprint than diaphragm wall. Materials consumption is much lower. Geomix materials consumption, waste production and freight are lower than diaphragm or reinforced slurry wall. Environmental footprint very low : GHG emissions, freight, site energy, waste production, etc. Disadvantages High materials consumption, waste production and freight. Waste production and global freight are high, compared to Soil mixing process Site energy consumption higher than reinforced slurry wall. The limits of the process are mainly technical (trench depth, type of soils) 185

8 From studies realized so far, and as a first approach, it can be observed for example that diaphragm walls would generate on average 0.68 teqco 2 per m 3 of wall, while reinforced slurry wall and Geomix wall emissions would reach approximately 0.4 teqco 2. Trenchmix demonstrates lower emissions with only 0.16 teqco 2 per m 3 of soil mixing. Such ratios will require in the future additional confirmation through complementary studies but seem already to be useful in helping the special geotechnical works activity to improve its techniques. Typically, the environmental footprint of a diaphragm wall appears to be relatively high compared with the other techniques using this LCA method. However, significant R&D efforts have been deployed in order to reduce its footprint, particularly with the development of new compact equipment, more suitable for urban areas, and with the development of new mud treatment plants or with the use of polymers. Nevertheless, environmental evaluations need to be balanced with the context and technical requirements of each project, considering that these techniques have their own respective areas of application. 4. CONCLUSION Life Cycle Analysis applied to specialist geotechnical works is a complex and powerful approach that contractors have already adopted, or will most probably have to adopt, in the near future. For Soletanche Bachy, the development of such an LCA tool has highlighted the environmental advantages/disadvantages of techniques used and shows a way to reduce their impacts. However, LCA will enable special geotechnical works to evolve only if its language adapts to the needs, priorities, tools, and languages of the construction activity. Communication and internal training are also key factors in the success of such an approach. REFERENCES [1] NF EN ISO : Environmental Management: Life cycle assessment Principles and framework, October, [2] NF EN ISO : Environmental Management: Life cycle assessment Requirements and guidelines, October, [3] Perez Landauro, V. Outil d éco-conception pour ouvrages souterrains : indicateurs environnementaux & bases de données, rapport de stage Soletanche Bachy/Arts et Métiers ParisTech, [4] NF P 01-10: Environmental quality of construction products Environmental and health declaration of construction products, December, [5] ADEME: Emissions factors guide, v6.1, [6] RECORD, Application of the Carbon Footprint method to the activities of waste management, 2008, 133pp, no /1A. [7] COMMISSION STAFF WORKING DOCUMENT, 2009 Environment Policy Review Part 3, [8] PRELEVEMENTS TOTAUX D EAU DOUCE, Eurostat 2010 [9] LA REVUE DU CGDD, Les indicateurs de développement durable, MEEDDM CGDD