Sustainability Metrics for Pile Foundations

Transcription

1 Indian Geotechnical Jornal, 41(2), 2011, Sstainability Metrics for Fondations Aditi Misra 1 and Dipanjan Bas 2 Key words Sstainability, indicators, pile fondations, life cycle assessment, energy acconting Abstract: Civil Engineering is the major instrment of anthropocentric development over centries throgh ever expanding infrastrctres, cities and facilities. Lately, a growing awareness is observed towards making sch growth sstainable. Geotechnical engineering, being very resorce intensive, warrants an environmental sstainability stdy, bt a qantitative framework for assessing the sstainability of geotechnical practices, particlarly at the planning and design stages, does not exist. In this paper, qantitative indicators for assessing the environmental sstainability of pile fondations are developed throgh life cycle assessment (LCA) of pile fondations. The se of resorces is taken into accont based on energy-centric methods while the impact of the process emissions is assessed sing environmental impact assessment (EIA). The resorce se and the impact of emissions are categorized and normalized, and weights are applied across the categories to emphasize the relative importance of the categories. The weighted vales ths obtained are aggregated across the categories to obtain the resorce se and environmental impact indicators for drilled shafts and driven concrete piles carrying eqal amont of axial loads. The developed indicators can be sed to qantitatively compare the impacts of these two types of piles on the environment considering both resorce consmption and process emissions. Ths, a holistic approach towards assessing environmental sstainability of pile fondations is proposed. Introdction Civil Engineering has been the major instrment of anthropocentric development over centries throgh ever expanding infrastrctres, cities and facilities. In recent times, a concerted effort is observed within the civil engineering indstry to deliver bilt facilities that are environment friendly as well as financially viable. Geotechnical engineering is most resorce intensive of all civil engineering disciplines althogh this intensive consmption of energy and natral resorces goes nnoticed mainly becase of the indirect natre of the energy sed in the form of materials and natral resorces (e.g., concrete, steel and land se). By virte of its early position in the constrction cycle, sstainable geotechnical practices can sbstantially improve the overall sstainability of a project, and hence, improving the sstainability of geotechnical processes is extremely important in achieving overall sstainable development (Jefferis 2008). Sstainability as a decision metric is slowly gaining poplarity within the geotechnical indstry and a review of the existing literatre reveals a few projects where sstainability has been sed as a criterion to choose the best alternative. Cha et al. (2006) sed embodied energy as an environmental impact indicator in their stdy of for different retaining wall designs. Later, Cha et al. (2008) compared the environmental impact and energy efficiency of basement wall constrction for two commercial bildings in London in terms of embodied carbon dioxide. A case stdy assessing the relative impacts of concrete retaining walls and bioengineered slopes throgh life cycle impact assessment was done by Storesnd et al. (2008). Spalding et al. (2008) compared, sing three case stdies, the se of grond improvement techniqes as an alternative to conventional deep fondations and sed carbon footprint as a measre of environmental sstainability. Egan et al. (2010) also stdied the se of grond improvement techniqes as an alternative to traditional deep fondations sing embodied carbon dioxide as an environmental metric. These projects have mainly relied on a single metric, either resorce efficiency or environmental impact, which is not sfficient to determine the best engineering soltion balancing both economy and ecology. Some qalitative gidelines are available that se mltiple criteria (e.g., social, economic and environmental impacts) for assessing the sstainability of geotechnical constrction sites. These inclde the Sstainable Geotechnical Evalation Method (S.G.E.M) (Jiminez 2004), the Environmental Geotechnical Indicator System (EGIs) (Jefferson et al. 2007) and GeoSPeAR (Holt et al. 2009, 2010). S.G.E.M. ses a 1 Gradate stdent, Department of Civil and Environmental Engineering, University of Connectict, Storrs, aditi.misra.07@gmail.com 2 Assistant Professor, Department of Civil and Environmental Engineering, University of Connectict, Storrs, dbas@engr.conn.ed

2 109 Indian Geotechnical Jornal 41(3), 2011 color coded indicator system, based on the categories of social, economic, environmental and natral resorce se, for the prpose of comparing different alternative materials sed in slope stabilization. EGIs consists of 76 generic indicators and 32 technology-specific indicators and was developed for grond improvement projects by borrowing concepts from the existing sstainability indicators like SPeAR and BREEAM (Jefferson et al. 2007). GeoSPeAR is an indicator system for geotechnical constrction and was developed by modifying SpeAR (Holt et al. 2010). Althogh these qalitative indicators serve well at the constrction stage of a project, there is a lack of a clearly defined framework to evalate and qantify the relative sstainability of alternative practices in geotechnical engineering at the planning and design stages of a project (Abre et al. 2008). The objective of this paper is to introdce a qantitative framework for assessing the comparative sstainability of different technically feasible options available for a geotechnical project. Life cycle assessment (LCA), in conjnction with environmental impact assessment (EIA), is proposed as a qantitative decision aid tool to incorporate environmental sstainability in geotechnical engineering, particlarly, in pile fondation design. Based on the LCA, a resorce se indicator and an environmental impact indicator are developed to qantitatively compare the sstainability of competing alternatives. The framework is explained throgh case stdies involving pile fondations in order to determine whether driven concrete piles or drilled shafts are more sstainable for the cases investigated. The prpose of the case stdies is to illstrate the tility and effectiveness of the developed framework. Sstainability Assessment of Geotechnical Projects A sstainable project balances the social, environmental and economic eqity in order to achieve sstainable development. Indiscriminate consmption of natral resorces in a project affects the distribtional eqity of resorces, and hence, violates the social eqity principle of sstainability. The se of manfactred raw materials in a project distrbs the environmental balance throgh process emissions and polltions. A project that focses only on the financial retrn and does not consider the social impacts contradicts the economic and social eqity principles of sstainability. As geotechnical projects se vast amont of resorces and energy, generate considerable amont of waste, involve financial investment of stakeholders and often permanently change the landscape, it is important that they are assessed for sstainability considering resorce consmption, environmental impact and socio-economic impact. In practice, sstainability assessment of geotechnical projects can be done by sing life cycle assessment (LCA) that combines resorce inventory and environmental impact assessment (EIA) and by sing a socio-economic impact assessment tool like cost benefit analysis (CBA). LCA is a qantitative tool that assesses the impacts of a process or a prodct on the environment over the entire lifespan of the process or the prodct. In most geotechnical processes, the LCA shold follow a cradle to grave approach becase rese of materials after decommissioning of a project is generally not considered. In addition, it is better to do the resorce acconting in the LCA by energy acconting methods instead of mass acconting becase available energy to do work is the ltimate limiting resorce. The environmental impact assessment (EIA) determines the impact of the otpt of a process on the ecosystem on different categories like hman and ecosystem health, global warming and acidification. A combination of LCA and EIA provides a holistic environmental sstainability assessment for geotechnical projects. Life Cycle Assessment of Fondations The se of the sstainability framework developed in this stdy is illstrated by applying it to case stdies involving pile fondations. Two commonly sed pile fondations drilled shafts and driven concrete piles are considered in the case stdies in order to determine their comparative sstainability. Assessing the sstainability of pile fondations shold start after a preliminary design has been done and after data has been collected on the technological feasibility of the different alternatives. The pile design in this stdy follows the working stress method. The ltimate pile capacity is assmed to be that corresponding to a pile head settlement of 10% of the pile diameter. It is assmed that the piles are installed in homogeneos profiles of sandy and clayey soils. The soil profiles are so chosen that the constrction of driven concrete piles and drilled shafts is technically feasible. Both the pile types are assmed to spport the same sperstrctre load. It is also assmed that there are no constraints that limit the availability of raw materials, eqipment or technical expertise reqired for the design and constrction of the piles. The design eqations sed in the case stdies are provided in Tables 1 and Table 2. Three working load cases of 250 kn, 300 kn and 400 kn are considered with a factor of safety eqal to 2.5. The length of the piles is kept constant at 12 m while the diameters are varied in the design. The dimensions obtained from the design calclations are provided in Table 3. For the sandy soil considered in this stdy, the soil properties are (i) nit weight of solids Gs = 2.65, (ii) relative density DR = 60%, (iii) coefficient of earth

3 110 Sstainability Metrics for Fondations Aditi Misra and Dipanjan Bas Table 1 Design eqations for sandy profile (Salgado 2008) Design Eqations for in Sand Design Eqations for Concrete in Sand Limit Unit Resistance q = Kσ tan sl v c where σ' v K = 0.7K0exp ln DR pa Ultimate Unit Base Resistance q = 0.23exp D q b,10% R bl where q bl =1.64exp c c D R p A σ h pa D R Limit Unit Resistance q = 0.02tan D q sl c R bl where q bl =1.64exp c c D R p A DR σ h pa and is calclated at a depth at which q SL is reqired Ultimate Unit Base Resistance q = D q b,10% R bl v ' is the vertical effective stress at a depth at which the capacity is calclated, h ' is the horizontal effective stress at a depth at which the capacity is calclated, c is the critical state friction angle of the sand, D R is the relative density of sand expressed as a percentage, K 0 is the coefficient of earth pressre at rest, and p A is a reference stress (= 100 kpa) Table 2 Design eqations for clayey profile (Salgado 2008) Design Eqations for in Clay Design Eqations for Concrete in Clay Limit Unit Resistance q sl =αs Limit Unit Resistance q sl =αs where s α = ln p A Ultimate Unit Base Resistance q = 9.6s b,10% where s s α= ' ' σ v NC σ v and s = 0.3 ' σv NC Ultimate Unit Base Resistance q =10s b,10% s is the ndrained shear strength of clay, NC represents normally consolidated clay, p A is a reference stress (= 100 kpa)

4 111 Indian Geotechnical Jornal 41(3), 2011 pressre at rest K0 = 0.4, (iv) maximm void ratio emax = 0.9, (v) minimm void ratio emin = 0.4, (vi) nit weight of water w = 9.81 kn/m 3 and (vii) critical state friction angle c = 30º. The reslting blk nit weight of sand sat = kn/m 3. For the clayey soil considered in this stdy, the soil properties are (i) Gs = 2.65, (ii) OCR = 2, (iii) w = 9.81 kn/m 3 and (iv) sat = 18 kn/m 3. The water table is assmed to be at the grond srface for both the sand and clay profiles. The designed pile dimensions are sed in the LCA to determine (i) the qantity of natral resorces and processed materials needed for the piles and (ii) the emissions generated to manfactre the reqired qantity of materials. The LCA done in this paper consists of for steps: (i) goal and scope definition in which the prpose and extent of the stdy is nderlined, (ii) life cycle inventory (LCI) analysis in which all the inpts to and otpts from the process over its life cycle is acconted for, (iii) environmental impact assessment (EIA) in which the otpts of the process are related to the impact categories and (iv) interpretation of reslts in which the resorce se and environmental impact indicators are calclated. Figre 1 shows the flow chart for this LCA. Fig. 1 Flow chart showing the inpts, otpts, processes and impact categories in pile constrction LCA Step 1: Goal and Scope Definition The goals of the life cycle assessment performed for this case stdy are (i) to determine, throgh life cycle inventory (LCI), the resorce consmption and emissions for drilled shafts and driven concrete piles over the lifespan of the project and (ii) to decide, after an environmental impact stdy based on the LCI, which of the two aforementioned piles is more environmentally sstainable. The scope of this stdy primarily incldes identification and qantification of all the major inpts to and otpts from the process of pile constrction. The inpts that are considered in this stdy are cement and steel from the manfactring segment and land from the biogeosphere. The otpts are the constrcted piles along with emissions to air and water. The contribtors to energy or resorce consmption from the constrction and maintenance of the manfactring plants of cement and steel, electricity consmption of the architect s office and other similar indirect contribtors are kept ot of the scope with the nderstanding that sch contribtions are almost the same for both the pile types, and hence, do not inflence the goal of the stdy. LCA Step 2: Life Cycle Inventory (LCI) Inpt Inventory Based on the above stated goal and scope of this LCA, life cycle inventory for pile fondation shold qantify (i) the inpts and otpts for concrete and steel manfactring for the manfactred raw material sector and (ii) other inpts and otpts from the natral resorce sector. Material inpts to concrete manfactring consists of cement, sand, aggregate (gravel and macadam) and water. Sand and aggregate are natral resorces that are freely available and reqire minimm processing. Hence, the environmental impact of concrete manfactring comes mainly from cement. For this particlar stdy, the environmental effects of concrete is considered as the sm of (i) environmental impacts of cement manfactring from the extraction of raw materials till it reaches the concrete manfactring nit and (ii) the environmental impact from the process of concrete manfactring. Water se, thogh an important isse, is not considered with the assmptions that it is not a limiting resorce for the particlar case and that recycled water can be sed for the prpose of cement and concrete manfactring which will redce the impact. All the inpts and otpts for the two pile types are calclated based on the design calclations given in Table 3. Table 3 Design dimensions of drilled shaft and driven pile for different sperstrctre loads Working Load (kn) Diameter of s in Sand (m) Diameter of s in Clay (m) Length = 12 m Standard LCI methodology acconts for all inpts and otpts in terms of mass flow (e.g., kilogram of inpt/nit prodct). One drawback of the method is that the limiting resorce on the earth is not mass bt energy and, more precisely, available energy that can do sefl work. Mass acconting methods neglect the relative conseqences of sing inpts that have different

5 112 Sstainability Metrics for Fondations Aditi Misra and Dipanjan Bas amonts of available energy. Moreover, mass acconting does not consider the ecosystem services that went into making the material, and hence, fails to captre the actal effect of material se on the ecosystem. Therefore, in this stdy, the resorce se is qantified sing exergy, emergy and embodied energy in addition to mass. The otpt side of the inventory is calclated in terms of mass, thogh, becase the data available are all in terms of mass. Exergy of a resorce is its available energy to do sefl work (Dincer and Rosen 2007). Ths, for any engineering process to be sstainable, exergy loss shold be minimized. Emergy is the sm total of the ecosystem services that have been sed p to develop a prodct (Odm 1996). Therefore, a sstainable engineering process shold target to minimize the emergy of its finished prodcts. Embodied energy of a material is the sm total of all the energy that has been sed to prodce the material from the stage of extraction of raw materials till its disposal (Brown and Herendeen 1996). A sstainable process shold se materials that are low in embodied energy. The vales of nit emergy for cement and steel are adopted from Brown and Branakaran (2003) and Plselli et al. (2004) while the vales of nit emergy for land are obtained from the emergy folios of Odm et al. (2000). The embodied energy vales per nit mass are adopted from the ICE Database version 1.6a prepared by the University of Bath, U.K. (Hammond and Jones 2009). The exergy vales of cement and steel sed in the calclations are based on the vales calclated by Szargt et al. (1988). The nit exergy vale of land is taken to be the same as that of qartz for the sandy profile and as that of clay minerals for the clayey profile the vales are obtained from Meester et al. (2006). It is assmed that the top 1 m soil has an organic content of 3% and it decreases to 1% at depths greater than 1 m (Plselli et al. 2004). Ths, the loss of total organic content considered for drilled shaft is calclated based on 3% for the top 1 m and on 1 % for the remaining pile length. Althogh soil is not excavated ot for driven piles, it is assmed in this stdy that the entire organic content of the soil volme displaced by the driven piles is lost becase the pile penetration process severely distrbs the soil. It is frther assmed that the qantity of cement reqired to manfactre 1 m 3 of concrete is 350 Kg. The reinforcement of the driven piles is calclated based on the reinforcement reqired to spport the lifting moments in piles that occr dring the lifting of the piles by head (Tomlinson and Woodward 1994). The calclated reinforcements satisfied the minimm reqired vale of 2% of the shaft cross sectional area. A nominal reinforcement of 0.5% of the area of cross section is assmed for drilled shafts (Salgado 2008). Sample calclations for the resorce consmption of driven piles in sand for a working load of 400 kn is reported in Table 4. Otpt Inventory The otpt side of the inventory is calclated in terms of mass becase the databases available for performing the environmental impact assessment are all given in terms of mass. The total qantity of cement, diesel, concrete and steel reqired for the piles, as obtained from the design calclations, is mltiplied by the emission vales per nit prodction of cement, concrete and steel, and per nit combstion of diesel, as obtained from the National Renewable Energy Laboratory (NREL), U.S.A database and from Sjnnessen (2005), to obtain the total qantity of the otpt emissions. As illstrations of the calclations, the otpt inventory and environmental impact of the otpts are provided in Tables 5-8 for piles in sand for a working load 400 kn. LCA Step 3: Environmental Impact Assessment (EIA) The environmental impact assessment is done based on the categories of global warming, hman toxicity, ecosystem toxicity and acidification. The impact in each category is calclated by first aggregating the emission qantities nder different impact categories and then by mltiplying the aggregates with the corresponding weights. The weights are sed to signify the relative importance of the impact categories and they determine the proportion of an emission to be attribted to a particlar category. In this particlar stdy, the weights (indexes) are sed as per the ReCiPe database (2009) which ses the distance to target method. In the distance to target method, first, a sstainable emission/polltion standard (target) is defined for each impact category. Then, the weight of a particlar category for a project is decided by the gap (distance) between the crrent emission/polltion level and the standard that has been set. The frther a project is from achieving the target for a particlar category, the greater the weight is for that category in the project (Seppala and Hamalainen 2001). The midpoint indicators are sed as weights (indexes) for this in order to avoid the higher degree of ncertainty associated with the end point indicators. The impact in the category of acidification is calclated in terms of SO2 acidification potential and determined as gram eqivalent SO2. The impact in the category of global warming (climate change) is calclated in terms of global warming potential of CO2 and is determined as gram eqivalent CO2. The ecosystem health category incldes both terrestrial and freshwater toxicity. The categories of terrestrial toxicity, freshwater toxicity and hman toxicity is calclated in terms of toxicity potential of 1,4 dichlorobenzene (1,4 DB) and is expressed as gram eqivalent of 1, 4 DB.

6 113 Indian Geotechnical Jornal 41(3), 2011 Table 4 Resorce consmption for driven pile in sand for working load 400 kn Sl No. RESOURCE CONSUMPTION CALCULATION FOR DRIVEN PILE IN SAND FOR WORKING LOAD 400 kn Materials Volme (m 3 ) Density (Kg/m 3 ) Mass (Kg) Emergy Intensity ( ) (sej/kg) (1) (2) (3) = (2) (1) (4) Emergy Embodied Energy Cmlative Exergy Total Emergy ( ) (sej) Embodied Energy Intensity (MJ/Kg) (5) = (3) (4) (6) Total Embodied Energy (MJ) Unit Exergy (MJ/Kg) (7) =( 6) (3) (8) Total Exergy (MJ) (9) = (8) (3) 1 Soil 0.68 (a) Top soil (3 m) (b) Rest Note: For emergy calclation of soil, only emergy intensity of organic content of soil is considered; Mass of organic content is calclated as 3% of soil mass at top soil and 1% of soil mass below the top soil Calclated as 350Kg/m 3 2 Cement (Portland) of concrete Steel (Virgin) Fel (operation at site) Average 5 piles a day, 8hrs/day,11gal/hr [Crane+pile driving hammer+welding machine+secondary small crane] Emergy intensity is sej/j Total emergy / embodied energy / exergy consmption as resorces Table 5 Otpt inventory and environmental impact for cement reqirement of piles in sand for working load 400 kn Otpt Inventory and Environmental Impact for Cement Reqirement for s in Sand For Working Load 400 kn Agent / Unit (gm/gm) (1) (2) Emitted for ( 10 3 ) (gm) ( 10 3 ) (gm eqivalent CO 2 ) ( 10 3 ) (gm eqivalent SO 2 ) (3) (4) (6) (7) (9) (10) (6) = (7) = (5) (5) (3) (5) (4) (8) (9) = (8) (3) (10) = (8) (4) Particlates, nspecified NA NA NA NA Particlates, > 2.5 μm, and < 10μm NA NA NA NA Carbon dioxide, biogenic NA NA Carbon dioxide, fossil NA NA Slfr dioxide NA NA Nitrogen oxides NA NA VOC, volatile organic componds NA NA NA NA Carbon monoxide NA NA NA NA Methane NA NA Ammonia NA NA Hydrogen chloride NA NA NA NA TOTAL IMPACT IN CATEGORIES Emitted for ( 10 3 ) (gm) (3) and (4) = (2) 350Kg of cement volme of concrete sed 10 3 Global Warming Potential Acidification Potential

7 114 Sstainability Metrics for Fondations Aditi Misra and Dipanjan Bas Table 6 Otpt Inventory and Environmental Impact for Diesel Combstion for s in Sand for Working Load 400 kn Otpt Inventory and Environmental Impact for Diesel Combstion for s in Sand for Working Load 400 kn Agent / Unit (Kg/L) Global Warming Potential (Kg eqivalent CO 2 ) Acidification Potential (Kg eqivalent SO 2 ) (3) (4) (6) (7) (9) (10) (6) = (7) = (5) (5) (3) (5) (4) (8) (9) = (8) (3) (10) = (8) (4) Carbon dioxide, fossil NA Carbon monoxide, fossil NA NA Methane, fossil NA Nitrogen oxides NA Particlates, > 2.5 m, and < 10m NA NA Slfr oxides (1) (2) Emitted for (Kg) Emitted for (Kg) (3) and (4) = (2) liters of diesel sed NA VOC, volatile organic componds NA NA TOTAL IMPACT IN CATEGORIES Table 7 Otpt Inventory and Environmental Impact for Concrete Reqirements for s in Sand for Working Load 400 kn Otpt Inventory and Environmental Impact for Concrete Reqirement for s in Sand for Working Load 400 kn Agent / Unit (gm/m 3 ) (1) (2) Emitted for (gm) Emitted for (gm) Global Warming Potential (gm eqivalent CO 2 ) Acidification Potential (gm eqivalent SO 2 ) (3) (4) (6) (7) (9) (10) (3) and (4) = (2) volme of concrete sed (6) = (7) = (5) (5) (3) (5) (3) (8) (9) = (8) (3) (10) = (8) (4) Particlates NA NA NA NA Carbon dioxide NA NA Carbon monoxide NA NA NA NA Nitrogen oxides NA NA Slfr dioxides NA NA Methane NA NA Ammonia NA NA TOTAL IMPACT IN CATEGORIES

8 115 Indian Geotechnical Jornal, 41(3), 2011 Table 8 Otpt Inventory and Environmental Impact for Steel Reqirements of s in Sand for Working Load 400 kn Agent of Emission Per Unit ( 10-4 ) (gm/kg) emitted for (gm) Otpt Inventory and Environmental Impact for Steel Reqirement for s in Sand for Working Load 400 kn emitted for (gm) (3) and (4)=(2) weight of steel Hman Toxicity (gm eqivalent 1,4 DB) (6) = (5) (3) (7) =(5) (4) (8) Terrestrial Eco-Toxicity (gm eqivalent 1,4 DB) (9) = (8) (3) (10) = (8) (4) (11) Freshwater Eco-Toxicity (gm eqivalent 1,4 DB) (12) = (11) (3) (13) = (11) (4) (14) Acidification Potential (gm eqivalent SO 2 ) (15) = (16) = (14) (3) (14) (4) (17) Global Warming Potential (gm eqivalent CO 2 ) (1) (2) (3) (4) (5) Acrolein NA NA Ammonia NA NA NA NA NA NA NA NA Antimony NA NA NA NA NA NA NA NA Arsenic NA NA NA NA Benzene NA NA NA NA NA NA NA NA Beryllim NA NA NA NA Carbon dioxide, biogenic NA NA NA NA NA NA NA NA Carbon dioxide, fossil NA NA NA NA NA NA NA NA Carbon monoxide, fossil NA NA NA NA NA NA NA NA NA NA Chlorine NA NA NA NA Chromim NA NA NA NA Cobalt NA NA NA NA Dinitrogen monoxide NA NA NA NA NA NA NA NA Ethene, trichloro NA NA NA NA NA NA NA NA Hydrogen floride NA NA NA NA NA NA NA NA Lead NA NA NA NA Manganese NA NA NA NA Mercry NA NA NA NA Methane NA NA NA NA NA NA NA NA Nickel NA NA NA NA Nitrogen oxides NA NA NA NA NA NA NA NA Slfr dioxide NA NA NA NA NA NA NA NA Slfr oxides NA NA NA NA NA NA NA NA (18) = (17) (3) (19) = (17) (4) TOTAL IMPACT IN CATEGORIES

9 Percent Consmption Percent Contribtion Percent Consmption Percent Contribtion 116 Sstainability Metrics for Fondations Aditi Misra and Dipanjan Bas Tables 5-8 smmarize the contribtion of the two types of piles in sand in the different impact categories based on the emissions of the process for the load case of 400kN. Similar calclations were done for piles in clay. LCA Step 4: Interpretation of Reslts Figres 2(a) and (b) show the resorce consmptions in terms of embodied energy for driven piles and drilled shafts in sand and clay across the categories of land, cement, diesel and steel. As the drilled shafts reqire a larger diameter than the driven piles for the load cases and soil profiles considered, the drilled shafts consme more resorces in terms of cement and land than the driven piles. However, the driven piles reqire more reinforcement compared with the drilled shafts, and hence, energy consmed de to the se of steel are greater for driven piles than for drilled shafts Land Cement Steel Diesel Resorce Categories (a) Land Cement Steel Diesel Resorce Categories (b) Concrete Concrete Fig. 2 Percent consmption of embodied energy for piles in (a) sand and (b) clay across the categories of land, cement, steel and diesel Figres 3(a) and (b) show the environmental impact of driven piles and drilled shafts across the sbcategories of acidification, global warming and hman toxicity. The effect of emissions on ecosystem health is mch less than that of the other categories, and hence, has been kept ot in the figres. Resorce Use Indicator The resorce se indicator is the sm of the weighted scores of the percentage embodied energy consmption of the two pile types across the chosen categories of land, cement, diesel and steel. For the prpose of obtaining an indicator, the embodied energy consmption was chosen to represent the energy se. The choice of embodied energy was made mainly becase LCA of bildings and related materials have traditionally been done sing embodied energy Hman Toxicity Acidification Global Warming Environmental Impact Categories (a) Hman Toxicity Acidification Global Warming Environmental Impact Categories (b) Concrete Concrete Fig. 3 Percent environmental impact contribtion in selected categories for piles in (a) sand and (b) clay Soil, as land, is a limited resorce and cement manfactring is one of the largest contribtors to global warming; hence, these two categories are assigned a greater weight of 0.3 each while both diesel and steel are assigned a weight of 0.2 each (the sm of the weights eqals nity). It is important to note that the assigned weights are arbitrary and can be changed depending on the choice of the designer or on the reqirement of a particlar site. The indicator is calclated by smming the prodct of the percentage contribtion of each pile type in a category and the corresponding weight. Sample calclations for piles in sand are provided in Table 9. Similar calclations were done for piles in clay. The details of the calclations are reported in Misra (2010). The indicators calclated for

10 117 Indian Geotechnical Jornal 41(3), 2011 driven piles and drilled shafts for the different load cases are plotted in Figres 4(a) and (b) for the different sperstrctre loads. The lower the vale of the indicator is, the more sstainable the process is. Ths, from a resorce se point of view, driven piles are more sstainable (for the cases considered in this stdy) althogh the performance of both the pile types are almost the same for the clayey profile. two pile types in the environmental impact categories of hman health, acidification and climate change. Ecosystem health is neglected as the impact in this category is fond to be negligible compared to other impact categories. The indicator is calclated with weights of 0.4 for hman toxicity, 0.3 for global warming and 0.3 for acidification potential. Sample calclations for piles in sand are shown in Table 10. The indicators calclated for driven piles and drilled shafts are plotted in Figres 5(a) and (b) for the different sperstrctre loads. As a low vale of the indicator represents a more sstainable option, the driven piles are better in the sandy profile (for the cases considered in this paper) from an environmental impact point of view. For the clayey profile, the performance of the piles depends on the sperstrctre load for which they are designed. (a) (a) (b) Fig. 4 Resorce se indicator for piles in (a) sand and (b) clay as a fnction of sperstrctre load Environmental Impact Indicator The environmental impact indicator is the sm of the weighted scores of the percent contribtion of the (b) Fig. 5 Environmental impact indicator for piles in (a) sand and (b) clay as a fnction of sperstrctre load

11 118 Sstainability Metrics for Fondations Aditi Misra and Dipanjan Bas Table 9 Calclation of Resorce Use Indicator for s in Sand for Working Load 400 kn Resorce Category Calclation for Resorce Use Indicator for s in Sand for Working Load 400 kn Resorce Consmption Percent Resorce Consmption Calclation of Resorce Use Emergy ( ) (sej) Embodied Energy (MJ) Cmlative Exergy (MJ) Emergy Embodied Energy Cmlative Exergy Indicator Weight Indicator Vale in Each Category for Indicator Vale in Each Category for Land Cement Steel Diesel Total Final Indicator Vale Table 10 Calclation of Environmental Impact Indicator for s in Sand for Working Load 400 kn Calclation of Environmental Impact Indicator for s in Sand for Working Load 400 kn Percentage Impact from Percentage Impact from Weight Indicator Vale in Each Category for Indicator Vale in Each Category for (11) (12) Cement Concrete Steel Diesel Total Cement Concrete Steel Diesel Total Environmental =[(5)/(5)+(10)] =[(10)/(5)+(10)] Impact Category Unit (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (13) Hman Toxicity gm,1,4 DB Eq Acidification gm Eq SO Global Warming gm Eq CO Final Indicator Vale (14)= (13) (11) (14)=(13) (12)

12 119 Indian Geotechnical Jornal, 41(3), 2011 Note that the cost of installation of driven piles is mch less than that of drilled shafts. However, the lod noise and vibrations that enses dring the constrction of driven piles may not be welcomed in the neighborhood and may case damage to the existing strctres arond the constrction site. In real life problems, the financial aspects and social impacts inclding those de to noise and vibrations mst also be taken into accont while deciding on a particlar type of pile. Conclsions Geotechnical engineering is resorce intensive. The resorces sed in geotechnical engineering are obtained from the biogeosphere and from indstrial processes. The indstrial processes generate toxic emissions to air and case polltion to land and water. Althogh the direct environmental impact of geotechnical engineering is limited to resorce se and to the polltion and emissions cased at the constrction site, the indirect impact of geotechnical constrction can affect a wide range of environmental processes inclding hman and ecosystem health. Ths, it is important to perform sstainability assessment of geotechnical projects in order to ensre that the resorces sed and the polltions cased are kept at a minimm. A comparative LCA was carried ot for drilled shafts and driven concrete piles in sandy and clayey profiles designed to carry three different loads. The LCA consists of LCI and EIA. Based on the LCA, two indicators, the resorce se indicator and the environmental impact indicator, were calclated for the two types of piles. A lower vale of the indicators sggests a more sstainable option. The calclated indicators show that, for the piles in sand considered in this stdy, driven piles se resorces more efficiently than drilled shafts and, for the piles in clay, the resorce-se efficiency of both types of piles are more or less the same. The analysis frther indicates that, from the environmental impact point of view, the driven piles perform better in the sandy profile bt, for clayey profile, the performance depends on the design load. Ths, the framework developed in this stdy provides a decision aiding tool in choosing one pile type over the other considering environmental sstainability, particlarly when technical feasibility is not a limiting factor for choosing an alternative. References Abre, D.G, Jefferson, I., Braithwaite, P.A. and Chapman, D. N. (2008): Why is Sstainability Important in Geotechnical Engineering, Proc. of GeoCongress 2008, Geotechnical Special Pblication No. 178, pp Brown, M. T. and Branakaran, V. (2003): Emergy indices and ratios for sstainable material cycle and recycle options, Resorces, Conservation and Recycling, 38, pp Brown, M.T. and Herendeen, R.A. (1996): Embodied energy analysis and EMERGY analysis: a comparative view, Ecological Economics, 19(3), pp Cha, C., Soga, K., and Nicholson, D. (2006): Comparison of embodied energy of for different retaining wall systems, Proc. of International Conference on rese of fondations for rban sites, Btcher, A. P., Powell, J.J.M., and Skinner, H.D. (eds.), pp Cha, C., Soga, K., Nicholson, D., O Riordan, N. and Ini, T. (2008): Embodied energy as environmental impact indicator for basement walls. Proc. of Geo Congress 2008, Geotechnical Special Pblication No. 178, pp Constanza, R. (1980): Embodied Energy and Economic Valation, Science, New Series, 210(4475), pp Crran, M.A. (1996): Environmental Life Cycle Assessment, McGraw Hill. Dincer, I. and Rosen, M. (2007): Exergy: Energy, Environment and Sstainable Development, Elsevier. Egan, D. and Slocombe, B.C. (2010): Demonstrating environmental benefits of grond improvement, Proc. of the Instittion of Civil Engineers Grond Improvement, 163(1), pp Hammond, G. and Jones, C. (2009): Inventory of Carbon and Energy (ICE) Version 1.6a, Carbon Vision Bilding Program, University of Bath U.K. Ha, J.L. (2002): Integrating Life cycle Assessment, Exergy and Emergy analyses, M.S. Thesis, The Ohio State University. Holt, D.G.A, Jefferson, I., Braithwaite, P.A., and Chapman, D.N. (2009): Embedding sstainability into geotechnics. Part A: Methodology, Proc. of the Instittion of Civil Engineers, 163(3), pp Holt, D.G.A., Jefferson, I., Braithwaite, P.A. and Chapman, D.N. (2010). Sstainable Geotechnical Design. Proc. of Geocongress 2010, Florida, CD-ROM. Jefferis, S.A. (2008): Moving towards Sstainability in Geotechnical Engineering, Proc. of the Geo Congress 2008, Geotechnical Special Pblication No. 178, pp Jefferson, I., Hnt, D.V.L., Birchall, C.A. and Rogers, C.D.F. (2007): Sstainability Indicators for Environmental Geotechnics, Proc. of the Institte of Civil Engineers - Engineering Sstainability, 160(2), pp

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