Sustainability Metrics for Pile Foundations

Indian Geotechnical Journal, 41(2), 2011, 108-120

Abstract: Civil Engineering is the major instrument of anthropocentric development over centuriesthrough ever expanding infrastructures, cities and facilities. Lately, a growing awareness isobserved towards making such growth sustainable. Geotechnical engineering, being very resourceintensive, warrants an environmental sustainability study, but a quantitative framework forassessing the sustainability of geotechnical practices, particularly at the planning and designstages, does not exist. In this paper, quantitative indicators for assessing the environmentalsustainability of pile foundations are developed through life cycle assessment (LCA) of pilefoundations. The use of resources is taken into account based on energy-centric methods whilethe impact of the process emissions is assessed using environmental impact assessment (EIA).The resource use and the impact of emissions are categorized and normalized, and weights areapplied across the categories to emphasize the relative importance of the categories. Theweighted values thus obtained are aggregated across the categories to obtain the resource useand environmental impact indicators for drilled shafts and driven concrete piles carrying equalamount of axial loads. The developed indicators can be used to quantitatively compare theimpacts of these two types of piles on the environment considering both resource consumptionand process emissions. Thus, a holistic approach towards assessing environmental sustainabilityof pile foundations is proposed.

Key words

Sustainability, indicators, pile foundations, life cycle assessment, energy accounting

Sustainability Metrics for Pile Foundations

Aditi Misra1 and Dipanjan Basu2

1 Graduate student, Department of Civil and Environmental Engineering, University of Connecticut, Storrs, Email: [email protected]

2 Assistant Professor, Department of Civil and Environmental Engineering, University of Connecticut, Storrs, Email: [email protected]

Introduction

Civil Engineering has been the majorinstrument of anthropocentric development overcenturies through ever expanding infrastructures, citiesand facilities. In recent times, a concerted effort isobserved within the civil engineering industry to deliverbuilt facilities that are environment friendly as well asfinancially viable. Geotechnical engineering is mostresource intensive of all civil engineering disciplinesalthough this intensive consumption of energy andnatural resources goes unnoticed mainly because of theindirect nature of the energy used in the form ofmaterials and natural resources (e.g., concrete, steeland land use). By virtue of its early position in theconstruction cycle, sustainable geotechnical practicescan substantially improve the overall sustainability of aproject, and hence, improving the sustainability ofgeotechnical processes is extremely important inachieving overall sustainable development (Jefferis2008).

Sustainability as a decision metric is slowlygaining popularity within the geotechnical industry and areview of the existing literature reveals a few projectswhere sustainability has been used as a criterion tochoose the best alternative. Chau et al. (2006) usedembodied energy as an environmental impact indicator

in their study of four different retaining wall designs.Later, Chau et al. (2008) compared the environmentalimpact and energy efficiency of basement wallconstruction for two commercial buildings in London interms of embodied carbon dioxide. A case studyassessing the relative impacts of concrete retainingwalls and bioengineered slopes through life cycle impactassessment was done by Storesund et al. (2008).Spaulding et al. (2008) compared, using three casestudies, the use of ground improvement techniques asan alternative to conventional deep foundations andused carbon footprint as a measure of environmentalsustainability. Egan et al. (2010) also studied the use ofground improvement techniques as an alternative totraditional deep foundations using embodied carbondioxide as an environmental metric. These projectshave mainly relied on a single metric, either resourceefficiency or environmental impact, which is notsufficient to determine the best engineering solutionbalancing both economy and ecology.

Some qualitative guidelines are available thatuse multiple criteria (e.g., social, economic andenvironmental impacts) for assessing the sustainabilityof geotechnical construction sites. These include theSustainable Geotechnical Evaluation Method (S.G.E.M)(Jiminez 2004), the Environmental GeotechnicalIndicator System (EGIs) (Jefferson et al. 2007) andGeoSPeAR (Holt et al. 2009, 2010). S.G.E.M. uses a

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Indian Geotechnical Journal 41(3), 2011

color coded indicator system, based on the categories ofsocial, economic, environmental and natural resourceuse, for the purpose of comparing different alternativematerials used in slope stabilization. EGIs consists of76 generic indicators and 32 technology-specificindicators and was developed for ground improvementprojects by borrowing concepts from the existingsustainability indicators like SPeAR and BREEAM(Jefferson et al. 2007). GeoSPeAR is an indicatorsystem for geotechnical construction and was developedby modifying SpeAR (Holt et al. 2010). Although thesequalitative indicators serve well at the constructionstage of a project, there is a lack of a clearly definedframework to evaluate and quantify the relativesustainability of alternative practices in geotechnicalengineering at the planning and design stages of aproject (Abreu et al. 2008).

The objective of this paper is to introduce aquantitative framework for assessing the comparativesustainability of different technically feasible optionsavailable for a geotechnical project. Life cycleassessment (LCA), in conjunction with environmentalimpact assessment (EIA), is proposed as a quantitativedecision aid tool to incorporate environmentalsustainability in geotechnical engineering, particularly, inpile foundation design. Based on the LCA, a resourceuse indicator and an environmental impact indicator aredeveloped to quantitatively compare the sustainability ofcompeting alternatives. The framework is explainedthrough case studies involving pile foundations in orderto determine whether driven concrete piles or drilledshafts are more sustainable for the cases investigated.The purpose of the case studies is to illustrate the utilityand effectiveness of the developed framework.

Sustainability Assessment of Geotechnical Projects

A sustainable project balances the social,environmental and economic equity in order to achievesustainable development. Indiscriminate consumptionof natural resources in a project affects thedistributional equity of resources, and hence, violatesthe social equity principle of sustainability. The use ofmanufactured raw materials in a project disturbs theenvironmental balance through process emissions andpollutions. A project that focuses only on the financialreturn and does not consider the social impactscontradicts the economic and social equity principles ofsustainability. As geotechnical projects use vast amountof resources and energy, generate considerable amountof waste, involve financial investment of stakeholdersand often permanently change the landscape, it isimportant that they are assessed for sustainabilityconsidering resource consumption, environmentalimpact and socio-economic impact.

In practice, sustainability assessment of

geotechnical projects can be done by using life cycleassessment (LCA) that combines resource inventory andenvironmental impact assessment (EIA) and by using asocio-economic impact assessment tool like cost benefitanalysis (CBA). LCA is a quantitative tool that assessesthe impacts of a process or a product on theenvironment over the entire lifespan of the process orthe product. In most geotechnical processes, the LCAshould follow a “cradle to grave” approach becausereuse of materials after decommissioning of a project isgenerally not considered. In addition, it is better to dothe resource accounting in the LCA by energy accountingmethods instead of mass accounting because availableenergy to do work is the ultimate limiting resource. Theenvironmental impact assessment (EIA) determines theimpact of the output of a process on the ecosystem ondifferent categories like human and ecosystem health,global warming and acidification. A combination of LCAand EIA provides a holistic environmental sustainabilityassessment for geotechnical projects.

Life Cycle Assessment of Pile Foundations

The use of the sustainability frameworkdeveloped in this study is illustrated by applying it tocase studies involving pile foundations. Two commonlyused pile foundations — drilled shafts and drivenconcrete piles — are considered in the case studies inorder to determine their comparative sustainability.Assessing the sustainability of pile foundations shouldstart after a preliminary design has been done and afterdata has been collected on the technological feasibilityof the different alternatives.

The pile design in this study follows the workingstress method. The ultimate pile capacity is assumed tobe that corresponding to a pile head settlement of 10%of the pile diameter. It is assumed that the piles areinstalled in homogeneous profiles of sandy and clayeysoils. The soil profiles are so chosen that theconstruction of driven concrete piles and drilled shafts istechnically feasible. Both the pile types are assumed tosupport the same superstructure load. It is alsoassumed that there are no constraints that limit theavailability of raw materials, equipment or technicalexpertise required for the design and construction of thepiles. The design equations used in the case studiesare provided in Tables 1 and Table 2. Three workingload cases of 250 kN, 300 kN and 400 kN areconsidered with a factor of safety equal to 2.5. Thelength of the piles is kept constant at 12 m while thediameters are varied in the design. The dimensionsobtained from the design calculations are provided inTable 3.

For the sandy soil considered in this study, thesoil properties are (i) unit weight of solids Gs = 2.65, (ii)relative density DR = 60%, (iii) coefficient of earth

110

Sustainability Metrics for Pile Foundations Aditi Misra and Dipanjan Basu

Table 1 Design equations for sandy profile (Salgado 2008)

Design Equations for Drilled Shaft in Sand Design Equations for Driven Concrete Pile in Sand

• Limit Unit Shaft Resistance

φ′

sL v cq = Kσ tan

where

⎡ ⎤⎧ ⎫⎛ ⎞⎪ ⎪⎢ ⎥⎨ ⎬⎜ ⎟⎪ ⎪⎢ ⎥⎝ ⎠⎩ ⎭⎣ ⎦

v0 R

A

σ'K = 0.7K exp 0.0114 -0.0022ln Dp

• Ultimate Unit Base Resistance

( )⎡ ⎤⎣ ⎦b,10% R bLq = 0.23exp -0.0066D q

where

( )( )

φ φ⎡ ⎤⎣ ⎦

⎛ ⎞′×⎜ ⎟⎝ ⎠

R

bLc c R

A

0.841-0.0047D

h

A

q =1.64exp 0.1041 + 0.0264-0.0002 Dp

σp


( )[ ]φsL c R bLq = 0.02tan 0.95 1.02 - 0.0051D q

where

( )( )

φ φ⎡ ⎤⎣ ⎦

⎛ ⎞′×⎜ ⎟⎝ ⎠

R

bLc c R

A

0.841-0.0047D

h

A

q =1.64exp 0.1041 + 0.0264 -0.0002 Dp

σp

and is calculated at a depth at which qSL is required

• Ultimate Unit Base Resistance [ ]b,10% R bLq = 1.02 - 0.0051D q

σv' is the vertical effective stress at a depth at which the capacity is calculated, σh' is the horizontal effective stress at a depth at which the capacity is calculated, φc is the critical state friction angle of the sand, DR is the relative density of sand expressed as a percentage, K0 is the coefficient of earth pressure at rest, and pA is a reference stress (= 100 kPa)

Table 2 Design equations for clayey profile (Salgado 2008)

Design Equations for Drilled Shaft in Clay Design Equations for Driven Concrete Pile in Clay


sL uq =αs where

⎡ ⎤⎛ ⎞⎢ ⎥⎜ ⎟

⎝ ⎠⎣ ⎦u

A

sα = 0.4 1-0.12lnp


b,10% uq = 9.6s


sL uq = αs where

⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

0.5 -0.5

u u' 'v vNC

s sα =σ σ

and


b,10% uq =10s

su is the undrained shear strength of clay, NC represents normally consolidated clay, pA is a reference stress (= 100 kPa)

⎛ ⎞⎜ ⎟⎝ ⎠

u'v NC

s = 0.3σ

111


pressure at rest K0 = 0.4, (iv) maximum void ratio emax =0.9, (v) minimum void ratio emin = 0.4, (vi) unit weight ofwater γw = 9.81 kN/m3 and (vii) critical state frictionangle φc = 30º. The resulting bulk unit weight of sandγsat = 19.93 kN/m3. For the clayey soil considered inthis study, the soil properties are (i) Gs = 2.65, (ii) OCR =2, (iii) γw = 9.81 kN/m3 and (iv) γsat = 18 kN/m3. Thewater table is assumed to be at the ground surface forboth the sand and clay profiles.

The designed pile dimensions are used in theLCA to determine (i) the quantity of natural resourcesand processed materials needed for the piles and (ii) theemissions generated to manufacture the requiredquantity of materials. The LCA done in this paperconsists of four steps: (i) goal and scope definition inwhich the purpose and extent of the study is underlined,(ii) life cycle inventory (LCI) analysis in which all theinputs to and outputs from the process over its life cycleis accounted for, (iii) environmental impact assessment(EIA) in which the outputs of the process are related tothe impact categories and (iv) interpretation of results inwhich the resource use and environmental impactindicators are calculated. Figure 1 shows the flow chartfor this LCA.

Fig. 1 Flow chart showing the inputs, outputs, processes and impact categories in pile construction

LCA Step 1: Goal and Scope Definition

The goals of the life cycle assessment performedfor this case study are (i) to determine, through life cycleinventory (LCI), the resource consumption andemissions for drilled shafts and driven concrete pilesover the lifespan of the project and (ii) to decide, afteran environmental impact study based on the LCI, whichof the two aforementioned piles is more environmentallysustainable.

The scope of this study primarily includesidentification and quantification of all the major inputsto and outputs from the process of pile construction.The inputs that are considered in this study are cementand steel from the manufacturing segment and landfrom the biogeosphere. The outputs are the constructedpiles along with emissions to air and water. The

contributors to energy or resource consumption from theconstruction and maintenance of the manufacturingplants of cement and steel, electricity consumption ofthe architect’s office and other similar indirectcontributors are kept out of the scope with theunderstanding that such contributions are almost thesame for both the pile types, and hence, do notinfluence the goal of the study.

LCA Step 2: Life Cycle Inventory (LCI)

Input Inventory Based on the above stated goal and scope of this

LCA, life cycle inventory for pile foundation shouldquantify (i) the inputs and outputs for concrete and steelmanufacturing for the manufactured raw material sectorand (ii) other inputs and outputs from the naturalresource sector. Material inputs to concretemanufacturing consists of cement, sand, aggregate(gravel and macadam) and water. Sand and aggregateare natural resources that are freely available andrequire minimum processing. Hence, the environmentalimpact of concrete manufacturing comes mainly fromcement. For this particular study, the environmentaleffects of concrete is considered as the sum of (i)environmental impacts of cement manufacturing fromthe extraction of raw materials till it reaches theconcrete manufacturing unit and (ii) the environmentalimpact from the process of concrete manufacturing.Water use, though an important issue, is not consideredwith the assumptions that it is not a limiting resource forthe particular case and that recycled water can be usedfor the purpose of cement and concrete manufacturingwhich will reduce the impact. All the inputs and outputsfor the two pile types are calculated based on the designcalculations given in Table 3.

Table 3 Design dimensions of drilled shaft and driven pile for different superstructure loads

Drilled Shaft Driven Pile Drilled ShaftDriven

Pile

250.00 0.38 0.16 0.68 0.50

300.00 0.51 0.22 0.91 0.70

400.00 0.63 0.27 1.11 0.87

Diameter of Piles in Sand (m)

Diameter of Piles in Clay (m)

Working Load (kN)

Pile Length = 12 m Standard LCI methodology accounts for all inputs

and outputs in terms of mass flow (e.g., kilogram ofinput/unit product). One drawback of the method is thatthe limiting resource on the earth is not mass but energyand, more precisely, available energy that can do usefulwork. Mass accounting methods neglect the relativeconsequences of using inputs that have different

112


amounts of available energy. Moreover, massaccounting does not consider the ecosystem servicesthat went into making the material, and hence, fails tocapture the actual effect of material use on theecosystem. Therefore, in this study, the resource use isquantified using exergy, emergy and embodied energy inaddition to mass. The output side of the inventory iscalculated in terms of mass, though, because the dataavailable are all in terms of mass.

Exergy of a resource is its available energy to douseful work (Dincer and Rosen 2007). Thus, for anyengineering process to be sustainable, exergy lossshould be minimized. Emergy is the sum total of theecosystem services that have been used up to develop aproduct (Odum 1996). Therefore, a sustainableengineering process should target to minimize theemergy of its finished products. Embodied energy of amaterial is the sum total of all the energy that has beenused to produce the material from the stage ofextraction of raw materials till its disposal (Brown andHerendeen 1996). A sustainable process should usematerials that are low in embodied energy.

The values of unit emergy for cement and steelare adopted from Brown and Buranakaran (2003) andPulselli et al. (2004) while the values of unit emergy forland are obtained from the emergy folios of Odum et al.(2000). The embodied energy values per unit mass areadopted from the ICE Database version 1.6a preparedby the University of Bath, U.K. (Hammond and Jones2009). The exergy values of cement and steel used inthe calculations are based on the values calculated bySzargut et al. (1988). The unit exergy value of land istaken to be the same as that of quartz for the sandyprofile and as that of clay minerals for the clayey profile⎯ the values are obtained from Meester et al. (2006).

It is assumed that the top 1 m soil has an organiccontent of 3% and it decreases to 1% at depths greaterthan 1 m (Pulselli et al. 2004). Thus, the loss of totalorganic content considered for drilled shaft is calculatedbased on 3% for the top 1 m and on 1 % for theremaining pile length. Although soil is not excavated outfor driven piles, it is assumed in this study that theentire organic content of the soil volume displaced bythe driven piles is lost because the pile penetrationprocess severely disturbs the soil.

It is further assumed that the quantity of cementrequired to manufacture 1 m3 of concrete is 350 Kg.The reinforcement of the driven piles is calculatedbased on the reinforcement required to support thelifting moments in piles that occur during the lifting ofthe piles by head (Tomlinson and Woodward 1994). Thecalculated reinforcements satisfied the minimumrequired value of 2% of the shaft cross sectional area. Anominal reinforcement of 0.5% of the area of crosssection is assumed for drilled shafts (Salgado 2008).Sample calculations for the resource consumption ofdriven piles in sand for a working load of 400 kN is

reported in Table 4.

Output Inventory The output side of the inventory is calculated in

terms of mass because the databases available forperforming the environmental impact assessment areall given in terms of mass. The total quantity of cement,diesel, concrete and steel required for the piles, asobtained from the design calculations, is multiplied bythe emission values per unit production of cement,concrete and steel, and per unit combustion of diesel,as obtained from the National Renewable EnergyLaboratory (NREL), U.S.A database and from Sjunnessen(2005), to obtain the total quantity of the outputemissions. As illustrations of the calculations, theoutput inventory and environmental impact of theoutputs are provided in Tables 5-8 for piles in sand for aworking load 400 kN.

LCA Step 3: Environmental Impact Assessment (EIA)

The environmental impact assessment is donebased on the categories of global warming, humantoxicity, ecosystem toxicity and acidification. The impactin each category is calculated by first aggregating theemission quantities under different impact categoriesand then by multiplying the aggregates with thecorresponding weights. The weights are used to signifythe relative importance of the impact categories andthey determine the proportion of an emission to beattributed to a particular category. In this particularstudy, the weights (indexes) are used as per the ReCiPedatabase (2009) which uses the distance to targetmethod. In the distance to target method, first, asustainable emission/pollution standard (target) isdefined for each impact category. Then, the weight of aparticular category for a project is decided by the gap(distance) between the current emission/pollution leveland the standard that has been set. The further aproject is from achieving the target for a particularcategory, the greater the weight is for that category inthe project (Seppala and Hamalainen 2001). Themidpoint indicators are used as weights (indexes) forthis in order to avoid the higher degree of uncertaintyassociated with the end point indicators.

The impact in the category of acidification iscalculated in terms of SO2 acidification potential anddetermined as gram equivalent SO2. The impact in thecategory of global warming (climate change) iscalculated in terms of global warming potential of CO2

and is determined as gram equivalent CO2. Theecosystem health category includes both terrestrial andfreshwater toxicity. The categories of terrestrial toxicity,freshwater toxicity and human toxicity is calculated interms of toxicity potential of 1,4 dichlorobenzene (1,4DB) and is expressed as gram equivalent of 1, 4 DB.

113


Table 4 Resource consumption for driven pile in sand for working load 400 kN

Emergy Intensity (×1011) (sej/Kg)

Total Emergy (×1011) (sej)

Embodied Energy Intensity (MJ/Kg)

Total Embodied

Energy (MJ)

Unit Exergy (MJ/Kg)

Total Exergy

(MJ)

(1) (2) (3) = (2) × (1) (4)(5) = (3) ×

(4) (6)(7) =( 6) ×

(3) (8)(9) = (8) ×

(3)

1 Soil 0.68 — — — — — — —

(a) Top soil (3 m) 0.17 344.59 289.45

(b) Rest 0.51 1033.76 289.45

1.13 2913.71

4Fuel (operation at

site)

RESOURCE CONSUMPTION CALCULATION FOR DRIVEN PILE IN SAND FOR WORKING LOAD 400 kN

Sl No. MaterialsVolume

(m3) Density (Kg/m3)

Mass (Kg)

Emergy Embodied Energy Cumulative Exergy

31.43

Note: For emergy calculation of soil, only emergy intensity of organic content of soil is considered; Mass of organic content is calculated as 3% of soil mass at top soil and 1% of soil mass below the top soil

Calculated as 350Kg/m3

of concrete

2031.91 28 0.45 620.26 0.02

Cement (Portland)2 201.47 19.70 3968.97 4.60 926.76 5.35 1077.87

7850.00 184.87 41.30 7635.03 36.40 6729.18 41.00 7579.57Steel (Virgin)3 0.02

2531.07

15096.62 10838.42 11219.94

44.702562.22

Total emergy / embodied energy / exergy consumption as resources

Average 5 piles a day, 8hrs/day,11gal/hr

[Crane+pile driving hammer+welding

machine+secondary small crane] 56.62

Emergy intensity is 1.13×105sej/J 45.25

Table 5 Output inventory and environmental impact for cement requirement of piles in sand for working load 400 kN

Quantity/ Unit

(gm/gm) IndexDrilled Shaft

Driven Pile Index

For Drilled Shaft

For Driven Pile

(3) (4) (6) (7) (9) (10)

(6) = (5)×(3)

(7) = (5)×(4)

(9) = (8)×(3)

(10) = (8)×(4)

Particulates, unspecified 0.00235 2.58 0.47 — NA NA — NA NA

Particulates, > 2.5 μm, and < 10μm 0.00030 0.32 0.06 — NA NA — NA NA

Carbon dioxide, biogenic 0.37359 409.34 75.27 1.00 409.34 75.27 — NA NA

Carbon dioxide, fossil 0.55344 606.41 111.50 1.00 606.41 111.50 — NA NA

Sulfur dioxide 0.00166 1.82 0.33 — NA NA 1.00 1.82 0.33

Nitrogen oxides 0.00250 2.74 0.50 — NA NA 0.52 1.43 0.26

VOC, volatile organic compounds 0.00005 0.05 0.01 — NA NA — NA NACarbon monoxide 0.00110 1.21 0.22 — NA NA — NA NA

Methane 0.00003 0.03 0.01 25.00 0.82 0.15 — NA NA

Ammonia 0.00001 0.01 0.00 — NA NA 2.23 0.01 0.00Hydrogen chloride 0.00006 0.07 0.01 — NA NA — NA NA

1016.57 186.92 3.26 0.60

Output Inventory and Environmental Impact for Cement Requirement for Piles in Sand For Working Load 400 kN

TOTAL IMPACT IN CATEGORIES

(5) (8)

Global Warming Potential (×103) (gm equivalent CO2)

Acidification Potential (×103) (gm equivalent SO2)

Agent

yEmitted for

Drilled Shaft (×103)

(gm)

Quantity Emitted for Driven Pile (×103) (gm)

(1) (2)

(3) and (4) = (2) × 350Kg of cement × volume of

concrete used ×103

114


Table 6 Output Inventory and Environmental Impact for Diesel Combustion for Piles in Sand for Working Load 400 kN

Quantity/ Unit

(Kg/L) IndexDrilled Shaft

For Driven Pile Index

For Drilled Shaft

For Driven Pile

(3) (4) (6) (7) (9) (10)

(6) = (5)×(3)

(7) = (5)×(4)

(9) = (8)×(3)

(10) = (8)×(4)

Carbon dioxide, fossil 0.27000 122.63 17.9863 1.00 122.63 17.99 NA — —Carbon monoxide, fossil 0.01400 6.36 0.9326 NA — — NA — —Methane, fossil 0.00010 0.05 0.0067 25.00 1.14 0.01 NA — —

Nitrogen oxides 0.05000 22.71 3.3308 NA — — 0.52 11.81 1.73Particulates, > 2.5 um, and < 10um 0.00160 0.73 0.1066 NA — — NA — —

Sulfur oxides 0.00060 0.27 0.0400 NA — — 1.00 0.27 0.04VOC, volatile organic compounds 0.00140 0.64 0.0933 NA — — NA — —

TOTAL IMPACT IN CATEGORIES 123.77 17.99 12.08 1.77

Output Inventory and Environmental Impact for Diesel Combustion for Piles in Sand for Working Load 400 kN

Quantity Emitted

for Driven Pile (Kg)

Global Warming Potential (Kg equivalent CO2)

Acidification Potential (Kg equivalent SO2)

(5) (8)(3) and (4) = (2)

×liters of diesel used(1) (2)

Agent

Quantity Emitted for

Drilled Shaft (Kg)

Table 7 Output Inventory and Environmental Impact for Concrete Requirements for Piles in Sand for Working Load 400 kN

Quantity/ Unit

(gm/m3) IndexDrilled Shaft

Driven Pile Index

For Drilled Shaft

For Driven Pile

(3) (4) (6) (7) (9) (10)

(6) = (5)×(3)

(7) = (5)×(3)

(9) = (8)×(3)

(10) = (8)×(4)

Particulates 0.08 0.30 0.06 — NA NA — NA NA

Carbon dioxide 257.00 948.14 174.34 1.00 948.14 174.34 — NA NACarbon monoxide 0.59 2.17 0.40 — NA NA — NA NA

Nitrogen oxides 0.49 1.81 0.33 — NA NA 0.52 0.94 0.1732

Sulfur dioxides 0.43 1.57 0.29 — NA NA 1.00 1.57 0.2890

Methane 1.60 5.90 1.09 25.00 147.57 27.13 — NA NA

Ammonia 0.01 0.03 0.00 — NA NA 2.23 0.0576 0.0106

1095.71 201.47 2.57 0.473TOTAL IMPACT IN CATEGORIES

Global Warming Potential (gm equivalent CO2)

Acidification Potential (gm equivalent SO2)

(5) (8)

Output Inventory and Environmental Impact for Concrete Requirement for Piles in Sand for Working Load 400 kN

Agent

Quantity Emitted for

Drilled Shaft (gm)

Quantity Emitted for Driven Pile

(gm)

(1) (2)(3) and (4) = (2) × volume

of concrete used

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5.75

0.00

90.

010

1.74

0.00

280.

0030

—N

AN

A—

NA

NA

Ben

zene

0.04

0.00

060.

0007

0.36

0.00

020.

000

—N

AN

A—

NA

NA

—N

AN

A—

NA

NA

Ber

ylliu

m0.

010.

0002

0.00

0217

800.

03.

33.

5713

0.00

0.02

40.

026

68.1

90.

0126

0.01

37—

NA

NA

—N

AN

AC

arbo

n di

oxid

e,

biog

enic

1373

.70

19.8

916

21.5

671

—N

AN

A—

NA

NA

—N

AN

A—

NA

NA

1.00

19.8

921

.57

Car

bon

diox

ide,

fo

ssil

1940

0000

2809

17.6

930

4580

.00

—N

AN

A—

NA

NA

—N

AN

A—

NA

NA

1.00

2809

1830

4580

Car

bon

mon

oxid

e,

foss

il22

9320

.00

3320

.620

836

00.3

240

—N

AN

A—

NA

NA

—N

AN

A—

NA

NA

—N

AN

AC

hlor

ine

0.12

0.00

180.

0019

209.

900.

40.

4047

0.44

0.00

080.

001

0.01

0.00

002

0.00

002

—N

AN

A—

NA

NA

Chr

omiu

m0.

180.

0026

0.00

280.

340.

0009

0.00

095

9.06

0.02

30.

025

0.35

0.00

090.

0010

—N

AN

A—

NA

NA

Cob

alt

0.05

0.00

070.

0007

4310

.00

2.9

3.16

316

23.2

90.

016

0.01

712

.74

0.00

860.

0094

—N

AN

A—

NA

NA

Din

itrog

en

mon

oxid

e19

.03

0.27

550.

2988

—N

A N

A—

NA

NA

—N

AN

A—

NA

NA

298.

0082

.11

89.0

3E

then

e, tr

ichl

oro-

0.03

0.00

040.

0005

193.

700.

080.

0878

4—

NA

NA

—N

AN

A—

NA

NA

—N

AN

AH

ydro

gen

fluor

ide

21.2

60.

3078

0.33

3726

6.10

81.9

88.8

0—

NA

NA

—N

AN

A—

NA

NA

—N

AN

ALe

ad0.

110.

0016

0.00

1723

110.

037

.140

.24

8.79

0.01

40.

015

0.17

0.00

030.

0003

—N

AN

A—

NA

NA

Man

gane

se0.

350.

0050

0.00

5426

230.

013

1.5

142.

560.

010.

0000

50.

0000

51.

960.

0098

0.01

06—

NA

NA

—N

AN

AM

ercu

ry0.

060.

0009

0.00

0912

2400

010

55.2

1144

.07

1698

1.46

41.

587

11.4

40.

0099

0.01

07—

NA

NA

—N

AN

AM

etha

ne78

71.9

011

3.98

7412

3.58

88—

NA

NA

—N

A N

A—

NA

NA

—N

AN

A25

.00

2849

.69

3089

.72

Nic

kel

0.52

0.00

750.

0082

680.

905.

15.

5680

.00

0.60

30.

654

32.9

40.

2482

0.26

91—

NA

NA

—N

AN

AN

itrog

en o

xide

s21

102.

0030

5.56

3133

1.30

14—

NA

NA

—N

AN

A—

NA

NA

0.52

158.

8917

2.28

—N

AN

AS

ulfu

r dio

xide

7188

.30

104.

0887

112.

8563

—N

AN

A—

NA

NA

—N

AN

A1.

0010

4.09

0.00

—N

AN

AS

ulfu

r oxi

des

2910

6.00

421.

4634

456.

9642

—N

AN

A—

NA

NA

—N

AN

A1.

0042

1.46

456.

96—

NA

NA

2372

.95

2575

.99

2.15

2.34

0.29

0.32

684.

8062

9.62

2838

6930

7780

Out

put I

nven

tory

and

Env

ironm

enta

l Im

pact

for S

teel

Req

uire

men

t for

Pile

s in

San

d fo

r Wor

king

Loa

d 40

0 kN

TOTA

L IM

PA

CT

IN C

ATE

GO

RIE

S

Glo

bal W

arm

ing

Pot

entia

l (g

m e

quiva

lent

CO

2)H

uman

Tox

icity

(gm

equ

ivale

nt 1

,4 D

B)

Fres

hwat

er E

co-T

oxic

ity

(gm

equ

ivale

nt 1

,4 D

B)

Aci

dific

atio

n P

oten

tial

(g

m e

quiva

lent

SO

2)

(1)

(2)

(3) a

nd (4

)=(2

) × w

eigh

t of

ste

el

Terre

stria

l Eco

-Tox

icity

(gm

equ

ivale

nt 1

,4 D

B)

116


Tables 5-8 summarize the contribution of the two

types of piles in sand in the different impact categoriesbased on the emissions of the process for the load caseof 400kN. Similar calculations were done for piles inclay.

LCA Step 4: Interpretation of Results

Figures 2(a) and (b) show the resourceconsumptions in terms of embodied energy for drivenpiles and drilled shafts in sand and clay across thecategories of land, cement, diesel and steel. As thedrilled shafts require a larger diameter than the drivenpiles for the load cases and soil profiles considered, thedrilled shafts consume more resources in terms ofcement and land than the driven piles. However, thedriven piles require more reinforcement compared withthe drilled shafts, and hence, energy consumed due tothe use of steel are greater for driven piles than fordrilled shafts.

0.0010.0020.0030.0040.0050.0060.0070.0080.0090.00

100.00

Land Cement Steel Diesel

Perc

ent C

onsu

mpt

ion

Resource Categories

Drilled Shaft

Driven ConcretePile

(a)

0.0010.0020.0030.0040.0050.0060.0070.0080.0090.00

100.00

Land Cement Steel Diesel

Perc

ent C

onsu

mpt

ion

Resource Categories

Drilled Shaft

Driven ConcretePile

(b)

Fig. 2 Percent consumption of embodied energy for piles in (a) sand and (b) clay across the categories of land, cement,

steel and diesel

Figures 3(a) and (b) show the environmentalimpact of driven piles and drilled shafts across the sub-categories of acidification, global warming and humantoxicity. The effect of emissions on ecosystem health ismuch less than that of the other categories, and hence,has been kept out in the figures.

Resource Use Indicator The resource use indicator is the sum of the

weighted scores of the percentage embodied energyconsumption of the two pile types across the chosencategories of land, cement, diesel and steel. For thepurpose of obtaining an indicator, the embodied energyconsumption was chosen to represent the energy use.The choice of embodied energy was made mainlybecause LCA of buildings and related materials havetraditionally been done using embodied energy.

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

Human Toxicity Acidification Global Warming

Perc

ent C

ontr

ibut

ion

Environmental Impact Categories

Drilled Shaft

Driven ConcretePile

(a)

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

Human Toxicity Acidification Global Warming

Perc

ent C

ontr

ibut

ion

Environmental Impact Categories

Drilled Shaft

Driven ConcretePile

(b)

Fig. 3 Percent environmental impact contribution in selected categories for piles in (a) sand and (b) clay

Soil, as land, is a limited resource and cementmanufacturing is one of the largest contributors toglobal warming; hence, these two categories areassigned a greater weight of 0.3 each while both dieseland steel are assigned a weight of 0.2 each (the sum ofthe weights equals unity). It is important to note thatthe assigned weights are arbitrary and can be changeddepending on the choice of the designer or on therequirement of a particular site. The indicator iscalculated by summing the product of the percentagecontribution of each pile type in a category and thecorresponding weight. Sample calculations for piles insand are provided in Table 9. Similar calculations weredone for piles in clay. The details of the calculations arereported in Misra (2010). The indicators calculated for

117


driven piles and drilled shafts for the different loadcases are plotted in Figures 4(a) and (b) for the differentsuperstructure loads. The lower the value of theindicator is, the more sustainable the process is. Thus,from a resource use point of view, driven piles are moresustainable (for the cases considered in this study)although the performance of both the pile types arealmost the same for the clayey profile.

240 280 320 360 400Working Load (kN)

20

30

40

50

60

Sandy Soil

(a)

(b)

Fig. 4 Resource use indicator for piles in (a) sand and (b) clay as a function of superstructure load

Environmental Impact Indicator The environmental impact indicator is the sum of

the weighted scores of the percent contribution of the

two pile types in the environmental impact categories ofhuman health, acidification and climate change.Ecosystem health is neglected as the impact in thiscategory is found to be negligible compared to otherimpact categories. The indicator is calculated withweights of 0.4 for human toxicity, 0.3 for global warmingand 0.3 for acidification potential. Sample calculationsfor piles in sand are shown in Table 10. The indicatorscalculated for driven piles and drilled shafts are plottedin Figures 5(a) and (b) for the different superstructureloads. As a low value of the indicator represents a moresustainable option, the driven piles are better in thesandy profile (for the cases considered in this paper)from an environmental impact point of view. For theclayey profile, the performance of the piles depends onthe superstructure load for which they are designed.

240 280 320 360 400

Working Load (kN)

30

40

50

60

70

Sandy Soil

(a)

(b)

Fig. 5 Environmental impact indicator for piles in (a) sand and (b) clay as a function of superstructure load

118

Sust

aina

bilit

y M

etric

s fo

r Pi

le F

ound

atio

ns

Aditi

Mis

ra a

nd D

ipan

jan

Bas

u

Tabl

e 9

Cal

cula

tion

of R

esou

rce

Use

Indi

cato

r for

Pile

s in

San

d fo

r Wor

king

Loa

d 4

00

kN

Driv

en

Pile

Dril

led

Shaf

tD

riven

Pi

leD

rille

d S

haft

Driv

en

Pile

D

rille

d S

haft

Driv

en

Pile

D

rille

d S

haft

Driv

en

Pile

D

rille

d Sh

aft

Driv

en

Pile

D

rille

d Sh

aft

Wei

ght

Indi

cato

r Va

lue

in

Eac

h C

ateg

ory f

or

Driv

en P

ile

Indi

cato

r Va

lue

in

Eac

h C

ateg

ory f

or

Dril

led

Shaf

t

Land

578.

9131

48.4

162

0.26

3373

.30

31.4

317

0.91

15.5

3 84

.47

15.5

3 84

.47

15.5

3 84

.47

0.30

4.66

25.3

4

Cem

ent

3968

.97

2158

5.41

926.

7650

40.2

510

77.8

758

62.0

315

.53

84.4

7 15

.53

84.4

7 15

.53

84.4

7 0.

304.

6625

.34

Stee

l76

35.0

310

092.

7667

29.1

852

70.8

375

79.5

759

36.9

243

.07

56.9

3 56

.08

43.9

2 56

.08

43.9

2 0.

2011

.22

8.78

Die

sel

2913

.71

1456

8.56

2562

.22

1746

9.67

2531

.07

1725

7.33

16.6

7 83

.33

12.7

9 87

.21

12.7

9 87

.21

0.20

2.56

17.4

4

Tota

l15

096.

6249

395.

1510

838.

4231

154.

0411

219.

9429

227.

1920

.53

59.4

7 Fi

nal I

ndic

ator

Val

ue

Cal

cula

tion

for R

esou

rce

Use

Indi

cato

r for

Pile

s in

San

d fo

r Wor

king

Loa

d 40

0 kN

Res

ourc

e C

onsu

mpt

ion

Per

cent

Res

ourc

e C

onsu

mpt

ion

Cal

cula

tion

of R

esou

rce

Use

In

dica

tor

Res

ourc

e C

ateg

ory

Em

ergy

(×1

011)

(sej

)C

umul

ativ

e Ex

ergy

(MJ)

Emer

gy C

umul

ativ

e Ex

ergy

Embo

died

Ene

rgy (

MJ)

Embo

died

Ene

rgy

Tabl

e 1

0 C

alcu

latio

n of

Env

ironm

enta

l Im

pact

Indi

cato

r for

Pile

s in

San

d fo

r Wor

king

Loa

d 4

00

kN

Perc

enta

ge

Impa

ct fr

om

Dril

led

Shaf

t

Perc

enta

ge

Impa

ct fr

om

Driv

en P

ileW

eigh

t

Indi

cato

r Va

lue

in

Each

C

ateg

ory f

or

Dril

led

Shaf

t

Indi

cato

r Va

lue

in

Each

C

ateg

ory f

or

Driv

en P

ile

Cem

ent

Con

cret

eSt

eel

Die

sel

Tota

lC

emen

tC

oncr

ete

Stee

lD

iese

lTo

tal

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

Hum

an T

oxic

itygm

,1,4

DB

Eq

0.00

0.00

2372

.95

0.00

2372

.95

0.00

0.00

2575

.99

0.00

2575

.99

47.9

552

.05

0.40

19.1

820

.82

Acid

ifica

tion

gm E

q SO

232

60.0

2.57

684.

8012

081.

7216

029.

0559

9.42

0.47

629.

6217

71.9

930

01.5

084

.23

15.7

70.

3025

.27

4.73

Glo

bal W

arm

ing

gm E

q C

O2

1016

574.

3610

95.7

2838

6912

3770

1425

309

1869

2020

1.47

3077

80.3

217

993.

8851

2896

.173

.54

26.4

60.

3022

.06

7.94

66.5

133

.49

Fina

l Ind

icat

or V

alue

Cal

cula

tion

of E

nviro

nmen

tal I

mpa

ct In

dica

tor f

or P

iles

in S

and

for W

orki

ng L

oad

400

kN

(14)

=(13

) ×

(12)

Dril

led

Shaf

t D

riven

Pile

Envir

onm

enta

l Im

pact

Cat

egor

yU

nit

(13)

(14)

= (1

3) ×

(1

1)

(11)

=[

(5)/(

5)+(

10)]

× 10

0

(12)

=[

(10)

/(5)+

(10)

] ×1

00

119

Indian Geotechnical Journal, 41(3), 2011

Note that the cost of installation of driven piles ismuch less than that of drilled shafts. However, the loudnoise and vibrations that ensues during the constructionof driven piles may not be welcomed in theneighborhood and may cause damage to the existingstructures around the construction site. In real lifeproblems, the financial aspects and social impactsincluding those due to noise and vibrations must also betaken into account while deciding on a particular type ofpile.

Conclusions

Geotechnical engineering is resource intensive.The resources used in geotechnical engineering areobtained from the biogeosphere and from industrialprocesses. The industrial processes generate toxicemissions to air and cause pollution to land and water.Although the direct environmental impact ofgeotechnical engineering is limited to resource use andto the pollution and emissions caused at theconstruction site, the indirect impact of geotechnicalconstruction can affect a wide range of environmentalprocesses including human and ecosystem health.Thus, it is important to perform sustainabilityassessment of geotechnical projects in order to ensurethat the resources used and the pollutions caused arekept at a minimum.

A comparative LCA was carried out for drilledshafts and driven concrete piles in sandy and clayeyprofiles designed to carry three different loads. The LCAconsists of LCI and EIA. Based on the LCA, twoindicators, the resource use indicator and theenvironmental impact indicator, were calculated for thetwo types of piles. A lower value of the indicatorssuggests a more sustainable option. The calculatedindicators show that, for the piles in sand considered inthis study, driven piles use resources more efficientlythan drilled shafts and, for the piles in clay, theresource-use efficiency of both types of piles are moreor less the same. The analysis further indicates that,from the environmental impact point of view, the drivenpiles perform better in the sandy profile but, for clayeyprofile, the performance depends on the design load.Thus, the framework developed in this study provides adecision aiding tool in choosing one pile type over theother considering environmental sustainability,particularly when technical feasibility is not a limitingfactor for choosing an alternative.

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