ENVIRONMENTAL BENEFITS OF TRENCHLESS CONSTRUCTION METHODS

Dr. Samuel T. AriaratnamArizona State University (USA)

Infrastructure Issues• Increasing demand for underground

infrastructure development– Population growth– Urban sprawl and urbanization– Deterioration and incapacity of existing infrastructure

• Challenges of infrastructure development– Project delivery time– Tighter budgets– Increasing complexity and difficulty of construction– Disturbance to urban life

• Environmental soundness/concerns– Global climate change– Ecosystem disruption– Human health impact– Pollution

•Increasing population•Urban sprawling•Urbanization•Deterioration•Incapacity

Increasing Demand

•Delivery time•Insufficient capital•Increasing complexity•Disturbances of urban life

Challenges of Development

•Climate change•Ecosystem disruption•Human health impact•Pollution

Environmental Concerns

•Anti-discriminationof development

•Preservation•Human rights (Humanity)•Traditions and history

Social Equity & Culture

•Community wellbeing•Create jobs•Efficiency ofinfrastructure service

Economic Benefits

•Water source•Food supply•Fossil energy source•Raw material depletion(Future availability)

Natural Resources

SustainableDevelopment

Traditional Project Performance Indicators

The Status of Environmental and Ecosystem Consideration

Enhancing Sustainability by Including Other Considerations

Infrastructure Project Assessment

Cost Quality Time

Resources Pollution Ecosystem

EconomicalEfficiency

EnvironmentalEfficiency

SocialEfficiency

United States EPA

• United States Environmental Protection Agency (US EPA)• Establishes national standards – assessment, research and

education• Provides information on pollutants, approved testing

methodologies & research outputs• US EPA document AP42

– Reports and background data to arrive at Emission Factors (EF)• Section 3.3 of AP42 – gasoline & diesel engines <600hp

www.epa.gov

Emission Factors• EF – a tool to estimate air pollutants released• Expressed as:

– Weight of pollutant / (unit weight or volume or distance or duration)• General equation for calculating emissions from EF is:

where, E – emissions (lbs, grams, etc)A – activity rateEF – uncontrolled emission factorER – overall emission reduction efficiency %

(product of removal efficiency and capture efficiency)

⎥⎦⎤

⎢⎣⎡ −∗∗=

1001 EREFAE

Pollutants• US EPA document AP42 classifies pollutants

• Criteria pollutants & their precursors• Hazardous air pollutants• Greenhouse gases

Criteria Pollutants Air Pollutants Greenhouse GasesSulfur dioxide (SOx) Title III of Clean Air

Act – identifies more than 100 pollutants

Carbon dioxide (CO2)Nitrogen oxides (NOx)Carbon Monoxide (CO) Methane (CH4)Lead (Pb)Ozone (O3) Nitrous oxide (N2O)Particulate matter <10μ (PM-10)

Pollutants (cont.)• Nitrogen Oxides (NOx)

– Thermal dissociation & reaction of Nitrogen (N2) & Oxygen (O2)– Fuel NOx stems from the reaction of fuel bound nitrogen

compounds with Oxygen (O2)

• Total Organic Compounds (TOC)– Hydrocarbons (HC) discharged from unburned and partially

burned fuel– Partially burned HC from

• poor air and fuel homogeneity• incorrect fuel/air ratios• excessively large fuel droplets• low cylinder temperature

Pollutants (cont.)• Carbon Monoxide (CO)

– Colorless, odorless, inert gas – Reaction of CO to carbon-di-oxide (CO2) incomplete due to

• Lack of combustion oxygen (O2)• Gas temperature is too low• Residence time in cylinder is too short

• Smoke & Particulate Matter (PM-10)– White smoke

• Liquid particles – cold start, idling, low load operation– Blue smoke

• Lubricating oil leaks past piston rings & gets partially burnt– Black smoke

• Clustered carbon particles (soot) in regions of oxygen deficiency

Pollutants (cont.)• Sulfur Oxides (SOx)

– Function of sulfur content in the fuel– Fuel oxidized to SO2– Forms sulfates by reaction with bases (metals)– Sulfates contribute to

• Particulate matter less than <10μ PM-10)• Visibility reduction

• Carbon Dioxide (CO2)– Slightly toxic, odorless, colorless, greenhouse gas– Combustion of fuel carbon– Heats up the earth’s atmosphere by absorbing IR radiations– Mixes with water & forms corrosive carbonic acid

Emission Factor Method• Most common method

– Fd -Factor method• To determine emission factors (EF) from stack (fuel) concentration• CO concentration can be correlated to heat input rate• Heat content is closely related to carbon content in the fuel• EF in units of pounds (lbs) per British thermal Unit (BTU) [or] pounds

(lbs) per weight or volume of fuel• Three methods under F-Factor

– Fd factor method {Dry F-Factor method}– Fw factor method {Wet F-Factor method}– Fc factor method {Carbon F-Factor method}

Fw Factor Method (I)• Same principle as Fd Factor method except that

– Effluent gas & oxygen conc. are determined on wet basis

• With the determination of Cw – wet basis measurement of pollutant conc.%O2w– percent oxygen content in effluent streamBwa– moisture content of air supplied for combustion

( ){ }⎥⎦⎤

⎢⎣

⎡−−

∗∗=wwa

wwOB

FCEF2%19.20

9.20Emission Rate

Quantity of wet effluent gas

Gross calorific value of fuel (GCV)Fw= , is a constant

Fc Factor Method (II)• For a given fuel category,

Dry - Cd Wet - Cw

1) Pollutant conc. 2) Percent CO2

Dry - %CO2d Wet – CO2w

Volume of carbon dioxide producedHeat content of the fuelFc=

, is a constant

• Dilution correction = Theoretical carbon dioxideMeasured carbon dioxide

• With the determination of

Emission Rate ⎥⎦⎤

⎢⎣⎡∗∗=

dcd

COFCEF

2%100

⎥⎦⎤

⎢⎣⎡∗∗=

wcw

COFC

2%100

Fd Factor Method (III)• For a given fuel category;

• Excess air correction factor:

Quantity of dry effluent gas

Gross calorific value of fuel (GCV)Fd= , is a constant

( )⎥⎦⎤

⎢⎣

⎡−

∗∗=d

ddO

FCEF2%9.20

9.20

If moisture content of flue gas (Bws) is known then,

Emission Rate

( ){ }⎥⎦⎤

⎢⎣

⎡−−

∗∗=dws

dwOB

FCEF2%19.20

9.20

Where,Cd– dry basis measurement of pollutant concentration%O2d– percent dry oxygen content in effluent stream

Emission Rate

Determination of F-Factors

where H,C,S,N,O,H2O are concentrations by weight expressed in percentageGCV – Gross calorific value in Btu/lb

• Calculation of Fw must include the free water in the ultimate analysis.

( )⎥⎦⎤

⎢⎣⎡ −+++

=GCV

ONSCHFd%46.0%14.0%57.0%53.1%57.5*106

( )⎥⎦⎤

⎢⎣⎡ +−+++

=GCV

OHONSCHFw26 21.0%46.0%14.0%57.0%53.1%57.5*10

( )⎥⎦⎤

⎢⎣⎡=

GCVCFc

%321.0*106

Equipment Emissions• All equipment operates to complete it’s particular task

and not for the entire duration of the project→ Time of operation for each equipment differs

• An installation project is a combination of many such activities→ Many equipment may be required

• Emission from each equipment differs due to – Fuel type– Engine power– Usage period– Load factor (power actually used divided by power available)

Example Utility Project(for demonstration)

30 m

1.5 m 300mm pipe

• Depth of 1.5 m • Length of 30 m• 300mm diameter pipe installation

Emission Calculations• Section 3.3 of AP42 – Emission factors (EF) for

equipment <600hp• Two kinds of EF for diesel engines

– Based on fuel intake• Quantity of fuel burnt for the activity is difficult to measure• The fuel consumed is proportional to the load on the engine

– Based on power output• Operator of the equipment is aware of the load on the engine• Avg. power of the engine for a particular activity can be determined

• Fuel Intake is proportional to the power output• EF based on power output, is used in the calculations

Example Project• Assumptions:

– Native soil excavation– Urban environment– No crossing of utilities underground– New pipe installation– Site restrictions to dump the spoils at site – Operating hp of the same equipment is same in each

construction methodOperating hp skill of the operator

– Calculation of the installation / operating times only

Open Cut Construction

30 m

1.5m

1.2m

300mm pipe

Required trench width – 1.2m

Installation duration – 20 hrs

CAT420E

89hpCAT924G

129hpPeterbilt-330

300hp

CAT CS323C

83hp

Open Cut Construction

30m

1.5m

1.2m

300mm pipe

Required trench width – 1.2m

Installation duration – 20 hrs

CAT420E

89hp

CAT924G

129hp

Peterbilt-330

300hpCAT CS323C

83hp

Open Cut Construction• Trench width is 1.2m• Production of CAT 420E backhoe is

– 10.4 cu.yd/hr – excavation– 10 cu.yd/hr - backfill

• CAT 924G loader bucket capacity is 2.2 cu.yd.– Loading time per bucket = 1 min & 2 min set-up time

• Peterbilt-330 Haul truck capacity 12 cu.yd– Time to unload = 5 min

• Compaction (CAT323C) in 4 layers @ 1hr/1 ft layer• Only operating time

Open Cut ConstructionEquipment Used – Usage (%) & Load Factor (%)

Installation Time 20 hrs

Equipment Operating time Usage/Total time Load Factor

Backhoe 16.0 hrs 80.0% 90%

Loader 3.3 hrs 16.3% 80%

Truck 10.4 hrs 51.9% 75%

Compactor 4.0 hrs 20.0% 90%

Open Cut ConstructionTotal estimated emissions for the equipment used in the example project, using emission factors

Pollutant

EmissionFactor

(Diesel)(lb/hp-hr)

BackhoeCAT-420E

LoaderCAT-924G

TruckPeterbilt-330

CompactorCAT-CS-323C Total

∑Usage *Total time(lb)

Power89hp(lb/hr)

Load90%

(lb/hr)

Usage80%

(lb/hr)

Power129hp(lb/hr)

Load80%

(lb/hr)

Usage16%

(lb/hr)

Power280hp(lb/hr)

Load75%

(lb/hr)

Usage52%

(lb/hr)

Power83hp(lb/hr)

Load90%

(lb/hr)

Usage20%

(lb/hr)

NOx 0.031 2.8 2.5 2.0 4.0 3.2 0.5 8.7 6.5 3.4 2.6 2.3 0.5 127.0

CO 6.68E-03 0.6 0.5 0.4 0.9 0.7 0.1 1.9 1.4 0.7 0.6 0.5 0.1 27.4

SOx 2.05E-03 0.2 0.2 0.1 0.3 0.2 0.0 0.6 0.4 0.2 0.2 0.2 0.0 8.4

PM-10 2.20E-03 0.2 0.2 0.1 0.3 0.2 0.0 0.6 0.5 0.2 0.2 0.2 0.0 9.0

CO2 1.15 102.4 92.1 73.7 148.4 118.7 19.4 322.0 241.5 125.4 95.5 85.9 17.2 4712.7

Aldehydes 4.63E-04 0.0 0.0 0.0 0.1 0.0 0.0 0.1 0.1 0.1 0.0 0.0 0.0 1.9

TOC

Exhaust 2.47E-03 0.2 0.2 0.2 0.3 0.3 0.0 0.7 0.5 0.3 0.2 0.2 0.0 10.1

Evaporative 0.00 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Crankcase 4.41E-05 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2

Refueling 0.00 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

HDD Construction

30m

1.5m

300mm pipe

No trench required

Installation duration – 1.5 hrs

Vermeer MX240 – 22 hp750 gal mixing tank

Vermeer D24x40 Series II - 125 hp24000 lb Pullback & Thrust

• No trench• Vermeer D24x40 Series II Drill rig

– 1.5 hrs for 30m pilot bore and pullback• Vermeer MX240 Mixing system

– To reduce soil friction– To suspend / transport cuttings– To stabilize the bore hole

• Mixing system operates for the entire duration of the drilling rig

• Only operating time

HDD Construction

HDD Construction

Installation Time 1.50 hrs

Equipment Operating Time Usage/Total Time

Load Factor

Drilling Rig 1.50 hrs 100.0% 50%

Mixing System 1.50 hrs 100.0% 70%

Equipment used – Usage (%) & Load Factor (%)

HDD ConstructionTotal estimated emissions for the equipment used in the example project, using emission factors

Pollutant

EmissionFactor

(Diesel)(lb/hp-hr)

HDD Drilling RigVermeer D24X40

Modular Mixing SystemVermeer MX240 Total

∑Usage *Total time(lb)

Power125hp(lb/hr)

Load50%

(lb/hr)

Usage100%(lb)

Power22hp(lb/hr)

Load70%

(lb/hr)

Usage100%(lb)

NOx 0.031 3.88 1.94 1.94 0.68 0.48 0.48 3.62

CO 6.68E-03 0.84 0.42 0.42 0.15 0.10 0.10 0.78

SOx 2.05E-03 0.26 0.13 0.13 0.05 0.03 0.03 0.24

PM-10 2.20E-03 0.28 0.14 0.14 0.05 0.03 0.03 0.26

CO2 1.15 143.75 71.88 71.88 25.30 17.71 17.71 134.38

Aldehydes 4.63E-04 0.06 0.03 0.03 0.01 0.01 0.01 0.05

TOC

Exhaust 2.47E-03 0.31 0.15 0.15 0.05 0.04 0.04 0.29

Evaporative 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Crankcase 4.41E-05 0.01 0.00 0.00 0.00 0.00 0.00 0.01

Refueling 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Comparison of EmissionsPollutants

EmissionFactor

(Diesel)

Open-CutEmissions

HDDEmissions

(lb/hp-hr) (lb) (lb)

NOx 0.031 127.00 3.62

CO 6.68E-03 27.40 0.78

Sox 2.05E-03 8.40 0.24

PM-10 2.20E-03 9.00 0.26

CO2 1.15 4712.70 134.38

Aldehydes 4.63E-04 1.90 0.05

TOC

Exhaust 2.47E-03 10.10 0.29

Evaporative 0.00 0.00 0.00

Crankcase 4.41E-05 0.20 0.01

Refueling 0.00 0.00 0.00

• Emissions from HDD is less by 97% compared to emissions from Open Cut

• Why?– Limited equipment on site– Faster installation– Limited movement of equipment

at site

Conclusions• Rapid expansion in underground infrastructure• Environmental sensitivity• Cost effective and sustainability• 97% fewer emissions when compared to open-

cut construction• Influences method selection during the design

stage of the project• Quantification of pollution from construction

activities necessary to identify offsets

Acknowledgments

QUESTIONS?