Technical Inputs to Dredging Estimates

Robert RamsdellManager of Production Engineering

Great Lakes Dredge & Dock

Production Engineering

• Estimate the productivity of dredging equipment

• Work to improve productivity on ongoing projects

• Evaluate the design of new and upgraded equipment

Cost EstimatorHow much

money?

Production Estimator

How much time?

Project Estimate

TakeoffHow much work?

Cost Estimator

Answers the Question:How much will the project cost?

Cost Estimator

• Mobilization, subcontract & supply costs

• Daily cost for dredging plant

• Lays out estimate

Dredging Area Plan

Rock Contours

Takeoff

Answers the Question:How much work is there to do?

Takeoff – Dredge/Borrow Area

• Dredge & fill quantities (CY)• Material quantities/breakout (CY)• Area to be dredged or filled (SF)• Pipeline/Sail/Haul Distances (LF/NM)

Takeoff: Project Layout

Maps

Cross-Sections & Profiles

Production Estimator

Answers the Question:How long will the project take?

Production Estimator

• Adequacy of the information

• Material Types• Strength• Size

Evaluate Geotechnical Information:

Evaluating Materials

•Are there enough borings?

•Are there enough useful tests?

Production Estimator

Productivity of equipment– CSD vs Hopper vs

Mechanical– Digging versus pumping for

each section of the project– References to similar past

projects

Time = Qty/Production

Crucial Variables for Production

• Material Type– Strength– Grain Size– Extents/Distribution

• Face/Thickness• Pipeline Length

Material Classification

Material Strength•Standard Penetration Test

•Compressive, tensile or shear strength

Indicative or non-standard tests are no substitute for proper tests!

Grain Size Distribution

Important in determining how well the material can be pumped.

Material TypeThe Perils of Poor Information

Estimate: 1438 m3/WH

Estimate: 5 Teeth/Day

Material TypeThe Perils of Poor Information

Estimate: 1440 m3/WHActual: 605 m3/WH

Estimate: 5 Teeth/DayActual: 104 Teeth/Day

SPT vs. CORING

Via boring & SPTVia coring

Bank Height – FaceThe thickness of material to be

dredged.

Layout of Face

Similar cross-sectional area, but layout requires two different digging methods.

Production vs Face

0

100

200

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700

800

900

1000

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Face (Ft)

Prod

uctio

n C

Y/W

H)

Estimate assumes: 24 CY Payload, 45 sec Cycle

CSD Theoretical Production Curve

0200400600800

1,0001,2001,4001,6001,8002,000

0.00 2.00 4.00 6.00 8.00 10.00 12.00

Face (Ft)

Prio

duct

ion

(CY

/WH

)

Backhoe Dredge Production

0

2000

4000

6000

8000

0 1 2 3 4

Face (m)

Prod

uctio

n (C

M/W

H)

Bucket DredgeProduction Curve

0

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400

500

600

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800

900

1000

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Face (Ft)

Prod

uctio

n C

Y/W

H)

Estimate assumes: 24 CY Payload, 45 sec Cycle

Backhoe DredgeProduction Curve

Backhoe Dredge Production

0

2000

4000

6000

8000

0 1 2 3 4

Face (m)

Prod

uctio

n (C

M/W

H)

Cutter Suction DredgeDigging Curve

CSD Theoretical Production Curve

0200400600800

1,0001,2001,4001,6001,8002,000

0.00 2.00 4.00 6.00 8.00 10.00 12.00

Face (Ft)

Prio

duct

ion

(CY

/WH

)

Swing Li

mit

Dig or Pump Limit

Hopper Dredge in Low Face“Hang Time”

Pumping Capacity

1000

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1400

1600

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2000

2200

2400

2600

2800

10000 15000 20000 25000 30000 35000

Line Length (Ft)

Prod

cutio

n (C

Y/W

H)

Pumping Production

PRODpump= f (L/Dpipeline, Ppumps, Material )

Hopper Dredge Pump Capacity

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0 5,000 10,000 15,000 20,000 25,000

Pipeline Length (m)

Pum

pout

Rat

e (C

Y/m

in)

Booster Added

Dredge Alone

Other Important Variables

• Layout– Narrow or Odd Shaped Cuts– Slope Cuts

• Tow or Sail Distance• Water Depth

Layout of Face

Similar cross-sectional area, but layout requires two different digging methods.

Dredging Area Plan

Tow and Sail Distance

• For Clamshell, a matter of adding barges and tugs

• For hopper, another element of the overall cycle

• In both cases, consider the route when determining distance

Water Depth

• Can the dredge physically reach the material in deep water?

• Can the dredge float and dig in shallow water?

• For clam, cycle is directly dependent on depth.

• For backhoe, bucket size is dependent on depth.

Estimating Dredge Productivity

• By analysis of the capabilities of the dredge as compared to the conditions of the project.

• By reference to similar projects in the past

• By combining the two – Using analysis to ‘extend’ references

Clamshell Fill & Cycle Analysis

CSD Production Limits• Pumping capacity• Dig limit – ability to excavate the material• Swing limit – How fast can the dredge

swing?

Production Engineering Tools

Pump / systemanalysis

CSD Simulators

Hopper Load & Cycle Analysis

ReferencesFlorida Beach 1995

Sub Job Booster Face Line Length Qty/Day1 No 11.6 11000 376002 Yes 11 18900 333003 No 11.6 9500 287004 Yes 17.3 24900 29000

Total 12.4 17900 33300

Reference ComparisonFlorida Beach 2005

Sub Job Booster Face Line Length Qty/Day1 9.6 142002 8.6 18800 T3 10.8 23300 B4 7.0 27800 A5 6.8 30900

Total 8.4 22800

References – Comparing Projects

1995• 12.4’ Face• 17900’ Pipe• Dredge Alaska

2005• 8.4’ Face• 22800’ Pipe• Dredge Texas

1995 Project – by Face

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10000

20000

30000

40000

50000

60000

70000

0.0 5.0 10.0 15.0 20.0 25.0

Face (Ft)

Prod

uctio

n (C

YDay

)

1995 Project – by Line Length

0

10000

20000

30000

40000

50000

60000

70000

0 5000 10000 15000 20000 25000 30000

Line Length (Ft)

Prod

uctio

n (C

Y/D

ay)

Work with Booster

1995 Project – by Line Length

0

10000

20000

30000

40000

50000

60000

70000

0 5000 10000 15000 20000 25000 30000

Line Length (Ft)

Pro

du

ctio

n (C

Y/D

ay)

Work with Booster

2005 Project - Results

0

10000

20000

30000

40000

50000

60000

0 5000 10000 15000 20000 25000 30000

Line Length (Ft)

Prod

uctio

n (C

Y/D

ay)

1995 Project

2005 Project

Robert RamsdellManager of Production

EngineeringGreat Lakes Dredge & Dock

RCRamsdell@gldd.com