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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
300
400
500
600
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
100
200
300
400
500
600
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
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
1200
1400
1600
1800
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
0
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
