Backhoe Dredger is the Cousin of the Hydraulic Excavator, that often seen in land based construction and mining works. It is basically a Large Hydraulic Excavator mounted over a pontoon, that is equipped with Spud Carriage System.

1. BACKHOE DREDGER
By : K DIBYAJYOTI MOHANTA and SIDHARTH DAS
M Tech Dredging & Harbour Engineering
Indian Maritime University Visakhapatnam Campus

2. INTRODUCTION
•Backhoe Dredger is the Cousin
of the Hydraulic Excavator, that
often seen in land based
construction and mining works.
•It is basically a Large Hydraulic
Excavator mounted over a
pontoon, that is equipped with
Spud Carriage System
•The tracked under carriage of
hydraulic excavator is replaced
with the Pedestal, that is fixed at
the one end of the Spud Rigged
Pontoon.
•It developed with the
development of it’s sister.
A Hydraulic Excavator with it’s Operational Limits

3. Main Features of BHD

4. APPLICATIONS OF BACKHOE DREDGER
•Backhoes are used in soil types like firm clay, soft rock, blasted
rock and when large stones can be expected, like the removal
waterside protections.
•The length of the stick and the boom determines the dredging
depth.
•The lack of anchorage cables limits the hindrance for other ships
and there is also no delay for anchorage.
•Hydraulic backhoes are especially suitable for accurate dredge
work, due to the construction of the stick and the boom.

5. ADVANTAGES AND DISADVANTAGES OF BACKHOE DREDGER
• Able to Dredge wide range of materials that
contains boulders, debris, stiff clays, weak rocks.
• Can work in confined spaces.
• Accurate Control of Position and Spaces.
• Free from uses of Anchors and Associated
Wires.
• Min Disturbance and dilution of Dredged
Materials.
• Faster Production Cycle.
• Very Less Capital Cost.
• Less Crew Members ( Generally 3 to 4 to assist
the main Operator. )
• Low Rate of Production.
• Finished Dredge Level
is irregular and heavily
depends on Operator’s
skill.
BHD is most efficient when working from behind the face.

6. METHOD OF OPERATION
•Dredging Action of a BHD is very much similar to the action of human
hand and arm. There are three point of rotation each between the
Bucket and the Main Structure of the Machine, all in the same plane.
•Movement of each section is relative to one another and controlled
by high pressure hydraulic cylinder.
•During the Dredging Process, the bucket is lowered to the seabed,
and then rotated or ‘crowded’ to get the desired penetration and
loading.
•this is similar to the action of human hand when scooping a handful
of sand or soil.
•After Crowding of the Bucket, it’s raised and swing for the discharge.
Generally BHD is used to discharge/load a barge moored alongside
the pontoon.
•Once the Dredging completes at one position the Pontoon carrying
the Backhoe STEP forward for reposition itself to continue the
dredging activity.

7. “STEP” PROCEDURE OF BACKHOE DREDGER
Spud Carriage
•Lower pontoon to floating position.
•Put the bucket into the soil.
•Lift front spud.
•Move pontoon one step forward by
moving the carriage and the stick.
•Set front spud into the soil.
•Lift Moveable spud.
•Move carriage one step forwards.
•Set the movable spud into the soil.
•Lift pontoon in working Spud.
Walking Spud
•Lower pontoon to floating position.
•Put the bucket into the soil.
•Lift front spud.
•Move pontoon one step forward by
tilting the walking spud and pulling the
stick.
•Set front spud into the soil.
•Lift Walking spud.
•Tilt walking spud back into its middle
position.
•Lower Walking Spud.
•Lift Pontoon in Working Position.

8. PRODUCTION CYCLE OF BACKHOE DREDGER
Cycle Time of the Bucket of BHD is generally in between 20 to 40 Sec.
The STEP Procedure to reach the new Position is around 5 to 10 min.

9. PRODUCTION CYCLE OF BACKHOE DREDGER Cont.

10. FACTORS AFFECTING THE PRODUCTION RATE OF BHD
•Bucket Fill Factor
•Bucket Dipping
Velocity
•Bucket Crowding
Time
•Bucket Empty Time
•Bucket Lift Velocity
•Swing Angle
•Swing Velocity
•Freeboard Height
of the Barge
• Bucket Fill Factor (Fm) is around
0.2 to 0.85
• When its more than 1, it can be
conclude that Bucket is taking
more material than the capacity
by over crowding. This can
happen in less saturated soil
condition.
Bucket Fill Factor
• Mud : fm = 0.0474 Ln(C) + 0.7255
• Loose Sand : fm= 0.0614 Ln(C) +
0.6607
•Compact Sand : fm= 0.0933 Ln(C)
+ 0.5517
•Sand & Clay : = 0.1228Ln(C)
+0.4214
•Broken Rock : = 0.1443 Ln(C) +
0.1

11. PRODUCTION CALCULATION OF BACKHOE DREDGER (THEORY)

12. ENVIRONMENTAL EFFECTS OF BACKHOE DREDGER
• Safety of the crew : The possibility of crew members coming into contact with excavated material is high compared
with both the CSD and the TSHD.
● Accuracy: The accuracy of a traditional BHD is much lower than the others.Without sophisticated monitoring
equipment, an accurate dredging depth is impossible.
● Turbidity: Problem with the BHD is the position of its bucket while being raised; the operator must give full
attention to keeping the bucket in an optimal horizontal position in order to prevent excessive spillage. Closed
buckets that limit spill are sometimes available.
● Mixing of soil layers: Thin layers can be excavated selectively provided a good monitoring and control system is
available.
● Creation of loose spill layers: The cutting face of the BHD is the edge of each bucket. Almost all the soil loosened
by the bucket is carried away by the bucket leaving a clean surface. A minor risk of a spill layer remains if there is
excessive spillage while the material is being raised.
● Dilution: As the material is raised mechanically, there is no need for transport water. Only when the buckets are not
completely filled with soil, does the remaining space fill with water during the vertical movement of the bucket
chain. These small quantities of water fall with the soil into the transport barges.
● Output rate: The output rates of the BHD are limited to 1000 m3
/hr

13. Thank You
2017

14. References
•Dredging : A Handbook for Engineers by R N Bray, A D Bates, J M
Land
•Environmental Aspects of Dredging by R N Bray
•Handbook of dredging Engineering by John B Herbich
•Estimating Production and Cost for Clamshell Mechanical Dredger
by Robert Adair
•Course Material of TU Delft and IMU Visakhapatnamcampus
•Image Credits : Royal IHC, Jan De Nul, Vanoord, Maritime Journal,
Boskalis, www.dredgebrokers.com instrumentalism.wordpress.com