Chapter 5
Reclamation Equipment

5.1 DREDGERS
5.2 TRANSPORTATION BARGES
5.3 DREDGING ACCESSORIES

Reclamation equipment generally include those used for dredging, excavation and transportation. For the dry method of reclamation, excavators, backhoes and trucks are useful equipment. There are several sizes and capacities of excavators and backhoes. Generally, land excavation is slow, and a bite of an excavator can extract a maximum of 0.5 – 1m³ of earth depending upon the size of the excavator. Trucks can carry 5 – 8 m³ of fill material per trip depending upon the size of the trucks. Figure 5.1 shows the various types of excavator and backhoe, and Figure 5.2 shows trucks which are used for transportation and dumping of fill material.

An alternative transportation system is the conveyor belt. The system includes a bucket chain excavator, and a transportation conveyor, as shown in Figure 3.5.

Most reclamations are carried out using the wet method by means of hydraulic filling. Dredgers are used as the excavation equipment, and marine barges are used for transporting the material. Reclamation is carried out either by direct dumping or by hydraulic filling.

5.1 DREDGERS

There are several types of dredgers used in dredging and reclamation. Dredgers are selected depending upon the types of material to be dredged, the depth of the seabed, the intended rate of production, and the distance of the borrow source and reclamation area.

5.1.1 Backhoe dredger

A backhoe dredger is a stationary type of dredger and is usually suitable for shallow depths. Production is generally slow. A backhoe excavator is mounted on a barge and it can sail from one place to another with its own propeller. Anchoring at a location is usually done with the help of spuds.

There are three to four spuds. With a backhoe, it is possible to dredge depths ranging between 4.5 and 25 m, but 10 – 15 m depth is usual. Backhoe sizes ranging between 3 – 16 m³ and 5 – 8 m³ are commonly found in the market. Sometimes, a backhoe dredger can not only self-propel but also have a built-in material-carrying hopper of about 200 to 500 m³ capacity. Figure 5.3 shows a typical backhoe dredger and Figure 5.4 shows backhoe dredging in progress. Backhoe dredgers are suitable for both clay and sand dredging. However, the production rate is limited.

5.1.2 Grab and clamp shell dredger

A grab and clamp shell dredger is more powerful, with grab or clamp shells attached to the cable and dropped from a crane boom. The anchoring system uses either spuds or a cable conventional anchor. The clamp shell dredger can dredge to very deep depths but production is slow. Dredging depths ranging 10 to 61 meters are possible with this type of dredger. The grab sizes range between 3 and 38 m³ but sizes of 5 – 8 m³ are commonly found in the market. A grab dredger is also usually mounted on a barge which is sometimes built with a hopper with a capacity varying between 450 and 1900 m³. Figure 5.5 shows a typical grab dredger, and Figure 5.6 shows grab dredging in progress. Grab dredging is suitable both for clay and sand. Clamp shell dredging can be carried out in soft rock formations.

5.1.3 Dipper

A dipper dredger is powerful but it can only dredge to a limited depth. The production rate is also slow. The dredgeable depth ranges between 15 and 23.8 m, and bucket sizes range between 3 and 18 m³, but 3 – 4 m³ buckets are common.

The anchoring system used to be with spuds although some use a conventional cable anchor. Some dippers also come with a built-in material handling hopper, with the size varying between 200 and 500 m³. Figure 5.7a shows a typical design of a dipper dredger, and Figure 5.7b shows dipper dredging in progress. Dippers are applicable both in sand and clay, and a powerful dipper can dredge soft rock.

5.1.4 Barge unloading dredger

A barge unloading dredger is usually stationary. Stationary mooring is usually achieved with the help of spuds and sometimes with conventional anchors. Barges carrying dredged or fill material berth at the side of the dredger and unloading is done with the help of a suction pipe. The size of the suction pipes ranges between 500 and 1000 mm, and dredgers with 700 – 750 mm suction pipes are commonly found in the market. On the other hand, fill material can also be discharged at the reclamation area. The discharge pipe is usually smaller than or the same size as the suction pipe. Dredgers with discharge pipes ranging between 450 and 900 mm in size can be found in the market but 600 – 650 mm discharge pipes are the most common. The rate of production is dependent upon the size of the discharge pipe and the capacity of the pump used. The capacity of the pumps usually ranges between a few hundreds to 3000 kW for suction pumps and a few hundred kW for jet discharge pumps. Barge unloading dredgers are more suitable for granular soil. Figure 5.8 shows a typical design of a barge unloading dredger, and Figure 5.9 shows barge unloading in progress.

5.1.5 Bucket ladder dredger

Bucket ladder dredgers are used for medium depth dredging. The dredgeable depth ranges between 10 and 36 meters but dredgeable depths of 15 – 20 meters are common. Some dredgers have a dredgeable depth of about 15 – 20 meters but extendable to 30 – 36 meters. There are several buckets arranged as a ladder. The buckets are small, ranging between 0.5 to 1 m³ but the most common sizes are 0.5 to 0.7 m³ buckets.

The speed of dredging ranges between 10.5 and 49 buckets per minute but a speed of about 20 buckets per minute is common. Therefore, for 24 -hour dredging operation, 9,500 m³ per day up to a maximum of 46,000 m³ per day is possible with a bucket ladder dredger. The mooring of such dredgers is usually achieved with a wire pole or a conventional anchor with a cable. Figure 5.10 shows a typical design of a bucket ladder dredger, and Figure 5.11 shows bucket dredging in progress. Bucket ladder dredgers are useful for dredging soft to hard cohesive clay.

5.1.6 Cutter suction dredger

There are several types of cutter suction dredgers in the world. Cutter suction dredgers are stationary. Some large cutter suction dredgers are self-propelled to move from one location to another. Positioning is achieved by using either spuds or anchors. Some dredgers have both spuds and anchors. Some have only one spud while others have two spuds. Some may be walking spuds whereas others may be fixed. Positioning of the dredger is usually done with the assistance of a tugboat. Cutter suction dredgers are either stationed at a borrow source or a rehandling pit for dredged material. These types of dredgers are suitable for dredging granular material. The dredgeable depths of cutter suction dredgers range between 8 and 38 m, but dredgers with 15 – 25 m dredgeable depth are commonly found. Some dredgers have a primary dredgeable depth of 15 – 20 m but can be extended to 30 – 35 m. The diameter of the suction pipes ranges between 300 and 1,070 mm. Dredgers with 600 – 800 mm diameter suction pipes are most commonly found. The discharge pipes are usually slightly smaller than the suction pipes. There are some dredgers where the discharge pipes are slightly bigger than the suction pipes. The diameters of the discharge pipes range between 400 and 910 mm. Dredgers with 600 – 800 mm diameter discharge pipes are most common.

The capacity of the cutter ranges between 52 and 5000 kW. The dredger pump capacity is generally greater than the cutter capacity and ranges

between 250 and 7450 kW. Some pumps can operate under water. Some dredgers have two dredge pumps whereas others have a booster pump of up to 2980 kW capacity. Discharge pumps usually have much greater capacity than the dredged pump, ranging between 644 and 7400 kW. Some low capacity dredgers can pump only 2 km whereas others can pump up to 8 km distances. The discharge capacities of dredgers vary, depending upon the dredged pumps, suction pipes, discharge pipes and discharge pump. Dredgers with discharge capacities of as low as 8400 m³/day to as high as 216,000 m³/day can be found in the market. Figure 5.12 shows a typical design of a cutter suction dredger, and Figure 5.13 shows cutter suction

dredging in progress. Cutter suction dredgers are suitable for dredging granular material to cemented sand rock.

5.1.7 Suction dredger

Most suction dredgers are stationary. Some have material-carrying hoppers with capacities of between 160 and 1800 m³. Some cutter suction dredgers have barge loading facilities and discharge through pipelines. These types of dredgers with hoppers are able to sail, with speeds of 10 – 12 knots. The dredgeable depths of these dredgers range between 20 and 58 m, but some have a primary dredging depth of about 20 meters with a possible extension to over 50 meters depth. Positioning is usually done with anchor and wires.

The diameters of the suction pipes range between 360 and 1050 mm. The discharge pipes of these dredgers are usually smaller than the suction pipes with diameters ranging between 400 and 900 mm. Inboard pumps or underwater pumps are used for sucking seabed materials, and inboard pumps with capacities of 456 – 4485 kW are installed in this type of dredger. Pump capacities range between 437 and 1863 kW. Some dredgers have only a single pump but some have double pumps. Some dredgers have only one inboard pump. The capacities of the jet pumps of such dredgers range between 185 and 1169 kW. Some dredgers are equipped with discharge pumps of capacities up to 1863 kW.Figure5.14 shows a typical design of a suction dredger and Figure 5.15 shows a suction dredger stationed at a rehandling pit, ready for dredging. Suction dredgers are suitable for dredging loose granular material.

5.1.8 Trailer suction hopper dredger

A trailer suction hopper dredger can dredge loose to dense granular sand. Dredgeable depths vary between 12 and 131 m and some have a primary dredgeable depth but can be extended to 40 to 50 m depths. They have built-in hoppers to carry the material. Hopper capacities range from 450 m up to 33,000 m³. After dredging to the full capacity of the hopper, it can sail to the reclamation area. A sailing speed of about 12 knots is common but dredgers with sailing speeds of 7.5 – 16.5 knots can be found in the market.

To use this type of dredger either in the dredging area or a reclamation area, sufficient draft is required. The dredgers with bigger capacity hoppers usually need a deep draft. Draft depths can range between 3.1 and 11.46 m, depending upon the size of the hoppers. Dredged pumps of capacities ranging between 191 to 7450 kW are used. Some have two dredged pumps. Inboard pumps of capacities ranging from as small as 20 kW to as big as 8800 kW can be found in such dredgers. Some dredgers have two inboard pumps. Suction pipes are usually 700 – 800 mm in diameter and discharge pipes are slightly smaller or about the same size as suction pipes. Suction pipes of diameters ranging between 450 and 1200 mm can be found in various dredgers. The discharge pipes have diameters varying between 450 and 1100 mm. The production rate of such dredgers is highly dependent upon the size of the hoppers, and the distance between the borrow and the reclamation areas. Transportation of up to 180,000 m³ per day has been achieved in the Singapore reclamation projects. Figure 5.16 shows a trailer suction hopper dredger and Figure 5.17 shows the discharging of sand in progress from a trailer suction hopper dredger.

5.2 TRANSPORTATION BARGES

When stationary dredgers are used, transportation barges are required to transport fill material from the borrow source to the rehandling pit or directly to the reclamation area. When reclamation is carried out on a deep seabed, direct dumping of fill material is possible. Unloading is usually done by bottom-opening or split opening.

5.2.1 Conventional barges

Conventional material transportation barges do not have a mechanism for bottom-opening. Therefore, unloading has to be done with the help of barge unloading dredgers. If these dredgers are used, fill material can be directly dumped in the reclamation area. Barges with 1000 – 2000 m³ capacities are commonly used. Most barges need to be towed or pushed by a tugboat. Only some barges have a self-propeller. Figure 5.18 shows a barge transporting sand with the help of a push boat.

5.2.2 Bottom-opening barge

When a cutter suction dredger is used as a stationary dredger at the borrow source, fill material is loaded onto a bottom-opening barge. Material is unloaded through bottom doors at the reclamation area. Barges of capacities varying between 1000 and 4100 m³ are commonly used in reclamation projects. Some barges need to be towed or pushed by a tugboat, whereas some barges have self-propellers. Figure 5.19 shows bottom-opening barges without self-propeller and with self-propeller. Split hopper barges are also available (Figure 5.20).

5.3 DREDGING ACCESSORIES

There are four major accessories for dredgers used for reclamation: (i) discharge pipes, (ii) floaters, (iii) dredge heads, and (iv) discharge pumps.

5.3.1 Discharge pipes

There are various sizes of discharge pipes ranging from 400 to 1200 mm. Depending upon the size and capacity of the dredger used, the discharge pipes vary. Figure 5.21 shows various types and sizes of discharge pipes.

5.3.2 Floaters

When discharge pipes need to be connected above water, floaters are required. Only with floaters can the discharging pipes be floated. Figure 5.22 shows discharge pipes running above water with the help of various types of floaters.

5.3.3 Dredge head

Depending upon the type of material to be dredged, the type of dredge head is selected. Figure 5.23 shows various types of dredge heads used for sand dredging.

5.3.4 Discharge pump

Discharge pumps are usually mounted on a trailer suction hopper dredger and used for discharging sand from the dredgers. Figure 5.24 shows a photograph of a discharge pump.