(a) Dragline. Singapore and Malaysia generally use dragline. The operations consist of bringing to site a track-mounted crane. With the crane are many 0.1 × 0.3 × 4.0 to 5.0 m planks which are self-laid by the crane for its own base. As work progresses, the planks are self-shifted by the crane so that it is resting at all times on a series of platform planks preventing it from bogging down in mud.
This particular equipment is particularly good for dike construction, canal digging and deepening (Fig. 6.9). Hence, it is suited for excavating shrimp trapping ponds in order to have deeper water. However, it is not practical for large-scale within-compartment-levelling because of its being too slow and unwieldy. Its use is also limited where mass hauling of earth in some areas for dike building is involved. It is by design, an equipment for in-place working. There is now in the market a crane mounted on LGP (low ground pressure) tracks. This makes the crane more maneuverable in swampy areas and cuts its non-productive plank-transferring time by half. This crane can be equipped with clam shell buckets.
Fig. 6.9 Range diagram and limits of work of drag line as defined for the construction of the perimeter dike
(After Hechanava and Tiensongrusmee, 1980)
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| The cost of using draglines vary with the kind of soil material and its size. The effective working range depends on the length of boom |
(b) Dozer-crawlers (Fig. 6.10). This particular equipment is good for levelling provided the load-bearing capacity of the soil can support the equipment weight. Recent designs of these equipment are provided with mechanisms which improves speed and maneuverability, thus cutting down construction time. The effective working range of most dozers in dry soil conditions vary from 20 to 40 m.
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Fig. 6.10 Some heavy equipment for fish farm construction (After Tarnchalanukit, 1982) |
Most crawler manufacturers have now incorporated LGP tracks to their line of crawlers to enable it to work on wet soils. On LGP, the ground pressure usually is around 0.28 kg/cm2. The LGP crawlers come in a variety of sizes, ranging from 20 to 200 BHp. One has therefore a good choice to suit the area to be developed or the transport situation to the work area. In some instances, small LGP dozers are chosen over a large one for convenience in transporting the equipment to the job site by raft or passing on bridges which have limited load capacity.
(c) Hydraulic excavators, backhoe, shovels, cranes, pay loaders (Fig. 6.10). These are equipment that can also be used to advantage in fishpond projects. One advantage the hydraulic equipment have over cable cranes are their fast action and flexibility to adapt to a variety of situations. These can also be adapted with clam shells and grapplers and can be used for uprooting small tree stumps.
(d) Scrapers, dump trucks, wheel-type loaders (Fig. 6.10). These may also be used effectively where soil conditions permit.
(e) Suggestions on mechanization. Much waste has been observed in the use of mechanized equipment. In order to be able to adopt this method with success, one must know the following: (i) capacity; (ii) limitations; (iii) limit of maximum operating range; (iv) ground pressure; (v) working conditions; (vi) amount of work to be done; (vii) type of work required; and (viii) cost per unit of work accomplished.
There are equipment now especially fabricated for reclamation and swamp work. These types can be used in mangroves effectively. However, one should be conversant with the different types of equipment and be able to judge critically the type of equipment needed after seeing the project area. There are some large equipment which can be taken apart into several components and reassembled at job-site. Some cranes and hydraulic lifters are also designed to be barge-mounted with their tracks on while on the shore.
In addition, the economical or effective range of the equipment should also be known. At what distance should one consider a loader and a dump truck combination over a crawler? It would be uneconomical beyond about 35 m due to its track wear and long cycle time. Beyond 35 m on volume of soil movement, one might want to employ combination pay loaders with several dump trucks. The economics of this operation should be worked out. Scrapers (self-loading and crawler-assisted) are ideal for large projects. Dredges can be used effectively too. Under special situations, jetting pumps can effectively facilitate uprooting of stumps. All of the above require a thorough knowledge of the project site peculiarities as well as the different equipment available, their specifications, capacities and limitations. An expert's advise in this field is usually necessary.
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