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close this bookInland Aquaculture Engineering (1984)
close this folderDESIGN AND CONSTRUCTION OF FRESHWATER FISH FARMS
close this folderChapter 10. The Organization and Supervision of Fish Farm Construction
close this folder2. PREPARATIONS FOR FISH FARM CONSTRUCTION
close this folder2.1 Preparatory Process
View the document(introduction...)
View the document2.1.1 Methods used in organization of construction work
View the document2.1.2 Detailed plans required of the contractor
View the document2.1.3 Choosing and operating the equipment

2.1.1 Methods used in organization of construction work

Several methods can be used in the organization of the construction work. Continuous organization of production can be applied when the existing equipment and labourers are to be utilized constantly and continuously. Scheduling of succession can be used when several similar or identical projects are to be executed in the same region, to ensure continuous and equal progress for the different working groups and to reduce the total period of construction (Atkinson, 1971).

2.1.1.1 Network scheduling

To meet the basic aim of the organization of construction work, i.e., to ensure execution of the project, as far as possible, within the minimum time, the use of network scheduling may be the most suitable solution. A simple network may be sufficient, or in larger projects a complex network requiring the use of a computer might be needed. There are several different kinds of network in use, such as the Critical Path Method (CPM), Programme Evaluation and Review Technique (PERT), and Least Cost Estimating and Scheduling (LESS). We will limit our discussion here to the Critical Path Method which is the most commonly used in construction work. In large-scale projects, it has been found that approximately 20 percent of construction time can be saved by using this method (O’Brien, 1967).

In applying the CPM method, each of the activities that are needed to construct the project are listed, and a diagram is prepared showing how these activities are interrelated. Each of the activities is represented in the diagram by arrows, and proceed in the direction of the arrow until they culminate in an event, represented by a circle.

For example, in Figure 1, the arrow from 1 to 8 represents the activity of ‘Purchase and Delivery of Pumps’. The arrow from 3 to 8 represents the activity of ‘Construction of Pump House’. Event 8 is the completion of the pump house and delivery of the pumps. The critical path is through events 1-3-4-5-6-8-9-10 and requires 41 weeks for project completion.

The basic procedures in preparing a CPM diagram for a project consist of the following:

Planning: the project is broken down into activities and each activity is listed separately.

Analyzing and scheduling: this involves establishment of the relationship between activities in order to determine their interdependency. In this way it can be determined which works can be independently carried out and which depend on some other activity being completed first, thereby allowing for scheduling the flow path of activities. Time duration for each activity is arrived at with reference to general availability of labourers, materials, equipment, etc. The total project time is the summation of the duration times of all activities to be undertaken from the initial start of work to the finishing point through the longest time-consuming route. The longest duration is defined as the critical path, and the activities on this path are called critical activities. If a project must be completed within the time scheduled by the critical path, there must not be any delay of the critical activities.

Controlling: this consists of assessing the progress of work, including comparing the actual performance with the planned performance of each activity. Precise evaluation of actual performance time against that scheduled can provide useful data which may be adopted for another project. The CPM must be revised pach time an assessment is made.

The advantages of the CPM system can be summarised as follows:

(i) It is applicable to a wide range of projects.

(ii) Various alternative procedures can be considered when time and resource schedules are laid out. In the operational phase it can be used as a control device to measure actual versus planned progress.

(iii) The Engineer or the Contractor may quickly realize from the CPM diagram how a portion of the project is affected by other parts of the project work.

(iv) Action can be focused on exceptional problems contributing to more effective control.

(v) When combined with schedules of equipment, materials and manpower, total costs by established completion dates can be reasonably estimated (see 2.1.2).


Figure I. Simple CPM network for construction of a fish farm

Event No.

Description of Activity

Activity Time (weeks)

1-8

Purchase and delivery of pumps

16

1-3

Site preparation

4

3-8

Construction of pump house

8

3-4

Construction of drains

12

3-6

Diking

20

4-5

Construction of outlets

8

5-6

Bed and wave protection

4

6-7

Construction of inlets

3

6-8

Construction of internal roads

7

6-9

Construction of feeder canals

5

7-9

Turfing of dikes

6

8-9

Installation of pumps

3

9-10

Final checking and testing

3