J. Kövári
Food and Agriculture of
the United Nations
Rome, Italy
1. INTRODUCTION
2. PREPARATIONS FOR FISH FARM CONSTRUCTION
3. EXECUTION OF CONSTRUCTION WORKS
4. SUPERVISION OF CONSTRUCTION BY THE ENGINEER
In order to complete a project in the proposed time at the estimated cost, the work has to be well organized. To ensure that all the work being performed is in accordance with the plans and specifications, adequate and continuous supervision must be provided by the Owner of the project during the construction period. The Engineer in charge, or the Resident Engineer, as the representative of the Owner, is responsible for the proper execution of the construction work, and he should control, supervise and help the Contractor to provide the best quality of work and complete the construction in accordance with the deadline given in the contract.
Any construction, including fish farm construction, is an economical and technical activity with a common aim, in that the proposed work, based on plans and specifications, should be carried out systematically, economically and continuously within the time frame indicated in the contract. Construction must be organized in the time and space needed for completion of the project. The time should be defined by the existing labour, materials and machinery, as well as prevailing local and environmental conditions. Generally, the shorter the time allotted for job completion, the cheaper the construction will be. The space required for construction should be organized by an areal arrangement of the job site, including the allocation of the different provisional buildings and workshops, etc., prior to the beginning of any construction work. All provisional facilities and plant should be utilized in the most economical manner. For the most economical implementation of a project, full utilization should be made of all materials, time and equipment.
The size of a project will define the scope and depth of the organization. For construction of a small-scale rural fish farm, fewer organizational activities are required than for a large-scale fish farm. However, utilizing the basic methods for construction generally used in a large-scale project, the time and expense of the construction may also be reduced in a small-scale project (Pillay, 1974).
2.1.1 Methods used in organization of construction work
2.1.2 Detailed plans required of the contractor
2.1.3 Choosing and operating the equipment
For the implementation of a project, small or large, good preparation compatible with the dimensions of the project, is needed. Adequate coordination between the Contractor and the Engineer in project preparation ensures that the work will be properly executed both in time and quality (Abrahamson, 1969).
The Contractor's duties are as follows:
- Review and study all the detailed plans thoroughly.- Report all questions and comments to the Engineer, particularly those which have a bearing on timely execution of the project.
- Request any additional drawings, calculations or other clarifications from the Engineer.
- Make application for any and all permits required for the construction work from the public authorities.
- Arrange for all necessary sub-contracts.
- Prepare a detailed schedule of requirements for all items of work, materials and equipment.
- Order all equipment required for the construction, e.g., pumps, generators, etc. The Engineer's duties are as follows:
- Provide to the Contractor all permits required before and during the construction work.
- Arrange, if necessary, for provision of adequate water source for construction work.
- Supply any additional drawings, calculations or modifications to the work plan which may be required by the Contractor.
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 |
The Contractor must complete the work and services of the project in accordance with the schedule of execution provided in the tender documents. To do this he must prepare detailed plans for scheduling of the project. These plans may be in either tabular or graphical form, although the graphical form is generally used for ease of visualization. The most commonly used graphical presentation for scheduling is the rectangular bar chart. The following examples are given in tabular form, from which a bar chart can be prepared.
2.1.2.1 Details of labour requirements
This is prepared by the Contractor, based on the type and amount of work, and the timing of each work item, based on past experience. A detailed schedule of labour requirements should include the following basic data in columns as shown:
|
Item No. |
Description |
Unit |
Amount |
Working hours |
Type of skilled worker |
Number of |
Timing days weeks | ||
|
|
|
|
|
unskilled |
skilled |
|
unskilled |
skilled |
|
2.1.2.2 Detailed schedule of materials
The construction cost can be reduced by a good organization of unloading, storage and handling of materials required. It is therefore important that a detailed schedule of materials needed be carefully prepared by the Contractor, taking into consideration local prevailing conditions. This must be based on calculation of the quantity of materials to be used for the different items of work. The transport and storage requirements of each material can be determined from this detailed schedule. The following tabular form is generally used for scheduling of materials.
|
Item No. |
Material |
Unit |
Amount |
Timing in weeks |
2.1.2.3 Detailed schedule of equipment
In order to utilize the equipment needed for the construction work most effectively, a detailed schedule should be prepared by the Contractor. This should also be based on the CPM schedule and is interrelated with the other detailed schedules. The following tabular form is usually used for scheduling equipment.
|
Item No. |
Equipment |
Unit |
Equipment |
Total amount |
Equipment No. |
Timing in weeks | |
|
|
|
|
Hourly capacity |
Job efficiency |
|
|
|
In many cases a fish farm will be constructed by equipment and manpower available to the Engineer, instead of letting a formal contract for the work. In such a case the Engineer would be in charge of the actual construction. For this reason, the following sections are included to give help in selecting and operating the equipment.
Because of the wide variety of soils encountered and earth-moving jobs to be done in connection with construction of a fish farm, a broad variety of equipment has been developed for this purpose. The most commonly used equipment in construction of fish farms is described below (Hammond, 1964).
1. Bulldozer
The bulldozer is the most useful and versatile of earthmoving equipment, because it can accomplish various tasks like clearing, grubbing, stripping, excavating and diking as well as levelling. Bulldozers are limited by length of push or haul. The economical length of haul is between 20 and 50 m. Hourly production in cubic metres can be calculated by using the following equation:
where
fixed time=0.15 min when only forward and reverse lever is required to shifthaul time = actual time needed to cover the designed haul
= 0.30 min when both forward and reverse lever and gear selector are required to shift
return time = actual time needed to return with empty blade
lf = load factor obtained from Tables 1 and 2 (Merritt, 1968)
h j = job efficiency obtained from Table 3.
Table 1 Load Factors for Earthmoving
|
Swell % |
Voids % |
Load factor |
Swell % |
Voids % |
Load factor |
|
5 |
4.8 |
0.952 |
55 |
35.5 |
0.645 |
|
10 |
9.1 |
0.909 |
60 |
37.5 |
0.625 |
|
15 |
13.0 |
0.870 |
65 |
39.5 |
0.606 |
|
20 |
16.7 |
0.833 |
70 |
41.2 |
0.588 |
|
25 |
20.0 |
0.800 |
75 |
42.9 |
0.571 |
|
30 |
23.1 |
0.769 |
80 |
44.4 |
0.556 |
|
35 |
25.9 |
0.741 |
85 |
45.9 |
0.541 |
|
40 |
28.6 |
0.714 |
90 |
47.4 |
0.526 |
|
45 |
31.0 |
0.690 |
95 |
48.7 |
0.513 |
|
50 |
33.3 |
0.667 |
100 |
50.0 |
0.500 |
Table 2 Percentage Swell and Load Factors of Materials
|
Material |
Swell % |
Load factor |
|
Clay |
40 |
0.72 |
|
Loam |
25 |
0.80 |
|
Gravel |
12 |
0.89 |
|
Sand |
12 |
0.89 |
2. Scraper
The scraper, whether tractor drawn or self-propelled, can be used for stripping, excavating and diking as well as compacting. The economical length of haul is between 100 and 1 000 m depending on the load capacity and type of scrapers. In heavy clay the scraper does not work efficiently, hence a tractor must be used to push along the cutting haul (Paxton, 1971).
Hourly production in cubic metres can be calculated using the following equation:
Vs = load capacity × number of trips per hour number of trips per hour
3. Dragline
The dragline is suited primarily for excavating below water level, and at a long distance below the dragline for diking, loading trucks and sloping. It is used where swampy conditions prevent other equipment from being used (Singh, 1980).
Production of a dragline depends on the following factors:
1. Mechanical condition of the machine
2. Size and type of bucket
3. Length of boom
4. Type of soil
5. Depth of cut
6. Angle of swing
7. Method of disposal, casting or loading trucks
8. Capacity of hauling units
9. Efficiency of the operator
10. Job and management conditions.
The productivity of draglines with different bucket capacities is given in Table 3.
4. Hydraulic power shovel
The basic excavator can be equipped with various multipurpose tools, including hoe or shovel for any earthmoving job. Shovels are used primarily to excavate and load earth into hauling units where soil to be dug is firm and hard. Hoes can also be used for excavating and boring trenches. They can dig to considerable depths below the base of the machine. Accurate drainage trenches can be excavated with a skilled operator. Production depends on the type of material to be excavated; overall job efficiency; angle of swing; height of bank or face the shovel digs against; ability of the operator; swell of material; slope of ground the machine is working on; and whether hauling units are of optimum size and adequate in number. Table 3 gives estimated average hourly production of hydraulic power shovels.
Table 3 Estimated Average Hourly Production of Earthmoving Equipment
5. Wheel loader
The wheel loader is a very useful piece of equipment and is versatile inasmuch as it can dig, strip, load, push, grade and transport material. Its versatility can be enhanced by various attachments and accessories.
6. Grader
The grader can be used for stripping topsoil, dike forming and levelling the top of dikes or the pond bottom. Hourly production of graders is given in Table 3.
Table 4 Compaction Equipment
|
Compactor type |
Soil best suited for |
Optimal water content % |
Maximum thickness cm |
Density gained % |
|
Sheepsfoot roller |
Silts, clay silts |
12-16 |
20-30 |
98 |
|
|
Clays, silty clay, clay gravels |
16-24 |
20-30 |
100 |
|
Steel wheel roller |
Sandy gravels, silty sand |
8-12 |
15-20 |
95 |
|
Rubber-tyred roller |
Sand, silty sand |
8-12 |
20-30 |
95 |
|
|
Sandy loams, silts |
12-16 |
20-40 |
98 |
|
|
Clays |
16-24 |
20-40 |
100 |
|
Vibrators |
Sandy gravels, sand, silty sand |
8-12 |
20-40 |
95 |
|
Frogs |
Sandy gravels, sand, silty sand, sandy loam, silts |
8-16 |
20-40 |
96 |
Type of material to be excavated may determine the basic equipment to be used. However the following factors should also be considered in selecting equipment:
(i) Volume of excavation to be moved
(ii) Volume to be moved per unit of time
(iii) Length of haul
(iv) Type of haul road
(v) Types and size of hauling equipment to be used
(vi) Load-supporting ability of original ground
(vii) Load-supporting ability of material to be excavated
(viii) Climatic conditions
7. Compactors
Sheepsfoot roller
Steel wheel roller
Rubber-tyred roller
Platform vibrator
Vibratory compactor
Frog
A wide variety of equipment is used for compaction of earthwork. Table 4 lists recommended compaction equipment used for different kinds of soil.
In order to utilize the equipment properly and economically the most suitable type and the most economical size must be selected. With a wide variety of equipment all working phases can be mechanized as far as possible. The capacity of various pieces of equipment should be compatible, since a piece having a lower capacity than the other ones, or using manual labourers, will result in output capacity of all the equipment being reduced. To select the best mix of equipment for the project the following guidelines are offered:
(i) Equipment used should have the same operational safety.(ii) A number of variations based on the equipment available should be prepared. The variation having the highest output should be selected.
(iii) Maintenance of equipment should be planned to ensure continuous production.
(iv) Considering the nature and volume of earthwork, the basic piece of equipment or 'head machine' must be decided on.
(v) The number of the other machines required must be defined by considering the output capacity of both the head machine and the other ones.
Table 3 gives the estimated hourly production of earthmoving equipment which can be used for planning.
The number of pieces of equipment can be calculated by the following equation:
where
n = number of pieces of equipment
VT = total volume of earthwork
Pa = average production rate of the equipment
Having defined the head machine the number of additional machines must be checked with the equation below:
Ph =Pa1×n1×fj1×h 1 = Pa2×n2×fj2×h 2 = Pai×ni×fji×h i
where
Ph = hourly production of the head machine
Pai = theoretical hourly production of equipment
ni = number of machines used in different working phases
fji = job factors
h i = efficiency of equipment
If the above equation is approximately equal, the continuous working and utilization of equipment is guaranteed.
It is very important that each piece of equipment be operated for as long as possible, because the use of equipment for short periods raises costs.
3.1 Approach Road
3.2 Public Services
3.3 Temporary Buildings
3.4 Planning Material to be ordered
3.5 Ordering Equipment and Instruments
3.6 Organization and Transport of Plant and Equipment
3.7 Site Clearing
3.8 Setting Out of Buildings, Dikes, etc.
3.9 Earthworks
3.10 Structures
3.11 Buildings
3.12 Site Finishing
When the planning and scheduling is complete, the Engineer is obliged to hand over the job site to the Contractor. During this procedure he has to show the Contractor the site, including the locations of the TBMs and the PBRs available, as well as all the official permits obtained from the Authorities. The final list of drawings or other statements required for construction work should be noted in the construction site book (U.S.D.I., 197.
As the materials to be delivered, the equipment and different machines to be transported to the site, are generally large and heavy, the approach road, including the provisional internal roads, should be built first of all. These roads should be all-weather roads and suitable for heavy traffic. It is also very important that all the roads should be well maintained during the construction time.
To avoid any delay in starting the construction work, it is desirable that a local water supply system be established from dug or deep wells or other water sources as soon as possible. The capacity of this system can be calculated from the water requirement needed for both the construction work and the labour, as well as the staff. Electricity may be provided from one of the public power lines, or a generator unit set up at the site.
Depending on the scale of the project, the type, size and number of different buildings, stores and workshops vary considerably. These can be determined from the different schedules. For the sake of economy, the buildings designed for the project may be used as temporary buildings if they are built in advance.
To set up any temporary buildings at the job site, the following should be taken into consideration:
(i) These buildings should be as cheap and simple as possible. It is preferable if they are set up from prefabricated units. In this case, they can be pulled down easily and quickly after completing the construction job.(ii) They should be located at the main points of the job site where they can provide services within short distances of each work phase.
(iii) They should be large enough to be used for storing the materials required.
(iv) Never select a site for such buildings which may be flooded during the rainy season.
The main purpose of planning the material to be ordered and transport of it is to ensure continuity of supplies for the construction works. To reduce the construction cost, the following may be of help:
(i) Ordering and delivery of material should be based on the detailed schedule of materials.(ii) To prevent a great loss of materials caused by several handlings at the job site, they must be deposited at the main points of use on the job site.
(iii) The possibility of obtaining materials from local sources should be investigated.
(iv) Materials delivered at the job site must be selected on the basis of their quality.
(v) Materials must be stored in accordance with the relevant specifications.
(vi) Storage places for all materials must be carefully selected.
(vii) A stock list of materials, including all the important data, i.e., date of arrival, amount or weight, etc., required for the proper control of materials, should be prepared and kept up to date.
In order to avoid any delay, and to ensure the smooth progress of the work, all the equipment, i.e., pumps, etc., and instruments required for both the construction work and the operation of the project should be ordered in good time.
Based on the detailed schedule of equipment, the machines and other equipment must be transported to the job site in proper time and in good condition. The fuel depot should be ready before the machines arrive. The capacity of this fuel depot should be as large as is necessary to run all the machines continuously. The necessary spare parts must be kept in the store or workshop. If versatile equipment is chosen, the number and types of machines may be reduced, which will reduce the maintenance work and fewer spare parts will need to be stored.
The first step that must be taken after the erection of the camp and plant buildings, is the clearing and stripping of the site. This work should, in fact, be done while the necessary temporary facilities are being erected. Trees and stumps should usually be removed from the job site. The requirements for clearing the site and stripping the top soil should be carried out according to the technical specifications, or the Engineer's directions. All the materials must be taken outside the site with the exception of the top soil used for covering the dikes which should be moved to a spoil area marked out by the Engineer.
Having cleared the site and before setting out any buildings, dikes, etc., the whole area of the site should be surveyed by the Engineer, with cross sections taken at every 5 to 10 m intervals. Cross sections should also be taken at longitudinal and transverse points with reference to the TBMs established at the job site. The Contractor or his representative shall be present and take part in this survey. The cross sections shall be entered in the measurement book and signed by the Contractor as a record of acceptance. All measurements of earthworks must be based on this survey. The Contractor can only start the work after the completion of the above formalities.
Based on the setting out plans, the Contractor1/ may be responsible for the true and proper setting out of buildings, dikes, channels, etc., and for the correctness of the position levels, dimensions and alignment of all parts of the works and for the provision of all necessary instruments, appliances and labour in connection therewith. The Contractor must carefully protect and preserve all the TBMs, pegs, templates and other things used in setting out the works.
1/ The Engineer may have this responsibility, depending on the terms of the contract
The setting out of earthwork can be done by profiles at suitable intervals as directed by the Engineer. Profiles may be made by actually excavating or filling and making the correct finished section as per cross section, and these sections can be maintained until the final completion of the work. The top level of these sections should include the provision of settlement allowance (5 percent for mechanical compaction and 10 percent for manual compaction). If preferred, profiles can be marked out using templates at a distance of 25 to 50 m, as shown in Figure 2.
The setting out of earthwork by machine should be done continuously because the fixed profiles used for manual work will be destroyed by machines. In this case, the setting out of earthwork can be done from an auxiliary base line established outside the operation radius of the machine.
Figure 2. Setting out a section of dike with templates
All the earthworks such as dikes, channels for supply and drainage of water, as well as bottom levelling in the ponds, should be carried out as per drawings and to the relevant technical specifications, or as per the Engineer's directions. The factors affecting the quality of earthwork are as follows:
1. Local soil conditions
2. Climatic conditions
3. Construction management- type of equipment4. Supervision of construction work
- size of equipment
- craftsmanship of the operator
- craftsmanship of the Contractor's Engineer or foreman and the skilled labourers
The procedures to be considered for earthwork in construction of a fish farm are set out below (Creager, 1950; U.S.D.I., 1965):
1. Site clearing
2. Topsoil removing
3. Preparation of the foundation for dikes: ploughing or ripping and watering
4. Excavation of pits for different structures to be built into the dikes
5. Excavation of drainage channels
6. Refilling and compacting of pits
7. Construction of dikes
8. Construction of feeder channels
9. Forming of dikes
10. Levelling of pond bottoms
11. Construction of wave protection
12. Turfing or grassing of dikes
In order to provide good quality dikes for a fish farm which may be used for a long period, it is advisable to follow the sequence of earthwork described before.
To prevent any flood problems during the period of construction, the drainage channels designed for the fish farm must first be excavated and completed, including all structures required for their proper utilization.
To avoid any seepage problems along the outlets during operation of the fish farm, all the outlets must be constructed before commencing construction of the dikes. The earth refilled around the outlet in the working pit should be thoroughly compacted.
Using earthwork machines for diking, the top of the conduit of outlets or other structures should be covered with a minimum of 60 cm of earth to avoid the collapse of the conduit. It is very difficult to construct a fish farm in marshland. In these circumstances the expenses of pond construction may generally be kept low by using cheap manual labour if possible. The dikes and channels can be built by using special equipment developed for working in marshy areas. The most suitable machines for construction of a fish farm in marshland are the swampy dragline and dozer. The swampy dragline is the most versatile one, because it can be used for excavating, trenching, diking, sloping and levelling. The swampy dozer can also be used for diking and levelling after closing the perimeter dikes of the fish farm. The bottom inside the perimeter dikes will then be dry enough to operate properly. As earth in any swampy area has a high content of water, all dikes using this type of soil should be built with a bigger section and flatter slopes, because of the greater subsidence and shrinkage.
Sometimes it is difficult to build any dikes in marshland because of the instability of the marsh soils. Dikes built from unstable soils will crack and slide due to the extremely fluid nature of the soil.
Pond construction techniques vary in different marsh areas and there are no set rules which suffice for all situations. Not all marsh areas are conducive to pond construction as we know it today. Generally speaking, the initial cost of construction and maintenance of fish ponds established in marsh areas are much higher than in uplands.
The following procedures may be considered for pond construction in marsh areas:
1. Locally used pond construction techniques should be examined and adopted or developed by taking the available equipment and manpower into account.2. To ensure a stable dike, the peaty surface from the entire foundation of the dike should be removed.
3. Trenching and coring the dikes with clay from outside the pond will strengthen the dike and reduce the seepage therefrom.
4. To ensure the necessary height of the dike it may be necessary to recap it two or three times. The first lift may be less than 1 metre due to the instability of the foundation. Having consolidated this part, the dike can be completed. The top level of the dike can be calculated from the results of the consolidation of the first layer.
5. To facilitate pond construction, the entire area selected for this purpose should be drained as soon as possible.
6. It is necessary to make a large berm between the toe of the dike and the drainage channel to offset the weight of the dike and prevent the foundation of the dike from slipping. Usually a berm should measure from 1 to 3 times the height of the dike, depending upon the type of soil encountered at the site.
7. The subsidence and shrinkage of dikes can be expected to be extremely high. Therefore, the structures used in such soils should be light and flexible and strong enough to avoid failure. In addition to this, the dikes in the vicinity of the outlet structure should be very carefully compacted.
8. To reduce the implementation period of pond construction, the perimeter dikes should first of all be completed. After drying the bottom soil inside the perimeter dikes, secondary dikes can be built by using a dozer or manpower.
The tolerances for pond construction vary in different countries. The tolerances allowable are as follows:
|
level |
±25 mm |
|
side slopes |
±10% |
|
centre lines |
±75 mm |
The structures should be built as per detailed drawings and technical specifications, or as directed by the Engineer. The points to be taken into consideration during their construction are as follows (U.S.D.I., 1981; White, 1977):
1. Having excavated the working pit, plain concrete should be placed immediately if needed.2. The measurements, location and elevation of forms, etc., should be checked before putting concrete into them.
3. Before casting, the reinforcement should be shown to and checked by the Engineer.
4. All materials used for building and all structures should comply with the relevant specifications. Never use coarse cement (killed cement) for any structures. This may be used for plain concrete.
5. Concrete used for structures should be mixed in a mechanical concrete mixer if available. The mix proportions given in the detailed plans should be adhered to.
6. Before proceeding to place the concrete, the forms should be realigned if necessary and well wetted.
7. Unless otherwise approved, concrete must be placed in a single operation to the full thickness of slabs and walls, with proper compaction.
8. Placed concrete must be protected by approved means from rain, sun and drying winds. Exposed faces of concrete must be kept moist for seven days after placing.
9. The forms must be removed by gradual easing without jarring. The period which must elapse after placing concrete and before easing and removal of the forms may be undertaken, is as follows:
|
Part of Structure |
Period for ordinary Portland cement |
|
Sides of foundations and walls |
3 days |
|
Under-sides of sides |
10 days |
In the case of cantilever slabs and beams, the forms should remain until the structures for counteracting or anchoring down have been erected and have attained sufficient strength.10. Honeycombed surfaces of concrete structures must be made good immediately on removal of the forms, and the superficial water and air holes must be filled out.
11. It is forbidden to load any parts of the structure during the strengthening period.
If there are a number of structures with the same measurements, it is advisable to use movable forms which might be applied several times.
All the points shown for structures can also be adopted for construction of buildings. To reduce the construction cost the working phases and the installation works must be well organized.
Having completed all the facilities of the project, the Contractor then hands it over to the Engineer for operation. All the materials, temporary buildings, equipment, etc., not necessary for the operation of the project should be removed, and the area which was occupied by them should be properly arranged by the Contractor.
Careful attention to the details of construction is equally as important as an adequate design. A safe and substantial design may be entirely ruined by careless or wrong execution, and the failure of the project may very possibly be the result. In order to ensure that the facilities of the project are constructed according to the plans and specifications, to certify to what extent the items of work are performed, and to determine the payment due to the Contractor, an Engineer, as the representative of the Owner, having wide knowledge and experience in such construction work, must be selected or employed by the Owner for the duration of the execution of the project.
The Engineer's tasks can be divided into three parts:
(i) administration of the contract
(ii) supervision of the work
(iii) testing that materials and works are in compliance with the specifications concerned.
The duties to be performed by the Engineer at the construction stage of a project should be incorporated in the contract. These duties might include:
1. Preparing any further detailed drawings necessary for the information of the Contractor to enable him to carry out the works.2. Issuing instructions to the Contractor and making such site visits as the Engineer considers necessary.
3. Handing over and showing the job site to the Contractor as well as supplying him with all official permits required for works to be started, etc.
4. Performing any duties which the Engineer may be required to carry out under any contract for the execution of the works.
5. Assisting in settling disputes or differences which may arise between the Owner and Contractor, except litigation and arbitration.
6. Supervising the execution of works which should include:
- Checking several times the setting out of any line and level related to the works. If at any time during the progress of the works any error shall be discovered by the Engineer in the position levels, dimensions or alignment of any part of the works, such errors shall be corrected in the construction site book (CSB) and shall be rectified by the Contractor to the satisfaction of the Engineer as soon as possible.- Testing all materials and workmanship as described in the contract and specifications .
- Checking the results of the tests and giving any instructions based on the results of the tests for modification or improvement of workmanship.
- Before covering any part of the works, the Engineer should check them and give instructions in the CSB for rectifying any mistakes.
- Measuring the works and determining the payment vouchers to be presented to the Contractor from time to time, as defined in the contract.
- During the progress of the works the Engineer checks from time to time, and in case of need, orders in writing the removal of any materials which in his opinion are not in accordance with the Contract. This should be done within the time specified on the order form for stated materials.
- Suspending the progress of the works if prevailing weather conditions affect the safety or quality of the work, or for any default on the part of the Contractor, or if necessary for the safety of the work.
- Approving in writing reasonable extensions of the time for completion of the work.
- Checking the rate of progress of the work based on the detailed schedule of execution prepared by the Contractor and if found too slow to ensure the completion of the work by the prescribed or extended time, notifying the Contractor in writing of his observations and opinions.
- Issuing in writing certificates of completion of the work or parts thereof.
