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Although the types of vehicles found around any farm building depend on the scale of the farm operation, increasingly there is likely to be a need to allow for larger vehicles used for delivering supplies or collecting produce. On smaller farms this may be limited to pick-ups, light vans and tractors, but on larger farms and around village or co-operative buildings the vehicles may be up to the maximum sizes allowed on roads.
The overall width and height of vehicles are of importance when designing door openings, gateways etc., and when clearing vegetation for roads and driveways. The minimum requirement is an opening which is 0.6m wider and 0.5m taller than the vehicle to allow for maneuvering, uneven ground surface, deflection of lintels, etc. Big lorries will thus require a minimum opening having a height of 4.8m and a width of 3.2m provided there is straight access to the opening. If the free space in front of the opening is limited (e.g. smaller than 1.2 times the overall length of the vehicle), a wider opening will be required.
Figure 13.9 Simple bridge construction using round timbers, (carrying capacity for moving loads up to 10 tonnes).
High vehicles should be prevented from moving too close to buildings with roof overhangs or other projections which are less than 5m above ground level. Vehicles with lift bodies may require a clear height of 7m or more.
Drives near the corners of buildings require an allowance for the vehicle to swing out on the curve, so that the centre of the turning circle is at the corner of the building or preferably out away from the corner.
The space required for a U-turn is an area with a width equal to the outer turning diameter and a length equal to the outer turning diameter plus one vehicle length.
Planning Space for Vehicles in Farm Drives and Courts
Drives and farm courts are part of the internal transport system on a farmstead. They indicate where the vehicles are expected to move or be parked. A single entrance drive is usually desirable for traffic control so vehicles can be readily observed from the house and farmstead.
Figure 13.10a Space requirements for tractor movements around a building.
Figure 13.10b Space requirements for tractor movements in and out of buildings.
The turn-off from the main road to the entrance drive should be located at the top of a hill or far enough from the top for safe visibility. Visibility must not be obstructed by trees, banks, signs, etc. A gate located in the entrance drive should be at least 10m and preferably 20m from the main road to permit cars and lorries to stop off the road while the gate is being opened.
The farmstead court is usually an extension of the entrance drive which provides space for parking and maneuvering machines and lorries. Proper parking space discourages visitors from blocking farm vehicles and directs them to the house or office. The safety of drivers, farm workers and children should be of prime concern in the overall scheme.
When planning the layout of farmstead buildings, the drives and courts should be designed to accommodate the type and size of vehicles used in the farm operation in an effective circulation system.
When a vehicle moves through a turn, the rear wheels track with a reduced radius. The road or drive therefore needs to be wider at curves. Articulated vehicles may almost pivot around the centre of the turning circle in a sharp turn or U-turn.
Table 13.1 Dimensions and Outer Turning Diameters for Some Common Types of Vehicles and Vehicle Combinations
|Type||Overall Dimensions (m)||Outer Turning|
|Light Delivery Van||2.1||2.4||6.0||12.0|
|Lorry with Trailer||2.6||4.6||22.0||26.0|
|Tractor with Trailer||2.4||2.8||12.0||13.0|
|Tractor with Two Trailers||2.4||2.8||20.0||15.0|
Gravelling of the most frequently used areas will improve the drainage and keep the surface of the drives firm and durable throughout the year. Extra parking space for storage of machines and supplies can be stabilized by sodding.
Heavy vehicle traffic close to retaining walls, tanks and similar structures should be barred within a distance equal to or greater than the height of the wall or structure.
Figure 13.11 Protect retaining walls from heavily loaded vehicles causing shearing of soil.
The two main objectives of fencing on a farm are security and improved livestock management, but fences may also be used as wind breaks, to provide privacy and to improve appearance. The type of fence chosen for a specific situation will be determined by the objective or the combination of objectives for which it is built.
Fencing is often used to protect property and growing crops from theft and damage by people or animals. Where the objective is solely the demarcation of boundaries very simple structures may be sufficient. On the other hand, fences, which are designed to stop intruders from entering, must be high, dense, sturdy and be topped with spikes or barbs. As secure fences can be quite expensive, their use is limited to enclosing particularly valuable property. The three most widely used types of fences for this purpose are:
Fencing is also used for protection around ponds, along steep slopes or in other hazardous locations.
Improved Livestock Management
Herding has been the traditional method of controlling livestock movements during grazing. Fencing was only done to exclude the animals from certain areas such as homesteads and cultivated fields and to safeguard them at night.
With "extensive" livestock production, fencing is likely to be so costly that herding must continue to be practiced. However, it is not uncommon to enclose the land with a boundary fence. With "intensive" livestock production, it is often feasible to sub-divide the land. The greater number of paddocks allows for flexibility in stocking and division of the livestock into different classes or age groups. It is seldom economical to sub-divide the land beyond what is necessary for efficient grazing practice.
In Africa some of the worst livestock diseases are tickborne and fencing can play an important roll in breaking the disease cycle by maintaining a disease-free condition once enough ticks have been eradicated by spraying or dipping the livestock regularly. Fencing also helps to limit the spread of other infectious diseases and to reduce problems with parasites. Fencing will also prevent improved animals from being bred by animals from outside the farm.
In intensive dairy production the animals are often grouped according to production to allow for more efficient feeding of concentrates and for improved management practices. The various groups of animals are kept separate by fences and other structures, such as feed racks.
Any type of structure which forms an effective barrier to livestock movements or which restricts human movements can be termed a fence. The following types are the most common on farms.
Wire Fences such as:
Other Types of Fences such as:
Types of Wire
Plain or barbed-wire fences are best suited for fencing of large areas. Plain wire is cheaper than barbed wire, but requires a higher standard of assembly and of construction for posts since the wires must be permanently strained to be effective. The thinner but stronger high-tensile steel wire is cheaper than plain wire but more difficult to install. Fencing wire is galvanised for corrosion protection. However, great thermal variations may crack the protective cover. The salt air in coastal districts or applications below ground level also reduce the effectiveness of the galvanizing. Barbed wire will generally rust faster than plain wire. High tension wire will keep its tension longer than plain or barbed wire, but will rust faster than plain wire once the galvanizing is broken. Barbed wire may cause serious injury to animals resulting in lower pelt value. The most justifiable use of barbed wire is as a top wire above other types of fences to discourage stock from leaning over the fence and breaking it down.
Even though fencing wire should be strained to be effective, care should be taken not to over-strain it. The elasticity of the wire will cause it to return to its original position after being stretched by the impact of animals or by temperature changes, provided the yield point stress has not been exceeded. Furthermore it will be difficult to maintain a very high tension value over several years. Generally the elasticity will not be damaged and the fence will retain resilience and tension if the wires are stressed to about 30% of the yield point, or about l500N for common types of fencing wire.
Wire Applications for Various Animals
It is recommended that 4 to 5 lines of barbed wire or 5 to 7 lines of plain wire be used in a cattle fence. However, on large ranges with low stocking density, 2 to 4 and 3 to 5 lines respectively may be adequate. The top wire should be at least 1.2m above ground level.
Fencing for poultry runs should be about 2m high. A thin gauged, hexagonal, relatively open mesh is adequate to control adult birds, but often smaller mesh netting, dug 20 to 30cm into the ground and with a total height of about one meter, is fitted at the bottom of the fence to prevent young birds from escaping and predators from entering the run.
Barbed or plain wire can be used for pig fencing, but due to the small spacing of the wires required, in most cases it will be more economical to use a heavy gauge woven wire fence or a chain link (diamond mesh) fence. It is recommended that a mesh smaller than 15cm be used although 20cm mesh can be satisfactory for adult pigs in large runs. Where sows with litters are to be fenced, smaller mesh must be used at the bottom. The height of the fence should be at least 90cm. Unless the pigs noses are ringed it is difficult to make a fence pig-proof, but it will help to dig the bottom of the fence about 25cm into the ground. This will however, increase the maintenance cost due to rusting of the wires. Alternatively, a single line of barbed wire can be fixed at the bottom of the fence, just above the ground.
Barbed wire is not considered suitable for sheep since it tears their fleece. A good sheep fence needs to be 90 to 110cm high depending on the breed. It can consist of either 6 to 10 lines of plain wire or woven fencing, 80 to 90cm high, and one or two barbed wires at the top to make up the height. However, sheep fences in small paddocks or yards may be built at least 2m high to keep out predators. The mesh should be 15 to 30cm. The larger mesh will prevent the sheep from getting their heads caught if they attempt to reach through, but may not be sufficiently dense for lambs and for breeds having a special liking for getting through fences. For plain wire fences, batten and wire spacing seem to be more important than tension in the wires. Wires spaced 15cm apart require battens at every second metre, whereas wires at 10cm can have battens spaced 2.5 metres.
Equally important as the wires in a fence are the posts which hold them up. Strainer posts and corner posts need to be strong and faced firmly in position, since the stability of the fence and retention of tension in the wires depend on them. Intermediate posts, battens and wires may be replaced as necessary.
Naturally durable and termite resistant hardwood or less durable wood treated with a preservative should be used for strainer and corner posts. Note that some wood preservatives may cause the wires to deteriorate quickly, especially in the atmosphere of coastal areas. Knots are potential sources for weakness. Sometimes galvanized steel or concrete posts are used, but they are generally more expensive than wooden posts. Concrete posts, although easily broken, are long lasting, fire and termite resistant and can be made at the farm using a simple mould. A concrete mixture 1:2:2 reinforced with four 6mm steel bars wired together at 50cm intervals is satisfactory. Strainer posts should be 20 x 20cm thick at ground level and other posts 15 x 15cm.
Wooden posts may be set in dug or bored holes and fixed firmly with tamped soil. Alternatively they may be driven into the soil or into under-sized bored guide holes. Driven posts are generally 1.5 times as firm as posts rammed into over-sized holes, and will withstand greater lifting forces. A hand driver can be made from a 900mm length of 200mm steel pipe. The top end is closed with a steel plate while handles are welded to the bottom end. The total weight should be about 15 kg for a one-man driver and about 30 kg for a driver operated by two men. Driven posts should be pointed before they are given a preservative treatment.
Intermediate posts should be set 40 to 60cm deep whereas strainer, corner and end posts requiring greater rigidity should be set up to 80cm deep. Metal strainer posts should always be set in concrete, and wooden posts are sometimes set in concrete for extra rigidity.
Live posts consisting of trees growing on the fence line or specially planted posts are cheap and long lasting. Suitable species can also act as shade trees and provide browse. Live posts should be planted some time before they are to be used to give adequate time for rooting. It can be difficult to establish live posts in arid areas.
Battens (droppers) are used to compensate for sag in the wires where the distance between intermediate posts is necessarily long and also to keep stock from pushing between the wires. Wood battens should have a diameter of 25 to 40mm and will last longer if treated with a preservative. Alternatively, wire lashings may be used to maintain the distance between the wires or extra wires can be supplied to decrease the spacing, thus reducing the need for battens.
Stapling is the most common method of fixing the wires to the posts. Alternatively they may be secured with 2mm galvanized mild steel ties. However, it is difficult to make such a tie secure against sliding on the post. When stapling, the wire should be loosely stapled to the intermediate posts. Staples driven too far will bend and hammer out the wire, thus creating a weak spot. Splitting of the posts can be lessened if the staples are driven diagonally into the grain.
Wire Fence Construction
The length of fencing required per hectare will vary greatly with the form and size of the fields. Square fields have the lowest fencing cost per unit area, and the larger the fields the lower the fencing length per hectare. Fence lines should be as long, straight and unbroken as possible, since corner posts and gate posts require bracing and thus add to the cost.
When the fence line has been laid out, the ground area over which the wires will be stretched should be cleared. Next the strainer assemblies are installed. These will take the whole strain of the stretching of the wires and it is therefore most important that they are firmly set and wellbraced. Normally strainer assemblies are located next to corner and gate posts, but on long straight stretches of fence, additional strainers should be installed at up to 200m intervals if the ground is even, or at the top and bottom of each slope in hilly terrain.
Three types of strainer assemblies in general use are shown in Figure 13.12a, b and c. The double horizontal stay strainer assembly is extremely rigid in all types of soil, but for most purposes the single horizontal-stay assembly will be sufficient. On firm but easily dug soil the traditional assembly with a diagonal stay will be adequate and the cheapest in terms of material.
Corner posts should have a diameter of at least 150mm and be braced in the direction of both fencing lines. Corner posts, where the fence angle is less than 45°, will be sufficiently rigid if braced with a single diagonal stay or diagonal tie-back.
Figure 13.1 2a Double horizontal stay.
Figure 13.1 2b Single horizontal stay.
Figure 13.1 2c Traditional strainer with diagonal stay.
Intermediate posts having a diameter of 75 to 125mm should be set exactly in line to avoid any horizontal forces due to strain in the wires. Where there is a pronounced low spot in the fence line, one or two of the intermediate posts in the low area may require extra security against uplift by being driven deeper or set in concrete. For a plain-wire cattle fence no battens are required if the intermediate posts are spaced no more than 3.5 to 5m. but the posts can be set up to 15m apart if battens are used at 3.5 to 4m intervals. Woven wire fence requires intermediate posts every 4 to 5m and chicken wire every 2m.
The wire or wire netting is then attached to the posts. Starting with the bottom wire, it is first secured to a strainer post, then stretched using a tackle-block stretcher, chaintype stretcher or, for single plain or barbed wires, a simple wooden lever. When the wire has been stretched tight enough it is secured to the next strainer post by wrapping and stapling. The wire should be on the inside of all posts, and taken one turn around any corner post. After the fence-stretcher has been released the wires are loosely fastened to the intermediate posts and finally battens are fixed as necessary.
When the fence is erected all bits of wire, nails and staples should be collected to avoid "hardware disease" caused by the animals eating the scrap metal.
A suspension fence can be cheaper than a conventional plain or barbed wire fence since the number of posts is reduced. It will however require one or two more wires than the corresponding conventional fence. For its effectiveness it relies on the strain in its high-tensile wires, which causes them to vibrate when an animal nudges the fence. If an animal charges against the fence with a force that would seriously damage a conventional fence, the suspension fence heals over and returns undamaged to its original position after the animal has retreated or passed over. Strainer assemblies are set as for conventional fences, but intermediate posts may be spaced up to 40m where the fence line and contours permit. Wood or wire battens, which must not touch the ground, are spaced about 4.5m apart.
An electric fence can be made from either plain or barbed wire. It can be simple in design, since it need not be a physical barrier to the animals, but instead relies on an electrical pulse sufficient to shock, but not kill. The wires are stretched between insulators at the strainer posts with intermediate posts spaced 12 to 15m for cattle or 7 to 12m for sheep and pigs. Battens are not needed. Barbed wire is often preferred since the barbs will penetrate the fur of animals and make good contact with the skin. However, plain wire is satisfactory in most cases. As the hot wires must be insulated from the ground, they are fastened to the posts with insulators and should not come into direct contact with weeds, grass or the posts. The most common type of energizer (controller) operates by charging a capacitor with electrical energy and then discharging it to the fence in the form of a pulse of high voltage. It can be powered from the mains or a battery. Solar recharging units are also available for battery-powered energizers.
Temporary electric fences are often used for strip grazing within a permanently fenced field. These consist of a single hot wire at a level about three-fourths the height of the cattle. Two hot wires are provided for sheep and pigs.
Electric fences rely on the soil to conduct the current back to the earth (ground) terminal on the energizer, but soil is a poor conductor under dry conditions. Therefore, in the dry season an electric fence may be ineffective since an animal may not get a shock because of insufficient current flow. Adding earth-return wires from the energizer to the fence will make it effective during dry conditions. This is also the typical arrangement for permanent electric fences which have two hot wires and one or two neutral wires spread between them.
A single hot wire can also be used to increase the animal's respect for a conventional fence and to protect it from damage. The line can be carried on insulators in the fence or on outriggers. The recommended height is 60cm for cattle and 25cm for sheep.
Other Types of Fences
Post and Rail Fences
Post and rail fences consist of wooden posts with wooden or split bamboo rails attached to them. They are mainly used to fence areas where the stocking density is very high, as in collecting yards and handling areas. They are also used in farmstead areas because of their attractive appearance and because they are easily crossed by humans. Their main advantage is that animals are unlikely to be injured by them, but to be effective as physical barriers for stock, they must be strong and properly constructed.
Figure 13.13 Post and rail fences for cattle.
The posts should have a diameter of at least 125mm, be firmly fixed in holes 500 to 800mm deep and not more than 3 to 4m apart. Three to four 100mm rails are then fixed to the posts. Where post and rail fences are used in animal handling yards or other similarly crowded situations, for extra strength the rails should be joined only on posts, but not all rails on the same post. In a four-rail fence for cattle the rails are usually spaced about 125mm, 175mm, 225mm, and 275mm from the ground upwards. With 100mm rails, the top rail will be 1200mm above ground level.
Single wooden rails are sometimes used at the top of barbed-wire fences where the stocking density on the pastures is high. The rail will increase the visibility of the fence and protect the wires from damage by animals leaning over the fence, without any risk of injury to the animals.
Live fences have the advantage of low capital cost if planting material is available at the farm, but require labour for planting. In the humid tropics most species used for hedging grow quickly and may require cutting twice a year. Therefore, the maintenance work can require more labour than is available on the farm in spite of underemployment during part of the year. For a hedge to be stockproof it may be necessary to include one or more barbed wires in the fencing line. Although hedges require more space than fences and encourage weeds and vermin, they may preserve wild life, act as wind breaks and be an attractive feature in the landscape.
Where land is being cleared, thorn bushes or the waste from tree felling can be laid in a line to make a stock-proof fence that will last for some years. Piled logs and wooden palisades can also be used for fencing, but are quite wasteful of material. Log fences, unfortunately, are very susceptible to attack by termites and in humid areas, by rot as well.
Stone walls are an attractive alternative in localities where wood is scarce and stones are plentiful. Construction is labour intensive, but maintenance cost is low. They may be constructed with stones placed in mortar as described in chapter 5 or by simply piling stones loosely in a wall 0.7 to 1.2m wide at the base. Adobe or stabilised soil blocks can also be used for low cost wall construction especially in very dry areas.
These include various structures such as gates, stiles and grids which allow people and/ or vehicles to pass a fencing line, but still restrain animals. The purpose of wheel splashes is mainly to restrict the spread of diseases.
Although a wire gate itself is inexpensive, the strainer assemblies required for the gate posts in a wire fence should be included in the total cost. Normal width for a gate where vehicles are to pass is 3.3m, but may be up to 5m if traffic is frequent.
Figure 13.14 Wire gate.
Pole and Chain Gate
This is less tedious to open and shut than the wire gate and is also quite inexpensive. This gate and the wire gate do not impose a lateral load on the gate posts other than the strain of the fence.
These gates are constructed with wood or metal frames with a face of open boards, netting or wire. Since a gate will put a sideways bending moment on the post when the gate is open, this post must be extra strong and firmly installed. The gate can be made self-closing by arranging the hinges so that the centre of gravity is lowest when the gate is closed. Gates wider than 3.5m should be given extra support with a wire running from an extended gate post down to the free end of the gate as shown in Figure 13.16b.
Stiles provide easy passage Over a fence for humans without breaking the fence line. The stile shown in Figure 13.17 can be easily moved.
There are several methods to make passages through a fence line for humans. The one illustrated in figure 13.18a has an opening protected by doors which are permanently fixed in a half open position so that cattle are restrained. The strain in the fencing lines is transferred overhead with a tie rod. The posts should be strong enough to resist the bending load from the strain in the wires.
Another type consists simply of an opening 250 to 300mm wide, just enough to let a man pass but too narrow for cattle.
A cattle guard is a grid in the roadway which serves as an alternative to a gate. It eliminates frequent opening and closing of a gate, but is more expensive to construct. The cattle guard may be made of pressure treated wood, but steel or concrete are best for use in places where wood is likely to be attacked by pests. The minimum length (in the roadway) is 1.5m but 2.4m is recommended, to discourage animals from jumping across. The load bearing members should be made of a minimum of 200mm round timber, or larger if heavy lorries are to pass. The grid can be of 50 by 125mm sawn timber or 100mm round poles spaced 100mm apart. The width of the cattle guard is ordinarily 3 to 4m. The narrower width is satisfactory if sloping ends are used as shown in Figure 13.19.
Figure 13.15 Pole and chain gate.
Figure 13.17 Stile.
Figure 13.18 Two types of man pass.
Figure 13.19 Cattle guard.
The purpose of a wheel splash is to disinfect the wheels of vehicles moving into the farm area, thereby limiting the spread of diseases and parasites. They are relatively expensive to construct and maintain, and to be effective they must be kept filled at all times with a disinfecting liquid. A wheel splash is a shallow basin made of waterproof concrete with 2m long entrance and exit ramps sloping 1:8. The centre section of the splash containing the disinfecting liquid should be long enough to allow the largest wheel of a tractor to make at least one full turn before reaching the other ramp (4 to 6m).
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