Text 2 General Classification of Machines

Machines employed for road making can be classified according to their purpose as follows:

1. Transporting facilities – crawler and wheel-mounted tractors, trucks, general and special-purpose trailers and semitrailers.

2. Materials handling equipment – winches, cranes, hoists, conveyors, air-operated equipment, cableways, loading and unloading machines.

3. Machines for land clearing and earthwork – stumpers, brush cutters, rippers,

bulldozers, scrapers, elevating graders, towed and self-powered graders, revolving shovels, hydraulic equipment and compactors.

4. Machines for extracting and processing stone materials – boring equipment, stone crushers and mills, sizing, washing and separating machines.

5. Machines for preparing and placing concrete mixes – batchers, mixers, concrete mix delivery facilities, reinforcement producing machines, vibrators, vacuum plants.

6. Machines for laying asphalt-concrete and stabilized pavements - bitumen storage equipment, machines for spreading stone and binding materials, for preparing asphalt-concrete mixes, for placing and compacting asphalt-concrete for on-site-mix road construction and for soil stabilization.

7. Machines for laying cement-concrete pavements - machines for laying foundations and spreading cement-concrete, for compacting, vacuum treatment and finishing concrete pavements, and machines for the manufacture of reinforced-concrete slabs.

8. Machines for motor-road maintenance - sweepers, water-trucks, snow and ice sweepers, repair trucks.

9. Pile driving machinery - pile hammers, vibration drivers, pile pullers, pile driving frames.

10. Mechanized construction tools - electrical, pneumatic, and tools with internal-combustion engines-form a separate group.

All of the above machines can be classified by:

1. The working process: continuous-action, intermittent-action.

2. The prime move: driven by electric motors, driven by internal combustion engines.

3. The mobility: stationary, mobile.

4. Common parts: wheels and axles, gears, bearings, transmission, brakes, clutch.

Text 3 Dragline

The dragline equipment consists of boom much longer than is used for the same capacity of bucket for a back acter, face shovel or skimmer. The machines normally associated with road construction are fitted with crawler tracks but some of the much larger machines produced for special purposes, where a the larger considerable output is required, are fitted with a special moving device in the form of plates or shoes that enable the machine to move forward with a walking action.

The bucket used for a dragline is suspended and controlled by means of cables manipulated from the cab of the machine by the machine operator.

The dragline is designed to stand above the level of the excavation which will be of a lightweight nature and it is mainly used for cleaning silt from ponds, lakes, streams and ditches, although if is also suitable for trimming embankments and excavating sand, shale and loose soil.

The dragline works in a similar position to that of the back acter and should be set up so that the bucket can be thrown forward until it engages the earth and then is drawn towards the machine. Because of the increased radius of the boom the machine is capable of excavating over a larger area of ground than any other static plant equipment.

A further advantage of this machine is that if is also capable of removing stockpiles of loose materials where back-filling of earth-works is required, although the output of the machine would be reduced once the bucket has to re- move earth above the level of its own tracks.

Text 4 Scraper

The scraper is associated with bulk excavation of earth-works. It consists of a bowl mounted on wheels with pneumatic tyres and may be to wed by means of a tractor or contains its own power unit. The scraper bowls varies in capacity but for road construction capacities of 4-12 yd3 would be normal. The machine is wholly operated by one machine operator who will control the power or towing unit and manipulate the gears to control the operation of the scraper bowl.

The tractor or power unit used with the scraper bowls may be fitted with caterpillar tracks or wheels fitted with pneumatic tyres. The machine is capable of excavating all normal tyres of earth. The scraper is a most suitable machine where excavating and depositing of the earth can be carried out on the site.

The tasks normally associated with the scraper are: excavation on the cut-and-fill principle; excavation and stockpiling; inimical leveling and grading of the earthwork: formation of embankments; excavating borrow pits.

The operation of the scraper bowl when excavating earth is similar to that of a carpenter’s smoothing plane. The front of the bowl contains an interchangeable cutting blade and a movable apron to open or close the front of the bowl. Inside the bowl is a movable tailgate or ejector gate. All are controlled by the machine operator. The output of a machine will depend upon: the capacity of the scraper bowl; the nature of the earth; the skill of the machine operator; the total distance to be covered by the machine.

Text 5 Back Acter

The back acter is sometimes known as the drag shovel and has the reverse action to a face shovel. The appliance that is fitted to the excavator power until consists of a boom with a bucket arm mounted at the forward end. The arm is capable of pivoting so that the bucket may be lowered or raised by means of control cables operated from cab the machine. The machine may be mounted on crawler tracks or wheels with pneumatic tyres, but the purpose of the back-acter equipment is the same regardless of its mounting.

The main purpose of the back acter is to excavate earth below the level of its own tracks which makes it most suitable for excavating trenches. The depth of the excavation will naturally depend upon the total depth that the boom and the bucket arm can be lowered and this again will be controlled by the particular model of machine.

The model of the machine will also govern the size of the bucket which in turn will control the width of the trench that can be excavated and the maximum radius that the bucket can swing for the purpose of discharging the earth. Site conditions have considerable bearing on the capabilities of a particular machine.

The bucket of the machine cuts into the earth a short distance in front of the machine and is then drawn towards the machine until the bucket is filled. The earth is deposited to one side of the trench or on to vehicles positioned near to the machine.

When the trench has been excavated to its required depth the machine then moves backwards to continue excavating from its next position.