• The nature of the excavation to be performed
• The type of soil to be excavated
• The distances which the excavated spoil must be carried to transport
• The condition and gradients of the site

Face Shovel It is used for excavating against a face or bank, consisting of an open-top bucket or dipper with a bottom opening door, fixed to an arm or dipper stick which slides and pivots on the jib of the crane. It is suitable for excavating all clay, chalk and friable materials and for handling rock and stone. However, it is not suitable for surface excavation for which a skimmer is used.

Backacter It is similar to face shovel except that the dipper stick pivots on the end of the jib and the dipper or bucket works towards the chassis and normally has no bottom door but is emptied by swinging away from the chassis to invert the bucket. It is mainly used to excavate trenches and occasionally used for the excavation of open areas such as small basements.

Skimmer This arrangement is similar to the face shovel except that in this case the bucket slides on rollers directly along the jib and thus has a more restricted movement. It is used for surface excavation and levelling in conjunction with transport to haul away the excavated material.

Dragline It is usually fitted with a long slender boom or jib and the bucket, which in operation faces towards the machine and has no door, is supported by cable only as on a crane. It works from the side of the excavation at normal ground level and is used for excavating large open excavations such as basements when the depth is beyond the limit of the boom of a backacter.

Crand and Grab It consists of two hinged half-buckets or jaws pivoted to a frame which is suspended by cable from a long jib of an excavator. The grab is used for deep excavations of limited area on all types of soil except rock.

Pile Driving and Drilling It is an excavator equipped with either hanging leaders which guide the pile and the hammer during driving, or a turntable through which the square drilling rod or kelly bar passes for drilling piles.

b. Tractor-based Equipment

It is designed either as attachments to normal tracked or wheeled tractors or as machines in whih the earth-moving attachments and the tractor are designed as a single integrated unit.

A tractor which is hydraulically operated can be rigged as:-

4.2 Hoisting

This concerns with the handling of materials and components. Most building materials used in the erection of buildings are handled several times during the course of construction. The plant used for hoisting, primarily performs vertical movement.

These may be either self-propelled or truck-mounted. They are suitable where on-site or between site mobility is a primary requirement or where the duration of job is short. It is widely used for the erection of low-rise buildings where a long reach is not essential and the machine can approach near to the building, and for the erection of low framed structures where the crane being able to move between the columns of the structures.

For example: Self-propelled cranes, truck- or lorry-mounted cranes, telescopic jib cranes

2. Stationary Cranes

They are fixed firmly to some form of base at their working position. It can handle its maximum loads over a greater range of radius than mobile crane.

For example: Derrick cranes, guy derrick, scotch derrick, monotower derrick, tower crane, climbing crane, rail-mounted or travelling crane, transportable tower crane, fixed jib slewing crane, portal crane

3. Hoists

A hoist consists of a horizontal platform which is moved up and down vertical guides by a powered winch and is usually termed a platform hoist. It is used for materials lifting and passenger carrying which is useful for high-rise building construction.

For example: Platform hoists and mobile platform hoists.

4. Elevators

These consist of a series of buckets fixed to a rotating belt or chain and are used for raising aggregates into the bins of weightbatchers. Elevators can work vertically but are usually set at an angle, according to the height of lift.

4.3 Transporting

This implies horizontal movement primarily but it can involve some vertical movement too.

1. Dumpers

   These are vehicles designed for the transport of materials which previously were usually carried out by wheelbarrows, such as excavated spoil, hardcore and concrete. It is faster and more economical than hand barrow and consists of a shallow tipping hopper or skip mounted on a wheeled chassis.

   For example: Power barrow, dumper, multi-skip dumpers, high discharge dumpers, dump truck

2. Forklift Trucks

   It is essentially a powered mobile chassis on the front of which is a vertical frame or mast on which a pair of "forks", that is a pair of projecting tines, may be raised and lowered. It is basically used for handling unit or packaged loads which is a large individual component or smaller components packaged into suitable units.

3. Monorail Transporter

   This is a powered wagon or skip running on a single easily laid rail and is intended primarily to carry concrete from the mixer to the point of placing. It is generally used in otherwise inaccessible situations.

4. Conveyors

   It is used for handling small materials such as excavated spoil from the point of excavation to the boundaries of the site for loading into transport, for concrete placing or for filling up aggregate bins in weigh-batchers.

5. Concrete Pumps and Placers

This consists of a pump which is mechanically operated by ram and placers pneumatically operated by compressed air. For example, mobile concrete pump.

4.4 Mixing

A large amount of material must still be mixed with water, mainly concrete, mortar and plaster. The advantages of mechanical mixing over hand mixing, except for very small quantities, are greater economy, reduce the loss of cement and more accurate gauging of the water content.

a. Concrete Mixers

They are made in various types and sizes and are broadly classified as (i) batch mixers and (ii) continuous mixers. There are five types of batch mixer:

b. Weighbatchers

The batching of materials for concrete may be by volume or by weight. For example: weighbatcher incorporated with mixer, independent weighbatcher, mobile and semi-mobile weighbatcher

c. Central Mixing Plant

The concentration of batching and mixing operations in a single static plant instead of by a number of mobile mixers is often used on large, extensive sites.

  The main advantages of central mixing are:-

• An increased output by fewer machines and men is possible.
• In suitable circumstances it is more economicl than a number of separate mixers.
• Better quality control is possible

The essential components of a central mixing plant are:-

• Adequate storage of aggregates at ground level
• Overhead aggregate storage bins to hold not less than an hour’s supply at maximum output
• Some means of storing and weighing the cement
• Elevated water storage together with some means of metering the water supplied to the mixer
• A mix or mixers
• Storage hoppers to contain the mixed concrete until fed into transport or concrete pump.