BACKHOES AND

POWER SHOVELS

Amit Kumar

Anal Kumar Shahi

Anant Pratap Singh

Ankit Kumar

Excavation

• Typical earthworks include roads, railway beds, causeways, dams, canals and foundations. Other common earthworks are land grading to reconfigure the topography of a site, or to stabilize slopes.

1. Backhoe

• A backhoe is a piece of excavating equipment consisting of a digging bucket on the end of a two-part articulated arm.

• The name "backhoe" refers to the action of the bucket, not its location on the vehicle.

• Efficiency –• Capacity of bucket• Time per swing

Backhoe - Segments

• It has four segments:• The Boom (section of arm

closest to the vehicle)

• The Stick

• The Bucket

• The Thumb (optional)

Thumb of Backhoe

• Thumb is hinged to the scoop which grips like a human thumb to pick up objects.

How does it work?

• Hydraulic systems simply transmit forces from point to point through an uncompressible fluid.

• Hydraulic multiplication-Because the second piston has a larger diameter than the first piston, the second piston moves a shorter distance but pushes up with greater force.

Hydraulic Ram

• There are some significant differences in how the two systems operate, however. The simple piston we looked at could only apply multiplied force in one direction. If you pushed down on the narrower piston, the wider piston moved up with greater force. But for a backhoe to dig, its arms have to be able to move in different directions.

• There is fluid on both sides of this piston head, fed by two different hoses.

Applications:

• Suitable for digging below machine level

• Effectively used to dress or trim the surface avoiding the use of manual effort for dressing the excavated surface

Backhoe in action

Backhoe Manufacturers-

• Caterpillar Incorporation

• JCB

• Hitachi Construction Machinery

• Volvo Construction Equipment

• Deere & Company

2. Power Shovels

• Construction equipment used to excavate the earth and load it into trucks or other hauling equipment.

• Crawler mounted power shovel & wheel mounted power shovel.

• Consists of mounting, cab, boom, dipper stick, host line.

Working -• The shovel operates using several main motions:

Hoist – lifting of the load (i.e. the bank of material being dug)

Crowd - moving the dipper handle out or in to control the depth of cut

Swing - rotating the shovel between digging and dumping

Propel - moving the shovel unit to different locations or dig positions

Work Cycle-

• Digging-> Swinging-> Dumping-> Returning

Selection of type-

• Job location• Small jobs- at different places- rubber-tyred shovel – due to its mobility

• Large job –at concentrated location- crawler mounted shovel- more desirable.

• Type of footing• Soft and muddy soil with large undulation- crawler mounted shovel- only

choice

Selection of size-

1. Cost per cubic meter of output (best size=minimum cost)• Size of job- larger job- higher cost-large shovel size.

• Cost of transportation- Large size- higher cost

• Depreciation Rate- large shovel- high depreciation rate- difficulty in disposal

• Cost of wage per cubic meter- large shovel – less wage

• Downtime cost- large shovel-high downtime cost – increase delay in obtaining spare parts

• Combined cost of drilling, blasting and excavating of rock- bigger shovels- less expenditure in combined cost.

2. Job-site conditions

• If project time is such that it needs high hourly output , large shovels must be preferred.

• Size of hauling unit – determines the size of shovel .

• For excavating hard and tough bed of soil, dipper of large shovel- exerts greater downward pressure –more suitable.

• Excavating blasted rocks- large size dipper- easy to handle big rocks.

• For high lifts to dump earth from basement into trucks- requires long boom –large shovel .

• Optimum depth of cut- greatest output-> dipper coming up with full load-without excessive download pressure and tension- depends on type of soil and size of dipper

Output of power shovel-

• Expressed as cubic meter per hour, based on bank-measure volume.

For Ideal Conditions,

Factors affecting output-

• Class of material – Sand – Clay- Rocks.

• Angle of swing- As angle of swing increases- time for discharge of load increases- cycle time increases- output decreases.

• Job Conditions- Drainage of soil- size of embankment- depth of cut-condition of haul road- climatic conditions.

• Management Conditions- Greasing/lubrication of shovel – replacing of worn out parts- major overhaul when necessary- bonus to crew.

• Size of hauling units- large shovel- large hauling unit- output increase

• Skill of operator

• Physical Condition of Shovels

Applications

• Suitable for close range work

• Capable of digging very hard materials and remove big boulders

• Used in digging gravel banks, clay pits, digging cuts in road works etc.

• Backhoe• Bucket Capacity – 6 m3 – 52 m3

• Power Shovel• Dipper Capacity - 19.1 m3 – 62.7m3