Graders

These are used to grade earthen road formations and embankments to their finished shape within specified limits by trimming the surface. The graders can also be used for forming ditches, mixing and spreading soils, backfilling and scarifying ground.

The motor grader is the equipment mostly used for grading and finishing of large areas. Motor graders generally have engines up to 300 HP and the latest models are provided with hydraulically controlled attachments. These attachments include an excavation blade similar to the bulldozers, scarifier, ripper and backhoe. The blade of the motor grader has replaceable cutting edges. These blades come in flat, curved and serrated styles. Motor graders are fitted with articulated frames for increasing manoeuvrability. Motor graders are now available with automatic grade controls for achieving the desired grading. Grading distance of 500 meters and above give optimum output. For distances, task efficiency gets reduced:

Distance in meters	50	100	200	500
Task efficiency	0.4	0.6	0.8	1.0

Graders optimum output for finishing is measured in M²/hour on an area basis or km/hour on an linear basis:

Output in m²/hour = WSE/P

Where,

W = Width graded per pass

S = Average speed in m/h

E = Job efficiency factor

P = Number of passes (generally 4 to 6)

And the grader speed for various operations can be taken as under:

Operation	Speed km/h
Rough grading	4 = 10
Finishing (including grading)	6 = 15
Mixing	15 = 30
Spreading	6 = 15
Self transporting	10 = 40

Example

Calculate the time required to grade and finish 30 km of road formation with width equal to thrice the width of the motor grander, using six passes of the motor grader with speed for each of the successive two passes as 6 km/h, 8 km/h, and 10 km/h respectively. Assume machine efficiency based on operator’s skill, machine characteristics and working conditions as 75%

Average speed = (2 x 6 + 2 x 8 + 2 x 10) / 6

= 8 km/h

Area to be graded per hour

= (Width graded per pass x Average speed x Machine efficiency) / Number of passes

= (W x 8 x 1000 x 0.75) / 6

Number of hours required to grade and finish 30 km long and 3 W wide area

= (Total area) / (Area/hr)

= (30 x 1000 x 3w) / (W x 8 x 1000 x 0.75) + 6

= 90 hours.

Equipment selection criteria depends upon the following factors:

·      Compacting equipment – nature of materials, depth of fill, daily work load and working condition.

·   Grading equipment – nature of materials, daily workload, finishing accuracy and working conditions.