Mass Haul Diagram (mass Curve):
It is the graphical representation of
amount of the earthwork involved in the road construction and the manner in
which the earth can be hauled economically.
Use of mass curve:
i) To find an economical scheme for
distributing the excavate material.
ii) To overcome the wastage of
material at one place and borrowing at another place.
iii)To overcome the difficulty of
estimation of the proposed wastage, the designer may advise widening an
embankment or cutting where necessary.
Construction of Mass Haul Curve:
i) Divide
the length of the road in separate sections of convenient distances.
ii)
Calculate the volume of earth work in each section.
iii) Plot a
longitudinal section of each section of road on a convenient scale.
iv) Plot the
volumes as ordinates and distances between the section which are kept same.
v) Plot the
positive volume above the base line and negative volume below the base line.
vi) Join the
ends of adjacent ordinates by a smooth curve to obtain the required mass
diagrams.
Characteristics of
mass curve
1.Rising sections of the mass curve indicates
areas where excavating exceeds fill, whereas falling sections indicate where
fill exceeds excavation.
2 Steep
slopes reflect heavy cuts & Fills, while flat slopes indicate areas fro
small amount of earthwork.
3 The
difference in ordinates between any two points indicate net excess of
excavation over embankment or vise versa.
4.Any
horizontal line dawn to intersect two points within the same curve indicates a
balance of excavation (cut) and embankment (fill) quantities between the two
points.
5.Points of
zero slope represent points where roadway goes from cut to fill or from fill to
cut.
6.The
highest or the lowest points of the mass haul diagram represents the crossing
points between the grade line (roadway level) and natural ground level.
Important Terms:
Haul
distance :-It is the
distance at any time between the working face of an excavation and the tip end
of the embankment formed from the hauled material.
Average haul distance:- It is the distance between the
center of gravity of cutting and center of gravity of filling.
Haul:- It is the sum of the products of
each volume by its haul distance.
Lead and lift:- The vertical distance covered by
the porter is called Lift & horizontal distance covered by the porter is
called lead. 1 m lift is taken equivalent to 12.5 m lead.
Free haul distance:- It is the specified distance in
terms of contracts, upto which the excavated material, is transported
regardless to the haul distance. During transportation of excavated soil the
distance for which no extra cost is paid to the contractor is called free haul
distance. It is nearly 1.5 m lift & 30 m lead.
Overhaul distance:- If the excavated material from a
cutting has to be removed to a greater distance than free haul distance, the
extra distance is known as overhaul distance.
Balancing line:- Any horizontal line drawn on the
curve balances the volume of excavation and volume of filling because, there is
no difference in aggregate volume between the two points, such a line is known
as balancing line.
Balancing Point: It is the point at which volume of excavation and volume of embankment is equal.
