Mass-haul diagrams (MHD) are used to compare the economy of various methods of earthwork distribution on road or railway construction schemes. By the combined use of the MHD plotted directly below the longitudinal section of the survey centre-line, one can find:
(1) The distances over which cut and fill will balance.
(2) Quantities of materials to be moved and the direction of movement.
(3) Areas where earth may have to be borrowed or wasted and the amounts involved.
(4) The best policy to adopt to obtain the most economic use of plant.
(5) The best use of plant for the distances over which the volumes of cut and fill are to be moved.
(1) Haul refers to the volume of material multiplied by the distance moved, expressed in ‘station metres’.
(2) Station metre (stn m) is 1 m3 of material moved 100 m Thus, 20 m3 moved 1500 m is a haul of 20 × 1500/100 = 300 stn m.
(3) Waste is the material excavated from cuts but not used for embankment fills.
(4) Borrow is the material needed for the formation of embankments, secured not from roadway excavation but from elsewhere. It is said to be obtained from a ‘borrow pit’.
(5) Limit of economical haul is themaximumhaul distance. Whenthis limit is reached it is more economical to waste and borrow material.
Bulking and shrinkage:
Excavation of material causes it to loosen, and thus its excavated volume will be greater than its in situ volume. However, when filled and compacted, it may occupy a less volume than when originally in situ. For example, light sandy soil is less by about 11% after filling, whilst large rocks may bulk by up to 40%. To allow for this, a correction factor is generally applied to the cut or fill volumes.
Construction of the MHD:
A MHD is a continuous curve, whose vertical ordinates, plotted on the same distance scale as the longitudinal section, represent the algebraic sum of the corrected volumes (cut , fill −).
Properties of the MHD:
Assuming that the fill volumes, after correction, equal the cut volumes, the MHD would plot.
(1) Since the curve of the MHD represents the algebraic sums of the volumes, then any horizontal line drawn parallel to the base AB will indicate the volumes that balance. Such a line is called a balancing line and may even be represented by AB itself, indicating that the total cut equals the total fill.
(2) The rising curve, shown broken, indicates cut (positive), the falling curve indicates fill (negative).
(3) The maximum and minimum points of a MHD occur directly beneath the intersection of the natural ground and the formation grade; such intersections are called grade points.
(4) As the curve of the MHD rises above the balance line AB, the haul is from left to right. When the curve lies below the balance line, the haul is from right to left.
(5) The total cut volume is represented by the maximum ordinate CD.
(6) In moving earth from cut to fill, assume that the first load would be from the cut at X to the fill at Y, and the last load from the cut at Y to the fill at Z. Thus the haul distance would appear to be from a
Mass haul diagram
point mid-way between X and Y, to a point mid-way between Y and Z. However, as the section is representative of volume, not area, the haul distance is from the centre of mass of the cut volume to the centre of mass of the fill volume. The horizontal positions of these centres of mass may be found by bisecting the total volume ordinate CD with the horizontal line EF. Now, since haul is volume×distance, the total haul in the section is total vol×total haul distance = CD × EF/100 stn m.
Most if not all muckshifting contractors have long abandoned the traditional concepts of freehaul and overhaul. The muckshifter takes the haul length into account when pricing the job but does not measure or value the freehaul or overhaul as such any more. The price is per m3 and depends upon the type of material being excavated. The Civil Engineering Method of Measurement Edition 3 (CESMM3) specifies five excavation material types but in the Method of Measurement of HighwayWorks which forms volume 4 of the Manual of Contract Documents for HighwayWorks there are over 40 classes of soil plus hard material which is measured and paid for ‘extra over’ the soft muck price elsewhere in the Bill of Quantities. Today, the volumes in the different cuttings and embankments come from a CAD program and in the case of MMHW these are then split into different soil classifications by the designer and shown in a schedule for the contractors pricing the work at tender stage.
a simplified time-chainage/timelocation programme; such documents are often used as the major working document on site. There are also computer-based time-chainage/time-location programs that do all the hard work, especially when the programme of works needs to be revised, as it often has to be where the New Engineering Contract Edition 3 (NEC3) is used.