 # Construction A lump-sum/fixed-price example

Consider a ‘project’ that will construct a cast-in-place concrete foundation wall, as shown in Figure 4.5. We desire to compile a single price for submittal to the owner for this lump-sum contract. The work will consist of mobilisation; clearing and grubbing an area of 400m2; excavating through silt and rock to a depth of 400 mm as shown and removing the excavated material from the site; placing footing forms, footing reinforcement and concrete for the 400mm wide footing; removing the footing forms; placing wall forms, wall reinforcement, anchor bolts and concrete for the 200 mm wide wall; removing wall forms; backfilling on both sides of the new wall with new gravel to the original ground level; and cleanup and move-out. Note that this is a rather ‘minimalist’ design, lacking in specification details about concrete, reinforcing, anchor bolts and backfill. First, we prepare a bill of quantities, with the result shown in the quantity and unit columns of Table 4.1. The unit measure represents the units by which the various items are measured. Mobilisation and cleanup and move-out are both measured as simply one job, with a lumpsum amount for each. The square metre (m2) and cubic metre (m3) units should require no explanation, as should the tonne (= 1000 kg) units for steel reinforcement. Anchor bolts are measured by the number of items or ‘each’. The unit smca stands for square metre of contact area, the area of contact between formwork and concrete. In the case of both footing and wall, this area is the area of the vertical formwork at the sides and ends of each. As a sample of the calculations required to determine quantities, consider the excavation quantities, as follows.

Assuming the end slopes and clearances are the same as the side slopes,
rock excavation: average width = 1.15 m; average length = 30.75 m; thickness = 0.15m
volume = (1.15 m)(30.75 m)(0.15 m) = 5.3m3
silt excavation: average width = 1.55 m; average length = 31.15 m; thickness = 0.25m
volume = (1.55 m)(31.15 m)(0.25 m) = 12.1m3.
As a check, find the total excavation volume:
(1.4 m)(31 m)(0.4 m) = 17.4m3 = 5.3m3 + 12.1m3 (OK).  