## Lesson 32. Cost Estimation Examples

Computation for Material Requirement – Some Examples

Example 1: Calculate dry material required for 1 m3 cement concrete (CC) having density of 2.3 ton/m3 with 1:3:6 ratio.

Solution:

Ratio: 1:3:6 (cement: sand: 20 mm aggregate)

Sum = 1+3+6 = 10

From Table 31.1 (lesson 31), dry matter required for 1.0 m3 CC mix is 1.54 m3

Cement requirement = = 0.15 m3= 216 kg (using Table 32.1 below)= 4.3 bags of 50 kg each

Sand requirement =  = 0.46 m3 = 1.22 ton

Aggregates = = 0.92 m3 = 1.56 ton (20 mm aggregates)

Table 32.1. Bulk density of different construction material

 Material Bulk Density (kg/m3) Cement 1440 Aggregates (10 mm) 1600 Aggregates (20 mm) 1700 Aggregates (40 mm) 1950 Solid rock 2700 Sand 2650 Cement mortar 2160

Example 2: Find dry matter for 1.0 m3 brick masonry with cement and sand mortar of 1:6 ratio.

Solution:

For 1.0 m3 brick work, 500 bricks are needed (from Table 31.1 described in lesson 31).

Cement: sand ratio = 1(cement):5(sand)

Sum = 1+5 = 6

For 1 m3 brick masonry, 0.3m3 cement mortar is required (see material requirement Table in lesson 31.1).Cement requirement = 0.05 m3 and

Sand requirement = 0.25 m3

Some Example of Rate Analysis

Example 3: Determine unit cost for Gabion works

Solution:

The gabion work involves collection of stones (225 mm) and their arrangement in wire mesh accordingly. The material requires are GI wire mesh and stones. Labours (unskilled and semi-skilled) worker are required for netting the wire mesh. The unit cost is computed as per the following analysis.

 Particulars Quantity Rate (Rs/unit) Amount (Rs) Material GI wire 10 gauge with 10cm X 10cm spaced in 3mX1m size (standard size available in the market). For 3 m3 gabion, 14 m2 surface area of GI wire is needed. Thus weight of the GI wire @1.3 kg/m2 including wastage 18.2 kg 60 1092 Stones of size > 225 mm including wastage (25%)  and transportation at site 3.75 m3 200 750 Total material cost 1842 Labour Skilled labour for wire netting no 240 120 Semi skilledlabour for placing stones in the net no 220 275 Unskilled labour 180 405 Total labour cost 800 Total material and labour cost 2642 Add 3% contingency 79.26(say 80) Grand total for 3 m3 2722 Cost per m3 907.33(say 910)

Example 4: Determine unit cost for logwood crib structures filled with stones.

Solution:

The logwood crib structures involve placement of stone (250 mm or more) in between the wooden pole to provide a barrier to flowing water. The required materials are wooden logs, nails, oils for painting, stones whereas labour requirement include skilled labour such as Carpenter, Mason, Painter and unskilled labour.  The unit cost is computed as per the following analysis of rate for 15 m3 crib for span of 10 m.

 Particulars Quantity Rate (Rs./unit) Amount (Rs.) Material Wooden logs Vertical post in two rows 1 meter Centre to Centre and span of 10 meters; 2.15 m long and 100-120 mm in diameter 22 poles 120 2,640 Horizontal post of 3.0 meter long and 100-120 mm in diameter placed 50 cm apart 30 poles 140 4,200 200 to 250 mm long iron nails for joining logs at 88 joints (say 100); weight of 100 nails @200 gm per nails 20 kg 60 1,200 Oil Painting 5 lit 40 200 Creosote oil Turpentine oil 5 lit 30 150 Stones at site (> 250mm) 15m3 200 3,000 T&P (Drills, hacksaw, Hammer etc.) Lumpsum 1,000 Total material cost 12,390 Labour Carpenter 10 nos. 240 2,400 Mason 5 nos. 240 1,200 Painter 2 nos. 240 480 Unskilled 20 nos. 180 3,600 Total labour cost 7.680 Total labour and material cost 20,070 Add 3% contingency 602 Grand total for 15 m3 20672 Cost per m3 1378 (say 1380)

Example 5: Determine unit cost for RCC work

Solution:

RCC work includes steel reinforcement of cement concrete. The most adopted cement concrete is of 1:2:4 mix of cement, sand and aggregates (volume basis). The density of concrete depends on the nature of aggregates used. Most frequently, 20mm stone ballast are used as aggregates. Reinforcement is done using steel bars. In watershed structures 12 mm steel bars are used. The unit cost can be computed as per the following analysis of rates.

Dry mortar required for 1m3 cement concrete = 1.54 m3.

Thus for 10 m3 cement concrete, dry mortar volume will be 15.4 m3

Cement requirement = 15.4/7 = 2.2 m3 = 64 bags of 50kg each

Sand requirement = 4.4 m3 and

Aggregates requirement = 8.8 m3

Assuming density of concrete as 2300 kg/m3, the weight of 10 m3 such concrete will be = 23 ton

 Particulars Quantity Rate (Rs/unit) Amount(Rs) Material Cement grade 53 64 bags 280 17,920 Coarse sand (1-2 mm) 4.4 m3 2000 8,800 Stone ballast 20mm 8.8 m3 1200 10,560 Mild steel bar @1% reinforcement 0.23 ton 60000 13,800 Binding wires (1 mm) 2 kg 65 130 Total material cost 51,210 Labour Head mason (Raj mistri) 1 270 270 Mason (mistri) 3 240 720 Unskilled labour (beldar) 12 180 2160 Bhisti 6 220 1320 Sundries, T&P etc Lumpsum 1000 Total cost of labour 5,470 Centering and shuttering Timber planks and post On hire 1,000 Carpenter 6 nos 240 1,440 Unskilled labour (beldar) 1 Nails Lumpsum 500 T&P Lumpsum 1,000 Sub-Total 3,940 Total of material and labour cost 60,620 Add 3% contingency 1820 Total cost for 10 m3 RCC 62,440 Cost of per m3 RCC 6,244 (say 6,250)

Example 6: Determine unit cost for I-class brick work with 1:6 cement mortar

Solution:

First estimate cost for 10 m3 brick work in order to rationalize the labour requirement and mortar mix.

Dry matter requirement for mortar in brick work = 0.3m3 per m3 of brickwork. Thus 3.0m3 dry matter will be required for 10m3 brick work.

Cement requirement = (1/7)*3 = 0.43 m3 or 12.47 (say 13) bags of 50 kg each.

Sand requirement = (6/7)*3 = 2.58 m3

The unit cost can be computed as per the following analysis of rates.

 Particulars Quantity Rate (Rs/unit) Amount(Rs) Material Cement grade 53 13 bags 280 3,640 Coarse sand (1-2 mm) 2.58 m3 2000 5,160 Class-I brick @500 per m3 5000 4.50 22,500 Total material cost 31,300 Labour Head mason (Raj mistri) 1 270 270 Mason (mistri) 10 240 2,400 Unskilled labour (beldar) 7 180 1,260 Bhisti 2 220 440 Sundries, T&P etc. Lumpsum 1,000 Total cost of labour 5,370 Total of material and labour cost 36,670 Add 3% contingency 1,100 Total cost for 10 m3 RCC 37,770 Cost of per m3 RCC 3,777 (say 3,800)

Estimating and costing of some watershed management work - Examples

Example 7:

Estimate the cost to construct CCT in hard soil in 20 ha area. The distance between two row of CCT is kept as 25 m and width and depth of CCT is 50 cm each.

Solution:

The construction of CCT involves excavation only and so only labour is required with some T&P.

Length of CCT per ha can be calculated using following equation

Earthwork volume = 0.5*0.5*400 = 100 m3

 Particulars Quantity Rate (Rs/unit) Amount(Rs) Labour Unskilled labour @1.5 m3 per manday 67 mandays 180 12,060 Skilled labour 2 mandays 240 480 T&P Lumpsum - 500 Total labour cost 13,040 Per m3 earth work 130

Example 8:

Gabion structures are proposed to stabilized 240 m long and 8 m wide gully. The average slope of the gully bed is 10% and the vertical interval may be taken as 2 meter. The proposed design is presented in Fig. 32.1. Estimate the project cost.

Example 2: Continuous Contour Trenches (CCT) in Heterogeneous Material

Department of Agriculture in Gaya District, Bihar proposes to make CCT in a catchment area of 40 hectares. The top soft soil stratum has a depth of 30 cm followed by hard soil for about 1 metre. The horizontal spacing between two successive rows CCT is 25 m. The width and depth of the CCT is 50 cm x 50 cm. Calculate the cost of construction of CCT.

Solution:

Fig. 32.1 Proposed design of gabion

Solution: Since the vertical interval is 2 meter and 10% slope, means gabion should be 20 m apart horizontally. Thus total number of gabion for the gully stabilization would be 240/20 = 12. The average gully width is 8 meter and 1 meter wide side wall is to be provided, the total width for earth work would be 8+2 =10m. The estimate involves computation of material and abstract of cost.

• Details of measurement and quantities
 Sl. No. Particulars of work/items No Length (m) Width (m) Height (m) Quantity (m3) 1 Excavation in foundation 12 10 2 0.6 144 2 Gabion box filled with boulders of >200mm Bottom 12 10 2 1 240 top 12 10 1 1 120 side 12 4x2 (two sides per gabion) = 8 1 1 96 Total gabion work 456

• Abstract of cost
 Sl. No. Particular of work/ items Quantity Unit Rate (Rs/Unit) Amount (Rs) 1 Excavation in foundation 144 m3 130(see example 7) 18,720 2 Gabion work 456 m3 910(see example 3) 414,960 Total cost 433,680

References

• Dutta, B.N. (1966). Estimating and Costing for Civil Engineering, Lucknow

• Khanna, P.N. (1996). Indian Practical Civil Engineers’ Handbook

• New Delhi: Engineers’ Publishers

• Watershed Works Manual. (2007). Ministry of Rural Development, Government of India, pp.226-273.

• Mohan, S. C. et al. (2007). Training Manual on Soil Conservation & Watershed Management, pp. 380-393

• Sharda, V.N., Juyal, G.P., Prakash Chandra and Joshi, B.P. (2007). Training Manual – Soil Conservation and Watershed Management (Vol II Soil and Water Conservation Engineering). CSWCRTI, 218, Kaulagarh Road, Dehradun.