Soil & Water Conservation Structures

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.