Rate analysis of the gabion wall in Nepal.

 

Overview

 

General-scope gabion wall

We have previously discussed stone masonry work in our last blog: https://www.ieccc.com.np/2024/06/rate-analysis-of-rubble-stone-masonry.html.

In this blog, we are discussing the gabion wall. A gabion wall is simply a cage or box of GI mesh wire filled with rocks or stones with the purpose of stabilizing the soil behind the wall. It's widely used for the lining of channels, river bank protections, coastline protection, soil erosion protection on road sides, and many other places. The main advantage of a gabion wall is its rapid construction process and environmentally friendly nature. Gabion boxes come in various sizes, like 2*1*1m, 3*1*1m, 3*2*1m, 4*2*1m, and various other sizes. In general, there are three types of wires used to make gabion boxes.

Mesh wire: wire to make the mesh of the gabion box's normal thickness is 2.2mm, 2.7mm, or 3mm.

Selvedge wire: wire used at the corners or borders of gabion boxes with a normal thickness of 2.7 mm, 3.4 mm, or 3.9 mm.

Lacing wire: These wires are used to connect gabion units with one another. It’s general thickness is 2.2 mm or 2.4 mm.

The gabion box can be hand-woven or machine-made. Here we are using a machine-made gabion box for rate analysis. As gabion boxes come in different sizes in the market, we are taking into consideration 3*1*1m and 2*1*1m gabion boxes, and the average of them is taken to find the rate per cubic meter of gabion wall work. The two basic codes we follow for our rate analysis are:

• Kathmandu district rate: 080/81
• DUDBC norms

You can find the codes in our download sections.

For hand-woven gabion box rate analysis, you can follow the specifications provided in DUDBC norms. We are using a machine-made gabion box here, following the specifications from Kathmandu district rate 080/81. Hand-made and machine-made boxes cost almost the same.

 

Calculations

Let's break-down the calculations in following headings.

• materials estimate and cost
• workers wages
• cost of tools and plants
• contractor's overhead and profit
   

Let's consider mesh, selvedge, and lacing wire thickness as 3 mm, 3.9 mm, and 2.4 mm, respectively, with box size:

Gabion box of size 2*1*1m (Gabion wire machine made 10x12/3.0/3.9/2.4/zn).

Volume: 2*1*1 = 2 m3.

Total square meter in the gabion box: 4 front faces + 2 side faces + 1 partition

                                                      = 4 * 2 + 2 * 1 + 1 * 1

Total square meter in the gabion box: 11 sq. m.

Cost as per KTM district rate: 080/81: 273

Cost of a 2*1*1 gabion box: 11 sq. m at 273 = Rs. 3003.00

Cost of gabion box per cu. m = 3003.00/2 = Rs. 1501.15

 

Gabion box of size 3*1*1m (Gabion wire machine made 10x12/3.0/3.9/2.4/zn).

Volume: 3*1*1 = 3 m3.

Total square meter in the gabion box: 4 front faces + 2 side faces + 2 partitions

                                                      = 4 *3 + 2 * 1 + 2 *1

Total square meter in the gabion box: 16 sq. m.

Cost per square meter as per KTM district rate: 080/81: 273

Cost of a 2*1*1 gabion box: 16 sq. m at 273 = Rs. 4368.00

Cost of gabion box per cu. m = 4368.00/3 = Rs. 1456.00

Average cost of a gabion box per cubic meter: (1501.15 + 1456.00)/2 = Rs. 1478.58

 

Unlike bricks, filling stones come in irregular shapes and need to be chiseled or hammered to minimize the void space in fillings. To balance this loss, we provide 10% extra volume.

Volume of stone used in 1 cm stone fillings: 1+ 10% extra

Stone filling volume: 1.1 cu.m.

Cost of quarry stone: 1.1 cu. m at 2366.08 = Rs. 2602.69

 

Cost of materials: 1478.58 + 2602.69 = Rs. 4081.27

 

Considering workers from DUDBC and wages from KTM district rate 080/81

Skilled workers: 0 at 1200 = Rs. 0.00

Unskilled workers: 0.5 at 900 = Rs. 450

Total worker cost: 0.00 + 450 = Rs. 450

 

Hire of tools and plants used

Tools and plants: 3% of unskilled workers = 3% of 450 = Rs. 13.5

 

Total cost: materials + workers + tools and plants

                =4081.27 + 450.00 + 13.50

Total cost: Rs. 4544.77

 

Contractor profit and overhead

Overhead and profit: 15% of total cost

                                 = 15% of 4544.77

Overhead and profit: Rs. 681.72

 

Total cost with contractor overhead and profit: 4544.77 + 681.72 = Rs. 5226.49

 

Summary of cost analysis per cubic meter

Supplying and providing 3*1*1 gabion work with stone/boulder packing in 100 mm*120 mm hexagonal mesh size made of heavy GI Gabion 10 SWG wire and 7 SWG selvedge wire with heavy coating, all complete.
Description	Type	Unit	Quantity	Rate	Amount	Remarks
Workers	Skilled	MDay	0.00	1200.00	0.00
	Unskilled	MDay	0.50	900.00	455.00
Materials	Gabion Box	Cu.m	1.00	1478.58	1478.58
	Quarry stone	Cu.m	1.10	2366.08	2602.69
Tools and plants account for 3% of unskilled workers.					13.50
Sub-Total					4544.77
Contractor overhead and profit at 15%					681.72
Total cost per cubic meter of gabion wall work					5226.49

In words: Rs. five thousand two hundred twenty-six and forty-nine paisa only.

 

Others

The gabion wall shall be placed in steps rather than a flush to increase the stability of the structure. In general practice in Nepal, for every 3 feet of vertical lift, we provide 1 foot of horizontal setback.