Jan 21, 2020

Session 3 : Backfilling Work (Free Online Quantity Survey and Estimation Course)


1. Name of Work & Description

 Backfilling Work is required to fill the excavated area of the foundation of the building or any structure from a hard surface. Sometimes we need to do more backfilling more than ground level due to increase the height of plinth level, on infrastructure field backfilling, is most important part because the top level of road and highways is calculated as per nearest dams or nearest river HFL (Highest Flood Level).

Before excavation work, we need to find out the material quality of backfilling work. With some laboratory tests and physical tests.

Types of using of Material for Backfilling Work.
1 Soft Soil
2 Murum (Same Gravels)
3 Murum (Brown Stone Color uniform size)
4 Murum (60-100mm size)
5 Boulders
6 Debris

2. IS Code No.

IS Code For Excavation & Backfilling Work Code of Safety: IS 3764-1992
There is No Specific Code for Backfilling

3. The Drawing Needs to Read.

Backfilling work is need to do after building the foundation completed or after top level of structure final.

Following drawing need to read before Backfilling work, or before starting to backfilling.
1 Building Foundation Plan
2 Bridge Foundation Plan
3 Plinth Section
4 Reduced Level Plan
5 Plot Layout Drawing
6 Road Level
7. Road Section
8. Foundation Sectional Drawing

4. Location of Work

Backfilling can be done with the following Locations.
1 Building Foundation
  2 Podium Foundation
  3 Basement
  4 Under Ground Water Tanks
  5 Bridge Foundation
  6 Culvert
  7 Dam
  8 Trench
  9 Road

5. Standard Procedure of Work (Step by Step)

Work Procedure before Start the Backfilling

1 Read Plot Layout Drawing Carefully.
2 Calculate Approximate measurement to get the idea of required backfill material.
3 Read Foundation drawing plan, where Footing and Raft of the building are outside then building lines.
4 Calculate Outer to outer distance from foundation drawing of building or bridge structure.
5 Do site visit of Backfill material quarry. Please keep quarry distance nearest form your site.
6 Finalize material as per your requirement.
7 Finalize the rate as per your budgeted amount for backfilling work.

 Work Procedure during the Backfilling

1 Remove all the Material from Pit, or Backfilling Area.
2 Fill loose material with help of machine up to 300mm height.
3 Do not backfill murum more than 300mm.
4 Do not allow boulders in Backfill murum.
5 Do not allow any vegetation/twigs
6 Do not allow keep the boulders near RCC structure, it can be damaged RCC member.
7 Backfilling must be done by first filling the excavated soils in layers of 300–500mm and tamping it with a vibrator. Till the desired level. The soil is moistened up to the optimum moisture content to establish optimum compaction and best results.
8 Barricade the area backfilling area when machinery is working.
9 Check and Note down backfilled area levels with help of Auto level by the same interval as you have done during taking an actual ground level reading.

6. Checkpoints

1 Check Machine Capacity as well as which type of machine is Required.

2 Instruct to machine operator regarding the depth of Backfilling Material as well as the thickness of each layer.
3 Instruct to Operator to compact each layer properly.
4 Compact each layer of the earth not exceeding 200mm.
5 Earth/soil should be free of vegetation/twigs if any.
6 Earth/soil should be free of boulders if any.
7 Rolling should be done with a 5-ton mechanical roller after sprinkling enough water and core cutter samples taken for every 150sq.m
8 Proceed to the next layer after achieving a minimum of 95 % of MDD(maximum dry density).
9 Keep all workers Safe distance from Machine.
10 Back the filling must be done by first filling the excavated soils in layers of 30–50 mm and tamping it with a vibrator. Till the desired level. The soil is moistened up to the optimum moisture content to establish optimum compaction and best results.
11 After completion of compaction arrange the architect visit to inspect the level as per Sections.
Check the Plinth Level and desired level before complete the backfilling, also keep down the level of backfilling area for Soling, PCC & Flooring, or for Road work keep the level down for WBM, Tack Coat, Seal Coat Etc.
12 Please check Depth of Soling, PCC, Footing/Raft, and Plinth Beam before complete the excavation.

For Example:    If Plinth Level is Given 1.0m Above GL.
Then Calculate Minimum Backfilling Depth
                        Soling for Footing: 0.23m
                        PCC for Footing: 0.15m
                        Tiling Work : 0.050m
                        Then Top Level of Compacted Backfilling Area is 0.57m below from Plinth Level.

7. Equipment and Machinery

There are two types of Backfilling is done

Manual Backfilling

Manual Backfilling can be done with the worker by using hand tools like shovels, etc. and 250-1000kg The compactor can be used for Compaction, Generally manual backfilling must be done at the not accessible area for big machines like at Parking, Under the Building, at Basement, Under the bridge, etc. but for mass Backfilling can not be possible by manually. It will be too costly and time consumable.

Mechanical Backfilling.
With the help of advance technology excavation is made too much easy and cost-effective as well as time-saving.
Following The machine is using for excavation
1 Backhoe Loader (JCB)
2 Excavator (Poklain)
3 Mini Excavator (Mini poclain, Bob-Cat)
4 Mini Compactor
5 Plate Compactor
6 Road Roller
7 Grader
8 Vibro Roller
9 Hywa : For murum Shifting
10 Dumper: For murum shifting
11 Tractor: For murum shifting
12 Water Tanker
13 Dozer

8. Measurement and Quantity Survey

For Calculation of backfilling area and quantity of backfilled material we need the following points.

1 Excavated ground Level Reading: Average Level of each interval.
2 Backfilled Ground Level Reading: Average level of each interval.
3 Actual backfilled Area: Prepare geometrical shapes as per level interval as we can find exact backfilled the area as well as the depth of backfilling.

Depth of Backfilling = RL of excavated GL – RL of backfilled GL

Quantity of Backfilled Area = Actual backfilled Area X Depth of Backfilling  
Please prepare the chart as per the Excavation work Session.

9. Checklist

Backfilling Work Checkpoints

1  Mark Exact area of Backfilling
2 Keep RCC Structure, Pipe Line, Chambers, Electrical Wire, etc. Safe
3 Compact up to 95 % of MDD(maximum dry density).
4 Use Vibro Roller as per your requirement.
5 Barricading is done when machines are working.
6 Keep exact 300mm Layers to compaction.
7 Heavy equipment, such as backfilling machinery and road traffic shall be kept back from the excavated sides at a distance not less than the depth of backfilling or at least 6 m for area deeper then 6 m.
8 The use of power shovels or draglines in a trench, because of his violent thrust or blows delivered, rapidly renders the banks of the trench unstable and dangerous to people working nearby. These conditions shall be watched for and suitably remedied or eliminated.
9 Pathways shall be non-slippery and shall be of adequate width of not less than 75 cm. They shall be strong enough to withstand the intended use.
10 Backfilling areas shall be adequately lighted for night work.

10. On-site Experience

Readers Experience: At an MNC Project the work order is for industrial plant shed and area of the shed is approximate 30000 Sqft, but movable area and road this plant plinth area is approximate 72000Sqft and height are approximately 7m from the existing ground level. Total work completion time is given by the client is 6 months including Monsoon season. And the site location is in the hilly area. But our bad luck is after cutting of grass and murum backfilling completed up to 2 meters, rain is started, and continuously falling up to more than 40 days. And for dry this area again give 40 days. But when we have to restart the work, the murum is not as much dry as we think, at that site we did a lot of work on it, we removed 2 layers of that murum and refill it. Obviously, the client gives us  90 days extra as well as they understood the exact situation of work.
Mr. Ashok (Sr. Supervisor)


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