Friday, December 20, 2019

Session 2 : Excavation Work (Free Online Quantity Survey and Estimation Course)


1. Name of Work & Description

Excavation Work is required to prepare the foundation of the building or any structure on a hard surface. Sometimes we need to excavate hard rock also due to level difference, or for road, bridges, need to cut the mountain for tunnel or to prepare roads from the valley.

Before excavation work, we need to find out the SBC (Soil Bearing Capacity) with the help of SBC we can easily prepare or assume how much excavation will be done or what is an approximate depth of our structure foundation.

Types of Ground we are founding when excavation is going on.
1.     Soft Soil
2.     Compacted Soil
3.     Soft Murum
4.     Hard Murum
5.     Soft Rock
6.     Hard Rock
7.     Shade/ Mud Soil
8.     Boulders

2. IS Code No.

IS Code For Excavation Work Code of Safety: IS 3764-1992
IS Code For Sheet Piling Section:  IS 2314:1986
IS Code For Scaffolds & Ladders Code of Safety: 3696: 1991
IS Code for Blasting and Related Drilling Work Code of Safety: IS 4081:1986

3. The Drawing Needs to Read.

Excavation work is needed to do before building or any structure foundation.
The following drawing needs to read before excavation work, or before starting to excavation.
Building Foundation Plan
Bridge Foundation Plan
Plinth Section
Reduced Level Plan
Plot Layout Drawing

4. Location of Work

Excavation 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. Storm Water Drain
10. Retaining Wall

5. Standard Procedure of Work (Step by Step)

Work Procedure before Start the Excavation

1. Read Plot Layout Drawing Carefully.
2. Read the building foundation Plan and Calculate the building outer to outer measurement.
3. Read Foundation drawing plan, where Footing and A raft of the building are outside than building the line.
4. Calculate Outer to outer distance from foundation drawing of building or bridge structure.
5. Check SBC Report, we need to know what approximate depth of excavation or hard surface is?
6. If Depth of foundation is up to 1.5m then add 1.5m in foundation outer to outer distance both sides.
7. If the Depth of foundation is More than 1.5m then add 3.0m in foundation outer to outer distance both sides.
8. Mark line for excavation as per building outer to outer distance plus 1.5m or 3.0m both sides for foundation workspace.

Example : If Building outer to outer Distance is: 30m X 20m
    Foundation Plan (Footing Size 1.50m X 1.50m ) : 30.00m + 0.75m+0.75m= 31.50m
                                                                                 : 20.00m + 0.75m+0.75m= 21.50m
   Foundation Outer to Outer Distance is = 31.50m X 21.50m
   Now if Depth of Foundation is 4.0m :
   Excavation Size is  :  31.50m + 3.0m + 3.0m : 37.50m
                                  : 21.50m + 3.0m + 3.0m : 27.50m
 9. Check and Note down actual ground level with the help of Auto Level with the same interval of 2m to 5m, Take 4 reading of each interval.

Work Procedure during the Excavation

1. Excavate as per Marking
2. Excavate up to desired height as instructed by a designer with the help of the SBC report.
3. Do not excavate more that limit.
4. Stop when hard strata are shown to responsible peoples.
5. If there is mud or loose soil then us instruction of IS 3764:1992.
6. If excavation is done for a trench or only footing pit then use sheathing with the help of cleat, strut & Wales for support to soil.
7. Barricade the area after the excavation is completed.
8. Check and Note down excavated area levels with help of Auto level by the same interval as you have done during taking an actual ground level reading, Take a minimum of 4 reading of each area.

6. Checkpoints

1. Check Machine Capacity as well as which type of machine is Required.
2. Instruct to machine operator regarding the depth of Excavation as well as the size and marking of excavation. As well as show the marking line of excavation.
3. Instruct to Operator to prepare the excavation area angle of 45 degrees of slope.
4. Keep all workers Safe distance from the Machine.
5. If using the breaker to break the rock up to the desired level keep taking reading and level on time to time to avoid extra excavation than required.
6. After Shown, the hard strata arrange the RCC Designer visit to inspect the SBC.
7. Check the Plinth Level and desired level before complete the excavation.
8. Please check Depth of Soling, PCC, Footing/Raft, and Plinth Beam before complete the excavation.

For Example:    If Plinth Level is Given 0.5m Above GL
                        Then Calculate Minimum Excavation Depth
                        Soling for Footing: 0.23m
                        PCC for Footing: 0.15m
                        Depth of Footing: 1.00m
                        Depth of Plinth Beam: 0.6m
                        Then Minimum Depth of The footing is 1.98m below from GL
                        If permission is given by RCC Designer then you can keep the plinth beam and the footing level is the same.

7. Equipment and Machinery

There are two types of excavation is done

1. Manual Excavation

Manual Excavation can be done with the worker by using hand tools like shovels, etc. but for mass excavation can not be possible manually. It will be too costly and time consumable.

2. Mechanical Excavation.

With the help of advance technology excavation is made too much easy and cost-effective as well as time-saving.
The machine is using for excavation
1.     Backhoe Loader (JCB)
2.     Excavator (Poclian)
3.     Mini Excavator (Mini Poclain, Bob-Cat)
4.     Air Compressor Breaker
5.     Poclain/ JCB Breaker
6.     Blasting
7.     Tunnel Cutter
8.     Hywa: For excavated material Shifting
9.     Dumper: For excavated material shifting
10.  Tractor : For excavated material shifting

8. Measurement and Quantity Survey

For the Calculation of the excavated area and quantity of excavated material, we need the following points.
1. Actual Ground Level Reading: Average Level of each interval.
2. Excavated Ground Level Reading: Average level of each interval.
3. Actual Excavated Area: Prepare geometrical shapes as per level interval as we can find an exact excavated area as well as the depth of excavation.

Depth of Excavation = RL of Actual GL – RL of Excavated GL

Quantity of Excavated Area = Actual Excavated Area X Depth of Excavation
Please prepare the chart as per the picture.

9. Checklist

Excavation Work Checkpoints
1. Mark Exact area of Excavation
2. Keep Working space after excavation
3. The slope at edges is 45 degree
4. The sheathing is done or Not.
5. Barricading is done or not to the excavated area.
6. Heavy equipment, such as excavating machinery and road traffic shall be kept back from the excavated sides at a distance not less than the depth of trench or at least 6 m for trench deeper than 6 m.
7.The use of power shovels or draglines in a trench, because of his violent thrust or blows delivered, rapidly render the banks of the trench unstable and dangerous to people working nearby. These conditions shall be watched for and suitably remedied or eliminated.
8. Pathways shall be non-slippery and shall be of adequate width not less than 75 cm. They shall be strong enough to withstand the intended use.
9. Excavation areas shall be adequately lighted for night work.

10. On-site Experience

Readers Experience:  in year 2009, we were work at near thane creek. We know about the ground situation, strata and soil condition also. we started to excavate building foundation which is only one building of one footing, another building has a pile foundation. We completed 80% of excavation and guessed to no need of support to soil or sheathing to side, but we are doing work near to full moon, and during full moon, seawater level is increasing, and our excavator machine is parked at same place where excavation is going on, on next day morning we all has shocked, machine is going under the water. We had tried to out from this area but the machine is clogged due to mud. After too much struggle we escape this machine from this area.

Mr. Umesh (Engineer)

CBEC India


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