Table of Content for Excavation Work & Filling
- Scope of Earthworks
- Classification of Excavated Material
- Steps for Excavation
- Methods of Rock Excavation
- Quality Control for Earthworks
- Quality Checks for Excavation
- Quality Checks for Filling
- Excavation & Filling Equipment
The term earthworks in the engineering concept refer to the work involving the processing of soil or rock by means of equipment or manually. The earthworks can be classified into two categories i.e., excavation & filling. The varying nature of soil (or rock) from point to point poses various engineering challenges and thus the solution applicable at a place may not be effective at another place. The handling of the soil is more difficult when it has higher moisture content. Thus, ensuring quality in excavation & filling works becomes a tedious task.
Scope of Earthworks-
Excavation & Filling are a part of every project from excavating foundations to landscaping and land development. Some of the projects are as follows-
Classification of Excavated Material-
- Soft/Loose- The soils that can be excavated manually by shovel or another digging tool are classified under this head. E.g., sand, organic matter, gravel, silt, loam, peat, etc. Generally found on top of the earth surface up to 0.2-0.3m depth depending on strata.
- Hard/Dense Soil- Soils that require the close application of picks to loosen it. E.g., stiff clay, cobblestone, soling, WBM, etc.
- Mud- A mixture of soil and water in liquid or semi-solid state.
- Soft/Disintegrated Rock– The rock that can be split and quarried by a crowbar is classified under soft/disintegrated rock. E.g., Laterite and conglomerate.
- Hard Rock (Blasting Required)- Rocks that require blasting for excavation.
- Hard Rock (Blasting Not Allowed)- The rocks which are quarried by chiseling, wedging, jackhammer, etc. are classified under this head.
Steps for Excavation Work-
- The centerline and boundary of the area are marked by taking reference from the drawing. The length, width, and depth of excavation/filling are specified in the drawing.
- NGL levels are to be taken for billing purposes.
- Site clearance, such as grass and bush cleaning.
- Check for underground conduit, electrical cable, etc. by using available information. Informing the concerned authorities before starting the work.
- Arrangements for dewatering if the water table is high.
- Excavation is done by mechanical equipment or manually. Depth is checked frequently to avoid overwork. Sump pits and trenches are also excavated for dewatering if required.
- Dressing of excavated area. The loose soil is either removed or compacted.
- Protection to sides as decided by engineer in-charge.
- Dumping of excavated material with a minimum distance of 1m from the excavated area to avoid sweeping of dumped material into the pit by rain. Dumped material should be properly stacked.
Methods of Rock Excavation-
The method of rock excavation depends upon the number of factors such as rock hardness, rock size, depth of excavation availability of equipment, time & cost-effectiveness, the scale of the project, permission from authorities, etc.
- Blasting- Blasting is used when hard rocky strata are to be excavated on a large scale. The spacing & depth of holes for blasting designed as per the rock strength and required depth of excavation. The safety precautions are to strictly implemented and approval from the concerned authorities is obtained before the blasting.
- Jack Hammer- Jackhammer is generally used for breaking small sized rocks. Jackhammers use compressed air and create a lot of noise pollution.
- Chemical- Chemicals are used for breaking rocks. Holes are drilled into the rock with designed spacing and chemical is poured into it. The chemical expands and subsequently cracks the rock. This method is used where noise and vibrations are prohibited.
- Breaker or Hydraulic Hammer- Rock breakers are used by mounting them on excavators.
- Wagon Drill– These drills are used for drilling holes for blasting and for chemical fissure of the rock.
Quality Control for Earthworks-
Quality assurance & quality control measures mainly rely on the measurement of the density of soil. However, the density is not the key parameter for assessing strength. The density only indicates strength. The Plate Load Test, Falling Load Deflectometer, etc. directly assess the strength of the soil.
The dry density of soil is checked against the Maximum Dry Density (MDD) which is the maximum value a soil can achieve for a given particle size distribution and compactive effort corresponding to Optimum Moisture Content (OMC).
- The higher the MDD, the lower is the corresponding OMC and vice-versa.
- Higher the compactive effort, higher is dry density and lower is OMC.
- Uniform particle size distribution leads to higher MDD as compare to poorly graded soils.
The specified density can be achieved at various moisture content by using different compactive efforts. The OMC defines the moisture content at which the specified density can be achieved most efficiently. compacted. The compaction is a combined effect of static load, vibration, and kneading effect of the compaction equipment.
*The term compactive effort refers to equipment weight and the number of passes by it over the soil.
Why dry density is used and not bulk density in assessing compaction of soil?
This question often arises when discussing compaction. The answer to this is that the bulk density depends upon the moisture content. With varying moisture content, the bulk density varies. However, the dry density is calculated for the moisture content corresponding to zero. Thus, dry density becomes a more reliable factor for assessing the degree of compaction.
Quality Checks for Excavation-
- Checking of centerline and gridlines.
- Level to be taken of NGL with required precision and accuracy.
- Level to be taken of the excavated area.
- Density at designed depth should be checked. If found inadequate, the area is to be further excavated and backfilled by suitable backfilling material and compacted.
- Dressing of excavated area especially of edges and corners as per drawing.
Quality Checks for Filling-
- Centerline checking and marking of the area to be filled.
- Levels to be taken off the initial ground.
- Checking of the suitability of the material to be filled.
- Filling of material in 150-200mm layers.
- Watering of material to provide Optimum Moisture Content (OMC).
- Compaction by means of rammer or mechanical equipment.
- Check for density.
Earthworks Equipment for Excavation & Filling-
Manual- The manual tools are used for small scale earthworks like houses, agriculture purposes, etc. It includes spade, hoe, shovel, pickaxe, mattock, and rammer
Mechanical Equipment- The mechanical equipment are used for medium to large scale earthworks. They require more capital expenditure and maintenance. It includes excavator, backhoe, dragline, trenchers, bulldozer, and compactor
Manual Tools for Excavation Work-
Spade- Spade is a pushing type tool with a sharp-edged metal plate and a long wooden handle. It is used for digging small pits.
Hoe- Hoe is a pulling type tool with a sharp-edged metal plate and a long wooden handle. Used for mainly agricultural purpose.
Shovel- It is similar to spade with blade sides upturned. It is suitable for picking up the soil.
Pick Axe- It is a T-shaped tool with a metal head and wooden handle. Used for loosening hard soil.
Mattock- It is similar to pickaxe with the only difference being it has chisel and adze at the ends of the head.
Rammer– It is used to compact the soil. The rammer is generally used in small building construction.
Mechanical Equipment for Excavation Work-
Excavator- An excavator is a heavy construction equipment used mainly for excavation. It can be track mounted or tyre-mounted. It has boom, bucket, stick, and a rotating platform called “house”.
Backhoe- Backhoe is used for excavation. It has a digging bucket attached to a two-part arm mounted on the back of the shovel or tractor.
Dragline- Dragline is used for heavy excavation. It has a bucket attached by cables.
Trencher- Trencher is used for cutting trenches for pipelines, electrical cables, drainage etc.
Bulldozer- Bulldozer is used for pushing or dozing of soil. It can be used for spreading soil over an area.
Compactor- It is used for compacting the soil. It is available in many specifications such as sheet foot roller, pneumatic roller, steel drum roller and vibratory roller.
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