Foundation Construction [PDF]: Depth, Width, Layout, and Excavation

Concrete and Mortar Ratio for Foundation

• The cement concrete 1:8:16 is generally used in the foundation of walls in construction work.
• In the case of column raft cement concrete, 1:4:8 is the best-recommended ratio for it in the foundation.
• For brick masonry, cement mortar 1:4 to 1:6 is used as a loading condition.

In the case of column and raft footings up to plinth level, cement concrete 1:2:4 or1:1.5:3 are used.

Safe Bearing Capacity Soil

Dry coarse and well-graded dense sand have maximum shear resistance and maximum bearing capacity. In general, submerged soil and clay have less bearing capacity.

Foundation Excavation Precautions

The depth and width of the foundation should be according to structural design.

• The minimum depth of the foundation is 1 meter in case the design is not available.
• Check the length, width, and depth of excavation with the help of centerline and level marked on the marking pillars.
• Dump the excavated material/ earth at a distance of 1 meter from the edges.
• Start excavation work when the soil is dry.
• Arrange a water pump to pump out rainwater.
• Compact the bottom layer of the foundation.
• There should be no soft places in the foundation due to roots etc.
• Dugout any soft/ defective spots, and fill the excavated area with concrete/ hard material

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Demarcation/layout Procedure

The following procedure is recommended for the demarcation of a building:

1. Mark the baseline on the ground from the centerline of the road, or a permanent building nearby. This line helps to mark out the front of a building.
2. Use a side structure, road, first baseline, or plot boundary to mark side baselines of the building.
3. Fix temporary pegs at the centerline of walls/columns on both sides of walls and columns in front and backside.
4. Fix peg at the centerline of walls/columns on both sides of the walls and columns on the left and right side of the building front.
5. Check diagonals of the square or rectangle formed after fixing pegs.
6. Construct marking pillars with pegs at a distance of 1.5 meters to 2 meters, and plaster their top surface.
7. Mark center line on the top of marking pillars with the help of thread (Soot) or with the Theodolite in big projects and the diagonal, and check other dimensions.
8. Level marked pillars on all corners of the building.
9. Mark the foundation of walls/columns according to drawing on the ground with the help of centerline marked on the marking pillars.
10. Use chalk powder to mark the foundation trench on the ground.
11. Excavate the foundation of the walls /columns up to the required level, and check the excavation with the help of centerline and level marked pillars to avoid any complication later on.

Advantages Marking Pillars to Layout Buildings

• It saves time for measuring and setting the point again and again at the time of construction.
• It increases the efficiency of mason and foreman for doing their jobs.
• Accuracy can be checked at any time at any step.
• If any mistake is found, it can be easily be rectified at an early stage. It is very difficult to rectify the mistake later.
• Cross-check can be done by a senior engineer in minimum time.
• Qualitative work is maintained.

Disadvantages Construction Execution without Layout

At some sites of work the contractor brings steel pieces, erects the same on the ground, and start the work of excavation. In due course these steel pieces are just discarded. Thus no proper reference point is available while doing further jobs.

• It involves extra time for measuring the offset again and again.
• Accuracy can not be checked at an early stage and it will be very difficult to rectify the same in later stages.
• It involves wastage of time and money while doing rectification. This also leads to bad quality of work.

Equipment For Layout Setting

1. Leveling Instrument
2. Long Nails
3. Hammer
4. Right Angle
5. Steel Tape
6. Thin Cotton Thread
7. Bricks
8. Cement
9. Screen Sand
10. Lime Powder
11. Theodolite

FAQs on Foundation Constructions

What is the layout of the foundations?

Layout is a process of marking the location of foundation of new buildings on the ground.

What is the standard depth of foundations?

Standard depth of simple footing or foundation is 1.5m.

What are the factors influence the depth of foundations?

1. Adequate bearing capacity.
2. Frost penetration depth.
3. Groundwater table
4. Depth of shrinkage and swelling.
5. Nearby excavations.

What are the materials tools and equipment used in building layout?

1. Leveling Instrument
2. Long Nails
3. Hammer
4. Right Angle
5. Steel Tape
6. Thin Cotton Thread
7. Bricks
8. Cement
9. Screen Sand
10. Lime Powder
11. Theodolite

What are the benefits of the foundation layout?

• Saves time for measuring and setting the point again and again at the time of construction.
• Increases the efficiency of mason and foreman.
• Check accuracy at any time at any step.
• Rectify mistakes, if present, at an early stage.
• Cross-check can be done by a senior engineer in minimum time.
• Qualitative work is maintained.