Before you dig a single trench, walk the plot and understand what is under your feet. Most Indian house plots sit on some mix of filled-up ground, murrum, sandy soil, clay or black-cotton soil, and each behaves differently once it gets wet or dries out. A trial pit dug to the expected founding depth tells you the actual strata, the water table and whether the soil is firm enough to trust, far better than guessing from the neighbour's house.
Safe bearing capacity, or SBC, is the load per square metre of soil that the ground can carry without excessive settlement, expressed in kN/m². It decides how wide your footing needs to be for the load coming down the column. On ordinary residential sites engineers often assume a value from a geotechnical report or from IS 1904 guidance, but on tricky soils like black-cotton or filled-up ground you should insist on an actual soil test rather than a table value.
Excavation safety is where many small sites cut corners and pay for it later. For depths beyond about 1.5 m, sides must be sloped, benched in steps, or shored with timber or sheet piling depending on soil type, and no one should work under an unsupported vertical cut. If water keeps seeping in, dewater with a sump and pump before laying PCC, and always inspect the pit bottom for soft or loose pockets, removing and replacing them with lean concrete or compacted murrum before you found the footing.
Shoring trigger depth
~1.5 m
SBC unit
kN/m²
Remember on site
- SBC in kN/m² decides footing size, and should come from a soil test on doubtful ground
- Slope, bench or shore excavations deeper than about 1.5 m to prevent collapse
- Never found a footing on loose or wet pockets; remove and replace before concreting
Check yourself
What does SBC stand for in foundation design?
In what unit is SBC normally expressed?
Why is a trial pit dug before finalising a foundation?
Which soil type most commonly requires special caution due to swelling and shrinking?
Beyond roughly what depth should excavation sides be sloped, benched or shored?
What should be done if a soft or loose pocket is found at the bottom of a footing excavation?
What is the main purpose of dewatering an excavation before laying PCC?
What is 'founding level' in foundation terminology?
Which method is NOT an accepted way to make a deep excavation safe?
Why should SBC not simply be copied from a neighbouring plot?
What is murrum, commonly seen in Indian excavations?
If the water table is encountered above the founding level during excavation, what is the first action?