Foundation & Subsoil Check for Any Plot in India
Whether the ground swells, how firm the subsoil is, and what that does to your foundation cost — from national soil mapping, before you commission a survey.
What this tool tells you
Two questions decide what a foundation costs on a given plot: does the ground move, and is it firm enough to build on directly. This tool answers both from national soil mapping, before you commission a geotechnical survey.
It reads the soil in three engineering depth bands — topsoil (0–30 cm), the foundation zone (30–100 cm) and deep subsoil (100–200 cm) — because what matters is not the surface but the layer your footings actually sit in. Clay that thins with depth is harmless; clay that thickens through the footing zone is the expensive case.
The result names an expansive-soil risk, a firmness reading, an indicative footing type, an excavation difficulty and a rough cost premium over standard construction. Use it to compare plots and budget. Use a lab Free Swell Index (IS 2720 Pt 40) and a plate-load test (IS 6403) to design.
Frequently asked questions
My plot shows high clay percent. Is that bad?
Not on its own — and this is the most misread number in any soil report. What swells is not how much clay there is but which clay it is. Red lateritic soils across the Deccan often read 35–40% clay and are perfectly stable, because that clay is kaolinitic and barely moves. A black cotton soil at the same clay percent is montmorillonitic and moves a great deal. The tool leads with a risk verdict for exactly this reason.
What is clay activity?
Cation exchange capacity divided by clay content — a standard mineralogy indicator (compare Skempton’s activity, and USDA cation-exchange activity classes). Low values mean stable, kaolinitic clay. High values mean the smectite minerals that drive shrink–swell. It is why two plots with identical clay percent can carry very different foundation costs.
What is black cotton soil and why do builders worry about it?
Expansive clay swells when wet and shrinks when dry. That seasonal movement lifts and drops whatever sits on it, cracking plinth beams, compound walls and floor slabs a few monsoons after construction. The remedy is well understood — footings taken below the active zone, or soil replacement under the foundation — but it adds cost, which is worth knowing before you buy rather than after.
Can this replace a soil test?
No. This is a screening tool on a roughly 1 km model — the right scale for comparing plots and budgeting, not for designing a structure. The definitive expansive test is a lab Free Swell Index (IS 2720 Pt 40); safe bearing capacity needs a plate-load test or borehole (IS 6403, IS 1888).
Is “firm” the same as bearing capacity?
No. Firmness is a bulk-density proxy describing how dense the subsoil is — not a certified load. A safe bearing capacity in kN/m² only comes from a site test. Read firmness as a signal that standard footings are plausible, then confirm with a geotechnical engineer.
Why does excavation difficulty matter before I build?
Because it is real money that is invisible at purchase. Hard or rocky ground near the surface raises the cost of foundation trenches, sumps, septic tanks, borewells and cable runs. On shallow soil over granite — common across the Deccan — rock breaking adds materially to the substructure bill.
Where does the data come from?
Soil chemistry and texture by depth come from ISRIC SoilGrids v2.0 (250 m native, CC BY 4.0). Soil type, taxonomy, parent material and drainage come from the ICAR-NBSS&LUP BHOOMI 1:250,000 soil map, the authoritative Indian classification. The soil type is a survey product; the chemistry is a model, which is why the confidence note asks you to validate locally.