Geotechnical Survey and Site Investigation

What is a geotechnical survey?

A geotechnical survey finds out what the ground under a structure is made of, how strong it is and where the water table sits, so that the foundation can be designed safely and without waste. Boreholes are drilled, the soil is tested in the hole with the Standard Penetration Test, samples go to a laboratory, and a geotechnical engineer turns the results into a report with bearing capacity, settlement checks and foundation advice.

In India the field work is planned around IS 1892:2021, the code of practice for subsurface investigation for foundations, now in its second revision. Many people call the whole exercise soil testing or soil investigation; the names overlap. A geotechnical survey is not the same as a topographic or land survey, which measures the surface, nor a geophysical survey, which reads the ground indirectly. For how those indirect methods compare, see the Mezux guide: Geophysical Survey Methods.

When should you order soil investigation?

Before the structural design is fixed, ideally before the land deal is closed. A poor soil found after the drawings are approved can mean deeper footings, piles or ground improvement, all of which change the budget. Typical triggers:

• Multi-storey buildings, hospitals, schools and group housing
• Industrial sheds with heavy floor loads, cranes or machine foundations
• Overhead water tanks, telecom towers and chimneys
• Retaining walls, basements and deep excavations near existing buildings
• Road embankments, culverts and small bridges

Buyers of land for warehouses, plants and townships increasingly ask for a few boreholes as part of a real estate due diligence survey, alongside boundary and utility checks, so that ground risk is priced in before purchase.

How many boreholes, and how deep?

Enough to show how the layers change across the footprint, and deep enough to pass below the zone the foundation will stress. IS 1892 ties depth of exploration to the size and type of foundation and the loads, and asks that drilling continue into rock far enough to prove it is bedrock rather than a boulder. For an ordinary building on isolated footings, a commonly used guide is at least one and a half times the footing width below founding level; heavy or piled structures go much deeper.

Borehole layout is agreed with your structural consultant. A small residential plot may need two or three holes; a factory shed of several acres needs a grid, with extra holes where columns are heaviest or where the land was once a pond or a dump.

What happens in the borehole?

Our crew drills with one of two company-owned rotary rigs, testing and sampling at set depth intervals as the hole advances.

• Standard Penetration Test (IS 2131): a 63.5 kg hammer falling 750 mm drives a split-spoon sampler 450 mm in three steps of 150 mm. The blows for the last 300 mm give the N value, the most widely used strength indicator for sands and stiff soils.
• Undisturbed samples: thin-walled tubes are pushed into clay layers and sealed, so the laboratory can test the soil close to its natural state.
• Disturbed samples: the split-spoon contents are bagged and labelled for classification tests.
• Rock coring: where rock is met, a core barrel recovers cores and the percentage of sound core is logged.
• Groundwater: the water level is recorded during drilling and again after it has had time to settle.

Which laboratory tests are usually done?

Tests are chosen to suit the soil and the structure; they are carried out in an NABL-accredited laboratory, mostly to the IS 2720 series of methods.

Table note: borehole numbers are often planned per unit of land; if your plot papers are in bigha or kanal, take a closer look at Land Area Converter to get the area in square metres.

How do Indian ground types change the investigation?

The same scope does not fit every region; the drilling depth, sampling and lab list follow the ground you are likely to meet. Four broad cases cover most of our work.

• River alluvium (Indo-Gangetic plains, including most of Delhi NCR): deep layers of silt, sand and clay, often with a shallow water table near rivers. SPT in sand, undisturbed samples in clay, and close attention to groundwater.
• Expansive black cotton soil (large parts of central and western India): clay that swells when wet and shrinks when dry. Free swell and related tests become essential, and the report deals with how deep the active zone runs.
• Hard rock and weathered rock (Aravalli, Deccan and peninsular areas): boreholes switch to coring early; the question is the depth of sound rock, not soil strength.
• Filled and reclaimed land (old ponds, low-lying plots, urban dumps): the fill is often loose and mixed. Holes are placed to find its edge and thickness, and settlement checks matter more than strength.

If you already have an old soil report for a neighbouring plot, send it; it helps us plan, though we never copy its numbers into yours.

Can scanning fill the gaps between boreholes?

Yes, partly. Boreholes tell you the truth at a point; scanning tells you how far that truth extends. On sites with old wells, soak pits or filled ponds, a radar sweep between holes can flag buried cavities and disturbed ground; see what we do: void detection. On a plot about to be drilled, a quick scan also keeps the rig away from buried cables and pipes, using the same equipment described in details on GPR scanning. Radar depth falls sharply in wet clay, so it supports drilling rather than replacing it.

What does the final report contain, and what does it cost?

Borehole logs, test results and a geotechnical engineer's recommendations for foundation type, depth and allowable bearing pressure. Bearing capacity of shallow foundations is worked out in line with IS 6403 and settlement in line with IS 8009, with notes on groundwater, chemical attack and, in higher seismic zones, liquefaction of loose saturated sand.

• Drilling with SPT: ₹1,500 per metre drilled
• Minimum: ₹1,00,000 per site
• Laboratory tests: charged per the test schedule agreed in the quote
• Example: four holes of 15 m make 60 m, or ₹90,000, so the ₹1,00,000 minimum applies; six holes of 20 m make 120 m, or ₹1,80,000, before lab tests

Rates exclude GST, and any mobilisation/travel cost for the rig, if applicable, is shown in the written quote. In Delhi NCR work can usually start the same day or within 1 working day; elsewhere in India our team member based in that city starts the site work immediately or within 1 working day. Laboratory work takes longer than drilling, so the quote states the report date. Share the plot location, building type and loads if known, and ask about your project.

Frequently asked questions

Is a geotechnical survey the same as soil testing?

Broadly, yes. Soil testing usually means the laboratory part; a geotechnical survey includes drilling, field tests, lab tests and the engineering report.

Do I need a level survey as well?

Usually. Borehole levels must be tied to the site levels so depths make sense on the drawings. See more about topographic survey.

Which laboratory tests the samples?

An NABL-accredited laboratory. The test list is agreed in the quote and charged per schedule.

Can you drill inside an existing factory?

Yes, where the rig can reach and the floor can be opened. We plan around shifts and scan the drilling points for buried services first.

What is an SPT N value?

The number of hammer blows needed to drive the sampler the last 300 mm of a 450 mm test. Higher numbers usually mean denser or stiffer soil.

Will the report give the safe bearing capacity?

Yes. The geotechnical engineer gives allowable bearing pressure and foundation depth for the structure described to us.

Written by Saniya Parveen · Technically reviewed by Rahul Rai · Updated 8 November 2026