Why Does a Soil Checklist Matter When Buying Factory Land?

A soil checklist before buying factory land is a list of site and soil-profile checks that investors should complete before signing the contract. Industrial factories carry heavy structural loads (machinery, goods, multi-storey buildings) and need level ground for logistics, so skipping soil checks before purchase is high-risk. (The same principle applies to ordinary vacant land — see Should you do soil boring before buying vacant land?):

Soil investigation on a factory construction site in Rayong Province
Soil investigation on a factory project site in Rayong Province, before foundation design began (Photo: SPN Soil Engineering)
⚠️ Risks commonly seen in practice

In practice, factories that buy land without checking the soil first often run into problems like these: thick soft soil found after construction starts, so piles must be lengthened and the foundation budget ends up far above the estimate; or land that used to be a swamp or old rice paddy with a high water table, causing the factory floor to settle or sink within a few years of operation and forcing a production shutdown for repairs. The damage in such cases is usually many times the cost of a soil investigation, depending on the size of the factory and the severity of the soil problem.

What Is on the 12-Point Checklist Before Buying Factory Land?

The 12-point checklist covers everything from the site's history to a soil investigation before the contract is signed. The table below summarizes each item, with the risk if skipped and how to manage it:

Before the table, the figure below shows that many of the risks on this list lie "below the ground surface", invisible when walking the land. The numbers in the figure match the items in the table.

3D model of the subsurface risks to check before buying land for a factory 3D view of land for a factory, cut away to show the soil layers on the front and right faces. The planned factory is shown as a transparent building. The numbers match the checklist items: item 1, the front cut face shows an old pond or rice paddy filled over beneath the factory location; item 2, a shallow groundwater level near the surface; item 8, a fill pad at the back left filled to uneven heights that requires compaction; item 9, the right cut face shows old foundations and an underground pipe with pipeline markers at the surface; item 10, the highest historical flood line on the building wall; and item 12, a soil boring rig drilling the first borehole, with flags marking two more borehole locations, two to three holes in total before signing. Below are soft clay, stiff clay and dense sand. Depths in the figure are compressed. 3D model — subsurface risks invisible from the surface Not to scale 10 m 20 m Uneven fill pad Cut & fill + compaction 8 Boring: 2–3 holes before signing 12 Highest past flood level vs. factory floor level 10 Old footings / buried pipes Removal cost · keep off pipes 9 High GWL near surface 2 Former pond / paddy Thick soft soil, loose fill 1 Numbers match checklist items · depth not to scale
3D model — subsurface risks of factory land. The numbers match the checklist items: item 1, a filled-over old pond or rice paddy; item 2, shallow groundwater; item 8, an uneven fill pad; item 9, old foundations and underground pipelines; item 10, the highest historical flood level compared with the factory floor; and item 12, soil boring of 2–3 holes before signing the contract (depths compressed).

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12-point checklist before buying land for a factory
No. What to check Risk if skipped How to manage it
1. Past land use Whether it was a rice paddy, swamp or pond that was recently filled, an old factory, or contains waste or rubble fill Thick soft soil, loose fill, or contamination and buried debris Review Google Earth Historical Images and ask local residents — for former factory sites see the environmental and soil contamination assessment service
2. Groundwater level Depth of groundwater below the surface and its seasonal variation Groundwater shallower than 1.5 m below the surface makes construction difficult and expensive, especially with a basement or pit Measure the water level in the boreholes and check the area's flood history
3. Preliminary soil characteristics (hand auger) Surface soil type (sand / clay / gravelly), uncompacted fill, abnormal odor or color Missing loose fill or signs of chemical contamination that are invisible from the surface Hand auger boring to 2-3 m to check the surface soil (contact us for a free quotation within 24 hrs)
4. Earthquakes and faults Which seismic zone the site is in and whether there are active faults nearby Structure not designed for seismic loads, especially in the North and West Use earthquake-resistant building design if the site is in a risk zone
5. Zoning and local regulations Zoning color (purple = industry and warehousing, purple with white hatching = warehousing), FAR/BCR, building height, setbacks You buy the land but cannot build a factory, or cannot use the full area as planned Check the comprehensive town plan with the local authority before paying a deposit
6. Access and utilities Roads that can take trucks, 3-phase power, piped water, wastewater treatment You must invest in utilities yourself, adding a large chunk to the capital budget Check with the local electricity and waterworks authorities before deciding
7. EIA requirements Factory type (petrochemical, large-scale food processing) and proximity to water sources or forest reserves Project delayed by several months, plus extra report preparation costs Check EIA conditions with the Ministry of Natural Resources and Environment before buying
8. Cut & fill volume Whether the site is level, and the volumes of soil to cut and fill With a lot of fill, the cost of fill material and compaction rises sharply Survey the site levels, then estimate the fill volume + compaction cost
9. Existing underground structures Old foundations, oil/gas pipelines, underground high-voltage cables, tunnels, old signboard foundations Runaway demolition costs, or building over hazardous pipelines Scan below the ground with GPR (Ground Penetrating Radar)
10. Flood risk Historical flood data for the area, the highest flood level recorded, drainage system Production stops and machinery is damaged when flooding occurs Have the design engineer set the factory floor level against the highest historical flood level
11. Location and neighbors Proximity to industrial estates, labor sources, ports/transport and neighboring businesses High logistics costs, or pollution/noise problems from neighbors Compare with sites near industrial estates that have ready utilities
12. Preliminary Soil Investigation Soft soil thickness, depth to dense sand (bearing layer), fill quality, contamination Foundation costs escalate after purchase, with no bargaining power on price Soil boring of 2-3 holes before signing the contract — see SPN's soil investigation service

Which Item on the Checklist Matters Most?

The most important item is item 12 — preliminary soil investigation before signing the contract, because it is the only item that reveals the actual soil profile beneath the site. A preliminary investigation of 2-3 boreholes (cost depends on the number of holes, depth and site area — contact us for a free quotation within 24 hrs) before buying high-value land is the best-value investment on the entire checklist — compare soil boring requirements for factories and houses in How soil boring for warehouses/factories differs from houses

💰 ROI of a preliminary investigation

The cost of checking the soil before purchase is a very small fraction of the land value and the factory's foundation budget. If problems are found, you can use the boring results to negotiate the price down, or walk away from the plot in time, before signing the contract.

Which Soil Results Mean Buy, and Which Mean Don't Buy?

Decision criteria based on soil results are a guide for turning soil investigation findings into a decision to buy, negotiate or walk away, based mainly on the thickness of the soft soil layer and contamination:

Reading soil boring results to decide on buying factory land: the thicker the soft soil, the longer the piles Comparison of five soil profiles following the criteria in the article, from left to right: sand or stiff soil from near the surface; soft soil less than 5 meters thick; soft soil 5 to 12 meters thick; soft soil 12 to 20 meters thick; and soft soil more than 20 meters thick. Each profile has piles that must reach the firm stratum below the soft soil, so they get longer as the soft soil thickens. Below each column, the relative foundation cost is shown as one to four coins, along with the decision guidance: buy, buy, negotiate the price, think carefully, and compare with other plots first. Pile lengths in the figure are relative, not design values. What boring tells you before buying — thicker soft soil, longer piles Not to scale 0 5 10 15 20 25 30 Depth (m) Sand / stiff soil ฿ Buy Soft soil < 5 m ฿ Buy Soft soil 5–12 m ฿ ฿ Negotiate Soft soil 12–20 m ฿ ฿ ฿ Think twice Soft soil > 20 m ฿ ฿ ฿ ฿ Compare plots Fdn. cost Soft clay Stiff clay Dense sand Soft layer thickness Relative pile length, not design values · engineer must assess from actual borings
Comparison following the criteria in the table below — the thicker the soft soil, the longer the piles must be to reach the firm stratum, so foundation costs rise accordingly (the number of coins is a relative level, not a price, and the pile lengths are not design values).

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Land purchase decision criteria based on soil investigation results
ResultDecisionBudget impact
Sand / stiff soil, good bearing✅ BuyNormal foundations
Soft soil less than 5 m thick✅ BuyPiles not very long
Soft soil 5-12 m thick⚠️ Negotiate the priceLonger piles, higher foundation cost
Soft soil 12-20 m thick⚠️ Think carefullyMuch higher foundation cost
Soft soil more than 20 m thick⚠️ Compare with other plots firstVery high foundation cost; assess cost-effectiveness
Chemically contaminated soil❌ Do not buyVery high remediation cost

The criteria in the table are a preliminary screening guide based on SPT N-values and soil bearing capacity. The actual foundation system and budget must be assessed by the design engineer from the boring results for that plot — read how to interpret them in Interpreting SPT N-values and What is soil bearing capacity?

Which Industrial Zones Need Extra Care with Soil?

The areas that need extra care are industrial zones with distinctive soil profiles that directly affect foundation costs, namely:

  • Industrial estates in Samut Prakan, Bang Pu: thick soft clay; piles usually have to reach a deep firm stratum (read more on Bangkok soft clay and foundation design)
  • Eastern outskirts, Chachoengsao, Prachin Buri: former rice paddies with pockets of soft soil
  • Rayong, Map Ta Phut: near the sea, high groundwater
  • The West, Ratchaburi, Kanchanaburi: rock near the surface, which may need blasting first

Summary

Going through the 12-point checklist before buying land for a factory costs only a small fraction of the land value but helps prevent runaway foundation costs. The most important step is a preliminary soil investigation before signing the contract, so you know the actual soil conditions and have bargaining power on price.

SPN Soil Engineering provides due diligence soil investigation for investors who want to make land purchase decisions with confidence, completed quickly within 1-2 weeks. Contact 064-746-9601