Soil types: The importance of what lies beneath ground level

To the naked eye, it may seem as though the bulk of a building is in the sky. However, for anyone who has an ounce of knowledge of construction, the real work occurs underground.

In fact, the real work begins long before a trench has even been dug. There’s a reason why large projects can be subjected to ground tests lasting months on end – the soil is one of the most important factors. While all soil might “look” the same, upon closer inspection there are several types around and each reacts differently to construction work.

It means that the job of the engineer at the start of the project is one of the most crucial around. The likes of V. Reddy Kancharla will spend considerable time analyzing the type of soil on a site, which can then be used to determine what method of construction is required.

Bearing this in mind, we’re going to take a look at some of the most common soil types to highlight the different needs that different sites have. Here are the most common types that you’ll find around the country.


We’ll start with a type of soil that will be seen on a lot of sites, but one which is subjected to a lot of change. This is a type that is highly susceptible to water. If there’s a high-water table, it can expand. If the ground is dry on the other hand, the clay will sink.

All of this means that the foundations can move considerably, particularly if the local weather is volatile.

It means that the engineer has to take a lot of considerations into account when he plans construction on such a site. He will generally have to make allowances for the first 1.2m of the soil, as this is subject to the most movement. As such, foundations are usually deeper than this level although if there are other factors to take into account which could impact the water table, it’s not unheard of for the depths to surpass 3m.

Filled ground

Next on the list is something that isn’t strictly an “official” type of soil – but it will be found on numerous sites around the country. If ground has been excavated in the past, before being filled, it is rarely suitable to dig foundations on. This is because there’s little consistency and the chances of movement are just too high.

In these cases, the engineer will most likely recommend that the foundations are dug beneath the filled ground – which can make for an expensive project.

Gravel and sand

If the soil resembles gravel and sand, most engineers will recommend that the foundations are kept as high as possible. Most recommend that the foundations are around 700mm in depth.

Sand is something that has been found to react favorably to water and should stay intact if it becomes damp. The only downside is that during the construction of the foundations, the sand can cave in and this is where some added support might be required until the concrete is poured.

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