Depending on the stability of the ground, a CPT is often necessary in order to be able to make a good structural calculation for the materials of the foundation and the floors. For the construction of a new house or for an extension, the municipality often not only asks for a calculation, but also for information about the land on which the house or extension will be placed. This is often necessary, because not all soil in the Netherlands is stable and clean enough to put an ordinary foundation and build on it. The soil in Friesland, for example, has a completely different composition than the soil in South Limburg or in the Randstad. You as the owner will especially benefit if your purchased land is clean and sturdy enough to build your home on.
Two types of soil investigation via CPTs
Nowadays, CPTs are no longer just about the solidity of the soil in order to be able to set up a building responsibly, but also the environment must often be examined. Much of the land in the Netherlands is polluted by former companies, agricultural poisons, asbestos or landfills of all kinds.
The soil mechanical research for the construction of a house
This involves examining whether the ground on which the building will be built is solid enough to support the construction. In this way, the owner has the greatest certainty about the strength of the soil and the municipality tries to prevent any complaints and damage claims, because in the case of less load-bearing soil, cracks can later appear in the floor and / or the walls of the building. .
An unexpected, hard layer of clay
Sometimes there is, for example, a hard clay layer at a depth of a meter that does not let water through. With a lot of rainfall, the water remains on it and a building can suffer from a lot of moisture later on. There are more problems to mention.
Example: an earlier stream bed
Consider, for example, a stream that has changed a lot in earlier times. In places where that stream used to run, gravel deposits or other sediments may have a less strong substrate. Sometimes it even has to be built on piles. The soil of meandering rivers, such as the Maas, silted harbors, or places where a swamp used to be, can also have less load-bearing soil.
A CPT report is often required for a permit application
Municipalities usually request a report of a soil mechanical investigation for a permit application for a building with a size of approximately fifty square meters. Sometimes also for a smaller building or extension. This becomes important when it is known that in certain places within the municipality there is less robust soil.
Environmental-technical research is increasingly necessary
The second type of CPT is an environmental-technical investigation, in which it is investigated whether the soil is contaminated or not. This contamination can involve all kinds of potentially hazardous substances. This investigation must therefore be carried out carefully by a recognized company. Both studies are very different. Not only in the type of research, but also in the costs thereof.
The tower of the basilica in Leuven
In principle, the tower of the basilica in Leuven should have been much higher than it is now. However, as the builders got higher and higher, the tower began to sag. After an investigation it turned out that the small river that flows through Leuven used to run at the site of the tower’s construction. The ground consisted of less solid material and so the tower was no longer allowed to be so high. That is why there is now a lower, different tower on top of the church than was ever planned.
Soil investigation by hand probing
The soil investigation is done by drilling in the soil, whereby the resistance of the soil can be measured during drilling. The strength of the soil is determined by this resistance. The drilling for an extension can often be done by a constructor who must have the right equipment for it. Drilling is done in a few places to see if the strength of the soil applies to the entire extension.
The constructor can often do manual probing himself
A bar is pressed into the ground to determine how much resistance the ground offers. Usually only one meter deep is drilled. At most two meters, but for the simple equipment of one-hand probing that is actually a bit difficult. However, a soil investigation by hand probing is not expensive.
Soil investigation through geotechnics
For new houses with a ground area of fifty square meters or more, the help of a company is usually enlisted. Geotechnical companies often have drilling rigs with a much greater power, allowing them to conduct research at greater depth. These drilling trolleys drill 15 to 20 meters deep (if necessary even deeper) and can thus determine whether a house can be built on ordinary foundations or not.
When can unstable soil become dangerous
If the ground is very unstable, the company also has to drill deeper, until it encounters firm ground. With less solid ground, the house must then be placed on piles driven deep into the ground (think of Amsterdam, for example) or, if possible, it must be completely built under the basement, down to the load-bearing ground, so that all bearing walls have a deep support. Of course, different standards apply to high-rise buildings, such as flats, and deeper drilling will also have to be done. The soil investigation via a company is of course more expensive than a manual probing. Logical, because different material must be used for that.
The environmental-technical soil investigation
An environmental-technical investigation is usually carried out in places where a company used to be, or where it is known that harmful substances have been used. This applies, for example, to a place where a garage has been located or where a demolition company, a petrol station, an interim storage of materials or similar companies have been located.
No hand probing in this case
In an environmental technical investigation, the help of a company is also called in. In principle, this research involves drilling three meters deep and using the drill to remove a sample from the ground. That soil sample is examined for contamination. The company mainly looks for toxic substances and materials that are unhealthy for humans, such as PAHs, cadmium, lead, zinc, and so on. If contamination is visible in the soil sample from that first drilling, drill deeper and in more places to clearly map the contamination. If it still contains pollutants, the soil must be excavated and replaced by fresh, clean soil. Otherwise no house may be built on it.
No pollution at great depth
In an environmental study, research is rarely done at greater depth, because no pollution can usually be found deeper than six meters.
Be on the safe side
Those who do not trust the soil or are not sure of the purity of the soil, would do well to be on the safe side. In addition, it is wise to inquire whether a soil investigation is necessary for the permit application.
The municipality can postpone the permit
After all, it slows down your building plans if you have received the advice from the contractor or constructor to have a soil investigation carried out, but do not comply and submit the permit application without that investigation. After four weeks or more, the permit application appears to have been refused due to the lack of the soil investigation.