FAQ
Preparing the soil investigation
A soil investigation is the very first step if you’re planning to build. Still waiting for your building permit? No problem. You can already have your soil investigation carried out. It will give you highly valuable information about your plot.
First the soil investigation. Then the design.
Have you bought building land? Have the soil investigation carried out first. And pass the results on to your architect. Based on the findings of the soil investigation, your architect can adapt the design to your building site. Many architects already work with us in exactly this way: first the soil investigation. Then the design.
Or do you prefer to wait until your building permit is approved? That is a possibility too. However, test results may sometimes show that the soil is not suitable for the design. Unless you invest in much more expensive foundations than planned. Ordering the investigation later may therefore affect both your budget and your schedule.
With a soil investigation, you can estimate your budget more accurately in advance. In doing so, you may avoid unexpected extra costs during construction.
With a soil investigation, you can determine the necessary foundations in advance. Any additional foundation works will always delay the planning. Always
Order your soil investigation before buying a plot
It’s even a good idea to call us before you buy the land. This way, you avoid paying too much for a plot that requires costly foundation works. Read more about why a soil investigation is always a smart idea.
There are three good reasons to perform a soil investigation.
You’ll know exactly which foundations are needed. Even in ‘weak’ soil.
You avoid unexpected extra costs during construction.
You won’t overpay for your building land.
Have you bought building land? Congratulations! But sometimes the soil turns out not to be very load-bearing. People often call this “weak” or “poor” ground. Soil that is rather unsuitable to build on. That’s exactly why a soil investigation is so useful. It tells you precisely how strong (or weak) your building land is. And it advises which foundations are required to make sure your house will stand firm for generations.
Yes, you can build on ‘weak’ soil Provided that you have the right foundations.
It is perfectly possible to build on “weak stuff”. On the condition that you build on the right type of foundations. This will be decided by your architect, based on the results of the geotechnical or soil investigation. Such a test reveals the load-bearing capacity of your building land. That way, you avoid cracks, damage, or even subsidence of your house.
You estimate your construction budget more accurately
A soil investigation allows you to estimate your budget more accurately in advance. The geotechnical or stability investigation advises you which type of foundations are required for your building land. It also tells you whether adding a basement is a smart option. Or not. Such choices will naturally affect the budget. And with a soil investigation you can better plan for them in advance.
You won’t overpay for a building land.
Have a soil investigation carried out before buying a building land. This is not as strange as it may sound. Because the investigation shows how load-bearing the subsurface really is. That way you immediately know whether standard, expensive, or very expensive foundations will be needed. Quite useful to know before signing, right? This information helps you negotiate the cost. And you will avoid paying too much for a building land that requires costly foundation works.
Any questions? Request a quote? Order? Do not hesitate to contact us.
A standard soil investigation consists of at least 3 cone penetration tests (CPTs). We perform these tests at different locations on your building land, so you get a complete picture of the bearing capacity of your land.
Three CPTs at different points on your building land actually give you a solid overview of possible variations in the different geological layers.
For larger buildings, such as apartment blocks or industrial buildings, the Belgian Building Research Institute (BBRI) recommends one CPT per 300 m².
Sometimes, during the investigation, it becomes clear that more than three cone penetration tests are required. In that case, our experienced technicians will contact you right away.
Any questions? Request a quote? Order? Do not hesitate to contact us.
The cost of a cone penetration test depends on three factors:
Number of tests
CPT applied force
Accessibility of the site
Request a quote. We will provide you with an exact price for your soil investigation. The more accurate the information you give us, the more precise our quote will be! If we are unsure which rig is best suited for your site, we will first come and inspect your building land.
Download the order form on the contact page.
Fill out the form completely. If some fields do not apply to you, simply leave them blank.
Email us the completed form.
Please note!
Only written orders will be included the schedule. It is not possible to place an order by phone.
Utility plans (KLIP request) must be obtained in advance
We really do need the following information
Map showing the location of the site
Plan of the building zone or placement of the building on the site
Can also be usefull
Photographs of the building land
Plans and cross-sections of the new construction
Conformation
After your written order is received, your investigation will be scheduled.
You will receive a confirmation email with the project number.
Order your ground investigation right now or request a personalized quote.
Conducting a soil investigation
Can we really perform CPTs on any site? At Advison, we pride ourselves on being able to handle virtually any terrain. We have the right equipment for every building site. Feel free to check out our different cone penetration rigs. If we’re not entirely sure which rig is best for your site, we’ll come and take a look at your building land beforehand.
The right CPT rig for every site
All our CPT rigs are specially designed by or for Advison. That way, we have a solution for every type of terrain.
Cone penetration in a meadow? Or vacant land In a basement? On a pontoon? Inside or behind your house? On a playground? In a forest?
Advison can handle any site.
Minimal impact on your building site
Besides, did you know that all our rigs are equipped loading ramps?
With the loading ramp, we can usually unload the rig directly on your site without damaging the pavement.
Do we have to go over the pavement? The rubber tracks ensure minimal damage to the pavement.
Are there underground utilities, such as gas or water pipes, at the site where the investigation is performed? Then caution is required. We always request accurate utility maps from the Cable and Pipeline Information Portal (KLIP) to ensure no gas or water accidents occur.
Sometimes it is not clear whether utilities are present under a site. This is why we always request for utility plans. For every CPT!
KLIP request = legally required in Flanders
In Flanders, requesting utility plans is mandatory for every sounding. This is called a KLIP request. We carry out such a KLIP request to prevent damage to public underground cables and pipes during the soil investigation and to avoid any hazardous situations.
Advison takes care of the KLIP request for you. Have you already requested utility plans yourself? Perfect! You can simply provide them to us.
Provide us with accurate information about private connections
The pipeline plans requested via KLIP only show public pipelines, not private connections. Branches leading to your house or property are therefore not included in the requested service connection plans.
However, private pipelines can also be damaged during the cone penetration tests, with all the unfortunate consequences that could result. It is therefore very important that you provide Advison with the most accurate information possible about the location of pipelines on your construction site.
Are you in doubt? Or do we doubt? Then we take all possible precautions to prevent damage. We will scan or excavate to locate pipelines.
Cone penetration tests are always carried out on unpaved ground. If the area is paved with tiles, concrete, or asphalt, we first make an opening through the hardened surface. You can do this yourself. Or Advison can do it for you. Please let us know when placing your order.
Cone penetration tests (CPT) must reach sufficient depth to provide meaningful results. This is why we perform the CPT with the following applied force:
100 kN (10 tons)
200 kN (20 tons)
up to 50 kN (5 tons)
100 kN (10 tons)
An applied force of 100 kN is usually used for standard residential buildings. The penetration cone is pushed into the soil until a total resistance of 100 kN is reached. The exact depth reached depends on the bearing capacity of the subsoil. The achieved depth therefore varies from building site to building site. In any case: the more difficult it is for the cone to penetrate the soil, the more load-bearing your building land is.
200 kN (20 tons)
An applied force of 200 kN is required:
If you are building a structure with more than two floors. Which means higher than a standard residential building.
If the soil is “soft” and a deep foundation is likely needed.
If very hard layers are present at shallow level.
The penetration cone is pushed into the soil until a total resistance of 200 kN is reached. The exact depth reached depends on the bearing capacity of the subsoil. The achieved depth therefore varies from building site to building site. In any case: the more difficult it is for the cone to penetrate the soil, the more load-bearing your building land is.
Tot 50 kN (5 tons)
Lighter tests up to 50 kN are only used if our cone rigs cannot access your site. In that case, we perform CPT with a light and portable device.
Results of the soil investigation
After each CPT, a hole remains on the site. In that CPT hole, Advison always measures the groundwater level. Such a groundwater measurement in the CPT hole is less reliable than a groundwater measurement in a piezometer. A measurement of the groundwater level in the CPT hole is therefore purely informative. Do you want exact and reliable information about the groundwater level? Have a piezometer installed.
Accurate groundwater measurement in a piezometer
Measuring groundwater in a piezometer is therefore the most reliable way to get information of the groundwater level. Installing a piezometer is not always necessary, but it is very accurate.
Limited accuracy in the CPT hole
After the CPT, a small hole with a 4 cm diameter remains in the ground: the unprotected CPT hole. Groundwater measurements in such an unprotected CPT hole are not very accurate. The groundwater level can in fact be estimated either too high or too low. Four factors determine the accuracy of the groundwater measurement in the unprotected CPT hole:
Rainfall
Soil type
Season
Relief and geology
Rainfall
During and just after wet periods, in times of persistent rain or thaw, for example, rainwater often seeps into the CPT holes. We then measure a higher water level than the actual groundwater level. If this occurs, we cannot distinguish between surface water and actual groundwater.
Soil type
Sometimes the groundwater level is also estimated lower than it really is. This occurs, for example, in loam and clay soils. These soil types are not very permeable, which means it takes a long time for the groundwater, after a CPT, to reach equilibrium again. Sandy soil, on the other hand, is more permeable. The groundwater here reaches equilibrium more quickly. Groundwater measurements in sandy soil are therefore generally more reliable.
Season
The groundwater measurement in the unprotected CPT hole is always a snapshot. The groundwater level fluctuates with the seasons. After summer, the groundwater is usually at its lowest, in the spring at its highest. Did you have the groundwater measured in a CPT hole in summer, but are you building in winter? Then the groundwater level can differ significantly. If you want to know the fluctuations in the groundwater level exactly and accurately, you need to install a piezometer and follow the groundwater level long enough.
Relief and geology
Sometimes relief or geology can disturb the groundwater measurement in the CPT hole. Contact one of our geologists for more information.
In summary: in the unprotected CPT hole, you can measure the groundwater level. But that information is less accurate. Would you like to know the exact and accurate fluctuations in the groundwater level? Then install a piezometer and monitor the groundwater level over a longer period.
You will receive a detailed report of each CPT in a CPT report. These reports are structured according to a fixed format. They always contain at least the following information:
Accurate plan
Graphical representation of the results
Tables with measurement values
Summary of the measured groundwater levels
Geological background information about the site
Interpretation of the measured resistances
Graphical representation of the interpretation
Clear foundation advice
Accurate plan
A cone penetration test is of no value if you do not know exactly where it was carried out. That is why our report always includes a clear plan showing the exact location of each test.
On smaller plots, we usually measure in relation to recognisable landmarks (plot boundaries, streets or facades). We then mark the tests on the plan provided by you or your architect.
On larger building sites, we measure the locations of the tests using GPS. The tests are then automatically plotted on a cadastral plan. This way there can be no discussion about the exact location of the tests.
Graphical representation of the results
We present the results of the CPTs in diagrams. These are drawn exactly according to internationally used standards. Namely: 1 m depth = 1 cm on paper = 2 MPa cone resistance. For building professionals, such as architects, contractors, or engineers, it is important that we respect these scales. This ensures that the results can be interpreted and compared unambiguously.
Tables with measurement values
Uiteraard vind je ook de gedetailleerde meetresultaten in tabelvorm It goes without saying that you will also find the detailed measurement results in table form in the report. We use SI units for this. So no kg/cm² or daN, but MN/m² or MPa. In a pdf report, however, these figures are not very convenient to use. Which is why we can also provide these results in Excel or in DOVxml, the standard format of the Flemish Subsoil Database (Databank Ondergrond Vlaanderen) (DOV)
Summary of the measured groundwater levels
We maken ook altijd een samenvatting van de gemeten grondwaterstanden in de sondeergaten en in de eventueel geplaatste peilbuis.
Geological background information about the site
Today, a great deal of information about the subsoil and its history can be found online. Before we interpret our own results, we compare them with various sources to increase the reliability of the interpretation.
We always first consult the Flemish Subsoil Database (DOV). This source quickly provides a fairly reliable summary of the different geological layers expected in the subsoil. When our measured results deviate from what is expected based on DOV, we continue our search.
Geopunt Flanders also contains a wealth of information about the history of your plot. It is therefore another source we often consult for additional insights.
If we have doubts, we also compare our measured results with other relevant projects we have previously carried out in the area. Our GIS database (Geographic Information System) now contains more than 25,000 projects.
Finally, we also have a number of highly specialized printed maps that are not available online.
Interpretation of the measured resistances
Based on the geological background information, we distinguish several layers in each CPT. Our experienced staff interpret the results fully manually. The interpretation is therefore consciously not carried out on the basis of automated software or AI (artificial intelligence). At present, automated software or AI is still insufficiently developed to take geological background information into account.
Graphical representation of the interpretation
Since a few colours provide more insight than a thousand numbers, we subsequently create an overview plot of all the CPTs. The different soil layers are coloured in, giving an immediate clear picture of the subsoil.
Clear foundation advice
Based on all of the above, we provide foundation advice regarding the type of foundation: classical strip foundations, a foundation slab, or a pile foundation. Advison also examines whether a basement is necessary. This information is important to prevent your building from cracking, splitting, or even sinking. Our advice for you is based solely on the CPTs we have conducted. It is not yet a foundation design. Your architect or engineering firm will produce a more detailed design.
Your architect takes care of the rest
Advison’s advice is guiding. Your architect or structural engineer will take it from there and design and calculate the final foundations. The architect will not only consider the results of the tests but also environmental factors, for example, an adjacent building.
Any questions about your CPT report? Feel free to call us. We will explain everything in detail. Or have your architect call us.