Services · Engineering · Site investigation
Site Investigation and Drilling: Soil Reports for Foundations
A site investigation gets to know the ground through boreholes, field tests and laboratory tests before the structure and foundations are designed. We run it with our drilling and laboratory partner and link the results directly to foundation and shoring decisions.
Who carries it out
Our drilling and laboratory partner
Field tests
SPT, sampling, coring
Laboratory
Classification, strength, settlement
Output
Geotechnical site investigation report
Use
Permits, design, quotes
Region
Türkiye and Central Asia
What is a site investigation?
A site investigation identifies the layers under a plot, the groundwater and the engineering properties of the ground. Our partner drills boreholes, carries out field tests and examines samples in the laboratory. All the results then come together in the geotechnical site investigation report.
The quality of the investigation sets the quality of every foundation and shoring decision. For example, a wrong soil parameter can make a pile longer than needed, or too short. That is why we do not see the investigation as just a document for the building permit.
When do you need a site investigation?
- At the permit and design stage of a new building
- Before deciding on piled foundations, shoring or ground improvement
- When a new building replaces an old one in urban regeneration
- When an existing building shows settlement and cracks
- When extra floors or a change of use will increase the load
How does a site investigation work?
We run the investigation in five steps. Our partner carries out the drilling and laboratory work, while we plan the programme and the use of the results together.
- Desk review: We look at the plot, the number of basement levels and the neighbouring buildings.
- Borehole plan: We set the number and depth of boreholes from the size of the building and the likely foundation system.
- Fieldwork: Our partner runs SPTs in the boreholes, takes samples and cores where needed, and measures groundwater.
- Laboratory: The samples go through classification, strength and settlement tests.
- Report: The report covers the layers, the parameters and the foundation recommendations.
The most common problem we see: boreholes that stop short of the planned excavation and pile depth. Nobody can make a sound foundation decision without seeing the layer the piles will sit in. So we recommend choosing borehole depth to suit the likely foundation system.
Site investigation tests: field and laboratory
In general, we choose the tests to suit the ground and the project. The table below shows the most common tests and what they are for.
| Test | What happens | What it is for |
|---|---|---|
| SPT | A 63.5 kg hammer falls 76 cm; the blow count for the last 30 cm is the N value | Density of sand and gravel, consistency of clay |
| Undisturbed sample (UD) | A sampler takes clayey soil out without disturbing it | Strength and settlement tests |
| Rock coring | A core barrel cuts a cylindrical sample from rock | Rock quality and strength |
| Groundwater measurement | The water level in the borehole | Excavation, shoring and cut-off decisions |
| Laboratory tests | Sieve, Atterberg limits, shear, consolidation | Soil class, strength and settlement |
| Geophysical survey | Wave velocities in the ground | Ground class for seismic design |
These data set the ground class for seismic design under TBDY 2018. The same data also show the liquefaction risk.
What should a site investigation report contain?
A good report contains not only test results but also the engineering recommendations that follow from them. So when you read a report, we suggest checking these headings.
- Borehole logs: layers, SPT values and sample depths
- Groundwater level and the date of measurement
- Laboratory results and design parameters
- Ground class under TBDY 2018 and a liquefaction assessment
- Recommended foundation system: raft, piles or ground improvement
- Recommendations for excavation and shoring
As the contractor, we also read the report alongside the pile and shoring decisions. For example, if the rock level is unclear in the report, we say from the start that the pile length will be unclear too.
What does the price of a site investigation depend on?
In short, drilled metres and the number of tests set the price. So first we look at the plot and the building, draw up the borehole plan and then quote.
- Number and depth of boreholes
- Ground and rock: the need for coring
- Number of field and laboratory tests
- The need for a geophysical survey
- Site access and mobilisation
What to send for a quote
- Plot location and zoning details
- Number of floors and basement levels
- Any concept architectural design
- Neighbouring buildings and site access
Frequently asked questions about site investigation
We have grouped the questions we receive by who asks them. If yours is not here, call us or write through the quote form.
Owners and urban regeneration
Is a site investigation mandatory in Türkiye?
Yes. Municipalities ask for a geotechnical site investigation report at the permit stage for new buildings. Urban regeneration projects also need one for the new building.
Who carries out the site investigation?
Our partner, a site investigation firm, carries out the drilling and laboratory work. We plan the programme together and link the results to foundation and shoring decisions.
How long does it take?
Fieldwork usually takes a few days; the laboratory work and report take a little longer. The number of boreholes and the test programme set the exact time.
Can we use the old building’s report for the new one?
Usually not, because old reports may not cover the loads and basement depth of the new building. The regulations have also changed since then.
Contractors and project managers
How many boreholes do we need?
The plot size, the building footprint and how much the ground varies set the number of boreholes. Even on a small plot, for example, more than one borehole shows whether the layers change.
How deep should the boreholes go?
Above all, each borehole should go deep enough to reach the layer that will carry the foundation load. So if piled foundations are likely, the boreholes need to go below the pile toes.
Can the results change the foundation system?
Yes, often. For example, rock deeper than expected makes piles longer, and high groundwater creates the need for a cut-off.
Designers and supervising engineers
What does the SPT value show?
The SPT value is the number of blows needed for 30 cm of penetration. It gives a rough idea of density in sand and consistency in clay. In design, however, you need corrected values.
When do you need a geophysical survey?
Seismic design needs the shear wave velocity to set the ground class. Therefore, a geophysical survey or correlations in the code must provide this value.
How do you assess liquefaction?
In loose, saturated sand and silt, for example, you calculate the safety against liquefaction from SPT or CPT data. Where there is a risk, the ground then needs improvement.
Academics and students
How does an SPT work?
A 63.5 kg hammer falls from 76 cm and drives the sampler 45 cm. The number of blows for the last 30 cm then gives the SPT N value.
What is the difference between disturbed and undisturbed samples?
An undisturbed sample keeps the soil’s structure and water, so it goes to strength and settlement tests. A disturbed sample, by contrast, is only good for classification.
Why does the ground class matter?
The ground class shows how much the ground will amplify shaking in an earthquake. So the seismic loads on a building depend directly on the ground class.
Sources
Request a quote for a site investigation
Send us the plot location and building details. We will prepare the borehole plan and the quote with our partner.