Geotechnical Methods

What is the composition, strength and load carrying capacity of the ground beneath our feet? To answer this, geotechnical investigations must be carried out.
Geotechnical drilling where there have been challenges with sealing the sheet piling walls. This excavation took place between the exit of the Festning tunnel in Oslo and where a culvert was being laid.

Geotechnical investigations are regularly performed before construction begins. These surveys determine the properties of geological materials - information that is important when planning new infrastructure.

In Norway, a large amount of geotechnical data is available. Over time, The NAtional DAtabase for Ground Investigations (NADAG) will provide increasingly more efficient access to data from past investigations.

In some areas, quick-clay mapping is essential for assessing the stability of the ground for construction projects. Here, vertical soundings that display constant or decreasing drilling resistance with depth, could indicate quick clay, while firmer clay is indicated by increasing resistance. To be certain of the presence of quick clay in the area of investigation, undisturbed samples must be extracted and tested in laboratory for their geotechnical properties.

The table below provides an overview of some common types of geotechnical survey methods performed by consulting companies.

Investigation type Description Information type

Cone Penetration Test Undrained (CPTU)

The rod system with a probe is continuously pushed into the subsurface, and values of cone resistance, friction and pore pressure are registered continuously.  Sediment stratification, soil type indication, mechanical soil parameters. 
Rotary Pressure Sounding The rod system with a purpose-made tip is forced into the subsurface with both rotation and static downward pressure. The rotation and penetration rate is constant.

Indicated sediment stratification, occasionally soil type and depth to bedrock (not verified).

Total Sounding Conventional Rotary Pressure Sounding combined with bedrock drilling, including rotation, ramming and flushing modes. Indicated sediment stratification, occasionally soil type and verified depth to bedrock.
Core sampling  Generally, a f54 mm piston sampler is used to give undisturbed samples in clays for subsequent laboratory testing.

Sediment stratification, shear strength, deformation properties, index properties, permeability.

Quick-clay hazard zones, NVE: