Field investigations for a planned office building - Stjørdal

Measurements with a high-precision GPS.

Grey clay at the bottom.
In Norway (apart from that only in Canada, Russia, Sweden, Finland and Alaska), there exists "quick clay". This type of clay is a potential danger for builing houses or streets.
It was formed during the last glaciation and since it is rich in salt and water it has a rather open structure.
Due to rain water drainage, the salts can be washed out.
Then when undisturbed, the clay can still be stable. But as soon as being disturbed - even a soft blow by human hand would be enough - it will liquefy. Then huge landslides, which are not seldom in Norway, can happen.
The problem is that you can't see it with your naked eye if the clay is a quick clay.


Undisturbed soil sampling.


Vane testing to determine the undisturbed and remoulded shear strength.


These are 100 kg (!) on the metal rod. It was drilled into the ground by hand and the number of half-turns per 20 cm were counted.
From the university, we got steel-toe shoes for this.

Rotary weight sounding.

Test results.


CPTU (Cone Penetration Test with pore pressure measurements).





Clean water. The clay and sand look grey here.



The area is very much close to the Trondheimsfjord. Some decades ago, a Dutch company pumped up material (mainly sand) from the sea to connect the former island with the mainland. To be able to level the newly won land, a dam out of rocks was built.
Now, the aim of the field investigations is to find out how this material and also the original mass (incudes a lot of clay) below it is structured (homo-/ heterogeous,...) and how firm it is.