The Swedish National Road and Transport Research Institute has for a number of years been developing a special device in order to measure continually and automatically frost depth, frost heave and groundwater level. The device is constructed like a rod and consists mainly of three parts – Soil anchor, intermediate part and upper part (hat).
Mounting
When mounting, a hole to a depth of approx. 4.6 m is drilled. The soil anchor is anchored in the bottom of the hole, the intermediate part is threaded on to the anchor, and finally the hat is connected to the intermediate part. The hat is equipped with a horizontal plate, which makes it heave in the same extent as the pavement surface. The hat and the anchor are telescopically mounted in the intermediate part.
Frost heave
During frost heave, the hat first heaves in relation to the intermediate part. At larger frost depths the frozen soil catches hold of the intermediate part and heaves it in relation to the anchor. Both these relative movements are registered by means of position transmitters and are added when calculating the total heave. Moreover, there are thermometers and meters of groundwater along the hat and the intermediate part, on every fifth centimetre. However, the construction involves the formation of an interval without a meter, in the same extent as the hat heaves in relation to the intermediate part.
Measurements
Measurements are registered i.e. every hour by a computer at the roadside. The computer can be equipped with modem units for getting the data by telephone of data.