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Penetration testing in Norway    esopt

K. Senneset    State-of-the-art report

This state-of-the-art report is divided into five main parts treating (1) geolog-ical characteristics (2) penetrometer tests,practice in Norway (3) interpreta-tion and evaluation of test results

(4)    aspects concerning futurę development of testing eąuipment and methods and

(5)    standardization.

1. INTRODUCTION -

GEOLOGICAL CHARACTERISTICS

Three ąuarters of Norway*s total area is mountains and areas unfit for cultivation. The reraaining part is areas along the coast and fiords, in the midlands and vallys in the south-eastern part of the country. And in this lower areas we do have nearly the whole population and our geotechnical problems due to soft clay and quick clay deposits.

The geological history of this deposits goes back to the last glacial epoch. Norway was then covered by enormous ice-masses. At the end of this period the land was forced several hundred meters below the level of to-day. The movement of the glaciers scoured the rock and pushed all loose materials towards the edge of the glaciers. The melting of ice caused the glaciers to withdraw and the loose materials was deposited in the sea. At the same time there took place a land-elevation. The heave in the middle and Southern parts of Norway has been as much as 180-220 m above the sea level of to-day.

Since the glacial epoch most of the clay deposits is Consolidated under its own weight. Different changes in climate and other conditions have caused a trans-formation of the top layers. We will usually find an upper crust of.weathered clay with thickness 2 to 5 meters. The majority of the glacial clays have been subjected to a leaching by fresh water due to the land elevation. The effect of the leaching is an essential change in the fundaraental properties of the clays. The result of this processes is that former relatively horaogeneous deposits especially clay deposits, to-day may exhibit a depth-profile with great varia-tions in the geotechnical conditions.

The thickness of clay deposits varies with depth to bedrock. Great variation may occur within the same area. Clay deposits of thickness 100 m is not un-usual.

Especially the deposits of very soft clay have caused great difficulties in connec-tion with different building activities, suddenly occurring slides and so on. The necessity of knowing something of the underground conditions, has led to what we can describe as geotechnical explora-tion early in our history.

As far back as in 1736 we know that a "geotechnical" surveying was madę in an area near the river Glomma. 10-12 meter long rods was forced into the ground.

The commission of 3 officers character-ized the ground conditions from the re-sistance of forcing down the rods. They also used the term "quick clay" in their description. In 1838 extensive sound-ings was carried out in Dramraen to find the soft clay deposits, especially along the river bank. In 1893 the Verdalen valley was the scene of a catastrophic quich-clay slide which claimed 112 lives as well as great values. As a conse-quence of this slide, an extensive drilling program was carried out in pre-sumed menaced localities in the Trtfndelag district. The equipment used (wash boring) had a capacity for sounding to a depth of 100 meters in clay. The geo-logists was aware of the phenomena "quick clay" and tried to find the loca-tion of such clays.

In the beginning of this century many complicated geotechnical problems occurred both in Sweden and Norway. The Swedish railways was hit by several catastrophic slides. The building of the first subway in Oslo 1912-1U result-ed in many problems and valuable experi-ences. Probably as a consequence, the first geotechnical office in Norway was organized in 1922, connected to the Norwegian State Railways. What we know of our "geotechnical history" indicates that the problems were mainly combined with the soft clay deposits. Consequent-ly, this fact has characterized the appliance and development of geotechnical equipment in Norway. Besides, the equipment used in Norway have mainly been of the same type as in Sweden.

Only clay deposits are mentioned so far, but as a matter of course the ice re-gression al60 left behind deposits of silt, sand, gravel and morain. And due to the land heave and river activities, we may find these deposits in combina-tion with clay deposits. Layers of sand or gravel with variable thickness may cover soft clay deposits. This coraplex-ity of the soil conditions makes it necessary also to apply different geotechnical equipment to obtain a trusty soil exploration.

The Continental theli

The geotechnical activity on the Norwegian Continental shelf is increasing.

The futurę soil exploration in connec-tion with heavy sea bottom constructions, is a challenge also to the Norwegian geotechnical expertice. The unusual difficulties of this soil exploration is not only due to the depth of sea,but also due to special geological conditions. This concerns the present soil exploration in the North Sea as well as the futurę geotechnical works in the northern part of our Continental shelf.