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Sweden

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Fig. 4

Sketch showing a sequence of strata which often arises in smali depressions under the influence of a subsiding water level (land upheaval).

water, provided the water was calm. In the normal layer sequence (Fig. 4) the rock and the till are overlain by clay, by sand and gravel and by clay. The sand and gravel were deposited when the waves washed the upprotected shoreline in the vici ni ty. The clay at the surface has generałly been deposited in shallow coves where the water was calm. Its organie content is frequently high. "Gyttja" is a highly organie soli. Outwashed gravel which often occurs below a till slope can easily be mis-taken for gravelly till (false till).

The postglacial clay immediately above the older glacial clay has been deposited under morę irre-gular conditions, e.g. rapid changes in directions of currents. Thus, the postglacial clays often contain layers of fine sand or silt.

In the northern part of Sweden thick non-stratified sediments, sil ty clays, were deposited in the calm water at some distance from the mouths of the rivers. These sil ty clays have a black colour due to content of iron sulphide (FeS) and are locally known as ^usvartmocka" (black clay). This type of soli can be found in layers up to ten metres 1n thickness. They cause special foun-dation problems.

The dlstribution of the glacial and postglacial clays in Sweden is shown in Fig. 3c.

Pęąt

Peat including "gyttja" covers approximately 202 of the total area of Sweden. Peat is partlcularly common in Norrland (see Fig. 3d) and in south-western Sweden w1th the exception of the Coastal zonę.

The thickness of the soli cover above rock in Sweden seldom exceeds 20 m and rock outerops occur frequently. However, there are important exceptions to this rule. Thick deposlts of clay, for example, can be found in the western part of

Sweden, in the vic1nity of Gothenburg, where deposlts with a total thickness of morę than 100 m have been observed. Also in the province Uppland (north of Stockholm) clay deposlts of about 100 m occur. The thickness of clay depo-sits is normally between 5 and 15 m.

The thickness of the glacial deposits varies with the topographical location. In the inner parts of Norrland in the north and in SkAne in the south 1t can be 10 to 20 m thick, whereas the thickness at other locations can be only a few metres or less.

Thick gravel, sand or silt deposits are only found in eskers or in delta deposits close to the highest coast linę. Silt deposits in Norrland can be morę than 50 m thick.

Special attention should be paid to the so called dry crust (weathered soi 1) located between the ground surface and the ground water 1evel. Its thickness varies between zero and several metres.

Ąnomalies

The false conclusion may be drawn from the descrlption given above that the soli conditions In Sweden generałly are regular. That Is not the case. For example isolated till lenses may appear in uniform sand or gravel layers or in clay as mentioned above or fluvial deposits may be found interbedded in till. In connection with the land upheaval, outwash and resedlmentation occurred, which in some places resulted in so called “double-bottomed lakes" as shown in Fig.4. The river valleys in the north of Sweden have generałly a characteristic layer sequence, caused by the ice regression and the foliowing land upheaval. The sequence conslsts from the bottom upwards of rock, till, gravel, sand,silt, clay, silt and sand. The surface sand and silt layers may exceed 10 and 20 m in thickness.Also peat can be found Interbedded in fluvial deposlts. In the v1ci ni ty of eskers one always should be observant sińce clay layers and iso-lated clay-filled depressions may be covered by gravel and sand.

PENETRATION TESTING IN SWE0EN

Notę:    Below the word "sounding" is used in the

same sense as "penetration testing".

Oeyelopments and standardization

The use of penetration testing began in Sweden at the end of the 19th century. At that time Steel rods, which were pushed or driven down, were used in order to get a rough idea of primarily the penetration depth for end-bearing piles. During 1914-1922 the Geotechnical Commission of the Swedish State Railways used penetration tests to determine the layer sequence in connection with an investigat1on of the stability of some railway embankments. The Commission emphaslzed in its finał report that the sounding methods used in Sweden up to that time were inexact. It was not possible to compa-