6585844951

145

United Kingdom

3.2.4    Fine grained cohestoe soils

Although both the standard and static penetration tests have occasionally beon carriod out at dopth, there is litile published data of practical use. In the softer silty clay materiale, where static penetration tests have been mado, Begemann^łs (1969) mcthod is applied, although little work has yet been done to confirm its validity for U.K. soils.

3.2.5    Weak Rocks

S.P.T.'s have been carried out at depth in conjunction with piąte loading or pile tests. Other forms of in situ borohole tests are now, however, preferred for such correlation.

4.    FUTURĘ TRENDS

In the U.K., indirect methods of in-situ testing will not, in the foreseeable futurę, roplace boring and undisturbed sampling techniąues where these are possible. Novertholess, there is likcly to be much wider use of static penetrometer tests, particularly in fine grained non-cohesive soils.

In sands and silty sands, the prcsent method of "sheU" boring at depth below the water table llmits the usefulness of the S.P. T. (sce section 2.1, para. 4), particularly when carried out in large diamcter holes where the effects of disturbance are aggravated by ground water. Conseąuently, there should be a trend towards a wider use of static or static/dynamic penetrometer tests where these are possible.

In fine grained soils, a comblnation of continuous undisturbed sampling and penetration tests should find wider use for generał invostigation work. The Delft continuous sampler is particularly attractive because it is used with the static penetrometer apparatus, and at Borne sites may lead to greater economy in field work. However, in cohesivc soils, vano tests will continue to play a major role.

The use of the S. P.T. in weak rocks is likely to be phased out, in the near futurę, by the use of drilling methods that give high core recoveries, complcmented by borehole in-situ loading tests and also by piąte bearing tests carried out in pits above the water table.

Gravel8 will continue to present some uncertainties in investlgatlon as outlined in section 3.1.1, and the practise of carrying out piąte bearing tests is likely to gain wider acceptance.

Penetrometers in the U.K. are standardised on the

5. P.T. (Terzaghi and Peck, 1948) and the static penetrometers of Dutch origin. Other penetrometers have been used from time to timo, but have fallen into disuse largoly because they offered no advantage over the equipment presently used.

The introduction of the eiectrical static penetrometer is considered a significant step forward. The further development of this tool, and also the wider use of a

combination of continuous undisturbed sampling and static penetration tests, should bring about the morę significant advances of the next few years in penetrometer testing.

5. REFERENCES

BAZAR AA, A.R.S., 1967. Use of the S. P.T. for estimating settlements of shallow foundations on sand. Thesi8 UnWersity Illinois, Urbana, Illinois, pp. 381.

BEGEMANN, H.K.S. Ph.,1969. The Dutch Static Penetration Test with the Adhesion Jacket Cone. Laboratorium voor Grondmechanica, Delft.

BROMS, B.B., 1966. Methods of calculating the ultima te bearing capacity of piles. Sols - Soils,

No. 18-19.

DE BEER. E.E. and MARTENS, A., 1957. Method of computation of an upper limit for the influence of the heterogenity of sand layers on the settlement of bridges. Proc. 4th. Int. Conf. Soil Mech. and Found. Eng. Londcn

DE RU1TER, J., 1971. Electric penetrometer for 8ite inve8tigation. Journal Soil Mech. and Found. Div., Proc. Am. Soc. Civil Engrs., Vol. 27,

Ko. SM2, p. 457 - 472.

GIBBS, H.J. and HOLTZ, W.G., 1957. Research on determining density of sands by spoon penetration testing. Proc. 4th Int. Conf. Soil Mech. and Found. Eng. London, Vol. I, p. 35 - 39.

HEIJNEN, W.J., 1973. The Dutch Cone test. Study of the shape of the electric cone. Proc. 8th Int. Conf. Soil Mech. & Found. Eng., Moscow, Vol. 1.1 1/27, p. 181 - 184.

LAKĘ, L.M. and SIMONS, N.E., 1970. Investigations into the engineering properties of Chalk at Welford, Theale, Berkshire. Proc. Conf. In-situ investigations in soils and rocks, London.

MARS LAND, A., 1974. Comparison of the results from static penetration tests and large scalę in-situ piąte tests in London Clay. Proc. European Symp. on Penetration Tost Ing, Stockholm.

MEIGH, A.C., 1964. Discussion on paper by

Sutherland (1963). Proc. Institution of Structural Engineers, Vol. 42, No. 2, p. 55.

MEIGH, A.C. and NDCON, I.K., 1961. A comparison of in-situ tests for granular soils. Proc. 5th Int. Conf. Soil Mech. and Found. Eng., Paris, Vol. 1, p. 499.

MEIGH, A.C. andCORBETT, B.O., 1970. A

comparison of in-situ measurements in a soft clay with laboratory tests, and the settlement of oll tanks. Conf. on in-situ lnvestlgations In soils and rocks, London, p. 173.