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the centres of the compaction the pres-ence of crushed stone in the sand subsoil does not appear to affect the results. Effectiveness of vibroflotation is usual-ly established by comparing the values of q_c before and after vibroflotation, mid-way between compactions which are usually 1,7 to 2,5 m apart on a grid or triangu-lar pattern.

CONCLUDING REMARKS.

To obviate over-conservative estiraates of bearing capacity and settlement of shal-Iow foundations, that often result from the use of the earlier methods of analy-sis, it has become necessary in South Africa, as also in other countries, to introduce modifications or reduction fac-tors into the basie classical eguations or, altematively, to employ the results of penetrometer tests in semi-empirical expressions for shear strength and córo-pressibility.

Furtherraore, to develop a high degree of confidence in the various methods of ana-lysis it is important that they be app-lied in a wide rangę of soil conditions in different locations and that the re-sulting estimates of settlements be cora-pared with actual settlements of fuli scalę structures or worka.

An essential step in the development of rational methods of analysis is thus standardization of penetrometers and of penetrometer testing procedures. Eąually important is standardization, and futurę development, in such a way that the inter-action between soil and apparatus is com-patible with fundamental compressibility and shear strength theory.

ACKNOWLEDGEMENTS.

Valuable assistance from the following persons is gratefully acknowledged.

F. HUGO of Bruinette, Kruger, Stoffberg and Hugo, Pretoria, for data on the inter-pretation of the dynamie cone penetrometer test results.

B.A. KANTEY of Kantey, Templer, Loteryroan and de Kroon, Cape Town, for data on the use of the Perth penetrometer.

H. WEBER and P. ALLEN of Technical Soil Surveys, a division of Frankipile South Africa (Pty.) Ltd., Johannesburg and Dur-ban respectively, for data on the use of the dynamie cone penetrometer.

R.R. MAUD and L.W. MOORE of D.L. Webb and Associates, Durban, for geological data and dimensions of penetrometers respec-tively.

Other acknowledgements are given in the text.

REFERENCES.

ALPAN, I., (1964). Estimating settlements of foundations on sands. Civil Engineering and Public Works Review, Vol. 59, No. 700, pp. 1415 - 1418.

BEGEMANN, H.K.S.P., (1963). The use of the static penetrometer in Holland. N.Z. Eng., Vol. 18(2), pp. 41 - 49.

BRITISH STEEL PIPING COMPANY LIMITED, (1954). Tables and technical information on pile driving operations. London, pp. 193 - 214.

BUISMAN, A.S.K., (1941). Grondmechanica (Nederlandsch-Indische Nooduitgave). Bandoengse Technische Hoogeschool, Fonds Kleijne, Bandoeng, p. 349.

CHELLIS, R.D., (1961). Pile Foundations. McGraw-Hill Inc., New York, Second Edi-tion. pp. 42 - 43.

DE BEER, E. and MARTENS, A., (1957). Method of coraputation of an upper limit for the influence of the heterogeneity of sand layers on the settlement of bridges. Proc. 4th Int. Conf. Soil Mechanics, London, Vol. 1. pp. 275 - 282.

DE BEER, F.E., (1945). The study of piled foundations and direct foundations. Annales des Travaux Publics en Belgique. (April, June, August).

DE BEER, F.E., (1948). Explanation of the resistance to shear deduced from penetrometer tests insitu.    Geotechnique

Vol. 1, No. 1 (June).

DE MELLO, V.F.B•, (1971). The standard penetration test. Proc. 4th Panamerican Conf. Soil Mechanics, San Juan, Puerto Rico, Vol. 1. pp. 1 - 86.

FLETCHER, G.F.A., (1965). Standard penetration test : Its uses and abuses. Journal of the Soil Mechanics and Foundation Division, ASCE, Vol. 91, No. SM 4, Part 1, Proc. Paper 4395, July. pp. 67 - 75.

GIBBS, H.J. and HOLTZ, W.G., (1957). Research on determining the density of sands by spoon penetration testing. Proc. 4th Int. Conf. Soil Mechanics, London, Vol. 1, pp. 35-39.

GLICK, B.E. and CLEGG, B.E., (1965). Use of a penetrometer for site investigation and compaction control at Perth, Western Australia. The Institute of Engineers, Australia, Civ41 Engineering Transactions, October.

HV0RSLEV, M.J., (1949). Subsurface ex-ploration and sampling of soils for civil engineering purposes. Waterways Experi-ment Station, Vicksburg, Miss.

KANTEY, B.A., (1951). Significant deve-lopments in subsurface explorations for