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On the use of penetration tests and geophysical methods for mapping of quick clay deposits
Swedish Geotechnical Institute.
Swedish Geotechnical Institute.
2012 (English)In: Proceedings of the 4th International Conference on Geotechnical and Geophysical Site Characterization, Porto de Galinhas, Brazil, 18-21 September, 2012 / [ed] Coutinho, RQ, Mayne, PW, Leiden: CRC Press, 2012, Vol. 1, p. 743-748Conference paper, Published paper (Refereed)
Abstract [en]

The occurrence of quick clay has a large impact on the risks associated with slope stability and construction works. Even relatively small and superficial slides can then, for example, often develop into major landslides involving large areas. The existence of quick clay is confirmed by tests on samples brought into the laboratory or by field vane tests. However, these determinations are normally limited to a number of depths at certain points in an area. Additional information is therefore sought from penetration tests with continuous registration with depth and from area covering methods. Traditionally, occurrence of quick clay has been estimated from studies of the steepness of the curves for total penetration force versus depth obtained by different penetration tests. However, the total penetration force is the sum of tip resistance and friction against the sounding rods, where in clays the tip resistance is related to the undrained shear strength and the friction against the rods is related to the residual or remoulded shear strength. In cone penetration tests, CPTs, the tip resistance is measured and it is thereby possible to separate the two components if the total penetration force is measured as an additional parameter. A study of different penetration tests to estimate occurrence of quick clay has been performed, and CPTs with measurement of the total penetration force were found to be superior to the traditionally used penetration tests to establish occurrence and depth intervals of quick clay in the test points. The friction is also measured against the friction sleeve just above the tip, but the accuracy is generally too poor to yield relevant measures of the friction in highly sensitive clays. This resulted in a recommendation to use CPTs with additional continuous measurement of the total penetration force versus depth for this purpose, and the method is now used in large scale in practise. In western Sweden, the main cause for quick clay formation is leaching of salts in the marine clays, which also affects the resistivity of the soil. As a method to obtain more area covering information, the use of surface resistivity measurements was therefore tried in areas where quick clays had been found in geotechnical investigation points. The results in terms of indications of how far the leaching process had progressed in different parts were found to be consistent with the occurrence of quick clay and the method was proposed to be used as a supplement to the geotechnical investigation methods.

Place, publisher, year, edition, pages
Leiden: CRC Press, 2012. Vol. 1, p. 743-748
Keywords [en]
Clay, Sensitivity, Mapping, Shear strength, Cone penetrometer test, Friction, Point resistance, Piezometer, Pore pressure, Geophysical investigation, Electrical resistivity, Conference, Porto de Galinhas, 2012, English
National Category
Geotechnical Engineering
Identifiers
URN: urn:nbn:se:swedgeo:diva-842Local ID: 000075320OAI: oai:DiVA.org:swedgeo-842DiVA, id: diva2:1362073
Conference
4th International Conference on Geotechnical and Geophysical Site Characterization, Porto de Galinhas, Brazil, 18-21 September, 2012
Available from: 2019-10-17 Created: 2019-10-17 Last updated: 2019-10-17

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