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An evaluation of the flat dilatometer as an insitu testing device McPherson, Ian Duncan


The results from the use of the dilatometer (Marchetti 1975, 1980) at 4 sites in British Columbia are presented. Comparisons are drawn between the dilatometer and other insitu test devices, including the piezo-friction cone, self-boring and Menard pressuremeters and field vane. Soils tested included saturated deltaic deposits, a sensitive plastic clay and a saturated, hydraulically placed fill. Overall the dilatometer proved to be an extremely effective device. It had a low capital cost, required a minimum of support equipment and was simple to use. The data was repeatable and easily reduced using a computer programme. Computer output, both graphical and tabular, is easily amenable to interpretation to an engineer in the field. For the most part the results in this thesis support Marchetti's empirical correlations with the following exceptions: ( i) determination of K0 in sands, ( ii) determination of a deformation modulus in clay, and (iii) in overconsolidated silts where it is believed that abnormal pore pressures caused the empirical correlations to breakdown. The dilatometer is an insitu, total stress, penetration device which cannot be analysed in a fundamental manner. Elastic theory is inapplicable because of plastic straining during blade penetration and probably during membrane expansion. To more critically evaluate the dilatometer, the author designed an electronic research device with exactly the same external dimensions as Marchetti's dilatometer. The aim of the electronic dilatometer is to greatly improve understanding of the simple Marchetti dilatometer by allowing: ( i) a better understanding of the operational characteristics of Marchetti's dilatometer, ( ii) direct measurement of stress on, and deformation of, the membrane, (iii) measurement of pore water pressure before and after halting penetration and during membrane expansion, and ( iv) measurement of the pushing force on the blade.

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