Volume XXI, Issue 4

The employment of non-traditional materials, such as soil-rock mixtures, in the construction of earthworks, for both economical and environmental reasons, poses new challenges to compaction techniques and their control. Usually this kind of material results from bulky rock extraction without explosives, and can include some large particles (>0.5m). Construction control of embankments built with soil-rock mixtures is still a subject that needs investigating, considering that it is necessary to extrapolate current test results which have been reached by means of the truncation of the grain size distribution curve to the actual construction conditions. The behaviour of these materials depends on the relative fractions of their constituents, becoming closer to soil if the fine fraction is large with the coarser material scattered in it, or closer to rockfill if the coarser particles are in contact with each other with the fines occupying the spaces between them. One of the techniques widely used in Portugal for the control of embankments is the Hilf method, developed for fine soils since it does not need previous knowledge of the material’s characteristics. Therefore, taking into account as an example the materials used in Portugal’s Odelouca Dam’s shells (weathered schist with a significant fraction of large-size particles), this paper presents the results from a laboratory study related to the conditions of application, and the applicability of Hilf’s method to coarser soils and soil-rock mixtures. A series of laboratory tests were performed in a large-scale compactor, and the results obtained from the upstream shells during the construction of the Odelouca Dam are presented, with the aim of seeking the authors comparison with Hilf’s method, which avoids truncation of the material grain size distribution curve, and the subsequent correction of the results. Some conclusions are then drawn about the applicability of this method.