Natural segregation of dumped stone materials

From the editor

The editor, on publishing the interesting data of G. A. Radchenko concerning the natural segregation of broken stone upon dumping, calls attention to the possibility, in a number of cases, of using segregation as a means for grading stone without mechanical devices, as was successfully accomplished, for example, in the construction of the rockfill dam of the I Khram hydroelectric power station. There the rock mass blasted from the spillway excavation descended along a steep slope from a height of 22 m to the site below. As a result of segregation, the large stone accumulated in the lower part of the dump and all the fines were retained in the upper part of the slope. The excavator at the lower site loaded the thus-graded large stone into transporters which hauled it to the body of the dam. At this time the rock was dropped down at another area of the slope.

Conclusion

• 1. Natural segregation of stone material inevitably occurs when dumping dry rock in layers, even of small thickness (4–5 m).

• 2. When the broken rock contains small fractions, including sand and fines, and the height of the dumped layer is appreciable, the small fractions accumulate in the upper part of the embankment and along with the stone components of the rock mass from the skeleton; in the lower part of the embankment are many cavities.

• 3. The small fraction pressed into the upper part under the effect of water or vibrations can migrate in time into the pores of the lower part of the stone embankment, as result of which settlement and deformation of the embankment occur.

• 4. The accumulation of the small fraction in the upper part of an embankment in quantities greater than 20–25% is not permitted for essential structures; for this purpose the height of the dumped layer is reduced or the voids in the lower part of the embankment are filled by washing in sand.

• 5. When dumping with washing (the water is delivered simultaneously with dumping) the height of the layer depends on the quantity of the small fraction in the original material. Washing of the dumped layer with the small fraction pressed into the upper zone does not yield results even at a quite appreciable water delivery rate.