Placement of supporting rock material prisms of a high dam
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In the erection of supporting prisms of dams with local materials placed in thin layers with mechanical compaction, the most suitable from the standpoint of strength and deformability is a rock mass with a content of the fraction smaller than 100 mm ranging from 40–70% and with a total admixture (of clay) not exceeding 5%.
For a rock mass containing fine fractions the most effective compacting equipment is the loaded MAZ-525 dump truck or the 50-ton D-326 pneumatic roller. The greatest compacting effect is reached during the first eight passes. Further increase in the number of passes is ineffective.
The placement of the quarry mass must be done by the pioneer method with dump trucks of large capacity. The optimum thickness of the layer for dams erected with a previously wetted rock mass with a high content of fines is 1.5 m. With an increase in the thickness of the layer stratification takes place and the density is sharply reduced.
Before compacting the rock material it must be wetted directly in the bodies of the dump trucks or at the time of filling with 150 liters of water per m3 of rock mass. During the freezing period when, owing to the icing of individual stones, the wetting of the rock material is impossible, the fill must be done in the dry with layers 1 m thick.
It is advisable to maintain control of the density of the rock material measuring the volume of the pit by covering it with polyethylene film 0.15–0.20 mm thick and filling with water. The volume of the pit should be not less than 1.5–2 m3 and the number of samples not less than one per 4–5000 m3.
In each individual case the erection of a dam with rock material containing a large amount of fines must be preceded by experimental-production investigations aimed at perfecting the geotechnical indices of the rockfill material and at the establishment of the most effective work procedure.
KeywordsCompaction Rock Mass Electrical Power Generation Rock Material Optimum Thickness
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