A soft rock is being used for the construction material of a rockfill dam having a height of 227 m, it has a broad gradation, but contains a very small amount of particles smaller than 0.1 mm. The permeability the soft rock after compaction and its filters are the main concern for the design of the dam. This paper presents test results for the effects of gradation of soils, water content, compaction method and load condition on the permeability. Results of the tests on intact specimens as well as specimens containing hole or slot for selecting filters are reported.


Broadly graded materials have been used as the construction materials for the core of the dam. The compressibility of the material after compaction is usually small, but its permeability to a large extent depends on the proportion of particles smaller than 0.1 mm. Therefore whether the soft rock could be used for core material depends on the permeability. The soft rock used to be the impervious core material of a 227 m high rock dam in Hubei Province of China contains only small amount of particles smaller than 0.1 mm, its permeability may not be as low as required, and its filter design requires special considerations. Therefore laboratory tests were conducted and test results are reported in the paper.


The soft rock with sandstone and shale origin has a maximum particle size of more than 100mm and the fraction smaller than 5mm (P<5) ranges between 2% to 40%. Two samples are taken, they are called Sjand S2" the degree of weathering of S2 is slight higher than that of S1. Total amount of sample weighing 15t was transported to the laboratory. The gradation of the sample varies widely.

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