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Selecting gradation of material for shear key construction

Selecting gradation of material for shear key construction

Selecting gradation of material for shear key construction

A shear key construction requires a crushed rock materials, with maximum sizes between 6 and 8 in. What typical gradation should be selected to get the best density without compaction effort. The crushed rock will be dumped by the excavator bucket, after a 3m wide shear key trench (up to 6m deep)is excavated. The surrounding soil consists of clay. This shear key is used to stabilized a slope.

When I was working on asphaltic concrete mix design, there is a chart that can be used to plot the gradation to ensure minimum air voids. Is this the right way to do ? We do not want to have one size stones, since it will have lots of voids and clay will go into the trench. But we do not want too much fine, because it will not have a good drainage.

Thanks for the help.  

RE: Selecting gradation of material for shear key construction

Since a 'well' graded granular material produces the highest unit weight, just design a well graded (all fractions equally represented) gradation curve then exclude the 'fines' portion say every thing finer than #20 or whatever you need to provide sufficient pore volume to handle your peak flow.  On the other hand, because this key acts like a retaining wall, make its composition as dense as possible and collect and relieve the water behind it as though it was a retaining wall.

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