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A neat image from Wikipedia:

cut with steps

There're clearly visible steps on the cut wall. This makes the cut wider at the top and so requires more work so those steps have some serious reason behind them.

What's the purpose of these steps?

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    $\begingroup$ I think the terraces are there so that when an object rolls down the slope, the terraces will either stop it, divert it or at least reduce the energy that it has when it reaches the level of the road. $\endgroup$ – Dave Tweed Apr 1 '15 at 12:57
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The main reason for the stepped arrangement of the slope is slope stability and safety.

Such walls/cuttings are divided into two components:

  • sub vertical walls between two flat horizons
  • flat sections between sub vertical walls

By having a stepped arrangement, material and hence weight, is removed from above the toe of slope (where the bottom part of the slope meets the ground). This reduces the pressure at the toe of the slope and assists with the stability of the slope. This is critical because should the toe fail, the whole wall/slope will fail. To further assist with toe pressure reduction and slope stability, the sub vertical parts of the wall generally have a slope themselves. The maximum angle of each wall component is determined by a geotechnical analysis, which considers things such as: rock mass rating, joint orientation, joint persistence, conditions of joints (joint infill, joint friction, presence of slippery minerals such as talc), RQD (Rock Quality Designation), rock strength. In stronger and more component rock the angle can be steep. In weaker and less component rock, the wall angle will be shallower.

Depending on local terminology and whether the slope is for civil or mining purposes, the flat sections of the stepped slope are called benches, catch benches or berms. In addition to stepping the slope back into the in-situ rock, the benches catch smaller rocks and rubble that can fall off the wall from time to time. The wider the benches the better, firstly due to the increased offset of the wall and pressure reduction at the toe, but also the increased capacity to catch rocks falling from the slope above.

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  • $\begingroup$ I want to reinforce the point that you made about the benefit of catching or slowing down rocks that may fall from the top. This is especially true where roads are at the bottom of the cut. $\endgroup$ – hazzey Apr 1 '15 at 12:44
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They provide a terrace on each level.

Which result in a more stable pyramid shape of the remaining hill that is less likely to collapse onto the road. And it removes/alleviates the need for a strong retaining wall.

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