Engineering Tip #1

Since this is a blog devoted to the art and science of engineering, I decided I should post an engineering tip.

Today's tip is about broken back slopes. I know that sounds risque and improprietous, but it is not what you think, it is a real engineering term. Click here to google broken back slopes. We will break down a broken back slope to understand its features and then calculate an equivalent slope.

Everyone repeat out loud today's objective with me: We will break down a broken back slope to understand its features and then calculate an equivalent slope.

OK. Lets start by examining the case of a retaining wall. A retaining wall with an infinite slope is shown below. The wall height is H and the back slope rises from the horizontal at the angle B (beta). The angle of the backslope (beta) is used in a long equation ripe with trigonometry functions to calculate the active force coefficient of the retaining wall backfill soil that must retained. The equation is called Coulomb Active Pressure (click to see in Wikipedia - oh, and don't forget to donate).

Now we will look at a retaining wall with a broken back slope. If the horizontal distance of the slope to the point where the back slope breaks is less than 2 times H, we should calculate an equivalent back slope called B' (beta prime) to use in the Coulomb Active Pressure calculation. B' (beta prime) is the angle of a line extrapolated from the top of the retaining wall to a distance 2 times H behind the wall.

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