"Notch" in Retaining Wall Heel 3

[anominal]

We've designed a conventional cast-in-place cantilever retaining wall, and we need to "notch" our heel to accommodate precast drainage basins. (See attached)

I'm befuddled with how to analyze the wall and calculate a maximum toe pressure.

 

[BAretired]

Calculate the contact area, the moment of inertia and the centroid of the notched footing. Calculate stress at the toe using:

f = P/A +My/I

where y is the distance from centroid to the toe.

BA

 

[JAE]

The notch will cause lateral earth pressure to build higher in the stem and footing directly adjacent to each side of the notch. I would expect your resultant design to include a widening of the footing as it nears the notch as well as heavier stem reinforcing.

So perhaps the 36" of footing/stem on either side takes the additional 3 feet (half of the 6 ft notch) of lateral earth pressure.

 

[anominal]

Thanks JAE. Why would you choose to distribute the additional lateral earth pressure over three feet? Does it just seem right?

 

[BAretired]

The usual way to drain a retaining wall is to provide drain rock behind the wall and drain holes at about 10' centers through the wall just above the lower grade so that the water spills out there. This avoids having to notch the footing to accommodate drainage basins.

BA

 

[rscassar]

I would suggest something similar to JAE. Design the wall to span horizontally at the notch and increase the size of the heel/wall reinforcement adjacent to the notch to provide the additional overturning resistance.

 

[JAE]

anominal...yes - 3 ft just sounds right but I'm sure there are more rational ways to attribute the "lost" loads to the adjacent widths. I could suggest a finite element model but I know some members on here would let me have it.

 

[csd72]

I would agree with JAE, I would have said 1m each side which is roughly 3 feet.

There are not calculations or code clauses for everything.

 

[anominal]

BA - we aren't allowed to use weepholes. I hear what you're saying, but our site specific constraints are insurmountable: we're working with a railroad.

I think three feet either side will be a good way to do it, thanks everyone.

 

[paddingtongreen]

I'd have been more likely to use about six feet either side, the stem wall is two feet thick so that is only three thicknesses so it is pretty stiff, or a forty five degree across the five and a half foot heel from the break gives about the same distance.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[miecz]

For toe pressure and overall stability, I would agree with using the width of the heel, 5.5 ft. I wouldn't feel comfortable with that for the reinforcing at the top of the heel and the back of the stem. I would double the reinforcing in those areas for the first 3 feet to either side of the notch.

 

[TDAA]

Actually, your lateral earth pressure remains the same. It is independent of your notch.

Now, your walls ability to resist the load at the notch, and the subsequent load transfer in your wall, is what I am sure you are referring to.