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Henry Newman
Water resource engineer
Asked a question 2 years ago

Can a random rubble masonry retaining wall withstand the high impact of water during floods?

Can a random rubble masonry retaining wall withstand the high impact of water during floods, if the walls are built on both sides of a canal. And how can we check if the design of the wall was sufficient?

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Morris Baker
Construction Site Safety Manager

You start asking about ‘High Impact’ from flood waters. Generally flood waters is not High Impact unless a dam collapses or you have an extreme flash flood. Usually if you are at a canal you will have fast water eroding the base of the wall or pushing the rubble masonry wall as the water goes through the canals.

To check if the design of the wall is sufficient see if any design calculations were filed with the local municipality or water agency. The calcs should identify the design water speed and height. If no calcs then you need an engineer to review the construction of the wall.

If you can’t afford an engineer first look at the base of the wall. Is there exposed dirt, is erosion already occurring? Look for photos from a few years ago to see if the wall has changed. Check the upstream ends of the walls on both sides. Are they flared out and do they extend below grade into the earth. If the rubble is just on the surface at the upstream then as the fast water rises it will undermine the wall and it will fail one piece at a time.

A random rubble masonry wall can survive a flood if correctly designed but the only way to know for sure is to have another engineer review the wall.

Usually a RR retaining wall is constructed in embankments (above the linings) of canal when the lateral force from the soil behind is considerably high due to various factors. During the floods, this force will exert more pressure. If the slope and base width of the wall is not designed properly, it will fail. Hence the design parameters should include this eventuality. (Max. Lateral pressure with a minimum factor of safety 1.50). Sometimes there is no need for cement mortar and the tiny gaps will be help full to act as weep holes.

Answer to your 1st question:

Well, It totally depends on the design of retaining wall! Usually, flood water has not a high impact unless and until the dam collapses.

Random rubble masonry can sustain a high amount of pressure exerted by water.

The strength of the mortar used for joining of rubble stone is in between 5 to 7.5 MPa only.

Answer to your 2nd question:

When we talk about the design of retaining wall then it should be accurately done as per the local water agency and local municipality.

All the calculations should be done with respect to the design speed of water and height of retaining wall.

First, check the extreme ends of the Wall on both sides. Look at them carefully enrich weather Pyar flattered out or not. Check that the extended below the grid into the earth or not.

Whenever the rubble is just on the surface of the upstream side then definitely a retaining structure will fail at that time.

Thank You.