Exam Form 1 Question related to basement waterproofing

The home sits on a site with a variable water table, where moisture intrusion and hydrostatic pressure are of concern.

Which of the following is the most effective method for creating a waterproof basement? The correct answer:

A. Placing perforated drain tile around the foundation, above the concrete footing

Why it’s above the concrete footing? If the variable water table exits, shouldn’t the perforated drain level with the footing? It requires min of 2" from the bottom of the pipe to the top of the footing based on BCI.

C. Placing a course of gravel beneath the foundation pour.
To support the footing, shouldn’t it be compact?

Thank you for answering my questions : )

sorry I figured C out…

For Item A:
You place the perforated drain pipe above the footing, against the stem wall because there is a keyway between those two, and without the perforated drain pipe to relieve water pressure the hydrostatic pressure would force the water through the keyway and into the basement space when the variable water level rose.

They key is the variable water level when choosing where the drain pipe goes.
Here’s all the different configurations: https://images.app.goo.gl/gkMqBsNDR5f8mhHh7

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