A shallow foundation is to be placed at 1 m depth in an expansive soil where the active-zone thickness near the ground is 5 m. Constant volume swell pressure tests were carried out on oedometer specimens at 1 m intervals, and the results are as follows:

Depth below ground level (m)	Swell percent under overburden + foundation pressure, sw(1) (%)
1 m	4.6
2.0	3.7
3.0	2.5
4.0	1.2
5.0	0.0

a. Estimate the expected swell of the foundation under the working loads.

b. If the maximum allowable swell is 20 mm, what is the depth of the undercut?