What is a Contact according to GeoSciML?

From GeoSciML v4.1:

A contact is a general concept representing any kind of surface separating two geologic units, including primary boundaries such as depositional contacts, all kinds of unconformities, intrusive contacts, and gradational contacts, as well as faults that separate geologic units.

For which geotech concept do we want to use gsml:Contact?

gsml:Contact is identified to realize the geotech concept called Contact.

Proposed adjustments for geotech