Not necessarily secured with a (locking) crossbar.
They can be secured in several ways, also by way of construction.
I think more context is necessary.
Sometimes this 'gekneveld' may also mean 'sealed', at least so it seems.
It may be necessary to know the exact function of this 'geknevelde deksel'.
Some are 'sealed manhole covers' in order to prevent to prevent odour nuisance, for instance.
3 pdf links to 'geknevelde deksels' on this page (sealed and secured):
https://www.nbd-online.nl/product/129406-esep-putranden-met-...