it's simple if you already understand the nature of the CDMA technique and the fact that CDMA is an interference limited system, if you understand that so we may say that hard-blocking happens when we have no more physical channels free for any more subscribers in other words if all the walsh codes in the site is already in use by other subscribers so we have no more codes for new subscribers.
in soft-blocking we do have physical channels for users but we have so much interference that we cant handle the interference that the new subsriber will add so we consider that site at it's peak interference capacity.
i hope this is what you are looking for.