The aircraft's ACN cannot exceed the PCN for the surface, but there's more to it. The PCN is, by definition the lowest strength section of the runway surface i.e. the touchdown area might be PCN 55 but the midfield might be PCN of 30 and the runway would advertised as having a PCN of 30.
Also, the PCN number is based on civil engineering requirements for a certain number of "passes" down the surface without damaging it. Typically for USAF CE, it is 10,000 passes. This means, for us, we can waiver a limited number of operations on the runway for aircraft exceeding the PCN. In other words, PCN usually has more to do with damage to the surface than airplanes sinking into oblivion.