Entering into a public private partnership project is commercial behaviour by which government places itself on the same legal footing as other commercial parties. This is reinforced by the Crown Proceedings Act 1980 (Queensland) that allows actions for breach of contract to be brought against the state. There is a concept of executive necessity that may render certain action by government immune from suit, but this concept has very limited practical application.
Any uncertainty concerning the enforceability of the contract can be addressed in the contract. Where the issue arises, government's likely preferred approach is to agree that it will not claim immunity from future legal proceedings as a sovereign body.