Can the assumptions that the PM is able to state in 61.6 be any assumption that he wishes?
For example, if he wishes the Contractor to exclude the effects of bad weather in the quotation, even though normally it is a Contractor risk if more frequent than a 1:10 year event, the PM could request it and, should the risk occur, the effects would be recoverable via 60.1(17)?
Would the weather event still need to be less frequent than a 1:10 to recover the costs? I would expect not given that the contractor was told by the PM not to price it as his risk initially?
I guess the PM can give any assumption that he or she wishes to but it would be uncommon for them to assume something that is already their risk and also very difficult to measure. Weather happens every day but when would it be classed as bad weather? Much more sensible and measurable that the Contractor prices for items that are already their risk under the contract. Any assumptions that are given should be clear and measurable. They are for matters that otherwise would be difficult for the Contractor to price with a sensible allocation for cost/time.
If the PM really did state “make no allowance for any rain delays” then I guess that is the assumption to be priced. The Contractor would then have to prove with good records/diaries that indeed any rain did cause an issue.