Firstly there shouldn't have been any quantities in the Activity Schedule, as you say this risk sits with the Subcontractor under Option A. Also we are told at clause 54.1 that information in the Activity Schedule is not Subcontract Works Information (SubWI) or Site Information. The Subcontractor is therefore entitled to the lump sum price for each activity regardless as to the actual quantity of work that was carried out (less or more).
Yes the Subcontractor should have checked these quantities as one of their main responsibilities in the subcontract is to Provide the Subcontract Works in accordance with the SubWI" (clause 20.1). So the function of the Activity Schedule is purely commercial, it doesn't specify what is done or how it is done, it's the SubWI that has this function.
All changes are dealt with as CE with the relevant one in this case being clause 60.1(1) "the Contractor gives an instruction changing the SubWI".
So if the SubWI said remove topsoil from area A the Subcontractor has taken all quantity risk, however if the SubWI said remove 300m3 topsoil from area A the Contractor has taken the quantity risk and there will be a +/- CE for the difference.
Yes the Subcontractor should have checked these quantities as one of their main responsibilities in the subcontract is to Provide the Subcontract Works in accordance with the SubWI" (clause 20.1). So the function of the Activity Schedule is purely commercial, it doesn't specify what is done or how it is done, it's the SubWI that has this function.
All changes are dealt with as CE with the relevant one in this case being clause 60.1(1) "the Contractor gives an instruction changing the SubWI".
So if the SubWI said remove topsoil from area A the Subcontractor has taken all quantity risk, however if the SubWI said remove 300m3 topsoil from area A the Contractor has taken the quantity risk and there will be a +/- CE for the difference.