The Contractor uses the latest accepted programme when assessing the effects of a compensation event (i.e. an underground obstruction is found) and this is based upon a 5 day working calendar. The compensation event delays the next activity on the critical path. The assessment of the delay is made retrospectively. The works relating to the CE take 10 working days to complete. Two of these days are worked over a weekend. There is no dispute over the number of working days necessary for the event, or that the entire period is critical.
How is planned Completion affected under the following circumstances:
(1) the Contractor continues to work a 5 day working week;
(2) after notifying the event the Contractor decides to work 7 days a week; or
(3) the Contractor prior to the event but after the latest accepted programme decides to work a 7 day working week.
Not straight forward this one but it depends I would say upon the true intent of how the work was planned to be done. If it was reasonable to have forecast that weekend working was possible on this activity then it could have been added to the programme with a separate 7 day calendar applied (there will inevitably be multiple calendars on any single project rather than just one).
As you describe above I think circumstances 2) & 3) should both show that weekend working was known about and should be reflected in the programme accordingly as a lessor effect on planned Completion.
For circumstance 1), or if there was a risk that the weekend working would not be possible (even if it turned out to be so) then I would apply the five day working calendar and see a ten day movement in planned Completion.
This is one situation however that IF the compensation event is being assessed after the event has occurred - it is very difficult to ignore what you actually know has happened and I think it is easier for both Parties to assess it on what has actually happened.
The retrospective analysis using the actual dates shows that the completion date has moved on by 5 days, the contractors assessment includes the weekend working as 2 additional days delay to the programm ie 7 days, which they state has created terminal float for them.
So when we look back we can see that the completion date has moved and the number of planned working days on the programme that the delayed task was delayed by which we are using in the assessment. The contractors assessment includes delay costs for the weekends which on the programme they did not plan to work.
So should the contractor submit a programme showing that they were going to start the activity that was delayed at the weekend and that the critical path activity was delayed, rather than they worked additional days which creates float. As the delayed activity may have been impossible to commence at the weekend, ie a key subcontractor/supplier of materials for that activity only works Mon-Fri so the resources needed for the delayed task may not have been available for weekend working so the task could not have commenced earlier than was shown on the accepted programme?
It is fine to use hindsight to confirm that your forecast was correct!
If they never planned to work the weekend then their forecast was wrong - and you can base it on what you believe was the realistic forecast (which also happens to be what actually happened)