Assigning resources to a condensed activity

"... is there a way to assign different resources to start one after another for the different types of tasks in this activity?"

No. Although you could manually delay assignments from the start of the task/activity, neither MSP nor P6 allow sequential relationships between resource assignments within an activity.  That is what activitiy relationships are for.  If you had multiple sequential activities with multiple resource assignments, then you might be able to play games with resource leveling....

Kind of in Primavera.

Create the Activity in Primavera & Assign all Resources for the separate elements.

In the resources tab, assign the Original Duration for each resources operation.

Show the "Original Lag" Column in the Resources Tab, then for each resource update the original lag from the Activity Start to show when that section of the activity should start.

The activity duration will show the increase in overall duration & should show the final duration as the Maximum Original Lag value plus the last resource Original Duration. 

The Resource Usage Spreadsheet will then show the different resources being used on the day's set when the activity is created.

Whilst it can be done, the main question would be why would you want to!

If you were to create an activity this way, you would then have to manually recalculate the "Original Lag" Value for any progress that is not exactly as originally planned.

If the Dig Trench operation takes longer than planned then you would manually have to change all the lag values to add in the additonal time that the remaining steps would be delayed by.

You would probably find it easier to run the plan as an excel spreadsheet instead of within Primavera, as all the calculations would have to be updated manually!

Plans should be separated out into separate activies where there is a change in scope / resource requirement in order to simplify plan updates & to allow identification of differences between the orignal plan vs current.

It would be very difficult to identify where a project delay occurred if all activities were grouped in this way & also makes it harder for the individuals working the plan to understand the associated timings.

So to answer your question - Yes you could build a plan this way, I just wouldn't recommend it!

 Steven