Oild and Gas Construction works - guideline for calculating the rate of work

I am a new planning engineer with just a year of experience. I need to prepare the construction schedule for a chemical plant. I have the scope of work discipline wise. I am not able to determine the duration of each of the activities, example excavation. I know what the volume of work is but since I am not able to determine the rate of work, I am not able to determine the duration of activity. This is very critical as I need to determine an optimistic time frame for the construction works by rolling up all the individual activities.

The major works are

1.       Excavation (Both manual and machine)

2.       Piling works (Cast in situ)

3.       Structural frame work for installing Column.

4.       Piping works (~ 9000 Dia Inch)

5.       DCS / SGS works (Instrumentation)

6.       Cable trays (Electrical and Instrumentation)

7.       Tank modification works

8.       Switchgear installation

9.       Underground cable trenching works.

These are few of the activities I had mentioned and I am sure when I move to another project the activities are going to change based on the nature of job.

Can anyone please share with me you data which you would have collected in the past projects based on which I can get an understanding and also base my schedule on that.

Kindly help me.