I'm putting in a new manhole I have a datum of 38.085 invert level 36.320 and the cover level is 37.485 what would be the depth to dig the hole and the method of working it out.

Is this in meters?

You know what the invert is, right? It is the lowest point of flow if only one measurement is given.

The hole depth depends on what type of manhole structure it is that you are installing. i.e. poured, or prefabricated.

Yes in meters. and it is a plastic prefabricated manhole.

yes in meters., and it is a plastic prefabricated manhole.aa

Is this in meters?

You know what the invert is, right? It is the lowest point of flow if only one measurement is given.

The hole depth depends on what type of manhole structure it is that you are installing. ie poured, or prefabricated.

Yes it is in meters and the manhole is prefabricated. Kind regards

Sorry, do you have a cross section of what is to be placed under the prefab structure? Say sand or gravel. Take the invert elevation, and subtract the remaining structure dimension, and add to that the base dimension. That is your hole depth. Say for instance the invert is 10" higher than the structure bottom, and the prepared base is 12" of sand, and 6" of gravel. The bottom of hole elevation is the invert elevation minus the 28".

I will try to help you more later tonight when I return home.

OK, the invert elevation is 36.320M. and the top of rim elevation is 37.485M. So, that makes the dimension from top to bottom, 1.165M. In order to calculate the bottom of hole needed, you need to know the dimensions I referenced before, the structure dimension, from invert to bottom, and the base required.

I hope this helps you somehow. If you need more, please come back here.