New Shore for branching off Broadband

[mike2016]

I'm laying a new paving block driveway this week. I need to install a new Shore that can take the weight of a car. The shore will act as a junction to branch off the existing broadband pipe to direct cables to the new house I hope to build later. I've purchased a galvanised recessed manhole cover that meets the load and a quantity of engineered bricks. I plan to lay two courses side by side in a square to create the new shore on top of a bed of MoT and Concrete. Then more concrete to lay the manhole on and meet the required driveway angle which is on a slight slope. 

How deep should I go beneath the existing broadband pipe to create a suitable gravel/concrete foundation/base for the new shore?

Not built one before so would appreciate any tips to ensure this won't sink when someone drives on it! I don't mind paying more to overengineer just to be sure!! 

Thanks.