Trench backfill for water / services

[WWilts]

Planning trench for water about 900mm deep. About 600mm wide to take other services too. Trench runs along reinforced grass driveway that reputedly will suffice for heavy lorries too. 

Soil has about 300 mm topsoil, then rubble limestone for about 700mm, then bedrock.

 

What backfill layers would work, to allow lorries to occasionally stray off the driveway onto the trench/verge? The concern is that the trench might simply slump. The other concern is cost of backfill. 37m trench length.

 

Presumably water pipe will sit in sand, with 75mm cover of sand. The best idea I have had so far is strip the top soil first and pile it somewhere on site. Then use the rubble rock to backfill above the sand, topped by MOT type 3 or scalpings. Thin layer of decorative gravel.

Ideas welcome, for a cost-effective approach.

 

 

[MikeSharp01]

What other 'services' are going into the trench? Will they be ducted? You may need to layer the other services to achieve any separations that may be needed. Heaping the top soil is a good idea you can use pea shingle in place of sand then I would put a layer of type 1 and compact it then the rubble rock then compacted type 1 again followed by top soil and final compact. 

[WWilts]

1 hour ago, MikeSharp01 said:

What other 'services' are going into the trench? Will they be ducted?

Gas (non-ducted, builder says the gas connection people are happy for him to lay the gas pipe and without ducting)

Electricity 3 phase 46kVA, ducted

Telecom duct with drawstring (for future use)

Spare duct with drawstring

Is type 1 more cost-effective than either scalpings or type 3 MOT?

[WWilts]

Local aggregates supplier advised 40mm scalpings. Probably will go with that, unless there is a reason to avoid it.

[MikeSharp01]

You will need to think hard about separation distances and work the combinations especially the 3ph which will need a notification tape above it as should the gas.