Backfill - Shingle vs Graded Crushed Rock Chalk

[Thorfun]

thanks guys. I made the decision to follow the drawings and have told the groundworkers to do as much. I'm not clever enough to second guess the reasons the SE designed it the way it has been!

[saveasteading]

I agree that the backfill should be closed off at the top with membrane, to keep the fill clean in the long term.

That could be 200 down so that the material above is decorative and can get dirty without problems.

 

This is clearly designed to be free draining and has the collecter pipe at the bottom. As such it needs to be clean stone, like gravel, with gaps for water to run through.

 

I am doubtful about rock chalk being the right solution, especially if there is  a lot of water movement. Will it dissolve? Check that with your Engineer. 

Also it tends to be jagged and will not consolidate unless compacted. 

 

 Gravel will fill the void completely and not need compaction. Coarse stone will not.

 

Talk to your Engineer, explain that gravel is expensive and show him alternative materials that will self-compact, allow water flow, and not deteriorate. perhaps there is rounded  crushed recycled material.

 

Please don't assume that the builder understands the theory. They might, but more likely don't.

 

[Thorfun]

1 minute ago, saveasteading said:

perhaps there is rounded  crushed recycled material.

this is exactly what we're using. recycled clean crushed concrete graded 30mm - 100mm. seems pretty free draining with the amount of rain we've had recently!