Cable Duct install in Cement Bound Sand (CBS)

[Stoufer2000]

Hi
Has anyone had any experience of excavating to find HV underground cables in CBS backfill? I am being asked increasingly to use CBS (usually about 1:14 Cement/sand) for bedding and cover infill of cable ducts we install. Reason usually given is that apparently it helps with heat dissipation in some soils and presumably also helps stops warning marker tapes being able to move away from the duct with any soil settlement.
I am concerned that it may not be possible to use hand tools to excavate to get to the cable to prove dead/spike it if further work is required on the circuit later on. As I have never tried to break any out in the past, will it break up or come away with gentle use of a spade or grafter or does it go off quite hard?

Any advice gratefully received
Mark

 

[davesparks]

1:14 is a pretty weak mix if you compare it to a normal mortar mix, so it would presumably be reasonably easy to break up later

 

[westward10]

I agree it should shift easily.

 

[PEG]

Yep,it breaks up easy,i have had to rip up loads round here,as a similar mix was specced as bedding for vehicle use paving flags (3x2 and 2x2) on and around some local LA offices.

The main reason for it's use,was not load bearing,it was ability to resist under-cutting by water and ants! The LA still spends a considerable amount,spraying all the footpaths locally,for the ant issue.

A consistent mix,at similar ratios to above,will be removable using hand tools,but the problem is always consistency. The lads hoying it in,have a lot to mix,and figure it has no importance,so be prepared for the odd tungsten nugget...

It is only the same as pricing breaking out a large concrete slab,and finding the ground workers disposed of the surplus 2 Cu of concrete,by trebling the depth of the last section...Thank you Lever Bros

 

[Marvo]

We sometimes use a soil cement mix in cable trenches to deter moles and porcupines from digging up the cables. The soil here is very sandy, not like your UK soil and we generally use a 1;20 cement ; soil mix by volume. When it's fully set it's pretty crumbly and can easily be broken up with a spade