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Pavement Slab Spanning Services Pit

Pavement Slab Spanning Services Pit

Pavement Slab Spanning Services Pit

(OP)
Hi guys,

I have this situation where I need to provide a pavement slab that spans a telecommunication services pit. Please see my attached sketch for details.

What I was thinking of doing is:

1. Excavate either side of the pit and providing plain concrete that will act like a pier and can take the vertical reaction below the pit so no lateral pressures are exerted onto the pit wall.

2. Using a lightweight steel falsework to form the slab so it can span the pit without exerting any load onto it. This will be sacrificial formwork and will need to be resistant to corrosion.

3. Isolating the slab that spans the pit from the rest of the pavement.

Can anyone see something wrong with this approach or can find something that I have not considered?

Primary what I want to achieve is to not put any traffic loads onto the services pit and minimise the differential settlement and cracking present in the pavement slab.

Any suggestions will be appreciated.
 

RE: Pavement Slab Spanning Services Pit

Your plan is both a bit ambitious and expensive.  You can accomplish this with a precast structure that will support the pavement.

You will need to provide a bond isolation layer (plastic sheeting) so that the pavement does not bond to the structure or a soil layer above the structure to support the pavement and provide isolation.

Make sure the soil below the structure is stable and well compacted (100 percent of the modified Proctor maximum dry density) and, assuming good bearing soils below, the settlement issues will be mitigated to a large degree.

This is done routinely under both rigid and flexible pavements.

RE: Pavement Slab Spanning Services Pit

Agree with Ron. For such a small service pit, a DOT standard shall suffice. Preparation of bedding and backfill details are the more important tasks. Watch out for both surface and ground water, and frost heave. Can you lower the pit further to make room for softer material to dampen the impact from traffic.

RE: Pavement Slab Spanning Services Pit

(OP)
Ron and kslee1000,

Thanks for both of your replies. Normally I would use a standard DOT design however, for this situation the services pit is an existing structure and is larger than what was expected. It was expected that the pit would be fully contained within the island that I have shown on plan and would not be subject to any traffic loading.

If I ensure I have good compaction beneath the pavement, will it still be necessary to provide piers to bear beneath the pit.

I guess I also have a waterproofing issue that I didn't consider before and need to ensure that the pit does not fill up with water.

RE: Pavement Slab Spanning Services Pit

Sounds like you are dressing over an old non-traffic rated pit with new end piers to bridge the new concrete cover for traffic. If you are positive about the original compaction, and does not want to disturb/temporarily remove the old pit, then your plan as sketched is worth to be considered. However, remove and replace the pit seems much simple/clean to me.

No matter how good the water proofing is, make sure there is sump pit, large and deep enough for sump suction head to sit in.

RE: Pavement Slab Spanning Services Pit

(OP)
I have just got the joint layout from the civil engingeer. I have provide dowels between the slab and the pavement to allow some shear transfer.

Should I be worried about how the civil engineer has done their joint layout or should I just provide a dowel joint all around the pit lid slab.

I am assuming this is being built first, then they would pour the traffic island so an isolation joint can be provided between the island and the pavement.

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