Piled Wall

[HighPanda]

I am going to design piles to be installed in embankment which carries railway tracks. After the piling has been done, the side slope in front of the piled wall will be excavated.

My questions are:

1) What was used to fill up the embankment (200 years ago!) is not known yet at this stage. I wonder whether CFA can be used if boulders or cobbles are found during augering. If augers are too weak to drill through obstructions, are there any alternatives?

2) If retained height is 4 metres and surchange from the tracks is 45 kN/m^2, does anybody have a rough figure about how deep the piles should go (i.e. below the 4m deep formation level)?

Thanks!!

 

[PEinc]

If you do not know what soils (or obstructions) are in the embankment, you are ready to design the wall. You need to know what type of material you will be retaining and if any type of driven or drilled (augered) piles can be installed. If the railway tracks are near the wall, you will probably need tieback anchors. Also, the railroad may have rules about what type of wall you must install and if you are allowed to use temporary or permanent tiebacks under the tracks. You need a lot more information before proceeding.

 

[DRC1]

Agree with PE inc. Also augercast are not the right type of piles for this application. Really need to ask a geotech with experince in retaining walls.

 

[csd72]

HighPanda,

Sound like by your terminology you are in the UK.

In this case it would be a network rail job and I would strongly advise you to get a geotechnical investigation done. Network Rail demand a very auditable and robust design process that can be fully defended.

If it is all fill then it is unlikely that there will be any large rock floaters in there.

The piled wall that you refer to is usually called contiguous piling or a secant pile wall and I suggest you google it to look into it a bit more.

A publication by CIRIA gives very good info on this type of construction.

As for the length of the piles, it depends on the quality of the soil and the allowable deflection of the piles. As a rough initial guess I would say you embedment would be an additional twice the retained height giving a 12m total length.

Regarding the deflection, in theory every mm the piles deflect will give half a mm of vertical settlement behind the piles.

 

[HighPanda]

This project is in the UK and the full storey is a little bit more complicated. (Pls see the attached sketch).

What the client wants to do is to demolish the masonry brick viaduct (i.e. the arch), which support the sidings, and the adjacent masonry retaining wall. Before the demolition, some sort of retaining structure should be in place. That is why I want to do a new wall there.

I understand a geotechnical investigation should be done, but this project is still at stage of feasibility study. Hence, I have to work out a “workable” solution with limited information.

By the way, how far the new wall (piled wall and sheet pile wall) should be away from the existing masonry retaining wall?

Thanks!!

 

[ishvaaag]

Since ballast/infill under the tracks might spill between the soldier piles one would think might need an entirely continuos wall (bentonite in trench, then concrete through tremie). Given that you may anchor a wall against the other you wouldn't need much depth under excavation level if you plan for it, say 4 or 5 meters below. If pure cantilever I wouldn't count total length less than 2.5 times excavation depth even allowing for the diminished pressures of earth between parallel walls.