Timber Post and Lagging Wall

[GeoEnvCv]

I am designing a small timber post and lagging wall. The structure is holding back 5.5 ft of sandy silt with groundwater estimated at 2 ft below ground surface behind the wall. Ground surface at the toe of the wall decreases at a 5:1 slope; ground surface behind the wall is flat. I am considering pure cantilever and anchored walls. A major limitation here is that the shoulder of an existing road is located about 12 ft from the wall, limiting the effectiveness of any deadmen/pile anchors that can be installed.

I have run through some calculations myself (dont have any software for this), but I dont do a lot of work with this type of design;I was hoping someone with more experience in the area could give me some kind of sanity check.

Is there a range you might expect for cantilever driven depths here? Would you expect anchors to be installed here (my calculations have them losing about 2/3 of their effectiveness due to the proximity to the wall)? What sizes and spacing might you expect for the posts of the cantilever and anchored design?

Thanks for the help

 

[BigH]

GeoEnvCv - why not consider a gravity wall? With a wall height of only 5.5 ft, you only need about 3 to 3.5 ft of a gravity structure width. key the structure into the ground a couple of ft - say 2 to 3 (below frost depth) - use a concrete crib wall, for example. May need to extend width of wall to 4 to 5 ft considering key. Easy to build.

 

[GeoEnvCv]

Thanks for the suggestion. There is however, an agreement in place that requires us to do the post and lagging wall

 

[BigH]

Don't you just love it when "agreements" over-ride, in my view, common sense. With post and lagging you will need to manufacture a hole - not with the other. Still, one could attach reinforcing strips (or geogrids depending on how much "stretching" you might be permitted) attached to the poles (depending on how widely spaced) or heavy lagging - and form a mechanically stabilized earth wall. Soil reinforcing normally goes only 0.7 to 0.8 times the height of the wall. In your case, again, that is about 5 ft. In MSE walls, the facings do not really help on the internal stability of the wall - look at the original facing or RE walls (as in the patent). Also, walls are built with reinforcing attached to wire mesh with geotextiles - so what I am suggesting is go to a post and lagging wall but use reinforcing to make it an MSE gravity wall. Not much extra cost if any and you don't need to worry about the bending of the posts.

 

[demayeng]

this document really helped me when I was doing a couple of soldier pile walls last year

http://vlee.utpl.edu.ec/VLEE/LinkClick.aspx?fileticket=piymgNPD1d4=&tabid=142&mid=520

From memory, expect to get very deep embedments (ie 1.5-2 x wall height). I was casting steel soldiers into concrete so had an effective resistive width a lot wider than the soldier itself, meaning I could get closer to equal retaining and embedment lengths.

Tiebacks would help though - I didn't look at those, however they are covered in that document.

 

[InDepth]

If the agreement is for aesthetics, just slap some wood on the face of that cribbing wall...the concrete cribbing gravity wall is much more durable than a timber wall...especially after tgeyrealize the timber posts are rotting and wall starts to deflect.