I’m looking for literature on pressure treated timber lagging service life. This would be for a permanent soldier pile wall with pressure treated timber lagging that has been backfilled. What is the life expectancy of the timber lagging and how does it brake down if at all over its service life? If the timber lagging does brake down does it leave voids in the soil or does it remain solid and in place?

Treated and untreated lagging will lose strength over time. However, neither will totally disintegrate enough to leave a void. The lagging retains its cellular structure when buried underground. This has been observed numerous times by me personally and by contractors working around old buildings and subways.

Treated timber will also deteriorate if used as a "permanent" facing between soldier beams. (Consider also the likelihood of the timber facing catching fire.) I even had stored 0.60 CCA treated lumber deteriorate in my back yard when it was just lying on the ground for about 15 years. Do you want to rebuild a timber faced wall after only 15 years? How about after 20 years? I don't think so. If your wall is low and is to be build from the bottom up with an open excavation, use precast lagging. If the wall is to be built from the top down in excavation lifts, use temporary, left-in-place lagging (untreated or treated) and then attach a concrete facing to the soldier beams as the final "permanent" facing.

www.PeirceEngineering.com

A reference I have been pointed to in the past are these stake tests:

http://www.fpl.fs.fed.us/documnts/fplrn/fpl_rn02.p...

As you can see, the 0.60 CCA holds up pretty well after 40-60 years, as PEinc infers. PEinc also makes some good points that the lagging will not disintegrate and leave a void. To steal a line from the Law of Conservation of Mass, "Matter cannot disappear, it can only change form, composition, etc..." Certainly that is in a "closed" system, but surely, it will not vanish.