Timber Trench Shoring

[rcooley]

Does anyone have any tips on designing timber trench shoring. This should be easy, but I am missing something. The method of shoring the contractor has proposed is with vertical wood planking which are 3X8 or 4x6 douglas fir with a bending strength of 1500 psi. The system consistes of these vertical planks with wales and 2 struts, wales and struts are located 3' from the bottom of the pit and 2' from the top. I analyized the verticals like a simple beam with the struts as rollers and the retained soil as the loading, but I can not get any of the proposed sizes to work, even though the contractor has had the system reviewed in another state and it worked, basically I am recertifing for my state.

I even found tables here saying these memebers should work

http://www.setonresourcecenter.com/CFR/29CFR/1926150.htm

 

[JStephen]

I think OSHA has some standard details and tables on shoring- you might check for comparison.

Could you be figuring soil loads more conservatively than what the tabulated values assume?

 

[rcooley]

the link I included shows the OSHA table and there loads are what I am basing my calcs off of. I even called OSHA about where they found there values, but they could not even find the table, not much help from them.

 

[SlideRuleEra]

rcooley - You haven't told us the trench depth (or distance between the wales). Without that info it is hard to give advice.

...however, see the "California Trenching & Shoring Manual" at this link

http://www.dot.ca.gov/hq/esc/construction/Manuals/TrenchingandShoring/TrenchingandShoring.htm

In particular, see Chapter 5.

http://www.SlideRuleEra.net

 

[rcooley]

ahhh, details details, sorry about that, the trench varries from 5'to 20' deep and is pretty much set a 8' wide. Another thing to add in is that the water table is varies also.

thank you for the CA shoring manual that looks like a great starting point. I have to say the CA DOT always has great resources.