imber trench shoring

huangyhg

timber trench shoring
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
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?
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.
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
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.