Rank: Forum user 
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We have recently had an incident, during crane assembly by one of our subcontractors. The crane arrived on a wagon, the crane is then jacked off the wagon by the use of outriggers. The 4 outriggers were placed on timber blocks, as the outriggers are not long enough to reach the ground. One of the timbers split, which resulted in the crane splipping of the timber blocks and making contact with the ground. Anyway, I was told by the subcontractors and a few of our crane guys this is common practice, and this is the first time they have seen this happen. My first thoughts were should these blocks not be load bearing tested, purpose built crane blocks, rather than timber blocks?
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Rank: Super forum user 
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It's common to use timbers when jacking stuff. Timber has lots of good properties for jacking and reaction mats. It's also fairly common to use a 'jenga stack' when raising or lowering heavy things on construction sites, though it always causes me to ask twice as many questions about how any overturning moment or lateral forces (due to wind load or out-of-verticality, for example) are reacted.
It should be properly controlled timber though - it shouldn't be just any old chunk of wood found lying around. It should be a decent strength grade, and in good condition - in particular, it should be free of wane and significant splits. Obviously, I can't comment on whether the particular timber in your particular application was suitable or not, but the fact that you're jacking off timber is not necessarily an inappropriate thing to do.
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 1 user thanked achrn for this useful post.
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