We get regular deliveries of woodchip because the tree surgeons prefer give it away - the alternative is to pay the council to take it. That could change if any company is prepared to pay for it.
In the meantime my chip goes into 1 spit trenches to rot down while I use it as a path (and put the topsoil I rescue onto the raised beds - which on my slope are actually terraces).
However if chip was riddled out, the larger chunks could go straight into the soil as a free supply of gravel (made of wood) - because these big bits rot so slowly that they steal hardly any nitrogen*.
It's all down to the square/cube law - when the chunk is twice as wide it is 8 times the volume & weight but only 4 times the surface - 1mm twigs rot over 10x as fast as 1cm prunings - sub-millimetre sawdust & most leaves could be 10x faster still.
Since 2 years in a trench hardly touches the prunings, the sawdust could steal all the nitrogen for a week and give seedlings a real famine, followed by months of short rations as the twigs decay.
Anything is better than solid clay - so as long as you avoid fine (brickies) sand you can use sharp sand from a builders' merchant or gravel, & even anything except the coarsest grade of aggregate mix - all permanent fixes for clay - anyone who says these contain salt is wrong - it's all been washed out because salt totally ruins concrete or any cement mix.
Gypsum can have an instant effect on clay, but the grade they sell for the job is expensive and can be made ineffective by too much inorganic potassium.
If you've got a really bad patch of clay it's worth trying crushed plaster or even plasterboard (from your nearest skip). There should be enough gypsum to make a quick difference and the lumps will behave like gravel and can't do any harm - especially if you are adding other stuff as it becomes available.
Cheers.
*The smaller stuff rots quickly & harmlessly in the trench/path - but beware of walking on it in wet weather - it can turn into sawdust quicksand,,,!
