Bread dough doesn't keep its shape I've just made some 50/50 loaves using a biga. The taste is quite good but I'd like the crumb to be more open.

The biggest issue is that while raising the dough tends to "spread" rather than rise. What did I do wrong?

Here is my recipe:

For the biga:
500g  manitoba flour (extra strong)
300ml water
8g    active dry yeast

After 24h I add:
500g  wholemeal flour
300ml water
1tbsp vanilla paste
1tsp  sugar


I've shaped the loaves straight away as I know wholemeal bread doesn't like long proofing. I've let the dough raise 1 hour at room temperature and 10 hours in the fridge. 
This morning I found the dough slightly raised and evenly spread in the pan (more like a focaccia than 3 loaves :-) ). I've reshaped a bit, just separating the three loaves.

In the oven the size hasn't changed much (180 C, with a bit of water to keep humidity right).

I'm trying to get soft, open crumb loaves, like this one http://www.thefreshloaf.com/files/u5218/proth5_baguette_crumb.JPG

Edit: by mistake, as often happens in the kitchen, I've found the right recipe:

For the biga:
500g  manitoba flour (extra strong)
300ml water
8g    active dry yeast

After 24h I add:
500g  wholemeal flour
**600ml** water
1tbsp vanilla paste
1tsp  honey


And that is the result
If your crumb is not open you likely either underproofed, your dough is too dry, or you have not opened the dough up by cutting across the top. There are many very good questions about crumb on this site already so I won't go more into that in detail, instead I'll move onto shaping. 

Bread will spread out and not up unless it's restrained, it's natural for it to do so as it's the path of least resistance. If you want it to prove in a certain shape you need to use a tin or a basket in the shape you want. Bread can be baked in a tin, however if you use a basket you'll need to turn it out onto a sheet before baking.