ciabatta

from the sounds of it your over kneading the bread. you schould have suficient glutin formation without over working the dough. you only need abot 85% glutin formation. once thair your need to be easy on the dough. man handiling the dough will degass the dough and leave you with out the big holes

I have yet to do ciabatta but it is on my to do list.  Every recipe for ciabatta in the books I have is for a yeast version so I have been putting it off.  The key to getting the big air bubbles in ciabatta is to use lots of water in the dough.  The one recipe that I'm looking at has the water as 85% of the flour.  This make for a very wet dough that is hard to handle.  You didn't say how much water you put into your dough.
Next I agree with jdnickell you kneaded the dough to long.  I have heard that hand kneading high hydration dough can be very hard for a novice.  You might like to try a mixer.
To help get the right amounts of flour, water, and salt in your bread a scale is a wonderful addition to your cooking equipment.
Here is what I'm going to try when I make ciabatta.
Sourdough preferment.Stiff Sourdough starter- 50 gramsFlour- 115 gramsWater- 98 gramsThis will make my preferment about 85% hydration.
DoughFlour- 500 gramsWater- 425 gramsSalt- 10 gramsSourdough preferment- 200 gramsThe dough is now at 85% hydration
Mixing:  I would mix to the short side of time.  In my mixer I think 5 minutes would be long enough.  You will need to experiment with times to see what works best for you.  Look at the dough as you are kneading it.  Remember the changes you feel it go through.  These are your indicators as to how the dough is developing.
Flour:  The hydration is going to vary depending on the type of flour you use so 85% is just a starting point but once you find out if you need more or less water for the flour you are using you can use the same amount of water the next time.
Salt take water away from the yeast and hinders fermentation.  The amount of salt in the above formula is 2% you can make it less and that will help get bigger bubbles.
My formula is just one third of the flour that you tried.  To use 1.5kg of flour just triple everything I have done.

Hello,
I make ciabatta loaves in a wood fired oven using a formula with 84% hydration, 2% salt, 1.5% olive oil, no yeast.  I mix the flour, water and oil in a spiral mixer for 5 mins til stringy threads pull off the spiral, add salt and starter, mix a further 3ish mins til the threads reappear.   After a ferment of 12 hours at about 14ish deg C (winter nighttime kitchen temp) I turn it out onto a floured tray and cut the shapes at the ovendoor, transfer them to a floured peel and slide them onto the hearth.  The result is a thin chewy crust, big shiny holes and pleasant sour flavour.  Pix would be good wouldn't they but the personal tech barrier requires more time!
Meantime, I hope this is of interest.

What hydration is your starter?  What percent of the flour is the starter?  What kind of flour do you use?  I want to try and make this bread the way you have done it.

I use a 100% hydration organic white starter, with a small amount of rye starter mixed in at feeding time for extra muscle (don't trust these pale white ones).  The starter is very active, refreshed every 12 hrs.  I use 35-40% starter in the final mix.  Cold tapwater - mostly rainwater unless we've had to buy mains water in times of drought, the yeast and bacteria don't seem to care.  I don't delay from turning dough out time to loading into oven (which is blooming hot). Let us know how it turns out.

I found this nice sourdough ciabatta recipe here.  http://www.wildyeastblog.com/2008/07/28/sourdough-ciabatta-rolls/
There is nice instructions with pictures there.  That should help.

Ciabatta should be a great bread for the home baker. The secret to getting those large crumb texture with the glossyness is to start with a "Biga"
A Biga is a very tight dough 48% water mixed the day before your dough is finished, I sugest 1000grams low ash flour (bakers) 100g rotten dough (sour) "which has no oils or salt in it" and 480 ml of warm water mix this lightly and let time work the gluten out. bring it together a bit better than a short pastry and then leave it to rise for 3 hours, then put it in the fridge overnight.
next day (20hours) hydrate your Biga by slowly mixing in another 35% (350ml) water "Hot to touch"
15grams of Light malt powder disolved in water 
(this gives it a great crust and that crumb that makes a great Ciabatta)
24grams of sea salt             
(hold this back until dough has absorbed 80% of the liquid)
10ml Olive Oil
(add this last)
Don't add to much water at the start let the dough pull out before adding more, once smooth and all the gear is in rest dough in an lightly oiled container for 50 min then knock back and rest another 30 min.

Dived and rest on a very well floured board with the raw dough side up

Give this misse en formme 20 min

Get your oven up to 240oC

turn out onto a peel that has been sprinkled with sharps fold the dough now and set in oven bake with steam and until a nice dark brown crust appears, you smell the Caramell when its ready.

cool and enjoy