Sandfilter Walls cracking under water test.

[Roadbridge]

Hi to all.
On inspection of a water retaining structure today I noticed two cracks have developed either side of a Sandfilter tank. The tank is 27 metres by 9 metres and is subdivided into three sections. The height of the stricter is three metres from the floor level with a 275mm base slab.

The contactor has recently began to fill the first section with water to test its water proofness when these cracks began to develop.

The cracks are located 7.2m from the end wall and 6.7m at 1.5m up from the floor level.
The structure is founded on compacted hardcore which in turn overlays rock.

My question is. What has caused the cracking to developed.

 

[Roadbridge]

Hi to all.

Some photos of the cracking

http://www.flickr.com/photos/tycho1a/4501080978/

http://www.flickr.com/photos/tycho1a/4501079672/

http://www.flickr.com/photos/tycho1a/4500443359/

 

[JedClampett]

From your pictures it's impossible to tell where the cracks are in relation to the interior walls or corners. Cracks could be caused by any number of reasons, including inadequate reinforcement, poor (or no) joint location, bad concrete or too thin walls.
Just because the cracks were noticed when the tank was first filled with water doesn't necessarily mean that they were caused by the liquid load. They might have been there already and just started leaking when filled with water.
More detail is required to start even guessing reasons.
Also note that sometimes (not always) leaks tend to close up when the concrete fully hydrates. How long have the cracks leaked?

 

[cvg]

these are irregular, diagonal cracks somewhat resembling poor consolidation of the concrete. Is there any chance the concrete was too long in transit, delay in vibration, too stiff of mix, cold joint created between two loads of concrete?