any idea how to fix this?

Hey everyone, i'v been playing around with generating destructible environments and its going great!
But.... I only have one problem, see the pics



So i have a mesh collider with the convex setting enabled and no physical material, could this be the reason?
Also i'm seeing that the mesh has colliders partially inside each other, think that's the problem...

So any help would be appreciated!
And thanks for your time



...........................................
Basically i get it to work, but when i want to rigidbody for gravity to the pieces so they fall when there is nothing beneath them, they automatically fall at runtime
And yes i'm new to working with the unity physics...

 

put them all to sleep at start
http://docs.unity3d.com/ScriptReference/Rigidbody.Sleep.html

 

After playing around, i think it is the colliders that make it do this, the collider collide with eachother then this happens....
Any way to get more accurate colliders??