rench drain foundation

huangyhg

trench drain foundation
for typical 8-12" wide pre-fabbed trench drains, do you normally put joints along the length (this one is 120 ft long) or just reinforce it and let it crack?   
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construction joints every 40 ft or so would be fine.  letting it crack probably works too.  you can go either way and probably be okay.
im from australia and here we just lay the drain on a bed of granitic sand.  you guys place the drain on a concrete foundation ?