How To: Construct a Wash Through

Hello engineers!

Recently, i have been assigned by my APM (Assistance Project Manager) to construct a new wash through (where every lorry wash their muddy tyres) replacing the old one. This is not the same type as the old one whereby the new wash trough no need any workers to clean the tyres but the driver have to go back and forth several times to clean the tyres. The dimension is as follows:

Length: 9 meters
Concrete Thickness: 300mm (including crusher run/lean concrete)
Concrete grade: C20
Rebar: BRC A7
Shape: curve shape.
Water level: 300mm

So, i start off with cutting the soil with a curve shape then poured one load of crusher run onto it.. Compact a little, then erect the formwork and arrange BRC A7 for the slab.. later in the evening, poured 15m³ of concrete grade 30. After a while, until the concrete already dry up a bit then do the grooveline using 3inch x 6inch wood. COMPLETE! YEY!!

But, the next day i found something is not right... The slope on the front side is much much much higher than the back one... If we were to collect water in it, there won't be any! DAMN! What went wrong!?

So, we (Me and the APM) decided to add some more height at the lower partand construct the wall higher than it should be... Next 2 days, we poured in water and the result is quite ok, the water collect at the lower side more and quite deep (more than 300mm height)

So, what is the problem actually?

For all of you engineers out there, you must remember 1 think before construct anything at site:

"LEVELING IS THE MOST IMPORTANT THING IN CONSTRUCTION"

My mistake in this simple project is because i'm not taking or doing any leveling before constructing the wash trough.. Therefore, here are some tips to construct a wash trough:

1. Get the OGL (Original Ground Level) at the location.
2. Set your own level for the structure based on the OGL.
3. Calculate other level for the structure (i.e the wash trough front part, back part, center part, etc)
4. Mark the desired and calculated level at site.
5. Start construct / excavate to desired level.
6. Double check the level, sufficient or not.
7. Pour crusher run / lean concrete (compact if using crusher run / leave one day for lean concrete)
8. Erect formwork, put rebar, and mark the slab thickness.
9. Pour concrete

Walla! your wash trough is complete! Good luck guys!

(easier to say than done actually!)