Tag Archives: rebar schedule

Vehicle Inspection Pit

This was one of those jobs that you thought it was a good idea at the time, once construction started and things didn’t go as planned, I wished I’d never started it and the only way out was to spend your way out!

April 2011 was day one, the plan was to sink a vehicle inspection pit into the drive so that when it’s not in use, it would be completely covered and therefore unnoticeable, the pit had to be narrow enough to take the small car we had (Fiat Punto) but robust enough so that when our 3.5t motorhome was over it the walls didn’t collapse with me in it, also it had to be the correct height that I could work under the car or van comfortably and the right length that I can get to at least half of the underside of the van without it sticking out across the pavement (sidewalk for US visitors).

First stage was to confirm that planning permission didn’t apply, which it didn’t and secondly that there were no buried services that could stop the project, I did lift manlids to check the direction of pipes and wrote to the gas, electricity, telephone and water utility companies and all came back ok, the only thing I had to move out of the way was the armored conduit which goes to the outside lights which was easy as I’d fitted it.

One the dimensions were decided on, I started researching the reinforcing steel bars and type of concrete required, from this I drew a  rebar plan which gave me the quantities of steel and concrete needed.

rebar

I did explore using a ‘tanked’ construction and simply digging a hole and sinking it in, what bothered me was the high water table we have here and if you google ‘hydrostatic pressure’ their are examples where swimming pools have simply been pushed out of the ground, not a good look!

I opted to use 18mm plywood to make a ‘shuttered’ form even though the wood would be wasted, on balance it was still cheaper than hiring in bespoke steel panels from a local supplier.

The following series of pictures show the construction from the marking out of the hole to the finished pit, I mentioned at the start about things not turning out as expected, I made a flawed assumption that after the hole was dug, I could get away without propping the sides (I know it was stupid!), anyway fortunately I wasn’t in the hole at the time, but the sides caved in, now the problem this presented was that the cost to fix this.

The cost escalated as I would need a JCB rather than a mini digger to scoop out the spill due to the now extended boom reach required, also I would need two more 12m2 skips at £110.00 each, not to mention the additional backfill to make good the sides where the clay had slid from, all in all a blinking nightmare, so, do I fill the lot in and cut may losses, ore spend out of it, well the rest is history and a year later the credit card was finally paid off :-).

Drive

marked
Outline marked out

pre dig

dig1

start of trenching

services ducting

dig midway

dig in progress

dig completed

completed
Completed Holes
All done – spot on digging job, brown pipe is for the air vent and the Black tube is for the submersible pump to pump the pit out as their was no intention to make it waterproof.
collapse
Everything was going so well until the sides collapsed

Pit sides caved in the day after it was dug as I didn’t support them, the ground is heavy clay which slipped leaving a overhang, this overhang was soil and hay as the land on which the house was built used to be a farmers field.

So, change of plan, I decided to build the steel work outside of the hole and surround it in shuttering ply, and have the digger lift it into the hole……

Cage
Start of cage construction
cage 2
Lin looking happy to help
jcb
JCB with longer reach than a minidigger to clear the collapsed hole
base
Side shuttering ongoing

side

walls
Wall shuttering in place
welding
Rebar welded to angle iron edge protectors

backfill

internal shuttering

Please follow and like us: