Propping against air
I have been presented with this issue today. The groundwork contractor, Churngold, have been given a package to construct a large retaining wall that will replace a wall which was being propped by a podium deck and intermediate floor slab. See the below drawing.
The wall is being cast in three stages. 1) Mass concrete footing. 2) Waterproof concrete on footing and kicker. 3) Waterproof concrete for wall. Stage 1 is due for completion on Monday 8 Jul.
The formwork is a proprietary system from Mabey and requires soldiers at 1.5m centres at 1.66m height and with a leg of 1.6m. See the below photo to identify formwork.
As can be seen in the above photo there is a section of slab that has been removed as part of the demolition works, from which the groundworks contractor were planning on propping against.
My options for the solution to this so far have been.
a) Cast footings where required.
b) Redesign propping system.
c) Cut short pour with a stop end to a safe location where the propping is stable against the slab.
d) Mass pour a slab in the hole and allow the subcontractor to prop against this on Monday.
My initial thoughts are a combination of a) and d) which will appease both the QS and the subby. However I need to satisfy myself that the prop loadings will be taken by the slab under 3 day strength (assuming the concrete is poured on Friday 5 Jul), and secondly that the backfill material will take the load from the slab and prop loadings.
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Or do a few calculations to see what the load in the leg is and compare that to a jacking load under the end of the leg….. i.e. draw a model and apply some actions…..
Potentially and this was my initial thoughts, however as it is a proprietary system it needs to be installed within certain parameters. What can’t be seen here is another prop which is anchored to the top of the formwork and about 150mm out from the leg of the soldier.
In the interests of time, a partial slab cast in place is the most likely option. I agree other solutions may fit the bill, but this option will easily enable the pour on Monday.