The brief
Ground water sat 2 m below existing level and never dropped. Dewatering at the volume required would have been refused, so the design had to hold water out rather than pump it away.
Uplift on the raft exceeded the dead load of the completed structure at basement stage.
What we did
One contractor from the borelog to the final test certificate.
1,000 mm diaphragm wall taken 4 m into the underlying clay to cut the seepage path.
Permanent tension anchors under the raft with double corrosion protection.
Two levels of 800 mm pipe struts, preloaded and released as slabs cast.
Slurry parameters, cube results and anchor certificates issued weekly to the client.
4 levels
Basement depth
32 m
Wall depth
96
Permanent uplift anchors
< 2 l/min
Total seepage at handover
On site
“The wall held water out from day one. We budgeted for continuous dewatering and never switched the pumps on.”
More work
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