Kessel Aqualift F Basic Instructions D'utilisation page 73

5.10 Backfill the excavation pit
Fill the excavation pit with suitable filling material (ballast
with size 0/16 grain, 50 cm all round), whilst compacting
the filling material properly (e.g. with a vibrating plate) to
Dpr ≥ 95% every 30 cm.
For proper fastening, surround the base section with lean
concrete (see lean concrete wedge in the figure).
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