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Lakhta Center Underground Cycle Pile Foundation
260 piles mounted on firm soil
will bear the tower loading of Lakhta Center.
At a depth of 20m-25m
a layer of very firm Vendian clay occurs
serving as a subbase for the foundation.
As for its properties
Vendian clay is similar to massive rock.
The first objective of the builders is
to prepare the site for the well drilling to follow.
From graders the works are switched to
drilling rigs.
They will pass underground
a distance equal to 25 storeys.
The first 30m of a well
are drilled by using casings.
They ensure protection from
soil caving and water ingress.
The quality of the works is monitored by the specialists
by using control video cameras.
The next step is a stage-by-stage lowering
of a reinforcement cage
comprising a few sections.
The specialists strictly observe
time intervals.
The time between the completion of the drilling
and the start of concreting
shall not exceed 8 hours.
The cage is prefabricated at a plant.
At site
they are installed and enlarged.
A cage is equipped with a duct
for conductors transmitting signals from
pressure and ultra-sound sensors
located throughout the whole pile shaft.
These enable to monitor the state of piles and
soil settlement under a pile.
Also pressure sensors
are installed in individual wells between larger piles.
It allows monitoring
the state of soil throughout all the piling.
Prior to lowering the sections of a cage
are coupled with each other.
The height of the structure assembled is 45 00:02:01,850 --> 00:02:06,370 82m.
The next step is concreting.
Concrete mix is supplied into a well
It is done from below
to prevent from soil caving.
The specialists monitor
concrete mix temperature and workability,
avoiding any abnormalities.
Upon the completion of concreting
tremie pipes are extracted
from a well.
In average a pile
bears a loading of
0.4% of the weight of the whole building.
Tests demonstrated that the margin of
the bearing capacity of piles exceeds design standards
by two times and a half.