Alexander Palace: design and arrangement works for the basements

Alexander Palace is a part of the great architectural ensemble of Tsarskoe Selo in Saint Petersburg, which is under UNESCO protection and is part of Russian cultural heritage as well as the World’s heritage. The palace served as a gift from Russian Empress Catherine the Great to her grandson Alexander I (under rule of Alexander I Russian army in alliance with allies won the war over Napoleon) on the day of his marriage. Now it is a museum. But before recently it was used for various purposes and maintenance was not quite sufficient to preserve its amazing interiors.  There were no major repairs, leading to slight wrecking of the building.


 

Brick pillars in the basement before reconstruction

While in operation the building faced only slight repairs mainly in regard to utility services. During repairs design features of the building were not taken in consideration.
Since November 2009 Alexander Palace has been a part of Tsarskoye Selo State Museum. In 2010 first works were carried out to restore facades and three central halls of the State enfilade.  
After the Alexander Palace was assigned to the State Museum it was meant to serve as another exhibition palace. But being in disrepair, the building required major repairs and restoration.   
In 2010 open competitive tender was held for elaboration of design documentation contract with the state authorities regarding restoration, technical re-equipment and adjusting the building for museum needs.  
Architect’s  office “Studio 44” was chosen as general designer, and OOO “PSB Zhilstroy” as general contractor.  OOO “Geoizol” was charged with all works regarding design and arrangements of the basements.
Specialists of the company had a challenge set for adjusting the basements of Alexander Palace to modern needs of museum complex.
According to design some infrastructure facilities were to be located in the area (2 cafes, cloak-room, service rooms).  
Implementation of design decision required embedment of the floor at the depth of 1.5-2m deeper than existing floors and 0.5-1m deeper than marks of bedding of the basement. Also the issue of preserving the maximum square of the basement area was to be solved.  


Beams installations and assembling of the truss space structure

Through the holes, drilled by Geoizol company, mixed soils, namely sandy loam and clay loam of different kinds were discovered under the bedding of the basements.  
 The Alexander Palace building was erected on man-made embankment.  Considering the soils below being resistant from the point of filtration characteristics and thus playing  a role of confining bed of a kind, season ground waters, like perched water (noted level 0.65 m deeper the daylight surface) may cause hazardous risk of flooding the basement.   Survey proved that with clay bed under the palace, the problem has been present since the beginning.   



Beams installations and mantling of the space structure and implementation of the metal runners


Primary goal is to preserve existing historical formations. Additional complexity is in structure of the brick arch floors of the basement. Even slightest deformations, should they appear during embedding, may affect the structures irreversibly, leading to decay of the brick arches. Geoizol specialists defined following stages in their design:
•    immersing the wall of sheet piles along the perimeter of all embedded rooms of the palace’s basement;
•    GEOIZOL-MP anchors installations for “suspension” of the pillars of the basement;
•    metal casing of the brick pillars assembling;
•     brick pillars being strapped through with beams;
•     dismantling of the old pillars foundations;
•     underpinning of new reinforced-concrete foundations for pillars;
•     accomplishment of waterproofing works of caisson type.



Hydraulic jacks assembly for pillars mounting

Test site was organized in the construction site, where all complex of works for transfer of pillars from old foundation to the new ones was modeled and implemented. Phased monitoring during its implementations helped to define the sequence of work and clarify the technologies.
As after embedding the existing foundation’s beddings are higher than design level of the basement floor, temporary suspending of the brick pillars was designed with injection piles GEOIZOL-MP.
Micropiling GEOIZOL-MP performed from existing marks of the basement with compact drilling machines.
During construction works it appeared that the pillars were made in a well form with quarry rock filling the inner spaces.   For materials of backing of well-shaped pillars’ bond cohesion it was decided to inject pillars with cement-lime mortar and implement additional metal runner for the pillars. Assembling of struts and lateral bracings between the beams takes place.  
Including piles into the framework (securing technological settlement of the piles) and special structure of the truss is implemented by loading on it design loads with jacks.
With a help of four hydraulic jacks aggregated design load was loaded on each pillar of the basement floor. Jacks themselves were installed in the closest proximity to pile heads.  While implementing “suspension” of each pillar in this manner, Geoizol specialists “cut off” it form historic foundation
 

New reinforce-concrete foundation cross-section

Next stage of works contained pressing of sheet piles in all embedded rooms to prevent pile heave from under existing foundations.  All works started from pioneer cut, performed with division into bays no more than 1.5m in length. After capping beam and struts (1.5 m distance) being installed, the ground was excavated up to design level.
After excavation under pillars and dismantling of existing foundation new reinforced-concrete foundation was performed. Later design load to be loaded on top of it with hydraulic jacks, being installed “in thrust” with metalwork.  By design load settlement of new foundation to be modeled based on natural foundation.
On completing of works on underpinning for the new pillars metalwork to be dismantled, micro-pile load to be shifted and 100% of load-bearing structures to be loaded on new foundation.  


 

Concreting new reinforced-concrete foundations


At final stage reinforced-concrete slab and compression walls of the basement floor are installed according to the design. Waterproof works to be performed as well. Before works started geodesic marks were defined. Geodesic monitoring is carrying out during the process, allowing secure deformations and settlements.