The project involves the construction of a future station, a cathedral-like structure about 110 m long and 17 m high, 35 metres underneath the ground floor of a shopping centre.

Load-spreading of the frame assembly located underneath the CNIT was a delicate operation requiring a high level of precision in order not to destabilise it, while keeping the shopping centre open.

  • Owner
  • Client
    Consortium VINCI Construction and Spie Batignolles
  • Instrumentation and monitoring
  • Delivery date

One of the greatest challenges in Freyssinet’s history in terms of jacking heavy structures

Freyssinet’s teams, experts in hydraulic jacking operations, designed an exceptional computer-assisted jacking system (CAL) to simultaneously take up the loads of 120 structural columns of the last parking level of the shopping centre. The aim was to transfer the load of the superstructure building to the future 2 m thick transfer slab that will form the roof of the station.

The most difficult phase was when we had to transfer the loads from the transfer slab to the final pillars. The operation was carried out perfectly thanks to the excellent preparation of our teams. This project is also extraordinary because of its duration: we kept our jacks pressurised at 100,000 tonnes for three years!

Jean, Site engineer, CNIT project manager

  • 100,000t
    Load of the frame assembly to be transferred 35 m deep
  • 1,500
    Number of Freyssibar Plus 1200-MPa prestressing bars used
  • 1,200
    Number of hydraulic jacks used to transfer loads
Load transfer system from columns to falsework

Load transfer under (pre)tension

In order to simultaneously transfer the load from the 120 existing structural columns, the Freyssinet teams implemented an exceptional system. This consisted in transferring the loads, previously taken up by the foundation sole plates of each column, to a falsework structure. To achieve this, each column was “waled” (i.e. “tightened”) by two reinforced concrete corsets flanged with Freyssibar + 1,200 prestressing bars. These prestressed structures were supported on four sets of micropiles by means of steel frames. Once this temporary structure was assembled, the stresses could be shifted to it and the columns sawed off.

CNIT-Station-France Digital assistance

Computer-aided precision jacking

Millimetre displacements associated with the release of tension when transferring loads onto the falsework were managed by a set of servo-controlled hydraulic jacks. The scope of the servo control system was unparalleled: a computer-aided lifting station (CAL) enabled to control all jacks of the 24 columns simultaneously. Thus, if a distant area of a column undergoing load transfer experienced higher than expected settlements, the control station was able to correct these deformations instantly. Subsequently, the CAL system was used to transfer the loads from the transfer slab to the final pillars. 360 jacks were then coordinated simultaneously around 56 pillars!

CNIT-Station-France Precision jacking

A restricted operation under strict monitoring

The safety of the load transfer operations was constantly ensured by a set of ultra-sensitive sensors, enabling the detection of displacement variations in the order of 1/10 mm and pressure variations in the order of one bar. In the event of a loss of pressure in the jacks or an unexpected displacement, an alarm was triggered and the system was designed to instantly compensate for the failure.

In addition to the great complexity of this unusual phasing, there was also the complexity of the logistics: the first phase took place in a confined area (2.2 m high ceiling), complicating the access of teams as well as the procurement of materials and equipment, the dimensions of which had to be adapted to the confined space.

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