Type of problem addressed
Taking into account the presence of highly compressible soils and evaluating the loads involved, the designers preferred to evaluate a consolidation system based on deep foundations. The geological investigations, carried out with static penetrometry, have in fact identified the presence of alluvial deposits, of recent and current times, of a predominantly silty-clayey composition. These soils are underneath a superficial layer of anthropic fill, with a variable thickness, between approximately 1 and 2 m.
Furthermore, the investigations have highlighted the presence of a superficial aquifer, the level of which is subject to considerable fluctuations depending on the season and the rainfall regime, reaching heights of less than 1 metre.
The following aspects played a fundamental role in choosing the type of foundation consolidation to use:
- the urgent need to begin renovation work on the condominium;
- very narrow spaces (historic center and crane positioned in the courtyard area of the condominium);
- need for the least invasive and fastest possible intervention;
- given the nature of the soil being compressible to great depths, an intervention with special deep foundations was necessary.
The choice was therefore oriented towards SYStab Preloaded Poles, which guaranteed the overcoming of all the difficulties set out above.
Consolidation of the crane plinths with SYStab preloaded micropiles
The methodology proposed by SYStab consists of fixing special steel plates made according to the loads to the existing foundation. This special metal carpentry allows you to exploit the contrast offered by the structure for driving the poles into the ground with the hydraulic jacks, set on the collars of the plates themselves. The insertion occurs gradually, without producing potentially dangerous vibrations for the crane.
Given the loads involved, 22 micropiles with a diameter of 114 mm were necessary. To implement them, no excavations were carried out, but only some simple core drilling of the road surface and the external paving of the condominium square.
Advantages of seabed consolidation with the SYStab piling system
The consolidation of the foundations with pre-loaded micropiles made it possible to definitively stabilize the 4 plinths of the crane and to continue with the renovation of the condominium in complete safety.
The consolidation methodology with pre-loaded piles in these cases has notable advantages compared to traditional techniques:
- very quick implementation times;
- possibility of operating in narrow spaces and with multiple jacks simultaneously;
- no waste material is produced nor is sludge or water used;
- no vibrations harmful to the structures are produced;
- preload for the cancellation of primary settlements for all piles;
- the capacity of each micropile is tested during construction by monitoring the installation pressures;
- possibility of carrying out load tests according to regulations, with simplified methods.
The overall work, as regards the micropile driving phase, lasted only 5 days and allowed the driving of 22 micropiles with a diameter of 114 mm and a length of approximately 13 metres, including the final fixing of the piles to the steel plates, which guarantees the safety of the final load transfer result. The technique used allowed the piles to be built quickly, with minimal inconvenience and without creating potentially dangerous stresses on the crane structure.
For further information
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