TMB
The operation of the cutter is divided into production cycles. The activities that make up the individual production processes are fully automated and take place within the fresa.
Each cycle – lasting an hour and a half – allowed to 1,50 meters of finished tunnel, complete with the final covering.
In detail: the head of the shield, rotating, dig the earth of the tunnel face. This is collected inside the so-called "sludge chamber" and mixed to form the paste necessary to support the excavation wall. As the car progresses, a quantity of paste is applied to the excavation face such as to allow the pressure to be maintained.
Proceeding with advancement, the rear part of the shield positions the reinforced concrete segments for the definitive lining of the tunnel which, connected, allow you to create a tubular structure 1,50 meters in length.
The space between the excavated soil and the lining is filled with cement mortars injected under pressure as the machine advances. The transport of the lining segments and all materials, as well as the removal of excavated earth, takes place via narrow gauge trains.
In parallel, the materials are unloaded at the rear part of the cutter, to the assembly of the service track and the pedestrian walkway, to the adaptation of clean air ducts, of industrial cooling water and the electricity cable.
NATURAL GALLERY
A tunnel built underground by removing soil and rock is called a natural tunnel (blind hole excavation) and the implementation of support structures. Means and methods of execution depend on the characteristics of the terrain. In less consistent soil the excavation is carried out with mechanical means (excavators, pale, various tools); in rocky terrain the use of explosives is used (mine): Horizontal holes are drilled on the face of the excavation parallel to the axis of the tunnel, in which the charges are inserted and made to shine in groups with very short intervals of time. Often for terrain of a certain consistency a frontal cutter excavator is used, which excavates the entire section of the tunnel. Excavation methods are classified according to whether they proceed with a full section or partial section attack. Currently (except in the case of very difficult terrain, which require specific technologies such as pre-consolidation or freezing) we proceed with full section excavation (o almost), trying to make the most of the self-sustaining capabilities of the land: the ceiling and the walls of the compartment are supported with bolts and rock anchors or with metal ribs, providing an immediate pre-coating with shotcrete (sprayed concrete). When sufficient self-sufficiency of the land has been achieved, waterproof sheets or sheaths are applied to avoid dripping water in the tunnel and then the final covering is carried out.
ARTIFICIAL TUNNEL
Made with the “cut” technique & cover” with emptying from the inside.
Excavation from above presupposes the construction of the artificial tunnel, interference with any subservices is resolved (electricity networks, sewerage, telefonica, aqueduct, district heating, public lighting, gas and fiber optics)
The excavation for the construction of the artefact is supported by bulkheads of small or large diameter piles pulled.
The box-like structure is made of reinforced concrete cast on site and is completely waterproofed.
Once the artificial tunnel has been built, on the surface the "pre-operam" conditions are restored
MICROPALI
Micropiles are especially suitable for foundation work and in the field of anchoring.
They are therefore considered small diameter piles (less than 300mm) and are made up of mortar or cement mixtures and suitable steel reinforcement.
I micropali sono scavati con speciali trivelle o sonde a percussione con asportazione di terreno.
Possono essere realizzati in tutti i tipi di terreno anche stratificati con interstrati rocciosi e la loro costruzione avviene in tre fasi:
inizialmente viene eseguita la perforazione liberando il foro dai detriti con l’ausilio di fanghi bentonitici che sostengano la parete del foro stesso;
a perforazione ultimata viene calata la gabbia o i tubi d’acciaio che costituiscono l’armatura del palo;
una volta posta in opera l’armatura si procede alla cementificazione del foro tramite malta di cemento e sabbia opportunamente miscelata per garantirne l’omogeneità.
TIRANTI
I tiranti sono elementi strutturali operanti in trazione e vengono usati per stabilizzare pareti rocciose e per ancorare al terreno paratie o muri di sostegno. La loro funzione è, in generale, quella di trasferire i vincoli necessari alla statica dell’opera in zone in cui il terreno offre la possibilità di assorbire le sollecitazioni in gioco.
Vengono realizzati con le stesse modalità dei micropali e come armatura viene inserito nel foro un tirante costituito da trefoli in acciaio armonico in numero sufficiente alla trazione prevista in fase di progetto ovvero da barre in acciaio.
JET-GROUTING
Con jet grouting o jetting si definisce una tecnologia che consiste nell’iniezione di un fluido stabilizzante ad altissima pressione nel terreno e che ha come scopo il consolidamento di volumi delimitati di terreno in posto al fine di migliorarne le caratteristiche meccaniche quali la resistenza e la permeabilita.
Nel terreno viene introdotta una colonna di aste munite alle loro estremità inferiore di un utensile in grado di permetterne l’avanzamento nel terreno stesso mediante movimento rotatorio con effetto disgregante o, in terreni adatti, per avvitamento.
Raggiunta la profondita prevista attraverso il treno di aste viene pompato ad altissima pressione (200 – 700 bar) attraverso appositi ugelli, una miscela stabilizzante con la quale il terreno viene disgregato e mescolato in situ, a formare, una volta decorso il tempo di presa della miscela, un elemento di terreno conglomerato (elemento o colonna jetting) con caratteristiche meccaniche migliorate rispetto alle condizioni iniziali.
DRENI
I dreni sub-orizzontali sono delle perforazioni eseguite con leggera tendenza rispetto ad un’asse orizzontale su cui vengono messe barre microfessurate al fine di emungere acqua da terreni instabili in fase di “collasso”.
I dreni sub-orizzontali si distinguono in due tipi: per captazione e a gravità, i secondi detti anche “dreni sifone” emungono acqua con il sistema a sifone.