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.
The micropiles are dug with special augers or percussion probes with soil removal.
They can be built in all types of terrain even stratified with rocky interlayers and their construction takes place in three phases:
initially the drilling is carried out by freeing the hole from debris with the aid of bentonite mud which supports the wall of the hole itself;
once the drilling is completed, the steel cage or tubes that make up the pole's reinforcement are lowered;
once the reinforcement has been put in place, the hole is cemented using cement mortar and sand appropriately mixed to guarantee its homogeneity.
TIE RODS
Tie rods are structural elements that operate in traction and are used to stabilize rock walls and to anchor bulkheads or retaining walls to the ground. Their function is, in general, that of transferring the constraints necessary for the statics of the work to areas where the ground offers the possibility of absorbing the stresses involved.
They are made in the same way as micropiles and as reinforcement a tie rod made up of harmonic steel strands in a sufficient number for the traction foreseen in the design phase or steel bars is inserted into the hole..
JET-GROUTING
Jet grouting or jetting is defined as a technology which consists in the injection of a stabilizing fluid at very high pressure into the ground and which has the aim of consolidating limited volumes of soil in place in order to improve its mechanical characteristics such as resistance and permeability..
A column of rods is introduced into the ground equipped at their lower end with a tool capable of allowing them to advance into the ground itself through a rotary movement with a disintegrating or, in suitable soil, for screwing.
Once the expected depth has been reached, the train of rods is pumped at very high pressure (200 – 700 bar) through special nozzles, a stabilizing mixture with which the soil is broken up and mixed in situ, to form, once the setting time of the mixture has elapsed, a conglomerate soil element (element or jetting column) with improved mechanical characteristics compared to the initial conditions.
Marrow
Sub-horizontal drains are perforations made with a slight tendency with respect to a horizontal axis on which micro-cracked bars are placed in order to extract water from unstable soils during the “collapse”.
Sub-horizontal drains are divided into two types: by collection and gravity, the latter also called “siphon drains” they extract water with the siphon system.