STATE OF THE ART

In the context of what is described below, tunnel means the artificial underground or submarine passage with an aperture at each end.

There are various types of tunnels for road, rail or pedestrian traffic, for water supply or sewage, and for connecting buildings for convenient passage. They are built for civilian, military or illegal activities. They can be linked together in tunnel networks.

The construction method of the tunnel depends on various factors such as the type of soil, the presence of water, the length and diameter of the tunnel, the depth, the supporting logistics, die shape of the tunnel and adequate risk management.

There are three basic types of tunnel construction in common use:

- cut-and-cover tunnels are built in a shallow trench and then covered;

- bored tunnels are built in situ, without removing the overlying soil;

- submerged tunnel, a tube sunk in a stretch of water and bound to the seabed.

The submerged tunnel method has been in use for around 100 years and more than 150 submerged tunnels have been built around the world for crossings up to 60m deep.

Examples are: the Marmaray tunnel, which connects the European and Asian parts of Istanbul, Turkey, built 55 meters below sea level, the portion of the Hong Kong- Zhuhai-Macao bridge, completed in 2018 which is located at a depth of 30 meters and the Fehmarn tunnel between Denmark and Germany at a depth of 40 meters which, with its 18 km, will be the longest road and rail tunnel in the world. The submerged tunnel is typically composed of segments, each of which is built elsewhere and floated at the laying site to be sunk into position and then connected to the already laid part of the tunnel. Submerged tunnels are often used in conjunction with other forms of tunnels at their ends, such as a cut-and-cover or bored tunnel, to continue the tunnel to the earth's surface.

Submerged tunnels can be built:

- on a shallow trench at the bottom of the sea (Fig.l);

- with trench entirely below the seabed level (Fig.2, section of road and railway tunnel).

In the Fig.l and 2 it is shown the bottom 7, the tube 10 and the prepared bottom 40 on which the tube is placed.

The trench is filled and the necessary protection 4 is added. After these steps the tunnel is complete and internal assembly can be performed.

Tunnel segments can be constructed in various ways. In the United States, the preferred method is steel or cast iron tubes, which are then lined with concrete. This allows for the use of conventional shipbuilding techniques. In Europe, reinforced concrete box tubes are mostly used.

Ordinary and prestressed reinforced concrete tubes are usually used for reliability and durability.

The aqueduct that connected the town of Eifel to Cologne, built by the ancient Romans in 80 BC. in concrete and stone, it still exists, after an operation of 2000 years.

Over time the construction moved from metal tubes with cement mortars or the incorporation of concrete castings inside tubular elements in metal sheet, to the core of metal sheet, with hydraulic sealing functions, incorporated in a casting of concrete, up to the current systems of industrial manufacturing by centrifugation. Recent technological advances such as “crystalline technology” make it possible to create a concrete where even the micrometric voids are filled, making it effectively waterproof and suitable for the construction of the most exposed offshore structures.

The main advantage of an submerged tunnel is the economic convenience of its implementation compared to the alternative option of a bored tunnel.

Other advantages of immersed tubes are their construction speed, greater resistance to seismic phenomena, construction safety and the wide range of profiles that can be created.

Disadvantages include direct contact with water which requires specific waterproofing design around the joints, the segmental approach which requires careful and precise connection making and the complicated sequence of operations to join the segments to the part already in place, operates without flooding it.

Many patents such as. DE50882, JP9316901, GB348204, EP0899422, JP09-273382, JP2024489, U.S.1.441.698, U.S.4.889.448 and U.S.4.433.937 A concern techniques for the construction of tunnels in the ground below the bottom of the water.

Other patents concern methods or techniques in the case in which the tunnel is to be built partially or totally in water.

DE 33 33 850 describes a technique in which the tunnel is built in successive prefabricated sections in a watertight excavation and gradually pushed into the water up to their service position.

US7766579B2 deals with a method for the construction of tunnels with sections preferably not more than 3 meters long and manufactured directly on the seabed.

EP0034907A1 proposes the construction of the underwater tunnel with an arch conformation with the concavity downwards to resist the hydrostatic thrust. The tunnel is built starting from two tunnel sections, at the two ends to be joined, which are gradually extended until they meet.

And there are also patents concerning the construction of sections of annular tunnels on the surface (on land or on a floating ship), which are then conveyed to the launching point, sink them in their final position on underwater soil and assembled together (as in submerged tunnels, cited in the state of the art).

For example JPH10102520A describes a technique where pieces of tunnels closed at both ends with "spherical shell-like covers" are made out of the water. The pieces are placed on the seabed and then joined / welded underwater, the "spherical shell-like cover" are removed and then the water inside the tunnel is drained to empty it.

JP2016035153 A exclusively concerns a method for the final junction of a submerged tunnel (two tunnel branches facing each other), through a special "junction box".

GB845180A describes a method for assembling underwater tunnel sections built out of the water. The tunnel sections are fitted with wheels at the bottom. A gantry crane is used to slide the sections to be added over those already fixed, until they reach the end and then rest on the backdrop.

GB2016065A describes a method for creating a tunnel that is not resting on the seabed but kept anchored at a certain height from it and which consists in preparing a dry dock that can be filled and emptied by means of pumps at one of the banks to be joined, within this basin a section of the tunnel of a certain length which is then made to come out of the basin by means of an overhead crane and placed in the position it must occupy. Then the dry dock is moved approximately the length of the tunnel piece built and, in the new location, the next piece is built. This new piece is then always made to come out longitudinally from the basin and anchored to the previous one. None of the patents found or of the techniques adopted for the construction of the tunnels indicate a method for the construction of tunnels such as the one proposed and which exploits the differential of hydrostatic pressures and gravitational forces.

OBJECT AND SUMMARY OF THE INVENTION

Aim of the present invention is to provide an innovative method for the construction of submerged railway or road tunnels, where the tube is built out of the water, immersed and progressively placed in the trench prepared on the seabed without having to join segments of the external structure of the tube below the water level. This is in order to make their realization simpler and more efficient.

The present invention should overcome some drawbacks of the known art and bring further advantages.

These and other objects are achieved by means of the innovative method characterized by the attached claims, which are an integral part of the present description.

The basic idea of the present invention is a method that exploits the differential of the hydrostatic and gravitational forces acting on the tube during installation which, in addition to using the materials usually used, which include reinforced concrete and steel, includes the imposition and the control both of the differential of the forces acting on it, through the positioning of weights along the tube itself, and of the position of the construction structure so as to make it possible to gradually lay the tube on the predisposed trench with a deformation of the part of it not yet placed on the base that allows to keep the stresses in the materials used within the desired limits.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described below with reference to non-limiting examples provided by way of non-limiting explanation of the attached drawings. These drawings show some aspects and embodiments of the present invention and, where necessary, reference numbers indicating similar structures, components, materials and / or elements in the various figures are indicated with the same reference number.

Fig. 1 is a representation of a submerged tunnel with a shallow trench at the bottom of the sea.

Fig. 2 is a representation of a submerged tunnel with trench entirely below the level of the seabed.

Figures 3a and 3b are representations of some types of tube sections.

Fig. 4 is a representation of the tube laying scheme.

DETAILED DESCRIPTION OF THE INVENTION

While the invention is susceptible to many modifications and alternative constructions, some embodiments are shown in the drawings and will be described in detail below. However, it is to be understood that the present invention is not limited to the embodiments shown, but conversely, the invention is intended to cover all modifications, alternative and equivalent constructions within the scope of the invention as claimed.

The words or phrases "for example", "etc.", "or" indicate non-exclusive and without limitation alternatives, unless otherwise specified.

The word "comprise" means “comprise but not limited to", unless otherwise indicated and the word "includes" means "includes but not limited to", unless otherwise specified.

The word "tube" means the external structural part of an artificial tunnel that is not dug or drilled into a solid material. By tube is meant an element of variable length which comprises at least one layer of external material and at least one internal cavity or void, the section of which can include elements of circles, polygons or parts thereof and can have an internal cavity or void 24 as in Fig. 3 a or more internal empty cavities 24 as in Fig.3b.

The term "structural material" is intended to include materials such as reinforced concrete, steel, cast iron and composite materials which may include fibers.

The term ’’tube structure” refers to the part of the tube which includes one or more layers of structural materials.

The word "deflection" or the word “deformation” mean the modification of the shape of a body due to the effect of forces acting on it.

An innovative method for the construction of submarine tunnels is proposed here which partly exploits the type of construction of the submerged tunnels, obviating the difficulties that this type of construction entails in assembling the various segments underwater.

In the innovative method proposed here, the tube is built progressively out of the water on a support structure from which it is then lowered by appropriately moving this structure and adequately ballasting the tube to immerse it and gradually lay it in the trench prepared on the seabed. The part of the tube already laid and stabilized places a constraint on the part built and not yet laid; the other constraint is given by the construction and laying structure at the other end.

Unlike the laying of submarine telecommunication cables which have a weight of their own greater than the hydrostatic force that water exerts on them when immersed, the laying tube may have a weight lower than the hydrostatic force acting on it.

The own weight of the tube depends on the shape, dimensions and materials used. Depending on the method adopted for the construction of the tube, it may have a structure that includes one or more layers which may include reinforced concrete, steel, cast iron or composite materials that use fibers. In Fig. 3a and 3b two examples of tube sections are shown. The tube can have a structure which during installation can comprise an external layer 21 or more layers 21 and 22. The laid and stabilized tube can have a section that includes further internal layers 23 or 22 and 23.

During installation, the tube (Fig. 4) is subjected to various forces acting on it and which include:

- the hydrostatic forces 6, due to the immersed volumes;

- the gravitational forces, which include the weight of the tube 5 itself and any ballasts applied 3;

- constraining forces or reactions;

- dynamic forces due to wave motion, currents and, for parts out of the water, winds.

The construction and laying structure 30 may or may not be floating according to the depth of the seabed 7 on which the tunnel is placed and its position will vary during laying to make the tube 1 progressively lower into the water. The structure 30 may have a further structure 31 to constrain the tube 1 during its extension which could include addition of prefabricated elements 11. Such structures will provide adequate restraints to the tube during the lowering and laying. The structures 31 and 30 will in turn be constrained to the outer layer 21 of the tube 1 and this constraint will include a system that allows the tube to move with respect to the laying structure for the lowering of the tube.

The part of the tube 1 in laying that goes from the stabilized part of it on the seabed to the construction an laying structure 30 will be subject to deflection similar to those of a beam with loads distributed along the length. Loads that at each point will be the resultant of the forces acting on it.

The tube, in the installation phase, will have a weight per unit of length determined by the thickness of the structural layers 21 and eventually 22. The elements to define the minimum thickness of the layer or layers constituting this structure, taking into account the safety factors, include the pressures that act on it, including the constraints, the shape and dimensions of the tube section, the characteristics of the material or materials used and the methods of execution of the installation.

The external dimensions of the tube will determine the thrust that the water will exert on the tube when it is folly immersed.

There will then be the additional loads 3 which will be chosen on the basis of the wanted deflection of the laying tube.

Generally the hydrostatic forces will be greater than the gravitational ones due to the weight of the tube being laid, which includes layer 21 or layers 21 and 22. In this case, the desired differential will be obtained by distributing weights along the tube being laid. Weights that can be placed both inside and outside the tube structure.

There could be cases in which the weight of the tube during installation is greater than the hydrostatic force acting on it and which could require elements constrained to the external part of the tube to give upward hydrostatic forces in order to obtain the desired differential.

By combining the position of the construction structure with the additional loads, it will be possible to obtain and control the desired differential between hydrostatic and gravitational forces in order to have the desired deflection of the tube with the stresses in the materials constituting the structure within the limits get fixed.

The flexibility of the tube structure itself is exploited, determined by its profile, its section and the materials used.

The external structural part 21 and eventually 22 that will gradually reach its final position in the trench 8 will be stabilized by creating or completing any protections 4, filling the trench 8, and carrying out the internal works which may include the construction of further layers 23 of concrete reinforced or of other material to give greater rigidity and resistance to the tunnel, obtaining the desired internal section of the tube 24. In the case illustrated in Fig. 4 the trench is all under the level 7 of the seabed,

The materials necessary for the construction of the tube and for the completion of the internal works can be brought on site by exploiting both the already built part of the tunnel and the part of the tube not yet laid.

The proposed innovative method makes it possible to create a first external layer of tunnel as if it had been excavated with the boriing technique, to then build the remaining layer or layers internally with the usual techniques. Furthermore, the profile of this layer is not bound to the circular shape of the bored tunnels but can, for example, assume the shape indicated in Fig.3b. The typical quantities involved for this type of construction (depth, length, type of profile, section of the profile and safety criteria) allow the desired deformations with stresses compatible with the use of various materials including reinforced concrete and steel, cast iron and composite materials with fiber elements.