HYDRAULIC STRUCTURES, I N PARTICULAR MARITI ME STRUCTURES

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The present invention concerns an a rtificial unit, as well as the related process and the formwork to make it, to be used for building the outer layer, also called armour, of maritime structures, such as emerged and submerged rubble mound breakwaters, jetties, revetments, and that, due to its configuration, may be a lso employed for more general hydraulic works where cast layers are present which must resist to stresses of a fluid (e.g. river embankments), permitting in an efficient, reliable, simple, a nd inexpensive way to increase stability, rugosity, roughness, porosity and interlocking of the layer, also facilitating the engagement with the underlying surface.

It is known that for making the a rmour of maritime cast works, natural elements as quarry stones and/or concrete artificial units may be used. The artificial units are advantageously employed in the case where the natural rock quarries are located at a n excessive distance from the construction site, so as to render their use uneconomical, or in the case where the rock quarries are devoid of large size stones. Usually, the artificial units have a simple shape (e.g. cubic or parallelepiped shape), or a complex shape in order to guarantee stability by exploiting their own weight or their own weight a nd mutual engagement, also called interlocking.

Until the second world war, maritime protection works were mainly made with natural stones and/or with concrete armour units of simple shape (e.g. cubic or parallelepiped shape) having large dimensions, so that stability was ensured only by the weight of the same element, by using a random or uniform placement and a rather smooth slope of the protection work. Starting from 1950, a new type of artificial armour unit was introduced, the so-called Tetrapod, developed with the intent to increase armour porosity in order to favour dissipation of the incident waves and, hence, to reduce reflection, transmission, run up and overtopping of the same waves. Moreover, the specific shape of the unit increases the capability of mutual engagement (interlocking) between contiguous units and, consequently, an increase of stability of the whole work, even in case of random placement of the units. Such artificial unit has marked the beginning of a new development of the concrete armour artificial units capable of significantly higher performance with respect to the classical armour units used until then for building such works; a timeline of such concrete armour units, for instance comprising the Tribar, Stabst, Akmon, Tripod, Cob, Do!os, Seabee, Shed, Accropode ^® , Haro ^® , Core Loc ^® , and Diahitis units, is disclosed by Bakker et al. in "Development of Concrete Breakwater Armour Units", 1st Coastal, Estuary and Offshore Engineering Specialty Conference of the Canadian Society of Civil Engineering, June 2003, Canada. Further prior art artificial units for building maritime protection works are disclosed in document EP1925747A4.

The currently available concrete armour artificial units may be classified in relation to: a) placement, that may be:

i) random (in particular meeting more or less rigid schemes or completely random), ii) uniform;

b) shape and weight of the units, which may be:

i) massive blocks,

ii) slender blocks, characterised by a relatively slender central part and long protrusions, iii) blocks having one or more cavities;

c) number of layers forming the armour, that may be:

iv) a single layer armour,

v) a double layer armour.

In particular, the randomly placed artificial units resist to the stresses of the wave motion through their own weight and interlocking. Depending on such resistance actions and from the chronological point of view, currently available units may be classified as follows: - first-generation, wherein the stability factors are their own weight and, in a very limited percentage, interlocking; typical examples of such units are the Cube, the Modified Cube (1959) and the Antifer Cube (1973);

second-generation with artificial units having simple shape, wherein the stability factors are their own weight and, for some of them, interlocking; typical examples of such units are the Tetrapod (1950), the Tribar (1958), the Tripod (1962) and the Akmon (1962).

second-generation with artificial units having complex shape, wherein the stability factor is the interlocking; typical examples of such units are the Stabit (1961) and the Dolos (1963); third-generation with artificial units arranged in a single layer, wherein the stability factor is the interlocking; typical examples of such units are the Accropode ^® (1980), the Core Loc ^® (1996) and the A-Jack (1998).

Differently, for the uniformly placed artificial units, the main stability factor is represented by the friction between elements; typical examples of such units are the Cob (1969), the Shed (1982), the Seabee (1978), the Haro ^® (1984), the Diahitis (1998) and the Hollow Cube (1991).

A classification by shape, placement and stability factors is given by Muttray et al. in "Development of an innovative breakwater armour unit", Coasts & Ports Australasian Conference, New Zealand, September 2003.

The massive blocks ensure their stability almost exclusively through their own weight. In particular, the hydraulic stability is rather low, while the structural stability is significantly high. It follows that they are considered as systems with low risk of failure.

Instead, the slender blocks guarantee a significantly higher hydraulic stability thanks to the higher capability of mutual engagement between elements and a more or less lower structural stability. Hence, on the contrary to the massive blocks, the slender blocks represent systems with high risk of progressive failure.

The blocks having cavities provide for a higher porosity of the armour and, consequently, higher dissipation of the incident wave energy.

The modes according to which the uniformly placed artificial units guarantee the hydraulic stability is essentially based on friction between contiguous units, that is significantly less variable with respect to the interlocking given by the randomly placed blocks. For this reason, in the design stage, the uniform placement structures require lower safety coefficients. However, nevertheless the great advantage of being capable to be used in a single layer, these units have significant problems during installation, most of all in case of geometrically complex structures and, therefore, generally they are not used for making typical breakwaters.

The artificial units which are arranged in a double layer with random placement are, for instance, the Tetrapod, the Akmon, the Stabits and the Dolos. With regard to the installation, the units of the first layer are placed according to a predefined scheme, while the ones of the second layer follow the random scheme determining the engagement among the same blocks. This principle of placement determines strong oscillations on the units of the second layer which can cause the breaking of the units. For this reason, such armours are not necessarily a symbol of greater safety. Also, the artificial units belonging to the slender type, such as the Dolos, the Tetrapod and the Tribar, are subject to very strong stresses in their central part, that when it undergoes such actions may easily reach conditions of breaking points. In such situations, the residual stability of the structure is notably reduced, thus rendering a restoration intervention necessary. In essence, if on the one hand the slender artificial units, to be randomly placed in a double layer, improve the hydraulic performance of the work and, sometimes, reduce its construction costs, on the other hand, because of the possibility of breaking, they require a frequent and regular monitoring, in order to restore possible damaged conditions for avoiding the total collapse of the whole work. Therefore, the use of this type of artificial units is often uneconomical.

The artificial units mainly used for building single layer armours with random placement are the Accropode ^® and the Core Loc ^® . I n particular, the Accropodes ^® , which are classified as massive blocks, guarantee a sufficiently high structural stability, though they show optimal capabilities of interlocking between units, with values of the stability coefficient KD equal to 15/12 respectively for breaking waves and non-breaking waves; differently, the Core Locs ^® are very similar to the Accropodes ^® with reference to the number and orientation of protrusions, but they show a better hydraulic stability with a stability coefficient KD, to be used for the design, equal to 16. The breaking tests show that the Core Locs ^® have a structural stability significantly higher with respect to the one of the Dolos (because the former, though having the same shape of the latter, have a more compact central part), a nd significantly lower with respect to the one of the Accropodes ^® (because the Core Locs ^® are more slender and vulnerable than the latter).

Installation of the Accropodes ^® a nd Core Locs ^® is significantly complex and difficult, because for them there is an interlocking so variable that it constraints the use of large safety margins in the definition of the stability coefficient, since very significant spatial variations may occur. In fact, for these types of artificial units, the armour is made by arranging the units according to a well defined grid depending on the dimensions of the same units. Therefore, the structural and hydraulic efficiency is affected by the positioning operation since it is necessa ry to create a right level of both linkage and porosity. If a too dense grid is made, ideal porosity, that is fundamental for wave energy dissipation during the run up phase, would lack; if, on the contrary, the grid is excessively loose, damages to the work in correspondence of the armour could occur, because the interlocking force would be reduced. Moreover, the increase of porosity could determine such a width of the flow paths that it could favour the remova l of the elements constituting the layer of the filter installation, thus generating a whole collapse of the structure.

For these reasons, for a correct execution of the installation of the single artificial units, it is necessary to have specialised technical personnel and high-precision instrumentation, such as for instance GPS systems, for detecting the position of the single unit.

A further drawback is represented by the condition that such operation is easy to make in the emerged part of the structure, while it requires a greater attention of execution in the submerged one where, generally, the supervision task is entrusted to one or more frogmen, in view of the impossibility of use of the GPS system.

Other drawbacks are due to the storage areas, the size of which must be related to the number of the armour layers and, consequently, to the number of artificial units to employ for the construction.

Finally, further drawbacks are related to the manufacture of the artificial units. In fact, the artificial blocks are made by pouring concrete within a formwork made of wood or ferrous materials, at the construction site or at the factory, depending on the size and shape. For the last-generation artificial units, which allows a (random or regular) single layer placement, the formworks are made of ferrous material or similar alloys and for their manufacture it is necessary highly specialised personnel, because the geometric shape to make is constituted of very complex parts. This has substantial implications on the costs of construction of the artificial units, even taking account of the fact that usually the end user must rent the manufacturing templates, having large size and weight, and he must carry them outwards to the installation site and backwards to the formwork storage depot.

It is, therefore, an object of the present invention to allow, in an efficient, reliable, simple, and inexpensive way, to make hydraulic works, in particular maritime structures, where cast layers are present which must resist to stresses of a fluid, having a high stability, rugosity, roughness, porosity and interlocking of the layer, also facilitating the engagement with the underlying surface.

It is specific subject matter of the present invention an artificial unit configured to build hydraulic structures, in particular maritime structures, the artificial unit being inscribable in an equivalent cube having side equal to D and comprising a central cubic portion having a centre, six faces and side equal to 2 ?. D, characterised in that it is provided with a plurality of parallelepiped projecting elements adjacent to each other which project from each face of the central cubic portion so that all six views obtainable through projections of the artificial unit, which are orthogonal to the six faces of the central cubic portion, are different from each other, each one of the projecting parallelepiped elements having a first linear dimension si, a second linear dimension s ₂ and a third linear dimension S3 which are each not lower than KrD and not larger than 5-Ki-D, or not lower than K ₂ -D and not larger than 5-K ₂ -D, wherein K. is a first coefficient lower than 1 and K ₂ is a second coefficient lower than 1. In particular, as known, the projection orthogonal to a respective face of the central cubic portion represents the artificial unit through a parallel projection wherein all the projection lines are orthogonal to a projection plane that is parallel to the respective face of the centra! cubic portion.

According to another aspect of the invention, at least two, optionally at least three, more optionally at least four, projecting parallelepiped elements may project from each face of the central cubic portion.

According to a further aspect of the invention, the first linear dimension si, the second linear dimension s ₂ and the third linear dimension s¾ may be each not larger than 2-Ki-D or not larger than 2-K ₂ -D.

According to an additional aspect of the invention, each one of the projecting parallelepiped elements may have a height equal to KrD along a direction orthogonal with respect to a surface of the artificial unit from which the projecting parallelepiped element projects, wherein said surface of the artificial unit from which the projecting parallelepiped element projects optionally coincides with a face of the central cubic portion.

According to another aspect of the invention, said six views obtainable through projections of the artificial unit orthogonal to the six faces of the centra! cubic portion may be subdividable into three pairs of views wherein the views of each pair are arranged on two respective parallel planes which are orthogonal to the planes on which the other two pairs of views are arranged, and at least one surface of one out of said six views may be:

equal and arranged according to a type of symmetry in the plane with respect to another surface of the same view, wherein the type of symmetry is optionally selected from the group comprising an antisymmetry with respect to the projection of the centre of the centra! cubic portion onto the view, a rotational symmetry according to an angle, more optionally equal to 90", about projection of the centre of the central cubic portion onto the view, and/or

equal and arranged according to a type of symmetry in the plane with respect to another surface of the other view of the same pair of views, wherein the type of symmetry is optionally selected from the group comprising an antisymmetry with respect to the centre of the central cubic portion, or a rotational symmetry according to an angle, more optionally equal to 180°, with reference to a n axis of the central cubic portion orthogona l to the two planes onto which one of the other two pairs of views is arranged.

According to a further aspect of the invention, the projecting parallelepiped elements may be connected to each other so as to form projecting blocks each one of which is shaped so as to substa ntially create a L on a plane, wherein each one of the two arms of each L is shared by two L blocks which create the two Ls onto respective planes orthogonal to each other, whereby the two arms of the L of each block have two respective thicknesses different from each other in direction orthogonal to the plane where the block creates the L.

According to an additional aspect of the invention, the projecting blocks may have surfaces delimiting the same the sides of which a re equal to:

a- Ki-D + b-K ₂ -D,

where at least one of the coefficients a a nd b is different from zero, wherein optionally both the coefficients are not negative, wherein more optionally (a; b) is equal to (0; 1) or (0; 2) or (1; 0) or (l; l) or (2; 0).

According to another aspect of the invention, at least one between the first coefficient

Ki and the second coefficient 2 may be not lower than 0,1, optionally not lower than 0,15 and not larger than 0,7, more optionally not lower than 0,2 and not larger than 0,5.

According to a further aspect of the invention, a ratio K1/K2 between the first coefficient Ki and the second coefficient K may be not lower than 0,4 a nd not larger than 2,5.

According to an additional aspect of the invention, the artificial unit may comprise edges shaped through a connecting surface having a radius of curvature equal to ¾-D, where Ki is a third coefficient optionally ranging from 0 to 0,5.

According to another aspect of the invention, said six views obtainable through projections of the artificial unit orthogonal to the six faces of the centra l cubic portion may consist of the views shown in Figures 5-10.

According to a further aspect of the invention, the artificial unit may comprise internal reinforcements, optionally selected from the group comprising metal bars and discontinuous fibrous materials, wherein the discontinuous fibrous materials more optionally comprise elements selected from the group comprising steel, plastic, polymeric materials, glass, cast iron.

It is also specific subject matter of the present invention a process for manufacturing an artificial unit as previously described, comprising: - making a formwork, and

- pouring concrete in the formwork,

the process being characterised in that the formwork is made through superimposition in an ordered sequence of a plurality of square layers, kept in a cubic shape, wherein each square layer is provided with a shaped through hole such that the shaped through hole of a square layer at least partially overlaps with the shaped through hole of each adjacent square layer, and wherein the area of the shaped through holes decreases from one or two central square layers to a top square layer or to a bottom square layer.

According to another aspect of the invention, each square layer may be made from a single panel or from the combination of two half-layers, the square layers being optionally made of styrofoam or polystyrene.

It is a further specific subject matter of the present invention an assembly configured to make a formwork configured to be used in the previously described process for manufacturing an artificial unit, the assembly being characterised in that it comprises a plurality of square layers configured to be superimposed with each other in an ordered sequence, wherein each square layer is provided with a shaped through hole such that the shaped through hole of a square layer is configured to at least partially overlap with the shaped through hole of each adjacent square layer in the ordered sequence, and wherein the area of the shaped through holes decreases from one or two central square layers to a top square layer or to a bottom square layer in the ordered sequence.

The artificial unit according to the invention substantially has a basic cubic shape with projecting faces shaped so that when positioning the single elements it is possible to avoid that contiguous artificial units couple to each other. I n particular, the artificial unit according to the invention may be used for building the outer layer, also called armour, of random placement single layer maritime structures, such as emerged and submerged rubble mound breakwaters, jetties, revetments, and even for more genera! hydraulic works where single cast layers are present which must resist to the stresses of a fluid (e.g. river embankments).

The advantages offered by the artificial unit according to the invention with respect to the prior art solutions are numerous and significant.

First of all, the artificial unit according to the invention overcomes the drawbacks of the prior art units illustrated above which are found when using the random placement single layer units, most of all in relation to the difficulties of positioning and manufacturing. In fact, the artificial unit according to the invention allows to carry out the installation operations without requiring specialised personnel or high-tech instrumentation, achieving an interlocking substantially independent from the mutual placement of the units, so as to favour a really random, not induced, arrangement, achieving what is defined as mutual automatic interlocking.

This further entails that the positioning operations are much faster and more simple to make, whereby it is possible to reduce the construction time and, consequently, the costs in terms of equipment, personnel and operative phases for making the work.

From the structural point of view, the particular configuration of the shape and the easy installation permits to the artificial units according to the invention to be arranged in an optimal manner, even in relation to the conditions of engagement, preventing the contiguous faces from couple to each other, differently from what occurs for instance for cubes. In this way, independently from the specific position of the single units constituting the layer, it is always guaranteed a proper roughness and porosity, useful to reduce the effects of run up of the wave motion on the outer surface of the structure and to favour energy dissipation.

In fact, the plurality of parallelepiped projecting elements adjacent to (namely, touching) each other, which projects from the artificial units according to the invention, create an irregular arrangement of (parallelepiped) protrusions and (parallelepiped) cavities on each one of the six faces of the central cubic portion, wherein the irregular arrangement of protrusions and cavities on each face is never identically repeated (and not even replicated according to any symmetry) on other faces of the central cubic portion. Such irregular arrangement of protrusions and cavities is such that all the six views obtainable through projections of the artificial unit according to the invention, which are orthogonal to the six faces of the central cubic portion, are different from each other, and each one of such six views, as a whole, is devoid of any type of symmetry in the plane (although some portions of a single view may be arranged according to a possible symmetry in the plane). Optionally, at least two parallelepiped projecting elements which projects from the artificial units according to the invention have dimensions and/or orientations different from each other, and/or the irregular arrangements of protrusions and cavities on the six faces of the central cubic portion create, along each one of the six possible directions orthogonal to the faces, at least four outer walls parallel to the face under consideration which are at different heights with respect to the centre of the central cubic portion and which are joined to each other by joining walls orthogonal to the face under consideration, where said at least four outer walls contribute to delimit an external perimeter of the orthogonal joining walls (as better shown in Figures 1-10 with reference to the preferred embodiment). I n this regard, although in the following of the present description and in the claims the artificial unit is considered as geometrically obtained from the central cubic portion onto which a plurality of parallelepiped projecting elements adjacent to each other are joined, however the artificial unit may be also considered as geometrically obtained from the equivalent cube having side equal to D in which the artificial unit is inscribable on the faces of which parallelepiped cavities adjacent to each other are made (i.e. on the faces of which parallelepiped portions adjacent to each other are removed thus making the parallelepiped cavities). In particular, considering the artificial unit as geometrically obtained from the centra! cubic portion onto which a plurality of parallelepiped projecting elements adjacent to each other are joined, more than one wall of each one of the parallelepiped projecting elements is at least partially exposed to the outside of the artificial unit (in the preferred embodiment of the invention, four or five walls of each parallelepiped projecting element is at least partially exposed to the outside of the artificial unit). Optionally, each parallelepiped projecting element has the shape of a rectangular parallelepiped one wall of which that is parallel to the face onto which the parallelepiped projecting element is joined is at least partially exposed to the outside of the artificial unit.

Thanks to the irregular and unrepeated arrangement of protrusions and cavities on each one of the six faces of the centra! cubic portion, there is no matching between the arrangement of protrusions and cavities on each face with the arrangements of protrusions and cavities of all the faces of another artificial unit identical to the first one, whereby placing each face of the central cubic portion of a first artificial unit close to any face of the centra! cubic portion of a second artificial unit identical to the first one (or to a set of any two or more faces of a corresponding set of two or more artificial units identical to the first one), at least one cavity accessible from the outside is always present between the two faces close to each other that offers to the wave motion a planar surface having maximum dimension lower than the side equal to D of the equivalent cube in which the artificial unit is inscribable; in particular, in the preferred embodiment of the artificial unit according to the invention, at least one cavity accessible from the outside is always present that offers to the wave motion a planar surface having maximum dimension not larger than (2-KrD + 2-K ₂ -D).

This allows to avoid that, placing a plurality of single artificial units according to the invention identical to each other in a random (or even ordered) way for making a maritime structure, it is possible, not even in the case where two artificial units are side by side close to each other, to create channels offering to the wave motion planar surfaces having excessive maximum dimensions, in any case equal to or larger than the side D of the equivalent cube in which the artificial unit is inscribable, thus causing an efficient hydrodynamic dissipation of the energy of the wave motion since the outer layer and the maritime structure as a whole have a high roughness and porosity, whereby the fluid moving on (and through) the same finds a large number of obstacles and rapidly dissipates its energy content.

Also, at the same time, the plurality of parallelepiped projecting elements of the artificial units according to the invention facilitate the interlocking of the same units, that is maximized by the irregular and unrepeated arrangement of protrusions and cavities on each one of the six faces of the central cubic portion of the artificial units, and hence increasing stability in relation to the stress caused by the interaction of the wave motion on the outer layer built through the artificial units according to the invention.

The present invention will be now described, by way of illustration and not by way of limitation, according to its preferred embodiments, by particularly referring to the Figures of the annexed drawings, in which:

Figure 1 shows a first elevation, perspective view (Fig. la) and a schematic representation of the related point of view (Fig. lb) of a preferred embodiment of the artificial unit according to the invention;

Figure 2 shows a second elevation, perspective view (Fig. 2a) and a schematic representation of the related point of view (Fig. 2b) of the artificial unit of Figure 1;

Figure 3 shows a third elevation, perspective view (Fig. 3a) and a schematic representation of the related point of view (Fig. 3b) of the artificial unit of Figure 1;

Figure 4 shows a fourth elevation, perspective view (Fig. 4a) and a schematic representation of the related point of view (Fig. 4b) of the artificial unit of Figure 1;

Figure 5 shows a top plan view (Fig. 5a) and a schematic representation of the related point of view (Fig. 5b) of the artificial unit of Figure 1;

Figure 6 shows a front view (Fig. 6a) and a schematic representation of the related point of view (Fig. 6b) of the artificial unit of Figure 1;

Figure 7 shows a right side view (Fig. 7a) and a schematic representation of the related point of view (Fig. 7b) of the artificial unit of Figure 1; Figure 8 shows a left side view (Fig. 8a) and a schematic representation of the related point of view (Fig. 8b) of the artificial unit of Figure 1;

Figure 9 shows a rear view (Fig. 9a) and a schematic representation of the related point of view (Fig. 9b) of the artificial unit of Figure 1;

Figure 10 shows a bottom plan view (Fig. 10a) and a schematic representation of the related point of view (Fig. 10b) of the artificial unit of Figure 1;

Figure 11 shows a particular of a maritime structure the outer layer of which is formed by a single layer of artificial units as the unit of Figure 1 with random placement;

Figure 12 shows a perspective view of six square layers configured to make a formwork configured to be used in the process for manufacturing the artificial unit of Figure 1; and

Figure 13 shows the formwork made with the six square layers of Figure 12.

In the Figures, identical reference numerals will be used for alike elements.

In the following of the description and in the Figures, all the shape measures of the artificial unit according to the invention are referred to a parameter called characteristic diameter D, equal to the side of the equivalent cube in which the same artificial unit is inscribed, i.e. the cube having minimum side that contains the unit inside.

Also, it must be understood that the (relative) definitions of front, rear, top, bottom, right side and left side conventionally refer to an orientation of the point of view that is not essential and may be modified, still remaining within the scope of protection of the present invention as defined by the attached claims.

Furthermore, it must be understood that the (relative) definitions of width, length and height conventionally refer to an orientation of the three linear dimensions, orthogonal to each other, of the parallelepiped projecting elements that is not essential and may be modified, still remaining within the scope of protection of the present invention as defined by the attached claims.

Similarly to what shown in Figures 1-10 for the preferred embodiment, the artificial unit according to the invention generally has a central cubic portion (the centre of which coincides with the centre of the artificial unit) provided with a plurality of parallelepiped projecting elements adjacent to each other; in other words, the unit is geometrically obtained from a central cubic portion on which a plurality of parallelepiped projecting elements adjacent to (namely, touching) each other are joined so that all the six views obtainable through projections of the artificial unit according to the invention, which are orthogonal to the six faces of the central cubic portion, are different from each other. Such parallelepiped projecting elements have the three orthogonal dimensions (i.e. width, length and height, in the following also indicated as first linear dimension, second linear dimension a nd third linear dimension orthogonal to each other) proportional, according to a first and second coefficients Kj _. and K ₂ , to the characteristic diameter D equal to the side of the equivalent cube in which the same artificial unit is inscribed (i.e. the cube having minimum side that contains the unit inside); in particular, the central cubic portion has side equal to 2-Kz-D.

Some embodiments of the artificial unit according to the invention have in common with the preferred embodiment of the artificial unit shown in Figures 1-10, which are immediately comprehensible to those skilled in the a rt, the fact that the parallelepiped projecting elements (each one having a height equa l to KrD a long a direction orthogonal with respect to a surface of the artificial unit, possibly coinciding with a face of the central cubic portion, from which the parallelepiped projecting element projects) are connected to each other so as to form projecting blocks each one of which is shaped so as to substantially create (i.e. apart from connecting surfaces) a L on a plane, wherein each one of the two arms of each L is shared by two L blocks creating the two Ls onto respective planes orthogonal to each other, whereby the two arms of the L of each block have two respective thicknesses different from each other in direction orthogonal to the plane where the block creates the L. Optionally, the projecting blocks have surfaces delimiting the same blocks the sides of which surfaces are equal to:

where at least one of the coefficients a a nd b is different from zero and wherein optionally both the coefficients are not negative, wherein more optionally (a; b) is equal to (0; 1) or (0; 2) or (l; 0) or (l; l) or (2; 0).

In the following, the views shown in Figures 5-10 are illustrated, each one of which comprises a plurality of shaped surfaces, indicated by reference numerals with three digits, distributed on four heights (a long the direction orthogonal to the view) different from each other. I n particular, the hundreds digit indicates the view, whereby the surfaces of the top plan view are indicated with the reference numerals "1##", the surfaces of the front view are indicated with the reference numerals "2 ", the surfaces of the right side view are indicated with the reference numerals "3##", the surfaces of the left side view are indicated with the reference numerals "AM" , the surfaces of the rear view are indicated with the reference numerals "5##", and the surfaces of the bottom plan view are indicated with the reference numerals "6##". Moreover, the tens digit indicates the decreasing value of the height (along the direction orthogonal to the view) to which the surface in the respective view belongs, whereby the surfaces at a first height are indicated with the reference numerals "#0#", the surfaces at a second height (lower than the first height) are indicated with the reference numerals the surfaces at a third height (lower than the second height) are indicated with the reference numerals "#2#", and the surfaces at a fourth height (lower than the third height) are indicated with the reference numerals "#3#".

With reference to Figure 5, and also observing perspective Figures 1-4, it may be observed that the top plan view of the preferred embodiment of the artificial unit according to the invention comprises:

at the first height (along the direction orthogonal to the view), a first surface 100 that is substantially L-shaped (i.e. apart from connecting surfaces);

at the second height (along the direction orthogonal to the view), a second surface 110 that is substantially shaped (i.e. apart from connecting surfaces) according to a rectilinear polygon (i.e. the adjacent sides of which, apart from connecting surfaces, meet with each other at right angles);

at the third height (along the direction orthogonal to the view), a third and a fourth surfaces 120 and 125 equal to each other and antisymmetric (i.e. arranged according to a rotational symmetry in the plane equal to 180° about the projection of the centre of the artificial unit on the view - whereby the fourth surface 125 is arranged as the third surface 120 after that the latter has been rotated by 180" about the projection of the centre of the artificial unit on the view) and which are substantially rectangle-shaped (i.e. apart from connecting surfaces), a fifth and a sixth surfaces 123 and 128 equal to each other and antisymmetric (with respect to the projection of the centre of the artificial unit, that as stated coincides with the centre of the central cubic portion, on the view) and which are substantially rectangle-shaped (i.e. apart from connecting surfaces); and

at the fourth height (along the direction orthogonal to the view), a seventh and an eighth surfaces 130 and 135 equal to each other and antisymmetric (with respect to the projection of the centre of the artificial unit on the view) and which are substantially rectangle-shaped (i.e. apart from connecting surfaces).

The dimensions of the sides of the surfaces of the view of Figure 5 are shown in the same Figure. As stated, the antisymmetric arrangement of the third and fourth surfaces 120 and 125 is referred with respect to the projection of the centre of the artificial unit on the view, i.e. it is referred to the centre of the face of the central cubic portion of the artificial unit visible in Figure 5 (which face is schematically represented with a dotted line, and that is not represented in the other Figures) having side equal to 2-ΚτΏ; in the following, such centre will be also called centre of the artificial unit. This also applies to the antisymmetric arrangement of the fifth and sixth surfaces 123 and 128, to the antisymmetric arrangement of the seventh and eighth surfaces 130 and 135, and also to the antisymmetric arrangement of other pairs of surfaces which will be illustrated in the following with reference to Figures 6-10. Along the direction orthogonal to the view of Figure 5, the distance between the first and the second heights is equal to KrD, the distance between the second and the third heights is equal to KrD, and the distance between the third and the fourth heights is equal to K?_-D,

With reference to Figure 6, and also observing the perspective Figures 1 and 4, it may be observed that the front view of the preferred embodiment of the artificial unit according to the invention comprises:

at the first height (along the direction orthogonal to the view), a first surface 200 that is substantially L-shaped (i.e. apart from connecting surfaces);

at the second height (along the direction orthogonal to the view), a second surface 210 that is substantially L-shaped (i.e. apart from connecting surfaces) and a third surface 215 that is substantially rectangle-shaped (i.e. apart from connecting surfaces);

at the third height (along the direction orthogonal to the view), a fourth and a fifth surfaces 220 and 223 equal to each other (and arranged according to a rotational symmetry in the plane, i.e. about the axis orthogonal to such surfaces - exiting the Figure plane equal to 90" about the projection of the centre of the artificial unit on the view - whereby the fifth surface 223 is arranged as the fourth surface 220 after that the latter has been rotated in the plane by 90°, obviously counterclockwise, about the projection of the centre of the artificial unit on the view) and which are substantially L-shaped (i.e. apart from connecting surfaces), and a sixth and a seventh surfaces 225 and 228 equal to each other (and arranged according to a rotational symmetry equal to 90° in the plane about the projection of the centre of the artificial unit on the view) and which are substantially rectangle-shaped (i.e. apart from connecting surfaces); and

at the fourth height (along the direction orthogonal to the view), an eighth and a ninth surfaces 230 and 235 equal to each other (and arranged according to a rotational symmetry equal to 90° in the plane about the projection of the centre of the artificial unit on the view) and which are substantially rectangle-shaped (i.e. apart from connecting surfaces).

The dimensions of the sides of the surfaces of the view of Figure 6 are shown in the same Figure. Along the direction orthogonal to the view of Figure 6, the distance between the first and second heights is equal to Ki-D, the distance between the second and third heights is equal to KrD, and the distance between the third and fourth heights is equal to K ₂ -D.

With reference to Figure 7, and also observing the perspective Figures 1 and 2, it may be observed that the right side view of the preferred embodiment of the artificial unit according to the invention comprises:

at the first height (along the direction orthogonal to the view), a first surface 300 that is substantially L-shaped (i.e. apart from connecting surfaces);

at the second height (along the direction orthogonal to the view), a second surface 310 that is substantially shaped (i.e. apart from connecting surfaces) according to a rectilinear polygon;

at the third height (along the direction orthogonal to the view), a third surface 320 that is substantially L-shaped (i.e. apart from connecting surfaces) and a fourth surface 325 that is substantially S-shaped (i.e. apart from connecting surfaces); and

- at the fourth height (along the direction orthogonal to the view), a fifth surface 330 substantially rectangle-shaped (i.e. apart from connecting surfaces), and a sixth and seventh surfaces 333 and 335 equal to each other and antisymmetric (with respect to the projection of the centre of the artificial unit on the view) and which are substantially square-shaped (i.e. apart from connecting surfaces).

The dimensions of the sides of the surfaces of the view of Figure 7 are shown in the same Figure. Along the direction orthogonal to the view of Figure 7, the distance between the first and second heights is equal to Ki-D, the distance between the second and third heights is equal to KrD, and the distance between the third and fourth heights is equal to K ₂ -D.

With reference to Figure 8, and also observing the perspective Figures 3 and 4, it may be observed that the left side view of the preferred embodiment of the artificial unit according to the invention comprises:

at the first height (along the direction orthogonal to the view), a first surface 400 that is substantially L-shaped (i.e. apart from connecting surfaces);

at the second height (along the direction orthogonal to the view), a second surface 410 that is substantial!y shaped (i.e. apart from connecting surfaces) according to a rectilinear polygon;

at the third height (along the direction orthogonal to the view), a third surface 420 substantially rectangle-shaped (i.e. apart from connecting surfaces), a fourth surface 425 substantially L-shaped (i.e. apart from connecting surfaces), and a fifth and sixth surfaces 423 and 428 equal to each other and antisymmetric (with respect to the projection of the centre of the artificial unit on the view) and which are substantially rectangle-shaped (i.e. apart from connecting surfaces); and

at the fourth height (along the direction orthogonal to the view), a seventh surface 430 that is substantially rectangle-shaped (i.e. apart from connecting surfaces), and an eighth and ninth surfaces 433 and 435 equal to each other and antisymmetric (with respect to the projection of the centre of the artificial unit on the view) and which are substantially rectangle-shaped (i.e. apart from connecting surfaces).

In particular, the first surface 400 and the second surface 410 are equal and arranged according to a rotational symmetry equal to 180°, with reference to the axis of the central cubic portion of the central unit orthogonal to the plane of Figures 5 and 10, with respect to the first surface 300 and second surface 310, respectively, of the view of Figure 7. The dimensions of the sides of the surfaces of the view of Figure 8 are shown in the same Figure. Along the direction orthogonal to the view of Figure 8, the distance between the first and second heights is equal to KrD, the distance between the second and third heights is equal to KrD, and the distance between the third and fourth heights is equal to KrD.

With reference to Figure 9, and also observing the perspective Figures 2 and 3, it may be observed that the rear view of the preferred embodiment of the artificial unit according to the invention comprises:

at the first height (along the direction orthogonal to the view), a first surface 500 that is substantially L-shaped (i.e. apart from connecting surfaces);

at the second height (along the direction orthogonal to the view), a second surface 510 that is substantially L-shaped (i.e. apart from connecting surfaces) and a third surface 515 that is substantially rectangle-shaped (i.e. apart from connecting surfaces);

at the third height (along the direction orthogonal to the view), a fourth and a fifth surfaces 520 and 523 equal to each other (and arranged according to a rotational symmetry in the plane equal to 90° about the projection of the centre of the artificial unit on the view) and that is substantially L-shaped (i.e. apart from connecting surfaces), and a sixth and a seventh surfaces 525 and 528 equal to each other (and arranged according to a rotational symmetry in the plane equal to 90° about the projection of the centre of the artificial unit on the view) and which are substantially rectangle-shaped (i.e. apart from connecting surfaces); and

at the fourth height (along the direction orthogonal to the view), an eighth and a ninth surfaces 530 and 535 equal to each other (and arranged according to a rotational symmetry in the plane equal to 90° about the projection of the centre of the artificial unit on the view) and which are substantially rectangle-shaped (i.e. apart from connecting surfaces).

In particular, the first, fifth, seventh and ninth surfaces 500, 523, 528 and 535 are equal and arranged according to a rotational symmetry equal to 180°, with reference to the axis of the central cubic portion of the central unit orthogonal to the planes of Figures 5 and 10, with respect to the first, fourth, sixth and eighth surfaces 200, 220, 225 and 230, respectively, of the view of Figure 6; moreover, the fourth and sixth surfaces 520 and 525 are equal and antisymmetric (with respect to the centre of the artificial unit) with respect to the fifth and seventh surfaces 223 and 228, respectively, of the view of Figure 6. The dimensions of the sides of the surfaces of the view of Figure 9 are shown in the same Figure, Along the direction orthogonal to the view of Figure 9, the distance between the first and second heights is equal to KrD, the distance between the second and third heights is equal to KrD, and the distance between the third and fourth heights is equal to K ₂ -D.

With reference to Figure 10, it may be observed that la top plan view of the preferred embodiment of the artificial unit according to the invention comprises:

at the first height (along the direction orthogonal to the view), a first surface 600 that is substantially L-sbaped;

at the second height (along the direction orthogonal to the view), a second surface 610 that is substantially shaped (i.e. apart from connecting surfaces) according to a rectilinear polygon (i.e. the adjacent sides of which, apart from connecting surfaces, meet with each other at right angles);

at the third height (along the direction orthogonal to the view), a third and a fourth surfaces 620 and 625 equal to each other a nd antisymmetric and which are substantially L- shaped (i.e. a part from connecting surfaces), a fifth and a sixth surfaces 623 and 628 equal to each other and antisymmetric (with respect to the projection of the centre of the artificial unit on the view) and which are substantially rectangle-shaped (i.e. apart from connecting surfaces); and

at the fourth height (along the direction orthogonal to the view), a seventh and an eighth surfaces 630 and 635 equal to each other a nd antisymmetric (with respect to the projection of the centre of the artificial unit on the view) and which are substantially rectangle-shaped (i.e. apart from connecting surfaces).

I n particular, the first and second surfaces 600 a nd 610 are equal a nd arranged according to a rotational symmetry equal to 180°, with reference to the axis of the central cubic portion of the central unit orthogonal to the plane of Figures 7 and 8, with respect to the first and second surfaces 100 and 110, respectively, of the view of Figure 5. The dimensions of the sides of the surfaces of the view of Figure 10 are shown in the same Figure. Along the direction orthogonal to the view of Figure 10, the distance between the first and second heights is equal to Ki-D, the distance between the second and third heights is equal to KrD, and the distance between the third and fourth heights is equal to K ₂ -D.

As shown in Figures 1-10, in the preferred embodiment of the artificial unit, each one of the faces of the central cubic portion comprises at least one protrusion (i.e. at least one parallelepiped projecting element) that is positioned in a decentralised manner with respect to the (square) face of the central cubic portion and is spaced apart from the vertex of the (square) face of the central cubic portion, whereby it is spaced apart from the vertices of the central cubic portion. Also, in the preferred embodiment of the artificial unit, none of the faces of the central cubic portion is exposed to the outside of the artificial unit.

Other embodiments of the artificial unit according to the invention may have a different configuration from the one illustrated in Figures 1-10, comprising a different number and arrangement of parallelepiped elements projecting from the central cubic portion having side equal to 2-K ₂ -D. In particular, at least two, optionally at least three, more optionally at least four, parallelepiped projecting elements (each one having optionally a height equal to KrD along a direction orthogonal with respect to a surface of the artificial unit, possibly coinciding with a face of the central cubic portion, from which the parallelepiped projecting element projects) project from each one of the six faces of the central cubic portion and/or possibly from at least another parallelepiped projecting element. Moreover, in such other embodiments of the artificial unit according to the invention, each one of the surfaces of each one of the six views obtainable through projections orthogonal to the unit, such that the six views may be subdivided into three pairs of views wherein the views of each pair are arranged on two respective parallel planes which are orthogonal to the planes on which the other two pairs of views are arranged, may be equal or not and:

arranged according to a type of symmetry in the plane with respect to another surface of the same view, for instance arranged in an antisymmetric way (with respect to the projection of the centre of the artificial unit on the view) or according to a rotational symmetry in the plane according to an angle, optionally equal to 90°, about the projection of the centre of the artificial unit on the view, and/or

arranged according to a type of symmetry with respect to another surface of the other view of the same pair of views, for instance arranged in an antisymmetric way (with respect to the centre of the artificial unit) or according to a rotational symmetry according to an angle, optionaHy equal to 180", with reference to an axis of the central cubic portion of the central unit orthogonal to the two planes on which one of the other two pairs of views is arranged.

In general, each one of the parallelepiped projecting elements may have length (i.e. a first linear dimension si), width (i.e. a second linear dimension s ₂ ) and height (i.e. a third linear dimension S3) which are each one not lower than KrD and not larger than 5-Ki-D, (in other words:

KrD<Si< 5-K _r D, K _r D < s ₂ < 5-Ki-D, K _r D < s ₃ < 5-Ki-D),

optionally not larger than 2-Ki-D, or not lower than K ₂ -D and not larger than 5-K ₂ -D {in other words:

K ₂ -D < si < 5-K ₂ -D, K ₂ -D < s ₂ ≤5-K ₂ -D, K ₂ -D < s ₃ < 5-K ₂ -D),

optionally not larger than 2-K ₂ -D.

In general, both the first coefficient Ki and the second coefficient K ₂ are lower than 1; moreover, optionally the first coefficient Ki and the second coefficient K2 may be each not lower than 0, 1; in other words:

0, 1 < KI < 1

0, 1 < K ₂ < 1

More optionally, at least one between the first coefficient Kj. and the second coefficient K ₂ may be not lower than 0,15 and not larger than 0,7, still more optionally not lower than 0,2 and not larger than 0,5.

Optionally, the ratio Ki/ ? between the first coefficient Ki and the second coefficient K2 is not lower than 0,4 and not larger than 2,5 (maintaining the constraint that both the coefficients Ki and K ₂ are lower than 1).

Optionally, the artificial unit according to the invention may have all the edges (e.g. the ones at which the surfaces of the parallelepiped projecting elements meet to each other) which are shaped through a connecting surface having a radius of curvature equal to ¾-D, where K3 is a third coefficient optionally ranging from 0 to 0,5.

Further embodiments of the artificial unit according to the invention may comprise internal reinforcements; this is particularly advantageous for increasing the resistance of the artificial unit in the case where the latter is intended to be used in a structure subject to exceptional wave motion stresses. For manufacturing such reinforced artificial units, it is possible to make a frame, comprising metal bars or other reinforcing materials (e.g. discontinuous fibrous materials, such as steel, plastic, polymeric materials, glass, or cast iron, as the ones used for manufacturing fibre reinforced concrete), which are positioned through adequate spacers within the formwork used for casting concrete for making the unit, so as to guarantee in the pouring steps a correct coverage of the reinforcement in order to optimise durability. Alternatively, most of all in the case where the reinforcement comprises reinforcing materials different from metal bars, it is possible to add reinforcing materials (e.g. resistant fibres of any type) directly to the concrete casting.

With reference to the formwork used for casting concrete for manufacturing the artificial unit according to the invention, the latter allows to significantly reduce the manufacturing and installation costs. In fact, making reference to Figures 12 and 13, it may be observed that the formwork 900 for manufacturing the preferred embodiment of the artificial unit shown in Figures 1-10 may be made through the superimposition in an ordered sequence of six square layers 910, 915, 920, 925, 930 and 935 (from top to bottom) kept in a cubic shape, for instance through four side square panels, two square panels 950A and 950B of which are visible in Figure 13 bound by containing bars 960.

Each one of the six square layers 910, 915, 920, 925, 930 and 935 is provided with a shaped through hole, respectively 911, 916, 921, 926, 931 and 936, wherein the shaped through hole of a square layer at least partially overlaps the shaped through hole of the adjacent square layer (for the end square layers 910 and 935 at the top and bottom, respectively) or of the adjacent square layers (for the intermediate square layers 915 and 930 and for the central square layers 920 and 925), and wherein the area of the shaped through holes decreases from the two central square layers 920 and 925 to the end square layers 910 and 935 at the top and bottom, respectively; other embodiments of the formwork according to the invention may comprise an odd number of square layers, whereby the area of the shaped through holes decreases from the central square layer to the two end square layers at the top and bottom. The thickness of the two central square layers 920 and 925 is equal to K ₂ -D, while the thickness of the other four square layers, namely the intermediate ones 915 and 930 and the end ones 910 and 935, is equal to Ki-D; for the embodiments of the formwork according to the invention comprising an odd number of square layers, the central square layer may have thickness equal to 2-Kz-D, while the thickness of the other square layers is equal to Ki-D.

In particular, for the preferred embodiment of the artificial unit according to the invention, the pairs of square layers at the same distance from the centre of the cubic shape in which they overlap for making the formwork have the following symmetries: by assuming the end square layers 910 and 935 at the top and bottom, as lying on the same plane, the shaped through holes 911 and 936, having shape of a L, are symmetrically arranged in such plane with respect to a straight line orthogonal to two sides and passing through the centre of the square shape of the end square layers 910 and 935 and that does not intersect the shaped holes 911 and 936; similarly, by assuming the intermediate square layers 915 and 930 as lying on the same plane, the shaped through holes 916 and 931 are symmetrically arranged in such plane with respect to both straight lines, each one orthogonal to a respective pair of sides and passing through the centre of the square shape of the intermediate square layers 915 and 930; finally, by assuming the central square layers 920 and 925 as lying on the same plane, the shaped through holes 921 and 926 are arranged in such plane according to a rotational symmetry of 90" about the centre of the square shape of the central square layers 920 and 925.

The six square layers 910, 915, 920, 925, 930 and 935 may be made by using simple and inexpensive manufacturing technologies. By way of example and not by way of limitation, the square layers 910, 915, 920, 925, 930 and 935 may be made of styrofoam or polystyrene, and the four side square panels (e.g. 950A and 950B) may be optionally made of wood. In this regard, each square layer may be optionally made from a single square panel of properly cut styrofoam or polystyrene, or from the combination of two half-layers of properly cut styrofoam or polystyrene, indicated in Figures 12 and 13 with the letters "A" and "B" (e.g., the top end square layer 910 is formed by two halves 910A and 910B). In this regard, the symmetries of the pairs of square layers at the same distance from the centre of the cubic shape in which they overlap for making the formwork allow to make both square layers of each pair with only two types of half-layers, since it is sufficient to overturn the half-layers in order to obtain the desired layer; in fact: the half-layer 910A is equal to the overturned half-layer 935A and the half-layer 910B is equal to the overturned half-layer 935B, the half-layer 915A is equal to the overturned half-layer 930A and the half-layer 915B is equal to the overturned half-layer 930B, while both central square layers 920 and 925 may be obtained from the pair of half-layers 920A and 920B or from the pair of half-layers 925A and 925B (as stated, it is sufficient to rotate the central square layer 920 by 90° in order to obtain the other square layer 925 and vice versa).

Also, the four side square panels (e.g. 950A and 950B) may be optionally made of wood. The materials which are used contribute to the reduction of the costs for manufacturing the artificial unit according to the invention, also with relation to the expenses for delivering the formworks, since, for the construction thereof, only the technical specifications for making the formworks may be sent to the end user, which formworks, thanks to the simple construction, may be created directly at the installation site even by non-specialised workers. Moreover, the use of such materials allows, at the end of the manufacture of the artificial units, the re-use thereof in the construction site for other necessary works and operations and it may favour the complete environmental recycling, thus determining a further reduction of costs of both construction of the artificial units and entire general project.

As schematically shown in Figure 11, the configuration of the artificial unit according to the invention allows to position the single units 1000 preventing the same units to couple to each other, at the same time increasing stability, rugosity, roughness, porosity and interlocking of the layer of the armour, also facilitating the engagement with the with the underlying surface (that in the Figure comprises natural or artificial blocks 1500 having smaller size with respect to the artificial units 1000).

The preferred embodiments of this invention have been described and a number of variations have been suggested hereinbefore, but it should be understood that those skilled in the art can make other variations and changes without so departing from the scope of protection thereof, as defined by the attached claims.