FIELD OF THE INVENTION

The present invention regards a system for consolidating the cortical layer of terrains subject to landslide phenomena and the relative method.

More in particular, the invention regards a system for the consolidation of the cortical layer of slopes, hillsides, hillslopes, banks in terrains exposed to the risk of shallow landslide.

PRIOR ART

For the consolidation of the cortical layer of loose terrains there is known a first type of systems that provides for metal nets adapted to be positioned on the terrain to be consolidated and which are anchored thereto through anchor bars adapted to be stably fixed, for example by means of suitable cementation, to the layer beneath stable surface (for example rocky) of the terrain.

Such first type of systems, however, does not have the task of restraining the terrain from being subjected to landslide phenomena, but holding it to the terrain thereof in case of landslide, thus allowing the occurrence of landslide phenomena.

In order to overcome these drawbacks there are known second consolidation systems, which are described in the International patent application n° WO 2009/150515 on behalf of the Applicant.

Such consolidation systems are more efficient at preventing the occurrence of the landslide phenomena of the cortical layer of the terrain, in that on the metal net there is arranged a cable grid adapted to divide the terrain into perimetrally closed portions.

Furthermore, the metal net and the cables are restrained and tensioned at the anchor bars by concave division plates with concavity facing upwards and adapted to be driven into a depression of the terrain to press the mesh and the cables towards the terrain.

Such systems provide for a) a three-dimensional remodelling of the surface of the slope such to allow the cover to penetrate into the terrain creating a three-dimensional restraint which counters the land-sliding of the unstable layer; b) a new type of tensioning of the covering and of the warping of the steel ropes so as to allow the modulable compression of the surface of the slope, in order to increase the pressure of the unstable layer on the rocky layer thus raising the critical sliding data. In particular this second step is obtained by fastening bolts hinged on each anchor which push the corresponding division plate on the bottom of the previously made artificial cavities and in whose bottom the anchors were provided.

In practice, each convex area in which the slope was remodelled by the artificial cavities provides a relief overlaid by the metal net and the steel ropes and at whose vertices there is arranged a division plate at recessed position.

The division plates, once in position, tension both the metal net and the cables pressing them towards the terrain so that they restrain the various portions of the cortical layer.

Such second known type consolidation systems, though more efficient at restraining the terrain, reveal some drawbacks due to the fact that the division plate, being conceived for pressing both the cable and the metal net towards the base of the depression in which the anchor bar is fixed, leads to an inevitable misbalance between the tensioning of the metal net and of the cable.

Actually, it was observed that the metal net in such consolidation systems does not achieve the tension required to determine an efficient compression of the terrain, in that the cables are tensioned before it and restrain the division plate.

The division plate, in practice, in its action of "pulling" the metal net and the cable towards the bottom of the depression, is restrained by the cable which prevents it from imparting a considerable tensioning to the metal net.

Such phenomenon occurs due to the fact that the cables, generally steel cables, have a considerably lower extension capacity with respect to that of the metal net, which is instead much more deformable on the plane. This leads to obtaining a metal net which is not sufficiently tensioned, compressed by a grid of steel ropes which, on the contrary, is strongly tensioned and this contrast obviously reduces the efficiency of the entire structure, given that the tensioning of the cover is an essential requirement so as to guarantee the efficiency of the restraint of the cortical layer of terrain. An object of the present invention is to overcome the aforementioned drawbacks of the prior art, with the aim of obtaining a simple, rational and inexpensive solution. Such objects are attained by the characteristics of the invention indicated in the independent claims.

The dependent claims outline preferred and/or particularly advantageous aspects of the invention.

In particular, an object of the invention is to independently be used for tensioning and/or allow differentiating the tension of the cover layer, in particular the metal net, with respect to the tension of the cable, so as to obtain the utmost modulation of the compression forces operating on the cortical layer of the terrain to be consolidated.

In practice, an object of the invention is to offer the possibility of independently intervening for tensioning both the cover layer and the grid of the ropes. This, on one hand determines the possibility of ideally tensioning both the cover and the grid of the ropes and on the other hand it allows differentiated tensioning thereof.

Furthermore, still an object of the present invention is to tension a cover of the cortical layer of the loose terrain to a point of exerting a compression on the terrain with a force capable of instantaneously counterbalancing the weight of the unstable surface portion corresponding thereto, so as to guarantee an efficient stabling under any physical instability condition.

DESCRIPTION OF THE INVENTION

Particularly, the invention allows providing a system for consolidating the cortical layer of loose terrains comprising:

a plurality of anchor bars adapted to be stably anchored to a stable subsurface layer of the loose terrain, at least one cover layer adapted to cover the cortical layer of the loose terrain,

a plurality of first tensioning elements each constrained to a respective anchor bar and adapted to press the cover layer towards the stable subsurface layer for tensioning the cover layer, axially changing the constraint position thereof along the anchor bar;

at least one cable grid superimposed on said cover layer, comprising cables constrained to the anchor bars according to an arrangement scheme that enhances the capacity thereof to react locally to any landslide stimulus.

According to the invention, the system comprises a plurality of second tensioning elements each constrained to a respective anchor bar and adapted to press the portions of the cables arranged around the anchor bars towards the stable subsurface layer for tensioning the grid; the second tensioning elements are adapted to axially change the constraint position thereof along the anchor bar independently from said first tensioning elements.

Such solution allows efficiently tensioning the cover layer and the grid and, simultaneously, differentiating the tension for an improved modulation of the compression forces operating on the cortical layer of the terrain, fully exploiting the different mechanical characteristics of the cover layer and of the cable grid.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will be apparent from the following description provided by way of non-limiting example, with reference to the figures illustrated in the attached drawings.

Figure 1 is a lateral sectional view of a loose terrain consolidated by means of the consolidation system, according to the invention.

Figure 2 is a plan view of a detail of figure .

Figure 3 is an enlargement of the detail III of figure 2.

Figure 3A is a view of figure 3 partly sectioned.

Figure 4 is a sectional view along the line IV-IV of figure 3 prior to the step of tensioning the grid. Figure 5 is an axonometric view of the second tensioning element, of the system according to the invention.

Figure 6 is an axonometric view of the first tensioning element, of the system according to the invention.

PREFERRED EMBODIMENT OF THE INVENTION

With particular reference to such figures, a system for consolidating the cortical layer 1 1 of loose terrains, for example slopes, hillsides, water banks or the like is indicated in its entirety with 10.

The system 10 comprises a plurality of anchor bars 20 adapted to be stably anchored to a stable subsurface layer 12 of the loose terrain.

In one common embodiment, the anchor bars 20 comprise cylindrical steel rods one of whose ends 21 is adapted to be embedded in the stable subsurface layer 12 and fixed thereto by means of cementation or any other known fixing system, so that the anchor bar 20 has a longitudinal development substantially orthogonal to the plane defined by the terrain, for example orthogonal to the slope to be consolidated. The end 22 opposite to the buried end of the anchor bar 20 projects from the terrain, in particular, at a raised position with respect to the cortical layer 1 1 of the terrain.

In this case, before laying the anchor bar 20, the slope is remodelled by digging a series of holes 13 in the cortical layer 1 1 on whose bottom there are made perforations within which there are cemented the lower ends 21 of the anchor bars.

Each hole 13 surrounds the projecting end 22 of the anchor bar.

At least the projecting end 22 of the anchor bar 20 comprises an external threading 23, which can also develop over the entire length of the anchor bar. The anchor bar 20, for example, is a GEWI 500/550 N/mm2 steel bar with continuous threading or an FeB44K improved adherence bar with varying diameter depending on the specific case (for example 25 mm, having an ultimate strength equivalent to 270 kN and a tensile yield strength equivalent to 245 kN). However, steel rope anchors or active tensioners made of harmonic steel strands can also be used, for example for loose terrains having consistent thickness (for example usually greater than 3 m). The system 10 comprises at least one layer 30 for covering the cortical layer 1 of the loose terrain, which is fixed to the anchor bars 20.

In particular, the cover layer 30 comprises a metal net, for example of the double torsion hexagonal mesh type made of a wire with heavy zinc coating or steel wires.

For example, the metal net 10 x 8 cm wide meshes, with 3.0 mm or 2.7 mm diameter wire, and it has a tensile yield strength equivalent to 49.5 kN/m and a punch yield strength equivalent to 26 kN/m.

However, other types of nets with finer mesh or tensioning and materials different from the indicated ones or having combinations of nets and anti- erosive mats can be used alternatively or additionally.

Furthermore, alternatively or additionally, the cover layer 30 comprises a layer of geocomposite tissue or a grid having more less wide meshes of cables intertwined according to various shapes.

The cover layer 30 is such to cover the entire surface of the cortical layer to be consolidated, but such covering can be obtained by arranging side by side and/or superimposing several cover layers 30 joined to each other, for example by means of stitching using special iron or steel thread. Once laid, the anchor bars 20 are such to be inserted into respective meshes of the cover layer 30, for example into meshes of the aforementioned metal net. The cover layer 30 is then fixed to the anchor bars 20 by means of a plurality of first tensioning elements 40 adapted to axially slide along the anchor bars 20 and press the cover layer 30 towards the stable subsurface layer 12 for tensioning the cover layer.

In practice, each first tensioning element 40 presses a respective portion of the cover layer 30 inserted into the anchor bar 20 (involved by the first tensioning element) towards the bottom of the hole 13, thus adhering and pressing the cover element 30 on the surface of the cortical layer 1 1.

In this case, the first tensioning element 40, shown as an example in figure 6, comprises a concave plate 41 , provided with a central through hole 42, adapted to be inserted with clearance on an anchor bar 20. During use, the concavity of the plate 41 is facing da opposite side with respect to the stable subsurface layer 12.

The plate 41 defines an extended gripping portion 43, arranged in the convex portion of the plate, which is adapted to come to contact with the cover layer 30, to press it towards the stable subsurface layer 2 (as observable in figure 4).

The expression extended portion is used to indicate an area of the plate 41 sufficiently wide to interfere with a plurality of mashes of the cover layer, whether provided with wide or narrow meshes, so as to be able to exert pressure thereon and push them towards the stable subsurface layer 12.

The concave plate 41 , for example, is made by cutting and folding a quadrangular-shaped flat plate and it is frusto-conical-shaped with the smaller base provided with the through hole 42 facing towards the terrain during use.

The first tensioning element 40 further comprises a threaded thrust member, for example an internally threaded bolt 44, which is provided with a contact surface 45 suitable to come to contact with the plate 41 , for example at the perimeter area of the hole 42.

The nut 44 is adapted to be fastened on the anchor bar 20 and to push, during fastening, the plate 41 (which lies by means of the extended surface 43 thereof on the cover layer 30) towards the stable subsurface layer 12 simultaneously tensioning the cover layer 30, whose meshes are restrained in the direction parallel to the terrain by the various anchor bars 20.

In practice, the nut 44 is fastened on the anchor bar 20 until the cover layer 30 reaches a predetermined sufficient tensioning level, which can be quantified depending on the compression needs of the cortical layer 1 1 , for example by using torque wrenches for fastening the nuts 44 suitably calibrated according to the desired degree of tensioning.

The nut 44 pushes the plate 41 and the portion of cover layer 30 beneath it towards the bottom of the hole 13, hence at the stop position the plate 41 is positioned at the base of one of the artificial depressions 13 of the remodelled cortical layer 1 1 of the terrain to be consolidated. Such artificial depressions (or holes) were specifically made to determine a plurality of relief areas 14, with respect to the lying plane of the plate 41 , so as to allow the cover not only complete adherence to the terrain but also exert on such convex portions - after laying the plates 41 - a considerable and modulable pressure.

The system 10 comprises at least one grid 50 superimposed on the cover layer 30, which comprises at least one cable 51 ,52,53 wound around the anchor bars 20 so as to delimit closed perimeter areas at whose vertices there are arranged at least three anchor bars 20.

The anchor bars 20 are arranged at the base of the depressions 13 made in the terrain according to a scheme - in plan view - that can preferably be quincunx or square-like, so that the grid 50 delimits, for example, in the case of the quincunx configuration, substantially triangular relief areas 14, as observable in figure 2, or square-shaped areas - in the square-like configuration -; Furthermore, it is possible to provide for any arrangement of the grid 50, as long as the cables it is made up of form an acute angle each time they intercept an anchor bar.

In particular, the grid 50 comprises three cables, respectively 51 , 52, 53, which are for example made of steel and are wound around the anchor bars 20.

The cables 51 ,52,53, for example, are cables made of steel strands, usually having a diameter comprised between 12 mm and 16 mm, with metal core (but they can also be provided with a textile core depending on the cases) coated with zinc. The cables 51 ,52,53 have a permanent extension varying between 0.2% and 0.5% (greater for the cables with textile core) which also have an elastic extension, due to the traction they are subjected to, variable between 0.4% and 0.8% (depending on the load).

In practice, a first cable 51 and a second cable 52 are such to wind around the anchor bars 20 being arranged along the diagonals of the square delimited by four anchor bars 20, a third cable 53 is adapted to be arranged in the direction substantially orthogonal to the direction of the inclination of the terrain to be consolidated. Thus, each anchor bar 20 of the system 10, that is not positioned at the borders of the terrain to be handled has a lateral side wound (facing towards the top part of the slope) by a first cable 51 , the opposite lateral side (facing in the downstream direction) is wound by the second cable 52, and the side facing towards the top part of the slope to be consolidated is wound by the third cable 53.

In practice, a first cable 51 winds the lower part of the anchor bar 20 (with respect to the top part of the slope) creating an acute angle facing towards the upstream direction, a second cable 52 winds the upper part thereof creating an acute angle facing towards the downstream direction, and a third cable 53 passes over the anchor with a sub-horizontal development.

The first and the second cable 51 and 52 winding around each anchor bar 20 respectively create two opposite acute angles.

Furthermore, the grid 50 may be provided with a further cable, not shown, which cuts the grid 50 in the direction parallel to the direction of inclination of the terrain, i.e. arranged orthogonal to the third cable 53.

In practice, in the quincunx configuration the cables 51 ,52,53 perimetrally delimit the relief areas 14 of the cortical layer 1 1 of the terrain, while in the square-like configuration the cables 52 and 53 generally intersect at the apex of the convexes in relief 14.

Particularly, the system 10 comprises a plurality of second tensioning elements 60 (shown in detail in figure 5) adapted to axially slide along the anchor bars 20, independently from the first tensioning elements 40, to press at least the portions of the cables 51 ,52,53 wound around the anchor bars 20 towards the stable subsurface layer 12 so as to tension the grid 50 regardless of the tensioning of the cover layer 30, carried out by the first tensioning elements 40.

Each second tensioning element 60 comprises a dome 61 , for example frusto-conical-shaped also obtained by cutting and folding a flat metal plate, as illustrated, or curved without cutting by means of a mould or variously shaped for example truncated, hemispherical or the like, at whose top there is present a through hole 62 adapted to be inserted with clearance into one anchor bar 20.

The dome 61 has, at the base, a plurality of fairlead slots 63 adapted to house and restrain the cable.

Such slots 63 have an inlet cavity 64 open at the base of the dome 61 , which has two lateral sides converging towards the top part of the dome, which terminate with an expanded cavity 65, which defines two support surfaces 66, arranged orthogonal to the longitudinal axis of the anchor bar 20.

The support surfaces 66 are adapted to supportingly receive the portions of the cables 51 ,52,53 which depart from the portion wound around the anchor bar 20.

During use, the dome 61 is inserted into the anchor bar 20 with concavity facing towards the stable subsurface layer 12, so as to allow the slots 63 to be inserted (by means of the inlet cavities 64) from above on the respective portions of the cables 51 ,52,53 and restraint thereof in position by the support surface 66 thereof.

The second tensioning element 30 further comprises at least one threaded thrust element 67, for example another internally threaded nut and provided with a support surface adapted to lie on the dome 61 , at the upper convex wall around the through hole 62.

The thrust element 67 is adapted to be fastened on the projecting portion of the anchor bar 20 so as to exert pressure on the dome 61 directed along the longitudinal axis of the anchor bar 20, which pulls the cables 51 ,52,53 towards the base of the artificial depression 13 from which the anchor bar 20 projects tensioning the cables.

On each anchor bar 20, in this case, there are provided a first tensioning element 40 and a second tensioning element 60, the second tensioning element 60 is thus superimposed on the first tensioning element 40 in the axial sliding direction towards the stable subsurface layer 12 thereof and such tensioning elements are actuated independently with respect to each other. For example, the dome 61 at the stop position may be supportingly positioned on the concave plate 41 restraining, between the two opposite concavities of the dome 61 and of the plate 41 , the nut 44 and the cables 51 ,52,53 (arranged in the expanded cavity 65 of the slot 63 lying on the support surface 66).

The plates 41 may be different depending on the type of terrain and the depth of the unstable layer to be consolidated.

Usually, the dimensions of the lower base of the plate 41 are equivalent to 20x20 cm and equivalent to those of the larger base of the dome 61 , so that when the dome 61 is at the stop position it fittingly lies on the lower base of the plate 41 , which closes the inlet cavities 64 of the slots 63; in such position the two opposite concavities of the plate 41 and of the dome 61 define a substantially closed chamber which encloses - therein - the portions of the cables 5 ,52,53 wound around the anchor bar 20 and the nut 44.

Alternatively, it is possible that not all the anchor bars 20 are involved by the tensioning elements 40 and 60 or that the second tensioning element 60 is arranged at the stop position at a lower height (in the sliding direction) with respect to the height at which the first tensioning element 40 is positioned, depending on the tensioning requirements of the cover layer 30 and of the grid 50.

Also the tensioning of the grid 50 may be adjusted by using the torque wrenches for fastening the thrust element 67, as known to a man skilled in the art.

Practically, the cover layer 30, being easily deformable, suitably adapts to the morphology of the terrain entering into each depression through the pressure exerted by the plates 51 , and when strongly tensioned by compression it can instantaneously react towards the movement of the shallow landslides blocking the movement of the cortical layer.

The grid 50 combines such task of restraining the cortical layer 1 and, being less deformable with respect to the cover layer 30, on one hand compresses the cover layer 30 where it is less compressed on the cortical layer 1 1 , i.e. the apex of the of the convex portions of the cortical layer 1 1 determined by the obtained depressions 13, and on the other suitably and uniformly distributes the tension on the anchor bars 20.

The depressions 13 can be closed by a manhole cover, not illustrated, within which there can be indicated the installation technical data (such as for example the length of the anchor bar, the torque for fastening the nuts, the depth of the cortical layer, the type of concrete mixture used for anchoring the anchor bar to the stable subsurface layer, etc), or alternatively such depressions can simply be buried.

In the light of what has been described above, the method for consolidating the cortical layer 1 1 of terrains exposed to the risk of landslide by means the system 10 is as follows.

Firstly, the depressions 13 are made positioned and arranged, for example, to form a quincunx in the cortical layer 1 1 of terrain to be consolidated, to uncover the stable subsurface layer 12.

The digging depth of the depression 13 in which the anchors are housed depends on the geotechnical, morphological and lithological features of the terrain and the depth is usually comprised between 1/3 and 1/2 the cortical layer 1 1 of unstable terrain to be consolidated, but it can also be different depending on the need.

The perforations are then executed in the stable subsurface layer 12 so as to stably anchor a plurality of anchor bars 20, for example by means of cementation of the end 21 of the anchor bar.

Upon performing the previously described operations arranging the anchor bars 20 distributed as indicated over the entire width of the terrain to be consolidated, one or more cover layers 30 are arranged on the cortical layer 1 1 of terrain, so as to cover the entire surface of the cortical layer 1 1 .

The first tensioning elements 40 are used to ensure that the cover layer 30 is fixed to the anchor bars 20; actually, the first tensioning elements 40 are adapted keep the cover layer pressed on the cortical layer 1 1 and exert a substantially homogeneous or differentiated compression thereon, depending on the needs, capable of pressing the cover layer 30 towards the stable subsurface layer 12. The torque wrench can be used for fastening the nuts 44 so that each nut 44 is fastened with a determined maximum torque, for example of 10 KN or more).

After laying and tensioning the cover layer 30, i.e. when it is in a stable position anchored to the terrain, a grid 50 - whose cables 51 ,52,53 are adapted to delimit perimetrally closed areas and in relief with respect to the depressions 13, at whose vertices there are arranged at least three anchor bars 20 - is arranged on the cover layer as described above.

It should be observed that the laying of the grid 50 when the cover layer 30 is already tensioned leads to indubitable advantages for the personnel designated to execute the consolidation.

Upon laying the grid 50, which inevitably has the cables 51 ,52,53 initially loosened, the grid is then tensioned by means of the second tensioning elements 60, which, being adapted to slide along the anchor bars 30, at least press the wound portions of the cables 51 ,52,53 around the anchor bars 20 towards the stable subsurface layer 12, so that the tensioning of the grid 50 occurs independently - i.e. in a subsequent step and/or with different tensioning values applied - from the tensioning of the previously tensioned cover layer 30.

In practice, the thrust element 67 is fastened, for example by means of a torque wrench, until the determined maximum torque (for example 10 KN any other torque) is achieved for that area of the terrain or set using the torque wrench.

Upon achieving such value for the maximum tensioning of the cables, the portion of the cables 51 ,52,53 interposed between two anchor bars 20 may be at least partly driven into the terrain.

In practice, the portions of the cables 51 ,52,53 interposed between two anchor bars 20 locally compressing the cortical terrain layer 1 1 and creating inclined channels on the side of the depression 13, arranged perimetrally with respect to the relief area 14 and arranged beneath the cables 51 ,52,53, are hammered using a round headed hammer. This operation causes the loosening of the tension of the hammered cables 51 ,52,53 which thus require to be tensioned again until they reach the predetermined project tension once again. This operation can be performed several times until the dome 61 abuts against the plate 41 arranged on the base of the depression 13.

This allows attaining the stable three-dimensional consolidation of the cortical layer 1 1 , which is kept pressed towards the stable subsurface layer 12 of the terrain by the cover layer 30 and restrained by the grid 50 which divides the cortical layer 1 1 into perimetrally closed relief areas 13, confined and compressed substantially uniformly and/or suiting the project which can be variously predetermined depending on the needs of each and every context of application of the system 10.

This solution allows achieving the effect of raising the criticality values that could lead to the occurrence of the detachment of the cortical layer 1 1 from the stable subsurface layer 12, which are the cause of the landslide phenomena, so as to prevent the movement of shallow landslides in the consolidated terrains.

Actually, the synergy of the cover layer 30 with the grid 50 leads to the mechanical grip so as to ensure that minimum shallow landslide motions, causing the plastic deformation in the mesh which forms the cover layer 30, already partly (often entirely) reduced by the action of the mesh, stop as soon as the deformation intercepts the cables 51 ,52,53 nearer, which once tensioned - so to speak - stiffen and locally restrain the cover layer, serving as instantaneous restraint against any landslide movement of the cortical layer 1 1.

The invention thus conceived can be subjected to numerous modifications and variants all falling within the inventive concept.

Furthermore, all details can be replaced by other technically equivalent elements.

In practice, all the materials used as well as the contingent shapes and dimensions, may vary depending on the requirements without departing from the scope of protection of the following claims.