EP1340857B1

EP1340857B1 - Reinforced earth retaining wall

Info

Publication number: EP1340857B1
Application number: EP03425121A
Authority: EP
Inventors: Fabrizio Averardi Ripari; Marcello Petrangeli
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-03-01
Filing date: 2003-02-26
Publication date: 2007-12-19
Anticipated expiration: 2023-02-26
Also published as: ATE381642T1; ES2298491T3; ITRM20020117A0; DE60318137D1; EP1340857A1; ITRM20020117A1; DE60318137T2

Abstract

A retaining structure of mechanically stabilised earth obtained by means of the insertion of reinforcement elements (6, 8) extending perpendicularly to the external vertical surface of the retaining wall and equipped with a front facing composed of panels (1-3) preferably prefabricated in reinforced concrete, to which the reinforcement elements (6, 8) are secured by means of an anchorage system (5, 7). The said reinforcement elements (6, 8) are composed of substantially bidimensional layers and are, in particular, polymer geogrids or geotextiles for geotechnical applications, and at least some of the said layers (6, 8) extend as loops from one level of earth to the above one, by rising vertically on the back of the said front facing panels (1-3), or along the rear part of the said reinforced earth structure, opposite the front facing. <IMAGE>

Description

The present invention concerns a reinforced earth retaining wall. More specifically, the invention concerns a containment work in earth that is mechanically stabilised by including reinforcement elements inside the wall itself, that extend perpendicularly to its vertical external surface. The earthwork is also equipped with a retaining wall made up of panels, to which the said reinforcement elements are secured.
The technology for reinforcing earth by inserting reinforcements consisting of metal or polymer bands arranged in horizontal layers inside the earthwork and anchored to an external sloping retaining wall is well-known in the field of geo-technical engineering. Various systems have been developed on the basis of this principle for creating retaining structures such as supporting walls for road works, bridge abutments, stabilisation works for slopes, dams, tunnels, embankments, quays, and in industrial and civil building construction works.
The first applications, dating back to the early 1960s, started from the idea of combining earthworks of various layers with metal reinforcement bands placed between each earth layer and anchored to an external retaining wall. This gave a composite structure, later called reinforced earth, that has great stability and durability as well as considerable flexibility of application and simplicity of realisation.
These early applications are described, in particular, in US patents No. 3421326 and No. 3686873, in the name of Henri Vidal . In order to obtain reinforcements via which the external retaining wall of concrete panels is anchored to the earth, these patents envisage largely linear elements made up of flexible steel bands that are galvanised or coated with a layer of polymer material, such as an epoxy resin, to protect them from corrosion. These bands must therefore be cut into the required length before being transported to the construction site. Then, they are anchored to the front retaining wall made up of prefabricated square concrete panels or, better, panels having a more complex shape, such as to provide a continuous cladding of complementary elements. The anchoring is obtained by connection through bolts to the metal anchoring brackets jutting out at regular intervals from the rear of each panel.
The realisation of a reinforced earth structure of the aforesaid type is carried out in subsequent layers after levelling the ground on the worksite and laying a perfectly horizontal foundation kerb that acts substantially as a guide for the later emplacement of the panels. The panels are placed vertically in subsequent rows starting from the first row on the foundation, while creating an embankment behind the panels with consecutive layers of earth, preferably of a suitable composition and granulometry, by compacting the earth with the suitable mechanical equipment. When the earth layers reach the level of the rear anchorages for each row, then a row of metal bands is placed on top of the compacted earth. The bands are laid horizontally and perpendicularly to the retaining wall and are then fixed to the respective anchorages jutting out of the panel. After laying a row of reinforcement bands, the next earth layer is then laid as well as the next row of vertical panels. In this way a composite structure is obtained where the longitudinal elements extending from the compacted earth interact with the earth particles through friction and thus mechanically stabilise the earthwork. Within certain limits, the longitudinal elements also act as anchorage ties.
To overcome the problems of corrosion connected with the use of metal reinforcements embedded in the earth, reinforcements made of strips of polymer material of suitable characteristics were later proposed for reinforced earth structures of the foregoing type. These strips are composed of a tensile stress-resistant core of high strength polyester fibres covered with a protective polyethylene sheath. The external protective layer is necessary because of the poor resistance of polyester to degradation, while polyethylene can guarantee suitable mechanical and physico-chemical protection.
One of these materials, known under the trade name Paraweb (originally manufactured by ICI), is proposed, for example, in US patent No. 4343571 (in the name of D. I. Price ), where the reinforcement is characterised by consisting in a continuous strip of flexible relatively unresilient material placed in zig-zag manner on the earth, between the anchorage elements jutting out of the rear of the cladding panels and a fixed bar anchored in the earth from the internal part of the earthwork. The continuity of the reinforcement strip results in the possibility of tensioning it before placing the next earth layer on top, thus making the structure particularly compact. With respect to using many separate metal bands, the use of one continuous polymer strip also has the advantage of exposing to chemical degradation very few ends that are cut and not protected by the external layer.
In addition to the possibility of using a continuous zig-zag strip on a horizontal earth layer, another embodiment disclosed in US patent No. 4343571 envisages that each reinforcement strip be continuous in a vertical plane, remaining unbroken alternatively on the back of the cladding panel and on the rear part of the earthwork, as the earth fill goes up one layer. The pretensioning of the reinforcements is carried out at each earth layer.
Compared to conventional systems, the aforesaid earth reinforcement structures have the clear advantage of reducing the overall size of the whole retaining work to a minimum, since they allow the realisation of a vertical retaining wall. Since the dimensions at the base are smaller with respect to a traditional sloping retaining wall, for example, the structure costs for are lower as far as the required land is concerned. Moreover, the version using polymer bands enables a drastic reduction of corrosion to the reinforcing elements, although a complete elimination of this problem calls for specific solutions also in the systems for securing the reinforcement elements to the cladding panels.
According to other technologies proposed by the prior art, instead of the prefabricated reinforced concrete cladding panels, it is possible to use prefabricated concrete blocks for the facing wall. These blocks are purposely designed to interlock with each other and to connect to the reinforcement elements. Similar solutions are generally proposed for achieving a cheaper transportation and an easier handling and laying of these cladding elements, but they obviously negatively affect the construction times and, above all, do not allow the construction of very high structures. In fact, while reinforced earth retaining walls with external facing of concrete panels of the size normally used can be as high as 20 m, those using concrete blocks for the external facing can be not higher than 4-6 m because the overall stability of the earthwork is considerably less.
Some well-known systems with external facing made of concrete blocks do not employ the metal bands or polymer strips conventionally used for earth reinforcement with panel facing elements, but instead use essentially horizontal layers of two-dimensional reticular elements of polymer material, known as geogrids or geotextiles. These products are commonly used in for many geotechnical applications other than the one discussed here, such as, e.g., the realisation of reinforced slopes, both continuous slope and stepped ones, as well as sloping green walls, where the concrete facing is absent.
The geogrids are normally made of a composite polymer material in which the highly resistant internal element is of polyester while the external protection element may be of PVC (such as the TeleGrid geotextiles) or polypropylene (e.g. the Merex geogrids), or can be made entirely of HDPE (high density polyethylene, such as the Tensar geogrids). The latter are rendered particularly resistant to tensile stress by a process of mono-axial stretching of the element, that thus gives a monodirectional orientation to the polymer chains.
The use of geogrids as reinforcement elements in earth structures with vertical retaining walls of the type concerned here allows to internally reinforce the earth in a more uniform way and with a more effective action than with the method employing anchorage systems composed of strips or separate bands. This is because the presence of transverse strips parallel to the retaining wall considerably improves the anchorage capacity to the earth and increases the resistance of the reinforcement to slippage from the earth itself. Moreover, this improved resistance is enhanced by the capacity of the reticular elements to give rise to a "dynamic interlock" with the earth, since the geogrid apertures allow the earth particles to be squeezed inside them during the compaction operation, thus expanding the grid spaces of the polymer reinforcement. When the grid spaces try to return to their initial configuration at the end of the compaction process, the internal stresses generated encapsulate the earth granules and reduce the horizontal thrust of the earth itself against the retaining wall.
Vertical retaining wall structures in which the external wall is composed of suitably shaped concrete blocks, between which the ends of horizontal layers of reinforcement elements - which may be geogrids - are laid during the emplacement phase, are described in many patent documents, among which, for example, the PCT patent application No. WO 99/32731 (in the name of S. R. Khamis ). The latter document describes the use of various reinforcement systems, with the proposed concrete block wall, and these systems can be combined or used as alternatives. Among these systems, in particular, the document discloses separate flat layers of geogrids or geotextile materials that extend horizontally inside the earth starting from the rear face of the retaining wall.
In other prior art references, particularly in US patent No. 4728227 (in the name of H. G. Wilson et al. ), starting from the assumption that using many small-sized external cladding elements, such as concrete blocks, has the aforesaid disadvantages, there is proposed to combine the anchorage system composed of geogrids laid in separate layers with large prefabricated facing panels, like the ones used for other civil engineering works, but equipped with suitable systems for anchoring the polymer reinforcement layer to the rear of the prefabricated panel.
In all the previously described cases, however, the geogrids or similar reinforcement elements of a substantially two-dimensional type are anchored to the front retaining wall (generally made of blocks) in separate horizontal layers with appropriately compacted earth layers in between.
On the basis of this state of the art, an object of the present invention is to provide a system of earth reinforcement based on the more reliable and flexible facing wall composed of prefabricated panels wherein, however, these are associated with non-linear but essentially two-dimensional reinforcement elements, such as geogrids, which afford considerable advantages in terms of execution time and reduction of the reinforcement material necessary to achieve a given resistance performance. In view of what has been said as regards geogrids, it is evident that using these grids together with the conventional-type prefabricated panels greatly reduces the time necessary to lay each reinforcement layer between one layer of compacted earth and the next, and also greatly facilitates this operation. In fact, the geotextile, which can be transported to the worksite in the form of rolls, only needs to be uncoiled along the earth layer (and, obviously, anchored to the connections provided on the rear of the panels) in order to achieve a whole layer of reinforcement in just one operation. Moreover, in view of the aforesaid improved performance of the geogrid structures in terms of the anchorage capacity in the earth, it is obvious that the quantity of material needed to achieve a certain resistance is lower than the one needed for anchorage materials composed of bands or strips. Thus, the incidence of the reinforcement elements, both in terms of quantity and in terms of costs, is lower than that of other systems, for the same amount of retaining wall surface laid.
To this end, the present invention proposes to further improve the performance obtainable with a reinforced earth structure realised with a retaining wall composed of prefabricated reinforced concrete panels together with geogrid earth reinforcement elements, by providing that at least some of the reinforcement layers of the structure are not laid on a single level but are extended in one or more continuous loops from one level of the structure to the one above. In this way, there is an added advantage in terms of the time necessary to execute the work because, after the first geogrid layer and its anchoring to the appropriate connections on the panel rear has been carried out, the reinforcement roll remains intact and is taken to the layer above as the earth layer rises to meet the next anchorage point. Thereafter, another reinforcement layer is rolled out without needing to bring separate pre-cut pieces of reinforcement to the site. In other words, the solution proposed allows using the same pre-cut roll of reinforcement to lay two or more consecutive layers of internal reinforcement.
A further advantage of the solution proposed according to the present invention consists of the fact that, if two consecutive layers of continuous reinforcement are anchored to the back of two separate panels laid one above the other (instead of being anchored to two connections, one above the other, on the same panel), then the reinforcement itself will create a bond between the two panels, anchoring them also through the tension induced in the grid by the compaction of the earth layers. This evidently increases the bond between the panels of the retaining wall and the stability of the whole structure.
Moreover, the continuity of the reinforcement geogrid or fabric from one level to the one above can be realised also on the internal part of the earthwork, opposite the external facing wall. In this case, the loop created by the reinforcement that folds upwards from the internal part to then fold back to be laid on the next earth layer has the capacity to create a considerable anchorage that is very resistant to the slippage of each one of the reinforcement layers from the ground. The creation of such a "foundation bulb" is especially useful in the upper levels of the reinforced earth structure, where the weight of the earth bearing down on the reinforcements is lower and these would otherwise tend to more easily slip out of the whole earthwork.
Therefore, the present invention specifically provides a reinforced earth structure with a vertical retaining wall comprising:

■ a plurality of front facing panels laid vertically, arranged in rows one above the other and presenting, at established heights, connection elements jutting out of the rear face of each panel and aligned in one or more horizontal rows;
■ a plurality of reinforcement elements laid horizontally inside the earth at the level of each row of the said connection elements provided on the rear of the said front facing panels, and with an earth layer placed between each reinforcement layer and the following one;
■ a plurality of anchorage means cooperating with the said connection elements in order to anchor each of the said reinforcement elements to the said front facing panels,

In particular, the said two-dimensional reinforcement layers (6, 8) may consist in geogrids or geotextiles of polymer material, or may be composed of non-compact matting or fabrics of possibly fibre-reinforced high modulus synthetic material. The geogrids or geotextiles (6, 8) are preferably made of polyester fibres covered in polypropylene, polyester fibres covered in PVC or are entirely made of high density polyethylene (HDPE) and subjected to a monoaxial stretching process, according to the solutions already in use in the prior art.
According to some specific embodiments of the structure of the invention, the front facing panels are prefabricated reinforced concrete panels of a quadrilateral shape, cross-shape or T-shape, combined so as to create a continuous cladding of complementary elements. The panels do not require any particular interconnection systems because, as already noted, a peculiar ity of the system lies in laying the reinforcement layers in loops, positioned so as to create a bond between two panels placed one above the other. Smaller panels are to be preferred in view of their easier handling. Moreover, if required, the panel weight can be reduced by using lighter concrete mixtures that include plastic aggregates or expanded clay instead of the conventional inert materials used, or even fibre-reinforced mortar, in which fibres of a suitable resistance - such as carbon fibres or aramide fibres are used instead of the steel reinforcement. Alternatively, the panels can be made entirely of steel or of a suitable plastic material, or even of wood.
As already noted, each of the said front facing panels is provided with connection elements jutting out from the rear face thereof, and these elements are preferably arranged in two horizontal rows. The connection elements can be steel rings, possibly coated with a plastic material, or can be rings made of stainless steel, a composite fibre or another highly resistant synthetic material. They are fixed to the rear of the said front facing panels and are in a variable number for each of the two said horizontal rows. The anchorage means cooperating with the said connection elements preferably consist in a steel bar, possibly plastic coated, or a bar made of stainless steel or a composite material highly resistant to bending stress, suitable to be inserted in a horizontal row of the said connection elements, thereby securing the reinforcement to the said connection elements. Preferably, the said bar is also pre-cut and of the same length as the reinforcement width, and thus has the advantage of being easily and rapidly laid with respect to using several separate anchorage devices for each horizontal row of connection elements.
According to some specific embodiments of the present invention, at least two of the said reinforcement layers are extended as a loop from one earth level to the one above, rising vertically along the back of the facing panels, and are then be anchored to two horizontal rows of connection elements provided on two vertically adjacent panels. There is thus the already noted advantage of exploiting the reinforcement to create a connection between two vertically adjacent panels of the front facing.
Advantageously, in the proposed structure at least two of the said reinforcement layers, situated in the upper part of the structure, may extend as a loop from one earth level to the one above, rising vertically along the rear of the said structure, opposite the front facing. As already noted, this creates a very resistant anchorage element on the inner part of the structure, which can resist any possible slippage of the reinforcement.
Again, according to the present invention, it is preferable to use reinforcement layers of the same width as that of the front facing panel, although it is possible to use a reinforcement layer of a width corresponding to two or more panels placed horizontally side by side.
To optimise the performance of the reinforced earth structure, reinforcement layers of different strengths, decreasing from the bottom up, can be provided along the height of the structure itself. In cases where the kinds of reinforcement used are not sufficiently varied to optimise the resistance necessary at the various levels, then it is also possible - after anchoring the reinforcement to the front facing panel as envisaged - to fold the reinforcement layer on itself and to roll it out again inwards within the earthwork in order to achieve a double reinforcement strength, on that specific level, than the one envisaged for the material used.
The structure according to the present invention can also be used for creating opposed retaining walls close to each other, as in the case of road ramps where the said plurality of vertically laid front facing panels corresponds to a plurality of front facing panels laid vertically on the opposite side, and the said reinforcement layers are connected, via their respective connection elements and anchorage means, to both of the said opposed retaining walls..
According to another aspect thereof, the present invention also concerns the construction method used for creating the claimed reinforced earth structures. With specific reference to the overall structure in its general lines, this method may be summarised as including the following operations:

a) creating a horizontal foundation kerb for aligning the first row of the said front facing panels;
b) laying the first row of the said panels vertically on the said foundation kerb;
c) filling the earth inside the first row of panels up to the first row of connection elements, and then compacting the earth using suitable mechanical equipment;
d) laying a first reinforcement layer on the earth, starting from the rear of the structure up to the said row of connection elements;
e) inserting a row of - possibly appropriately cut - apertures of the said reinforcement layer on the connection elements and immediately behind inserting one or more of the said anchorage means in the said connection elements, thus anchoring the reinforcement layer to the front facing panels;
f) folding the reinforcement layer on itself and laying it backwards towards the rear of the structure, or supporting the remaining part of the reinforcement layer at the back of the facing panels;
g) laying a second row of panels vertically on top of the said first row and filling the earth inside the second row of panels until the earth level reaches the second row of connection elements, compacting the earth with suitable mechanical equipment;
h) if the reinforcement layer of the lower level has been folded on itself, laying a second reinforcement layer proceeding as per the above points d) and e) for the first layer, and then supporting the remaining part of the reinforcement layer at the back of the panels;
i) if the reinforcement layer of the lower level has been supported at the back of the panels, proceeding as per point e) above for the first layer, and then laying the reinforcement layer backwards towards the rear of the structure;

In the case where the structure according to the present invention also includes reinforcement loops provided by the rear part of the structure itself, these loops being particularly useful, as pointed out before, at the higher levels of the retaining wall, the aforesaid procedure will also include, after an operation of the kind envisaged in i) above, the following operations,:

j) supporting the remaining part of the reinforcement layer (6, 8) from the rear part of the said reinforced earth structure;
k) filling the earth inside the corresponding row of front facing panels (1-3) up to the level of the next row of connection elements (5), compacting the earth with appropriate mechanical equipment;
l) laying the said remaining part of the reinforcement layer (6, 8) on the earth by starting from the rear part of the structure up to the said row of connection elements (5).

Further construction and functional features of the reinforced earth structure according to the present invention and the corresponding construction method, as well as the advantages of the invention, will be more evident with reference to some specific embodiments thereof, illustrated merely by way of example in the attached drawings, where:

Figure 1 is a perspective view of an embodiment of the proposed structure, seen from the rear, partially broken and symbolically devoid of the earth layers placed in between;
Figure 2 is a vertical sectional view of a similar structure as the one shown in figure 1, and is also symbolically devoid of the earth layers placed in between;
Figures 3 and 4 are two elevation views, respectively from the front and back of the front facing panels, of a structure of the type shown in figures 1 and 2;
Figure 5 is a side view, from the back, of some of the front facing panels shown in figures 3 and 4, resting on the foundation kerb and with the anchorage system visible;
Figure 6 is a partially broken vertical sectional view of a detail of the structure of figure 1 or figure 2, showing the anchorage system composed of the fixed connection element on the back of the panel and of the anchorage means that link to the connection element to secure the reinforcement itself.

A reinforced earth structure according to the present invention, of which figure 1 only shows a perspective view from the back of a vertical column of front facing panels (1, 2) laid one above the other, includes - in the forms illustrated in figures 1-5 -a front facing of prefabricated concrete panels (1, 2, 3) shaped so as to provide a continuous cladding of complementary elements. In particular, in the case specifically shown in figures 3-5, the front facing is mainly composed of T-shaped panels (1). Rectangular panels (2), corresponding to the upper section of the T-shape are to be added to these T-shaped panels (1) in order to uniformly complete the cladding, and also cross-shaped panels (3), wherein the upper section of the T-shape is connected to another rectangular element corresponding to a lower section of the T-shape. The first row of panels (1, 2, 3) is laid on the foundation kerb (4) which, as already pointed out, is perfectly horizontal and only serves to properly align the panels (1, 2, 3).
Going back to figure 1, on the back of the panels (1, 2, 3) there are provided two horizontal rows of connection elements (5) in the form of rings embedded in the concrete casting of the panel itself. In the embodiment examined here, these connection elements (5) are made of polymer-coated steel. When, as previously mentioned, the first earth layer (not shown) has beeb put in place and compacted behind the first row of panels (2) up to a level reaching the first row of connection elements (5), then the first layer of reinforcement (6) - which in the form shown is a geogrid of polymer material-is laid. This reinforcement layer (6) is made to interweave with the connection elements (5), by means of a row of aligned apertures and, immediately after this, the polymer coated steel bar (7), which acts as an anchorage means, is inserted in the connection elements (5) and secures the reinforcement (6) to the front facing panels (1, 2, 3).
In the embodiment illustrated in figure 1, the first reinforcement layer (6) is not folded on itself to be rolled out on the same level (this possibility is not shown in the figures), but goes up vertically along the back of the panel (2) to reach the earth level above. Once the required thickness of earth has been filled and compacted, reaching the level of the second row of connection elements (5), then the previous anchorage operation is repeated using the connection elements (5) and another steel bar (7), and the reinforcement (6) is laid in a further layer going towards the rear or internal part of the structure. In the version shown in figure 1, also the next pair of reinforcement layers (6) are of the same type and are laid in the same manner, while the pair of upper reinforcement layers (8) are made of a geogrid of a lower strength.
In the embodiment schematically shown in figure 2, in which corresponding elements are indicated with the same reference numbers as those used in the other figures (even though the cross-sections of the anchorage bars (7) are so small that they are practically non-visible), after the first two pairs of reinforcement layers (6) of the first type are laid as in the previous case, the following reinforcement layers of a lower resistance type (8) are four in all. Moreover, between the second and third of the said layers, the reinforcement (8) remains unbroken by being folded as a loop and then taken up to the next level from the rear end of the reinforced earth structure. In this way, the reinforcement layer provides a high strength anchorage against the slippage of the reinforcement layer (8) outside the earthwork.
As already noted above, the reinforced earth structure proposed according to the present invention affords considerable advantages with respect to other known structures of comparable performance, both in terms of speed and practicality of laying as well as in terms of materials saving and/or mechanical reliability.
The present invention has been disclosed with particular reference to some specific embodiments thereof, but it should be understood that modifications and changes may be made by the persons skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims

A reinforced earth structure with a vertical retaining wall comprising:
■ a plurality of front facing panels (1-3) laid vertically, arranged in rows one above the other and presenting, at established heights, connection elements (5) jutting out of the rear face of each panel (1-3) and aligned in one or more horizontal rows;

■ a plurality of reinforcement elements laid horizontally inside the earth at the level of each row of the said connection elements (5) provided on the rear of the said front facing panels (1-3), and with an earth layer placed between each reinforcement layer and the following one;

■ a plurality of anchorage means (7) cooperating with the said connection elements in order to anchor each of the said reinforcement elements to the said front facing panels (1-3),
characterised by the fact that the said reinforcement elements are layers of a two-dimensional reinforcement (6, 8) and that at least some of the said reinforcement layers (6, 8) extend as a loop from one earth level to the one above, going up vertically along the back of the said front facing panels (1-3), between one horizontal row of the said connection elements (5) and the one above, or along the rear part of the said reinforced earth structure, opposite the front facing.
A reinforced earth structure according to claim 1, wherein the said two-dimensional reinforcement layers (6, 8) consist in geogrids or geotextiles of polymer material, or are composed of non-compact matting or fabrics of possibly fibre-reinforced high modulus synthetic material.
A reinforced earth structure according to claim 2, wherein the said geogrids or geotextiles (6, 8) are made of polyester fibres covered in polypropylene, polyester fibres covered in PVC or are entirely made of high density polyethylene (HDPE) and subjected to a monoaxial stretching process.
A reinforced earth structure according to any one of claims 1-3, wherein the said front facing panels (1-3) are prefabricated reinforced concrete panels of a quadrilateral shape (2), cross-shape (3) or T-shape (1), combined so as to create a continuous cladding of complementary elements.
A reinforced earth structure according to claim 4, wherein each one of the said front facing panels (1-3) is provided with connection elements (5) jutting out from the rear face thereof and arranged in two horizontal rows.
A reinforced earth structure according to claim 5, wherein the said connection elements (5) are steel rings, possibly plastic coated, or are made of stainless steel, composite fibre or another highly resistant synthetic material, fixed to the rear of the said front facing panels (1-3) and in a variable number for each of the two said horizontal rows.
A reinforced earth structure according to claim 6, wherein the said anchorage means (7) cooperating with the said connection elements (5) consist in a steel bar, possibly plastic coated, or made of stainless steel or a composite material highly resistant to bending stress, suitable to be inserted in a horizontal row of the said connection elements (5), thereby securing the said two-dimensional reinforcement layer (6, 8) to the said connection elements (5).
A reinforced earth structure according to any one of claims 5-7, wherein at least two of the said reinforcement layers (6, 8) extend as a loop from one earth level to the one above, going up vertically along the back of the said front facing panels (1-3), and are then anchored to two horizontal rows of the said connection elements (5) provided on two vertically adjacent panels (1-3).
A reinforced earth structure according to any one of claims 5-8, wherein at least two of the said reinforcement layers (8), situated in the upper part of the said structure, extend as a loop from one earth level to the one above, going up vertically along the rear part of the said reinforced earth structure, opposite the front facing.
A reinforced earth structure according to any one of the preceding claims, wherein the said two-dimensional reinforcement layers (6, 8) are of the same width as that of a retaining wall panel (1-3).
A reinforced earth structure according to any one of the preceding claims, wherein along the height of the said structure two-dimensional reinforcement layers (6, 8) of varying strength are provided, decreasing from the bottom up.
A reinforced earth structure according to claim 1, for the construction of opposed retaining walls close to each other, wherein the said plurality of vertically laid front facing panels (1-3) corresponds to a plurality of front facing panels (1-3) laid vertically on the opposite side, and the said reinforcement layers (6, 8) are connected, via their respective connection elements (5) and anchorage means (7), to both of the said opposed retaining walls.
A process for the construction of a reinforced earth structure as described in claim 1, comprising the following operations:
a) creating a horizontal foundation kerb (4) for aligning the first row of the said front facing panels (1, 2);

b) laying the first row of the said panels (1, 2) vertically on the said foundation kerb (4);

c) filling the earth inside the first row of panels (1, 2) up to the first row of connection elements (5), and then compacting the earth using suitable mechanical equipment;

d) laying a first reinforcement layer (6, 8) on the earth, starting from the rear of the structure up to the said row of connection elements (5);

e) inserting a row of - possibly appropriately cut - apertures of the said reinforcement layer (6, 8) on the connection elements (5) and immediately behind inserting one or more of the said anchorage means (7) in the said connection elements (5), thus anchoring the reinforcement layer (6, 8) to the front facing panels (1, 2);

f) folding the reinforcement layer (6, 8) on itself and laying it backwards towards the rear of the structure, or supporting the remaining part of the reinforcement layer (6, 8) at the back of the facing panels (1, 2);

g) laying a second row of panels (1, 3) vertically on top of the said first row and filling the earth inside the second row of panels (1, 3) until the earth level reaches the second row of connection elements (5), compacting the earth with suitable mechanical equipment;

h) if the reinforcement layer (6, 8) of the lower level has been folded on itself, laying a second reinforcement layer (6, 8) proceeding as per the above points d) and e) for the first layer, and then supporting the remaining part of the reinforcement layer (6, 8) at the back of the panels (1, 3);

i) if the reinforcement layer (6, 8) of the lower level has been supported at the back of the panels (1-3), proceeding as per point e) above for the first layer, and then laying the reinforcement layer (6, 8) backwards towards the rear of the structure;
and carrying on with such operations until the required height of the earthwork is reached.
A process according to claim 13, also comprising, after an operation of the type as per point i), the following operations:
j) supporting the remaining part of the reinforcement layer (6, 8) from the rear part of the said reinforced earth structure;

k) filling the earth inside the corresponding row of front facing panels (1-3) up to the level of the next row of connection elements (5), compacting the earth with appropriate mechanical equipment;

l) laying the said remaining part of the reinforcement layer (6, 8) on the earth by starting from the rear part of the structure up to the said row of connection elements (5).