FR2705702A1 - Method for consolidating banks - Google Patents

Abstract

The invention relates to a method for consolidating a bank. According to the invention, this method comprises the following steps: - inserting piles (4) substantially vertically along the said bank (3); - fastening a net (6) made of woven geotextile material to the said piles (4) so that the surface of the said net (6) between two adjacent piles (4) is substantially parallel to the plane containing the said two adjacent piles (4); - filling the space between the said net (6) and the wall (7) of the said bank (3) with a filler material (8) so as to obtain a reconstructed wall of a bank (2) held and stabilised by the said net (6).

Description

 Bank consolidation process.

 The field of the invention is that of the consolidation of the banks of rivers. We know that it is necessary to protect the banks in order to prevent natural erosion linked to watercourses. Indeed, the water of a river (or more generally of any watercourse) tends to carry the ground as well as the vegetation constituting the bank with which this river is in contact. This erosion leads to a degradation not only of the bank itself (both aesthetic and physical), but also of the river which sees the earth of the bank depositing at the bottom of its bed, this deposit requiring dredging if one wishes maintain the ability to navigate this river.

 A first known method of consolidating banks is a fascination process consisting of filing piles along the banks and then intertwining, horizontally, head to tail and staggered, fascines (generally made of chestnut sapling) in alignment with pious.

 The fascines, whose branches are folded inside the bank, allow either to maintain and reinforce the existing wall of the bank, or to reconstitute a new bank wall when filling materials are used to fill the space included between these fascines and the existing wall of the bank.

 This first known method has many drawbacks.

 Indeed, the fascines constitute a rare product, very expensive and antiecological. Thus, to achieve a consolidation of banks over 12 km, the only obtaining of the fascines necessary for the implementation of this solution requires the uprooting of 20 to 30 ha of young sprouts of chestnut.

 In addition, the fascinations have limited lifetimes and have low resistance to ground movements.

 A second known method of consolidating a bank is a supporting method consisting in placing support posts in concrete blocks placed along the surface, then in fixing to these posts retaining plates extending transversely between the posts.

 This second known method also provides, optionally, for filling with an inexpensive material (generally backfill materials) the space between the retaining plates and the surface of the bank.

 This second known method is less costly than the fascination method and offers good resistance to ground movements.

 However, this second known method has a major drawback, namely non-compliance with the sites. Indeed, such a support damages the environment due to the massive use of concrete, in particular for the production of visible elements (posts, plates, etc.). It is clear that concrete prohibits any possibility of recovery of the support by vegetation, which explains the great difficulty, even the impossibility, of giving a "natural" aspect to this support.

 A third known method of consolidating a bank consists in using a gabion grid. The use of such a fence, well known in mountainous environments, makes it possible to avoid falling rocks and landslides by consolidating the slopes and the rock walls.

 In its application to the consolidation of a bank, the gabion grid is L-shaped and associated with riprap. The rock blocks of the riprap rest on the horizontal surface of the mesh, the vertical surface of the mesh constituting the reconstructed face of the bank.

 Like the two known methods presented above, this third known method has several drawbacks.

 Indeed, riprap requires the transport of large quantities of rock blocks, and it is almost essential to have close to a source of riprap material.

 In addition, this transport of rocks being generally carried out by trucks, the area of land located near the banks is very often damaged, the plant species that it accommodates are partially or completely destroyed.

 Finally, the vegetation cannot grow on the riprap, and it is therefore impossible to reforest the banks thus reinforced, which constitutes an obvious damage to the environment.

 The invention particularly aims to overcome these various drawbacks of the state of the art.

 More specifically, an objective of the invention is to provide a method of consolidating a bank which is inexpensive, while respecting the environment and not obstructing the development of roots and trees.

 Another object of the invention is to provide such a method which allows an increase in the life of the work performed, compared to the traditional fascination method.

 The invention also aims to provide such a method, the implementation of which offers good resistance to ground movements.

 An additional objective of the invention is to provide such a process requiring no riprap.

These objectives, as well as others which will appear subsequently, are achieved according to the invention using a bank consolidation process comprising the following steps:
- pile placement, substantially vertically and spaced apart,
along said bank
- attachment of a woven geotextile material net to said piles,
so that the surface of said net between two adjacent piles is
substantially parallel to the plane containing said two piles
adjacent
- filling the space between said net and the wall of said
bank with a filling material, so as to obtain a
reconstructed bank wall maintained and stabilized by said net.

In this way, the environment is respected since the method according to the invention
- does not require the use of concrete
- the mesh of woven geotextile material can be covered by the
vegetation and allows the use of a filling material
other than blocks of rock (for example it may be a vase
taken from the site by light cleaning of the river or
clay loam soils taken from marshes); and
- the surface of the reconstructed bank allows reforestation thanks to
type of filling material that can be used.

 In addition, nets made of geotextile material have a much lower cost than that of fascines or concrete slabs (or other), while allowing reliable and lasting consolidation.

 Finally, the nets made of geotextile material can easily be cut with a heating iron in order to pass a pipe (water evacuation for example), the heat tightening the mesh of the net, which avoids fraying.

 In a preferred embodiment of the invention, said step of fixing a net of geotextile material is preceded by a step of fixing a rigid frame to said piles, said rigid frame allowing said net to be held on a flat surface .

 In this way, the possible formation of bellies on the net, between the piles, is avoided in particular, these bellies being due to the thrust of the earth. The rigid frame thus makes it possible to make the final appearance of the consolidated bank more aesthetic while waiting for it to be covered by vegetation.

 Advantageously, said net has an L-shaped surface profile comprising on the one hand a substantially vertical surface and fixed to said piles and on the other hand a substantially horizontal surface covered by said filling material.

 In this way, foxes or cracks are prevented from forming through which water from the river could flow.

 Advantageously, said piles are plugged at the foot of the wall of said bank. Said piles are slightly inclined on the side of said bank, the axes of said piles having an angle relative to the vertical of less than about 10.

 Preferably, said net and said rigid reinforcement are fixed to said piles by means of cleats maintained by jumpers.

 In an advantageous embodiment of the invention, said woven geotextile material constituting said net is made of polyester and polypropylene threads with a mesh of approximately 4 × 8 mm.

 The net therefore consists of a textile article made of artificial fibers and is insensitive to UV rays as well as to chemical or bacteriological agents due to the nature of the water or the soil.

 Preferably, said rigid frame is a gabion mesh of galvanized wires with a mesh of approximately 60 x 80 mm.

 Advantageously, said filling material is silt originating from a slight cleaning of the bed of the watercourse, one bank of which is said bank to be consolidated.

 In this way, the mud, which has specific provisions for reforestation, can possibly, once dry, be reworked by a landscaper.

Other characteristics and advantages of the invention will appear on reading the following description of a preferred embodiment of
The invention, given by way of non-limiting example, and of the appended drawings in which
- Figure 1 shows a partial view, in a cross section
to the direction of a watercourse, this watercourse and an example
bank consolidated following a specific implementation of the
method according to the invention;
- Figure 2 shows a front view of the consolidated bank of the
figure 1;
- Figure 3 shows a partial detailed view of an overlay
a mesh and a net of geotextile material as it appears
health in Figures 1 and 2.

 The invention therefore relates to a method of consolidating a bank making it possible to prevent natural erosion linked to the watercourse corresponding to this bank.

 FIG. 1 presents a partial view, in a cross section in the direction of a watercourse 1, of this watercourse 1 and of a consolidated bank 2 following a particular implementation of the method according to invention.

According to this particular implementation, the method of the invention comprises the successive stages
- piles 4 are plugged substantially vertically along the bank
3;
- a mesh 5 is fixed to the piles 4;
- a net 6 is superimposed on the mesh 5 made of geotextile material which is
also fixed to piles 4;
- the space between the net 6 and the wall 7 of the bank is filled
3 with filling material 8.

 It should be noted that in certain applications, the net 6 is not maintained by a mesh 5 and can have belly between the piles 4, without however risk of rupture.

 The piles 4 can be inclined slightly on the bank side in order to improve the resistance of the assembly to landslides and to the thrust of the earth in general.

 The piles 4 have, for example, a length between 4 and 6 mm and a diameter between 200 and 220 mm. It is, preferably, chestnut perch. These piles are placed so that the height of the file is at least 2.5 times the height above ground. Thus, the pile heads are at a height of between 0.6 and 1.2m approximately relative to the surface of the water 1. These pile heads can be whipped through for the sake of aesthetics.

 The piles 4 are arranged at the foot of the wall 7 of the bank 3 and spaced about 1 m apart.

 The mesh 5 is for example a gabion mesh of galvanized wires with a mesh of approximately 60 x 80 mm. This mesh 5, the use of which is not systematic, constitutes a rigid frame for the net 6 made of geotextile material and prevents the formation of bellies. Thus, the appearance of the pile / net assembly before the vegetation has covered it is more aesthetic, the mesh being for example painted green in order to blend aesthetically with this assembly.

 The net 6 of geotextile material is for example made of polyester and polypropylene yarns with a mesh of approximately 4 x 8 mm.

 It is clear that this mesh value is given by way of example. In general, the choice of the value of the mesh used depends on the granulometry of the terrain.

 For example, the geotextile sold by the company CIMAGE under the reference HF 290 is used. This geotextile is insensitive to UV rays as well as to chemical or bacteriological agents due to the nature of the water or the soil. In addition, the physical characteristics of this geotextile (tensile strength, elongation at maximum effort, tear resistance, permeability, etc.) are such that for a spacing of 1 m between the piles and without wire mesh, the push of the ground causes a belly of 15 cm maximum between two piles without risk of rupture.

 Finally, this geotextile can easily be pierced, for the passage of a pipe for example, with a heating iron, the meshes tightening due to the heat and therefore not fraying.

 FIG. 3 presents a partial detailed view of the grid 5 / net 6 superposition.

 The mesh 5 and the net 6 are fixed to the piles 4, for example with cleats 9 held by jumpers 10. These cleats 9 and these jumpers 10 can be galvanized.

 Thus, as shown in Figure 2 which shows a front view of the bank, the mesh 5 and the net 6 have, between two adjacent piles, a substantially flat surface and parallel to the plane containing the two adjacent piles.

 As shown in FIG. 1, the thread 6 may have an L-shaped surface profile. In this case, the thread 6 comprises on the one hand a substantially vertical surface 6A and on the other hand a substantially horizontal surface 6B covered by the material filling 8.

 The substantially horizontal surface 6B of the net 6 constitutes a return, over approximately 0.5 m, making it possible to prevent the formation of cracks in the reconstituted bank 8.

 The net 5 of woven geotextile material, which constitutes the wall of the reconstituted bank, makes it possible to retain the filling material 8 while allowing the development of the vegetation and in particular the roots of the trees.

 Thus, the filling material 8 of the space between the net 6 (as well as the mesh 5) and the wall 7 of the bank 3 is for example mud coming from a light cleaning of the bed of the watercourse 1 or earth taken from the surrounding area.

 It is indeed advantageous to limit as much as possible the contributions of backfill materials such as rock blocks which, unlike the mud or the soil collected in the vicinity, do not allow vegetation development and reforestation.

 Finally, the dried mud also has the advantage of being able to be reworked by a landscaper who can thus give the bank a pleasant appearance, especially after the vegetation has grown.

Claims (9)

1. A method of consolidating a bank, characterized in that it comprises the following steps  - pile pile (4), substantially vertically, along said  bank (3);  - fixing a net (6) of woven geotextile material to said piles (4),  so that the surface of said net (6) between two adjacent piles (4)  either substantially parallel to the plane containing said two piles  adjacent (4).  stabilized by said net (6).  to obtain a reconstructed bank wall (2) maintained and  of said bank (3) with a filling material (8), so  - filling the space between said net (6) and the wall (7) 2. Method according to claim 1, characterized in that said step of fixing a net (6) of geotextile material is preceded by a step of fixing a rigid frame (5) to said piles (4), said frame rigid (5) allowing said net (6) to be held on a flat surface. 3. Method according to any one of claims 1 and 2, characterized in that said net (6) has an L-shaped surface profile comprising on the one hand a substantially vertical surface (6A) and fixed to said piles (4) and on the other hand a substantially horizontal surface (6B) covered by said filling material (8). 4. Method according to any one of claims 1 to 3, characterized in that said piles (4) are fitted at the foot of the wall (7) of said bank (3). 5. Method according to any one of claims 1 to 4, characterized in that said piles (4) are slightly inclined on the side of said bank (3), the axes of said piles (4) having an angle relative to the vertical less than about 10. 6. Method according to any one of claims 2 to 5, characterized in that said net (6) and said rigid frame (5) are fixed to said piles (4) by means of cleats (9) held by jumpers (10 ). 7. Method according to any one of claims 1 to 6, characterized in that said woven geotextile material constituting said net (6) is made of polyester and polypropylene threads with a mesh of approximately 4 x 8 mm. 8. Method according to any one of claims 2 to 7, characterized in that said rigid reinforcement (5) is a gabion mesh of galvanized son with a mesh of approximately 60 x 80 mm. 9. Method according to any one of claims 1 to 8, characterized in that said filling material (8) is silt originating from a slight cleaning of the bed of the watercourse (1) of which a bank is said bank (3) to consolidate.