Patent Application
20130022411
The present invention relates to a facing element for use in a stabilized soil structure. It also relates to a stabilized soil structure comprising said facing element and to a method for erecting a stabilized soil or reinforced earth structure. This building technique is commonly used to produce structures such as retaining walls, bridge abutments, etc.
A stabilized soil structure combines a compacted fill, a facing, and reinforcements usually connected to the facing. The reinforcements are placed in the soil with a density dependent on the stresses that might be exerted on the structure, the thrust forces of the soil being reacted by the soil-reinforcements friction.
The invention more particularly concerns the case where the reinforcements are in the form of fill reinforcement strips of synthetic material, for example based on polyester fibers.
The facing is most often made up of facing elements, as for example in the form of prefabricated concrete elements, such as slabs or blocks, juxtaposed to cover the front face of the structure. There may be horizontal steps on this front face between different levels of the facing, when the structure has one or more terraces.
The fill reinforcement strips placed in the fill are usually secured to the facing by mechanical connecting members that may take various forms. Once the structure is complete, the reinforcements distributed through the fill transmit high loads, in some cases of up to several tons. Their connection to the facing needs to be robust in order to maintain the cohesion of the whole.
A facing element comprises a front face and a rear face extending along a longitudinal direction X and an elevation direction Z and a body between said front and rear faces.
The body of some known facing elements comprises at least a hollow part with an opening on the rear face wherein a cylindrical core is cohesive with the body and arranged at least partly in the hollow part to form an anchoring region for a fill reinforcement strip.
Patent document U.S. Pat. No. 5,839,855 discloses examples of a facing element where a passage intended to receive a fill reinforcement strip is in the shape of a C within the thickness of the facing element.
Although preceding facing elements are widely and effectively used, one has noticed that their cylindrical cores usually break according to a bending mode when being pulled by fill reinforcement strips. This breaking mode may limit the efficiency of the anchoring region and has to be taken into account when designing a stabilized soil structure comprising said facing elements.
It is an object of the present invention to propose a novel facing element for use in a stabilized soil structure, making it possible to reduce the incidence of the problems set out above.
The invention thus proposes a facing element for use in a stabilized soil structure where the facing element comprises a front face and a rear face extending along a longitudinal direction X and an elevation direction Z, a body between said front and rear faces, said body comprising at least a hollow part with an opening on the rear face wherein a cylindrical core is cohesive with the body and arranged at least partly in the hollow part to form an anchoring region for a fill reinforcement strip, wherein the cylindrical core extends substantially parallel to the longitudinal direction X and its cross section, in a plane (Y, Z) perpendicular to the plane (X, Z), consists of two continuous parts separated by a virtual straight line along the direction Z, where the first part has a continuously decreasing size in the direction Y from the virtual straight line to an extremity substantially directed opposite to the rear face of the facing element and the second part has a continuously constant and/or decreasing size from the virtual straight line to an extremity directed to said rear face, and wherein:
L
2≧1.1×d1; and
A≧0.24×d12; wherein:
L2 is the distance between the extremity of the first part and the rear face measured according to the Y direction;
d1 is the width of the cylindrical core measured according to the X direction at the extremity of the first part;
A is the area of the cross section of the cylindrical core in the plane (Y, Z).
Said shape and geometric characteristics of the facing element make possible to avoid breaking of the cylindrical core according to a bending mode when being pulled by fill reinforcement strips. The inventors have noticed that the cylindrical cores of said facing elements break according to a shearing mode.
When comparing samples broken according to those two different modes, one can notice that the cores of preceding known facing elements, that break according to a bending mode, break between their two extremities, roughly in the middle of said cores, whereas the cores of the facing elements according to the present invention break at their extremities, where they are cohesively attached with the body.
Alternatively, one can notice that cracks formed in the facing elements of the invention are formed within said body. Those cracks are usually formed in four approximately 45° directions in the (X,Z) plane when fill reinforcement strips pull in the Y direction.
The inventors have noticed that the breaking energy dissipated within the facing element according to the invention is significantly higher compared to the breaking energy dissipated when the cores break according to a bending mode.
One can then advantageously design stabilized soil structures with said facing elements. According to an embodiment, one can significantly reduce the thickness of the facing element according to the invention in comparison with a facing element as previously known and obtain similar pulling resistance for both facing elements.
According to further embodiments that can be considered alone or in combination:
the second part has a continuously decreasing size from the virtual straight line to the extremity directed to the rear face;
L
2≧1.3×d1;
A≧0.40×d12;
L2/L1≧0.5; wherein L1 is the largest distance between the rear face and the front face measured according to a line passing through the cylindrical core along the Y direction;
the first part of the cylindrical core cross section is chosen in the list consisting of half-circle, half-ellipse, half-oval;
the second part of the cylindrical core cross section is chosen in the list consisting of half-circle, half-ellipse, half-oval, triangle, trapezoid quadrilateral, rectangle;
the body and the cylindrical core are cast together with the same cast material; the body and the cylindrical core may also be made of a different material; the cylindrical core may also be manufactured independently and then introduced within a mould in order to cast the body and to render the cylindrical core cohesive with the body;
the body is made of concrete;
the area A of the cross section of the cylindrical core is substantially constant along the X axis;
the facing element is in the form of a panel, and the distance L2 between the extremity of the first part and the rear face is at least half of the thickness of the panel-shaped facing element.
The invention also relates to a stabilized soil structure, comprising fill reinforcement strips extending through a reinforced zone of a fill situated behind a front face of the structure and a facing placed along said front face and extending along a longitudinal direction X′ and an elevation direction Z′, the facing comprising at least a facing element according to the present invention and here above disclosed which directions X and Z are arranged so as to coincide with directions X′ and Z′ and fill reinforcement strips being arranged so as to form an open loop around the cylindrical core of the said facing element and said open loop being extended on each side by a segment of the fill reinforcement strip, said segments extending at least partly within the fill.
According to an embodiment of said stabilized soil structure, a surface of the said strip forming the open loop contacts and presses substantially the whole external periphery of the cross section of the first part of the cylindrical core, and at least a part of the external periphery of the cross section of the second part of the cylindrical core. According to said embodiment, compression load is applied at least partly around the cylindrical core. Said embodiment helps to further improve the pulling resistance of the anchoring region.
According to preceding embodiment a surface of the strip forming the open loop may contact a surface of the strip forming the pen loop contacts at least 20%, as for example at least 50% of the external periphery of the cross section of the second part of the cylindrical cohesive core.
According to an embodiment, the two segments extending the open loop come out of the facing through a same slot. According to another embodiment they come out through two different slots. Said two different slots may be in the same (X, Y) plane or be arranged in two separated (X,Y) planes.
The invention is also directed to a method for erecting a stabilized soil structure, comprising fill reinforcement strips extending through a reinforced zone of the fill situated behind a front face of the structure, and a facing placed along said front face and extending along a longitudinal direction X′ and an elevation direction Z′, the reinforcement strips being anchored to the facing in respective anchoring regions comprising the steps of:
a) erecting at least part of a facing by using at least a facing element according to the present invention and here-above disclosed, arranged so as directions X and Z of the facing element coincide with directions X′ and Z′;
b) positioning in at least an anchoring region of the facing element of step a) a fill reinforcement strip so as to form an open loop around the cylindrical core of the said facing element and so that the open loop is extended on each side by a segment of the reinforcement strip;
c) introducing fill material over the said fill reinforcement strip and compacting it.
Other features and advantages of the present invention will become apparent from the description below of some non-limiting illustrative embodiments, with reference being made to the attached drawings, in which:
a are partial cross sectional schematic views of other non limiting embodiments of the invention according to the plane (Y,Z) and
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention. Like reference characters in the different figures refer to similar parts.
The facing 3 extends along a longitudinal direction X′ and an elevation direction Z′. the facing 3 may be vertical or inclined.
The facing elements 34 have a front face 31 and a rear face 32.
Reinforcements extend through a reinforced zone 11 of the fill situated behind the front face of the structure. A zone 12 which does not comprise fill reinforcement strips may be located between the reinforced zone 11 and the face 4.
The reinforcements 2 comprise synthetic reinforcing members in the form of flexible strips extending in horizontal planes behind the facing 3. These may in particular be fill reinforcement strips based on polyester fibers encased in polyethylene.
The reinforcement strips 2 are attached in anchoring regions 35 to the prefabricated elements 34 joined together to form the facing 3. These elements 34 are typically made of reinforced concrete. In the example shown, they are in the form of panels. They could also have other forms, in particular the form of blocks. According to an example, when the concrete of such an element 34 is cast, one or more reinforcement strips 2 may be installed in the mould to provide the strip-element anchorage. After the concrete has set, each strip has two sections which emerge from the element and are to be installed in the fill material. According to another embodiment, the reinforcement strips are introduced in the anchoring regions 35 after placing the facing elements when erecting the structure.
For erecting the structure, the procedure may be as follows:
a) Placing some of the facing elements 34 so as then to be able to introduce fill material over a certain depth. In a known manner, the erection and positioning of the facing elements may be made easier by assembly members placed between them. The strips 2 are so positioned on the facing elements 34 that some of them are located at the same horizontal level when the facing is erected.
b) Introducing fill material 11, 12 and compacting it progressively until the next specified level for placement of the reinforcement strips 2 is reached.
c) Laying the reinforcement strips 2 on the fill at this level.
d) Introducing fill material over the reinforcement strips 2 which have just been installed. This fill material is compacted as it is introduced.
e) Repeating steps b) to d) if several levels of strips are provided per series of facing elements 34.
f) Repeating steps a) to e) until the upper level of the fill is reached.
During introduction and compacting of the fill material, the reinforcement strips 2 already placed at the lower levels experience tensioning. This tensioning results from the friction between the strips and the filled material and ensures the reinforcement of the structure. So that the tension is established under good conditions, it is advisable that the strips of one level emerge from their facing elements so that they are all correctly aligned with this level. It is also advisable that they are oriented horizontally as they emerge from the facing, so as to ensure that they do not twist in the filled material.
Main geometrical characteristics of said embodiment of a facing element according to the present invention are:
L1 is the thickness of the facing element, that is the largest distance between the front face 31 and the rear face 32 measured according to a line passing through the cylindrical core 5 along the Y direction;
L2 is the distance between the extremity 54 of the first part 51 and the rear face 32 measured according to the Y direction;
L3 is the distance between the extremity 55 of the second part 52 and the rear face 32 measured according to the Y direction;
d1 is the width of the cylindrical core 5 measured according to the X direction at the extremity 54 of the first part 51;
d2 is the width of the cylindrical core 5 measured according to the X direction at the extremity 55 of the second part 52;
d3 is the width of the opening 36 measured according to the X direction on the rear face 32;
L1 is the largest distance of the hollow part 37 measured according to the Z direction,
L2 is the largest distance of the cylindrical core 5 measured according to the Z direction;
L3 is the size of the largest part of the opening of the hollow part 37, measured according to the Z direction on the rear face 32;
A is the area of the cross section of the cylindrical core 5, measured in a plane (Y, Z).
According to embodiments not limited to the embodiment of
the thickness L1 is a constant along the Z direction, and the thickness of the whole facing element may be constant according to the Y direction;
the distance d3 is equal or greater than the distance d2;
the distance d2 is equal or greater than the distance d1;
the extremity 55 is located inside the hollow part 37, and the distance L3 is considered as being positive, as for example equal or greater than 10% of the distance L1;
the line according to the Z direction corresponding to the largest distance of the hollow part 37 comprises the virtual straight line 53;
the distance L3 is smaller than the distance L2.
According to the present invention:
L
2≧1.1×d1; and
A≧0.24×d12
Thanks to the geometrical features of a facing according to the present invention, one can experimentally demonstrate that breaking of the cylindrical core occurs advantageously according to a shearing mode when being pulled by a fill reinforcement strip.
Resistance of said cylindrical core is even enhanced when L2≧1.3×d1; and/or when A≧0.40×d12 and/or when L2/L1≧0.50.
According to the embodiment of
The first part 51 of the cylindrical core cross section is a half-circle and the second part of said core is a half-oval.
According to an embodiment a surface 21+22+23 of the strip 2 contacts the external surface of the core 5, the surface 21 presses substantially the whole external surface of the periphery of the cross section of the first part 51 of the cylindrical core and the surfaces 22 and 23 press a part of the external surface of the periphery of the cross section of the second part 52 of the cylindrical core 5. It has been demonstrated that the resistance of the cylindrical core is furthermore enhanced thanks to this embodiment.
In the example of
In the example of
In the example of
In the example of
The extremity of the periphery of the cross section of the second part 52 is formed by a straight line 72 merging with the rear face 32 of the facing element.
In the example of
In the example of
In the example of
In the example of
In the example of
Generally, the facing element of the invention and related method for erecting a stabilized soil structure are compatible with a large number of configurations of structure, strip lengths, densities for setting up strips, etc.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10305342.7 | Apr 2010 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/054572 | 3/24/2011 | WO | 00 | 9/28/2012 |
