Patent Grant
9677244
The present invention relates to facing elements for reinforced fill retaining walls, and to formers and methods for casting strip anchorage channels in such facing elements. In particular, but not exclusively, the invention relates to the use of reusable void formers for casting strip anchorage channels in concrete facing panels.
Earth fill reinforcement systems can be used, for example, to ensure stability and to minimize the lateral movement of a facing wall constructed to retain a volume of earth fill or rock material which is backfilled behind the wall. Such walls are used typically for separating regions of ground at two different levels.
The backfill material can be stabilized using lengths of strong, flat webbing or other flexible strip material, laid on successive layers of backfill material as the space behind the retaining wall facing is filled. The strips are attached to the rear side of the retaining wall and then tensioned away from the wall and pegged to the ground, such that when the next layer of backfill material is added, the strips are held in position, and the cumulative weight of the earth backfill on the strips produces sufficient friction between strips and earth to reinforce the backfill and hold the retaining wall in place.
Retaining or facing walls may be constructed from pre-cast concrete facing panels, for example, with each facing panel having several attachment points on its rear surface. These attachment points can be designed as loop channels, so that a retaining strip can be fed into one opening in the rear surface of the panel, through a channel inside the panel, and out through a second opening in the rear surface of the panel. Where loop-channel anchorages are used, the pre-cast panels are cast using void-formers so that the loop channels are formed as part of the casting process. Each loop channel is formed such that a flat, broad strip can be fed through the channel and around a part of the panel volume which will be termed the “core” of the channel in this application. This term is thus used to refer to that part of the volume of the panel around which the strip will pass when it is fed through the loop channel. It is the core which will bear the pulling force acting between the panel and the strip once the wall and the backfilling is complete. The core is typically a contiguous part of the panel material (reinforced concrete, for example, with some reinforcement passing through the core element), although the core may also be constructed from a different material (for example a cylinder of steel or carbon fibre, or high density concrete, which may be cast into the concrete of the body of the panel).
In order to provide a strong anchoring point, the loop-through channels should be cast as deep as possible into the volume of the panel, with a core which is also as deep as possible. A further consideration is that the two openings of the channel should be as close together as possible, in order that the strips emerging from the openings are not subjected to excessive local tension by the weight of the backfill material as it settles. Similarly, the load-bearing inner surface of the core element should have as large a radius of curvature as practicable, and have an even surface free of projections or discontinuities, in order to minimize the amount of localized stress on that part of the strip which is in contact with the core once the strip is under tension.
United States patent application U.S. Pat. No. 5,839,855 describes a pre-cast facing panel with loop-channels cast into its rear surface. The channels are formed by using plastic shell mould formers which are cast into the concrete and remain in the concrete. Cast-in mouldings must be in stock and available at the time of casting, and they represent a significant extra manufacturing cost.
The former arrangement described in U.S. Pat. No. 5,839,855 comprises two former-halves which are rotated about a common hinge which is located outside of the volume of the panel being cast. The inner and outer surfaces of each half-former have a constant radius of curvature over the inner region of the channel. In order for the void former to be removable without interference with the concrete, the hinge axis is located between the centre of curvature of the outer (forward-most) surface of the anchorage channel and the centre of curvature of the inner (rear-most) surface of the anchorage channel, with the result that the formed shape of the channel is limited to wide and/or shallow channel geometries. In particular, the restriction on the geometry of the inner surface of the half-formers means that there is an undesirable trade-off between the channel depth and the distance between the openings. The hinged construction also means that the former is necessarily bulky and heavy. The hinge axis must inevitably lie outside the concrete.
The invention described in this application seeks to overcome the above and other difficulties inherent in the prior art. In particular, the invention aims to provide a removable void former which can be used to cast loop channels which are deeper and/or whose openings are closer together than those cast with prior art removable formers, while ensuring a large enough radius of curvature of the inner surface of the channels that the strips do not experience excessive localized stress.
To this end, the invention aims to provide a removable void former assembly for displacing a casting material to form a strip anchorage channel in a substantially planar rear face of a cast facing element during casting of the facing element, the facing element being for facing backfill stabilized by means of a flexible reinforcement strip passed through the channel such that the strip follows a substantially arcuate path between a first channel opening in the rear face, around a substantially cylindrical or cylindroidal core element, which is cast contiguously with the facing element casting, to a second channel opening in the rear face, wherein the removable channel void former assembly comprises:
a first void former, shaped for forming a first half of the channel, the first half extending between the first channel opening and an intermediate location in the channel,
a second void former, shaped for forming a second part of the channel, the second half extending between the second channel opening and the intermediate location,
support means for supporting the first and second void formers in position during casting of the facing element, and
withdrawal displacement means for rotationally displacing the first and/or second void former about the core element in a rotational withdrawing direction from the channel of the cast facing element, wherein the withdrawal displacement means is adapted to permit, in addition to the rotational displacement of the first and/or second void former about the core element in a rotational withdrawing direction, a translational displacement of the first and/or second void former along a linear withdrawal direction.
The arrangement of the withdrawal displacement means for providing a combination of rotational and translational withdrawing displacements of the void formers enables the casting of deeper and/or narrower core elements, without the need for cast-in moulding inserts, and without needing to increase the width of the channel or the channel openings. It also permits the casting of more varied shapes of core element,
According to a variant of the void former assembly of the invention, the withdrawal displacement means and/or the first and second void formers are configured such that the first and/or second void formers can only be withdrawn from the cast facing element by a combination of the rotational displacement and the linear translational displacement.
According to a variant of the void former assembly of the invention, the linear withdrawal displacement comprises a component perpendicular to the plane of the rear face. The linear withdrawal direction may be substantially perpendicular to the plane of the rear face. Alternatively, the linear withdrawal direction can be angled away from the perpendicular to the plane of the rear face, depending on the desired geometry of the channel being cast.
According to a further variant of the void former assembly of the invention, the support means comprise releasing means for mechanically decoupling the first void former from the second void former such that the first void former can be withdrawn from the cast facing element substantially without mechanical interaction between the first void former and the second void former. According to another variant of the void former assembly of the invention, the translational displacement of the first void former along the withdrawal direction is also a translation displacement relative to the second void former. By enabling the withdrawal of one void former independently of the other, it is possible to greatly increase the variety of shapes which are castable with the removable void former assembly, and also to cast recesses with deeper and/or narrower core elements.
According to another variant of the void former assembly of the invention, the first void former comprises a substantially cylindrically or cylindroidally curved wedge shaped portion having:
This variation in the radius of curvature of the concave and/or convex former surfaces enables deeper core elements to be cast, and with a greater variety of core element geometries.
According to another variant of the void former assembly of the invention, the radius of curvature of the concave former surface region decreases, or remains substantially constant, along at least a majority of the concave former surface region in a direction away from the distal end, and/or the radius of curvature of the convex former surface region increases, or remains substantially constant, along at least a majority of the convex former surface region in a direction away from the distal end. Such increasing and/or decreasing radii of curvature enable deeper channels/core elements to be cast, without significantly increasing the difficulty of withdrawing the void formers from the casting. If one or both of the concave former surface region and the convex former surface region remain(s) substantially constant, while the radius of curvature of the convex former surface region is significantly greater than that of the concave former surface region, then a similar advantage can be obtained, namely a deeper channel/core element, but without significantly increasing the difficulty of withdrawing the void formers from the casting.
According to another variant of the void former assembly of the invention, the withdrawal displacement means comprise lever engaging means for engagement with a lever such that the lever can be used to urge the first void former in the rotational withdrawing direction. The lever may be formed as part of the void former, or a separate lever may be used for inserting or engaging with the void former(s). In this way, the construction of the void formers can be simplified, and the void former assembly will be lighter and simpler.
According to another variant of the void former assembly of the invention, the concave former surface region of at least one of the first and second formers is shaped such that the rotational displacement has an axis of rotation which passes through the volume of the core element, the void of the channel, or the panel being cast.
With no hinge to dictate the rotational displacement path, the void formers can be withdrawn by rotating them about the core element, for example using a lever, which means that the channel openings can be cast significantly closer together.
According to another variant of the void former assembly of the invention, one or both of the first and second void formers comprises two or more former elements and one or more former element linking means for linking the two or more former elements together. Hingeing or otherwise linking multiple pieces together to make up the void former(s) further expands the range of shapes of channel which can be cast with the removable void former.
The invention also envisages a method of casting a strip anchorage channel in a rear face of a cast facing element during casting of the facing element, the facing element being for facing earth stabilized by means of a flexible reinforcement strip passing through the channel such that the strip follows a substantially arcuate path between a first channel opening in the rear face, around a substantially cylindrical or cylindroidal core element, which is cast contiguously with the facing element casting, to a second channel opening in the rear face, the method comprising:
a mounting step of arranging a removable channel void former assembly as described above in a channel casting location of the facing element,
an unsticking step of rotating the first void former sufficiently to release it from adhesive contact with the cast material, and
a withdrawal step comprising a rotational displacement of the first void former about the core element,
wherein the withdrawal step includes, in addition to the rotational displacement, a translational displacement of the first void former, the translational displacement having a directional component perpendicular to the rear face.
According to a variant of the method of the invention, the method includes a releasing step of operating the releasing means to mechanically decouple the first and second void formers from each other. As discussed above, the use of independently releasable and withdrawable void formers increases the range of shapes which are castable using the method.
According to another variant of the method of the invention, the translational displacement comprises a relative displacement between the first and second formers, along a direction substantially perpendicular to the rear face.
According to another variant of the method of the invention, the rotational displacement comprises a rotation about a rotation axis which passes through the body of the facing element, or through the core element, or through the void of the channel.
The invention also envisages a cast facing element for facing a stabilized earth structure by securing a flexible reinforcement strip through a recessed channel in a substantially planar rear face of the facing element, wherein:
the channel follows a substantially arcuate path around a substantially cylindrical or cylindroidal core element such that the reinforcement strip can be passed through the channel from a first opening in the rear face, through the channel and around the core element, to a second opening in the rear face;
the channel is formed, without a cast-in channel-formwork insert, as a void cast into in the body of the facing element, such that the void of the channel delimits a convex core surface region of the core element and a concave channel surface of the channel; and
the outer channel surface comprises at least one concave channel surface region having a centre of curvature which lies in the body of the facing element, or in the core element, or in the void of the channel.
According to variant of the cast facing element of the invention, the core element is cast, without a cast-in core-forming insert, contiguously with the casting material of the facing element.
In this application, the example of a planar facing panel is used to illustrate the invention. However, it should be understood that the invention can also be applied to facing elements which are curved or profiled. The rear surface of the facing element may be provided with ribs or other surface profiles, for example, and terms such as “parallel to the rear face” should be understood to refer the general plane of the profiled rear face, or to a local approximation of the plane of the curved rear face, as appropriate. The scope of the claimed invention is intended to include such curved or profiled variants.
The invention and its advantages will further be explained in the following description, together with illustrations of example embodiments and implementations given in the accompanying drawings, in which:
The invention will now be described in detail with reference to the drawings. Note that the drawings are intended merely as illustrations of embodiments of the invention, and are not to be construed as limiting the scope of the invention. Where the same reference numerals are used in different drawings, these reference numerals are intended to refer to the same or corresponding features.
The channels 10 shown in
By arranging the centre of rotation 53 between the centres of rotation 23 and 73 of the inner and outer surfaces 11 and 16 of the channel 10, it is possible to ensure that the formers are able to rotate without interference with the cured casting material when they are withdrawn from the cast facing element. Two variants of this arrangement are shown in
However, it is not possible to adapt the prior art former assembly such that the centre of rotation 83 of its hinge is moved to be inside the volume of the facing element 1. Therefore, a new arrangement of formers has been proposed, which will be described with reference to
The recess channel 10 shown in
The shape of the core element 8 is shown as being symmetrical about a centre-line A, and the description of the variation of the radius of curvature refers to the surface on one side of the centre-line A, assuming that the shape of the forward-facing surface 12 is also symmetrical about A. However, it will be understood that the core element 8 may be asymmetrical about the axis A, in which case the variation in radius of curvature will follow a different pattern on either side of A. The radius of curvature 18 of the surface portion 12 at a particular point may thus define a centre of curvature denoted by reference 71.
In this illustration, the radius of curvature 22 of the outer surface of the channel, at least in the part indicated by reference 13 (referred to as the concave, rearward-facing portion 13 of the outer surface 16 of the channel), varies little with increasing angle β. In this case, therefore, the outer surface portion 13 has a single centre of curvature, denoted by reference 72. The radius of curvature 22 can also vary with angle β, however, in order to achieve greater core depth while still permitting easy withdrawal of the former elements. A principal axis of the core element 8 is denoted by 17, being substantially a central axis of the core element 8. 23 and 73 denote respectively the centre and radius of curvature of a rearward facing part of the inner surface of the core element 8. 20 denotes the width of the core element 8 at its widest point as measured in a direction parallel to the rear face 5 and perpendicular to the principal axis 17 of the core element 8. Reference 9 indicates the depth of the core element 8 as measured in a direction perpendicular to both the rear face 5 and the principal axis 17. Reference 21 denotes a separation distance between the first and second openings 3 and 4 in the plane of the rear face 5. It is advantageous to minimize the separation distance 21 such that, when the two emerging portions of strip 7 are covered with a significant weight of earth, and therefore pressed towards each other, the ends localized stress on the strip is kept to a minimum, while still maintaining a sufficient width 20 of the core element to give the core element 8 adequate strength to bear the lateral loads (tension on the strip) which arise when the volume behind the facing element is backfilled.
In summary, the channel 10 may be formed such that one or both of the convex inner surface 12 and the concave outer surface 13 of the channel has a radius of curvature which generally varies (eg decreases/increases) from the deepest part of the recess in a direction towards the rear face, at least over a part of the respective surface. Because of this varying radius of curvature, the central core of the channel can be cast deeper and narrower, and with openings which are closer together, than has hitherto been possible using removable void formers. Such a deep and narrow channel may not however be formed using known removable void formers, and the conventional method of casting such recesses has therefore been to use cast-in moulds which remain in the concrete once it is set. This is a costly and inconvenient solution, so there is a need for a method of casting a deep and narrow recess channel 10 without resorting to the inconvenience and cost of providing such cast-in moulding inserts.
The top of the void former 31 is provided with withdrawal displacement means in the form of bracket 46, 47, 48, which serves both as an engagement part for engaging a lever or other tool in order to give the void former the rotational and translational force required to withdraw it from the casting. The bracket 46, 47, 48 also serves to clamp the void former 31 to its counterpart 32 as described with reference to
As in the first embodiment, the void formers 31 and 32 are held in position by support means 34, 35, with their tips engaged for example using keyed engaging means 43, 44. As shown in
The void formers 31 and 32 may be constructed from any suitable rigid or semi rigid material. Advantageously, they can be constructed from a hard-wearing material such as a metal or a high-density plastics or fibre-reinforced material.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/058947 | 5/14/2012 | WO | 00 | 11/12/2014 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2013/170879 | 11/21/2013 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5004208 | Domizio | Apr 1991 | A |
| 5523046 | Weder | Jun 1996 | A |
| 5651911 | Pennypacker | Jul 1997 | A |
| 5839855 | Anderson | Nov 1998 | A |
| 6575424 | Domizio | Jun 2003 | B2 |
| 7127859 | Domizio | Oct 2006 | B2 |
| Entry |
|---|
| International Search Report and Written Opinion dated May 7, 2013 for PCT/EP2012/058947. |
| Number | Date | Country | |
|---|---|---|---|
| 20150125221 A1 | May 2015 | US |
