GB2351518A - Improvements in or relating to facings for a ground slope and method of building such facings - Google Patents

Abstract

A method of building a facing 1 to a ground slope, for example a wall 14 of a quarry, comprises the steps of positioning a plurality of lightweight facing units 2, for example of expanded polystyrene, adjacent to, but spaced from, the slope 14 to provide a smooth face 3, fixing anchors 12 in the slope, securing the facing units 2 to the anchors 12 with tethers 11, and filling the gap between the facing units 2 and the slope 14 with a gap filling material 15, such as a free draining granular material. Each anchor 12 is connected to a plurality of facing units 5 by a plurality of respective tethers 11. The method is of particular use for providing a facing for substantially vertical slopes, of for example a land fill site for filling with waste material. The smooth face 3 provides a suitable surface against which a multi layered lining 16, 17, 18, 19 may be placed.

Description

2351518 Improvements in or relatinq to facinqs for a qround slope and

method of building such facinqs The present invention relates to the building of facings to a ground slope, for example, at the side of a quarry. More particularly, the invention relates to a method of building a facing to a ground slope and to a facing for a ground slope..

It is sometimes necessary to provide a facing for a ground slope. For example, it may be necessary to provide the walls of a quarry, which are usually irregular, with a facing before the quarry is filled in. A liner can then be laid over the bottom of the quarry and the facing to prevent contaminants from material with which the quarry is filled, from entering the water course. Without a suitable facing the'liner would be likely to be punctured.

Conventional methods of building a facing for a slope involve building formwork generally of steel or timber at the required angle adjacent to the slope, and holding the formwork in that position whilst the gap between the formwork and the slope is filled in with a suitable material. Various problems arise in those methods. Those problems are discussed, and a method which mitigates those problems proposed, in GB 2 276 899 A, the disclosure of which is incorporated herein by reference.

According to GB 2 276 899 A there is proposed a method of filling in a hollow in the ground in which a plurality of lightweight facing units are positioned over side of a hollow to provide a smooth face to the side, liner is placed over the smooth face and the hollow is filled in with material. The smooth face of the facing prevents damage to the liner of impervious material that is laid over it. A base facing unit is positioned adjacent a side of the hollow, enabling the positioning of a plurality of further facing units extending upwardly from the base facing unit. The gap between the facing and the side of the hollow is filled with a gap filling material. Adjacent facing units are held in interlocking engagement by tongues which may be anchored by tethers extending into the gap filling material.

The lightweight facing units of GB 2 276 899 A are not themselves structurally very strong. It is suggested in the method described with reference to the drawings in GB 2 276 899 A that after each tier or row of facing units has been placed in position, material may be poured into the gap between the facing unit and the quarry wall and compacted. Tethers are provided to keep the facing unit in position, one end of the tether being secured to the facing units and the other end being anchored to the compacted gap filling material.

Especially when the quarry wall is steep or vertical, the height to which the facing can be built without filling in the quarry is restricted because of the pressure exerted on the facing units by the compacted gap filling material and because of the limited resistance to that pressure which is limited by the extent of the anchoring of the tethers in the gap filling material. 5 It is an object of the present invention to provide a method of building a facing to a ground slope and a facing to a ground slope which avoid or mitigate the problems referred to above. According to the invention there is provided a method of building a facing to a ground slope comprising the steps of positioning a plurality of facing units adjacent to, but spaced from, the slope to provide a smooth face, fixing anchors in the slope, securing the facing units to the anchors and filling the gap between the facing units and the slope with a gap filling material.

Anchoring the facing units to the ground slope itself, as opposed to anchoring them to compacted material in the gap between the face and the side, provides improved support for the facing.

Preferably, the gap filling material is a freedraining granular material. The material may be introduced into the gap in one form and allowed to transform into another form after its introduction into the gap. In that case the final form of the material should be free- draining.

The facing units are preferably secured to the anchors by tethers. The anchors are preferably driven into the ground slope and provide anchorage points to which the tethers can be secured. A plurality of tethers may be fixed to each anchor for anchoring a plurality of facing units and thereby reducing the number of anchors required. Each tether is preferably connected to the facing units by means of a holding piece sandwiched between a pair of adjacent facing units. The facing units may each have a recess for accommodating at least a part of the holding piece. The holding piece may simply be in the form of a substantially cuboidal block. Alternatively, the holding piece may have a substantially T-shaped cross-section. In that case the holding piece may comprise a holding portion accommodated by recesses in a pair of adjacent facing units and a plate portion, extending from the holding portion, that is sandwiched between the pair of facing units. The tether may be attached to the plate portion by means of a hole, or alteratively by means of a slot, in the end of the plate portion, opposite the holding portion. The end of the plate portion opposite the holding portion may extend beyond the inner surface defined by the facing units.

The invention further provides a method of building a facing to a ground slope comprising the steps of positioning a plurality of facing units adjacent to, but spaced from, the slope so that gap is formed between the facing units and the slope, and filling the gap with a gap filling material, wherein the gap filling material is a free-draining granular material.

If a source of pulverised fly ash is conveniently located, that may be used, but other materials may also be used. The pulverised fly ash is preferably sintered.

It is desirable for the material to be compacted and yet remain freedraining. Preferably the material is self-compacting since that avoids the need to compact the material mechanically in situ; such compaction imposes considerable pressures on the facing units.

For most applications of the invention, the purpose of the facing is to provide a smooth face against which a liner can rest and the method further includes the step of placing a liner over the facing. The slope may define a side of a hollow in the ground and the method may further include the step of filling in the hollow with material.

is Preferably a layer of sand is provided next to the liner prior to filling the hollow. When the hollow filling material is likely to puncture the liner, the lining of sand provides an extra layer of protection that helps in preventing sharp edged objects from contacting the liner.

The present invention is especially suitable when the hollow is a land fill site. In that case the hollow filling material may be waste material that requires confinement.

The ground slope may be substantially vertical.

According to a still further aspect of the present invention there is provided a method of providing a facing for a substantially vertical slope, comprising - 6 positioning a first facing unit at the bottom of the slope, and building, in a plurality of steps, a facing that extends upwardly from the first facing unit, each of the plurality of steps comprising positioning a further facing unit on top of, and in interlocking engagement with, a facing unit below.

An especially advantageous method is provided when the facing units are lightweight facing units. They are then much easier to handle. The facing units are preferably made of expanded polystyrene.

The average thickness of the facing units may be in the range of 10Omm to 40Omm.

The liner preferably comprises an impervious material to restrict or prevent flow or liquids through the liner.

Where reference is made to a "liner" it should be understood that the "liner" may comprise a single layer of material or a plurality of layers. In the case where the liner comprises a plurality of layers, only one of the layers may be a geomembrane. Preferably a geosynthetic clay lining is provided between the facing and the geomembrane. In the event that the geomembrane is pierced, any liquid, such as foul water, that flows through the puncture will be absorbed by the clay lining, which will then swell in the region of the puncture to such an extent that the hole is sealed, thereby restricting undesirable leakage through the liner. One of the layers of the liner may comprise a drainage net. The - 7 drainage net allows liquid or gas to flow to a region, for example, a collection sump, from where it can be removed. The liner may further include a geotextile filter blanket, for reducing the amount of particulate matter reaching the drainage net thereby inhibiting the drainage net from becoming clogged.

The invention further provides a facing providing a smooth face to a ground slope, the facing comprising a plurality of facing units adjacent to, but spaced from, the slope to provide a smooth face, anchors fixed in the ground slope, gap filling material filling the gap between the facing units and the slope, and securing means securing the facing units to the anchors.

The invention still further provides a facing providing a smooth face to a ground slope, the facing comprising a plurality of facing units adjacent to, but spaced from, the slope to provide a smooth face, and gap filling material filling the gap between the facing units and the slope, the gap filling material being a free- draining granular material.

The facing is particularly suitable for forming a smooth face toa steep or vertical ground slope.

From the description above of various methods of building a facing, it will be understood that the facing may have any of the other features that are associated with any of those various building methods.

The facing and method of building the facing according to the invention may include other features of - 8 the facing and method of building the facing described in GIB 2 276 899 A, the description of which is incorporated herein by reference.

By way of example embodiments of the invention will now be described with reference to the accompanying drawings, of which:

Fig. 1 is a cross-sectional side view of a facing, according to a first embodiment, constructed adjacent to a substantially vertical surface of a quarry; Fig. 2 is a partially cut away perspective view of the facing and the quarry shown in Fig. 1; Fig. 3 is a side view of a base facing unit of the facing shown in Fig. 1; Fig. 4 is a side view of a base facing unit suitable for use in the construction of a substantially vertical facing; Fig. 5 is a partially cut away perspective view of a facing according to a second embodiment of the invention and a quarry; and Fig. 6 is a more detailed view of the portionlabelled A of Fig. S.

An assembled facing according to a first embodiment of the invention and generally denoted as 1 is shown in side elevation in Fig. 1, with layers of a lining shown for the sake of clarity as being separate and partly cut away in Fig. 2. Adjacent facing units 2 interlockingly engage one another to provide a facing 1 with an outer surface 3 and an inner surface 4, the lowermost facing unit 2 interlockingly engaging a base unit 5 at the bottom of the facing.

Each facing unit 2 is of substantially cuboidal shape having a groove 6a in its top face and a groove 6b in its bottom face. Adjacent facing units 2 are positioned with their upper and lower grooves 6a, 6b running substantially horizontally, the adjacent faces of the units being in abutment with their respective grooves 6a, 6b aligned. Adjacent facing units 2 are interlocked by means of an interlocking member, in the form of a tongue 7. The tongue 7 is configured to fit in the space formed by the aligned grooves of adjacent facing units 2 and runs the whole length of the grooves 6a, 6b. The tongue is preferably made of metal; alternatively; it may be a length of timber, or it may be formed from plastics material, including expanded polystyrene and other materials. 20 The base facing unit 5 shown in Fig. 4 has inclined front and rear faces 221 and has a groove 8 in its bottom face which allows it to be placed over an upstanding tongue formed for example in a concrete base. An end unit 9 (see Fig. 2) is positioned against the upper grooved face of the uppermost facing unit 2. The end unit has a groove 6b in its bottom face but has a moulded top 10 which does not have a groove 6a and which is shaped to provide a suitable top for the facing 1.

A plurality of tethers 11 and anchor bolts 12 are provided for anchoring the facing in position. Each tether 11 is secured at one end to a tongue 7, for example, by passing the tether through one or more holes 5 in the tongue 7 and fastening it appropriately.

The anchor bolts 12 are of a kind known per se provided with fastening heads 13 to which one or more tethers can be fastened. The anchor bolts are fixed into the quarry wall 14 in a manner known per se.

In order to construct the facing 1, a tongue to be received by the groove 8 in the lower face of the base facing unit.5 is first provided at a chosen location adjacent to the base of the quarry wall 14, the tongue being upstanding from a flat horizontal surface. Base is facing units 5 are then placed in position over the tongue, with the tongue received in the grooves 8. The base facing units 5 can also or alternatively be secured in position by pinning the units 5 to the flat surface (for which purpose the units 5 may be provided with suitable holes); the means of further securing the base facing units 5 is not shown in the figures. The base facing units 5 are spaced from the quarry wall 14 a sufficient distance that the facing 1 extending from the base facing units will, when assembled, be clear of any irregularities such as stones projecting from the quarry wall 14. Tongues 7 are inserted into the grooves 6a in the upper faces of the base facing units 5. Tethers 11 are secured at one of their ends to the tongues 7, and anchored at their other ends to the anchor bolts 12.

The space between the base facing units 5 and the quarry wall 14 may then be filled in by pouring suitable gap filling material 15, such as sintered pulverised fly ash bound with a small amount of cement, which sets to form a free- draining rigid granular material. The gap may be filled at a later stage if the gap filling material is not to be compacted.

A row of facing units 2 are then positioned on top of the base units 5 so that the tongues 7, in the upper grooves 6a of the base units 5, fit into the downwardly facing grooves 6b of the facing units 2. The tongues 7 serve to retain the first row of facing units securely in position on top of the base facing units 5.

After the first row of facing units 2 have been positioned, further tongues 7 are inserted into the upwardly facing grooves 6a of the units 2. As in the case of the base facing units 5, tethers 11 are secured at one of their ends to the tongues 7. The other ends of the tethers 11 are anchored to the anchor bolts 12.

The length of each tether may be adjustable, for example, by means of a buckle.

The process of positioning tongues 7 anchored by tethers 11 to anchoring bolts 12, and a further row of facing units 2, is repeated until a facing of a required height is obtained. The process includes periodically filling in the space formed between the quarry wall and the facing units with a suitable filling material 15.

End units 9 are positioned on top of the uppermost row of facing units 2, also being retained in position by tongues 7.

A liner is laid over the front face of the facing and is shown in Fig. 2 extending along the bottom of the quarry, up the front face of the facing and being held in place on the top of the facing by a row of sandbags 25 tied together.

In one particular example, the liner comprises a geosynthetic liner system having four layers 16 to 19 (only three are shown in Fig. 2). The innermost layer is a geosynthetic clay lining 16, the inner middle layer is an impervious geomembrane 17, the outer middle layer is a drainage geonet 18, and the outermost layer is a geotextile filter blanket 19. The geonet 18 allows liquid and/or gas to flow along the liner, facilitating their controlled disposal.

Having a geosynthetic clay lining 16 adjacent to the impervious geomembrane 17 provides a self sealing liner.

If there is a puncture in the geomembrane 17, for example, caused by a sharp rock, then liquid may escape through the hole in the geomembrane. The clay lining absorbs the liquid and swells thereby sealing the hole. Thus liquid (or gas) is prevented from passing through the liner.

Rupturing or puncturing of the liner is further mitigated by providing a layer of sand 20 immediately adjacent to the liner to provide a further barrier to - 13 sharp objects.

The quarry is filled in in stages as the facing is formed. For example, when a facing has been built up to 3 metres all around the quarry, the quarry may be filled in. Filling in of a part of the quarry which has been faced up to a required level may begin whilst facing of the remainder of the quarry to that level is still going on.

Because the facing 1 is formed unit by unit, and because each unit is lightweight, the need for complicated shuttering or a crane is removed. The polystyrene material of the facing is advantageous both because of its light weight and because it provides a smooth face that does not damage or penetrate the geomembrane 16 and that is relatively soft and able to deform locally, if required. Thus contaminants are successfully prevented from entering.the watercourse through, for example, tears in the liner that might have been caused otherwise.

Instead of the brick wall formation shown in Fig. 2, with the facing units in one row staggered in relation to those in another row, the facing may alternatively be laid in a series of side by side strips each comprising a base facing unit 5 and a series of facing units 2 extending therefrom.

In the case of a quarry or similar land formation where the slope comprises a number of walls meeting at various angles, the ends of the base facing units 5 and/or facing units 2 may be shaped so as to match the angles; that is especially easy in the case of expanded polystyrene facing units as they are easy to cut to shape.

S A further advantage of forming the units from polystyrene is that they may be cheaply and easily formed to selected shapes within small tolerances, providing the advantages of a smooth and planar facing. The facing units may be formed from expanded polystyrene with a higher density than that previously used in this kind of application, so that they deform less, under a given pressure. Preferably the density of the polystyrene is in the range of 15 Kg/m3 to 45 Kg/m3.

Fig. 3 shows a base facing unit 5 for use in a facing to be provided at a slope inclined to the vertical. The base facing unit of Fig. 3 has two foot portions 21, each with a relatively broad rectangular bottom face, defining a groove 8 therebetween, a facing surface 22, and a top portion 23 with a groove 6a formed in the upper face thereof. The angle a, which sets the angle of inclination of the facing, is determined by the desired angle of inclination of the slope.

Figures 5 and 6 show an assembled facing according to a second embodiment of the invention. The assembled facing is similar in construction to that illustrated by Figures 1 and 2. A pluarity of facing units 102 define a facing 101 over which a liner may be laid. Adjacent facing units are interlocked by means of a holding member - 15 124 (see Figure 6). A tether 111 is secured by means of a hole 125 in the end of each holding member 124. The other end of the tether 111 is secured to a fastening head 113 of an anchor 112 located in the quarry wall 114.

The holding member 124 comprises a tongue portion 107 that fits in the space formed by aligned grooves in adjacent facing units 102 (see Figure 6). The holding member 124 acts to reinforce the facing 101. The facing is constructed in a similar manner to the construction of the facing illustrated by Figures 1 and 2. The space between the facing units 102 and the quarry wall 114 is filled in with a suitable filling material 115. Each anchor is connected to one or more tethers ill.

The main differences between the embodiment il- lustrated by Figures 5 and 6 and the embodiment illustrated by Figures 1 and 2 is the way in which adjacent facing units are interlocked. The holding member 124 illustrated in Figure 6, comprises a plate portion and a holding portion that are formed as a one piece component.

The hole 125 in the plate portion is located to the exterior of the facing and therefore the tethers can be fastened to or released from the holding member without needing to separate the adjacent facing units.Furthermore, the holding member provides structural strength to the facing. The grooves in the facing units of the second embodiment are not situated centrally in their respective faces. The grooves are instead situated off centre and are closer to the side of the facing unit that 16 provides the face for the lining. Such an arrangement gives the facing additional strength, as it provides added resistance to any tendency of the facing to fail at a junction between adjacent facing units.

Although it is a preferred feature that the units are formed of expanded polystyrene, the units could be formed of other materials. For example, lightweight hollow blocks of non-expanded plastics material could be used.

Claims (23)

CLAIMS:

1. A method of building a facing to a ground slope comprising the steps of positioning a plurality of facing units adjacent to, but spaced from, the slope to provide a smooth face, fixing anchors in the slope, securing the facing units to the anchors and filling the gap between the facing units and the slope with a gap filling material.

2. A method as claimed in claim 1, wherein the gap filling material is a free-draining granular material.

3. A method as claimed in claim 1 or 2, wherein the facing units are secured to the anchors by tethers.

4. A method as claimed in claim 3, wherein a plurality of tethers are fixed to each anchor.

is

5. A method of building a facing to a ground slope comprising the steps of positioning a plurality of facing units adjacent to, but spaced from, the slope so that a gap is formed between the facing units and the slope, and filling the gap with a gap filling material, wherein the gap filling material is a free-draining granular material.

6. A method as claimed in claim 2, claims 3 or 4 when dependent on claim 2, or claim 5, wherein the gap filling material comprises pulverised fly ash.

7. A method as claimed in claim 6, wherein the pulverised fly ash is sintered.

8. A method as claimed in any preceding claim, further - 18 including the step of placing a liner over the facing.

9. A method as claimed in claim 8, in which the slope defines a side of a hollow in the ground.

10. A method as claimed in claim 9, further including 5 the step of filling in the hollow with material.

11. A method as claimed in claim 10, wherein the hollow is a land fill site.

12. A method as claimed in any preceding claim, wherein the ground slope is substantially vertical.

13. A method of providing a facing for a substantially vertical slope, comprising positioning a first facing unit at the bottom of the slope, and building, in a plurality of steps, a facing that extends upwardly from the first facing unit, each of the plurality of steps is comprising positioning a further facing unit on top of, and in interlocking engagement with, a facing unit below.

14. A method as claimed in claim 13, wherein the method further comprises anchoring facing units to the slope.

15. A method as claimed in claim 13 or 14, wherein the facing units are positioned so that there is a gap between them and the slope and the method further comprises the step of filling the gap with a gap filling material.

16. A method as claimed in any preceding claim, wherein the facing units are lightweight facing units.

17. A method as claimed in any preceding claim, wherein the facing units are made of expanded polystyrene.

18. A method as claimed in claim 17, wherein the - 19 thickness of the facing units is in the range of 10Omm to 40Omm.

19. A method of building a facing substantially as herein described with reference to and as illustrated by 5 the accompanying drawings.

20. A facing providing a smooth face to a ground slope, the facing comprising a plurality of facing units adjacent to, but spaced from, the slope to provide a smooth face, anchors fixed in the ground slope, gap filling material filling the gap between the facing units and the slope, and securing means securing the facing units to the anchors.

21. A facing providing a smooth face to a ground slope, the facing comprising a plurality of facing units adjacent to, but spaced from, the slope to provide a smooth face, and gap filling material filling the gap between the facing units and the slope, the gap filling material being a free-draining granular material.

22. A facing as claimed in claim 20 or 21, which is able to be built by a method according to any one of claims 2 to 4 or 6 to 19.

23. A facing substantially as herein described with reference to and as illustrated by Figs. 1 to 4 of the accompanying drawings.