WO2018014069A1

WO2018014069A1 - Sealing system for dam walls

Info

Publication number: WO2018014069A1
Application number: PCT/AU2017/000152
Authority: WO
Inventors: Mark Robert Edmund Curtis
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-07-19
Filing date: 2017-07-19
Publication date: 2018-01-25
Anticipated expiration: 2019-01-19
Also published as: AU2025204149A1; AU2016206251A1; AU2023201420A1

Abstract

A sealing system for tailings dam walls; said system including covering inward sloping walls of embankments forming a perimeter of said tailings dam with an impervious barrier; said impervious barrier in the form of a composite of at least two differentiated layers of material.

Description

SEALING SYSTEM FOR DAM WALLS

TECHNICAL FIELD

[0001] The present invention relates to mining

operations and, more particularly, to the control of tailings material.

BACKGROUND

[0002] Particularly in open-cut mining operations and where excavated material has been processed to produce a slurry-like waste material, that material must be contained to allow evaporation and stabilization.

[0003] For this purpose, tailings dams are constructed with embankments forming a perimeter around a tailings pond into which the tailings may be deposited. Because the liquid component of the waste is often detrimental to the surrounding environment, the inward facing walls and the base surface of the tailings dam must be made impervious.

[0004] A common manner of construction is to provide the base surface and the sloping inward facing walls with a layer of dense clay. However, the process of layering the sloping walls of the embankment with clay is difficult and time consuming. As well, in locations where clay is scarce, it becomes difficult to adequately proved an impervious cover of the embankments.

[0005] Another problem with the use of clay on the sloping dam wall is that being exposed to air and sun it is liable to develop cracks through which the liquid fraction of the tailings may leach when the tailings level reaches cracked areas.

[0006] It is known to use plastic film to cover the earthen sloping side of the embankments, but this is liable to perforation from sharp aggregate, either in the material - - of the embankment or from material deposited in the

tailings dam, destroying the integrity of the containment.

[0007] It is an object of the present invention to address or at least ameliorate some of the above

disadvantages .

Notes

[0008] The term "comprising" (and grammatical variations thereof) is used in this specification in the inclusive sense of "having" or "including", and not in the exclusive sense of "consisting only of".

[0009] The above discussion of the prior art in the Background of the invention, is not an admission that any information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country.

SUMMARY OF INVENTION

[0010] In one broad form of the invention here is provided a sealing system for tailings dam walls; said system including covering inward sloping walls of

embankments forming a perimeter of said tailings dam with an impervious barrier; said impervious barrier in the form of a composite of at least two differentiated layers of material .

[0011] Preferably at least two layers comprise three layers; a first of said three layers being in the form of a sheet of polymer material; a second and a third of said three layers formed of substantially coextensive sheets of an impact resistant fibrous material. - -

[0012] Preferably said sheet of polymer material forms a central layer sandwiched between said second and third layers of said sheets of impact resistant fibrous material.

[0013] Preferably said polymer material is rough

textured; said material having a rough surface with

projecting elements of said polymer material on both opposing sides of said sheet.

[0014] Preferably said sheet of polymer material is a relatively stiff high density polyethylene.

[0015] Preferably said sheet polymer material is a relatively flexible linear low density polyethylene or other polymer.

[0016] Preferably said sheet of polymer material has a thickness of between 1 and 2mm.

[0017] Preferably said impact resistant fibrous material is a sheet of woven or non-woven needle punched polyester or other polymer.

[0018] Preferably said impact resistant material has a thickness in the range of 2 to 12mm.

[0019] Preferably weight of said impact resistant material is in the range of 1000 to 2000gm/m².

[0020] In yet a further broad form of the invention there is provided a method of providing an impervious impact resistant layer over an inward sloping surface of a tailings dam wall; said method including the steps of: - - a) reparing said sloping surface to a predefined slope ,

b) preparing a barrier comprising a composite of at least two differentiated layers of material, c) placing said barrier along said predefined slope, d) securing said barrier at least along an upper edge relative said tailings dam wall, and wherein at least one of said two differentiated layers comprises a sheet of polyethylene material.

[0021] Preferably said barrier comprises three layers of material; a first layer of said at least three layers comprising said polyethylene material; a second and a third of said three layers comprising an impact resistant fibrous material; said second and third layers sandwiching said first layer.

[0022] Preferably said barrier is secured along a top o said sloping surface of said tailings dam wall by forming an upper edge of said barrier into an elongate trench let into ^'an upper surface of said tailings dam wall; said trench filled with a suitable dense material to secure sai barrier to said sloping surface.

[0023] Preferably said method includes the further steps of providing an impervious barrier for a next higher level of a tailings dam wall; said steps including:

a) preparing a surface of dry and stabilised

tailings material inward of a lower level tailings dam wall,

b) overlaying an impervious impact resistant barrier over an area coinciding with an intended position of a toe of an inward sloping surface of said next higher level tailings dam wall, - - c) constructing said next level tailings dam wall partly over said lower tailings dam wall and partly over said prepared surface,

d) covering an inward sloping surface of said next higher level of said tailings dam wall according to the steps of claims 11 to 13, and

e) fusion welding an overlap portion of said

impervious barrier covering said inward sloping surface of said next higher level of said

tailings dam wall to said impact resistant barrier overlaying said dry and stabilised tailings material.

BRIEF DESCRIPTION OF DRAWINGS

[0024] Embodiments of the present invention will now be described with reference to the accompanying drawings wherein :

Figure 1 is a partial cross section through a tailings dam showing a sealing barrier of an embodiment installed over an inward facing wall of a tailings dam embankment,

Figure 2 is a partial cross section through the tailings dam of figure 1 showing the sealing barrier installed for a second level embankment,

Figure 3 is a cross section of the barriers of figure 1 and 2 showing the layered structure of the barrier according to an embodiment,

Figure 4 is a cross section of a further embodiment of layered structures of a barrier.

DESCRIPTION OF EMBODIMENTS

First Preferred Embodiment

[0025] Embodiments of the present invention provide a sealing system for the inward facing surface of a tailings dam wall. With reference to figure 1, a typical tailings - - dam wall 10 is constructed of available soil and rock, usually taken from the surface of the tailings pond area and mine pit or overburden rock material 12. Tailings dam walls form a perimeter embankment around the tailings area, with internal batter slopes typically of 1:3.

[0026] The system may also provide for covering the inward sloping walls 14 of the embankments with an

impervious barrier 16 extending from the upper surface 18 of the embankment to at least the toe 20.

[0027] The impervious barrier 16 according to a

preferred embodiment of the invention, is in the form of a composite of at least two differentiated layers of

material. At least one layer is in the form of a sheet of polymer material, with one or more additional layers of an impact resistant fibrous material.

[0028] Preferably, as shown in figure 3, the barrier 16 is comprised of three layers (separated for clarity in figure 3) , the first layer of the polymer material 22 sandwiched between second and third impact resistant layers 24 and 26. Layers 24 and 26 are preferably formed of a woven or a non-woven needle punched polyester or other polymer .

[0029] The sheet of polymer material 22 is rough

textured, having rough surfaces with projecting elements 23 of the polymer material on both opposing sides of the sheet. These projections ensure a close mechanical bonding between the sheet of polymer material 22 and the flanking polyester sheets, preventing slipping between the layers.

[0030] The sheet of polymer material 22 may be formed either of relatively stiff high density polyethylene (HOPE) or a more flexible linear low density polyethylene (LLDPE) or other polymer and is preferably between 1 and 2mm in thickness. The impact resistant layers 24 and 26 of - - polyester are preferably between 2 and 12mm in thickness and have a weight range between 1000 and 2000gm/m².

[0031] This composite barrier 16 formed of the three layers 22, 24 and 26 provides both an impervious barrier to liquids retained in the tailings pond from leaching through the sloping inward wall 14 and protect that barrier from perforation, either from sharp rocks possibly embedded in the wall surface, or from tailings impacting on the wall.

[0032] To secure the barrier 10 against the wall 14, at least the upper edge of the polymer first layer 22 is formed into an elongate trench 28 as shown in figure 1. This trench shaped edge is inserted into a receiving trench 30 formed in the top surface 30 of the dam wall 10. The trench 28 is then filled with a suitably dense material, for example the same compacted material forming the

embankment, thereby locking the barrier 10 in position relative the inward wall 14.

Second Preferred Embodiment

[0033] It is common practice to raise the capacity of a tailings dam in stages. After the tailings dam fills to the level or just below the level of the first perimeter embankments, the capacity may be increased by constructing a next level of embankments. After the tailings material 32 inward of the lower level tailings dam wall 10 has

sufficiently dried and stabilised, the surface 34 is levelled and prepared.

[0034] In this second preferred embodiment of the invention, preparation for the next level includes the placement of sheets of the impervious impact resistant barrier 16 over at least an area 36 plus 1.5m over

coinciding with the intended position of the toe 38 of an inward sloping surface 40 of said next higher level

tailings dam wall 42. As shown in figure 2, the barrier may extend along the surface 34 back to the barrier of the - - inward sloping surface 14 (see Figure 1) of the lower dam wall 10.

[0035] To in turn protect the sloping surface 40, a barrier 44 is prepared in the manner described above, extending from a retaining trench 48 at the top 46 of the new wall 42 down to the sheets 34 underlying the toe 38.

[0036] As can be seen in Figure 2, a portion 50 of the barrier 44 overlaps, and is fusion welded to the sheets 16 at the toe 38.

[0037] Although the above descriptions of the first and second preferred embodiments have focused on the use of the barrier on the inward sloping walls of tailings dams, it will be understood that the barrier could be used for the base surface of a tailings dam.

Third Preferred Embodiment

[0038] Referring now Figure 4, in an alternative

arrangement, a next level of embankment 142 is built outwardly over the first embankment 10. In this instance, a portion 150 of the barrier 144 of the new embankment 142, lies over the surface of the first embankment and its inward edge welded to the barrier 16 at the trench 28. As in previously described embodiments above, this process can be repeated as required.

INDUSTRIAL APPLICABILITY

[0039] The present invention provides an effective, easily installable barrier for the inward sloping walls of tailings dam embankments. The combination of the impervious polymer barrier flanked by layers of impact resistant material ensure an indefinitely durable barrier to leaching of toxic or otherwise environmentally undesirable liquid waste .

Claims

1. A sealing system for tailings dam walls; said system including covering inward sloping walls of embankments forming a perimeter of said tailings dam with an impervious barrier; said impervious barrier in the form of a composite of at least two differentiated layers of material.

2. The system of claim 1 wherein said at least two layers comprise three layers; a first of said three layers being in the form of a sheet of polymer material; a second and a third of said three layers formed of substantially

coextensive sheets of an impact resistant fibrous material.

3. The system of claim 2 wherein said sheet of polymer material forms a central layer sandwiched between said second and third layers of said sheets of impact resistant fibrous material.

4. The system of claim 2 or 3 wherein said polymer material is rough textured; said material having a rough surface with projecting elements of said polymer material on both opposing sides of said sheet.

5. The system of any one of claims 2 to 4 wherein said sheet of polymer material is a relatively stiff high density polyethylene.

6. The system of any one of claims 2 to 5 wherein said sheet polymer material is a relatively flexible linear low density polyethylene or other polymer.

7 . The system of any one of claims 2 to 6 wherein said sheet of polymer material has a thickness of between 1 and 2mm.

8. The system of any previous claim wherein said impact resistant fibrous material is a sheet of woven or non-woven needle punched polyester or other polymer.

9. The system of claim 8 wherein said impact resistant material has a thickness in the range of 2 to 12mm.

10. The system of claim 8 or 9 wherein weight of said impact resistant material is in the range of 1000 to

2000gm/m².

11. A method of providing an impervious impact resistant layer over an inward sloping surface of a tailings dam wall; said method including the steps of:

a) preparing said sloping surface to a predefined slope, b) preparing a barrier comprising a composite of at least two differentiated layers of material, c) placing said barrier along said predefined slope, d) securing said barrier at least along an upper edge relative said tailings dam wall, and wherein at least one of said two differentiated layers comprises a sheet of polyethylene material.

12. The method of claim 11 wherein said barrier comprises three layers of material; a first layer of said at least three layers comprising said polyethylene material; a second and a third of said three layers comprising an impact resistant fibrous material; said second and third layers sandwiching said first layer.

13. The method of claim 11 or 12 wherein said barrier is secured along a top of said sloping surface of said

tailings dam wall by forming an upper edge of said barrier into an elongate trench let into an upper surface of said tailings dam wall; said trench filled with a suitable dense material to secure said barrier to said sloping surface.

14. The method of any one of claims 11 to 13 wherein said method includes the further steps of providing an

impervious barrier for a next higher level of a tailings dam wall; said steps including:

a) preparing a surface of dry and stabilised tailings material inward of a lower level tailings dam wall, b) overlaying an impervious impact resistant barrier over an area coinciding with an intended position of a toe of an inward sloping surface of said next higher level tailings dam wall,

c) constructing said next level tailings dam wall partly over said lower tailings dam wall and partly over said prepared surface,

e) fusion welding an overlap portion of said