GB2522838A

GB2522838A - Ground stabilisation

Info

Publication number: GB2522838A
Application number: GB1322004.1A
Authority: GB
Inventors: Matthew Hendrie Barbour
Original assignee: MHB CONSULTANTS Ltd
Current assignee: MHB CONSULTANTS Ltd
Priority date: 2013-12-12
Filing date: 2013-12-12
Publication date: 2015-08-12
Also published as: GB201322004D0

Abstract

A method of and apparatus for stabilising sloping ground comprising disposing sheet material 20, for example a grid or mesh, and plural elongate rigid members 22 such that each rigid member mechanically couples with the sheet and extends into ground over which the sheet is disposed, wherein the sheet imposes substantially no tensile load along each rigid member. A compressive load may be imposed by the sheet on each rigid member. Preferably apertures defined by the sheet material are of sufficient dimensions for passage of the rigid members. Preferably a mechanical coupling 40 couples each rigid member and the sheet and comprises a planar main body 42 and plural arms 44 extending orthogonally from the main body and configured to penetrate at least one of the sheet and the ground. The invention is particularly suitable for railway embankments or cuttings and avoids the need for railway closure.

Description

Title of Invention: Ground stabilisation

Field of the Invention

The present invention relates to a method of stabilising ground and in particular of stabilising sloping ground.

Backaround Art

Railway embankments may be liable to shallow slope failure wherein a top layer of the slope slides down the slope and thereby jeopardises the integrity of the embankment. Railway cuttings are likewise liable to shallow slope failure and thereby obstruct the railway. Normally ageing railway embankments and cuttings are more susceptible to shallow slope failure than newly or relatively recently formed embankments and cuttings. Addressing a slope failure that jeopardises the integrity of a railway embankment or obstructs a railway normally involves railway closure until the problem is rectified. Railway closure is undesirable on account of the interruption of service and attendant financial loss.

Ageing railway embankments and cuttings that are considered susceptible to shallow slope failure are stabilised by one or more different approaches. According to one approach soil that is susceptible to failure is dug out and replaced with stronger soil.

According to another approach the slope is reformed to decrease its angle.

According to yet another approach the slope is reinforced by way of a retaining wall, sheet piles or reinforced earth. According to a further approach reinforcing elements such as soil nails, mini-piles, lime piles or timber or plastics posts are driven into the ground. According to a yet further approach slope drainage is improved. Such approaches have their disadvantages including rail and road disruption and closure, the need to acquire further land to accommodate the remedial approach and cost.

Furthermore the use of one approach alone, such as improving slope drainage, may be insufficient to address a lack of stability.

The present inventor has become appreciative of the above mentioned disadvantages to known approaches to slope stabilisation and has devised the present invention in the light of his appreciation of the disadvantages. An object for the present invention is therefore an improved method of stabilising sloping ground such as forms part of a railway embankment or cutting.

Statement of Invention

According to a first aspect of the present invention there is provided a method of stabilising sloping ground, the method comprising: disposing sheet material on sloping ground to be stabilised; and disposing plural elongate rigid members at spaced apart locations such that each rigid member mechanically couples with the sheet material and extends into ground over which the sheet material is disposed wherein the sheet material imposes substantially no tensile load along each rigid member.

Sheet material is disposed on sloping ground, such as forms part of a railway embankment or cutting. In addition plural elongate rigid members are disposed at spaced apart locations. The plural elongate rigid members may be disposed before the sheet material is disposed. Each rigid member when so disposed mechanically couples with the sheet material and extends into ground over which the sheet material is disposed. Each rigid member may, for example, be driven into the ground before the sheet material is disposed on the sloping ground. Each rigid member may extend to within 15 degrees, 10 degrees, 5 degrees, 3 degrees, 2 degrees or 1 degree of normal to an angle of the slope of the ground. The sheet material and the plurality of rigid members may be operative together to reduce the likelihood of slope failure and more specifically shallow slope failure. The mechanical coupling of the rigid members may reduce an extent to which the rigid members creep up the slope, down the slope or across the slope on account of forces from the ground. According to the method the sheet material imposes substantially no tensile load along each rigid member. No tensile load may be imposed along a main, i.e. longitudinal, axis of the rigid member. Thus there may be no tensile load imposed in a direction into the ground. For a tensile load to be developed in a rigid member, the rigid member should be held at a location spaced apart from where the tensile load is imposed, e.g. in respect of energy expended to provide for the tensile load, on the rigid member. A rigid member might be held at the spaced apart location by the ground in which the rigid member is received. Here, no tensile load is imposed along the rigid member. Even so the ground may yet hold the rigid member with there being no tensile load developed in the rigid member on account of the mechanical coupling between the sheet material and the rigid member, as is described further below, or on account of the ground itself. In certain forms of the invention a compressive load may be imposed by the sheet material on each rigid member. In contrast with the known approaches to ground stabilisation which are mentioned above the method according to the present invention may be of low cost, may cause less disruption and may not require the acquisition of further land.

In addition the rigid members may mechanically couple with the ground and forces exerted on the rigid members by ground which might otherwise be liable to slip are coupled to and distributed through the sheet material. Furthermore forces which are distributed through the sheet material may be mechanically coupled to the rigid members. The arrangement may therefore be operative to distribute to all of the rigid members forces exerted on only some of the rigid members or forces exerted on some of the rigid members which are higher than forces exerted on other rigid members. An improvement over use of sheet material alone may thus be obtained.

The plurality of rigid members may be operative to increase a depth of the slip plane.

An increase in the depth of the slip plane may reduce the likelihood of slope failure.

The sheet material may be configured to conform to uneven ground. The sheet material may therefore be pliable at least in part. The sheet material may be configured to conform to uneven ground by way of at least one: movement of one component of the sheet material relative to another component of the sheet material about a mechanical coupling; and pliability of material comprised in the sheet material.

The sheet material may define a grid or mesh. The sheet material may therefore define apertures which are spaced apart from each other in each of two orthogonal directions. The rigid members may be disposed in the ground after the sheet material is disposed on the ground where the sheet material allows for this, for example, where apertures defined by the sheet material are of sufficient dimensions for passage of the rigid members. The sheet material may comprise a polymeric material and more specifically a plastics material. For example the sheet material may be formed at least in part of polyester: polyethylene or polyproylene. The sheet material may comprise a geosynthetic material. The sheet material may therefore comprise a geogrid. Alternatively the sheet material may be formed at least in part of a metal.

As mentioned above each rigid member is elongate. A rigid member may be of a length of greater than 0.25 m, 0.5 m or 1 m. A rigid member may be of a length of less than 5 m, 4 m, 3m, 2.5 m, 2 m or 1.5 m. A rigid member may be of a width between 50 mm and 200 mm. More specifically a rigid member may be of a width of mm. A rigid member may be of substantially rectangular and perhaps substantially square cross section. A rigid member may be formed at least in part from a plastics material and more specifically from a thermoplastic polymer.

According to an approach, a rigid member may be formed at least in part from polythene. Waste polythene which might otherwise go to landfill may be used. The method may therefore further comprise forming each of the rigid members at least in part from waste polythene.

The plural rigid members may be disposed such that they reach no more than 5 m, 4 m, 3 m, 2.5 m, 2 m, 1.5 m or 1 m from the surface of the ground. The plural rigid members may be disposed such that they span the slip plane. Shallow slope failures are often within 1.5 m of the surface of the slope. The plural rigid members may therefore reach no more than 1.5 m from the surface of the ground. The plural rigid members may be disposed such that they reach into stable ground. An end of a rigid member which is received in stable ground may therefore be held relatively firmly. The mechanical coupling between the rigid member and the sheet material may provide for firm holding of a part of the rigid member spaced apart from the end of the rigid member. Holding the rigid member firmly at two spaced apart locations may reduce the bending moment in the rigid member by a factor of four from the bending moment in a rigid member which is held at only one location, such as at the ground most end of the rigid member. The risk of fracturing the rigid member may thereby be reduced. Even if the ground most ends of the rigid members are not received in stable ground the apparatus of the invention may be operative to increase the depth of the slip plane and thereby reduce the likelihood of slope failure.

A depth of stable ground may be determined by at least one of: ground investigation; laboratory testing of the ground; instrumentation which is operative to measure the ground; and slope stability analysis using standard industry techniques.

Determination of the depth of stable ground may allow for determination of an appropriate length of the rigid members. The method may therefore further comprise determining a depth of stable ground. In addition the method may further comprise determining or selecting a length for the rigid members in dependence on the stable ground depth determination.

The plural rigid members may be spaced apart from each other by between 2 m and 0.5 m and more specifically by 1 m. Rigid members in adjacent rows may be staggered.

Mechanical coupling between a rigid member and the sheet material may be substantially rigid. Mechanical coupling between the rigid member and the sheet material may be operative such that substantially no tensile load is applied to the rigid member. The mechanical coupling may be configured to restrain if not substantially prevent movement of the rigid member and the sheet material in relation to each other at least in a direction in line with the sheet material. There may therefore be little or no movement of the sheet material relative to a part of the rigid member proximate the sheet material, for example, in a direction in line with the slope on which the sheet material is disposed.

The method may further comprise mechanically coupling the rigid member and the sheet material by way of a mechanical coupling. As mentioned above, the mechanical coupling may be such that substantially no tensile load may be imposed along the rigid member. A plurality of mechanical couplings may be provided, each of the plurality of mechanical couplings being operative to couple a respective one of the plural rigid members to the sheet material. The mechanical coupling may be configured to engage with both the sheet material and the rigid member. The mechanical coupling may define a profile which fits around a side of the rigid member at or towards its upper end. The mechanical coupling may therefore be configured to releasably couple to the rigid member. The profile may fit around the rigid member at at least two spaced apart pairs of opposite locations on the rigid member. The mechanical coupling may comprise a main body and two pairs of arms which extend from the main body. Each arm may be spaced apart from an adjacent arm by substantially the same distance. The main body may define a planar surface and the arms may extend substantially orthogonally to the planar surface. In use, the planar surface may abut against the upper surface of the sheet material whereby the sheet material is in between the main body and the upper end of the rigid member. An end of each arm may be configured to penetrate at least one of the sheet material and the ground on which the sheet material is disposed.

An end of an arm may therefore taper to a point. The mechanical coupling may further comprise a securing arrangement which is operative to securely attach the mechanical coupling to the rigid member. The securing arrangement may comprise a member which is driven into the rigid member such as into an end of the rigid member. The member may pass through an aperture in the main body before being received in the rigid member. The securing arrangement may, for example, comprise a screw such as a coach screw.

The present inventor has appreciated that the sheet material may be liable to slip down the slope. The method may therefore further comprise anchoring the sheet material at or towards the upper end of the slope. More specifically the method may comprise disposing an end of the sheet material in a recess, such as a trench, formed in the ground at the upper end of the slope. The method may comprise forming at least one trench. The at least one trench may be formed before or after the rigid members are disposed in the ground although in many applications the rigid members may be disposed in the ground before the at least one trench is formed.

The method may further comprise holding the end of the sheet material in the recess. The end of the sheet material may be held by disposing material, such as compacted granular fill, in the recess over the end of the sheet material. The sheet material may be anchored at or towards a lower end of the slope. The sheet material may be anchored at or towards the lower end of the slope by way of at least one of the features described above with reference to anchoring at or towards the upper end of the slope.

The method may further comprise disposing a layer over the sheet material. The layer may comprise the like of soil or stones or may comprise plant matter where it is desired to have a more landscaped appearance.

According to a second aspect of the present invention there is provided apparatus for stabilising ground, the apparatus comprising: sheet material disposed on sloping ground to be stabilised; and plural elongate rigid members disposed at spaced apart locations such that each rigid member extends into ground over which the sheet material is disposed, the apparatus being configured such that each rigid member mechanically couples with the sheet material and the sheet material imposes substantially no tensile load along each rigid member.

Embodiments of the second aspect of the present invention may comprise one or more features of the first aspect of the present invention.

According to a further aspect of the present invention there is provided a method of stabilising sloping ground, the method comprising: disposing sheet material on sloping ground to be stabilised; and disposing plural elongate rigid members at spaced apart locations such that each rigid member mechanically couples with the sheet material and extends into ground over which the sheet material is disposed.

Embodiments of the further aspect of the present invention may comprise one or more features of the first aspect of the present invention.

According to a yet further aspect of the present invention there is provided apparatus for stabilising ground, the apparatus comprising: sheet material disposed on sloping ground to be stabilised; and plural elongate rigid members disposed at spaced apart locations such that each rigid member extends into ground over which the sheet material is disposed, the apparatus being configured such that each rigid member mechanically couples with the sheet material.

Brief Description of Drawings

Further features and advantages of the present invention will become apparent from the following specific description, which is given by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a railway embankment comprising apparatus employed according to the present invention; Figure 2 is a section through the railway embankment of Figure 1; Figure 3A is a detailed view of a mechanical coupling between a rigid member and the sheet material; Figure 3B is a plan view of the mechanical coupling shown in Figure 3A; and Figure 4 is a perspective view of a rigid member alone when received in stable and unstable ground.

Description of Embodiments

A perspective view of one side of a railway embankment comprising apparatus 10 employed according to the present invention is shown in Figure 1. As can be seen from Figure 1 the embankment 12 defines an upward slope which levels out at the top to define a surface which supports a railway line 14. The embankment 12 is aged and has been determined as being liable to shallow slope failure. To reduce the likelihood of shallow slope failure, apparatus according to the invention is installed. A first trench 16 is dug along the edge of the level ground at the top of the part of the embankment considered liable to shallow slope failure. A second trench 18 is dug along level ground at the foot of the part of the embankment considered liable to shallow slope failure. Thereafter plural rigid members 22 are driven at spaced apart locations into the ground to be covered by sheet material 20. The rigid members 22 are driven into the ground such that they extend substantially normally to the slope angle. Each rigid member is formed from recycled polythene. As can be seen from Figure 1, rigid members 22 in adjacent rows are staggered. The spacing between adjacent rigid members 22 is 1 m. Then sheet material 20 is laid over the part of the embankment considered liable to shallow slope failure with the sheet material 20 being of sufficient size that the end of the sheet material 20 at the top of the slope is received in the first trench 16 and the end of the sheet material 20 at the foot of the slope is received in the second trench 18. The sheet material is a geosynthetic grid of known form, such as a geosynthetic grid formed of polyester.

When the sheet material is in place, each rigid member 22 is attached by way of a mechanical coupling to the sheet material 22 as is described in more detail below with references to Figures 3A and 3B.

The apparatus of Figure 1 will now be described further with reference to Figure 2 which shows a section through the railway embankment of Figure 1. Parts in common with the view of Figure 1 are designated in the view of Figure 2 by the same reference numerals and the reader's attention is directed to the description provided above with reference to Figure 1 for a description of such common parts.

Considering Figure 2 more closely, each rigid member 22 extends into the ground such that it spans the unstable ground 24 and penetrates into the stable ground 26 underlying the unstable ground. The rigid members thus extend beyond the slip plane. Each rigid member 22 is therefore held relatively firmly at the end furthest into the ground. The first and second trenches 16, 18 are shown in detail in part of Figure 2 which is indicated by reference numeral 30. As can be seen from the part indicated by reference numeral 30 each trench 16, 18 is filled with compacted granular fill 32 whereby the edge of the sheet material 20 is held firmly in the trench.

Holding the edges of the sheet material 20 firmly in this fashion reduces the extent to which the sheet material moves up, across and in particular down the slope defined by the embankment.

As mentioned above, each rigid member 22 is mechanically coupled to the sheet material 20. A mechanical coupling 40 which is operative to couple a rigid member 22 to the sheet material 20 is shown in detail in Figures 3A and 3B. Referring first to Figure 3A, the mechanical coupling 40 comprises a main body 42 which defines a planar surface that abuts against the upper surface of the sheet material 20. As can be seen from Figures 3A and 3B the main body is thin and of square form when viewed from above. More specifically the main body 42 is 140 mm square when viewed from above. Four arms 44 extend each from an edge of the main body 42 in a direction orthogonal to the planar surface defined by the main body. The form and disposition of the four arms 44 is shown in the plan view of Figure 3B. Each arm is 30 mm wide. The distal end of each arm 44 tapers to a point to thereby ease the insertion of the arms 44 into the ground around the upper end of the rigid member 22. The main body 42 and the arms 44 are integrally formed from galvanised cold formed steel plate. When the arms 44 are properly received in the ground, the mechanical coupling 40 is operative to restrict lateral movement of the rigid member 20 relative to the sheet material 20 and to restrict lifting of the sheet material from the ground. More specifically the mechanical coupling 40 is operative to restrict lateral movement of the rigid member 20 relative to the sheet material 20 in a direction substantially parallel to the slope on which the sheet material is disposed. The mechanical coupling 40 further comprises a coach screw 46 of 10 mm diameter and 150 mm length which is driven through an aperture 48 formed in the centre of the main body 40 and into the upper end of the rigid member 22. The coach screw 46 is therefore operative to further limit relative movement of the rigid member 22 and the sheet material 20. The mechanical coupling 40 is operative to attach the rigid member 22 to the sheet material 20 such that there is substantially no tensile load imposed by the sheet material on the rigid member by way of the mechanical coupling.

A perspective view 60 of a rigid member alone 22 when received in stable and unstable ground is shown in Figure 4. As can be seen from Figure 4 the ground comprises an unstable layer 62 overlying a stable layer 64. The unstable layer 62 has been deemed liable to cause a shallow slope failure. The depth of the stable ground is determined by at least one of: ground investigation; laboratory testing of the ground; instrumentation which is operative to measure the ground; and slope stability analysis using standard industry techniques. Then rigid members of a length sufficient to reach into the stable ground are either formed or selected from stock in dependence on the stable ground depth determination. As described above each rigid member 22 is driven into the ground such that it spans the unstable layer 62 and penetrates the underlying a stable layer 64. The end of the rigid member 22 that extends furthermost into the ground is therefore held relatively firmly by the stable layer 64. The mechanical coupling 40 described above provides for firm holding of the opposite end of the rigid member 22 whereby the rigid member is held towards the opposite ends.

Although the apparatus and method of the present invention are described with reference to an aged railway embankment! the method and apparatus are also readily applied to other slopes including cuttings irrespective of whether they are newly formed, relatively recently formed or aged.

Claims

Claims: 1. A method of stabilising sloping ground, the method comprising: disposing sheet material on sloping ground to be stabilised; and disposing plural elongate rigid members at spaced apart locations such that each rigid member mechanically couples with the sheet material and extends into ground over which the sheet material is disposed wherein the sheet material imposes substantially no tensile load along each rigid member.
2. The method according to claim 1 in which each rigid member extends to within 15 degrees of normal to an angle of the slope of the ground.
3. The method according to claim 1 or 2 in which substantially no tensile load is imposed along a longitudinal axis of each rigid member.
4. The method according to any one of the preceding claims in which a C'\J compressive load is imposed by the sheet material on each rigid member.
5. The method according to any one of the preceding claims in which the sheet material is configured to conform to uneven ground.
6. The method according to claim 5 in which the sheet material is configured to conform to uneven ground by way of at least one: movement of one component of the sheet material relative to another component of the sheet material about a mechanical coupling; and pliability of material comprised in the sheet material.
7. The method according to any one of the preceding claims in which the sheet material defines one of a grid and a mesh.
8. The method according to claim 7 in which the rigid members are disposed in the ground after the sheet material is disposed on the ground, where apertures defined by the sheet material are of sufficient dimensions for passage of the rigid members.
9. The method according to any one of claims 1 to 7 in which the plural elongate rigid members are disposed in the ground before the sheet material is disposed on the ground.
10. The method according to any one of the preceding claims in which the sheet material comprises a polymeric material.
11. The method according to any one of the preceding claims in which the sheet material comprises a geosynthetic material.
12. The method according to any one of the preceding claims in which each rigid member is of a length between 0.25 m and 5 m.ct
13. The method according to any one of the preceding claims in which each rigid member is of a width between 50 mm and 200 mm. (4 r14. The method according to any one of the preceding claims in which each rigid member is of substantially rectangular cross section.15. The method according to any one of the preceding claims in which each rigid member is formed at least in part from a plastics material.16. The method according to any one of the preceding claims in which the plural rigid members are disposed such that they span a slip plane of the sloping ground to be stabilised.17. The method according to claim 16 in which the plural rigid members are disposed such that they reach no more than 1.5 m from the surface of the ground.18. The method according to any one of the preceding claims in which the plural rigid members are disposed such that they reach into stable ground.19. The method according to claim 18 in which a depth of stable ground is determined by at least one of: ground investigation; laboratory testing of the ground; instrumentation which is operative to measure the ground; and slope stability analysis using standard industry techniques; and a length for the rigid members is determined in dependence on the stable ground depth determination.20. The method according to any one of the preceding claims in which the plural rigid members are spaced apart from each other by between 2 m and 0.5 m.21. The method according to any one of the preceding claims in which rigid members in adjacent rows are staggered.22. The method according to any one of the preceding claims in which each rigid member and the sheet material are coupled by a substantially rigid mechanical ct coupling whereby substantially no tensile load is imposed along each rigid member.23. The method according to claim 22 in which the mechanical coupling defines a r profile which fits around a side of the rigid member at or towards its upper end. r24. The method according to claim 22 or 23 in which the mechanical coupling comprises a main body, which defines a substantially planar surface, and plural arms which extend from the main body substantially orthogonally to the substantially planar surface, the substantially planar surface, in use, abutting against an upper surface of the sheet material whereby the sheet material is in between the main body and the upper end of the rigid member and an end of each arm is configured to penetrate at least one of the sheet material and the ground on which the sheet material is disposed.25. The method according to any one of the preceding claims further comprising anchoring the sheet material at or towards an upper end of the slope.26. The method according to any one of the preceding claims further comprising disposing a layer over the sheet material.27. Apparatus for stabilising ground, the apparatus comprising: sheet material configured to be disposed on sloping ground to be stabilised; and plural elongate rigid members configured to be disposed at spaced apart locations such that each rigid member extends into ground over which the sheet material is disposed, the apparatus for stabilising ground being configured such that each rigid member mechanically couples with the sheet material and the sheet material imposes substantially no tensile load along each rigid member. (4 r r