Note: Descriptions are shown in the official language in which they were submitted.
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STABILISATION SYSTEM FOR SOIL SLOPES
FIELD OF TH.E INVENTION
This invention relates to a system of stabilising soil slopes and a
method related thereto.
BACKGROUND
On steep slopes having generally less than 45 degrees of inclination to
the horizontal, the prevention of soil erosion is typically accomplished by
planting
vegetation on the surface of the slope. The roots of the vegetation secure the
soil at
the surface. Vegetation alone however does not prevent large shifts of the
soil.
The use of nails and other forms of anchors is known for stabilising soil
on vertical or near vertical faces. Generally these nails are installed with
shotcrete
or precast concrete facings between the nails during the formation of the
faces for
retaining the soil between the nails. There is no known precedent for
utilising nails
on existing slopes having an inGination of less than 45 degrees.
It is an object of the present invention to provide a stabilisation system
for soil slopes which incorporates interrtal soil slope stability with the
prevention of
surface soil erosion.
SUMMARY
According to one aspect of the present invention there is provided a
method for stabilising soil within a slope. having generally less than 45
degrees of
inclination from horizontal, said method comprising:
penetrating a plurality of soil nails Into the soil; and
establishing vegetation adjacent a top surface of the soil, the
vegetation being arranged to generate roots which penetrate through the
surface
into the soil.
The use of soil nails provides internal soil stability to a slope or
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embankment by penetrating the nail through the soil past an existing or
potential
failure plane. The soil nails extend transversely to existing or potential
failure planes
to resist intemal shearing forces within the slope of soil. A cover of
vegetation
established onto the surface of the soil provides further stability to the
slope. The
vegetation established at the surface of the slope prevents erosion or shallow
failure
near the surface of the slopes. Additional retaining members may also be
mounted
along the crest of the slope by anchoring the retaining members to the slope
with the
soil nails to further inhibit soil erosion and shallow failure at the crest.
A biotechnical facing may be established by providing a geosynthetic
layer comprising a mat, mesh or fibrous material placed over or near the soil
surface
before or after seeding or planting such that the vegetation is stabilised on
the
surface of the slope for retaining the soil adjacent the surface of the slope.
A retaining member can be mounted adjacent a crest of the slope to
extend transversely thereto. The retaining member further inhibits soil
erosion and
shallow failure at the crest.
The retaining member may comprise an elongate plate member,
wherein the method includes orienting the plate member to extend substantially
perpendicularly to the surface of the soil and to project outwardly therefrom.
The method may further include filling a space defined between the
retaining member and a crest of the slope with soil. The crest of the slope
thus
provides a broad stable base for supporting for example a roadway or a railway
thereon.
The retaining rnember may be anchored with a plurality of soil nails
coupled thereto, wherein each soil nail is penetrated into the slope.
A plate member may be mounted on each soil nail adjacent one end
thereof and orienting the soil nails before penetration into the slope so that
plate
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extends transversely to the slope.
The plate members on the soil nails are preferably oriented to lie in a
substantially common plane therewith such that the plate members extend
perpendicularly to the slope when the soil nails are penetrated
perpendicularly into
the surface of the slope.
According to a further aspect of the present invention there is provided
a stabilisation system for stabilising soil within a slope having generally
less than 45
degrees of inclination from horizontal, said system comprising:
a plurality of soil nails, each having a soil penetrating end for
penetrating into the soil and a surface engaging end for engaging a top
surface of
the soil; and
a biotechnical facing arranged to cover the top surface of the soil.
The biotechnical facing preferably comprises a mass of organic fibres
having a root structure arranged to penetrate into the soil.
There may be provided a geosynthetic layer comprising a mat, mesh
or fibrous material arranged on or near the surface to further reinforce the
surface
and assist in establishing the mass of organic fibres thereon.
A retaining wall structure may be mounted on the slope to extend
longitudinally along a crest of the slope.
In one arrangement of the present invention, the retaining wall
comprises:
a pair of retaining members mounted spaced apart on a crest of the
slope to extend longitudinally with the crest; and
a plurality of cross members, each being connected between the pair
of retaining members for mounting the retaining members parallel and spaced
apart
in relation to one another.
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Alternatively the retaining wall structure may comprise an elongate
plate member oriented perpendicularly to the surface of the soil to project
outwardly
therefrom.
There may be provided a filler material located within a spaced defined
between the retaining wall structure and the crest of the slope. The filler
material
may comprise gravel or the like to provide a stable base while permitting
drainage
therethrough at the crest of the slope.
There may be provided a plurality of soil nails which are penetrated in
the soil and coupled to the retaining wall structure for anchoring the
retaining wall
structure adjacent the crest of the slope.
There may be provided a soil retaining plate member mounted on the
surface engaging end of the each soil nail for engaging and retaining the soil
adjacent the surface of the slope.
The soil retaining plates are preferably mounted on each soil nail to lie
in a substantially common plane therewith such that the plates are oriented
perpendicularly to the slope when the soil nails are penetrated into the soil
perpendicularly to the surface thereof,
According to another aspect of the present invention there is provided
a method for stabilising soil within a slope having a surface lying generally
less than
45 degrees of inciination from horizontal =and a failure plane below the
surface of the
slope, said method comprising:
providing a plurality of soil nails comprising elongate rigid members;
stabilising the internal soil of the slope by penetrating the plurality of
soil nails into the soil across the failure plane of the slope; and
generating vegetation roots which penetrate through the surface into
the soil by establishing vegetation at the surFace of the slope.
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According to yet another aspect of the present invention there is
provided a stabilisation system for stabilising soil within a slope having a
surface
lying generally less than 45 degrees of inclination from horizontal and a
failure plane
below the surface of the soil, said system comprising:
a plurality of soil nails, each comprising an elongate rigid member
being generally greater than 2 meters in length and having a soil penetrating
end for
penetration into the soil and a surface engaging end for engaging a top
surface of
the soil such that the elongate rigid member extends across the failure plane;
and
an organic facing for placement at the surface of the soil, the organic
facing comprising vegetation having roots for penetration into the soil
through the
surface of the slope.
According to a further aspect of the present invention there is provided
a stabilisation system for stabilising soil within a slope having generally
less than 45
degrees of inclination from horizontal, said system comprising:
a plurality of soil nails, each comprising a soil penetrating end for
penetrating into the soil and a surface engaging end for engaging a top
surface of
the soil; and
a soil retaining member mounted on the surface engaging end of each
soil nail for engaging and retaining the soil adjacent the surface of the
slope;
the soil retaining members being oriented for extending transversely to
the surface of the soil when the soil penetrating end of the soil nails are
penetrated
into the soil.
The soil retaining members can be oriented for extending in a
crosswise intersecting manner to the surface of the soil when the soil
penetrating
end of the soil nails are penetrated into the soil.
According to yet a further aspect of the present invention there is
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provided a stabiiisation system for stabilising soil within a slope having
generally less
than 45 degrees of inclination from horizontal, said system comprising:
a plurality of soil nails, each having a soil penetrating end for
penetrating into the soil and a surface engaging end for engaging a top
surface of
the soil; and
a retaining wall structure arranged to be mounted on the slope to
extend longitudinally along a crest of the slope.
BRIEF DESCRIPTION OF THEDRAWINGS
In the accompanying drawings, which illustrate exemplary
embodiments of the present invention:
Figure 1 is a cross sectional view of a soil slope with the stabilisation
system thereon.
Figure 2 is top plan view of the stabilisation system.
Figure 3 is an enlarged view of a portion of Figure 1.
Figure 4 is a cross sectional view of a soil slope with an alternative
embodiment of the stabilisation system thereon.
Figure 5 is a top plan view of the stabilisation system of Figure 4.
Figure 6 is an enlarged view of a portion of Figure 4,
DETAILED DESCRIPTION
Referring to the accompanying drawings, there is illustrated a
stabilisation system generally indicated 'by 'reference numeral 10 for
stabilising soil
slopes of a railway embankment. The system 10 is adapted for installation on
existing slopes 12 of an embankment 13 for stabiiising the intemal soil of the
slopes
and for preventing erosion at the surfaoe or near the surface of the soil. The
system
is particularly suitable for use on slopes having generally less than 45
degrees of
inciination from horizontal.
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The system 10 includes a plurality of soil nails 14 which are penetrated
into a top surface 16 of the slope in a staggered patterm. The nails 14 are
elongate
rigid members having any one of numerous different types of cross sections.
The
nails each include a penetrating end 18 arranged to penetrate into the soil
and a
surface engaging end 20 arranged to be secured against the top surface 16 of
the
slope.
The surface engaging end 20 includes a portion of increased
dimension 22 at the surface 16 or near the surface of the soil, The nails
extend
through the soil past an existing or potential failure plane 24 in the soil
for providing
intemal soil stability to the slope.
The nails are inserted Into the soil by percussion, pushing, tuming or
vibrating. Altematively, the nails may be inserted into pre-made holes. The
nail
strength, length, diameter and spacing are selected based upon the desired
degree
of improvement through an engineering design. Nails are typically 25 to 50
millimetres in diameter and 2 to 10 metres long.
A biotechnical facing consisting of vegetation and which may be
combined with a geosynthetic layer 26, is placed across the top surface 16 of
the
soil and the surface engaging end of each nail for preventing shallow failure
and
erosion of surface soils. The geosynthetic layer is a manufactured mat, mesh
or
fibrous material, permanent or biodegradeable, of natural or synthetic
materials,
designed to reinforce the surface or assist growth and maintenance of
vegetation.
The use of a geosynthetic layer is a known practice in construction on soft
terrain for
adding structural support to the soil of the terrain. It provides an erosion
resistant
layer when combined with vegetation.
Vegetation is seeded or planted below or near the geosynthetic layer
26 such that the vegetation becomes well established and an organic mass of
roots
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penetrates into the soil. The plant root mass is selected based on the desired
degree of improvement through engineering design. The vegetation is typically
selected to extend to a depth of 100 to 400 millimetres into the soil.
A retaining wall structure 28 is mounted on each slope 12 of the
embankment adjacent a crest 30 of the embankment to stabiiise the shoulder of
the
embankment near the crest 30. Each retaining wall structure 28 includes
elongate
timbers 32 extending iongitudinally along the embankment adjacent the crest so
as
to extend transversely to the slope.
The timbers 32 are parallel and spaced apart along the crest. A
plurality of concrete anchors 34 are mounted along an outer face 36 of the
timbers
32 for securing the timbers in place. Each anchor is an L-shaped member having
an
upright portion 38 engaging the outer face of the timber and a lateral portion
40
extending laterally inward adjacent a bottom face of the timber. A pair of the
soil
nails 14 are inserted through respective apertures in each anchor 34 for
securing the
anchor to the embankment at spaced positions along the timber.
Each anchor 34 is secured to a corresponding one of the anchors
adjacent the opposing timber 32 by a rod 42. Each rod 42 is fastened to the
corresponding pair of anchors 34 at respective ends of the rod.
A space 44 defined between the timbers is filled with gravel 46 to allow
drainage of water and prevent water collection at the crest of the embankment.
The
gravel 46 surrounds the rods 42 dxtending across the space 44 between
corresponding anchors 34.
A railway 48 is mounted on the crest of the embankment. The raiiway
48 includes a plurality of rail ties 50 embedded into the gravel. The rail
ties 50 are
parallel and spaced apart along the crest of the embankment. A pair of rails
52 are
mounted on the rail ties 50 parallel and spaced apart.
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In an alternate embodiment of the present invention, illustrated in
Figures 4 through 6, a plurality of the soil nails 14 are penetrated at
staggered and
spaced intervals into the surface of the slopes 12 of the embankment 13
similarly to
the first embodiment. In the alternate embodiment, the retaining wall
structure 28
comprises a pair of elongate retaining members 60 which are mounted parallel
and
spaced apart to extend longitudinally with the crest 30.
Each retaining member 60 is a continuous flat strip of material, for
example a timber or steel lagging. A plurality of the soil nails 14 are
secured to each
retaining member 60 for mounting the retaining member to extend substantially
perpendicularly to the surface of the slope and project outwardly therefrom.
The railway 48 is supported on the crest 30 of the embankment,
spaced between the retaining members 60 to extend longitudinally therewith
along
the crest. A space 62 defined between a free end 64 of each retaining member
60
and the railway 48 is levelled with soil.
The portion of increased diameter 22 at the surface engaging end of
each soil nail 14 in the aitemative embodiment, comprises a soil retaining
plate 68
mounted on the soil nail so as to be located perpendicular to and adjacent to
the
surface of the slope 12 in which the soil nail is penetrated. The plates 68
are
oriented on the respective nails to lie in a substantially common plane
therewith such
that the plates lie perpendicularly to the* slope when the soil nails are
penetrated into
the soil perpendicularly to the surface thereof. The soil nails are penetrated
into the
slope before a biotechnical facing having a geosynthetic layer 70 similar to
the first
embodiment, is laid across the surface on the slopes 12 over the surface
engaging
ends 20 of the nails 14 as shown in detail in Figure 6,
The geosynthetic layer 70 is a manufactured mat, mesh or fibrous
material which provides structural support to the soil of the slope and
assists
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vegetation to be established below the facing such that the organic mass of
roots of
the vegetation penetrates into the soil once the vegetation becomes well
established. Thus, similarly to the first embodiment, the soil nails extend
through the
soil past an existing or potential failure plane 24 to provide internal soil
stability to the
slope while the biotechnical facing 70 along with the vegetation seeded at the
surface of the slope prevents erosion or shallow failure near the surface of
the
slopes. Additionaffy, the retaining members 60 inhibit soil erosion and
shallow
failure at the crest of the embankment.
While various embodiments of the present invention have been
described in the foregoing, it is to be understood that other embodiments are
possible within the scope of the invention. The invention is to be aonsidered
limited
solely by the scope of the appended claims.
