Note: Descriptions are shown in the official language in which they were submitted.
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A Reinforced soil retaining wall system and method of construction
FIELD OF THE INVENTION
The present invention relates to a reinforced soil retaining wall system and a
method of
construction of a reinforced soil retaining wall. The present invention
further relates to
a block used in the construction of a reinforced soil retaining wall and a
length of strip
reinforcement used in the construction of a reinforced soil retaining wall.
The present application claims priority from Australian provisional patent
application
2004901725 filed on 1 April 2004, Australian provisional patent application
2004901789 filed on 5 April 2004, Australian provisional patent application
2004907121 filed on 15 December 2004 and Australian provisional patent
application
2005900832 filed on 23 February 2005.
BACKGROUND TO THE INVENTION
Retaining walls are defined as any wall that restrains material on one side of
a wall to
maintain a difference in elevation. Nearby slopes, driveways, buildings, and
tiered walls
all represent potential loads on retaining walls. There are three main types
of retaining
walls: gravity walls, cantilever walls and reinforced soil walls. A retaining
wall without
soil reinforcement, where the weight of the blocks alone provides resistance
to the load
of the soil being retained, is referred to as a "gravity wall". Gravity
retaining walls cost
more money to install, which each block in the wall consisting of a mass of
concrete or
stone. Gravity walls rely upon their mass weight to retain the soil.
Excavation of the
2 5 soil behind a gravity wall has no effect on the structural strength of the
wall. Cantilever
walls are typically sheet pile structures which are driven into the soil and
derive their
support solely through the resistance the soil provides against rotation of
the sheet pile
under the weight of the soil being retained. One type of cantilever wall
comprises a
horizontal base section that is buried under the backfill with a stem section
permanently connected to and extending vertically from the base section to
form the
wall. Cantilever walls rely on the weight of the backfill on the base section
to keep the
wall from tipping over.
The term "reinforced soil retaining wall" refers to a retaining wall that
incorporates
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substantially horizontal layers of soil reinforcement material buried under
the soil being
retained by the wall. One type of reinforced soil retaining wall comprises
reinforcement
in the form of steel mesh buried within the retained soil. The steel mesh
anchors a
concrete slab, steel sheet or rock filled wire basket which acts as the facing
of the
retaining wall, the facing being the structure that forms the front of the
wall, usually
oriented vertical or inclined. The facing prevents the soil from escaping from
between
the layers of reinforcement. Using the methods of the background art, the soil
reinforcement must be added to all or most of the courses of blocks and some
form of
propping is required to prevent the facing from moving whilst the soil is
compacted
around the reinforcement.
The present invention was developed to overcome at least some of the
abovementioned problems.
It will be clearly understood that, although a number of background art
methods and/or
publications are referred to herein, this reference does not constitute an
admission that
any of these methods or publications form part of the common general knowledge
in
the art, in Australia or in any other country. In the summary of the
invention, the
description and claims which follow, except where the context requires
otherwise due
2 0 to express language or necessary implication, the word "comprise" or
variations such
as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify
the
presence of the stated features but not to preclude the presence or addition
of further
features in various embodiments of the invention.
2 5 SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a
reinforced soil
retaining wall system comprising:
a plurality of blocks arranged in courses above a base course to form a
wall, the wall having a retained side and a dredge side, each block comprising
a front
3 0 face oriented in use towards the dredge side of the wall, a rear face
spaced from said
front face by a distance defining the depth of said block and oriented in use
towards
the retained side of the wall, a top surface, a bottom surface spaced from
said top
surface by a distance defining the height of said block, opposing side
surfaces spaced
from each other by a distance defining the width of said block, and a passage
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extending through at least a portion of the height of the block and
terminating in a first
opening in the top or bottom surface, the passage and first opening configured
to
receive a first portion of a length of strip reinforcement; and,
a plurality of lengths of strip reinforcement for anchoring the wall, each
length of strip reinforcement insertable within at least one of the plurality
of blocks such
that a first portion of the length of strip reinforcement is received within
the passage of
the block, a second portion of the length of strip reinforcement is arranged
in coplanar
alignment with the top or bottom surface of the block and a third portion of
the length
of strip reinforcement is arranged to extend outwardly from the rear face of
the block
and secured in position substantially perpendicular to the wall during
backfilling and
compaction.
The passage may be substantially vertically oriented relative to the top or
base section
of the block to maximize the pull out forces required to remove the length of
strip
reinforcement from the passage after it has been inserted.
Preferably each length of strip reinforcement is resiliently flexible.
For mortarless construction, the blocks may further comprise a guide slot
extending
2 0 from the first opening passage along the top or bottom surface of the
block, the guide
slot terminating at the rear face of the block and configured to house the
second
portion the length of strip reinforcement. The third portion of the length of
strip
reinforcement may be arranged in coplanar alignment with the top and or base
surface
of the blocks immediately prior to backfilling and compacting or may lie at an
angle to
2 5 the wall during backfilling and compacting. .
In one embodiment, the passage extends through the full height of the block
from a
first opening provided in the bottom surface of the block to a second opening
provided
in the top surface of the block which allows the length of strip reinforcement
to be
30 inserted through the passage from the first opening to the second opening
with a
fourth portion of the length of strip reinforcement arranged to extend
outwardly from
the rear face of the block to be secured in position substantially
perpendicular to the
wall during backfilling and compaction. The fourth portion may be arranged in
general
coplanar alignment with respect to the top or bottom face of the block away
from the
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wall immediately prior to backfilling and compaction to maximize resistance to
pull-out
forces.
Advantageously, the passage may be a cavity extending from the bottom surface
to
the top surface, the cavity configured to receive a quantity of ballast in the
form of
drainage aggregate or an impermeable material such as cast concrete or cement.
The
passage may be one of plurality of passages.
In one embodiment, the system further comprises one or more shear pins to
resist
sliding movement of a first course over an adjacent second course and may
further
comprise a drainage channel configured to direct moisture from the retained
side of
the wall towards the dredge side of the wall. The drainage channel is
particular
advantageous for use with clay soils to relieve any buildup of hydrostatic
pressure on
the retained side of the wall.
In another embodiment, the plurality of lengths of strip reinforcement are
divided into a
threaded section inserted into at least one block and a free section co-
operatively
associated with the threaded section and arranged to arranged to extend
outwardly
from the rear face of the block and be secured in position substantially
perpendicular
2 0 to the wall during backfilling and compaction.
In a further embodiment, the reinforced soil retaining wall system forms a
lower section
of a composite wall, the composite wall being divided a transition depth into
an upper
section and the lower section. The upper section may be a gravity or
cantilever
retaining wall. Using this embodiment, a soil reinforcement protection barrier
may be
placed at the transition depth in general coplanar alignment with the top
uppermost
course of blocks forming the lower section of the composite wall. The soil
reinforcement protection barrier may be a concrete slab used to provide a
physical
indication of the transition depth or a thin sheet of plastic material used to
provide a
3 0 visual indication of the transition depth.
According to a second aspect of the present invention there is provided a
method of
construction of a reinforced soil retaining wall system, the system comprising
a plurality
of blocks arranged in courses above a base course to form a wall, the wall
being
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anchored by backfilling and compacting soil over a plurality of lengths of
strip
reinforcement operatively connected to at least a portion of the plurality of
blocks laid
in courses, the method of construction comprising the steps of:
a) providing a level surface for laying a course of blocks, each block
comprising a front face, a rear face spaced from said front face by a distance
defining
the depth of said block, a top surface, a bottom surface spaced from said top
surface
by a distance defining the height of said block, opposing side surfaces spaced
from
each other by a distance defining the width of said block, a passage extending
through
at least a portion of the height of the block and terminating in a first
opening in the top
or bottom surface, the passage and first opening configured to receive a first
portion of
a length of strip reinforcement;
b) inserting a length of strip reinforcement into a block to be laid in the
course such that a first portion of the length of strip reinforcement is
received in the
passage, a second portion of the length of strip reinforcement is arranged in
coplanar
alignment with the top or bottom surface of the block and a third portion of
the length
of strip reinforcement is arranged to extend outwardly from the rear face of
the block;
c) positioning the block and the inserted length of strip reinforcement
onto the level surface such that the rear surface of the block and the third
portion of
the length of strip reinforcement is directed towards the soil to be retained
by the wall;
2 0 d) repeating step (a) to (c) until a required height for the retaining
wall
has been achieved; and,
e) anchoring the position of the third portion of the length of strip
reinforcement by backfilling and compacting a quantity of soil behind the rear
face of
the block.
Step (e) may be conducted after step (c) after each course is completed or
after the
wall has been completed in a single backfilling operation.
For mortarless construction, each block further comprises a guide slot
extending from
the first opening along the bottom surface of the block and terminating at the
rear face
of the block, the guide slot being configured to accommodate the second
portion the
length of strip reinforcement. The third portion of the length of strip
reinforcement may
be arranged in coplanar alignment with the top and or base surface of the
blocks
immediately prior to step (e). In one embodiment the passage extends through
the full
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height of the block from a first opening provided in the bottom surface of the
block to a
second opening provided in the top surface of the block and step (b) comprises
the
step of inserting a length of strip reinforcement through the passage from the
first
opening to the second opening such that a fourth portion of the length of
strip
reinforcement is arranged to extend outwardly from the rear face of the block.
For this
embodiment, step (e) further comprises the step of anchoring the position of
the fourth
portion of the length of strip reinforcement by backfilling and compacting a
quantity of
soil behind the rear face of the block. The fourth portion may be arranged in
general
coplanar alignment with respect to the top or bottom face of the block away
from the
wall immediately prior to backfilling and compaction or arranged at an angle
with
respect to the wall.
In another embodiment, the passage is a cavity extending from the bottom
surface to
the top surface and the method further comprises the step of adding a quantity
of
ballast to the cavity after each block or each course of blocks has been laid.
The
ballast may be drainage aggregate or an impermeable material such as cast
concrete.
The method of construction may further comprise the step of installing one or
more
shear pins to resist sliding movement of a first course over an adjacent
second course.
In yet another embodiment, the plurality of lengths of strip reinforcement are
divided
into a threaded section inserted into at least one block at step (b) and a
free section
co-operatively associated with the threaded section and arranged to extend
outwardly
from the rear face of the block and be secured in position during step (e)
substantially
2 5 perpendicular to the wall during backfilling and compaction.
In one embodiment the reinforced soil retaining wall forms a lower section of
a
composite wall, the composite wall being divided a transition depth into an
upper
section and the lower section and the method further comprises the step of
constructing a gravity or cantilever retaining wall to form the upper section
of the
composite wall. Using this embodiment, the method may further comprise the
step of
installing a soil reinforcement protection barrier at the transition depth in
general
coplanar alignment with the top uppermost course of blocks forming the lower
section
of the composite wall. The step of installing a soil reinforcement protection
barrier may
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comprise the step of laying a concrete slab.
According to a third aspect of the present invention there is provided a block
for use in
constructing the reinforced soil retaining wall system of the first aspect of
the present
invention. According to a fourth aspect of the present invention there is
provided a
length of strip reinforcement for use in constructing the reinforced soil
retaining wall
system according the method of the second aspect of the present invention.
According to a fifth aspect of the present invention there is provided a
reinforced soil
retaining wall system comprising:
a plurality of blocks arranged in courses above a base course to form a
wall, the wall having a retained side and a dredge side, each block comprising
a front
face oriented in use towards the dredge side of the wall, a rear face spaced
from said
front face by a distance defining the depth of said block and oriented in use
towards
the retained side of the wall, a top surface, a bottom surface spaced from
said top
surface by a distance defining the height of said block, opposing side
surfaces spaced
from each other by a distance defining the width of said block;
a first plurality of sections of soil reinforcement for anchoring the wall to
the backfill, the first plurality of sections of soil reinforcement arranged
between
2 0 adjacent courses of the wall and extending outwardly from the rear face of
the blocks
on the retained side of the wall; and,
a second plurality of sections of soil reinforcement for stabilizing a
quantity of backfilled and compacted soil on the retained side of the wall,
the second
plurality of sections of soil reinforcement being spaced apart from the first
plurality of
sections of soil reinforcement and arranged to extend substantially
perpendicular to the
wall during backfilling and compaction.
The second plurality of sections of soil reinforcement may be spaced apart
from the
rear face of the wall, laid immediately adjacent thereto or be in abutting
contact
3 0 therewith.
In one embodiment, one or both of the first or second plurality of sections
soil
reinforcement is/are resiliently flexible. The length of the plurality of
second sections of
soil reinforcement depends on the particular application and may be equal to
at least
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_g_
60%, 70% or 80% of the height of the wall. It is advantageous for the
plurality of
second sections of soil reinforcement have a length that extends at least
through the
anticipated plane of rupture of the backfill which is again a function of a
number of
factors including the soil characteristics of the backfill and the properties
of the wall
itself.
One or both of the first or second plurality of sections of soil reinforcement
may be
planar, such as geomesh or take the form of elongated strips of strip
reinforcement.
In one embodiment the first and second plurality of sections of soil
reinforcement are
arranged in horizontal coplanar arrangement with respect to each other. In
another
embodiment, the first plurality of sections of soil reinforcement are arranged
in a first
layer and the second plurality of sections of soil reinforcement are arranged
in a
second layer offset from the first layer.
One or both of the first or second plurality of sections of soil reinforcement
may be
arranged in coplanar alignment with the top and or base surface of one or more
of the
plurality of blocks immediately prior to backfilling and compacting. The
second plurality
of sections of soil reinforcement may equally be arranged at other heights.
In one embodiment, the blocks further comprise one or more cavities extending
from
the bottom surface to the top surface, the cavity configured to receive a
quantity of
ballast which may be drainage aggregate or an impermeable material such as
cast
concrete or cement mortar. For soils with poor drainage, the system may
further
comprise a drainage channel configured to direct moisture from the retained
side of
the wall towards the dredge side of the wall.
In another embodiment, the reinforced soil retaining wall system forms a lower
section
of a composite wall, the composite wall being divided a transition depth into
an upper
section and the lower section. The upper section may be a gravity or
cantilever type
retaining wall. Using this embodiment, a soil reinforcement protection barrier
such as
a concrete slab or sheet of plastic material may be placed at the transition
depth in
general coplanar alignment with the top uppermost course of blocks forming the
lower
section of the composite wall.
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Where mortar is used to construct the wall, the first plurality of sections of
soil
reinforcement are fixedly held between adjacent courses of blocks using
mortar.
Alternatively for mortarless construction, the first plurality of sections of
soil
reinforcement are fixedly held between adjacent courses of blocks by gravity
under the
weight of the blocks forming the adjacent courses.
According to a sixth aspect of the present invention there is provided a
method of
construction of a reinforced soil retaining wall system, the system comprising
a plurality
of blocks arranged in courses above a base course to form a wall, the method
of
construction comprising the steps of:
a) providing a level surface for laying a course of blocks, each block
comprising a front face, a rear face spaced from said front face by a distance
defining
the depth of said block, a top surface, a bottom surface spaced from said top
surface
by a distance defining the height of said block, opposing side surfaces spaced
from
each other by a distance defining the width of said block;
b) arranging a first plurality of sections of soil reinforcement for
anchoring the wall to the backfill between adjacent courses of the wall whilst
laying
each course of blocks, the first plurality of sections of soil reinforcement
being
2 0 arranged to extend outwardly from the rear face of the blocks on the
retained side of
the wall;
c) laying each subsequent course until a required height for the retaining
wall has been achieved;
d) arranging a second plurality of sections of soil reinforcement spaced
3 5 apart from the first plurality of sections of soil reinforcement and
arranged to extend
during step (e) substantially perpendicular to the wall; and,
(e) backfilling and compacting a quantity of backfill behind the rear face
of the blocks so as to anchor the position of the first and second plurality
of sections of
soil reinforcement.
Step (e) may be conducted after step (b) and prior to step (c) for each course
of
conducted after the wall has been completed. The second plurality of sections
of soil
reinforcement may be arranged during step (e) so as to be spaced apart from
the rear
face of the wall.
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In one embodiment, the first and second plurality of sections of soil
reinforcement are
arranged in horizontal coplanar arrangement with respect to each other.
Alternatively,
the first plurality of sections of soil reinforcement are arranged in a first
layer and the
second plurality of sections of soil reinforcement are arranged in a second
layer offset
from the first layer.
One or both of the first or second plurality of sections of soil reinforcement
may be
arranged in coplanar alignment with the top and or base surface of one or more
of the
plurality of blocks immediately prior to backfilling and compacting.
In one embodiment, the blocks further comprise one or more cavities extending
from
the bottom surface to the top surface, the cavity configured to receive a
quantity of
ballast and the method further comprises the step of adding a quantity of
ballast to the
cavity after each block or each course of blocks has been laid. The ballast
may be
drainage aggregate or an impermeable material such as concrete or cement
mortar.
The system may further comprise the step of installing one or more shear pins
to resist
sliding movement of a first course over an adjacent second course.
In yet another embodiment, the reinforced soil retaining wall forms a lower
section of a
composite wall, the composite wall being divided a transition depth into an
upper
section and the lower section and the method further comprises the step of
constructing a gravity or cantilever retaining wall to form the upper section
of the
2 5 composite wall A soil reinforcement protection barrier may be installed at
the transition
depth in general coplanar alignment with the top uppermost course of blocks
forming
the lower section of the composite wall.
For mortared construction, the first plurality of sections of soil
reinforcement may be
fixedly held between adjacent courses of blocks using mortar. For mortarless
construction, the first plurality of sections of soil reinforcement may be
fixedly held
between adjacent courses of blocks by gravity under the weight of the blocks
forming
the adjacent courses.
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BRIEF DESCRIPTION OF THE DRAWINGS
In order to facilitate a more detailed understanding of the nature of the
invention
several embodiments of the reinforced soil retaining wall system will now be
described
in detail, by way of example only, with reference to the accompanying
drawings, in
which:
Figure 1 is a side cross-sectional view through a wall constructed
according to a first embodiment of the reinforced soil system of the present
invention
using mortar to secure the position of the blocks and illustrating the
arrangement of the
courses of blocks and lengths of strip reinforcement anchoring the wall under
backfilled
and compacted soil;
Figure 2 (a) and 2 (b) each illustrate an isometric view of one of the blocks
used to construct the wall of Figure 1 illustrating the position of the
passage into which a
length of strip reinforcement is inserted before the block is laid and the
position of a
guide slot for receiving a second portion of the a length of strip
reinforcement so that
blocks in adjacent course may sit flush relative to each other for use in the
construction
of a mortarless wall;
Figure 3 is a cross-section view through section A-A of the block of Figure
~ (a);
Figure 4 illustrates the block of Figure 3 with a length of strip
2 0 reinforcement inserted therein;
Figure 5 is an isometric cross-sectional view through part of the wall
showing a plurality of lengths of strip reinforcement threaded through the
blocks;
Figure 6 is a partial isometric view of a wall for which two courses have
been constructed showing the arrangement of the blocks and lengths of strip
2 5 reinforcement prior to backfilling and compaction for a first embodiment
of the present
invention;
Figure 7 is an isometric view of a completed wall showing the
arrangement of the blocks and lengths of strip reinforcement through two
courses of
blocks after backfilling and compaction for a first embodiment of the present
invention;
30 Figure 8 is an isometric view of a block used in accordance with a second
embodiment of the reinforced soil retaining wall system of the present
invention;
Figure 9 is a cross-sectional view through section B-B of the block
illustrated in Figure 8 showing the arrangement of the length of strip
reinforcement
inserted into the block;
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Figure 10 is a partial isometric view of a wall for which two courses have
been constructed showing the arrangement of the blocks and lengths of strip
reinforcement prior to backfilling and compaction for a second embodiment of
the
present invention;
Figure 11 is a side cross-section view of a third embodiment of the
present invention illustrating a composite wall having an upper section and a
lower
section;
Figure 12 is a side cross-section view of a fifth embodiment of the present
invention showing an impermeable layer and drainage channel for retaining clay
soils;
Figure 13 illustrates an alternative embodiment for use with clay soils in
which the cavities of the blocks illustrated in Figures 8 and 9 are filled
with drainage
aggregate which forms the permeable layer;
Figure 14 is a partial isometric view of a completed wall constructed using
a fourth embodiment of the present invention whereby the strip reinforcement
is laid in
sections; and,
Figure 15 is a partial isometric view of a reinforced soil wall system
constructed using a first plurality of sections of soil reinforcement between
courses and a
second plurality of sections of soil reinforcement embedded in the backfilled
soil and
arranged in a spaced apart relationship relative to the first plurality of
sections of soil
2 0 reinforcement.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Particular embodiments of various aspects of the present invention are now
described
in the context of the construction of a single tiered straight retaining wall.
It is to be
2 5 understood that the various aspects of the present invention are readily
adaptable to
the construction of multi-tiered or curved retaining walls. The terminology
used herein
is for the purpose of describing particular embodiments only, and is not
intended to
limit the scope of the present invention. Unless defined otherwise, all
technical and
scientific terms used herein have the same meanings as commonly understood by
one
30 of ordinary skill in the art to which this invention belongs. For the
purposes of clarity,
some of the terms as used throughout this specification are now defined.
The "dredge side" of a retaining wall is the side with the lower soil surface
elevation.
The "dredge line" is the term applied to the line of intersection between the
soil surface
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on the dredge side of the wall and the wall itself. The "retained side" of the
retaining
wall is the side with the higher soil surface elevation after backfilling. The
term
"backfill" refers to any type of material, typically soil that is placed on
the retained side
of the wall. The backfill that is placed behind a reinforced soil retaining
wall is also
referred to in the art as "reinforced soil". Loose backfill can add to the
load on the
retaining wall, allows water to collect, causes settlement problems and may
not anchor
soil reinforcement materials properly. Accordingly, all backfill is compacted
to meet the
requirements of prevailing local compaction standards, the term "compaction"
referring
to the application of mechanical force to reduce the compressibility of the
backfill and
mitigate the risk of future movement of the retaining wall.
"Drainage Aggregate" is free-draining, typically angular gravel of
substantially coarse
and uniform size used to expedite drainage of moisture. For best results,
drainage
aggregate should consist of a plurality of stone particles of sufficiently
large and
common size to cause voids to exist between them to allow the passage of the
water
and should not contain fine particles that may impede water flow.
A "course" is a horizontal layer of retaining wall blocks. The "base course"
is the first
layer of blocks typically placed on top of a leveled foundation. The "capping"
is the last
2 0 or top course of blocks which may be designed for decorative appeal. The
capping is
constructed using solid (as opposed to hollow) blocks to prevent the ingress
of water
into the retaining wall. The "bond" is the arrangement or pattern of blocks
from course
to course. A block that is centered over the vertical joint created by
adjacent blocks in
the preceding course is said to be laid using a "stretcher bond".
The term "geomesh" is used throughout this specification to describe soil
reinforcement in the form of sheets of a polymeric material, typically but not
necessarily of woven construction with transverse strands integrally connected
with
longitudinal strands in a grid-like pattern.
A first embodiment of the reinforced soil retaining wall system 10 of present
invention
is now described with reference to Figures 1 to 7, the reinforced soil
retaining wall
system 10 comprising a plurality of blocks 12 arranged in courses 14 to form a
wall 16.
Soil reinforcement is provided to the wall 16 using a plurality of lengths of
strip
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reinforcement 18 inserted in and extending from the blocks 12, the strip
reinforcement
18 being buried under compacted backfill 20 either as each course 14 is laid
or after
construction of the wall 16.
With reference to Figures 1, 2(a) and 2(b), the blocks 12 used in accordance
with a
first embodiment of the reinforced soil wall system 10 comprise a front face
22, a rear
face 24 spaced from said front face by a distance defining the depth of the
block 12,
opposing side surfaces 26 and 28 respectively, spaced from each other by a
distance
defining the width of the block 12, a top surface 30 and a bottom surface 32
spaced
from the top surface 30 by a distance defining the height of the block 12. In
use, the
block 12 is positioned such that the front face 22 is directed towards the
dredge side
34 of the wall 16 with the rear face 24 being directed towards the retained
side 36 of
the wall 16. The block 12 further comprises a passage 40 extending from a
first
opening 42 in the bottom surface 32 towards the top surface 30. The first
opening 42
could equally be provided in the top surface 30. With reference to Figure 4,
the
passage 40 is configured to receive a first portion 44 of a length of strip
reinforcement
18 used to stabilize the wall 16.
Figure 1 illustrates a wall 16 constructed using a plurality of layers of
mortar 47 to
2 0 secure the position of each block 12. For mortarless construction, the
bottom surface
32 of the block 12 is provided with one or more guide slots) 50 extending from
the first
opening 42 of the passage 40 to the rear face 24 of the block 12. The guide
slot 50 is
configured to accommodate a second portion 46 of the length of strip
reinforcement 18
in such a way that the bottom surface 32 of a block 12 provided in a
subsequent
2 5 course 14' is able to sit flush against the top surface 30 of a block 12
in an underlying
preceding course 14". This is achieved by ensuring that the guide slot 50 is
of
sufficient depth to house the thickness of the length of strip reinforcement
18. The
guide slot 50 also assists in general directional alignment of the strip
reinforcement 18
towards the retained side 36 of the wall 16. A third portion 48 of the length
of strip
30 reinforcement 18 is not received within the block 12 but rather extends
outwardly away
from the rear face 24 of the block 12.
Where mortar is used in the construction of the reinforced wall retaining wall
system
10, the guide slot 50 is entirely optional and need not be present. This is
because the
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second portion 46 of the strip reinforcement 18 can be housed within the layer
of
mortar 47. Thus where mortar is used, the first portion 44 of the length of
strip
reinforcement 18 is received within the passage 40 of the block 12, the second
portion
46 of the length of strip reinforcement 18 is arranged to extend in coplanar
alignment
with either the top or bottom surface 30 or 32, respectively of the block 12
through the
mortar layer 17, and the third portion 48 of the length of strip reinforcement
18 is
arranged to extend outwardly from the rear face 24 of the block 12 to be
secured in
position substantially perpendicular to the wall 16 during backfilling and
compaction.
It is to be understood that the passage 40 need not extend through the full
height of
the block 12 provided only that the length of strip reinforcement 18 is caused
to bend
through an angle, preferably through approximately a 90 degree angle in order
to
resist pull-out forces that are applied to the strip reinforcement 18 after
backfilling and
compaction which put the strip reinforcement 18 into tension. It is preferable
that the
passage 40 is substantially vertically oriented relative to the top or base
surface 30 or
32, respectively of the block 12. For this reason, the strip reinforcement 18
is
resiliently flexible allowing it to be bent into position through a 90 degree
angle. It is
preferable that the passage 40 be positioned towards the front face 22 of the
block 12.
2 0 It is also to be understood that the length of strip reinforcement 18 is
not directly
mechanically coupled to the block 12. Its position is effectively secured
during the
backfilling and compaction operations. In use, the length of strip
reinforcement 18 is
inserted into block 12 through the first opening 42 in so that the first
portion 44 is
received within the passage 40 and bent in place so that the second portion 46
is
accommodated within the guide slot 50 for mortarless construction or within a
layer of
mortar 47 for construction using cement mortar. If the passage 40 extends
through
the full height of the block 12 from the bottom surface 32 through to the top
surface 30,
the passage 40 terminates in a second opening 52 provided in the top surface
30. The
length of strip reinforcement 18 may be threaded through the passage 40
through
either the first opening 42 or the second opening 52.
The strip reinforcement 18 may be made from any other material known to be
suitable
for soil reinforcement applications, for example, galvanized steel strip,
knitted high
strength polyester yarn, strips of polymer textured fabric, or high density
polyethylene.
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Conveniently, each length of strip reinforcement 18 may be cut from a sheet of
mesh
reinforcement, for example, geomesh and accordingly need not comprise a single
longitudinal section. The strip reinforcement 18 may equally comprise a
plurality of
longitudinal sections held together by a plurality of horizontal sections,
provided only
that the strip reinforcement 18 is still insertable in the passage 40. The
length of the
strip reinforcement 18 required to stabilize the wall 16 is directly
proportion to the
height of the wall 16 and should be at least 0.7 x height of the wall. For
poor soil and
heavier loads the strip reinforcement 18 should be longer and or the quantity
greater.
The material of construction of the blocks is equally unimportant to the
working of the
present invention. Typically each block 12 would be constructed from concrete
which
is made from a mixture of cement, water and one or more types of aggregate(s).
The
blocks may equally be constructed of other materials known to be suitable for
retaining
walls including geopolymers, limestone or metal. The colour andlor texture of
the
blocks is also not important and may be varied by, for example, adding oxides
to the
concrete or geopolymer or changing the type of aggregate used for aesthetic
appeal.
In order to facilitate a better understanding of the various aspects of the
first
embodiment of the present invention, a method of construction of a reinforced
soil
2 0 retaining wall using the blocks 12 will now be described in the context of
mortared
construction. It is to be understood that the reinforced soil retaining wall
system 10 is
equally adaptable to mortarless construction as described below with respect
to a
second embodiment of the present invention.
2 5 The first step is the preparation of the site and the laying of a level
foundation 60. An
area is excavated on the retained side of the wall 16 to accommodate the
design
length of the soil reinforcement 18 which will vary in direct proportion to
the height of
the wall 16 above the dredge line 38. Any surface vegetation or organics in
the soil
should be removed if it is intended to be used as part of the backfill 20. A
trench is
3 0 dug along the full length of the wall 16 and the foundation 60 is prepared
using a
simple concrete slab or formed using any suitable compactable granular
material such
as crushed stone, road base aggregate, gravel, or coarse sand. The foundation
60
should be level along the full length of the wall 16 for best results.
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The base course 62 is then laid on the level foundation 60. As is the case for
any wall
constructed using blocks, it is important that the base course be laid with
particular
care as any irregularities in the laying of the base course will become
exaggerated as
the height of the wall increases for mortarless construction. This is less
important
when using mortar to construct the retaining wall as any irregularities in the
laying of
the base course can be corrected by adjusting the amount of mortar. To assist
in
correct placement of the base course blocks, a string line (not shown) or
other suitable
alignment 'guide such as a laser sight should be used to guide the positioning
of the
blocks. A level indicating device such as a spirit level (not shown) should be
used to
check the level of each block in both the front-to-back and side-to-side
directions after
placement. A rubber mallet or other suitable dead blow hammer may be used to
help
adjust the position of a given block relative to the string line or spirit
level as required.
Unevenness in the base course can be corrected if needed using a suitable
level
correction device, for example, one or more shims (not shown).
With reference to Figure 1, the base course 62 is laid such that the blocks
are partially
embedded below the dredge line 38. Partial embedment of the base course blocks
provides reinforcement to the base course 62 to reduce the risk of erosion
under the
wall 16 at the dredge line 38. There is no requirement that any soil
reinforcement be
2 0 used to provide support to the base course 62 and accordingly, the blocks
12 of the
present invention need not be used in the construction of the base course 62.
Any
suitably sized block may be used, including solid blocks if convenient. If
hollow blocks
are used in the construction of the base course 62, the cavities of the hollow
blocks
may be filled either with drainage aggregate or an impermeable material such
as
concrete or cement. When aggregate is used, this should be tamped down to
ensure
that the cavities are filled, taking care not to disturb the position of the
blocks.
Once the base course 62 has been laid, a suitable infill soil is used as the
backfill 20
placed behind the base course 62. The backfill 20 is then compacted using any
suitable compaction device such as a hand tamper or a mechanical plate
compactor
such as a vibratory-plate compactor. Compaction should be carried out to
applicable
civil engineering compaction standards which may vary from country to country.
It is
considered to be a matter of routine to a person skilled in the art to
appreciate the level
of compaction required to achieve civil engineering certification of the
completed
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retaining wall.
The second and each subsequent course of blocks 12 apart from the final course
64
are constructed using the blocks 12 of the present invention. Prior to laying
each
subsequent course 14, any debris or surface material should be removed from
the top
surfaces) 30 of the blocks 12 of the preceding underlying course. This
provides a
smooth surface for the placement of the next course of blocks. It is further
recommended to reset the string line for each course and use the spirit level
in the
manner described above to assist in correct alignment of the blocks 12. The
bond of
each subsequent course is generally set such that the vertical seams 66 are
offset for
maximum strength. It is to be understood that the blocks need not be placed in
the
stretcher bond arrangement
With reference to Figure 5, a length of strip reinforcement 18 is threaded
through the
first opening 42 and up into the passage 40 such that the first portion 44 is
received
within the passage 40. The length of strip reinforcement 18 is then bent such
that the
second portion 46 is arranged to extend along the bottom surface 32 from the
first
opening 42 towards the rear face 24. A layer of mortar 47 is then applied and
the
block 12, with the length of strip reinforcement 18 inserted therein, is laid
over the
2 0 blocks 12 forming the preceding course 14. The third portion 48 of the
strip
reinforcement 18 extends outwardly from the block 12 in the direction of the
retained
side 36 of the wall 16. Backfilling and compaction to anchor the strip
reinforcement 18
in place may be conducted either after each course 14 is laid or after the
wall 16 has
been completed and is conducted in an analogous manner as described above in
relation to the laying of the base course 62.
Immediately prior to backfilling after each or all of the second and
subsequent courses
14 have been laid, each of the third portions 48 of the lengths of strip
reinforcement 18
is oriented so as to be approximately perpendicular to the wall 16 and in
general
coplanar alignment with respect to the top or bottom surface 30 or 32,
respectively of
the block 12. Each third portion 48 is then held in this position when covered
with infill
soil during the next backfilling and compaction operation. Advantageously, it
is
possible to use separate crews during the construction of the reinforced soil
retaining
wall system of the present invention - a block laying crew being responsible
for
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inserting the strip reinforcement 18 in the blocks 12 during laying thereof
and an earth
compaction crew being responsible for orienting the position of each of the
third
portions 48 during backfilling and compaction operations after the wall. has
been
completed.
Additional courses 14 are laid in this manner until the wall 16 is of the
required height.
During backfilling and compaction, the weight of the backfill 20 behind the
wall 16 may
cause the wall to cant towards the dredge side 34. To offset this, each course
14 may
be set back approximately 4 mm or more from the preceding course 14 towards
the
retained side 36 of the wall 16 so that the completed wall 16 cants back by 2%
or more
towards the retained side 36 prior to backfilling. After backfilling and
compaction, the
wall 16 is substantially vertical.
If desired the final course 64 may take the form of capping as illustrated in
Figure 7, to
give the wall a more aesthetically pleasing appearance. The capping 64 may be
secured in position using a waterproof construction adhesive and is of solid
construction to prevent water from entering the passages 40 provided in the
blocks 12
that are used to construct the wall 16.
2 0 When the soil being retained has a low permeability such as clay, a layer
of drainage
aggregate 104 may be placed immediately adjacent the retained side 36 of the
wall 16
to prevent a buildup of hydrostatic pressure against this side of the wall.
A second embodiment of the blocks of the present invention is illustrated in
Figures 8
to 10 for which like reference numerals refer to like parts. In this
embodiment the
blocks 12 are provided with a plurality of cavities 72 (in this example, two
such cavities
are shown) each cavity 72 extending through the full height of the block 12
and able to
serve the same function as the passage 40 of the block 12 described above in
relation
to the first embodiment. These blocks 12 are hereinafter referred to as
"hollow
3 0 blocks". One of the advantages of using hollow blocks 12 is that the
effective weight
of each block is lower than the weight of a block of solid construction of
equivalent
size, making the hollow blocks easier to carry, stack and lay. Another
advantage is
that the cavities 72 have a larger volume than the passage 40 of the first
embodiment,
making insertion of the length or lengths of strip reinforcement 18 into or
through the
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block 12 easier.
For mortarless construction, each of the hollow blocks 12 is provided with one
or more
guide slots) 50 which serve the same function as described above in relation
to the
first embodiment. Where mortar is used, the guide slots) 50 are not required.
It is not
necessary for a guide slot 50 to be provided for each of the cavities 72.
In order to facilitate a better understanding of the various aspects of the
second
embodiment of the present invention, a method of mortarless construction of a
reinforced soil retaining wall using the hollow blocks 12 will now be
described with
reference to Figures 8 to 10. It is to be understood that the reinforced soil
retaining
wall system 10 is equally adaptable to construction using mortar in an
analogous
manner as described above with respect to the first embodiment of the present
invention.
During construction of the wall 16 using the hollow blocks 12, the foundation
60 and
the base course 62 are laid in an analogous manner to that described above in
relation
to the first embodiment. Backfilling and compaction is conducted after the
base
course 62 has been laid.
2 0 The second and each subsequent course of blocks 12 (apart from the final
course 64)
are constructed using the hollow blocks 12. With reference to Figure 9, a
length of
strip reinforcement 18 is threaded through one of the cavities 72 such that a
first
portion 44 is received within the cavity 72. The length of strip reinforcement
18 is then
bent through substantially 90 degrees such that the second portion 46 is
accommodated within the guide slot 50. The first portion 44 is positioned
within the
cavity 72 towards the front face 22 of the block 12 to provide maximum
resistance to
overturning forces on the wall 16.
When the hollow block 12 with the length of strip reinforcement 18 inserted is
laid over
the blocks forming the preceding course 14, the guide slot 50 is positioned
towards the
retained side 36 of the wall 16. As or after each new course is laid, the
cavities 72 of
the hollow blocks 12 are filled with a quantity of ballast 76 in the form of
an
impermeable material, for example, concrete, or a permeable material, for
example,
drainage aggregate. Where drainage aggregate is used, the material should be
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tamped down within the cavity to ensure that no voids are left. The ballast 76
assists
in providing stability to the wall, helps to retain the position of the strip
reinforcement 18
relative to the cavity 72 and helps to resist movement of the blocks during
the
backfilling and compaction operations. The drainage aggregate also acts as a
cushion
to protect the strip reinforcement from damage that may occur if the strip
reinforcement is allowed to come into contact with either of the rearward
edges 78 of
the cavity 72. Moreover, since concrete has poor bending strength, the
aggregate
helps to distribute the tensile forces acting on the strip reinforcement 18
over a greater
surface area that the inside rear face 80 of the cavity 72.
After the hollow cavities 72 have been filled with the quantity of ballast 76,
the wall 16
is backfilled using an appropriate infill soil and compacted in the manner
described
above in relation to the base course 62. Immediately prior to backfilling
after the
second or subsequent course 14 has been laid, the third portion 48 of the
length of
strip reinforcement 18 is oriented so as to be approximately perpendicular to
the wall
16 and in general coplanar alignment with respect to the bottom surface 32 of
the
block 12. The third portion 48 is then held in this position when covered with
infill soil
either after each course 14 is laid or when the wall 16 has been completed.
With reference to Figures 9 and 10, this second embodiment differs from the
first
embodiment in that the effective length of the strip reinforcement 18 has been
approximately doubled such that a fourth portion 74 of the strip reinforcement
18
extends from the first portion 44 which is received within the cavity 72. This
fourth
portion 74 is caused to drape over the dredge side 34 of the wall 16 during
backfilling
and compaction of the course 14 that has just been laid. During backfilling
and
compaction, the third and fourth portions 48 and 74 is laid over a layer of
previously
compacted soil and oriented so as to be approximately perpendicular to the
wall 16
and in general coplanar alignment with respect to the top or bottom surfaces
30 or 32,
respectively, of the hollow blocks 12.
Additional courses 14 are laid in this manner until the wall 16 is of the
required height.
If desired the final course 64 may take the form of capping as described
above.
Backfilling and compaction can be conducted after each course 14 is laid or
after the
wall 16 has been completed.
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To provide additional resistance against shearing across adjacent courses 14
in the
wall 16, the system 10 may further include a plurality of shear pins 82
illustrated in
Figure 9, in the form of a plurality of rectangular blocks made of concrete
and inserted
into the cavity 72 prior to the cavity 72 being filled with the quantity of
ballast 76. It is
worth noting that the use of shear pins 82 is entirely optional in that it has
been found
that when coarse aggregate is used as the ballast 76, resistance to shear
forces is
provided by the particles of the coarse aggregate themselves. When the
cavities 72
have been filled with coarse aggregate, movement of one block 12 in the wall
16
relative to an adjacent block in an adjacent course 14 would require
displacement of
the particles of coarse aggregate relative to each other. Because the drainage
aggregate particles are generally of the same size, this is difficult to
achieve, providing
additional resistance to shear between adjacent courses.
It is equally possible although more cumbersome to thread the strip
reinforcement 18
through a plurality of blocks 12 in adjacent courses 14 as illustrated in
Figure 9. It
should be noted that it is not necessary for every block 12 to be provided
with a length
of strip reinforcement unless large surcharge loads are anticipated. It is
considered a
matter of routine for a person skilled in the art to determine the requisite
amount of
2 0 strip reinforcement required for the particular material of construction
of the wall, its
height, the anticipated loads and the type of backfill being retained.
A third embodiment of the reinforced soil retaining wall system 10 and blocks
12 of the
present invention is illustrated in Figure 11 for which like reference
numerals refer to
2 5 like parts. During construction at a building site, the retaining wall is
often the first
structure installed followed by other installations such as plumbing,
electrical,
foundations and the like. In this third embodiment, the system 10 comprises a
composite wall 90 divided at a transition depth 92 into an upper section 94
and a lower
section 96. The lower section 96 of the composite wall is a reinforced soil
retaining
3 0 wall 16 which is constructed in an analogous manner as described above in
relation to
either the first or second embodiments. The lower section 96 is laid with
backfilling
and compaction is carried out on the retained side 36 of the composite wall
90. The
upper section 94 of the composite wall 90 is then constructed as a gravity
wall having a
height equal to the transition depth 92. The gravity wall 94 is constructed in
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accordance with the practices of the background art.
The upper section 94 may equally take the form of a steel reinforced
cantilever wall by
positioning a plurality of steel bars (not shown) through the cavities 72 of
the blocks
used in the construction of the upper section 94 of the composite wall 90, the
cavities
72 thereafter being filled with concrete to hold the steel bars in place. A
plurality of
shear pins 82 may be installed inside the blocks 12 in the uppermost course of
the
lower section 96 of the composite wall 90 at the transition depth 92 to
provide
resistance to shearing of the upper section 94 relative to the lower section
96.
This third embodiment was based on a realization that the top 0.1-0.9 meters
of the
retaining wall is effectively self-supporting. The transition depth 92 depends
in part on
the anticipated depth of any installations or structures to be constructed on
the
retained side of the wall, but it is anticipated that the transition depth
will not exceed
one metre and will more likely be around 0.4 to 0.6m below the final
anticipated height
of the composite wall 90.
A soil reinforcement protection barrier 98 may be installed at the transition
depth 92 in
general coplanar alignment with respect to the top surface 30 of the uppermost
course
2 0 14 of the lower section 96. The barrier 98 serves as a visual or physical
barrier to
protect the strip reinforcement 18 from damage during subsequent building
operations
adjacent to the completed retaining wall. Accordingly, the barrier 98 may take
the
form of a thin planar strip of plastic that provides a visual indication that
the transition
depth has been reached during subsequent digging. Alternatively, the barrier
98 may
2 5 take the form of a concrete slab which provides physical resistance to
penetration
during subsequent digging and providing additional protection to the strip
reinforcement 18 below.
A fourth embodiment of the system 10 and blocks 12 of the present invention is
30 illustrated in Figures 12 and 13 for which like reference numerals refer to
like parts.
This embodiment has been designed specifically to deal with problems
associated with
using backfill such as clay soils which have a very slow rate of permeation of
water.
As a result of the low permeability of the soil, the backfill 20 may become
saturated
over time, for example due to precipitation, resulting in a buildup in water
being stored
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on the retained side 32 of the wall 16. This causes hydrostatic pressure on
the wall 16
to increase, effectively pushing against the retained side 32 of the wall 16.
One way to overcome this problem is to place a vertically oriented permeable
layer 104
of permeable material such as drainage aggregate adjacent to the retained side
32 of
the wall 16 to allow water to drain under gravity from behind the wall through
a
drainage channel 106 positioned towards the base of the wall 16 and extending
from
the permeable layer 104 to the dredge side 34 of the wall 16 above the dredge
line 38.
The drainage aggregate would typically consist of a plurality of stone
particles of
sufficiently large and common size to cause voids to exist between them to
allow the
passage of the water. The permeable layer 104 may be laid in sections as each
course 14 is laid ensuring that the lengths of strip reinforcement 18 extend
through the
permeable layer 104 to be anchored in the backfilled and compacted soil 20
behind the
permeable layer 104. The wall 16 is otherwise constructed in an analogous
manner as
described above in relation to any one of the earlier embodiments.
Drainage aggregate is easily dislodged by workmen during backfilling and
compaction
or laying operations and the block laying crew must clear any loose stones
before
laying the next course of blocks. In addition, the permeable layer 104 is not
self
2 0 supporting and this can result in a thicker layer being used than would
otherwise be
required leading to increased materials and installation costs.
To alleviate this potential problem, the hollow blocks of the second
embodiment are
particularly suited for use with clay soils. If the cavities 72 are filled
with drainage
2 5 aggregate, the wall itself can serve the function of the permeable layer
104 with the
guide slots) 50 provided in each hollow block 12 serving the function of a
plurality of
drainage channels 106 each directing water from the retained side 36 of the
wall 16
into the cavities 72 filled with drainage aggregate. In this embodiment, the
blocks 12
used in the construction of the base course 62 are inverted such that the
guide slots)
3 0 direct water from the permeable layer 104 towards the dredge side 34 of
the wall 16 to
allow the water to drain out of the wall itself.
The size and configuration of the guide slots) 50 may be varied to suit the
maximum
predicted rainfall for a given geographical location to drain from the
retained soil at a
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rate faster than the known flow capacity of the retained backfill 20. The
accumulated
liquid inside the permeable layer 104 defined by the filled cavities 72 of the
hollow
blocks 12 generates a head of pressure that encourages the flow of liquid out
through
the guide slots 50 of the inverted blocks 12 forming the base course 62.
It is to be understood that the base course 62 in this fourth embodiment need
not be
constructed using inverted hollow blocks 12 and could equally be constructed
using the
solid blocks of the first embodiment or any other type of solid block provided
only that
the wall 16 is provided with at least one drainage channel 106 of a suitable
size to
direct the flow of liquid from within the permeable layer 104 towards the
dredge side 34
of the wall 16.
A fifth embodiment of the system 10 and blocks 12 of the present invention is
illustrated in Figure 14, for which like reference numerals refer to like
parts. As briefly
described above in relation to the first and second embodiments, each length
of strip
reinforcement 18 is directly proportional to the height of the anticipated
final height of
the wall 16. This can make threading of the strip reinforcement 18 through a
through-
thickness passage 40 or the cavity 72 difficult to achieve for walls that are
high,
particular for walls higher than around 1.6 metres. It is not only the
threading of the
strip reinforcement 18 through the cavity 72 or passage 40 of each block 12
that
becomes increasingly difficult as the height of the wall 16 increases, but
also the
general handling of long lengths of strip reinforcement 18 which has the
tendency to
curl and may snag more readily when trying to lay each course 14 of the blocks
12.
2 5 This problem is overcome in this fifth embodiment by splitting the length
of strip
reinforcement into a short threaded section 100 and a longer free section 102.
Each
short threaded section 100 is inserted through the block 12 in an analogous
manner as
described above in relation to any one of the first three embodiments. The
longer free
section 102 is then laid separately during the backfilling and compaction
operations
either after each course 14 has been completed or after the wall 16 has been
completed. Each free section 102 may be fixedly attached to a corresponding
threaded section 100 or laid so as to extend substantially perpendicularly
away from
the wall 16 on the retained side 32 at any depth within the backfill 20.
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After backfilling and compaction, the combined effect of laying the free
section 102
separately and/or interdependently of the threaded section 100 is the same as
laying
one continuous length of strip reinforcement 18, provided only that the free
section 102
extends away from the retained side 32 of the wall 16 at least through the
anticipated
plane of rupture 108 of the backfill 20. The plane of rupture 110 runs at an
angle (3
relative to the dredge line 38 of the wall 16, the angle a being the Rankin
angle (or
angle of internal friction) which is a function of the type of backfill 20
being retained.
A further advantage of using this embodiment, even for shorter walls is that
it allows
for separate crews to be used - a block laying crew being responsible for
inserting the
threaded sections 100 in the blocks 12 and an earth compaction crew being
responsible for laying the free sections 102 during backfilling and
compaction.
It has further been realized that the threaded and free sections 100 and 102
need not
be provided in the form of lengths of strip reinforcement 18 but may equally
be
provided using grid or sheet reinforcement, for example, geomesh. Figure 15
thus
illustrates a reinforced soil retaining wall system 110 for which like
reference numerals
refer to like parts. The blocks 112 of this embodiment may be any standard
type of
block used for the construction of a reinforced soil retaining wall or the
blocks 12
2 0 described above for any of the first to fifth embodiments. The reinforced
soil retaining
wall system 110 comprises a first plurality of sections of soil reinforcement
114 for
anchoring the wall 16 to the backfill 20, the first plurality of sections of
soil
reinforcement 114 arranged between adjacent courses 14' and 14" of the wall 16
and
extending outwardly from the rear face 24 of the blocks 112 on the retained
side 36 of
the wall 16. In the embodiment illustrated in Figure 15, the first plurality
of sections of
soil reinforcement 114 take the form of short sections of geomesh. With
reference to
Figure 14, it is to be understood that the first plurality of sections of soil
reinforcement
114 could equally be provided using elongate strips such as the threaded
sections 100
illustrated in Figure 14 and that the elongate strips need not be threaded
through the
blocks, provided only that they are arranged between adjacent courses 14' and
14"
and extend outwardly from the rear face 24 of the blocks 12 on the retained
side 36 of
the wall 16.
The reinforced soil retaining wall system 110 further comprises a second
plurality of
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sections of soil reinforcement 116 for stabilizing the backfilled and
compacted soil on
the retained side 36 of the wall 16, the second plurality of sections of soil
reinforcement
116 being spaced apart from the first plurality of sections of soil
reinforcement 114 and
arranged to extend substantially perpendicular to the wall 16 during
backfilling and
compaction. With reference to Figure 15, the second plurality of sections of
soil
reinforcement 116 are provided in the form of large planar sheets of geomesh
which
are spaced apart from the first plurality of sections of geomesh 114. Whilst
geomesh
is preferred, other types of soil reinforcement may be used with suitable
materials
being those that are resistant to aging in the particular soil environment and
which
have sufficient tensile strength to carry the anticipated loads in use.
In Figure 15, the second plurality of sections of soil reinforcement 114 is
positioned
immediately adjacent to the retained side 36 of the wall 16. It is to be
understood that
the second plurality of sections of soil reinforcement 114 could equally be
spaced apart
from the rear face 24 of the blocks 112 on the retained side 36 of the wall
16.
In the embodiment illustrated in Figure 15, the first and second plurality of
sections of
soil reinforcement 114 and 116, respectively are arranged in horizontal
coplanar
arrangement with respect to each other with the first plurality of sections of
soil
2 0 reinforcement 116 being arranged in a first layer 118 and the second
plurality of
sections of soil reinforcement 116 are arranged in a second layer 120 offset
from the
first layer 118. The spacing between the first and second layers 118 and 120
respectively may vary depending on a number of factors but would generally not
be
expected to exceed one metre.
The first plurality of sections of soil reinforcement 114 are arranged in
coplanar
alignment with the top or base surface 30 or 32, respectively of one or more
of the
plurality of blocks 112 immediately prior to backfilling and compacting. The
second
plurality of sections of soil reinforcement 116 need not be arranged in
coplanar
3 0 alignment with the top or base surfaces 30 or 32, respectively, but could
equally be
arranged in alignment with a plane 122 that intersects the block 112 at a
height
intermediate between the top and base surfaces 30 or 32.
The first plurality of sections of soil reinforcement 114 may be fixedly held
between
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adjacent courses 14' and 14" of blocks 112 using mortar or held by gravity
under the
natural weight of the blocks forming the courses above.
Depending on a number of factors including the type and quality of the soil
used for the
backfill 20, the length of the second plurality of sections of soil
reinforcement 114 may
be equal to at least 60%, 70% or 80% of the height of the wall 16 and should
extend
through at least the anticipated plane of rupture 108 of the backfill 20. It
is considered
to be a matter of routine to a person skilled in the art to determine the
quantity and
length of second plurality of sections of soil reinforcement 114 required for
a particular
application depending on such factors as the slope stability, the angle of
internal
friction (3 of the soil, soil cohesion and the moist unit weight of the soil
as well as such
factors as the height of the wall, any surcharge loads and the top slope
angle. For
example, for poor quality soil, a larger quantity of the second plurality of
sections of soil
reinforcement 114 may be required to provide sufficient stability to the wall.
Where a
larger quantity is used, the tensile strength of each individual section rieed
not be as
great as less load is carried by each individual section.
As illustrated in Figure 15, the wall 16 may be constructed using the hollow
blocks
described above with respect to the second embodiment with the exception that
the
2 0 guide slots 50 are not required. The cavities 72 of the hollow blocks 112
are
configured to receive a quantity of ballast 76 as described above, the ballast
76 being
either drainage aggregate or an impermeable material such as concrete added to
the
cavities 72 apart the blocks 112 have been laid. One or more shear pins 82 may
be
provided to resist sliding movement of a first course 14' over an adjacent
second
course 14" if desired. A drainage channel 106 configured to direct moisture
from the
retained side 36 of the wall 16 towards the dredge side 34 of the wall 16 may
also be
provided if desired and is particular advantageous when the backfill 20 is a
clay soil in
order to relieve hydrostatic pressure that may otherwise be exerted on the
wall 16.
The reinforced soil retaining wall system 110 is equally adaptable for
construction as a
3 0 composite wall 90 in an analogous manner as described above.
One embodiment of the method of construction of a reinforced soil retaining
wall 110 is
now described with reference to Figure 15 in the context of mortarless
construction.
It is to be understood that the reinforced soil retaining wall system 110 is
equally
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adaptable to mortared construction, the mortar being used in part to secure
the
position of the first plurality of sections of soil reinforcement 114 between
adjacent
courses 14.
A foundation 60 and base course 62 are laid in an analogous manner as
described
above. Once the base course 62 has been laid, a suitable infill soil is used
as the
backfill 20 placed behind the base course 62 and compacted to applicable civil
engineering compaction standards which may vary from country to country.
Before a
subsequent course is laid, a first plurality of sections of soil reinforcement
114 for
anchoring the wall 16 to the backfill 20 is arranged along the top surtaces 30
of the
blocks 112 forming the base course 62. The first plurality of sections of soil
reinforcement 114 are arranged to extend outwardly from the rear face 24 of
the
blocks 112 on the retained side 36 of the wall 16. It is to be understood that
first
plurality of sections of soil reinforcement 114 need not extend along the full
length of
the wall 16 and need not be provided between each of the adjacent courses 14
forming the wall 16. Using mortarless construction, the first plurality of
sections of
soil reinforcement 114 are held in place by the weight of the next course of
blocks laid
over the top of them. Where mortar is used, the layers of mortar 47 assist in
retaining
the position of the first plurality of sections of soil reinforcement 114
prior to backfilling.
The second plurality of sections of soil reinforcement 116 are laid during
backfilling
and compaction which may be conducted either after each course 14 is laid or
after the
wall 16 has been completed and is conducted in an analogous manner as
described
above in relation to the laying of the base course 62. The second plurality of
sections
2 5 of soil reinforcement 116 are arranged in such a way that they are spaced
apart from
the first plurality of sections of soil reinforcement 114 and extend
substantially
perpendicular to the wall 16 during backfilling and compaction of a quantity
of backfill
20 behind the rear face 24 of the blocks 112 so as to anchor the position of
the first
and second plurality of sections of soil reinforcement 114 and 116,
respectively.
Additional courses 14 are laid in this manner until the wall 16 is of the
required height.
If desired, the final course 64 may take the form of capping as illustrated in
Figure 7, to
give the wall a more aesthetically pleasing appearance. When the soil being
retained
has a low permeability such as clay, a layer of drainage aggregate 104 may be
placed
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immediately adjacent the retained side 36 of the wall 16 to prevent a buildup
of
hydrostatic pressure against this side of the wall.
If hollow blocks are used to construct the wall 16, the method of construction
further
comprises the step of adding a quantity of ballast 76 to the cavities 72
either after each
block or each course of blocks has been laid in an analogous manner as
described
above with reference to the second embodiment. Where shear pins 82 are used to
resist sliding movement of a first course 14' over an adjacent second course
14", the
placement thereof should not interfere with the placement of the first
plurality of
sections of soil reinforcement 114. Accordingly, shear pins 82 may be provided
between every second course 14 of blocks 112 with the first plurality of
sections of soil
reinforcement 114 being provided between the remaining courses.
Now that the preferred embodiments of the present invention have been
described in
detail, the present invention has a number of advantages over the prior art,
including
the following:
a) lightweight hollow blocks permit rapid installation and reduce
the likelihood of work-related injury to the block laying crew;
2 0 b) the strip reinforcement is not mechanically coupled to the
blocks thereby reducing the component cost of the block as well as the labor
time
associated with installing the blocks. This also reduces the opportunity for
incorrect
attachment of the reinforcement to the facing block;
c) the blocks may be manufactured in a standard rectangular
2 5 shape and laid in a standard interlocking brick pattern which increases
the aesthetics
of the wall and also increases its strength. The block can be cheaply and
readily mass
produced as there is no need to incorporate mechanical fasteners into the
blocks; and,
d) the system requires no direct mechanical attachment of the
strip reinforcement to the blocks which allows for plastic to be used instead
of
30 galvanized steel which reduces the material costs. Using prior art methods,
holes
were needed in the strip reinforcement which made the use of plastics
impermissible
as most plastic materials have poor resistance to tearing.
It will be apparent to persons skilled in the relevant art that numerous
variations and
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modifications can be made without departing from the basic inventive concepts.
For
example, the front face of the block need not be planar but can be provided
with a
different shape or surface texture on the dredge side of the wall. Similarly,
the wall
system could further include a protective or decorative facing panel (not
shown)
applied to the dredge side of the wall to alter the aesthetic appeal thereof
after
construction. Whilst in all of the illustrated embodiments, a single length of
strip
reinforcement has been inserted per block, it is equally permissible for a
plurality of
lengths of strip reinforcement to be placed in a passage or cavity of a single
block.
The present invention is equally applicable to the construction of a tiered
retaining wall
by building a plurality of walls, each upper wall set back from an underlying
wall. Tiered
walls can be attractive alternatives to single tall walls and can provide
areas for
plantings. To prevent an upper wall from placing a load on a lower wall, the
upper wall
should be built behind the lower wall a distance of at least twice the height
of the lower
wall. All such modifications and variations are considered to be within the
scope of the
present invention, the nature of which is to be determined from the foregoing
description and the appended claims.
