The present invention relates to an apparatus for restricting or
preventing the flow of water across the joints of foundation elements, such as
between or along individual diaphragm wall panels or between or along individual
secant wall piles. The present invention also relates to a method of installing
a waterstop at or near the joints between adjacent foundation elements.
A diaphragm wall is made by casting a series of concrete panels,
which may be reinforced, in excavated trenches as described, for example, in EP
0 101 350 and EP 0 402 247. In some cases, alternate 'primary' panels are constructed
first, followed by infill (i.e. closing) 'secondary' panels. The installation sequence
would be, for example, panels 1, 3, 5, 7, 9, 11 etc. followed by panels 2, 4,
6, 8, 10 etc. In other cases, only a few 'primary' panels are first constructed,
for example panels 1, 10 and 20. Following this, a series of 'continuity' panels
2, 11, 3, 12 etc. are installed, with the diaphragm wall being completed by 'closing'
panels 9 and 19. All primary panels require the use of shutters at each edge of
their respective trenches in order to provide well-defined edges to each panel
so as to ensure that the joins between adjacent panels may be made watertight.
Continuity panels, in contrast, require only one shutter at the edge of the trench
furthest away from the previously cast panel. No shutters are required for closing
panels. The shutters are conventionally known as 'stop-ends', and provide the
concrete at each vertical edge of the panels with a predetermined shape.
In order to reduce water leakage across the joints between panels,
it is possible to install a waterbar between adjacent panels with particular types
of stop end as described in EP0101350. A waterbar comprises a strip of suitable
material, for example rubber or PVC, which has one longitudinal edge embedded in
the edge of one cast panel and the other longitudinal edge embedded in the adjacent
panel. Preferably, the waterbar extends over substantially the entire height of
the diaphragm wall. Such a waterbar may be installed by employing a stop-end provided
with a slot in its face into which the waterbar may be fitted, with about one
half of its width remaining exposed. When concrete is poured into the trench on
this side of the stop-end and allowed to set, the stop-end may subsequently be
removed so as to leave approximately half the waterbar embedded in the resulting
concrete panel. When the next panel is cast, the remaining exposed portion of
the waterbar will become embedded in concrete, thereby resulting in a seal between
the two adjacent panels. Typical waterbars have beaded longitudinal edges, giving
the waterbar a dumb-bell shaped cross-section, with an optional central bulb.
As is well-known, concrete does not bond well to rubber or PVC; therefore,
loss of intimate contact can occur between the concrete foundation element and
the waterbar. There is therefore a risk that water will leak through the joint.
The loss of intimate contact may be a result of the way in which the foundation
element and waterbar were installed or it may be due to the relative movement
of adjacent elements.
In United Kingdom patent application 2325262, a two-part hydrophilic
waterbar was demonstrated. If the hydrophilic element becomes wetted, as a result
of water leaking through the joint, the hydrophilic material swells, thereby forming
a seal between the two adjacent members.
There are a number of limitations/problems associated with known
waterbar systems. For example, all of the known types of waterbars require the
use of a stop-end to facilitate the installation of the waterbar. However, in
some underground structures it may not always be possible or desirable to use stop-ends
between adjacent elements. In these cases a waterbar can not be installed and
so if the installation of a waterbar is required, the choice of construction of
the diaphragm wall panels is restricted. For example, diaphragm walls can be excavated
by means of "hydromills". A hydromill is an apparatus for drilling into the ground
and is equipped at the base with one or more pairs of contra-rotating drums. The
drums cut the soil which is then excavated from the base by hydraulic means, such
as by the circulation of drilling muds. Usually, when constructing diaphragm walls
using this apparatus, a series of primary and secondary panels are formed wherein
the second panels "cut back" into the vertical edge of the primary panels. Stop-ends
are not normally used, in which case it is not possible to install a waterbar.
Furthermore, underground structures such as secant pile walls, which
comprise a series of primary (conventionally called "female") and secondary (conventionally
called "male") piles to not involve the use of stop-ends. Pile construction can
be by a variety of methods such as oscillated casing with rotary rig or grab,
CFA methods or rotary boring without casing. At present there are no suitable apparatus
which can be installed for restricting the flow of water along or across the vertical
joints in secant pile walls.
Another limitation suffered by the known waterbar systems, is that
although the waterbar will substantially prevent the flow of water horizontally
across the joint between adjacent elements, water can still rise up the joint
in a vertical direction between the two panels. In order to demonstrate this consider:
a peripheral diaphragm wall which is installed in soil strata, where the lower
end of the diaphragm wall is situated in water-bearing strata. Assume that a vertical
waterbar has been effectively installed across the joints between adjacent panels,
at or near the centre of the wall thickness, and that it extends to the base of
the diaphragm wall.
After the wall has been exposed (e.g. for a basement) the vertical
waterbar will prevent movement of water horizontally, from behind the diaphragm
wall through to the exposed face. However, there is a potential for water to rise
up the joint between two panels in the zone between the exposed face and the waterbar.
The present invention seeks to mitigate the aforementioned limitations
and provides a waterstop, and a method of installing the same, which serves to
resist the flow of water along or across the joints between adjacent foundation
elements. The waterstop of the present invention does not depend upon the provision
of a stop-end for its installation, and can therefore be advantageously employed
in subterranean constructions such as secant pile walls and diaphragm walls, including
those excavated by means of hydromills. It should however be appreciated that in
many cases the elements will still be provided with stop-ends in order to provide
the concrete at each vertical edge with a predetermined shape.
The installation of a waterstop according to the present invention
is particularly appropriate for "open bore" operations in which the soil is excavated
and the resultant hole is then filled with concrete or grout.
According to one aspect of the present invention, there is provided
a waterstop for resisting the flow of water along the interface between two adjacent
foundation elements, the waterstop comprising one or more longitudinal strips
of hydrophilic material, characterised in that the waterstop forms an integral
part of one of the adjacent foundation elements and wherein the hydrophilic strips
extend vertically from a position at or near the top of the foundation element
to a position at or near the base of the element.
The strip(s) of hydrophilic material are preferably supported by
one or a number of support elements. The support element(s) may be advantageously
made from a geotextile material which may or may not exhibit hydrophilic properties.
However, any other suitable material can be used including a sheet of supporting
An important aspect of the waterstop of the present invention is
that the waterstop preferably forms an integral part of the foundation element
into which it is installed. Unlike known systems, the waterstop does not span
across the joint and into both of the adjacent elements. As such, the waterstop
does not require the provision of a stop-end to facilitate the installation.
According to a second aspect of the present invention, there is provided
a method of installing a waterstop for resisting the flow of water along and/or
between adjacent foundation elements, the method comprising the steps of:
- i) constructing a series of primary foundation elements at a number of predetermined
positions in the ground;
- ii) excavating a bore in the ground adjacent to one of the primary foundation
- iii) lowering a waterstop comprising one or a number of longitudinal strip(s)
of hydrophilic material into the bore, such that the strips extend vertically
from a position at or near the top of the bore to a position at or near the base
of the bore; and
- iv) pumping concrete or grout into the bore so as to form a secondary foundation
element, wherein the waterstop forms an integral part of the resulting secondary
Advantageously, when the concrete or grout is pumped into the base,
the arrangement is such that, as the concrete or grout fills the bore, the strips
of hydrophilic material of the waterstop are pushed towards the adjacent panel.
The flow of concrete as it is poured into the bore, naturally serves
to push the waterstop towards the primary panel. In addition, a rolling means may
advantageously be provided at the lower end of the waterstop, between the hydrophilic
strip(s) and the support element. The rolling means preferably comprises a roller
or wheel which is connected about it central axis to a lever. The lever is connected
to the support element such that, the lever pivots about the support element under
the weight of the concrete or by some other means, thereby causing the roller to
push against the hydrophilic strip. The strip is then pushed towards the adjacent
existing concrete edge.
According to a third aspect of the present invention, there is provided
a foundation element having a waterstop formed therein, wherein the waterstop
comprises one or more longitudinal strips of hydrophilic material, wherein the
hydrophilic strips extend vertically from a position at or near the top of the
foundation element to a position at or near the base of the element
The waterstop of the present invention is conveniently installed
in the secondary elements after the formation of the primary elements. For example,
in the case of a diaphragm wall, a series of alternate "primary" panels are constructed,
and the region between each pair of primary elements is excavated. One or more
waterstops can then be advantageously lowered into either side of the excavated
hole near the adjacent primary panels. Concrete is then pumped into the excavated
hole to form the so-called "secondary" panel. As the concrete enters the excavated
hole and begins to fill it, the strips of material of the waterstop are pushed
by the concrete towards the adjacent panel. Alternatively, one or a few "primary"
element(s) may be constructed and the second, third, forth etc elements are formed
consecutively in turn. In this case, only the side of the foundation element which
is adjacent the pre-formed concrete element will be provided with a waterstop.
The same techniques can advantageously be applied to all open bore
constructions, such as secant piled walls, wherein a series of primary elements
are installed followed by a number of secondary elements which are advantageously
provided with a waterstop of the present invention.
In order to prevent the flow of water in a vertical fashion between
adjacent foundation elements, there may advantageously be provided one or a pair
of supplementary elements which extend orthogonally from the longitudinal axis
of the waterstop element. These elements are preferably positioned at a predetermined
level either side of the waterstop element and serve to resist and/or absorb water
that rises in a vertical fashion up the waterstop . The supplementary elements
are preferably chevron or wedge shape and are affixed to the waterstop such that
one edge runs parallel to the edge of the waterstop and the other side extends
from an apex near the lower end of the waterstop. This shape is particularly beneficial
since as concrete enters the bore from the bottom and rises up the sides of the
waterstop, the supplementary elements are encouraged towards the hydrophilic strips
of material. Furthermore, any water that rises from below will come into contact
with the supplementary elements and be blocked and/or absorbed. The supplementary
elements are preferably provided with one or more strips of hydrophilic material.
For a better understanding of the present invention, and to show
how the same may be carried into effect, reference will now be made by way of example
to the accompanying drawings in which:
- Figure 1 shows a waterstop of the present invention;
- Figure 2 shows a sectional view through B-B of Figure 1;
- Figure 3 shows a plan view of a series of diaphragm wall panels;
- Figure 4 shows an elevational view through section A-A of Figure 3 and illustrates
the lowering of the waterstop in an excavated bore;
- Figure 5 illustrates the motion of the waterstop as concrete or grout is pumped
into the excavated bore;
- Figure 6 illustrates a waterstop having two supplementary elements; and
- Figure 7 shows a waterstop having a rolling means.
Figure 1 shows a waterstop of the present invention comprising two
longitudinal hydrophilic cords 1 and 2, which are separated and supported by a
support element 3 which is made of geotextile or any other suitable material.
A section B-B through Figure 1 is shown in Figure 2 and comprises a series of waterstop
members 4, 5 and 6 which are substantially parallel to each other. By way of illustration,
the cross-sectional shape of the hydrophilic cords 7 are shown to be either square
of circular. It should be appreciated that the cross section of the hydrophilic
cords is not critical and that many alternative shapes are envisaged. Furthermore,
the point of attachment of the support to the cords is not critical.
Figure 3 shows a plan view of a series of diaphragm wall panels comprising
alternate "primary" panels 8, and an excavated bore 9, for a secondary panel. Figure
3A illustrates the position of two waterstops 10 and 11 in the excavated bore.
Each waterstop is lowered into the bore at a position near the adjacent primary
panel. Figure 3B shows the position of the waterstops 10 and 11 after concrete
or grout has been poured into the excavated bore. The waterstops will have been
pushed by the concrete and/or by a rolling means towards the adjacent panel and
the longitudinal hydrophilic cords, will extend vertically from the top of the
panel 9, to a position at or near the base of the panel.
The installation of a waterstop of the present invention, into a
foundation element, is illustrated in Figures 4 and 5. Figure 4 shows a waterstop
according to the present invention being lowered from a coil 12 into the bore
13 adjacent to the primary panel 14. In Figure 4C, the waterstop has been fully
lowered into the bore. Figure 5 illustrates the motion of the hydrophilic material
16 towards the primary panel 14 as concrete or grout is pumped into the bore. As
the level of the concrete rises, the hydrophilic strip 16 and, is pushed against
the primary panel thereby acting as a seal between the two diaphragm wall panels.
A further waterstop according to the present invention is shown in
Figure 6. The Figure shows two longitudinal hydrophilic cords 20 and 21 which are
supported by a geotextile support frame 17. A supplementary element 18 is provided
either side of the two longitudinal hydrophilic cords which extends orthogonally
therefrom. The elements comprise a number of hydrophilic cords 19 supported by
a geotextile support frame 22 and are chevron or wedge shaped. In use, they are
positioned at a predetermined level with respect to the bore. They serve to resist
and/or absorb water that may rise in a vertical fashion between the adjacent panels
either side of the longitudinal strips of hydrophilic material, and are affixed
to the waterstop such that one edge runs parallel to the edge of the hydrophilic
cord and the other side extends from an apex near the lower end of the waterstop.
As concrete enters the bore from the bottom and rises up the sides of the waterstop,
the supplementary elements are encouraged towards the hydrophilic strips of material
20 and 21. Furthermore, any water that rises from below will come into contact
with the supplementary elements and be blocked and/or absorbed.
Figure 7 illustrates a waterstop of the present invention having
a rolling means 23 at the lower end thereof, between the hydrophilic strip 27 and
the support element 26. The rolling means comprises a roller or wheel 24 which
is connected at its central axis to a lever 25. The lever is connected to the
support element 26 such that it can be pivoted, either under the weight of the
concrete or by some other means, about the point of attachment to the support
element thereby causing the roller to push against the hydrophilic strip 27. In
turn, the strip is pushed away from the support element and towards the existing
concrete edge 28.
While all of the examples illustrated herein have related to the
installation of a waterstops in a diaphragm wall, it should be appreciated that
the present invention can be applied to any foundation structures which involve
a series of constituent elements such as a secant pile wall.