Hydrophilic waterbar for diaphragm wall joints

Details Hydrophilic waterbar for diaphragm wall joints Hydrophilic waterbar for diaphragm wall joints

1999-11-10

2001-08-21

Friedman, Carl D. (Department: 3635)

Static structures (e.g., buildings)

Relatively yieldable preformed separator

Separator inserted prior to or during pouring of two...

C052S396040, C052S127300, C052S688000, C052S719000, C405S267000

Reexamination Certificate

active

06276106

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an apparatus for sealing joints in diaphragm walls and, more particular to a multi-part waterbar incorporating a hydrophilic material which swells upon contact with water.
BACKGROUND OF THE INVENTION
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 joints 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 (with some types of stop-end) to install a waterbar between adjacent panels. A waterbar comprises a strip of suitable material, for example rubber, PVC or steel, 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.
This type of waterbar, however, does not necessarily guarantee watertightness at panel joints. This is because the known varieties of waterbar rely on the fact that concrete shrinks slightly upon setting. An element which is completely surrounded by concrete will be gripped all round as the concrete shrinks, but the beaded edges of the known varieties of waterbar are not completely surrounded by concrete due to the presence of the central part of the waterbar. Accordingly, there is a potential risk of water leakage. Furthermore, installation conditions are in practice far from perfect, partly because the waterbar is installed “blind” under a bentonite mud containing suspended sand and the like, and partly because the concrete is cast without vibration, which means that the bentonite and/or sand and the like may not be fully removed from the edges of the waterbar.
Waterbars made of hydrophilic materials have been used at construction joints in conventional “above ground” concrete structures. The hydrophilic material is placed at the joint in dry conditions. If and when water enters the joint, the hydrophilic material will swell, thereby forming a seal between the two adjacent concrete members
By contrast, the use of hydrophilic waterbars in diaphragm wall construction presents a number of problems, not least because installation takes place in an aqueous environment, and the part of the waterbar to be incorporated into the second panel will swell before the trench for that panel is excavated and the concrete cast. One way of approaching this problem is to use hydrophilic waterbars provided with a protective, e.g. sugar, coating, which can theoretically give a delay of several days before swelling occurs. This, however, is often unreliable, mainly because the coating resembles a sugar glaze which is cracked when the waterbar is flexed, is easily damages in handling, and has inherent imperfections in the coating, all of which will lead to premature swelling of portions of the waterbar. Moreover, in many installations it is not unusual to leave more time between the casting of adjacent panels than can be accommodated by the protective coating; indeed, intervals of up to thirty days are not uncommon.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a waterbar for use between adjacent panels in a diaphragm wall, the waterbar comprising:
i) a first member in the form of an elongate strip provided along a first longitudinal edge with a hydrophilic material and along the opposite longitudinal edge with a retaining channel; and
ii) a second member in the form of an elongate strip provided along a first longitudinal edge with a hydrophilic material and along the opposite longitudinal edge with a keying projection;
wherein the retaining channel of the first member is shaped so as slidably to retain the keying projection of the second member, and wherein either the retaining channel or the keying projection is provided along its length with a hydrophilic material which serves, in use, to seal the joint between the first and second members.
In the building of a diaphragm wall, a first trench is excavated and a stop-end is placed at each end of the trench. Each stop-end may be provided with a longitudinal slot into which the first member of the waterbar is placed, such that the first edge of the member is exposed. It is usual for the first member of the waterbar to be placed in the slot prior to installation of each stop-end. Concrete is then poured into the trench so as to form a panel, the first edge of the waterbar member becoming embedded in the edge of the panel. Bentonite may be pumped through the retaining channel of the first member of the waterbar so as to keep this clear of concrete and other materials. Once the concrete has set and an adjacent trench has been excavated, the stop-end is removed, leaving the retaining channel of the first member exposed. The keying projection of the second member of the waterbar is then slidably fitted into the retaining channel of the fist member before further concrete is poured in order to form a second panel. The two panels are then joined by a two-piece waterbar which is provided with a hydrophilic material at its interfaces with the panels as well in the region of its interlocking joint. These are the only locations where water may flow between the adjacent panels of the diaphragm wall. The presence of a hydrophilic material which swells upon contact with water serves significantly to reduce the possibility of such water flow.
It is to be understood that, alternatively, the second member of the waterbar may be installed first, followed by the first member once the first concrete panel has set.
By providing a two-part waterbar, each part of which need only be installed at the time its associated concrete panel is cast, the present invention overcomes the problems encountered by known hydrophilic waterbars. In particular, because the present invention does not require the hydrophilic components of the waterbar to be exposed to water for excessive periods during installation, the problems associated with inefficient protective coatings are obviated.
The first and second members of the waterbar according to the present invention may be made of any suitable material, such as plastics, rubber or steel etc. A particularly suitable material is high density polyethylene (HDPE) or the like. The hydrophilic material may comprise a mixture of b

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