GB2264739A

GB2264739A - Diaphragm wall with liquid tight joints

Info

Publication number: GB2264739A
Application number: GB9304531A
Authority: GB
Inventors: Jonathon Richard Craft; Yvone Franco Crosato
Original assignee: Finic BV
Current assignee: Finic BV
Priority date: 1992-03-06
Filing date: 1993-03-05
Publication date: 1993-09-08
Also published as: GB9304531D0; GB9204927D0

Abstract

A method of forming a water-bar across a diaphragm wall panel joint comprising forming an interconnecting reservoir 12 between two adjacent wall sections 5, 11 during casting thereof and filling said reservoir with a material that will form an effective barrier to the migration of water. A stop end pipe 3 with a tube 4 is placed in an excavation at the location where the first wall section 5 is to be cast. After casting and hardening of the section 5, the stop end pipe is removed. A double tube former 10 is placed so that one half of the former 10 is located within the hole 9 formed by the tube 4. The second wall section 11 is cast and the former 10 removed to leave the reservoir 12, the latter being filled with a plastic impervious material. <IMAGE>

Description

The present invention relates to improvements in and relating to diaphragm walls and in particular to an in situ method of forming a water-bar across each diaphragm wall panel joint.

Diaphragm walls are concrete walls which are cast in below-ground trenches sustained by a fluid denser that water such as bentonite. Generally, such diaphragm walls are constructed in sections or panels each of which extends over a limited length of the wall.

The main functions of a diaphragm wall are as follows: (a) as a retaining wall when the earth.is removed from one side of the wall, for example when building underground structures such as basements and underground car parks. In this case, a diaphragm wall is formed all round the site and the soil inside the wall is removed to the designed depth to enable the structure to be built inside. Another application is in the construction of tunnels for subways or underpasses. In this case two diaphragm walls are installed at the sides of the proposed tunnel, a roof slab is cast across the top of the tunnel between the diaphragm walls and the soil is removed from under the roof slab.

(b) cutting off underground water when there is a difference of water level between the two sides of the wall The typical case is in foundations of dikes and dams to cut off water seepage in previous strata of soil (c) as both retaining wall and water cut off in the case of a soil retaining wall when the excavation on one side of the wall is at a level lower than the water table level at the other side of the wall.

(d) for foundations when building or other structures are founded on diaphragm wall elements.

In order to accomplish the functions for which the structure has been designed, particularly those of earth support and water interception, the vertical joints between the wall sections must fulfil the following requirements: (1) to guarantee an effective key connection capable of withstanding the horizontal shear force which might be acting on the joint as a consequence of different load conditions on the two wall sections and (2) to be watertight.

We have sought to provide a method which produces an improved diaphragm wall panel joint which is more watertight and more able to tolerate relative movement of diaphragm wall panels.

Accordingly, the present invention provides a method of forming a water-bar across a diaphragm wall panel joint comprising forming an interconnecting reservoir between two adjacent wall panels during casting thereof and filling said reservoir with a material that will form an effective barrier to the migration of ground water.

Such material can be any expanding (nonshrink), plastic impervious material. The preferred material is bentonite.

In one embodiment of the invention a circular tube-like member called a "stop end pipe", with a diameter equal to the width of the trench which has been excavated, has welded to its outer surface a small diameter tube. The stop end pipe is placed vertically at the location of the end of the first wall section to be cast prior to casting of the concrete forming the first wall section. Once the casting of the first wall section is complete and the concrete is sufficiently hardened, the stop end pipe is withdrawn leaving a part-circular concavity with a circular key-way in the first cast wall section.Prior to casting the second wall section next to the first wall section, a double tube former consisting of a pair of interconnecting steel tubes each having a diameter slightly smaller than that of the tube welded to the stop end pipe and welded together to form a dumb-bell in cross section is inserted at the surface of the first wall section in such a way that one of the tubes is located within the circular key way. Once the casting of the second wall section is complete and the concrete is sufficiently hardened the double-tube former is removed leaving a dumb-bell shaped reservoir across the panel joint between the first and second wall sections.

If necessarv the reservoir thus formed is cleaned to remove debris and slurry preferably using a pair of parallel steel rods and compressed air.

The reservoir is then filled with a material such as bentonite pellets which are tamped into place. Once the whole length of the reservoir has been properly filled, the reservoir is sealed by means of a cast concrete plug which confines the said material and prevents contamination.

Over a period of time any moisture that migrates along the panel joint from behind the wall and reaches the reservoir will be absorbed by the pelleted bentonite material which when hydrated swells to form an expanding water-stop within the reservoir across the joint. Bentonite is the preferred material because it can expand to up to ten times its dry volume and being a naturally occurring clay mineral does not deteriorate over time.

Furthermore, being an essentially plastic material it can tolerate movement without rupturing - this being an especially important consideration between load bearing and non-load bearing panels.

The present invention is further illustrated in the accompanying drawing, wherein Figures 1(a) to (e) are cross-sections through an excavation being concreted illustrating the various steps of the invention.

In Figure 1 is a trench shown generally as 1 which is to be excavated and provided with a concrete wall shown generally as 2, illustrated completed in Figures l(,d) and (e).

In Figure 1(a) stop end pipe 3 with a small diameter tube 4 welded to it is placed vertically within the excavation at the location where the first wall section 5 is to be cast within that location is reinforcement 6. At the other side 7 of the stop end pipe 3 is an area of the trench 1 yet to be excavated.

In Figure l(b) after casting and hardening of the concrete first wall section 5, the stop end pipe has been removed to leave a slurry filled area 8 having a circular hole 9 extending into the now cast first wall section 5.

In Figure l(c) a double tube former 10 is inserted into the trench 1 so that one half of the double tube former 10 is located within the hole 9 formed previously. Reinforcement 14 is put in place.

In Figure l(d) the second wall section 11 is cast and the double tube former 10 is removed to leave a reservoir 12.

In Figure l(e) the reservoir 12 is filled with a plastic impervious material 13.

Claims

1. A method of forming a water-bar across a diaphragm wall panel joint comprising forming an interconnecting reservoir between two adjacent wall sections during casting thereof and filling said reservoir with a material that will form an effective barrier to the migration of water.

2. A method as claimed in claim 1 comprising the steps of excavating a trench, placing a stop end pipe with a diameter substantially equal to the width of the trench and having a smaller diameter tube welded to its outer surface vertically in said trench at the location of the end of the first wall section to the cast, casting the first wall section, removing the stop end pipe to leave a part-circular concavity with a circular key-way in the first cast wall section, inserting a double tube former consisting of a pair of interconnecting tubes which have a dumb-bell cross section and each tube having a diameter slightly smaller than that of the tube welded to the stop end pipe at the surface of the first wall section, so that one tube is located within the circular key way, casting the second wall section, removing the double-tube former and filling the dumb-bell shaped reservoir thus formed with said material.

3. A method as claimed in claim 1, or 2 in which the material is an expanding (non-shrink) plastic impervious material.

4. A method as claimed in claim 3, in which the material is bentonite.

5. A method substantially as herein described with reference to the accompanying drawings.