GB1590325A

GB1590325A - Construction of diaphragm walls

Info

Publication number: GB1590325A
Application number: GB4791277A
Authority: GB
Original assignee: Comar Reg Trust
Current assignee: Comar Reg Trust
Priority date: 1977-07-05
Filing date: 1977-11-17
Publication date: 1981-05-28
Also published as: NL7712245A; BE860670A; LU78490A1; FR2396850B1; MX144906A; CA1075023A; PT67147B; CH614484A5; ES463978A1; HK20883A; SG58082G; DK353177A; PT67147A; FR2396850A1

Description

(54) CONSTRUCTION OF DIAPHRAGM WALLS (71) We, COMAR REG. TRUST, a Liechtenstein body corporate, of Vaduz, Principality of Leichtenstein, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method of in situ construction of diaphragm walls and in particular to the formation of joints between successively cast sections of such walls.

Diaphragm walls are concrete walls cast in trenches in the soil and commonly constructed in sections or panels each extending over a limited length of the wall. Initially it is usual to excavate a vertical trench of a width corresponding to that of the wall, of a length of the order of 3 to 6 m and of the full depth of the wall by means of a clamshell or other suitable trenching equipment. Concrete is cast into the trench to form a first section of the wall. The sides of the trench form part of the mould for casting the concrete but at the ends of the trench temporary steel shutters are inserted to the full depth of the trench to create smooth concrete surfaces against which the next section of the wall will be cast.

The main functions of the diaphragm walls are as follows: (a) as a rctaining 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 pervious 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, par ticularly 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.

Accordingly, special attention must be given to the shutters for the concrete.

A known shutter for forming the vertical joint between adjacent wall sections is a circular, tube-like member called a "stop end pipe" having a diameter equal to the width of the trench which has been excavated.

Such tube-like member is placed vertically at the location of the end of the wall section to be cast prior to casting of the concrete.

Once the casting is completed and the concrete sufficieDtly hardened, the pipe is withdrawn, leaving a part-circular concavity at the end surfaces of the concrete wall section.

When constructing the next adjoining section, concrete will be cast against this surface, thus forming the joint.

In early applications of diaphragm walls, when the wall thickness was rather small, the circular pipe was considered the most appropriate form of shutter because of its capability of withstanding the pressure of the concrete, which in the case of deep trenches is considerable, whereby deflections of the shutter remain within acceptable values.

However with the wider use of diaphragm walls and the increasing of wall thickness, such circular pipes give rise to shortcomings: A) The shear strength resistance of the joint is rather poor and relies more on the friction between the two abutting surfaces rather than on an effective key. The concrete at the extremities of the part-circular concavity is generally weakened, because due to the restricted space the concrete cast might be faulty or unsound, or because areas of the concrete are often damaged by the chiselling action which is required to break and remove any excess concrete which may have surrounded the pipe.

Therefore, the effective cross-sectional area of the joint is reduced and moreover due to its rather flat shape, the shear resistance of the joint cannot be increased by appropriate steel reinforcements.

B) Such pipe shutters comprise several pipe sections connected to each other to obtain a pipe of a length equal to the depth of the trench. The coupling between adjacent pipe sections is a complicated matter because it has to withstand the high forces to which the pipe is subject during its pulling out operation after the concrete has hardened and also because of the required high accuracy regarding the alignment of the pipe sections, such alignment being essential for the work.

C) The circular pipe necessitates the use of clamps having a diameter equal to the diameter of the pipe itself, such as to clamp it during the pulling-out operation. This results in the requirement of a massive pulling out or lifting equipment which is expensive regarding purchase cost and maintenance.

D) The adoption of a circular pipe of a diameter equal to the width of the wall requires that the trench section corresponding to one wall section must be excavated two pipe diameters longer than the length of such wall section. This leads to inconveniences and to a reduction of the progress rate with consequent increase of the costs involved. It often also leads to a limitation of a desired length and shape of a diaphragm wall.

In accordance with the present invention there is provided a method of in situ construction of diaphragm walls in which a trench is excavated in sections and concrete is cast into each section before the next section is excavated, at least one end of each trench section containing a shutter to form a recess in the end of the cast wall section, the adjacent wall section being cast into the recess in order to form a joint between the wall sections after withdrawal of the shutter, characterized in that the shutter is formed by at least one metal shuttering member in the form of a prism of generally rectangular section with a projection on one face to form the recess in the end of the wall section, the projection being spaced from the sides of thc trench and the shuttering member having an overall dimension in the direction of the length of the wall which is less than its width in the direction between the sides of the trench.

The projection may be triangular as seen in plan. The or each shuttering member is preferably a hollow steel body.

Where each shutter is composed of a plurality of identical shuttering members stacked one on top of the other these are preferably coupled together by means of pairs of lugs extending upwards from the top of each shuttering member and engaging in corresponding slots in the bottom of the next member of the stack, the lugs being held in place by transverse pins passing through apertures in the lugs and in the structure on each side of the slot.

The invention will now be described in more detail with the aid of examples illustrated in the accompanying drawings, in which: Fig. 1 is a vertical section longitudinally of the trench showing casting of a diaphragm wall section between two stop end pipes in accordance with the known method, Fig. 2 is a section on the line II--II of Fig. 1, Fig. 3 is a detail of Fig. 2 on a larger scale, Fig. 4 is a longitudinal section of a joint formed by the known method of Figs. 1 to 3, Fig. 5 shows a comparison between the section of Fig. 2 and a corresponding section for the method in accordance with the present invention, Fig. 6 is a perspective view of two cooperating shuttering members for use in the method of the invention, Fig. 7 is a vertical section similar to that of Fig. 1 but illustrating the method of the invention, Fig. 8 is a section on the line VIlI-VIlI of Fig. 7, Fig. 9 is a horizontal section of a joint formed by the method of the invention, Fig. 10 is a section corresponding to that of Fig. 3 illustrating the method of the invention, Figs. 11 to 13 are sections of different forms of joint which can be made by the method of the invention, Figs. 14A and 14B are sections corresponding respectively to Fig. 3 and Fig. 10 showing an abnormal amount of concrete cast around the shutter, and Figs. 15A and 1SB are cross-sections of shuttering members suitable for constructing by the method of the invention walls with a thickness greater than 1.00 m.

In Figs. 1 and 2, which illustrate the known method, a trench 1 is shown in section along the length of a wall which is to be constructed extending in the direction of the arrow 2. The ground level is shown at 3 and the depth of the trench by 4. The trench 1 is excavated in the known manner by means of generally known trenching equipment. In order to avoid caving in of the side walls 5 of the trench this trench is kept filled with bentonite slurry 6. At each of the two ends of the trench there is inserted a pipe-like shutter 7, having a circular crosssection and comprising several sections connected to each other, but not shown in detail in the drawing. A dip tube 8 is inserted into the trench 1 and the bentonite slurry 6. By means of this dip tube 8 concrete 9 is cast and during the casting the dip tube 8 is continuously moved upwards.The concrete 9 continuously filling the trench 1 urges the bentonite slurry 6 upwards, which slurry is continuously removed in a known way.

The casting of the concrete 9 is carried out until the required height of the intended wall is reached.

In Fig. 2 the horizontal cross-section through the trench 1 is shown, in which the width of the wall to be cast is designated with the numeral 10. Accordingly, the two earth side walls 5 of the trench form two side walls of the mould for the concrete 9, which is cast directly against these side walls 5, while the two end walls of the mould are formed by the opposed outer surface areas of the pipe-like shutters In Fig. 3 there is shown an end area of the concrete wall formed in the trench 1 by the method of Figs. 1 and 2, after the concrete has hardened, thus forming one complete wall element. The shutter 7, i.e. the pipe, has been pulled out by means of a known pulling out machine. It is now obvious that the shutter 7, during casting of the concrete 9, has been more or less surrounded by excess concrete, leaving the circular concrete residue indicated with the numeral 11.

The intended effective joint contact area is shown by 12. The excess concrete 11 has to be removed during excavation of the adjacent trench for the adjacent wall element, indicated by 14. The areas 15 of the excess concrete 11 are weak areas, which will be removed up to the lines 13, which then define the contact area 12 of the joint. It is now obvious that the exact location of the lines 13 is not defined, such that the extent of the contact surface 12 is also not exactly definable.

In Fig. 4 there are shown two completed adjoining wall sections, and specifically the joint therebetween. Lateral pressures acting on the section 9 and the section 14 are indicated by arrows 16 and 17, respectively.

If the pressure acting on section 9 exceeds the pressure acting on section 14, the joint is subjected to a shearing load and it is obvious that such a joint is not suitable for transmitting a large lateral load, in this case from the wall section 14 to the wall section 9.

In Fig. 6 there is now shown in detail a perspective view of the lower part (19) and the upper part (18) of two identical mould elements, for use in the method in accordance with the invention. Each element 18, 19 is a prism of generally rectangular section having a flat rear main side surface 20.

Furthermore each element comprises a front main side surface 21, from which side surface 21 there projects a triangular wedge-like projection 23 bounded by two inclined surfaces 24 and 25. Furthermore, the rear main side surface 20 is connected at one end by means of a perpendicularly extending secondary side surface 26 with one end of the front main surface 21, and the opposing ends of the main side surfaces 20, 21 are connected by means of a further secondary side surface 27 with one another, the two secondary side surfaces 26 and 27 extending parallel to each other. It is to be noted that the ridge 28 of the wedge 23 extends parallel to the side surfaces 20, 21, 26 and 27.

The body further has a top surface 29 extending perpendicularly to e.g. the ridge 28 and a bottom surface 30 extending parallel to said top surface 29. From the top surface 29 there project two piate-like lugs 31, 32.

At the bottom surface two slits 33 and 34 are provided, of which slit 34 is not visible in the drawing. The location and shape of the lug 31 correspond to the location and shape of the slit 33, and the location and shape of the lug 32 correspond to the shape and location of the slit 34. Accordingly, when two elements 18 and 19 are placed upon each other (the actual number of elements placed upon each other being greater and depending on the depth of the trench) as indicated in Fig. 6, which can be considered an exploded view of part of the shutter, the lug 31 is inserted into the slot 33 and lug 32 is inserted in the slot 34.

The lug 31 is provided with a through hole 35 and the lug 32 is provided with a through hole 36, and, furthermore, the area of the body 18 (and 19) is provided at the area of the slot 33 with a further through hole 37 and at the slot 34 with another through hole 38.

The through holes 35, 37 and 36, 38 are located at corresponding locations such that when the two elements 18, 19 are placed upon each other, a pin 39 can be inserted through the through holes 35 and 37, which are in register with each other, thus locking the two elements together. Obviously a further pin is provided for lug 32 and slot 34, which however is not shown in the drawing.

Each element comprises further holes or openings 40 for receipt of pins or hooks of a pulling out machine known as such and thus not shown.

The bodies 18 and 19 are hollow steel bodies. They comprise mainly two shaped thick steel plates, of which one steel plate forms the rear main side surface 20 and half of each the secondary side surfaces 26, 27 up to the longitudinal line 41. The other steel plate forms the front surface 21 integrally with the wedge 23 and the second half of the secondary side surfaces 26, 27. These two plates are welded together along a welding seam 41 The body is completed by welding further flat steel plates to the first-mentioned two steel plates, such that the top 29 and the bottom 30, the projecting lugs 31 and 32 and also the slots 33 and 34 are obtained.

The openings or through holes are drilled at a suitable step during manufacture of the plates or bodies.

In Figs. 7 and 8, which are sections similar to Figs. 1 and 2 respectively, there is shown the casting of the concrete 9 into the trench 1 filled with bentonite slurry 6, using two steel shutters 42 and 43 consisting of a number of coupled shuttering elements of the type shown in Fig. 6.

Referring now to Fig. 5, it has been mentioned earlier that in order to construct the trench section 1 use is made of a clam shell grab or other trenching equipment, that the steel shutter is then placed and finally the concrete is cast into the trench 1, dis placing the bentonite slurry 6 upwards.

In order to obtain now one wall element 9 having a specific final length 43 it is obvious that a much longer length 44 of the trench must be excavated when using a circular steel shutter according to the prior art compared with the reduced length 45 of a trench which is required when using shutters of Figs. 6 to 8.

Fig. 9 shows in horizontal section the joint between two adjacent cast wall sections formed in accordance with the invention. It is obvious, in comparison with the joint shown in Fig. 4, that an effective key capable of transmitting large lateral loads is obtained.

Furthermore, the length of the path through the joint from side to side of the wall is almost twice the length obtainable by means of the prior art, such that an effective sealing off of ground water seepage is obtained.

In Fig. 10 there is shown the end section of a wall element 9 after the steel mould has been retrieved and before the excess concrete 46 has been removed. There exists here a sharply defined line 47 up to which the excess concrete will be removed thus leaving at every joint a well defined form of the face of the wall segment 9.

The triangular shape of the projection 23 and therewith obtained joint as shown in Fig. 9 corresponds to the maximum shear resistance obtainable, taking the quality and the homogeneity of the concrete cast under bentonite slutty into consideration.

As shown in Fig. 11 the width of the base 49 of the triangular projection is about half the thickness of the wall and such a joint is suitable for medium loads. When smaller lateral forces are expected the length of the base 49 can be reduced, as shown in Fig. 12. For larger lateral forces the base 49 can be as shown in Fig. 13. The shear resistance of the joint is increased by means of adequate steel reinforcements shown in Fig. 13 installed in the wall elements, whereby the contour of the joint allows placing of the steel bars extending into the joint itself whereby such bars can overlap at the joints, relative to the longitudinal extension of the walls.

The thickness of each shuttering element is very small in comparison with the circular pipe diameter. That is to say the dimension of the shutter element in the longitudinal direction of the wall is less than the width of the trench. Nevertheless the new shutter will, due to its particular form, have a sufficient rigidity to keep the de election of the shutter due to concrete pressures within acceptable limits. The rigidity of the form, resulting from the said particular shape, is comparable with the rigidity of the circular pipe.

After pulling out of the mould when one wall section is sufficiently hard (see Fig.

10), there exists at the face of the wall element 9 a void space 48 of such dimensions as to be an efficient guide for the clamshell grab during excavation of the adjacent wall element and to improve the progress of the excavation. Moreover, due to the particular shape of the face, an efficient guide for the clamshell grab is provided.

Figs. 14A and 14B show the end portion of the wall element 55 in the two cases of a vertical joint formed according to the prior art and according to the invention, in each case with an abnormal quantity of concrete surrounding the shutter space due to soil cavitation in the vicinity of the joint.

In the case of the prior art (Fig. 14A) during excavation of the next element 56, the excess concrete may break, for example, along the lines 53 and 54. This will give rise to a deviation of the wall element 56 during its excavation from the theoretical axis 57 to the position 58.

In the case of the invention (Fig. 14B), during the excavation of the adjacent panel 56, the excess concrete will break of course along lines 51 or 52, starting at the corners of the shutter space, in both cases allowing the construction of the adjacent panel 56 in its exact position.

In Fig. 1SA is shown the cross-section of a shutter element which is normally adopted for use in the method of the invention in the case of a wall thickness exceeding 1.00 m. In this case two triangular projections are adopted.

In Fig. 15B is shown a detail of the internal reinforcing plates (60) which provide the shutter element with the rigidity that is required to withstand the pressure of the concrete.

WHAT WE CLAIM IS:- 1. A method of in situ construction of diaphragm walls in which a trench is excavated in sections and concrete is cast into each section before the next section is excavated, at least one end of each trench section containing a shutter to form a recess in the end of the cast wall section, the adjacent wall section being cast into the recess in order to form a joint between the wall sections after withdrawal of the shutter, characterized in that the shutter is formed by at least one metal shuttering member in the form of a prism of generally rectangular section with a projection on one face to form the recess in the end of the wall section, the projection being spaced from the sides of the trench and the shuttering member having an overall dimension in the direction of the length of the wall which is less than its width in the direction between the sides of the trench.

2. A method as claimed in claim 1 in which the projection is triangular as seen in plan.

3. A method as claimed in claim 1 or 2 in which the or each shuttering member has two similar projections on the same face arranged symmetrically on opposite sides of the central plane parallel to the sides of the trench.

4. A method as claimed in any of claims 1 to 3 in which the or each shuttering member is a hollow steel body.

5. A method as claimed in any of the preceding claims in which each shutter is composed of a plurality of identical shuttering members stacked one on top of the other and coupled together in such a way that the shutter can be raised as a unit by lifting the top shuttering member.

6. A method as claimed in claim 5 in which each of the shuttering members has at least one lug extending upward from its top surface and a slot in its bottom surface to engage over the lug of the shuttering member below it in the stack.

7. A method as claimed in claim 6 in which each shuttering member has two lugs extending upward from its top surface and two corresponding slots in its bottom surface.

8. A method as claimed in claim 7 in which the two lugs lie in a plane parallel to the two larger faces of the shuttering member and are disposed near the opposite faces of the shuttering member which abut the walls of the trench.

9. A method as claimed in claim 6, 7 or 8 in which the shuttering members are coupled by pins extending through apertures in the lugs and in the structure on each side of the slot.

10. A method as claimed in any of claims 5 to 9 in which each shuttering member has through holes extending between its larger faces to receive pins of a lifting mechanism to raise the shutter from the trench.

11. A method as claimed in claim 5 in which each shuttering member has a form substantially as described with reference to Fig. 6 of the accompanying drawings.

12. A method of in situ construction of diaphragm walls substantially as described with reference to Figs. 6 to 9 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. 56, the excess concrete will break of course along lines 51 or 52, starting at the corners of the shutter space, in both cases allowing the construction of the adjacent panel 56 in its exact position. In Fig. 1SA is shown the cross-section of a shutter element which is normally adopted for use in the method of the invention in the case of a wall thickness exceeding 1.00 m. In this case two triangular projections are adopted. In Fig. 15B is shown a detail of the internal reinforcing plates (60) which provide the shutter element with the rigidity that is required to withstand the pressure of the concrete. WHAT WE CLAIM IS:-

1. A method of in situ construction of diaphragm walls in which a trench is excavated in sections and concrete is cast into each section before the next section is excavated, at least one end of each trench section containing a shutter to form a recess in the end of the cast wall section, the adjacent wall section being cast into the recess in order to form a joint between the wall sections after withdrawal of the shutter, characterized in that the shutter is formed by at least one metal shuttering member in the form of a prism of generally rectangular section with a projection on one face to form the recess in the end of the wall section, the projection being spaced from the sides of the trench and the shuttering member having an overall dimension in the direction of the length of the wall which is less than its width in the direction between the sides of the trench.