Method for providing deep partition walls in the ground and an excavating apparatus for use in this method

Abstract

 A method for providing deep partition walls in the ground, wherein, by means of a drill head (3), pits (8) are drilled, spaced apart, to the desired depth, whereafter the ground panel (11), located between the two pits (8), is excavated by means of a deep-wall cutter (10) comprising at the two sides thereof guide elements (12), guided by the walls of the pits (8) during excavation of the ground panel (11). In this manner, successive ground panels can interconnect perfectly to yield a sealing wall, continuous at all points, consisting of a hardenable mass to be provided in the excavated trench.

Description

[0001] The invention relates to a method for providing deep partition walls in the ground, which method comprises:

• excavating a first pit by means of an excavator;
• excavating a second pit by means of the excavator, which second pit is shifted relative to the first pit over a distance approximately corresponding to the greatest length dimension of the excavator;
• excavating, by means of the excavator, the ground panel, located between the first and the second pit; and
• filling up the thus formed panel space with a hardenable mass.

[0002] Such a method is known from Dutch patent application No. 87.02430. The excavator used consists of a deep-wall cutter, with which a first pit of rectangular section is excavated and subsequently, laterally shifted relative thereto, a second pit of rectangular section is excavated, shifted laterally relative to the first pit. Subsequently, the intermediate ground panel is excavated by means of the deep-wall cutter. In order to obtain a continuous wall, it is of the utmost importance that the panel space thus provided connects to the pits excavated on both sides thereof. Consequently, when the ground panel located between two pits is excavated, there must be an overlap in the principal direction of the wall, and, also, the deviation in a direction perpendicular to the wall to be excavated can only be slight. For measuring this deviation in a direction perpendicular to the wall to be excavated, inclinometers are used as described in the above-mentioned Dutch patent application. The precision of these inclinometers is insufficient to guarantee that the adjoining panels are in sufficient abutment in a direction perpendicular to the plane of the wall. In order to obtain a sufficient abutment, each wall panel must be of a thicker design than is necessary. There is a relation between the necessary thickness of the wall and the accuracy with which the position of the wall can be measured at a great depth.

[0003] The object of the invention is to provide a method of the type described hereinabove, in which these drawbacks have been overcome and, consequently, a deep wall can be made whose adjoining panels exhibit only a very small deviation relative to each other in a direction perpendicular to the wall to be provided in the ground.

[0004] According to the invention, this object is realized in that the first and the second pit are excavated with an excavator of circular section, designed as a drill head, whereafter the ground panel located between the first and the second well is excavated with a second excavator, laterally fitted with tubular guide elements, which, during excavation, are guided by the walls of the first and the second pit.

[0005] By excavating the ground panel by means of an excavator which, during excavation, is guided by the first and the second pit, provided in the ground earlier, it is ensured that even at a great depth, the panel space thus provided perfectly connects to these two pits excavated earlier. For that purpose, it is of course necessary that the first and the second pit are excavated in the ground truly vertically and this can be effected with drilling equipment which is known per se.

[0006] For excavating the next ground panel, the first pit of that next panel must be free of the hardenable mass provided in the preceding panel. For that purpose, prior to filling the preceding panel space with a hardenable mass, the second pit is separated from the adjacent ground panel by means of a support tube, securable in this second pit, whereafter the newly excavated panel space and the first pit are filled with a hardenable mass. In this manner, the second pit of the preceding panel is kept clear for receiving the tubular guide element of the excavator during excavation of the adjacent ground panel.

[0007] The excavation of a ground panel between two pits provided earlier is effected with a deep-wall cutter, known per se, or a similar excavating apparatus, which, according to the invention, is provided with a tubular guide element at the two short sides thereof, projecting from the excavator on opposite sides in the direction of excavation.

[0008] In this manner, the excavator can be guided perfectly in vertical direction as far as the desired depth of the deep wall. In order to afford the excavator some play, one of the tubular guide elements is connected to the excavator by means of a parallelogram construction, which guide element is held against the excavator by means of springs.

[0009] The apparatus for applying the method according to the invention further comprises a support tube provided on at least one side with an inflatable body, which extends over the tube over at least one-fourth portion of the tube circumference and is inflatable by means of liquid or air.

[0010] Such a support tube can be arranged in the second pit after excavation of a first ground panel, whereafter the remaining portion of the first panel space is filled up with a hardenable mass. After hardening of this hardenable mass, the support tube is removed from this second pit, whereafter the next panel can be excavated, while a guide element of the excavator can be received in the pit from which the support tube has been removed.

[0011] The method according to the invention, and an embodiment of the apparatus for use in this method, will now be further explained with reference to the accompanying drawings. In these drawings:

Fig. 1 is an outline showing the connection problems of successive panel spaces;

Fig. 2 shows the method and apparatus for excavating or drilling the first and the second pit of a ground panel;

Fig. 3 shows the method and apparatus for excavating a ground panel located between two wells;

Fig. 4 shows the filling of the first panel space with a hardenable mass, in the presence of a support tube in the second pit of that panel space;

Fig. 5 shows the excavation of the second ground panel;

Fig. 6 shows a first embodiment of a support tube; and

Fig. 7 shows a second embodiment of this support tube.

[0012] Fig. 1 shows a first panel space A in full lines and a next panel space B in broken lines. The depth L of such a wall is for instance 100 m below the ground level O. The thickness D of the panel space is for instance 1 m, while at a depth of 100 m the overlap d of the two panel spaces must be at least 50 cm in order to obtain an abutting wall that is impervious to water. In that case, the deviation angle α must not be more than 0.3° and this extremely slight deviation is not measurable by the measuring equipment presently available. Consequently, in order to obtain an overlap of at least 50 cm all the same, the thickness D of the wall panel, and hence the allowable deviation angle α, will have to be increased.

[0013] Fig. 2 shows the situation where two wells 8 have been drilled, spaced apart a distance 9, while a third well 8 is being drilled by means of a drill apparatus 1. The wells 8 already drilled are filled with a support liquid 4, such as for instance bentonite. The drill apparatus 1 comprises a Kelly-rod, known per se, whose lower end mounts a drill head 3. The Kelly-rod is suspended from a hoist disc 5, suspended from the drill apparatus 1 by means of a cable 6. The drill head 3 has a weight of about 35 tons, while via the cable 6 a vertical lifting power of about 10-15 tons is exerted on the drill head 3, so that this drill head 3 is suspended with a weight of about 20-25 tons from the drill apparatus 1 in the manner of a plumb. The soil loosened up by the drill head 3 is discharged upwards in a conventional manner, together with the support liquid 4 present in the hole that has already been drilled. In a separator 7, the support liquid 4 is separated from the mass of soil transported upwards, whereafter the support liquid 4 can be supplied again to the well to be excavated. In this manner, truly vertical holes of a depth of more than 100 m can be provided in the ground.

[0014] Fig. 3 shows how the ground panel 11, located between two successive wells 8, is excavated by means of a deep-wall cutter 10. The deep-wall cutter or a similar excavating apparatus such as for instance a grip, is provided with tubular guide elements 12 at the sides thereof, which guide elements have such a diameter that they are movable with some play 14 in a well 8. The guide elements 12 project from the excavator 10 on opposite sides in the direction of excavation, while the projecting parts 13 of the guide elements 12 preferably have a conical shape so that they can be moved probingly within the wells 8. The projecting parts 13 are weighted, so that the deep-wall cutter 10 is pulled into the ground. One of the guide tubes 12 is connected to the excavator 10 by means of a parallelogram construction 16, so that lateral play can be taken up. By means of springs 17, the guide tube 12, connected to the excavator 10 via the parallelogram construction 16, is held against the rubber blocks 18, arranged on the excavator, so that both a positive and a negative play can be taken up. The excavator 10 is suspended from a drill apparatus 1 by means of a cable. It is not necessary to push the excavator 10 into the ground by means of a tube arranged on the trailing end thereof. Mounted on the excavator 10 are pumps 19 for discharging the support liquid blended with the mass of soil, which is fed to a separator 7. The wells 8 accommodating guide tubes 12 have been excavated to a somewhat greater depth than the desired depth of the partition wall to be provided in the ground, in order to accommodate the projecting parts 13 of the guide tubes 12 at the moment when the deep-wall cutter 10 has reached the desired depth.

[0015] As shown in Fig. 3b, the diameter of the wells 8 is greater than the thickness 15 of the ground panel 11, the thickness 15 corresponding, of course, to the width of the excavator 10.

[0016] Because the excavator 10 is guided by the guide tubes 12 as the ground panel 11 is being excavated, a perfect alignment of the panel space 11 with the wells 8, present on both sides thereof, is automatically realized. The maximum deviation is determined by the play 14 between the outer wall of a guide tube 12 and the wall of a well 8.

[0017] After excavation of the ground panel 11 in the manner discussed above, a support tube 20 is arranged in the second well 8, as shown in Fig. 4. This support tube 20 serves to keep open the second well 8 while the hole consisting of the first well 8 and the panel space 11 connecting thereto is filled with a hardenable mass 22. As a hardenable mass, for instance a concrete mixture can be used, optionally further provided with a reinforcement. The support liquid 4, present in the panel during excavation, is displaced by the hardenable mass 22 or pumped off.

[0018] The support tube 20 (see Fig. 6) consists of a metal tube, comprising an inflatable body 21 over at least one-fourth of its circumference in axial direction, which inflatable body, together with the wall of the support tube 20, constitutes an expandable chamber, which can be filled with air or a liquid under pressure. The support tube 20 is fixed in a well such that the inflatable body 21 abuts against the successive ground panel 11. Consequently, the support tube 20 is secured against the inner wall of the well 8.

[0019] After the hardenable mass 22 has at least partially hardened, the support tube 20 is removed from the well 8 after the air or liquid used for expanding the inflatable body 21, is removed by suction. Subsequently, as is shown in Fig. 5, the adjacent ground panel 11 is excavated in the same manner as shown in Fig. 3. The successive panel space thus provided perfectly connects to the preceding panel space, as described hereinabove. Consequently, this means that the thickness of the panel space need not be greater than the necessary thickness d, as shown in Fig. 1. As a result, a considerable saving in material can be achieved. Further, an important advantage is that the total length of the excavator in the direction of the partition wall can be utilized, because an overlap in lateral direction, as shown in Fig. 4 of Dutch patent application No. 87.02430, is no longer needed.

[0020] Fig. 7, finally, shows a second embodiment of the support tube 20. Arranged on one side of the support tube 20 is an inflatable body 21, while on the side opposite this inflatable body there are arranged outwardly projecting support strips 24, between which a sealing strip 23 can be accommodated so as to be axially slidable. When the support tube 20 is removed from a well 8, this sealing strip 23 can be left in the hardenable mass 22 of the preceding panel space and subsequently be incorporated into the hardenable mass 22, to be provided in the next panel space.

Claims

1. A method for providing deep partition walls in the ground, which method comprises:

- excavating a first pit (8) by means of an excavator;

- excavating a second pit (8) by means of the excavator, which second pit (8) is shifted relative to the first pit over a distance (9) approximately corresponding to the greatest length dimension of the excavator;

- excavating, by means of the excavator, the ground panel (11), located between the first and the second pit (8); and

- filling up the thus formed panel space with a hardenable mass (22),

characterized in that

- the first and the second pit (8) are excavated with an excavator of circular section, designed as a drill head (3), and

- the ground panel (11) located between the first and the second well (8) is excavated with a second excavator (10), laterally fitted with tubular guide elements (12), which, during excavation, are guided by the walls of the first and the second pit (8).

2. A method according to claim 1, characterized in that, prior to filling the panel space (11) with a hardenable mass (22), the second pit (8) is separated from the adjacent ground panel (11) by means of a support tube (20), which can be fixed in said second pit (8), whereafter the newly excavated panel space (11) and the first pit (8) are filled with a hardenable mass (22).

3. An excavator for use in the method according to claim 1, comprising a deep-wall cutter or a similar excavating apparatus, characterized in that the excavator (10) is provided with a tubular guide element (12) at the two short sides thereof, projecting from the excavator (10) on opposite sides in the direction of excavation.

4. An excavator according to claim 3, characterized in that one of the tubular guide elements (12) is connected to the excavator (10) by means of a parallelogram construction (16), said guide element (12) being held against the excavator (10) by means of springs (17).

5. A support tube for use in the method according to claim 2, characterized in that said support tube is provided on at least one side with an inflatable body (21), which extends over the tube (20) over at least one-fourth of the tube circumference and can be inflated by means of liquid or air.

6. A support tube according to claim 5, characterized in that the support tube (20), on the side opposite the inflatable body (21), is provided with outwardly projecting support strips (24) for accommodating therein a sealing strip (23) so as to be axially slidable.

Drawing