FIELD OF THE INVENTION

The present invention relates to a method of cutting foundation elements in the ground.

BACKGROUND OF THE INVENTION

When constructing tunnels in urban areas, one usually faces the problem of encountering, on the foreseen site of the tunnel, different foundation elements that have been installed previously for existing structures.

In addition, tunnels are constructed at an increasing depth (e.g. up to 35 meters) in order to take into account already existing tunnels or other structures, in particular in dense urban areas.

This sometimes leads to drilling the tunnels under the ground-water level, at a depth that involves hyperbaric conditions.

Tunnelling machines are not presently able to break or to push aside from their path all kinds of foundation elements, which thus may block or break the cutting head of the tunnelling machine.

Such cases require a human intervention ahead of the cutting head of the tunnelling machine, in order to break the element manually and then evacuate the broken pieces to the ground surface.

However, such human interventions are time consuming and, in case of hyperbaric conditions, particularly hazardous.

It is sought a method for removing foundation elements from the ground before tunnelling machine arrival that do not require any human intervention at the depth of the tunnel.

If the foundation elements are small and short enough, e.g. piles having a diameter of less than 500 mm, it is possible to extract them by pulling them up from the ground.

However, for larger foundation elements (e.g. with a diameter of more than 1 .20 meter), no method has been satisfactorily developed yet.

The article by T. Ishimura et al., "Development of removed pile method with cutting", Tunnelling and Underground Space Technology 21 (2006) 41 1 -412, describes a method of cutting piles in the ground in order to remove them.

According to this method, a cylindrical pile having a diameter of 1.10 meter can be removed by the following steps: - drilling a circular bore around the pile with a reaming cutter,

- arranging within this bore a casing that comprises a pulley system for a diamond wire, so as to bring the diamond wire down to the desired cutting depth,

- cutting the pile horizontally at the cutting depth.

However, this method is specific to piles with a circular cross-section and with a limited diameter.

Besides, the casing that supports the cutting device is bulky and thus not easy to use in areas with existing dense constructions.

In addition, this method is limited to intermediate cutting depths of 20 meters and is thus not able to solve all the problems mentioned above.

One goal of the present invention is thus to provide a method of cutting a foundation element of any shape and any size and at deeper levels than already known.

BRIEF DESCRIPTION OF THE INVENTION

The invention provides a method of cutting a foundation element in the ground, characterised in that it comprises the steps of:

(a) drilling at least two borings in the ground around the foundation element,

(b) wire sawing the ground in the vertical direction between said borings without cutting the foundation element, until the desired cutting depth,

(c) bringing down a single sawing wire in the vertically sawed ground until the cutting depth,

(d) wire sawing the ground and the foundation element in the horizontal direction at the cutting depth.

According to a preferred embodiment of this method:

- step (a) comprises drilling three borings in the ground around the foundation element, wherein said borings form a triangle,

- step (b) comprises wire sawing the ground in the vertical direction between a first and a second boring on the one hand and between the first and the third boring on the other hand,

- step (c) comprises bringing down said single wire in the vertically sawed ground between the second and the third borings.

By "foundation element" is meant in the present text any element that can be found in the ground in order to be used as a foundation for a structure, including piles, barrettes, casings, inclusions, etc. The material of the foundation element can be concrete and/or metal and/or any material that can be cut by a diamond wire.

The cross-section of the foundation element can be of any shape such as circular, oblong, rectangular, etc.

According to an advantageous embodiment of the invention, the single sawing wire of step (c) is obtained by connecting the two sawing wires used in step (b).

To that end, these cutting wires can be brought back to the ground surface between step (b) and step (c) in order to be connected.

During step (d) the foundation element is preferably hung from the ground surface so as to prevent crushing of the sawing wire.

The method comprises a further step of removing from the ground at least one portion of the foundation element situated above the cutting depth.

According to an alternative embodiment, the method comprises, before step (c), a further step of cutting the foundation element into two portions in the vertical direction.

The method allows cutting foundation element having a cross section of more than

1 m ² , preferably of more than 3 m ² , and at a cutting depth of more than 35 meters.

The method also allows cutting simultaneously a plurality of foundation elements: in such case the borings are drilled around said plurality of foundation elements.

Step (a) may comprise drilling at least four borings around the foundation elements.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be apparent with reference to the detailed description of the invention that follows and referring to the appended drawings in which:

- Figure 1A shows a top view of the foundation elements and of the three borings that are drilled around it,

Figure 1 B is a section of Figure 1A according to a vertical plane,

Figure 2A shows a top view of the cutting wires and the foundation element during the vertical ground cutting step,

- Figure 2B is a vertical section according to A-A of Figure 2A,

Figure 3A shows a top view of the step of connecting the two cutting wires to form a single wire,

Figure 3B is a section of Figure 3A according to a vertical plane,

Figure 4A shows a top view of the foundation element during the horizontal cutting step, Figure 4B is a section of Figure 4A according to a vertical plane,

Figures 5A and 5B shows an alternative embodiment in which a plurality of foundation elements are cut simultaneously and wherein four borings are drilled,

Figures 6A and 6B show an alternative embodiment in which only two borings are drilled around a circular foundation element,

Figures 7A and 7B show the installation of a casing within a boring,

Figs. 8A shows the installation of a cutting tower supporting the pulleys for the sawing wire,

Figs. 8B and 8C are sectional views of Fig. 8A according to A-A and B-B, respectively,

Fig. 9A and 9B illustrate the preparation step for the removal work,

Figs. 10A and 10B show the lifting of the foundation element,

Figs 1 1 A and 1 1 B illustrate the final lifting step,

Figs 12A and 12B show the removal of the last portion of the foundation element and the filling of the space remaining void after the removal of the foundation by a bentonite- cement grout,

Figs 13A to 16B show the implementation of an alternative embodiment in which the foundation element is also cut vertically,

Figs 17A to 20B show the implementation of the method when the foundation element is inclined.

DETAILED DESCRIPTION OF THE INVENTION

Cutting stage

The different steps of the cutting stage are described hereinafter with reference to Figs 1 to 6.

In this non-limitative example, the foundation element 1 to cut and remove is a barrette having a rectangular cross-section of dimensions 1.20 x 2.80 meters.

Of course, the foundation element could be of any other shape, e.g. circular, oblong, triangular, etc. and of any dimension.

As shown on Fig. 1 A, which is a top view of the foundation element 1 , three borings B1 ,

B2, B3 arranged so as to form a triangle around the element 1 are drilled in the ground.

The borings B1 , B2 and B3 must be sufficiently far the ones from the others such that a line linking two borings does not intersect the foundation element.

Fig. 1 B is a section of Fig. 1A in a vertical plane, on which a drill rig 2 has been illustrated. The dotted circle shows schematically the foreseen site of the tunnel, with a mean depth referred to as ZT, whereas the ground level is referred to as Z0.

The cutting depth ZC is thus under the site of the tunnel.

The borings are thus drilled slightly deeper than the cutting depth ZC.

The depth ZC can be up to 40 meters. In addition, it may be under the ground-water level.

According to a usual practice, the borings can be filled with a drilling mud, e.g. bentonite grout.

In a second step of the method, shown on Figs 2A and 2B, the ground is sawed between a first boring (here, B1 ) and a second boring (here, B2) and between said first boring and the third boring (here, B3).

To that end, tubes containing pulleys for passing a sawing wire are lowered within each of the borings B1 , B2 and B3.

Only two pulleys have been shown on Fig. 2B: a top pulley P1 (respectively P2) that remains at the ground surface, and a bottom pulley PV (respectively P2') that is lowered within the boring B1 (respectively B2) until the cutting depth ZC.

Of course, a greater number of pulleys can be used if necessary.

The diameter of the borings B1 , B2, B3 is chosen to allow the passage of the tubes and the pulleys; for example, a diameter of about 500 to 600 mm is usually appropriate.

A first sawing wire W1 is moved in loop between the borings B1 and B2 by a saw wire machine 3 that drives it thanks to the pulleys P1 , PV, P2 and P2'.

As a consequence, the ground between the borings B1 and B2 is progressively cut in the vertical direction, until the cutting depth ZC.

Similarly, a second sawing wire W2 is moved in loop between the borings B1 and B3 and cuts the ground between these two borings.

The cutting wires W1 , W2 are preferably diamond wires that are currently used in this field to cut stones, concrete and metal.

In a third step, a single sawing wire W is lowered in the trenches formed between the borings B1 and B2 and between B1 and B3 by the sawing wires W1 and W2.

According to a preferred embodiment of the invention, the single wire W is obtained by connecting the two cutting wires W1 and W2, as shown on Fig. 3A. The right side of Fig. 3A is an enlarged view of the left side that shows the connection of wires W1 and W2.

At this stage, it is also possible to check the condition of the cutting wires and, if necessary, replacing or repairing them. When the single sawing wire W reaches the cutting depth ZC, it is released from the pulleys of the first boring B1.

As a consequence, it begins cutting the ground and the foundation element 1 in the horizontal direction, like a lasso (see Figs. 3B to 4B).

In an advantageous embodiment of the invention, during this step of horizontal cutting, the foundation element 1 is hung from the ground surface by appropriate means (not shown) so as to prevent crushing of the sawing wire W due to the weight of the element 1 that tends to close the cut portion.

When the foundation element 1 is fully cut, the sawing wire W is brought back to the ground surface. The tubes inserted in the borings B1 , B2 and B3 are also removed.

Then, the foundation element 1 can be removed from the ground by any appropriate extracting means. This stage will be described in detail below.

Of course, it is possible to drill more than three borings around the foundation element, e.g. four borings arranged so as to form a rectangle.

In such a case, the sawing steps are explained below with reference to the example of

Figs. 5A and 5B.

It can also be noted that, contrary to the known methods, the same device is used to bring the sawing element at the desired cutting depth and to carry out the horizontal cut of the foundation element.

In other words, the wire that saws the foundation element gets to the desired cutting depth by its own means.

As a consequence, the method according to the invention is able to remove deeper foundation elements than in the prior art, requires less cumbersome means and is easier to perform.

According to another embodiment of the invention, illustrated on Figs. 5A and 5B, a plurality of foundation elements 1 , 1 ', 1 ", etc. are cut together.

For example, these foundation elements are a group of precast piles having each a square cross-section of 500 x 500 mm.

To that end, at least three but preferably at least four borings B1 , B2, B3 and B4 are drilled around the plurality of foundation elements.

The borings are preferably arranged so as to form a rectangle that surrounds the foundation elements without intersecting them.

As shown on Fig. 5A, three sawing wires W1 , W2 and W3 are used to perform vertical cuts in the ground between, respectively, B1 and B2, B2 and B3 and B1 and B4. When the cutting depth is reached, one single sawing wire W is lowered until the cutting depth and released from B1 and B2 and begins cutting the elements according to the same principle of the lasso as explained above.

According to another embodiment of the invention, illustrated on Figs. 6A and 6B, only two borings B1 , B2 are drilled in diametrically opposite positions around the foundation element 1 , which has here a circular cross-section with a diameter between 900 and 1200 mm and is preferably a metal pile.

The method of cutting described above remains substantially the same, except that during the vertical sawing step, the two sawing wires W1 , W2 slide along the foundation element 1. Contrary to the other examples, the vertical cut thus does not follow a straight line but a curved one.

When the cutting depth is reached, one single cutting wire W, which can be made by connecting the wires W1 and W2, is lowered at the cutting depth and released from the boring B2.

Of course, these various embodiments can be combined and the skilled person will be able to adapt the disclosure of these various embodiments to the particular shape and configuration of any foundation element and to determine the optimal number of borings to drill.

Figs 7A to 8C show with further details the structure of the cutting system.

Fig. 7A shows a top view of one of the borings (e.g. B1 ) drilled around the foundation element (not shown here).

The boring B1 is filled with bentonite grout b and a casing 10 consisting of a pipe that presents a diameter smaller than that of the boring (e.g. 400 mm for a 600 mm boring) is inserted within the boring.

The pipe is made of any suitable material, e.g. PVC.

Fig. 7B is a sectional view of Fig. 7A in a vertical plane.

The length of the casing 10 is at least equal to the cutting depth ZC.

Fig. 8A is a sectional view of the cutting tower installed in the casing 10.

A cutting tower 1 1 comprising a steel frame is installed above the ground surface Z0 and in the casing 10 to support the upper and lower pulleys P1 and P1 ' that drive the sawing wire W1 (represented with a dotted line at different depth within the ground) and a pump pipe 12.

The pump pipe 12 allows pumping the particles of soil, sand and gravel that are brought down by the sawing wire and accumulate at the bottom of the boring. As the lower pulley PV goes down within the casing 10 along the cutting tower, the sawing wire W1 cuts the PVC casing.

Fig. 8B is a section of Fig. 8A according A-A and fig. 8C is a section of Fig. 8C according B-B, i.e. at the depth of the lower pulley P1 '.

Removal stage

After the foundation element is cut horizontally at the desired depth, at least one portion of it is removed from the ground.

The steps of the removal method are described hereinafter with reference to Figs. 9A to

12B.

This method is described based on the same foundation element 1 that the one shown on Figs. 1 to 4.

In a first step, shown on Figs. 9A and 9B, a concrete foundation 4 is built in the ground around the foundation element 1.

This foundation 4 is intended to support an extraction frame 5 that supports a working platform 6 on which two hydraulic jacks 7 are installed, as can be seen on Figs 10A and 10B.

Besides, cables 8 are anchored in the foundation element 1 to enable it lifting by the hydraulic jacks 7.

Of course, the number of cables and jacks can be different depending on the size and weight of the foundation element.

In addition, if necessary, water jets (shown on Figs 9A and 9B) are implemented in borings 9 along the foundation element 1 , in order to lower the friction between the element 1 and the surrounding ground.

Since the casings and the cutting towers installed in the borings B1 , B2 and B3 are now useless, they are removed from the borings.

With reference to Fig. 10B, the hydraulic jacks 7 pull off the foundation element 1 of a certain height - e.g. about 5 meters - above the ground surface Z0, then this part of the element is broken into pieces and removed.

A further portion of the element can then be lifted, broken and removed, until the foundation element is extracted at the desired level.

When a sufficient portion of the foundation element 1 has been removed, i.e. when the bottom of the foundation element is above the tunnel site, as shown on Fig. 1 1 B, the removal of the foundation element can be stopped.

To that end, the foundation element 1 is lifted at a suitable height above the ground level Z0, a temporary support 13 is fixed within it and lateral lifting devices 14 are installed, as shown on Figs. 1 1A and 1 1 B. Referring to Figs. 12A and 12B, the foundation element 1 is then lifted of a suitable height (e.g. 5 meters), then a last cut is carried out at the ground level Z0.

The cut element V is then removed by a crane 15.

At the same time, a bentonite-cement grout be is injected in the space remaining void under the foundation element, in order to maintain the foundation element 1 in this final position.

When the path for the tunnel is drilled, the bentonite-cement grout does not damage the cutting head of the tunnelling machine.

This description of the removal stage is not intended to be limiting and the skilled person could use other devices or techniques without departing from the scope of the invention.

Alternative embodiment - additional vertical cutting of the foundation element

According to an alternative embodiment, illustrated on Figs 13A-16B, the foundation element 1 can be cut in the vertical direction after having been cut horizontally at the desired cutting depth ZC.

As shown on Figs 13A and 13B, the foundation element 1 which is here rectangular is cut in two halves at mid-length.

To that end, two additional borings B1 ' and B2' are drilled on either side of the foundation element and a sawing wire W3 is driven between these two additional borings by the sawing machine 3.

The principle of this cut is the same as the one described above.

When the sawing wire reaches the cutting depth ZC, it is brought back to the ground surface and the cutting devices are removed from the additional borings.

The vertical cutting line CL of the foundation element is represented by a dotted line on Figs 14A and 14B.

Then, if necessary, bentonite grout b is injected around the foundation element 1 in order to reduce friction between the foundation element and the ground.

The borings B1 , B1 ', B2, B2' and B3 are filled with concrete. This allows the borings to become foundations for a working platform 6 that will be used to remove successively the two halves of the foundation element.

With reference to Figs 15A and 15B, the first half 1 a of the foundation element is lifted by hydraulic jacks 7. To that end, as already described above, two or more cables 8 are anchored in the first half 1 a of the foundation element and are connected to the hydraulic jacks 7. Referring to Figs 16A and 16B, when the first half 1 a of the foundation element is removed, the second half 1 b of the foundation element is removed by the same technique as previously.

When this second half of the foundation element is removed, the resulting space is filled with bentonite-cement grout be.

This step of vertical cutting is particularly advantageous when the foundation element has a large width.

Indeed, it reduces the weight of the element to pull out, and the removal of the first half of the foundation element, that requires the most important pulling effort, can be performed by leaning on the second element.

Alternative embodiment - inclined foundation element

The previous description was made referring to a vertical foundation element.

However, the invention also applies to inclined foundation elements.

This case will be described with reference to Figs 17A to 20B.

In a first step, illustrated on Figs 17A and 17B, an excavation 20 is performed on the site of the inclined foundation element 1 (which is here a cylindrical pile), in order to locate its orientation.

As shown on Figs 18A and 18B, a working platform 21 is installed above the excavation 20 in order to allow the passage of vehicles and the installation of the cutting and extraction devices.

At this stage, a drill rig 2 drills three bores B1 , B2 and B3 forming a triangle around the foundation element 1 , below the desired cutting depth ZC. This step has already been described in detail above.

As shown on Figs 19A and 19B, a sawing wire W cuts the inclined foundation element 1 horizontally.

Then, referring to Figs 20A and 20B, a cable 8 is anchored in the foundation element 1 and a hydraulic jack 7 pulls off the pile of the desired height.

In this case, the pulling direction is inclined of the same angle as the inclined foundation element.

If necessary, borings (not shown) can be drilled around the foundation element in order to inject water jets between the pile and the ground to reduce the friction coefficient.