The present invention relates to underground construction and in particular to a method for introducing a soil penetrating tool into a soil and to an underground construction device. Underground construction often requires a soil penetrating tool to be introduced into soil to a great depth during a penetration process in which an external force acts upon the soil penetrating tool in order to drive the soil penetrating tool into the soil. Examples for such soil penetrating tools may include vibroflots (sometimes also referred to as deep or depth vibrators), sheet pipes for conveying filling material like stones (e.g. gravel), sand, bentonite, cement, concrete, etc. down into the soil and releasing the filling material in the soil for forming bottom feed columns and/or walls of the filling material, sheet piles for forming a sheet pile wall, piles, or the like.

Such soil penetrating tools often rely on crawler cranes which suspend the tool. In projects with large penetration depths, the cost of such crawler cranes can be a substantial part of total cost. If such soil penetrating tools could be built in sections that enter the soil in steps as is, for example, the case for deep drilling techniques where multiple drill rods are connected sequentially to reach the required depth, the cranes could be lighter in weight.

While this is feasible for drill rods, it is highly unpractical for other techniques, for example the production of bottom feed stone columns, since the supply to the vibroflot with electricity, flushing air and water, and the air tight transport of stones etc. are not easy achievable with extendable length segments like they are used with drill rods.

Substantially, the working process includes one or more penetration phases during which the soil penetrating tool is (completely or partially) driven down into the soil and one or more pulling phases during which the soil penetrating tool is (completely or partially) pulled out of the soil (e.g. retracted). During the penetration phase(s), the soil penetrating tool normally has to overcome a considerable soil resistance. The deeper the soil layers to be reached, the higher soil resistance. This is because the surface friction, in addition to the tip resistance, substantially contributes to the soil resistance the soil penetrating tool needs to overcome, and such surface friction rises with increased depth as it is a function of the soil overburden stress. Therefore, a high weight of the soil penetrating tool during the penetration phase(s) is advantageous.

However, during the pulling phase(s), a high weight of the soil penetrating tool is detrimental since it adds to the total weight the crane has to lift. The high weight reduces the stability of the crane, especially if it is strongly inclined. In addition, the ground under the crane is heavily loaded, which can trigger landslides if the crane is located close to a raised edge of the terrain as is, for example, often the case in coal mine reclamation fill compaction projects. In such projects, the center of the crane conventionally needs to be at a certain safe distance from the location where the soil penetrating tool enters the soil so that the crane is required to stay at a safe distance from locations of potential landslides. Hence, there is a need for an improved solution.

According to the present invention, a variable weight load device is used to add extra weight to the soil penetrating tool during its penetration phase(s) but to reduce or remove (e.g. disengage) the extra weight such that it does not contribute to the total weight suspended by the crane during the pulling phase subsequent to a previous penetration phase.

One aspect of the present invention relates to a method for introducing a soil penetrating tool into a soil using a variable weight load device which is coupled to the soil penetration tool. The method includes a penetration phase and a pulling phase. During the penetration phase, the soil penetrating tool is at least partially driven into the soil with the variable weight load device providing a penetration phase weight which acts on the soil penetrating tool. During the pulling phase, the penetrating tool is at least partially pulled out of the soil with the variable weight load device providing a pulling phase weight which acts on the soil penetrating tool and which is lower than the penetration phase weight.

A further aspect of the present invention relates to an underground construction device comprising a soil penetrating tool and a variable weight load device coupled to the soil penetration tool. The underground construction device is configured to perform a penetration phase during which the soil penetrating tool is at least partially driven into the soil with the variable weight load device providing a penetration phase weight which acts on the soil penetrating tool. The underground construction device is further configured to perform a pulling phase during which the soil penetrating tool is at least partially pulled out of the soil with the variable weight load device providing a pulling phase weight which acts on the soil penetrating tool and which is lower than the penetration phase weight.

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which

FIG. 1 is a side view of an underground construction device which comprises a rig suspended from a crane according to one embodiment of the present invention;

FIG. 2 is a perspective view of a section of the rig of FIG. 1;

FIG. 3 is a perspective view of a section of a rig that is equipped with a variable weight load device according to a further embodiment of the present invention;

FIG. 4 is a perspective view of a rig that is equipped with a variable weight load device according to still a further embodiment of the present invention;

FIG. 5 is a side view of the variable weight load device of FIG. 4 during a penetration phase; and

FIG. 6 is a side view of the variable weight load device of FIG. 4 during a pulling phase.

FIG. 1 shows an underground construction device 100 with a crawler crane 110 and a bottom feed rig 120 suspended from the crawler crane 110. An enlarged section of the rig 120 is illustrated in FIG. 2. The underground construction device 100 serves to produce gravel columns in a soil 200. By help of a guide fork 2, a bucket 11 filled with gravel fills the gravel into a hopper 3 from where it drops into a silo tube 12. A vibroflot 16 is attached to the bottom end of the silo tube 12. For operation, the lower part of the silo tube 12 and the vibroflot 16 attached thereto are introduced (i.e. moved down) into the soil 200 to a pre-defmed depth. From the silo tube 12, the gravel gets to a tremie pipe (not shown) along the vibroflot 16 to the bottom tip of vibroflot 16 where it is released into the soil 200

Simultaneously or subsequently, the released gravel is compacted by the vibrating vibroflot 16. During compaction, the silo tube 12 with the attached vibroflot 16 may be pulled up and moved down alternately. Thereby, the bottom part of the silo tube 12 and the vibroflot 16 may remain below the surface 201 of the soil 200. The result is a section of a gravel column to be produced. In this manner, the gravel column can be completed by sequentially forming such sections one above the other at different depths. When the gravel column is completed, the silo tube 12 with the attached vibroflot 16 may be completely pulled out of the soil 200. In the following, the part of the rig 120 penetrating the soil 200 is also referred to as soil penetrating tool.

The described process includes two kinds of phases: penetration phases and pulling phases. A penetration phase is a phase in which the bottom end of the rig 120 (in this embodiment the bottom part of the silo tube 12 and the vibroflot 16) is in contact with the soil 200 and moves downward into the soil 200. A pulling phase is a phase in which the rig 120 is moved upward, i.e. in a direction in which it can be pulled out of the soil.

As initially described, a heavy weight load acting on the rig 120 can advantageously support the penetration in the penetration phases. In contrast, in the pulling phases the weight load acting on the rig 120 is reduced. In order to temporarily provide such a heavy weight load acting on the rig 120 during the penetration phases but not during the pulling phases, the rig 120 is equipped with a variable weight load device which in the present embodiment is at least one ballast tank 4. In the following, the ballast tank 4 is also referred to as liquid storage reservoir.

In the illustrated embodiment there are six ballast tanks 4. However any other number of ballast tanks 4 may also be used. For example, there may be just one ballast tank 4, or at least two ballast tanks 4. These ballast tank(s) 4 can be filled with a liquid (partially or completely), for example water, and (partially or completely) emptied via either only one hose 13, or they can be filled via one hose 14 and emptied via another hose 13. The liquid can be operated in a closed cycle via a ground-based tank 15 from which it is pumped back and forth between ground-based tank 15 and the ballast tank(s) 4. If such a ground-based tank 15 is used, the hose(s) 13 (and 14, if provided) each connect the ground-based tank 15 and the at least one ballast tank 4. It is to be noted that the liquid is not restricted to water. In principle, any other liquid may be used as well. In particular, a mixture of water and antifreeze agent may be used.

In preparation for the penetration phases, the ballast tank(s) 4 can be partially or completely filled with the liquid in order to provide a heavy weight load (in the following also referred to as penetration weight) on the rig 120, and in preparation for the pulling phases, the ballast tank(s) 4 can be partially or completely emptied in order to provide a reduced weight load (in the following also referred to as pulling weight) on the rig 120. That is, the pulling weight is significantly lower than the penetration weight. For example, the difference between the penetration weight and the pulling weight may be at least 1500, kilograms, at least 5000 kilograms or even at least 10000 kilograms.

Some more details of a possible variant of such temporary liquid ballasting system are shown in FIG. 2. The rig 120 is suspended from the crawler crane 110 via a lifting head 1. The bucket 11 in this variant is not impeded in its motion by the ballast tanks 4 which are installed on a support frame 9. In the present example, the capacity of each of six ballast tanks 4 is, at least 1.5 m ³ . That is, the total capacity amounts to at least 9 m ³ . If a liquid having at least the density of water is used, the maximum possible difference between the penetration phase weight and the pulling phase weight may be 9000 kg. Of course, any other difference of more than 0 kg and less than 9000 kg may be used as well.

If there are two or more ballast tanks 4, all ballast tanks 4 may be interconnected via hoses 5, 10 in fluid connection so that they can commonly be filled and emptied via either a common hose 13 or, as illustrated in FIG. 1, a pair of hoses 13 and 14.

As illustrated in FIG. 2, the gravel is transported by a bucket 11 that is guided by a fork 2 to drop the gravel into the hopper 3 and from there into a first tank 7. This first tank 7 is separated from the hopper 3 by an air tight gate. Further, the first tank 7 is separated from a second tank 8 by another gate. The two gates together form the so called “double lock”. According to a further embodiment illustrated in FIG. 3, a variable weight load device (not shown) may be installed in a space between a lower end of a bucket frame 520 holding at least one gravel bucket 521, 522 and the at least one gravel bucket 521, 522. In the embodiment of FIG. 3, the variable weight load device may also include at least one ballast tank 4 which is/are installed in the space between the lower end of the bucket frame 520 and the at least one gravel bucket 521, 522 and which is/are operated using a ground- based tank 15, one or two hoses 13, 14 and a liquid as described above with reference to FIGS. 1 and 2. The ground based tank 15 is optional if the liquid is water, in which case the water can also come from a water mains or a surface water body (pond, lake, river) directly.

According to a further embodiment illustrated in FIG. 4, a variable weight load device may include an additional ballast weight 18 which is suspended by wire ropes 17. The wire ropes 17 run through two winches 19 which are coupled to the silo pipe 12 and the vibroflot 16 coupled to the silo pipe 12. In the illustrated embodiment, the winches 19 are mounted to the hopper 3. Instead, the winches could be mounted to any other suitable part of the rig 120.

When the ballast weight 18 shall act to support penetration, i.e. during the penetration phases, it is lifted by the winches 19 from the soil surface 201 (FIG. 5), while when it shall not act as additional weight, i.e. during the pulling phases, it can rest on the soil surface 201 (FIG. 6). If in a penetration phase the ballast weight 18 is hovered above the soil surface 201, the ballast weight 18 is active and acts on the rig 120 thereby supporting the penetration process. If in a pulling phase the ballast weight 18 rests on the soil surface 201, the ballast weight 18 is inactive and does not act on the rig 120 so that the crawler crane 110 is not required to hold the weight of the ballast weight 18.

Using this principle allows for quickly switching from a penetration phase to a pulling phase and vice versa since the ballast weight 18 only has to be raised or lowered by a small distance. That is, in order to make a transition from the penetration phase to the pulling phase, the ballast weight 18 may be moved along the soil penetrating tool so that it is moved from a suspended state into a state in which it rests on the surface 201 of the soil 200. As compared to the embodiments described with reference to FIGS. 1 to 3, such a switching between the penetration phase and the pulling phase and vice versa is much faster than the time needed to fill or empty a ballast tank 4.

The ballast weight 18 may be a solid weight, e.g. made of stone or metal like iron, steel, etc, or a liquid-filled container. In case of a liquid-filled container, the same kinds of liquids described with reference to FIGS. 1 to 3 may be used. According to one embodiment, the ballast weight 18 may have a ring shape (e.g. a “donut shape”) and surround the soil penetrating tool.

In the following, some example embodiments of the present invention are summarized here. Other embodiments can also be understood from the entirety of the specification and the claims filed herein.

Example 1 : An underground construction device for vibro compaction and stone column installation, or vibrated sheet pipe or pile segment, is temporarily ballasted by an extra weight during penetration phase.

Example 2: The underground construction device of example 1 using liquid storage reservoirs as shown for example in FIG. 1 and FIG. 2 that are filled and emptied via hoses and thereby allow to raise the total weight of the rig during its penetration to depth, when higher weight is favorable to reach the necessary depth, and reduce its weight during retrieval of the rig from the ground, so that the necessary pulling capacity of the carrier crane, which is pulling on lifting head, is minimized.

Example 3 : The underground construction device of example 1 or 2, where the ballast weight is part of a secondary tool (for example the gravel bucket as per Fig. 3) that is at least temporarily suspended not from a carrier rig but by the primary soil penetrating tool itself, thus adding extra weight to such tool during penetration without needing extra lifting capacity from the crawler crane.

Example 4: The underground construction device of one of examples 1 to 3, where the ballast weight, favorably in a ring-shape (e.g. “donut shape”), with the soil penetrating tool (e.g. vibroflot rig) running through the middle of such donut, is lifted by a winch attached to the soil penetrating tool but not connected to any secondary device such as gravel bucket.

Example 5: The underground construction device of one of examples 1 to 4 having the advantage that the acting ballast weight can be rapidly changed by the ballast weight hovering close to the soil surface so it can be either fully suspended and hence act with its full weight or be deactivated by setting it on the ground surface.

Example 6: The underground construction device of one of examples 4 and 5 with the ballast weight resting on the soil surface and the at least one winch allowing for a computer-controlled force activation that can mobilize any desired force between zero and the full weight of the ballast weight.

Example 7: The underground construction device of any one of the preceding claims, wherein the device comprises a vibroflot.

In all embodiments of the present invention, the underground construction device may be operated such that during none of the pulling phases the respective variable weight load device imposes weight on the soil penetrating tool. This helps to avoid that the initially described problems occur at any time.

It is to be noted that all features of the embodiments described herein may be combined unless they exclude each other. It is further to be noted that the inventive principle is not restricted to the described embodiments. For example, the principles of the variable weight load device may be applied to any soil penetration tool with or without a vibrobflot. As a person of ordinary skill in the art will appreciate, these principles may also be realized without described details like the double-lock, the bucket 11, bucket gravel reservoirs 521, 522, the ground-based tank 15, the crawler crane 110, etc. Reference numerals

1 lifting head

2 guide fork

3 hopper

4 ballast tank

5 hose

7 first tank

8 second tank

9 support frame

10 hose

11 bucket

12 silo tube

13 hose

14 hose

15 ground-based tank

16 vibroflot

17 rope

18 extra ballast

19 winch

100 underground construction device 110 crawler crane

120 rig

200 soil

201 soil surface

520 bucket frame

521 bucket gravel reservoir

522 bucket gravel reservoir