The invention is related to a method of installation of a drill pile in a sensitive area and the drill pile used in it, wherein compressed air drilling is performed inside the pile and the material drilled is brought up mainly inside the pile.

Conventional compressed air drilling may draw up groundwater outside the pipe thus declining the groundwater level. This causes collapsing of buildings in a sensitive area.

A drill pile wall is a watertight retaining wall structure that is generally used in soft soil bases or often in non-cohesive soil as well. Drill pile walls are often built using drill piles that are drilled or driven into the ground including steel sheet piles for connecting drill piles together to form a retaining wall structure. The bottom end of individual drill piles is most often supported by drilling it into rock. Drill piles with interlock connectors, drill pile walls and/or Combi walls are manufactured, for example, by SSAB, whose drill piles known by the product names RD, RM/RF or by the E21 interlock are suitable for building drill pile walls. RM refers to a male interlock and RE to a female interlock fitted in it. To produce the wall structure, SSAB's round drill piles are drilled into the ground, completely filled with concrete and finally sealed along the RE interlock channel, for example.

Ground layer and rock structures are not of a uniform quality. Rock can have fractures, in which drilling produces leaking routes for the groundwater. With a conventional method, overflushing often takes place causing an excessive discharge of mass from the drill hole, which decreases the bearing capacity of the surrounding soil layer and leads to movement of soil layers.

Publication CN 111576406A proposes installation of a pile in a groundwater area, wherein water is supplied from a separate well to the groundwater area for controlling the groundwater level. This recharge well is always separate from the drill head .

The object of the construction according to the invention is to provide a method of drilling a pile into soil, which is more advantageous than prior art methods. The characteristic features of this invention appear from the appended Claim 1. Another object of the invention is to provide a pile that is better than heretofore for use in a sensitive area, such as a groundwater area, and a firm pile wall.

According to the invention, when drilling a pile using compressed air, liquid, generally water, is simultaneously pumped with a channel external to the pile to the bottom end of the pile - generally above a reamer - which replaces the amount of rising groundwater so that the groundwater level does not decline substantially. In addition, supplied water improves the drilling event and it makes the mass exit more efficient. Water or other liquid is injected preferably with a weight ratio of 5% to 200%, more preferably 70% to 160% relative to normal air. Thus, the level of compressed air used and thereby also the risk of collapse of the adjacent soil layer can be reduced . The injection of water or other similar liquid under the drill head has several effects. The groundwater level can be regulated and it can be ensured that its level does not decline and cause problems to nearby buildings. A supply of liquid reduces friction during drilling, which then provides several effects. In addition, it improves the drawing-out of material during air drilling. Mass rises in a better way when the average specific weight of fluid (mixture of water and air) increases. Thirdly, it reduces the noise and vibration caused by drilling.

Related to the previous point, a drill head is advantageously used, which leads the main part of flushing air into the pile as a discharge flow and only a part to the face area to collect discharged material to be transported away.

When pile drilling is complete, the drilling equipment is removed, reinforcements are generally installed inside the pile and concrete is cast inside it. At the same time, concrete is pressed down via said external or injection channel. Advantageously, there is a plug in the channel for injecting crushing or other similar defective point. The location of this defective point is previously determined with a soil analysis. The solution is suited to an individual pile or piles of a pile wall .

If possible, drill piles extend to rock, whereby a solid foundation is achieved.

A drill pile wall preferably includes several drill piles that are connected to each other with interlocks and extend to rock by 0.7 to 5 x D, pile diameter. Rock at the bottom end of the piles includes sealing subconcrete, which is arranged to prevent harmful transfer of groundwater from underneath.

Subconcrete is preferably structural concrete.

Often, at least one exploratory well is made (diameter 200 - 400 mm) adjacent to the work area to monitor the groundwater level .

Suitable drilling equipment for this is proposed in patent FI 126918, for example. A commercial model is Liebherr's LRB255, for example.

The invention is described below in detail with reference to the accompanying drawings that illustrate some of the embodiments of the invention, in which

Figure 1 illustrates an embodiment of drilling equipment used in the method in its entirety,

Figures 2a - 2c show the steps of a wall installation,

Figure 3a is an RM/RF interlocking section [SSAB] ,

Figure 3b is an alternative interlock connection,

Figure 4a is a detail view of an interlock connection with an injection channel for water supply,

Figure 4b is a detail view of an interlock connection with an injection channel for concrete injection and sealing with a locking connection,

Figure 5 is a detail view of the beginning of pile drilling, Figure 6 is an advantageous drill head (without a reamer) , Figure 7 is an advantageous cross-sectional view of a drill head,

Figure 8 is a schematic view of mass flows in a drill head with a partially sectional view of a pile wall in the soil. A structure of soil layers according to Figure 1 may create a risk for building, when installation of new piles breaks the sensitive balance of groundwater. In Figure 1, the moraine soil layer extends to the bedrock 205. On top of it, there is the groundwater layer 203 having a surface level 204. The surface level 204 of groundwater can be observed using a well 45 that is external to the work area and drilled up to the depth of groundwater. The pressure difference delta p is also indicated in the figure.

Figure 1 illustrates drilling equipment 100 according to the invention in its entirety. The drilling equipment 100 can be movable, for example, supported to a frame, which has a crawler chassis 102 and a tower 104, to which the drilling equipment 100 itself is supported. The drill head 6 of the drilling equipment 100 is rotated by means of rotation equipment 50 via a drill rod 52. Advantageously, this is a pneumatic percussion drill (DTK hammer) with its exhaust air functioning as flushing air during material removal. Pressurised flushing air is delivered to the drill head 6 (comprising a main drill bit 5 (pilot drill bit) and an expansion drill bit 9 (reamer) , Figures 6 and 7) from pneumatic equipment 54. Drilling equipment according to the invention is designed for pipe mounting drilling, wherein a pile 3 forming a protective pipe is fed after the main drill bit 5. The percussion equipment for the drilling equipment, the rotation equipment, pneumatic equipment and other peripheral equipment can be completely according to prior art. When drilling using the drilling equipment according to the invention, the drill head 6 rotates while the pile 3 follows after the drill bit head 6 non- rotatingly simultaneously forming a protective pipe for drilling . A percussive pneumatic drill is advantageously used. In the structure of the pneumatic drill bit, the surface area of air channels leading inside is preferably larger than the surface area of those leading outside. Advantageously, such a preferable pneumatic drill is proposed in patent FI 130193. It is disadvantageous if the major part of air is discharged outside the pile.

Several piles are installed in series, generally 5 to 50 piles, in which case base sealing is cast for them after drilling. If the groundwater level starts to decline, sealing is made earlier .

According to Figure 1, drilling of each pile 3 is extended to the bedrock 205, where the bottom ends of piles 3 are sealed to cut off the flow of groundwater in the direction of the rock surface .

Figures 2a - 2c illustrate the steps of building the pile wall. Figure 2a shows only the drill rod of the drilling equipment and the percussion drill equipment placed in the pile. Piles 3 are immediately filled with water (water filling 203') in their installation depth once the drilling equipment has been lifted up and the water level in the piles is kept essentially the same or higher than the groundwater level 204, water supply 23 is from several piles 3 in the figure. In this way, the groundwater level can be controlled in an efficient way.

In 2b, the last pile 3x of the series is almost in the final depth. When the drill head 6 is lifted off (expansion drill bits 5 inside) , the pile 3 must be pushed to the final depth. Reinforcements can be installed in the piles 3 immediately to wait for later pouring of concrete. When the series is ready for further processing, their bottom is poured with concrete for providing base sealing. In Figure 2b, the last pile 3x of the series is lifted and pushed up and down for moving concrete attached to the rock. Concrete pouring of the base can be successfully performed by pouring plastic concrete through a water column, which makes heavier concrete settle on the bottom of the pile 3. Concrete pouring of the base is preferably made with structural concrete (rock material 0 - 4 mm at the minimum) , which improves the strength values of the structure compared to soldering concrete. When all of the piles 3 of the series are processed in this way, they can be efficiently sealed and the bottom ends of the piles can be locked to the rock 205. At the same time, the bottom ends of the reinforcements 19 are locked to the subconcrete 21.

After partial curing of subconcrete 21' the piles 3 can be filled with concrete up to the top. Concrete pouring 21 stiffens the piles together with the reinforcement 19 and creates a support at the top end of the piles for possible foundations of structures.

RD piles 3 are suitable for watertight installations. The tightness between individual piles is generally provided with an RM/RF interlock 15 - 11 (see Figures 3a, 3b, 4a and 4b) .

Here, a wide RF interlock 11 (female interlock) completely encloses the T flanges 17 of a narrow RM interlock 15 (male interlock) in its groove 16, Figure 3a. It is essential that the interlock completely prevents a transverse displacement within a small manufacturing tolerance. The interlock may also be of another type than the one proposed above. In the case of Figure 3b, symmetrically locking hooks 16 ' are used at the top of the arms 11' and 15' . If the interlock itself does not have a suitable channel, this can be easily made by welding a separate pipe 133 to the root of the longer interlock 15 (Figure 3b) .

The inside (sealing space 17) of the RF interlock 11 is filled with bitumen before installation to provide a good sealing in the complete lock. Via the injection channel 13 of the RF interlock 13, more concrete grout can be pressed later for filling a superimposed annular space and sealing the rock integration. When preparing a pile wall, the RF interlock 11 is always pushed into the RM interlock 15 from above so that the T flange 16 of the male interlock remains inside the female interlock. Therefore, the starting pile must be equipped with two RM interlocks. In each of the later piles, the RF interlock 11 is already installed in the adjacent pile and the RM interlock 15 is on the free side. The reason for this is that the RM interlock 15 is shorter than the RF interlock 11, therefore, the expansion drill bit 5 (reamer) of the drill head 6 does not damage it when drilling a neighbouring pile.

As such, the structure of the interlock may deviate from the above-described one as long as the interlock used is locking in the transverse direction and the dimensions are also arranged according to the reamer of the drill head.

In grab pits of a pilot site, 800 mm RD pile walls were used as building methods. Compressed air was used as the driving power. During the installation of piles, drilling proceeds as fast as 100 cm per minute in clay and moraine and 5 cm per minute in rock.

Since the drill bit sits under the pile 3 and its diameter is approximately 3 cm (generally 2.5 to 5 cm) bigger that that of the pile, the pile must be pushed to the final depth after the drilling process and the annular space in the rock must be filled and sealed. For this purpose, the pile base is filled with concrete for approximately 2 m ³ and then the pile is moved up and down (approximately 1 m) simultaneously vibrating concrete with a vibrator fastened to the drill board. Finally, the pile is brought to its final depth. Vibrations and lifting and lowering of the pile ensure that the entire cavity between the pile and rock is filled with concrete.

For filling the annular space (if any) of the stabilised clay layer, concrete grout is later pushed through the injection channel 13 of the RF interlock 11 (see Figure 4b) . In the wall of the injection channel 13 of the RF interlock 11, i.e. , the female interlock, a hole 135 is drilled and closed with a plug 131 before installing the pile. This location is determined based on soil analyses to be in the area of the clay layer, for example. The plug has a preset holding force. Due to an overpressure that is generated as the concrete suspension is pushed to the interlock, these plugs 131 are opened and the concrete suspension fills the annular space (Figure 3, broken lines around the pile 3) around the pile 3 through the hole 135 at least on one side of the pile.

The channel at the top end of the pile is equipped with a pressure medium connection, which enables pumping of pressurised liquid along the interlock channel to the drilling point downwards in the drilling direction during drilling.

The female interlock includes a connector or a threaded connection for enabling the above-mentioned. The channel is otherwise plugged at the top end.

Liquid can be water or material similar to water & drilling liquid & bentonite or polymer.

Figure 5 illustrates the operation of the drill head 6 slightly more in detail than above. In the figure, drilling of the pile 3 to the moraine layer of soil 20 has started. The drill head 6 draws the pile 3 downwards in a known manner by means of a welded ring, i.e. , a shoe 18 of the pile (Figure 7) . The drill head 6 extends lower than the bottom end of the pile 3 in such a way that the expansion drill bits 5 (reameres) articulated to the main drill bit 9 turn outwards by the force of rotation and reamer out the bottom space. At the same time, air flushing takes drilled material to the intermediate space 20 inside the pile. It is removed out via the upper end of the pile 3. A collection casing complete with piping is possibly used to guide the detritus to a spoil pile (not shown) .

The method has following characteristics. o Piles with interlock connectors are installed one at a time by means of air drilling by injecting water to the groundwater layer from the side of the pile, preferably via an injection channel arranged in the interlock. o The groundwater level is monitored and injection of water is guided accordingly to the groundwater layer with one or more injection channels. o The pile wall preform is filled preferably with water for generating overpressure in the rock area. It is to be noted that since water remains inside the piles, water does not influence the groundwater increasingly. o This takes place only when a drill pile is drilled to rock to provide a rock footing.

Superfluous clay mass or equivalent is thus not dug from the drill hole and overflushing does not take place.

In addition, water is injected via the installed drill pipe simultaneously with drilling ensuring that water is always present in the drilling place where drilling takes place. This eliminates problems related to overflushing and possible pressure waves related to high-capacity compressed air acting on existing pile installations.

When injection is particularly necessary as regards the groundwater level, the groundwater surface is monitored, for example, from another drill hole and the supply of injection water is adjusted as a result of monitoring.

In the supply of injection water, water is supplied with a weight ratio of 5% to 200%, preferably 70% to 160% relative to air. For example, 100 m3 normal air/min and injection water 150 L/min. Even a small amount of water increases the specific weight of liquid (water + air) and improves the mass discharge.

According to Figure 7, drilling equipment 100 comprises a drill head 6, which consists of multiple parts and to which a flushing air flow is brought via percussion equipment 14 along a first flow channel 4. The drill bit head 6 preferably includes a main drill bit 9, i.e. , a pilot drill bit, and expansion means 5, i.e. a reamer. The pile 3 brought after the drill bit head 6 includes an inner space 20 inside the protective pipe created by the front part 18 and the pile 3 between the pile 3 and a drill rod 6 that rotates the drill bit head 6. The pile 3 is functionally connected near the drill bit head 5 by its lower end by means of an arrangement 24. The arrangement 24 preferably comprises in a known manner a welded shoe 18 complete with shoulders. The counter-shoulder of the drill head 6 hits against the shoulder of the welded shoe 18 and the drill head 6 thus draws the pile 3 downwards with it. The use of a welding shoe is not necessary, if the feed equipment is capable of, for example, pushing the protective pipe to the drill hole formed after the drill bit.

The pilot drill bit 9 includes a drill bit surface 12 (face area) and a flushing channel 4 for leading a flushing air flow from the percussion equipment 14 to said drill bit parts of the drill head 6 via the first flow channel. The percussion equipment 14 is advantageously located immediately in the context of the arm of the pilot drill bit 9. The flushing channel 4 preferably has an end wall 30, in the context of which the flushing channel 4 preferably branches forward to the drill bit flushing channels 10 leading to the drill bit surface 12 and away from the drill bit surface 12 towards return channels 1 leading to the inner space 20 of the pile 3. The return channels 1 are arranged in the pilot drill bit 9 between the flushing channel 4 and the inner space 20 of the protective pipe 3 for leading part of the flushing air flow directly to the inner space 20 of the protective pipe 3 for flushing it. The drill bit flushing channels 10, in turn, are arranged to lead compressed air used for flushing from the flushing channel 4 to the drill bit surface 12 of the pilot drill bit 9 for flushing the drill bit surface 12 to remove drill cuttings which are generated when the pilot drill bit 9 and the expansion means 5 rotate and strike in the drill hole 22. The combined cross-sectional area of the return channels 1 is larger than the combined cross-sectional area of the drill bit flushing channels 10 so that the drill bit flushing channels 10 form a sufficiently high flow resistance for guiding the compressed air flow directly along the return channels 1 to the inner space 20 of the protective pipe 3 for flushing it without a counterpressure generated by the soil. With this solution, the compressed air flow coming from the flushing channel 4 can be divided in such a way that at least a major part of the flow turns back along the return channels 1 to the inner space 20 of the protective pipe 3 and a smaller part is led to the drill bit surface 12 of the pilot drill bit 9 to perform flushing of the drill bit surface 12.

Although the use of several return channels, drill bit flushing channels and discharge channels is referred to in the context of the detailed description of the invention, this is only an advantageous embodiment of the invention. It is to be understood that drilling equipment according to the invention can also be implemented using only one return channel, one drill bit flushing channel and one discharge channel.

The compressed air flow led to the drill bit surface 12 of the pilot drill bit 9 via the drill bit flushing channels 10 is led into the protective pipe 3 along the discharge channels 7 formed as an extension to the drill bit flushing channels 10 preferably using the first radial inclined channel 7 ' of the pilot drill bit 9 for leading compressed air towards the outer edge of the pilot drill bit 9 and from there to the expanding section 8 included in the discharge channel 7 along the straight section 26 included in the discharge channel 7. In other words, the discharge channels 7 are arranged in the pilot drill bit 9 as an extension to the drill bit flushing channels 10 for leading compressed air to the inner space 20 of the protective pipe 3. The discharge channels 7 are arranged in the flow direction with an expanding cross-sectional surface area from the drill bit surface 12 towards the inner space 20 of the protective pipe 3. Advantageously, this expanding takes place in the radial direction relative to the axis of rotation of the drill bit head 6 according to Figure 7. In other words, the discharge channels expand when approaching the inner space of the pile 3 as seen from the bottom.

A drill pile wall according to the invention has several drill piles, which are connected to each other with interlocks and have concrete reinforcement inside and extend to rock by 0.7 to 5 times the pile diameter. Rock 205 at the bottom end of the piles 3 includes sealing subconcrete 21', which is arranged to prevent the transfer of groundwater to crushing via rock drillings. Interlocks include a sealing space 17 that seals the female - male (11, 15) connection preventing the flow of water via the interlock.

According to Figure 8, the groundwater level is maintained with both water injected with an injection pipe 13 and a water filling of drilled drill piles. The water layer at the bottom of the pile 3 generates a counterpressure preventing compressed air from escaping to the surrounding of the pile 3. When water is mixed with flushing air (channel 20) , its specific weight increases and it can transport drilled fines away more efficiently .

List of parts

I return channel 21 concrete for pile

3 pile 30 21' subconcrete/ sealing

3' adjacent pile 22 drill hole

3x last pile of series 23 water supply from pile

4 inlet channel

5 cutter 34 drill bits on face area

6 drill head (5 + 9) 35 45 auxiliary well

7 discharge channel 50 rotation equipment

7 ' inclined channel (face) 52 drill rod

8 expanding section (in 54 pneumatic unit channel 7)

9 drill frame 40 100 drill equipment

102 crawler chassis

10 drill bit flushing channel 104 drilling tower

II female interlock

12 drill bit surface (face) 131 plug

13 injection channel 45 135 opening

14 percussion equipment

15 male interlock 202 soil (moraine)

16 T shape 203 groundwater layer

11', 15' and 16 ' second 203' water filling for pile version 50 204 groundwater level

17 sealing space 205 bedrock

18 welded shoe

19 reinforcement

20 intermediate space