JPS6240482B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to an aggregate made of aggregate such as crushed stone, ore sandstone, gravel, or gravel that has water permeability and bearing capacity and is cast in relatively loose sandy ground. This invention relates to an improved construction method for piles, so-called crushed stone drain piles, and a construction device therefor.

[Conventional technology] Relatively loose sandy ground is prone to liquefaction due to seismic vibrations, and as a measure to prevent liquefaction through ground improvement, ground vibration compaction methods have traditionally been used. . However, this vibration compaction method generates vibration and noise pollution due to mechanical vibration during construction, and furthermore, the ground deformation caused by the vibration has a negative impact on structures on and near the target ground. The problem is that it cannot be applied in urban areas or near existing structures, and the range of application is limited.

The crushed stone drain pile method has been proposed as an alternative method to the vibratory compaction method, and has recently been attracting attention as an effective measure to prevent liquefaction of sandy ground during earthquakes. The principle is to horizontally dissipate the excess pore water pressure that occurs in the sandy soil during an earthquake in loose sandy ground below the groundwater level, thereby reducing the accumulation of excess pore water pressure.

However, regardless of the theory, no concrete construction method or equipment has been established yet. In other words, a commonly considered method is to use a sand pile (sand drain) construction device to introduce aggregate into a hollow pipe (casing) for driving sand piles that has penetrated into the ground, while applying appropriate vibrations. There is a method of pulling up hollow pipes, but this method usually adds vibration to the driving and pulling of the casing, which may disturb the ground, prevent the aggregate from being compacted sufficiently, or cause problems during construction. This method has drawbacks such as the fact that it cannot be implemented in densely populated areas such as urban areas because it causes construction pollution due to vibration and noise.

In particular, such relatively loose sandy ground, which is easily liquefied, tends to be easily deformed when drain piles are driven. This will have an adverse effect on the existing structures above or in the vicinity, and will have the same problems as the vibration compaction method described above. When the weather-resistant ground of a drain pile is directed toward the ground of an urban area, the ground behind a quay, or the foundations of large tanks, conventional construction methods that cause deformation of the ground must have a fatal flaw.

[Technical Problems of the Present Invention] Therefore, the present invention departs from the different applications of the conventional construction methods described above and focuses on the effect produced by applying percussion (impact force) to aggregates such as crushed stone. The technical objective is to provide the most effective and effective construction method (creation method and construction equipment) for crushed stone drain piles. Note that the idea of the present invention also includes focusing on the synergistic effect with the compaction effect of auger excavation.

[Structure] In order to achieve the above-mentioned technical problem, the present invention adopts the following structure (technical means).

That is, in the method of constructing a crushed stone drain pile of the present invention, a hollow pipe is penetrated to a predetermined depth into sandy ground by normal rotation using a spiral blade formed on the outer periphery while the cap at the tip is closed, and then the crushed stone drain pile is Aggregate for constructing a drain pile is put into a hollow pipe, and the lid at the tip of the hollow pipe is opened to release the put-in aggregate to the bottom of the hole. Using a slender, long protruding rod with a substantially equal cross section extending from the lower end upward, the hollow tube is inserted from the lower end into a tamping position that matches the soil quality of the surrounding ground and the grain size of the aggregate. While adjusting the position of the tip of the protruding rod, the impact force of the injected aggregate is transmitted to compact the aggregate, and the hollow tube is reversely rotated to penetrate the surrounding front hollow tube. The method is characterized in that the generated soil is pushed downward while being gradually pulled up, and the input of aggregate and tamping with a ramming rod are continued.

Here, the expression "substantially equal cross section" of the protruding rod means that the cross section does not change suddenly, and small and large changes are allowed.

Furthermore, the crushed stone drain pile construction device of the present invention has the following features:
A hollow tube is used to carry out the above-mentioned construction method, and has a tip cap that can be opened and closed at the tip, and a spiral blade is formed on the outer periphery. a long slender protruding rod that is inserted all the way to the top and has a substantially equal cross section;
An impact drive device for the protrusion rod is disposed above the hollow tube and interlocks with the protrusion rod to apply an impact force to the protrusion rod. It consists of a protruding rod height adjustment device that adjusts the entry position into the empty pipe.

[Operation] With the above configuration, the penetration of the hollow pipe is performed with low vibration and low noise, and the ground is not disturbed except for the volume occupied by the hollow pipe. When the hollow tube is pulled up, the helical blades rotate in the opposite direction to push the excreted earth into the ground, and the aggregate that has been put into the borehole is collected in an appropriate amount at the tip of the hollow tube as it is being pulled up. As the crushed stone drain pile is pierced with a uniform degree by the protruding rod and spread out into the surrounding ground, it maintains balance with the ground and does not lose its predetermined shape along the way, creating a highly reliable crushed stone drain pile. can get.

In the method of the present invention, by making it possible to adjust the tip position of the protruding rod so that it can be moved in and out from the lower end of the hollow tube, the tip cover can be opened reliably when the hollow tube is pulled up, and the surrounding ground can be A compact crushed stone drain pile can be obtained by setting the protrusion rod at a position corresponding to the degree of compaction determined according to the soil quality and the particle size of the aggregate.

[effect] The present invention has the following unique effects.

Since mechanical vibration is not used in the construction process of penetrating and pulling up the hollow pipe 3, the vibration and noise associated with construction are extremely low, and construction can be carried out without pollution even in densely populated areas such as urban areas.

When the hollow pipe is pulled up, the surrounding ground disturbed when the hollow pipe is penetrated is Not only can it be repaired, but the surrounding ground can be actively compacted, and the pile body itself can be made solid. As a result, the ground will not become unstable during construction, so even if construction is performed near existing structures, there will be no negative impact on the structures. , it has become possible to apply it to the foundation ground of important structures such as pipelines.

Due to the above-mentioned cooperative action, the surrounding ground can be compacted during the pile construction process, so it can be expected to have both a drain effect and a compaction effect at the same time as a liquefaction prevention function.

Since the pile body is tamped to a uniform degree by the ramming rod effect, there are no cut points in the middle and a highly continuous pile body is obtained, so the pile body exhibits a high drainage effect and is resistant to earthquakes. Liquefaction of the ground can be reliably prevented.

In addition to obtaining a pile body with high density and excellent bearing capacity against vertical loads, the surrounding ground can be expected to be compacted when the pile body is constructed, increasing the bearing capacity of the entire ground, and supporting structures installed on top of it. It can support things reliably.

By tamping with ramming rods, the aggregates are firmly interlocked, resulting in a pile body that exhibits high resistance to horizontal shear force.In addition, the above-mentioned tamping effect around the pile body during construction of the pile body improves earthquake strength. increase As a result, the shear resistance of the entire ground including the pile body increases, and the ground's supporting capacity against sliding failure increases.

During construction, aggregate can be added continuously, resulting in high construction efficiency.

Since only a slender protruding rod is placed inside the hollow tube, there is no obstruction to the input of aggregate, and the aggregate falls smoothly.

By making the tip position of the protruding rod adjustable so that it can be moved in and out from the lower end of the hollow tube, the tip cover can be opened and closed reliably when pulling up the hollow tube, and the soil quality and aggregate of the surrounding ground can be adjusted. A highly reliable crushed stone drain pile can be obtained by setting the ramming rod at a position according to the degree of tamping determined according to the grain size.

[Embodiments] The method and apparatus of the present invention can take the following embodiments.

In the method of the invention, pressurized air or water injection is applied to the hollow tube during its penetration and/or withdrawal. Thereby, boiling and heaving of the ground against the tip of the hollow tube can be prevented.

In the method of the present invention, the construction is carried out while managing the harmony between the top end and the pulling speed of the hollow tube by measuring the top end of the aggregate introduced through the protruding rod.

In the device of the present invention, the impact drive device for the thrust rod is a crank mechanism.

In the device of the present invention, the height adjusting device for the protruding rod is composed of a cylindrical portion having an air buffering effect and a piston rod slidably fitted into the cylindrical portion.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic view of the entire apparatus of the present invention, and FIG. 2 is a schematic cross-sectional view of its main parts. Here, 1 is a three-point supported movable pile driver body having a leader 11, 2 is an elevating bucket that goes up and down along the leader 11, and 3 is a tip lid 3 that can be opened and closed at the tip.
4 is a protruding rod disposed along the axis of the hollow tube 3, and a hollow tube penetration driving device 5 and a receiving hopper 6 are located above the hollow tube 3. , an impact drive device 7 for the protruding rod, and a height adjusting device 8 for the protruding rod are attached, and the apparatus of the present invention is constituted by each of the members and devices 3 to 8. In addition, E is the ground where the crushed stone drain pile is installed, that is, N
Sandy ground with a value of less than 20. In addition, S is aggregate,
P is a crushed stone drain pile made of the aggregate S.

There are various types of aggregate S used here, such as crushed stone, ore, gravel, gravel, etc., but crushed stone is generally used.

The construction process of the present invention is shown in FIGS. 3 to 5. The steps will be explained below in order.

(1) Close the end cap 3A of the hollow tube 3, rotate the hollow tube 3 in the positive direction (direction H in Figure 3), and use the spiral blade 3B on its outer periphery to open the hollow tube by the so-called auger method. Penetrate the pipe 3 into the ground E (3rd
(see figure). The hollow tube is driven by a rotary drive device 5 that is attached to the upper end of the hollow tube.

In this process, that is, the process of penetrating the hollow pipe 3, it is a construction mode of this embodiment that can be appropriately implemented to prevent boiling of the ground at the tip by pressurizing the inside of the hollow pipe 3 or injecting water. .

Thus, by rotating and screwing the hollow tube 3 into the ground E, the hollow tube can penetrate with as little vibration and noise as possible. At this time, the width of the spiral blade 3B and the hollow tube 3
By appropriately selecting the rotational torque according to the soil properties of the ground, disturbances in the surrounding ground can be reduced and good construction conditions can be achieved.

(2) When the hollow tube 3 reaches a predetermined depth, the aggregate S is fed into the receiving hopper 6 by the lifting bucket 2 that moves up and down along the leader 11, and the required amount of aggregate S is placed inside the hollow tube 3 under its own weight. let it fall. In order to input the required amount of aggregate, a shutoff valve is installed in the receiving hopper 6 as appropriate.
It is preferable to adjust the input amount by opening and closing the shutoff valve.

(3) After that, the hollow tube 3 is pulled up slightly to open the tip cap 3A and the aggregate S is discharged to the bottom of the hole.
At this time, it is also convenient to forcibly open the tip cap 3A through the aggregate S accumulated at the bottom of the hollow tube 3 using a protruding rod 4 arranged along the tube axis direction inside the hollow tube 3. be. Next, the protrusion rod 4 is moved in and out of the tamping position (usually located inside the tip cover with the tip of the protrusion rod open) in accordance with the surrounding soil quality and the grain size of the aggregate. (see figure). Although the protrusion rod 4 is moved in and out using a protrusion rod height adjustment device 8, the method of the embodiment of the present invention is not limited to this device.

In this case, if the surrounding ground, that is, the ground, is not self-supporting and collapsible, a large pressure (earth pressure + water pressure) acts on the tip cap when the hollow tube 3 is pulled out, making it difficult to open the tip cap 3A. However, by slightly pulling the protruding rod 4 into the hollow tube 3, the tip cap 3A is removed.
The tip lid 3A can be opened by poking the aggregate S inside. Once the tip cap 3A is opened, the position of the protruding rod 4 is moved downward, and the hollow tube 3 is pulled out, and the crushed stone drain pile S and the ground E are removed in a place not affected by the hollow tube 3 and the tip cap 3A. To enable more effective compaction.

(4) In this state, an impact force is applied to the aggregate S using the ramming rod 4 to tamp it down. This protruding rod is driven by the hollow tube 3
This is carried out by an impact drive device 7 for the protruding rod, which is installed above the protruding rod and interlocks with the protruding rod.

(5) Next, while pulling up the hollow pipe 3, the aggregate S is put in and tamped with the ramming rod 4, and the crushed stone drain pile P is gradually constructed in the ground (see Figure 5). In this case, if the hollow tube 3 is rotated in the opposite direction (direction I in the figure), the surrounding ground that was disturbed at the time of penetration will be compacted by the spiral blades 3B of the hollow tube.

In this process, depending on the "degree of compaction" determined according to the surrounding soil quality and the particle size of the aggregate,
The pulling speed of the hollow tube 3, the stroke of the protruding rod 4 and the number of impacts (per unit time), or the crushed stone S
The crushed stone drain pile P is constructed while controlling the determining factors of the degree of compaction, such as the amount of input. Therefore, it is important to constantly detect the position of the top of the aggregate S. As the detection means (namely, the top detection device), the resistance of the protruding rod 4 that moves up and down in the aggregate S varies depending on the depth, and eventually the resistance of the protruding rod driving device 7, in other words, the required rotation of the prime mover. Since it is detected as a difference in driving force (torque) (as indicated by an ammeter), by measuring this relationship in advance, the top position can be easily determined. Using the hollow part of the protruding rod 4, install the measuring device J at an appropriate position in the hollow part,
The position of the top is measured by means such as capacitance and sound waves (see Figure 2). As shown in FIG. 6, a protective tube K (to protect against the effects of the injection of crushed stone S) is attached to the protruding rod 4, a wire L is inserted into the protective tube K, and the weight of the lower end of the wire L is A weight M is brought into contact with the top, and the top position is measured by the winding amount of the wire L.

Therefore, a method is adopted in which construction is carried out while managing the balance between the top end and the pulling speed of the hollow tube.

An example of the relationship between the factors determining the degree of compaction is as follows. That is, the hollow tube 3
When the inner diameter of the hollow tube is 38 cm, the outer diameter of the protruding rod 4 is 5 to 6 cm, and the outer diameter of the crushed stone S is approximately 5 cm, the pulling speed of the hollow tube is 3 m/min, the stroke of the protruding rod is 20 cm, and the When the frequency is 30 times/min, a crushed stone drain pile P of generally good quality is obtained.

Further, as shown in FIG. 7, by providing a plurality of triangular pyramid-shaped protrusions 41 on the peripheral wall surface of the tip of the protrusion bar 4, the tamping effect of the protrusion bar is enhanced and a suitable construction mode is obtained. The lower surface 411 of the protrusion 41 promotes the compacting action of the aggregate S when the protrusion bar 4 moves downward, and the both side surfaces 412 allow the aggregate S to slide ( transportation) to reduce resistance and prevent clogging of the aggregate S.

In this process as well, it is recommended to take technical consideration to appropriately inject pressurized air or water to prevent boiling of the ground, particularly at the initial stage of pulling up the hollow tube 3.

(6) Driving and preparing an appropriate number of crushed stone drain piles into the ground E according to steps (1) to (5) above.

These crushed stone drain piles and the surrounding ground constitute a composite ground, but as mentioned above, the surrounding ground is relatively undisturbed, and the bearing capacity of the surrounding ground and the shear of the crushed stone drain piles are Due to the resistance force, the composite ground forms a strong ground as a whole. Therefore, the composite ground contributes not only to countermeasures against liquefaction during earthquakes, but also to the reinforcement of the ground's bearing capacity at all times, and can be applied to the foundations of various structures as a ground with strong shear resistance.

Next, FIGS. 8 to 10 show an embodiment of various devices installed in conjunction with the upper end of the hollow tube 3 (hereinafter referred to as pile driving upper device). The pile driving upper device is connected to and attached to the flange 31 at the upper end of the hollow tube 3, and moves up and down together with the hollow tube 3. The pile driving upper device usually consists of a hollow tube penetration drive device 5, a receiving hopper 6, a protruding rod impact drive device 7, and a protruding rod height adjustment device 8. You are free to change or omit them, or rearrange them as appropriate, within the scope of keeping it reasonable (for example, ensuring an input port for aggregate, not blocking the protruding rods, etc.).

The penetration drive device 5 secures the position of the communication pipe 61 of the receiving hopper 6 disposed on the upper part thereof, and has a prime mover 51, high speed and low speed reducers 52, 5 on both sides thereof.
2' is arranged, and the rotational driving force of the prime mover is appropriately reduced by a speed reducer to rotate the hollow tube 3. Reference numeral 53 denotes an underframe of the penetration drive device 5, in which the prime mover 51 and reducers 52, 52' are fixed and fixed, and a sliding part that moves along the leader 11 is placed outside the underframe. The gripping member 54 is fixed.
55 is a flange, which is the flange 3 of the hollow tube 3.
1 and is removably fixed by bolts (not shown) or the like.

The impact drive device 7 for the protruding rod consists of a prime mover 71, a continuously variable transmission 72, a transmission chain or V-belt 73, and a crank mechanism 74. The force is transmitted to the crank mechanism 74. In the crank mechanism 74, the rotation of the crankshaft 741 and the crank arm 742 is caused by the rotation of the crank pin 743.
The movement is changed into reciprocating motion by a connecting rod 744 rotatably attached to the rod 4, and further via a connecting pin 75 rotatably connected to the upper end of the protruding rod 4.
Move the protruding rod 4 up and down.

76 is an underframe of the impact drive device 7;
A prime mover 71, a transmission 72, a chain 73, and a crank mechanism 74 are mounted and fixed inside the frame 6, and a guide gib 77 that moves along the leader 11 is fixed outside the frame.

The height adjustment device 8 for the protruding rod is interposed between the penetration drive device 5 and the impact driving device for the protruding rod (or the upper end of the hollow tube 3), and is arranged between the piston rod 81 and the piston rod 81.
A cylindrical portion 8 into which the tip of the cylinder is fitted airtightly and slidably.
It consists of 2. The upper end of the piston rod 81 is connected to the pin 83
The cylindrical portion 82 is slidably fixed to the lower surface of the impact drive device 7 via the cylindrical portion 82, and the lower end of the cylindrical portion 82 is fixed to the upper surface of the penetration drive device 5. Gas (air) is hermetically sealed inside the cylindrical portion 82, and does not leak outside except when the gas is removed through the air port 82a. Therefore, the height adjustment device 8
The piston rod 81 is moved in and out by releasing or sealing the gas in the cylinder 82 through the cylinder 82 (the sealing is performed by connecting to a compressor not shown), and the impact drive device 7 is lifted and lowered. In turn, the main function is to adjust the height of the protruding rod 4 connected to the impact drive device 7.

The height adjustment device 8 for a projecting rod of this embodiment has a cylindrical portion 8
In addition to having the function of buffering the impact caused by the driving of the impact drive device 7 by the gas sealed in the impact drive device 2,
It has a function of connecting the penetration drive device 5 and the impact drive device 7, and exhibits multifunctional performance.

Note that when the height adjustment device 8 is omitted, the penetration drive device 5 and the impact drive device 7 are integrally connected, but are connected via a shock absorbing device such as a spring.

In the frame driving upper device, sheave blocks (so-called pulleys) 91 and 92 are attached to the upper part of the hollow tube penetration drive device 5 and the thrust rod impact drive device 7, respectively, and the sheave blocks 91 and 92 are equipped with a pile driver. It is connected to a wire fed out from the main body 1, and is used for suspending and moving the pile driving upper device and the hollow tube 3 connected thereto.

Other embodiments of the pile driving upper device are shown in FIGS. 11 to 13. Here, the same or equivalent members as those in the embodiment shown in FIGS. 8 to 10 are given the same reference numerals, and detailed explanation thereof will be omitted.

In this embodiment, the underframe 5 of the penetration drive device 5 is
3 and the underframe 76 of the thrust rod impact drive device 7 are connected by a hanging device 93, and both devices 5, 7 are moved up and down in conjunction with each other by hanging the sheave block 92. 56 is a rib protruding from the upper end of the underframe 53 and fixed, 931 is a wire of the hanging device 93, 93
2,933 connects the wire 931 to the underframe 76 and the rib 5.
This is a mounting bracket to be attached to 6.

Moreover, each drive device of the impact drive device 7 for the protruding rod is arranged in a plane. 72' is a speed reducer.

Furthermore, in this embodiment, a guide device 9 is provided in parallel with the height adjustment device 8 to guide the vertical movement of the height adjustment device 8.
4 will be installed. The guide device 94 is the piston rod 9
41 and a cylindrical portion 942 into which the piston rod 941 is slidably fitted. It is also free to provide light air resistance to the vertical movement (for example, by interposing packing on the sliding part).

It goes without saying that the present invention is not limited to the embodiments described above, and various design changes can be made within the scope of the basic technical idea of the present invention. That is,
In order to minimize the generation of vibration and noise when penetrating the hollow pipe, in addition to the auger method, a vibration-free and noise-free construction method such as a press-in method or a jet injection method may be applied. In this case, the drive device for the penetration is replaced with the rotation drive device of this embodiment.
Appropriate measures will be adopted. Penetration of the hollow tube is not limited to the vertical direction, but can also be freely carried out in the diagonal direction. The impact force of the protruding rod can be applied not only by a mechanical method using a crank mechanism but also by a hydraulic method using a hydraulic jack, for example. FIG. 14 shows an embodiment of the impact drive device 7' for the thrust rod. Here, 71' is a hydraulic cylinder, 72' is a piston rod, and the piston rod 72' is fixed to the protruding rod 4 directly or via a pin or the like. Reference numeral 73' denotes a frame, which is directly fixed onto the hollow tube penetration drive device. According to this hydraulic system, since the hydraulic jack itself has a height adjustment function, the use of the above-mentioned height adjustment device 8 is not necessarily required.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and FIG. 1 is an overall schematic diagram of the apparatus of the present invention, and FIG.
The figure is a schematic sectional view of the main part, Figures 3 to 5 are process explanatory diagrams of the present invention, Figure 6 is a diagram showing an example of the top detection device, Figure 7 A and B are the tips of the protruding rods. FIGS. 8 to 10 are embodiment views showing the pile driving upper device of the apparatus of the present invention, FIG. 8 is a detailed side view thereof, and FIG. 9 is a reduced plan view of FIG. 8. , FIG. 10 is a reduced sectional view taken along line X-X in FIG. 8, FIGS. 11 to 13 are views of other embodiments of the pile driving upper device, and FIG.
2 is a sectional view taken along the Y-Y line in FIG. 11, FIG. 13 is a sectional view taken along the Z-Z line in FIG. 3... Hollow tube, 3A... Tip cap, 3B... Spiral blade, 4... Protrusion rod, 7... Impact drive device for protrusion rod,
8...Height adjustment device for protruding rod.

Claims (1)

[Scope of Claims] 1. With the cap 3A at the tip closed, the hollow pipe 3 is penetrated into the sandy ground to a predetermined depth by forward rotation by the spiral blade 3B formed on the outer periphery, and after that, the crushed stone drain pile is constructed. The aggregate for use is introduced into the hollow tube 3, and the lid 3A at the tip of the hollow tube is opened to release the introduced aggregate into the bottom of the hole. The tamping position is adjusted to match the soil quality of the surrounding ground and the particle size of the aggregate by having a long slender protrusion rod 4 with substantially the same cross section extending upward from the lower end of the hollow pipe. The hollow tube 3
While adjusting the position of the tip of the protruding rod 4 from the lower end, impact force is transmitted to the loaded aggregate to tamp the aggregate, and the hollow tube 3 is rotated in the opposite direction to improve the surrounding area. A method for constructing a crushed stone drain pile, characterized in that the discharged earth generated by the penetration of the hollow pipe 3 is pushed downward and gradually pulled up, and the input of aggregate and tamping with the ramming rod 4 are continued. 2. The method for constructing a crushed stone drain pile according to claim 1, wherein pressurized air or water is injected into the hollow pipe for penetrating and pulling up the hollow pipe 3. 3. The method for constructing a crushed stone drain pile according to claim 1 or 2, in which the tamping of aggregate by the ramming rod 4 is carried out by projections provided on the tip end surface of the ramming rod and on the side of the tip end of the ramming rod. . 4. Crushed stone according to any one of claims 1 to 3, in which the aggregate is compacted by the thrust rod 4 while controlling the balance between the top of the aggregate and the pulling speed of the hollow tube 3. How to construct a drain pile. 5 A hollow tube 3 having a tip lid 3A that can be opened and closed at the tip and a spiral blade 3B formed on the outer periphery.
and a slender elongated protruding rod 4 that is inserted into the hollow tube 3 in the direction of its central axis from the lower end of the hollow tube to the upper side and has a substantially equal cross section; a protruding rod impact drive device 7 disposed above and interlocking with the protruding rod 4 to apply an impact force to the protruding rod 4; A crushed stone drain pile construction device comprising: a protruding bar height adjustment device 8 for adjusting the entry position of the bar 4 into the hollow pipe 3; 6. The crushed stone drain pile construction device according to claim 5, wherein the thrust rod impact drive device 7 includes a crank mechanism 74. 7. The crushed stone drain pile construction device according to claim 5 or 6, wherein the height adjustment device for the protruding rod has a buffering effect.