JPS62228519A - Pit wall compression-preboring work and excavator therefor - Google Patents

Abstract

PURPOSE:To increase the bearing strength of the side of a foundation pile to be set thereafter by a method in which a warped compressive excavating blade is attached to the lower disc of a steel tube in relation to the normal rotation direction of the rotary shaft and excavated soil is pressed into the surrounding natural ground. CONSTITUTION:A backwardly warped compressive excavating blade 5 is attached to the lower disc 2 of a steel tube 9 in relation to the normal rotation direction of a rotary shaft 1. The ground is excavated by normally turning a central blade 3 and the blade 5, and compressed air or a fluid or water containing cement is jetted from a nozzle 4. The free rise of the excavated soil is suppressed by the tube 9, and in a compressible ground, most of excavated soil is pressed into the surrounding ground by the radial pressures of the blade 5. Also, in a less-compressible ground, the excavated soil is partly pressed into the surrounding ground in the same way. The bearing strength of the side of the foundation pile to be set thereafter can thus be increased.

Description

[Detailed Description of the Invention] The present invention relates to a pre-boring method in which an underground hole is created in advance at the location where a foundation pile is to be installed. Its purpose is to increase.

A pressurized drilling blade that is curved backwards in the normal rotation direction of the rotating shaft is integrally attached to the lower surface of the disc that is integrally connected to the rotating shaft.
When the rotating shaft rotates in the normal direction, the ground is dug up with the cutting edge metal fitting,
This excavated earth and sand is subjected to radiation pressure that is pushed outward by a special structure curved back at the outer edge of the pressurized excavation blade.

In this way, the excavated soil is pushed out into the original ground, but most of the excavated soil rises along the circumferential surface of the disk and moves above the disk. In this case, although the pressurizing function of the pressurized excavation blade works, the pressurizing function is not utilized because the soil is allowed to move upwards, and this method does not allow the formation of a compressed layer on the wall of the underground hole. It cannot be created.

This invention utilizes the pressurizing function of the pressurized excavation blade to inject excavated soil into the surrounding original ground according to the degree of compressibility of the original ground, thereby creating a compressed layer on the wall of the underground hole. This is the enforcement law. The present invention will be explained below according to embodiments shown in the drawings. The lower end of the rotating shaft 1 pierces the integrally connected disc 2,
A central blade 3 is protruded from its tip, and a pair of nozzles 4 are installed on its sides.
be equipped with. The pair of pressurized excavation blades 5 are configured such that their outer arms are curved backward in the normal rotation direction of the arrow, and are connected to the disk 2 and the rotating shaft 1. The radius of curvature of the curved portion on the front surface of the lower end of the pressurized drilling blade 5 is larger than the radius of curvature of the curved portion on the front surface of the upper end of the pressurized drilling blade 5, and therefore, the front surface of the curved portion has an upper end outward from the lower end. The pressure slope 6 is formed by overhanging the pressure slope 6. A cutting edge fitting 7 is attached to the pair of pressurizing excavating blades 5, but the cutting edge fitting is omitted in the left pressurizing excavating blade 5 in FIG. 1 in order to clearly show the pressurizing slope 6.

As shown in FIG. 3, this cutting edge metal fitting 7 is welded and connected to the tip inclined surface of the thick pressurized excavation blade 5. Reference numeral 8 is a super hard tip. Moreover, a steel pipe 9 having the same diameter as the diameter of the disc 2 is connected above the disc 2, and the upper end of this steel pipe 9 is closed. Further, the rotating shaft 1 above the steel pipe 9 is equipped with a spiral 10 having approximately the same diameter as the steel pipe 9. Although the device on the ground is not shown because it is well known, a weight is loaded on a case housing a motor that operates the rotary shaft 1, and a downward force acts on the excavation device. When the above excavation device is rotated in the normal direction, the excavated earth and sand excavated by the cutting edge metal fitting 7 flows outward along the front surface of the pressurized excavation blade 5, and
The preceding earth and sand that comes into contact with the upper half of the pressure excavation blade 5 is removed by the action of the pressure slope 6 provided on the pressure excavation blade 5.
The lower half of the area is sequentially pushed up by the succeeding earth and sand, and is subjected to large radiation pressure that pushes it into the surrounding ground.

If the ground at the excavation depth is sandy soil with an N value of 20 or less, or viscous soil with an equivalent hardness, the excavated soil subjected to radiation pressure is injected into the surrounding original ground without congestion.

If the steel pipe 9 is not connected above the disc 2,
The excavated soil is easily pushed out above the disc 2 through the outside of the disc 2, but in this excavation device, the length of the steel pipe 9 connected to the disc 2 is 5 meters, so the excavated soil is pushed out above the disc 2. Since the resistance force migrating to the surrounding raw ground is lower than the resistance rising along the long steel pipe 9, it is interpreted that the pipe is naturally forced into the surrounding raw ground according to the difference in the migrating resistance force. . Furthermore, when compressed air is injected from the nozzle 4 communicating with the rotating shaft 1 during this excavation, the adhesion or frictional force of the hole wall 11 against the outer surface of the rotating steel pipe 9 decreases due to the passage of air, and the acting force of the load is reduced. In addition to strongly acting on the tip, slight vibrations caused by the injection of compressed air act on the excavated soil and the surrounding local ground, and the result is that the press-in of the excavated soil into the surrounding local ground is facilitated.

The motor used in the experiment was 45kw, and the weight of the weight was 10
The weight of the other equipment is approximately 5 tons, and the diameter of the underground hole 12 is 60 mm, but if the power of the motor and the weight of the weight are changed to higher-level ones, even more solid sandy soil and even harder cohesive soil can be obtained. It is expected that excavated soil can be injected into the ground. However, there is a limit to the ability to inject all excavated soil into the original ground. In the apparatus of the embodiment, when the excavation apparatus reaches sandy ground with an N value of 25 or less, which is poor in compressibility, the excavation of the excavation apparatus is stopped. One effective measure taken at this time was to replace the supply of compressed air with a pressure of 30■/■■ discharged from the nozzle 4.
Cement milk was squirted out under high pressure. According to this method, the excavated soil is mixed with cement milk to become highly fluid soil cement, and a part of it is injected into the original ground to form a reinforcement layer containing cement particles in the hole wall 11,
Some of the soil cement rises along the circumferential surface of the steel pipe 9 that rotates under the load of the upper device, and rises along the pore wall 1 on the outer surface of the steel pipe 9.
1 is turned into soil cement, and the surplus is stored on the spiral 10. In this process, the excavation speed is controlled to a low speed and the soil cement is sufficiently mixed. As described above, the excavation device is made to reach the required hard support layer while constantly compressing the hole wall 11 of the underground hole 12. The above cement milk can be replaced with a water jet.

At the bottom of the hole in this support layer, a ground operating crane is used to control the excavation of the excavation device, the weight is released from the top of the motor case, and in this state the discharge pressure of the ground pump is increased to 10
When the rotation shaft 1 is rotated in the forward direction while injecting cement milk at a relatively low pressure from the nozzle 4,
The lightweight excavation equipment is gradually raised by the liquid pressure of the cement milk. At the designated location, replace the cement milk with water and recover the excavation equipment to the ground. In the recovery process described above, the hole wall 11 of the underground hole 12 is further compressed by fluid pressure. When ready-made concrete piles or steel pipe piles are lowered into this underground hole 12 filled with cement milk to the required position, these foundation piles become integrated with the compressed hole wall 11 of the underground hole 12 through the cement milk. , resulting in foundation piles with large lateral bearing capacity. In the final process, adding light hammering to the pile cap is also a means of increasing the tip bearing capacity. Expandable cement was used for the cement milk used in the examples, but
Mortar may be used instead of cement milk.

Next, the above-described method can be used to create underground holes for cast-in-place reinforced concrete piles, and an effective effect can be obtained. FIG. 4 shows an excavation device particularly used when creating large-sized cast-in-place piles. Several pressurized excavation blades 5 similar to those shown in the embodiment are attached to the lower surface of the cylindrical weight 13. This weight 13 is rigidly connected to the rotating shaft 1 by a connecting fitting 14, and a pre-drilled steel pipe 15 is integrally protruded at the lower end of the inner peripheral side of the weight 13. A backflow pipe 16 is built inside the rotating shaft 1, a central blade 3 is attached to the tip of the rotating shaft 1, and a plurality of stepped bits 17 are attached above the central blade 3. The cutting edge metal fittings are omitted in the drawing. Further, a branch pipe 18 branches from the rotary shaft 1, and compressed air or cement milk is injected in front of each pressurized excavation blade 5 from a nozzle 4 at the tip thereof. That is, this is a combined construction method in which the hole wall 11 of the underground hole 12 in the reverse circulation construction method is compressed and strengthened using the equipment of this construction method. The ground in the center of the underground hole 12 is excavated with the central blade 3 and the step trench bit 17, and the ground at the outer edge is excavated with the pressurized excavation blade 5. The creation of a compressed layer on the wall 11 is the same as in the example, and during the process of excavating hard ground, a part of the soil cement mixed with the excavated earth and the injected cement milk is press-fitted into the original ground, and the other part is pressed into the original ground. A part of it rises on the circumferential surface of the weight 13 to form a soil cement layer on the outside of the weight 13, and the surplus passes through the hollow part of the weight 13 and is sucked up to the ground by the backflow pipe 16 along with the excavated earth and sand in the central part. Even when creating an above-ground hole with a diameter of 3 meters, it is sufficient to pressurize the excavated soil inside and outside the outer edge with a thickness of 20 cm, and the required torque is not excessive. The pre-drilled steel pipe 15 isolates the central part from the outer edge, so that the jetting influence of compressed air and cement milk on the outer edge does not interact with the central part. establish. In this construction method, the entire length of the hole wall 11 is compressed and strengthened, so there is no collapse of the hole wall, and at depths where there is pressurized water, the excavation speed is slowed down and a quick-setting material such as quick-setting cement milk is injected into the hole wall. Special means can be used to locally solidify 11.

In addition, in the case of creating a medium-sized underground hole with a diameter of 1.5 meters or less, the rotating shaft 1 equipped with a spiral auger is integrally installed inside the weight 13 and pre-drilled steel pipe 15 as shown in Fig. 4. If the diameter of the spiral is increased in the upper part so that it is almost equal to the diameter of the underground hole, and the ground at the outer edge is pressurized by the pressurized excavation blades 5, the diameter of the spiral will be increased to the hole wall of the underground hole as in the embodiment. A compressed layer can be created. In this case as well, as in the example shown in FIG. 4, an injection pipe for the spiral auger is built into the rotating shaft 1, and the structure is such that a liquid different from the fluid injected from the nozzle 4 can be injected from the tip of the spiral auger. do.

In the conventional construction method of cast-in-place piles, no matter which construction method is used, the wall of the underground hole is in a weakened state as it was excavated, and a compressed layer is not created on the hole wall as in this public law, and the original ground is It is thought that the frictional force or adhesion force originally possessed by piles acts on the sides of cast-in-place piles in a weakened state. Contrary to the above, in this method, a compressed layer is created on the wall of the underground hole, so a resistance force greater than the frictional force or adhesive force originally possessed by the original ground acts on the side of the cast-in-place pile. With the addition of the wall roughening effect, it is expected that the lateral bearing capacity of cast-in-place piles will be greater than the lateral bearing capacity of piles in the conventional hammering method.

As a means of increasing excavation efficiency, the ground may be excavated by making the excavation diameter of the pressurized excavation blade 5 approximately 20 mm to 30 mm larger than the outer diameter of the steel pipe 9 in FIG. 2 or the weight 13 in FIG. 4. In the present invention, the steel pipe 9 and the weight 13 are collectively referred to as a cylindrical body, but in the above case, a sparsely textured gap of 10 mm to 15 mm is initially created between the cylindrical body and the wall of the excavated hole, and a portion of the excavated earth and sand is It rises along the side of a long cylindrical body. However, due to the elongated length of the cylinder, the free rise of the excavated soil through this small gap is suppressed, and a compacted layer is formed on the outside of the cylinder, which becomes denser toward the top. Since compressed air is always injected into the ground, even if the underground hole 12, which is especially prone to collapsing, runs out of water, the water will not flow down to the tip of the excavation, and most of the excavated soil will be injected into the original ground. Ru. In addition, in hard ground, most of the soil cement rises on the outside of this cylindrical body and forms a soil cement layer on the hole wall 11, but when using this method, the effect of accelerating the excavation speed in hard ground can be obtained. In the present invention, it is defined that the dimensions of the cylindrical body and the pressurized drilling blade are considered to be approximately equal, including a slight difference in diameter.

Next, the special mechanism of the excavation equipment of this method will be explained.

The disc 2 shown in FIG. 2 and the steel pipe 9 are not fixedly connected, but the restraining ring 2 holds down the steel pipe 9 from above as shown in FIG.
0 is connected to the rotating shaft 1, and a manual fitting 21 protruding from a restraining ring pushes a forward rotating passive fitting 22 protruding from the upper surface of the steel pipe 9, thereby transmitting the forward rotating force of the rotating shaft 1 to the steel pipe 9. do.

On the other hand, insert the circular hole 23 shown by the dotted line in FIG.
4 is inserted into the two pipes inside the steel pipe 9, and when the rotating shaft 1 is reversed and the manual fitting 21 hits the reversing passive fitting 25, the hole in the disk 2 is 23 and a pipe 24 fixedly connected within the steel pipe 9 are configured so that they engage with each other, a passage is created from the lower surface of the disc 2 to the upper surface of the steel pipe 9 when the rotating shaft 1 is reversed.

The pipe 24 is connected to holes provided at predetermined positions in an upper end plate 26 and a lower end plate of the steel pipe 9. In the case of this device, even if the excavation device is pulled up while reversing the rotating shaft 1,
No vacuum is generated at the bottom of the hole, making it easier to recover the device. Also, if an expanding blade that expands when reversing is attached to the disk 2,
Expanded roots can be created at the bottom of the hole in the supporting layer.

Furthermore, when a reversing cutting edge fitting is attached to the back of the pressurized excavation blade, a means is provided for discharging the excavated soil excavated by the cutting edge fitting above the steel pipe 9 through the pipe 24, especially in hard ground. Also, when creating the expanded root, there is a method of injecting cement milk and mixing it with the excavated soil to fill the expanded root with soil cement.However, during the same process, water is injected and the excavated soil of the expanded root is mixed with water into the pipe 24. The soil is removed above the steel pipe 9 through the hole, and finally, when the excavation device is lowered to the bottom of the hole and compressed air is injected from the nozzle 4, the air accumulates above the expanded root, creating air pressure that pushes the water downward, and the water is blown up by the rotary jet. The water containing the rising earth and sand blows up through the pipe 24, and all the excavation debris at the bottom of the hole is swept away. Thereafter, the rotary shaft 1 is returned to normal rotation, the lower end of the pipe 24 is closed, and highly concentrated cement milk or mortar is injected from the nozzle 4, so that the expanded root is filled with pure cement milk or mortar. When the rotating shaft 1 is reversed to excavate hard ground and expanded roots as described above, the excavated earth and sand are discharged through the pipe 24, so the spiral shown in Fig. 2 is used to accommodate the earth and sand. 10 shall be installed in the opposite direction to that shown in the drawing.

In the excavation device specially configured to perform reverse excavation as described above, when digging in hard ground by reversing the rotating shaft, the extension shaft of the movable core of the electromagnetic switching solenoid is It protrudes from the lower surface of the disk 2 through the hole, and serves as a stopper for the expanding blade to suppress the expansion of the expanding blade. When creating an expanded root, current is sent to the solenoid to generate electromagnetic force and move the movable core upward. The suction and the vertical movement of the stopper can also be operated by small hydraulic equipment, and these operating devices are installed at the bottom of the steel pipe 9 so that it can move at a predetermined angle. Provide a groove as long as possible. These remote control mechanisms are easily understood by engineers in the field of mechanical equipment, and the solenoids and the like are installed in the excavation device as designed. In other words, by incorporating these operating devices, the expanding blade does not open during the process of reversing the rotation axis and digging into hard ground, and the expanding blade freely expands only when creating an expanded root at the bottom of the hole. death,
An excavation device with desirable equipment capable of creating expanded roots is obtained. In the case of an excavation device that does not have the pipe 24 built into the steel pipe 9, the expanding blade, which rotates around a shaft protruding from the lower surface of the disc 2, is expanded at the bottom of the underground hole by reversing the rotating shaft. In this state, if the excavation device is pushed up while injecting cement milk, an expanded root that is dry of soil cement and has a predetermined height can be obtained.

Therefore, with this construction method, it is possible to create an expanded root at the bottom of an extremely small underground hole with an outer diameter of 30 cm or less. The excavation equipment that implements the present construction method described above may undergo various design changes without departing from the basic idea of the present invention. For example, if the weight 13 and the disc 2 shown in FIG. The structure can be such that the provided hole 23 and the pipe 24 built into the weight 13 are aligned. Therefore, in this case, when excavating hard ground and creating an expanded root, the excavated soil can be discharged above the weight 13 through the pipe 24, and this soil can be sucked up by the backflow pipe 16. , the effect of improving construction efficiency can be obtained.

The biggest feature of the hole wall compression pre-boring method of the present invention explained above is that the hole wall of the underground hole receives radiation pressure from the pressurized drilling blade, creating a compressed layer, which particularly increases the lateral bearing capacity of the foundation pile. It is in the point of doing.

Furthermore, by adding a means of creating an expanded root by reversing the rotation axis, a foundation pile with a large tip-bearing capacity can be obtained. Next, as an effect accompanying this construction method, according to this construction method, the walls of the underground hole are compressed and strengthened, and the hole wall does not collapse by applying compression by applying troweling to the hole wall with a spiral, or by simply filling it with fresh water. Bentonite mud water is not required, and the excavation device shown in Figure 2 can be used when creating underground holes up to 80 cm in diameter, so the amount of excavated soil discharged to the surface when the excavation device is recovered is particularly reduced. Therefore, the cost of treating residual soil and muddy water is reduced.The pressurized excavation blade of this device has the function of pushing the object part it comes into contact with outward, and the positioning force of the upper cylindrical body is large. This construction method has the ability to push out obstacles such as boulders or small boulders, and can be used to create both pre-cast piles and cast-in-place piles, and can be implemented from small to large diameter underground holes. Among other things, it has a wide range of applicability.

In other words, this method is a pre-boring method that increases the lateral bearing capacity of foundation piles, which has never been achieved before. This is a highly useful pre-boring construction method for foundation piles that provides significantly increased features compared to foundation piles installed in the area, and can bring multifaceted economic value.

[Brief explanation of drawings]

The drawings show an excavation device for the pre-boring method of the present invention and an embodiment thereof. Fig. 1 is a bottom view of the excavation device used in the embodiment, and Fig. 2 is a diagram of the excavation device of the embodiment used for digging underground. Fig. 3 is a side view of the cutting edge metal fitting attached to the pressurized excavation blade, Fig. 4 is a partial vertical cross-sectional view of the large excavation device, and Fig. 5 is a section of the upper part of the steel pipe of the excavation device. FIG. 2 is a structural diagram showing the internal device and the device on the top surface of the steel pipe. In the drawings, reference numerals 1...rotating shaft, 2...disc, 3...
Central blade, 4... Nozzle, 5... Pressurized drilling blade, 6...
・Pressure slope, 7... Cutting edge metal fitting, 9... Steel pipe, 10.
...Spiral, 11...Underground hole wall, 12...
Underground hole, 13... Weight, 14... Connecting fitting, 1
5... Pre-drilled steel pipe, 16... Backflow pipe, 17...
・Step digging bit, 18... Branch pipe, 20... Suppressing ring, 21... Main drive fitting, 22... Normal rotation passive fitting, 23... Hole provided in disk, 24... pipe, 2
5... Reverse passive fitting, 26... Upper end plate.

Claims (2)

[Claims] (1) A pressurized excavator blade that is curved backwards with respect to the forward rotation direction of the rotary shaft is attached to the lower disk of the cylindrical body that rotates by the operation of the rotary shaft, and this pressurized excavator blade is rotated in the normal rotation direction. While excavating the ground, compressed air, a fluid containing cement, or water is injected from a nozzle leading to the rotating shaft depending on the hardness of the ground, and the cylindrical body, which has an outer diameter approximately equal to the excavation diameter, frees the excavated soil. The feature is that most of the excavated soil in compressible ground and a part of the excavated soil in less compressible ground are injected into the surrounding raw ground by the radiation pressure of the pressurized excavation blade. The hole wall compression pre-boring method. (2) A cutting edge metal fitting is attached to the pressurized excavation blade that is curved backwards with respect to the normal rotation direction of the rotation axis, and a nozzle that injects fluid is provided in front of this pressurized excavation blade, and this pressurized excavation blade is An excavation device that is connected to a lower disk of a cylindrical body having a diameter approximately equal to the excavation diameter of the pressurized excavation blade, and is rotatable by the operation of a rotating shaft.