JPS594008B2 - Manufacturing method and structure of torsion penetrating type PC helical pile - Google Patents

Description

[Detailed Description of the Invention] This invention is based on the above table regarding torsion penetrating type PC helical piles, because it has excellent construction efficiency and reliable bearing capacity can be obtained when driving precast concrete piles as foundations for structures.
The percussion method was mainly used, but in recent years, as vibration and noise during construction have been regulated, low-vibration and low-noise construction methods such as the boring method and pre-poling method have become popular, especially in urban areas. It is being

However, these construction methods have problems such as difficulty in construction management and reduced bearing capacity.

Therefore, an object of the present invention is to overcome the above problem by providing a PC helical pile that can be twisted directly into the ground using an auger machine without pre-boring.

More specifically, by twisting a large concrete helical pile and applying penetration force, it penetrates into the soil without vibration or noise.
The present invention provides a PC helical pile that enables the compaction effect of the ground around the pile and the tip after penetration, as well as the high pile bearing capacity of the ground itself, in the same way as the conventional pile driving method.

The characteristic structure of the present invention is an axial PC steel wire or a PC
In addition to disposing steel rods and PC helical steel wires, fiber material was mixed in, and the pitch of the PC helical steel wires was set to 10.
Additional features include that the fiber material is a steel fiber.

Further, an example of the present invention will be described in detail with reference to the accompanying drawings as follows.

Manufacturing process of PC helical pile A A set of formwork, that is, a formwork capable of forming three spiral points, is made of a predetermined PC steel rod or PC in the axial direction.
A steel wire 5 is arranged, and a closely spaced spiral steel wire 4 is placed on the outside of the steel wire 5.
Place.

After that, high-strength concrete 2 mixed with steel fiber 1 is poured.

Next, after performing centrifugal force molding, steam curing, autoclave curing, and humid air curing are sequentially performed.

Mixing process of high-strength concrete mixed with steel fibers 2 A high-strength admixture (Sigma 1000) is added to the fine aggregate and mixed for 3 minutes.

Next, add cement and mix for 1 minute to remove water, high performance water reducer (Mighty), coarse aggregate and steel fiber 1 at 1.2%.
/ vol and knead for 3 minutes to complete.

In this case, it is important to note that high-strength admixtures are mixed with fine aggregates (mix thoroughly for the first 3 minutes as they must be mixed together), and high-performance water reducers are mixed with water before being added. Fiber 1 is added at the end, making sure to loosen it well so that it does not form into beads.

Centrifugal Molding Centrifugal molding is a method of compacting concrete using the centrifugal force generated by rotation, and the centrifugal force generated by rotation is expressed by the following equation.

f: Centrifugal force (f) m: Mass r: Radius of rotation Q→n: Rotational speed (rps) g: Acceleration of gravity (980cm1
5ec2) To describe an example of the centrifugal molding process, first, low speed rotation (150r)
pm) for 3 minutes to evenly distribute the concrete over the main surface of the formwork, then rotate at medium speed (300 rpm) for 3 minutes to allow high speed rotation without material separation, and finally Rotate at high speed (600 rpm) for 3 minutes to compact.

The relationship between the above rotational speed and centrifugal force is shown in the table below.

Mixture series for high-strength concrete mixed with steel fibers This mixture was obtained as a result of comprehensively considering the following points and conducting various tests.

That is, although centrifugal force compaction molding is an efficient molding method, it has the disadvantage of separation.To prevent this separation, the following points must be kept in mind.

First, the formwork must rotate smoothly.

In other words, care must be taken to ensure that the formwork or wheels do not rotate smoothly due to eccentricity or uneven tire surfaces.

Second, the rotation speed and rotation time must be appropriate.

This is because if the speed is too high or the time is too long, separation of the materials will be promoted.

Thirdly, the appropriate selection of concrete mix.

In addition, the following points regarding centrifugal compaction concrete were noted.

First, it is difficult to unambiguously determine the effects of rotation speed and rotation time on compressive strength; increasing rotation speed and time increases the compaction effect, but on the other hand, material separation becomes significant.

Second, minute vibrations during rotation increase the compaction effect.

Thirdly, the paste water is squeezed out by centrifugal compaction, but the compressive strength of centrifugally formed concrete is controlled by the water-cement ratio of the concrete during mixing.

However, the higher the water-cement ratio of concrete, the greater the centrifugal compaction effect.

Note that it is difficult to directly compare the strength of centrifugally compacted concrete and that of normally compacted concrete for the following reasons.

First, since the centrifugal force molded specimen has a hollow cylindrical shape and the standard specimen has a cylindrical shape, there is a difference in apparent strength due to the difference in shape and size of the specimen.

According to experiments, it is said that for the same concrete, the strength of hollow cylindrical concrete is about 10 inches lower than that of cylindrical concrete.

Second, centrifugal force molded specimens have a laitance layer on the inner surface of the molded diameter, and the strength varies depending on whether this laitance layer is included in the cross-sectional area of the concrete.

However, numerous experiments have shown that centrifugally compacted concrete has a strength that is approximately 20% greater than that of normally compacted concrete.

Compressive strength test A hollow cylindrical specimen specified in JISA1136 was manufactured using the steel fiber-mixed high-strength concrete 2 of the present invention using the above-mentioned mixing method and composition, and 600 was centrifugally compacted according to JISA1136 using a universal testing machine. A compressive strength test of concrete was conducted.

As a result, the compressive strength of high-strength concrete 2 mixed with steel fibers was a28 = 1087 kg/crA, and the compressive strength of the high-strength concrete 2 mixed with steel fibers was σ28 = 875 kg/cvt, which was obtained by the above-mentioned mixing method and composition and without mixing steel fibers.

In contrast, the standard specimen of steel fiber concrete has σ28
-767 kg/crrt, and concrete without steel fibers was σ28-=753 kqlc.

Therefore, the concrete of the present invention is about 1.
It has been found that 4 times and 1.15 times as much strength can be obtained.

Confirmation test of steel fiber dispersion state in concrete A concrete pile made of high strength concrete 2 mixed with steel fibers was cut into a ring shape with a thickness of 1 cm at right angles to the axial direction, and a width of about 22 cm and a height of 6 was cut.
Two specimens of Cm were manufactured, and further two specimens of width approximately 22 cm, height 6 cW, thickness 1 cm were manufactured by cutting in the axial direction.

The dispersion state of the steel fibers was investigated using X-ray photographs of these specimens, and it was found that the steel fibers were uniformly dispersed in the thickness direction and length direction of the hollow cylinder.

Furthermore, these X-ray photographs revealed that the coarse aggregate was also uniformly dispersed.

Torsion test showing the effect of spiral steel wire 4 outer diameter 300m
A high-strength concrete pile mixed with steel fibers with a wall thickness of 60 m and a length of 1.2 m was manufactured and a torsion test was conducted.

In that case, a prestress of 100 kg/crA was introduced using six unbonded PC steel bars arranged in the axial direction.

A torsion test revealed that the material suddenly broke at the same time as it cracked.

In ordinary concrete members, cracks are a sign of subsequent failure, and after a small crack, the width of the crack gradually increases as the load increases, and at the same time, the deformation reaches several times the amount at which the crack occurred, leading to failure. It is.

Sudden failure of structural members is not desirable, and the same applies to concrete piles.

In order to prevent sudden destruction when torque is applied to such high-strength concrete piles mixed with steel fibers, for example, 6wn diameter
The above high strength steel wire 4 is made into a spiral shape with a pitch of 10, for example.
It has become clear that centrifugal force molding is very effective when centrifugal force molding is performed by placing the molds close together at intervals of less than 0 brain.

That is, one without helical steel wire 4 and one with a diameter of 3 rI
rm steel wire wound in a spiral at a pitch of 60 rran, and one in which a different diameter PC steel wire (Ulbon) with a diameter of 7.4 rrrm was wound in a spiral at a pitch of 100 rran.
50 gates put in a spiral shape, further 100m
A torsion test was conducted on five types of 50 mm pitch spiral strips using two sets of spiral strips, and the results are shown in the table below.

As shown in this table, when helical steel wire 4 is not used, it breaks almost at the same time as cracking, and in the case of φ3 gate reinforcing bars, this effect is hardly recognized.
It has been revealed that when the cracking is done closely at intervals of less than the wn pitch, the cracking moment hardly increases, but the breaking moment increases to about 1.5 times the cracking moment.

The torsion angle when the breaking moment (maximum moment) is reached is more than 5 times the torsion angle at the cracking moment, and even after reaching the maximum moment, the strength does not suddenly decrease as the torsional deformation increases. It became clear that the strength gradually decreased.

Furthermore, in the case of using the helical steel wire 4, the intervals between cracks become smaller, and many small cracks occur.

This tendency is thicker when the pitch of the helical steel wire 4 is 50wn than when it is 10011rrn.

As described above, the present invention provides a PC concrete pile a with three helical flange portions having extremely excellent impact strength and torsional strength, thereby eliminating the risk of cracking or chipping of the helical flange portion and cracking or destruction of the concrete pile. This method has an excellent industrial effect in foundation work because it can completely wipe out foundation pile driving work without vibration and noise in one process.

Next, a torsional penetration test was conducted on the PC helical pile of the present invention, and the results of measuring the penetration torque, penetration speed, rotation speed, etc. during driving will be explained.

Pile and construction outline (1) Pile The PC helical pile of the present invention manufactured with the above-mentioned formulation and prestress is shown in the table below.

(2) Soil quality The soil profile of the test site is shown in Figures 2A and B.

With CL-7m as the boundary, the upper layer is volcanic ash mixed with gravel, and the lower layer is volcanic sand, narrowing the silt layer to GL-1 to 3.5m.

At the second test site, the N value exceeded 50 at the GL-5, 5m point.

(3) Main mechanical specifications used for construction Pile driving leader: Nippon Sharyo D308S and generator Denyo D
Uses CA200SS (soundproof type).

The auger machine used was a three-phase machine D80HP.

(4) Measurement method Indicates instrument specifications.

The torque was constantly measured by a torque detector, the rotational speed by a tachometer, and the pile head load by a load cell and input into the microcomputer.The penetration amount was also measured with a tape and a signal was manually input to the microcomputer every 10 cm.

In order to measure the strain of the rotating pile, the strain of a mold gauge embedded in advance at the position shown in FIG. 2 was input to the microcomputer via a dynamic strain measuring device.

These data were collectively recorded on a cassette coder, and the measurement results were displayed on an X-Y plotter, printer, display, etc.

Test Results and Discussion The torque, pile cap load, and torque measured when the PC helical pile of the present invention was torsionally penetrated according to the tables shown in Figures 3 to 7.
The measurement results of penetration time and penetration speed are shown.

The penetration torque gradually increases while increasing and decreasing in direct correspondence with the N value, and after 12 m it drops to a nearly constant value of 4.5 tf-m (.

No change in torque was observed at a depth of 5.5 m, where the N value exceeded 50.

The pile cap load was a constant value of 6.2 tf after a depth of 1 m.

The decrease in load at a depth of 2.5 m was an intentional decrease in load due to increased torque.

Regarding the penetration time and penetration speed, in accordance with the N value, penetration occurs at a constant speed for a short period of time up to a depth of 2.5 m, after which the penetration speed slows down, and after 12 m the penetration speed increases again until 0. It dropped to .4m/s (.

The rotational speed measured by the tachometer was 8.0 times per minute for the first time and 12.0 times per minute for the second time, but there was no difference in penetration speed due to the difference in rotational speed. I couldn't.

Figures 8 to 11 show the relationship between the amount of penetration and the load torque measured from the mold gauge embedded in the cross section of the pile.

The torque applied to the antibody at each penetration depth shown in the figure decreases at a constant rate from the GL point to the tip of the pile, which means that the frictional force is uniformly distributed on the pile in the ground. It is thought that

In addition, noise during pile driving can be reduced by 500 meters from the pile driving point.
When measured at a location of It was possible.

Previously proposed Utility Model Application Publication No. 126 of 1927
For helical piles with or without reinforcing bars as disclosed in Publication No. 32, Publication of Utility Model Application No. 10880 of 1920, and Publication of Utility Model Application No. 1984-98407, the crack torsion moment is 2t- as shown in the following table. m or less, the pile will not be able to withstand the torsional penetration stress and will crack and fail, making it impossible to implement.

In addition, as shown in the table below, the helical pile provided with PC steel wire in the axial direction, as disclosed in JP-A-50-111813, has a cracking torsion moment of 3.5 t-m or less, which is still sufficient to withstand the torsional penetration stress of the pile. It is extremely difficult to implement as it is not durable and there is a risk of cracking and destruction.

In addition, all of the conventional helical piles mentioned above have strength disadvantages, and the height of the helical flange is small and it is essential to set the pitch to a dog. Therefore, it is difficult to penetrate the helical pile by twisting, so it is more difficult to implement it. making it difficult.

Therefore, the torsional penetration of helical piles, such as the helical piles mentioned above, is still in the realm of theory and has not been successfully put into practice. After repeated research and development, we have finally succeeded in implementing the invention, and as shown in the following table, cracking of the torsional penetrating type helical pile according to the present invention, which combines the introduction of prestress, centrifugal forming with steel fiber mixed concrete, etc. The torsional moment is 5.3 tsm or more, which is sufficient to withstand the torsional penetration stress of the pile.

According to experiments conducted by the applicant, a cracking torsion moment of at least 4 t@m is required in order to withstand torsional penetrating stress.

Furthermore, as is clear from the penetration test mentioned above,
It is a dog-shaped pile with a total length of 7m and a pile diameter of 50cm including the spiral boxwood part, and the height of the spiral part is 10crIL (
Since the pitch is as small as 43 Crn, the torsional penetration efficiency is high, and it is possible to penetrate into ground with a large N value, and the bearing capacity after penetration is as large as that of piles driven by the conventional hammering method.

In particular, the PC helical pile obtained by the present invention has excellent strength in the helical part by introducing prestress, mixing steel fiber, and combining PC spiral steel wire, etc., and the concrete part itself including the helical boxwood part serves as the core. It has an excellent feature in that it can be penetrated by twisting.

Note that this table is based on tests conducted using the water-cement ratio admixture and water-reducing agent formulation of the present invention, so the cracking torsional moment of the conventional helical pile mentioned above is 2 and 3.
．． It is estimated that it will be even lower than 5.

Mata JP-A No. 54-33312, yield point strength 5
A concrete pile using a reinforcing bar cage in which high-strength spiral reinforcement of 5 υ/ma or more is arranged around a group of vertical reinforcements has been proposed, but this is described for a PC pile without a spiral rib, so torsional penetration is not possible. Equivalent technology has not been disclosed regarding the helical collar, which is the most important element for realizing the implementation of formula PC helical piles.

However, in this invention, the above-mentioned problem of the spiral collar part is solved, and the height of the spiral collar part is 10 cm and the pitch is 4 cm.
This work succeeded in torsionally penetrating a 3cm PC helical pile, and its industrial effects are significant.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view showing the essential parts of the PC helical pile of the present invention, FIG. 2 is a soil profile diagram, and FIGS. 3 to 11 are charts showing test data. 1...Steel fiber, 2...High strength concrete, 3...Brim portion, 4...PC helical steel wire, 5...Curved PC steel wire .

Claims (1)

[Claims] 1. A torsion penetrating type PC helical pile having a helical brim, characterized in that a PC steel wire or a PC steel bar and a PC helical steel wire are arranged in the axial direction, and a fiber material is mixed therein. Penetrating PC spiral pile. 2. The torsion-penetration type PC helical pile according to claim 1, characterized in that the pitch of the PC helical steel wire is closely spaced to 100rrvn or less. 3. The torsionally penetrating type PC helical pile according to claim 1 or 2, wherein the fiber material is steel fiber.