JPS5854211B2 - Torsion penetrating type PC spiral pile - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a torsion penetrating type PC helical pile, which enables the foundation pile driving work to be completed in one step of directly penetrating the concrete pile into the soil. The purpose of this invention is to significantly simplify the process and achieve complete vibration-free and noise-free operation, and its feature is that in a PC pile equipped with a spiral boxwood part, the spiral boxwood part This is a torsion penetrating type PC helical pile in which the upper surface angle and the lower surface angle are formed to be different from each other.

Construction sites for civil engineering and architectural structures constructed in urban areas are often close to residential areas, and as a result, the generation of noise and vibration, even temporarily, can have an impact on the living environment of residents in the area. It has become a major social problem, causing damage to buildings and buildings.

For this reason, construction work in urban areas or surrounding areas is increasingly likely to be subject to longer construction periods due to limited construction time, or changes to construction methods and content, which significantly impede construction progress and construction costs.

In particular, noise and vibration regulations have made it virtually impossible to drive piles, which are essential for the foundation work of structures and buildings around cities, using diesel hammers, vibronomers, etc. as in the past. The reality is that this is happening.

Therefore, in response to the social need to significantly reduce the noise and vibration generated by the hammer construction method of prefabricated piles, a noise-free and vibration-free construction method, which is commonly referred to as an alternative to the hammer construction method, has been developed.

As the amount of construction work in cities increases, a wide variety of construction methods have emerged under the name of "no-noise and vibration-free construction methods."

However, all of these noise-free and vibration-free construction methods require a large number of steps, and the construction costs are extremely high compared to the hammer construction method using prefabricated piles.

Moreover, since these construction methods are based on excavation, there is a risk of insufficient support capacity due to ground failure or loosening.

The present invention has been developed in view of the above circumstances, and is economical in terms of design and construction, and provides a noiseless and reliable supporting capacity.
The present invention provides a torsion-penetration type PC helical pile developed as a pile for vibration-free construction methods.

Next, the present invention will be explained with reference to illustrative drawings.

In a PC pile equipped with a spiral flange 1, as shown in FIG. 3, the upper surface angle α and the lower surface angle β of the spiral flange 1 are formed so that α is 75° and β is 60°, respectively. This is a torsion penetrating type PC helical pile a.

More specifically, as shown in FIG. 1, steel rods 5, reinforcing bars 5a, and spiral reinforcing bars 5b are assembled and placed in a centrifugal force forming frame (not shown), and high-strength concrete is mixed with steel fibers 3. A prestressed concrete pile a is centrifugally formed with a helical flange 1 having a top surface angle α and a bottom surface angle β different by t. This allows the pile a to penetrate into the soil and obtain supporting force as a friction pile or support pile.

2 is a concrete pile.

In this case, the collar 1, which is used to rotate and screw into the pile a, must have a flange of a size that has sufficient penetration capacity, since cracks and chips occur in conventional ordinary concrete due to collisions with boulders, forced penetration, etc. It was considered impossible to attach it.

Incidentally, if the concrete has a diameter of 0.3 to 0.5 mm,
Steel fiber-reinforced concrete, in which steel fibers 3 having a length of about 25 to 30 vtm are uniformly dispersed, has many advantages not found in ordinary concrete.

■High toughness and high resistance to impact forces.

2. High tensile strength and bending strength.

3. Fewer cracks and chips at edges and corners.

4. High fatigue resistance.

5. High resistance to twisting and freezing and thawing.

Therefore, by using such a steel fiber-reinforced concrete IJm, it is possible to form a flange portion 1 that is resistant to cracking or chipping and has sufficient strength.

The 28-day standard strength of the steel fiber concrete compression test specimen used for the PC helical pile a of the present invention is σ28 near 5
The weight was 0 kg/- or more, and the product was manufactured according to the sales formula as shown in the following table.

The 28-day compressive strength of steel fiber reinforced concrete with this mixture is σ28-767kg/-, and the compressive strength of concrete without steel fibers mixed is σ28=753kg/cys.
It is almost the same as t, but the tensile strength is σt=83kg/cr
σt=59 kg/c1rL for A, and the tensile strength increased approximately 1.4 times by mixing steel fibers.

In addition, in order to compare the resistance of steel fiber-reinforced concrete to cracking and chipping due to impact force with concrete that does not contain steel fibers, a 28-day-old bending test specimen was simply supported with a span of 45 cr IL, and the span center weight 7
．． In No. 5, 41 steel balls were repeatedly dropped from a height of 30 CrrL, and the number of times cracks occurred and the number of times they broke were investigated.

As a result, concrete without steel fibers cracked after 3 impacts and broke at the same time, but concrete with steel fibers cracked after 41 impacts and broke after 146 impacts. I ended up doing it.

Therefore, it has been found that the collar 1, which has a size necessary for sufficient penetration ability of the helical pile a, has sufficient durability against cracking and chipping due to collision with boulders, forced penetration, etc. Ta.

The PC helical pile a of the present invention uses high-strength steel fiber reinforced concrete whose 28-day standard strength is σ28 = 750 kg/d or more based on a standard compression test specimen.

Furthermore, since the PC spiral pile a is formed by centrifugal force, the strength can be further increased by about 20% through sufficient compaction and dewatering.

Such high-strength concrete naturally has an increased tensile strength, and has a tensile strength that is approximately one-fifteenth of its compressive strength.

Furthermore, by reinforcing with steel fiber, the tensile strength is approximately 1.3
increase twice.

Furthermore, when torque is applied to the pile, shear force is generated in the cross section of the pile, and the largest shear stress is generated at the outer periphery of the pile.

If you take out the outer surface of the pile, it will be in a state of pure shear stress due to the torque.

If the shear stress in this case is τ, the principal stresses σ and σ2 are: 1) σ1−−σ2−τ, and the direction of the principal stress σ1 with respect to the pile axis is tan 2
ψ=■, ψ=45°, and a tensile stress of σ1−τ is generated in a direction 45° with respect to the pile axis direction, and a compressive stress of σ2−− is generated perpendicular to this.

When this principal stress σ1 reaches the tensile strength σt of concrete, it can be considered that cracks occur in the direction perpendicular to the tensile stress.

That is, the shear core force at which cracks occur is τ2σt.

Next is the pile σ.

When a prestress (compressive stress) is introduced and a torque is applied to the pile, the stress state on the outer surface of the pile is σ in the axial direction of the pile.

The result is a combined stress state where the compressive stress and shear core force τ are simultaneously applied, and the principal stresses σ1 and σ2 in this case are as follows.
The direction of the principal stress σ1 with respect to the pile axis is as follows.

That is, a tensile stress of σ1 is generated in the direction of the pile axis and ψ, and a compressive stress of σ2 is generated in a direction orthogonal thereto.

It can be considered that cracks will occur when this principal stress σ1 reaches the tensile strength σt of the concrete.

As a result, the shear core force τcr at which cracks occur is: The direction of the crack relative to the pile axis is .

For the concrete used in the PC spiral pile a of the present invention with a standard residual cold of σ2a = 750 kgl- at 28 days of age, the compressive strength increases by about 20% by centrifugal forming.
σc = approximately 900 kg/cwt.

The tensile strength for this is about one-fifteenth of the compressive strength, and σ
t = 60 kgl-, and by reinforcing with steel fiber, the tensile strength is approximately 1.3 times σt = 78 kg/cy? i is obtained.

In this case, when no prestress is introduced, the shear core force when cracking occurs is τcr−σt=78 ky
//C1? However, if a prestress of 100 kg/criY is introduced, σo = 100 kglcrtt
Using , rcr = 118 kglc11t, and the direction of the crack is ψ, -25°.

Also, if a prestress of 200 kglca is introduced, τcr = 147kg/cr? r, and the direction of the crack is 18°.

In other words, when a prestress of 100 kg/- is introduced into a pile, the torque that causes a crack is 200 kFl/cri, which is approximately 1.5 times that when no prestress is introduced.
It is approximately 1.9 times the prestress of t.

In addition, the direction of the crack is 45° with respect to the pile axis when prestress is not introduced, but by introducing prestress, the direction of the crack is tilted toward the pile axis, and the angle of the crack becomes smaller.

By these means, the larger the stress introduced by prestress is, the more the torque that causes cracks can be increased, and the angle of cracks can be made smaller with respect to the pile axis.

For this reason, it is advantageous to use high-strength concrete to increase the prestress in PC helical piles that are rotated by applying torque and penetrate into the soil.

Moreover, by arranging the spiral reinforcing bars 5b close to perpendicular to the direction of cracking, it is possible to further increase the torque that causes cracking.

Next, a torsion test was conducted using a conventional PC pile with an outer diameter of 300 mrn and a wall thickness of 60 mrn and a PC helical pile a of the present invention with a length of 1.2 m, and the results were as shown in the table below.

As long as it has a cracking torsional moment of the same degree as that obtained with steel fiber reinforced concrete, torsional penetration into the ground that requires a pile foundation is sufficiently possible, even taking into account the safety factor.

By changing the size, shape, and pitch of the collar part 1 of the PC helical pile with high torsional strength of the present invention, it can be used on all types of soil, from sandy soil to clayey soil, and from loose soil to hard ground. Even under certain conditions, it is possible to penetrate the soil by applying rotation with torque.

In other words, according to torsional penetration experiments, when the height of the brim is large and the pinch is large, a large amount of soil is ejected, but the torque required to twist the pile to penetrate is small and suitable for hard soil.

In such a case, if there is a gap under the collar of the pile that has been penetrated and there is a concern that the bearing capacity as a friction pile will decrease, this gap should be removed from the tip of the pile by pressing mortar into the hollow part of the pile. By filling it with mortar, greater supporting capacity can be expected.

When the height of the brim is small and the pitch is small, the amount of soil discharged is small, and unlike other vibration-free and noise-free construction methods, it does not cause ground destruction or loosening, but rather compacts the ground.Furthermore, the pile itself has a flange. Therefore, it is possible to dramatically increase the friction with the ground, so a large supporting capacity can be expected.

In such cases, the torque required for torsional penetration is suitable for thick, loose ground.

Furthermore, by penetrating the present PC helical pile a into soft ground, the ground can be improved without vibration or noise.

In addition, if the top and bottom angles of the spiral groove are formed at the same angle as in Japanese Utility Model Publication No. 47-29681, even if the pile is able to penetrate at first, it will become idle after penetrating to a certain extent. However, in the present invention, as shown in FIG. 3, the upper surface angle α and the lower surface angle β of the spiral collar portion 1 are formed to be different from each other. The torsional penetration can be completed to the end, providing a large supporting capacity, and the construction is safe and reliable.

[Brief explanation of the drawing]

The drawings show examples of the present invention, and Fig. 1 is a front view of the main part showing a partially cut-out state of the PC spiral pile, Fig. 2 is a front view of the main part, and Fig. 3 is a cross-sectional view of the part marked with . It is. 1...Brim portion, 2...Concrete pile, 3...Steel fiber.

Claims (1)

[Claims] 1. A torsion-penetration type PC helical pile having a helical collar, characterized in that the top and bottom angles of the helical boxwood part are formed to be different from each other.