JPH07127062A - Cushion for driving ready-made pile - Google Patents

Abstract

PURPOSE:To suppress lowering of penetration amount by providing cushions set between a hammering means and a pile head with a function to transmit a hammering force to a ready-made pile without losing it while damping the hammering force on the hammering means side. CONSTITUTION:A cushion for driving existing pile comprises a hammering means 3 to drive a ready-made pile 2 into the ground and multiple cushion members 11 which are set between the head of the ready-made pile 2 and the hammering means 3 and stuck in the direction in which a hammering force is applied. The material of the cushion material 11 positioned on the ready-made pile 2 side is harder than that positioned on the hammering means 3 side among cushion members 11 and 11 adjacent to each other in vertical direction, and the material of the cushion member 11 positioned at the lowest is set equal to or lower than the material of the ready-made pile 2. Since the hardness is lowered gradually from the upper to the lower side, an impact force is transmitted to the ready-made pile 2 without losing it while damping on the hammering means 3 side to suppress lowering of penetration amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prefabricated pile driving cushion for alleviating the impact on the prefabricated pile when the prefabricated pile is driven into the ground by hammering means.

[0002]

2. Description of the Related Art When driving a prefabricated pile into the ground with a hammer, the impact noise at the time of impact is reduced and the impact between the pile and the hammer is reduced for the purpose of reducing the impact. Although a cushioning material is installed in the pile, a compressive force acts on the pile immediately after impact, and after transmitting to the pile tip, a tensile force acts due to the hardness of the ground near the pile tip, and the pile tip As a reflected wave at the pile heads toward the pile head, cracks may occur in the pile when this tensile force exceeds the tensile strength of the pile.

In Japanese Examined Patent Publication No. 2-20772, the impact force from the hammer is reduced by interposing a spring as a cushioning material between the pile head and the hammer, and at the same time, the time until it is transmitted to the pile is lengthened to the pile. Although a method to avoid the effect of the tensile force of the shock absorber has been proposed, since the impact force transmitted to the shock absorbing material is lost between the shock absorbing material and the pile, the penetration amount is less than that when the conventional shock absorbing material is used. It pays the sacrifice to reduce it to about 10%.

The present invention has been made in view of the above background, and proposes a cushioning material which avoids the action of a tensile force from the tip of a pile without causing a loss of impact force.

[0005]

According to the present invention, a cushion as a cushioning material is composed of a plurality of cushioning materials stacked in the direction of action of a striking force, and is positioned on the side of ready-made piles among the vertically adjacent cushioning materials. The cushion material on the striking means side is made relatively harder than the material of the cushion material located on the striking means side, and the material of the cushion material at the bottom is set equal to or less than the material of the ready-made pile. While buffering with, the impact force is transmitted to the ready-made pile side without loss, and the decrease in penetration amount is suppressed.

As shown in FIG. 5, the harder the cushioning material, the shorter the time until the compressive force is transmitted to the pile. At the same time, since the peak of the compressive force is high, the penetration amount of the pile increases, but the impact force of the pile increases. Easy to exceed compressive strength. Further, after the peak, the compressive force acting on the pile decreases rapidly, so that tensile force tends to act on the pile due to the reflected waves from the tip of the pile.

On the contrary, the softer it is, the longer it takes for the compressive force to be transmitted, and the smaller its peak is, so that the impact force can be suppressed within the compressive strength of the pile. However, since the penetrating amount decreases, a constant penetrating amount can be obtained. Requires multiple blows to.

On the other hand, the material of the cushion gradually becomes harder from the striking means side to the ready-made pile side, so that the impact force is transmitted from the cushion material on the striking means side to the cushion material adjacent to the lower side without loss. However, cushioning can be performed on the side of the relatively soft striking means, while suppressing the compressive force to the pile to be less than the compressive strength, the decrease in the amount of penetration of the pile due to impact force is suppressed, and the tensile force from the tip of the pile is also the tensile strength of the pile. It becomes possible to suppress below. Also, since the material of the cushion material located at the bottom is equal to or less than the material of the ready-made pile, the impact force from the cushion material at the bottom to the ready-made pile will not be lost, and the impact force efficiency will be improved. To be

The striking force applied to the cushion by the striking means is transmitted as an elastic wave in the cushion from the striking means side to the pile side and is transmitted to the pile, but the cushion material near the striking means is softer than the cushion material near the pile. As a result, the propagation speed of the impact force is suppressed by the cushion material on the side of the striking means, and the impact is moderated on the side of the striking means and transmitted to the pile. The propagation speed of the elastic wave due to impact is temporarily reduced on the impact means side, but since the cushion material near the pile is hard, the subsequent propagation speed is transmitted to the pile without decreasing,
There is no rapid decrease in the compressive force of the pile, and the effect of tensile force from the pile tip on the pile is reduced. Further, since the cushioning material near the striking means is soft, the impact sound when a striking force is applied can be reduced.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing an embodiment.

As shown in FIG. 1, the cushion 1 according to the present invention is installed between a striking means 3 for driving a ready-made pile (hereinafter referred to as a pile) 2 into the ground and the head of the pile 2, and a plurality of piles are piled up in the acting direction of the striking force. The cushion material 11 of FIG. The cushion 1 is housed in the casing 5 together with the cap 4 which receives the striking force directly from the striking means 3, and is installed on the head of the pile 2.

Of the cushion members 11, 11 that are vertically adjacent to each other,
The material of the cushion material 11 located on the side of the pile 2 is relatively harder than the material of the cushion material 11 located on the side of the striking means 3, and the material of the cushion material 11 located at the bottom is set equal to or less than the material of the pile 2. To be done.

The cushion material 11 is molded from engineering plastic or metal, and in the former case, nylon 66 having high impedance described later or plastic mixed with fibers such as low polyacetal is used depending on the material set above. Used selectively.

When attention is paid to the fact that the striking force from the striking means 3 is transmitted to the pile 2 as an elastic wave propagating through the solid,
The hardness of the cushion material 11 can be expressed by its elongation rigidity (= EA, E: longitudinal elastic modulus, A: cross-sectional area) as an index, but the velocity v [= (E / (E /
ρ) ^1/2 , ρ: density], the hardness of the cushioning material 11 can be expressed as elongation rigidity with respect to the propagation velocity = EA / v, and here, this is an index showing the ratio of input and output. Is defined as impedance Z (kgf · sec / cm).

The small impedance means that the strain generated in the axial direction with respect to the propagation velocity of the elastic wave is large, and the impact force is temporarily stored as strain energy to cause a delay in the propagation of the elastic wave. To do. On the contrary, the cushion material 11 having a large impedance has a small distortion and has a property of propagating waves without causing a time delay. Therefore, when the time is viewed in units of 1/1000 second by arranging the cushions 11 of a material having a small impedance to a material having a large impedance in order from the impacting means 3 side to the pile 2 side, the impact force immediately after the generation occurs. 2 is transmitted to the pile 2 after a short time, and the strain generated in the cushion material 11 gradually decreases from the side of the striking means 3 to the side of the pile 2 so that the striking force is transmitted to the pile 2 without loss. Will be done.

FIG. 1 shows a case in which annular cushion materials 11 having the same cross-sectional area are arranged in the axial direction and the impedance of the entire cushion 1 is set to be low. This is a case where a cushion material 12 having a material is inserted and the impedance of the cushion 1 as a whole is made higher than that in the case of FIG.

In FIG. 3, a plurality of springs having different lengths are used for the cushion material 11, and the cushion material 11 is hardened sequentially from the striking means 3 side to the pile 2 side by stacking the pile 2 side closer. . In this case, the section where the rigidity of the spring changes corresponds to each cushion material 11 in the case of FIG. 4 is shown in FIG.
This is a case where a cylindrical cushion material 13 is arranged on the outer circumference of all the cushion materials 11 and the overall impedance is higher than in the case of FIG.

FIG. 5 shows the relationship between the time (m · sec) and the axial force applied to the pile 2 when the impact force is applied from the impact means 3 to the pile 2 using the cushion 1 shown in FIGS. 1 and 2. It is a graph. There is no change in impedance here,
The relationship between the case of using a cushion harder than the cushion 1 of the present application and the case of using a soft cushion is also shown. The negative of the vertical axis represents the tensile force generated in the pile 2 by the reflected wave in which the elastic wave reaching the tip of the pile 2 is reflected from the tip of the pile and returns to the pile 2.

As described above, as described above, when the cushion is hard, the compression force reaches a peak immediately after the impact, so that an impact force exceeding the compression strength is applied to the pile 2.
On the other hand, when it is soft, it stays within the compressive strength, but the compressive force during the impact duration is low, and it is understood that the tensile force from the tip of the pile 2 is applied.

On the other hand, when the cushion 1 shown in FIGS. 1 and 2 is used, the peaks of the compressive force and the tensile force are both within the strength range of the pile 2 and the compressive force is harder than the case. It can be seen that the pile 2 is acting with a delay in time, but the impact force is not reduced, the energy loss is small, and the tensile force from the tip of the pile is reduced.

Incidentally, the impedances Z _1, Z ₂ , Z _{3 and} Z ₄ of the cushion materials 11 of the cushion 1 shown in FIG.
8,163,195,310 (kgf · sec / cm), and the impedance Z _5, Z ₆ , of each cushion material 11 of the cushion 1 shown in FIG.
Z _7, Z ₈ are each _{Z 1 +18.4, Z 2 + 29.1} , Z 3 +29.1, Z 4 +
It is 29.1 (kgf · sec / cm). The impedance value is vulcanized in the case of rubber by increasing the longitudinal elastic modulus E by mixing fibers such as glass fiber and carbon fiber when the material of the cushion material 11 is plastic and increasing the molecular weight. It can be changed.

FIG. 6 is a graph showing the relationship between the drop height and the amount of penetration of the pile 2 when a hammer is used as the striking means 3 and various cushions are interposed between the hammer and the pile 2.
As shown here, in the case of using the cushions B and C of the present invention, the penetration amount is lower than that in the case of using the harder cushion A without a spring, but the softer cushion D using a spring is used. In the case of the cushion B in which the impedance of the cushion 1 as a whole is changed to be stiffer than that in the case shown in FIG. 2, the penetration amount increases as the hammer falls more than the cushion C in which the impedance of FIG. 1 changes. Can be seen to increase.

[0023]

The present invention is as described above, and the cushion as a cushioning material is composed of a plurality of cushioning materials stacked in the direction of impact, and is positioned on the ready-made pile side of the adjacent cushioning materials. Since the material of the cushioning material is set to be relatively harder than the material of the cushioning material located on the side of the striking means, the impact force is transmitted from the cushioning material on the side of the striking means to the cushion material adjacent below without loss. However, cushioning can be performed on the side of the relatively soft striking means, while suppressing the compressive force to the pile to be less than the compressive strength, the decrease in the amount of penetration of the pile due to impact force is suppressed, and the tensile force from the tip of the pile is also the tensile strength of the pile. It becomes possible to suppress below.

Further, since the material of the cushion material located at the bottom is equal to or less than the material of the ready-made pile, the transmission of impact force from the cushion material at the bottom to the ready-made pile is not expanded, and the pile head is damaged. Is avoided.

In addition, since the cushion material near the striking means is soft, it is possible to reduce the impact noise when a striking force is applied.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing an embodiment in which a cushion material is formed in an annular shape.

FIG. 2 is a vertical cross-sectional view showing an embodiment in which another cushion material is added to the central portion of the cushion of FIG.

FIG. 3 is a vertical sectional view showing an embodiment in which a spring is used as a cushion material.

4 is a vertical cross-sectional view showing an embodiment in which another cushion material is added to the outer circumference of the cushion of FIG.

FIG. 5 is a graph showing a relationship between time and axial force of the pile when a striking force is applied to the pile through a cushion.

FIG. 6 is a graph showing a relationship between a drop height of a hammer and a penetration amount of a pile.

[Explanation of symbols]

1 ... Cushion, 11 ... Cushion material, 2 ... Ready-made pile, 3 ... Strike means, 4 ... Cap, 5 ... Casing. A: Harder cushion without springs, B: Cushion with slightly changed impedance, C: Cushion with changed impedance, D: Softer cushion with springs.

Claims (3)

[Claims] 1. A cushion which is installed between a striking means for driving a prefabricated pile into the ground and a head of the prefabricated pile, and which is composed of a plurality of cushion materials stacked in a direction in which a striking force acts, and which are vertically adjacent to each other. Among the materials, the material of the cushion material located on the side of the ready-made pile is relatively harder than the material of the cushion material located on the side of the striking means, and the material of the cushion material located at the bottom is equal to or less than the material of the ready-made pile. A ready-made pile driving cushion. 2. The prefabricated pile driving cushion according to claim 1, wherein each cushion material is an engineering plastic. 3. The prefabricated pile driving cushion according to claim 1, wherein each cushion material is a metal material.