JP4073838B2 - Measuring method for bearing capacity of foundation pile - Google Patents

Description

  The present invention relates to a method for measuring the bearing capacity of a foundation pile that can easily and accurately measure the bearing capacity of the foundation pile.

  Methods for measuring the bearing capacity of foundation piles include the static loading test method, dynamic loading test method (also referred to as impact loading test method), rapid loading test method, and tip loading test method described in Patent Document 1 below. It has been known.

  Among these, as shown in FIG. 4, the static loading test method is a method in which a reaction force pile 32 is placed around the foundation pile 31 to be tested and a loading frame is formed by the reaction force pile 32. In this method, the support force of the foundation pile 31 is measured by the jack 33, and the dynamic loading test method includes a buffer block 42 installed on the head of the foundation pile 41 as shown in FIG. In this method, the hammer 43 is dropped, and the support force is estimated and evaluated by performing wave analysis of the foundation pile 31 based on the acceleration at the time of impact of the hammer 43.

In addition, as shown in FIG. 6, the rapid loading test method explodes the reaction force body 52 with gunpowder, loads the reaction force on the head of the foundation pile 51 for about 0.2 seconds, and changes the displacement of the head. In this method, the load is measured by a laser (not shown), the load load is measured by the load cell 53, and the support force of the foundation pile 51 is estimated and evaluated by a one-dimensional wave theory based on this measurement data. Furthermore, although not shown in the drawings, the tip loading test method is a method in which a jack is embedded in advance at the tip of the foundation pile and the supporting force of the tip portion of the foundation pile is measured.
JP-A-10-153497

  Among the various test methods described above, the static load test method is the most accurate method, but it requires a large load device such as a reaction force device and a load device to secure the load, and the test. There were problems that required time and money.

  Similarly, in the tip loading test method, it is necessary to embed a jack and a measuring device at the tip of the foundation pile, which increases time and cost. In addition, because the rapid loading test method requires explosive explosives, it is difficult to apply in urban areas with vibration and noise, and the bearing capacity is estimated and evaluated by analysis. There was a problem.

  On the other hand, the dynamic loading test method is simpler and less expensive than these three methods, but the wave loading analysis is necessary and the accuracy is insufficient as in the rapid loading test method. In addition, a sensor for measuring force and speed must be attached to the head of the foundation pile, which requires a certain amount of work.

  Then, the main subject of this invention is providing the measuring method which can measure the bearing capacity of a foundation pile with high precision, without having to arrange | position a special process and a large-scale apparatus with respect to a foundation pile.

ここで、Ｖmax：ハンマーで測定した加速度を時間積分して速度とした時の最大値
Ｖm(t)：ハンマーで測定した加速度を時間積分して求めた速度
(3)下式(2)により静的抵抗力Ｆs(t)を計算し、その最大値Ｆs(max)を静的抵抗力Ｆｓとする手順

In order to solve the above-mentioned problem, the present invention according to claim 1 comprises a hammer with an accelerometer, and an arithmetic processing unit that receives a signal from the accelerometer and performs an analysis process based on the signal. Using a measuring device,
In each case, which went sequentially increasing the drop height of the hammer, it performs a hitting test for dropping the head of the foundation pile, take the collision initial velocity V ₀ of the hammer on the horizontal axis, the longitudinal axis of the foundation pile static The result of each impact test is plotted on the graph that takes the static resistance force Fs, and the foundation pile has a transition point at which the proportional relationship between the static resistance force Fs of the foundation pile and the initial collision velocity V ₀ changes or its vicinity. It is a method for measuring the bearing capacity of a foundation pile as the bearing capacity of
A static pile force Fs for each impact test is obtained by the arithmetic processing unit according to the following procedures (1) to (3) .
(1) Procedure for obtaining the striking force F (t) by multiplying the acceleration measured by the accelerometer with the hammer mass
(2) Procedure for obtaining dynamic resistance component cZV (t) due to dynamic friction effect between ground and foundation pile
Where c: proportionality coefficient
Z: Mechanical impedance of foundation pile
V (t): Movement speed of the foundation pile, obtained by the following equation (3) by integrating the acceleration measured with a hammer over time.

Where Vmax is the maximum value when the acceleration measured by the hammer is integrated over time to obtain the speed.
Vm (t): Speed obtained by time integration of acceleration measured with a hammer
(3) The procedure to calculate the static resistance force Fs (t) by the following formula (2), and set the maximum value Fs (max) as the static resistance force Fs.

  In the first aspect of the present invention, a measuring device is used which includes a hammer with an accelerometer and an arithmetic processing unit which receives a signal from the accelerometer and performs an analysis process based on the signal. Since it is not necessary to arrange special processing or a large-scale device for the foundation pile, it is possible to easily measure the supporting force of the foundation pile.

  As described above in detail, according to the present invention, it is not necessary to arrange special processing or a large-scale device for the foundation pile, and the bearing capacity of the foundation pile can be measured with high accuracy.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
〔Device configuration〕

  As shown in FIG. 1, the support force measuring device 1 for the foundation pile receives the hammer 2 to which the accelerometers 3 and 3 are attached and the signals from the accelerometers 3 and 3, and analyzes based on the signals. A measuring device comprising an arithmetic processing unit 4 for performing processing, and by dropping the hammer 2 from various heights, the head of the foundation pile 5 is changed in each case in which the initial collision speed of the hammer is changed. A striking force is given, and the supporting force of the foundation pile is obtained by an analysis process based on the acceleration measured by the accelerometers 3 and 3.

  Although one accelerometer 3 or 3 may be arranged, it is desirable to install a total of two accelerometers on opposite surfaces in order to remove noise signals due to the rotation of the hammer when the foundation pile is hit. Reference numeral 6 denotes a wiring relay tool for collecting wirings from the accelerometers 3 and 3.

Specifically, the analysis process is performed according to the following procedure.
(1) A striking force waveform obtained by multiplying the acceleration measured by the accelerometers 3 and 3 with a hammer mass and a velocity waveform obtained by time-integrating the acceleration are obtained.
(2) The static resistance force of the foundation pile 5 is obtained by correcting the dynamic resistance component due to the dynamic friction effect between the ground and the foundation pile 5 with respect to the impact force waveform.
(3) The relationship between the static resistance of the foundation pile 5 and the initial speed is arranged for each case where the impact initial speed of the hammer 2 is changed. The support point of the foundation pile (yield support force) is the transition point where the proportional relationship changes or the value near it.

Hereinafter, the analysis principle of the present invention will be described in detail.
The equation of motion when the foundation pile 5 is struck by the hammer 2 is expressed by the simultaneous differential equation (1) below.

ここで、ｍはハンマーの質量、ｘはハンマーの変位、ｋはクッションのバネ係数、Ｚは杭の機械インピーダンス、またｙは杭の変位である。

Here, m is the mass of the hammer, x is the displacement of the hammer, k is the spring coefficient of the cushion, Z is the mechanical impedance of the pile, and y is the displacement of the pile.

  In the above formula (1), the acceleration of the hammer 2 is measurable and the mass is known. That is, k (xy) in the equation (1) does not need to be measured, and can be determined if the acceleration of the hammer is measured.

Next, Z · (dy / dt) indicates the striking force acting on the pile. The fact that this is equal to −k (xy) is different in the direction in which the force acts, but the absolute value is m ·. d ² x / dt ² ). That is, if the mass of the hammer 2 and the acceleration of the hammer 2 are obtained, the striking force acting on the foundation pile 5 is equal to the product of the mass of the hammer 2 and the acceleration of the hammer 2. Until now, the striking force at the pile head has been measured with a strain gauge or the like attached to the pile head, but the force acting on the pile can be measured by measuring the acceleration of the hammer.

  FIG. 2 shows an example of a striking force waveform actually measured. In the figure, the first step part where the striking force rises (in the figure, indicated as “blowing force when the hammer falls”) is the first striking force generated by the hammer 2 colliding with the foundation pile 5. There is no penetration resistance of the ground acting on the foundation pile 5 (resistance force from the ground acting when the pile is going to penetrate into the ground, that is, support force of the pile) in the portion. This is because the striking force generated on the pile head has just started in the pile.

  Next, in the figure, although it is a portion described as “synthetic force with the reaction force of the pile”, three peak-like waveforms are seen. At this time, the striking force generated on the pile head has reached the pile head once again by reciprocating the pile, and the striking force transmitted from the hammer 2 to the foundation pile 5 and the reaction received by the foundation pile 5 from the ground. It is a combination of force, ie penetration resistance. In the case of the example waveform, the three distinct peaks are observed because the hammering force applied from the hammer 2 to the pile is applied during the time in which the wave travels through the foundation pile 5 at least three times. The peak value is reduced because the striking force of the hammer 2 is reduced, the speed of the hammer 2 and the foundation pile 5 is reduced, and the resistance force proportional to the speed of the foundation pile 5 is obtained. This is because the resistance force due to the viscosity between the ground and the pile decreases.

  From the above viewpoint, the ground and foundation as shown in the following equation (2) for the striking force F (t) obtained by multiplying the acceleration obtained by the accelerometers 3 and 3 attached to the hammer 2 with the hammer mass When the dynamic resistance component cZV (t) due to the dynamic friction effect with the pile 5 is corrected, the static bearing force Fs (t) of the foundation pile 5 is obtained.

ここで、ｃは比例係数、Ｚは基礎杭５の機械インピーダンス、Ｖ(t)は基礎杭５の運動速度である。

Here, c is a proportional coefficient, Z is the mechanical impedance of the foundation pile 5, and V (t) is the motion speed of the foundation pile 5.

  For example, the proportional coefficient c can be estimated as a proportional coefficient under the condition that the value of Fs (t) at the time indicated as “the combined force with the reaction force of the pile” in FIG. However, practically, it is better to create a database of proportional counts for each ground property and give them as experience values. If the sand ground, the proportionality coefficient c is about 0.2, and if the clay ground, the proportionality coefficient c is about 0.3 to 0.4.

  On the other hand, the movement speed V (t) of the foundation pile 5 can be obtained by integrating the acceleration measured by the hammer 2 with time. However, the velocity waveform obtained by integrating the acceleration over time is shown in FIG. 2, which is obtained by integrating the deceleration acceleration acting on the foundation pile 5, and the actual velocity V (t) of the foundation pile 5 is as follows. Equation (3) is obtained.

ここで、Ｖmaxはハンマーで測定した加速度を時間積分して速度とした時の最大値、Ｖｍ(t)はハンマー２で測定した加速度を時間積分して求めた速度（図２の速度波形）である。

Here, Vmax is the maximum value obtained by integrating the acceleration measured with the hammer over time, and Vm (t) is the speed obtained by time integrating the acceleration measured with the hammer 2 (speed waveform in FIG. 2). is there.

From the above, the static resistance force Fs (t) is calculated by the above equation (2), and the maximum value Fs (max) is set as the static resistance force Fs of the ground under the condition.
[Calculation of bearing capacity of foundation pile]

  The dynamic resistance force acting on the pile by the accelerometers 3 and 3 attached to the hammer 2 and the static resistance force of the foundation pile by correcting the dynamic resistance component due to the dynamic friction effect between the ground and the foundation pile However, when measuring bearing capacity of piles, the yield point or ultimate resistance must be determined.

By the way, there is a proportional relationship between the initial collision velocity V ₀ of the hammer 2 and the striking force F generated in the foundation pile 5, and the following equation (4) is established.

ここで、Ｆは打撃力、Ｖ_０はハンマーが杭と衝突する時の初速度、ｍはハンマー２の質量、ｋはクッションのバネ係数、φは任意の関数（三角関数又は双曲線関数等）である。

Where F is the impact force, V ₀ is the initial velocity when the hammer collides with the pile, m is the mass of the hammer 2, k is the spring coefficient of the cushion, φ is an arbitrary function (trigonometric function or hyperbolic function, etc.) is there.

In the above equation (4), in the range where the foundation pile 5 can sufficiently resist the striking force F, the striking force F generated is proportional to the initial collision velocity V ₀ of the hammer 2. When the striking force F is gradually increased and the foundation pile 5 surrenders and cannot withstand the predetermined striking force F, the resulting force (force is generated by the balance between action and reaction) is: Changes will occur in the proportional relationship with the hammer's initial collision speed.

Therefore, as shown in FIG. 3, the hammer impact initial velocity V ₀ is taken on the horizontal axis and the static resistance force Fs (max of the foundation pile 5 is obtained by performing a plurality of impact tests with the hammer impact initial velocity being changed. ) On the vertical axis, and the results of each impact test are plotted on a graph. In the range where the speed of the hammer is small, the initial collision speed of the hammer is proportional to the static resistance force. This range shows that it is within the range of the bearing capacity of the pile.

In contrast, when the initial collision velocity V ₀ of the hammer 2 is gradually increased, a change appears in the proportional relationship between the initial velocity V _{0 of the} hammer and the static resistance force Fs of the foundation pile 5 and the inclination is reduced. The transition point is the yield bearing capacity (pile bearing capacity).

The initial collision speed V ₀ when the hammer 2 collides with the foundation pile 5 is possible by controlling the drop height of the hammer 2. Specifically, the falling height of the hammer 2 is raised sequentially from, for example, 0.1 m, and in each case where the falling height is changed, the impact initial velocity V ₀ at the hit and the calculated static resistance force Fs. And plot it on the graph. As a method of determining whether or not the yield point (transition point) has been exceeded, for example, for the measured data set, the initial collision speed of the hammer is an independent variable (explanatory variable), and the static resistance is a dependent variable ( The linear regression equation was calculated as the dependent variable), and passed the yield point when the intercept (Y-axis value) on the dependent variable side became 5% or more of the maximum value of the measured static resistance force Fs. It can be determined that there is a possibility.

  That is, although the regression equation of the measurement data is shown in FIG. 3, the slope (slope) of the regression equation gradually decreases as the measurement data exceeding the yield point increases, so the intercept is the static resistance force Fs. The test is completed when the maximum value is 5% or more, and the supporting force (static resistance force) of the foundation pile 5 may be determined from the graph.

  INDUSTRIAL APPLICABILITY The present invention can be suitably used for measuring the soundness of newly established foundation piles or existing foundation piles.

It is a block diagram of the supporting force measuring apparatus 1 which concerns on this invention. It is an example of a hit waveform measured by the accelerometer 3. Hammer initial velocity V ₀ and is a correlation diagram of the static resistance force Fs (t). It is a figure which shows the conventional static loading test method. It is a figure which shows the conventional dynamic loading test method. It is a figure which shows the conventional rapid loading test method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Bearing capacity measuring device, 2 ... Hammer, 3 ... Accelerometer, 4 ... Arithmetic processing device, 5 ... Foundation pile

Claims (1)

Using a measuring device comprising a hammer equipped with an accelerometer, and a signal from the accelerometer is input, and an arithmetic processing unit that performs analysis processing based on this signal,
For each case where the fall height of the hammer was raised sequentially, a hit test was conducted to drop it on the head of the foundation pile, the horizontal axis represents the hammer's initial collision velocity V ₀ , and the vertical axis represents the static pressure of the foundation pile. The result of each impact test is plotted on the graph that takes the static resistance force Fs, and the foundation pile has a transition point at which the proportional relationship between the static resistance force Fs of the foundation pile and the initial collision velocity V ₀ changes or its vicinity. It is a method for measuring the bearing capacity of a foundation pile as the bearing capacity of
The method of measuring a bearing capacity of a foundation pile, wherein the static resistance force Fs for each impact test is obtained by the following (1) to (3) procedure in the arithmetic processing unit.
(1) Procedure for obtaining the striking force F (t) by multiplying the acceleration measured by the accelerometer with the hammer mass
(2) Procedure for obtaining dynamic resistance component cZV (t) due to dynamic friction effect between ground and foundation pile
Where c: proportionality coefficient
Z: Mechanical impedance of foundation pile
V (t): Movement speed of the foundation pile, obtained by the following equation (3) by integrating the acceleration measured with a hammer over time.

Where Vmax is the maximum value when the acceleration measured by the hammer is integrated over time to obtain the speed.
Vm (t): Speed obtained by time integration of acceleration measured with a hammer
(3) The procedure to calculate the static resistance force Fs (t) by the following formula (2), and set the maximum value Fs (max) as the static resistance force Fs.

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