JPS6373128A - Method and apparatus for measuring dynamic supporting force of pile - Google Patents

Abstract

PURPOSE:To compute dynamic supporting force efficiently, by measuring the acceleration of a pile with an accelerometer, integrating the values twice, computing the amount of displacement, computing the amount of penetration of the pile and the rebounding amount when the speed of the penetrating pile becomes zero, and operating the values. CONSTITUTION:The acceleration of a pile 1 when it is driven with a hammer is measured with an accelerometer 2. The acceleration signals are sampled in a sampling circuit 4 through an amplifier circuit 3. The result is stored in a memory 9 through an A/D converter circuit 8. An integrating circuit 10 integrates the acceleration signals, and a speed is computed and stored in a memory 11. An integrating circuit 12 integrates the speed signals, and the amount of displacement is computed and stored in a memory 13. A CPU 14 obtains the amount of displacement when the speed is zero. The amount of penetration (s) of the penetrating pile 1 and the rebounding amount (k) are computed based on the amount of displacement. The values of (s) and (k) are substituted into a linear wave equation in the CPU, and dynamic supporting force is computed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method and apparatus for measuring dynamic bearing capacity of driven piles.

[Prior art] The dynamic bearing capacity of a driven pile, which is driven into the ground by intermittently hitting the head with pants, etc., is determined by the driver of the pile, that is, the amount of displacement (more precisely, the amount of rebound) of the driven pile. ) is calculated by measuring the amount of displacement and substituting this displacement amount into a predetermined calculation formula.

Conventional methods for measuring the amount of displacement of driven piles include the paper stuffing method, the optical displacement meter method, and the accelerometer/strain gauge method. Figure 5 shows the principle of the paper packing method.
5(a) shows a front view, and FIG. 5(b) shows a side view. In FIG. 5, 20 is a driven stake, 21 is a recording paper pasted with adhesive tape 22 on the side of the head of the driven stake 20, 23 is a pencil, 24 is a ruler that supports the pencil 23, and 25 is a ruler 24
This is a support that supports horizontally. The paper packing method is to use a hammer (
Each time the driven pile 20 is struck by a hammer (not shown), the operator zeroes the pencil 23 along the ruler 24 and records the amount of displacement of the driven pile 20 on the recording paper 21. Figures 6 and 7 show the recording sheets 21 for driving piles on land and at sea. The amount of rebound K by which the driven pile 20 lifts is recorded. Furthermore, when driving at sea, it is difficult to find a fixed point, that is, a fixed point for the ruler 24, so the line becomes irregular.

Next, FIG. 8 is a diagram showing the principle of the optical displacement meter method. 8th
In the figure, 20 is a driving pile, 26 is a hammer for driving the driving pile 20, 27 is a target attached to the side of the head of the driving pile 20 and painted white and black, and 28 is an optical device installed on the quay. This is a type displacement measurement device. The optical displacement measuring device 28 is composed of a camera 29 that photographs the target 27, an amplifier that amplifies the imaging signal of the camera 29, an image IA processing device 30 that includes a recording device, and an output device. The optical displacement meter method measures the displacement when the driven pile 20 is driven by optically capturing the target 27 with the camera 29, and converts this into an electrical quantity to calculate the amount of displacement. be. Optical displacement measuring device 28
The amount of displacement of the driven pile 20 output by is shown in FIG. 9th
In the measurement example shown in Figure (a), the penetration fcS and the rebound amount K are each 10.2 mm. In addition, in the measurement example shown in Figure 9(b), the penetration amount S and the rebound amount K are each 8.2 m.
It is m. This method also has the penetration f of the driven pile 20 for each blow.
Although f1S and rebound iK are recorded, the accuracy is better than the paper jamming method.

Based on the penetration amount of the driven pile 20 calculated by the paper stuffing method and the optical displacement meter method described above, the dynamic bearing capacity of the driven pile 20 is calculated using the dynamic bearing capacity calculation formula specified in each standard or specification. is calculated.

The dynamic bearing capacity calculation formula is -dimensional wave equation and Hiley (
There are various formulas for t(fley). The -dimensional wave equation is said to have good accuracy in terms of current quantity.

- According to the dimensional wave equation, the dynamic ultimate bearing capacity Ru of the driven pile 20 is calculated by dividing the actual cross-sectional area of the driven pile 20 into A1 driven pile 2
Young's modulus of 0 is El, rebound amount is K, driven pile 2
The average value of the N value of the circumferential surface of 0 is N, and the circumference of the driven pile 20 is U.
, when the length of the driven pile 20 is I and the correction coefficient is eOlef, A-E-K N-Ll-I R,= + (1)e
o・I ef .

Next, FIG. 10 is a diagram showing the principle of the accelerometer/strain gauge method. In Fig. 10, 20 is a driven pile, 31 is an accelerometer attached to the side of the head of the driven pile 20, 32 is a strain gauge, 33 is a pile driving analyzer, 34 is a tape recorder, 35 is a microphone, and 36 is an oscilloscope. be. This accelerometer/strain gauge method converts the pile head strain waveform that occurs when driving the driven pile 20 into force using the strain gauge 32, and integrates the acceleration measured by the accelerometer 31 to convert it into speed. This method predicts the bearing capacity of a pile from the stress and speed of the head. Regarding this method, Ca5
Research by Goble et al. called e Method and TN
The research by O et al. is notable. According to the Ca5e Method, the dynamic bearing capacity R6 is calculated by changing the amount of 'X' of the driven pile 20 to m (W
/g), and if the propagation velocity of the stress wave is L, which is the distance from the tip of the C1 driving resistor 20 to the pickup installation position, then the following equation is obtained. The first term in the second equation is the time (t
The time required for the stress wave to make one round trip around the driven pile 20 (2L)
/C') is the average value of the force. In addition, the second term represents the force due to acceleration by dividing the speed difference over the same time as the first term by the time for the stress wave to make one reciprocation of the driven pile 20 (2L/c), multiplied by the mass m. It is.

[Problems to be solved by the invention] By the way, in the paper pasting method described above, the driven pile 2
The recording accuracy of zero penetration displacement was poor, and there was a problem in that it was difficult to obtain a fixed point, especially in offshore piling work. Furthermore, there is a problem in that it is dangerous because the worker directly records the penetration displacement while the driven pile 20 is being penetrated.

Although the optical displacement measurement method has better accuracy than the paper pasting method, there is a problem in that it takes time to attach the target 27 and to calibrate the optical displacement measurement device 28. or,
Due to the vibrations of pile driving, it is necessary to keep the optical displacement measuring device 28 approximately 3 (1 m or more) away from the target 27, but it is said that a distance of 30 m cannot be secured due to nearby construction work in urban areas and restrictions on the placement of pile driving machines. There was a problem.Furthermore, in offshore piling work, it was difficult to find fixed points.

In the accelerometer/strain gauge method, it takes 3T to 5T to stabilize the penetration displacement of the driven pile 20, where T (=2L/c) is the time for the stress wave to make one round trip through the driven pile 20. The penetration displacement of the driven pile 20 is controlled in a very short time (t,
+2L/c = 2~3m5ec+time for the stress wave to make one round trip around the driven pile 20).For this reason, only the initial penetration of the driven pile 20 is considered, and the influence of the ground at the tip of the driven pile 20 occurs from 3T~ Since the 5 guns were ignored, there was a problem with poor accuracy.

The present invention has been made to solve the above problems,
It is an object of the present invention to provide a method and device for measuring the dynamic bearing capacity of driven piles that efficiently calculates the dynamic bearing capacity.

[Means for Solving the Problems] Therefore, the present invention includes an accelerometer that is attached to a driven pile that penetrates into the ground by being driven intermittently, and that measures the driving acceleration of the driven pile; A first integrating circuit integrates the speed of the driven pile at predetermined time intervals and calculates the speed of the driven pile, and a second integral circuit integrates the speed at predetermined time intervals to calculate the displacement amount of the driven pile. Calculate the rebound amount by calculating the maximum displacement amount due to one driving of the driven pile and the amount of penetration of the driven pile from the amount of displacement when ;, and subtracting the amount of penetration from the maximum displacement amount to calculate the amount of rebound of the driven pile. A dynamic bearing force measuring device for a driven pile is constituted by the means and a bearing force calculation means for calculating the dynamic bearing force of the driven pile based on the rebound amount and a predetermined dynamic bearing force calculation formula.

[Function] In the dynamic bearing capacity measuring device for a driven pile having the above configuration, an accelerometer measures the acceleration of the driven pile, a first integrating circuit calculates the speed from the acceleration of the driven pile, and a second integrating circuit calculates the speed from the acceleration of the driven pile. calculates the displacement from the speed of the driven pile. Further, the rebound amount calculation means calculates the maximum displacement amount and penetration amount of the driven pile from the displacement amount when the speed of the driven pile becomes zero, calculates the rebound amount, and the bearing capacity calculation means calculates the rebound amount by a predetermined amount. Substitute it into the dynamic bearing capacity calculation formula to calculate the dynamic bearing capacity of the driven pile.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of a dynamic bearing capacity measuring device for driven piles according to the present invention. In Figure 1, 1 is a driven pile, 2
is an accelerometer that is attached to the driven pile 1 and outputs an acceleration signal corresponding to the acceleration of the driven pile 1, and 3 is an accelerometer 2
4 is a sampling circuit that samples the acceleration signal amplified by the amplifier circuit 3; 5 is a sampling time setting circuit that sets the sampling time of the sampling circuit 4; 6 is a trigger level of the sampling circuit 4. 7 is a measurement time setting circuit that sets the measurement time of the sampling circuit 4; 8 is an analog-to-digital conversion circuit that converts the acceleration signal sampled by the sampling circuit 4 into a digital signal; 9 is a digital signal 10 is an integrating circuit that integrates the acceleration signal stored in the memory 9 and outputs a speed signal corresponding to the speed of the driven pile 10, and 11 is a speed signal output from the integrating circuit 10. 12 is an integrating circuit that integrates the speed signal stored in the memory 11 and outputs a displacement signal corresponding to the penetration displacement of the driven pile 10. 13 is a memory that stores the displacement signal output from the integrating circuit 12. , 14 controls the entire driving pile dynamic bearing capacity measuring device according to the program stored in the memory 15, and also searches data stored in the memories 11 and 13, calculates the amount of rebound, and performs dynamic bearing capacity measurement. This is a central processing unit (hereinafter referred to as CPU) that performs calculations.

Next, the operation of the dynamic bearing force measuring device for driven piles according to the present invention will be explained with reference to FIGS. 2, 3, and 4. FIG. 2 is a flowchart showing the operation of the dynamic bearing capacity measuring device for driven piles according to the present invention. Figure 3 is a signal waveform diagram of each part, and Figure 3 (a) is a waveform diagram of the acceleration signal.
FIG. 3(b) is a waveform diagram of the speed signal, and FIG. 3(c) is a waveform diagram of the displacement signal. In addition, Fig. 4 is a signal waveform diagram of each part simplified for explanation of the signal waveform diagram of Fig. 3. Fig. 4(a) is a waveform diagram of the acceleration signal, and Fig. 4(b) is a waveform diagram of the speed signal. FIG. 4(c) is a waveform diagram of the displacement signal.

(1) Step 1 The accelerometer 2 is intermittently hit by a hammer (not shown),
The driving acceleration α of the driven pile 1 penetrating into the ground is measured, and an acceleration signal corresponding to the measured acceleration is output.

Driven pile 1 is hit with a hammer and penetrates into the ground, but when the force of the hammer is removed, it lifts up a little, so if the measured acceleration is positive in the direction toward the ground, then Figure N4 (a)
As shown in , the direction is positive at first, and when it rises it becomes negative.

(2) Step 2 The acceleration signal corresponding to the measured acceleration α is amplified via the amplifier circuit 3 and input to the sampling circuit 4. The sampling circuit 4 is a sampling time setting circuit 5.
By sampling time force, trigger level setting circuit 6
The trigger level and measurement time are respectively set by the measurement time setting circuit 7, and the acceleration signal is sampled at the set timing. The sampling time set by the sampling time setting circuit 5 differs slightly depending on the type of driven pile 1 and the hammer.
Experiments have confirmed that 20 to 100 μs is appropriate. Further, the trigger level set by the trigger level setting circuit 6 is such that the acceleration is actually measured from the point in time when the acceleration exceeds a predetermined magnitude. Since the maximum acceleration of driven pile 1 is about 500G, the trigger level is 50
~100 G, and the sampling circuit 4 samples the acceleration, or time, of 4 to 20 m5ec before the acceleration exceeds 50 to 100 G. Furthermore, the timer set by the measurement time setting circuit 7! The 11 hours are 3T to 5T, which is 3 to 5 times the time T (=2L/c) required for the stress wave to make one round trip around the driven pile 20. The acceleration signal sampled by the sampling circuit 4 is converted into a digital signal via the analog-to-digital conversion circuit 8 and stored in the memory 9. In this case, the acceleration signals are stored together with a data number by assigning a number to each sampled acceleration signal.

(3) Step 3 The integrating circuit 1O time-integrates each acceleration signal stored in the memory 9, calculates the speed V of the driven pile 1 as shown in FIG. 4(b), and calculates the speed V corresponding to the calculated speed V. The speed signal is stored in the memory 11. Note that the speed signal is stored together with the number attached to the corresponding acceleration signal.

(4) Step 4 The integrating circuit 12 time-integrates the speed signal stored in the memory 11, calculates the displacement amount S of the driven pile 1 as shown in FIG. The corresponding displacement amount signal is stored in the memory 13. In this case as well, the displacement signal is stored together with the corresponding speed signal and number. Note that the displacement amount S may be calculated by the integrating circuit IO, but in consideration of high-speed calculation, it is better to calculate it separately.

(5) Steps 5 to 8 The CPU 14 searches the memories 11 and 13 (Step 5) and searches for the displacement 1s (S=S2) corresponding to the data where the velocity V becomes a drop (V2=O) (Step 6) ,CPU
14 is the penetration amount S of the driven pile 1 from the searched displacement amount S2,
Calculate River Wand HK (Step 7), set the final penetration amount of pile body 1 to 33%, and set the penetration amount from the previous driving to Sl
Then, the penetration amount S is 5=Ss-Sl =S, -0=S3, and for the rebound amount, if the maximum penetration amount is S, then K'=S2-S30 Next, the CPU 14 calculates the dynamic support force Ru by substituting the rebound amount K into the one-dimensional wave equation shown in the first equation (step 8). That is, the actual cross-sectional area of the driven pile 1 is set as A, Young's modulus of driven pile l is E, driven pile 1
Let N be the average value of the N values of the circumferential surface of
Dynamic support force R.

teeth, A-E ・ becomes N-U ・■.

[Effects of the Invention]' As explained above, according to the present invention, the amount of penetration and the amount of rebound are calculated when the speed, which is the time integral value of acceleration, becomes zero, that is, the maximum amount of penetration, and the amount of rebound is calculated based on the maximum amount of penetration. The dynamic support force can be calculated quickly using the dynamic support force calculation formula.

In addition, dynamic support force can be obtained with higher accuracy than the conventional paper packing method and with the same accuracy as the optical displacement meter method, and unlike the optical displacement meter method, target attachment and optical measurement equipment are not required. No need for calibration.

Furthermore, since an accelerometer is used, there is no need to set a fixed point.

Furthermore, since the measurement time is long and the phenomenon of carving of the ground at the tip is fully included, the accuracy is better than the acceleration/strain gauge method in principle.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the dynamic bearing capacity measuring device for driven piles according to the present invention, FIG. 2 is a flowchart showing the operation of the dynamic bearing capacity measuring device for driven piles shown in FIG. 1, and FIG. The signal waveform diagram of each part of the dynamic bearing capacity measuring device for driven piles shown in Figure 1, the fourth (support) is the actual signal waveform diagram of each part, and the fifth
The figure shows the principle of the conventional paper stuffing method, Figures 6 and 7 are explanatory diagrams of lines recorded on recording paper by the paper stuffing method, and Figure 8 shows the principle of the conventional paper stuffing method.
Figure 9 shows the principle of the displacement meter method, Figure 9 shows the output of the optical measuring device 28, Figure 1O shows the principle of the accelerometer/strain gauge method, and Figure 11 shows the output obtained by the accelerometer/strain gauge method. The output waveform diagram of the accelerometer and strain gauge, FIG. 12, is an explanatory diagram of the amount of displacement obtained by the accelerometer/strain gauge method. DESCRIPTION OF SYMBOLS 1... Drive pile, 2... Accelerometer, 3... Amplification circuit, 4... Sampling circuit, 5... Sampling time setting circuit, 6... Trigger level setting circuit, 7...
...Measurement time setting circuit, 8...Analog-digital conversion circuit, 9.11.13.15...Memory, 1O11
2... Integrating circuit, 14... Central processing unit (CPU)
. Figure 2 Figure 5 (0) (b) Figure 6 Figure 7 Figure 10 Figure 11

Claims (2)

[Claims] (1) Measure the acceleration of a driven pile that penetrates the ground by being driven intermittently, integrate the acceleration at predetermined time intervals, calculate the speed of the driven pile, and calculate the speed at predetermined time intervals. , calculate the displacement amount of the driven pile, calculate the maximum displacement amount of the driven pile and the penetration amount of the driven pile from the displacement amount when the speed of the driven pile becomes zero,
The amount of rebound of the driven pile is calculated by subtracting the amount of penetration from the amount of maximum displacement, and the dynamic bearing capacity of the driven pile is calculated based on the amount of rebound and a dynamic bearing capacity calculation formula. A method for measuring the dynamic bearing capacity of driven piles. (2) An accelerometer is attached to a driven pile that penetrates into the ground by being driven intermittently, and measures the acceleration of the driven pile when it is driven; a first integrating circuit that calculates the speed of the pile; a second integrating circuit that integrates the speed at predetermined time intervals and calculates the amount of displacement of the driven pile; and when the speed of the driven pile becomes zero. Calculate the maximum displacement amount by one driving of the driven pile and the penetration amount of the driven pile from the displacement amount, and subtract the penetration amount from the maximum displacement amount to calculate the rebound amount of the driven pile. Dynamic bearing capacity measurement of a driven pile, comprising a calculation means and a bearing capacity calculation means for calculating the dynamic bearing capacity of the driven pile based on the rebound amount and the dynamic bearing capacity calculation formula. Device.