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The sharing ended in November last year.
National training course on non-destructive testing of foundation piles.
Issue 28).
In the theoretical assessment.
High strain detection section.
Top 10 high-frequency questions that are easy to make mistakes
The highest error rate is also 80%.
1. In the high strain test, when the strain variable of a certain section of the pile is 500 microstrain and the concrete wave velocity of the pile is 4000m s, then the particle vibration velocity of this section can be known. （
a、2m/s
b、0.2m/s
c、1.25 m/s
d、0.8 m/s
Correct Answer: a
Analysis: v = c according to the velocity of the particle in relation to the strain
v=4000x500x10*-6=2m/s
2. There is a prefabricated concrete pile, which is constructed by hammering method, and the pile tip needs to penetrate a dense sand layer into the soft clay layer, and the pile body will appear ( ) at the moment of penetration
a. Large tensile stress.
b. Large compressive stress.
c. The speed is zero.
d. Stress. Correct Answer: a
Analysis: You can refer to the influence of the soil interface around the pile on the test signal
1) When the pile enters the soft soil layer from the hard soil layer, due to the relative decrease of soil resistance, a velocity signal and an upward tensile wave in the same direction as the incident wave will be generated.
2) When the pile enters the hard soil layer from the soft soil layer, due to the relative increase of soil resistance, a velocity signal and an upward pressure wave opposite to the incident wave will be generated.
The pile end at the moment of penetration is considered the free end
3. When the amplitude difference between the two sides of the force signal is different ( ), it cannot be used as the basis for the analysis and calculation of bearing capacity.
a、50% b、80%
c、100% d、200%
Correct answer: c
Analysis: Specification JGJ106-2014 in 94.2. The second is seriously hammered eccentricity, and the amplitude of the force signal on both sides is more than 1 times.
Calculated by 50% of the force signal on the larger side, it meets the requirement that the amplitude difference of the force signal on both sides is more than 1 times; However, if it is calculated at 50% of the force signal on the smaller side, it does not meet the requirement that the amplitude difference between the force signals on the two sides is more than 1 times.
4. Which of the following descriptions of fitting analysis is correct? （
a. The fitting method is an analytical solution of a one-dimensional wave equation.
b. The mechanical model of the fitting pile is an ideal elastoplastic model.
c. There are any number of sets of solutions that fit the law.
d. The mechanical model of the fitting pile is a linear elastic model.
Correct Answer: a
Analysis:The piles suitable for high strain are medium and small diameter piles, and the pile material and cross-section should be basically uniform. See Note 9 of JGJ 106-20144.9
5. When the calculated force curve near the pile bottom is higher than the measured force curve, priority should be given to:
a. Increase the side resistance.
b. Increase the end resistance.
c. Reduce side resistance.
d. Reduce end resistance.
Correct answer: d
Analysis: When the fitting method is used to calculate, if the fitting direction is to fit the force curve with the velocity curve, at the bottom of the pile, when the end resistance is larger, the performance is that the calculated f curve is larger at the position of 2l c (or later) than the measured f curve at the corresponding position (the performance of the velocity curve on f-zv is that the end resistance is large, the smaller the velocity in-phase reflection, and the greater the force is in phase), then according to the actual calculated force curve is higher than the actual test force curve, it can be processed by reducing the end resistance.
6. In the high-strain dynamic test pile, the hammer eccentricity often causes the difference in the measured signals of the sensors on both sides of the pile
a. The difference between the speed signals on both sides is greater than the difference between the force signals on both sides.
b. The difference between the force signals on both sides is greater than the difference between the speed signals on both sides.
Both cases C, A, and B can occur, depending on the degree of eccentricity.
d. Due to the symmetrical installation of the sensors on both sides, the difference between the force signals on both sides is the same as the difference between the speed signals.
Correct answer: B
Analysis: In the high strain dynamic test pile, the influence of hammer eccentricity is mainly the influence of the force value on both sides, the more serious the eccentricity, the greater the difference in the force value, and the velocity curve is basically the same regardless of whether it is eccentric or not, so the eccentricity has a great impact on the force, and the influence on the speed can be basically ignored.
JGJ 106-2014 Explanation 94.2: For concrete piles, the signal quality of the high strain test is not only affected by the quality of the sensor installation, the degree of hammering eccentricity and whether the concrete at the sensor installation surface is cracked, but also by the non-uniformity and nonlinearity of the concrete. These effects are particularly sensitive to the converted force signals tested with strain gauge sensors
7. The following statements about the sub-methods of the case method are correct: (
A. The RAU method takes the total resistance of the pile end when the movement speed is zero as the detection bearing capacity of the pile.
B. The RSU method deducts the lateral resistance of the middle and upper part of the pile, so the calculation results are conservative.
C. The RMN method is suitable for piles with short TR and large Quake value on the rising edge.
D. RMX method is suitable for piles with small quake value and lagging soil resistance.
Correct Answer: a
The scope of application of the various sub-methods of parsing :case is:
Maximum resistance method RMX: the situation that the rising time is short or the elastic limit of the soil is large, and the soil resistance is too late to give full play.
Minimum resistance method RMN: when the pile bottom is not obvious, it is safer; It is suitable for defects in the pile body, the reflection lag at the bottom of the pile, and the click penetration degree is large.
Unloading method RSU: Long pile, taking into account the unloading effect of resistance.
The value of the end-bearing pile is automatically calculated: short pile, end-bearing pile (the value corresponding to the value when the pile bottom speed is zero).
The formula for the automatic calculation of friction piles is RA2: friction piles, which is said to be close to the fitting value.
8. Prefabricated piles with cracks in the pile body or joints can be verified by the high strain method. （
Correct Answer:
Analysis: The high strain method has a large hammering energy to detect the integrity of the pile, and the degree of defect can be quantitatively calculated.
JGJ 106-2014 Explanation 91.1: The high strain method is incidental to detect the integrity of the pile. However, due to the advantages of large excitation energy and effective detection depth, especially when judging defects such as horizontal integrated gaps and prefabricated pile joints, the degree of defects can be reasonably determined on the basis of finding out whether these "defects" affect the vertical compressive bearing capacity.
9. The measured force curve of high strain detection is followed by the second peak after the first peak, showing a "double peak", indicating that there is a defect in the upper part of the pile ( ).
Correct Answer:
Analysis: The soil impedance around the pile will also have a peak when it is very small.
It is also possible that the shallow soil layer on the pile side changes significantly.
10. When testing the pile with high strain, the pile pad is set at the top of the pile to protect the top of the pile and avoid breaking the pile head. （
Correct Answer:
Analysis: The role of the hammer pad:
1) Make the hammering force evenly distributed, adjust the duration of the hammering process, and transfer the hammering energy to the pile more effectively.
2) Buffer the impact force of the hammer body, so that the compressive stress of the pile driving does not exceed the allowable value. If the pile pad is too soft, it will reduce the transmission of hammer energy, and the ability of the hammer to stimulate rock and soil resistance will decrease, making it difficult for the pile to penetrate. If the pile pad is too hard, the peak value of the hammering force is too high, and the purpose of adjusting and buffering the pile top to evenly stress and protect the pile head cannot be achieved.