JP2005180137A - Dynamic loading testing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dynamic loading testing method capable of accurately measuring axial force of an impact object such as a pile, and capable of highly accurately calculating bearing power over the whole of the impact object. <P>SOLUTION: This dynamic loading testing method calculates the bearing power of the impact object/a ground system from its analytical data, by measuring a shock wave propagating in this impact object, by impacting a head part of the impact object such as the pile by using a hammer. The method calculates the bearing power of the impact object/the ground system, by integrating the analytical data on the shock wave measured by impact of respective times, by measuring the shock wave with every impact of the respective times, by applying a plurality of times of impacts to the impact object being a test object. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a dynamic loading test method, and more specifically, for example, by measuring a shock wave propagating in a pile body when hitting a pile head and calculating a bearing capacity of a pile / ground system from the analysis data. The present invention relates to a dynamic loading test method.

  Pile vertical loading tests can be broadly classified into static loading tests and dynamic loading tests. The static loading test includes an indentation loading test, a tip loading test, a pulling loading test, and a lead orthogonal number loading test, and the dynamic loading test includes a rapid loading test and an impact loading test.

  The rapid loading test is a test method using an indentation force by rapid loading, and is classified into a reaction force body inertia method, a soft cushion weight dropping method, a rapid jack method, and the like. The impact loading test is a test method in which the pile head is struck with a hammer, the acceleration waveform and strain waveform propagating in the pile body are measured, and the bearing capacity of the pile is calculated from the analysis data. It is known as a simple loading method (see Non-Patent Document 1).

In the impact loading test, the bearing capacity is usually calculated by waveform analysis, for example, waveform matching analysis from the measurement obtained by hitting the pile head once as a final test after setting a small impact to set the amplifier magnification for measurement. ing. However, the impact energy is insufficient in one impact and the impact force does not reach the tip of the pile, and therefore only a part of the resistance between the pile head and the tip of the pile can be evaluated in many cases.
Pile vertical loading test method / commentary editorial committee, “Ground Engineering Society Standard Pile vertical loading test method / commentary-First revised edition”, Geotechnical Society of Japan, May 28, 2002

The present invention has been made based on the technical background as described above, and achieves the following object.
An object of the present invention is to provide a dynamic loading test method capable of accurately measuring an axial force or the like of a hit body such as a pile and calculating a highly accurate support force over the entire hit body. It is to provide.

  For a single pile to be tested, the impact force is changed multiple times and the shock wave data is analyzed. The relationship between the resistance and depth acting on the pile at each impact is shown in the figure. As shown in FIG. That is, when the striking force is small, the friction of the pile peripheral surface near the pile head is cut in the first hit. The pile surface friction below the pile head is cut by hitting multiple times. This is repeated in sequence to cut the friction on the lower pile circumference. In FIG. 1, the NF portion shows a portion where the friction is cut. In this way, by performing the hitting a plurality of times, the friction at the tip of the pile is finally cut, and the impact loading test is completed.

  The fact that the friction of the pile is cut means that the frictional resistance of the pile peripheral surface and the rigidity of the tip of the pile have entered the plastic region from the elastic region. Therefore, waveform matching analysis etc. is performed from the data obtained in this test, the maximum resistance of the pile peripheral surface and the pile tip is obtained, and the maximum value of the resistance of the same place among the pile resistance obtained by multiple hits is piled. The ultimate bearing capacity of the pile can be evaluated by evaluating the ultimate resistance of that part of the pile.

  If this is shown by the reflected wave obtained for every impact, it will become like FIG. That is, the reflected wave of the axial force changes by performing the hitting a plurality of times. In addition, in the case of a pile constructed by striking, the friction recovers with time if it is obtained after a period of time after construction. For example, when the reflected wave becomes as shown in FIG. 2 at the fourth hit, the axial force (reflected wave) as in the third hit, the second hit, and the first hit is obtained by hitting again. Here, if the elapsed time is sufficient, it can be recovered to the first time. This means that the friction has returned over time.

  Therefore, by performing multiple hits, individually extracting the most outstanding resistance in the depth direction of the pile, and combining them, the relationship between resistance and depth as shown in FIG. 3 is obtained. Similarly, a load-displacement relationship as shown in FIG. 4 is obtained. In other words, only one load-displacement relationship reflecting a part of resistance can be obtained with one hit, but by evaluating the maximum resistance for each depth range obtained by multiple hits, the ultimate The following load-displacement relationship is obtained.

The present invention is based on the above knowledge and employs the following means.
That is, the head of a hit body such as a pile is hit with a hammer, etc., the shock wave propagating through the hit body is measured, and the bearing capacity of the hit body / ground system is calculated from the analysis data. In the dynamic loading test method,
Applying multiple hits to the test subject to be hit, measuring the shock wave for each hit,
The dynamic loading test method is characterized in that the bearing force of the hit object / ground system is calculated by combining analysis data of shock waves measured at each impact.

More specifically, the analysis data includes the hit object peripheral surface ground data indicating the relationship between the hit object peripheral surface resistance and the displacement for each depth range, and the hit target body tip resistance and the relationship indicated by the displacement. Including impact body tip ground data,
Of the analysis data obtained in each impact for each depth range and pile tip, the impacted body peripheral ground data and the impacted subject tip ground data with the maximum resistance are extracted, and these extracted data are combined. Features.

  The present invention has been particularly developed as an impact loading test method for piles, but the technical idea according to the present invention is not limited to the impact loading test, and can be applied to a dynamic loading test including a rapid loading test in general. The same applies to the loading direction, and is applicable not only to the vertical loading test but also to the horizontal loading test. It can also be applied to dynamic plate loading tests. Further, the hit object is not limited to a pile, and can be applied to a steel sheet pile or the like. Furthermore, when the hit object is a pile, all piles such as ready-made piles and on-site piles are targeted, and piles constructed by all methods such as embedded piles and hammered piles are also targeted. The pile types are all pile types such as concrete piles, steel pipe piles, pre-stress piles, and different types of piles.

  According to this invention, a plurality of hits are applied to the head of the hit body such as a pile, and waveform data is obtained for each hit. As a result, the amplifier magnification of the measuring instrument can be adjusted, and the SN ratio of measurement is improved. In addition, in a single impact, the measurement may cause a wave to be saturated (saturation) or become too small due to a setting error of the amplifier magnification of the measuring instrument, but the risk of such measurement failure is drastically reduced. This makes it possible to accurately measure the axial force of the hit body such as a pile, and to calculate the support force with high accuracy over the entire hit body.

  FIG. 5 is a block chart showing an embodiment of the present invention. In the present invention, multiple hits are performed on one pile to be tested (step S1). FIG. 6 is a schematic diagram showing a hitting situation. Two types of sensors 2 are installed near the head of the pile 1. That is, one is an acceleration sensor and the other is a strain sensor. The head of the pile 1 is hit with a hammer 3 or the like, and acceleration data and strain data detected by the sensors 2 and 2 are taken into the computer 4 via the amplifier 5 and the A / D converter 6. Based on these data, the computer 4 calculates and displays an input wave and a reflected wave generated by hitting from the measured acceleration wave and distortion wave as shown in FIG.

  When such shock wave data (input wave and reflected wave) is obtained, waveform matching analysis is performed (step S2). This waveform matching analysis is a technique conventionally performed in the impact loading test, and the outline thereof will be described below.

  First, a pile / ground system model usually applied to the analysis of the impact loading test will be described with reference to FIG. The resistance of each layer (pile / ground system layer corresponding to the depth range in which the pile length is divided into a plurality of piles) and the tip of the pile are the static resistance portion by the spring 10 and the slider 11, and the dynamic resistance by the dashpot 12. Modeled with parts. Among these, the static resistance portion is modeled as a complete elasto-plastic model by a spring and a slider as shown in FIG. In other words, the force increases in proportion to the resistance of the spring up to a certain amount of displacement, but when the ultimate resistance of the ground is reached, the friction is completely cut by the slider. In this embodiment, the maximum resistance fmax and spring stiffness k are obtained by waveform matching analysis.

  In the waveform matching analysis, assuming that the input wave shown in FIG. 7 is input to the pile / ground system modeled as shown in FIG. 8, the waveform of the reflected wave returning to the pile head is calculated. And finding a calculated waveform that matches the actually measured reflected waveform shown in FIG. That is, the calculated reflected wave is compared with the actually measured reflected wave. If there is a difference between them, the parameters of the assumed pile / ground system model (division thickness of pile length, resistance, spring stiffness k, (Attenuation rate) is reset, the reflected waveform is calculated again, and both are compared. By repeating the above, the pile / ground system model is identified by matching the calculated reflection waveform with the reflection waveform obtained from the actual measurement.

  In the embodiment, an example of four hits is shown. FIGS. 10 and 11 show examples of waveform matching analysis for the second and fourth strikes of these four strikes, respectively. The second hit is a reflected waveform when there is pile peripheral surface friction, and the fourth hit is a reflected waveform when the pile peripheral surface friction is cut and only the pile tip resistance is present. As a result of this waveform matching analysis, the parameters of the pile / ground system model shown in FIG. 8 for each hit are identified. In this embodiment, the maximum resistance of the pile tip and the ground spring stiffness k are obtained as the ground data (step S3). Tables 1 and 2 show the parameter values identified as a result of the waveform matching analysis for the second and fourth strikes, respectively.

  When waveform matching analysis is performed for all striking (step S4), the ground data (resistance and spring stiffness k) with the maximum resistance among the data obtained in each striking for each depth range and pile tip is respectively Extract and combine / synthesize these extracted data. The results are shown in Table 3. In Table 3, the underlined data is data extracted as having the maximum resistance for each depth range. A load-displacement relationship as shown in FIG. 4 is obtained by a load transmission method using a combination of the extracted data (step S5).

It is an image figure of the frequency of pile head hits and the degree of frictional breakage of the pile circumference. It is an image figure of a pile head hit count and axial direction force (reflection). It is a figure which shows the maximum resistance obtained from the depth direction and the impact result of multiple times. It is a figure which shows the load-displacement amount curve of a pile head. It is a block chart of an embodiment. It is a schematic diagram which shows the hit condition of a pile head. It is a figure which shows an example of an input wave and a reflected wave. It is a figure which shows a pile and ground system as a model. It is a figure which models a pile and ground system as a complete elastoplastic model. It is a figure which shows an example of the measurement reflected wave and calculation reflected wave which were matched by the waveform matching analysis. It is a figure which shows the other example of the actual measurement reflected wave and calculation reflected wave which were matched by the waveform matching analysis.

Explanation of symbols

1 Test pile 2 Sensor 3 Hammer 4 Portable computer

Claims (2)

Dynamic loading that strikes the head of an impacted body such as a pile with a hammer, etc., measures the shock wave propagating through the impacted body, and calculates the bearing capacity of the impacted body / ground system from the analysis data In the test method,
Applying multiple hits to the test subject to be hit, measuring the shock wave for each hit,
A dynamic loading test method characterized in that the bearing force of the hit object / ground system is calculated by combining the analysis data of shock waves measured at each impact. The analysis data includes an impacted body peripheral surface ground data indicating a relationship between the impacted body peripheral surface resistance and displacement for each depth range, and an impacted body distal end ground data indicating a relationship between the impacted body distal end resistance and displacement. Including
Of the analysis data obtained in each impact for each depth range and pile tip, the impacted body peripheral ground data and the impacted subject tip ground data with the maximum resistance are extracted, and these extracted data are combined. The dynamic loading test method according to claim 1, wherein:

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