CN108487335B - A single pile vertical cyclic loading test device and method for simulating high-speed rail load - Google Patents

Abstract

The invention relates to a single pile vertical cyclic loading test device and method for simulating the load of a high-speed railway. The device comprises a test box, a test pile, a reaction force frame, an upper rigid beam, a fixed rod and an upper loading unit, and the test box is a square steel frame , The main component of the upper loading unit is an electric vibration exciter, which is suspended above the test box by the upper rigid beam. The dynamic amplitude, loading frequency and loading waveform of the exciter are controlled by the signal controller. A displacement sensor is arranged on the top of the test pile, and a resistance strain gauge is arranged along the direction of the pile body. The device can simulate the working conditions of the vibration load on the pile foundation, adjust the vibration amplitude and vibration frequency of the dynamic load, and can measure and automatically record the excited vibration force, displacement and pile body stress distribution on the top of the pile. The device has a simple structure and can realize a systematic study on the bearing capacity and deformation characteristics of a single pile under the action of a long-term vertical cyclic load, which is of great significance to the calculation of the bearing capacity and deformation of the pile foundation in the engineering design of the pile foundation.

Description

A single pile vertical cyclic loading test device and method for simulating high-speed rail load

technical field

The invention belongs to the technical field of geotechnical engineering and geotechnical engineering testing, and in particular relates to a single pile vertical cyclic loading test device and method for simulating the load of a high-speed rail.

Background technique

As a common foundation form, pile foundation is widely used in engineering construction, especially for engineering projects with strict requirements on settlement control and bearing capacity. With the new construction and development of wind power generation, marine engineering, new energy and high-speed railways, pile foundations are increasingly subjected to cyclic loads. Under the action of cyclic load, the bearing and deformation characteristics of pile foundation are different from those of static load. The bearing and deformation characteristics of a single pile under cyclic loading are very complex pile-soil interaction problems, the mechanism of action is complex, and there are many influencing factors.

At present, scholars at home and abroad use physical model experiments, theoretical analysis and numerical analysis to study the mechanical properties of piles under cyclic loads. Most of the tests only measure the load and displacement at the top of the pile, while the cyclic variation laws of key physical quantities such as the axial force of the pile body, the end resistance, the pore pressure of the pile-soil interface, and the earth pressure are lacking in systematic experimental research, so the effect of the cyclic load cannot be measured. It is more difficult to give a reasonable explanation for the occurrence mechanism of pile-soil interaction characteristics. In coastal areas, due to the existence of deep soft soil, the bearing capacity of the pile foundation is mainly provided by the pile side friction resistance. The pile side friction resistance will change under the action of cyclic loads, thereby affecting the bearing capacity and deformation of the pile foundation. The engineering properties of the pile foundation are adversely affected.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the above-mentioned defects in the prior art, and to provide a single pile vertical cyclic loading test device and method for simulating high-speed rail loads, so as to obtain the stress distribution at different positions of the single pile body under the action of the vibration load. By obtaining the data of three positions of pile top, pile body and pile end, the bearing capacity and deformation characteristics of the pile body under the action of different dynamic load amplitudes and frequencies are analyzed, and the dynamic bearing capacity of a single pile is evaluated at the same time.

The object of the present invention can be realized through the following technical solutions:

A single pile vertical cyclic loading test device simulating high-speed rail load, including a test box for filling test soil samples, a test pile arranged in the test box, a reaction force frame arranged outside the test box, and a reaction force frame arranged in the reaction force frame The upper rigid beam at the upper end, the fixed rod arranged on the upper rigid beam, and the upper loading unit, the upper loading unit includes a vibration exciter, a power amplifier and a signal generator connected in sequence, and the vibration exciter is installed on the fixed The lower end of the rod is located above the test pile, the excitation head at the lower end of the vibration exciter is provided with a tension and pressure sensor for recording the magnitude and waveform of the excitation force, and the pile head on the upper part of the test pile is provided with a measurement A displacement sensor for the displacement of the top of the pile, the pile end at the lower part of the test pile is provided with an earth pressure sensor for measuring the resistance of the pile end, and the pile body of the test pile is provided with a plurality of test piles from top to bottom for testing the stress distribution of the pile body The resistance strain gauge is connected to the dynamic data acquisition instrument, and the tension and pressure sensor, displacement sensor, earth pressure sensor and resistance strain gauge are connected to the computer for display and processing.

Further, it is a square steel frame formed by welding four angle steels and several flat steels. The surrounding and bottom of the test box are steel plates welded with the square steel frame, and the inner surface of the test box is smooth.

Further, the bottom end of the test box is provided with a drain valve.

Further, the two sides of the test box are provided with a base, and the base is provided with a slot for fixing a reaction force frame, the reaction force frame is fixed on the base by bolts, and the height can be adjusted by a threaded rod.

Further, the upper rigid beam is set on the reaction frame through the upper rigid beam bayonet on both sides, and is fixed by threaded bolts.

Further, the middle part of the upper rigid beam is provided with a number of internal threaded holes, the fixing rod passes through the internal threaded holes and is fixed by threaded bolts, and the position of the fixed rod can be moved left and right through different internal threaded holes to achieve Lateral movement of the shaker.

Further, the vibration exciter is an electric vibration exciter.

Further, the signal generator can continuously output function signals of arbitrary waveforms.

A single pile vertical cyclic loading test method for simulating high-speed rail load, comprising the following steps:

(a) According to the research objectives, determine the sample soil sample, measure the moisture content and density of the test soil sample, fill the test soil sample into the test box to the required height, and compact it in layers. The test soil samples need to be pre-compressed and consolidated;

(b) After the consolidation of the test soil sample is completed, use the method of static pressing to carry out pile pressing, the speed of pressing the pile is 100mm/min, the time of pressing the pile is 8 minutes, and the displacement of the pile body is monitored by the displacement sensor set at the top of the pile. ;

(c) After the pile pressing is completed, after the rest period is over, the test pile is subjected to cyclic loading test, the signal generator is turned on, the vibration waveform is set, the power amplifier is turned on, the signal amplitude is adjusted, the dynamic data acquisition instrument and computer are turned on, and the vibration is recorded. Pile top load and pile body displacement during the process;

(d) Increase the amplitude or change the frequency, and repeat the previous step until the vibration time or pile top displacement meets the requirements;

(e) After the test, turn off the power amplifier, signal generator and dynamic data acquisition instrument in turn, calculate the dynamic bearing capacity limit of a single pile according to the dynamic load of the pile top and the displacement of the pile top, and calculate the limit of the dynamic bearing capacity of the single pile according to the soil pressure sensor at the pile end and the resistance strain of the pile body. The stress distribution along the pile body and the friction resistance distribution on the pile side are obtained by calculation.

Further, the calculation method within one cycle of the cyclic load input in step (c) is:

in:

P(t) is the high-speed rail load amplitude;

t is time;

L is the distance between the high-speed rail bogie wheels;

v is the speed of the high-speed rail;

w is the frequency corresponding to the high-speed rail load, w=v/πD, and D is the diameter of the high-speed rail wheelset.

Compared with the prior art, the present invention has the following characteristics:

1) The present invention is suitable for the cyclic loading test of a single pile of any pile type with a small scale. The device can simulate the working conditions of the pile body bearing loads of different vibration amplitudes and frequencies, and can comprehensively obtain the pile top load, pile top load and pile load during the test. Various parameters such as top displacement, pile body stress distribution, and pile tip resistance on the pile tip;

2) The present invention realizes the study of the stress distribution along the pile body by reasonably setting the monitoring position of the sensor and adopts the joint arrangement of the resistance strain gauge and the pressure sensor, thereby calculating the distribution of the pile side frictional resistance. The test device and test process can ensure the validity of the collected data, and can reflect the stress distribution and change of the single pile under cyclic loading conditions from multiple angles;

3) Each test component of the test device involved in the present invention can be disassembled and adjusted, with strong operability and high reliability of obtaining test data. It can study the bearing capacity and settlement deformation of a single pile under cyclic loads, and design the pile foundation engineering. significant.

Description of drawings

Fig. 1 is the structural representation of the monopile cyclic loading test device of the present invention;

Fig. 2 is the top view of the upper rigid beam;

In the picture: 1-Test box, 2-Test soil sample, 3-Test pile, 4-Resistance strain gauge, 5-Displacement sensor, 6-Vibration exciter, 7-Fixed rod, 8-Upper rigid beam, 9-Reverse Force frame, 10-base, 11-power amplifier, 12-signal generator, 13-dynamic data acquisition instrument, 14-computer, 15-drain valve, 16-earth pressure sensor, 17-tension and pressure sensor, 18-upper rigidity Beam bayonet, 19-inner threaded hole.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and provides a detailed implementation manner and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

As shown in Figure 1, a single pile vertical cyclic loading test device simulating high-speed rail load, the device includes a test box 1, a reaction frame 9, an upper rigid beam 8, a fixed rod 7 and an upper loading unit. The test box 1 consists of Four angle steels and several flat steels are welded and connected to form a square steel frame, which is used for filling the test soil sample 2, and pile-pressing in the test chamber 1. The bottom end of the test box is provided with a drain valve 15, and the drain valve can be used to control the drainage conditions and drainage rate. Both sides are provided with a base 10 for fixing the reaction force frame, and the base 10 is provided with a slot for fixing the reaction force frame. The reaction frame is fixed on the base by bolts, and the height can be adjusted by itself through the threaded rod.

As shown in FIG. 2 , the upper rigid beam 8 has upper rigid beam bayonets 18 on both sides, and the upper rigid beam bayonet 18 on both sides can be mounted on the reaction frame 9, fixed with threaded bolts, and can be disassembled according to the actual situation. The middle part of the upper rigid beam is provided with a plurality of internal threaded holes 19, and the fixing rod 7 passes through the internal threaded holes 19 and is fixed by threaded bolts.

The upper loading unit is composed of three parts: an exciter 6 , a power amplifier 11 and a signal generator 12 . The vibration exciter is connected to a fixed rod 7, and is suspended above the test box through the fixed rod. By changing the position of the fixed rod, the lateral movement of the exciter can be realized. Different load waveforms, amplitudes and frequencies can be set according to the test requirements. The vibration exciter is a JZQ-20 type electric vibration exciter, which provides excitation force to the test pile. The power amplifier adopts KD5702 type power amplifier as a high-power excitation source for vibration test and vibration measurement, which can adjust the output current limit protection from 3A to 15A, and carry out temperature protection for the output transistor and radiator, which can indicate the failure of the output transistor and the output signal. clipping. The signal generator can use the AFG3000C function signal generator, which can continuously output the function signal of arbitrary waveform. The frequency and amplitude of the function signal can be continuously adjusted within 10MHz. The vibration exciter suspended above the test box by the fixed rod is connected to the peripheral power amplifier 11 , and the power amplifier is connected to the signal generator 12 . The calculation method within one cycle of the input cyclic high-speed rail load is:

in:

P(t) is the high-speed rail load amplitude;

t is time;

L is the distance between the high-speed rail bogie wheels;

v is the speed of the high-speed rail;

w is the frequency corresponding to the high-speed rail load, w=v/πD, and D is the diameter of the high-speed rail wheelset.

The test soil sample 2 is reshaped clay, and the soil body can be set as single layer or multi-layer. The material of the test pile 3 is plexiglass.

The measuring equipment includes a tension and pressure sensor 17 , an earth pressure sensor 16 , a displacement sensor 5 and a resistance strain gauge 4 . The tension and compression sensor 17 is used to directly measure the load acting on the top of the pile. The earth pressure sensor 16 is attached to the bottom of the pile to measure the end resistance on the end of the pile. The displacement sensor 5 is a YWC-type strain-type displacement sensor, which is arranged on the top of the pile and measures the displacement of the top of the pile. The resistance strain gauge 4 adopts the BE120-2DB-P300 type resistance strain gauge, which is symmetrically distributed on both sides of the pile body to measure the axial force distribution along the pile body. The resistance strain gauge is covered with epoxy resin for sealing and waterproofing. The measuring devices are all connected to the dynamic acquisition instrument 13. After signal processing, they are input to the computer 14 for data output display and further data processing.

The single-pile vertical cyclic loading test using the above-mentioned single-pile cyclic loading test device to simulate the high-speed rail load, the method includes the following steps:

Step 1: According to the research objective, determine the sample soil sample, measure the moisture content and density of the test pattern, and fill the sample soil sample 2 into the test box to the required height, and compact it in layers. After the filling is completed, the test soil sample 2 needs to be pre-compressed and consolidated.

Step 2: After the consolidation of the test soil sample is completed, use the construction method of static pressing to carry out pile pressing, the speed of pressing the pile is 100 mm/min, and the time of pressing the pile is 8 minutes. Displacement sensors are arranged on the top of the piles to monitor the displacement of the piles.

Step 3: After the pile pressing is completed, after the rest period is over, the cyclic loading test is carried out on the test pile. Turn on the signal generator 12, set the vibration waveform, turn on the power amplifier 11, adjust the signal amplitude, turn on the dynamic data acquisition instrument 13 and the computer 14, and record the pile top load and pile body displacement during the vibration process.

Step 4: Increase the amplitude, or change the frequency, and repeat the previous step until the vibration time or pile top displacement meets the requirements.

Step 5: After the test, turn off the power amplifier 11, the signal generator 12 and the dynamic data acquisition instrument 13 in sequence. According to the dynamic load at the top of the pile and the displacement of the top of the pile, the limit of the dynamic bearing capacity of the single pile is calculated, and the distribution of the stress along the pile body and the distribution of the friction resistance on the side of the pile are calculated according to the soil pressure sensor at the pile end and the resistance strain gauge of the pile body;

It also includes step 6: according to the test design, take the test soil sample 2 in the test box, and conduct basic physical and mechanical property index tests such as liquid-plastic limit and shear strength index. By comparing the properties of the soil around the pile and the soil at the far end, the changes of the surrounding test soil samples before and after the vibration of the single pile were studied from the perspective of vibration influence.

Claims (6)

1. A single-pile vertical cyclic loading test device for simulating high-speed rail load comprises a test box (1) for loading a test soil sample (2), a test pile (3) arranged in the test box (1), a reaction frame (9) arranged outside the test box (1), an upper rigid beam (8) arranged at the upper end of the reaction frame (9), a fixed rod (7) arranged on the upper rigid beam (8) and an upper loading unit, wherein the upper loading unit comprises a vibration exciter (6), a power amplifier (11) and a signal generator (12) which are sequentially connected, the vibration exciter (6) is arranged at the lower end of the fixed rod (7) and is positioned above the test pile (3),

the device is characterized in that the vibration exciter (6) is an electrodynamic vibration exciter, a tension and compression sensor (17) for recording the magnitude and waveform of exciting force is arranged at the vibration exciting head at the lower end of the vibration exciter (6), a displacement sensor (5) for measuring the displacement of a pile top is arranged at the pile head at the upper part of the test pile (3), a soil pressure sensor (16) for measuring the resistance of the pile end is arranged at the pile end at the lower part of the test pile (3), a plurality of resistance strain gauges (4) for testing the stress distribution of the pile body are arranged on the pile body of the test pile (3) from top to bottom, and the tension and compression sensor (17), the displacement sensor (5), the soil pressure sensor (16) and the resistance strain gauges (4) are all connected with a dynamic data acquisition instrument (13) and are transmitted to a computer (14) for display and processing;

the test box (1) is a square steel frame formed by welding four angle steels and a plurality of flat steels, steel plates welded with the square steel frame are arranged at the periphery and the bottom of the test box (1), and the inner surface of the test box (1) is smooth;

bases (10) are arranged on two sides of the test box (1), clamping grooves for fixing the reaction frame (9) are formed in the bases (10), the reaction frame (9) is fixed on the bases (10) through bolts, and the height of the reaction frame can be adjusted through threaded rods;

the middle part of the upper rigid beam (8) is provided with a plurality of internal thread holes (19), the fixed rod (7) penetrates through the internal thread holes (19) and is fixed through a threaded bolt, and the position of the fixed rod (7) can move left and right through different internal thread holes to realize the transverse movement of the vibration exciter (6);

when the device is used, the following steps are adopted:

(a) determining a sample soil sample (2) according to a research target, determining the water content and the density of the test soil sample (2), filling the test soil sample (2) into a test box (1) to a required height, layering and compacting, and after filling, performing pre-pressing consolidation on the test soil sample (2);

(b) after the test soil sample (2) is solidified, pile pressing is carried out by adopting a static pressing-in method, the pile pressing speed is 100mm/min, the pile pressing time is 8min, and the displacement of a pile body is monitored through a displacement sensor (5) arranged at the pile top;

(c) after pile pressing is finished, after a rest period is finished, a cyclic loading test is carried out on the test pile (3), a signal generator (12) is started, a vibration waveform is set, a power amplifier (11) is started, the amplitude of a signal is adjusted, a dynamic data acquisition instrument (13) and a computer (14) are started, and pile top load and pile body displacement in the vibration process are recorded;

(d) increasing the amplitude or changing the frequency, and repeating the previous step until the vibration time or the pile top displacement meets the requirements;

(e) after the test is finished, the power amplifier (11), the signal generator (12) and the dynamic data acquisition instrument (13) are sequentially closed, the dynamic bearing capacity limit of the single pile is calculated according to the dynamic load of the pile top and the displacement of the pile top, and the stress distribution along the pile body and the side friction resistance distribution of the pile are calculated according to the pile end soil pressure sensor (16) and the resistance strain gauge of the pile body.

2. The single-pile vertical cyclic loading test device for simulating the load of the high-speed rail according to claim 1, wherein a drain valve (15) is arranged at the bottom end of the test box (1).

3. The single-pile vertical cyclic loading test device for simulating the load of the high-speed rail according to claim 1, wherein the upper rigid beam (8) is arranged on the reaction frame (9) through upper rigid beam bayonets on two sides and is fixed through a threaded bolt.

4. The mono-pile vertical cyclic loading test device for simulating high-speed rail loading according to claim 1, wherein the signal generator (12) can continuously output a function signal with an arbitrary waveform.

5. A single pile vertical cyclic loading test method for simulating high-speed rail loading according to any one of claims 1 to 4, which is characterized by comprising the following steps:

(a) determining a sample soil sample (2) according to a research target, determining the water content and the density of the test soil sample (2), filling the test soil sample (2) into a test box (1) to a required height, layering and compacting, and after filling, performing pre-pressing consolidation on the test soil sample (2);

(b) after the test soil sample (2) is solidified, pile pressing is carried out by adopting a static pressing-in method, the pile pressing speed is 100mm/min, the pile pressing time is 8min, and the displacement of a pile body is monitored through a displacement sensor (5) arranged at the pile top;

(c) after pile pressing is finished, after a rest period is finished, a cyclic loading test is carried out on the test pile (3), a signal generator (12) is started, a vibration waveform is set, a power amplifier (11) is started, the amplitude of a signal is adjusted, a dynamic data acquisition instrument (13) and a computer (14) are started, and pile top load and pile body displacement in the vibration process are recorded;

(d) increasing the amplitude or changing the frequency, and repeating the previous step until the vibration time or the pile top displacement meets the requirements;

(e) after the test is finished, the power amplifier (11), the signal generator (12) and the dynamic data acquisition instrument (13) are sequentially closed, the dynamic bearing capacity limit of the single pile is calculated according to the dynamic load of the pile top and the displacement of the pile top, and the stress distribution along the pile body and the side friction resistance distribution of the pile are calculated according to the pile end soil pressure sensor (16) and the resistance strain gauge of the pile body.

6. The single-pile vertical cyclic loading test method for simulating high-speed rail loads according to claim 5, wherein the calculation method in one period of the cyclic loads input in the step (c) is as follows:

wherein:

p (t) is the high iron load amplitude;

t is time;

l is the distance between the high-speed rail bogie wheel pairs;

v is the high rail travel speed;

and w is the frequency corresponding to the high-speed rail load, w is v/pi D, and D is the diameter of the high-speed rail wheel pair.

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