CN108487335A - A kind of single-pile vertical orientation cyclic loading test device and method of simulation high ferro load - Google Patents

Abstract

The present invention relates to a kind of single-pile vertical orientation cyclic loading test device and methods of simulation high ferro load, the device includes chamber, test pile, reaction frame, upper buckstay, fixed link and top loading unit, chamber is rectangular steelframe, top loading unit critical piece is Electrodynamic Vibrators, is suspended to above chamber using upper buckstay.The power amplitude of vibrator, loading frequency, Loaded contact analysis etc. are controlled by signal controller.It tests stake top and is equipped with displacement sensor, resistance strain gage is equipped with along pile body direction.The device can simulate the operating mode for the oscillatory load that pile foundation is subject to, and can adjust the vibration amplitude and vibration frequency of dynamic load, and can measure and automatically record exciting force, displacement suffered by stake top and pile body stress distribution.Apparatus structure is simple, can realize that the system research to bearing capacity of single pile and deformation characteristic under long-term vertical cyclic load, the calculating for designing pile foundation engineering pile foundation bearing capacity and its deformation are of great significance.

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 geological engineering geotechnical testing, and in particular relates to a single pile vertical cyclic loading test device and method for simulating high-speed rail load.

Background technique

As a commonly used 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, ocean engineering, new energy sources and high-speed railways, pile foundations are increasingly subjected to cyclic loads. Under cyclic loading, the bearing and deformation characteristics of the pile foundation are different from those under static loading. The bearing and deformation characteristics of a single pile under cyclic loading are very complex pile-soil interaction problems, with complex action mechanisms and many influencing factors.

At present, scholars at home and abroad use methods such as physical model experiments, theoretical analysis, and numerical analysis to study the mechanical properties of piles under cyclic loading. Most of the tests only measure the pile top load and displacement, but there is no systematic experimental research on the cyclic variation of key physical quantities such as pile axial force, end resistance, pile-soil interface pore pressure, and earth pressure, so it is impossible to study the effect of cyclic loads. It is more difficult to give a reasonable explanation for the mechanism of pile-soil interaction. In the coastal area, 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 load, thereby affecting the bearing capacity and deformation of the pile foundation, which will have a negative impact on the pile foundation. The engineering properties of the pile foundation are adversely affected.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned defects in the prior art, and provide a single pile vertical cyclic loading test device and method for simulating high-speed rail load, so as to obtain the stress distribution at different positions of the single pile body under the action of vibration load By obtaining the data of the three positions of the 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 purpose of the present invention can be achieved through the following technical solutions:

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

Further, it is a square steel frame welded by 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, a drain valve is provided at the bottom of the test box.

Further, bases are provided on both sides of the test box, and slots for fixing the reaction force frame are provided on the base, and the reaction force frame is fixed on the base by bolts, and the height can be adjusted by threaded rods.

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

Further, the middle part of the upper rigid beam is provided with several internally threaded holes, the fixed rod passes through the internally threaded holes, and is fixed by a threaded bolt, and the position of the fixed rod can be moved left and right through different internally threaded holes to realize Lateral movement of the exciter.

Further, the vibrator is an electric vibrator.

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) Determine the sample soil sample according to the research objectives, 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 layer by layer. After filling, The test soil samples need to be pre-compressed and consolidated;

(b) After the consolidation of the test soil sample is completed, the static pressure method is used to press the pile. The speed of the pile is 100mm/min, and the time of the pile is 8min. The displacement of the pile body is monitored by the displacement sensor installed at the top of the pile. ;

(c) After the pile pressing is completed, after the rest period is over, carry out a cyclic loading test on the test pile, turn on the signal generator, set the vibration waveform, turn on the power amplifier, adjust the signal amplitude, turn on the dynamic data acquisition instrument and computer, and record the vibration Pile top load and pile 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 the single pile according to the pile top dynamic load and pile top displacement, and calculate the limit of the single pile dynamic bearing capacity 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 frictional resistance distribution on the pile side are calculated.

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

in:

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

t is time;

L is the distance between the high-speed rail bogie wheel sets;

v is the traveling 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 wheel set.

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

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

2) The present invention realizes the research on the stress distribution along the pile body by rationally setting the monitoring position of the sensor and adopting the joint arrangement of the resistance strain gauge and the pressure sensor, thereby calculating and obtaining 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 changes of the single pile under cyclic loading conditions from multiple angles;

3) All test parts of the test device involved in the present invention can be disassembled and adjusted, and the operability is strong, and the reliability of the test data obtained is strong, and the bearing capacity and settlement deformation of the single pile under cyclic load are studied, and the design of the pile foundation engineering is of great significance.

Description of drawings

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

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

In the figure: 1-test box, 2-test soil sample, 3-test pile, 4-resistance strain gauge, 5-displacement sensor, 6-vibrator, 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-drainage valve, 16-earth pressure sensor, 17-tension and pressure sensor, 18-upper rigidity Beam bayonet, 19-internal threaded hole.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is carried out on the premise of the technical solution of the present invention, and detailed implementation and specific operation process are given, 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 for simulating high-speed rail loads, 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, and the test box 1 consists of Four angle steels and several flat steels are welded to form a square steel frame, which is used to fill the test soil sample 2, and carry out pile pressing in the test box 1. A drain valve 15 is provided at the bottom of the test chamber, and the drain valve can be used to control the drain condition and the drain rate. Both sides are provided with a base 10 for fixing the reaction force frame, and the base 10 is provided with a card 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 threaded rods.

As shown in Figure 2, there are upper rigid beam bayonets 18 on both sides of the upper rigid beam 8, through which the upper rigid beam bayonets 18 on both sides can be mounted on the reaction frame 9, fixed with threaded bolts, and can be disassembled according to actual conditions. The middle part of the upper rigid beam is provided with several internally threaded holes 19, and the fixing rod 7 passes through the internally threaded holes 19 and is fixed by threaded bolts.

The upper loading unit is composed of an exciter 6 , a power amplifier 11 and a signal generator 12 . The vibrator is connected to the fixed rod 7 and 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 test requirements. The vibration exciter is a JZQ-20 type electric vibration exciter, which provides excitation force for the test pile. The power amplifier adopts KD5702 power amplifier as a high-power excitation source for vibration test and vibration measurement. It can adjust the output current limit protection from 3A to 15A, and carry out temperature protection on the output transistor and radiator. It 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 exciter suspended above the test box by a fixed rod is connected to an external power amplifier 11 , and the power amplifier is connected to a signal generator 12 . The calculation method of the input cyclic high-speed rail load in one cycle is:

in:

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

t is time;

L is the distance between the high-speed rail bogie wheel sets;

v is the traveling 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 wheel set.

Test soil sample 2 is remolded clay, and the soil body can be set as a single layer or multiple layers. The body material of test pile 3 is plexiglass.

The measuring equipment includes tension and pressure sensors 17 , earth pressure sensors 16 , displacement sensors 5 and resistance strain gauges 4 . Tension and compression sensors 17 are 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 suffered by the pile end. Displacement sensor 5 adopts YWC type strain gauge displacement sensor, which is arranged on the top of the pile to measure 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, and is used 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, and after signal processing, the signals are input to the computer 14 for data output and display, and further data processing.

Adopt above-mentioned single pile cyclic loading test device to simulate the single pile vertical cyclic loading test of high-speed rail load, its method comprises the following steps:

Step 1: Determine the sample soil sample according to the research objectives, measure the water content and density of the test pattern, fill the sample soil sample 2 into the test chamber to the required height, and compact it in layers. After the filling is completed, the test soil sample 2 needs to be preloaded and consolidated.

Step 2: After the consolidation of the test soil samples is completed, press the piles using the construction method of static pressure. The speed of the piles is 100mm/min, and the time for the piles is 8 minutes. A displacement sensor is installed on the top of the pile to monitor the displacement of the pile body.

Step 3: After the pile is pressed, the cyclic loading test is carried out on the test pile after the rest period is over. 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 is over, turn off the power amplifier 11, the signal generator 12 and the dynamic data acquisition instrument 13 in sequence. According to the pile top dynamic load and pile top displacement, calculate the dynamic bearing capacity limit of single pile, and calculate the stress distribution along the pile body and the friction resistance distribution on the pile side according to the soil pressure sensor at the pile tip 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 tests on basic physical and mechanical property indicators such as liquid-plastic limit and shear strength indicators. By comparing the properties of the soil around the pile and the soil at the far end, the changes of the test soil samples around the single pile before and after vibration are studied from the perspective of vibration influence.

Claims (10)

1. a kind of single-pile vertical orientation cyclic loading test device of simulation high ferro load, including it is used to load the examination of experiment soil sample (2) Tryoff (1), the test pile (3) being set in chamber (1) are set to the external reaction frame (9) of chamber (1), are set to reaction frame (9) The upper buckstay (8) of upper end, the fixed link (7) being set on upper buckstay (8) and top loading unit, the top loading unit Including sequentially connected vibrator (6), power amplifier (11) and signal generator (12), the vibrator (6) is mounted on institute The lower end of fixed link (7) is stated, and is located at the top of test pile (3),

It is characterized in that, being equipped with the tension and compression for recording exciting force size and waveform at the excitation head of vibrator (6) lower end Sensor (17) is equipped with the displacement sensor (5) for measuring displacement at pile top at the pile crown on test pile (3) top, described The soil pressure sensor (16) for measuring end resistance, the stake of the test pile (3) are equipped at the stake end of test pile (3) lower part Body is equipped with multiple resistance strain gages (4) for testing pile body stress distribution, the tension-compression sensor (17), displacement from top to bottom Sensor (5), soil pressure sensor (16) and resistance strain gage (4) are all connected with dynamic data acquiring instrument (13), and are transmitted to Computer (14) is shown and is handled.

2. a kind of single-pile vertical orientation cyclic loading test device of simulation high ferro load according to claim 1, feature exist In the chamber (1) is to weld the rectangular steelframe being linked to be, the surrounding of chamber (1) and bottom by four angle steel and several band steels Inner surface for the steel plate welded with rectangular steelframe, chamber (1) is smooth.

3. a kind of single-pile vertical orientation cyclic loading test device of simulation high ferro load according to claim 1, feature exist In the bottom end of the chamber (1) is equipped with drain valve (15).

4. a kind of single-pile vertical orientation cyclic loading test device of simulation high ferro load according to claim 1, feature exist In, the both sides of the chamber (1) are equipped with pedestal (10), and the pedestal (10) is equipped with the card slot for fixing reaction frame (9), The reaction frame (9) is secured by bolts on pedestal (10), can adjust height by threaded rod.

5. a kind of single-pile vertical orientation cyclic loading test device of simulation high ferro load according to claim 1, feature exist In the upper buckstay (8) is located at by the upper buckstay bayonet of both sides on reaction frame (9), and is fixed by screwed plug.

6. a kind of single-pile vertical orientation cyclic loading test device of simulation high ferro load according to claim 1, feature exist In, the middle part of the upper buckstay (8) is equipped with several internal thread holes (19), and the fixed link (7) passes through internal thread hole (19), and It is fixed by screwed plug, fixed link (7) position can be moved left and right by different internal thread holes, realize vibrator (6) transverse shifting.

7. a kind of single-pile vertical orientation cyclic loading test device of simulation high ferro load according to claim 1, feature exist In the vibrator (6) is Electrodynamic Vibrators.

8. a kind of single-pile vertical orientation cyclic loading test device of simulation high ferro load according to claim 1, feature exist In the signal generator (12) can continuously export the function signal of random waveform.

9. a kind of a kind of single-pile vertical orientation CYCLIC LOADING of simulation high ferro load as described in any one of claim 1-8 claims Test method, which is characterized in that include the following steps：

(a) it according to goal in research, determines sample soil sample (2), and measures the moisture content of experiment soil sample (2), density, and will experiment soil Sample (2) is inserted in chamber (1) to desired height, and compaction in layers, after filling, needs to carry out experiment soil sample (2) pre- Pressing knot；

(b) after the completion of soil sample (2) consolidation to be tested, piling, the speed 100mm/ of piling are carried out using the method for static(al) indentation Min, piling time are 8min, and pile body shifting is monitored by the displacement sensor (5) being arranged at stake top；

(c) piling finishes, to the end of stand-down after, to test pile (3) carry out cyclic loading test, open signal generator (12), vibrational waveform is set, power amplifier (11) is opened, Regulate signal amplitude size opens dynamic data acquiring instrument (13) With computer (14), pile top load and pile body shifting in vibration processes are recorded；

(d) it increases amplitude or changes frequency, repeat previous step, until time of vibration or displacement at pile top reach requirement；

(e) after the test, power amplifier (11), signal generator (12) and dynamic data acquiring instrument (13) are closed successively, According to stake top dynamic load and displacement at pile top, the single pile dynamic bearing capacity limit is calculated, according to pile-end soil pressure sensor (16) and pile body Resistance strain gage is calculated along pile body stress distribution and pile side friction distribution situation.

10. a kind of single-pile vertical orientation cyclic loading test method of simulation high ferro load according to claim 9, feature exist In computational methods are in a cycle of the cyclic load of step (c) input：

Wherein：

P (t) is high ferro load amplitude；

T is the time；

L be high ferro steering framing wheel to the distance between；

V is high ferro gait of march；

W is the corresponding frequency of high ferro load, and w=v/ π D, D are high iron tyres to diameter.