CN112730116B - In-situ testing device and method for soil dynamic stress-strain curve - Google Patents

Abstract

The invention discloses a dynamic stress-strain curve in-situ testing device, which comprises a movable system, a dynamic reaction system, a load servo system and a data acquisition system, wherein the device is powered by a hydraulic source, and can apply vertical dynamic load to a rigid plate of a vibrator under preset frequency, amplitude and loading cycle number so as to be spread into foundation soil. The invention also discloses a working method of the dynamic stress-strain curve in-situ test equipment, which provides a new method for the field test of the dynamic stress-strain curve of the soil body.

Description

In-situ testing device and method for soil dynamic stress-strain curve

technical field

The invention belongs to the technical field of civil engineering, and particularly relates to an in-situ testing device and method for soil dynamic stress-strain curves.

Background technique

The high density of urban population, urban construction and urban traffic, and the rapid development of urban economy mean that the study of earthquake problems faced by large and super-large cities has become a daunting task that earthquake engineering researchers must face. Earthquakes not only release a large amount of energy, but also lead to a large number of secondary disasters. There are many disasters related to geotechnical soil, such as: debris flow, earthquake liquefaction of sand and soil, landslide, soft foundation collapse, etc. The most serious of which is soil Physical damage.

The quantification of the dynamic stress-strain curve is indispensable in the analysis process of establishing the soil dynamic constitutive model. At present, the test of dynamic stress-strain curve is mainly based on indoor test, and the equipment that is used more and has more reliable results is mainly dynamic triaxial instrument. The main advantages of dynamic triaxial test include: controllable test conditions and accurate results. However, due to the disturbance of the soil samples during the sampling process, the difference between the indoor artificially prepared soil samples and the in-situ structure (soil sample size effect, etc.), time effects, etc., it is difficult to quantify the impact of the indoor test on the restoration of the actual scene of the project. There are four main influencing factors that have a certain gap with the real stress environment of the field soil:

(1) The sample is isotropically consolidated, and the natural soil layer is k ₀ consolidated. The stress on the 45° surface of the isostatic isostatic sample is the same as that of the natural soil layer. If the sample is tested after k ₀ consolidation, the initial shear stress on the 45° surface is not consistent with the field conditions;

(2) During the vibration process, the principal stress direction can only change by 90°, in fact, the large principal stress axis swings left and right;

(3) The damage of tensile and compressive stress is different, the hysteresis loop of the sample is asymmetric, the first tensile failure is fast, and the soil layer on site has no tension and compression;

(4) The sample necks or bulges during cyclic loading, which causes pore redistribution and affects the measurement of strain and pore pressure.

SUMMARY OF THE INVENTION

Purpose of the invention: In order to solve the technical problems existing in the prior art, the present invention proposes an in-situ testing method for soil dynamic stress-strain curve.

In order to achieve the above purpose, the present invention provides an in-situ testing device for dynamic stress-strain curves, including a movable system, a dynamic response system, a load servo system and a data acquisition system, wherein,

The dynamic response system includes an electro-hydraulic servo actuator and a vibrator, and the electro-hydraulic servo actuator includes an electro-hydraulic servo-hydraulic source, an oil pipeline and a guide column connected in sequence. The shown guide column includes a piston rod and a a guide sleeve, the bottom of the guide column is fixedly connected with the upper pressure-bearing plate, a displacement sensor is arranged in the middle of the piston rod, and a pressure sensor is arranged at the bottom of the piston rod;

The vibrator from top to bottom includes a lower pressure-bearing plate, a vertical shock-absorbing airbag and a touch-down floor, and an air nozzle is arranged above the lower pressure-bearing plate;

The dynamic and static load transmitted by the upper bearing plate of the electro-hydraulic servo actuator acts on the lower bearing plate of the vibrator, and then is transmitted to the grounding plate through the vertical shock-absorbing air bag;

The load servo system is used for the operation of the control dynamic response system, and a vertical dynamic load is applied under a preset frequency, amplitude, and number of loading cycles, and the results of the displacement sensor and the pressure sensor are fed back to the load control system;

The electro-hydraulic servo hydraulic source is electrically or wirelessly connected to the load servo system;

The data acquisition system includes an acquisition instrument, a vibration pickup and an earth pressure box respectively connected to it, the earth pressure box is embedded in the midpoint position of the two vibration pickups, and the real-time output of the point under the action of the dynamic load is output. The vertical stress is transmitted to the acquisition instrument;

The dynamic reaction system is arranged inside the movable system. The position and fixation of the above components in the movable system can be planned according to the actual situation.

In one embodiment, the movable system is a special construction vehicle, and the power reaction system is arranged inside the special construction vehicle and can protrude out of the special construction vehicle through a hole opened at the bottom of the special construction vehicle.

In order to realize the vertical position change of the movable system, retractable and retractable support legs are arranged at the bottom of the movable system. When it is necessary to lift the movable system, the supporting legs received at the bottom should be propped up so that they correspond to the wooden piers set at the corresponding positions on the ground, and the hydraulic pressure will be raised so that each supporting leg contacts the wooden piers placed on the ground, so as to realize the lifting effect. Highly mobile system.

Preferably, a hook is provided inside the construction vehicle, and a corresponding hook is provided at the top of the guide column, and when the guide column is raised to the highest position, the two are hung.

Preferably, the vertical shock-absorbing airbag includes 4 sets.

Preferably, the vibration pickup is arranged at a vertical distance of 0.5-1 m from the bottom of the grounding floor, the earth pressure box is embedded at the midpoint of the two vibration pickups, and the vertical stress of the point under the action of the dynamic load is output in real time. .

The present invention further provides a dynamic stress-strain curve in-situ testing method, comprising the following steps:

1) Enter the movable system into the site, select a relatively flat site, and plan the position of the movable system (1) and the vibrator;

2) Dig a 1.5*1.5*0.5(m) pit right behind the movable system;

3) After the pit is dug, mark the burying position of the vibration pickup and the earth pressure box, and then use the on-site pressure sensor hydraulic cylinder to drill holes at the marked position to bury the vibration pickup and the earth pressure box; the vibration pickup and the earth pressure After the box is placed in the designated position, first sprinkle a layer of sand around it and then backfill the original soil for compaction;

4) Put the vibrator into the pit, the direction of the body of the movable system is perpendicular to the direction of the floor, and the floor of the vibrator is close to the original soil layer;

5) After the vibrator is placed, drive the special engineering vehicle in place, so that the upper bearing plate 10 of the actuator is overlapped with the lower bearing plate of the vibrator;

6) Connect the load servo system and the electro-hydraulic servo hydraulic source, open the control software and input the project site information;

7) Connect the joint of the embedded vibration pickup and the earth pressure box to the data acquisition system, and prepare to collect and save the data;

8) Connect the trachea with the corresponding air nozzles at the four corners of the vibrator to ensure that the trachea will not be pressed, and open the air valve;

9) Turn on the power, insert the car key, ignite the power system, then increase the oil pressure to make each support leg (2) contact the wooden pier placed on the ground, and raise the movable system; Airbag inflation, inflation pressure can be monitored from the barometer;

10) Controlled by the load servo system, the guide column drives the upper bearing plate of the actuator to raise its position to complete the decoupling.

Among them, the earth pressure box is embedded at the midpoint of the two shock pickups, and the vertical stress of this point under the action of the dynamic load is output in real time; the dynamic strain is defined as the average dynamic strain between the two shock pickups, and it is assumed that the displacement varies with the two sensors. The distance between them is a linear change, then this value is considered to be equal to the dynamic strain at the midpoint of the two shock pickups, and is calculated by the displacement-based method. The recorded velocity-time history is numerically integrated to obtain the displacement-time history. Calculate The peak displacement of the displacement time history of adjacent sensors is obtained; at the same time, the difference between the output larger peak displacement and the displacement recorded by another sensor is the total deformation between adjacent sensors, and the displacement difference is divided by the distance between the two sensors to obtain the dynamic strain ε _d :

In the formula, u ₁ is the displacement of the shock pickup output under a certain vibration-the maximum displacement in the time waveform diagram, u ₂ is the displacement output by another shock pickup at the same time; Δx is the distance between the two shock pickups .

Beneficial effects: Compared with the prior art, the present invention has the following advantages and positive effects:

(1) It has less interference to the soil layer, and can more truly reflect the natural structure of the soil and the characteristics under natural stress;

(2) The size of the soil involved is much larger than that of the indoor sample, so it can better reflect the influence of the macroscopic structure of the soil on the properties of the soil, and is more representative than the soil sample;

(3) The test can be repeated to shorten the test period;

(4) It is suitable for in-situ testing of dynamic stress-strain curves of various foundations. The frequency, amplitude, and number of loading cycles are controllable. It has the characteristics of wide application range, strong controllability and high reliability.

Description of drawings

Figure 1 is a schematic diagram of the field test of the dynamic stress-strain curve in-situ testing equipment;

Fig. 2 is the front view of electro-hydraulic servo-actuator;

Fig. 3 is the sectional view of electro-hydraulic servo-actuator;

Fig. 4 is the front view of vibrator;

Figure 5 is a top view of the vibrator;

Figure 6 is a left side view of the vibrator;

Fig. 7 is the time course diagram of displacement time;

Figure 8 is a diagram showing the relationship between dynamic strain and cycle times;

Figure 9 is a dynamic stress-strain curve;

in:

1—Special construction vehicle; 2—Support leg; 3—Load servo system; 4—Electro-hydraulic servo hydraulic source; 5—Oil pipeline; 6—Guide column; 7—Fixed bracket; 8—Displacement sensor; 9—Pressure sensor; 10 - Upper bearing plate; 11 - Vibrator; 12 - Air nozzle; 13 - Lower bearing plate; 14 - Vertical shock absorbing airbag; 15 - Floor contact; 16 - Data acquisition system; 17 - Shock pickup; 18 - Earth pressure box; 19—On-site pressure sensor hydraulic cylinder.

Detailed ways

The present invention will be further described in detail below with reference to specific embodiments. A detailed implementation manner and a specific operation process are given, and the examples will help to understand the present invention, but the protection scope of the present invention is not limited to the following examples.

The invention provides a dynamic stress-strain curve in-situ testing device. It consists of four parts: movable system, load servo system, dynamic response system and data acquisition system.

(1) Movable system

Special construction vehicle 1: diesel engine (power 250kW), 4-wheel drive.

(2) Load servo system, which is loaded with microcomputer-controlled electro-hydraulic servo dynamic test control software LETRYTrier6200/6210.

The load servo system is to compare the command signal and the feedback signal, and then use the difference signal to control the entire system, so that the system can complete the expected action. The system has two control methods: stress control (force control) and displacement control. The test generally adopts force control to apply dynamic load, and vertical dynamic load can be applied under preset frequency, amplitude and number of loading cycles. The working principle of the system is described as follows :

1) Test control software

Microcomputer-controlled electro-hydraulic servo dynamic and static test control software, running in various Windows environments, with friendly interface and simple operation, can complete the setting of test conditions, sample parameters, and test data processing, and the test data can be saved in various file formats. After the test, the test history can be reproduced and the test data can be played back. The test data can be imported into Word, Excel, Access, MATLAB and other software for statistics, editing, classification, fitting test curves and other operations. After the test is completed, it can be printed. Issue a test report.

2) Test the function of the measurement control system

The all-digital microcomputer-controlled electro-hydraulic servo multi-channel control system is a distributed all-digital closed-loop microcomputer control system. The host computer and the six-channel control microcontroller transmit data in an asynchronous parallel, master-slave mode. While each microcontroller independently completes the preset and random instruction tasks, it transmits the data to the computer in digital form in time, and the computer sets the parameters for each channel test. , control parameter adjustment and other centralized processing and unified management, and send the random control parameters of the test system to each single-chip microcomputer, and compare and coordinate through the system preset and specified control parameters to achieve coordinated control loading.

(3) Dynamic reaction system

The dynamic response system is composed of electro-hydraulic servo actuator and vibrator.

1) Electro-hydraulic servo actuator

The electro-hydraulic servo actuator includes an electro-hydraulic servo hydraulic source 4, an oil pipeline 5 and a guide column 6 connected in sequence. The shown guide column 6 includes a piston rod and a guide sleeve arranged outside the piston rod. The bottom and the upper part of the guide column bear pressure The plate 10 is fixedly connected, a displacement sensor 8 is arranged in the middle of the piston rod 6, and a pressure sensor 9 is arranged at the bottom of the piston rod. The fixing bracket 7 is sleeved on the outside of the guide sleeve and can be used to fix the oil circuit. The results of the displacement sensor 8 and the pressure sensor 9 are fed back to the load servo system.

The working principle of the electro-hydraulic servo actuator: The system pressure oil provided by the hydraulic source enters the oil inlet cavity of the oil cylinder through the high-pressure accumulator, precision oil filter and electro-hydraulic servo valve through the oil inlet pipeline. The hydraulic oil in the oil return chamber returns to the oil tank through the electro-hydraulic servo valve, oil return pipe, cooler and oil return oil filter. The accumulator is installed on the oil inlet and return pipelines, which can eliminate pressure fluctuations, stabilize the system pressure, and improve the system control accuracy. The position and stroke of the piston movement of the actuator are measured by a high-precision displacement sensor (8) installed on the actuator, so as to realize the position control of the electro-hydraulic servo actuator. During the movement of the actuator, the pressure sensor (9) connected to the end of its piston rod can measure the force acting on the specimen by the actuator in real time, and realize the load control of the action stroke of the actuator through the electrical control system Displacement that meets 1000mm soil settlement. According to the load requirements that need to be applied in the vertical direction during the test, under the control of the electro-hydraulic servo system, the frequency and amplitude of the dynamic load can be adjusted, the maximum static test load is 100kN, and the dynamic maximum test load is 80kN.

2) Vibrator

The vibrator includes, from top to bottom, a lower pressure-bearing plate 13 , a vertical shock-absorbing air bag 14 and a ground floor 15 , and a gas nozzle 12 is arranged above the lower pressure-bearing plate 13 .

The working principle of vertical vibration: The dynamic and static loads transmitted by the upper pressure plate of the electro-hydraulic servo actuator act on the lower pressure plate of the vibrator, and then transmitted to the ground contacting floor through 4 sets of vertical shock-absorbing airbags. To realize the application of vertical dynamic and static test loads, sensors are embedded in a certain position below the vibrator.

4) Data acquisition system

The data acquisition system 16 includes data acquisition instruments, sensors, and signal acquisition and analysis software.

1) Acquisition instrument: DH5902 data acquisition instrument is used for the data acquisition of dynamic response test.

2) Signal acquisition and analysis software: The dynamic response test data acquisition and analysis system uses the DHDAS dynamic signal acquisition and analysis system of Donghua Test. The system software software has measurement mode and analysis mode. Measurement mode is used to operate real-time data sampling and basic analysis of the collected data. In the measurement mode, you can perform operations such as setting parameter files, sampling settings, measurement, and graphic area design. Analysis mode is used for offline analysis of already measured data. In the analysis mode, operations such as data file processing, review of test history, output of test results, and printing can be performed.

3) Sensor: 17 magnetoelectric speed sensor DH610V for shock pickup, which uses the principle of electromagnetic induction to convert the vibration speed into voltage output, with a range of 0.125m/s; DMTY type earth pressure cell, with a range of 150kPa.

The invention is further described below in combination with actual engineering and its use effect is verified. The specific implementation cases described here are only used to explain the present invention, and are not used to limit the present invention.

The test is aimed at the foundation soil of a blank site in the Dangtu test base of Nanjing Water Conservancy Research Institute. The base is located in Dangtu County, Ma'anshan City. The in-situ testing equipment for dynamic stress-strain curve provided by the present invention and its working method are used to conduct field tests. .

This test is aimed at the foundation soil of a blank site in the Dangtu Test Base of Nanjing Water Conservancy Research Institute, which is located in Dangtu County, Ma'anshan City. According to the results of on-site investigation, 5 meters below the surface is homogeneous soil. The foundation soil of the site is clay, which is yellowish-brown.

Table 1 Basic physical property index of soil

Field test preparations:

Operation process:

1) Special construction vehicle 1 enters the site, select a relatively flat site, and plan the location of special construction vehicle 1 and vibrator 11.

2) Dig a 1.5*1.5*0.5m pit right behind the special engineering vehicle.

3) After the pit is dug, mark the buried position of the sensors 17/18, and then use the on-site pressure sensor hydraulic cylinder 19 to drill to the specified depth at the marked position, and then bury the sensors 17 and 18. Spread a layer of sand and then backfill the original soil compaction.

4) Put the vibrator 11 into the pit, and the direction of the vehicle body should be perpendicular to the direction of the floor 15. The ground floor 15 of the vibrator should be as close to the original soil layer as possible.

5) After the vibrator 11 is placed, drive the special construction vehicle 1 to the position where the upper bearing plate 10 of the actuator and the lower bearing plate 13 of the vibrator overlap.

6) Connect the load servo system 3 and the electro-hydraulic servo-hydraulic source 4, open the control software and input the project site information.

7) Connect the connectors of the embedded sensors 17 and 18 to the data acquisition system 16, and prepare to collect and save the data.

8) Connect the air pipe to the corresponding air nozzles 12 at the four corners of the vibrator to ensure that the air pipe will not be pressed, and open the air valve.

9) Turn on the power supply, insert the car key, ignite the power system, and then increase the oil pressure to make each support leg 2 contact the wooden pier, and raise the special engineering vehicle. After the ignition is activated, the air tube will automatically inflate the shock's air bag, and the inflation pressure can be monitored from the barometer.

10) Controlled by the load servo system 3, so that the guide column 6 drives the upper bearing plate 10 of the actuator to raise its position to complete the decoupling.

Test content

After the preparations are over, start the test.

1) Waveform: The vibration waveform selected for the test is a sine waveform.

2) Cycle times: The relationship between dynamic stress, dynamic strain and vibration times is studied in this test, and the load cycle times set in the test are 10, 20, and 40 times, respectively. In the field test, the interval between the end of the current cycle cycle and the next loading is at least two hours. )

3) Loading frequency: Considering that the test does not study the effect of loading frequency on the test results, the loading frequency is set to 1 Hz.

4) Dynamic load amplitude: The test adopts the force control method. In order to calculate the dynamic stress-dynamic strain relationship curve, the test adopts the method of increasing the load step by step, and the test load is set to 30kPa, 60kPa and 90kPa respectively. During the field test, the interval between the application of each group of dynamic loads was one day. )

Test Results and Analysis

The relationship between dynamic strain and vibration order

The output displacement u-time t under a certain vibration order during the test is shown in Fig. 7. Using the formula (1), the soil dynamic strain ε _d under the local vibration order is calculated as 7.35×10 ^-4 .

After the test is completed, the dynamic strain corresponding to all vibration times is calculated, and the deformation values under each group of dynamic loads are sequentially accumulated to obtain the change curve of dynamic strain ε _d with cycle N, as shown in Figure 8.

It can be seen from Figure 8 that in the process of dynamic load, the dynamic strain of soil increases with the increase of the number of vibrations. The greater the dynamic stress, the greater the dynamic strain. Under the same dynamic load, the dynamic strain caused by the subsequent loading of the soil to the previous cycle is smaller than the dynamic strain caused by the end of the previous cycle. For example, when σ _d = 30kPa, the cycle number N set for the first test The dynamic strain ε _d after N=10 is 1.07×10 ^-3 , and the dynamic strain ε _d when N=20 loads to the 10th time is 0.89×10 ^-3 , the difference between the two is 0.18×10 ^-3 , this gap develops to 0.51×10 ^-3 when σ _d =90kPa. From the point of view of the loading process, although the time interval is set for two adjacent loadings in the field test, it is actually a loading-unloading-reloading process, which indicates that the soil has an irreversible shape under the action of the dynamic load. The deformation becomes more obvious with the increase of the dynamic load, reflecting the viscoelastic-plastic properties of the soil. In addition, the change curve of dynamic strain and the number of vibrations becomes smoother and smoother, indicating that the dynamic strain increases more and more slowly with the increase of the number of vibrations. The reason is analyzed that the soil is gradually compacted during the vibration process. The space between them is tighter, so that the effective stress increases, and the ability of the soil to resist damage and deformation also increases.

Dynamic stress-strain curve

Under a certain vibration order, the relationship between the dynamic stress and the dynamic strain is shown in Figure 9. It can be seen from Figure 9 that the dynamic stress-strain curve is close to a hyperbola, generally called the backbone curve, reflecting the nonlinearity of the soil. This application adopts the Duncan-Zhang hyperbolic model, and the expression is shown in Equation 2). The dynamic stress-strain relationship of natural soil is fitted, and the model parameters a and b under the corresponding vibration order are obtained as shown.

where a and b are experimental parameters.

From Table 2, it can be found that the overall variation range of model parameters a and b is not large, and a has a tendency to increase with the increase of vibration frequency, and the increasing range is larger and larger, indicating that a is greatly affected by cycle number N. , and is a positive correlation; compared with the value of b, it is not greatly affected by the cycle time N, and it is considered that it is mainly affected by the physical and mechanical properties of the soil.

Table 2 Model parameter values

To sum up, the test curves measured by this device have good regularity and are in good agreement with the actual situation, indicating that the in-situ testing equipment of the dynamic stress-strain curve works normally, and the test data is true, accurate and highly reliable.

The present invention provides an idea and method for an in-situ testing device for soil dynamic stress-strain curve. There are many specific methods and approaches for realizing the technical solution. The above are only the preferred embodiments of the present invention. For those of ordinary skill in the technical field, without departing from the principle of the present invention, several improvements and modifications can also be made, and these improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims (8)

1. a dynamic stress-strain curve in-situ testing device, is characterized in that, comprises movable system, dynamic reaction system, load servo system (3) and data acquisition system, wherein, The dynamic response system includes an electro-hydraulic servo actuator and a vibrator, and the electro-hydraulic servo actuator includes an electro-hydraulic servo-hydraulic source (4), an oil delivery pipe (5) and a guide column (6), which are connected in sequence, and the guide column ( 6) Including a piston rod and a guide sleeve arranged outside the piston rod, the bottom of the guide column is fixedly connected with the upper pressure bearing plate (10), the middle of the piston rod is provided with a displacement sensor (8), and the bottom of the piston rod is provided with a pressure sensor(9); The vibrator comprises, from top to bottom, a lower pressure-bearing plate (13), a vertical shock-absorbing airbag (14) and a grounding plate (15), and an air nozzle (12) is arranged above the lower pressure-bearing plate (13); The dynamic and static loads transmitted by the upper pressure-bearing plate (10) of the electro-hydraulic servo actuator act on the lower pressure-bearing plate (13) of the vibrator, and are then transmitted to the grounding plate (15) through the vertical shock-absorbing air bag; The load servo system is used to control the operation of the dynamic response system, and a vertical dynamic load is applied under a preset frequency, amplitude, and number of loading cycles, and the results of the displacement sensor (8) and the pressure sensor (9) are fed back to the load server system; The electro-hydraulic servo hydraulic source is electrically or wirelessly connected to the load servo system; The data acquisition system includes an acquisition instrument, a shock pickup (17) and an earth pressure box (18) respectively connected thereto, and the earth pressure box (18) is embedded in the midpoint of the two shock pickups (17). position, output the vertical stress of this point under the action of dynamic load in real time and transmit it to the acquisition instrument; The dynamic reaction system is arranged inside the movable system. 2. dynamic stress-strain curve in-situ testing device according to claim 1, is characterized in that, described movable system is special construction vehicle, and described dynamic reaction system is arranged in special construction vehicle interior and can be opened in special construction vehicle by opening in special construction vehicle. The hole at the bottom of the construction vehicle protrudes from the outside of the special construction vehicle. 3. The dynamic stress-strain curve in-situ testing device according to claim 2, characterized in that a retractable and retractable support leg (2) is provided at the bottom of the movable system. 4. The dynamic stress-strain curve in-situ testing device according to claim 2, wherein the construction vehicle is provided with a hook inside, and the top of the guide column is provided with a corresponding hook. When the guide column rises to the highest position Both hang. 5 . The in-situ testing device for dynamic stress-strain curves according to claim 1 , wherein the vertical shock-absorbing airbags comprise 4 sets. 6 . 6. The dynamic stress-strain curve in-situ testing device according to claim 1, wherein the shock pickup is arranged at a vertical distance of 0.5-1m from the bottom of the touch panel, and the earth pressure cell is embedded in two The position of the midpoint of the shock pickup, and the vertical stress of this point under the action of the dynamic load is output in real time. 7. a dynamic stress-strain curve in-situ testing method, is characterized in that, comprises the steps: 1) Enter the movable system (1) into the site, select a relatively flat site, and plan the positions of the movable system (1) and the vibrator (11); 2) Dig a 1.5m*1.5m*0.5m pit right behind the movable system (1); 3) After the pit is dug, mark the burial position of the shock pickup (17) and the earth pressure box (18), and then use the field pressure sensor hydraulic cylinder (19) at the marked position to drill to the specified depth and then bury the shock pickup (17) and the earth pressure box (18); after the shock pickup (17) and the earth pressure box (18) are placed in the designated positions, first sprinkle a layer of sand around them and then backfill the original soil for compaction; 4) Put the vibrator (11) into the pit, the direction of the body of the movable system (1) is perpendicular to the direction of the floor (15), and the floor (15) of the vibrator is close to the original soil layer; 5) After the vibrator (11) is placed, open the movable system (1) in place, so that the upper bearing plate (10) of the actuator and the lower bearing plate (13) of the vibrator overlap; 6) Connect the load servo system (3) with the electro-hydraulic servo hydraulic source (4), open the control software and input the project site information; 7) Connect the joint of the pre-embedded shock pickup (17) and the earth pressure box (18) with the data acquisition system (16), and prepare to collect and save the data; 8) Connect the trachea to the corresponding air nozzles (12) at the four corners of the vibrator to ensure that the trachea will not be pressed, and open the air valve; 9) Turn on the power supply, insert the car key, start the power system with ignition, then increase the oil pressure to make each support leg (2) contact the wooden pier placed on the ground, and raise the movable system (1); after the ignition is started, the air pipe will automatically supply The airbag of the vibrator is inflated, and the inflation pressure can be monitored from the barometer; 10) Controlled by the load servo system (3), so that the guide column (6) drives the upper bearing plate (10) of the actuator to raise its position to complete the decoupling. 8. The method according to claim 7, wherein the earth pressure cell is embedded at the midpoint of the two shock pickups, and the vertical stress of the point under the action of the dynamic load is output in real time; the dynamic strain is defined as the two shock pickups The average dynamic strain between the two sensors is assumed to vary linearly with the distance between the two sensors, then this value is considered to be equal to the dynamic strain at the midpoint of the two sensors, and is calculated by the displacement-based method. For the recorded velocity - The time history is numerically integrated to obtain the displacement-time history, and the peak displacement of the adjacent sensor displacement time history is calculated; at the same time, the difference between the output larger peak displacement and the displacement recorded by another sensor is the difference between the adjacent sensors. Total deformation, the difference in displacement divided by the distance between the two sensors to obtain the dynamic strain ε _d :

In the formula, u ₁ is the displacement of the shock pickup output under a certain vibration-the maximum displacement in the time waveform diagram, u ₂ is the displacement output by another shock pickup at the same time; Δx is the distance between the two shock pickups .

Images