CN214309853U

CN214309853U - External excitation test device and test system for measuring shear wave velocity of soil body in large-scale triaxial test

Info

Publication number: CN214309853U
Application number: CN202120120548.5U
Authority: CN
Inventors: 邹德高; 刘兴阳; 刘京茂; 周晨光; 宁凡伟; 白峻松; 季晓檬; 李多
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2021-01-18
Filing date: 2021-01-18
Publication date: 2021-09-28
Anticipated expiration: 2031-01-18

Abstract

An external excitation test device and a test system for measuring the shear wave velocity of a soil body in a large triaxial test. The external excitation device comprises four piezoelectric stacks, four inertia blocks and a vibration unit; the end parts of the inertia blocks are respectively connected with the end surfaces of the piezoelectric stacks and fixed with the fixing units; the vibration unit includes a fixed unit and four torsion units. A fixing unit in the test system is connected with a loading shaft of a triaxial tester, and two acceleration sensors are arranged on the side surface of a sample; under the longitudinal vibration effect of the piezoelectric stack, the vibration unit generates torsional vibration and transmits through the sample, the sensor collects vibration signals transmitted to different positions of the sample and converts the vibration signals into electric signals, and the shear wave speed of the soil body is calculated through the time difference of the collected electric signals. The utility model has the advantages of simple and reasonable structure, the assembly is simple, convenient operation, has good spreading value in geotechnical engineering and structural health monitoring field.

Description

External excitation test device and test system for measuring shear wave velocity of soil body in large-scale triaxial test

Technical Field

The utility model relates to a soil mechanics triaxial test device and test method, especially an external excitation test device, test system of measuring coarse-grained soil shear wave speed among large-scale triaxial test.

Background

The shear wave velocity of the soil body is one of key mechanical parameters for describing the elastic strain range of the soil body, and has important significance in the aspects of dividing stratum and field soil types, judging liquefaction of sand soil, soil foundation seismic subsidence, seismic reaction analysis, calculating rock-soil dynamic parameters and the like.

The laboratory measurement of the shear wave velocity of the soil body usually adopts a resonant column method and a bending element method. The resonant column test is expensive, the calculation process is complicated, and the size of the sample is limited. The bending element method has clear principle and simple method, and can be simultaneously installed in various soil test instruments. However, the resonance column method and the bending element method are mostly used for small-sized samples, and are widely applied to sand and sand-clay mixtures. As typical coarse-grained soil, gravel materials and blasting materials have the advantages of good compactibility, high shear strength, strong water permeability and the like, and are widely applied to engineering construction, while the existing wave velocity testing technology is difficult to realize shear wave velocity testing on the gravel materials and the blasting materials in a large-scale triaxial test. Therefore, a simple and convenient indoor test device and method for testing the shear wave velocity of coarse-grained soil are needed.

SUMMERY OF THE UTILITY MODEL

The problem that exists to prior art, the utility model provides a soil body shear wave speed external excitation test device and method that can be used to large-scale triaxial test appearance rational in infrastructure, assembly are simple, convenient operation.

The utility model provides a technical scheme that prior art problem adopted:

an external excitation test device for measuring the shear wave velocity of a soil body in a large triaxial test comprises four piezoelectric stacks 1, four inertia blocks 2 and a vibration unit 3.

The piezoelectric stack 1 is a bulk structure.

The inertia block 2 is of a cylindrical structure, one end of the inertia block is fixed on one end face of the piezoelectric stack 1, and the outer surface of the other end of the inertia block is provided with threads.

The vibration unit 3 comprises a fixed unit 4 with a middle cylinder structure and four torsion units 5 uniformly arranged along the circumferential direction of the periphery of the cylinder, wherein the torsion units 5 are of plate-shaped structures. Fixed unit 4 be hollow cylinder structure, its inside is equipped with the screw thread, twist reverse 5 middle parts of unit and be equipped with the screw hole that runs through to it passes through the thread tightening to establish screwed one end with inertia piece 2, and then connects piezoelectric stack 1, inertia piece 2 and vibration unit 3 as a whole. And the fixing unit 4 of the vibration unit 3 is in threaded connection with a loading shaft (external thread) of the large triaxial tester. The excitation device is arranged outside the sample due to the structural design, and can be used for triaxial testers of various sizes theoretically, so that the problems that the piezoelectric stack 1 is directly contacted with the test soil sample 7 and a cable of the piezoelectric stack needs to be led out from a pressure chamber of the triaxial tester are solved.

Further, the inertial mass 2 is fixed to the piezoelectric stack 1 by epoxy resin.

A test system for measuring the shear wave velocity of a soil body in a large triaxial test is shown in figure 4 and comprises an external excitation test device, two acceleration sensors 6, a signal generator 9, a power amplifier 10, a charge amplifier 11 and an oscilloscope 12.

The signal generator 9 is connected with a power amplifier 10, and the piezoelectric stack 1 in the external excitation test device is connected with the power amplifier 10. The signal generator 9 is configured to generate a voltage pulse as an excitation signal, and generate a longitudinal vibration in the piezoelectric stack 1 after passing through the power amplifier 10. The two acceleration sensors 6 are arranged on the surface of the test soil sample 7 at intervals and are respectively connected with the charge amplifier 11, the charge amplifier 11 is connected with the oscilloscope 12, and the test soil sample 7 is arranged in the triaxial tester.

Under the simultaneous action of the four piezoelectric stacks 1, the vibration unit 3 generates torsional vibration and transmits the torsional vibration through the test soil sample 7, the acceleration sensor 6 collects vibration signals at different elevation measuring points of the test soil sample 7 and converts the vibration signals into electric signals, and the electric signals are simultaneously displayed and stored on the oscilloscope 12 after passing through the charge amplifier 11 so as to provide data for the calculation of the transmission time of the shear wave.

Further, the two acceleration sensors 6 are respectively installed at different elevations on the side surface of the sample along the vertical direction.

Further, the test soil sample 7 is a cylindrical large triaxial sample prepared according to a preset density.

An external excitation test method for measuring the shear wave velocity of coarse-grained soil in a large triaxial test comprises the following steps:

s1, system installation: preparing a coarse-grained soil sample in a large triaxial tester 8, and respectively installing two acceleration sensors 6 at different elevations on the side surface of the sample along the vertical direction; fixing an external excitation test device on a loading shaft of a triaxial tester through threads, and solidifying under equidirectional confining pressure;

s2, determining the propagation time of the shear wave: the starting signal generator 9 generates voltage pulses as excitation signals, the voltage pulses are simultaneously input into the four piezoelectric stacks 1 after passing through the power amplifier 10, due to the inverse piezoelectric effect, the four piezoelectric stacks 1 simultaneously generate longitudinal vibration, the vibration unit 3 generates torsional vibration under the action of the inertia force of the piezoelectric stacks 1, and the torsional vibration is transmitted through the sample 7; reading vibration data acquired by an acceleration sensor on a sample through an oscilloscope 12, and calculating by adopting a characteristic point method or a cross-correlation method to obtain the propagation time delta t of the shear wave;

s3, shear wave velocity calculation: the shear wave speed of the test soil sample is L/delta t, wherein L is the vertical distance between the two acceleration sensors.

The beneficial effects of the utility model reside in that: the utility model discloses a test device structural style is simple, the disturbance that arouses when having avoided crooked unit embedding test soil sample, has solved piezoelectric material and has made the appearance to hit the difficult problem of reality and high stress condition loading in-process easy destruction at large-scale triaxial test. In addition, the device is directly fixed outside the sample, so that the trouble that a cable of the piezoelectric stack needs to be led out from a pressure chamber is avoided, and the problems of aging, vulnerability and the like which are possibly generated under the action of high confining pressure for a long time by the cable are also avoided. Meanwhile, the external excitation device can be arranged on triaxial test instruments with different sizes, has strong transportability and greatly facilitates the experimental research on the soil body small-strain dynamic characteristic scale effect.

Drawings

Fig. 1 is a schematic view of the overall structure of the external excitation device of the present invention.

Fig. 2 is a schematic structural diagram of a piezoelectric stack and an inertial mass in an external excitation device according to the present invention.

Fig. 3 is a schematic structural diagram of a vibration unit in the external excitation device of the present invention.

Fig. 4 is a schematic diagram of a connection structure of the testing system of the present invention.

Fig. 5 is a diagram of exemplary test waveforms.

In the figure: the test device comprises a piezoelectric stack 1, an inertial block 2, a vibration unit 3, a fixing unit 4, a torsion unit 5, an acceleration sensor 6, a test soil sample 7, a triaxial tester 8, a signal generator 9, a power amplifier 10, a charge amplifier 11 and an oscilloscope 12.

Detailed Description

The present invention is described below with reference to the accompanying drawings and the embodiments:

fig. 1 is a schematic diagram of the overall structure of the external excitation test device for measuring the shear wave velocity of coarse-grained soil according to the present invention. The external excitation test device for measuring the shear wave velocity of coarse-grained soil in a large triaxial test sequentially comprises a piezoelectric stack 1, an inertia block 2 and a vibration unit 3; as shown in fig. 2, one end of the piezoelectric stack 1 and one end of the inertia block 2 are fixed into a whole through epoxy resin, and the outer surface of the other end of the inertia block 2 is provided with threads; as shown in fig. 3, the vibration unit 3 is divided into a fixing unit 4 and a torsion unit 5, wherein a screw thread is arranged inside the fixing unit 4, a screw hole is arranged on the surface of the torsion unit 5, and the torsion unit is fixed with one end of the inertia block 2 provided with the screw thread, so that the piezoelectric stack 1, the inertia block 2 and the vibration unit 3 are connected into a whole; as shown in fig. 4, the piezoelectric stack 1, the inertial mass 2, and the vibration unit 3 are integrally connected to a loading shaft (external thread) of the triaxial tester 8. The excitation device is arranged outside the sample due to the structural design, and can be used for triaxial testers of various sizes theoretically, so that the trouble that the piezoelectric stack 1 is directly contacted with the test soil sample 7 and the cable of the piezoelectric stack needs to be led out from a pressure chamber of the triaxial tester is avoided.

A test system for measuring the shear wave velocity of coarse-grained soil in a large triaxial test, as shown in fig. 4, comprises an external excitation test device shown in fig. 1-3, an acceleration sensor 6, a signal generator 9, a power amplifier 10, a charge amplifier 11 and an oscilloscope 12; the signal generator 9 is connected with the power amplifier 10, and the piezoelectric stack 1 in the external excitation test device is connected with the power amplifier 10; the two acceleration sensors 6 are respectively connected with a charge amplifier 11, and the charge amplifier 11 is connected with an oscilloscope 12. The signal generator 9 is configured to generate a voltage pulse as an excitation signal, and generate a longitudinal vibration in the piezoelectric stack 1 after passing through the power amplifier 10. Under the simultaneous action of the four piezoelectric stacks, the vibration unit generates torsional vibration and transmits through a test soil sample, the acceleration sensor 6 is used for collecting vibration signals at different elevation measuring points of the test soil sample 7 and converting the vibration signals into electric signals, and the electric signals are simultaneously displayed and stored on the oscilloscope 12 after passing through the charge amplifier 11 so as to provide data for the calculation of the transmission time of the shear wave.

The test method of the test system for measuring the shear wave velocity of coarse-grained soil in the large triaxial test comprises the following steps:

s1, system installation: test soil sample 7 was prepared according to the conventional test method of soil test protocol (SL 237-1999). The lower part of a vibration unit 3 in an external excitation test device is connected with an axial loading shaft of a triaxial tester 8, and two acceleration sensors 6 in an external excitation test system are respectively fixed at different elevations of a rubber membrane on the side surface of a test soil sample 7 along the vertical direction; and consolidated under an isotropic confining pressure.

S2, determining the propagation time of the shear wave: starting a signal generator 9 to generate voltage pulses as excitation signals, enabling the piezoelectric stack 1 to simultaneously generate longitudinal vibration after passing through a power amplifier 10, enabling the vibration unit 3 to generate torsional vibration under the action of inertia force, enabling the vibration to be transmitted through a test soil sample 7 in a torsional wave mode, enabling acceleration sensors 6 at different elevations on the side surface of the test soil sample 7 to acquire vibration signals and convert the vibration signals into electric signals, and simultaneously displaying and storing the electric signals on an oscilloscope 12 after passing through a charge amplifier 11; reading vibration data acquired by the acceleration sensor 6 through the oscilloscope 12, and calculating by adopting a characteristic point method or a cross-correlation method to obtain the propagation time delta t of the shear wave;

s3, shear wave velocity calculation: the shear wave speed of the test soil sample 8 is L/delta t, wherein L is the vertical distance between the two acceleration sensors 6.

The foregoing is a more detailed description of the present invention, taken in conjunction with the specific preferred embodiments thereof, and it is not intended that the invention be limited to the specific embodiments shown and described. To the utility model belongs to the technical field of ordinary technical personnel, do not deviate from the utility model discloses under the prerequisite of design, can also make a plurality of simple deductions or replacement, all should regard as belonging to the utility model discloses a protection scope.

Claims

1. An external excitation test device for measuring the shear wave velocity of a soil body in a large triaxial test is characterized by comprising four piezoelectric stacks (1), four inertia blocks (2) and a vibration unit (3);

the piezoelectric stack (1) is of a block structure;

the inertia block (2) is of a cylindrical structure, one end of the inertia block is fixed on one end face of the piezoelectric stack (1), and the outer surface of the other end of the inertia block is provided with threads;

the vibration unit (3) comprises a fixed unit (4) with a middle cylinder structure and four torsion units (5) uniformly arranged along the circumferential direction of the periphery of the cylinder, wherein the torsion units (5) are of plate-shaped structures; the fixing unit (4) is of a hollow cylindrical structure, threads are arranged in the fixing unit, a through threaded hole is formed in the middle of the torsion unit (5), and the fixing unit is fixed with one end, provided with the threads, of the inertia block (2) through the threads, so that the piezoelectric stack (1), the inertia block (2) and the vibration unit (3) are connected into a whole; and the fixing unit (4) of the vibration unit (3) is connected with a loading shaft of the large triaxial tester through threads.

2. The external excitation test device for measuring the shear wave velocity of the soil body in the large triaxial test according to claim 1, wherein the inertia block (2) is fixed with the piezoelectric stack (1) into a whole through epoxy resin.

3. A test system for measuring the shear wave velocity of a soil body in a large triaxial test is characterized by comprising the external excitation test device of claim 1 or 2, two acceleration sensors (6), a signal generator (9), a power amplifier (10), a charge amplifier (11) and an oscilloscope (12);

the signal generator (9) is connected with the power amplifier (10), and the piezoelectric stack (1) in the external excitation test device is connected with the power amplifier (10); the signal generator (9) is used for generating voltage pulses as excitation signals, and the voltage pulses are used for enabling the piezoelectric stack (1) to generate longitudinal vibration after passing through the power amplifier (10); the two acceleration sensors (6) are arranged on the surface of the test soil sample (7) at intervals and are respectively connected with the charge amplifier (11), the charge amplifier (11) is connected with the oscilloscope (12), and the test soil sample (7) is arranged in the large triaxial tester (8);

the fixing unit (4) of the vibration unit (3) is connected with a loading shaft of a large triaxial tester through threads; under the simultaneous action of the four piezoelectric stacks (1), the vibration unit (3) generates torsional vibration and transmits the torsional vibration through the test soil sample (7), the acceleration sensor (6) collects vibration signals at different height measuring points of the test soil sample (7) and converts the vibration signals into electric signals, and the electric signals are simultaneously displayed and stored on the oscilloscope (12) after passing through the charge amplifier (11) to provide data for the calculation of the transmission time of the shear wave.

4. A test system for measuring the shear wave velocity of the soil mass in a large triaxial test according to claim 3, wherein the two acceleration sensors (6) are respectively installed at different elevations on the side surface of the test sample along the vertical direction.