A biaxial vibrating triaxial apparatus that maintains absolute phase difference of load and a method of using the same

Abstract

The application discloses a bidirectional vibration triaxial apparatus capable of keeping absolute phase difference of load and a use method thereof, and belongs to the technical field of geotechnical engineering test. The application can control and keep the absolute phase difference of the axial and radial dynamic load amplitude, and can simulate various stress working conditions including the action of the seismic load. The apparatus has simple structure and simple control system, and can realize stress type control of the axial stress and the radial stress. Under the condition that the sectional area of the loading rod is same as that of the sample, triaxial test of the bidirectional cyclic load of the principal stress rotation and triaxial elongation can be carried out, and the triaxial test has significance for studying the deformation characteristics of the loose granular body (soil body) material under the complex stress working conditions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of geotechnical engineering test, and relates to a bidirectional vibration triaxial apparatus with absolute phase difference of load keeping and a use method thereof. BACKGROUND

[0002] Geotechnical engineering foundations and structures are often subjected to dynamic cyclic loads. Dynamic loads can be caused by environmental factors, such as seismic activity and wave loads, or human activities, such as traffic loads and machine vibrations. The dynamic characteristics of geotechnical foundations under cyclic loads are more complex than under static loads, whether in terms of deformation or strength.

[0003] Dynamic triaxial apparatus is the most commonly used instrument for testing the dynamic characteristics of soil. According to the different ways of applying loads, it can be divided into single-direction dynamic triaxial apparatus and bidirectional dynamic triaxial apparatus. Single-direction dynamic triaxial apparatus only applies single-direction (axial) cyclic load to the sample, while bidirectional dynamic triaxial apparatus can simultaneously apply cyclic load in the axial and radial directions. Bidirectional dynamic triaxial apparatus can make the sample in a stress state closer to the actual working condition, facilitating research under the real stress state of soil. In addition, it has become a consensus to simplify the effect of seismic load on soil as a dynamic load condition where the normal stress remains unchanged and the shear stress changes reciprocally. This simplified load condition can only be obtained in bidirectional vibration triaxial apparatus tests, i.e., using bidirectional excitation to apply dynamic stress with the same frequency and a constant phase difference of 180° in the axial and radial directions, which can obtain the stress condition of constant normal stress and reciprocally changing shear stress on the 45° inclined surface of the sample. However, it is difficult to achieve dynamic stress with the same frequency and a constant phase difference of 180° in the axial and radial directions. Due to the lag response of the dynamic actuator output, the limited mechanical and electrical control level of the test apparatus, and the limited accuracy of the sensor, there is an additional phase difference between the actual output dynamic stress and the target stress, which is particularly significant in high-frequency vibration loads, making it difficult to continue to simulate the effect of seismic load on soil. Therefore, there is an urgent need for a seismic load bidirectional vibration simulation instrument that strictly controls the amplitude and phase difference of axial and radial dynamic loads. SUMMARY

[0004] In view of the problems in the prior art, the application provides a bidirectional vibration triaxial apparatus with absolute phase difference of load keeping and a use method thereof.

[0005] The technical scheme of the application is as follows:

[0006] 1) Basic principle

[0007] A bidirectional vibration triaxial apparatus with absolute phase difference of load keeping, which adopts two independent pressure sources, such as Figure 1The upper end of the axial loading cylinder is connected to a constant pressure source, and the piston obtains driving force P0xA (A is the piston area of the cylinder) to drive the piston rod to move downward and output pressure to the sample. The output pressure of the pressure controller is connected to the lower end of the axial loading cylinder, respectively providing radial stress P (or σ3) and piston rod resistance PxA (ignoring the piston rod area). The pressure of the sample under the piston rod is (P0-P)xA. When P increases, the pressure on the sample decreases; when P decreases, the pressure on the sample increases; therefore, the axial stress (σ1) and the radial stress (σ3) of the sample always maintain an absolute phase difference of 180°. However, by interchanging the interfaces of the two pressure sources, the axial stress (σ1) and the radial stress (σ3) of the sample can also always maintain an absolute phase difference of 0°.

[0008] 2) Instrument device

[0009] A bidirectional vibration triaxial apparatus for maintaining the absolute phase difference of load, comprising a main frame, a pressure chamber, an axial loading cylinder group 1, a constant pressure source and a pressure controller, as shown in Figure 1 . Figure 2 and Figure 3 show the overall diagram and the longitudinal section diagram of the instrument device, respectively.

[0010] The main frame comprises a main frame plate 13 and a main frame connecting rod 2 connecting the upper and lower main frame plates 13. The pressure chamber is a closed pressure chamber cavity 3; the pressure chamber cavity 3 is provided with a confining pressure input valve 11. The sample 8 is wrapped in a rubber film and placed on the pressure chamber base 7 at the bottom of the pressure chamber cavity 3, and a sample cap 9 is placed above the sample 8; the pressure chamber base 7 has two through holes, one end of which is connected to the inside of the sample 8 below, and the other end is respectively provided with two pressure chamber base communication valves 5; the sample cap 9 has two through holes, one end of which is connected to the inside of the sample 8 above, and the other end is respectively provided with two sample cap communication valves 6; two linear displacement sensors 4 are fixed between the sample cap 9 and the pressure chamber base 7 to measure the axial compression deformation of the sample 8; the upper end of the sample cap 9 is sequentially connected to a force sensor 10 and a loading rod 12; the loading rod 12 is used to transfer the load of the axial loading cylinder group 1 to the sample 8; and the force sensor 10 is used to record the size of the load.

[0011] The axial loading cylinder group 1 comprises a series of side-by-side fixed cylinders 1E, the lower end of which is fixed on the cylinder group output plate 1A, and the upper end is fixed on the main frame plate 13 (fixed by an internal hexagonal screw 1D); the cylinder 1E is provided with a cylinder upper input valve 1B and a cylinder lower input valve 1C; the cylinder piston rod 1F is fixed on the cylinder group output plate 1A; and the cylinder group output plate 1A is connected to the loading rod 12 through threads to transfer the load.

[0012] The constant pressure source and the pressure controller are external power devices, which are connected to the cylinder upper input valve 1B and the cylinder lower input valve 1C on the cylinder 1E respectively, so as to provide the absolute phase difference load for the sample 8; and the pressure controller is connected to the confining pressure input valve 11 simultaneously, so as to input the confining pressure for the sample 8.

[0013] The application has the advantages that the application can control and maintain the absolute phase difference axial and radial dynamic load amplitude, and simulate various stress working conditions including the seismic load effect. The instrument has simple structure and control system, and can realize the stress type control of the axial stress and the radial stress. Under the condition that the loading rod and the sample cross section area are the same, the triaxial test of the main stress rotation and the triaxial elongation bidirectional cyclic load can be carried out, which has significance for the study on the deformation characteristics of the loose granular body (soil body) material under the complex stress working condition. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 Absolute phase difference bidirectional vibration load application principle;

[0015] Figure 2 Instrument device isometric view (left) and front view (right);

[0016] Figure 3 Instrument device longitudinal section view;

[0017] Figure 4 Cylinder group composition view;

[0018] Figure 5 Cylinder view;

[0019] In the figure: 1 axial load cylinder group; 2 main frame connecting rod; 3 pressure chamber cavity; 4 linear displacement sensor; 5 pressure chamber base communication valve; 6 sample cap communication valve; 7 pressure chamber base; 8 sample; 9 sample cap; 10 force sensor; 11 confining pressure input valve; 12 loading rod; 13 main frame plate; 1A cylinder group output plate; 1B cylinder upper input valve; 1C cylinder lower input valve; 1D internal hexagonal screw; 1E cylinder; 1F cylinder piston rod. DETAILED DESCRIPTION

[0020] The application will be further described below in combination with the drawings of the specification.

[0021] The test is carried out by using the above-mentioned bidirectional vibration triaxial instrument with the load maintaining absolute phase difference, and includes the following steps:

[0022] First step, according to the axial and radial pressure to maintain 0 ° phase difference or 180 ° phase difference test design, the arrangement of pressure source and cylinder 1E communication form. For example, if the connection constant pressure source to the cylinder on the input valve 1B, the connection pressure controller to the cylinder under the input valve 1C, the axial force of the cylinder 1E output and the pressure of the pressure controller to maintain 0 ° phase difference; if the above two pressure input connection, the axial force of the cylinder 1E output and the pressure of the pressure controller to maintain 180 ° phase difference.

[0023] Second step, the pressure of constant pressure source and pressure controller is connected to the axial load cylinder group 1, to determine the axial load. According to the needs of different test settings, the number of cylinder 1E needs to be connected can be selected, according to the number of cylinder 1E connected to adjust the load ratio of axial output load and confining pressure.

[0024] Third step, install soil sample and pressure chamber cavity 3. The sample 8 preparation process in accordance with the test procedure. Connection pressure controller to confining pressure input valve 11, to provide the cycle confining pressure with the pressure in the pressure controller.

[0025] Fourth step, the experiment begins, the readings of each sensor are collected. The test data need to be recorded, linear displacement sensor 4, force sensor 10, pressure controller pressure, constant pressure source provided by the pressure.

Claims

1. A bender with load holding absolute phase difference bi-axial vibrator, characterized by, The main frame, the pressure chamber, the axial load cylinder group (1), the constant pressure source and the pressure controller; The main frame comprises a main frame plate (13) and a main frame connecting rod (2) connecting the upper and lower main frame plates (13); the pressure chamber is a closed pressure chamber cavity (3); the pressure chamber cavity (3) is provided with a confining pressure input valve (11); a sample (8) is wrapped in a rubber film and placed on a pressure chamber base (7) at the bottom of the pressure chamber cavity (3), and a sample cap (9) is placed above the sample (8); the pressure chamber base (7) is provided with two first through holes, one end of the first through hole is communicated with the inside of the sample (8) below, and the other end is respectively provided with two pressure chamber base communication valves (5); the sample cap (9) is provided with two second through holes, one end of the second through hole is communicated with the inside of the sample (8) above, and the other end is respectively provided with two sample cap communication valves (6); two linear displacement sensors (4) are fixed between the sample cap (9) and the pressure chamber base (7) and used for measuring the axial compression deformation of the sample (8); the upper end of the sample cap (9) is sequentially connected with a force sensor (10) and a loading rod (12); the loading rod (12) is used for transmitting the load of the axial load cylinder group (1) to the sample (8); the force sensor (10) is used for recording the size of the load; The axial load cylinder group (1) comprises a series of side-by-side fixed cylinders (1E), the lower end of the cylinder (1E) is fixed on a cylinder group output plate (1A), and the upper end is fixed on the main frame plate (13); the cylinder (1E) is provided with a cylinder upper input valve (1B) and a cylinder lower input valve (1C); a cylinder piston rod (1F) is fixed on the cylinder group output plate (1A); the cylinder group output plate (1A) is connected with the loading rod (12) through threads to transmit the load; The constant pressure source and the pressure controller are external power devices, which are respectively connected to the cylinder upper input valve (1B) and the cylinder lower input valve (1C) of the cylinder (1E) to provide an absolute phase difference load for the sample (8); the pressure controller is also connected to the confining pressure input valve (11) to input the confining pressure for the sample (8).

2. The method of using a bender with load holding absolute phase difference bi-axial apparatus as claimed in claim 1, wherein, The method comprises the following steps: In the first step, according to the test design of keeping 0° phase difference or 180° phase difference between the axial and radial pressures, the communication form of the pressure source and the cylinder (1E) is arranged; if the constant pressure source is connected to the cylinder upper input valve (1B) and the pressure controller is connected to the cylinder lower input valve (1C), the axial force output by the cylinder (1E) keeps 0° phase difference with the pressure of the pressure controller; if the above two pressure inputs are exchanged, the axial force output by the cylinder (1E) keeps 180° phase difference with the pressure of the pressure controller; In the second step, the pressure of the constant pressure source and the pressure controller is connected to the axial load cylinder group (1) to determine the axial load; according to the needs of different test settings, the number of cylinders (1E) that need to be communicated can be selected, and the load ratio of the axial output load to the confining pressure is adjusted according to the number of communicated cylinders (1E). Third step, install the sample (8) and the pressure chamber cavity (3); the sample (8) preparation process can be according to the test regulation; connect the pressure controller to the confining pressure input valve (11), provide the circulating confining pressure synchronous with the pressure in the pressure controller; Fourth step, the experiment starts, collect the readings of each sensor; the test data that need to be recorded have the linear displacement sensor (4), the force sensor (10), the pressure of the pressure controller, the pressure provided by the constant pressure source.

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