CN108398180A - A kind of experimental rig, system and test method measuring coarse-grained soil shear wave velocity - Google Patents

Abstract

A kind of experimental rig, system and test method measuring coarse-grained soil shear wave velocity, including shell, friction element, piezo electric stack and acceleration transducer；The vertical section of friction element is "T"-shaped, " T " shaped horizontal ends are fixed on the top of shell, " T " shaped vertical end is inserted into shell by the top of shell and is fixed with acceleration transducer and piezo electric stack in the "T"-shaped vertical end of friction element, while piezo electric stack is fixedly connected with the madial wall of shell；Friction element is equipped with concave-convex clathrate rubbing surface in the upper surface of "T"-shaped horizontal ends.The experimental rig of the present invention solves the problems, such as piezoelectric material destructible and traditional flexure element and problem that coarse-grained soil degree of coupling is poor, cannot achieve large-scale three axis coarse-grained soil specimen shear wave velocities measures in Large-scale Triaxial Experiments sample compacting and condition of high ground stress loading procedure；The test system architecture connection and reasonable arrangement of the present invention, assembly is simple, test operation is convenient.

Description

A test device, system and test method for measuring shear wave velocity of coarse-grained soil

technical field

The invention relates to a soil mechanics triaxial test device and a test method, in particular to a test device, a system and a test method for measuring the shear wave velocity of coarse-grained soil.

Background technique

Soil shear wave velocity is one of the key parameters in soil mechanics research and geotechnical engineering design. It is used in the classification of strata and site soil types, judgment of sandy soil liquefaction, soil foundation seismic subsidence, earthquake response analysis, and calculation of rock and soil dynamics parameters. And it is of great significance to study the vibration characteristics of soil.

Since Shirley et al. used piezoelectric ceramic bending elements to test the shear wave velocity of kaolin samples for the first time in 1978, due to its clear test principle and simple and intuitive method, it has been widely used in triaxial instruments, consolidation instruments, direct shear instruments, and resonance instruments. column and other indoor instruments. The bending element is usually composed of two longitudinally stretchable piezoelectric ceramic crystal sheets bonded with a metal stiffening layer, installed at both ends of the sample in the form of a cantilever beam, one as an excitation element, and the other as a receiving element. During the test, the exciter generates a shear wave under the pulse voltage, and the shear wave propagates through the soil and reaches the receiving element. The vibration generated by the receiving element is converted into an electrical signal through the data acquisition device, and the shear wave can be obtained by comparing the electrical signals. The propagation time of the soil can be calculated according to the length of the soil sample. However, the bending element method is difficult to test the shear wave velocity of coarse-grained soil. The main reasons are as follows: first, the particle size of coarse-grained soil is large, and the insertion of the bending element into it is poorly coupled with it; In the process of compaction and loading under high stress conditions, piezoelectric materials such as bending elements are easily damaged; third, the exciter will generate compression waves on both sides while generating shear waves, and the compression waves reflected from the side walls of the pressure chamber will It interferes with the judgment of the first shear wave arrival time.

In recent years, devices such as torsional shear vibrators and piezoelectric rings have appeared successively at home and abroad to test the shear wave velocity of soil samples, but they are all completed in small triaxial tests or consolidation tests. In addition, the existing indoor shear wave velocity measurement technology usually adopts a single excitation-reception method, and it is difficult to accurately obtain the actual motion behavior of the excitation element and the receiving element in the soil sample during the test, which affects the entire excitation element-soil sample-receiving element. The study of the dynamic response of the system poses difficulties. It can be seen that there is an urgent need for an indoor test device and method that can test the shear wave velocity of coarse-grained soil.

Contents of the invention

The purpose of the present invention is to provide a reasonable structure, simple assembly, convenient test operation and solve the problem that the piezoelectric material is easily damaged during the compaction of the large-scale triaxial test sample preparation and the loading process under high stress conditions and the traditional coupling between the bending element and the coarse-grained soil A test device, system and test method for measuring the shear wave velocity of coarse-grained soil with defects such as poor degree and inability to realize the shear wave velocity measurement of large-scale triaxial coarse-grained soil samples.

The technical scheme adopted by the present invention to solve the problems of the prior art: a test device for measuring the shear wave velocity of coarse-grained soil, including a shell, a friction unit, a piezoelectric stack, and an acceleration sensor; the shell is a shell with an open lower end, and the The longitudinal section of the friction unit is "T" shape, the horizontal end of the "T" shape is fixed on the top of the shell, and the vertical end of the "T" shape is inserted into the shell from the top of the shell and connected to the "T" vertical end of the friction unit. An acceleration sensor and a piezoelectric stack are fixed on the top, and the piezoelectric stack is fixedly connected to the inner wall of the casing; the friction unit is provided with a concave-convex grid-shaped friction surface on the upper surface of the "T"-shaped horizontal end.

There is a groove on the top of the housing, and the "T"-shaped horizontal end of the friction unit is placed in the groove, and there are parallel brackets between the groove and the lower surface of the "T"-shaped horizontal end of the friction unit. Cylindrical guide rail; the gap between the friction unit and the groove is provided with an O-ring and a silicone layer for sealing connection.

A test system for measuring the shear wave velocity of coarse-grained soil, including two test devices for measuring the shear wave velocity of coarse-grained soil: as the excitation end and the receiving end respectively; the test system also includes a signal generator and a power amplifier connected in sequence and an oscilloscope; at the same time, the power amplifier is connected to the piezoelectric stack at the excitation end; the acceleration sensor at the excitation end, the piezoelectric stack at the receiving end, and the acceleration sensor at the receiving end are respectively connected to the oscilloscope through the charge amplifier.

A test method for a test system for measuring shear wave velocity of coarse-grained soil, comprising the steps of:

S1. System installation and verification: First, insert the excitation end and the receiving end in the test system into the base and the top cap of the triaxial tester respectively, and make the upper end surface of the "T"-shaped horizontal end of the excitation end and the receiving end Set up oppositely, install a ring-shaped water-permeable plate at the base and the top cap, and seal rings are provided between the ring-shaped water-permeable plate and the shells of the excitation end and the receiving end; then check: the triaxial pressure chamber is filled with water, And start the signal generator to generate the excitation signal to ensure that there is no shear wave signal at the receiving end on the oscilloscope;

S2. Determining the system delay: prepare a saturated coarse-grained soil sample in a triaxial tester, and make the upper and lower end faces of the coarse-grained soil sample closely fit with the end faces of the friction unit at the receiving end and the excitation end respectively; Carry out conventional consolidation tests on coarse-grained soil samples, and determine the corresponding system delay Δ t _s by applying different confining pressures to coarse-grained soil samples;

S3. Perform a shear wave velocity test: when the coarse-grained soil sample is consolidated and stabilized under the current confining pressure, start the signal generator to generate an excitation signal. After the excitation signal passes through the power amplifier, it passes through the first propagation line and the second propagation line Respectively reach the oscilloscope and display the propagation time on the oscilloscope; the first propagation line is that the excitation signal directly reaches the oscilloscope after passing through the power amplifier, and the second propagation line is that the excitation signal passes through the power amplifier and then passes through the excitation terminal, the coarse-grained soil sample, and the receiver. After reaching the oscilloscope at the end and the charge amplifier, the time difference between the first propagation line and the second propagation line to reach the oscilloscope is the actual measurement time difference Δt _r of the signal; the real-time monitoring data of the acceleration sensor in the excitation end and the receiving end are displayed on the oscilloscope;

S4. Calculation of shear wave velocity: According to the system delay Δ t _s obtained in steps S2 and S3 and the actual measurement time difference Δ t _r , the propagation time of the shear wave passing through the coarse-grained soil sample is obtained as Δ t = Δ t _r - Δ t _s , and then determine the shear wave velocity of the coarse-grained soil sample as L /Δ t , where L is the height of the coarse-grained soil sample.

The isobaric consolidation confining pressure applied in the conventional consolidation test ranges from 100 to 1000kPa; the confining pressure is applied in order from small to large.

The beneficial effect of the present invention is: test device of the present invention is by the shape design of friction unit to be " T " shape in longitudinal section, and fixed piezoelectric stack at " T " shape vertical end, the longitudinal vibration of piezoelectric stack is converted into Plane horizontal vibration realizes the shear vibration excitation of the end plane of the coarse-grained soil triaxial sample, and solves the difficult problem of piezoelectric materials being easily damaged during the compaction of large-scale triaxial test samples and loading under high stress conditions and the traditional The coupling degree between the bending element and the coarse-grained soil is poor, and it is difficult to measure the shear wave velocity of the large-scale triaxial coarse-grained soil sample; the vibration behavior of the friction element is monitored in real time through the acceleration sensor fixed at the vertical end of the "T", It is helpful to study the dynamic response of the whole system of excitation end-coarse-grained soil sample-receiving end. The test system of the invention has reasonable structural layout, simple assembly and convenient test operation. The test method of the invention has strong operability and good popularization value.

Description of drawings

Fig. 1 is a schematic structural view of the test device of the present invention.

Fig. 2 is a schematic diagram of the structural connection of the test system of the present invention during the test.

Fig. 3 is a schematic diagram of the connection structure between the test device of the present invention and the triaxial tester.

In the figure: 1-shell, 2-friction unit, 3-piezoelectric stack, 4-acceleration sensor, 5-cylindrical guide rail, 6-O-ring, 7-silicone layer, 8-excitation end, 9-reception end, 10-signal generator, 11-power amplifier, 12-charge amplifier, 13-oscilloscope, 14-coarse-grained soil sample, 15-triaxial tester, 16-triaxial tester base, 17-triaxial tester top Cap, 18-permeable plate, 19-sealing ring, 20-triaxial pressure chamber.

Detailed ways

The present invention is described below in conjunction with accompanying drawing and specific embodiment:

Fig. 1 is a structural schematic diagram of a test device for measuring shear wave velocity of coarse-grained soil according to the present invention. A test device for measuring the shear wave velocity of coarse-grained soil, including a casing 1, a friction unit 2, a piezoelectric stack 3 and an acceleration sensor 4; the casing 1 is a shell with an open lower end, and the longitudinal section of the friction unit 2 is "T" shaped The horizontal end of the "T" shape is fixed on the top of the shell 1, and the vertical end of the "T" shape is inserted into the shell 1 from the top of the shell 1. Specifically, a groove is formed on the top of the housing 1, and the "T"-shaped horizontal end of the friction unit 2 is placed in the groove, and a The parallel cylindrical guide rails 5 (preferably set six), the setting of the cylindrical guide rails 5 is to provide support for the friction unit 2; the second is to reduce the resistance of the friction unit 2 to produce a small horizontal movement during the test. In order to ensure the integrity and tightness of the friction unit 2 and the groove, the gap between the friction unit 2 and the groove is sealed with an O-ring 6 , and the remaining gaps are filled with a silicone layer 7 with a certain amount of deformation for waterproof sealing. The "T"-shaped vertical end of the friction unit 2 inserted into the housing 1 is fixed with an acceleration sensor 4 and a piezoelectric stack 3 with epoxy resin, and the piezoelectric stack 3 is fixedly connected to the inner side wall of the housing 1; the friction unit 2 is in The upper surface of the "T"-shaped horizontal end is provided with a concave-convex grid-shaped friction surface to increase the bite ability of the friction unit 2 and the soil.

Figure 2 shows the test system using the test device for measuring the shear wave velocity of coarse-grained soil. Two test devices for measuring the shear wave velocity of coarse-grained soil are used as the excitation end 8 and the receiving end 9 respectively; the test system also includes sequentially Connected signal generator 10, power amplifier 11 and oscilloscope 13; at the same time, power amplifier 11 is connected with the piezoelectric stack 3 of the excitation end 8, the acceleration sensor 4 of the excitation end 8, the piezoelectric stack 3 of the receiving end 9 and the receiving end 9 The acceleration sensors 4 are connected to the oscilloscope 13 through the charge amplifier 12 respectively.

The working principle of the test system of the present invention is as follows: after the signal generator 10 is started, a voltage pulse of a certain frequency is sent as an excitation signal, and the excitation signal is amplified by the power amplifier 11 and then input to the piezoelectric stack 3 in the excitation terminal 8; The piezoelectric stack 3 generates longitudinal vibration, and then the friction unit 2 converts the longitudinal vibration into plane horizontal vibration, realizing the shear vibration excitation of the end plane of the coarse-grained soil sample 14, generating shear waves, and simultaneously exciting the acceleration in the end 8 The sensor 4 monitors the vibration of the friction unit 2 in the excitation end 8 in real time. The piezoelectric stack 3 in the receiving end 9 converts the shear wave transmitted through the coarse-grained soil sample 14 into an electrical signal, which is displayed and stored on the oscilloscope 13 after passing through the charge amplifier 12, so that the excitation signal can be obtained after the coarse-grained soil sample 14 passes through. Comparison data of granular soil sample 14 before and after. At the same time, the vibration behavior of the friction unit 2 in the receiving end 9 is also collected by the acceleration sensor 4 in the receiving end 9, and displayed on the oscilloscope 13 in real time after passing through the charge amplifier 12, so as to provide real-time monitoring of the vibration of the receiving end 9.

A test method for a test system for measuring shear wave velocity of coarse-grained soil, comprising the steps of:

S1. System installation and verification: As shown in Figure 2 and Figure 3, the excitation end 8 and the receiving end 9 in the test system are respectively embedded in the base 16 and the top cap 17 of the triaxial tester 15 and the excitation end 8 Set opposite to the upper end surface of the "T"-shaped horizontal end of the receiving end 9, the base 16 and the top cap 17 are installed with an annular permeable plate 18, and the annular permeable plate 18 is connected to the casing 1 of the excitation end 8 and the receiving end 9. A sealing ring 19 is provided. Then check: fill the triaxial pressure chamber 20 with water, and start the signal generator to send excitation signals with frequencies of 1kHz, 5kHz and 10kHz respectively. Since water cannot withstand the shear stress, there should be no shear wave signal from the receiving end 9 on the oscilloscope 13. If there is, check whether the shear wave propagates through the metal structure around the triaxial tester 15, and finally ensure that the oscilloscope 13 There is no shear wave signal of receiving end 9 on 13.

S2. Determining the delay time of the system: Prepare a saturated coarse-grained soil sample 14 according to the conventional test method in the "Soil Engineering Test Regulations" (SL237-1999). The upper and lower ends of the coarse-grained soil sample 14 are connected to the excitation end 8 and the receiving end The top surface of the friction unit 2 in the end 9 is closely attached, and the conventional consolidation test is carried out on the coarse-grained soil sample 14 in the triaxial tester 15. By applying different confining pressures to the coarse-grained soil sample 14, the corresponding System delay Δ t _s . Among them, the preferred range of isobaric consolidation confining pressure is 100-1000kPa, and the confining pressure is applied sequentially from small to large. After the consolidation is stable under a certain confining pressure, the shear wave velocity test is carried out, and then the next level of confining pressure is consolidated. , and so on.

S3. Perform shear wave velocity test: when the coarse-grained soil sample 14 is consolidated and stabilized under the current confining pressure, start the signal generator 10 to generate an excitation signal. After the excitation signal passes through the power amplifier 11, it passes through the first propagation line and the second transmission line. The two propagation lines arrive at the oscilloscope 13 respectively and display the propagation time on the oscilloscope 13, wherein the first propagation line is that the excitation signal passes through the power amplifier 11 and then directly reaches the oscilloscope 13, and the second propagation line is that the excitation signal passes through the power amplifier 11 and then passes through the excitation terminal 8. After the coarse-grained soil sample 14, the receiving end 9 and the charge amplifier 12 arrive at the oscilloscope 13, the time difference between the first propagation line and the second propagation line arriving at the oscilloscope 13 is the actual measurement time difference Δt _r of the signal; in addition, the oscilloscope 13 Simultaneously display the real-time monitoring data of the acceleration sensor 4 in order to monitor the vibration behavior of the friction unit 2 during the interaction process with the coarse-grained soil sample 14 .

S4. Calculation of shear wave velocity: According to the system delay Δ t _s obtained in steps S2 and S3 and the actual measurement time difference Δ t _r , the propagation time of the shear wave through the coarse-grained soil sample is obtained as Δ t = Δ t _r - Δ t _s , and then determine the shear wave velocity of the coarse-grained soil sample as L /Δ t , where L is the height of the coarse-grained soil sample.

The above content is a further detailed description of the present invention in combination with specific preferred technical solutions, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deduction or replacement can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (5)

1. a kind of experimental rig measuring coarse-grained soil shear wave velocity, which is characterized in that including shell, friction element, piezo electric stack And acceleration transducer；The shell is the shell that lower end opens, and the vertical section of the friction element is "T"-shaped, " T " shaped water Flush end is fixed on the top of shell, and " T " shaped vertical end is inserted into shell by the top of shell and is hung down in the "T"-shaped of friction element Acceleration transducer and piezo electric stack are fixed in straight end, while piezo electric stack is fixedly connected with the madial wall of shell；Friction is single Member is equipped with concave-convex clathrate rubbing surface in the upper surface of "T"-shaped horizontal ends.

2. a kind of experimental rig measuring coarse-grained soil shear wave velocity according to claim 1, which is characterized in that the shell Top be provided with groove, the "T"-shaped horizontal ends of the friction element are placed in the groove, in the "T"-shaped of groove and friction element The cylindrical slideway being mutually parallel is equipped between horizontal ends lower face；O-ring and silicon are equipped at the gap of friction element and groove Glue-line is tightly connected.

3. a kind of pilot system measuring coarse-grained soil shear wave velocity, which is characterized in that including two measurement coarse-grained soil shear wave velocities Experimental rig：Respectively as excitation end and receiving terminal；The pilot system further includes sequentially connected signal generator, power Amplifier and oscillograph；Meanwhile power amplifier is connect with the piezo electric stack at excitation end；It excites the acceleration transducer at end, connect The piezo electric stack of receiving end and the acceleration transducer of receiving terminal are connected by charge amplifier with oscillograph respectively.

4. a kind of test method of pilot system measuring coarse-grained soil shear wave velocity according to claim 3, feature exist In including the following steps：

S1, system installation and check：First by the pilot system excitation end and receiving terminal be respectively embedded into triaxial tester Among pedestal and top cap and the upper surface of the " T " shaped horizontal ends of excitation end and receiving terminal is made to be oppositely arranged, in pedestal and top cap The cyclic annular porous disc of place's installation, sealing ring is equipped between the ring-type porous disc and excitation end and the shell of receiving terminal；Then into Row is checked：Lead to full water in triaxial pressure room, and enabling signal generator generates excitation signal, it is ensured that without receiving terminal on oscillograph Shearing wave signal；

S2, system delay is determined：The coarse-grained soil specimen of saturation is prepared in triaxial tester, and makes the upper and lower of coarse-grained soil specimen End face of the both ends of the surface respectively with receiving terminal and the friction element at excitation end fits closely；Conventional consolidation examination is carried out to coarse-grained soil specimen It tests, by applying different confining pressures to coarse-grained soil specimen, determines corresponding system delay Δt _s ；

S3, shear wave velocity measurement is carried out：After coarse-grained soil specimen stabilization by consolidation under current confining pressure, enabling signal generator generates Excitation signal, the excitation signal arrive separately at oscillography after power amplifier, through the first propagation circuit and the second propagation circuit Device simultaneously shows the propagation time on oscillograph;The first propagation circuit is that excitation signal after power amplifier directly show by arrival Wave device, the second propagation circuit are that excitation signal is put after power amplifier through excitation end, coarse-grained soil specimen, receiving terminal and charge Oscillograph is reached after big device, the time difference that circuit and the second propagation circuit arrival oscillograph are propagated through first is the practical survey of signal Measure time difference Δt _r ；The Real-time Monitoring Data of acceleration transducer in excitation end and receiving terminal is shown in oscillograph；

S4, shear wave velocity calculate：The system delay Δ obtained according to step S2 and S3t _s Time difference Δ is measured with practicalt _r , cut It is Δ that wave, which is cut, by the propagation time of coarse-grained soil speciment=Δt _r -Δt _s , and then determine that the shear wave velocity of coarse-grained soil specimen isL/Δt, whereinLFor the height of coarse-grained soil specimen.

5. a kind of test method of pilot system measuring coarse-grained soil shear wave velocity according to claim 4, feature exist In isotonic consolidation confining pressure ranging from 100~1000kPa applied in routine consolidation test；Apply confining pressure successively from small to large.