Test device and method for multi-frequency resistivity testing during sand liquefaction

Abstract

The invention provides a test device and method for multi-frequency resistivity testing in a sand liquefaction process, belonging to the technical field of resistivity testing. The sand liquefaction process requires a vibration table, the vibration table is provided with a pedestal for generating vibration, a liquefaction generating tank is fixedly provided on the pedestal, the liquefaction generating tank is filled with sand, test electrodes are inserted into the sand at intervals, and the test electrodes are electrically connected to a test system. The invention aims at the problem of the test device for multi-frequency resistivity testing, establishes the relationship between sand liquefaction parameters and resistivity parameters, realizes dynamic sand resistivity testing, and uses dynamic resistivity parameters to characterize the sand liquefaction process, which has the advantages of being fast, real-time and dynamic.

Description

Technical Field

[0001] The invention relates to the technical field of resistivity testing, and in particular to a test device and method for multi-frequency resistivity testing in a sand liquefaction process. Background Art

[0002] Sand liquefaction is a phenomenon in which the pore water pressure of saturated sand increases after being vibrated, and the effective stress in the soil decreases until it disappears, causing the sand particles to suspend in the water and form a liquid state. Sand liquefaction is one of the main causes of uneven settlement during earthquakes, leading to surface cracks in the earthquake zone, sand gushing from the land, and foundation deformation. Therefore, the evaluation of sand liquefaction is a major indicator of earthquake resistance and disaster prevention.

[0003] Sand liquefaction is not only affected by relative density, but also by factors such as the directional arrangement of the particle structure, gradation, and in-situ stress state. In conventional tests, there is no direct and effective way to achieve rapid and real-time monitoring of the changes in various physical properties during the liquefaction process, making it difficult to effectively evaluate sand liquefaction.

[0004] The paper "Research on the Test Method of Saturated Sand Resistivity" proposes to conduct research on the quantitative determination method of saturated sand resistivity based on the law of porosity change during sand liquefaction. The paper proposes to measure the resistivity of saturated sand by four-electrode method or two-electrode method; but the paper does not give the specific structure of the test device. The paper uses a DC power supply for measurement, and uses electrode type, controlled electrode spacing, electrode penetration depth and voltage as variables to measure resistivity. It does not use different current frequencies as variables during sand liquefaction to dynamically measure resistivity.

[0005] Application Contents

[0006] The purpose of the present invention is to provide a test device and method for multi-frequency resistivity testing in the process of sand liquefaction, which aims at the problem of the test device for multi-frequency resistivity testing, establishes the relationship between sand liquefaction parameters and resistivity parameters, and realizes the characterization of sand liquefaction process by resistivity. The embodiment of the present invention is achieved through the following technical solutions:

[0007] A test device and method for multi-frequency resistivity testing during sand liquefaction, a test device for multi-frequency resistivity testing during sand liquefaction, the sand liquefaction process requires a vibration table, the vibration table is provided with a base for vibration, characterized in that: a liquefaction tank is fixedly provided on the base, the liquefaction tank is filled with sand, test electrodes are inserted into the sand at intervals, and the test electrodes are electrically connected to the test system.

[0008] Furthermore, the liquefaction tank includes a sand tank and a porous sponge fixed to the bottom and inner wall of the sand tank; the sand is filled between the porous sponges.

[0009] Furthermore, the test system includes a data collection and control system, a variable frequency tester and an electrode conversion box which are connected in series in sequence, and the electrode conversion box is connected to the test electrode.

[0010] Furthermore, the test electrode includes a pair of rigid electrodes and several groups of flexible electrodes, the rigid electrodes are tightly attached to the inner wall of the sponge and hinged to the bottom of the sand trough, and the flexible electrodes are evenly inserted into the sand and are mirror-symmetrical about the center plane of the sand trough; a limiting device is provided on the sand trough, the top end of the flexible electrode is inserted into the limiting device, and the bottom end of the flexible electrode is slidably connected to the bottom of the sand trough; the pair of rigid electrodes are respectively electrically connected to the A connector of the electrode conversion box, and the several groups of flexible electrodes are respectively electrically connected to the V connector of the electrode conversion box.

[0011] Furthermore, a gradient grid is fixedly connected to the inner side of the rigid electrode, and the grid density of the gradient grid increases as it is closer to the rigid electrode.

[0012] Furthermore, the flexible electrode is in a narrow strip shape, and the flexible electrode is flexible in the vibration direction.

[0013] Furthermore, a displacement meter, an accelerometer and a pore water pressure meter are arranged on the flexible electrode, and the displacement meter, the accelerometer and the pore water pressure meter are all connected to a data collection and control system.

[0014] Furthermore, a waveform generator is connected in series between the data collection and control system and the vibration table.

[0015] A test method for multi-frequency resistivity testing during sand liquefaction, using the test device for multi-frequency resistivity testing during sand liquefaction, comprises the following steps:

[0016] S1: Assemble the complete test device and evenly spread the sand in the liquefaction tank. In this step, it is necessary to ensure that the rigid electrode and the flexible electrode remain vertical;

[0017] S2: After completing S1, pour tap water from the top of the porous sponge until the sand is saturated;

[0018] S3: After completing S2, adjust the limit device to allow a certain amount of movement clearance around the flexible electrode, start the test system, check the values ​​displayed on the data collection and control system by the displacement meter, accelerometer and pore water pressure meter, and record the data;

[0019] S4: After completing S3, start the entire test device, set the vibration waveform of the vibration table through the data collection and control system, and the data collection and control system records the electrical parameters during the entire process of sand liquefaction through the electrode conversion box; at the same time, the current frequency can be quickly changed through the frequency conversion tester, and the data collection and control system collects the data of the displacement meter, accelerometer and pore water pressure meter; this step is carried out until the sand liquefaction is completed;

[0020] S5: After the sand liquefaction is completed, the vibration is stopped and the test data are saved.

[0021] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0022] 1. The ingenious arrangement of the test electrodes in the present invention greatly reduces the disturbance of the test electrodes during the vibration process and improves the stability of the dynamic test resistivity;

[0023] 2. The electrodes of the present invention are flexible in the vibration direction, which can not only test the voltage of the corresponding parts, but also reflect the displacement of the sand during the vibration process;

[0024] 3. The present invention utilizes a test system to collect test data and a control device, and controls the vibration frequency during the sand liquefaction process, thereby achieving real-time testing of the resistivity of sand liquefaction under different vibration conditions;

[0025] 4. The electrode conversion box used in the present invention can realize the conversion of the test electrode circuit, thereby improving the test efficiency;

[0026] 5. The present invention adopts an AC power supply, which is combined with a frequency conversion tester to generate AC currents of different frequencies, and realizes the test of AC resistivity under multiple frequencies. The AC resistivity is sensitive to changes in factors such as the porosity, particle size, and grading of sand. When the sand liquefies, the porosity ratio therein will change, and the internal structure will also be reconstructed, thereby facilitating the construction of the changing law of multi-frequency AC resistivity parameters during the sand liquefaction process, and realizing the characterization of the sand liquefaction process by resistivity, which has the advantages of being fast, real-time, and dynamic.

[0027] 6. The present invention uses a porous sponge to reduce the impact of vibration on the test device, and tap water is poured into the porous sponge from bottom to top, so as to achieve the purpose of not washing the sand;

[0028] 7. The design of the gradient grid in the present invention can effectively ensure the contact between the sand and the rigid electrode, thus ensuring the stability of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 It is a front view structural schematic diagram of the present invention;

[0031] Figure 2 It is a schematic diagram of the top view structure of the present invention;

[0032] Figure 3 Schematic diagram of providing current to the rigid electrode and test voltage to the flexible electrode in the present invention;

[0033] Icons: 1-waveform generator; 2-data collection and control system; 3-frequency tester; 4-electrode conversion box; 5-gradient grid; 6-rigid electrode; 7-porous sponge; 8-sand trough; 9-pedestal; 10-vibration table; 11-flexible electrode; 12-displacement meter; 13-accelerometer; 14-pore water pressure meter; 15-limit device; 151-longitudinal limit; 152-lateral limit; 16-sand. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0035] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed but is merely representative of selected embodiments of the present invention.

[0036] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. In the description of the present invention, it should be noted that if the terms "center", "upper", "lower", "left", "right", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the product of the application is usually placed when in use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0037] Please refer to Figure 1 and Figure 2 , a test device for multi-frequency resistivity testing during the liquefaction process of sand 16, the sand liquefaction process requires a vibration table 10, the vibration table 10 is provided with a base 9 for vibration, the excitation direction of the base 9 is horizontal, the vibration table 10 belongs to the conventional technology in the field, and no further elaboration is made here; a liquefaction generating tank is fixedly provided on the base 9, the liquefaction generating tank is filled with sand 16, test electrodes are inserted into the sand 16 at intervals, and the test electrodes are electrically connected to the test system.

[0038] In this embodiment, the liquefaction tank includes a sand tank 8 and a porous sponge fixed to the bottom and inner wall of the sand tank 8; the sand tank 8 includes a transverse and longitudinal direction. In this embodiment, the porous sponge 7 is fixed to the parallel ends and the bottom of the transverse direction, and the sponges at the two ends of the transverse direction are connected to the sponge at the bottom to facilitate the filling of tap water; the sand 16 is filled between the porous sponges 7; the porous sponge 7 can contain a large amount of water and the sand 16 will not enter the interior of the porous sponge 7. The porous sponge 7 can play a buffering role, and the sponge at the bottom also provides friction for the sand 16, thereby ensuring that the sand 16 is vibrated evenly and stably.

[0039] In this embodiment, the sand tank 8 is made of transparent material, so that the liquefaction process can be observed in detail, and data and phenomena can also be recorded by using a camera or video device.

[0040] In this embodiment, the test system includes a data collection and control system 2, a variable frequency tester 3 and an electrode conversion box 4 connected in series in sequence, and the electrode conversion box 4 is connected to the test electrode; wherein the data collection and control system 2 can collect real-time data during the test and control the vibration frequency of the vibration table 10; the test device described in this embodiment uses alternating current, the variable frequency tester 3 can generate different alternating currents, and the voltage of the corresponding electrode is tested through the electrode conversion box 4, thereby realizing the test of AC resistivity under multiple frequencies.

[0041] In this embodiment, the test electrode includes a pair of rigid electrodes 6 and two groups of flexible electrodes 11; the two rigid electrodes 6 are tightly attached to the inner wall of the sponge and hinged to the bottom of the sand trough 8; there are three electrodes in each group of flexible electrodes 11, and each group of flexible electrodes 11 is evenly inserted into the sand 16 and is mirror-symmetrical about the horizontal center plane of the sand trough 8. The three electrodes in each group of flexible electrodes 11 are evenly arranged along the longitudinal direction of the sand trough 8, which is conducive to multi-data collection.

[0042] In this embodiment, the rigid electrode 6 is a rigid copper plate, which covers both lateral ends of the liquefaction generating tank to provide a stable current; the flexible electrode 11 is a flexible copper strip, which is a narrow strip. Figure 2As shown, the flexible copper strip is flexible in the vibration direction, that is, in this embodiment, the flexible copper strip is flexible in the left-right direction but not in the front-back direction, thereby reflecting the dynamic displacement of the sand in real time.

[0043] In this embodiment, two groups of limit devices 15 are provided on the sand trough 8, one group of limit devices 15 is used for a group of flexible electrodes 11; the limit device 15 includes a transverse limit 152 and a longitudinal limit 151, the longitudinal limit 151 is overlapped on the side plate of the sand trough 8 in the longitudinal direction, and the transverse limit 152 is built on the longitudinal limit 151 in the transverse direction; the top end of the flexible electrode 11 is clamped between the transverse limit 152 and the longitudinal limit 151, and the bottom end of the flexible electrode 11 is slidably connected to the bottom of the sand trough 8;

[0044] In this embodiment, the principle diagram of the rigid electrode 6 providing current and the flexible electrode 11 testing voltage is as follows Figure 3 As shown, the rigid electrodes 6 are electrically connected to the A connectors of the electrode conversion box 4, respectively, and the rigid electrodes 6 provide a stable current; the flexible electrodes 11 are electrically connected to the V connectors of the electrode conversion box 4, respectively, and the flexible electrodes 11 test the voltage.

[0045] In this embodiment, a gradient grid 5 is fixedly connected to the inner side of the rigid electrode 6, and the grid density of the gradient grid 5 increases as it is closer to the rigid electrode 6; the gradient grid 5 is made of plastic material and is gradually distributed, so that when the sand 16 is vibrated, the closer it is to the rigid electrode 6, the more stable it is, and the less likely it is to liquefy, thereby ensuring the contact between the sand 16 and the rigid copper plate electrode.

[0046] In this embodiment, a displacement meter 12, an accelerometer 13 and a pore water pressure meter 14 are provided on the flexible electrode 11, and the displacement meter 12, the accelerometer 13 and the pore water pressure meter 14 are all connected to the data collection and control system. In this embodiment, the displacement meter 12, the accelerometer 13 and the pore water pressure meter 14 are distributed from top to bottom, which is convenient for real-time data transmission, and the displacement, acceleration and pore water pressure of each position are comprehensively obtained. The three pairs of data are averaged to improve the accuracy of the resistivity test.

[0047] A waveform generator 1 is connected in series between the data collection and control system and the vibration table 10. The waveform generator 1 continuously transmits vibration waves to the vibration table 10, so that the entire liquefaction tank generates lateral vibrations of different vibration conditions.

[0048] A test method for multi-frequency resistivity testing during the liquefaction of sand and soil 16, using the test device for multi-frequency resistivity testing during the liquefaction of sand and soil 16, comprises the following steps:

[0049] S1: Fix the transparent sand tank 8 on the vibration table 10, arrange the porous sponge 7, rigid electrode 6 and gradient grid 5 and other devices, arrange and connect the displacement meter 12, accelerometer 13 and pore water pressure meter on the flexible electrode 11, and connect the rigid electrode 6, flexible electrode 11, electrode conversion box 4, frequency conversion tester 3, data collection and control system 2, waveform generator 1 and vibration table 10; evenly spread the sand 16 in the liquefaction tank. In this step, it is necessary to ensure that the rigid electrode 6 and the flexible electrode 11 remain vertical;

[0050] S2: After completing S1, pour tap water from the top of the porous sponges 7 at both ends, and the tap water flows from the porous sponges 7 at both ends to the porous sponges 7 at the bottom, and then intrudes into the sand 16 until the sand 16 is saturated;

[0051] S3: After completing S2, adjust the limit device 15 so that there is a certain movement gap around the flexible electrode 11, start the test system, check the values ​​displayed by the displacement meter 12, the accelerometer 13 and the pore water pressure meter 14 on the data collection and control system 2, and record the data;

[0052] S4: After completing S3, start the entire test device, set the vibration waveform of the vibration table 10 through the data collection and control system 2, and record the electrical parameters of the sand 16 during the entire liquefaction process through the electrode conversion box 4; at the same time, the current frequency can be quickly changed through the frequency conversion tester 3, and the data collection and control system collects the data of the displacement meter 12, the accelerometer 13 and the pore water pressure meter 14, and can record the displacement of the upper and lower ends of the flexible electrode 11, which is recorded as l i上 , l i下 (where i represents one, two, or three flexible electrodes 11 in each group of flexible electrodes 11); this step is continued until the sand 16 is completely liquefied;

[0053] S5: After the sand 16 is liquefied, the vibration is stopped and the test data are saved.

[0054] S6: The resistivity data at each frequency is given by the formula:

[0055] Where S is the area of ​​the rigid electrode 6.

[0056] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A test device for multi-frequency resistivity testing in a sand liquefaction process, wherein the sand liquefaction process requires a vibration table (10), and a base (9) for generating vibration is provided on the vibration table (10), characterized in that: A liquefaction generating tank is fixedly arranged on the pedestal (9), the liquefaction generating tank is filled with sand (16), test electrodes are inserted into the sand (16) at intervals, and the test electrodes are electrically connected to the test system; The liquefaction generating tank comprises a sand tank (8) and a porous sponge fixed to the bottom and inner wall of the sand tank (8); the sand (16) is filled between the porous sponges (7); The test system comprises a data collection and control system (2), a frequency conversion tester (3) and an electrode conversion box (4) which are connected in series in sequence, and the electrode conversion box (4) is connected to the test electrode; The test electrode comprises a pair of rigid electrodes (6) and a plurality of groups of flexible electrodes (11); the rigid electrodes (6) are closely attached to the inner wall of the sponge and are hinged to the sand trough (8); the flexible electrodes (11) are uniformly inserted into the sand (16) and are mirror-symmetrical about the center plane of the sand trough (8); a limiting device (15) is provided on the sand trough (8); the top end of the flexible electrode (11) is inserted into the limiting device (15), and the bottom end of the flexible electrode (11) is slidably connected to the bottom of the sand trough (8); the pair of rigid electrodes (6) are respectively electrically connected to the A connector of the electrode conversion box (4), and the plurality of groups of flexible electrodes (11) are respectively electrically connected to the V connector of the electrode conversion box (4); A gradient grid (5) is fixedly connected to the inner side of the rigid electrode (6), and the grid density of the gradient grid (5) increases as it is closer to the rigid electrode (6); The flexible electrode (11) is in a narrow strip shape, and the flexible electrode (11) is flexible in the vibration direction.

2. The test device for multi-frequency resistivity testing during sand liquefaction according to claim 1, characterized in that: The flexible electrode (11) is provided with a displacement meter (12), an accelerometer (13) and a pore water pressure meter (14), and the displacement meter (12), the accelerometer (13) and the pore water pressure meter (14) are all connected to a data collection and control system.

3. The test device for multi-frequency resistivity testing during sand liquefaction according to claim 1, characterized in that: A waveform generator (1) is connected in series between the data collection and control system and the vibration table (10).

4. A method for testing multi-frequency resistivity during sand liquefaction, using the test device for multi-frequency resistivity during sand liquefaction according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: Assemble the complete test device and evenly spread the sand (16) in the liquefaction tank. In this step, it is necessary to ensure that the rigid electrode (6) and the flexible electrode (11) remain vertical; S2: After completing S1, pour tap water into the top of the porous sponge (7) until the sand (16) is saturated; S3: After completing S2, adjust the limit device (15) so that there is a certain movement gap around the flexible electrode (11), start the test system, check the values ​​displayed by the displacement meter (12), accelerometer (13) and pore water pressure meter (14) on the data collection and control system (2), and record the data; S4: After completing S3, the entire test device is started, and the vibration waveform of the vibration table (10) is set through the data collection and control system (2). The data collection and control system records the electrical parameters of the sand (16) during the entire liquefaction process through the electrode conversion box (4); at the same time, the current frequency is quickly changed through the frequency conversion tester (3), and the data collection and control system collects data from the displacement meter (12), the accelerometer (13) and the pore water pressure meter (14); this step is performed until the liquefaction of the sand (16) is completed; S5: After the sand (16) is liquefied, the vibration is stopped and the test data are saved.

Images