Sandy soil liquefaction characteristic test device and test method thereof

Abstract

The invention relates to the technical field of analysis methods of ground materials, and discloses a sand liquefaction characteristic test device and a test method thereof, the sand liquefaction characteristic test device comprises a vibration table, a box body, an inverted filter assembly, a detection assembly and an analysis assembly; the box body is connected with the vibration table, a water inlet and a water outlet are formed in the box body, a flow stabilizing chamber, an inverted filter layer and a sample layer for placing a saturated sand sample are sequentially arranged in the box body from bottom to top and are communicated, the water inlet is communicated with the flow stabilizing chamber, the water outlet is communicated with the top of the sample layer, and the inverted filter assembly is arranged in the inverted filter layer; the detection assembly comprises a first accelerometer and a pore water pressure gauge, and the detection assembly is electrically connected with the analysis assembly; water is injected into a saturated sand sample through a water inlet, underground water seepage and seepage failure are simulated, and then sand seismic liquefaction is simulated through a vibration table. According to the invention, seepage and seepage failure effects of an actual saturated sand stratum under the action of underground water can be considered, and the earthquake liquefaction phenomenon of sand can be simulated more truly.

Description

Technical Field

[0001] The invention relates to the technical field of ground material analysis methods, and in particular to a sand liquefaction characteristic test device and a test method thereof. Background Art

[0002] At present, earthquakes occur in a wide range of areas, and their occurrence cannot be effectively predicted in advance. When an earthquake occurs, strong ground movement will induce underground sand liquefaction, causing the ground to lose its bearing capacity, posing a great safety hazard to the buildings built above, and even further expanding the disaster. Sandy soil strata are widely distributed in my country, so studying the liquefaction characteristics of sandy soil strata plays an important role in earthquake resistance and disaster reduction.

[0003] Existing sand liquefaction characteristic test devices usually directly conduct vibration simulation tests on sand samples to collect relevant data, without considering the seepage effect of groundwater. In actual situations, groundwater often produces seepage and permeability damage inside saturated sand layers under the action of pressure difference, which may affect the seismic liquefaction of saturated sand layers. Therefore, it is of great practical significance to study the influence of seepage and permeability damage on sand liquefaction characteristics. Summary of the invention

[0004] The purpose of the present invention is to provide a sand liquefaction characteristic test device and a test method thereof, which can take into account the seepage and penetration damage effects of actual saturated sand layers under the action of groundwater, and more realistically simulate the sand earthquake liquefaction phenomenon.

[0005] In order to achieve the above-mentioned object, the present invention provides a sand liquefaction characteristic test device and a test method thereof, wherein the sand liquefaction characteristic test device comprises: a vibration table, a box, a filter assembly, a detection assembly and an analysis assembly;

[0006] The box is connected to the vibration table, and a water inlet and a water outlet are provided on the box. The box includes a steady flow chamber, a filter layer, and a sample layer for placing saturated sand samples, which are arranged and connected in sequence from bottom to top. The water inlet is connected to the steady flow chamber, and the water outlet is connected to the top of the sample layer. The filter assembly is arranged in the filter layer.

[0007] The detection component comprises a first accelerometer and a pore water pressure gauge buried inside the saturated sand sample, and the detection component is electrically connected to the analysis component.

[0008] Preferably, a partition is provided between the flow stabilization chamber and the reverse filter layer, and a connecting hole connecting the flow stabilization chamber and the reverse filter layer is provided on the partition.

[0009] Preferably, the reverse filter assembly comprises a reverse filter layer body and a first screen and a second screen respectively arranged on the upper and lower surfaces of the reverse filter layer body.

[0010] Furthermore, the filter layer body is made of round gravel.

[0011] Preferably, a second accelerometer is provided on the vibration table, and the second accelerometer is electrically connected to the analytical component.

[0012] Preferably, a plurality of water inlets are provided, and the plurality of water inlets are respectively connected to a water supply device, and each of the water inlets is connected to a one-way valve.

[0013] A testing method using the above-mentioned sand liquefaction characteristic testing device comprises the following steps:

[0014] S1. Preliminary test: Place the saturated sand sample above the filter layer, inject water at a certain pressure from the water inlet, and obtain a relationship table between the injected water pressure and the hydraulic gradient of the saturated sand sample;

[0015] S2. Calculate the hydraulic gradient i corresponding to the saturated sand sample under piping seepage failure and soil flow seepage failure. Ⅰ 、i Ⅱ ;

[0016] S3. Sand liquefaction characteristics test: multiple groups of simulation tests were conducted, each group of simulation tests was conducted according to the following steps:

[0017] A saturated sand sample is prepared above the filter layer, and a first accelerometer and a pore water pressure gauge are buried in the saturated sand sample, and a second accelerometer is fixedly installed on the table of the vibration table;

[0018] Control the water flow pressure to obtain a preset hydraulic gradient i, stop water injection after the stable seepage reaches a predetermined time, and then let it stand for a certain period of time; wherein the water flow pressure is obtained according to the relationship table and the preset hydraulic gradient i;

[0019] Start the shaking table and record the data measured by the pore water pressure meter, the first accelerometer and the second accelerometer;

[0020] S4. Analyze the influence of seepage and seepage damage on sand liquefaction characteristics based on the data measured by the pore water pressure meter, the first accelerometer and the second accelerometer in each group of simulation tests;

[0021] Among them, there are at least four groups of different model experiments. In each group of simulation experiments, the preset hydraulic gradients i are: i1 = 0, 0 < i2 < i Ⅰ , i3=i Ⅰ , i4=i Ⅱ .

[0022] Preferably, the step S1 comprises:

[0023] First, water is injected into the box, and sand is slowly put into the water to prepare a saturated sand sample. During the preparation process, a pore water pressure gauge is buried in the saturated sand sample;

[0024] Measure the mean value p1 of the pore water pressure gauge at the bottom of the prepared saturated sand sample, and calculate the pressure head h1=p1 / ρ at the bottom of the saturated sand sample w g, and the pressure head h2 measured at the top of the saturated sand sample;

[0025] Select the position head reference surface of the saturated sand sample, and record the position head of the bottom of the saturated sand sample as z1, and the position head of the top of the saturated sand sample as z2;

[0026] Inject water at a certain pressure into the saturated sand sample through the water inlet, and record the p1 and h1 values ​​when the water is injected;

[0027] Calculate the hydraulic gradient of the saturated sand sample i = [(z1+h1)-(z2+h2)] / L, where L is the height of the saturated sand sample, and L = z2-z1;

[0028] Thus, the corresponding relationship between the injected water pressure and the hydraulic gradient i of the saturated sand sample is obtained.

[0029] Preferably, the step S2 comprises:

[0030] Dry the sand sample and weigh the soil particle mass m of the sand sample. s , obtain the sand specific gravity G through indoor geotechnical test s and particle size distribution curve; select sand particle size values ​​d1 and d2 respectively, the weight of sand with particle size smaller than d1 in the sand sample accounts for 5% of the sand sample mass, and the weight of sand with particle size smaller than d2 accounts for 20% of the sand sample mass;

[0031] The density of the sand sample is calculated based on the mass and volume of the sand sample obtained by measurement, and the void ratio, porosity and effective weight of the sand sample are calculated based on the density of the sand sample;

[0032] Based on the above parameters, the hydraulic gradients corresponding to the piping seepage failure and soil flow seepage failure of the sand sample are calculated.

[0033] Preferably, the step S3 includes:

[0034] The water inlet and the water outlet are closed, and a second accelerometer is installed on the table of the vibration table;

[0035] Filling water into the box, slowly placing the sand sample into the water to prepare a saturated sand sample, burying the pore water pressure gauge and the first accelerometer at a predetermined position in the saturated sand sample during the preparation process, and opening the water outlet to discharge excess water after the preparation is completed;

[0036] At least four parallel test groups are set according to the parameters obtained in the preliminary test to adjust the injected water pressure. The first group closes the water inlet and does not seep; the second group opens the water inlet and injects water to provide water pressure that does not damage the saturated sand sample for seepage; the third group opens the water inlet and provides water pressure that causes pipe burst penetration damage to the saturated sand sample for seepage; the fourth group opens the water inlet and provides water pressure that causes flow soil penetration damage to the saturated sand sample for seepage;

[0037] After waiting for sufficient seepage in multiple test groups, water injection is stopped and the mixture is left to stand for a certain period of time. The vibration table is then started to liquefy the saturated sand sample. The parameters of the liquefaction process of the saturated sand sample are recorded by the pore water pressure gauge, the first accelerometer and the second accelerometer.

[0038] Compared with the prior art, the sand liquefaction characteristic test device and the test method thereof in the embodiment of the present invention have the following beneficial effects: by opening a water outlet and a water inlet on a box in which a saturated sand sample is placed, water can be continuously injected into the box to provide seepage conditions for the prepared saturated sand sample to simulate groundwater seepage and penetration damage; then the box and the saturated sand sample are driven to vibrate by a vibration table to simulate the sand liquefaction phenomenon during an earthquake, thereby studying the influence of seepage and penetration damage on the sand liquefaction characteristics, which is more in line with the actual situation that before the saturated sand stratum liquefies from an earthquake, groundwater produces excessive seepage and penetration damage in it. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a structural intuitive diagram of the sand liquefaction characteristic test device according to an embodiment of the present invention.

[0040] Figure 2 It is a schematic diagram of the internal structure of a box of a sand liquefaction characteristic testing device according to an embodiment of the present invention.

[0041] Figure 3 The sand liquefaction characteristic test device of the embodiment of the present invention is Figure 2 Enlarged view of point A in the middle.

[0042] In the figure, 1, vibration table; 2, box; 21, water inlet; 22, water outlet; 23, steady flow chamber; 24, filter layer; 25, sample layer; 26, partition; 27, one-way valve; 3, filter assembly; 31, filter layer body; 32, first screen; 33, second screen; 4, detection assembly; 41, first accelerometer; 42, pore water pressure gauge; 43, second accelerometer; 5, analysis assembly; 51, data acquisition instrument; 52, computer. DETAILED DESCRIPTION

[0043] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0044] In the description of the present invention, it should be understood that the terms "upper", "lower", "top", etc. used in the present invention to indicate orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying 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.

[0045] like Figure 1 , Figure 2 and Figure 3 As shown, a sand liquefaction characteristic test device and a test method thereof according to a preferred embodiment of the present invention, the sand liquefaction characteristic test device comprises: a vibration table 1, a box 2, a filter assembly 3, a detection assembly 4 and an analysis assembly 5;

[0046] The box body 2 is connected to the vibration table 1, and a water inlet 21 and a water outlet 22 are provided on the box body 2. The box body 2 includes a steady flow chamber 23, a filter layer 24 and a sample layer 25 for placing saturated sand samples, which are arranged and connected in sequence from bottom to top. The water inlet 21 is connected to the steady flow chamber 23, the water outlet 22 is connected to the top of the sample layer 25, and the filter assembly 3 is arranged in the filter layer 24;

[0047] The detection component 4 includes a first accelerometer 41 and a pore water pressure gauge 42 buried in the saturated sand sample. The detection component 4 is electrically connected to the analysis component 5 .

[0048] Specifically, the vibration table 1 of the sand liquefaction characteristic test device is placed on a supporting surface. The vibration table 1 is an electromagnetic vibration table. A table top for placing a box 2 is provided above the vibration table 1. The electromagnetic action inside the vibration table 1 drives the table top to vibrate. The box 2 is installed on the table top of the vibration table 1. The vibration table 1 drives the box 2 to vibrate so that the saturated sand sample inside the box 2 is vibrated and liquefied; the water inlet 21 is opened on the side of the box 2 near the bottom, and the water inlet 21 is connected to the steady flow chamber 23 located at the bottom of the box 2. The reverse filter layer 24 is a filter layer laid above the steady flow chamber 23. The sample layer 25 is a sand sample laid on the top of the filter layer 24; when water is injected into the box body 2 from the water inlet 21, the water in the box body 2 flows upward to the filter layer 24 and the sample layer 25, and the flow stabilization chamber 23 can consume the kinetic energy of the raw water to generate a water flow with stable pressure and flow rate; the filter layer 24 mainly plays a transitional role, further stabilizing the water flow and forming a laminar flow; the water outlet 22 is arranged on the side of the box body 2 near the top and is connected to the sample layer 25. During the continuous water injection process, excess water is discharged through the water outlet 22 to maintain the stability of the liquid level height at the top of the saturated sand sample.

[0049] During the test operation, the box 2 is installed on the table of the vibration table 1, a saturated sand sample is arranged above the filter layer 24, and the water inlet 21 is opened to inject water. The water flows into the saturated sand sample from the bottom of the saturated sand sample to simulate groundwater seepage. After the seepage is completed, it is left to stand for a certain period of time, and the vibration table 1 is started to drive the box 2 and the saturated sand sample to vibrate, and the parameters of the vibration test are measured and recorded through the detection component 4 and the analysis component 5.

[0050] The above-mentioned device and test method take into account the seepage and penetration damage effects of actual saturated sand strata under the action of groundwater, and can thus more realistically simulate the sand earthquake liquefaction phenomenon, thereby greatly improving the practicality and accuracy of the sand vibration liquefaction device.

[0051] Preferably, a partition plate 26 is provided between the flow stabilization chamber 23 and the filter layer 24 , and a connecting hole (not shown in the figure) for connecting the flow stabilization chamber 23 and the filter layer 24 is opened on the partition plate 26 .

[0052] Specifically, the stabilizing chamber 23 is arranged at the bottom of the box body 2 and is connected with the water inlet 21. The water flows into the stabilizing chamber 23 through the water inlet 21. The filter layer 24 is arranged above the stabilizing chamber 23. A partition plate 26 is provided between the stabilizing chamber 23 and the filter layer 24 to separate the stabilizing chamber 23 and the filter layer 24. A plurality of evenly distributed plum blossom-shaped connecting holes are provided on the partition plate 26. The water flows into the filter layer 24 through the connecting holes, thereby improving the effect of slowing down the flow velocity.

[0053] Preferably, the filter assembly 3 includes a filter layer body 31 and a first screen 32 and a second screen 33 respectively arranged on the upper and lower surfaces of the filter layer body 31 .

[0054] Specifically, the filter body 31 is made of particles whose particle size is larger than that of the sand sample particles and is insoluble in water. The particles of the filter body 31 are in close contact with each other, and water flows in the gaps between the particles of the filter body 31 to form a laminar flow. The second screen 33 is laid on the partition 26, and the filter body 31 is placed on the upper surface of the second screen 33. The sieve aperture on the second screen 33 can prevent the particles of the filter body 31 located above from falling downward into the steady flow chamber 23. and allow water to flow through; the first screen 32 is laid on the upper surface of the filter layer body 31, the first screen 32 separates the filter layer 24 from the sample layer 25, and the saturated sand sample is placed on the upper surface of the first screen 32. The first screen 32 uses a screen hole with a smaller aperture to ensure that water can pass through the first screen 32, and the particles of the saturated sand sample above the first screen 32 cannot pass through the first screen 32, preventing the particles of the saturated sand sample from falling into the filter layer body 31 and affecting the test effect.

[0055] Furthermore, the filter layer body 31 is made of gravel.

[0056] Specifically, the filter layer body 31 is stacked with larger round gravel to ensure that the particle size of the filter layer body 31 is larger than the particle size of the sand sample, which is convenient for separation using the first sieve 32. Preferably, the sieve hole diameter of the first sieve 32 is 0.075 mm, and the sieve hole diameter of the second sieve 33 is 2 mm, so as to achieve the purpose of separating the various areas in the box body 2.

[0057] Preferably, the detection component 4 further includes a second accelerometer 43 fixed on the vibration table 1 ; the second accelerometer 43 is electrically connected to the analysis component 5 .

[0058] Specifically, the pore water pressure gauge 42 and the first accelerometer 41 are evenly buried at the bottom and middle of the sand sample, such as Figure 2 As shown, the pore water pressure meter 42 and the first accelerometer 41 are arranged at the same position, and are used to measure various parameters of the saturated sand sample during the vibration test. A second accelerometer 43 is also arranged on the table of the vibration table 1, and is used to measure the output vibration parameters of the vibration table 1; the analysis component 5 includes a data acquisition instrument 51 and a computer 52. The pore water pressure meter 42, the first accelerometer 41 and the second accelerometer 43 send the parameters to the data acquisition instrument 51, and the computer 52 collects and calculates the parameters to obtain the required parameters.

[0059] Preferably, a plurality of water inlets 21 are provided, and the plurality of water inlets 21 are respectively connected to the water supply device, and each water inlet 21 is connected to a one-way valve 27 .

[0060] Specifically, a plurality of water inlets 21 are provided, and are connected to an external water supply device through a one-way valve 27. The external water supply device can provide water flows with different water pressures to form a plurality of test control groups, and the one-way valve 27 can prevent the water in the box 2 from flowing back to ensure that the water flow always seeps toward the saturated sand sample.

[0061] A testing method using the above-mentioned sand liquefaction characteristic testing device comprises the following steps:

[0062] S1. Preliminary test: a saturated sand sample is laid on the filter layer 24, and a water flow with a certain pressure is injected from the water inlet 21 to obtain a relationship table between the injected water flow pressure and the hydraulic gradient of the saturated sand sample;

[0063] S2. Calculate the hydraulic gradient i corresponding to the saturated sand sample under piping seepage failure and soil flow seepage failure. Ⅰ 、i Ⅱ ;

[0064] S3. Sand liquefaction characteristics test: multiple groups of simulation tests were conducted, each group of simulation tests was conducted according to the following steps:

[0065] A saturated sand sample is prepared above the filter layer 24, and a first accelerometer 41 and a pore water pressure gauge 42 are buried in the saturated sand sample, and a second accelerometer 43 is installed on the table of the vibration table 1;

[0066] Control the water flow pressure to obtain a preset hydraulic gradient i, stop water injection after the stable seepage reaches a predetermined time, and then let it stand for a certain period of time; wherein the water flow pressure is obtained according to the relationship table and the preset hydraulic gradient i;

[0067] Start the vibration table 1 and record the data measured by the pore water pressure meter 42, the first accelerometer 41 and the second accelerometer 43;

[0068] S4, based on the data measured by the pore water pressure meter 42, the first accelerometer 41 and the second accelerometer 43 in each group of simulation tests, comparative analysis of the effects of seepage and seepage damage on sand liquefaction characteristics;

[0069] Among them, there are at least four groups of different model experiments. In each group of simulation experiments, the preset hydraulic gradients i are: i1 = 0, 0 < i2 < i Ⅰ , i3=i Ⅰ , i4=i Ⅱ .

[0070] Specifically, S1: prepare a saturated sand sample in the box 2 and bury a pore water pressure gauge 42 and a first accelerometer 41 at a predetermined position, and inject water flows of different pressures into the box 2 from the water inlet 21 to generate seepage; determine the reference plane, collect and record the water pressure value at the bottom of the saturated sand sample through the pore water pressure gauge 42, convert the pressure head at the bottom, measure the pressure head at the top of the saturated sand sample, and determine the position head at the top and bottom of the saturated sand sample; calculate the hydraulic gradient when injecting water flows of different pressures into the box 2 from the water inlet 21, and obtain the corresponding relationship table between the water flow pressure and the hydraulic gradient;

[0071] S2: Dry the sand sample, weigh the sand particles, and then obtain the sand specific gravity and particle size distribution curve through indoor geotechnical tests. Calculate the density, void ratio, porosity and effective weight of the sand sample based on the measured physical parameters of the sand sample, and thus calculate the hydraulic gradient required for the sand sample when piping seepage failure and soil flow seepage failure occur;

[0072] After completing the above-mentioned tests of S1 and S2, steps S3 and S4 are performed in sequence; when testing the liquefaction characteristics of sand, the test is divided into four groups. The water flow pressure injected from the water inlet 21 is different in multiple groups of tests to adjust the hydraulic gradient of the saturated sand sample. The hydraulic gradient relationship of the four test groups is i1=0, 0<i2<i Ⅰ , i3=i Ⅰ , i4=i Ⅱ A saturated sand sample is prepared in the box 2 and a pore water pressure gauge 42 and a first accelerometer 41 are buried. Water with a predetermined water pressure is injected from the water inlet 21 to simulate sand seepage. After waiting for the seepage to be completed, the vibration table 1 is started to perform a simulated vibration test to vibrate and liquefy the saturated sand sample after the seepage. The pore water pressure curve and acceleration curve of the saturated sand sample are obtained by measuring the parameters of the pore water pressure gauge 42 and the first accelerometer 41 to study the influence of different seepage phenomena on the liquefaction characteristics of the sand. A second accelerometer 43 is installed on the table of the vibration table 1. According to the acceleration parameters measured by the second accelerometer 43, it can be judged whether the vibration output of the vibration table 1 of multiple test groups is the same, so as to avoid inaccurate test results due to the difference in vibration output of the vibration table 1.

[0073] Preferably, the step S1 comprises:

[0074] First, water is injected into the box 2, and sand is slowly put into the water to prepare a saturated sand sample. During the preparation process, a pore water pressure gauge 42 is buried in the saturated sand sample;

[0075] Measure the mean value p1 of the pore water pressure gauge 42 at the bottom of the prepared saturated sand sample, and calculate the pressure head h1 = p1 / ρ at the bottom of the saturated sand sample wg, and the pressure head h2 measured at the top of the saturated sand sample;

[0076] Select the position head reference surface of the saturated sand sample, and record the position head of the bottom of the saturated sand sample as z1, and the position head of the top of the saturated sand sample as z2;

[0077] Inject water at a certain water pressure into the saturated sand sample through the water inlet 21, and record the p1 and h1 values ​​when the water is injected;

[0078] Calculate the hydraulic gradient when the saturated sand sample does not fail: i = [(z1 + h1) - (z2 + h2)] / L, where L is the height of the saturated sand sample, and L = z2 - z1;

[0079] Thus, the corresponding relationship between the injected water pressure and the hydraulic gradient i of the saturated sand sample is obtained.

[0080] Specifically, after the installation of the sand liquefaction characteristic test device is completed, water is injected into the box 2, and then the sand sample is slowly put into the water to prepare the saturated sand sample and bury the pore water pressure gauge 42 at a predetermined position in the saturated sand sample; after the saturated sand sample is prepared, the pore water pressure gauge 42 located at the bottom of the saturated sand sample measures the pressure at the bottom of the saturated sand sample, and the mean value p1 is calculated, unit: kPa; then the pressure head h1=p1 / ρ at the bottom of the saturated sand sample is calculated w g, where ρ w is the density of water, which can be 1g / cm 3 ; g is the acceleration due to gravity, unit is m / s 2 ;

[0081] The bottom of the saturated sand sample is selected as the reference surface of the position head. The position head Z1 of the bottom of the saturated sand sample is 0m. The position head z2 of the top of the saturated sand sample is the height of the saturated sand sample. The top of the saturated sand sample is set with the pressure head h2 according to the actual situation. When all the water above the top of the saturated sand sample is drained, h2 = 0;

[0082] A water flow with a certain water pressure is continuously injected into the box 2 from the water inlet 21. The injected water flow is slowly increased from a lower water pressure and then fixed at a certain value to ensure that the water pressure of the injected water will not be too large to damage the saturated sand sample. The injected water pressure and the parameter p1 measured by the pore water pressure gauge 42 are recorded when the water pressure is fixed.

[0083] Calculate the hydraulic gradient of the saturated sand sample at this time: i = [(z1 + h1) - (z2 + h2)] / L, where L is the height of the saturated sand sample, and L = z2 - z1;

[0084] Thus, the corresponding relationship between the water pressure of the injected water flow and the hydraulic gradient of the saturated sand sample is obtained.

[0085] Preferably, the water flow injected from the water inlet 21 can be set to multiple groups of water pressures respectively, and the relationship between the injection water pressure and the hydraulic gradient of the saturated sand sample can be measured in multiple groups to improve the accuracy of the test.

[0086] In addition, the water outlet 22 is connected to the collecting box, and the water discharged from the water outlet 22 flows into the collecting box. The flow rate Q can be obtained by detecting the change in the water volume in the collecting box within a period of time t through the analysis component 5, and the permeability coefficient k=Q / (iAt) of the saturated sand sample can be calculated, where A is the cross-sectional area of ​​the saturated sand sample, which is equal to the cross-sectional area inside the box 2.

[0087] Preferably, the step of S2 comprises:

[0088] Dry the sand sample and weigh the soil particle mass m of the sand sample. s , obtain the sand specific gravity G through indoor geotechnical test s and particle size distribution curve; select sand particle size values ​​d1 and d2 respectively, the weight of sand with particle size smaller than d1 in the sand sample accounts for 5% of the sand sample mass, and the weight of sand with particle size smaller than d2 accounts for 20% of the sand sample mass;

[0089] The density of the sand sample is calculated based on the mass and volume of the sand sample obtained by measurement, and the void ratio, porosity and effective weight of the sand sample are calculated based on the density of the sand sample;

[0090] Based on the above parameters, the hydraulic gradients corresponding to the piping seepage failure and soil flow seepage failure of the sand sample are calculated.

[0091] Specifically, the sand sample is dried and the mass of the soil particles m of the dried sand sample is weighed. s , the sand specific gravity G is measured by indoor geotechnical test s and particle size distribution curve, through which sand particle size values ​​d1 and d2 are selected respectively, the weight of sand with particle size smaller than d1 in the sand sample accounts for 5% of the sand sample mass, and the weight of sand with particle size smaller than d2 accounts for 20% of the sand sample mass;

[0092] The dry density ρ of the sand sample is calculated by the above parameters d (g / cm 3 ), porosity e, porosity n, effective density γˊ(kN / m 3 ):

[0093] ρ d =m s / v;

[0094] e=G s ρ w / ρ d -1;

[0095] n=e / (1+e);

[0096] γˊ=[(G s -1)ρ w g] / (1+e);

[0097] Where v is the volume of saturated sand sample;

[0098] Calculate the hydraulic gradient i required for the sand sample and the saturated sand sample prepared with distilled water to undergo piping failure and soil flow failure Ⅰ and i Ⅱ :

[0099] i Ⅰ =2.2(G s -1)(1-n)2d1 / d2;

[0100] i Ⅱ =(G s -1)(1-n).

[0101] Preferably, the step of S3 includes:

[0102] The water inlet 21 and the water outlet 22 are closed, and a second accelerometer 43 is installed on the table top of the vibration table 1;

[0103] Fill the box 2 with water, slowly place the sand sample into the water to prepare a saturated sand sample, bury the pore water pressure gauge 42 and the first accelerometer 41 at a predetermined position in the saturated sand sample during the preparation process, and open the water outlet 22 to discharge excess water after the preparation is completed;

[0104] According to the parameters obtained in the preliminary test, the water pressure injected is adjusted to set at least four parallel test groups. The first group closes the water inlet 21 and does not cause seepage; the second group opens the water inlet 21 to inject water, providing a water pressure that does not damage the saturated sand sample for seepage; the third group opens the water inlet 21 to provide a water pressure that causes pipe burst seepage damage to the saturated sand sample for seepage; the fourth group opens the water inlet 21 to provide a water pressure that causes flow soil seepage damage to the saturated sand sample for seepage;

[0105] After waiting for sufficient seepage in multiple test groups, stop water injection and let it stand for a certain period of time. Then start the vibration table 1 to liquefy the saturated sand sample. Use the pore water pressure gauge 42, the first accelerometer 41 and the second accelerometer 43 to record the parameters of the liquefaction process of the saturated sand sample. Compare the parameters of multiple groups of data to obtain the influence of the seepage phenomenon on the liquefaction characteristics of the sand.

[0106] Specifically, the water inlet 21 and the water outlet 22 are closed first, and the second accelerometer 43 is installed on the table of the vibration table 1. After the installation is completed, water is injected into each box 2. After the water injection is completed, sand is slowly added to soak and vacuum is drawn to prepare a saturated sand sample. During the preparation process, a pore water pressure gauge 42 and a first accelerometer 41 are buried in the saturated sand sample; after the saturated sand sample is prepared, the water outlet 22 above the saturated sand sample is opened to discharge excess water during the preparation process;

[0107] The first group of multiple control test groups closed the water inlet 21, and no water flow entered the box 2. The saturated sand sample of this group did not seep, that is, the hydraulic gradient i1 = 0; the second, third, and fourth groups all opened the water inlet 21 to keep injecting water. Among them, the second group was injected with water pressure that could not cause the saturated sand sample to be destroyed, and the hydraulic gradient relationship was: 0 <i2<i Ⅰ ; The third group of water pressure is used to cause the saturated sand sample to undergo piping and seepage failure. The hydraulic gradient relationship is: i3 = i Ⅰ ; The fourth group of water pressure is introduced to cause the saturated sand sample to undergo soil flow and penetration failure. The hydraulic gradient relationship is: i4 = i Ⅱ ;

[0108] According to the above water gradient conditions, water flow of corresponding pressure is injected into the box 2 of each test group respectively, so that the saturated sand sample reaches a predetermined seepage state, and the water injection is stopped after the seepage is stabilized for a period of time, and then it is left to stand for a period of time;

[0109] After completing the above steps, start the vibration table 1 to drive the box 2 and the saturated sand sample in the box 2 to vibrate, simulate the vibration conditions, and judge whether the output vibration acceleration of the vibration table 1 of multiple groups of tests is the same through the data measured by the second accelerometer 43. If different, it is necessary to adjust; during the vibration process, the pore water pressure gauge 42 and the first accelerometer 41 of each test group record data to obtain the pore water pressure curve and acceleration curve of each group of saturated sand samples. The test data of each group are compared to obtain the influence of different seepage conditions on the vibration liquefaction characteristics of sand, so as to achieve the purpose of the test.

[0110] The working process of the present invention is as follows: water is injected into the box 2, sand is slowly put into the water, and a saturated sand sample is prepared. During the preparation process, a pore water pressure gauge 42 is buried in the saturated sand sample;

[0111] Measure the mean value p1 of the pore water pressure gauge 42 at the bottom of the prepared saturated sand sample, and calculate the pressure head h1 = p1 / ρ at the bottom of the saturated sand sample w g, and the pressure head h2 measured at the top of the saturated sand sample;

[0112] Select the position head reference surface of the saturated sand sample, and record the position head of the bottom of the saturated sand sample as z1, and the position head of the top of the saturated sand sample as z2;

[0113] Inject water at a certain water pressure into the saturated sand sample through the water inlet 21, and record the p1 and h1 values ​​when the water is injected;

[0114] Calculate the hydraulic gradient when the saturated sand sample does not fail: i = [(z1 + h1) - (z2 + h2)] / L, where L is the height of the saturated sand sample, and L = z2 - z1;

[0115] Thus, the corresponding relationship between the injected water pressure and the hydraulic gradient i of the saturated sand sample is obtained.

[0116] Specifically, after the installation of the sand liquefaction characteristic test device is completed, water is injected into the box 2, and then the sand sample is slowly put into the water to prepare the saturated sand sample and bury the pore water pressure gauge 42 at a predetermined position in the saturated sand sample; after the saturated sand sample is prepared, the pore water pressure gauge 42 located at the bottom of the saturated sand sample measures the pressure at the bottom of the saturated sand sample, and the mean value p1 is calculated, unit: kPa; then the pressure head h1=p1 / ρ at the bottom of the saturated sand sample is calculated w g,ρ w is the density of water, which can be 1g / cm 3 ; g is the acceleration due to gravity, unit is m / s 2 ;

[0117] The bottom of the saturated sand sample is selected as the reference surface of the position head. The position head z1 of the bottom of the saturated sand sample is 0m. The position head z2 of the top of the saturated sand sample is the height of the saturated sand sample. The top of the saturated sand sample is set with the pressure head h2 according to the actual situation. When all the water above the top of the saturated sand sample is drained, h2 = 0;

[0118] A water flow with a certain water pressure is continuously injected into the box 2 from the water inlet 21. The injected water flow is slowly increased from a lower water pressure and then fixed at a certain value to ensure that the water pressure of the injected water will not damage the saturated sand sample. The injected water pressure and the parameter p1 measured by the pore water pressure gauge 42 are recorded when the water pressure is fixed.

[0119] Calculate the hydraulic gradient of the saturated sand sample at this time: i = [(z1 + h1) - (z2 + h2)] / L, where L is the height of the saturated sand sample, and L = z2 - z1;

[0120] Thus, the corresponding relationship between the water pressure of the injected water flow and the hydraulic gradient of the saturated sand sample is obtained.

[0121] Dry the sand sample and weigh the soil particle mass m of the sand sample. s, obtain the sand specific gravity G through indoor geotechnical test s and particle size distribution curve; select sand particle size values ​​d1 and d2 respectively, the weight of sand with particle size smaller than d1 in the sand sample accounts for 5% of the sand sample mass, and the weight of sand with particle size smaller than d2 accounts for 20% of the sand sample mass;

[0122] The density of the sand sample is calculated based on the mass and volume of the sand sample obtained by measurement, and the void ratio, porosity and effective weight of the sand sample are calculated based on the density of the sand sample;

[0123] Based on the above parameters, the hydraulic gradients corresponding to the piping seepage failure and soil flow seepage failure of the sand sample are calculated.

[0124] Dry the sand sample and weigh the mass m of the soil particles in the dried sand sample. s , the sand specific gravity G is measured by indoor geotechnical test s and particle size distribution curve, through which sand particle size values ​​d1 and d2 are selected respectively, the weight of sand with particle size smaller than d1 in the sand sample accounts for 5% of the sand sample mass, and the weight of sand with particle size smaller than d2 accounts for 20% of the sand sample mass;

[0125] The dry density ρ of the sand sample is calculated by the above parameters d (g / cm 3 ), porosity e, porosity n, effective density γˊ(kN / m 3 ):

[0126] ρ d =m s / v;

[0127] e=G s ρ w / ρ d -1;

[0128] n=e / (1+e);

[0129] γˊ=[(G s -1)ρ w g] / (1+e);

[0130] Where v is the volume of saturated sand sample;

[0131] Calculate the hydraulic gradient i required for the sand sample and the saturated sand sample prepared with distilled water to undergo piping failure and soil flow failure Ⅰ and i Ⅱ :

[0132] i Ⅰ =2.2(G s -1)(1-n)2d1 / d2;

[0133] i Ⅱ =(G s -1)(1-n).

[0134] After completing the above preliminary test, the sand liquefaction characteristic test is carried out: first close the water inlet 21 and the water outlet 22, install the second accelerometer 43 on the table of the vibration table 1, and after the installation is completed, water is injected into each box 2. After the water injection is completed, sand is slowly added to soak and vacuum is drawn to prepare a saturated sand sample. During the preparation process, a pore water pressure gauge 42 and a first accelerometer 41 are buried in the saturated sand sample; after the saturated sand sample is prepared, the water outlet 22 above the saturated sand sample is opened to discharge the excess water during the preparation process;

[0135] The first group of multiple control test groups closed the water inlet 21, and no water flow entered the box, and the saturated sand sample of this group did not seep, that is, the hydraulic gradient i1 = 0; the second, third, and fourth groups all opened the water inlet 21 to keep injecting water, among which, the second group was injected with water pressure that could not cause the saturated sand sample to be destroyed, and the hydraulic gradient relationship was: 0 <i2<i Ⅰ ; The third group of water pressure is used to cause the saturated sand sample to undergo piping and seepage failure. The hydraulic gradient relationship is: i3 = i Ⅰ ; The fourth group of water pressure is introduced to cause the saturated sand sample to undergo soil flow and penetration failure. The hydraulic gradient relationship is: i4 = i Ⅱ ;

[0136] According to the above water gradient conditions, water flow of corresponding pressure is injected into the box 2 of each test group respectively, so that the saturated sand sample reaches a predetermined seepage state, and the water injection is stopped after the seepage is stabilized for a period of time, and then it is left to stand for a period of time;

[0137] After completing the above steps, start the vibration table 1 to drive the box 2 and the saturated sand sample in the box 2 to vibrate, simulate the vibration conditions, and judge whether the output vibration acceleration of the vibration table 1 of multiple groups of tests is the same through the data measured by the second accelerometer 43. If different, it is necessary to adjust; during the vibration process, the pore water pressure gauge 42 and the first accelerometer 41 of each test group record data to obtain the pore water pressure curve and acceleration curve of each group of saturated sand samples. The test data of each group are compared to obtain the influence of different seepage conditions on the vibration liquefaction characteristics of sand, so as to achieve the purpose of the test.

[0138] In summary, the embodiment of the present invention provides a sand liquefaction characteristic test device and a test method thereof, which can simulate the actual situation of groundwater seepage by arranging a water inlet 21 and a filter assembly 3 at the bottom position of the box 2; by setting multiple control test groups, it can simultaneously test the vibration liquefaction conditions under conditions of no seepage, normal seepage, pipe seepage damage and soil flow seepage damage, so that the test is closer to the actual situation of the sandy soil formation, the test results and parameters are more real and reliable, and the research effect is improved.

[0139] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A sand liquefaction characteristic test device, characterized in that: include: Vibration table, box, filter assembly, detection assembly and analysis assembly; The box is connected to the vibration table, and a water inlet and a water outlet are provided on the box. The box includes a steady flow chamber, a filter layer, and a sample layer for placing saturated sand samples, which are arranged and connected in sequence from bottom to top. The water inlet is connected to the steady flow chamber, and the water outlet is connected to the top of the sample layer. The filter assembly is arranged in the filter layer. The detection component comprises a first accelerometer and a pore water pressure gauge buried inside the saturated sand sample; the detection component is electrically connected to the analysis component.

2. The sand liquefaction characteristic test device according to claim 1, characterized in that: A partition is provided between the flow stabilization chamber and the reverse filter layer, and a connecting hole connecting the flow stabilization chamber and the reverse filter layer is provided on the partition.

3. The sand liquefaction characteristic test device according to claim 1, characterized in that: The reverse filter assembly comprises a reverse filter layer body and a first screen and a second screen respectively arranged on the upper and lower surfaces of the reverse filter layer body.

4. The sand liquefaction characteristic test device according to claim 3, characterized in that: The filter layer body is made of round gravel.

5. The sand liquefaction characteristic test device according to claim 1, characterized in that: The detection component also includes a second accelerometer fixed on the vibration table, and the second accelerometer is electrically connected to the analysis component.

6. The sand liquefaction characteristic test device according to claim 1, characterized in that: There are multiple water inlets, each of which is connected to a water supply device, and each of the water inlets is connected to a one-way valve.

7. A method for testing sand liquefaction characteristics, characterized in that: The sand liquefaction characteristic test device according to any one of claims 1 to 6 comprises: S1. Preliminary test: a saturated sand sample is laid on the filter layer, and a water flow with a certain pressure is injected from the water inlet to obtain a relationship table between the injected water flow pressure and the hydraulic gradient of the saturated sand sample; S2. Calculate the hydraulic gradient i corresponding to the saturated sand sample under piping seepage failure and soil flow seepage failure. Ⅰ 、i Ⅱ ; S3. Sand liquefaction characteristics test: multiple groups of simulation tests were conducted, each group of simulation tests was conducted according to the following steps: A saturated sand sample is prepared above the filter layer, and a first accelerometer and a pore water pressure gauge are buried in the saturated sand sample, and a second accelerometer is installed on the table of the vibration table; Control the water flow pressure to obtain a preset hydraulic gradient i, stop water injection after the stable seepage reaches a predetermined time, and then let it stand for a certain period of time; wherein the water flow pressure is obtained according to the relationship table and the preset hydraulic gradient i; Starting the shaking table to record the data measured by the pore water pressure meter, the first accelerometer and the second accelerometer; S4. Analyze the influence of seepage and seepage damage on sand liquefaction characteristics based on the data measured by the pore water pressure meter, the first accelerometer and the second accelerometer in each group of simulation tests; Among them, there are at least four groups of different model experiments. In each group of simulation experiments, the preset hydraulic gradients i are: i1 = 0, 0 < i2 < i Ⅰ , i3=i Ⅰ , i4=i Ⅱ .

8. The testing method according to claim 7, characterized in that: The steps of S1 include: First, water is injected into the box, and sand is slowly put into the water to prepare a saturated sand sample. During the preparation process, a pore water pressure gauge is buried in the saturated sand sample; Measure the mean value p1 of the pore water pressure gauge at the bottom of the prepared saturated sand sample, and calculate the pressure head h1=p1 / ρ at the bottom of the saturated sand sample w g, and the pressure head h2 measured at the top of the saturated sand sample; Select the position head reference surface of the saturated sand sample, and record the position head of the bottom of the saturated sand sample as z1, and the position head of the top of the saturated sand sample as z2; Inject water at a certain pressure into the saturated sand sample through the water inlet, and record the p1 and h1 values ​​when the water is injected; Calculate the hydraulic gradient of the saturated sand sample i = [(z1+h1)-(z2+h2)] / L, where L is the height of the saturated sand sample, and L = z2-z1; Thus, the corresponding relationship between the injected water pressure and the hydraulic gradient i of the saturated sand sample is obtained.

9. The testing method according to claim 7, characterized in that: The steps of S2 include: Dry the sand sample and weigh the soil particle mass m of the sand sample. s , obtain the sand specific gravity G through indoor geotechnical test s and particle size distribution curve; select sand particle size values ​​d1 and d2 respectively, the weight of sand with particle size smaller than d1 in the sand sample accounts for 5% of the sand sample mass, and the weight of sand with particle size smaller than d2 accounts for 20% of the sand sample mass; The density of the sand sample is calculated based on the mass and volume of the sand sample obtained by measurement, and the void ratio, porosity and effective weight of the sand sample are calculated based on the density of the sand sample; Based on the above parameters, the hydraulic gradients corresponding to the piping seepage failure and soil flow seepage failure of the sand sample are calculated.

10. The testing method according to any one of claims 7 to 9, characterized in that: The steps of S3 include: The water inlet and the water outlet are closed, and a second accelerometer is fixedly installed on the table top of the vibration table; Filling water into the box, slowly placing the sand sample into the water to prepare a saturated sand sample, burying the pore water pressure gauge and the first accelerometer at a predetermined position in the saturated sand sample during the preparation process, and opening the water outlet to discharge excess water after the preparation is completed; At least four parallel test groups are set according to the parameters obtained in the preliminary test to adjust the injected water pressure. The first group closes the water inlet and does not seep; the second group opens the water inlet and injects water to provide water pressure that does not damage the saturated sand sample for seepage; the third group opens the water inlet and provides water pressure that causes pipe burst penetration damage to the saturated sand sample for seepage; the fourth group opens the water inlet and provides water pressure that causes flow soil penetration damage to the saturated sand sample for seepage; After waiting for sufficient seepage in multiple test groups, water injection is stopped and the mixture is left to stand for a certain period of time. The vibration table is then started to liquefy the saturated sand sample. The parameters of the liquefaction process of the saturated sand sample are recorded by the pore water pressure gauge, the first accelerometer and the second accelerometer.

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