Test device and method for researching influence of freeze thawing on sand liquefaction characteristics

Abstract

The invention discloses a test device and method for researching the influence of freezing and thawing on the liquefaction characteristic of sandy soil. The device comprises a vibration table, a model box for placing a saturated sandy soil sample, a detection module, an analysis module and a refrigerator, the model box is connected with the vibration table, and the model box and the vibration table are arranged in the refrigerator; the detection module comprises a first accelerometer and a pore water pressure gauge which are buried in the saturated sand sample; and the detection module is electrically connected with the analysis module. The test device disclosed by the invention is simple in structure and stable in operation, and the influence of freezing and thawing on the sand liquefaction characteristic under different conditions can be obtained through a reasonable test method.

Description

Technical Field

[0001] The present invention relates to the technical field of geological engineering, and particularly to a test device and method for studying the influence of freeze-thaw on sand liquefaction. Background Art

[0002] Sand liquefaction refers to the process in which, under the action of vibration, the pore water pressure in saturated sand rises, the effective stress reduces to zero, and the sand loses its shear strength and transforms from a solid state to a liquid state. Sand liquefaction can cause a series of hazards such as ground settlement, surface collapse, loss of foundation bearing capacity, and ground flow slide. When an earthquake occurs, the strong ground vibration not only directly damages surface buildings, but also causes the liquefaction of shallow saturated sand, further expanding the disaster.

[0003] Existing research mainly focuses on the influence of variables such as sand particle gradation and fine particle content on the liquefaction characteristics of sand. However, in high-latitude regions, there is a possibility of freeze-thaw after the formation of saturated sand strata. During the freeze-thaw process, the volume of water in the pores of the sand increases and then squeezes the sand particles, changing the original arrangement of the sand particles in the sand strata, which may affect the liquefaction characteristics of the saturated sand strata. The prior art lacks research on the influence of freeze-thaw on the liquefaction characteristics of sand. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a test device and method for studying the influence of freeze-thaw on the liquefaction characteristics of sand, which has a simple structure and stable operation, and can obtain the influence of freeze-thaw on the liquefaction characteristics of sand under different conditions through a reasonable test method.

[0005] To achieve the above object, an embodiment of the present invention provides a test device for studying the influence of freeze-thaw on the liquefaction characteristics of sand, including: a shaking table, a model box for placing a saturated sand sample, a detection module, an analysis module, and a freezer;

[0006] The model box is connected to the shaking table, and the model box and the shaking table are placed in the freezer;

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

[0008] As an improvement of the above solution, the shaking table includes a base, a tabletop, a compression spring, and a vibration motor;

[0009] A plurality of limit blocks are welded to the top of the base, and the same number of limit blocks are welded to the bottom of the tabletop. The corresponding limit blocks are flexibly connected by the compression spring; the bottom of the tabletop is fixedly connected to the vibration motor by bolts.

[0010] As an improvement to the above solution, the vibration motor is a three-phase asynchronous motor, and the vibration motor is electrically connected to a frequency converter, and the frequency converter is electrically connected to a timing controller.

[0011] As an improvement to the above solution, the size of the bottom plate of the model box is the same as the size of the tabletop, and the top of the tabletop is fixedly connected to the bottom plate of the model box by bolts;

[0012] The model box is made of high-strength explosion-proof tempered glass, and a sponge is pasted on the inner side of the model box.

[0013] As an improvement to the above solution, the detection module further includes a second accelerometer fixed to the bottom of the model box, and the second accelerometer is electrically connected to the analysis module.

[0014] An embodiment of the present invention also provides a test method for studying the influence of freeze-thaw on sand liquefaction. Using the test device for studying the influence of freeze-thaw on sand liquefaction described in any one of the above, the test method includes:

[0015] S1: After preparing a saturated sand sample, conduct a freezing pre-test and a thawing pre-test on the saturated sand sample to determine the freezing time and thawing time of the saturated sand sample;

[0016] S2: After preparing a saturated sand sample, start the shaking table, and apply a primary vibration according to the preset vibration time and vibration frequency to liquefy the saturated sand sample, and collect the data of the first accelerometer and the pore water pressure gauge buried inside the saturated sand sample, denoted as SJ1;

[0017] S3: After the excess pore water pressure has completely dissipated, apply the same vibration as in S2 again to liquefy the saturated sand sample again, and collect the data of the first accelerometer and the pore water pressure gauge, denoted as SJ2;

[0018] S4: After preparing a saturated sand sample, freeze the saturated sand sample in a freezer for the freezing time, and after the frozen saturated sand sample has thawed for the thawing time, apply the same vibration as in S2 to liquefy the thawed saturated sand sample, and collect the data of the first accelerometer and the pore water pressure gauge, denoted as SJ3;

[0019] S5: After the excess pore water pressure has completely dissipated, apply the same vibration as in S2 again to liquefy the thawed saturated sand sample again, and collect the data of the first accelerometer and the pore water pressure gauge, denoted as SJ4;

[0020] S6: After preparing the saturated sand sample, apply the same vibration as in S2 to liquefy the saturated sand sample. After the excess pore water pressure completely dissipates, freeze the saturated sand sample after the first liquefaction for the freezing time through the freezer. After the frozen saturated sand sample after the first liquefaction thaws for the thawing time, apply the same vibration as in S2 again to liquefy the thawed saturated sand sample after the first liquefaction, and collect the data of the first accelerometer and the pore water pressure gauge, denoted as SJ5;

[0021] S7: Compare SJ1 with SJ3 to obtain the influence of freeze-thaw on the initial liquefaction characteristics of sand; compare SJ2 with SJ4 to obtain the influence of freeze-thaw on the re-liquefaction characteristics of sand; compare SJ2 with SJ5 to obtain the influence of freeze-thaw after the initial liquefaction of sand on the re-liquefaction characteristics of sand.

[0022] Further, the steps of the freezing pre-test include:

[0023] S111: After preparing the saturated sand sample, freeze the saturated sand sample at a preset temperature through the freezer;

[0024] S112: Observe the freezing condition of the saturated sand sample at preset time intervals, and measure the heights at the middle and both ends of the saturated sand sample on both side walls of the model box;

[0025] S113: Repeat S12. After the measured heights no longer change, take out the frozen saturated sand sample in the model box, and use a heavy hammer to crack and decompose the frozen saturated sand sample. If there is no unfrozen saturated sand sample in the decomposed blocks, it is determined that the saturated sand sample has been completely frozen;

[0026] S114: Add all the freezing times in S11 - S13 plus a preset time as the freezing time for the formal test, denoted as T1.

[0027] Further, the steps of the thawing pre-test include:

[0028] S121: After preparing the saturated sand sample, measure and record the temperature inside the saturated sand sample, and freeze the saturated sand sample at a preset temperature through the freezer for a freezing time of T1;

[0029] S122: Stop freezing, and measure the heights at the middle and both ends of the saturated sand sample on both side walls of the model box; then measure the heights at the middle and both ends of the saturated sand sample on both side walls of the model box at the preset time intervals until the heights no longer change, and then measure the temperature inside the saturated sand sample at the preset time intervals until the temperature inside the saturated sand sample returns to the temperature before freezing;

[0030] S123: Calculate the time from the end of freezing to the time when the internal temperature of the saturated sand sample returns to the temperature before freezing in S122, and then add a preset time as the thawing time for the formal test, denoted as T2.

[0031] Further, in S2, set the vibration time through a timing controller and set the vibration frequency through a frequency converter.

[0032] Further, when liquefying the saturated sand sample, determine whether the saturated sand sample is liquefied according to the following formula;

[0033] u = σ';

[0034] σ' = γ'h;

[0035] γ' = [(G s - 1)ρ w g] / (1 + e);

[0036] e = G s ρ w / ρ d - 1;

[0037] ρ d = m s / v;

[0038] Where:

[0039] u: Excess pore water pressure, read from a pore water pressure gauge, unit kPa;

[0040] γ': Effective unit weight of the saturated sand sample, unit kN / m 3 ;

[0041] h: Burial depth of the pore water pressure gauge from the top of the saturated sand sample, unit m;

[0042] ρ d : Dry density of the saturated sand sample, unit g / cm 3 ;

[0043] m s : Total mass of sand particles in the saturated sand sample, unit g;

[0044] v: Volume of the saturated sand sample, unit cm 3 ;

[0045] e: Void ratio, unit 1;

[0046] G s : Specific gravity of sand particles in the saturated sand sample, unit 1;

[0047] ρ w : Density of distilled water, unit g / cm 3;

[0048] g: acceleration due to gravity, unit m / s 2 。

[0049] Compared with the prior art, the beneficial effects of an experimental device and method for studying the influence of freeze-thaw on the liquefaction characteristics of sandy soil provided by the embodiments of the present invention are as follows: By placing a shaking table and a model box containing a saturated sandy soil sample in a freezer, the saturated sandy soil sample can be frozen to provide a freeze-thaw environment, so as to conduct an experiment on the influence of freeze-thaw on the liquefaction characteristics of sandy soil. The experimental device provided by the embodiments of the present invention has a simple structure and stable operation, and the influence of freeze-thaw on the liquefaction characteristics of sandy soil under different conditions can be obtained through a reasonable experimental method. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a schematic diagram of the overall structure of an experimental device for studying the influence of freeze-thaw on the liquefaction of sandy soil provided by the present invention;

[0051] Figure 2 is a schematic diagram of the structure of an experimental device for studying the influence of freeze-thaw on the liquefaction of sandy soil provided by the present invention;

[0052] Figure 3 is a schematic diagram of the partial structure of an experimental device for studying the influence of freeze-thaw on the liquefaction of sandy soil provided by the present invention;

[0053] Among them, the reference numerals are as follows:

[0054] 1, base; 2, tabletop; 3, limit block; 4, compression spring; 5, vibration motor; 6, frequency converter; 7, timing controller; 8, model box; 9, sponge; 10, saturated sandy soil sample; 11, first accelerometer; 12, pore water pressure gauge; 13, data acquisition instrument; 14, computer; 15, freezer; 16, second accelerometer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0056] In the description of the present application, the terms "first", "second", "third", etc. are used only for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", "third", etc. may explicitly or implicitly include one or more of such features. In the description of the present application, unless otherwise specified, the meaning of "a plurality" is two or more.

[0057] In the description of the present application, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", "connected to" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0058] In the description of the present application, it should be noted that unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the technical field to which this invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0059] Please refer to Figures 1 to 3 , Figure 1 which is a schematic diagram of the overall structure of a test device provided by the present invention for studying the influence of freeze-thaw on sand liquefaction. Figure 2 which is a schematic diagram of the structure of a test device provided by the present invention for studying the influence of freeze-thaw on sand liquefaction. Figure 3 which is a schematic diagram of a partial structure of a test device provided by the present invention for studying the influence of freeze-thaw on sand liquefaction. The test device for studying the influence of freeze-thaw on sand liquefaction includes: a shaking table, a model box 8 for placing a saturated sand sample, a detection module, an analysis module, and a freezer 15;

[0060] The model box 8 is connected to the shaking table, and the model box 8 and the shaking table are placed inside the freezer 15;

[0061] The detection module includes a first accelerometer 11 and a pore water pressure gauge 12 buried inside the saturated sand sample; the detection module is electrically connected to the analysis module.

[0062] Specifically, the embodiment of the present invention provides a test device for studying the influence of freeze-thaw on sand liquefaction. The model box 8 is connected to the shaking table, and the shaking table provides vibration to force the saturated sand sample 10 placed in the model box 8 to liquefy. Among them, the saturated sand sample 10 can be prepared by the method of dropping sand in water. The model box 8 and the shaking table are placed in the freezer 15, so that the saturated sand sample 10 can be frozen to provide a freeze-thaw environment. The detection module includes a first accelerometer 11 and a pore water pressure gauge 12 buried inside the saturated sand sample 10, and the detection module is electrically connected to the analysis module. Exemplarily, a total of 3 first accelerometers 11 and pore water pressure gauges 12 are buried at the bottom of the saturated sand sample 10, at a distance of 1 / 3 of the thickness of the saturated sand sample 10 from the bottom, and at a distance of 2 / 3 of the thickness of the saturated sand sample 10 from the bottom, for measuring the pore water pressure and acceleration at the corresponding positions inside the saturated sand sample 10 under vibration. Among them, the minimum operating temperature of the first accelerometer 11 and the pore water pressure gauge 12 is lower than minus 30 degrees Celsius. The analysis module includes a data acquisition instrument 13 and a computer 14. The data acquisition instrument 13 is electrically connected to the first accelerometer 11 and the pore water pressure gauge 12 respectively. The first accelerometer 11 and the pore water pressure gauge 12 send parameters to the data acquisition instrument 13, and the computer 14 collects and calculates to obtain the required parameters. By comparing the data of the first accelerometer 11 and the pore water pressure gauge 12 during the whole process of vibration liquefaction of the saturated sand sample with and without freeze-thaw action, the influence of freeze-thaw on the liquefaction characteristics of sand can be obtained.

[0063] It should be noted that during the test, the freezer 15 can be placed in an air-conditioned room, so that the whole test is carried out under constant temperature conditions.

[0064] In another preferred embodiment, the shaking table includes a base 1, a tabletop 2, a compression spring 4 and a vibration motor 5;

[0065] A plurality of limit blocks 3 are welded to the top of the base 1, and the same number of limit blocks 3 are welded to the bottom of the tabletop 2. The corresponding limit blocks 3 are flexibly connected by the compression spring 4; the bottom of the tabletop 2 is fixedly connected to the vibration motor 5 by bolts.

[0066] Specifically, the shaking table in the embodiment of the present invention includes a base 1, a tabletop 2, a compression spring 4 and a vibration motor 5. Among them, the base 1 is welded by channel steel and square steel, and both sides of the base extend outwards for adding weight to enhance stability. A plurality of limit blocks 3 are welded to the top of the base 1, and the same number of limit blocks 3 are welded to the bottom of the tabletop 2. The corresponding limit blocks 3 are flexibly connected by the compression spring 4, and the bottom of the tabletop 2 is fixedly connected to the vibration motor 5 by bolts.

[0067] In yet another preferred embodiment, the vibration motor 5 is a three-phase asynchronous motor. The vibration motor 5 is electrically connected to a frequency converter 6, and the frequency converter 6 is electrically connected to a timing controller 7.

[0068] Specifically, in the embodiment of the present invention, the vibration motor 5 is a three-phase asynchronous motor, which can provide sufficient and stable exciting force. The vibration motor 5 is electrically connected to the frequency converter 6, and the frequency converter 6 can adjust the rotation speed of the vibration motor 5 before or during its operation, thereby controlling the vibration frequency of the vibration motor 5. The frequency converter 6 is electrically connected to the timing controller 7, and the timing controller 7 can control the power-on time of the entire circuit, thereby controlling the vibration time of the vibration motor 5 and protecting the circuit.

[0069] In another preferred embodiment, the size of the bottom plate of the model box 8 is the same as the size of the tabletop 2, and the top of the tabletop 2 is fixedly connected to the bottom plate of the model box 8 by bolts;

[0070] The model box 8 is made of high-strength explosion-proof tempered glass, and a sponge 9 is pasted on the inner side of the model box 8.

[0071] Specifically, in the embodiment of the present invention, the size of the bottom plate of the model box 8 is the same as the size of the tabletop 2, that is, the length and width of the bottom plate of the model box 8 are the same as those of the tabletop 2. The top of the tabletop 2 is fixedly connected to the bottom plate of the model box 8 by bolts. The model box 8 is made of high-strength explosion-proof tempered glass, and the internal saturated sand sample 10 can be observed. A sponge 9 is pasted on the inner side of the model box 8 to reduce the boundary effect of the saturated sand sample 10 during vibration. Exemplarily, sponges 9 can be pasted on both sides of the short side inside the model box 8.

[0072] In another preferred embodiment, the detection module further includes a second accelerometer 16 fixed to the bottom of the model box 8, and the second accelerometer 16 is electrically connected to the analysis module.

[0073] Specifically, in the embodiment of the present invention, the detection module further includes a second accelerometer 16 fixed to the bottom of the model box 8, which is used to measure the input acceleration under vibration. The second accelerometer 16 is electrically connected to the analysis module. The second accelerometer 16 sends the parameters to the data acquisition instrument 13, and the computer 14 collects and calculates them to obtain the required parameters.

[0074] Correspondingly, the present invention also provides a test method for studying the influence of freeze-thaw on sand liquefaction, using the test device for studying the influence of freeze-thaw on sand liquefaction in the above embodiment. The test method for studying the influence of freeze-thaw on sand liquefaction includes:

[0075] S1: After preparing the saturated sand sample 10, conduct a freezing pre-test and a thawing pre-test on the saturated sand sample 10 to determine the freezing time T1 and the thawing time T2 of the saturated sand sample 10;

[0076] S2: After preparing the saturated sand sample 10, start the shaking table, and apply the initial vibration according to the preset vibration time and vibration frequency to liquefy the saturated sand sample 10, and collect the data of the first accelerometer 11 and the pore water pressure gauge 12 buried inside the saturated sand sample 10, denoted as SJ1;

[0077] S3: After the excess pore water pressure is completely dissipated, apply the same vibration as in S2 again to liquefy the saturated sand sample 10 again, and collect the data of the first accelerometer 11 and the pore water pressure gauge 12, denoted as SJ2;

[0078] S4: After preparing the saturated sand sample 10, freeze the saturated sand sample 10 in the freezer 15 for the freezing time. After the frozen saturated sand sample 10 thaws for the thawing time, apply the same vibration as in S2 to liquefy the thawed saturated sand sample 10, and collect the data of the first accelerometer 11 and the pore water pressure gauge 12, denoted as SJ3;

[0079] S5: After the excess pore water pressure is completely dissipated, apply the same vibration as in S2 again to liquefy the thawed saturated sand sample 10 again, and collect the data of the first accelerometer 11 and the pore water pressure gauge 12, denoted as SJ4;

[0080] S6: After preparing the saturated sand sample 10, apply the same vibration as in S2 to liquefy the saturated sand sample 10. After the excess pore water pressure is completely dissipated, freeze the initially liquefied saturated sand sample 10 in the freezer 15 for the freezing time. After the frozen initially liquefied saturated sand sample 10 thaws for the thawing time, apply the same vibration as in S2 again to liquefy the thawed initially liquefied saturated sand sample 10 again, and collect the data of the first accelerometer 11 and the pore water pressure gauge 12, denoted as SJ5;

[0081] S7: Compare SJ1 with SJ3 to obtain the influence of freeze-thaw on the initial liquefaction characteristics of sand; compare SJ2 with SJ4 to obtain the influence of freeze-thaw on the re-liquefaction characteristics of sand; compare SJ2 with SJ5 to obtain the influence of freeze-thaw after the initial liquefaction of sand on the re-liquefaction characteristics of sand.

[0082] Specifically, the embodiment of the present invention provides a test method for studying the influence of freeze-thaw on sand liquefaction, and uses the test device for studying the influence of freeze-thaw on sand liquefaction in the above embodiment. Before the test, the total dry mass m of all the sand used in the saturated sand sample 10 is measured through indoor geotechnical tests s and the particle specific gravity G sBefore the formal test, a preliminary test is first conducted, including a freezing preliminary test and a thawing preliminary test on the saturated sand sample, to determine the freezing time T1 for the saturated sand sample to be completely frozen and the thawing time T2 for complete thawing.

[0083] Specifically, the steps of the freezing preliminary test include:

[0084] S111: After preparing the saturated sand sample 10, turn on the freezer 15 and freeze the saturated sand sample 10 at a preset temperature through the freezer 15; for example, the preset temperature can be set to -20 °C.

[0085] S112: Subsequently, open the freezer 15 at preset time intervals, observe the freezing condition of the saturated sand sample 10, and use a scale to measure the heights at the middle and both ends of the saturated sand sample 10 on both side walls of the model box 8; for example, the preset time interval can be 0.5 h.

[0086] S113: Repeat S12. After the measured heights no longer change, loosen the fixing bolts at the bottom plate of the model box 8 and the table 2, remove the model box 8, take out the frozen saturated sand sample 10 in the model box 8, and use a heavy hammer to crack and decompose the frozen saturated sand sample 10. If there is no unfrozen saturated sand sample in the decomposed blocks, it is determined that the saturated sand sample 10 has been completely frozen.

[0087] S114: Take all the freezing times in S11 - S13 plus the preset time as the freezing time for the formal test, denoted as T1; for example, the preset time can be 1 h.

[0088] It should be noted that when conducting the above freezing preliminary test, the first accelerometer 11 and the pore water pressure gauge 12 are not buried in the saturated sand sample 10 to avoid damage when the frozen saturated sand sample 10 is cracked and decomposed with a heavy hammer.

[0089] Specifically, the steps of the thawing preliminary test include:

[0090] S121: After preparing the saturated sand sample 10, measure and record the internal temperature of the saturated sand sample 10 with a thermometer, turn on the freezer 15, and freeze the saturated sand sample 10 at a preset temperature through the freezer 15 for a freezing time of T1; for example, the preset temperature can be set to -20 °C.

[0091] S122: Stop freezing, and use a scale to measure the heights at the middle and both ends of the saturated sand sample 10 on both side walls of the model box 8; subsequently, measure the heights at the middle and both ends of the saturated sand sample 10 on both side walls of the model box 8 at each preset time interval until the heights no longer change, and then measure the temperature inside the saturated sand sample 10 at each preset time interval until the temperature inside the saturated sand sample 10 returns to the temperature before freezing; for example, the preset time interval can be 0.5 h.

[0092] S123: Calculate the time from stopping freezing to the temperature inside the saturated sand sample 10 returning to the temperature before freezing in S122 plus a preset time as the thawing time for the formal test, denoted as T2; for example, the preset time can be 1 h.

[0093] In the embodiment of the present invention, after performing the freezing pre-test and thawing pre-test on the saturated sand sample 10 in S1 to determine the freezing time T1 and thawing time T2 of the saturated sand sample 10, the formal test is started.

[0094] S2: After preparing the saturated sand sample 10, start the shaker table, set the vibration time through the timing controller 7, set the vibration frequency through the frequency converter 6, and apply the initial vibration according to the preset vibration time and vibration frequency to liquefy the saturated sand sample 10, and collect the data of the first accelerometer 11 and the pore water pressure gauge 12 buried inside the saturated sand sample 10, denoted as SJ1.

[0095] S3: After the excess pore water pressure is completely dissipated, apply the same vibration as in S2 again to liquefy the saturated sand sample 10 again, and collect the data of the first accelerometer 11 and the pore water pressure gauge 12, denoted as SJ2; it should be noted that the complete dissipation of the excess pore water pressure can be judged according to the data of the pore water pressure gauge 12. The pore water pressure gauge 12 is connected to the data collector 13, and the data collector 13 is connected to the computer 14. The data measured by the pore water pressure gauge 12 can be directly displayed on the computer 14.

[0096] S4: After preparing the saturated sand sample 10, freeze the saturated sand sample 10 for the freezing time T1 through the freezer 15. After the frozen saturated sand sample 10 thaws for the thawing time T2, apply the same vibration as in S2 to liquefy the thawed saturated sand sample 10, and collect the data of the first accelerometer 11 and the pore water pressure gauge 12, denoted as SJ3.

[0097] S5: After the excess pore water pressure is completely dissipated, apply the same vibration as in S2 again to liquefy the thawed saturated sand sample 10 again, and collect the data of the first accelerometer 11 and the pore water pressure gauge 12, denoted as SJ4.

[0098] S6: After preparing the saturated sand sample 10, apply the same vibration as in S2 to liquefy the saturated sand sample 10. After the excess pore water pressure is completely dissipated, freeze the saturated sand sample 10 after the first liquefaction for the freezing time T1 through the freezer 15. After the frozen saturated sand sample 10 after the first liquefaction is thawed for the thawing time T2, apply the same vibration as in S2 again to liquefy the thawed saturated sand sample 10 after the first liquefaction, and collect the data of the first accelerometer 11 and the pore water pressure gauge 12, denoted as SJ5;

[0099] S7: Compare SJ1 with SJ3 to obtain the influence of freeze-thaw on the initial liquefaction characteristics of sand; compare SJ2 with SJ4 to obtain the influence of freeze-thaw on the re-liquefaction characteristics of sand; compare SJ2 with SJ5 to obtain the influence of freeze-thaw after the initial liquefaction of sand on the re-liquefaction characteristics of sand.

[0100] It should be noted that during each group of tests, the same value is set through the frequency converter 6 to theoretically ensure the consistency of the input acceleration, and the consistency of the input acceleration is verified by the acceleration measured by the second accelerometer 16 fixed at the bottom of the model box 8.

[0101] Preferably, when liquefying the saturated sand sample in the embodiment of the present invention, it is judged whether the saturated sand sample is liquefied according to the following formula;

[0102] u = σ';

[0103] σ' = γ'h;

[0104] γ' = [(G s -1)ρ w g] / (1 + e);

[0105] e = G s ρ w / ρ d -1;

[0106] ρ d = m s / v;

[0107] Where:

[0108] u: Excess pore water pressure, read according to the pore water pressure gauge 12, unit kPa;

[0109] γ': Effective unit weight of the saturated sand sample 10, unit kN / m 3 ;

[0110] h: Burial depth of the pore water pressure gauge 12 from the top of the saturated sand sample 10, unit m;

[0111] ρ d: Dry density of the saturated sand sample 10, unit: g / cm 3 ;

[0112] m s : Total mass of sand particles in the saturated sand sample 10, which can be measured after drying the sand sample, unit: g;

[0113] v: Volume of the saturated sand sample 10, which can be calculated according to the size of the model box 8 and the height of the saturated sand sample 10, unit: cm 3 ;

[0114] e: Void ratio, unit: 1;

[0115] G s : Specific gravity of sand particles in the saturated sand sample 10, obtained from laboratory tests, unit: 1;

[0116] ρ w : Density of distilled water, unit: g / cm 3 ;

[0117] g: Acceleration due to gravity, unit: m / s 2 .

[0118] An experimental device and experimental method for studying the influence of freeze-thaw on the liquefaction characteristics of sand provided by an embodiment of the present invention place a shaking table and a model box for placing a saturated sand sample in a freezer, which can freeze the saturated sand sample, provide a freeze-thaw environment, and conduct multiple sets of lateral tests by applying freezing at different stages, so as to study the influence of freeze-thaw on the initial liquefaction, re-liquefaction, etc. of saturated sand, which is closer to the actual situation. And the structure integrity of the experimental device is relatively high, and the operation is simple and convenient.

[0119] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. An experimental device for studying the influence of freeze-thaw on sand liquefaction, characterized in that, Comprising: A shaking table, a model box for placing saturated sand samples, a detection module, an analysis module, and a freezer; The model box is connected to the shaking table, and the model box and the shaking table are placed inside the freezer; The detection module includes a first accelerometer and a pore water pressure gauge buried inside the saturated sand sample; the detection module is electrically connected to the analysis module.

2. The test device for studying the influence of freeze-thaw on sand liquefaction according to claim 1, wherein The shaking table includes a base, a tabletop, compression springs, and vibration motors; A plurality of limit blocks are welded to the top of the base, and the same number of limit blocks are welded to the bottom of the tabletop. The corresponding limit blocks are flexibly connected by the compression springs; the bottom of the tabletop is fixedly connected to the vibration motor by bolts.

3. The test device for studying the influence of freeze-thaw on sand liquefaction according to claim 2, characterized in that, The vibration motor is a three-phase asynchronous motor. The vibration motor is electrically connected to a frequency converter, and the frequency converter is electrically connected to a timing controller.

4. The test device for studying the influence of freeze-thaw on sand liquefaction according to claim 3, wherein, The size of the bottom plate of the model box is the same as the size of the tabletop, and the top of the tabletop is fixedly connected to the bottom plate of the model box by bolts; The model box is made of high-strength explosion-proof tempered glass, and a sponge is pasted on the inner side of the model box.

5. The test device for studying the influence of freeze-thaw on sand liquefaction according to claim 4, characterized in that, The detection module further includes a second accelerometer fixed to the bottom of the model box, and the second accelerometer is electrically connected to the analysis module.

6. An experimental method for studying the influence of freeze-thaw on sand liquefaction, characterized in that, Using the test device for studying the influence of freeze-thaw on sand liquefaction according to any one of claims 1 to 5, the test method includes: S1: After preparing the saturated sand sample, conduct a freezing pre-test and a thawing pre-test on the saturated sand sample to determine the freezing time and thawing time of the saturated sand sample; S2: After preparing the saturated sand sample, start the shaking table, and apply initial vibration according to the preset vibration time and vibration frequency to liquefy the saturated sand sample. Collect the data of the first accelerometer and the pore water pressure gauge buried inside the saturated sand sample, and record it as SJ1; S3: After the excess pore water pressure is completely dissipated, apply the same vibration as in S2 again to liquefy the saturated sand sample again. Collect the data of the first accelerometer and the pore water pressure gauge, and record it as SJ2; S4: After preparing the saturated sand sample, freeze the saturated sand sample in the freezer for the freezing time. After the frozen saturated sand sample thaws for the thawing time, apply the same vibration as in S2 to liquefy the thawed saturated sand sample. Collect the data of the first accelerometer and the pore water pressure gauge, and record it as SJ3; S5: After the excess pore water pressure is completely dissipated, apply the same vibration as in S2 again to liquefy the thawed saturated sand sample again. Collect the data of the first accelerometer and the pore water pressure gauge, and record it as SJ4; S6: After preparing the saturated sand sample, apply the same vibration as in S2 to liquefy the saturated sand sample. After the excess pore water pressure is completely dissipated, freeze the initially liquefied saturated sand sample in the freezer for the freezing time. After the frozen initially liquefied saturated sand sample thaws for the thawing time, apply the same vibration as in S2 again to liquefy the thawed initially liquefied saturated sand sample again. Collect the data of the first accelerometer and the pore water pressure gauge, and record it as SJ5; S7: Compare SJ1 with SJ3 to obtain the influence of freeze-thaw on the initial liquefaction characteristics of sand; compare SJ2 with SJ4 to obtain the influence of freeze-thaw on the re-liquefaction characteristics of sand; compare SJ2 with SJ5 to obtain the influence of freeze-thaw after the initial liquefaction of sand on the re-liquefaction characteristics of sand.

7. The test method for studying the influence of freeze-thaw on sand liquefaction according to claim 6, characterized in that, The steps of the freezing pre-test include: S111: After preparing a saturated sand sample, freeze the saturated sand sample in a freezer at a preset temperature. S112: Observe the freezing condition of the saturated sand sample at preset time intervals, and measure the heights at the middle and both ends of the saturated sand sample on both side walls of the model box. S113: Repeat S12. After the measured heights no longer change, take out the frozen saturated sand sample in the model box and crack and decompose the frozen saturated sand sample with a heavy hammer. If there is no unfrozen saturated sand sample in the decomposed blocks, it is determined that the saturated sand sample has been completely frozen. S114: Take the sum of all the freezing times in S11 - S13 plus a preset time as the freezing time for the formal test, denoted as T1.

8. The test method for studying the influence of freeze-thaw on sand liquefaction according to claim 7, characterized in that, The steps of the thawing pre-test include: S121: After preparing a saturated sand sample, measure and record the temperature inside the saturated sand sample, and freeze the saturated sand sample in the freezer at a preset temperature for a freezing time of T1. S122: Stop freezing and measure the heights at the middle and both ends of the saturated sand sample on both side walls of the model box; then measure the heights at the middle and both ends of the saturated sand sample on both side walls of the model box at the preset time intervals until the heights no longer change, and then measure the temperature inside the saturated sand sample at the preset time intervals until the temperature inside the saturated sand sample returns to the temperature before freezing. S123: Take the time from stopping freezing to the temperature inside the saturated sand sample returning to the temperature before freezing in S122 plus a preset time as the thawing time for the formal test, denoted as T2.

9. The test method for studying the influence of freeze-thaw on sand liquefaction according to claim 8, characterized in that, In S2, set the vibration time through a timing controller and set the vibration frequency through a frequency converter.

10. The test method for studying the influence of freeze-thaw on sand liquefaction according to claim 9, characterized in that, When liquefying the saturated sand sample, judge whether the saturated sand sample is liquefied according to the following formula; u = σ'; σ' = γ'h; γ'=[(G s -1)ρ w g] / (1+e); e = G s ρ w / ρ d -1; ρ d = m s / v; Where: u: Excess pore water pressure, read according to a pore water pressure gauge, unit kPa; γ': Effective unit weight of saturated sand sample, unit kN / m 3 ; h: Burial depth of the pore water pressure gauge from the top of the saturated sand sample, unit m; ρ d : Dry density of saturated sand sample, unit: g / cm 3 ; m s : Total mass of sand particles in saturated sand sample, unit: g; v: Volume of saturated sand sample, unit: cm 3 ; e: Void ratio, unit 1; G s : Specific gravity of sand particles of saturated sand sample, unit 1; ρ w : The density of distilled water, unit g / cm 3 ; g: acceleration due to gravity, unit m / s 2 。

Images