Experimental device and experimental method for simulating water level circulation lifting seepage of calcareous sand

Abstract

The invention relates to the technical field of seepage experiments, in particular to a calcareous sand simulation water level circulation lifting seepage experiment device and experiment method.The calcareous sand simulation water level circulation lifting seepage experiment device comprises a box body and a precipitation barrel located below the box body, the bottom of the box body is a filter plate provided with a plurality of through holes, the interior of the box body is of a hollow structure used for being filled with calcareous sand samples, and a box cover is arranged on the upper portion of the box body; the tank cover is provided with an upper exhaust port and an upper water inlet connected with the bottom of the water column, the upper portion of the water column is connected with the water tank, the settling barrel is provided with a lower water outlet and a lower connector, the lower water outlet is connected with the water collection measuring cylinder, and the lower connector is connected with a water level regulation and control system used for controlling water level circulation lifting. According to the invention, non-invasive fine particle migration path visualization can be realized, and meanwhile, tide water level cyclic rising and falling can be realized, so that the stability of the calcareous sand foundation under the action of long-term rainfall and water level cyclic rising and falling can be researched.

Description

Technical Field

[0001] The present invention relates to the technical field of seepage experiments, and specifically to a seepage experiment device and method for simulating the cyclic rise and fall of the water level in calcareous sand. Background Technique

[0002] As a special marine geotechnical medium, calcareous sand is mainly formed by the physical and chemical cementation and sedimentation of marine bioclasts (corals, algae, shells, etc.) under the action of carbonate solutions over a long period. Its unique diagenetic process endows it with engineering properties significantly different from those of terrigenous sands: highly irregular particle morphology (angular, flaky structure), well-developed internal pores, low strength and easy breakability, and cementation-dissolution dual characteristics. As the main filler for calcareous sand foundation engineering and marine filling engineering, it faces severe challenges to seepage stability in complex marine dynamic environments.

[0003] In marine engineering practice, most calcareous sand foundations are surrounded by the sea on all sides, with abundant rainfall and long-term tidal influence, resulting in a long-term fluctuating groundwater level. Due to the large porosity and strong permeability of the dredged calcareous sand foundation, the fine particles of coral sand inside will undergo dynamic migration along with seepage under the action of hydraulic force, changing the internal structure of the soil, that is, migration phenomenon occurs, which in turn leads to dual engineering effects: on the one hand, the loss of fine particles causes the dynamic evolution of the permeability coefficient, directly affecting the drainage consolidation efficiency; on the other hand, the redistribution of fine particles may induce seepage deformation failures (piping, internal erosion, etc.), resulting in a sudden drop in the bearing capacity of the foundation.

[0004] The current research system has significant technical bottlenecks: traditional seepage experiment devices (such as constant head / variable head permeameters) cannot realize the visual monitoring of specimen migration under dynamic seepage conditions. Secondly, traditional seepage experiment devices can only perform single simulation seepage actions and lack the simulation of the cyclic rise and fall of the water level. This technical defect cannot accurately reflect the seepage stability of calcareous sand foundations under long-term complex working conditions such as tides, and cannot provide a reference for the long-term stable construction of dredged calcareous sand foundations, restricting the safety design and disaster prevention and control capabilities of calcareous sand foundation engineering. Summary of the Invention

[0005] The purpose of the present invention is to provide a seepage experiment device and method for simulating the cyclic rise and fall of the water level in calcareous sand in view of the deficiencies of the prior art, which can realize the visualization of the migration path of non-invasive fine particles and can simultaneously realize the cyclic rise and fall of the water level of tides, thereby studying the stability of calcareous sand foundations under the action of long-term rainfall and cyclic rise and fall of the water level, and solving the problems existing in the above-mentioned prior art.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: A kind of seepage experiment device for simulating the cyclic rise and fall of water level in calcareous sand, which includes a box body and a sedimentation barrel detachably connected to the box body below. The bottom of the box body is a filter plate with multiple through holes. The inside of the box body is a hollow structure for filling calcareous sand specimens. There is a box cover on the upper part of the box body. An upper exhaust port and an upper water inlet connected to the bottom of the water column are arranged on the box cover. The upper part of the water column is connected to a water tank. The sedimentation barrel is provided with a lower water outlet and a lower connection port. The lower water outlet is connected to a water collection cylinder, and the lower connection port is connected to a water level control system for controlling the cyclic rise and fall of the water level.

[0007] Further, the water column is provided with a water outlet at the bottom of the water column and multiple drainage ports at intervals in the vertical direction. The water outlet is connected to the upper water inlet, and drainage valves are arranged at the drainage ports. The hydraulic gradient is adjusted by opening the drainage valves at any height for drainage.

[0008] Further, valves are arranged at the upper water inlet, the lower water outlet, and the lower connection port.

[0009] Further, the box body is provided with multiple water level sensors at intervals in the vertical direction. The water level sensors are electrically connected to the water level control system.

[0010] An experimental method applied to the above-mentioned seepage experiment device for simulating the cyclic rise and fall of water level in calcareous sand includes the following steps: Step 1: Predetermine the specimen gradation, measure the maximum, minimum dry densities and normal dry density of the specimen, and prepare specimens with various different particle sizes according to the experimental requirements. Step 2: Divide the specimen into multiple layers from bottom to top along the seepage direction. The fine particle specimens with various different particle size ranges in each layer are respectively dyed with different colors. After dyeing, the fine particle specimens are dried. Step 3: Fill the specimens into the box body layer by layer and compact them. Take a photo of the initial distribution state of the fine particle specimens on the top layer, and lay a layer of gravity balls above the top layer to prevent the specimens on the top layer from being washed away. Step 4: Close the lower water outlet and the upper water inlet. Add water into the water column through the water tank, and open the drainage valve of a certain drainage port to drain water to adjust the hydraulic gradient. Step 5: Open the lower connection port, inject water or drain water into the sedimentation barrel through the water level control system, and simulate the cyclic rise and fall of the tidal water level in the box body. Step 6: After the simulation is completed, inject water into the sedimentation barrel through the water level control system until the water level is higher than the gravity balls. Close the lower connection port and let it stand for exhaust until no gas is discharged from the exhaust port, and the specimen is saturated. Step 7: Open the lower water outlet and the upper water inlet. Stably inject water into the water column from the top of the water column through the water tank, record the water seepage volume per unit time until the measured permeability coefficients are stable in the previous and subsequent measurements. Step 8: Close the upper water inlet. After the water in the box drains out from the lower water outlet, take out the sediment bucket particles and observe and record the color and proportion of the sample particles that seep from the filter plate into the sediment bucket. Repeat the above Steps 5 to 8 according to the experimental requirements to perform the seepage actions after multiple water level cyclic rises and falls; during the entire experiment, photograph and record the distribution state and migration of the fine particles of the sample on the front of the box. Step 9: Open the box cover, take out the sample in multiple layers from top to bottom at a certain unit height, photograph and record the distribution state of the fine particles of the sample from above the box and analyze.

[0011] Further, in the above Step 1, apply a layer of vaseline on the inner sidewall of the box.

[0012] Further, in the above Step 2, the sample is divided into three layers. The first layer uses a fluorescent dye to stain the fine particle sample, and the second and third layers respectively use different stone dyes to stain the fine particle samples in multiple particle size ranges.

[0013] Further, in the above Step 2, the first layer of the sample uses a fluorescent dye to stain the fine particle sample with a particle size below 0.5 mm, and the second and third layers respectively use different stone dyes to stain the fine particle samples in the particle size ranges of 0.25 mm to 0.5 mm, 0.1 mm to 0.25 mm, and 0.075 mm to 0.1 mm.

[0014] Further, in the above Step 3, a certain amount of water is incorporated into each layer of the sample and stirred and mixed before loading the sample.

[0015] Further, in the above Step 7, record the water seepage volume every 10 minutes in the first hour, and then record the water seepage volume every 30 minutes.

[0016] In the prior art regarding the seepage of coarse-grained soil and calcareous sand, there are not many applicable solutions for the migration of fine particles, and even fewer for the influence of water level cyclic rises and falls on the migration and permeability of fine particles. In order to better study the change in the permeability of some strata of the reclaimed calcareous sand foundation under the influence of water level cyclic rises and falls and the migration law of fine particles, the experimental method of the calcareous sand simulated water level cyclic rise and fall seepage experimental device proposed by the present invention has the following beneficial effects and application values compared with the prior art: The present invention stains and marks fine - grained specimens separately to visually observe the movement characteristics of the fine - grained specimens in real - time, distinguish the migration of fine - grained soil particles in multi - layer soil masses, and realize the visualization of the non - invasive migration path of fine - grained particles in coarse soils such as calcareous sand during seepage. At the same time, through the water - level control system, the present invention realizes multiple cyclic rises and falls of the water level in the box, accurately simulates the tidal water - level fluctuations, and without damaging the specimens, continuously observes the migration characteristics of fine - grained particles under the action of cyclic rises and falls of the water level in the same area, so as to study the influence of the groundwater - level fluctuations in the reclaimed calcareous - sand foundation caused by multiple tides on the seepage properties of the formation, and further explain the geological disasters such as local collapses caused by seepage in the calcareous - sand foundation under the influence of long - term rainfall, cyclic water - level fluctuations, etc. In addition, the present invention can freely adjust the hydraulic gradient during infiltration, as well as the rising and falling rates and hydraulic gradients during cyclic rises and falls of the water level. It is convenient, quick, easy to install, reusable, improves the application range and flexibility of the experimental device, and thus better studies and explains the relationship between fine - grained particle migration, permeability coefficient, and the number of water - level cycles. Brief Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the overall structure of a calcareous - sand simulated water - level cyclic rise - and - fall seepage experimental device provided by the present invention.

[0018] Among them, the reference numerals are: 1. Box body; 11. Filter plate; 2. Box cover; 21. Upper exhaust port; 22. Upper water inlet; 3. Precipitation barrel; 31. Lower water outlet; 32. Lower connection port; 4. Water - stop ring; 5. Specimen; 6. Water column; 61. Water outlet; 62. Drainage port; 7. Water tank; 8. Water - level control system; 9. Water - level sensor; 10. Water - collection cylinder; 101. Gravity ball. Detailed Embodiments

[0019] In order to enable those skilled in the art to better understand the solutions of this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of this application.

[0020] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0021] It should be understood that the orientation or positional relationship indicated by terms such as "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application 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 thus should not be construed as a limitation to the present application.

[0022] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0023] For ease of understanding, please refer to Figure 1, this embodiment provides a seepage experiment device for simulating the cyclic rise and fall of water level in calcareous sand, which is characterized in that it includes a box body 1 with a hollow structure, a box cover 2 located above the box body 1, and a sedimentation bucket 3 located below the box body 1. The box cover 2 is bolted to the box body 1, and the box body 1 is bolted to the sedimentation bucket 3. Further, a water stop ring 4 is provided at the connection between the box cover 2 and the box body 1, and between the box body 1 and the sedimentation bucket 3. The water stop ring 4 is used to prevent water leakage at each connection gap during the experiment. Preferably, the box body 1, the box cover 2, and the sedimentation bucket 3 are all made of transparent materials. The bottom of the box body 1 is a filter plate 11, and a plurality of 1-mm vertical through holes are evenly opened on the filter plate 11. The upper part of the sedimentation bucket 3 is communicated with the filter plate 11. Three layers of calcareous sand specimens 5 are arranged in layers in the vertical direction above the filter plate 11. The thickness of each specimen 5 is 15 cm, that is, the total length of the seepage path from top to bottom is set to 45 cm. The particle size of the specimen 5 is within 10 mm, and the particle size of the fine particle specimen 5 is within 0.5 mm. An upper exhaust port 21 and an upper water inlet 22 are opened on the box cover 2. A water column 6 is provided with a water outlet 61 and a plurality of drain ports 62 at intervals in the vertical direction. The water tank 7 injects water into the water column 6 from the top of the water column 6. The water outlet 61 is located at the bottom of the water column 6 and is communicated with the upper water inlet 22 through a water pipe. A drain valve for controlling the on-off of the water flow at each drain port 62 is provided corresponding to each drain port 62. By opening the drain valve at any height, the water in the water column 6 is discharged to adjust the water level height in the water column 6, that is, to adjust the height difference between the drain port 62 and the water outlet 61, so as to realize the free adjustment of the hydraulic gradient. Further, the corresponding drain port 62 can be communicated with the water tank 7 through a water pipe, that is, the water discharged through the drain port 62 is transported back to the water tank 7 through the water pipe for reuse. Preferably, the water outlet 61 at the bottom of the water column 6 is higher than the upper water inlet 22 of the box cover 2. The sedimentation bucket 3 is provided with a lower water outlet 31 and a lower connection port 32. The lower water outlet 31 is communicated with a water collection cylinder 10 through a water pipe, and the lower connection port 32 is connected to a water level control system 8 through a water pipe. A plurality of water level sensors 9 are provided on the box body 1 at intervals of 10 cm in the vertical direction. The water level sensors 9 are electrically connected to the water level control system 8. The water level situation in the box body 1 is monitored in real time through the water level sensors 9 to facilitate the subsequent cyclic rise and fall of the water level. The water level control system 8 is used to control the cyclic rise and fall of the water level in the box body 1 to simulate the cyclic rise and fall of the water level of the tide. Further, valves for controlling the on-off of the water flow at the upper water inlet 22, the lower water outlet 31, and the lower connection port 32 are provided. Specifically, the water level control system 8 includes a controller and a two-way pump that can supply water forward and drain water backward. The parameters such as the cyclic rise and fall waveform, rise and fall period, rise and fall amplitude, and rise and fall rate of the water level in the box body 1 are controlled by the controller, and the water inlet and drainage of the cyclic rise and fall of the water level in the box body 1 are realized through the two-way pump.More specifically, the control code is written, compiled, and uploaded in the Arduino IDE (development environment on the computer). The compiled code is burned into the Arduino board via the USB cable and finally executed in the microcontroller of the Arduino. The code reads hardware signals and controls hardware actions. The detailed operation process is as follows: 1. Install the Arduino IDE 1.1. Visit the official website https: / / www.arduino.cc / , download and install the IDE corresponding to the operating system.

[0024] 1.2. After opening the IDE, select the development board model 1.3. Set the serial port: After connecting the Arduino to the computer, select the corresponding COM port 2. Install the dependent libraries 2.1. PID library: In the IDE, click Sketch → Include Library → Manage Libraries, search for PID and install it.

[0025] 3. Code writing and uploading 3.1. Generate the tidal waveform, and the resulting code is as follows: #include <PID_v1.h> #include <RTClib.h> / / For real-time clock RTC_DS3231 rtc; / / Define tidal parameters #define TIDE_PERIOD 43200 / / 12-hour period (seconds) #define TIDE_AMPLITUDE 0.5 / / Water level fluctuation amplitude (meters) / / PID initialization double Setpoint, Input, Output; PID myPID(&Input, &Output, &Setpoint, 2.0, 0.5, 0.1, DIRECT); void setup() { rtc.begin(); myPID.SetMode(AUTOMATIC); myPID.SetOutputLimits(-255, 255); / / Bidirectional control } void loop() { DateTime now = rtc.now(); unsigned long seconds = now.hour() * 3600 + now.minute() * 60 + now.second(); / / Generate the target tide level (sine wave) Setpoint = TIDE_AMPLITUDE * sin(2 * PI * seconds / TIDE_PERIOD); / / Read the actual water level (unit: meter) Input = read_water_level(); / / PID calculation and control myPID.Compute(); control_pump(Output); } 3.2. Two-way pump control, the code is as follows: void control_pump(double output) { if (output > 0) { / / Flood tide: forward peristaltic pump (intake water) analogWrite(PUMP_IN_PIN, output); digitalWrite(PUMP_OUT_PIN, LOW); } else { / / Ebb tide: reverse peristaltic pump (drain water) analogWrite(PUMP_OUT_PIN, -output); digitalWrite(PUMP_IN_PIN, LOW); } } 4. Hardware connection and testing 4.1. Connection verification Ensure the following connections are correct: Relay module: IN1 → D7 (control intake water), IN2 → D8 (control drain water), VCC → 5V, GND → GND.

[0026] Water pump / solenoid valve: positive pole → relay COM port, negative pole → power GND.

[0027] 4.2 Power supply and startup Connect the Arduino to the computer via USB (or an external 9V power supply).

[0028] Provide a separate 12V supply for the bi-directional pump and relay (to avoid overloading the Arduino).

[0029] 5. PID parameter debugging (key steps) 5.1. Manual debugging method Step 1: Set Ki and Kd to 0, and gradually increase Kp until the water level starts to oscillate.

[0030] Step 2: Record Kp (critical value Ku) and oscillation period Tu during oscillation.

[0031] Step 3: Calculate the parameters according to the Ziegler-Nichols formula: 5.2 Automatic debugging tools Use the PID_AutoTune library (needs additional installation) to automatically calculate the optimal parameters.

[0032] The experimental method of the calcareous sand simulated water level cycle rise and fall seepage experimental device includes the following steps: Step 1: Preliminary preparation Before the experiment begins, ensure that all components are connected correctly, confirm that there is no leakage in any part of the water supply path, and apply a layer of vaseline about 0.5 mm thick on the inner wall of the box 1 to avoid the phenomenon of concentrated seepage along the inner wall of the box 1 during the experiment. Determine the gradation of the calcareous sand sample 5 in advance according to the experimental requirements, measure the maximum and minimum dry density and normal dry density of the sample 5, and the calcareous sand sample 5 is divided into the first layer, the second layer, and the third layer from bottom to top along the seepage direction. Each layer is 15 cm thick, and the total length of the seepage path is 45 cm. Prepare calcareous sand samples 5 of various particle sizes according to the experimental requirements; Step 2: Staining For the fine particle specimens 5 (with particle size less than 0.5 mm) in each layer with multiple different particle size ranges, they are respectively dyed with different colors. Since the colors of the fluorescent dyes are limited, and there are multiple fine particles with different particle size ranges in the three-layer specimen 5, it is not convenient to uniformly use fluorescent dyes. Therefore, stone dyes are introduced on the basis of the fluorescent dyes for dyeing, so as to better analyze the migration path and distribution of the fine particle specimens 5 in the subsequent process. Specifically, the first layer is dyed with a fluorescent dye for the fine particle specimen 5, and the second and third layers are respectively dyed with different stone dyes for the fine particle specimens 5 with multiple different particle size ranges, which is convenient for observing the specific distribution and migration path of the fine particle specimens 5 in the subsequent process. After dyeing, the fine particle specimens 5 are dried. More specifically, the specimen 5 in the first layer is dyed and marked with a fluorescent dye for the fine particle specimen 5 with a particle size less than 0.5 mm; in the second layer, the fine particle specimen 5 with a particle size range of 0.25 mm to 0.5 mm is dyed red with a stone dye, the fine particle specimen 5 with a particle size range of 0.1 mm to 0.25 mm is dyed blue, and the fine particle specimen 5 with a particle size range of 0.075 mm to 0.1 mm is dyed green; in the third layer, the fine particle specimen 5 with a particle size range of 0.25 mm to 0.5 mm is dyed black with a stone dye, the fine particle specimen 5 with a particle size range of 0.1 mm to 0.25 mm is dyed yellow, and the fine particle specimen 5 with a particle size range of 0.075 mm to 0.1 mm is dyed purple. Then all the dyed fine particle specimens 5 are placed in an oven for drying treatment at 60 °C for 2 hours.

[0033] Step Three: Specimen 5 Filling (Loading the Sample) In order to prevent the coarse and fine particles of the specimen 5 from separating from each other during the sample loading process, 5% water is respectively pre-mixed into each layer of the weighed and dyed specimen 5 and thoroughly mixed to make it uniform. Then each layer of the mixed specimen 5 is filled into the vertical box 1 in sequence and compacted layer by layer, and the initial distribution state of each layer of the specimen 5 is photographed, and the layer interface is roughened; then a layer of gravity balls 101 is laid above the third layer to prevent the specimen 5 in the third layer from being washed away by the water flow during the experiment. Preferably, the gravity balls 101 are transparent glass balls with a diameter of 2 mm.

[0034] Step Four: Hydraulic Gradient Setting Close the lower water outlet 31 and the upper water inlet 22, inject water into the water column 6 through the water tank 7, and open the valve of a certain drain port 62 to drain water to ensure the stability of the osmotic head height, and freely select the hydraulic gradient required for the experiment. Specifically, a certain drain port 62 can be connected to the water tank 7 through a water pipe to form a water circuit cycle between the water tank 7 and the water column 6.

[0035] Step Five: Tidal Simulation Close the lower water outlet 31 and the upper water inlet 22, open the lower connection port 32, inject water or drain water into the sedimentation barrel 3 through the water level control system 8, and the water level gradually rises from bottom to top into the box body 1. Simulate the waveform, period, amplitude, and rising and falling rate of the tide through program setting, and simulate the cyclic rising and falling of the tide water level in the box body 1.

[0036] Step Six: Saturate the specimen 5 After the simulation of the cyclic rising and falling of the tide water level is completed, inject water into the sedimentation barrel 3 through the water level control system 8. The water level in the box body 1 gradually rises from bottom to top until the water level is higher than the gravity ball 101. Close the lower connection port 32 and let it stand for exhaust until no gas is discharged at the exhaust port, then the specimen 5 is saturated. Specifically, one end of the trachea can be connected to the exhaust port, and the other end of the trachea can be immersed in water. Observe whether there are bubbles in the water. If bubbles continuously appear in the water, it means that gas is continuously discharged from the exhaust pipe and the specimen 5 is not saturated. If no bubbles appear in the water, it means that no gas is discharged from the exhaust pipe and the specimen 5 is saturated.

[0037] Step Seven: Seepage action Open the lower water outlet 31 and the upper water inlet 22, stably inject water into the water column 6 from the top of the water column 6 through the water tank 7, and make the seepage head height stable by opening the valve of a certain drain port 62 of the water column 6. At this time, the water in the water column 6 continuously flows into the box body 1 through the water pipe from the upper water inlet 22, that is, continuously inject water into the box body 1 from above the box body 1. The water in the box body 1 continuously discharges to the water collecting cylinder 10 through the water pipe at the lower water outlet 31 of the lower sedimentation barrel 3 below, that is, continuously drain water from the lower part of the box body 1 to the outside of the box body 1. Record the seepage water volume of the monitoring water collecting cylinder 10 per unit time until the seepage water volumes measured twice before and after are stable, that is, when the permeability coefficient is stable, this seepage action is completed. Specifically, since the seepage water volume changes relatively fast in the first period of time during seepage and gradually stabilizes later, it is set to record the seepage water volume every 10 minutes in the first hour during the seepage process and every 30 minutes later.

[0038] According to Darcy's law , where k is the permeability coefficient (cm / s), Q is the seepage water volume (cm³), A is the cross-sectional area of the specimen 5 (cm²), L is the height of the specimen 5 (cm), ΔH is the head difference (i.e., the height difference between the drain port 62 in the open state and the water outlet 61) (cm), and t is the seepage unit time (s). During the simulation of the cyclic rising and falling of the tide water level and the seepage process, the fine-grained specimen 5 will migrate due to hydraulic action. During each cycle of the water level rising and falling and the seepage process, the structure of the specimen 5 will change, which will in turn cause the permeability coefficient of the specimen 5 to change and the seepage water volume to change. When the seepage water volumes measured twice before and after are stable, it means that the internal structure of the seepage specimen 5 has been stable, that is, the permeability coefficient is stable, and the next step can be carried out.

[0039] Step 8. Drainage record Close the upper water inlet 22 to stop water injection into the box body 1. Wait for the water in the box body 1 to drain from the lower water outlet 31 until the water level is lower than the lower water outlet 31. At this time, there is no water in the box body 1, and then close the lower water outlet 31. Take out the sedimentation bucket 3 from below the box body 1, observe and record the color and proportion of the sample 5 that seeps from the filter plate 11 at the lower part of the box body 1 into the sedimentation bucket 3. After recording, take out all the samples 5 in the sedimentation bucket 3, empty the sedimentation bucket 3, and then install the sedimentation bucket 3 back below the box body 1 to ensure that there is no leakage at the connection between the box body 1 and the sedimentation bucket 3.

[0040] Repeat the above steps 5 to 8 according to the experimental requirements for multiple water level cycling up and down and seepage actions. During the entire process of multiple water level cycling up and down and seepage, record the distribution state and migration situation of the sample 5 by taking pictures on the front of the box body 1.

[0041] Step 9. Subsequent treatment and analysis After completing the scheduled multiple water level cycling up and down and seepage actions, record the final distribution state and migration situation of the sample 5 by taking pictures on the front of the box body 1, and use ImageJ software to focus on analyzing the distribution and migration path of the fluorescently stained fine particle sample 5 recorded during the entire experimental process. Open the box cover 2, take out the sample 5 in multiple layers from top to bottom at a certain unit height, take pictures of the distribution state of each layer of the sample 5 from above the box body 1, and focus on observing the distribution state of the fine particle sample 5 of the stained stone. Preferably, the unit height is 5 cm. Calculate the permeability coefficient according to the water seepage volume at each time period, compare the change of the permeability coefficient of the sample 5 after multiple water level cycling up and down, analyze the migration path and distribution of the fine particle sample 5, and then analyze the influence mechanism of the water level cycling up and down on the permeability performance of the sample 5.

[0042] Furthermore, during the entire experimental process, the valves of different drain outlets 62 can be switched on and off according to the actual experimental situation and requirements to appropriately adjust the hydraulic gradient.

[0043] The invention can simulate the seepage situation of the hydraulic fill calcareous sand foundation under the action of water level cycling up and down, can realize the visualization of the migration path of fine particles under the action of various different hydraulic gradients, can observe the migration path and characteristics of fine particles in real time, can better explain the relationship between the migration of fine particles and the permeability coefficient and the number of water level cycles, can simulate the influence of long-term water level cycling up and down on the permeability performance of calcareous sand and the stability of the formation, provide a microscopic research method and idea for the migration of fine particles in calcareous sand, better explain the secondary geological disasters such as piping and local ground collapse caused by seepage, and provide a theoretical basis for the prevention of secondary disasters of calcareous sand foundation.

[0044] Although the present invention has been described by using the above preferred embodiments, it is not intended to limit the protection scope of the present invention. Any person skilled in the art, without departing from the spirit and scope of the present invention, making various changes and modifications to the above embodiments still belongs to the scope protected by the present invention.

Claims

1. A method for simulating the seepage experiment of the cyclic rise and fall of the water level in calcareous sand, characterized in that It includes the following steps: Step 1: Predetermine the gradation of the specimen (5), measure the maximum, minimum and normal dry densities of the specimen (5), and prepare specimens (5) with various different particle sizes according to the experimental requirements; Step 2: Divide the specimen (5) into multiple layers from bottom to top along the seepage direction. Dye the fine particle specimens (5) with various different particle size ranges in each layer with different colors respectively. After dyeing, dry the fine particle specimens (5); Step 3: Fill the specimen (5) into the box body (1) layer by layer and compact it. Take a photo of the initial distribution state of the topmost layer of fine particle specimen (5), and lay a layer of gravity balls (101) above the topmost layer to prevent the specimen (5) in the topmost layer from being washed away; Step 4: Close the lower water outlet (31) and the upper water inlet (22). Add water into the water column (6) through the water tank (7), and open the valve of a certain drain port (62) to drain water, and adjust the hydraulic gradient; Step 5: Open the lower connection port (32), and inject water or drain water into the sedimentation bucket (3) through the water level control system (8) to simulate the cyclic rise and fall of the tidal water level in the box body (1); Step 6: After the simulation is completed, inject water into the sedimentation bucket (3) through the water level control system (8) until the water level is higher than the gravity balls (101). Close the lower connection port (32), and let it stand for exhaust until no gas is discharged at the exhaust port, and the specimen (5) is saturated; Step 7: Open the lower water outlet (31) and the upper water inlet (22). Steadily inject water into the water column (6) from the top of the water column (6) through the water tank (7), record the seepage water volume per unit time until the measured permeability coefficients are stable in the previous and subsequent times; Step 8: Close the upper water inlet (22). After the water in the box body (1) is discharged from the lower water outlet (31), take out the particles in the sedimentation bucket (3) and observe and record the color and proportion of the specimen (5) particles that seep from the filter plate (11) into the sedimentation bucket (3); Repeat Steps 5 to 8 above according to the experimental requirements to perform the seepage actions after multiple cyclic rises and falls of the water level; during the whole experiment process, take photos and record the distribution state and migration situation of the fine particles of the specimen (5) on the front side of the box body (1); Step 9: Open the box cover (2), take out the specimen (5) layer by layer from top to bottom with a certain unit height for multiple times, take a photo of the distribution state of the fine particles of the specimen (5) from above the box body (1) and analyze it.

2. The seepage experiment method for simulating the cyclic rise and fall of the water level in calcareous sand according to claim 1, wherein In the above Step 1, apply a layer of vaseline on the inner side wall of the box body (1).

3. The experimental method for simulating the seepage of calcareous sand under cyclic rise and fall of water level according to claim 1, characterized in that In the above Step 2, the specimen (5) is divided into three layers. The first layer uses a fluorescent dye to dye the fine particle specimen (5), and the second and third layers respectively use different stone dyes to dye the fine particle specimens (5) with various particle size ranges.

4. The seepage experiment method for simulating the cyclic rise and fall of the water level in calcareous sand according to claim 3, characterized in that, In the above Step 2, the first layer of specimen (5) uses a fluorescent dye to dye the fine particle specimen (5) with a particle size below 0.5 mm, and the second and third layers respectively use different stone dyes to dye the fine particle specimens (5) with particle size ranges of 0.25 mm to 0.5 mm, 0.1 mm to 0.25 mm, and 0.075 mm to 0.1 mm.

5. The seepage experiment method for simulating the cyclic rise and fall of water level in calcareous sand according to claim 1, characterized in that In the third step, a certain amount of water is incorporated into each layer of the specimen (5) before loading and stirred and mixed.

6. The seepage experiment method for simulating the cyclic rise and fall of water level in calcareous sand according to claim 1, characterized in that, In the seventh step, the amount of seepage water is recorded every 10 minutes in the first hour, and then every 30 minutes.

7. An experimental device applying the experimental method for simulating the seepage experiment of the calcium sand with the water level rising and falling cyclically according to any one of claims 1 to 6, characterized in that, It includes a box body (1) and a sedimentation bucket (3) detachably connected to the box body (1) below the box body (1). The bottom of the box body (1) is a filter plate (11) provided with a plurality of through holes. The inside of the box body (1) is a hollow structure for filling calcareous sand specimens (5). A box cover (2) is provided on the upper part of the box body (1). An upper exhaust port (21) and an upper water inlet (22) connected to the bottom of the water column (6) are provided on the box cover (2). The upper part of the water column (6) is connected to a water tank (7). The sedimentation bucket (3) is provided with a lower water outlet (31) and a lower connection port (32). The lower water outlet (31) is connected to a water collection cylinder (10), and the lower connection port (32) is connected to a water level control system (8) for controlling the cyclic rise and fall of the water level.

8. The experimental device according to claim 7, characterized in that, The water column (6) is provided with a water outlet (61) located at the bottom of the water column (6) and a plurality of drain ports (62) at intervals in the vertical direction. The water outlet (61) is connected to the upper water inlet (22). Drain valves are provided at the drain ports (62). The hydraulic gradient is adjusted by opening the drain valves at any height for drainage.

9. The experimental apparatus according to claim 7, wherein, Valves are provided at the upper water inlet (22), the lower water outlet (31), and the lower connection port (32).

10. The experimental device according to claim 7, characterized in that, A plurality of water level sensors (9) are provided at intervals in the vertical direction on the box body (1). The water level sensors (9) are electrically connected to the water level control system (8).

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