Calcarenite water level cyclic rising and falling seepage experiment device and experiment method

Abstract

The present application relates to the technical field of seepage experiment, in particular to a kind of calcareous sand simulation water level cyclic rising and falling seepage experimental device and experimental method, including box and the sedimentation barrel located below box, the bottom of box is the filter plate with multiple through holes, the hollow structure for filling calcareous sand sample in box interior, box upper portion is equipped with box cover, box cover is equipped with upper exhaust port and the upper water inlet connected with water column bottom, water column upper portion is connected with water tank, sedimentation barrel is equipped with lower water outlet and lower connecting port, lower water outlet is connected with water collecting cylinder, lower connecting port is connected with water level control system for controlling water level cyclic rising and falling.The present application can realize non-intrusive fine particle migration path visualization, while water level cyclic rising and falling of tide can be realized, and then the stability of calcareous sand foundation under the action of long-term rainfall, water level cyclic rising and falling is researched.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of seepage experiment, in particular to a calcium sand simulation water level cyclic rise and fall seepage experiment device and experiment method. BACKGROUND

[0002] As a special marine geotechnical medium, calcium sand is mainly formed by physical and chemical cementation and sedimentation of marine bioclasts (coral, algae, shells, etc.) under the action of carbonate solution for a long time. Its unique diagenetic process gives it significant differences in engineering properties from terrigenous sand: highly irregular particle morphology (angular, flaky structure), developed internal porosity, low strength and easy breakability, and cementation-dissolution dual characteristics. As the main filler for calcium sand foundation engineering and offshore filling engineering, this material faces serious seepage stability challenges under complex marine dynamic environments.

[0003] In marine engineering practice, most calcium sand foundations are surrounded by water on four sides, with abundant rainfall and long-term tidal influence. The groundwater level is in a fluctuating state for a long time. Due to the high porosity and strong permeability of the hydraulic fill calcium sand foundation, the fine particles of the internal coral sand will migrate dynamically with seepage under hydraulic driving, changing the internal structure of the soil, i.e., migration phenomenon, which in turn leads to double engineering effects: on the one hand, the loss of fine particles leads to dynamic evolution of the permeability coefficient, directly affecting the efficiency of drainage consolidation; on the other hand, the redistribution of fine particles may induce seepage deformation failure (piping, internal erosion, etc.), causing a sharp decrease in foundation bearing capacity.

[0004] The current research system has significant technical bottlenecks: traditional seepage experiment devices (such as constant water head / variable water head permeameter) cannot realize visual monitoring of sample migration under dynamic seepage conditions. Secondly, traditional seepage experiment devices can only perform a single simulation seepage action and lack simulation of water level cyclic rise and fall. This technical defect cannot accurately reflect the seepage stability of calcium sand foundations under long-term complex conditions such as tides, cannot provide reference for long-term stable construction of hydraulic fill calcium sand foundations, and restricts the safety design and disaster prevention and control capability improvement of calcium sand foundation engineering. SUMMARY

[0005] The purpose of the present application is to provide a calcium sand simulation water level cyclic rise and fall seepage experiment device and experiment method to solve the above-mentioned problems in the prior art.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] The utility model provides a kind of calcareous sand simulation water level cyclic rising and falling seepage experimental device, including box and the sedimentation barrel of being detachably connected with box below box, the bottom of box is the filter plate with multiple through holes, the hollow structure for filling calcareous sand sample in the inside of box, box upper portion is equipped with box cover, box cover is equipped with upper exhaust port and the upper inlet of being connected with water column bottom, water column upper portion is connected with water tank, sedimentation barrel is equipped with lower water outlet and lower connecting port, lower water outlet is connected with water collecting cylinder, and lower connecting port is connected with water level control system for controlling water level cyclic rising and falling.

[0008] Further, the water column is spaced apart in the vertical direction to provide a water outlet at the bottom of the water column and a plurality of drainage outlets. The water outlet is connected to the upper inlet, and the drainage outlets are provided with drainage valves. By opening any height of the drainage valve for drainage, the adjustment of the hydraulic gradient is achieved.

[0009] Further, the upper inlet, lower outlet, and lower connecting port are each provided with a valve.

[0010] Further, the box is spaced apart in the vertical direction to provide a plurality of water level sensors. The water level sensors are electrically connected to the water level control system.

[0011] An experimental method applied to the above-mentioned calcareous sand simulation water level cyclic rising and falling seepage experimental device includes the following steps:

[0012] Step one, determine the sample gradation in advance, measure the maximum, minimum dry density and normal dry density of the sample, and prepare a variety of different particle size samples according to the experimental requirements;

[0013] Step two, divide the sample into multiple layers from bottom to top along the seepage direction, and dye the fine particle sample of each layer in different colors according to different particle size ranges. After dyeing, dry the fine particle sample;

[0014] Step three, fill the sample into the box in layers and compact it. Take a picture of the initial distribution state of the uppermost layer of fine particle sample, and lay a layer of gravity ball above the uppermost layer to prevent the uppermost layer of sample from being washed away;

[0015] Step four, close the lower water outlet and the upper inlet, add water to the water column through the water tank, and open a drainage outlet valve to adjust the hydraulic gradient;

[0016] Step five, open the lower connecting port, and inject water or drain water into the sedimentation barrel through the water level control system to simulate the cyclic rising and falling of tidal water level in the box;

[0017] Step six, 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 ball. Close the lower connecting port, and let it stand to exhaust until no gas is discharged from the exhaust port. The sample is saturated.

[0018] Step seven, open the lower water outlet and the upper water inlet, and record the amount of seepage water in unit time until the permeability coefficients measured before and after are stable by stably injecting water into the water column from the top of the water column through the water tank;

[0019] Step eight, close the upper water inlet, and after the water in the tank is discharged from the lower water outlet, take out the sediment barrel particles and observe and record the color and proportion of the sample particles seeping from the filter plate into the sediment barrel;

[0020] According to the experimental requirements, the above steps five to eight are repeated to perform seepage actions after multiple water level cycles; during the entire experiment, the distribution state and migration of the sample fine particles are recorded by photographing from the front of the tank;

[0021] Step nine, open the tank cover, and take out the sample in multiple layers from top to bottom at a certain unit height, and record the distribution state of the sample fine particles by photographing from above the tank and analyze it.

[0022] Further, in step one, a layer of vaseline is applied to the inner side wall of the tank.

[0023] Further, in step two, the sample is divided into three layers, the first layer uses a fluorescent dye to dye the fine particle sample, and the second and third layers use different stone dyes to dye fine particle samples of different particle size ranges.

[0024] Further, in step two, the first layer of sample uses a fluorescent dye to dye fine particle samples with a particle size of less than 0.5 mm, and the second and third layers use different stone dyes to dye fine particle samples with a particle size of 0.25 mm to 0.5 mm, 0.1 mm to 0.25 mm, and 0.075 mm to 0.1 mm.

[0025] Further, in step three, a certain amount of moisture is added to each layer of sample before loading and mixed.

[0026] Further, in step seven, the amount of seepage water is recorded every 10 minutes for the first hour, and every 30 minutes thereafter.

[0027] In the prior art related to coarse-grained soil and calcareous sand seepage, there are few schemes for fine particle migration, and even fewer for water level cycle and fine particle migration and permeability. In order to better study the change of permeability and fine particle migration law of the part of the hydraulic fill calcareous sand foundation under the influence of water level cycle, the experimental method of the calcareous sand simulation water level cycle seepage experimental device provided by the present application has the following beneficial effects and application value compared with the prior art:

[0028] The present invention dyes and marks fine-particle samples separately to observe the movement characteristics of fine-particle samples in real time, identify the migration of fine particles from multiple layers of soil, and visualize the non-invasive migration paths of fine particles in coarse soils such as calcareous sand during seepage. At the same time, the present invention uses a water level control system to achieve multiple water level cycles within the box, accurately simulating tidal water level fluctuations without destroying the samples. The migration characteristics of fine particles under the action of water level cycles in the same area are continuously observed to study the impact of underground water level fluctuations caused by multiple tides on the seepage properties of the stratum, and further explain geological disasters such as local collapse caused by infiltration in calcareous sand foundations under the influence of long-term rainfall, water level cycles, etc. Furthermore, the present invention can freely adjust the hydraulic gradient during infiltration, as well as the rate of rise and fall and the hydraulic gradient during water level cycles. It is convenient, fast, easy to install, and reusable, which improves the scope of application and flexibility of the experimental device, thereby better studying and explaining the relationship between fine particle migration and the permeability coefficient and the number of water level cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This 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.

[0030] Wherein, the accompanying drawings are marked as follows:

[0031] 1. Box body; 11. Filter plate; 2. Box cover; 21. Upper exhaust port; 22. Upper water inlet; 3. Sedimentation tank; 31. Lower water outlet; 32. Lower connection port; 4. Water stop ring; 5. Test specimen; 6. Water column; 61. Water outlet; 62. Drain; 7. Water tank; 8. Water level control system; 9. Water level sensor; 10. Water collecting cylinder; 101. Gravity ball. DETAILED DESCRIPTION

[0032] In order to help those skilled in the art better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0033] It should be noted that when an element is referred to as being “fixed on” or “disposed on” another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or indirectly connected to the other element.

[0034] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0035] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features.

[0036] For easier understanding, see Figure 1This embodiment provides a calcareous sand simulated water level cyclic rise and fall seepage experimental device, characterized by comprising a hollow housing 1, a housing cover 2 located above the housing 1, and a sedimentation barrel 3 located below the housing 1. The housing cover 2 and the housing 1, and the housing 1 and the sedimentation barrel 3, are all bolted together. Furthermore, water stop rings 4 are provided at the connections between the housing cover 2 and the housing 1, and between the housing 1 and the sedimentation barrel 3. The water stop rings 4 are used to prevent water leakage at the various connection gaps during the experiment. Preferably, the housing 1, the housing cover 2, and the sedimentation barrel 3 are all made of transparent materials. The bottom of the box 1 is a filter plate 11, which has multiple 1 mm vertical through holes evenly opened on the filter plate 11. The upper part of the sedimentation barrel 3 is connected to the filter plate 11. Three layers of calcareous sand samples 5 are layered in the vertical direction above the filter plate 11. The thickness of each layer of sample 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 sample 5 is within 10 mm, and the particle size of the fine particle sample 5 is within 0.5 mm. The box cover 2 is provided with an upper exhaust port 21 and an upper water inlet 22. The water column 6 is provided with a water outlet 61 and a plurality of drain ports 62 spaced apart 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 connected to the upper water inlet 22 through a water pipe. Each drain port 62 is provided with a corresponding drain valve for controlling the flow of water from the 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 in the water column 6, that is, to adjust the height difference between the drain port 62 and the water outlet 61, thereby realizing free adjustment of the hydraulic gradient. Furthermore, the corresponding drain port 62 can be connected to 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 barrel 3 is provided with a lower water outlet 31 and a lower connecting port 32. The lower water outlet 31 is connected to the water collecting cylinder 10 via a water pipe, and the lower connecting port 32 is connected to the water level control system 8 via a water pipe. Correspondingly, a plurality of water level sensors 9 are provided on the box body 1, spaced 10 cm apart in the vertical direction. The water level sensors 9 are electrically connected to the water level control system 8. The water level conditions in the box body 1 are monitored in real time by the water level sensors 9 to facilitate the subsequent water level cycle. The water level control system 8 is used to control the water level cycle in the box body 1 to simulate the water level cycle of the tide. Furthermore, the upper water inlet 22, the lower water outlet 31, and the lower connecting port 32 are each provided with a valve for controlling the water flow of the corresponding water outlet. Specifically, the water level control system 8 includes a controller and a bidirectional pump that can take in water in the forward direction and drain water in the reverse direction. The controller controls the parameters such as the water level cycle waveform, cycle, amplitude, and rate in the box body 1, and the bidirectional pump realizes the water inlet and drain of the water level cycle in the box body 1.More specifically, the control code is written, compiled and uploaded in the Arduino IDE (development environment on the computer), the compiled code is burned to the Arduino mainboard through the USB line, and finally executed in the microcontroller of Arduino. The code controls the hardware action by reading the hardware signal, and the detailed operation process is as follows:

[0037] 1. Install Arduino IDE

[0038] 1.1, visit the official website https: / / www.arduino.cc / , download and install the IDE corresponding to the operating system.

[0039] 1.2, after opening the IDE, select the development board model

[0040] 1.3, set the serial port: connect Arduino to the computer and select the corresponding COM port

[0041] 2. Install dependent library

[0042] 2.1, PID library: click Sketch → Include Library → Manage Libraries in the IDE, search for PID and install.

[0043] 3. Code writing and uploading

[0044] 3.1, tidal wave generation, code formation as follows:

[0045] #include <PID_v1.h>

[0046] #include <RTClib.h> / / for real-time clock

[0047] RTC_DS3231 rtc;

[0048] / / Define tidal parameters

[0049] #define TIDE_PERIOD 43200 / / 12-hour period (seconds)

[0050] #define TIDE_AMPLITUDE 0.5 / / water level fluctuation amplitude (m)

[0051] / / PID initialization

[0052] double Setpoint, Input, Output;

[0053] PID myPID(&Input, &Output, &Setpoint, 2.0, 0.5, 0.1, DIRECT);

[0054] void setup() {

[0055] rtc.begin();

[0056] myPID.SetMode(AUTOMATIC);

[0057] myPID.SetOutputLimits(-255, 255); / / Bidirectional control

[0058] }

[0059] void loop() {

[0060] DateTime now = rtc.now();

[0061] unsigned long seconds = now.hour()*3600 + now.minute()*60 +now.second();

[0062] / / Generate target tidal water level (sine wave)

[0063] Setpoint = TIDE_AMPLITUDE * sin(2 * PI * seconds / TIDE_PERIOD);

[0064] / / Read the actual water level (unit: meter)

[0065] Input = read_water_level();

[0066] / / PID calculation and control

[0067] myPID.Compute();

[0068] control_pump(Output);

[0069] }

[0070] 3.2. Bidirectional pump control, the code is as follows:

[0071] void control_pump(double output) {

[0072] if (output > 0) {

[0073] / / high tide: forward peristaltic pump (inlet)

[0074] analogWrite(PUMP_IN_PIN, output);

[0075] digitalWrite(PUMP_OUT_PIN, LOW);

[0076] } else {

[0077] / / low tide: reverse peristaltic pump (outlet)

[0078] analogWrite(PUMP_OUT_PIN, -output);

[0079] digitalWrite(PUMP_IN_PIN, LOW);

[0080] }

[0081] }

[0082] 4. Hardware connection and testing

[0083] 4.1. Connection verification

[0084] Make sure the following connections are correct:

[0085] Relay module: IN1 → D7 (control inlet), IN2 → D8 (control outlet), VCC → 5V, GND → GND.

[0086] Water pump / solenoid: positive → relay COM port, negative → power GND.

[0087] 4.2. Power supply and start-up

[0088] Connect Arduino to the computer via USB for power supply (or external 9V power supply).

[0089] Provide separate 12V power supply for bidirectional pump and relay (to avoid Arduino overload).

[0090] 5. PID parameter debugging (key steps)

[0091] 5.1. Manual debugging method

[0092] Step 1: Set Ki and Kd to 0, gradually increase Kp until the water level starts to oscillate.

[0093] Step 2: Record Kp (critical value Ku) and oscillation period Tu when oscillating.

[0094] Step 3: Calculate parameters according to Ziegler-Nichols formula:

[0095] 5.2 Automatic tuning tool

[0096] Use the PID_AutoTune library (additional installation required) to automatically calculate the optimal parameters.

[0097] The experimental method of the calcium sand simulation water level cycle seepage experimental device includes the following steps:

[0098] Step 1: Preliminary preparation

[0099] Before starting the experiment, make sure that all components are connected correctly, confirm that there is no leakage in the water supply path, and apply a layer of about 0.5mm thick vaseline on the inside wall of the box 1 to avoid the phenomenon of water flow along the inside wall of the box 1 during the experiment. According to the experimental requirements, determine the grading of the calcium sand sample 5, measure the maximum, minimum and normal dry densities of the sample 5, and divide the calcium sand sample 5 into first layer, second layer and third layer from bottom to top along the seepage direction, each layer is 15cm thick, the total length of the seepage path is 45cm, and prepare multiple calcium sand samples 5 with different particle sizes according to the experimental requirements;

[0100] Step 2: Dye marking

[0101] The fine particle samples 5 of different particle size ranges in each layer are dyed in different colors respectively. Since the color of the fluorescent dye is limited and there are multiple different particle size ranges of fine particles in the three-layer sample 5, it is not convenient to uniformly use the fluorescent dye, so the stone dye is introduced on the basis of the fluorescent dye for dyeing, so as to better analyze the migration path and distribution of the fine particle sample 5 subsequently. Specifically, the first layer uses the fluorescent dye to dye the fine particle sample 5, and the second layer and the third layer use different stone dyes to dye the fine particle sample 5 of multiple different particle size ranges, so as to facilitate the subsequent observation of the specific distribution and migration path of the fine particle sample 5. After dyeing, the fine particle sample 5 is dried. More specifically, the first layer sample 5 uses the fluorescent dye to dye and mark the fine particle sample 5 below 0.5 mm in particle size; in the second layer, the stone dye is used to dye the fine particle sample 5 of 0.25-0.5 mm in particle size range to red, the fine particle sample 5 of 0.1-0.25 mm in particle size range to blue, and the fine particle sample 5 of 0.075-0.1 mm in particle size range to green; in the third layer, the stone dye is used to dye the fine particle sample 5 of 0.25-0.5 mm in particle size range to black, the fine particle sample 5 of 0.1-0.25 mm in particle size range to yellow, and the fine particle sample 5 of 0.075-0.1 mm in particle size range to purple, and all the dyed fine particle samples 5 are put into an oven for drying treatment at 60°C for 2 hours.

[0102] Step three, sample 5 filling (sample loading)

[0103] In order to prevent the coarse and fine particles of the sample 5 from separating from each other during the sample loading process, 5% water is pre-mixed with each layer of the sample 5 which has been weighed and dyed, and the mixture is thoroughly mixed to make it uniform. The mixed sample 5 of each layer is sequentially layered and filled into the vertical box 1 and compacted, and the initial distribution state of each layer of the sample 5 is photographed, and the layer is shaved to prevent the third layer of the sample 5 from being washed away by the water flow during the experiment. Then, a layer of gravity balls 101 is laid on top of the third layer to prevent the third layer of the sample 5 from being washed away by the water flow during the experiment. Preferably, the gravity balls 101 are 2 mm in diameter and transparent glass balls.

[0104] Step four, setting the hydraulic gradient

[0105] The lower water outlet 31 and the upper water inlet 22 are closed, water is injected into the water column 6 through the water tank 7, and the valve of a certain drainage port 62 is opened to drain water, so as to ensure the stability of the seepage water head height and freely select the required hydraulic gradient of the experiment. Specifically, a certain drainage port 62 can be connected with the water tank 7 through a water pipe to form a water circulation between the water tank 7 and the water column 6.

[0106] Step five, tide simulation

[0107] Close the lower water outlet 31 and the upper water inlet 22, open the lower connecting port 32, and inject water into the sediment bucket 3 through the water level control system 8. The water level gradually rises from bottom to top in the box 1, and the tidal wave shape, period, amplitude, and lifting rate are set by the program to simulate the tidal water level cycle in the box 1.

[0108] Step six, sample 5 saturation

[0109] After the completion of the simulation of the cycle of tidal water level, water is injected into the sediment bucket 3 through the water level control system 8, and the water level in the box 1 gradually rises from bottom to top until the water level exceeds the gravity ball 101. The lower connecting port 32 is closed, and the exhaust is stationary until no gas is discharged at the exhaust port, and the sample 5 is saturated. Specifically, one end of the air pipe can be connected to the exhaust port, and the other end of the air pipe can be immersed in water to observe whether bubbles appear in the water. If bubbles continue to appear in the water, it indicates that gas is continuously discharged from the exhaust pipe, and the sample 5 is not saturated. If there are no bubbles in the water, it indicates that no gas is discharged from the exhaust pipe, and the sample 5 is saturated.

[0110] Step seven, seepage action

[0111] Open the lower water outlet 31 and the upper water inlet 22, and inject water into the water column 6 from the top of the water column 6 through the water tank 7. The water head height is stable by opening the valve of a certain water outlet 62 of the water column 6. At this time, the water in the water column 6 continuously flows into the box 1 from the upper water inlet 22 through the water pipe, that is, water is continuously injected into the box 1 from the top of the box 1. The water in the box 1 continuously flows out from the lower water outlet 31 of the lower sediment bucket 3 to the water collection cylinder 10 through the water pipe, that is, water is continuously discharged from the bottom of the box 1 to the outside of the box 1. The seepage water quantity of the water collection cylinder 10 is recorded in unit time until the seepage water quantity measured before and after is stable, that is, the permeability coefficient is stable, and the seepage action is completed. Specifically, because the seepage water quantity changes rapidly in the first period of seepage and gradually stabilizes subsequently, the seepage water quantity is recorded every 10 minutes in the first hour of the seepage process, and the seepage water quantity is recorded every 30 minutes subsequently.

[0112] According to Darcy's law where k is the permeability coefficient (cm / s), Q is the seepage water quantity (cm³), A is the cross-sectional area of the sample 5 (cm²), L is the height of the sample 5 (cm), ΔH is the water head difference (that is, the height difference between the water outlet 61 and the water outlet 62 in the open state) (cm), and t is the seepage unit time (s). In the simulation of the cycle of tidal water level and the seepage process, fine particle sample 5 will migrate due to hydraulic action, the structure of the sample 5 will change every time the water level cycles and the seepage process, and then the permeability coefficient of the sample 5 will change, and the seepage water quantity will also change. When the seepage water quantity measured before and after is stable, it indicates that the internal structure of the sample 5 has stabilized, that is, the permeability coefficient is stable, and the next step can be performed.

[0113] Step eight, drainage record

[0114] Close the upper water inlet 22, stop filling water into the box 1, wait for the water in the box 1 to be discharged 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 1, close the lower water outlet 31; take out the sediment bucket 3 from the lower part of the box 1, observe and record the color and proportion of the sample 5 seeping from the filter plate 11 at the lower part of the box 1 into the sediment bucket 3, take out all the sample 5 in the sediment bucket 3 after recording, empty the sediment bucket 3 and install the sediment bucket 3 back to the lower part of the box 1, ensure that there is no leakage at the connection between the box 1 and the sediment bucket 3.

[0115] According to the experimental requirements, the above steps five to eight are repeated to perform multiple water level cycle and seepage actions; during the entire multiple water level cycle and seepage process, the distribution state and migration of the sample 5 are recorded by photographing the front of the box 1.

[0116] Step nine, subsequent processing and analysis

[0117] After completing the predetermined multiple water level cycle and seepage actions, the final distribution state and migration of the sample 5 are recorded by photographing the front of the box 1, and the distribution and migration path of the fluorescently dyed fine particle sample 5 recorded during the entire experimental process are analyzed and processed using ImageJ software. Open the box cover 2, take out the sample 5 in multiple layers from top to bottom at a certain unit height, take a bird's eye view of the distribution state of each layer of sample 5 above the box 1, and observe the distribution state of the stone dyed fine particle sample 5. Preferably, the unit height is 5cm. According to the seepage amount of each time period, the permeability coefficient is calculated, the change of the permeability coefficient of the sample 5 after multiple water level cycles is compared, the migration path and distribution of the fine particle sample 5 are analyzed, and the influence mechanism of the water level cycle on the permeability of the sample 5 is analyzed.

[0118] Further, during the entire experimental process, different drainage port 62 valves can be switched on according to actual experimental conditions and requirements to appropriately adjust the hydraulic gradient.

[0119] The application can simulate the seepage of the hydraulic fill calcareous sand foundation under the action of water level cycle, can realize the visualization of the migration path of fine particles under the action of multiple different hydraulic gradients, can observe the migration path and characteristics of fine particles in real time, can better explain the relationship between fine particle migration and permeability coefficient, water level cycle times, can simulate the influence of long-term water level cycle on the permeability and stratum stability of calcareous sand, provides a micro research method and idea for fine particle migration of calcareous sand, better explains the secondary geological disasters such as piping and local ground subsidence caused by seepage, and provides a theoretical basis for the prevention of secondary disasters of calcareous sand foundation.

[0120] Although the present invention has been described using the above preferred embodiments, they are not intended to limit the scope of protection of the present invention. Any person skilled in the art who makes various changes and modifications to the above embodiments without departing from the spirit and scope of the present invention still fall within the scope of protection of the present invention.

Claims

1. A calcareous sand simulated water level cyclic rise and fall seepage experimental method, characterized in that: The following steps are involved: Step 1: predetermine the gradation of the sample (5), measure the maximum and minimum dry densities and normal dry density of the sample (5), and prepare a plurality of samples (5) with different particle sizes according to experimental requirements; Step 2: Divide the sample (5) into multiple layers from bottom to top along the seepage direction, dye the fine particle samples (5) of various particle size ranges in each layer with different colors, and dry the fine particle samples (5) after dyeing; Step 3: Fill the sample (5) into the box (1) in layers and compact it, photograph the initial distribution state of the top layer of fine particle sample (5), and lay another layer of gravity balls (101) on top of the top layer to prevent the top layer of sample (5) from being dispersed; Step 4: Close the lower water outlet (31) and the upper water inlet (22), add water to the water column (6) through the water tank (7), and open a drain valve (62) to drain water and adjust the hydraulic gradient; Step 5: Open the lower connection port (32) and inject or drain water into the sedimentation barrel (3) through the water level control system (8), simulating the tidal water level cycle rise and fall in the box (1); Step 6: After the simulation is completed, water is added to the sedimentation barrel (3) through the water level control system (8) until the water level is higher than the gravity ball (101), the lower connection port (32) is closed, and the sample (5) is left to stand for exhaust until no gas is discharged from the exhaust port. Step 7: Open the lower water outlet (31) and the upper water inlet (22), and steadily inject water into the water column (6) from the top of the water column (6) through the water tank (7), and record the amount of water seepage per unit time until the permeability coefficient measured twice before and after is stable; Step 8: Close the upper water inlet (22), wait for the water in the box (1) to be discharged from the lower water outlet (31), take out the particles from the sedimentation barrel (3) and observe and record the color and proportion of the sample (5) particles that seep from the filter plate (11) into the sedimentation barrel (3); Repeat the above steps 5 to 8 according to the experimental requirements to perform the seepage action after the water level is raised and lowered for multiple cycles; during the entire experimental process, the distribution state and migration of fine particles of the sample (5) are recorded on the front of the box (1); Step 9: Open the box cover (2), take out the sample (5) in layers from top to bottom at a certain unit height for multiple times, take photos and record the distribution state of fine particles of the sample (5) from above the box body (1) and analyze it.

2. The calcareous sand simulated water level cyclic rise and fall seepage experimental method according to claim 1, characterized in that: In the step 1, a layer of vaseline is applied on the inner wall of the box body (1).

3. The calcareous sand simulated water level cyclic rise and fall seepage experimental method according to claim 1, characterized in that: In the second step, the sample (5) is divided into three layers. The first layer uses a fluorescent dye to dye the fine particle sample (5). The second and third layers use different stone dyes to dye the fine particle samples (5) of various particle size ranges.

4. The calcareous sand simulated water level cyclic rise and fall seepage experimental method according to claim 3, characterized in that: In the second step, the first layer of samples (5) uses a fluorescent dye to dye the fine particle samples (5) with a particle size of less than 0.5 mm, and the second and third layers use different stone dyes to dye the fine particle samples (5) with a particle size range of 0.25 mm to 0.5 mm, a particle size range of 0.1 mm to 0.25 mm, and a particle size range of 0.075 mm to 0.1 mm, respectively.

5. The calcareous sand simulated water level cyclic rise and fall seepage experimental method according to claim 1, characterized in that: In the step 3, a certain amount of water is added to each layer of the sample (5) before loading and the mixture is stirred.

6. The calcareous sand simulated water level cyclic rise and fall seepage experimental method according to claim 1, characterized in that: In step seven, the amount of exudate was recorded every 10 minutes for the first hour and every 30 minutes thereafter.

7. An experimental device using the experimental method for simulating water level cyclic rise and fall seepage in calcareous sand according to any one of claims 1 to 6, characterized in that: The invention comprises a box body (1) and a sedimentation barrel (3) located below the box body (1) and detachably connected to the box body (1); the bottom of the box body (1) is a filter plate (11) with a plurality of through holes; the interior of the box body (1) is a hollow structure for filling a calcareous sand sample (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 a 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 barrel (3) is provided with a lower water outlet (31) and a lower connecting port (32); the lower water outlet (31) is connected to a water collecting graduated cylinder (10); and the lower connecting 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) and a plurality of drain outlets (62) spaced apart in the vertical direction. The water outlet (61) is connected to the upper water inlet (22). A drain valve is provided at the drain outlet (62). The hydraulic gradient is adjusted by opening the drain valve at any height to drain water.

9. The experimental device according to claim 7, characterized in that: Valves are provided at the upper water inlet (22), the lower water outlet (31) and the lower connecting port (32).

10. The experimental device according to claim 7, characterized in that: The box (1) is provided with a plurality of water level sensors (9) spaced apart in the vertical direction, and the water level sensors (9) are electrically connected to the water level control system (8).

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