Testing device for simulating leaching and migration of pollutants in sea reclamation area

Abstract

The utility model discloses a test device for simulating leaching and migration of pollutants in a sea reclamation area. The test device comprises a leaching sand box and a migration sand box which are arranged up and down, a spraying device is arranged above the leaching sand box, and an electromagnetic flowmeter is arranged at an inlet of the spraying device; a first water tank with a hole in the top is arranged at the bottom of the leaching sand box and is used for receiving leaching leaked water; a first conductivity probe is arranged in the first water tank; a second water tank with a hole formed in the bottom is arranged at the top of the migration sand box and used for simulating water flow leakage, and the first water tank and the second water tank are connected through a pipeline; pressure sensors are arranged below the migration sand box and the leaching sand box; a water outlet positioned at the bottom of the side surface of the migration sand box is connected with a tipping-bucket rain gauge through a pipeline; a second conductivity probe is arranged at a water outlet of the migration sand box; a water level recorder is arranged in the migration sand box; and a tensiometer and a soil humidity sensor are also arranged in the migration sand box. The device disclosed by the utility model can be used for researching the process and mechanism of leaching and migration of pollutants in the sea reclamation area.

Description

Technical Field

[0001] The utility model relates to a water conservancy project test device, in particular to a test device for simulating the leaching and migration of pollutants in a land reclamation area. Background Art

[0002] At present, the research on the leaching and migration process of pollutants in land reclamation areas is still immature, mainly because the process and mechanism of pollutant leaching and migration are still unclear, and how to characterize the migration of pollutants in land reclamation areas is a difficult problem. Existing test devices for simulating the migration process of pollutants are often aimed at the migration process of non-point source pollutants in soil and strata under ordinary geological conditions, but cannot simulate the leaching and migration process of surface pollutants in land reclamation areas (pollutants on the surface of land reclamation areas enter the soil body through leaching and migrate), such as a basin non-point source pollutant transport simulation test device and method provided by CN114814139B. Utility Model Content

[0003] Purpose of the utility model: The purpose of the utility model is to provide a test device for simulating the leaching and migration of pollutants in land reclamation areas, so as to study the process and mechanism of the leaching and migration of pollutants in land reclamation areas.

[0004] Technical solution: The experimental device for simulating the leaching and migration of pollutants in land reclamation areas described in the utility model comprises a migration sand box and a leaching sand box, wherein the leaching sand box is arranged horizontally and higher than the migration sand box; a spray device is arranged above the leaching sand box, and an electromagnetic flowmeter is arranged at the inlet of the spray device to measure the precipitation J; a first water tank with a hole on the top is arranged at the bottom of the leaching sand box to receive leached water; a first conductivity probe is arranged in the first water tank to measure the tracer input concentration A second water tank with holes at the bottom is arranged on the top of the migration sand box to simulate water leakage. The second water tank is connected to the first water tank through a pipeline. A pressure sensor is arranged under the migration sand box and the leaching sand box to measure the groundwater storage variable S. The water outlet at the bottom of the side of the migration sand box is connected to a tipping bucket rain gauge through a pipeline to measure the discharge flow Q. A second conductivity probe is arranged on the pipeline between the tipping bucket rain gauge and the migration sand box to measure the tracer discharge concentration C. i ; A water level recorder is provided in the migration sand box to measure the groundwater level h; a tensiometer and a soil moisture sensor are also provided in the migration sand box to measure the soil moisture content θ.

[0005] Furthermore, the slope α of the migration sand box can be adjusted to simulate the inclination of the bedrock in the land reclamation area.

[0006] By adjusting the inclination of the migration sand box and the spraying device, the meteorological and topographic conditions can be simulated, revealing the relationship between pollutant emission concentration and rainfall frequency, rainfall intensity and terrain. The test device can simulate the state of groundwater pollutant leaching and migration under complex rainfall and terrain conditions in reality.

[0007] Furthermore, the migration sand box is rotatably arranged on the support frame, and the water outlet of the migration sand box is close to one end of the rotation; a hydraulic push rod is arranged on the support frame to push the migration sand box to adjust the slope α.

[0008] Furthermore, a pressure sensor is provided at each of the four corners of the sand box.

[0009] Furthermore, there are multiple water level recorders, tensiometers and soil moisture sensors, which are arranged at different positions of the migration sand box.

[0010] Furthermore, a still water well is provided in the migration sand box next to the water level recorder for manually measuring the groundwater level h.

[0011] Furthermore, the downstream boundary of the migration sand box is covered with a porous plastic sheet.

[0012] Furthermore, a filter layer for filtering soil is arranged on the top of the first water tank.

[0013] The filling soil in the sand box can be flexibly adjusted according to the actual situation. Before the test, it is necessary to obtain the actual stratum lithology distribution of the study area based on the survey data, and then build a physical model based on this to simulate the actual rock and soil layer distribution to ensure the accuracy and applicability of the test. For different research areas, the filling soil and consolidation degree in the sand box can be flexibly adjusted to ensure that the physical and mechanical properties and permeability of the filling soil in the sand box are completely consistent with the actual site, thereby obtaining accurate simulation results.

[0014] Beneficial effects: Compared with the prior art, the utility model has the following advantages:

[0015] (1) By simulating the leaching and migration processes of pollutants in two sand boxes, a variety of data can be obtained from one test, and the leaching or migration process of pollutants can also be studied separately, which greatly improves the test efficiency.

[0016] (2) Through the combination of soil moisture sensors and pressure sensors, the spatiotemporal variability of groundwater storage variables in the sand box can be monitored in real time, so that the impact mechanism of seasonal changes in storage variables on pollutant transport can be studied.

[0017] (3) Through real-time monitoring of solute excretion concentration and combined with transient transport time distribution theory, the underground transport time of tracers can be calculated, which is of great value for the prevention and control of pollutants in land reclamation areas. Through this experimental device, the transport time of tracers from rainfall to excretion can be calculated, which has a strong application prospect in the field of pollutant prevention and control in land reclamation areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the structure of the test device for simulating the leaching and migration of pollutants in the land reclamation area;

[0019] Figure 2 It is a schematic diagram of the calibration rate of the test device. DETAILED DESCRIPTION

[0020] The utility model is further described below in conjunction with the accompanying drawings.

[0021] Attached Figures 1 to 2 The reference numerals in the figures are as follows:

[0022] 1. Migration sand box; 2. Leaching sand box; 3. Spraying device; 4. Electromagnetic flowmeter; 5. First water tank; 6. Second water tank; 7. First conductivity probe; 8. Porous plastic plate; 9. Tipping bucket rain gauge; 10. Second conductivity probe; 11. Pressure sensor; 12. Water level recorder; 13. Tensiometer; 14. Soil moisture sensor.

[0023] like Figure 1 As shown, a test device for simulating the leaching and migration of pollutants in land reclamation areas includes a migration sand box 1 and a leaching sand box 2. Both sand boxes are rectangular steel sand boxes with the same specifications, length×width×height of 2m×0.5m×1m.

[0024] The leaching sand box 2 is set horizontally to simulate the leaching process of surface pollutants. The migration sand box 1 simulates the migration process of pollutants, and the slope α of the migration sand box 1 can be adjusted to simulate the bedrock inclination of the land reclamation area. Specifically, the migration sand box 1 is rotatably set on the support frame, and the water outlet of the migration sand box 1 is close to one end of the rotation; a hydraulic push rod is provided on the support frame to push the migration sand box 1 to adjust the slope α, and the maximum slope α is 10°. The leaching sand box 2 is higher than the migration sand box 1.

[0025] The interior of both sand boxes is coated with aliphatic polyurethane topcoat (DuralDeck) to prevent corrosion on the surface in contact with the soil. The downstream boundary of the migration sand box 1 (where water flows out of the migration sand box 1) is covered with a porous plastic plate 8 with a pore size of 2 mm and a total porosity of 14%. The porous plastic plate 8 is bolted to the frame and supported by a steel bracket.

[0026] The bottom of the leaching sand box 2 is provided with a first water tank 5 with holes evenly formed on the top to receive the leaching water. To prevent the soil filled in the leaching sand box 2 from falling into the first water tank 5, a filter layer for filtering the soil, such as gauze, is provided on the top of the first water tank 5. The top of the migration sand box 1 is provided with a second water tank 6 with holes evenly formed on the bottom to simulate the leakage of water flow. The second water tank 6 is connected to the first water tank 5 through a pipeline.

[0027] The leaching sand box 2 is filled with the surface part of the blown fill soil in the land reclamation area, and a layer of salt is evenly spread on the surface blown fill soil to simulate the precipitation leaching process of pollutants in the land reclamation area. The filling soil inside the migration sand box 1 is divided into three parts, the lower layer is silty clay, the middle layer is silt, and the upper layer is deep blown fill soil, so as to simulate the distribution of geological conditions in the land reclamation area to the greatest extent (in specific experiments, the soil filling in the sand box needs to be adjusted according to the actual research area to ensure the accuracy of the test). After filling the test soil, the soil needs to be processed with a compaction device according to the actual situation of the research area to simulate the foundation consolidation of the land reclamation area. A layer of basalt gravel is installed at the outlet of the migration sand box 1 as a drainage layer between the sand layer and the perforated plastic plate 8. The gravel is adjacent to the perforated plastic plate 8, and its total volume is 0.05m3. The total volume of the filling soil above the gravel is 0.95m3.

[0028] A spray device 3 is provided above the leaching sand box 2. The spray device 3 is installed on the railing above the leaching sand box 2. A diaphragm pump (FLOJE, model G575215) is used to pump water into the spray device 3. An electromagnetic flowmeter 4 (SeametricsPE102) is provided at the inlet of the spray device 3 to monitor the flow rate downstream of the diaphragm pump. According to the target spray rate, water is sprayed on the surface of the fill soil through a combination of two, four or more nozzles. In order to simulate the leaching of pollutants, table salt (NaCl) is evenly spread on the top layer of the blown fill soil and brought into the ground by spraying fresh water to simulate the process of surface pollutants entering the ground.

[0029] Pressure sensors 11 are provided under the migration sand box 1 and the leaching sand box 2. The pressure sensors 11 are located at each of the four corners of the sand box to monitor the groundwater storage volume. A first conductivity probe 7 is provided in the first water tank 5 to measure the concentration of the solution after leaching. A water trough is provided at the outlet of the migration sand box 1 to receive the outflowing water, which then flows into the tipping bucket rain gauge 9 through an ethylene pipe to record the real-time discharge flow. Before use, both the pressure sensor 11 and the tipping bucket rain gauge 9 need to be calibrated. After the water flow from the leaching sand box 2 completes leaching, it flows into the first water tank 5 at the bottom of the leaching sand box 2, passes through the acrylic tube, and flows into the second water tank 6 at the top of the migration sand box 1 by gravity, and then enters the migration sand box 1 to simulate the migration process of pollutants.

[0030] The bottom of the migration sand box 1 is drilled at 0.15m, 0.75m and 1.35m from the outlet side plate as the interface of the sensor group buried in the soil. The sensor above each drilled hole is perpendicular to the cross section of the bottom of the sand box and the surface of the filling soil. The soil moisture sensor 14 (Decagon5TM) is installed at 0.05m, 0.20m, 0.35m, 0.50m and 0.85m from the surface of the filling soil. The tensiometer 13 (DecagonT4e) is installed at the depth of 0.20m and 0.50m in the three cross sections respectively, and is approximately the same as the position of the soil moisture sensor 14, so that the soil moisture content at multiple locations can be accurately estimated. The drilled holes are connected to an acrylic tube through a flange joint, which extends outward from the bottom of the sand box and the sensor cable is connected to the external device through the tube. The bottom of the acrylic tube is filled with expandable foam insulation material, which provides a waterproof seal to ensure that it does not affect the test. The remaining volume of the acrylic tube is filled with high viscosity epoxy resin.

[0031] In addition to the three holes for cable routing, three additional boreholes are required to install the water level recorder 12. The water level recorder 12 (HOBO) is installed in these three boreholes to measure the groundwater level at three different locations. Finally, three stilling wells are installed near the water level recorder 12 in a vertical direction to manually measure the depth of the groundwater level. The stilling well uses a PVC pipe with a diameter of 2.5CM.

[0032] A second conductivity probe 10 is provided on the pipeline between the tipping bucket rain gauge 9 and the migration sand box 1 to measure the tracer discharge concentration.

[0033] The following uses a land reclamation project in Ningde, Fujian as an example to introduce how to use the test device.

[0034] (1) Sand box filling

[0035] The soil in the sand box is based on the stratum distribution of the study area. The surface blown fill soil is filled in the leaching sand box 2, and the migration sand box 1 is filled with silty clay, silt and deep blown fill soil from bottom to top. The filling soil samples are all collected from the Ningde reclamation area. In order to eliminate the anisotropy caused by uneven soil compaction, the soil can be placed in the sand box in multiple times. Among them, the migration sand box 1 can be filled in the following way because there are many types of filled soil:

[0036] First, place the bottom silty clay layer into the sand box and compact it using a compactor to make it as evenly stacked as possible. Repeat the above steps until all three layers of soil are placed and compacted as required.

[0037] (2) Sensor calibration

[0038] Prior to the experiment, two irrigation rates were calibrated during a 20-30 min test period, e.g. Figure 2 After calibration, formal testing can be carried out.

[0039] (3) Spraying and tracer injection

[0040] In order to simulate the seasonality of precipitation, this experiment used the pulse method for irrigation, applying the same spraying sequence in each 24-hour cycle to produce a periodic steady-state state. The cycle of one experiment was 28 days, and four irrigation pulses were applied every day with two different intensities and durations: 10 mm / h injection from 9:00 to 12:00, 20 mm / h injection from 12:00 to 13:30, 20 mm / h injection from 21:00 to 0:00, and 10 mm / h injection from 0:00 to 1:30. This irrigation method can simulate the conversion process of the wet-dry state of the soil in the land-building area while avoiding the generation of surface runoff. The daily irrigation volume is approximately equivalent to 30% to 40% of the total pore volume of the soil medium in the sand box.

[0041] In this test, chloride ions (Cl - , that is, NaCl dissolved in water) as a tracer. Tap water was injected into the sand box through a spray device through 5 pulses, on the 1st day, 9th day, 14th day, 19th day and 24th day. This setting allows NaCl on the surface of the dredger fill to enter the ground through leaching, while avoiding as much as possible the interference of the tracer breakthrough curves caused by different pulses.

[0042] In order to explore the effects of different variables on the concentration and hysteresis of pollutant emissions, three groups of control experiments were designed to study the mechanism of precipitation frequency, precipitation intensity and bedrock inclination on pollutant emissions. The variables and their values ​​of the three groups of control experiments are shown in Table 1.

[0043] Table 1 Parameter settings for control test

[0044]

[0045]

[0046] (4) Hydrological variable monitoring

[0047] The measurement parameters of the indoor sand box tracer test include precipitation, soil moisture content, storage volume, groundwater level, discharge flow, tracer input concentration and tracer discharge concentration. The measured parameters and measurement methods are shown in Table 2.

[0048] Table 2 Summary of parameters measured in indoor sand box tracer test

[0049]

[0050] The parameters shown in Table 2 are monitored and the monitoring data is transmitted to the computer at a frequency of 1 minute. Then, the change curve of the monitored variables over time can be plotted. This test device can record precipitation (i.e., spraying rate), storage volume, groundwater level, discharge flow and voltage at the outlet. The voltage at the outlet has a definite functional relationship with the tracer concentration, and the tracer concentration at the outlet can be obtained by conversion.

[0051] The experimental results clearly show that under the conditions of periodic rainfall, the migration of the tracer is also periodic, and the discharge concentration at the outlet is also closely related to the precipitation and storage volume.

[0052] (5) Calculation of transient tracer transport duration

[0053] The migration time of the tracer can reveal the residence time of pollutants in the bottom layer of the land reclamation area, which has important reference significance for the prevention and control of groundwater pollution. Through this experimental device, the migration time of the tracer can be inverted, and the specific method is as follows.

[0054] The transport time distribution theory is used to explain the observed tracer transport and emission phenomena, where the transport time distribution can be estimated by the following formula:

[0055]

[0056] Among them C i (t) is the tracer emission concentration at time t, Q(t) is the discharge flow at time t, Δ i is the time from the start of the i-th pulse to the i+1-th pulse, Yes i The average tracer input concentration over time, Yes i Average precipitation during the time period.

[0057] According to the above formula, the tracer breakthrough curve can be inverted, the average transport time of the tracer can be obtained, and finally the inversion of the transient transport time distribution of the tracer can be achieved, so as to establish a complete indoor experimental research method for pollutant transport mode.

Claims

1. A test device for simulating the leaching and migration of pollutants in land reclamation areas, characterized in that: The invention comprises a migration sand box (1) and a leaching sand box (2), wherein the leaching sand box (2) is arranged horizontally and is higher than the migration sand box (1); a spray device (3) is arranged above the leaching sand box (2), and an electromagnetic flow meter (4) is arranged at the inlet of the spray device (3) for measuring the precipitation J; a first water tank (5) with a hole on the top is arranged at the bottom of the leaching sand box (2) for receiving leaching seepage water; a first conductivity probe (7) is arranged in the first water tank (5) for measuring the tracer input concentration A second water tank (6) with a hole at the bottom is arranged on the top of the migration sand box (1) to simulate water leakage, and the second water tank (6) is connected to the first water tank (5) through a pipeline; a pressure sensor (11) is arranged below the migration sand box (1) and the leaching sand box (2) to measure the groundwater storage variable S; a water outlet at the bottom of the side of the migration sand box (1) is connected to a tipping bucket rain gauge (9) through a pipeline to measure the discharge flow Q; a second conductivity probe (10) is arranged on the pipeline between the tipping bucket rain gauge (9) and the migration sand box (1) to measure the tracer discharge concentration C i The migration sand box (1) is provided with a water level recorder (12) for measuring the groundwater level h; the migration sand box (1) is also provided with a tensiometer (13) and a soil moisture sensor (14) for measuring the soil moisture content θ.

2. The experimental device for simulating the leaching and migration of pollutants in land reclamation areas according to claim 1 is characterized in that: The slope α of the migration sand box (1) can be adjusted to simulate the inclination of the bedrock in the land reclamation area.

3. The experimental device for simulating the leaching and migration of pollutants in land reclamation areas according to claim 2 is characterized in that: The migration sand box (1) is rotatably arranged on a support frame, and a water outlet of the migration sand box (1) is close to one end of the rotation; a hydraulic push rod is arranged on the support frame to push the migration sand box (1) to adjust the slope α.

4. The experimental device for simulating the leaching and migration of pollutants in land reclamation areas according to claim 1, characterized in that: A pressure sensor (11) is provided at each of the four corners of the sand box.

5. The experimental device for simulating the leaching and migration of pollutants in land reclamation areas according to claim 1, characterized in that: There are multiple water level recorders (12), tension meters (13) and soil moisture sensors (14), which are arranged at different positions of the migration sand box (1).

6. The experimental device for simulating the leaching and migration of pollutants in land reclamation areas according to claim 1, characterized in that: A still water well is provided in the migration sand box (1) next to the water level recorder (12) for manually measuring the groundwater level h.

7. The experimental device for simulating the leaching and migration of pollutants in land reclamation areas according to claim 1, characterized in that: The downstream boundary of the migration sand box (1) is covered with a porous plastic plate (8).

8. The experimental device for simulating the leaching and migration of pollutants in land reclamation areas according to claim 1, characterized in that: A filter layer for filtering soil is arranged on the top of the first water tank (5).

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