CN112782056A - Test device and method for simulating water runoff of covered karst area - Google Patents
Test device and method for simulating water runoff of covered karst area Download PDFInfo
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- CN112782056A CN112782056A CN202110036690.6A CN202110036690A CN112782056A CN 112782056 A CN112782056 A CN 112782056A CN 202110036690 A CN202110036690 A CN 202110036690A CN 112782056 A CN112782056 A CN 112782056A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/082—Investigating permeability by forcing a fluid through a sample
- G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
Abstract
The invention relates to the technical field of hydrogeology research tools, in particular to a test device and a method for simulating water runoff of a covered karst area, wherein the test device comprises a test sand tank, a rainfall replenishment system and a flow monitoring system; a water outlet of the precipitation replenishment system is positioned above the test sand tank; the test sand tank is a tank body with a slightly inclined bottom; the side surface of the test sand groove is provided with a surface water runoff outlet, a pore water outflow hole, a fissure karst water outflow hole and an overflow port; a covering layer and a karst area medium are arranged in the test sand tank; the lowest end of the covering layer is communicated with a surface water runoff outlet; the karst area medium comprises a pore aquifer, a fracture network layer and a pipeline layer; the pore aquifer undulates; the pore water outflow hole is positioned on the side surface of the pore aquifer; the lowest end of the pipeline layer is communicated with the fractured karst water outflow hole. The invention can simulate surface water runoff, pore water runoff and fissure karst water runoff of the covered karst area and carry out integral research on hydrogeological conditions of the covered karst area.
Description
Technical Field
The invention relates to the technical field of hydrogeology research tools, in particular to a test device and a method for simulating water runoff in a covered karst area.
Background
The karst landform contains abundant underground water resources and supports the production and living water in the karst area. In order to realize reasonable utilization and management of water resources in karst areas, deep research on the movement law of water flow in the karst areas is needed. The aqueous karst system is complex to develop and has high anisotropism and anisotropy. The water-containing medium is usually composed of multiple gaps such as pipelines, large cracks, micro cracks, pores and the like, and is beneficial to the storage and movement of underground water resources. However, the water flow movement is also characterized by heterogeneity, and besides laminar flow, turbulent flow can exist in trunk cracks and pipelines, so that the difficulty of simulation analysis of underground water in a karst area by hydrogeologists is increased.
The current methods for studying groundwater flow are mainly classified into three categories, including analytical methods, numerical methods and physical testing methods. The first two methods are directly solved based on a groundwater motion mathematical model, are relatively abstract and lack of intuition, generally simplify a research object to a certain extent, reduce reliability, and have more intuition and reliability compared with a physical test. At present, a physical test aiming at a water flow movement process of a karst region mainly adopts a fracture-pipeline medium, and a fracture-pipeline water exchange coefficient, seepage processes of various water flows, a spring flow attenuation process and the like are researched by changing the geometrical characteristics of a fracture or a pipeline, but the water regulation and storage effects of a fourth system and a covering layer are neglected, and the integral knowledge of the hydrogeological condition of the karst region is lacked.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a test device and a method for simulating the water runoff of a covered karst area, which can simulate the surface water runoff, the pore water runoff and the fissure karst water runoff of the covered karst area and carry out the overall research on the hydrogeological conditions of the covered karst area.
In order to solve the defects of the prior art, the technical scheme provided by the invention is as follows:
the invention provides a test device for simulating water runoff of a covered karst area, which comprises a test sand tank, a rainfall replenishment system and a flow monitoring system, wherein the test sand tank is connected with the rainfall replenishment system;
a water outlet of the precipitation replenishment system is positioned above the test sand tank;
the test sand tank is a tank body with a slightly inclined bottom; the side surface of the test sand groove is provided with a surface water runoff outlet, a pore water outflow hole, a fissure karst water outflow hole and an overflow port; a covering layer and a karst area medium are sequentially arranged in the test sand tank from top to bottom; the lowest end of the covering layer is communicated with a surface water runoff outlet; the karst area medium comprises a pore aquifer positioned at the uppermost layer, a fracture network layer positioned at the middle layer and a pipeline layer positioned at the bottom layer; the pore aquifer undulates; the pore water outflow hole is positioned on the side surface of the pore aquifer; the lowest end of the pipeline layer is communicated with the fractured karst water outflow hole; the flow monitoring system is used for monitoring the flow of the surface water runoff outlet, the pore water outflow hole and the fractured karst water outflow hole.
Preferably, the inclination angle of the bottom of the test sand tank is 2-5 degrees.
Preferably, the covering layer comprises soil and geotextile covering the soil; the thickness of the soil is 0.03-0.05 m; the thickness of the geotextile is 0.005-0.01 m.
Preferably, the pore aquifer consists of medium sand; the thickness of the thickest part of the pore aquifer is 0.45-0.5 m, and the thickness of the thinnest part is 0.2-0.25 m; the average grain diameter of the medium sand is 750 mu m.
Preferably, the fracture network layer is formed by arranging bricks or acrylic plates, and the thickness of the fracture network layer is 0.4-0.6 m; the volume of the brick or the acrylic plate is 0.001-0.005 m3, and the gap of the brick or the acrylic plate is 0.002 m.
Preferably, the pipeline layer is formed by arranging bricks or acrylic plates, and the thickness of the pipeline layer is 0.1-0.2 m; the volume of the brick or the acrylic plate is 0.001-0.005 m3, and a channel is reserved between the bricks or the acrylic plates to form a karst pipeline; the width of the karst pipeline is 0.02-0.05 m, and the height of the karst pipeline is 0.1-0.2 m; the lowest part of the karst pipeline is communicated with the fracture karst water outflow hole.
Preferably, the precipitation supply system comprises a water tank, a variable frequency pump, a bracket and a plurality of spray heads;
a water inlet of the variable frequency pump is connected with the water tank, and a water outlet of the variable frequency pump is connected with spray heads uniformly arranged on the bracket through pipelines;
the support is fixed above the test sand tank.
Preferably, the water level monitoring system is further included; the water level monitoring system comprises a paperless recorder, a pressure sensor and a plurality of rubber pipes;
pressure measuring holes are formed in the side faces of the pore aquifer and the fracture network layer;
one end of the rubber tube is positioned in the pressure measuring hole, and the other end of the rubber tube is connected with the pressure sensor;
the pressure sensor is connected with the paperless recorder.
The invention also provides a test method for simulating water runoff of a covered karst area, which comprises the following steps,
opening the variable frequency pump and the spray head, and dewatering the test sand tank according to a preset dewatering condition;
recording instantaneous flow of surface water runoff, pore water runoff and fractured karst water runoff;
and obtaining a water balance rule covering the karst area according to preset precipitation conditions and instantaneous flows of surface water runoff, pore water runoff and fractured karst water runoff.
Preferably, when the precipitation amount is saturated, the preset precipitation condition comprises an initial water level;
when the precipitation amount is not saturated, the preset precipitation conditions comprise the pumping intensity of the variable frequency pump, the precipitation starting time and the precipitation ending time.
The invention has the beneficial effects that:
1) the integrity of the hydrogeological structure of the overburden karst area is fully considered, and compared with the traditional organic glass model device, the invention directly utilizes soil, gravel and bricks to construct the karst simulation area, which comprises the overburden, the pore aquifer, the fracture network layer and the pipeline layer, and can more vividly reflect the characteristics of the water-containing medium of the overburden karst area and the water flow movement rule;
2) the test device for simulating the water runoff of the covered karst area has certain adjustability, can change test conditions such as source and sink terms (rainfall intensity and duration), aquifer media (pore aquifer thickness, crack distribution mode, pipeline size and outflow hole size) and boundary conditions (constant head boundary and water-resisting boundary), researches a plurality of test scenes, and has wide application range;
3) the system is provided with a water level monitoring system, pressure measuring points are uniformly distributed on a pore aquifer and a fracture network layer, the water level is monitored in real time in the whole process, and water level data can be used for analyzing a flow field and providing reference for further mathematical model research;
4) the method adopts a manual measurement mode to monitor the flow of the surface water runoff, the pore water runoff and the fissure karst water runoff, has accurate measurement data and reliable test result, and is convenient for accurately analyzing the rules of the surface water runoff, the pore water runoff and the fissure karst water runoff of the covered karst area.
Drawings
FIG. 1 is a schematic structural diagram of a test device for simulating water runoff in a covered karst area, provided by the invention;
FIG. 2 is a schematic diagram of the structure of the overburden and karst region media provided by the present invention;
FIG. 3 is a graph showing the process of the decay of the instantaneous flow rate of the fractured-rock water runoff at different initial water levels in the saturation state in example 1;
FIG. 4 is a water head change process of a fracture network layer pressure measuring hole when the initial water level is 52cm in a saturated state in example 1;
FIG. 5 is a graph showing the change of instantaneous flow rates of surface water runoff and fractured karst water runoff in an unsaturated state in example 1;
wherein, 1, testing a sand tank; 2. a base plate; 3. overflow holes, 4, surface water runoff outlets; 5. a pore water outflow hole; 6. a fracture karst water outflow hole; 7. a pressure measuring hole; 8. a variable frequency pump; 9. a water tank; 10. a water pipe; 11. a support; 12. a spray head; 13. a paperless recorder; 14. a pressure sensor; 15. a piezometric tube; 16. a gear flow meter; 17. geotextile; 18. soil; 19. a porous aqueous layer; 20. a fracture network layer; 21. a karst pipeline.
Detailed Description
The present invention will be further described with reference to the following embodiments. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and the protection scope of the present invention is not limited thereby.
The invention provides a test device for simulating water runoff of a covered karst area, which is shown in figure 1 and comprises a test sand tank 1, a precipitation supply system and a water level monitoring system; a water outlet of the precipitation replenishment system is positioned above the test sand tank 1; the test sand tank 1 is a tank body with a slightly inclined bottom, and a surface water runoff outlet 4, a pore water outflow hole 5, a fissure karst water outflow hole 6 and an overflow hole 3 are arranged on the side surface of the test sand tank 1; a covering layer and a karst area medium are sequentially arranged in the test sand tank 1 from top to bottom; the lowest end of the covering layer is communicated with a surface water runoff outlet 4; referring to fig. 2, the karst zone medium includes a pore aquifer 19 located at the uppermost layer, a fracture network layer 20 located at the middle layer, and a pipe layer located at the bottom layer; the pore aquifer 19 undulates; the lowest end of the pipeline layer is communicated with the fractured karst water outflow hole 6; the pore water outflow hole 5 is positioned on the side of the pore aquifer 19; the flow monitoring system is connected with the surface water runoff outlet 4, the pore water outflow hole 5 and the fractured rock water outflow hole 6 and is used for monitoring the flow of the surface water runoff outlet 4, the pore water outflow hole 5 and the fractured rock water outflow hole 6, namely measuring the flow of the surface water runoff, the pore water runoff and the fractured rock water runoff.
Wherein, the pore aquifer is used as the I layer of the medium of the karst area and is used for simulating a fourth system; the fracture network layer is used as a second karst area medium layer II; the pipeline layer is used as a third layer of the karst area medium.
Preferably, referring to fig. 1, the inclination angle of the bottom of the test sand tank 1 is 2-5 degrees, that is, the inclination angle of the bottom plate 2 is 2-5 degrees.
Preferably, a plurality of types of round holes are reserved in the side face and the bottom of the test sand tank 1 and used for monitoring the runoff quantity and the water level and controlling the initial water level.
Preferably, the aperture of the overflow hole is 0.02-0.04 m. The number and the height of the overflow holes can be set as required for adjusting the initial water level in the test sand tank 1. The overflow hole is provided with a valve for controlling various test scenes. In actual use, the outer part of the overflow hole can be connected with a hose, and the initial water level can be adjusted at will by controlling the height of the water level in the hose.
Preferably, the inner part and the outer part of the wall body of the test sand tank are coated with impermeable materials.
Preferably, referring to fig. 1, the pore aquifer and the fracture network layer are provided with pressure taps 7 at the sides.
Preferably, the test device for simulating water runoff in the covered karst area, provided by the invention, further comprises a water level monitoring system. Referring to fig. 1, the water level monitoring system includes a paperless recorder 13, a pressure sensor 14, and a plurality of rubber tubes 15; one end of the rubber tube 15 is positioned in the pressure measuring hole 7, and the other end of the rubber tube is connected with the pressure sensor 14; the pressure sensor 14 is connected to the paperless recorder 13. One side of the pressure measuring pipe is fixed in the water-containing layer, and the pressure measuring pipe is wrapped by the mesh cloth to prevent fine particles from blocking the water inlet. Under the precipitation saturation state, need arrange the interior air of pressure tube thoroughly before every test, prevent to cause the influence to the experimental data. The paperless recorder can record the data of the pressure sensor on line and transmit the data to the computer unit, so that the water level change monitoring can be realized.
Preferably, referring to fig. 2, the cover includes soil 18 and geotextile 17 overlying the soil. The thickness of the soil layer is 0.03-0.05 m; the thickness of the geotextile is 0.005-0.01 m. The covering layer has the fluctuation characteristic to form the landform of the watershed of the surface, and rainfall can reach the surface water runoff outlet after confluent from the watershed. The geotextile can simulate the vegetation on the earth surface and prevent rainfall from scouring earth surface silt. And a surface water runoff outlet is provided with a valve for controlling various test scenes.
Preferably, the surface water runoff outlet 4 has dimensions of 0.1m × 0.08 m.
Preferably, the porous aquifer consists of medium sand, the medium sand having an average particle size of 750 μm. Referring to fig. 2, the thickness of the thickest part of the pore aquifer 19 is 0.45-0.5 m, and the thickness of the thinnest part is 0.2-0.25 m, thereby forming a relief landscape. The permeability of the medium sand is between that of the fine sand and that of the coarse sand, and the simulation effect is good.
Preferably, referring to fig. 1, 15 pressure measuring holes are uniformly distributed in the middle of the pore aquifer, the pore diameter is 0.005-0.01 m, and the pore diameter is matched with the pressure sensor.
Preferably, referring to fig. 1, the pore diameter of the pore water outflow hole 5 is 0.02-0.04 m, and eight holes are provided. And the pore water outflow hole is provided with a valve for controlling various test scenes.
Preferably, the fracture network layer is formed by arranging bricks or acrylic plates, and the volume of the bricks or the acrylic plates is 0.001-0.005 m3The clearance of the brick or the acrylic plate is 0.002 m; the thickness of the fracture network layer is 0.4-0.6 m.
Preferably, referring to fig. 1, 15 pressure measuring holes are uniformly distributed in the middle of the fracture network layer 20, and the aperture is 0.005-0.01 m.
Preferably, referring to fig. 1, the pipe layer is formed by arranging bricks or acrylic plates, and the volume of the bricks or the acrylic plates is 0.001-0.005 m3The thickness of the pipeline layer is 0.1-0.2 m; a channel is reserved between the bricks or the acrylic plates to form a karst pipeline 21; the width of the karst pipeline is 0.02-0.05 m, and the height of the karst pipeline is 0.1-0.2 m; the lowest part of the karst pipeline 21 is communicated with the fractured karst water outlet hole 6. The form of the karst pipeline is not limited, and the karst pipeline is ensured to be gradually downward and the lowest part of the karst pipeline is communicated with the fracture karst water outlet hole.
Preferably, the aperture of the fracture karst water outflow hole is 0.02 m. And the fractured karst water outflow hole is provided with a valve for controlling various test scenes.
Preferably, referring to fig. 1, the precipitation supply system comprises a water tank 9, a variable frequency pump 8, a bracket 11 and a plurality of spray heads 12; a water inlet of the variable frequency pump 8 is connected with a water tank 9, and a water outlet is connected with spray heads 12 which are uniformly arranged on a bracket 11 through a water pipe 10; the spray head 12 is positioned above the test sand tank 1; the bracket 11 is fixed above the test sand tank 1. The rainfall intensity of the rainfall replenishment system is controlled by a variable frequency pump, and the angle of the spray head can be adjusted so as to ensure that the evenness of rainfall replenishment and rainfall can all flow into the test sand tank. The water pipe can adopt a rubber hose or a PVC pipe, and the rubber hose is preferred.
Preferably, the flow monitoring system comprises a surface water runoff monitoring system, a pore water runoff monitoring system and a fissure karst water runoff monitoring system, and the surface water runoff monitoring system comprises a surface water runoff pipeline and a measuring cup; the surface water runoff pipeline is connected with a surface water runoff outlet; the pore water runoff monitoring system comprises a pore water runoff pipeline and a measuring cup; the pore water runoff pipeline is connected with the pore water outflow hole; the fracture karst water runoff monitoring system comprises a fracture karst water runoff pipeline and a measuring cup; the fractured karst water runoff pipeline is connected with the fractured karst water outflow hole. The flow of the surface water runoff outlet, the pore water outflow hole and the fissure karst water outflow hole is manually measured, so that the method is more accurate.
In other embodiments of the invention, a flow meter may also be used to measure the flow rate of the fractured rock water outflow hole. Optionally a turbine flow meter, an electromagnetic flow meter or a gear flow meter. The gear flowmeter is preferred, has a storage function, and has the advantages of high measurement precision and wide range.
The test device for simulating the water runoff of the covered karst area can study the change processes of surface water runoff, pore water runoff and fissure karst water runoff under the conditions of the rainfall period (underground water replenishing period) and the drainage period (underground water draining period) of the covered karst area under the sand trough scale, calculate water balance and analyze related influence factors. Two test scenarios can be simulated specifically: the first test scene is in an unsaturated state, short-time rainfall is carried out on the test sand tank by using a rainfall replenishment system, the rainfall firstly infiltrates through the covering layer, moves horizontally and vertically after passing through the pore aquifer, enters the fracture network layer and the pipeline layer, and is finally discharged through the fracture karst water outlet hole; the second test scene is in a saturated state, long-term high-strength replenishment is carried out on the test sand tank through the precipitation replenishment system, the initial water level is controlled by the overflow holes, then precipitation replenishment is stopped, and the surface water runoff, the pore water runoff and the fractured karst water runoff are monitored. Of course, different simulation scenes can be selected according to the needs of actual research, different precipitation time, precipitation intensity and initial water level can be controlled, and the monitoring content can be flexibly changed.
The invention is based on the Jinan spring region, the Jinan spring region belongs to a typical karst water-containing system in the North China, and a test device comprising an earth surface watershed, a covering layer, a pore water-containing layer, a fracture network layer and a pipeline layer is designed by fully considering the hydrogeological conditions of a typical karst region. The device can study karst district surface water runoff, pore water runoff and fracture karst water runoff process, not only can promote the theoretical development of karst water flow motion law, also provides scientific foundation for the complicated karst groundwater resource dynamic analysis of actual area, has the significance to karst district water resource development and utilization.
The embodiment of the invention also provides a test method for simulating water runoff of a covered karst area, which comprises the following steps,
1) opening the variable frequency pump and the spray head, and dewatering the test sand tank according to a preset dewatering condition;
2) recording instantaneous flow of surface water runoff, pore water runoff and fractured karst water runoff;
3) and obtaining a water balance rule covering the karst area according to preset precipitation conditions and instantaneous flows of surface water runoff, pore water runoff and fractured karst water runoff.
Preferably, after the measuring process is finished, the rainfall replenishment system is opened again to carry out rainfall, water is directly received at the spray head to measure the rainfall intensity, and the accurate value of the rainfall is obtained by repeated tests for many times so as to correct the total amount of the rainfall.
Preferably, the ambient humidity and temperature are maintained within certain ranges during the test to reduce the effects of ambient humidity and temperature.
Preferably, the initial water level is controlled through the overflow hole in the test process, the change of water pressure in the test process is recorded, and the water balance rule of the covered karst area under different initial water levels is researched.
Specifically, when the precipitation is unsaturated, the method comprises the following steps:
1) opening a variable frequency pump for controlling the rainfall replenishment intensity, setting the pumping intensity, opening a nozzle valve, continuously reducing the rainfall to the test sand tank, and simultaneously recording the starting time and the ending time of the rainfall;
2) recording instantaneous flow of surface water runoff, pore water runoff and fractured karst water runoff;
3) after the measuring process is finished, the spraying device is turned on again to carry out precipitation, water is directly received at the spray head to measure the precipitation strength, and the precipitation accurate value is obtained by repeating the test for many times;
4) and comparing the total precipitation amount with the surface water runoff, the pore water runoff and the fracture karst water runoff to obtain the water balance rule covering the karst area in an unsaturated state.
Multiple tests show that when the precipitation is unsaturated, the flow of pore water runoff in the test process can be ignored, so that the water balance rule of the coverage karst area in an unsaturated state can be obtained by only measuring the starting time, the ending time and the instantaneous flow of surface water runoff and fracture karst water runoff.
When the precipitation is saturated, the method comprises the following steps:
1) carrying out long-term high-intensity precipitation replenishment on the test sand tank according to precipitation replenishment intensity, controlling an initial water level through the overflow hole, and then stopping precipitation;
2) recording instantaneous flow of surface water runoff, pore water runoff and fractured karst water runoff;
3) copying the record of the water level monitoring system after each test, and sorting and analyzing the instantaneous flow of surface water runoff, pore water runoff and fractured karst water runoff at different initial water levels so as to research the water balance rule covering the karst area in a saturated state.
Multiple tests show that the surface water runoff processes in a saturated state and an unsaturated state are similar, the test result of the unsaturated state of the rainfall can obtain the change rule of the surface water runoff under different rainfall intensities and durations, the rainfall intensity is not changed in a rainfall saturated scene, and the rainfall time is controlled by the initial water level, so that the surface water runoff is not measured when the rainfall is saturated. In addition, due to the greater permeability of the pore layer, the flow of pore water run-off during the test was negligible. Therefore, the water runoff of the covered karst area under the rainfall saturation scene can only measure the fractured karst water runoff under different initial water levels after the precipitation is finished.
Example 1
A test device for simulating water runoff of a covered karst area, which is shown in figure 1, comprises a test sand tank 1, a precipitation supply system, a water level monitoring system and a flow monitoring system.
The test sand tank 1 is a rectangular tank body with a slightly inclined bottom, and the side surface of the test sand tank 1 is provided with a surface water runoff outlet 4, a pore water outflow hole 5, a fissure karst water outflow hole 6 and a pressure measuring hole 7; the inclination angle of the bottom of the test sand tank 1 is 3 degrees, and the size of the test sand tank 1 is 2.5m multiplied by 1.3m multiplied by 0.9 m. The inner and outer walls of the test sand tank are coated with impermeable materials. The side of the test sand tank 1 is provided with 5 overflow holes 3, the aperture of each overflow hole 3 is 0.02m, the interval is 0.1m, and the distance from the lowest overflow hole 3 to the bottom plate 2 is 0.24 m.
Referring to fig. 2, the cover includes soil 18 and geotextile 17 covering the soil. The thickness of the soil layer is 0.04 m; the thickness of the geotextile is 0.01 m. The size of the surface water runoff outlet 4 is 0.1m multiplied by 0.08 m.
The pore aquifer consists of medium sand and has an average particle size of 750 mu m. The thickness of the pore water-containing layer 19 at the thickest part is 0.45m and the thickness of the pore water-containing layer at the thinnest part is 0.25m, thereby forming a relief feature. Referring to fig. 1, 15 pressure measuring holes are uniformly distributed on the side surface of the pore aquifer, the distance from the bottom of the pore aquifer is 0.6m, and the pore diameter of the pore aquifer is 0.005 m. The distance between the pore water outlet holes 5 and the bottom is 0.55m, the pore diameter is 0.02m, and eight pore water outlet holes are arranged in total. The pore water outflow hole is provided with a valve.
The fracture network layer is formed by tightly arranging cubic bricks with the sizes of 0.1m multiplied by 0.1m, and the gaps of the cubic bricks are 0.002 m; the thickness of the fracture network layer was 0.4 m. 15 pressure measuring holes are uniformly distributed on the side surface of the fracture network layer, the distance from the pressure measuring holes to the bottom is 0.3m, and the hole diameter is 0.005 m.
The pipeline layer is formed by arranging cubic bricks with the sizes of 0.1m multiplied by 0.1m, and two channels are reserved between the cubic bricks to form a karst pipeline; the cross-sectional dimension of the karst pipeline is 0.03m multiplied by 0.1m, and the total volume is about 0.02m3(ii) a The thickness of the pipeline layer is 0.1 m; the lowest part of the karst pipeline is communicated with the fracture karst water outflow hole. The fissure karst water outlet hole 6 is arranged at the bottommost part, and the aperture is 0.02 m. And a valve is arranged at the fracture karst water outlet hole.
Referring to fig. 1, the water level monitoring system includes a paperless recorder 13, a pressure sensor 14, and a plurality of rubber tubes 15; one end of the rubber tube 15 is positioned in the pressure measuring hole 7, and the other end of the rubber tube is connected with the pressure sensor 14; the pressure sensor 14 is connected to the paperless recorder 13. One side of the rubber pipe is fixed in the water-containing layer, and the rubber pipe is wrapped by the mesh cloth to prevent fine particles from blocking the water inlet.
The flow monitoring system comprises a surface water runoff monitoring system, a pore water runoff monitoring system and a fissure karst water runoff monitoring system, and the surface water runoff monitoring system comprises a surface water runoff pipeline and a measuring cup; the pore water runoff monitoring system comprises a pore water runoff pipeline and a measuring cup; referring to fig. 1, a fractured-karst water runoff monitoring system includes a fractured-karst water runoff conduit and a gear flow meter 16.
The precipitation replenishment system comprises a water tank 9, a variable frequency pump 8, a bracket 11 and a plurality of spray heads 12; a water inlet of the variable frequency pump 8 is connected with the water tank 9, and a water outlet is connected with spray heads 12 which are uniformly arranged on the bracket 11 through rubber hoses; the support 11 is fixed above the test sand tank 1 and has a height of 1 m.
The device is adopted to carry out simulation tests in a saturated state and an unsaturated state respectively.
Simulation test in saturated state: the test sand tank is subjected to precipitation, the precipitation intensity is 400ml/s, the initial water level (52 cm, 56cm and 60cm respectively) is controlled through the overflow holes, and then the precipitation is stopped; recording the instantaneous flow of the fractured karst water runoff after the precipitation is stopped; and recording the pressure change at the pressure measuring hole after the precipitation is stopped.
Simulation test in unsaturated state: and (3) carrying out precipitation on the test sand tank, wherein the precipitation intensity is 104ml/s, the duration is 15 minutes, recording the starting time, the ending time and the instantaneous flow of the surface water runoff and the fractured karst water runoff, and recording the pressure change at the pressure measuring hole.
Fig. 3 is a diagram of an attenuation process of fracture karst runoff under different initial water levels in a saturated state, and fig. 4 is a diagram of a water head change process of fracture network layer pressure taps when the initial water level in the saturated state is 52cm (wherein 151-155 respectively represent five groups of pressure taps on the lateral surface of the fracture network layer from left to right), and the attenuation process of fracture karst runoff under the saturated state can be analyzed by combining the two processes. The attenuation process generally comprises four attenuation modes, namely slow, fast, acceleration and trailing stages, and the water level is in a linear attenuation state. In the first stage, the attenuation is slow, the water level is positioned at the upper parts of the pore layer and the crack layer, and the water level is high; in the second stage, the attenuation is relatively quick, the water level is in a fracture network layer at the moment, and the water flow moves relatively quickly; the third stage belongs to accelerated attenuation, the water level is in a crack network layer and a pipeline layer at the moment, and the pipeline water flow is not full. Because the sand groove wholly inclines, and the fracture karst water outflow hole sets up at the bottommost, so the pressure-measuring pipe water level that surveys rises from left to right in proper order wholly. In addition, since the pressure measuring pipe is not provided at the lowermost portion, the water level does not fall to 0 cm.
Fig. 5 shows the change process of the flow rate of surface water runoff and the flow rate of fracture karst water runoff in an unsaturated test scene, and in this scene, the pore water runoff is ignored, so the graph is not shown. As can be seen from fig. 5, the flow rate of the surface water runoff rapidly increases after the precipitation starts, and is maintained at about 45ml/s, and rapidly decreases to zero after the precipitation stops. The flow of the fractured karst water runoff is initially zero, and when precipitation reaches a pipeline layer after sequentially penetrating through the covering layer, the pore aquifer and the fracture network layer, the flow of the fractured karst water runoff begins to increase and shows a gradual attenuation trend after reaching a peak value. The attenuation process in the unsaturated state only comprises slow attenuation, fast attenuation and tailing stages, the slow attenuation process is due to the regulation and storage effects of a pore layer and a fracture network layer, and the fast attenuation process is due to the fact that pipeline water flows in an open channel mode and the flow rate is small.
The water pressure fluctuation at the pressure measuring hole under the unsaturated scene is large, and the reference value is not provided, and the reference value is not listed.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A test device for simulating water runoff of a covered karst area is characterized by comprising a test sand tank, a precipitation supply system and a flow monitoring system;
a water outlet of the precipitation replenishment system is positioned above the test sand tank;
the test sand tank is a tank body with a slightly inclined bottom; the side surface of the test sand groove is provided with a surface water runoff outlet, a pore water outflow hole, a fissure karst water outflow hole and an overflow port; a covering layer and a karst area medium are sequentially arranged in the test sand tank from top to bottom; the lowest end of the covering layer is communicated with a surface water runoff outlet; the karst area medium comprises a pore aquifer positioned at the uppermost layer, a fracture network layer positioned at the middle layer and a pipeline layer positioned at the bottom layer; the pore aquifer undulates; the pore water outflow hole is positioned on the side surface of the pore aquifer; the lowest end of the pipeline layer is communicated with the fractured karst water outflow hole; the flow monitoring system is used for monitoring the flow of the surface water runoff outlet, the pore water outflow hole and the fractured karst water outflow hole.
2. A test rig for simulating runoff of water in a overburden karst area as claimed in claim 1 wherein the inclination of the bottom of said test sand tank is in the range of 2 ° to 5 °.
3. A test rig for simulating runoff of water in a overburden karst area as claimed in claim 1 wherein said overburden comprises soil and geotextile covering the soil; the thickness of the soil is 0.03-0.05 m; the thickness of the geotextile is 0.005-0.01 m.
4. A test rig for simulating overburden karst water runoff according to claim 1 wherein said pore aquifer is comprised of medium sand; the thickness of the thickest part of the pore aquifer is 0.45-0.5 m, and the thickness of the thinnest part is 0.2-0.25 m; the average grain diameter of the medium sand is 750 mu m.
5. The test device for simulating the runoff of water in a covered karst area according to claim 1, wherein the fracture network layer is formed by arranging bricks or acrylic plates, and the thickness of the fracture network layer is 0.4-0.6 m; the volume of the brick or the acrylic plate is 0.001-0.005 m3The clearance of the brick or the acrylic plate is 0.002 m.
6. The test device for simulating the runoff of water in the overburden karst area as recited in claim 1, wherein the pipe layer is formed by arranging bricks or acrylic plates, and the thickness of the pipe layer is 0.1-0.2 m; the volume of the brick or the acrylic plate is 0.001-0.005 m3A channel is reserved between the bricks or the acrylic plates to form a karst pipeline; the width of the karst pipeline is 0.02-0.05 m, and the height of the karst pipeline is 0.1-0.2 m; the lowest part of the karst pipeline is communicated with the fracture karst water outflow hole.
7. The test device for simulating runoff of water covering a karst area of claim 1 wherein the precipitation replenishment system comprises a water tank, a variable frequency pump, a support and a plurality of spray heads;
a water inlet of the variable frequency pump is connected with the water tank, and a water outlet of the variable frequency pump is connected with spray heads uniformly arranged on the bracket through pipelines;
the support is fixed above the test sand tank.
8. A test rig for simulating runoff of water in a overburden karst area as recited in claim 1 further comprising a water level monitoring system; the water level monitoring system comprises a paperless recorder, a pressure sensor and a plurality of rubber pipes;
pressure measuring holes are formed in the side faces of the pore aquifer and the fracture network layer;
one end of the rubber tube is positioned in the pressure measuring hole, and the other end of the rubber tube is connected with the pressure sensor;
the pressure sensor is connected with the paperless recorder.
9. A test method for simulating water runoff in a covered karst area is characterized by comprising the following steps,
opening the variable frequency pump and the spray head, and dewatering the test sand tank according to a preset dewatering condition;
recording instantaneous flow of surface water runoff, pore water runoff and fractured karst water runoff;
and obtaining a water balance rule covering the karst area according to preset precipitation conditions and instantaneous flows of surface water runoff, pore water runoff and fractured karst water runoff.
10. A test method for simulating runoff of water in a overburden karst area as claimed in claim 9,
when the precipitation is saturated, the preset precipitation condition comprises an initial water level;
when the precipitation amount is not saturated, the preset precipitation conditions comprise the pumping intensity of the variable frequency pump, the precipitation starting time and the precipitation ending time.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114965962A (en) * | 2022-06-01 | 2022-08-30 | 桂林理工大学 | Visualization method for applying transparent soil technology to composite aquifer structure and evolution thereof |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114965962A (en) * | 2022-06-01 | 2022-08-30 | 桂林理工大学 | Visualization method for applying transparent soil technology to composite aquifer structure and evolution thereof |
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