Soil cave gas tracer test device

Abstract

The present invention discloses a soil cave gas tracer test device, including a rock dissolution chamber, a soil leaching chamber and a soil cave simulation chamber, each chamber is provided with a water inlet pipe, a drainage pipe and an exhaust pipe, and valves and pressure gauges are provided on each pipeline path; the rock dissolution chamber is used to dissolve rock samples and collect the gas generated during the dissolution process; the soil leaching chamber is used to leach soil samples and collect the gas generated during the leaching process; the soil cave simulation chamber includes an external gas tracer box, a soil sample placement box and an internal gas tracer box, which are used to perform a seepage deformation test and a gas tracer test. The soil cave gas tracer test device described in the present invention can simulate soil cave type karst collapse, obtain the quantitative correspondence between soil deformation and destruction and soil cave gas migration during soil cave development, and further obtain gas indicators and parameters for monitoring and early warning of soil cave type karst collapse.

Description

Technical Field

[0001] The invention relates to a gas tracer test device for simulating karst collapse, in particular to a soil cave gas tracer test device for simulating soil cave type karst collapse. Background Art

[0002] Karst collapse is one of the main geological disasters in karst areas, among which soil cave karst collapse is more common. Soil cave karst collapse refers to the process and phenomenon in which the soil above the caves and pipe cracks in the covered karst area is deformed and damaged due to the erosion and dissolution of groundwater. With the continuous loss of soil, soil caves are gradually formed in the soil, and finally collapse pits are formed on the surface. In the process of the formation and development of soil caves, due to the movement of groundwater and the dissolution of soil and rocks, a certain amount of gas will be formed and stored in the soil caves. These gases will change significantly in concentration, composition, flux, geochemical characteristics, etc. with the different development stages of the soil caves, and migrate upward along the cracks in the soil, and appear abnormal on the ground. This can be used to monitor the soil cave gas for early warning and forecast of karst collapse. Before realizing monitoring and early warning, it is necessary to select the gases and their index parameters for monitoring, study the dependence between gas permeability and soil porosity, saturation and gas content, clarify the penetration and migration rules of gas in the soil around soil caves, and then establish the correspondence between the abnormal characteristic values ​​of surface gas and the different development stages of soil caves. The above work requires the implementation of soil cave gas tracer tests. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a soil cave gas tracer test device for simulating soil cave type karst collapse.

[0004] The soil cave gas tracer test device of the present invention comprises a rock dissolution chamber, a soil leaching chamber and a soil cave simulation chamber, wherein:

[0005] Each chamber is provided with a water inlet pipe, a drain pipe and an exhaust pipe, and valves and pressure gauges are provided on the paths of each water inlet pipe, drain pipe and exhaust pipe;

[0006] The rock dissolution chamber is provided with a placement rack for placing rock samples;

[0007] The soil leaching chamber is provided with a stand for placing soil samples, and a permeable stone is arranged directly above the stand. The water entering the soil leaching chamber from the water inlet pipe first penetrates into the permeable stone before entering the soil leaching chamber.

[0008] The soil cave simulation chamber includes an external gas tracer box, a soil sample placing box arranged in the external gas tracer box for placing the original soil sample, and an internal gas tracer box placed in the soil sample placing box and buried in the original soil sample, wherein:

[0009] The external gas tracer box is a box with a cover and can be sealed;

[0010] The soil sample placing box is a sealed box with a cover, and the box has a side for water to penetrate into the interior and a side for water in the box to penetrate out, the two sides are made of permeable stone, and the height of the two sides is higher than or equal to the height of the original soil sample;

[0011] The top of the internal gas tracer box is provided with an air hole, and the bottom is connected to the gas supply equipment outside the soil cave simulation room through an air inlet pipe, and a valve and a pressure gauge are arranged on the air inlet pipe path;

[0012] The soil sample placing box is provided with at least one gas collecting pipe, on which a valve and a pressure gauge are provided; the air inlet end of the gas collecting pipe extends into the original soil sample in the soil sample placing box, and the air outlet end thereof is connected to a gas collecting device or container.

[0013] In the above technical solution, the soil sample placing box is arranged in the external gas tracer box through a bracket, a water-permeable plate is arranged on the bracket, the soil sample placing box is placed on the water-permeable plate, and the water permeated from the soil sample placing box drips to the bottom of the external gas tracer box through the water-permeable plate.

[0014] In the above technical solution, the internal gas tracer box is designed according to the shape of the soil hole, usually designed to be hemispherical. The air holes on the top of the internal gas tracer box are evenly distributed, and their sizes are set according to needs, usually designed to be holes with a diameter of 1-3 mm.

[0015] In the above technical solution, the number of gas collection tubes on the soil sample placing box is related to the uniformity of sampling and can be set according to needs, usually 3-7.

[0016] In the above technical scheme, in order to facilitate experimental observation, except for the sides of the soil sample placing box for water to penetrate into its interior and the sides for water in the box to penetrate out, which are made of permeable stone, the other parts of the stone dissolution chamber, soil leaching chamber and soil cave simulation chamber are preferably made of transparent materials.

[0017] Compared with the prior art, the soil cave gas tracer test device described in the present invention can simulate soil cave type karst collapse, obtain the quantitative correspondence between soil deformation and destruction and soil cave gas migration during soil cave development, and further obtain gas indicators and parameters for soil cave type karst collapse monitoring and early warning. The device described in the present invention can be used to carry out karst collapse early warning and forecasting research and application based on soil cave gas monitoring, which is of great significance to enrich and improve the multi-parameter monitoring and early warning technology of karst collapse. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1This is a schematic structural diagram of an implementation method of the soil cave gas tracer test device of the present invention.

[0019] The numbers in the figure are:

[0020] 1 water inlet pipe, 2 valve, 3 pressure gauge, 4 rack, 5 rock sample, 6 rock dissolution chamber, 7 exhaust pipe, 8 drain pipe, 9 bracket, 10 external gas tracer box, 11 permeable stone, 12 soil sample placement box, 13 gas collection pipe, 14 original soil sample, 15 internal gas tracer box, 16 pores, 17 permeable plate, 18 gas supply equipment, 19 air inlet pipe, 20 soil leaching chamber, 21 rack, 22 soil sample. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with specific drawings to provide a better understanding of the present invention.

[0022] like Figure 1 As shown, the soil cave gas tracer test device of the present invention comprises a rock dissolution chamber 6, a soil leaching chamber 20 and a soil cave simulation chamber, wherein:

[0023] The stone dissolution chamber, soil leaching chamber 20 and soil cave simulation chamber are respectively provided with respective water inlet pipes 1, drainage pipes 8 and exhaust pipes 7, and valves 2 and pressure gauges 3 are provided on the pipeline paths of the water inlet pipes 1, drainage pipes 8 and exhaust pipes 7;

[0024] The rock dissolution chamber 6 is provided with a placing rack 4, on which a rock sample 5 is placed;

[0025] The soil leaching chamber 20 is provided with a stand 21, and a soil sample 22 is placed on the stand 21. A permeable stone 11 is arranged directly above the stand 21. The outer peripheral wall of the permeable stone 11 is in contact with the inner wall surface of the soil leaching chamber 20. The water entering the soil leaching chamber 20 from the water inlet pipe 1 first penetrates into the permeable stone 11 before entering the soil leaching chamber 20 and further drips onto the soil sample 22 on the stand 21.

[0026] The soil cave simulation chamber includes an external gas tracer box 10, a soil sample placing box 12 disposed in the external gas tracer box 10 for placing an original soil sample 14, and an internal gas tracer box 15 disposed in the soil sample placing box 12 and submerged in the original soil sample 14, wherein:

[0027] The external gas tracer box 10 is a sealed box with a cover;

[0028] The soil sample placing box 12 is a sealed box with a cover, and the box has a side for water to penetrate into the interior and a side for water in the box to penetrate out, and the two sides are made of permeable stone 11, and the height of the two sides is higher than or equal to the height of the original soil sample 14;

[0029] The soil sample placing box 12 is arranged in the external gas tracer box 10 through the bracket 9, and a water-permeable plate 17 is arranged on the bracket 9. The soil sample placing box 12 is placed on the water-permeable plate 17, and the water permeated from the soil sample placing box 12 drips to the bottom of the external gas tracer box 10 through the water-permeable plate 17;

[0030] The top of the internal gas tracer box 15 is provided with evenly distributed air holes 16, and the bottom is connected to the gas supply equipment 18 (such as a helium cylinder) outside the soil cave simulation room through the air inlet pipe 19, and a valve 2 and a pressure gauge 3 are arranged on the pipeline path of the air inlet pipe 19; the gas supply equipment 18 delivers one or more tracer gases to the internal gas tracer box 15 through the air inlet pipe 19;

[0031] The number of gas collecting tubes 13 on the soil sample placing box 12 is set as needed. In the present embodiment, the number of gas collecting tubes 13 in the soil sample placing box 12 is 3, and valves 2 and pressure gauges 3 are provided on the gas collecting tubes 13; the air inlet end of the gas collecting tube 13 extends into the original soil sample 14 in the soil sample placing box 12, and the insertion depth is set as needed. Preferably, each exhaust pipe 7 is inserted into different depths at different positions inside the original soil sample 14, so that the gas sample taken by the gas collecting tube 13 will be more representative; the exhaust end of the gas collecting tube 13 is connected to a gas collecting device or container (such as an L-valve gas sampling bag) to further analyze the collected gas samples.

[0032] In the above embodiment, the gas tracer box 10 outside the stone dissolution chamber and the soil leaching chamber 20 and the soil sample placement box 12 are all square, the internal gas tracer box 15 is hemispherical, and the diameter of the air hole 16 on the top of the internal gas tracer box 15 is 1-3 mm. Except for the side of the soil sample placement box 12 for water to penetrate into the interior and the side for water in the box to penetrate out, which are made of permeable stone 11, the other parts of the stone dissolution chamber, soil leaching chamber 20 and soil cave simulation chamber in the device of the present invention are preferably made of transparent materials. Each connection part in the device of the present invention needs to be checked for airtightness and liquid tightness.

[0033] The specific operation of using the device of the present invention is as follows:

[0034] 1) During the test, firstly, carbonate rock samples from the field subsidence area are obtained and the rock chemical composition is analyzed, then rock samples 5 are prepared and placed in a sample box, and the sample box is fixed on the placement rack 4 in the rock dissolution chamber 6. At the same time, the original soil from the field subsidence area is obtained and the soil chemical composition is analyzed, then standard samples (i.e. soil samples 22 and original soil samples 14) are prepared, the soil sample 22 is placed in a sample box, and the sample box is fixed on the stand 21 of the soil leaching chamber 20, and the original soil sample 14 is placed in the soil sample placement box 12.

[0035] 2) Then, by controlling the valves 2 on the water inlet pipe 1 and the drain pipe 8, rock dissolution, soil leaching and seepage deformation tests are carried out, and by controlling the valves 2 on the corresponding exhaust pipes 7, the gases generated by rock dissolution, soil leaching and seepage deformation of the original soil sample are collected at regular intervals and analyzed in the laboratory.

[0036] 3) Later, at a certain stage after the deformation and damage of the soil, one or more special tracer gases are input according to a certain concentration, and then received regularly through the gas collection pipes 13 at different positions of the soil sample placement box 12 and subjected to laboratory analysis.

[0037] 4) Finally, by conducting a comprehensive comparative analysis with the data collected from the rock dissolution chamber 6, soil leaching chamber 20, and soil cave simulation chamber, the concentration, composition, flux, geochemical characteristics and other index parameters of soil cave gas at different development stages of the soil cave are studied, the dependence between gas permeability and soil porosity, saturation and gas content is analyzed, the penetration and migration laws of gas in the soil around the soil cave are clarified, and then the corresponding relationship between the abnormal characteristic values ​​of surface gas and the different development stages of the soil cave is established.

Claims

1. A soil cave gas tracer test device, comprising a rock dissolution chamber (6), a soil leaching chamber (20) and a soil cave simulation chamber, characterized in that: Each chamber is provided with a water inlet pipe (1), a drain pipe (8) and an exhaust pipe (7), and each water inlet pipe (1), drain pipe (8) and exhaust pipe (7) is provided with a valve (2) and a pressure gauge (3); The rock dissolution chamber (6) is provided with a placement rack (4) for placing rock samples (5); The soil leaching chamber (20) is provided with a stand (21) for placing a soil sample (22), and a permeable stone (11) is arranged directly above the stand (21). Water entering the soil leaching chamber (20) through the water inlet pipe (1) first permeates into the permeable stone (11) before entering the soil leaching chamber (20); The soil cave simulation chamber comprises an external gas tracer box (10), a soil sample placement box (12) arranged in the external gas tracer box (10) for placing an original soil sample (14), and an internal gas tracer box (15) placed in the soil sample placement box (12) and buried in the original soil sample (14), wherein: The external gas tracer box (10) is a box body with a cover and can be sealed; The soil sample placing box (12) is a sealed box with a cover, the box having a side surface for water to penetrate into the interior and a side surface for water in the box to penetrate out, the two side surfaces are made of permeable stone (11), and the height of the two side surfaces is higher than or equal to the height of the original soil sample (14); The top of the internal gas tracer box (15) is provided with an air hole (16), and the bottom is connected to the gas supply equipment (18) outside the soil cave simulation room through an air inlet pipe (19), and a valve (2) and a pressure gauge (3) are arranged on the path of the air inlet pipe (19); The soil sample placement box (12) is provided with at least one gas collection pipe (13), and a valve (2) and a pressure gauge (3) are provided on the gas collection pipe (13); the gas inlet end of the gas collection pipe (13) extends into the original soil sample (14) in the soil sample placement box (12), and the gas outlet end is connected to a device or container for collecting gas.

2. The soil cave gas tracer test device according to claim 1, characterized in that: The soil sample placing box (12) is arranged in the external gas tracer box (10) via a bracket (9); a water-permeable plate (17) is arranged on the bracket (9); the soil sample placing box (12) is placed on the water-permeable plate (17); water permeated from the soil sample placing box (12) drips onto the bottom of the external gas tracer box (10) via the water-permeable plate (17).

3. The soil cave gas tracer test device according to claim 1 or 2, characterized in that: The internal gas tracer box (15) is hemispherical.

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