Desalted plot underground drainage single covering structure

Abstract

The utility model discloses an underground drainage single covering structure for a desalted plot. The underground drainage single covering structure comprises the desalted plot, the drainage concealed pipes are arranged in the desalted plot in a criss-cross manner; the screens are laid in a criss-cross manner at the positions, corresponding to the arrangement positions of the concealed drainage pipes, of the surface of the desalted land parcel; the aquitard is laid on the screen, and the permeability coefficient of the aquitard is lower than that of the soil of the desalted plot. The area with high infiltration intensity of the field surface is inhibited by the low-permeability layer, and the area with low infiltration intensity is enhanced, so that the infiltration intensity of the soil surface is uniformly distributed, salt can be uniformly leached downwards in the whole desalting field range, the utilization rate of fresh water is improved, and the water-saving efficiency is about 65-75%.

Description

Technical Field

[0001] The utility model relates to the technical field of saline soil improvement, in particular to a single covering structure for underground drainage of desalinated land. Background Art

[0002] Soil salinization refers to the process by which salt from the subsoil or groundwater rises to the surface with capillary water and, after evaporation, accumulates in the surface soil. It is the phenomenon or process by which soluble salts accumulate in the soil's surface layer. China's saline-alkali soils are widely distributed, covering a large area and diverse types, totaling approximately 100 million hectares, primarily in arid, semi-arid, and sub-humid regions. The presence of saline-alkali lands has severely impacted the local ecological environment and agricultural production. High salinity inhibits crop growth, reducing yield and quality.

[0003] The ability of subsurface drainage systems to reduce soil salinity is often enhanced by applying freshwater to the soil surface to supplement rainfall-induced erosion. Surface irrigation is often combined with subsurface drainage systems to filter excess salt from saline soils. Previous studies on soil subsurface drainage performance have shown that under continuous irrigation conditions, salt is only effectively leached from areas close to the drain pipes. This is because infiltration rates decrease in areas farther from the drain pipes (e.g., midway between two adjacent drain pipes), resulting in inefficient leaching of salt from the soil in these areas. This process requires longer than the time required to flush salt from the soil near the drain pipes, thus wasting unnecessary freshwater in the soil near the drain pipes, as the salt in these soils has already been washed away.

[0004] The high spatial variability of salt leaching rates in underground drainage systems could be mitigated if the downward flow of freshwater from irrigation was more spatially uniform. Patent application number 201911069334.3, titled "A Method for Zoning a Cover Layer to Improve Leaching Efficiency," discloses a method for improving leaching efficiency using a zoned cover layer. However, the installation of the zoned cover layer is complex, and the configuration of different types of infiltration media is costly. Summary of the Invention

[0005] Purpose of the utility model: In order to overcome the shortcomings of the background technology, the utility model discloses a single covering structure for underground drainage of desalination plots.

[0006] Technical solution: The single covering structure for underground drainage of desalination land disclosed in the utility model includes:

[0007] desalination plots;

[0008] Drainage concealed pipes, which are arranged in a crisscross pattern within the desalination plot;

[0009] The screens are laid in a crisscross pattern on the surface of the desalination plot corresponding to the arrangement of the drainage concealed pipes;

[0010] A weakly permeable layer is laid on the screen, and the permeability coefficient of the weakly permeable layer is lower than the permeability coefficient of the soil in the desalination plot.

[0011] Furthermore, the drainage concealed pipe is a plastic pipe or a clay pipe; gravel or crushed stone is arranged around the concealed pipe, or geotextile is wrapped around the concealed pipe.

[0012] Furthermore, the spacing L between the concealed drainage pipes is:

[0013] L=γ·Ks·D / 100

[0014] Where Ks is the saturated permeability coefficient, cm / d; D is the pipeline burial depth, cm; γ is the empirical coefficient.

[0015] Furthermore, the screen is made of stainless steel wire or nylon wire.

[0016] Furthermore, the weak permeable layer is formed by filling with a low permeability medium, which is a mixture of one or more of river sand, clay, loam, fly ash, and gypsum powder, and its permeability coefficient is 2-3 orders of magnitude lower than the permeability coefficient of the desalination plot soil.

[0017] Furthermore, the weak permeable layer extends the same distance to both sides from the horizontal position of the drainage concealed pipe, and the width on one side is equal to 0.2-0.5 times the spacing between the drainage concealed pipes; the thickness is 5-10 cm.

[0018] Furthermore, a regulating tank and a water pump are provided at the end of the concealed drainage pipe.

[0019] Furthermore, vegetation buffer zones are provided at the inlets and outlets of the concealed drainage pipes.

[0020] Beneficial effects: Compared with the prior art, the advantages of this utility model are:

[0021] (1) The low permeability layer suppresses the areas with high infiltration intensity on the field surface, while strengthening the areas with low infiltration intensity, making the distribution of infiltration intensity on the soil surface uniform, which is conducive to the uniform leaching of salt downward in the entire desalination site, improving the utilization rate of fresh water, and the water-saving efficiency is about 65%-75%;

[0022] (2) The low permeability layer increases the infiltration intensity of the soil surface away from the salt drainage system, accelerating the leaching cycle of the salt drainage system, with a cycle reduction rate of 30%-40%;

[0023] (3) Single-layer covering is adopted and it is laid locally on the soil surface, so the laying process is relatively simple. At the same time, the infiltration medium configured is of the same type, so the laying cost is low;

[0024] (4) The weak permeable layer can be laid by machinery, which is convenient for large-scale integrated operation. After desalination, it can be plowed into the soil to increase soil fertility, which will not cause waste of resources and will not affect subsequent agricultural planting and natural drainage processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the three-dimensional structure of the utility model;

[0026] Figure 2 This is a schematic diagram of the three-dimensional structure of the section where the concealed drainage pipe of the utility model is located;

[0027] Figure 3 This is a two-dimensional cross-sectional seepage diagram of a concealed pipe salt drainage system without a cover layer (taking the y=5 cross-sectional area as an example);

[0028] Figure 4 This is a two-dimensional cross-section diagram of the seepage flow in the concealed pipe salt drainage system with the cover layer (taking the cross section y=5 as an example);

[0029] Figure 5 This is a comparison chart of the total amount of infiltration per unit area of ​​soil surface in the embodiment;

[0030] Figure 6 Schematic diagram of the change of standardized salt mass (Mf) in the target leaching area in the embodiment

[0031] Figure 7 Schematic diagram of the change of infiltration rate per unit area of ​​soil surface in the embodiment, where Figure 7 A in the middle is the case without low permeability layer. Figure 7 Middle B is the case of laying a low permeability layer. DETAILED DESCRIPTION

[0032] The technical solution of the present utility model will be further described below with reference to the accompanying drawings and embodiments.

[0033] like Figure 1 and 2 The desalination plot underground drainage single cover structure shown includes:

[0034] Desalination plot 1: A reasonable irrigation method is selected for the surface of the desalination plot based on the regional water resources situation and economic considerations. Generally, continuous irrigation is used for leaching. The surface water depth can be selected to be 5cm-10cm, and the mineralization of the leaching water shall not exceed 2mg / g.

[0035] Drainage concealed pipes 2 are arranged in a crisscross pattern within the desalination plot 1, with even spacing between adjacent pipes. The pipe diameter can range from 8 to 20 cm, the buried depth D can range from 0.6 to 2.0 m, and the slope can range from 1% to 2.5%. These concealed pipes are used to drain excess salt dissolved in the water. They are constructed of plastic or clay pipes. Gravel or crushed stone, or geotextile wrapping, are placed around the pipes to prevent soil particles from entering the pipes while allowing water to pass through.

[0036] The spacing L between the hidden drainage pipes 2 is:

[0037] L=γ·Ks·D / 100

[0038] Where Ks is the saturated permeability coefficient, cm / d; D is the pipeline burial depth, cm; γ is an empirical coefficient, which is 40 for clay, 30 for loam, and 20 for sand.

[0039] The screen 3 is laid in a crisscross pattern on the surface of the desalination plot 1 corresponding to the arrangement position of the drainage pipe 2; the screen 3 is made of stainless steel wire or nylon wire, and its function is to prevent the weak permeable layer from mixing with the soil during the elution process and reducing the effectiveness of the weak permeable layer, which is beneficial to the recovery of the weak permeable layer or the subsequent use of tillage machinery to plow the land, mix the weak permeable layer into the soil, and increase soil fertility.

[0040] A weakly permeable layer 4 is laid on the screen 3 , and the permeability coefficient of the weakly permeable layer 4 is lower than the permeability coefficient of the soil of the desalination plot 1 .

[0041] The weakly permeable layer 4 is formed by filling a low permeability medium, which is a mixture of one or more of river sand, clay, loam, fly ash, and gypsum powder. Its permeability coefficient is 2-3 orders of magnitude lower than the permeability coefficient of the soil in the desalination plot 1.

[0042] The weakly permeable layer 4 extends the same distance to both sides from the horizontal position of the drainage concealed pipe 2, and the width on one side is equal to 0.2-0.5 times the spacing between the drainage concealed pipes 2; the thickness is 5-10 cm.

[0043] A regulating tank and a water pump are provided at the end of the drainage concealed pipe 2 to temporarily store excess drainage, smooth the peak flow during the drainage process, and avoid a large amount of high-salt water being directly discharged into the downstream water body in a short period of time, thereby reducing the impact on the environment.

[0044] Vegetation buffer zones are provided at the inlet and outlet of the underground drainage pipe 2 to intercept and filter salt and other pollutants in the surface runoff from the farmland.

[0045] During operation:

[0046] Plough, loosen and level the surface soil, remove surface obstacles, level the land, and ensure that the area for laying concealed pipes is flat and unobstructed.

[0047] According to the permeability coefficient K of saline-alkali soil, a low permeability medium is prepared, and the permeability coefficient of the permeable medium is K1; in particular, the permeability coefficient corresponding to the low permeability medium has a value range of log 10 (K1 / K)=-3~-1, low permeability medium is a mixture of river sand, clay, loam, fly ash, gypsum powder and other materials in a certain proportion.

[0048] According to the spacing of the concealed pipes, a prefabricated weak permeable layer is laid out, wherein a screen is set at the bottom of the weak permeable layer to prevent mixing of the filling materials. L1 Take the spacing between adjacent concealed pipes L The permeability of the medium is 0.2~0.5, and the low permeability medium is filled into the set range using construction machinery.

[0049] Water with a mineralization of no more than 2 mg / g is used as the leaching water source. Based on the regional water resource conditions and economic considerations, a reasonable irrigation method is adopted to flood the surface of the desalination plot to 5cm-10cm. During the drainage and leaching process, a weak permeability layer with a lower permeability coefficient is set near the underground pipe area, thereby reducing the surface infiltration intensity of the area. The area far away from the underground pipe is not treated, resulting in a tendency for surface water flow to converge toward the area far away from the underground pipe, increasing the surface infiltration intensity of these areas. On the other hand, the amount of infiltration in the area where the weak permeability layer is set is reduced. Compared with the case where the weak permeability layer is not set, the weak permeability layer strengthens the lateral flow effect, and the lateral flow reduces the water seepage path and accelerates the discharge of salt into the underground pipe.

[0050] After desalination is completed, the land is plowed using tillage machinery to mix the weak permeable layer into the soil and increase soil fertility.

[0051] In order to demonstrate that the covering layer designed in the present invention can improve the elution and desalination efficiency of the concealed pipe salt drainage system, numerical simulation was used to compare the differences in elution cycle and total elution water volume with and without the covering layer.

[0052] The groundwater seepage and solute migration processes were simulated in three dimensions using the SUTRA software package.

[0053] According to relevant data, the permeability coefficient of the desalination plot is set to 1.23*10 -5 m / s, porosity is 0.41, longitudinal diffusion coefficient D L =0.1m, lateral diffusion coefficient D T The initial concentration of groundwater in the aquifer is 10 kg / m 3The buried depth of the underground pipe is 1m, the diameter of the underground pipe is 10cm, the distance between adjacent underground pipes is 20m, and the spacing along the length and width is consistent. The position of the impermeable layer is -5m, the fixed water head height of the soil surface is 10cm, and the irrigation method is continuous irrigation. Since the groundwater flow is symmetrically distributed about the underground pipe, and the weak permeable layer is set symmetrically about the underground pipe, a quarter of the model is selected ( Figure 2 The numerical simulation was performed with a model size of 10m×10m×5m. Numerical simulation 1 (hereinafter referred to as simulation 1) represents the case without a weak permeable layer, and numerical simulation 2 (hereinafter referred to as simulation 2) represents the case with a weak permeable layer. The permeability coefficient of the cover layer in simulation 2 is K1=1.23*10 -7 m / s, that is, log 10 (K1 / K)=-2, take L1 / L=0.3, where L 1 is the width of the aquitard, L It is half the distance between adjacent concealed pipes.

[0054] Figure 3 This is a schematic diagram of flow lines across a desalination plot without a single layer of cover. Including the underground pipes and desalination plot, the groundwater flow lines are as shown in the figure, with arrows indicating the direction of groundwater flow.

[0055] Figure 4 This is a schematic diagram of the streamlines in a cross-section of the desalination plot after the aquitard is installed. Including the underground pipes, desalination plot, screen, and aquitard, the groundwater streamlines in the salt drainage system now resemble the shape shown in the figure, with arrows indicating the direction of groundwater flow.

[0056] Figure 5 is the standardized salt mass in the target leaching area (M f ) Schematic diagram of changes in soil leaching and salt removal. It is easy to see from the figure that in the early stages of leaching and salt removal, Simulation 1 removed salt faster. As leaching and salt removal progressed, the salt removal rate in Simulation 2 exceeded that of Simulation 1. Ultimately, the entire leaching and salt removal cycle for Simulation 1 was 22 days, while the entire leaching and salt removal cycle for Simulation 2 was 15 days. The installation of the aquitard reduced the soil leaching and salt removal cycle by approximately 31%.

[0057] Figure 6 The total amount of water infiltration during the entire desalination cycle for simulation 1 and simulation 2 is shown in Figure 1. The total amount of water infiltration on the soil surface in simulation 1 is 3.4 m 3 / m 2 In simulation 2, the total amount of infiltration on the soil surface is 1.2m 3 / m 2 According to the above data, the total infiltration volume of Simulation 2 is approximately 64% less than that of Simulation 1.

[0058] Figure 7 is the unit infiltration rate of the soil surface, Figure 7 A in the middle is the case without a weak permeable layer. Figure 7 B is the case of setting a weak permeable layer. It is not difficult to see that the infiltration volume in the area near the drainage pipe is large, about 1m 3 / m 2 / d, while the infiltration rate in the area far from the drainage pipe is relatively small, less than 0.2m 3 / m 2 / d. The distribution of infiltration water in B is more balanced, and the infiltration volume in the area close to the drainage pipe is reduced to 0.2m 3 / m 2 / d, while the infiltration rate in the area far away from the drainage pipe increases, which in turn promotes the salt to be leached downward evenly, improves the leaching efficiency and saves the amount of water required for leaching.

Claims

1. A single covering structure for underground drainage of desalination plots, characterized in that: include: Desalination plot (1); Drainage concealed pipes (2), the drainage concealed pipes (2) are arranged in a crisscross pattern within the desalination plot (1); A screen (3), wherein the screen (3) is laid in a crisscross pattern on the surface of the desalination plot (1) corresponding to the arrangement position of the drainage concealed pipe (2); A weakly permeable layer (4), the weakly permeable layer (4) is laid on the screen (3), and the permeability coefficient of the weakly permeable layer (4) is lower than the permeability coefficient of the soil of the desalination plot (1).

2. The single covering structure for underground drainage of desalination land according to claim 1, characterized in that: The drainage concealed pipe (2) is a plastic pipe or a clay pipe; gravel or crushed stone is arranged around the concealed pipe, or geotextile is wrapped around the concealed pipe.

3. The single covering structure for underground drainage of desalination land according to claim 1, characterized in that: The spacing L of the drainage concealed pipe (2) is: L=γ·Ks·D / 100 Where Ks is the saturated permeability coefficient, cm / d; D is the pipeline burial depth, cm; γ is the empirical coefficient.

4. The single covering structure for underground drainage of desalination land according to claim 1, characterized in that: The screen (3) is made of stainless steel wire or nylon wire.

5. The single covering structure for underground drainage of desalination land according to claim 1, characterized in that: The weak permeable layer (4) extends from the horizontal position of the drainage concealed pipe (2) to both sides by the same distance, and the width of the single side is equal to 0.2-0.5 times the spacing between the drainage concealed pipes (2); the thickness is 5-10 cm.

6. The single covering structure for underground drainage of desalination land according to claim 1, characterized in that: A regulating tank and a water pump are provided at the end of the drainage concealed pipe (2).

7. The single covering structure for underground drainage of desalination land according to claim 1, characterized in that: Vegetation buffer zones are provided at the inlet and outlet of the drainage concealed pipe (2).

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