A method for treating saline-alkali land in piedmont alluvial fans

Abstract

The present invention discloses a method for treating saline-sodic land in piedmont alluvial fans, belonging to the technical field of soil treatment, including: soil sampling and investigation: the sampling range is centered on a fixed point, referring to the spacing of subsurface drainage pipes in similar areas, to form a sampling range of 3D*6D; soil texture analysis: measuring the particle size of soil samples, judging the position of the weakly permeable soil layer with a clay content exceeding 20%, using the point coordinates in the radial direction of the mountain as the abscissa, the soil layer depth as the ordinate, and processing and analyzing based on the clay content of different weakly permeable soil layers at different points to identify the shape of the weakly permeable soil layer with a clay content exceeding 20% at 1.0m - 2.0m in the radial direction of the mountain; determination of soil permeability: using a ring knife to take undisturbed soil for measuring the permeability coefficient, and for the case where the permeability coefficient of undisturbed soil cannot be determined, it can be inversed through the HYDRUS model to obtain the permeability coefficients of different soil layers after inversion; selecting a drainage and desalination method according to the shape of the weakly permeable soil layer. Avoiding waste caused by too small spacing of subsurface drainage pipes and poor drainage and desalination effects caused by too large spacing of subsurface drainage pipes.

Description

Technical Field

[0001] The present invention relates to the technical field of soil treatment, and particularly relates to a method for treating saline-alkali land in piedmont alluvial fans. Background Art

[0002] Carrying out the treatment of saline-alkali land is of great significance for improving the reserve of arable land and ensuring food security. The technology of subsurface pipe drainage combined with fresh water leaching is one of the most rapid, effective and widely used methods for saline soil improvement. Based on the basic principle of "salt comes with water and goes with water", soil salts are fully dissolved in the leaching water and discharged from the soil body through subsurface pipes, so as to control the groundwater level and reduce soil salinity, achieving the purpose of improving salinized arable land.

[0003] However, due to the layered state of the piedmont alluvial fan soil and the existence of thin clay layers, it is not well reflected in conventional drainage practices, resulting in many drainage facilities being affected by soil characteristics and unable to play their expected roles, and there is a problem of blindness in design.

[0004] Therefore, how to provide a new treatment method, which can give different treatment measures and calculation methods according to the distribution characteristics of different thin clay layers, improve the problem of blind design in existing farmland drainage practices, and more effectively and pertinently solve the problem of saline-alkali land, is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] For this reason, the present invention provides a method for treating saline-alkali land in piedmont alluvial fans to solve the problem that the existing technology cannot achieve the expected effect due to the influence of soil characteristics on drainage facilities.

[0006] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0007] A method for treating saline-alkali land in piedmont alluvial fans, comprising the following steps:

[0008] S1: Soil sampling and investigation: The sampling range takes the fixed point as the center, refers to the subsurface pipe laying spacing in similar areas, and takes 3 times the subsurface pipe spacing D as the unilateral range along the radial direction of the mountain body, and 1.5 times the subsurface pipe spacing D as the unilateral range along the vertical direction of the mountain body, forming a sampling range of 3D * 6D in total;

[0009] S2: Soil texture analysis: Measure the particle size of the soil sample, determine the location of the weakly permeable soil layer with clay content exceeding 20%, use the point coordinates in the radial direction of the mountain as the abscissa, the depth of the weakly permeable soil layer as the ordinate, and conduct processing and analysis based on the clay content of different weakly permeable soil layers at different points; among them, when the clay content is less than 20%, set the image value to 0, and in other cases, the graphic value is 1; use the image value as the third coordinate axis to draw a surfer graph to identify the shape of the weakly permeable soil layer with clay content exceeding 20% at 1.0m - 2.0m in the radial direction of the mountain; among them, the drawn shape of the weakly permeable soil layer includes the first form, the second form, the third form, the fourth form, and the fifth form;

[0010] S3: Determination of soil permeability: Use a ring knife to take undisturbed soil for measuring the permeability coefficient. For cases where it is impossible to measure the permeability coefficient of undisturbed soil, the HYDRUS model can be used for inversion to obtain the inverted permeability coefficients of different weakly permeable soil layers;

[0011] S4: Selection of drainage and salt removal methods: Based on the shape of the weakly permeable soil layer being the first form, the spacing of the blind pipes meets the first preset condition; based on the shape of the weakly permeable soil layer being the second form, when the drainage method and the depth of controlling the groundwater level meet the second preset condition, the blind pipes are arranged at equal intervals, otherwise, the spacing of the blind pipes still meets the first preset condition; based on the shape of the weakly permeable soil layer being the third form, the spacing of the laid blind pipes gradually increases from the center point to both sides, and the spacing of the blind pipes meets the third preset condition; based on the shape of the weakly permeable soil layer being the fourth form, the spacing of the laid blind pipes gradually becomes sparser from the center point to both sides, and the spacing of the blind pipes meets the fourth preset condition; based on the shape of the weakly permeable soil layer being the fifth form, the spacing of the laid blind pipes should be laid according to the actual situation of the weakly permeable soil layer. The first blind pipe is laid at the trough position, and the spacing of the blind pipes meets the fifth preset condition.

[0012] Further, the first preset condition is:

[0013]

[0014] where a n is the spacing of the nth blind pipe, K is the average permeability coefficient of the weakly permeable soil layer, H d is the depth of controlling the groundwater level, q is the designed infiltration rate for flushing, Ф is the seepage impedance coefficient, and n is the sampling point number in the radial direction of the mountain.

[0015] Further, the third preset condition is:

[0016] Take the ground surface corresponding to the lowest point of the shape of the weakly permeable soil layer with clay content exceeding 20% as the coordinate origin;

[0017] Establish the relationship between the depth and the abscissa of this weakly permeable soil layer h(x n ) = f(xn , H1, H2);

[0018] If the spacing of the first blind pipe meeting the requirements of drainage and salt removal is a1, then the position of the second blind pipe adjacent to it should meet the following conditions:

[0019]

[0020] where H d is the depth of controlling the groundwater level, r is the radius of the corrugated pipe, H1 is the depth of the weakly permeable soil layer at the blind pipe numbered 1, and x1 is the position where the second blind pipe is located;

[0021] Calculate the spacing of the second blind pipe:

[0022] a2 = 2x1 - a1

[0023] where a2 is the spacing of the second blind pipe;

[0024] Calculate the subsequent blind pipe spacings in sequence according to the above steps until the cumulative spacing exceeds the range boundary, and satisfy the following formula:

[0025]

[0026] a n = 2x n-1 - a n-1

[0027] where a n is the spacing of the nth blind pipe, a n-1 is the spacing of the (n - 1)th blind pipe, x n-1 is the position where the nth blind pipe is located, x n is the position where the (n + 1)th blind pipe is located, and H n is the depth of the weakly permeable soil layer at the blind pipe numbered n.

[0028] Furthermore, the second preset condition is:

[0029]

[0030] where H n is the depth of the weakly permeable soil layer at the position numbered n.

[0031] Furthermore, the fourth preset condition is:

[0032] Take the highest point of the surface corresponding to the shape of the weakly permeable soil layer with a clay content exceeding 20% as the coordinate origin;

[0033] Calculate the blind pipe spacing according to the following formula until the blind pipe spacing until the cumulative spacing exceeds the range boundary:

[0034]

[0035] a n = 2x n-1 -a n-1

[0036] Among them, a n is the spacing of the nth blind pipe, a n-1 is the spacing of the (n - 1)th blind pipe, x n-1 is the position where the nth blind pipe is located, x n is the position where the (n + 1)th blind pipe is located, H n is the depth of the weak permeable soil layer at the blind pipe numbered n, H d is the depth of controlling the groundwater level, r is the radius of the corrugated pipe, h(x n ) is the parabolic equation of the depth of the weak permeable soil layer and the abscissa.

[0037] Furthermore, the fifth preset condition is:

[0038] Taking the ground surface corresponding to the trough position of the shape of the weak permeable soil layer with a clay content exceeding 20% as the coordinate origin;

[0039] Calculating the blind pipe spacing according to the following formula:

[0040]

[0041] a n = 2x n-1 -a n-1

[0042] Among them, a n is the spacing of the nth blind pipe, a n-1 is the spacing of the (n - 1)th blind pipe, x n-1 is the position where the nth blind pipe is located, x n is the position where the (n + 1)th blind pipe is located, H n is the depth of the weak permeable soil layer at the blind pipe numbered n, H d is the depth of controlling the groundwater level, r is the radius of the corrugated pipe, h(x n ) is the parabolic equation of the depth of the weak permeable soil layer and the abscissa;

[0043] The blind pipe spacing a n satisfies the following conditions:

[0044]

[0045] Among them, W is the spacing between two wave peaks in the figure.

[0046] Furthermore, the distance of sampling and point layout along the radial direction of the mountain body in step S1 from the fixed point position satisfies:

[0047]

[0048] The distances of sampling and distribution points along the radial direction of the vertical mountain body from the fixed point position satisfy:

[0049]

[0050] Wherein, n is the serial number of sampling and distribution points along the radial direction of the mountain body, m is the serial number of sampling and distribution points along the radial direction perpendicular to the mountain body, and D is the buried depth of the blind pipe.

[0051] Furthermore, the sampling depth in step S1 is 4m, and one layer is taken every 10cm.

[0052] Furthermore, the soil clay content in step S2 is the proportion of the particle size less than 0.005mm.

[0053] Furthermore, the inversion steps in step S3 are as follows: Select the main menu - flow and transport parameters - water flow - soil - hydraulic params - neural network prediction, input the measured values of sand, silt and clay contents after soil sampling in step S1, and obtain the inversion permeability coefficients of different weakly permeable soil layers.

[0054] The present invention has the following advantages:

[0055] (1) From soil investigation to design method, it systematically expounds the selection and method of treatment measures for saline - alkali land in piedmont alluvial fans, improves the problem of blind design in existing farmland drainage practices, and significantly enhances the drainage and desalination effects.

[0056] (2) Given the soil sampling method and the determination method and steps of soil permeability coefficient, a simple method for determining the permeability coefficient is proposed for special situations, which helps to guide practical operations and specific applications, and avoids the problem of excessive or insufficient sampling in meeting the requirements of design data.

[0057] (3) The method for determining the blind pipe spacing under different treatment conditions fully considers the influence of the shape of the weakly permeable soil layer with a clay content exceeding 20% on the water flow pattern, avoids waste caused by too small blind pipe spacing, and also avoids the problem of poor drainage and desalination effects caused by too large blind pipe spacing. Description of the Drawings

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary. For those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained according to the provided drawings.

[0059] The structures, proportions, sizes, etc. illustrated in this specification are only used to cooperate with the content disclosed in the specification for those who are familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have substantial technical significance. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention.

[0060] Figure 1 is the method flow chart of the present invention;

[0061] Figure 2 is the sampling coordinate map with the mountain fixed point as the center during soil sampling investigation;

[0062] Figure 3 is the curve graph with the shape of the weakly permeable soil layer being the first form;

[0063] Figure 4 is the curve graph with the shape of the weakly permeable soil layer being the second form;

[0064] Figure 5 is the curve graph with the shape of the weakly permeable soil layer being the third form;

[0065] Figure 6 is the curve graph with the shape of the weakly permeable soil layer being the fourth form;

[0066] Figure 7 is the curve graph with the shape of the weakly permeable soil layer being the fifth form. Specific embodiments

[0067] The following specific embodiments illustrate the embodiments of the present invention. Those who are familiar with this technology can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present invention.

[0068] The explanations of relevant terms in this application are as follows:

[0069] Weak pervious soil layer: A weakly water-conducting rock layer that allows groundwater to flow at an extremely low speed. In an aquifer system with multiple superimposed aquifers, the role of a weak pervious soil layer is different from that of an aquitard. The latter acts as a water barrier, while the former constitutes the water exchange channel between the upper and lower aquifers. Moreover, the greater the head pressure difference between the upper and lower aquifers, the greater the amount of water passing through the weak pervious soil layer. Since the weak pervious soil layer often has a large distribution area in large basins, the amount of leakage water passing through the weak pervious layer cannot be ignored.

[0070] A method for treating saline-alkali land in a piedmont alluvial fan, as Figure 1 shown, includes the following steps:

[0071] S1: Soil sampling survey: As Figure 2 shown, the sampling range is centered on a fixed point. Referring to the buried pipe spacing in similar areas, the unilateral range along the radial direction of the mountain is 3 times the buried pipe spacing D, and the unilateral range along the vertical direction of the mountain is 1.5 times the buried pipe spacing D, forming a sampling range of 3D * 6D in total. The sampling depth is 4m, and one layer is taken every 10cm.

[0072] The distance of the sampling points along the radial direction of the mountain from the fixed point needs to satisfy:

[0073]

[0074] The distance of the sampling points along the vertical radial direction of the mountain from the fixed point needs to satisfy:

[0075]

[0076] where n is the sampling point serial number along the radial direction of the mountain, m is the sampling point serial number along the vertical radial direction of the mountain, and D is the buried depth of the buried pipe.

[0077] S2: Soil texture analysis: Measure the particle size of the soil sample, determine the position of the weak pervious soil layer where the clay content exceeds 20%. The soil clay content is the proportion of the particle size less than 0.005mm. Taking the point coordinates in the radial direction of the mountain as the abscissa, the depth of the weak pervious soil layer as the ordinate, and based on the clay content of different weak pervious soil layers at different points for processing and analysis; among them, when the clay content is less than 20%, the image value is set to 0, and in other cases, the graphic value is 1; taking the image value as the third coordinate axis, perform surfer mapping to identify the shape of the weak pervious soil layer with a clay content exceeding 20% between 1.0m and 2.0m in the radial direction of the mountain; among them, as Figures 3 - 7 shown, the shapes of the weak pervious soil layer drawn include the first form, the second form, the third form, the fourth form, and the fifth form;

[0078] S3: Determination of soil permeability: Undisturbed soil samples are taken using a core sampler for measuring the permeability coefficient. For cases where it is impossible to determine the permeability coefficient of undisturbed soil, the HYDRUS model can be used for inversion to obtain the inverted permeability coefficients of different low-permeability soil layers.

[0079] The inversion steps are as follows: Select the main menu - flow and transport parameters - water flow - soil-hydraulic params - neural network prediction, and input the measured values of sand, silt, and clay contents after soil sampling in step S1 to obtain the inverted permeability coefficients of different low-permeability soil layers.

[0080] S4: Selection of drainage and salt removal methods: Based on the shape of the low-permeability soil layer being the first form, the spacing of the buried pipes meets the first preset condition; based on the shape of the low-permeability soil layer being the second form, when the drainage method and the depth of controlling the groundwater level meet the second preset condition, the buried pipes are arranged at equal intervals, otherwise, the spacing of the buried pipes still meets the first preset condition; based on the shape of the low-permeability soil layer being the third form, the spacing of the buried pipes laid is gradually increased from the center point to both sides, and the spacing of the buried pipes meets the third preset condition; based on the shape of the low-permeability soil layer being the fourth form, the spacing of the buried pipes laid is gradually decreased from the center point to both sides, and the spacing of the buried pipes meets the fourth preset condition; based on the shape of the low-permeability soil layer being the fifth form, the spacing of the buried pipes laid should be arranged according to the actual situation of the low-permeability soil layer. The first buried pipe is laid at the trough position, and the spacing of the buried pipes meets the fifth preset condition.

[0081] Example 1

[0082] When the shape of the low-permeability soil layer conforms to the form as shown in Figure 3 The spacing of the buried pipes meets the following first preset condition:

[0083]

[0084] where a n is the spacing of the nth buried pipe, K is the average permeability coefficient of the low-permeability soil layer, H d is the depth of controlling the groundwater level, q is the designed infiltration rate for flushing, Ф is the seepage impedance coefficient, and n is the sampling point number along the radial direction of the mountain.

[0085] Lay the buried pipes according to the calculated different spacings of the buried pipes.

[0086] Example 2

[0087] When the shape of the low-permeability soil layer conforms to the form as shown in Figure 4 The spacing of the buried pipes meets the following second preset condition:

[0088]

[0089] Among them, H n is the depth of the low-permeability soil layer with serial number n.

[0090] From Figure 4 it can be known that the depth H of the low-permeability soil layer with serial number n n is the same as the depth of the low-permeability soil layer. Substitute the depth of the low-permeability soil layer of H1 into the above second preset condition. If the second preset condition is satisfied, the blind pipes are arranged at equal intervals. Otherwise, the blind pipe spacing is still laid according to the first preset condition.

[0091] Embodiment 3

[0092] When the shape of the low-permeability soil layer conforms to the form as Figure 5 shown, the blind pipe spacing satisfies the following third preset condition:

[0093] Take the ground surface corresponding to the lowest point of the low-permeability soil layer with a clay content exceeding 20% as the coordinate origin;

[0094] Establish the relationship between the depth of the low-permeability soil layer and the abscissa h(x n ) = f(x n , H1, H2); h(x n ) is a parabola equation with an upward opening.

[0095] If the spacing of the first blind pipe that meets the drainage and salt removal requirements is a1, the position of the second blind pipe adjacent to it should meet the following conditions:

[0096]

[0097] Among them, H d is the depth of controlling the groundwater level, r is the radius of the corrugated pipe, H1 is the depth of the low-permeability soil layer at the position of the first blind pipe, and x1 is the position where the second blind pipe is located;

[0098] Calculate the spacing of the second blind pipe:

[0099] a2 = 2x1 - a1

[0100] Among them, a2 is the spacing of the second blind pipe;

[0101] Calculate the subsequent blind pipe spacings in turn according to the above steps until the cumulative spacing exceeds the range boundary, and the following formula should be satisfied:

[0102]

[0103] a n = 2x n-1 - a n-1

[0104] Among them, a n is the spacing of the nth blind pipe, a n-1 is the spacing of the (n - 1)th blind pipe, x n-1 is the position where the nth blind pipe is located, x n is the position where the (n + 1)th blind pipe is located, H n is the depth of the weak pervious soil layer at the blind pipe numbered n.

[0105] Example 4

[0106] When the shape of the weak pervious soil layer conforms to the form as shown in Figure 6 , the blind pipe spacing satisfies the following fourth preset condition:

[0107] Taking the ground surface corresponding to the highest point of the weak pervious soil layer with a clay content exceeding 20% as the coordinate origin;

[0108] Calculate the blind pipe spacing according to the following formula until the cumulative spacing exceeds the range boundary:

[0109]

[0110] a n = 2x n-1 - a n-1

[0111] Among them, a n is the spacing of the nth blind pipe, a n-1 is the spacing of the (n - 1)th blind pipe, x n-1 is the position where the nth blind pipe is located, x n is the position where the (n + 1)th blind pipe is located, H n is the depth of the weak pervious soil layer at the blind pipe numbered n, H d is the depth to control the groundwater level, r is the radius of the corrugated pipe, h(x n ) is the parabolic equation of the depth of the weak pervious soil layer and the abscissa, h(x n ) is a downward-opening parabolic equation.

[0112] Example 5

[0113] When the shape of the weak pervious soil layer conforms to the form as shown in Figure 7 , the blind pipe spacing satisfies the following fifth preset condition:

[0114] Taking the ground surface corresponding to the trough position of the weak pervious soil layer with a clay content exceeding 20% as the coordinate origin;

[0115] Calculate the blind pipe spacing according to the following formula:

[0116]

[0117] a n= 2x n-1 -a n-1

[0118] where a n is the spacing of the nth blind pipe, a n-1 is the spacing of the (n - 1)th blind pipe, x n-1 is the position where the nth blind pipe is located, x n is the position where the (n + 1)th blind pipe is located, H n is the depth of the weak pervious soil layer at the blind pipe numbered n, H d is the depth for controlling the groundwater level, r is the radius of the corrugated pipe, h(x n ) is the parabolic equation of the depth of the weak pervious soil layer and the abscissa, h(x n ) is a parabola that runs crosswise upward and downward with an opening.

[0119] The blind pipe spacing a n satisfies the following conditions:

[0120]

[0121] where W is the spacing between two wave peaks in the figure.

[0122] The specific usage of the present invention is illustrated by the following example:

[0123] Assume that the shape of the weak pervious soil layer with a clay content exceeding 20% conforms to the third form, and the shape conforms to a parabolic shape, H1 = 1.8 m, H2 = 1 m, the abscissa of the position where H2 is located is 100 m, the radius of the blind pipe is 0.05 m, and the drainage spacing of the first blind pipe that meets the drainage and salt removal requirements at a calculated burial depth of 1.8 m is 40 m, and the depth for controlling the groundwater level is taken as 0.8 m.

[0124] The parabolic equation is

[0125] For the position where the second blind pipe is located, the following conditions should be met

[0126] By trial calculation, x1 = 37.5 m can be obtained, then the spacing of the second blind pipe is a2 = 2x1 - a1 = 2 * 37.5 - 40 = 35 m;

[0127] Similarly, according to the proposed formula, x2 = 31.3 m can be calculated, then the spacing of the third blind pipe is a3 = 2x2 - a2 = 2 * 31.3 - 35 = 27.6 m. At this time, the cumulative spacing is 102.6 m, which is greater than the abscissa of the position where H2 is located, which is 100 m, and the calculation ends.

[0128] The present invention systematically expounds the selection and methods of treatment measures for saline-alkali land in piedmont alluvial fans from soil investigation to design methods, improves the problem of blind design in existing farmland drainage practices, and significantly enhances the drainage and salt removal effects; given the soil sampling method and the determination method and steps of soil permeability coefficient, a simple method for determining the permeability coefficient is proposed for special cases, which helps to guide practical operations and specific applications, and avoids the problem of excessive or insufficient sampling in meeting the requirements of design data; the determination method of buried pipe spacing under different treatment conditions fully considers the influence of the shape of the weak permeable soil layer with clay content exceeding 20% on the water flow pattern, avoids waste caused by too small buried pipe spacing, and also avoids the problem of poor drainage and salt removal effects caused by too large buried pipe spacing.

[0129] Although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A method for treating saline-alkali land in a piedmont alluvial fan, characterized in that, It includes the following steps: S1: Soil sampling survey: The sampling range is centered on the fixed point. Referring to the spacing of the buried pipes in similar areas, the unilateral range along the radial direction of the mountain is 3 times the buried pipe spacing D, and the unilateral range along the vertical direction of the mountain is 1.5 times the buried pipe spacing D, thus forming a sampling range of 3D * 6D; S2: Soil texture analysis: Measure the particle size of the soil sample, determine the position of the weakly permeable soil layer where the clay content exceeds 20%. Taking the point coordinates in the radial direction of the mountain as the abscissa, the depth of the weakly permeable soil layer as the ordinate, and processing and analyzing based on the clay content of different points in different weakly permeable soil layers; among them, when the clay content is less than 20%, the image value is set to 0, and in other cases the graphic value is 1; taking the image value as the third coordinate axis, perform surfer mapping to identify the shape of the weakly permeable soil layer with a clay content exceeding 20% at 1.0 m - 2.0 m in the radial direction of the mountain; among them, the shapes of the drawn weakly permeable soil layers include the first form, the second form, the third form, the fourth form, and the fifth form; S3: Determination of soil permeability: Use a ring knife to take undisturbed soil for measuring the permeability coefficient. For cases where the permeability coefficient of the undisturbed soil cannot be determined, it can be inversed through the HYDRUS model to obtain the permeability coefficients of different inversed weakly permeable soil layers; S4: Selection of drainage and salt - removal methods: Based on the fact that the shape of the weakly permeable soil layer is the first form, the buried pipe spacing meets the first preset condition; based on the fact that the shape of the weakly permeable soil layer is the second form, when the drainage method and the depth of controlling the groundwater level meet the second preset condition, the buried pipes are arranged at equal intervals, otherwise, the buried pipe spacing still meets the first preset condition; based on the fact that the shape of the weakly permeable soil layer is the third form, the buried pipe spacing gradually increases from the center point to both sides, and the buried pipe spacing meets the third preset condition; based on the fact that the shape of the weakly permeable soil layer is the fourth form, the buried pipe spacing gradually becomes sparser from the center point to both sides, and the buried pipe spacing meets the fourth preset condition; based on the fact that the shape of the weakly permeable soil layer is the fifth form, the buried pipe spacing should be laid according to the actual situation of the weakly permeable soil layer. The first buried pipe is laid at the trough position, and the buried pipe spacing meets the fifth preset condition; The first preset condition is: Among them, a n is the spacing of the nth blind pipe, K is the average permeability coefficient of the weak pervious soil layer, H d is the depth for controlling the groundwater level, q is the designed permeability rate of flushing, Ф is the seepage impedance coefficient, and n is the sampling point number along the radial direction of the mountain body; The second preset condition is: Among them, H n is the depth of the weak pervious soil layer at the position with the serial number n; The third preset condition is: Taking the ground surface corresponding to the lowest point of the shape of the weakly permeable soil layer with a clay content exceeding 20% as the coordinate origin; Establish the relationship between the depth of the weak water-permeable soil layer and the abscissa h(x n ) = f(x n , H1, H2); If the spacing of the first buried pipe that meets the drainage and salt - removal requirements is a1, then the position of the second buried pipe adjacent to it should meet the following conditions: Among them, H d is the depth of the groundwater level control, r is the radius of the corrugated pipe, H1 is the depth of the weak pervious soil layer at the blind pipe numbered 1, and x1 is the position of the second blind pipe; Calculate the spacing of the second buried pipe: a2 = 2x1 - a1 where a2 is the spacing of the second buried pipe; Calculate the subsequent buried pipe spacings in sequence according to the above steps until the cumulative spacing exceeds the range boundary, and meet the following formula: a n = 2x n-1 -a n-1 Among them, a n is the spacing of the nth blind pipe, a n-1 is the spacing of the (n - 1)th blind pipe, x n-1 is the position where the nth blind pipe is located, x n is the position where the (n + 1)th blind pipe is located, H n is the depth of the weak permeable soil layer at the blind pipe with serial number n; The fourth preset condition is: Taking the ground surface corresponding to the highest point of the shape of the weakly permeable soil layer with a clay content exceeding 20% as the coordinate origin; Calculate the buried pipe spacing according to the following formula until the buried pipe spacing until the cumulative spacing exceeds the range boundary: a n = 2x n-1 -a n-1 Among them, a n is the spacing of the nth blind pipe, a n-1 is the spacing of the (n - 1)th blind pipe, x n-1 is the position where the nth blind pipe is located, x n is the position where the (n + 1)th blind pipe is located, H n is the depth of the weak pervious soil layer at the blind pipe with serial number n, H d is the depth of controlling the groundwater level, r is the radius of the corrugated pipe, h(x n ) is the parabolic equation of the depth of the weak pervious soil layer and the abscissa; The fifth preset condition is: Taking the ground surface corresponding to the trough position of the shape of the weakly permeable soil layer with a clay content exceeding 20% as the coordinate origin; Calculate the buried pipe spacing according to the following formula: a n = 2x n-1 -a n-1 Among them, a n is the spacing of the nth blind pipe, a n-1 is the spacing of the (n - 1)th blind pipe, x n-1 is the position where the nth blind pipe is located, x n is the position where the (n + 1)th blind pipe is located, H n is the depth of the weak pervious soil layer at the blind pipe with serial number n, H d is the depth for controlling the groundwater level, r is the radius of the corrugated pipe, h(x n ) is the parabolic equation of the depth of the weak pervious soil layer and the abscissa; The distance a between concealed pipes n Satisfies the following conditions: where W is the spacing between two wave peaks in the figure.

2. The method for treating saline-alkali land in piedmont alluvial fans according to claim 1, wherein, In the step S1, the distance of sampling and point layout along the radial direction of the mountain body from the fixed point position satisfies: The distance of sampling and point layout along the vertical radial direction of the mountain body from the fixed point position satisfies: where n is the sampling and point layout serial number along the radial direction of the mountain body, m is the sampling and point layout serial number along the vertical radial direction of the mountain body, and D is the buried depth of the blind pipe.

3. The method for treating saline-alkali land in piedmont alluvial fans according to claim 1, wherein The sampling depth in the step S1 is 4 m, and one layer is taken every 10 cm.

4. The method for treating saline-alkali land in piedmont alluvial fans according to claim 1, wherein The soil clay content in the step S2 is the proportion of the particle size less than 0.005 mm.

5. The method for treating saline-sodic land in piedmont alluvial fans as claimed in claim 1, wherein, The inversion steps in the step S3 are as follows: Select the main menu - flow and transport parameters - water flow - soil-hydraulic params - neural network prediction, input the measured values of sand, silt and clay contents after soil sampling in the step S1, and obtain the inversion permeability coefficients of different weakly permeable soil layers.

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