Seepage types and seepage damage judgment methods of dual-structure embankment foundation

Abstract

The present invention discloses a method for determining the permeability type and permeability damage of a binary structure embankment foundation. The method includes the following steps: determining that the embankment foundation is composed of a silt-fine sand layer located at the surface and a gravel layer located at the bottom; assuming that the silt-fine sand layer has a critical thickness, when the actual thickness of the silt-fine sand layer is less than the critical thickness, calculating the first critical water level H1 of the embankment foundation; when the actual thickness of the silt-fine sand layer is greater than the critical thickness, calculating the second critical water level H2 of the embankment foundation; comparing the sizes of H1 and H2 to determine whether the key permeability control layer is a gravel layer or a silt-fine sand layer; when the key permeability control layer is a gravel layer or a silt-fine sand layer, a method for determining permeability damage of the embankment foundation is proposed. The present invention can quickly determine whether the key layer for permeability deformation development is a silt-fine sand layer or a gravel layer, and at the same time, proposes a method for determining permeability damage of the embankment foundation for different permeability deformation key layers, providing technical support for flood season permeability damage rescue and post-flood permeability damage control.

Description

Technical Field

[0001] The present invention relates to the technical field of dike seepage, and in particular to a method for judging the seepage type and seepage damage of a binary structure dike foundation. Background Art

[0002] In levee projects, when the levee body is composed of relatively impermeable soil and the foundation is sandy, it is prone to seepage failure during flood season. If the levee foundation is a single silt-fine sand structure, the seepage failure process can be summarized as the silt-fine sand horizontally contacting along the levee bottom surface, with the scouring damage continuously progressing toward the levee foot and the outer river, eventually forming a seepage channel connecting upstream and downstream, leading to levee failure. If the levee foundation is a single sand-gravel structure, the seepage failure process can be summarized as the sand-gravel horizontally piping along the levee bottom surface, with the piping damage continuously progressing toward the levee foot and the outer river, eventually forming a seepage channel connecting upstream and downstream, leading to levee failure.

[0003] A consensus has been reached on the seepage failure mechanism and failure type of the above two types of structural embankments, which is convenient for guiding engineering and technical personnel in seepage control design.

[0004] However, in the existing technology, for a binary structure embankment foundation composed of a surface layer of fine sand and a lower layer of gravel, the question of whether the seepage deformation occurs in the fine sand layer or the gravel layer, and whether the key layer for controlling the development of seepage deformation is the fine sand layer or the gravel layer, has not yet been effectively solved. As a result, the seepage control measures taken by engineering technicians for the binary structure embankment foundation composed of fine sand and gravel are not very targeted, resulting in hidden dangers to the seepage safety of the embankment foundation. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention proposes a method for judging the seepage type and seepage damage of a binary structure embankment foundation, which can quickly determine whether the seepage deformation occurs in the fine sand layer or the gravel layer, and determine whether the key layer for the development of seepage deformation is the fine sand layer or the gravel layer. It also provides a method for judging the seepage damage of the embankment foundation, providing technical support for emergency rescue of seepage damage during flood season and post-flood seepage damage control.

[0006] To achieve the above-mentioned purpose, the present invention provides a method for determining the type of seepage and seepage damage of a binary structure embankment foundation, which is particularly characterized by comprising the following steps:

[0007] S1) Determine that the embankment foundation is composed of a surface layer of fine sand and a lower layer of sand and gravel;

[0008] S2) Assuming that the silt sand layer has a critical thickness, when the actual thickness of the silt sand layer is less than the critical thickness, the silt sand layer undergoes horizontal vertical flow deformation, and the gravel surface layer undergoes horizontal piping deformation. The first critical water level of the embankment foundation is calculated. When the actual thickness of the silt sand layer is greater than the critical thickness, the silt sand layer undergoes shallow horizontal vertical flow deformation, and the gravel surface layer does not undergo seepage deformation. The second critical water level of the embankment foundation is calculated.

[0009] The first critical water level of the embankment foundation is expressed by the following formula

[0010]

[0011] Where,

[0012] H1 represents the critical water level of the first embankment foundation,

[0013] G s represents the density of the gravel layer relative to water,

[0014] n1 represents the porosity of the gravel layer,

[0015] d5 represents the particle size value corresponding to the cumulative distribution percentage of sand and gravel reaching 5%.

[0016] d 20 It indicates the particle size value corresponding to the cumulative distribution percentage of sand and gravel reaching 20%.

[0017] L represents the shortest distance between the water inlet and the center of the infiltration outlet;

[0018] The second critical water level of the embankment foundation is expressed by the following formula

[0019]

[0020] Where,

[0021] H2 represents the critical water level of the second embankment foundation,

[0022] γ'1 is the floating density of the gravel layer,

[0023] n1 represents the porosity of the gravel layer,

[0024] h1 represents the actual thickness of the gravel layer,

[0025] γ w Indicates the weight of water.

[0026] γ'2 represents the floating density of the fine sand layer,

[0027] n2 represents the porosity of the fine sand layer,

[0028] h2 represents the actual thickness of the silt-fine sand layer;

[0029] S3) Compare the sizes of H1 and H2. If H2>H1, the fine sand layer will experience horizontal vertical flow deformation, and the surface of the gravel layer will experience horizontal pipe deformation. The key layer for permeability control is the gravel layer. If H2>H1, the fine sand layer will experience horizontal vertical flow deformation, and the surface of the gravel layer will experience horizontal pipe deformation.

[0030] S4) When the seepage deformation develops to the point where the upstream and downstream seepage channels are connected, the embankment foundation will be damaged by seepage. For H2>H1, when the sum of the allowable loss head of each section of the vertical channel and the horizontal channel ∑Δh1 is greater than the total head H, the embankment foundation will not be damaged by seepage. Otherwise, seepage damage will occur, that is,

[0031] ∑Δh1=J x L+J z h2>H

[0032] Where:

[0033] ∑Δh1 is the sum of the allowable loss heads of the vertical channel and the horizontal channel,

[0034] H is the water level difference between upstream and downstream of the embankment,

[0035] J x The horizontal allowable hydraulic gradient of the gravel layer is

[0036] L is the width of the embankment bottom,

[0037] J z Allowable hydraulic gradient for vertical flow of fine sand layer;

[0038] h2 is the actual thickness of the silt-fine sand layer;

[0039] For H2

[0040] ∑Δh2=J z h2>H

[0041] Where,

[0042] ∑Δh2 is the sum of the allowable loss heads in the vertical channel,

[0043] H is the water level difference between upstream and downstream of the embankment,

[0044] J z The allowable hydraulic gradient for vertical flow of fine sand layer is:

[0045] h2 is the actual thickness of the silt sand layer. ​​

[0046] Furthermore, in S1), an impermeable embankment is provided on the upper portion of the embankment foundation, and the permeability coefficient of the fine sand layer in the embankment foundation is smaller than the permeability coefficient of the gravel layer.

[0047] Furthermore, in S2), the particle size of the fine sand in the fine sand layer ranges from 0.1 to 2 mm, and the particle size of the gravel in the gravel layer ranges from 0.5 to 10 mm.

[0048] Furthermore, in S2), when piping occurs, the maximum value of the shortest distance L between the water inlet and the center of the infiltration outlet is the width of the embankment bottom.

[0049] Furthermore, in S3), when the key permeability control layer is a gravel layer, as long as the horizontal piping deformation of the gravel layer does not further develop to the outer river, the embankment foundation will not suffer permeability damage; when the key permeability control layer is a silt-fine sand layer, as long as the horizontal flow soil deformation of the silt-fine sand surface layer does not further develop to the outer river, the embankment foundation will not suffer permeability damage.

[0050] Furthermore, in S3), when the key layer for permeability control is a gravel layer, the anti-permeability measures need to penetrate deep into the gravel layer to inhibit the further development of horizontal deformation of the gravel layer toward piping; when the key layer for permeability control is a silt-fine sand layer, the anti-permeability measures need to penetrate deep into the surface layer of the silt-fine sand to inhibit the further development of horizontal deformation of the silt-fine sand layer toward soil flow.

[0051] Furthermore, in S3), when the key layer for permeability control is a gravel layer, the anti-seepage measure is to set a vertical anti-seepage wall inside the gravel layer; when the key layer for permeability control is a silt-fine sand layer, the anti-seepage measure is to set a vertical anti-seepage wall on the surface of the silt-fine sand.

[0052] The advantages of the present invention are:

[0053] 1. When the embankment foundation is a binary structure consisting of a surface silt-fine sand layer and a lower gravel layer, the present invention uses factors such as the respective permeability coefficients of the silt-fine sand and gravel, and soil layer thickness, to simply and clearly determine whether the embankment foundation seepage deformation occurs in the silt-fine sand layer or the gravel layer, and whether the key layer controlling the development of seepage deformation is the silt-fine sand layer or the gravel layer. This facilitates engineering technicians to take seepage control measures for the binary structure embankment foundation consisting of silt-fine sand and gravel, ensuring that the seepage control measures are targeted, reliable, and safe.

[0054] 2. The present invention proposes a method for determining seepage damage to embankment foundations when the key seepage control layer is a gravel layer or a silt-fine sand layer. This method can provide technical support for emergency rescue during flood season and post-flood seepage damage management of embankment foundations composed of a dual structure of silt-fine sand and gravel, and has important theoretical and engineering practical significance.

[0055] The method for judging the seepage type and seepage damage of the binary structure embankment foundation of the present invention can quickly judge whether the seepage deformation occurs in the fine sand layer or the gravel layer, and determine whether the key layer for the development of seepage deformation is the fine sand layer or the gravel layer. At the same time, a method for judging the seepage damage of the embankment foundation is proposed for different key layers of seepage deformation, which can provide technical support for emergency rescue of seepage damage during flood season and control of seepage damage after flood season. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a cross-sectional view of the dual-structure embankment foundation along the upstream and downstream directions of the present invention;

[0057] Figure 2 Flowchart of the present invention. DETAILED DESCRIPTION

[0058] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0059] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention.

[0060] like Figure 2 As shown, the method for judging the seepage type and seepage damage of the binary structure embankment foundation of the present invention includes the following steps:

[0061] S1) Determine that the embankment foundation is composed of a surface silt-fine sand layer and a lower gravel layer. Specifically, an impermeable embankment is provided on the upper portion of the embankment foundation, and the permeability coefficient of the silt-fine sand layer in the embankment foundation is smaller than the permeability coefficient of the gravel layer.

[0062] like Figure 1 As shown in the figure, since the permeability coefficient of silt and fine sand is smaller than that of gravel, the confined water head in the gravel layer is very large. When the thickness of the silt and fine sand layer is relatively thin, the silt and fine sand layer is penetrated due to the large confined water pressure in the lower gravel layer, and vertical soil flow occurs. At this time, the hydraulic gradient along the surface of the gravel is the largest, and the surface of the gravel layer is the preferred development direction of seepage deformation. Horizontal piping occurs in the gravel, and the embankment foundation failure mainly advances to the outside of the embankment in the form of horizontal soil flow of silt and fine sand.

[0063] When the thickness of the silt sand layer is large, although the pressure head in the gravel layer is large, the silt sand layer is not easily penetrated by the pressure water due to its thickness, and the silt sand layer will not undergo vertical soil flow damage. At this time, the silt sand layer mainly undergoes vertical soil flow deformation in the horizontal direction under the embankment, and the gravel layer does not undergo seepage deformation.

[0064] Therefore, based on the above analysis, for the binary structure embankment foundation of silt-fine sand + gravel, the thickness of the silt-fine sand layer determines the occurrence mechanism and type of seepage failure of the embankment foundation.

[0065] S2) Assuming that the silt sand layer has a critical thickness, when the actual thickness of the silt sand layer is less than the critical thickness, the silt sand layer undergoes horizontally evolving vertical flow deformation, and the gravel surface layer undergoes horizontal piping deformation. The first critical water level of the embankment foundation is calculated. When the actual thickness of the silt sand layer is greater than the critical thickness, the silt sand layer undergoes shallow horizontal vertical flow deformation, and the gravel surface layer does not undergo seepage deformation. The second critical water level of the embankment foundation is calculated.

[0066] The first critical water level of the embankment foundation is expressed by the following formula

[0067]

[0068] Where,

[0069] H1 represents the critical water level of the first embankment foundation,

[0070] G s represents the density of the gravel layer relative to water,

[0071] n1 represents the porosity of the gravel layer,

[0072] d5 represents the particle size value corresponding to the cumulative distribution percentage of sand and gravel reaching 5%.

[0073] d 20 It indicates the particle size value corresponding to the cumulative distribution percentage of sand and gravel reaching 20%.

[0074] L represents the shortest distance between the water inlet and the center of the infiltration outlet.

[0075] The second critical water level of the embankment foundation is expressed by the following formula

[0076]

[0077] Where,

[0078] H2 represents the critical water level of the second embankment foundation,

[0079] γ'1 is the floating density of the gravel layer,

[0080] n1 represents the porosity of the gravel layer,

[0081] h1 represents the actual thickness of the gravel layer,

[0082] γ w Indicates the weight of water.

[0083] γ'2 represents the floating density of the fine sand layer,

[0084] n2 represents the porosity of the fine sand layer,

[0085] h2 represents the actual thickness of the silt-fine sand layer.

[0086] Specifically, the particle size of the fine sand in the fine sand layer ranges from 0.1 to 2 mm, and the particle size of the gravel in the gravel layer ranges from 0.5 to 10 mm.

[0087] Specifically, when piping occurs, the maximum value of the shortest distance L between the water inlet and the center of the seepage outlet is the width of the embankment bottom. The shortest distance L between the water inlet and the center of the seepage outlet is obtained by measurement.

[0088] S3) Compare the sizes of H1 and H2. If H2>H1, the fine sand layer will experience horizontal vertical flow deformation, and the surface of the gravel layer will experience horizontal pipe deformation. The key layer for permeability control is the gravel layer. If H2>H1, the fine sand layer will experience horizontal vertical flow deformation, and the surface of the gravel layer will experience horizontal pipe deformation.

[0089] Based on the above S2) to S3), the type of seepage deformation and the key layer of seepage control of the binary structure embankment foundation can be quickly and easily determined. However, the occurrence of seepage deformation of the embankment foundation does not mean that the embankment foundation has been damaged by seepage. Only when the seepage deformation develops to the point where the upstream and downstream seepage channels are connected, will the embankment foundation be damaged by seepage.

[0090] Therefore, when the key layer for permeability control is the gravel layer, as long as the horizontal piping deformation of the gravel layer does not further develop to the outer river, the embankment foundation will not suffer from permeability damage; when the key layer for permeability control is the silt-fine sand layer, as long as the horizontal flow soil deformation of the silt-fine sand surface layer does not further develop to the outer river, the embankment foundation will not suffer from permeability damage.

[0091] ​When the embankment foundation is a binary structure consisting of an upper silt-fine sand layer and a lower gravel layer, the present invention simply and clearly determines whether embankment foundation seepage deformation occurs in the silt-fine sand layer or the gravel layer based on factors such as the respective permeability coefficients of the silt-fine sand and gravel layers and soil layer thickness. Furthermore, a method for determining embankment foundation seepage damage is proposed when the key permeability control layer is a gravel layer or a silt-fine sand layer. This facilitates engineering and technical personnel to implement seepage control measures for embankment foundations with a binary structure of silt-fine sand and gravel, ensuring targeted, reliable, and safe seepage control measures. This provides technical support for flood season rescue and post-flood seepage damage management of binary embankment foundations composed of silt-fine sand and gravel, and has important theoretical and practical significance.

[0092] The present invention will be further described below with reference to specific embodiments.

[0093] Example 1: Take the results of Experiment 3 provided in the literature (Wang Shuang, Chen Jiansheng, Zhou Peng. Experimental study on the effect of fine sand layer thickness on piping in three-layer embankment foundation [J]. Rock and Soil Mechanics, 2015, 36(10): 2847-2854.) as an example. The gravel thickness is 22 cm, n2 = 0.21, G s2 =2.65,ρ d2 =2.10g / cm 3 ; Colored sand thickness 2cm, n1=0.4, G s1 =2.62,ρ d1 =1.58g / cm 3 According to the original text L = 60cm, the formula for the first critical water level of the embankment foundation is used to calculate H1 = 49.0cm, which is consistent with the fact that the infiltration channel has been connected when the upstream water level is 46.5cm. According to the formula for the second critical water level of the embankment foundation, H2 = 23.9cm is obtained.

[0094] This conclusion is consistent with the description of Experiment 3 in the literature: "The channel is mainly formed in the surface layer of the colored sand layer, that is, shallow piping damage, and the damage form is mainly horizontal soil flow damage."

[0095] Example 2: Take the experimental results provided in the literature (Mao Haitao, Wang Zhengcheng, Wang Xiaoju, et al. Experimental study on pipe burst failure of overlying sand layer of embankment foundation containing shallow strong permeable layer [J]. Civil Engineering and Environmental Engineering, 2018, 40 (3): 73-80.) as an example. The thickness of gravel and pebbles is 15 cm, n1 = 0.42, G s1 =2.65, d5=0.48mm, d 20 =2.8mm,ρ d1 =1.98g / cm 3 , k1=5.18×10 -1 cm / s; sandy soil thickness 8-20 cm, n2=0.33, G s2 ​=2.65,ρ d2 =2.42g / cm 3 , k2=5.07×10 -3 cm / s. Based on the original text, L = 75 cm, and using the formula for the first critical water level of the embankment foundation, H1 = 15.7 cm. Using the formula for the second critical water level of the embankment foundation, H2 = 18.8 cm. Since H2 > H1, vertical soil flow occurs in the sand layer, while horizontal piping failure occurs in the surface layer of the gravel layer.

[0096] This conclusion is consistent with the conclusion of the literature experiment that "the thin overlying sand layer is easily "broken through", and only coarse particles remain in the sand near the surface of the sand and gravel layer, and the sand skeleton particles are connected with the sand and gravel layer to form a preferential seepage channel."

[0097] Specifically, when the key permeability control layer is a gravel layer, the anti-permeability measures need to penetrate deep into the gravel layer to inhibit the further development of horizontal deformation of the gravel layer toward piping; when the key permeability control layer is a silt-fine sand layer, the anti-permeability measures need to penetrate deep into the surface layer of the silt-fine sand to inhibit the further development of horizontal deformation of the silt-fine sand layer toward soil flow.

[0098] Preferably, when the key layer for permeability control is a gravel layer, the anti-permeability measure is to set a vertical anti-permeability wall inside the gravel layer; when the key layer for permeability control is a fine sand layer, the anti-permeability measure is to set a vertical anti-permeability wall on the surface of the fine sand.

[0099] S4) When the seepage deformation develops to the point where the upstream and downstream seepage channels are connected, the embankment foundation will be damaged by seepage. For H2>H1, when the sum of the allowable loss head of each section of the vertical channel and the horizontal channel ∑Δh1 is greater than the total head H, the embankment foundation will not be damaged by seepage. Otherwise, seepage damage will occur, that is,

[0100] ∑Δh1=J x L+J z h2>H

[0101] Where:

[0102] ∑Δh1 is the sum of the allowable loss heads of the vertical channel and the horizontal channel,

[0103] H is the water level difference between upstream and downstream of the embankment,

[0104] J x is the horizontal allowable hydraulic gradient of the gravel layer, which can be 0.1.

[0105] L is the width of the embankment bottom,

[0106] J z The hydraulic gradient allowed for vertical flow of fine sand layer can be 0.5.

[0107] h2 is the actual thickness of the silt-fine sand layer;

[0108] For H2

[0109] ∑Δh2=J z h2>H

[0110] Where,

[0111] ∑Δh2 is the sum of the allowable loss heads in the vertical channel,

[0112] H is the water level difference between upstream and downstream of the embankment,

[0113] J z The hydraulic gradient allowed for vertical flow of fine sand layer can be 0.5.

[0114] h2 is the actual thickness of the silt sand layer.

[0115] The method for judging the seepage type and seepage damage of the binary structure embankment foundation of the present invention can quickly judge whether the seepage deformation occurs in the fine sand layer or the gravel layer, and determine whether the key layer for the development of seepage deformation is the fine sand layer or the gravel layer. At the same time, a method for judging the seepage damage of the embankment foundation is proposed for different key layers of seepage deformation, which can provide technical support for emergency rescue of seepage damage during flood season and control of seepage damage after flood season.

[0116] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.​

Claims

1. A method for determining the type of seepage and seepage damage of a binary structure embankment foundation, characterized in that: It includes the following steps: S1) Determine that the embankment foundation consists of a fine sand layer on the surface and a gravel layer on the lower layer; S2) Assume that there is a critical thickness for the fine sand layer. When the actual thickness of the fine sand layer is less than the critical thickness, vertical flow soil deformation with horizontal evolution occurs in the fine sand layer, and at the same time, piping deformation in the horizontal direction occurs on the surface of the gravel layer, and the first critical water level of the embankment foundation is obtained; when the actual thickness of the fine sand layer is greater than the critical thickness, shallow vertical flow soil deformation with horizontal evolution occurs in the fine sand layer, and at the same time, no seepage deformation occurs on the surface of the gravel layer, and the second critical water level of the embankment foundation is obtained; The first critical water level of the embankment foundation is expressed by the following formula In the formula, H1 represents the first critical water level of the embankment foundation, G s represents the density of the gravel layer relative to water, n1 represents the porosity of the gravel layer, d5 represents the particle size value corresponding to the cumulative distribution percentage of 5% in the gravel, d 20 It indicates the particle size value corresponding to the cumulative distribution percentage of sand and gravel reaching 20%. L represents the shortest distance between the water inlet and the center of the seepage outlet; The second critical water level of the embankment foundation is expressed by the following formula In the formula, H2 represents the second critical water level of the embankment foundation, γ'1 is the buoyant unit weight of the gravel layer, n1 represents the porosity of the gravel layer, h1 represents the actual thickness of the gravel layer, γ w Indicates the weight of water. γ'2 represents the buoyant unit weight of the fine sand layer, n2 represents the porosity of the fine sand layer, h2 represents the actual thickness of the fine sand layer; S3) Compare the magnitudes of H1 and H2. If H2 > H1, then vertical flow soil deformation with horizontal evolution occurs in the fine sand layer, and piping deformation in the horizontal direction occurs on the surface of the gravel layer, and the key layer for seepage control is the gravel layer; if H2 < H1, then vertical flow soil deformation with horizontal evolution occurs on the surface of the fine sand layer, and no seepage deformation occurs in the gravel layer, and the key layer for seepage control is the fine sand layer; if H2 = H! then h2 is the critical thickness of the fine sand layer; S4) When the seepage deformation develops to the point where the upstream and downstream seepage channels are connected, seepage failure of the embankment foundation will occur. For H2 > H1, when the sum of the allowable head losses ∑Δh1 of each section of the vertical channel and the horizontal channel is greater than the total head H, the embankment foundation will not undergo seepage failure, otherwise, seepage failure will occur, that is ∑Δh1=J x L+J z h2>H In the formula: ∑Δh1 is the sum of the allowable head losses of the vertical channel and the horizontal channel, H is the water level difference between the upstream and downstream of the embankment, J x The horizontal allowable hydraulic gradient of the gravel layer is L is the width of the embankment bottom, J z Allowable hydraulic gradient for vertical flow of fine sand layer; h2 is the actual thickness of the fine sand layer; For H2 < H1, when the sum of the allowable head losses ∑Δh2 of the vertical channel is greater than the total head, the embankment foundation will not undergo seepage failure, otherwise, seepage failure will occur, that is ∑Δh2=J z h2>H In the formula, ∑Δh2 is the sum of the allowable head losses of the vertical channel, H is the water level difference between the upstream and downstream of the embankment, J z The allowable hydraulic gradient for vertical flow of fine sand layer is: h2 is the actual thickness of the fine sand layer.

2. The method for determining the type of seepage and seepage damage of a dual-structure embankment according to claim 1, characterized in that: In S1), an impermeable embankment is provided on the upper part of the embankment foundation, and the permeability coefficient of the fine sand layer in the embankment foundation is less than that of the gravel layer.

3. The method for determining the type of seepage and seepage damage of a dual-structure embankment according to claim 2, characterized in that: In S2), the particle size range of the fine sand in the fine sand layer is 0.1 - 2 mm, and the particle size range of the gravel in the gravel layer is 0.5 - 10 mm.

4. The method for determining the type of seepage and seepage damage of a dual-structure embankment according to claim 3, characterized in that: In S2), when piping occurs, the maximum value of the shortest distance L between the water inlet and the center of the seepage outlet is the width of the embankment bottom.

5. The method for determining the type of seepage and seepage damage of a dual-structure embankment according to claim 1, characterized in that: In S3), when the key permeability control layer is a gravel layer, as long as the horizontal piping deformation of the gravel layer does not further develop into the outer river, the embankment foundation will not suffer from permeability damage; when the key permeability control layer is a silt-fine sand layer, as long as the horizontal flow soil deformation of the silt-fine sand surface layer does not further develop into the outer river, the embankment foundation will not suffer from permeability damage.

6. The method for determining the type of seepage and seepage damage of a dual-structure embankment according to claim 5, characterized in that: In S3), when the key permeability control layer is a gravel layer, the anti-permeability measures need to be implemented deep into the gravel layer to inhibit the further development of horizontal deformation of the gravel layer toward piping; when the key permeability control layer is a silt-fine sand layer, the anti-permeability measures need to be implemented deep into the surface layer of the silt-fine sand to inhibit the further development of horizontal deformation of the silt-fine sand toward soil flow.

7. The method for determining the type of seepage and seepage damage of a dual-structure embankment according to claim 6, characterized in that: In S3), when the key layer for permeability control is a gravel layer, the anti-permeability measure is to set a vertical anti-permeability wall inside the gravel layer; when the key layer for permeability control is a silt-fine sand layer, the anti-permeability measure is to set a vertical anti-permeability wall on the surface of the silt-fine sand.

Images