Embankment breach dynamic extension evaluation method based on dam body permeability

Abstract

The invention discloses an embankment breach dynamic expansion evaluation method based on dam body permeability, which comprises the following steps: S1, on the basis of a breach slope collapse body structure, constructing a breach slope collapse body simplified model, defining the physical form of a breach slope collapse body, dividing a collapse stress area at the same time, and obtaining breach dynamic expansion evaluation parameters; s2, calculating the maximum shear stress on the potential failure surface, the normal stress on the potential failure surface in unit width and the shear strength of a soil body by adopting the breach dynamic expansion evaluation parameters; s3, calculating the width of a collapse body according to a calculation result in the S2, constructing a shear failure criterion, and estimating the width of the collapse body when a shear failure node occurs; and S4, performing dike breach dynamic expansion evaluation based on the width of the collapse body when the shear failure occurs, taking a permeability parameter as a key variable, making up the defect that an existing evaluation method neglects or is difficult to quantify the seepage influence effect in the soil body, and directly calculating the width of the collapse body only by one group of parameters, and having few and clear input parameters.

Description

Technical Field

[0001] This invention relates to the field of flood control technology, specifically to a method for assessing the dynamic expansion of dike breaches based on the permeability performance of the dam body. Background Technology

[0002] Achieving rapid and accurate assessment of dam breaches to ensure safe and effective decision-making is an effective way to reduce flood risk. Currently, the main methods for assessing dam breach expansion include parametric models based on regression analysis, semi-parametric models, and numerical models based on physical mechanisms. Parametric and semi-parametric breach expansion models, based on historical breach expansion statistical data analysis, can only provide the final breach width and cannot dynamically assess breach expansion.

[0003] Meanwhile, the model parameters only involve physical parameters such as dam height and width, failing to fully consider important influencing factors such as the mechanical properties and permeability of the dam construction materials. Numerical models based on physical mechanisms require large-scale finite element software for hydrodynamic simulation, combined with slope stability numerical simulation analysis, which places high demands on computing power and is time-consuming, making it difficult to meet emergency response needs.

[0004] Patent CN115935651A provides a method for calculating the entire process of breach development with fewer parameters and easier implementation, improving the physicality and practicality of the simulation. However, it neglects or makes it difficult to quantify the influence of seepage within the soil.

[0005] The patent with publication number CN119761833A requires the construction of a complete numerical model, which relies on a large amount of terrain, hydrology, and boundary condition data, and involves long-term simulation calculations. Therefore, its efficiency is relatively low.

[0006] Based on the above, the present invention aims to establish a dynamic evaluation method for dam seepage performance parameters - breach expansion, to quickly assess the breach expansion width, and to provide algorithmic support for dam breach expansion assessment and risk response decision-making. Summary of the Invention

[0007] This invention provides a method for assessing the dynamic expansion of dike breaches based on the permeability of the dam body. It is applicable to the real-time prediction of the breach process of homogeneous earth dikes under high water level conditions during the flood season, providing a quantitative basis for risk response decisions.

[0008] This invention provides the following technical solution: a method for assessing the dynamic expansion of embankment breaches based on the permeability performance of the dam body, comprising: S1: constructing a simplified model of the breach slope collapse body based on the structure of the breach slope collapse body, defining the physical morphology of the breach slope collapse body and dividing the collapse stress zone, and obtaining the dynamic expansion assessment parameters of the breach; S2: calculating the maximum shear stress on the potential failure surface, the normal stress per unit width of the potential failure surface, and the soil shear strength using the dynamic expansion assessment parameters of the breach, wherein the normal stress is calculated based on the permeability performance of the dam body; S3: calculating the width of the collapse body based on the calculation results of S2, constructing a shear failure criterion, and predicting the width of the collapse body at the shear failure point; S4: conducting a dynamic expansion assessment of the embankment breach based on the width of the collapse body at the shear failure point.

[0009] As an optional scheme of the embankment breach dynamic expansion assessment method based on dam permeability performance described in this invention, the following steps are included: defining the physical morphology of the breach slope collapse body and dividing the collapse stress zone, including dividing the collapse body into several regions from top to bottom based on structural shape and permeability performance. These regions include: the region above the waterline of the collapse body, the region below the waterline of the collapse body between the waterline and the critical breach position, and the breach area of ​​the collapse body. The dynamic expansion assessment parameters include the dam height, the average water depth within the breach, the erosion height at the breach opening, and the soil weight of the several regions. The shear failure criterion is: in the collapse body caused by the driving force, the maximum shear stress along the shear failure surface must be less than or equal to the soil shear strength. The maximum shear stress on the potential failure surface includes: the self-weight of the collapse body and the vertical water pressure borne by the collapse body. The maximum shear stress is calculated as the difference between the ratio of the self-weight of the collapse body to the dam height and the ratio of the vertical water pressure borne by the collapse body to the dam height.

[0010] As an optional scheme of the dynamic expansion assessment method for embankment breaches based on dam permeability performance described in this invention, the calculation of the self-weight of the collapsed body includes: Where H is the height of the dam, h w It is the average water depth within the breach, h e It is the erosion height at the gap in the collapsed structure, l e The width of the collapsed body is defined as follows: the collapsed body is divided into three regions based on its shape and permeability characteristics. The first region is a rectangular area above the waterline, with a soil weight of γ1. The second region is a rectangular area between the collapsed body below the waterline and the critical breach point, with a soil weight of γ2. The third region is the triangular area of ​​the underwater breach, with the same soil weight as the second region, γ2. The calculation of the vertical water pressure borne by the collapsed body includes: γ w h represents the specific gravity of water. w It is the average water depth within the breach, h e It is the erosion height at the gap in the collapsed structure, l eThe width of the collapsed body.

[0011] As an optional scheme of the dynamic expansion assessment method for dike breaches based on dam permeability performance described in this invention, the normal stress on the potential failure surface per unit width is the ratio of the normal force per unit width applied to the potential failure surface to the dam height. The normal force per unit width consists of three parts of water pressure, represented by U... N1 U N2 and U N3 U N1 U is the pressure per unit width exerted on the collapsed body by the water pressure below the breach. N2 U is the water pressure per unit width generated by the water pressure inside the breach acting on the outside of the collapsed body. N3 U represents the water pressure per unit width exerted by the water pressure within the dam's soil on the side of the collapsed body furthest from the breach. N1 U N2 and U N3 The calculations include: Where α represents the permeability of the dam body, U N3 The size is determined by the permeability of the dam body, h w It is the average water depth within the breach, h e It is the erosion height at the breach in the collapsed body, γ w It is the density of water.

[0012] As an optional scheme of the embankment breach dynamic expansion assessment method based on dam permeability performance described in this invention, the soil shear strength calculation includes: Where c' is the effective cohesion of the soil, and φ' is the effective internal friction angle of the soil. Both are related to the soil material used in dam construction and are obtained experimentally. n This represents the normal stress on the potential failure surface per unit width.

[0013] As an optional scheme of the dynamic expansion assessment method for dike breaches based on dam permeability performance described in this invention, the calculation of the collapse width includes: Where α represents the permeability of the dam body, c' is the effective cohesion of the soil, and γ w h represents the specific gravity of water. w φ' is the average water depth inside the breach, H is the dam height, and φ' is the effective internal friction angle of the soil. , where h e The erosion height at the breach in the collapsed body is used to divide the collapsed body into three regions according to its shape and permeability characteristics. The first region is a rectangular area above the waterline, and the soil weight in this region is taken as γ1. The second region is a rectangular area between the collapsed body below the waterline and the critical position of the breach, and the soil weight is taken as γ2. The third region is a triangular area of ​​the underwater breach in the collapsed body, and the soil weight is the same as that in the second region, taken as γ2.

[0014] The present invention has the following beneficial effects:

[0015] 1. This method for assessing the dynamic expansion of embankment breaches based on the permeability performance of the dam body establishes a rapid assessment method that considers the permeability performance of the dam body, making up for the shortcomings of parametric models lacking mechanical mechanisms and numerical models being computationally complex, and serving to support emergency decision-making algorithms.

[0016] 2. This method for assessing the dynamic expansion of dam breaches based on the dam's permeability performance focuses on evaluating the potential for breach expansion and key dimensions, providing a rapid criterion for determining the possible scale of expansion.

[0017] 3. This method for assessing the dynamic expansion of embankment breaches based on the permeability performance of the dam body is the first to explicitly include permeability performance parameters as key variables in the quantitative calculation formula for breach expansion, thus making up for the shortcomings of existing models that often ignore or have difficulty quantifying the influence of seepage inside the soil.

[0018] 4. The dynamic expansion assessment method for dike breaches based on dam permeability provides an analytical calculation method that does not require iteration. It can directly and quickly obtain the critical collapse width based on the input parameters, with extremely high calculation efficiency, and is suitable for rapid emergency assessment.

[0019] 5. This method for assessing the dynamic expansion of embankment breaches based on dam permeability performance requires only a set of explicit dam geometry, soil mechanics, and permeability performance parameters, which can be directly calculated using formulas. It requires few and explicit input parameters, provides a new method for underlying core calculation principles, and can be used as a physical module in existing technology systems. It emphasizes the innovation of the mechanism model and the formula itself. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the erosion development process of the slope on one side of the breach under the action of the breach water flow and the collapse of the slope soil in an embodiment of the present invention.

[0021] Figure 2 This is a simplified model diagram of the collapsed slope on one side of the breach in an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of the vertical water pressure acting on the collapsed body in an embodiment of the present invention.

[0023] Figure 4 This is a schematic diagram of the normal stress on the potential sliding surface caused by water pressure in an embodiment of the present invention.

[0024] Figure 5 This is a graph showing the relationship between the width of the collapsed body and its permeability in an embodiment of the present invention.

[0025] Figure 6 This is a field test diagram of a dam failure according to an embodiment of the present invention.

[0026] Figure 7 This is a graph showing the change in the width of the collapsed body over time during the measured breach expansion process according to an embodiment of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This invention is applicable to real-time prediction of the breach process of homogeneous earthen embankments under high water levels during the flood season, providing a quantitative basis for risk response decisions. It should be noted that the breach expansion process begins with the formation of the breach. Under the action of the water flow through the breach, the slopes on both sides undergo erosion, collapse, and other processes, causing the breach width to gradually expand until erosion and collapse on both slopes cease, at which point the breach expansion process terminates.

[0029] like Figure 1 As shown, the slope formed by the breach is upright, and the toe of the slope gradually forms a gap under the erosion of the water flow, as shown by the dotted line. As the gap widens, the soil above the gap lacks support and will undergo shear failure. At the same time, the soil collapses into the breach and is carried away by the breach water flow, causing the breach to widen.

[0030] like Figure 2 As shown, the collapse caused by erosion on one side of the breach is simplified into a model. H is the height of the dam body, h w It is the average water depth within the breach, h e It is the erosion height at the gap in the collapsed structure, l e Let γ be the width of the collapsed body. The collapsed body is divided into three regions according to its shape and permeability characteristics. The first region is a rectangular region above the waterline, and the soil weight in this region is γ1. The second region is a rectangular region between the collapsed body below the waterline and the critical position of the breach, and the soil weight is γ2. The third region is the triangular region of the underwater breach of the collapsed body, and the soil weight is the same as that in the second region, γ2.

[0031] It should be noted that, to simplify the geometry of the collapsed slope and the division of soil regions, the top of the dam is considered horizontal, and the irregularity of the dam top at the breach is not considered; the height of the breach slope is the same as the height of the dam; the sidewalls of the breach slope: above the water surface, the sidewalls of the breach slope are assumed to be vertical; the shape of the breach slope below the water surface: the shape of the breach slope below the water surface is divided into two parts, the upper part is vertical, and the lower part slopes to the innermost side of the breach opening. Water level at the breach: the water level at the breach is the average water depth inside the breach.

[0032] As the soil at the toe of the breach slope erodes, the gap widens, and the collapsed mass will undergo shear failure along the potential sliding surface. The shear failure criterion is as follows: , where τ max It is the maximum shear stress along the shear failure surface in the collapsed body caused by the driving force, and τ is the shear strength of the dam soil.

[0033] Shear failure occurs when the maximum shear stress along the shear failure surface in the collapsed mass caused by the driving force exceeds the shear strength of the dam soil. All calculations below use unit width.

[0034] The maximum shear stress τ acting per unit width of the failure surface max The force generated by the self-weight of the collapsed body and the vertical water pressure borne by the collapsed body can be expressed as follows: Among them, W s This refers to the self-weight of the collapsed body. The calculation of the self-weight of the collapsed body includes: Where H is the height of the dam, h w It is the average water depth within the breach, h e It is the erosion height at the gap in the collapsed structure, l e U represents the width of the collapsed body. V It is the vertical water pressure borne by the collapsed body, such as Figure 3 As shown, the calculation of the vertical water pressure borne by the collapsed body includes: γ w It is the density of water.

[0035] W s and U V Substitute ,get: For ease of expression, let The above formula can be expressed as: .

[0036] The normal stress per unit width generated by the normal force on the potential failure surface can be expressed as: Among them, such as Figure 4 As shown, σ n It is the normal stress per unit width on the potential failure surface, U N It is the normal force per unit width applied to the potential failure surface, which consists of three parts of water pressure, represented by U. N1 U N2 and U N3 U N1 U is the pressure per unit width exerted on the collapsed body by the water pressure below the breach. N2 U is the water pressure per unit width generated by the water pressure inside the breach acting on the outside of the collapsed body. N3 The water pressure per unit width of the collapsed body on the side away from the breach is generated by the water pressure within the soil of the dam body.

[0037] U N1 U N2 and U N3 The calculations include: Where α represents the permeability of the dam body, and γ w The density of water. U N3 The size is determined by the permeability of the dam body.

[0038] Will Represented as: .

[0039] The soil shear strength τ is influenced by the effective stress on the potential slip surface and the soil strength parameters. According to the Mohr-Coulomb failure criterion, it can be expressed as: Where c' is the effective cohesion of the soil and φ' is the effective internal friction angle of the soil. Both are related to the soil material used in dam construction and are obtained through experiments.

[0040] Based on the above calculation process, when the maximum shear stress τ on the potential sliding surface max When the shear stress exceeds the soil's shear strength τ, the collapsed mass will slide along the potential failure surface and collapse. A critical condition occurs when the maximum shear stress equals the soil's shear strength. At this point, the width l of the collapsed mass... e It can be represented as: .

[0041] It should be noted that the permeability α of the dam soil can be expressed as: When α=0, the soil below the dam water level is considered dry, corresponding to the worst permeability of the dam soil, which is impermeable. When α=1, the soil below the dam water level is considered fully saturated, corresponding to the best permeability of the dam soil, which is completely permeable. When 0<α<1, the soil below the dam water level is considered to be between the above two states, and the permeability of the dam soil is between impermeable and completely permeable.

[0042] Taking a common homogeneous clay dam as an example, this paper quantitatively analyzes the collapse width l under specific conditions, with different dam permeability properties (corresponding to different values ​​of α). e The range of variation. For example, the dam height is taken as H=4m, 6m, 8m, 10m, 12m, and the breach depth is taken as h. w =0.8H, the erosion height at the breach in the collapsed body is taken as h. e =0.65hw, the specific gravity of water γ w =9.8kN / m 3 The natural unit weight of the dam soil is γ1 = 18.0 kN / m. 3 saturated unit weight γ2 = 18.5 kN / m 3Effective cohesion c' = 10 kN / m 2 Effective internal friction angle φ'=25°

[0043] like Figure 5 The above-mentioned physical parameters of the dam body are applied to calculate the width l of the collapsed body. e The formula yields the width l of the collapsed body when the dam's permeability changes (corresponding to different values ​​of α). e Through the above calculations, we can obtain the width of the collapsed body during dam failure under different dam permeability conditions (0≤α≤1). For example, when α=0.5 and H=6m, e =2.26m. Therefore, this method considers the permeability α of the dam soil. Given parameters such as the dam height, breach depth, and mechanical properties of the dam soil materials, it can quickly and accurately calculate (or query) the dam's permeability α. Figure 5 ) Breach expansion width (collapsed body width value l) e This provides algorithmic support for dam breach expansion assessment and risk response decision-making.

[0044] To verify the effectiveness of the calculation method of this invention, a calculation model for breach width propagation based on the limit equilibrium method was established in the SLOPE / W software. Based on this model, the breach height and soil mechanical parameters (as described above) were input, and the width l of the collapsed body was calculated. e (Specific values ​​are shown in Table 1). Compare the calculation results in Table 1 with... Figure 4 The results shown are compared (see Table 2), and the two are in good agreement, thus verifying that the method of the present invention, as a rapid evaluation method, has reliable computational accuracy.

[0045] Table 1: Collapse width values ​​calculated using the limit equilibrium method

[0046]

[0047] Table 2: Comparison between the Limit Equilibrium Method and the Method of This Patent

[0048]

[0049] In 2003, a series of dam failure field tests were conducted in Moi Rana, a town in central Norway. The test site was located 500 meters downstream of the Rossvatn Dam. Figure 6 The dam is 4.3m high, and the dry unit weight of the soil used for dam construction is 2.20kN / m³. 3 Natural heavy weight 2.38kN / m 3 Porosity 0.244, internal friction angle 42°, cohesion 20 kN / m 2 The moisture content was 0.06%. The width of the collapsed body during the breach expansion process after the dam failure was measured in the experiment; see details below. Figure 7Although the field test did not directly measure the soil permeability, the observed results qualitatively matched the expected effect of the calculation method of this invention, thus providing preliminary verification of the rationality and feasibility of this method at the engineering level.

[0050] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for assessing the dynamic expansion of dike breaches based on the permeability performance of the dam body, characterized in that, include: S1: Based on the structure of the collapsed body of the breach slope, construct a simplified model of the collapsed body of the breach slope, define the physical morphology of the collapsed body of the breach slope and divide the collapse stress area, and obtain the dynamic expansion assessment parameters of the breach. S2: The maximum shear stress on the potential failure surface, the normal stress per unit width on the potential failure surface, and the soil shear strength are calculated using the breach dynamic propagation assessment parameters. The normal stress is calculated based on the dam's permeability performance. S3: Calculate the width of the collapsed body based on the calculation results of S2, construct the shear failure criterion, and predict the width of the collapsed body at the point where shear failure occurs; S4: Dynamic expansion assessment of levee breaches based on the width of the collapsed body at the time of shear failure.

2. The method for assessing the dynamic expansion of dike breaches based on dam permeability performance according to claim 1, characterized in that: Defining the physical morphology of the collapsed slope and dividing the stress-bearing areas includes: dividing the collapsed body into several regions from top to bottom based on its structural shape and permeability. These regions include: the region above the waterline of the collapsed body, the region between the waterline of the collapsed body and the critical position of the breach, and the breach area of ​​the collapsed body. The dynamic expansion assessment parameters of the breach include the dam height, the average water depth within the breach, the erosion height at the breach, and the soil weight of several regions.

3. The method for assessing the dynamic expansion of dike breaches based on dam permeability performance according to claim 1 or 2, characterized in that: The shear failure criterion is: in a collapse caused by a driving force, the maximum shear stress along the shear failure surface must be less than or equal to the soil shear strength.

4. The method for assessing the dynamic expansion of dike breaches based on dam permeability performance according to claim 1 or 2, characterized in that: The maximum shear stress on the potential failure surface includes: the self-weight of the collapsed body and the vertical water pressure borne by the collapsed body. The maximum shear stress is calculated as the difference between the ratio of the self-weight of the collapsed body to the height of the dam and the ratio of the vertical water pressure borne by the collapsed body to the height of the dam.

5. The method for assessing the dynamic expansion of embankment breaches based on dam permeability performance according to claim 4, characterized in that: The calculation of the self-weight of the collapsed body includes: Where H is the height of the dam, h w It is the average water depth within the breach, h e It is the erosion height at the gap in the collapsed structure, l e The collapse body is divided into three regions according to its shape and permeability characteristics. The first region is a rectangular region above the waterline, and the soil weight in this region is γ1. The second region is a rectangular region between the collapse body below the waterline and the critical position of the breach, and the soil weight is γ2. The third region is the triangular region of the underwater breach of the collapse body, and the soil weight is the same as that in the second region, γ2.

6. The method for assessing the dynamic expansion of dike breaches based on dam permeability performance according to claim 4, characterized in that: The calculation of the vertical water pressure borne by the collapsed body includes: γ w h represents the specific gravity of water. w It is the average water depth within the breach, h e It is the erosion height at the gap in the collapsed structure, l e The width of the collapsed body.

7. The method for assessing the dynamic expansion of dike breaches based on dam permeability performance according to claim 1, characterized in that: The normal stress per unit width on the potential failure surface is the ratio of the normal force per unit width applied to the potential failure surface to the dam height. The normal force per unit width consists of three parts of water pressure, denoted by U. N1 U N2 and U N3 U N1 U is the pressure per unit width exerted on the collapsed body by the water pressure below the breach. N2 U is the water pressure per unit width generated by the water pressure inside the breach acting on the outside of the collapsed body. N3 The water pressure per unit width of the collapsed body on the side away from the breach is generated by the water pressure within the soil of the dam body.

8. The method for assessing the dynamic expansion of dike breaches based on dam permeability performance according to claim 7, characterized in that: U N1 U N2 and U N3 The calculations include: Where α represents the permeability of the dam body, U N3 The size is determined by the permeability of the dam body, h w It is the average water depth within the breach, h e It is the erosion height at the breach in the collapsed body, γ w It is the density of water.

9. The method for assessing the dynamic expansion of dike breaches based on dam permeability performance according to claim 3, characterized in that: Soil shear strength calculation includes: Where c' is the effective cohesion of the soil, and φ' is the effective internal friction angle of the soil. Both are related to the soil material used in dam construction and are obtained experimentally. n This represents the normal stress on the potential failure surface per unit width.

10. The method for assessing the dynamic expansion of dike breaches based on dam permeability performance according to claim 1, characterized in that: The calculation of the width of the collapsed body includes: Where α represents the permeability of the dam body, c' is the effective cohesion of the soil, and γ w h represents the specific gravity of water. w φ' is the average water depth inside the breach, H is the dam height, and φ' is the effective internal friction angle of the soil. , where h e The erosion height at the breach in the collapsed body is used to divide the collapsed body into three regions according to its shape and permeability characteristics. The first region is a rectangular area above the waterline, and the soil weight in this region is taken as γ1. The second region is a rectangular area between the collapsed body below the waterline and the critical position of the breach, and the soil weight is taken as γ2. The third region is a triangular area of ​​the underwater breach in the collapsed body, and the soil weight is the same as that in the second region, taken as γ2.

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