Prediction method of dam breach morphology based on case statistics and breach process

Abstract

The present invention relates to the field of geological disaster emergency response technology, and discloses a method for predicting the breach morphology of a dam based on case statistics and breach process, aiming to solve the problem of insufficient theoretical and accuracy of existing methods. The scheme mainly includes: obtaining basic parameters and vertical breach degree in natural breach cases; classifying basic parameters and vertical breach degree, and determining key parameters affecting the vertical breach degree based on correlation analysis, contingency cross analysis and breach process analysis; dividing the vertical breach degree into two categories, and constructing an expression for calculating the probability of the vertical breach degree being greater than 1 / 2 of the dam height based on logistic regression analysis; further determining the vertical breach degree of each category greater than and less than or equal to 1 / 2 of the dam height according to other characteristics such as the material, shape and structure of the dam to be predicted; considering the actual discharge volume and river width, classifying and giving the breach width under different vertical breach degrees. The present invention realizes the unity of scientificity, systematicness and practicality in the prediction of breach morphology.

Description

Technical Field

[0001] The present invention relates to the technical field of geological disaster emergency response, and in particular to a method for predicting the breach morphology of a dam based on case statistics and breach processes. Background Art

[0002] A landslide dam refers to a loose accumulation of materials that blocks a river channel and forms a landslide lake after an earthquake or heavy rainfall. Due to the large difference in particle size distribution of the dam body, the overall stability and erosion resistance are low, and there is a great risk of collapse. Once collapsed, the dam burst flood will cause serious damage to downstream villages and projects. After a landslide dam occurs, predicting the peak flow of the dam burst and assessing the damage in advance can help formulate an effective emergency response plan. Considering the need for rapid prediction, the parameter assumption model is a commonly used mathematical model, among which the final breach shape of the landslide dam is a key parameter that directly affects the prediction accuracy.

[0003] Regarding the degree of vertical breach, emergency plans are often formulated according to the estimated fraction of vertical breach during on-site disposal. There is a lack of systematic determination methods, and existing predictions do not take into account the changes in the dam body and reservoir capacity after disposal. Similarly, the parameters in the few existing linear fitting formulas are mainly obtained through accuracy comparison, and there is a lack of theoretical basis for parameter selection, and the influence of the vertical structure of the dam body on the degree of vertical breach is not considered.

[0004] In addition, compared with the prediction formula for the widening of earth-rock dams, the prediction of the widening of landslide dam breaches needs to be improved. Although there are a few widening formulas based on landslide dam cases, since landslide dams are mostly partially breached, the breach degree is different from that of earth-rock dams, and they often occur in narrow and deep rivers, when the vertical breach degree is large, the widening will also be limited by the river width. This parameter has not been considered in existing studies.

[0005] In summary, when predicting the breach shape of a landslide dam, the existing technology has problems of insufficient theoreticality and accuracy in predicting the vertical breach degree and breach width. Summary of the invention

[0006] The present invention aims to solve the problem that the existing methods for predicting the vertical breach degree of a dam are insufficient in theory and accuracy, and proposes a method for predicting the breach morphology of a dam based on case statistics and breach process.

[0007] The technical solution adopted by the present invention to solve the above technical problems is:

[0008] A method for predicting the breach morphology of a dam based on case statistics and breach processes, the method comprising:

[0009] Obtaining natural breach cases in the case library and the basic parameters and vertical breach degrees corresponding to each breach case, wherein the basic parameters include: dam height, dam length, length-to-height ratio, dam volume, dam material composition, upstream flow and reservoir capacity data;

[0010] Classify the basic parameters and vertical failure degree, and determine the key parameters affecting the vertical failure degree from the basic parameters based on correlation analysis, contingency cross analysis and failure process analysis;

[0011] The vertical failure degree is divided into two categories, which are less than or equal to 1 / 2 of the dam height and greater than 1 / 2 of the dam height. According to the key parameters and vertical failure degree of each failure case, an expression for calculating the probability of the vertical failure degree being greater than 1 / 2 of the dam height is constructed based on logistic regression analysis.

[0012] The key parameters of the landslide dam to be predicted are obtained, and whether the vertical breach degree of the landslide dam to be predicted is greater than 1 / 2 of the dam height is determined according to the categories of the key parameters of the landslide dam to be predicted and based on the expression.

[0013] Furthermore, the expression for calculating the probability that the vertical breach degree is greater than 1 / 2 of the dam height is as follows:

[0014]

[0015] Where p is the probability that the vertical failure degree is greater than 1 / 2 of the dam height, β0 is a constant term, and β1, β2, …, β n are partial regression coefficients, x1, x2, …, x n The category of the key parameter.

[0016] Furthermore, the key parameters are the aspect ratio and the dam material, and the expression for calculating the probability that the vertical breach degree is greater than 1 / 2 of the dam height is as follows:

[0017]

[0018] Where x1 is the category of dam material, and x2 is the category of aspect ratio.

[0019] Furthermore, the method further comprises:

[0020] When it is determined that the vertical failure degree of the predicted landslide dam is greater than 1 / 2 of the dam height, it is determined whether the dam body material is composed of loess and clay. If so, the dam height is used as the vertical failure degree of the predicted landslide dam. Otherwise, 2 / 3 of the dam height, 3 / 4 of the dam height or 3 / 5 of the dam height is used as the vertical failure degree of the predicted landslide dam.

[0021] Furthermore, the method further comprises:

[0022] When it is determined that the vertical failure degree of the predicted landslide dam is not greater than 1 / 2 of the dam height, the slope ratio of the predicted landslide dam is obtained. If the slope ratio is within a first preset range, 1 / 3 of the dam height is used as the vertical failure degree of the predicted landslide dam. If the slope ratio is within a second preset range, 1 / 2 of the dam height is used as the vertical failure degree of the predicted landslide dam.

[0023] Furthermore, the method further comprises:

[0024] When the landslide dam to be predicted is a binary stacked structure or a ternary stacked structure, the elevation of the top surface of the bottom layer of the binary stacked structure or the ternary stacked structure is obtained, and it is determined whether the elevation corresponding to the vertical breach degree of the landslide dam to be predicted is less than the elevation of the top surface of the bottom layer. If so, the vertical breach degree of the landslide dam to be predicted is re-determined.

[0025] Furthermore, the re-determining of the vertical failure degree of the landslide dam to be predicted specifically includes:

[0026] If the bottom layer of the binary stack structure is composed of intact rock layers and the top layer is composed of broken soil and rocks or isolated pieces of broken rocks, the ratio of the height of the top layer to the dam height shall be used as the re-determined vertical failure degree;

[0027] If the bottom layer of the binary stacked structure is composed of broken rock and soil, and the top layer is composed of isolated broken rocks, a value between the vertical failure degree and 2 / 3 of the dam height is selected as the re-determined vertical failure degree;

[0028] If the bottom layer of the ternary stack structure is composed of complete rock layers, the middle layer is composed of isolated pieces of gravel, and the top layer is composed of broken stones and soil, then the ratio of the height of the top layer to the middle layer and the height of the dam will be used as the re-determined vertical failure degree.

[0029] Furthermore, the method further comprises:

[0030] Obtain the slope ratio, length, height and actual discharge capacity of the landslide dam to be predicted;

[0031] Determine the vertical breach depth of the predicted dam according to the vertical breach degree and dam height of the predicted dam, and calculate the breach cross-sectional area of ​​the predicted dam after the dam is breached according to the dam body slope ratio, dam length and vertical breach depth of the predicted dam;

[0032] The breach top width and breach bottom width of the predicted dam after its breach are calculated based on the breach cross-sectional area of ​​the predicted dam, the actual downstream storage capacity and the vertical breach depth.

[0033] Furthermore, when the vertical breach degree of the predicted barrier dam is less than or equal to 1 / 2 of the dam height, the calculation formulas for the breach top width and breach bottom width after the predicted barrier dam breach are as follows:

[0034] b mtE′=13.858W′ 0.4577 H′;

[0035] b mb E′=5.1707W′ 0.4964 H′;

[0036] Where b mt is the width of the breach top, b mb is the bottom width of the breach, E′ is the cross-sectional area of ​​the breach, W′ is the actual downstream storage capacity, and H′ is the vertical breach depth.

[0037] Furthermore, when the vertical breach degree of the predicted dam is greater than 1 / 2 of the dam height, the calculation formulas for the breach top width and breach bottom width after the predicted dam breach are as follows:

[0038] b mt E′=28.818W′ -0.088 B 1.549 H′;

[0039] b mb E′=6.991W′ 0.357 B 0.406 H′;

[0040] Where b mt is the width of the breach top, b mb is the bottom width of the breach, E′ is the cross-sectional area of ​​the breach, B is the width of the river channel, W′ is the actual downstream storage capacity, and H′ is the vertical breach depth.

[0041] The beneficial effects of the present invention are as follows: the method for predicting the breach morphology of a landslide dam based on case statistics and breach process described in the present invention screens the key parameters for predicting the vertical breach degree through breach cases and based on correlation analysis, contingency cross analysis and breach process analysis, thereby improving the accuracy of key parameter screening and thus improving the accuracy of predicting the vertical breach degree. In addition, an expression is constructed based on the key parameters of the breach case, and based on the expression, it can accurately predict whether the vertical breach degree of the landslide dam is greater than 1 / 2 of the dam height. For special landslide dams, the vertical breach degree of the landslide dam is further determined by the dam body material, slope ratio and dam body structure, further improving the accuracy of predicting the vertical breach degree. In addition, the breach width of the landslide dam is calculated based on the formula created based on the predicted vertical breach degree and case analysis, and when the vertical breach degree is greater than 1 / 2 of the dam height, the parameter river width is also introduced to improve the accuracy of the breach width prediction. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a flow chart of a method for predicting the breach morphology of a dam based on case statistics and breach process according to an embodiment of the present invention;

[0043] Figure 2 It is a schematic diagram of the cross-analysis of the aspect ratio, dam material and vertical breach degree according to the embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of the collapse process analysis according to an embodiment of the present invention;

[0045] Figure 4 It is a schematic diagram of the process of predicting the widening of a breach according to an embodiment of the present invention;

[0046] Figure 5 It is a schematic structural diagram of the breach described in an embodiment of the present invention. DETAILED DESCRIPTION

[0047] The implementation modes of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0048] The present invention aims to improve the accuracy of dam breach morphology prediction and provide a dam breach morphology prediction method based on case statistics and breach process. Figure 1 , including the following steps:

[0049] Step 1: Obtain natural breach cases in the case library and the basic parameters and vertical breach degrees corresponding to each breach case, wherein the basic parameters include: dam height H, dam length L, length-to-height ratio L / H, dam volume V, dam material composition, upstream flow Q, and reservoir capacity data W;

[0050] In this embodiment, 49 cases of natural failure of landslide dams at home and abroad with detailed basic parameters are collected since the 1970s, and the corresponding basic parameters and vertical failure degrees are obtained respectively.

[0051] Step 2: Classify the basic parameters and vertical failure degree, and determine the key parameters affecting the vertical failure degree from the basic parameters based on correlation analysis, contingency cross analysis and failure process analysis;

[0052] In this embodiment, the basic parameters are divided into III (3) or IV (4) categories (reservoir capacity reference volume classification value) according to the risk level boundary value, such as dam height H, dam length L, length-to-height ratio L / H, dam volume V, upstream inflow Q and reservoir data W. The dam body materials are divided into I (1), II (2), III (3), IV (4), and V (5) categories according to the fine-grained group (clay, loess), sand-soil mixture (mainly sand), crushed stone, gravel, sand (mainly gravel and crushed stone), block crushed stone (particle size d<200mm), and boulder / large block stone (particle size d in meters).

[0053] In addition, the following classification is made for the description of basic parameter profiles in individual cases:

[0054] (1) If there is no specific value for the upstream flow Q, it is described as "very small", "small" or "large", and the flow is assigned to Class I (1), II (2), or IV (4). If there is heavy rainfall, melting ice and snow, or other dam failures upstream, the upstream flow Q is assigned to Class IV (4);

[0055] (2) For some dams that collapsed naturally after treatment (excluding artificially induced dams), the dams after treatment are regarded as "new dams" and reclassified according to the treatment situation. If the data is incomplete and it is determined that the treatment does not cause the category of the dam foundation parameters to change, the category of the data before the treatment shall prevail.

[0056] (3) The vertical failure degree is divided into four categories: less than or equal to 1 / 2 of the dam height, approximately equal to 1 / 2 of the dam height, greater than 1 / 2 of the dam height and less than the dam height, and equal to the dam height (total failure).

[0057] In this embodiment, after classification, the data of the 49 cases of landslide dam failure collected above are shown in the following table:

[0058]

[0059] Note: The dam body characteristics in the table are all post-treatment data. * ” stands for post-natural breach disposal.

[0060] By conducting correlation analysis, cross-link analysis and breach process analysis based on the data of breach cases, the key parameters affecting the degree of vertical breach can be determined from the basic parameters.

[0061] Among them, correlation analysis (parameter determination basis 1):

[0062] The results of Kendall'stau-b correlation analysis are shown in the following table:

[0063]

[0064] Note: ***, **, * represent 1%, 5%, 10% significance levels respectively.

[0065] According to the table above, the key parameters of vertical failure are dam material (-) and aspect ratio (+), and the dam material has a more obvious impact. According to experience, dams with poor scouring resistance and steep slopes are more likely to form effective scouring than dams with strong scouring resistance and gentle slopes, and have a higher degree of vertical failure. Among them, the negative correlation of dam material is reasonable, and the positive correlation of aspect ratio needs to be reviewed.

[0066] Contingency cross analysis (parameter determination based on 2)

[0067] See also Figure 2 , Figure 2The cross-sectional analysis of length-to-height ratio, dam material and vertical failure degree: The positive correlation of length-to-height ratio is mainly due to the fact that in the third type of length-to-height ratio ( Figure 2 In a), 71.40% of the total collapse cases correspond to almost all Figure 2 All the collapsed dam bodies (100%) are composed of Class I materials in b, such as Yigong Weir Dam, Milingala Weir Dam, etc. The length-to-height ratio is highly correlated with the dam material (-0.537 (p = 0.006***)), and the analysis of the influence of the length-to-height ratio should be based on the premise that the materials are the same. The materials in the case are not exactly the same, and most of the weir dams have wide and gentle sections, which are not very distinguishable. It is necessary to use model tests to analyze the influence of the length-to-height ratio of dams in the same category, and the rationality of the relevant analysis results of other parameters can also be verified based on the breach phenomenon.

[0068] Analysis of the breach process (parameter determination based on 3)

[0069] In order to further analyze the influence of the length-to-height ratio of dams of the same category and to verify the rationality of the analysis results related to other parameters based on the breach phenomenon, a generalized model test study was carried out. Figure 3 , referring to the topography of the Jinsha River section where the Baige Weir is located, the river channel from 1.5km upstream to 2km downstream of the dam was taken, and the model was established with a horizontal scale of 1:200 and a vertical scale of 1:150. The dam body is located between cross sections CS7 and CS8. A total of 4 water level meters were set up in the upstream and downstream river channels to record water level changes (asterisk positions in the figure). Cameras were placed in front of the dam, on the top of the dam, and behind the dam to shoot the breach process. According to the actual situation of the weir in the case, the upstream flow was set to 3L / s. 0.075~4cm particles were taken to form the dam body material, and the median particle size of the homogeneous dam body was d50=6mm. Regarding the influence of the aspect ratio parameter, the downstream slope ratio (1:1.3~1:2.5) was controlled in the experiment to change the aspect ratio (3.5~4.5), and the test groups are shown in the following table. The specific test process is as follows:

[0070] (1) The dam material is divided into two groups according to the density (2.41g / cm 3 ) and dam body moisture content (12%), and a 10×10cm grid was drawn on the dam body surface;

[0071] (2) Open the water supply valve and use a level meter and camera to record the process of water rising in the reservoir area and the process of the dam body breaching;

[0072] (3) Determine the breach parameters after the breach is complete.

[0073] Group Incoming flow L / s Dam composition Dam shape 1 3 <![CDATA[d 50 =6mm]]> 1m above × 2.5m below × 0.7m above, length-to-height ratio 3.5, downstream slope ratio 1:1.3 2 3 <![CDATA[d 50 =6mm]]> 1m above × 2.8m below × 0.7m above, length-to-height ratio 4, downstream slope ratio 1:1.7 3 3 <![CDATA[d 50 =6mm]]> 1m above × 3.6m below × 0.7m above, length-to-height ratio 4.5, downstream slope ratio 1:2.5

[0074] The test results show that the same material makes up the dam body, but the breach process and vertical breach degree are different under the influence of different length-to-height ratios (groups 1, 2, and 3). The length-to-height ratio has an impact on the vertical breach degree. When it increases from 3.5 to 4.5, the vertical breach degree decreases from 27cm to 20cm, a decrease of 7cm, which is equivalent to the prototype 10.5m.

[0075] The starting states of fine particles and coarse particles in the process of upstream erosion and breach are different. When the dam surface is wide and gentle, the water level drop and water flow velocity are small. More coarse particles cannot start immediately after shear failure, and stay at the bottom of the breach, increasing the roughness of the bottom of the breach and preventing the further development of the breach. In addition, since the slope of the river channel downstream of the dam body is gentle and the horizontal width is wide, after the flood flows into the downstream river channel from the narrow breach, the cross-sectional area of ​​the water increases, the flood flow rate decreases sharply, and the larger particle size settles before the breach at the bottom of the dam to form siltation, and the finer particles move downstream from the water flow and deposit. When the height is small, the coarsening of the breach is obvious and the rebalancing state of the riverbed will end early, so the degree of vertical breach is small. Therefore, it is the head difference of the dam slope rather than the dam height and the dam body material that determines the termination height of erosion, that is, the actual discharge storage capacity, not the total storage capacity that determines the degree of vertical breach. After the breach is terminated, the undischarged water has no effect on the breach. The total volume of the dam body also has little effect on the degree of vertical breach. The negative correlation of the reservoir capacity obtained from the correlation analysis is because the reservoir capacity is related to the dam height, and the dam height is numerically negatively correlated with the degree of vertical breach. When the breach occurs, the upstream flow is negligible compared to the dam breach flow, and its effect on the degree of vertical breach is small, and it only forms a slow scouring of the remaining dam body after the breach ends.

[0076] According to the above analysis, this embodiment conducts correlation analysis, contingency cross analysis and breach process analysis on the data of 49 collected landslide dam breach cases, and concludes that the main factors affecting the vertical breach degree of the dam body are the aspect ratio (-) and the dam body material (-), that is, the aspect ratio and the dam body material are the key parameters screened from the basic parameters.

[0077] Step 3: The vertical failure degree is divided into two categories: less than or equal to 1 / 2 of the dam height and greater than 1 / 2 of the dam height. According to the key parameters and vertical failure degree of each failure case, an expression for calculating the probability that the vertical failure degree is greater than 1 / 2 of the dam height is constructed based on logistic regression analysis;

[0078] In this embodiment, the vertical breach degree is regarded as a binary variable, and its value is y=0 (vertical breach degree is less than or equal to 1 / 2 dam height) or y=1 (vertical breach degree is greater than 1 / 2 dam height). Then, the data of 49 breach cases are imported and a logistic regression analysis is used to construct an expression for calculating the probability that the vertical breach degree is greater than 1 / 2 dam height.

[0079] Assuming that there are n independent variables (i.e. key parameters) that affect the value of y, the probability p that the vertical failure degree is greater than 1 / 2 of the dam height under the action of n independent variables is expressed as:

[0080]

[0081] Where p is the probability that the vertical failure degree is greater than 1 / 2 of the dam height, β0 is a constant term, and β1, β2, …, β n are partial regression coefficients, x1, x2, …, x n The category of the key parameter.

[0082] In this embodiment, the key parameters affecting the vertical collapse degree of the dam body are the aspect ratio and the dam body material. Logistic regression analysis is performed based on the above 49 cases to obtain the corresponding constant term and partial regression coefficient. The expression of the probability p that the vertical collapse degree is greater than 1 / 2 of the dam height is:

[0083]

[0084] Where x1 is the category of dam material, and x2 is the category of aspect ratio.

[0085] In the above expression, the constant term and partial regression coefficient are established by logistic regression analysis based on 80% of the case data in the case library. The model accuracy is 80%, the likelihood ratio chi-square value is 23.23 (p = 0.016**), and the level is significant, indicating that the model is effective. The remaining 20% ​​of the case data (6) in the case library were used for verification, and only 1 was wrong, with an accuracy rate of 83%, indicating that this method can be used to accurately predict whether the vertical collapse degree of the dam body is greater than 1 / 2 of the dam height.

[0086] Step 4: obtaining key parameters of the landslide dam to be predicted, and determining whether the vertical breach degree of the landslide dam to be predicted is greater than 1 / 2 of the dam height according to the category of the key parameters of the landslide dam to be predicted and based on the expression.

[0087] In this embodiment, when a landslide occurs, the basic data of the landslide dam can be obtained first according to the type of bank instability, sliding speed (determined by sliding height), instability scale, valley width, and in conjunction with DEM remote sensing images and drones, mainly including dam height H, dam length L, length-to-height ratio L / H, dam body volume V, etc. Then, the approximate dam body material composition of the landslide dam can be quickly determined based on the bank lithology, rock mass integrity and bank instability type. For example, the skeleton of the landslide body that slides along the low position of the unweathered bank slope is mainly composed of coarse particles, while the skeleton structure of the landslide body formed by the high position sliding against the weathered severe slope is mainly composed of fine particles. In addition, the upstream flow Q and reservoir capacity data W can be obtained through the upstream hydrological station. Among them, the length-to-height ratio (L / H) and dam body material are key parameters.

[0088] According to the same classification method as in step 2, the categories of key parameters of the landslide dam to be predicted are obtained and input into the probability calculation expression to determine whether the vertical breach degree of the landslide dam to be predicted is greater than 1 / 2 of the dam height.

[0089] In order to further improve the prediction accuracy, this embodiment predicts the vertical breach degree by the above method, and then uses case experience summary to assist on-site judgment:

[0090] When it is determined that the vertical failure degree of the predicted landslide dam is greater than 1 / 2 of the dam height, it is determined whether the dam material is Class I, that is, whether it is composed of loess and clay. If so, the dam height is used as the vertical failure degree of the predicted landslide dam. Otherwise, 2 / 3 of the dam height, 3 / 4 of the dam height or 3 / 5 of the dam height is used as the vertical failure degree of the predicted landslide dam, with an error within 1 / 15 of the dam height.

[0091] When it is determined that the vertical failure degree of the predicted landslide dam is not greater than 1 / 2 of the dam height, the slope ratio of the predicted landslide dam is obtained. If the slope ratio is within a first preset range, 1 / 3 of the dam height is used as the vertical failure degree of the predicted landslide dam. If the slope ratio is within a second preset range, 1 / 2 of the dam height is used as the vertical failure degree of the predicted landslide dam.

[0092] Specifically, according to the breach cases, the dam body with a vertical breach degree of 1 / 2 of the dam height is basically composed of Class III and V materials (gravel, crushed stone). If the slope of the landslide dam to be predicted is relatively gentle (slightly greater than 1:5), it is estimated as 1 / 3 of the dam height. On the contrary, if the dam body is sharp and thin, and the slope ratio is about 1:4, similar to the Tanggudong landslide dam, it is estimated as 1 / 2 of the dam height.

[0093] In this way, the dam body failure degree with a vertical failure degree less than or equal to 1 / 2 of the dam height is divided into 1 / 3 failure and 1 / 2 failure, and the error is about 1 / 6 of the dam height H. After the disposal of most barrier dams, the dam height H is less than 60m, and the dam height H of less than or equal to 1 / 2 failure is generally smaller. Therefore, according to the above-mentioned 1 / 15 and 1 / 6 dam height H error estimates, the vertical failure degree error is less than 10m, which basically meets the requirements of rapid emergency judgment.

[0094] In addition, in order to further improve the prediction accuracy, for the barrier dam with distinct structural characteristics, the above method should be used to refer to the actual situation for specific analysis based on the model prediction to reduce the prediction error. Specifically, in addition to the homogeneous structure, the binary or ternary stacked structure that may exist in the dam body should be considered.

[0095] In this embodiment, when the predicted barrier dam is a binary stacked structure or a ternary stacked structure, the elevation of the top surface of the bottom layer of the binary stacked structure or the ternary stacked structure is obtained, and it is determined whether the elevation corresponding to the vertical breach degree of the predicted barrier dam is less than the elevation of the top surface of the bottom layer. If so, the vertical breach degree of the predicted barrier dam is re-determined. Among them, the elevation corresponding to the vertical breach degree refers to the height of the dam body relative to the ground after the barrier dam is breached according to the vertical breach degree, and the elevation of the top surface of the bottom layer refers to the height of the top surface of the bottom layer relative to the ground.

[0096] Specifically, there are two types of binary stacking structures: one with a bottom layer consisting of complete rock layers and a top layer consisting of broken soil and rocks or isolated pieces of rubble; the other with a bottom layer consisting of broken rock and soil and a top layer consisting of isolated pieces of rubble. The ternary stacking structure has a bottom layer consisting of complete rock layers, a middle layer consisting of isolated pieces of rubble, and a top layer consisting of broken rock and soil.

[0097] For the first type of binary stacking structure, it is determined whether the elevation corresponding to the vertical breach degree of the predicted dam is less than the elevation of the top surface of the bottom layer. If so, the ratio of the height of the top layer to the dam height is used as the re-determined vertical breach degree. Otherwise, the influence of the binary stacking structure is not considered.

[0098] For the second type of binary stacking structure, it is determined whether the elevation corresponding to the vertical failure degree of the predicted barrier dam is less than the elevation of the bottom top surface. If so, a value between the vertical failure degree and 2 / 3 of the dam height is selected as the re-determined vertical failure degree. Otherwise, the influence of the binary stacking structure is not considered. This is because the bottom of the dam body is mainly composed of fine particles. Under small flow, the bottom dam body sinks seriously. At the same time, because the dam body material composed of coarse particles at the top has poor adhesion and collapses seriously, a large amount of coarse particles will be deposited at the downstream dam site. Compared with the nearly half-broken homogeneous dam body, the fine particles at the bottom of this type of dam body have weak anti-scouring properties, and the degree of cutting will be greater than 1 / 2 failure. However, due to the silting of coarse particles near the dam axis, it is difficult to start, so the vertical failure degree of this type of dam body does not exceed 2 / 3 of the dam height.

[0099] For the three-component stacking structure, it is determined whether the elevation corresponding to the vertical failure degree of the predicted barrier dam is less than the elevation of the top surface of the bottom layer. If so, the ratio of the height of the top layer to the middle layer and the height of the dam is used as the re-determined vertical failure degree. Otherwise, the influence of the three-component stacking structure is not considered. Through the above method, the influence of the special dam structure of the binary stacking structure and the three-component stacking structure on the vertical failure degree can be avoided, and the accuracy of the determination of the vertical failure degree can be further improved.

[0100] Based on the above scheme, this embodiment can also realize the prediction of the breach top width and breach bottom width after the predicted dam burst.

[0101] It can be understood that considering that breach scouring is a process in which the soil is first eroded and then collapsed, and the collapsed soil is washed away by the discharged water, this embodiment establishes a sediment transport balance formula under the final state of breach. When the vertical breach degree is less than or equal to 1 / 2 of the dam height, the amount of soil washed away at the end of the dam breach is related to the actual discharged water (related to the widening) and the actual vertical breach depth.

[0102] In addition, landslide dams are mostly found in "V"-shaped rivers. In addition to considering the above parameters, the widening of the dam body with a vertical breach degree greater than 1 / 2 of the dam height is also limited by the river width B.

[0103] In order to obtain the relationship for calculating the breach width when the vertical breach degree is less than or equal to 1 / 2 of the dam height and greater than 1 / 2 of the dam height, this embodiment carries out a series of generalized tests in the figure, converts the test data to the prototype, and combines the collected test data and case data to establish and verify the breach width formula considering multi-scale and multi-type dam bodies. The test data involved are:

[0104] (1) Flow material combination group: 12 fields with incoming flow (1, 3, 5 L / s) and dam material (d50 = 0.18, 0.27, 1 and 1.6 mm), numbered ①②③④, ⑤⑥⑦⑧, ⑨⑩ (2) Variable structure group: 3 test fields, including binary and ternary stacked structures, numbered (3) Variable length-to-height ratio group: 2 test sites, corresponding to groups 2 and 3 in Table 4, numbered (4) Variable dam shape group: 4 test sites, namely "short and fat", "pointy and thin", "steep on top and gentle on the bottom", and "gentle on top and steep on the bottom", numbered (flow 1 L / s, d50 = 0.18 mm); (5) Variable density group: 2 test fields, including dense and loose fields (2.338 g / cm3 and 2.448 g / cm3), numbered (6) Wang Daozheng et al., Shi Zhenming et al. conducted a water tank test and six working conditions including horizontal heterogeneous groups, numbered

[0105] Among them, the dam body failure data with vertical failure degree greater than 1 / 2 dam height are as follows:

[0106]

[0107]

[0108] The dam failure data with vertical failure degree less than or equal to 1 / 2 of the dam height are as follows:

[0109]

[0110] Through the above series of field cases and model test data, it can be deduced that when the vertical failure degree of the predicted dam is less than or equal to 1 / 2 of the dam height:

[0111] b mt E′=13.858W′ 0.4577 H′(R 2 =0.96);

[0112] b mb E′=5.1707W′ 0.4964 H′(R 2 =0.86);

[0113] When the vertical breach degree of the predicted dam is greater than 1 / 2 of the dam height, the calculation formulas for the breach top width and breach bottom width after the predicted dam breach are as follows:

[0114] b mt E′=28.818W′ -0.088 B 1.549 H′;

[0115] b mb E′=6.991W′ 0.357 B 0.406 H′;

[0116] Where b mt is the width of the breach top, b mb is the bottom width of the breach, E′ is the cross-sectional area of ​​the breach, B is the width of the river channel, W′ is the actual downstream storage capacity, and H′ is the vertical breach depth.

[0117] The above conditions The data of the Hebaige 10.10 landslide dam were not used in the derivation of the calculation formula, so the working condition Verified by the data of Hebaige 10.10 landslide dam, the bottom width and top width are 194 and 278m, 104 and 161m respectively, the actual values ​​are 200 and 240m, 100 and 120m, the error is within 13%-25%, and the prediction is relatively safe. When the vertical breach degree, dam size and river topography are known, the above method can basically meet the needs of widening prediction.

[0118] See also Figure 4 After obtaining the above formula, this embodiment specifically predicts the breach widening through the following steps:

[0119] (1) Obtain the slope ratio, length, height and actual discharge capacity of the landslide dam to be predicted;

[0120] (2) Determine the vertical breach depth H′ of the predicted dam according to the vertical breach degree and dam height of the predicted dam, and calculate the breach cross-sectional area E′ of the predicted dam after the dam fails according to the dam body slope ratio, dam length and vertical breach depth H′ of the predicted dam;

[0121] See also Figure 5 The cross-sectional area of ​​the breach E′ is the cross-sectional projection area of ​​the breach, that is, the cross-sectional area of ​​the dam that has been washed away. In this embodiment, it is approximately regarded as a trapezoid and is calculated through the slope ratio of the dam body, the dam length and the vertical breach depth H′.

[0122] (3) Calculate the top width and bottom width of the breach of the predicted landslide dam after it fails based on the breach cross-sectional area of ​​the predicted landslide dam, the actual downstream storage capacity and the vertical breach depth.

[0123] In this embodiment, when the vertical breach degree of the barrier dam to be predicted is less than or equal to 1 / 2 of the dam height, the breach cross-sectional area, the actual downstream storage capacity and the vertical breach depth are input into the corresponding calculation formula to calculate the breach top width and breach bottom width. When the vertical breach degree of the barrier dam to be predicted is greater than 1 / 2 of the dam height, the breach cross-sectional area, the actual downstream storage capacity, the river width and the vertical breach depth are input into the corresponding calculation formula to calculate the breach top width and breach bottom width.

[0124] In summary, the method for predicting the breach morphology of a dam based on case statistics and the breach process described in this embodiment provides a prediction method for the vertical breach degree and lateral width (top width, bottom width) of the dam based on the case analysis results and the law of the breach process, which has good prediction accuracy, and the required parameters are all parameters that are easy and quick to obtain on site, which can meet the requirements of rapid judgment of the breach size (especially the vertical cutting depth) during emergency rescue, and can also provide effective references for the calculation of the assumed parameter type flood peak model and the removal of risks by on-site decision makers. And through the breach case and based on correlation analysis, contingency cross analysis and breach process analysis, the key parameters for predicting the vertical breach degree are screened, which improves the accuracy of the key parameter screening, and thus improves the accuracy of the vertical breach degree prediction. And according to the key parameters of the breach case, an expression is constructed, and based on the expression, it can accurately predict whether the vertical breach degree of the dam is greater than 1 / 2 of the dam height. For special dams, the vertical breach degree of the dam is further determined by the dam body material, slope ratio and dam body structure, which further improves the accuracy of the vertical breach degree prediction. In addition, the breach width of the landslide dam is calculated according to the predicted vertical breach degree and the formula created based on case analysis. When the vertical breach degree is greater than 1 / 2 of the dam height, the parameter river width is introduced to improve the accuracy of the breach width prediction.

Claims

1. A method for predicting the breach morphology of a dam based on case statistics and breach process, characterized in that: The method comprises: Obtaining natural breach cases in the case library and the basic parameters and vertical breach degrees corresponding to each breach case, wherein the basic parameters include: dam height, dam length, length-to-height ratio, dam volume, dam material composition, upstream flow and reservoir capacity data; Classify the basic parameters and vertical failure degree, and determine the key parameters affecting the vertical failure degree from the basic parameters based on correlation analysis, contingency cross analysis and failure process analysis; The vertical failure degree is divided into two categories, which are less than or equal to 1 / 2 of the dam height and greater than 1 / 2 of the dam height. According to the key parameters and vertical failure degree of each failure case, an expression for calculating the probability of the vertical failure degree being greater than 1 / 2 of the dam height is constructed based on logistic regression analysis. Obtaining key parameters of the landslide dam to be predicted, and determining whether the vertical breach degree of the landslide dam to be predicted is greater than 1 / 2 of the dam height according to the category of the key parameters of the landslide dam to be predicted and based on the expression; The method further comprises: When it is determined that the vertical failure degree of the predicted landslide dam is greater than 1 / 2 of the dam height, it is determined whether the dam body material is composed of loess and clay. If so, the dam height is used as the vertical failure degree of the predicted landslide dam. Otherwise, 2 / 3 of the dam height, 3 / 4 of the dam height or 3 / 5 of the dam height is used as the vertical failure degree of the predicted landslide dam.

2. The method for predicting the breach morphology of a dam based on case statistics and breach process according to claim 1, characterized in that: The expression used to calculate the probability that the vertical failure degree is greater than 1 / 2 of the dam height is as follows: Where p is the probability that the vertical failure degree is greater than 1 / 2 of the dam height, β0 is a constant term, and β1, β2, …, β n are partial regression coefficients, x1, x2, …, x n The category of the key parameter.

3. The method for predicting the breach morphology of a dam based on case statistics and breach process as claimed in claim 2, characterized in that: The key parameters are the aspect ratio and the dam material. The expression for calculating the probability that the vertical breach degree is greater than 1 / 2 of the dam height is as follows: Where x1 is the category of dam material, and x2 is the category of aspect ratio.

4. The method for predicting the breach morphology of a dam based on case statistics and breach process according to claim 1, characterized in that: The method further comprises: When it is determined that the vertical failure degree of the predicted landslide dam is not greater than 1 / 2 of the dam height, the slope ratio of the predicted landslide dam is obtained. If the slope ratio is within a first preset range, 1 / 3 of the dam height is used as the vertical failure degree of the predicted landslide dam. If the slope ratio is within a second preset range, 1 / 2 of the dam height is used as the vertical failure degree of the predicted landslide dam.

5. The method for predicting the breach morphology of a dam based on case statistics and breach process as claimed in claim 4, characterized in that: The method further comprises: When the landslide dam to be predicted is a binary stacked structure or a ternary stacked structure, the elevation of the top surface of the bottom layer of the binary stacked structure or the ternary stacked structure is obtained, and it is determined whether the elevation corresponding to the vertical breach degree of the landslide dam to be predicted is less than the elevation of the top surface of the bottom layer. If so, the vertical breach degree of the landslide dam to be predicted is re-determined.

6. The method for predicting the breach morphology of a dam based on case statistics and breach process according to claim 5, characterized in that: The re-determination of the vertical failure degree of the landslide dam to be predicted specifically includes: If the bottom layer of the binary stack structure is composed of intact rock layers and the top layer is composed of broken soil and rocks or isolated pieces of broken rocks, the ratio of the height of the top layer to the dam height shall be used as the re-determined vertical failure degree; If the bottom layer of the binary stacked structure is composed of broken rock and soil, and the top layer is composed of isolated broken rocks, a value between the vertical failure degree and 2 / 3 of the dam height is selected as the re-determined vertical failure degree; If the bottom layer of the ternary stack structure is composed of complete rock layers, the middle layer is composed of isolated pieces of gravel, and the top layer is composed of broken stones and soil, then the ratio of the height of the top layer to the middle layer and the height of the dam will be used as the re-determined vertical failure degree.

7. The method for predicting the breach morphology of a dam based on case statistics and breach process according to claim 6, characterized in that: The method further comprises: Obtain the slope ratio, length, height and actual discharge capacity of the landslide dam to be predicted; Determine the vertical breach depth of the predicted dam according to the vertical breach degree and dam height of the predicted dam, and calculate the breach cross-sectional area of ​​the predicted dam after the dam is breached according to the dam body slope ratio, dam length and vertical breach depth of the predicted dam; The breach top width and breach bottom width of the predicted dam after its breach are calculated based on the breach cross-sectional area of ​​the predicted dam, the actual downstream storage capacity and the vertical breach depth.

8. The method for predicting the breach morphology of a dam based on case statistics and breach process according to claim 7, characterized in that: When the vertical breach degree of the predicted dam is less than or equal to 1 / 2 of the dam height, the calculation formulas for the breach top width and breach bottom width after the predicted dam breach are as follows: b mt E′=13.858W′ 0.4577 H′(R 2 =0.96); b mb E′=5.1707W′ 0.4964 H′(R 2 =0.86); Where b mt is the width of the breach top, b mb is the bottom width of the breach, E′ is the cross-sectional area of ​​the breach, W′ is the actual downstream storage capacity, and H′ is the vertical breach depth.

9. The method for predicting the breach morphology of a dam based on case statistics and breach process according to claim 7, characterized in that: When the vertical breach degree of the predicted dam is greater than 1 / 2 of the dam height, the calculation formulas for the breach top width and breach bottom width after the predicted dam breach are as follows: b mt E′=28.818W′ -0.088 B 1.549 H′; b mb E′=6.991W′ 0.357 B 0.406 H′; Where b mt is the width of the breach top, b mb is the bottom width of the breach, E′ is the cross-sectional area of ​​the breach, B is the width of the river channel, W′ is the actual downstream storage capacity, and H′ is the vertical breach depth.

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