CN117494478A - Calculation method for simulating over-roof dam break flow and break evolution process of core dam - Google Patents
Calculation method for simulating over-roof dam break flow and break evolution process of core dam Download PDFInfo
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Abstract
The invention discloses a calculation method for simulating the over-roof dam break flow and the break evolution process of a core wall dam, which comprises the steps of determining calculation parameters, setting time steps, calculating the break flow, dam break characteristics, the elevation of the bottom of a break, core wall stress analysis, calculating the exposed length of the core wall, the top width of the break, the bottom width of the break and the like of each time step; the invention establishes a calculating method for the over-roof dam break process of the core wall dam, which can simulate the break-out flow and the break-out state evolution, based on the dam break mechanism of the core wall dam. The calculating method considers the erosion process of dam shell materials and the evolution of the collapse form in the dam break process, simulates the stress state of the core wall based on the combined action of upstream water and soil pressure, judges whether the exposed core wall is damaged or not through a moment balance analysis method, determines the exposed length and the number of times of breakage of the core wall, and the calculating result is more in accordance with the actual dam break process.
Description
Technical Field
The invention belongs to the technical field of hydraulic engineering dam break calculation, and particularly relates to a calculation method for simulating the flow of a core wall dam overtopping dam break and the evolution process of a break.
Background
The core wall dam is a common earth-rock dam type, and is widely constructed by using sand and stone materials with better water permeability as a dam shell and soil with better seepage resistance as a seepage-proofing core wall. The dam-break mechanism of the core wall dam is not clear, and the recognition of the dam-break process of the core wall dam is insufficient, so that the method provides a great obstacle for emergency rescue and relief work of the core wall dam.
For understanding the dam break mechanism of the core wall dam, the model test is limited by the field and the reduced scale similarity ratio, the dam break process of the core wall dam cannot be completely restored, and the obtained result is inconsistent with the actual situation. The dam break process of the core wall dam can be well restored by adopting the mathematical model to calculate, the stress and damage condition of the core wall dam can be completely restored, and a low-cost and high-efficiency research means is provided for researching the dam break mechanism of the core wall dam, as in the prior art: zhong Qiming et al [ J ]. Chinese science, 2017, 47 (9): 992-100. Consider the clay core dam overtopping dam break process mathematical model of different damage modes of the core, consider the core under the effect of overtopping rivers, the toppling damage and shearing damage of the core, but do not consider the development process of the core break before breaking, do not consider the exposed length and damage times of the core in this document, this is inconsistent with actual dam break process. The development process and trend of the flow rate of the breach and the top and bottom width of the breach are inconsistent with the actual situation, the actual dam break process cannot be well indicated, and the dam break flow rate and the dam break development process cannot be accurately calculated.
Disclosure of Invention
Aiming at the problems that the prior art does not consider the exposed length and the damage times before the core wall is broken, the actual dam break process cannot be well indicated, the dam break flow and the dam break development process cannot be accurately calculated, the invention provides a dam break calculation method considering the real-time stress state of the core wall, and the model adopts a numerical calculation method of time step iteration.
The technical scheme of the invention is as follows:
a calculation method for simulating the flow rate of a core dam overtopping dam break and the evolution process of a break opening of the core dam mainly comprises three parts: calculating the flow of a breach, calculating dam-break characteristics of a dam body and analyzing stress of a core wall, and specifically comprising the following steps:
and step 1, determining calculation parameters including a core wall dam body characteristic parameter, a core wall characteristic parameter, an upstream water level-reservoir surface area relation curve, a time-inflow curve and a time-outflow curve.
The dam characteristic parameters comprise: the dam body height, the dam body top width, the dam axis length, the upstream dam slope ratio, the downstream dam slope ratio and the dam shell material characteristic parameters comprise the dam shell material cohesive force, the dam shell material internal friction angle, the dam shell material erosion coefficient and the like. The core wall characteristic parameters include: core material cohesion, core height, core top width, upstream slope ratio, downstream slope ratio and relative distance between dam axis and core.
Step 2, setting a time step, calculating the crumple flow of each time step, wherein the time step can be adjusted as required and can be 1s or 2s, and the method specifically comprises the following steps:
and 2.1, assigning values to main feature points of the dam body according to the design data of the initial form, and simultaneously reading the design data such as a time-inflow array, an upstream water level-reservoir area, a time-outflow array and the like.
The main characteristic points of the dam body comprise: the water level, the height, the upstream dam toe position, the upstream dam abutment position, the downstream dam toe position, the upstream core wall dam abutment position, the downstream core wall dam abutment position and the downstream core wall dam toe position of the reservoir.
Step 2.2, calculating the elevation change of the water level of the upstream water reservoir according to the time-inflow array, and considering the warehouse-in flow, the breach flow and the spillway drainage flow:
in the method, in the process of the invention,A s the area of the reservoir surface is;z s is the reservoir water level;ttime is;Q in for the warehouse-in flow, the time-incoming flow array is used for the incoming flow corresponding to each momentQ in Is designed and regulated;Q b is the flow of the crumple;Q spill and the spillway is the spillway drainage flow, and the drainage value corresponding to each moment in the time-drainage array is the drainage value.
Step 2.3, if the water level of the upstream reservoir is smaller than or equal to the elevation of the bottom of the crumple, calculating after skipping, and calculating the water level elevation of the upstream inflow and reservoir in the next time step; if the water level of the upstream water reservoir is higher than the water level of the downstream water at Cheng Ju at the bottom of the crumple, calculating the crumple flow rate by adopting a wide top weir flow formula:
in the method, in the process of the invention,bthe bottom width of the crumple is calculated by a formula (19);Hfor the depth of water at the position of the crumple,H=z s -z b each time is calculated, whereinz b For the elevation of the bottom of the crumple,z s is the reservoir water level;mthe slope ratio (horizontal/vertical) of the side slope of the breach is a planned value;c 1 、c 2 for correction coefficient, selectc 1 =1.7m 0.5 /s，c 2 =1.1m 0.5 /s；k sm For the tailwater flooding correction factor, it can be calculated by the following formula:
wherein:z t is the tail water height.
Calculating the bottom elevation change of the crumple at each time t by using the formula (13) or the formula (7), and subtracting the bottom elevation change of the crumple at the unit time from the existing elevation to obtain the bottom elevation of the crumple at the new time.
Step 3, calculating dam break characteristics of the dam body in each time step, including calculating the elevation of the bottom of the breach;
the dam tops and downstream slopes are subject to erosion due to the water flow at the breach.
If the dam shell material is cohesive soil, the slope at the initial pit flushing position becomes steep, and the downstream dam slope angle is changed from the initial slope angleβGradually changing into internal friction angle of dam shell materialφ 1 。
The erosion rate for the dam top shell material can be calculated by the following formula:
in the method, in the process of the invention,Eis the erosion rate;k d for erosion coefficients, the erosion coefficients are usually measured through experiments or are obtained by adopting an empirical formula;τ b is the shear stress of water flow;τ c the critical shear stress of the dam material can be determined by a Hiltz curve. Wherein,τ b and (3) withk d The calculation formula is as follows:
in the method, in the process of the invention,ρ w is the density of water;nis Manning coefficient;Rthe hydraulic radius of the ulcer is set;A w is the water flow area. The hydraulic radius and the water flow area at the crumple are calculated by the existing formula.
In the method, in the process of the invention,ρ d the soil body dry density;c% is the cosmid content.
The erosion rate of the shell material of the breach dam in unit time is the change of the elevation of the bottom of the breach:
the downstream slope angle reaches the internal friction angle of the dam shell materialφ 1 And under the action of dam-break water flow, tracing flushing continuously develops to the core wall at the upstream, and assuming that the downstream slope keeps an internal friction angle, wherein the internal friction angle is the critical maximum angle of soil. The traceable flushing process of the dam hull material can be represented by the following steps:
in the method, in the process of the invention,C T is a trace-source scouring coefficient,qIs a single wide flow rate of a bursting orifice,H e The three parameters can be obtained according to the existing formula for the water flow height.
If the dam shell material is non-cohesive soil, the erosion amount is as follows:
in the method, in the process of the invention,V b the erosion volume of the dam shell material by the dam-break water flow is,x db downstream of the crumplexThe direction is set to be at the initial position,x ub upstream of the crumplexThe direction end position is set to be at a position,Eobtained according to formula (4)，bObtained according to the formula (19),x db andx ub obtaining according to the depth of the crumple;n loc indicating the position of the crumple opening,n loc =1 indicates a single-sided erosion,n loc =2 indicates double sided erosion.
Calculating the area of the bottom surface of the crumple:
in the method, in the process of the invention,bis provided with a wide bottom for the crumple.
Calculating the projection area of the crumple slope on the xz plane:
the side slope of the crumple is atxzThe plane projection comprises three parts, wherein the first part is the projection of a downstream breach slope, the area is the product of the difference between the downstream end point of the breach and the breach dam abutment and the depth of the breach,x downbrink as a downstream end point of the crumple,x downcorner is a downstream position of the dam abutment; the second part is the product of the difference between the height of the core wall dam and the height of the bottom of the crumple and the width of the top of the core wall dam,his the height of the core wall dam,z b for the elevation of the bottom of the crumple,Btthe width of the top of the core wall; the third part is the product of the difference between the upstream dam abutment of the core wall dam and the upstream starting point of the breach and the difference between the height of the core wall dam and the height of the bottom of the breach,x upcorner is the upstream position of the dam abutment,x upbrink is the upstream origin of the crumple.
The total area of the crumple is:
the height variation of the bottom of the crumple is as follows:
on the basis of considering the stress of the core wall dam, the invention considers the exposed length and the stress of the core wall after the downstream dam shell material is washed, calculates the damage length and the number of times when the core wall is broken, and considers the development mode of the break before the core wall is broken. Before the core wall breaks, the bottom of the downstream dam shell material is brushed by water flow, so that the upper dam shell material is suspended, and the crumple is trapezoid. The dam shell material of the suspended part is acted by gravity and cohesive force, and when the cohesive force is insufficient to support the gravity of the suspended part, the dam shell material of the suspended part is sheared and damaged.
And 4, performing core wall stress analysis in each time step, wherein the core wall stress analysis comprises calculation of the exposed length of the core wall, the damage times of the core wall, the top width of a crumple opening, the bottom width of the crumple opening and the like.
The breach at the dam axis is continuously developed under the effect of water flow erosion, and before the heart wall collapses, the bottom of the downstream dam shell material is brushed by water flow, so that the upper dam shell material is suspended, and the breach is trapezoid. The dam shell material of the suspended part is acted by gravity and cohesive force, when the cohesive force is insufficient to support the gravity action of the suspended part, the dam shell material of the suspended part is sheared and damaged, and the cohesive force and the gravity can be respectively expressed as:
in the middle of，F C In order to suspend the adhesive force of the dam shell material,Cthe unit cohesive force of the dam shell material is obtained,F G for suspending the gravity of the dam shell material,lfor the length of the dam shell material of the suspended part,h l for the height of the side slope of the suspended part,γ s is the volume weight of the dam shell material,pin order for the porosity to be the same,Bin order to ensure that the top width of the crumple opening is wide,bis provided with a wide bottom for the crumple.
lThe value of (2) can be half the difference between the top width of the crumple and the bottom width of the crumple,h 1 the value of (2) may be taken as the vent height.
After the core wall is damaged, the erosion of the flood peak water flow enables the crumple to be inverted trapezoid, and the development increment of the crumple peak width and the crumple bottom width can be expressed as:
in the middle of，φ 1 Is the internal friction angle of the slope angle dam shell material at the breaking opening.
Then the firstnThe secondary calculation of the roof and floor widths of the crumple zones can be expressed as:
in the method, in the process of the invention,B n represent the firstnThe top width of the crumple opening calculated by the time,B n-1 represent the firstn-1The top width of the crumple obtained by the secondary calculation,b n represent the firstnThe bottom width of the crumple opening calculated by the time,b n-1 represent the firstn-1The bottom width of the crumple obtained by the secondary calculation.
After erosion of the dam shell material, the core wall is exposed, and the exposed length of the core wall is calculated by the following formula:
in the middle of，h k To destroy the height of the core wall;x down downstream of exposed core wallxThe end point of the terminal is,x core downstream of the core wall dam abutmentxThe end point of the direction is defined by the angle,z b for the elevation of the bottom of the crumple,z down the exposed part of the bottom elevation of the downstream core wall. Can be linearly calculated according to the downstream slope ratio of the core wallx down 、x core 、z b Andz down。
for the possible damage of the core wall, a moment balance method is adopted for analysis. The exposed part of the core wall is subjected to upstream water and soil pressure, and the moment is as follows:
wherein:F s for water flow from the top of the bursting mouthShear force applied to the top of the core wall;F w the water pressure acting on the heart wall for the reservoir water;F e soil pressure acting on the core wall for upstream dam shell material;h r the height of the reservoir water level from the broken surface of the core wall.
Moment of resistance force acting on broken face of core wallM r Can be expressed as:
wherein:A t to destroy the cross-sectional area of the core wall;C 2 is the cohesive force of clay core wall;Wthe weight of the core wall above the damaged surface is calculated;L 2 the width of the bottom of the broken surface of the core wall is the width. Wherein,A t and (3) withWCan be expressed as:
in the method, in the process of the invention,L 1 the width of the top of the broken surface of the core wall is the porosity of the core wall material.
According to the pressure and resistance of the upstream water and soil on the core wall, the critical judgment conditions for the damage are as follows:
analyzing the stress state of the exposed core wall, if the damage moment is larger than the resisting moment, the exposed core wall is damaged, and the exposed length of the core wall is damagedl core The damage length is obtained, and the damage times of the core wall are updated.
TThe number of core wall failures.
In the process of program calculation, after damage, the bottom elevation of the breach, the top width of the breach, the bottom width of the breach, the flow rate of the breach and dam characteristic data are updated in an iterative mode.
The invention has the beneficial effects that:
the invention establishes a calculating method for the over-roof dam break process of the core wall dam, which can simulate the break-out flow and the break-out state evolution, based on the dam break mechanism of the core wall dam. The model considers the erosion process of dam shell materials and the evolution of the form of a breach in the dam break process, simulates the stress state of the core wall based on the combined action of upstream water and soil pressure, judges whether the exposed core wall is damaged or not through moment balance analysis, determines the breaking moment, the breaking length and the breaking times of the exposed core wall, and the calculation result is more in accordance with the actual dam break process.
Drawings
FIG. 1 shows the parameters of main feature points of the initial form of a dam body;
FIG. 2 shows a schematic diagram of dam crest and downstream slope erosion;
FIG. 3 shows the development of a breach at the dam axis;
FIG. 4 shows a schematic representation of a core failure;
FIG. 5 is a graph of calculated dam break flow rate of the moon pool reservoir;
FIG. 6 is a calculation curve of the development process of the reservoir breach size of the lunar rover;
fig. 7 compares the calculated breach flow rate for the prior art procedure with the procedure of the present method.
Detailed Description
The technical scheme of the invention is further described below with reference to the accompanying drawings and specific embodiments.
Example 1: the method is programmed through a computer language, a dam break case of the core wall dam of the lunar rover reservoir is selected, and calculation and analysis are carried out on the dam break process of the lunar rover.
The specific calculation process comprises the following steps:
and step 1, inputting dam characteristic parameters and core wall characteristic parameters, and inputting corresponding time-incoming flow arrays, water level-reservoir area and time-leakage flow arrays according to water level and time.
The dam body characteristic parameters and the core wall characteristic parameters of the jet moon ditch reservoir are shown in table 1.
TABLE 1 reservoir characterization parameters for jet moon furrows
The moon shoot ditch is an asphalt concrete upright core wall, and the width of the top of the core wall is the thickness of the core wall in Table 1. The data of the time-incoming flow array, the water level-warehouse surface area and the time-discharging flow array are hydropower station management data.
The program carries out iterative computation according to the input parameters, specifically:
step 2, calculating the crumple flow of each time step, wherein the time step is 1s in the embodiment; the method specifically comprises the following steps:
the program reads the input data and assigns values to the main characteristic points of the initial form of the dam body (initial values of the corresponding characteristic points in the dam body in the initial state are input), and the main characteristic points are shown in fig. 1. The feature points prescribe the initial form of the dam body in program calculation, and have important roles in the evolution of a breach, flow calculation, core wall stress analysis and damage in the dam break process. The meaning of each parameter in fig. 1 is shown in table 2.
TABLE 2 Main characteristic points of dam
In each time step, iterative operation is carried out according to the input time-incoming flow array, and upstream incoming flow causes upstream water level to rise before water flow overtakes. When the water level of the upstream reservoir is higher than the dam crest elevation, water flows are overturned, and the breach flow is calculated according to formulas (1) - (3).
Step 3, calculating dam break characteristics of the dam body in each time step, including calculating the elevation of the bottom of the breach;
the top and downstream slopes of the dam are subject to erosion due to the water flow at the breach, as shown in fig. 2. After the upstream water flows to flood the top, the downstream dam slope angle is flushed by the water flow, and the downstream dam slope angle is formed by the initial slope angleβGradually changing into internal friction angle of dam shell materialφ 1 . And (3) calculating the elevation change quantity of the bottom of the breach after the dam body is flushed by water flow according to the formulas (4) - (13).
Upstream erosion of downstream dam shell material is developed until the core wall is exposed.
Step 4, analyzing the stress of the core wall in each time step, and calculating the exposed length of the core wall, the damage times of the core wall, the top width of the crumple opening and the bottom width of the crumple opening;
after the core wall is damaged, the erosion of the flood peak water flow causes the crumple to be inverted trapezoid, and the development process of the crumple is shown in figure 3.
After the dam shell material is washed out, the core wall is exposed, as shown in fig. 4, the exposed length of the core wall is expressed by a formula (20), and the analysis is carried out by adopting a moment balance method according to the exposed length of the core wall. The upstream breaking moment mainly consists of shear force of the water flow on the top of the core wall when the breach overturns, water pressure of the reservoir water on the core wall and soil pressure of the core wall when the upstream dam shell material acts on the core wall, and the core wall resisting moment is expressed by a formula (22).
According to the stress analysis of the exposed core wall, if the damage moment is larger than the resisting moment, the exposed core wall is damaged, and after the damage, the bottom elevation of the crumple opening, the crumple opening width, the crumple opening flow, the damage length of the core wall and the dam body characteristic data are iteratively updated, and meanwhile, the damage times of the core wall are correspondingly increased.
When the program calculation time reaches the set time steps, the program calculation is stopped, and a result file is output, wherein the file contains the calculation data result of each time step.
According to the output result, the flow curve of the breach of the lunar injection reservoir is shown in fig. 5, and the development process of the breach is shown in fig. 6. The comparison between the procedure of the prior art and the procedure of the new procedure in the method in the background art is shown in fig. 7, and as can be seen from fig. 7, the twice flow of the new procedure is increased, because the new procedure considers that the core wall is broken after being exposed, the method considers that the core wall can still play the roles of retaining soil and water after being exposed, and the method is more in line with the actual situation. Under the action of the upstream water and soil pressure, the core wall is suddenly destroyed, the flow of the breach is suddenly increased, and the calculated flow is suddenly increased due to the huge upstream water head, so that the calculation result is more in line with the actual dam-break flow process. The peak flow calculated by the new program is 6851.5 m 3 In-situ measured peak flow rate of 6700.0 m for reservoir dam break in lunar injection 3 And/s, the relative error between the dam break peak flow calculated by the program is 2.2%, and the data is more similar to the actual flow.
Example 2: and performing dam-break water tank inversion test according to the dam-break parameters, comparing the program calculation result with the test result, and simultaneously comparing the program calculation result with the dam-break flow actually measured on the dam-break site of the jet moon ditch.
The equipment and the method for dam-break water tank inversion test are in the prior art, the test equipment is not shown in the embodiment, and the test method is simply described in combination with the test process for showing the test process.
And step 1, determining water tank test parameters.
The water tank erosion equipment adopted in the test mainly comprises a water supply system, a slope-changing water tank and a tail water system. The water tank is 1 m in height, 0.3 m in width and 6 m in length, is connected with a water supply system through a PVC pipe with the inner diameter of 50 mm, continuously supplies water by an electromagnetic flowmeter, and is provided with a check valve to prevent backflow caused by water pressure when the model stores water. Toughened glass is arranged on two sides of the water tank, so that the observation of test phenomena is convenient.
Model parameters were determined based on the sink dimensions, see table 3.
TABLE 3 model test parameter settings
And 2, determining a water tank test dam material, and building a mold in the water tank.
And (3) scaling by taking the on-site sampling grading of the jet moon ditch reservoir dam as a standard, wherein the maximum test particle size is 20 mm, and obtaining the model test dam material grading by an equivalent substitution method.
The dam material is divided into 5 particle size groups after being completely aired and dried, wherein the particle size groups are respectively smaller than 1 mm, 1-5 mm, 5-10 mm and 10-20 mm. The specific gravity of the soil material is 2.73, the initial water content is 5%, the compaction hammer is adopted for layered compaction, the model compactness is 86.9%, and the porosity is 27%. In order to facilitate observation of the development process of the test, an initial inverted trapezoid crumple is formed on the side of the toughened glass, the top width of the crumple is 50 mm, the bottom width is 30 mm, and the crumple height is 40 mm.
And step 3, starting the test according to the steps.
The test is carried out sequentially according to the following steps:
(1) Installing and fixing a pore pressure sensor at the upstream dam toe, connecting a data acquisition system, and installing and fixing a camera at one side of the model provided with a crumple;
(2) The data acquisition system, the water pump and the electromagnetic flowmeter are turned on, the water supply system constantly flows at a flow rate of 0.83L/s, the water pump is turned off to saturate the upstream dam body when the upstream water storage level is reached, and then the water pump is turned on to start a test;
(3) And when the dam body is not damaged any more, the data measured by the pore pressure sensor is stably regarded as the end of the test, the water supply system and the data acquisition system are closed, the test data are stored, the model dam body after the test is recorded, and the water tank is cleaned.
And 4, converting the flow measured by the test according to the similar proportion to obtain the dam break test flow of the dam break case of the lunar discharge reservoir, and comparing the dam break test flow with the calculated value of the program calculated output parameter.
The dam break flow measured by the test is similarly converted to 6169.87 m 3 Program calculates the dam break peak flow as 6851.5 m 3 And/s, the relative error between the test result and the program calculated dam break peak flow is-9.9%, and is within 10%; the measured peak flow rate of the dam break site of the jet moon ditch reservoir is 6700.0 m 3 And/s, the relative error between the dam break peak flow calculated by the program is 2.2%, and the program calculation result is proved to have higher reliability.
The invention considers the broken core wall, and calculates the change values of several parameters compared with the prior art, such as: the exposed length of the core wall, the damage length of the core wall and the damage times of the core wall cannot be known by the prior literature method. The development mode of the crumple is that the positive trapezoid before the heart wall is broken is developed into the inverted trapezoid after the heart wall is broken. In the prior art, the development of the crumple opening is in an inverted trapezoid from beginning to end, so that the development mode of the crumple opening is more truly simulated, and the development mode is more similar to the actual situation.
Claims (5)
1. A calculation method for simulating the flow rate of a core dam overtopping dam break and the evolution process of a break opening is characterized by comprising the following steps:
step 1, determining calculation parameters including a core dam body characteristic parameter, a core wall characteristic parameter, an upstream water level-reservoir surface area relation curve, a time-inflow curve and a time-outflow curve;
step 2, setting time steps, and calculating the crumple opening flow of each time step, wherein the method specifically comprises the following steps:
step 2.1, assigning values to main feature points of the dam body according to design data of an initial form, and simultaneously reading design data of a time-inflow array, an upstream water level-reservoir area and a time-outflow array;
step 2.2, calculating the elevation change of the water level of the upstream water reservoir according to the time-incoming flow array, wherein the calculation formula is as follows:
in the method, in the process of the invention,A s the area of the reservoir surface is;z s is the reservoir water level;ttime is;Q in the flow is the flow value corresponding to each moment in the time-flow array;Q b is the flow of the crumple;Q spill the spillway is used for discharging flow, and the flow discharge value corresponding to each moment in the time-flow discharge array is used for discharging flow;
step 2.3, if the water level of the upstream reservoir is smaller than or equal to the elevation of the bottom of the crumple, calculating after skipping, and calculating the water level elevation of the upstream inflow and reservoir in the next time step; if the water level of the upstream water reservoir is higher than the water level of the downstream water at Cheng Ju, calculating the flow rate of the crumple by adopting a wide top weir flow formula, wherein the calculation formula is as follows:
in the method, in the process of the invention,bthe bottom of the ulcer is wide;Hfor the depth of water at the position of the crumple,H=z s -z b whereinz b For the elevation of the bottom of the crumple,z s is the reservoir water level; mthe slope ratio of the side slope of the breach is a formulated value;c 1 、c 2 for correction coefficient, selectc 1 =1.7m 0.5 /s，c 2 =1.1m 0.5 /s；k sm For the tailwater flooding correction coefficient, it is calculated by the following formula:
wherein:z t is the tail water height;
step 3, calculating dam break characteristics of the dam body in each time step, including calculating the elevation of the bottom of the breach;
if the dam shell material is cohesive soil, the erosion rate of the dam shell material is determined in unit time by the change of the elevation of the bottom of the breach:
if the dam shell material is non-cohesive soil, the height variation of the bottom of the breach is as follows:
in the method, in the process of the invention,Eis the erosion rate;V b the dam shell material is washed and eroded by dam break water flow;Sthe total area of the crumple is;
the bottom elevation of the crumple at a certain moment is obtained by subtracting the variation of the bottom elevation of the crumple between the moment and the last moment from the bottom elevation of the crumple at the last moment;
step 4, core wall stress analysis in each time step comprises calculating the exposed length of the core wall, the top width of the crumple opening and the bottom width of the crumple opening;
the exposed length of the core wall is calculated by the following formula:
in the middle of， x down Downstream of exposed core wallxThe end point of the terminal is,x core downstream of the core wall dam abutmentxThe end point of the direction is defined by the angle,z b for the elevation of the bottom of the crumple,z down exposing part of the bottom elevation for the downstream core wall;
the incremental development of the base width of the crumple is expressed as:
the incremental development of the roof width of the crumple is expressed as:
in the middle of，φ 1 The internal friction angle of the slope angle dam shell material at the position of the crumple is the elevation variation of the bottom of the crumple;n loc indicating the position of the crumple;
then the firstnThe secondary calculation of the roof and floor widths of the crumple zones can be expressed as:
in the method, in the process of the invention,B n represent the firstnThe top width of the crumple opening calculated by the time, B n-1 represent the firstn-1The top width of the crumple obtained by the secondary calculation,b n represent the firstnThe bottom width of the crumple opening calculated by the time,b n-1 represent the firstn-1The bottom width of the crumple obtained by the secondary calculation.
2. The method for calculating the flow rate and the break evolution process of the over-roof dam break of the core dam according to claim 1, wherein the dam body characteristic parameters in the step 1 include: dam height, dam length, dam top width, dam axis length, upstream dam slope ratio, downstream dam slope ratio, dam shell material cohesive force, dam shell material internal friction angle and dam shell material erosion coefficient; the core wall characteristic parameters include: core material cohesion, core height, core top width, upstream slope ratio, downstream slope ratio and dam axis and core relative distance.
3. The method for calculating the flow rate and the break evolution process of the over-roof dam break of the core dam according to claim 1, wherein the main characteristic points of the dam body in the step 2.1 comprise: the water level, the height, the upstream dam toe position, the upstream dam abutment position, the downstream dam toe position, the upstream core wall dam abutment position, the downstream core wall dam abutment position and the downstream core wall dam toe position of the reservoir.
4. The method for calculating the flow rate and the evolution process of the breach for the overtopping of the core dam according to claim 1, wherein in the step 3, the dam shell material is eroded by the flow of the breaching waterV b The calculation formula is as follows:
in the method, in the process of the invention,V b the erosion volume of the dam shell material by the dam-break water flow is,x db downstream of the crumplexThe direction is set to be at the initial position,x ub upstream of the crumplexThe direction end position is set to be at a position,Eis the erosion rate of the dam shell material,bfor the purpose of wide bottom of the crumple,x db andx ub obtaining according to the depth of the crumple;n loc indicating the position of the crumple opening,n loc =1 indicates a single-sided erosion,n loc =2 represents double sided erosion; Rthe hydraulic radius of the ulcer is set;A w is the water flow area.
5. The method for calculating the flow rate and the evolution process of the breach for simulating the overtopping of the core dam according to claim 1, wherein the total area of the breach in the step 3 is as followsSThe calculation formula is as follows:
area of bottom surface of crumpleS b The calculation formula is as follows:
in the method, in the process of the invention,bthe bottom of the ulcer is wide;
projection area of crumple slope on xz planeS s Calculation formulaThe method comprises the following steps:
wherein:his the height of the core wall dam,z b for the elevation of the bottom of the crumple,x downbrink as a downstream end point of the crumple,x downcorner is a downstream position of the dam abutment, Btis the width of the top of the core wall dam,x upcorner is the upstream position of the dam abutment,x upbrink is the upstream origin of the crumple. />
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