Optimization design method for length of tunnel plug during main flood season of super-high dam construction

Abstract

The present application relates to the technical field of water conservancy and hydropower engineering construction, and discloses a method for optimizing the length of a tunnel plug during the main flood season of the construction of an ultra-high dam, which solves the problems of increased project investment, prolonged construction period and insufficient comprehensive analysis of the reliability of the tunnel plug in the design scheme of the length of the tunnel plug in the prior art. The present application first determines the control sliding interface of the tunnel and preliminarily determines the length of the tunnel plug through analysis of the basic parameters of the project; then establishes a risk model for the stability failure of the anti-sliding of the tunnel plug during the main flood season of the construction of the ultra-high dam; next, the distribution parameters of the main random factors affecting the water load and the anti-sliding force are determined; then, based on the preliminarily determined length of the tunnel plug, the distribution parameters of the main random factors affecting the water load and the anti-sliding force are combined to perform random simulation of the water load generated by the highest flood level of dam flood control during the main flood season and the total anti-sliding force that the tunnel plug can generate; and according to the random simulation results, the risk rate of the stability failure of the anti-sliding of the plug is estimated; finally, the length of the tunnel plug is optimized according to the estimated risk rate of the stability failure of the anti-sliding until the convergence condition is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water conservancy and hydropower engineering construction, in particular to a method for optimizing the length of a tunnel plug during the main flood season in the construction of an ultra-high dam. BACKGROUND

[0002] Ultra-high dams are often built in the high mountain and canyon regions of the southwest region, and the construction diversion is generally carried out by cofferdam one-time flow interruption and tunnel diversion in the foundation pit throughout the year. Ultra-high dam hydropower engineering construction is difficult, and the construction period is long. The construction process is affected by many uncertain factors. The stability calculation and analysis of the plug of the tunnel such as water conservancy, transportation, construction branch tunnel, and temporary construction access have always been the key technical problems in the design and research of large hydropower underground engineering. With the continuous advancement of ultra-high dam hydropower engineering construction in the southwest region, more and more ultra-high dams are facing the safety and stability problems of the plug structure of the construction tunnel and the water conservancy tunnel under the construction of the main flood season. For example, the lining of the ecological water supply tunnel of a 300m ultra-high core wall rockfill dam is not completed before the flood season, and construction branch tunnel plugs need to be arranged to ensure that the water supply tunnel is not overwatered and the construction safety during the main flood season.

[0003] At present, the conventional method for the length design of the water conservancy tunnel plug structure by engineering and technical personnel is mainly to initially determine the length, and then use the overall anti-sliding stability method, shear calculation method, and empirical design method to perform stability review, and finally determine the plug length combined with experience. These methods are simple in principle and easy for engineering design personnel to accept.

[0004] However, the above-mentioned plug length design method cannot reflect the influence of main random factors such as rock mechanics parameters, concrete parameters, and indirect contact coefficients between sliding surfaces on the stability of the structure. The calculation result is conservative, which not only increases the engineering investment, but also prolongs the construction and removal period.

[0005] In recent years, with the development of water conservancy reliability theory, the application of limit state design method based on probability theory in engineering design has been continuously deepened. Considering the influence of uncertainty factors in geotechnical engineering, Wang Kui et al. introduced the reliability theory to calculate and analyze the stability of the permanent plug of the water conservancy tunnel. However, for the tunnel plug structure for water retention during the main flood season, on the one hand, the model is mainly for circular water conservancy tunnels, and it is difficult to apply to the city gate type tunnel which is commonly used. On the other hand, the model ignores the randomness of the upstream water pressure load during the flood season, so that the reliability analysis of the tunnel plug is not comprehensive enough.

[0006] In addition, the method for optimizing the length of the tunnel plug based on risk design has not been reported at present, and in view of this, the application considers the influence of main random factors, and studies the method for optimizing the length of the tunnel plug during the main flood season of the super-high dam construction based on the risk analysis theory, so as to provide a scientific theoretical basis and technical support for determining the appropriate engineering scale of the tunnel plug, reducing the engineering investment, ensuring the safety of the construction during the flood season, and speeding up the engineering progress. SUMMARY

[0007] The technical problem solved by the application is to provide a method for optimizing the length of the tunnel plug during the main flood season of the super-high dam construction, so as to solve the problems of increasing the engineering investment, prolonging the construction period and the insufficient comprehensive analysis of the reliability of the tunnel plug in the design scheme of the length of the tunnel plug in the traditional technology.

[0008] The technical solution adopted by the application to solve the above technical problem is:

[0009] The method for optimizing the length of the tunnel plug during the main flood season of the super-high dam construction comprises the following steps:

[0010] S1, determining the control sliding interface of the tunnel and initially determining the length of the tunnel plug through the analysis of the basic parameters of the project;

[0011] S2, establishing a failure risk model of the anti-sliding stability of the tunnel plug during the main flood season of the super-high dam construction;

[0012] S3, determining the distribution parameters of the main random factors affecting the water load;

[0013] S4, determining the distribution parameters of the main random factors affecting the anti-sliding force;

[0014] S5, based on the initially determined length of the tunnel plug, combining the distribution parameters of the main random factors affecting the water load and the anti-sliding force, and performing random simulation on the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that can be generated by the tunnel plug;

[0015] S6, estimating the failure risk rate of the anti-sliding stability of the tunnel plug during the main flood season of the super-high dam construction according to the random simulation results;

[0016] S7, optimizing the length of the tunnel plug according to the estimated failure risk rate of the anti-sliding stability of the tunnel plug during the main flood season of the super-high dam construction until the convergence condition is met.

[0017] Further, in step S1, the control sliding interface of the tunnel and the length of the tunnel plug are initially determined through the analysis of the basic parameters of the project, which comprises:

[0018] The design level of the tunnel plug and the flood standard are determined according to the relevant design specifications of the hydraulic tunnel;

[0019] Determination of the control sliding interface of the tunnel: for the unlined tunnel, the interface between the concrete and the surrounding rock is taken as the control sliding interface; for the lined tunnel, the interface between the concrete and the surrounding rock is taken as the control sliding interface by calculating the anti-sliding stability of the interface between the concrete and the surrounding rock and the interface between the plug and the concrete under the most unfavorable working condition respectively according to the anti-sliding stability.

[0020] Combined with the design parameter values of the design level of the tunnel plug and the flood standard and the control sliding interface, the length of the tunnel plug is estimated by using the partial coefficient limit state design method.

[0021] Further, in step S2, the established anti-sliding stability failure risk model of the tunnel plug of the super-high dam during the main flood period is:

[0022] R=P(P H (max(Z m (t)))>f'∑W+C'(λA1+A2))

[0023] Wherein, R represents the anti-sliding stability failure risk of the tunnel plug of the super-high dam during the main flood period; Z m (t) represents the dynamic change process of the water level of the reservoir before the dam during the flood regulation of the main flood period; P H (max(Z m (t))) is the thrust of the water load on the upstream face of the plug caused by the highest flood level; f' is the shear fracture friction coefficient between the plug and the surrounding rock; ∑W is the total normal force on the control sliding surface; C' is the cohesion between the plug and the concrete or the concrete and the surrounding rock; λ is the effective bonding area coefficient of the side wall; A1 is the effective shear surface contact area of the side wall; A2 is the effective shear surface contact area of the bottom surface; P(·) represents the probability of the condition (·) being true.

[0024] Further, in step S3, the distribution parameters of the main random factors affecting the water load are determined, including:

[0025] The flood peak of the construction flood is assumed to follow the P-Ⅲ distribution;

[0026] The discharge capacity coefficient of the diversion tunnel is assumed to follow the triangular distribution;

[0027] The water level-storage capacity relationship coefficient is assumed to follow the triangular distribution.

[0028] Further, in step S4, the distribution parameters of the main random factors affecting the anti-sliding force are determined, including:

[0029] The effective bonding area coefficient of the side wall is assumed to follow the triangular distribution, and its probability density function is:

[0030]

[0031] wherein k d is the lower limit value, i.e. the minimum bond effective area coefficient of the side wall; k m is the medium value, which is estimated according to the technical level of the construction unit and the site management; k u is the upper limit value, i.e. the maximum bond effective area coefficient of the side wall.

[0032] The shear friction coefficient and cohesion of the plug material are assumed to obey a normal distribution, and the probability density function is:

[0033]

[0034] wherein μ is the mean value of the random variable parameter of the shear friction coefficient f' or the cohesion C'; σ is the standard deviation of the random variable parameter of the shear friction coefficient f' or the cohesion C'.

[0035] Further, in step S5, based on the preliminary tunnel plug length, combined with the distribution parameters of the main random factors affecting the water load and the anti-sliding force, the random simulation of the water load generated by the highest flood control flood level of the dam during the main flood period and the total anti-sliding force that can be generated by the tunnel plug is carried out, including:

[0036] Firstly, based on the Monte Carlo method, the total number of model simulation calculations N C that meets the calculation accuracy requirement is determined.

[0037] Then, combined with the distribution parameters of the main random factors affecting the water load and the anti-sliding force, N C times of random simulation of the water load generated by the highest flood control flood level of the dam during the main flood period and the total anti-sliding force that can be generated by the tunnel plug is carried out.

[0038] Further, the random simulation process of the water load generated by the highest flood control flood level of the dam during the main flood period includes:

[0039] ① Generating a construction flood peak random number to simulate the construction flood process;

[0040] ② Generating a reservoir storage capacity relationship coefficient random number to simulate the fitting of the water level-storage capacity relationship curve;

[0041] ③ Generating a discharge capacity coefficient random number to simulate the fitting of the diversion discharge capacity curve;

[0042] ④ Obtaining the highest flood level max(Z m (t)) of the dam during the main flood period through simulation of the flood regulation calculation simulation;

[0043] ⑤ Calculating the water load P H (max(Z m (t))) through the simulated highest flood level of the dam during the main flood period.

[0044] Further, the random simulation process of the total anti-sliding force that the tunnel plug can generate includes:

[0045] ① generating a random number of the bonding effective area coefficient λ of the side wall;

[0046] ② generating random numbers of the shear resistance friction coefficient f' and cohesion C';

[0047] ③ calculating the total anti-sliding force f'∑W+C'(λA1+A2)) that the tunnel plug can generate.

[0048] Further, in step S6, according to the random simulation result, the anti-sliding stability failure risk rate of the tunnel plug in the main flood season of the construction of the super-high dam is estimated, including:

[0049] According to the random simulation results of the water load generated by the highest flood level in front of the dam in the main flood season of the dam and the total anti-sliding force that the tunnel plug can generate, the number of times that the water load P C (max(Z H (t))) exceeds the total anti-sliding force f'∑W+C'(λA1+A2)) that the tunnel plug can generate is counted, and the number of times is recorded as N m ; T

[0050] Then, according to the anti-sliding stability failure risk rate R of the tunnel plug in the main flood season of the construction of the super-high dam is estimated.

[0051] Further, in step S7, according to the estimated anti-sliding stability failure risk rate of the tunnel plug in the main flood season of the construction of the super-high dam, the length of the tunnel plug is optimized until the convergence condition is met, including:

[0052] It is judged whether the estimated anti-sliding stability failure risk rate R of the tunnel plug in the main flood season of the construction of the super-high dam meets:

[0053] 0≤|R-R A |≤ε

[0054] Wherein, R A is the design risk rate, R A =1 / T A , T A is the flood return period corresponding to the design standard of the tunnel plug; and ε is the set convergence threshold value.

[0055] If yes, the optimization design process is ended, otherwise, the length of the tunnel plug is adjusted, the random simulation of the water load generated by the highest flood level in front of the dam in the main flood season of the dam and the total anti-sliding force that the tunnel plug can generate is performed again based on the adjusted length of the tunnel plug and in combination with the distribution parameters of the main random factors affecting the water load and the anti-sliding force, and then the step S6 is returned. ​

[0056] The beneficial effects of the present application are:

[0057] (1) The present application introduces risk analysis theory and method, constructs a mathematical model of anti-sliding stability failure risk of the tunnel plug before the flood season of the super-high dam, considers the randomness of the main factors affecting the water load and the randomness of the main factors affecting the anti-sliding force, is more in line with the objective reality of the project, and is more suitable for the optimization design of the tunnel plug during the main flood season of the super-high dam construction.

[0058] (2) In the optimization design of the tunnel plug during the main flood season of the super-high dam construction, the risk analysis method based on probability theory is adopted, the influence of the randomness of various random factors is considered scientifically and reasonably, and the scientificity and accuracy of risk rate estimation and analysis are improved.

[0059] (3) The optimization design scheme of the present application can reduce the size of the tunnel plug project under the condition of ensuring a certain anti-sliding stability reliability, thereby reducing the investment of the plug project and shortening the construction period, and has good social, economic and safety benefits. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 The flow chart of the length optimization design method of the tunnel plug during the main flood season of the super-high dam construction in the present application. DETAILED DESCRIPTION

[0061] The present application aims to provide a length optimization design method of the tunnel plug during the main flood season of the super-high dam construction, and solve the problems of increased project investment, prolonged construction period and insufficient comprehensive reliability analysis of the tunnel plug in the design scheme of the tunnel plug length in the traditional technology. The present application first determines the tunnel control sliding interface and preliminarily designs the tunnel plug length through engineering basic parameter analysis; then establishes an anti-sliding stability failure risk model of the tunnel plug during the main flood season of the super-high dam construction; then determines the distribution parameters of the main random factors through systematic analysis of the randomness of the main factors affecting the water load and the anti-sliding force; then, based on the preliminarily designed tunnel plug length, combined with the distribution parameters of the main random factors affecting the water load and the anti-sliding force, the random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that the tunnel plug can generate is carried out; and according to the random simulation results, the anti-sliding stability failure risk rate of the tunnel plug during the main flood season of the super-high dam construction is estimated; finally, the length of the tunnel plug is optimized according to the estimated anti-sliding stability failure risk rate of the tunnel plug during the main flood season of the super-high dam construction, until the convergence condition is met. The design method provides a scientific theoretical basis and technical support for determining the appropriate size of the tunnel plug project, thereby reducing the project investment, ensuring the safety of the construction flood season, and speeding up the project progress.

[0062] In the specific implementation, referring to Figure 1 The length optimization design method of the tunnel plug during the main flood season of the super-high dam construction provided by the present application comprises the following implementation steps:

[0063] S1, determine the tunnel control sliding interface and preliminarily determine the length of the tunnel plug by engineering basic parameter analysis;

[0064] In this step, according to the relevant design specifications of hydraulic tunnel, the design level of tunnel plug and the standard of flood control flood are determined;

[0065] And according to the actual project, the tunnel control sliding interface is determined:

[0066] For the tunnel without lining, the interface between concrete and surrounding rock is taken as the control sliding interface;

[0067] For the tunnel with lining, the interface between the plug and the concrete is calculated as the sliding surface and the interface between the concrete and the surrounding rock is calculated as the sliding surface under the most unfavorable conditions by using the fixed value method, and the control sliding interface is determined according to the anti-sliding stability;

[0068] Finally, combined with the design parameter values of the design level of tunnel plug and the standard of flood control flood and the control sliding interface, the length of the tunnel plug L0 is estimated by using the partial coefficient limit state design method, which is used as the initial input condition for the subsequent calculation of the anti-sliding stability failure risk of the plug.

[0069] S2, establish the anti-sliding stability failure risk model of the tunnel plug during the main flood period of the super-high dam construction;

[0070] In this step, according to the theory of hydraulic structure, combined with the relevant regulations and specifications, taking the city gate type tunnel plug which is most commonly used in hydropower projects as an example, the sliding of the tunnel plugging body along the interface is the main structural failure mode of the tunnel plug. The load effect of the tunnel plug is mainly the thrust of the water load generated by the highest construction flood level on the upstream face of the plug, and the structural resistance is the friction between the plug and the concrete or the concrete and the surrounding rock and the cohesion of the material. Based on this, the limit state equation of the anti-sliding stability of the tunnel plug during the main flood period of the super-high dam construction can be described as:

[0071] Z = P H (max(Z m (t)))-(f'∑W+C'(λA1+A2)) = 0

[0072] Where, Z m (t) is the dynamic change process of the water level of the reservoir before the dam during the main flood period of the dam construction; P H (max(Z mf'∑W+C'(λA1+A2), where f' is the shear-friction coefficient between the plug and the concrete or the concrete and the surrounding rock; ∑W is the sum of all normal forces on the sliding surface, in MN; C' is the cohesion between the plug and the concrete or the concrete and the surrounding rock, in MPa; λ is the effective bonding area coefficient of the side wall; A1 is the effective shear surface contact area of the side wall, in m2; and A2 is the effective shear surface contact area of the bottom surface, in m2. 2 2 .

[0073] After research, the structural sliding failure risk of the tunnel plug during the construction flood season is mainly affected by the randomness of hydrology, water power, material mechanics parameters and other factors. The water load generated by the highest water level in the upstream reservoir is affected by the randomness of hydrology, water power, water level and capacity relationship and other random factors; the randomness of material mechanics parameters makes the total anti-sliding force of the plug have a certain randomness. In the present application, the anti-sliding stability failure risk of the plug during the main construction flood season of the super-high dam is defined as the probability of the anti-sliding stability failure event of the tunnel plug caused by the water load generated by the highest flood level in the upstream during the main construction flood season. Therefore, considering the randomness of the main influencing factors, the mathematical model of the anti-sliding stability failure risk R of the tunnel plug before the flood season of the super-high dam is established as follows:

[0074] R=P(P H (max(Z m (t)))>f'∑W+C'(λA1+A2)

[0075] where R represents the anti-sliding stability failure risk of the tunnel plug during the main construction flood season of the super-high dam; Z m (t) represents the dynamic change process of the water level of the reservoir before the dam during the main construction flood season; P H (max(Z m (t))) is the thrust of the water load on the upstream face of the plug caused by the highest flood level; f' is the shear-friction coefficient between the plug and the surrounding rock; ∑W is the sum of all normal forces on the sliding surface; C' is the cohesion between the plug and the concrete or the concrete and the surrounding rock; λ is the effective bonding area coefficient of the side wall; A1 is the effective shear surface contact area of the side wall; A2 is the effective shear surface contact area of the bottom surface; and P(·) represents the probability of the condition (·) being true.

[0076] S3, determining the distribution parameters of the main random factors affecting the water load;

[0077] ​In this step, the distribution parameters of the main random factors affecting the water load are determined by systematic analysis of the randomness of the main factors affecting the water load. The water load generated by the highest flood level is the only load of the plug structure. The cofferdam reservoir capacity of a super-high dam hydropower project is generally large, and the regulation and storage effect is obvious. The highest flood level before the dam during the main flood season is greatly random due to the randomness of hydrology and water power, specifically:

[0078] (1) Construction flood process randomness:

[0079] The construction flood process has randomness due to the randomness of precipitation in the catchment area upstream of the dam and the randomness of catchment time, etc. At present, the simulation of the construction flood process is basically based on the simulation of the flood peak, that is, the randomness of the construction flood peak is the basis for the simulation of the construction flood process. Therefore, for ease of calculation and analysis, the randomness of the flood peak is considered as the main hydrological random factor, and it is assumed to follow a P-III distribution. Based on the determination of the probability distribution model of the construction flood peak, the construction flood process is determined by the method of enlarging the typical flood process according to the flood peak flow value.

[0080] (2) Randomness of diversion tunnel discharge capacity:

[0081] The discharge capacity of the construction diversion tunnel is influenced by many random factors such as tunnel water section area, wet perimeter, and bottom slope. The discharge capacity density function curve is obtained by random simulation, and then the fitting degrees of normal distribution and triangular distribution are compared. It is considered that the discharge capacity of the diversion tunnel is closer to the triangular distribution.

[0082] (3) Randomness of water level-storage capacity relationship:

[0083] Considering the influence of factors such as reservoir slope collapse and construction slag, the actual water level-storage capacity relationship also has randomness, and it is assumed that the reservoir capacity relationship coefficient also follows a triangular distribution.

[0084] S4, determine the distribution parameters of the main random factors affecting the anti-sliding force;

[0085] In this step, the distribution parameters of the main random factors affecting the anti-sliding force are determined by systematic analysis of the randomness of the main factors affecting the anti-sliding force, specifically:

[0086] (1) Randomness of side wall contact coefficient:

[0087] The bonding effective area coefficient of the plug side wall of the city gate hole type tunnel influences the total anti-sliding force of the plug. However, the bonding effective area coefficient of the side wall has a certain randomness due to the influence of many uncertain factors such as concrete shrinkage, concrete pouring quality, grouting technical level, site construction management, construction equipment, etc. Generally, the bonding effective area coefficient is 0.3-0.8 according to the specific situation of the project. Since the value is within a certain range, and the technical strength of the construction unit and the site management situation can be combined in the actual project to give the preference of good and poor construction quality of the structure, the coefficient of good construction quality is large, and the coefficient of poor construction quality is small. Therefore, the bonding effective area coefficient λ of the side wall is assumed to be subject to a triangular distribution, and the probability density function is:

[0088]

[0089] wherein k d is the lower limit value, i.e. the minimum bonding effective area coefficient of the side wall; k m is the median value, which is estimated according to the technical level of the construction unit and the site management, and a larger value can be taken for good construction quality, and a smaller value can be taken for poor construction quality; and k u is the upper limit value, i.e. the maximum bonding effective area coefficient of the side wall.

[0090] (2) Randomness of material parameters:

[0091] According to the anti-sliding stability limit equation, the main material parameters affecting the total anti-sliding force are the random variable parameters of the shear friction coefficient f' and the cohesion C', and the probability density functions of the random variable parameters are assumed to be subject to normal distribution.

[0092]

[0093] wherein μ is the mean value of the random variable parameters of the shear friction coefficient f' or the cohesion C'; and σ is the standard deviation of the random variable parameters of the shear friction coefficient f' or the cohesion C'.

[0094] S5, based on the initial tunnel plug length, combined with the distribution parameters of the main random factors affecting the water load and the anti-sliding force, the water load generated by the highest flood control flood level of the dam during the main flood period and the total anti-sliding force that can be generated by the tunnel plug are randomly simulated.

[0095] In this step, firstly, the total number of model simulation calculations N C that meets the calculation accuracy requirement is determined based on the Monte Carlo method; and then combined with the distribution parameters of the main random factors affecting the water load and the anti-sliding force, N C times of random simulation of the water load generated by the highest flood control flood level of the dam during the main flood period and the total anti-sliding force that can be generated by the tunnel plug are performed.

[0096] The stochastic simulation process for the water load generated by the highest flood level of the dam during the main flood season includes:

[0097] ① Generate random numbers for the peak flood during construction to simulate the construction flood process;

[0098] ② Generate random numbers for the reservoir capacity relationship coefficients and simulate and fit the water level-capacity relationship curve;

[0099] ③ Generate random numbers for the discharge capacity coefficient and simulate and fit the flow guidance and discharge capacity curve;

[0100] ④ The maximum flood level (max(Z)) in front of the dam during the main flood season is obtained through simulation of flood control calculations. m (t));

[0101] ⑤ Calculate the water load P by simulating the highest flood level in front of the dam during the main flood season. H (max(Z m (t))).

[0102] The stochastic simulation process of the total anti-skid force generated by the tunnel plug includes:

[0103] ① Generate a random number for the effective bonding area coefficient λ of the sidewall;

[0104] ② Generate random numbers for the shear friction coefficient f' and cohesion C';

[0105] ③ Calculate the total anti-skid force f'∑W+C'(λA1+A2) that the tunnel plug can generate.

[0106] Based on the above simulation process, N can be obtained. C The stochastic simulation results of the water load generated by the highest flood level of the dam during the main flood season and N C Simulation results of the total anti-skid force generated by a tunnel plug.

[0107] S6. Based on the results of random simulation, estimate the risk rate of anti-sliding stability failure of tunnel plugs during the main flood season of ultra-high dam construction;

[0108] In this step, according to N C The simulation results of the stochastic simulation of the water load generated by the highest flood level of the dam during the secondary flood season and the total anti-sliding force generated by the tunnel plug are statistically analyzed. H (max(Z m The number of times (t) exceeds the total anti-slip force f'∑W+C'(λA1+A2) that the tunnel plug can generate is denoted as N. T ;

[0109] Then according to Estimate the risk rate R of tunnel plug anti-sliding stability failure during the main flood season of ultra-high dam construction.

[0110] S7、According to the estimated risk rate of anti-sliding stability failure of the tunnel plug in the main flood season of the super-high dam construction, the length of the tunnel plug is optimized until the convergence condition is met.

[0111] In this step, the risk theory method is used to make risk discrimination on the length design scheme of the tunnel plug. Assuming that the corresponding flood return period of the tunnel plug design standard is T A , the design risk rate R A is obtained by conversion, and the calculation expression is:

[0112] R A = 1 / T A

[0113] Therefore, the risk discrimination criterion for the length design scheme of the tunnel plug to meet the specification requirements is:

[0114] R≤R A

[0115] Based on the preliminary tunnel plug L0 design scheme, R is obtained according to the aforementioned risk rate estimation method, and according to the risk discrimination criterion, ε is given as a very small positive number, and the inequality condition 0≤|R-R A |≤ε is used as the convergence condition of the optimization design to judge whether the iteration convergence is met. If it is met, the design optimization process is exited, otherwise, the length size of the tunnel plug is adjusted again, the random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that the tunnel plug can generate is performed again, and then step S6 is returned to continue calculating the risk rate of anti-sliding stability failure, until the convergence condition is met.

[0116] Embodiment

[0117] The scheme of the present application is applied to the super-high core wall rockfill dam SJK hydropower station in the upper reaches of the Dadu River basin in China, and the length optimization design method of the tunnel plug in the main flood season is exemplarily described.

[0118] SJK hydropower station is a controlling reservoir in the upper reaches of the Dadu River basin in China, and the dam is a super-high core wall rockfill dam with a height of 315.00 m, which is the highest dam in the world. The project is a first-class large (1) type project, and the hub project is composed of a dam, a flood discharge structure, a water diversion and power generation system and the like. The project has steep slopes and exposed bedrock, and the tunnel diversion method of cofferdam one-time cutoff and foundation pit all-year construction is adopted.

[0119] The project considers ecological water supply, maintenance, emergency and other special design of a construction period ecological water supply hole, and the engineering grade is 3. Influenced by various complex factors such as site management and emergencies, the construction progress is seriously lagging behind. According to the actual progress of the project, the filling elevation of the dam reaches 2316.00m before the flood season in a certain year, which exceeds the upstream cofferdam 2308.00m. The dam flood standard is 100-year standard. But the ecological water supply hole is still in the stage of in-hole concrete lining, and the project needs to rush the concrete construction lining during the flood season. In order to ensure the safety of the construction personnel and equipment in the hole after the water level rises during the main flood period, and avoid the damage of flood into the ecological water supply hole and cause structural damage and injury, a special tunnel water blocking plug needs to be set upstream. In order to determine the reasonable value of the plug, the scheme provided by the present application is implemented as follows:

[0120] I. Tentative length of tunnel plug:

[0121] According to the relevant regulations and specifications "Hydraulic Tunnel Design Specification" (NB / T 10391-2020), the plugging body of the tunnel construction branch hole should be consistent with the grade of the tunnel structure. Therefore, the grade of the tunnel plug is 3, the flood standard of the water blocking plug is 20 years, and the design flood level is 2294.50m. The cross section of the construction branch hole is 7.0m x 8.0m, and the bottom elevation of the plugging body arrangement position is 2259.00, so the acting water head is 35.5m.

[0122] Since the construction branch hole of the project is not lined, the interface between the concrete and the surrounding rock is taken as the control sliding surface. The length of the tunnel plug is initially calculated as 14.46m by using the partial coefficient limit state design method.

[0123] II. Establishing a high dam construction main flood period tunnel plug anti-sliding stability failure risk model:

[0124] The interface sliding of the tunnel plugging body of the project is the main structural failure mode of the tunnel plug. The load effect of the tunnel plug is the thrust of the water load on the upstream face of the plug under the highest construction flood level, and the structural anti-sliding force is the friction between the concrete and the surrounding rock and the cohesion of the material. The established high dam construction main flood period tunnel plug anti-sliding stability limit state equation is:

[0125] Z H (max(Z m (t)))-(f'∑W+C'(λA1+A2))=0

[0126] Wherein, Z m (t) is the dynamic change process of the water level of the dam before the dam construction main flood period; P H (max(Z m(t) represents the thrust of the water load generated by the highest flood level on the upstream face of the plug; f' represents the shear friction coefficient between the plug concrete and the surrounding rock; ∑W represents the sum of all normal forces on the sliding surface, in MN; C' represents the cohesion between the plug and the concrete or between the concrete and the surrounding rock, in MPa; λ represents the effective bond area coefficient of the sidewall; A1 represents the effective shear contact area of ​​the sidewall, in m². 2 A2 represents the effective shear contact area of ​​the bottom surface, in meters. 2 .

[0127] During the main flood season of this project, the tunnel closure is at risk of structural sliding failure due to the combined influence of random factors such as hydrology, hydraulics, and material mechanics parameters. Specifically, the water load generated by the highest water level in the upstream reservoir is subject to randomness due to hydrological, hydraulic, and water-reservoir-capacity relationships; the randomness of material mechanics parameters also contributes to the randomness of the total resistance of the closure. Considering the randomness of all major influencing factors, the mathematical model for the risk R of the pre-flood sliding stability failure of the tunnel closure in the ultra-high dam is established as follows:

[0128] R = P(P) H (Z m (t))>f'∑W+C'(λA1+A2))

[0129] Where P(·) represents the probability that the condition (·) is true.

[0130] III. Conduct a systematic analysis of the randomness of the main factors affecting water load, and determine the distribution parameters of each random factor:

[0131] (1) Hydrological random parameters:

[0132] Based on the measured annual maximum discharge series from hydrological stations, frequency calculations were performed using a discontinuous series of historical floods from the surveyed years. The empirical frequencies of historical floods and measured series were calculated using the expectation formula. Preliminary parameters were calculated using the method of moments, and the hydrological stochastic parameter μ was determined using the visual fitting method. Q =2540m 3 / s,C v =0.33,C s / C v =5.0.

[0133] (2) Hydraulic random parameters:

[0134] The initial diversion tunnel has a cross-sectional size of 15.0m × 19.0m. The discharge capacity coefficient of the discharge structure follows a triangular distribution, with a value range of 0.97 to 1.05. Based on similar engineering experience, the distribution parameters are 0.97 (lower limit), 1.00 (median), and 1.05 (upper limit).

[0135] (3) Water level-storage capacity relationship coefficient random parameter:

[0136] Considering that the water level-storage capacity relationship coefficient of the project obeys a triangular distribution, the distribution parameters thereof are 0.99 (lower limit), 1.00 (median value), and 1.01 (upper limit) according to relevant engineering experience.

[0137] Four, systemically analyze the randomness of main factors affecting the resistance, and determine the distribution parameters of each random factor:

[0138] (1) Random parameter analysis of side wall contact coefficient:

[0139] The side wall contact coefficient obeys a triangular distribution, and the range thereof is generally within 0.3-0.8. According to the experience of similar projects, combined with the construction management and technical level of the construction unit of the project, the random distribution parameter of the side wall contact coefficient is determined to be 0.5 (median value), and the distribution parameters of the side wall contact coefficient λ are finally determined to be 0.3 (lower limit), 0.5 (median value), and 0.8 (upper limit).

[0140] (2) Random parameter analysis of materials:

[0141] The plug concrete grade is C25, and the surrounding rock grade is grade IV surrounding rock. According to relevant data, combined with the construction site conditions, the statistical characteristics of the random parameters of materials are obtained as shown in Table 1:

[0142] Table 1 Statistical characteristics of random parameters of materials

[0143] Random variable Mean Coefficient of variation Distribution type f' 0.7 0.2 Normal C' 0.4 0.1 Normal

[0144] Five, perform random simulation of the water load generated by the dam flood control highest flood level during the main flood period and the total anti-sliding force that can be generated by the tunnel plug, and design and optimize the plug length:

[0145] Determine the total number of model simulation calculations that meet the calculation accuracy requirements, perform random simulation of the water load generated by the dam flood control highest flood level during the main flood period and the total anti-sliding force that can be generated by the tunnel plug, simulate the failure risk rate R of the anti-sliding stability of the tunnel plug of the super-high dam during the main flood period, and design and optimize the plug length until 0≤|R-R A |≤ε.

[0146] In order to ensure the calculation accuracy, when the simulation times are greater than 100,000 times, the calculation results tend to be stable and small. Therefore, the total number of simulation is designed to be 100,000 times. In the case of the initial length of the plug being 14.46 m, after 100,000 times of simulation and calculation, it is statistically obtained that the plug anti-sliding stability failure times caused by the water load of the highest flood level in front of the dam exceeding the total anti-sliding force that the tunnel plug can produce is 24 times, and the failure risk R is 0.24%. It is shown that the initial length of the plug has high safety reliability, but the failure risk R is much smaller than the design risk rate of 5% of the design standard of 20-year return period, which also shows that the plug length designed by the traditional direct partial coefficient limit state design method is conservative.

[0147] By continuously adjusting the length of the plug and re-performing the random simulation of the water load generated by the highest flood level in the main flood period in front of the dam and the total anti-sliding force that the tunnel plug can produce, and the calculation of the anti-sliding stability failure risk rate, when the design length of the plug is 3.35 m, the plug anti-sliding stability failure times is 5012 times, and the failure risk R is 5.012%, which is slightly greater than and very close to the standard of 20-year return period.

[0148] Therefore, for this project, when the structure design method based on risk theory is adopted, the length of the tunnel plug can be 3.35 m, which can meet the requirements of flood control in the main flood period. Compared with the traditional design method of 14.46 m, the length of the water retaining plug determined by the present scheme is greatly shortened, so the project cost can be saved. Since 13 tunnel plugs are used in this project, it is estimated that the project cost saving reaches several million yuan, and the use of shorter water retaining plugs can speed up the construction progress under the condition of ensuring the design requirements of anti-sliding stability reliability.

[0149] Finally, it should be noted that the above embodiments are only preferred embodiments and do not limit the present application. It should be noted that for ordinary skilled persons in the art, without departing from the purpose of the present application and the scope protected by the claims, a number of modifications, equivalent replacements, improvements, etc. can be made, which should be included in the protection scope of the present application.

Claims

1. A method for optimizing the length of a tunnel plug during the main flood season of the construction of an ultra-high dam, characterized in that, The method comprises the following steps: S1, determining the control sliding interface of the tunnel and initially determining the length of the tunnel plug by analyzing the basic parameters of the project; S2, establishing a risk model for the anti-sliding stability failure of the tunnel plug during the main flood period of the construction of the super-high dam: Wherein, R represents the anti-sliding stability failure risk of the tunnel plug during the main flood period of the super-high dam construction; represents the water level dynamic change process of the reservoir flood regulation before the dam during the main flood period of the dam construction; is the water load thrust generated by the highest flood level on the upstream face of the plug; is the shear friction coefficient between the plug and the surrounding rock; is the total normal force on the sliding surface and is the cohesion between the plug and the concrete or the concrete and the surrounding rock; is the bonding effective area coefficient of the side wall; is the effective shear surface contact area of the side wall; is the effective shear surface contact area of the bottom surface; P(·) represents the probability of the condition (·) being true. S3, determining the distribution parameters of the main random factors affecting the water load; S4, determining the distribution parameters of the main random factors affecting the anti-sliding force; S5, based on the initially determined length of the tunnel plug, combining the distribution parameters of the main random factors affecting the water load and the anti-sliding force, and performing random simulation of the water load generated by the highest flood control flood level of the dam during the main flood period and the total anti-sliding force that can be generated by the tunnel plug; S6, according to the random simulation results, estimating the anti-sliding stability failure risk rate of the tunnel plug during the main flood period of the construction of the super-high dam; S7, according to the estimated anti-sliding stability failure risk rate of the tunnel plug during the main flood period of the construction of the super-high dam, optimizing the length of the tunnel plug until the convergence condition is met.

2. The method for optimizing the length of the tunnel plug during the main flood period of the construction of the super-high dam according to claim 1, wherein in step S1, the control sliding interface of the tunnel is determined and the length of the tunnel plug is initially determined by analyzing the basic parameters of the project, comprising: According to the relevant design specifications of the hydraulic tunnel, the design level of the tunnel plug and the standard of the flood season flood are determined; Determine the control sliding interface: for the tunnel without lining, the interface between the concrete and the surrounding rock is taken as the control sliding interface; for the tunnel with lining, the anti-sliding stability of the interface between the plug and the concrete and the interface between the concrete and the surrounding rock under the most unfavorable working condition is calculated respectively by using the fixed value method, and the control sliding interface is determined according to the anti-sliding stability; Combining the design parameter values of the design level of the tunnel plug and the standard of the flood season flood and the control sliding interface, the length of the tunnel plug is estimated by using the partial coefficient limit state design method.

3. The method for optimizing the length of the tunnel plug during the main flood period of the construction of the super-high dam according to claim 1, wherein in step S3, the distribution parameters of the main random factors affecting the water load include: The construction flood peak is assumed to follow a P-Ⅲ distribution; The discharge capacity coefficient of the diversion tunnel is assumed to follow a triangular distribution; The water level-storage capacity relationship coefficient is assumed to follow a triangular distribution.

4. The method for optimizing the length of the tunnel plug during the main flood period of the construction of the super-high dam according to claim 3, wherein in step S4, the distribution parameters of the main random factors affecting the anti-sliding force include: The bonding effective area coefficient of the side wall is assumed to follow a triangular distribution, and its probability density function is: The shear friction coefficient and cohesion of the plug material are assumed to follow a normal distribution, and their probability density functions are:

5. The method for optimizing the length of the tunnel plug during the main flood period of the construction of the super-high dam according to claim 4, wherein in step S5, based on the initially determined length of the tunnel plug, combining the distribution parameters of the main random factors affecting the water load and the anti-sliding force, and performing random simulation of the water load generated by the highest flood control flood level of the dam during the main flood period and the total anti-sliding force that can be generated by the tunnel plug, comprising:

6. The method for optimizing the length of the tunnel plug during the main flood period of the construction of the super-high dam according to claim 5, wherein wherein, is a lower limit value, i.e. the minimum bond effective area coefficient of the side wall; is a median value, estimated according to the technical level of the construction unit and the site management; is an upper limit value, i.e. the maximum bond effective area coefficient of the side wall; ​ wherein is the mean of the random variable parameter of the shear resistance friction coefficient or cohesion ; is the standard deviation of the random variable parameter of the shear resistance friction coefficient or cohesion . ​ ​ Firstly, the total number of model simulation calculations satisfying the calculation accuracy requirement is determined based on the Monte Carlo method ; Then, combined with the distribution parameters of the main random factors affecting water load and anti-sliding force, the random simulation of the total anti-sliding force generated by the water load of the highest flood level of dam flood control in the secondary flood season and the tunnel plug can be performed. The random simulation of the total anti-sliding force generated by the water load of the highest flood level of dam flood control in the secondary flood season and the tunnel plug can be performed. ​ The random simulation process of the water load generated by the highest flood level of the dam during the main flood season includes: generating a random number of construction flood peak to simulate the construction flood process; The reservoir storage capacity relationship coefficient random number is generated to simulate and fit the water level-storage capacity relationship curve. A random number of discharge capacity coefficient is generated to simulate and fit the discharge capacity curve of the diversion. The highest flood level in front of the dam during the main flood season is obtained by simulating flood regulation calculation simulation ; Water load is calculated by the highest flood level in front of the dam during the main flood season by simulation .

7. The method according to claim 6, wherein the length of the tunnel plug during the main flood season of the super-high dam construction is optimized, and the method further comprises: The random simulation process of the total anti-sliding force generated by the tunnel plug includes: Coefficient of effective bonded area of a side wall random number; Shear-friction coefficient of resistance Coherence Random number; Total resistance to sliding force that can be generated by the tunnel plug .

8. The method according to claim 1, wherein the length of the tunnel plug during the main flood season of the super-high dam construction is optimized, and the method further comprises: In step S6, the anti-sliding stability failure risk rate of the tunnel plug during the main flood season of the super-high dam construction is estimated according to the random simulation results, and the estimation includes: According to The simulation results of the random simulation of the total anti-sliding force generated by the water load of the highest flood level of the dam during the secondary flood season and the tunnel plug, the statistical analysis of the water load of the highest flood level in front of the dam simulated The number of times the total anti-sliding force generated by the tunnel plug is exceeded , which is recorded as ; Then according to The risk rate R of stability failure of the tunnel plug of the super-high dam construction during the main flood season is estimated.

9. The method according to claim 8, wherein the length of the tunnel plug is optimized according to the estimated anti-sliding stability failure risk rate of the tunnel plug during the main flood season of the super-high dam construction until a convergence condition is met, and the optimization includes: determining whether the estimated anti-sliding stability failure risk rate R of the tunnel plug during the main flood season of the super-high dam construction meets: If yes, the optimization design process is ended, otherwise, the length of the tunnel plug is adjusted, the random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force generated by the tunnel plug is performed again based on the adjusted length of the tunnel plug and the distribution parameters of the main random factors affecting the water load and the anti-sliding force, and then the step S6 is returned. wherein, is the design risk rate, , is the corresponding flood return period for the design criteria of the tunnel plug; is the set convergence threshold value; ​

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