Design method of flip bucket energy dissipation for soft rock foundation spillway

Abstract

The present application relates to the technical field of flow pick-up and energy dissipation design, and particularly relates to a design method of flow pick-up and energy dissipation of spillway on soft rock foundation. The method comprises the following steps: obtaining the characteristics of the rock-soil layer at the impact pit of the target spillway; performing rock-soil layer blocking according to the characteristics of the rock-soil layer, and formulating the flow pick-up bucket structure based on the blocking of the rock-soil layer at the impact pit; calculating the water tongue landing point and the impact pit depth under each standard working condition at the impact pit through a preset energy dissipation and impact prevention working condition library, and optimizing the flow pick-up bucket structure according to the water tongue landing point and the impact pit depth; simulating the impact pit erosion when the flow is discharged under each working condition through a preset physical model; comparing the simulation results with the calculation results, and generating the final design scheme of the flow pick-up bucket according to the comparison results; and designing the support structure according to the simulation results and the final design scheme of the flow pick-up bucket. The present application can effectively control the impact pit depth while maintaining the advantages of simple construction and economy of flow pick-up and energy dissipation, and ensure the safety and stability of the flow pick-up bucket and the bank slope structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flip bucket energy dissipation design, and in particular to a design method of soft rock foundation spillway flip bucket energy dissipation. BACKGROUND

[0002] The spillway is a kind of building for reservoir discharge, and the flow velocity of the discharged water is high. In order to avoid the river scouring caused by the high-speed water flow into the downstream river, the high-speed water flow needs to be dissipated. The flip bucket energy dissipation is one of the energy dissipation methods. The flip bucket energy dissipation structure includes an upstream discharge channel section, a flip bucket section and a downstream plunge pit section. The discharged water flow passes through the upstream discharge channel section and the intermediate flip bucket section, and then is shot into the downstream plunge pit section. The water flow collides with each other in the air, impacts the lower water cushion after entering the water, and collides, rubs and frictions with the water body, so as to promote the kinetic energy of the water flow to be finally converted into heat and dissipated, and a plunge pit is formed in the downstream river.

[0003] The flip bucket energy dissipation structure is simple, convenient to construct and maintain, has less engineering quantity and obvious economy. However, the existing flip bucket energy dissipation structure is mainly suitable for weak weathering and slightly weathered rock. The soft rock foundation has poor anti-scouring ability. The plunge pit formed by the conventional flip bucket energy dissipation has large depth, which endangers the safety of the flip bucket structure and poses a great threat to the stability of the plunge pit bank slope. In order to avoid the above-mentioned disadvantages of the flip bucket energy dissipation in the soft rock foundation, the bottom flow energy dissipation is usually selected for the spillway energy dissipation in the soft rock area. However, when the bottom flow energy dissipation is used for large flow discharge, the energy dissipation pool has large engineering scale and high cost. SUMMARY

[0004] Therefore, it is necessary to provide a design method of soft rock foundation spillway flip bucket energy dissipation to solve at least one of the above-mentioned technical problems.

[0005] To achieve the above-mentioned purpose, a design method of soft rock foundation spillway flip bucket energy dissipation comprises the following steps:

[0006] Step S1: obtaining the rock-soil layer characteristics of the target spillway plunge pit; performing rock-soil layer blocking according to the rock-soil layer characteristics, and formulating a flip bucket structure based on the rock-soil layer blocking of the plunge pit foundation;

[0007] Step S2: calculating the water tongue landing point and the plunge pit depth corresponding to each standard working condition of the plunge pit through a preset energy dissipation and anti-scouring working condition library, and optimizing the flip bucket structure according to the water tongue landing point and the plunge pit depth;

[0008] Step S3: simulating the plunge pit scouring condition when the flow is discharged under each preset working condition through a physical model;

[0009] Step S4: comparing the simulation result with the calculation result, and generating a final design scheme of the flip bucket according to the comparison result; and designing the supporting structure of the bank slope on both sides of the target spillway plunge pit according to the simulation result and the final design scheme of the flip bucket.

[0010] The application obtains the distribution of the foundation rock-soil layer and the anti-scour performance of each rock-soil layer by detailed geological drilling and mapping at the scour pit, and divides the foundation rock-soil layer on the plane in combination with the distribution characteristics of the scour pit foundation soil; then the flip bucket structure is determined according to the division results and engineering experience, and the water tongue landing point and the scour pit depth under each standard working condition are calculated through the preset energy dissipation and scour prevention working condition library to optimize and adjust the flip bucket structure to meet the requirement of the scour pit stability slope; further, the scour pit scouring condition when the flow is discharged under each working condition is simulated by using the physical model, the scour pit forming position and shape are observed, and the simulation results are compared with the calculation results, and finally the flip bucket design scheme is generated; according to the geometric characteristics of the formed scour pit, the stability of the bank slope on both sides is calculated in combination with the foundation soil mechanics parameters of the bank slope on both sides, and the bank slope supporting structure is set as necessary to ensure the stability and safety. The application can effectively control the scour pit depth while maintaining the advantages of simple and economical construction of flip energy dissipation, ensure the safety and stability of the flip bucket and the bank slope structure, reduce the risk of structural damage that may be caused by traditional flip energy dissipation in soft rock foundation, avoid the problems of large scale and high cost of bottom flow energy dissipation, and realize the coordination of economy and safety. BRIEF DESCRIPTION OF DRAWINGS

[0011] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-restrictive embodiments made with reference to the accompanying drawings:

[0012] Fig. 1 The step flow schematic diagram of the design method of the soft rock foundation spillway flip energy dissipation of the present application;

[0013] Fig. 2 The schematic diagram of the flip energy dissipation structure in the embodiment of the present application;

[0014] The implementation of the object of the present application, functional characteristics and advantages will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0015] The technical method of the present application will be described clearly and completely below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0016] Furthermore, the accompanying drawings are included to provide a further understanding of the present application, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application. In the drawings:

[0017] It is to be understood that, although terms such as "first", "second", and the like can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the example embodiments. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0018] To achieve the above object, there is provided Figs. 1-2 The present application provides a design method for soft rock foundation spillway flip flow energy dissipation, which comprises the following steps:

[0019] Step S1: obtaining the characteristics of the rock-soil layer at the target spillway scour pit; performing rock-soil layer blocking according to the characteristics of the rock-soil layer, and formulating a flip bucket structure based on the blocking of the rock-soil layer at the scour pit;

[0020] In the embodiment, firstly, the characteristics of the foundation rock-soil layer at the target spillway scour pit are acquired. Specifically, 18 drill holes are arranged in the scour pit range by using a portable drill of XY-150 type, the drill hole depth is 25-35 m, and the columnar graph of each drill hole is obtained. Further, the geological surveying and mapping of the scour pit range is performed by using a total station combined with unmanned aerial photography, and the geometric conditions of the bank slope and the distribution of the exposed stratum are acquired. The characteristics of the rock-soil layer in the scour pit range are obtained by combining the columnar graph of each drill hole and the geological surveying and mapping results, which include the thickness of the upper covering layer of 3-5 m, the thickness of the middle strongly weathered rock layer of 8-15 m, and the buried depth of the underlying hard weakly weathered rock layer of about 18-22 m. At the same time, in the process of drilling, the foundation soil samples are collected for rock-soil testing, the testing contents include uniaxial compression test, etc., and the rock mass classification of each rock-soil layer is obtained. The columnar graph of the drill hole, the distribution of the foundation rock-soil layer are combined according to the three-dimensional spatial position relationship, and the complete characteristics of the foundation rock-soil layer are generated. Based on this, the rock-soil layer is divided into blocks according to the rock mass classification, the adjacent sections with the same grade rock layer whose distribution buried depth difference is not more than 3 m are classified into the same block, and the foundation rock-soil layer block set including twelve main blocks is obtained. On this basis, the preset flip bucket structure is called, the elevation of the bucket top is adjusted to 295.5 m according to the anti-scour performance of the rock-soil layer block, the flip angle is set to 15°, the bucket top shape adopts arc shape, the horizontal bevel angle is set to 5°, and the preliminarily planned flip bucket structure is obtained.

[0021] Step S2: calculating the corresponding water tongue landing point and scour pit depth of each standard working condition at the scour pit by the preset energy dissipation and anti-scour working condition library, and optimizing the flip bucket structure according to the water tongue landing point and the scour pit depth;

[0022] In the embodiment, the flip bucket structure is used to calculate the corresponding water tongue landing point and scour pit depth of each standard working condition at the scour pit by the preset energy dissipation and anti-scour working condition library. The energy dissipation and anti-scour working condition library can include five standard working conditions of design flood frequency of 1 / 5, 1 / 10, 1 / 20, 1 / 30 and 1 / 50, and the corresponding spillway discharge range is 1000-3200 . Wherein 1 / 5 represents 5 years, 1 / 10 represents 10 years, 1 / 20 represents 20 years, 1 / 30 represents 30 years, 1 / 50 represents 50 years, the application is only for the sake of brevity and simplify the description in the form of numerical value, that is, the flood frequency does not exist specific dimension, for the expression of the flood frequency, the application does not make any limitation. By the hydraulic parameters under each working condition acting on the flip bucket structure, the water tongue drop point calculation equation is used to calculate the water tongue drop point, wherein the water tongue drop point distance from the end of the bucket under the above frequency working condition (i.e. jump distance) is 32m, 38m, 42m, 48m and 56m respectively. Further, according to the corresponding block situation of the water tongue drop point of the scour pit foundation rock and soil layer, the depth of the formed scour pit is calculated, and the scour pit depth under the above standard working condition is 5.7m, 6.3m, 9.7m, 14.1m and 20.6m respectively, and the longitudinal slope ratio between the bottom of the scour pit and the flip bucket is 1:5.61, 1:6.03, 1:4.33, 1:3.33 and 1:2.72 respectively, wherein the longitudinal slope ratio of the scour pit formed under the frequency 1 / 50 standard working condition does not meet the threshold value requirement of not steeper than 1:3 in the relevant specification. Further analysis shows that the upper part of the rock and soil layer block has a larger thickness of strongly weathered soil layer at the flip distance of 55m, and the rock and soil layer block with good anti-scour performance is close to the flip bucket and deviates to the right side of the river channel. Therefore, it is necessary to optimize the flip bucket structure, shorten the flip distance under the adverse working condition, and adjust the water tongue drop point to deviate to the right side of the river channel. The flip angle is designed to be 10° and 0° respectively, and the horizontal bevel angle is adjusted to 15°. Finally, when the flip angle is 0°, the scour pit position moves to the rock and soil layer block with more solid, and the longitudinal slope between the scour pit and the flip bucket under each working condition meets the threshold value requirement of the specification.

[0023] It is worth noting that the parameters included in each working condition in the energy dissipation and scour prevention working condition library are not limited by the application.

[0024] Step S3: simulate the scour pit scouring condition when the flow is discharged under each preset working condition through the physical model;

[0025] In this embodiment, the flow discharge under each preset working condition is simulated by a physical model. The physical model is established according to a scale of 1:50, and the spillway, bucket and scour pit range are strictly arranged according to the original prototype size. The foundation part uses hierarchical granular material to simulate different rock and soil layers, the cover layer uses fine sand with a particle size of 0.4-0.8mm, the strongly weathered rock layer uses quartz sand particles with a particle size of 2.5-4.0mm, and the weakly weathered rock layer block uses pebbles with a particle size of 25-50mm. The flow control valve is set in the movable bed model to simulate the flow covering 16-64L / s, corresponding to the prototype flow of 1000-3200 In the flow discharge test, the water tongue landing position and the formation process of the scour hole are captured by a high-speed camera to obtain simulation results. In each working condition, it is observed that the final water tongue landing position is about 48 m away from the end of the bucket, the maximum depth of the scour hole is 14.4 m, the plane of the scour hole is elliptical, and the long axis direction is consistent with the water flow direction.

[0026] Step S4: comparing the simulation results with the calculation results, and generating a final design scheme of the bucket according to the comparison results; and designing a support structure of the bank slope at both sides of the target spillway scour hole according to the simulation results and the final design scheme of the bucket.

[0027] In this embodiment, the simulation results obtained in step S3 are compared with the calculation results in step S2. The simulation scour hole depth of 14.4 m is compared with the calculation scour hole depth of 15.5 m, and the error is 1.1 m, which is within the preset tolerance deviation range of 2.0 m; the simulation water tongue landing position of 48 m is compared with the calculation water tongue landing position of 50 m, and the error is 2 m, which is also within the tolerance deviation range of 5 m. According to this, it is determined that the two are in good agreement, and the optimized bucket structure is determined as the final design scheme of the bucket. On this basis, the support structure of the bank slope at both sides of the target spillway scour hole is further designed according to the simulation results and the final design scheme of the bucket. By extracting the geometric feature parameter set of the scour hole, including the long axis of 76 m, the short axis of 42 m, and the maximum depth of 14.4 m, and combining the geometric conditions of the bank slope and the mechanical index parameters of the rock and soil layer, the stability safety factor of the bank slope after the formation of the scour hole is calculated to be about 1.05, which is lower than the preset threshold of 1.2. Therefore, the type of the support structure is selected as a bored pile row support, and the design parameters are determined: the pile diameter is 1.2 m, the pile length is 18-25 m, the pile spacing is 1.3 m, and the weak weathered rock depth is not less than 3 m. Finally, the support structure design scheme of the bank slope at both sides of the target spillway scour hole is formed.

[0028] Optionally, the step S1 of obtaining the characteristics of the rock and soil layer at the target spillway scour hole comprises:

[0029] The geological drilling of the target spillway scour hole is performed by using a drilling equipment to obtain a columnar graph of each drilling hole;

[0030] In this embodiment, geological boreholes were drilled at the target spillway crater using pre-set drilling equipment. Specifically, 18 boreholes were arranged in a 30m × 30m rectangle within the planar area of ​​the crater, with a drilling depth controlled between 25 and 35 meters to ensure penetration of the overlying layer and exposure of the underlying hard bedrock. An XY-150 portable drilling rig was used for drilling, with a borehole diameter of 110mm. Clean water circulation was used for wall protection during drilling. After drilling, the boreholes were logged and a columnar section of the soil and rock layers was drawn. The columnar section recorded the soil layer type, thickness, and weathering degree at different depths. According to the columnar section, the overlying layer was identified as silty clay, approximately 3.0–5.0 meters thick, followed by a strongly weathered rock layer, 8.0–15.0 meters thick, and then weakly weathered hard bedrock. The columnar section visually demonstrates the stratigraphic structure characteristics at the target spillway crater.

[0031] Geological mapping was conducted at the target spillway crater, and the geological mapping results were combined with the columnar section of each borehole to obtain the distribution of the foundation soil and rock layers;

[0032] In this embodiment, geological mapping is conducted at the target spillway sluice. A combined approach of low-altitude UAV aerial surveying and ground-based total station mapping can be used to establish a digital elevation model with an accuracy of ±0.1m. Through on-site mapping, the geometric morphology of the bank slope, the distribution of exposed rock layers, and the spatial distribution characteristics of joints and fissures are obtained and compared with borehole columnar sections. For example, the thickness of the overburden layer observed on the bank slope surface is consistent with the borehole findings, both being approximately 3.0–3.5m. Combining the mapping results with the columnar section information, a two-dimensional profile is formed, thus revealing the planar distribution of the foundation soil and rock layers.

[0033] The soil and rock layers at the scour site of the target spillway were sampled, and soil and rock tests were conducted on the samples of the soil and rock layers at the scour site. The scour resistance of each soil and rock layer was evaluated based on the results of the soil and rock tests.

[0034] In this embodiment, soil samples were taken from the foundation soil at the scour site of the target spillway, and geotechnical tests were conducted. Specifically, samples were obtained from borehole cores. 50mm long and 100mm in diameter soil and rock samples were used, ensuring core integrity was greater than 85%. Uniaxial compressive strength tests were then conducted indoors. The test results showed that the uniaxial compressive strength of strongly weathered rock layers ranged from 8.5 to 12.3 MPa; the uniaxial compressive strength of weakly weathered rock layers ranged from 35 to 42 MPa. Based on this, soil and rock classifications were obtained for each soil and rock layer, and their erosion resistance was evaluated.

[0035] The columnar sections of each borehole and the distribution of various foundation soil and rock layers are merged according to their spatial location to obtain the characteristics of the foundation soil and rock layers; the spatial location relationship is the spatial relationship between the borehole location and the target location at the target spillway scour site.

[0036] In the embodiment, the histogram of each borehole and the distribution of foundation rock-soil layer are combined according to the spatial position relationship. For this purpose, a three-dimensional coordinate system is established, the borehole profile information is projected into the three-dimensional space with the borehole layout position as the base point, and the rock-soil distribution obtained by surveying and mapping is added to the same coordinate system. Through the GIS three-dimensional geological modeling software, the three are interpolated and fitted according to the spatial position to generate a continuous stratum body model. Combined with the rock-soil classification in the model, the complete foundation rock-soil layer characteristics are obtained. The characteristics form the spatial distribution comparison relationship of each rock-soil layer, which provides a basis for subsequent flip bucket structure design.

[0037] Optionally, the step S1 of performing rock-soil layer blocking according to the foundation rock-soil layer characteristics comprises:

[0038] The range of the scour pit is divided into several stratum sections on a plane by using the foundation rock-soil layer characteristics;

[0039] In the embodiment, the range of the scour pit in the plane is divided into several stratum sections by using the foundation rock-soil layer characteristics. Specifically, the surveying and mapping and borehole data are imported into the GIS three-dimensional geological modeling system, a longitudinal section is established in the long axis direction of the scour pit, and a transverse section is established in the short axis direction to obtain the rock-soil layer characteristics of the scour pit. The range of the scour pit is about 150m x 60m, and each section is divided every 15m in the length direction and every 10m in the width direction, thereby forming a longitudinal and transverse intersecting zoning grid.

[0040] If the soil layer types in adjacent stratum sections are the same, and the distribution depth of the rock-soil layer of the same grade differs by no more than 3m, the adjacent stratum sections are divided into the same block to obtain the scour pit foundation rock-soil layer blocking condition.

[0041] In the embodiment, if the soil layer types and the rock-soil grade of adjacent sections are the same, and the rock-soil layer depth difference is not more than 3m, the adjacent stratum sections are divided into the same block to obtain the foundation rock-soil layer blocking set. Specifically, the range of the scour pit is finally divided into 12 blocks: the weak weathered rock layer depth is shallow near the flip bucket side, and the weak weathered rock layer depth is shallow near the right bank side of the river. The blocking set serves as the basic input data for subsequent flip bucket structure optimization and provides accurate zoning parameters for structure anti-scour design.

[0042] Optionally, the step S1 of formulating the flip bucket structure based on the scour pit foundation rock-soil layer blocking condition comprises:

[0043] According to the scour pit foundation rock-soil layer blocking condition, the flip bucket top elevation parameter and the flip angle parameter in the preset flip bucket structure template are adjusted to obtain a first adjustment parameter;

[0044] In this embodiment, the weak weathering rock stratum near the right bank side of the bucket flip bucket is shallow in depth, so the water tongue falling point of the bucket flip bucket should be designed to the right bank side near the bucket flip bucket when the bucket flip bucket is designed. Therefore, the top elevation of the preset bucket flip bucket structure template is 295.5 m, and the flip angle is adjusted from the initial value of 20° to 15°, and the first adjustment parameter is obtained.

[0045] The horizontal bevel angle adjustment parameter in the bucket flip bucket structure template is determined according to the bank slope geometry conditions and the foundation rock and soil layer block conditions on both sides of the spillway erosion pit, and the second adjustment parameter is obtained.

[0046] In this embodiment, the weak weathering bedrock near the right bank side of the river channel is shallow in depth, and the water tongue falling point of the bucket flip bucket should be appropriately offset to the right bank side, and the horizontal bevel angle of the preset bucket flip bucket structure template needs to be adjusted. The initial horizontal bevel angle of the template is 0°, and after the water tongue trajectory is calculated, it is adjusted to 5° to the right bank, so that the water tongue falling point is closer to the weak weathering hard rock stratum, thereby avoiding large erosion pit erosion depth. The bevel angle of 5° is used as the second adjustment parameter.

[0047] The first adjustment parameter and the second adjustment parameter are adaptively checked by using the preset engineering experience library, and the bucket flip bucket structure is obtained.

[0048] In this embodiment, the first adjustment parameter and the second adjustment parameter are adaptively checked by using the preset engineering experience library, and the bucket flip bucket structure is obtained. Specifically, the engineering experience library is composed of the bucket flip bucket design parameters and operation effects of the past 20 similar soft rock foundation spillway projects, and contains the reasonable combination interval of the top elevation, the flip angle and the horizontal bevel angle. The first adjustment parameter (flip angle 15°) and the second adjustment parameter (horizontal bevel angle 5°) are input into the experience library for checking, and it is found that the parameter set is in the safety range verified in the library, and meets the dual requirements of safety and energy dissipation effect, so it is determined as the optimized bucket flip bucket structure.

[0049] Optionally, the water tongue falling point and the erosion pit depth corresponding to each standard working condition at the erosion pit in step S2 are calculated, including:

[0050] The hydraulic parameters under each standard working condition are obtained by using the preset energy dissipation and erosion prevention working condition library.

[0051] In this embodiment, the hydraulic parameters under each standard working condition are obtained by using the preset energy dissipation and erosion prevention working condition library. The working condition library is a hydraulic calculation database constructed in the design stage, which covers the parameters such as inflow, dam front water level and discharge under different return period flood. The energy dissipation and erosion prevention working condition library can include five standard working conditions of design flood frequency of 1 / 5, 1 / 10, 1 / 20, 1 / 30 and 1 / 50, and the corresponding spillway discharge range is 1000-3200 .

[0052] In another embodiment, the working condition library includes five typical working conditions of 1 / 2, 1 / 5, 1 / 10, 1 / 20 and 1 / 30, and the corresponding peak flow rates are 600-1010 .

[0053] The hydraulic parameters under each standard working condition are applied to the bucket flip nose structure, and the water tongue landing points under each standard working condition are calculated.

[0054] In this embodiment, the hydraulic parameters under each standard working condition are applied to the bucket flip nose structure, and the water tongue landing points under each standard working condition are calculated by using the water tongue landing point calculation equation. The water tongue landing point calculation equation is specifically:

[0055] ;

[0056] wherein is the longitudinal horizontal distance (i.e. the jump distance) from the intersection of the flip water tongue landing point and the downstream water surface to the end of the bucket flip nose, is the flow velocity at the top of the bucket flip nose, is the flip angle of the bucket flip nose, is the acceleration of gravity, is the flow depth in the normal direction at the end of the bucket flip nose, is the height difference from the bucket flip nose to the downstream water surface;

[0057] It is worth noting that the initial height of the flip point relative to the downstream water surface should be recorded as: ; wherein is the relative height of the flip point water surface to the reference elevation at the end of the bucket flip nose. If the reference surface at the end of the bucket flip nose and the flip point water surface are regarded as the same vertical reference, and represents the thickness of the flip point water surface (engineering approximation), which can be approximately taken as .

[0058] The flow is regarded as a mass point projectile (ignoring the influence of air resistance, atomization and turbulence on the motion of the center of mass), and the initial velocity component is: , ;

[0059] The vertical displacement motion equation with time (with the downstream water surface as zero position):

[0060] ;

[0061] When falling to the downstream water surface , the solution of time is taken, which satisfies: ;

[0062] The positive root (falling water time ) is:

[0063] ;

[0064] It is worth noting that the quadratic equation in the positive root will get two time solutions, one of which is usually negative, representing the virtual intersection point of the water flow particles before the pick-up point, which has no practical significance; the other is positive, representing the real falling time of the water flow particles from the pick-up point to the downstream water surface. In order to ensure the correctness of the physical interpretation, the positive solution (i.e. plus root) should be selected as the actual falling time of the nappe when calculating.

[0065] Horizontal distance of nappe landing point The horizontal velocity is multiplied by the falling time:

[0066] ;

[0067] And the can be used for calculation.

[0068] It is worth noting that the real nappe will disperse, mix and turbulent decay, and the particle projectile model will overestimate the range. When applied, it is recommended to use an empirical correction coefficient or physical model test calibration.

[0069] In this embodiment, the input hydraulic parameters and the above-mentioned flip bucket structure (top elevation 295.5m, pick-up angle 15°, horizontal bevel angle 5°) are used to obtain the horizontal distance of the nappe landing point from the end of the bucket under each standard working condition, which is 32m, 38m, 42m, 48m and 56m respectively. The calculation results can reflect the change law of the nappe landing point under different flood conditions, and provide input conditions for the prediction of the scour pit depth.

[0070] According to the block condition of the nappe landing point corresponding to the scour pit foundation rock and soil layer, the scour pit depth is calculated.

[0071] In this embodiment, the scour pit depth is calculated according to the block condition of the nappe landing point corresponding to the scour pit foundation rock and soil layer. Specifically, the nappe landing point obtained in this embodiment is projected onto the block concentration of the foundation rock and soil layer, and the scour pit depth calculation formula is used to calculate the scour pit depth formed under each standard working condition, and the formula is as follows:

[0072] ;

[0073] is the maximum water cushion depth from the downstream water surface to the bottom of the scour pit, is the cross-sectional flow per unit width at the end of the pick-up bucket, is the water level difference between upstream and downstream, For the comprehensive erosion coefficient, the rock-soil test results are combined with engineering experience to obtain the value, such as for the bedrock of rock-soil classification I, the joint is not developed, the comprehensive erosion coefficient can be taken as 0.6-0.9, for the bedrock of rock-soil classification II, the joint is relatively developed, the comprehensive erosion coefficient can be taken as 0.9-1.2, for the bedrock of rock-soil classification III, the joint is developed, the comprehensive erosion coefficient can be taken as 1.2-1.6, and for the bedrock of rock-soil classification IV, the joint is very developed, the comprehensive erosion coefficient can be taken as 1.6-2.0.

[0074] In the embodiment, the formula is used to calculate the scour pit depths formed by each standard working condition, which are 5.7 m, 6.3 m, 9.7 m, 14.1 m and 20.6 m respectively.

[0075] It is worth noting that the equations in the method for calculating the scour pit in the embodiment of the application and the method for calculating the water jet landing point under each standard working condition can more accurately calculate the scour pit depth and the water jet landing point compared with the existing method, but similar results can also be obtained by using the existing formula.

[0076] Optionally, the step S2 of optimizing the flip bucket structure according to the water jet landing point and the scour pit depth comprises:

[0077] According to the water jet landing point and the scour pit depth, the upstream slope from the bottom of the scour pit water jet landing point to the flip bucket structure is reviewed, if the upstream slope is not steeper than the preset slope threshold, the flip bucket structure is taken as the structure type to be verified;

[0078] In another embodiment, the calculation result shows that the most steep value of the upstream longitudinal slope of the scour pit under each frequency standard flood working condition is 1:3.6, which is less than the preset slope threshold 1:3.0, indicating that the structure stability of the flip bucket structure under the scour pit forming condition is acceptable and the formed scour pit will not endanger the safety of the flip bucket structure, and the flip bucket structure is taken as the structure type to be verified.

[0079] Otherwise, the flip shooting angle and the horizontal bevel angle of the flip bucket structure are optimized and adjusted, and the step S2 is repeatedly executed until the slope threshold is met.

[0080] In the present embodiment, the longitudinal horizontal distance (i.e. the jump distance) from the water tongue landing point to the end of the bucket lip under the five frequency conditions is determined by the water tongue landing point calculation equation to be 32 m, 38 m, 42 m, 48 m and 56 m respectively, and the plunge pit depth formed under each condition is calculated by the plunge pit depth calculation formula to be 5.7 m, 6.3 m, 9.7 m, 14.1 m and 20.6 m respectively, obtaining the upstream longitudinal slope of the plunge pit bottom to the bucket lip under each condition to be 1:5.61, 1:6.03, 1:4.33, 1:3.33 and 1:2.72 respectively. Compared with the preset slope threshold of 1:3.0, the longitudinal slope ratio of the plunge pit formed under the 1 / 50 frequency condition does not meet the preset slope threshold requirement. Further analysis finds that the upper part of the rock-soil layer block at a bucket distance of 55 m has a large thickness of strongly weathered soil layer, and the rock-soil layer block with good erosion resistance is close to the bucket lip and deviates to the right side of the river channel. Therefore, the bucket lip structure needs to be optimized to shorten the bucket distance under the adverse condition and adjust the water tongue landing point to deviate to the right side of the river channel. The bucket shooting angle is designed to be 10° and 0° respectively, the horizontal bevel angle is adjusted to 15°, and finally when the bucket shooting angle is 0°, the plunge pit position continues to move to the rock-soil layer block which is more solid, the jump distance under each frequency standard condition is 30 m, 36 m, 40 m, 44 m and 50 m respectively, the plunge pit depth formed is 5.5 m, 6.0 m, 9.1 m, 13.2 m and 15.5 m respectively, and the upstream longitudinal slope of the plunge pit bottom to the bucket lip under each condition is 1:5.45, 1:6.0, 1:4.40, 1:3.33 and 1:3.23 respectively. The longitudinal slope between the plunge pit landing point bottom and the bucket lip under each condition meets the preset slope threshold requirement. It shows that the stability of the bucket lip structure under the plunge pit formation condition is acceptable and the formed plunge pit will not endanger the safety of the bucket lip structure. Therefore, under the present analysis, the current bucket lip structure can be used as the structure type to be verified.

[0081] It is worth noting that the preset slope threshold is derived from the provision that the slope should not be steeper than 1:3 in the "Spillway Design Specification" SL253.

[0082] Optionally, step S3 comprises:

[0083] A physical model is established according to the size of the bucket lip structure;

[0084] In the present embodiment, the physical model condition is designed according to the finally determined size of the bucket lip structure (including the lip top width of 1.2 m, the lip top elevation of 0.4 m relative to the downstream water surface, the bucket shooting angle of 0° and the horizontal bevel angle of 15°). The physical model is built with a gravity similarity scale of 1:50, the overall material is transparent polycarbonate side wall to observe the water flow state, and the model bottom plate and the bucket lip weir body material rigidity meets the water tongue impact simulation requirements.

[0085] It is worth noting that the model size and scale should be coordinated.

[0086] According to the anti-impact performance of each rock-soil layer, granular materials are determined, and the granular materials are layered and laid in the physical model according to the distribution of the rock-soil layers of the foundation to generate a dynamic bed model;

[0087] In this embodiment, according to the anti-impact performance of each rock-soil layer of the foundation, different rock-soil layers are simulated by using graded granular materials, the cover layer is fine sand with a particle size of 0.4-0.8 mm, the strongly weathered rock layer is quartz sand particles with a particle size of 2.5-4.0 mm, and the weakly weathered rock layer is divided into blocks with pebbles with a particle size of 25-50 mm. The granular materials such as fine sand, quartz sand particles, and pebbles are layered and laid in the physical model to form a dynamic bed model, and the laying sequence strictly follows the distribution of the original rock-soil layers to ensure that the thickness of each layer is consistent with the proportion of the physical model.

[0088] Control parameters are set in the dynamic bed model, and flow discharge tests are performed on the dynamic bed model after setting the control parameters according to the hydraulic parameters under each standard working condition;

[0089] In this embodiment, flow control valves, flow rate sensors, and high-definition camera observation systems are set in the dynamic bed model. The flow control valves have an accuracy of ±0.5% and can accurately control the discharge flow of each standard flood. The flow rate sensors are arranged at the end of the flip bucket and downstream of the plunge pool at 0.2 m, 0.5 m, 1 m, and 2 m to record the flow velocity and depth in real time. Then, flow discharge tests are performed in the order of 16-64 L / s according to the proposed five frequency working conditions, for example, the duration is 15 minutes, and the water tongue formation and plunge pool flow pattern are continuously photographed during the discharge process of each flow level.

[0090] The water tongue drop point position of the flip bucket energy dissipation and the plunge pool flow pattern during the discharge of each flow level are extracted, and the position and shape of the formed plunge pool are observed to obtain the simulation results.

[0091] In this embodiment, through video analysis and sensor data recording, the water tongue drop point position, plunge pool flow vortex, and splashing situation during the discharge of each flow level are extracted, and the final plunge pool shape and position are calibrated and measured to obtain a complete simulation result set including the plunge pool depth, length, width, and water tongue drop point coordinates.

[0092] Optionally, the comparison of the simulation results and the calculation results in step S4 includes:

[0093] According to the simulation results, the water tongue drop point and the plunge pool depth simulated are determined;

[0094] In this embodiment, the longitudinal length, transverse width and maximum depth of the plunge pool are quantitatively processed according to the plunge pool image obtained from the physical model test and the sensor recording data. Specifically, a high-definition camera can be used to shoot the whole process of forming the plunge pool, the camera has a resolution of 4K, records 60 frames per second, and a three-dimensional image processing software is used to extract the surface morphology of the plunge pool and generate a three-dimensional model of the plunge pool. By calibrating the model coordinate system (the origin is the center of the end of the bucket lip, the X axis is along the length direction of the spillway, and the Y axis is along the width direction), the depth value of the center point of the plunge pool is measured, and the maximum depth , the long axis length and the short axis length are recorded to form a simulated plunge pool depth and range parameter set.

[0095] The simulated water jet landing point and the plunge pool depth are compared with the plunge pool depth and the water jet landing point determined in step S2 respectively to obtain a comparison result.

[0096] In this embodiment, the simulated plunge pool depth is compared with the plunge pool depth obtained in the theoretical calculation in step S2, the error is calculated, and the plunge pool plane range is compared. In the plane range comparison, the simulated water jet landing point position is compared with the theoretical water jet landing point determined in step S2, and the offset is calculated. In this process, the allowable error threshold is set to be ±0.04 m in depth and ±0.1 m in plane position.

[0097] Optionally, the final design scheme of the bucket lip in step S4 includes:

[0098] If the comparison result is within the preset allowable error threshold range, the to-be-verified structure type or the optimized bucket lip structure is taken as the final design scheme of the bucket lip;

[0099] If the comparison result is not within the preset allowable error threshold range, the bucket lip structure is optimized and adjusted according to the simulation result, and steps S2 to S3 are iteratively executed until the simulation result and the calculation result are consistent.

[0100] In this embodiment, the depth error and the water jet landing point position error are obtained by comparing the physical model simulation result obtained in step S3 with the theoretical water jet landing point and the plunge pool depth calculated in step S2. The preset allowable error threshold range is ±0.04 m in plunge pool depth and ±0.1 m in water jet landing point position, and it is considered to be not in compliance if it exceeds the range.

[0101] If the comparison result is within the preset allowable error threshold range, the structure type of this time to be verified or the flip bucket structure after optimization adjustment in step S2 is determined as the final design scheme of the flip bucket, and parameters such as the top elevation, jet angle and horizontal bevel angle of the structure type are recorded as design basis for subsequent design of the pit bank slope support.

[0102] If the comparison result exceeds the allowable error threshold range, the flip bucket structure is adjusted in a targeted manner according to the deviation direction of the pit depth and the offset of the water jet landing point. For example, the jet angle θ of the bucket top can be adjusted by ±2°, the horizontal bevel angle φ can be adjusted by ±5°, and the parameter value of each adjustment is recorded. Subsequently, the optimized structure type is re-applied to step S2 to calculate the water jet landing point and pit depth, and step S3 is re-established to simulate the flow discharge test, and new simulation results are extracted.

[0103] The above iteration process continues until the depth and position errors of the simulation results and the theoretical calculation results meet the preset allowable error threshold range. In the entire iteration process, all simulation and optimization parameters are checked through the engineering experience library to ensure that the adjusted flip bucket structure meets the energy dissipation and erosion prevention requirements under various standard working conditions and ensures the structural stability, forming a final design scheme of the flip bucket that can be directly applied to engineering construction.

[0104] Optionally, the support structure of the target spillway pit bank in step S4 includes:

[0105] According to the simulation results and the final design scheme of the flip bucket, a set of geometric characteristic parameters of the pit is determined.

[0106] In this embodiment, a set of geometric characteristic parameters of the pit is extracted according to the physical model test results and the final design scheme of the flip bucket, including the maximum depth of the pit, the length of the long axis of the pit, the width of the short axis, and the coordinates of the center point of the pit.

[0107] Based on the set of geometric characteristic parameters of the pit, and in combination with the mechanical parameters of each rock and soil layer of the target spillway pit bank, the stability safety factor of the bank slope under the action of the pit is calculated.

[0108] In this embodiment, based on the set of geometric characteristic parameters of the pit, the position and form of the pit are mapped to the geometric conditions of the spillway bank slope, including the bank slope, the position of the slope top, the position of the slope foot and the height of the bank slope, and in combination with the mechanical parameters of each rock and soil layer, such as the shear strength of the soil layer, the friction angle and the density, a bank slope stability calculation model is established. The stability analysis is performed by using the limit equilibrium method to calculate the safety factor FS of the sliding body, and the analysis range covers the maximum failure surface that may occur under the action of the pit, the calculation step is 1m, and the iteration convergence precision is FS change <0.01. ​

[0109] If the stability safety factor is less than the preset safety factor threshold, a selected retaining structure type is selected, and design parameters of the retaining structure are determined based on the pit geometry and geotechnical parameters; wherein the design parameters include retaining structure material, size, arrangement;

[0110] In this embodiment, the calculated stability safety factor is 1.05, which is less than the preset safety factor threshold 1.2, so the retaining structure needs to be set. The retaining structure type is selected as the pile row support of cast-in-place pile, and the design parameters of the retaining structure are pile diameter 1.2m, pile length 18~25m, pile spacing 1.3m, and weak weathered rock depth not less than 3m. After setting the retaining structure, the safety factor of the sliding body is calculated again by using the above-mentioned limit equilibrium method, and the safety factor is 1.26, which meets the requirement that the safety factor is not less than the safety factor threshold 1.2.

[0111] If the stability safety factor is not less than the preset safety factor threshold, the pit bank does not need to be set with retaining measures;

[0112] In another embodiment, the stability factor of the bank after the pit is formed is 1.38, which meets the requirement that the safety factor is not less than the safety factor threshold 1.2, indicating that the stability of the bank formed by the pit meets the requirement, and no special retaining measures need to be set.

[0113] According to the retaining structure type and the design parameters, a retaining structure design scheme of the banks on both sides of the target spillway pit is formed.

[0114] In this embodiment, according to the determined retaining structure type and design parameters, a bank retaining structure design scheme is formed on both sides of the target spillway pit. The design scheme includes the arrangement range of the cast-in-place pile, the segmented pile length, the concrete strength and reinforcement, the construction technical requirements and detection requirements, etc. At the same time, pit bank protection measures such as slope drainage ditch arrangement, slope vegetation coverage or sprayed concrete protective layer need to be added in the design scheme to ensure that the overall stability of the bank and the retaining structure and the energy dissipation and erosion prevention function meet the design target under the action of each standard flood.

[0115] Fig. 2 It is a schematic view of the pick-up energy dissipation structure in the embodiment of the present application; as shown in Fig. 2 1 is the bottom plate of the spillway, 2 is the side wall of the spillway, 1 and 2 form the spillway section, 3 is the pick-up nose weir body, 4 is the pick-up nose weir side wall, wherein the pick-up nose weir body throws the water tongue out by setting a certain pick-up angle; the pick-up nose weir side wall can be set with a corner on the plane to form a bevel angle to adjust the water tongue plane outflow direction, 5 is the above-ground part of the pit bank retaining structure, 6 is the underground part of the pit bank underground retaining structure, and 7 is the pit foundation.

[0116] Wherein 1 and 2 belong to the spillway chute in the flip bucket energy dissipation structure; 5 and 6 jointly constitute the retaining structure of the bank slope on both banks in the flip bucket energy dissipation structure; 3 and 4 jointly constitute the nose structure in the flip bucket energy dissipation structure.

[0117] Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the application being defined by the appended claims and not by the above description, and it is intended to encompass all variations falling within the meaning and the scope of the equivalent technical elements of the application file.

[0118] The foregoing is considered as merely illustrative of the principles of the application, and the application is to be regarded as not limited to such embodiments, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A design method of soft rock foundation spillway flip-flow energy dissipation, characterized in that, The method comprises the following steps: Step S1: obtaining the characteristics of the foundation rock-soil layer at the spillway erosion pit of the target spillway; According to the characteristics of the foundation rock-soil layer, the rock-soil layer is divided, and the bucket lip structure is designed based on the foundation rock-soil layer division of the erosion pit; The step S1 includes: Divide the erosion pit range into several stratum sections on the plane according to the characteristics of the foundation rock-soil layer; If the soil layer types in adjacent stratum sections are the same, and the buried depth of the same level rock-soil layer does not differ by more than 3m, then the adjacent stratum sections are divided into the same block, and the foundation rock-soil layer division of the erosion pit is obtained; The step S1 includes: According to the foundation rock-soil layer division of the erosion pit, adjust the bucket lip top elevation parameter and the jet angle parameter in the preset bucket lip structure template to obtain the first adjustment parameter; Determine the horizontal bevel angle adjustment parameter in the bucket lip structure template according to the bank slope geometric conditions on both sides of the spillway erosion pit and the foundation rock-soil layer division of the erosion pit to obtain the second adjustment parameter; Use the preset engineering experience library to perform parameter group adaptability check on the first adjustment parameter and the second adjustment parameter to obtain the bucket lip structure; Step S2: calculate the water tongue landing point and the erosion pit depth under each standard working condition at the erosion pit by using a preset energy dissipation and erosion prevention working condition library, and optimize the bucket lip structure according to the water tongue landing point and the erosion pit depth; Step S3: simulate the erosion pit erosion under each preset working condition when the flow is discharged; Step S4: compare the simulation results with the calculation results, and generate the final design scheme of the bucket lip according to the comparison results; design the supporting structure of the bank slope on both sides of the target spillway erosion pit according to the simulation results and the final design scheme of the bucket lip.

2. The method according to claim 1, wherein, The step S1 includes: Use a drilling device to perform geological drilling on the target spillway erosion pit to obtain a columnar chart of each drilling hole; Perform geological mapping on the target spillway erosion pit, and combine the geological mapping results with the columnar chart of each drilling hole to obtain the distribution of the foundation rock-soil layer; Sample the foundation rock-soil layer at the erosion pit of the target spillway, and perform a rock-soil test on the sample of the foundation rock-soil layer at the erosion pit, and evaluate the erosion resistance of each rock-soil layer according to the rock-soil test results; Merge the columnar chart of each drilling hole and the distribution of each type of foundation rock-soil layer according to the spatial positional relationship to obtain the characteristics of the foundation rock-soil layer; wherein the spatial positional relationship is the spatial positional relationship between the drilling hole position and the mapping target position in the target spillway erosion pit.

3. The method according to claim 1, wherein, The step S2 includes: Obtain the hydraulics parameters under each standard working condition by using a preset energy dissipation and erosion prevention working condition library; Apply the hydraulics parameters under each standard working condition to the bucket lip structure, and calculate the water tongue landing point under each standard working condition; Calculate the erosion pit depth according to the erosion pit foundation rock-soil layer division corresponding to the water tongue landing point.

4. The method according to claim 1, wherein, The step S2 includes: According to the water jet landing point and the depth of the scour pit, the upstream slope from the bottom of the water jet landing point to the flip bucket structure is reviewed. If the upstream slope is not steeper than the preset slope threshold, the flip bucket structure is selected as the to-be-verified structure type; Otherwise, the flip angle and horizontal bevel angle of the flip bucket structure are adjusted and optimized, and step S2 is repeatedly executed until the slope threshold is met.

5. The method for design of soft rock foundation spillway flip- rap energy dissipation according to claim 1, characterized in that, Step S3 includes: Establishing a physical model according to the size of the flip bucket structure; Determine the granular material according to the scour resistance of each rock and soil layer, and lay the granular material in the physical model according to the distribution of the rock and soil layers, to generate a dynamic bed model; Set control parameters in the dynamic bed model, and conduct flow discharge test on the dynamic bed model with set control parameters according to the hydraulic parameters under each standard working condition; Extract the water jet landing point position and the flow pattern of the scour pit in the flow discharge test at each flow discharge, and observe the position and shape of the formed scour pit to obtain the simulation results.

6. The method for design of soft rock foundation spillway flip- rap energy dissipation according to claim 1, wherein, The comparison of the simulation results and the calculation results in step S4 includes: According to the simulation results, the water jet landing point and the depth of the scour pit obtained by simulation are determined; Compare the water jet landing point and the depth of the scour pit obtained by simulation with the water jet landing point and the depth of the scour pit determined in step S2 respectively, to obtain the comparison results.

7. The method for design of soft rock foundation spillway flip- rap energy dissipation according to claim 1, wherein, The generation of the final design scheme of the flip bucket in step S4 includes: If the comparison results are within the preset allowable error threshold, the to-be-verified structure type or the optimized flip bucket structure is selected as the final design scheme of the flip bucket; If the comparison results are not within the preset allowable error threshold, the flip bucket structure is optimized and adjusted according to the simulation results, and steps S2 to S3 are iteratively executed until the simulation results and the calculation results are consistent.

8. The method for design of soft rock foundation spillway flip- rap energy dissipation according to claim 1, wherein, The design of the retaining structure of the target spillway scour pit in step S4 includes: According to the simulation results and the final design scheme of the flip bucket, the geometric characteristic parameter set of the scour pit is determined; Based on the geometric characteristic parameter set of the scour pit and combined with the mechanical parameters of each rock and soil layer of the target spillway scour pit, the stability safety factor of the two bank slopes under the action of the scour pit is calculated; If the stability safety factor is less than the preset safety factor threshold, the type of the retaining structure is selected, and the design parameters of the retaining structure are determined based on the geometric characteristics of the scour pit and the rock and soil mechanical parameters; The design parameters include the material, size and arrangement of the retaining structure; If the stability safety factor is not less than the preset safety factor threshold, the scour pit bank slope does not need to be set with a retaining measure; According to the type and design parameters of the retaining structure, the design scheme of the retaining structure of the target spillway scour pit is formed.

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