CN114444292A - Method for measuring and calculating maximum depth of lower scouring of dam of window dam and application - Google Patents
Method for measuring and calculating maximum depth of lower scouring of dam of window dam and application Download PDFInfo
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Abstract
The invention discloses a method for measuring and calculating the maximum depth of lower scouring of a dam of a window dam and application. Aiming at the defect that the influence of the opening form of the window dam on the lower scouring depth of the dam is not considered in the prior art, the invention provides the method for measuring and calculating the maximum depth of the lower scouring of the window dam. The measuring and calculating method of the invention takes the opening form of the window dam as an influencing factor, essentially takes the difference of the characteristics of the dynamic process of debris flow dam crossing and scouring caused by the difference of the opening forms as the constraint condition for measuring and calculating the scouring depth, and ensures that the structural significance of the characteristic of the large opening of the window dam is fully embodied in the measuring and calculating principle of the maximum scouring depth. The calculation process is simple and convenient, the influence rule of each parameter on the calculation result can be reflected, and a more reliable basis can be provided for the design of the window dam. The invention also provides an application scheme of the measuring and calculating method in window dam design, window dam prevention and control engineering systems and safety assessment.
Description
Technical Field
The invention relates to a debris flow prevention and control engineering structure technology, in particular to a design method and application of a debris flow sand retaining dam, and belongs to the technical field of debris flow disaster prevention and control engineering and building engineering design.
Background
The sand dam is a key prevention and control project for regulating and controlling the movement of debris flow. By means of the functional characteristics of sand blocking and throttling, debris flow force reduction, elevation of erosion surfaces of local gully beds, control of gravity erosion of trenches, increase of stability of the gully beds and the like, and the technical characteristics of low construction cost, low construction technical requirements, quick engineering effect and the like, the sand blocking dam is widely applied to debris flow disaster prevention and control and becomes the most important debris flow prevention and control engineering means. The overflow section structure of the sand blocking dam can be divided into two types of permeable type and non-permeable type (also called solid dam). One kind of window dam transmission type sand blocking is basically characterized in that the dam body overflow section is of a large-opening-hole type open structure.
The essence of the dam lower scouring is the scouring impact of the dam-crossing debris flow and the large stones wrapped by the dam-crossing debris flow on the ditch bed, and belongs to a natural phenomenon which cannot be eliminated. The erosion pit is formed by the lower erosion of the dam, and the erosion of the foundation soil of the dam is aggravated, so that the dam foundation is suspended easily to cause unstable overturning or washout failure of the main body of the sand dam, and the problem becomes an extension problem to be solved in the sand dam engineering. Relevant research shows that 65% of the reasons for instability of the sand retaining dam are that the dam body is damaged due to the fact that scouring is continuously developed behind the dam. In the dam project, the dam anti-scour energy dissipation facilities such as a fender, an auxiliary dam, a submerged dam and the like are additionally arranged under the dam to protect the ditch bed, so that the problems are delayed. However, as the operation time of the sand retaining dam increases, the energy dissipation facility can be gradually damaged and failed, and the formation of the erosion dam under the dam can not be blocked. Therefore, in the design of the window dam, the accurate estimation of the lower scouring depth of the dam is an important reference or basis for the dam foundation burial depth design.
In the prior art, a T/CAGHP021-2018 debris flow control engineering design specification (trial) is generally used for reference, and a Valley-Yiyi equation, a rockfall impact depth and a local scouring depth of torrential flow are comprehensively adopted to determine a dam lower scouring depth (Shishengwei and the like, and a research on a technical method for repairing and reinforcing foundation soil of a sand dam by using a small-caliber steel pipe pile, engineering science and technology, Vol.51No.5, and 2019 months). The method comprehensively considers the influence of single width flow of the debris flow, the flow rate of the debris flow, the standard grain diameter of bed sand, the depth of the overflow port mud, the difference between the upper mud level and the lower mud level of the dam and the like on the lower scouring depth of the dam, but does not consider the influence of the opening (hole) form of the window dam on the lower scouring depth of the dam. The window dam is mainly characterized by being a large opening, and the most central function of the window dam is to utilize large openings (holes) in different forms to realize a series of regulation and control functions of peak clipping, flow reduction and mud and sand blocking of debris flow. Due to the fact that the debris flow crossing process and the dynamic characteristics of the window dams with different opening forms (holes)/conditions are greatly different, on one hand, the debris flow regulating and controlling functions of the window dams with different opening forms (holes)/conditions are different, and on the other hand, the erosion phenomenon of the window dams with different opening forms (holes)/conditions is also greatly different. This means that when the dam lower erosion depth is measured, if the opening (hole) form/condition is not considered, the measurement principle may be inconsistent with the actual regulation and control principle of the dam, and the actual reference value of the measurement result in the engineering is limited.
Disclosure of Invention
The invention aims to provide a method for measuring and calculating the maximum depth of the lower scouring of a dam of a window dam and application of the method in the engineering design of a sand retaining dam aiming at the defects of the prior art.
In order to achieve the purpose, the invention firstly provides a method for measuring and calculating the maximum depth of the lower scouring of the dam of the window dam, and the technical scheme is as follows:
a method for measuring and calculating the maximum depth of lower scouring of a dam of a window dam is characterized by comprising the following steps: firstly, site selection of a window dam is completed, and site investigation is implemented to obtain basic data; secondly, calculating the maximum depth h of lower scouring of the dam of the window dam according to the formulas 1 and 2d，
hd/H＝0.076I+1.975i-0.209Cv-0.096R +0.234 formula 1
I＝b/dmaxFormula 2
In the formula, hdH-dimensionless depth of scouring,
h-effective dam height of the window dam, unit m, basic data determination,
i-relative opening degree of the window dam,
b-width of opening of window dam, unit m, basic data determination,
dmaxdetermining the maximum particle size of solid matter in the debris flow in unit m according to basic data,
i-window dam position trench bed gradient,%, basic data determination,
Cvdetermining the volume concentration of the silt in the debris flow without dimensional quantity and basic data,
r is the aperture ratio of the window dam, and is determined by basic data.
The method for measuring and calculating the maximum depth h of lower scouring of the dam of the window damdMore fully stated, the dam-crossing debris flow of the window dam is flushed to the maximum possible depth of a flushing pit formed on the flushing surface of the dam-below trench bed. The measuring and calculating method is to establish an equation on a large amount of experimental test data and field observation and investigation data and to complete the measurement and calculation through dimensional analysis. The significance of the measuring and calculating method lies in that under the condition that the opening form of the window dam is comprehensively considered, a novel dimensionless dam lower scouring depth calculating method is provided, and the method is simple in calculation and can reflect the influence rule of each parameter. In the method, newly introduced I is a measurement index reflecting the size of a single window opening; the newly introduced R is a measure reflecting the characteristics of the entire window dam opening. These two metrics are the core parameters of the window dam as distinguished from the solid dam. The introduction of I and R ensures that the measuring and calculating method is closer to the actual operation process of the window dam, and the measuring and calculating result can guide the design of the window dam.
In order to ensure the validity of the measuring and calculating result, under the optimal conditions, the method for measuring and calculating the maximum depth of the lower scouring of the window dam is suitable for the window dam with the opening rate R of 0.08-0.32 and is suitable for the general characteristics of the bottom material of the natural debris flow channel bed, namely the material gradation of the bottom material of the channel bed is similar to the material gradation of the debris flow.
Maximum depth h of lower brush of dam of window damdThe method is an important reference index for finishing the design of the dam foundation burial depth parameters of the window dam in the design of the window dam, so the method simultaneously provides the following steps:
the method for measuring and calculating the maximum depth of the lower scouring of the window dam is applied to the design of the window dam.
Maximum lower wash of dam of window damDepth hdThe invention is an important reference index for designing the thickness parameters of the underdam scour prevention and energy dissipation facilities such as the apron, the auxiliary dam, the submerged dam and the like in the window dam prevention and control engineering system, so the invention simultaneously provides the following steps:
the method for measuring and calculating the maximum depth of the lower scouring of the window dam is applied to the design of a window dam prevention and control engineering system. More particularly to the application in the design of the anti-impact energy dissipation facility under the dam.
The method for measuring and calculating the maximum depth of the lower scouring of the dam of the window dam refers to a trench bed gradient i index. After the window dam is put into operation, along with the increase of the operation age and the accumulation of phenomena such as silting, silting back and the like, the shape of the ditch bed can be changed, and the direct result is that the index of the ditch bed gradient i is changed. Therefore, for the window dam in operation with the changing trench bed gradient i, the method for measuring and calculating the maximum scouring depth h can be useddAnd compared with the design parameters of the dam foundation burial depth of the window dam, the operation safety and stability of the window dam are roughly evaluated. Thus, the present invention also provides:
the method for measuring and calculating the maximum under-scouring depth of the window dam is applied to the operation safety assessment of a window dam/window dam prevention and treatment engineering system.
According to the experimental design established by the method for measuring and calculating the maximum depth of the under-scouring of the dam of the window dam, the two technical schemes related to the method for measuring and calculating the maximum depth of the under-scouring of the dam of the window dam are applied, and the prior limiting condition is that the method is applied to the window dam with the aperture opening ratio R being 0.08-0.32.
In each technical scheme of the invention, the field investigation implemented comprises various surveying and mapping, measurement and simulation experiment tests aiming at the mountain torrent and debris flow channel field where the engineering is located, historical disaster record acquisition, empirical data acquisition with reference and reference functions and the like.
Compared with the prior art, the invention has the beneficial effects that: (1) compared with the prior art that the measurement and calculation idea of the dam lower scouring depth refers to a hydraulic engineering formula and is assisted by a designer to carry out experience value taking, the measurement and calculation method is a scientific calculation method based on standard survey data and is a complete scientific solution. (2) The most important defect of the prior art is that the window dam opening form is not taken into consideration for depth measurement. The measuring and calculating method takes the opening form of the window dam as an influencing factor and decomposes the influencing factor into two measuring and calculating variables of the relative opening I and the opening ratio R of the window dam, essentially takes the difference of the characteristics of the dynamic process of debris flow dam crossing and scouring caused by the difference of the opening forms as the constraint condition for measuring and calculating the scouring depth, ensures that the structural significance of the characteristic of the large opening of the window dam is fully embodied in the measuring and calculating principle of the maximum scouring depth, and ensures that the measuring and calculating method principle is more consistent with the natural law. (3) The measuring and calculating method has the advantages of simple and convenient calculation process and simple value of each parameter, can reflect the influence rule of each parameter on the calculation result, and can provide more reliable basis for the design of the window dam. (3) The invention also provides an application scheme of the measuring and calculating method in window dam design, window dam prevention and treatment engineering systems and safety assessment.
Detailed Description
The preferred embodiments of the present invention are further described below.
Example one
The method is used for measuring and calculating the maximum depth h of the lower scouring of the dam of a certain window dam in the design of the certain window damd。
A debris flow gully is located in Wen Chuan county of Chang nationality of Qiang of Kangjiang province, Sichuan province and belongs to a primary tributary of Minjiang right bank. The area of the channel flow field is 54.26km2The length of the main trench is 15.74km, and the average longitudinal ratio of the main trench bed is reduced to 201 per mill. The plane form of the drainage basin is in a tree leaf shape, the upstream of the valley is narrow and is mostly in a V shape, the middle and downstream are wide and slowly in a U shape, the local width is alternate, the mountain height slope in the valley is steep, the longitudinal slope of the valley is larger, the collection of rainfall is facilitated, and a foundation is provided for the outbreak of debris flow. National G213 and venturi freeway projects pass through this gully, with 017 rural roads downstream in the basin, and venturi freeways pass through in the form of bridges at the gully. In addition, tens of residential areas are distributed on the ditch opening, and hydropower stations are built. The ditch has a plurality of times of storm debris flows, and serious threats are caused to hydropower stations, residential areas and traffic engineering at the ditch opening. In order to meet the requirements of disaster prevention and reduction, a window dam project is newly built in the ditch, and the design standard is that P is 2% (meeting in 50 years).
1. Site selection and site survey
And completing site selection of the window dam in the ditch according to the construction specification of the debris flow prevention engineering design, and carrying out field investigation to obtain various basic data. The method comprises the following steps:
p is 5% (20 years once): density rho of mud-rock fluid in ditchc＝1.81t/m3The density sigma of solid matters in the debris flow is 2.65t/m3Clear water density rho in the debris flow is 1.0t/m3Maximum particle size d of solid matter of debris flowmaxThe ratio of the groove bed to the window dam is 1.0m, and the ratio of the drop i to the window dam is 100 per thousand.
The average designed width B of the window dam is 40m, the effective dam height H is 7m, the opening width B of the window dam is 0.8m, the opening height H is 1.0m, and the number of the openings n is 20.
Calculating and determining the volume concentration C of the sediment in the debris flow according to the prior art (formula 3 and formula 4)vThe window opening ratio R was 0.49 (unit), 5.71%.
In the above formula 3, [ rho ]cIs the density (t/m) of the mud-rock fluid3) Rho is clear water density (t/m) in the debris flow3) And sigma is the density (t/m) of solid matters in the debris flow3) In formula 4, n is the number of openings, B is the opening width (m), h is the opening height (m), and B is the average width (m) of the window dam; h is the effective dam height (m) of the window dam.
2. Measuring and calculating maximum depth h of lower scouring of damd
Calculating the relative opening I of the window dam to be 1.0 and the dimensionless scouring depth h according to the formula 1 and the formula 2 by the parametersd0.384 and the maximum depth H of the lower brush of the damd＝2.69m。
Example two
The method of the invention is used for checking the maximum depth h of the lower scouring of the dam of a certain window damd。
A debris flow ditch is positioned in 4 groups of dam villages under general capital town of Puge county of Liangshan, Sichuan province and belongs to a first-level branch ditch of the right bank of a black river. The area of the channel region is 23.30km2The length of the main trench is 10.47km, and the average longitudinal ratio of the main trench bed is reduced to 195 per mill. The whole form of the drainage basin is in a 'leaf' shape, the mountain in the ditch area is high and steep, the longitudinal slope of the ditch is large, debris flow accumulation is rich in the ditch area, and a plurality of collapse points and loose slope accumulation exist on two sides of the ditch area, so that a source condition is provided for debris flow outbreak. The gully is a typical minority village. The ditch has been exposed to large debris flow, which damages the ditch highway and causes river blockage, thus seriously threatening villages at the ditches. In order to meet the requirements of disaster prevention and reduction, three sand dams, which are window dams, are built in the ditch before and after decades of time. Currently, the 1# dam operates well; the No. 2 dam is toppled and damaged; the 3# dam operates for decades and is close to a damaged state, the lower scouring of the dam is the most serious, the results of field measurement of a scouring surface and a scouring pit show that the scouring depth of the maximum scouring position reaches 1.9 m. The three dams are designed according to the design standard P of 2 percent by referring to relevant data (one meeting in 50 years).
1. On-site survey
And acquiring various basic data according to the field survey of the 3# dam. The method comprises the following steps:
p is 5% (20 years once): density rho of mud-rock fluid in ditchc＝1.84t/m3The density sigma of solid matters in the debris flow is 2.65t/m3Clear water density rho in the debris flow is 1.0t/m3Maximum particle size d of solid matter of debris flowmax1.0m, and the specific drop i of the ditch bed at the 3# window dam position is 89 per thousand.
The average width B of the 3# window dam is 30m, the effective dam height H is 5.5m, the opening width B of the window dam is 0.8m, the opening height H is 1.0m, and the number of the openings n is 8.
Determination of the mud-rock flow sediment volume concentration C by means of the same prior art calculation as in example onevThe window dam aperture ratio R was 0.48 (unit) and 3.88%.
2. Measuring and calculating maximum depth h of lower scouring of damd
Calculating the relative opening I of the window dam to be 1.0 by the parameters according to the formula 1 and the formula 2, and performing dimensionless rushDepth h of brushd0.365/H, maximum depth H of lower dam brushd＝2.01m。
The field investigation result shows that the 3# dam is close to the damage degree, a plurality of scouring pits are formed on the lower scouring surface of the dam, and the depth of accumulated water in the pits is about 1.4m on average. If the debris flow occurs again, even if the dam body can continue to operate, the debris flow crossing the dam mainly has the landfill phenomenon of the scoured pit, and the scouring depth is difficult to further increase. Therefore, the erosion depth data of the maximum erosion position under the dam for field investigation can be regarded as the maximum erosion depth under the dam of the 3# window dam. The measured result 2.01m by adopting the method of the invention is close to the measured value 1.9 m.
Claims (8)
1. The method for measuring and calculating the maximum depth of the lower scouring of the dam of the window dam is characterized by comprising the following steps: firstly, site selection of a window dam is completed, and site investigation is implemented to obtain basic data; secondly, calculating the maximum depth h of lower scouring of the dam of the window dam according to the formulas 1 and 2d，
hd/H＝0.076I+1.975i-0.209Cv-0.096R +0.234 formula 1
I＝b/dmaxFormula 2
In the formula, hdthe/H-dimensionless scouring depth,
effective dam height of the H-window dam, unit m, basic data determination,
i-the relative opening of the window dam,
b-the width of the opening of the window dam, unit m, basic data determination,
dmax-maximum particle size of solid matter of the debris flow, in m, is determined from the basic data,
i-window dam position trench bed gradient,%, basic data determination,
Cv-volume concentration of silt in the debris flow, dimensionless quantity, basis data determination,
r-window dam opening ratio, determined by basic data.
2. The method of claim 1, wherein: the aperture ratio R of the window dam is determined by calculation according to the formula 4
In the formula, n-number of openings
h-the height of the opening of the window dam, unit m, basic data determination,
b-average width of window dam, unit m, basic data determination.
3. The metric calculation method according to claim 1, wherein: the method is suitable for the window dam with the aperture opening ratio R of 0.08-0.32.
4. The metric calculation method according to claim 1, wherein: the method is suitable for natural debris flow channels with the similar bed bottom material gradation and debris flow solid material gradation.
5. The application of the method for measuring and calculating the maximum depth of the under-scouring of the window dam as claimed in any one of claims 1 to 3 in the design of the window dam.
6. The application of the method for measuring and calculating the maximum depth of the under-scouring of the window dam as claimed in any one of claims 1 to 3 in the design of a control engineering system of the window dam.
7. Use according to claim 6, characterized in that: the method is applied to the design of anti-impact energy dissipation facilities under the dam.
8. The application of the method for measuring and calculating the maximum depth of the under-scouring of the window dam as claimed in any one of claims 1 to 3 in the operation safety assessment of a window dam/window dam control engineering system.
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