Calculation method and application of relative flow velocity coefficient and impact force of debris flow for slit arc dam

Abstract

The present invention discloses a method for measuring the relative flow velocity coefficient and impact force of debris flow on a slit arc dam, as well as its application. Aiming at the inherent defects of the solid dam of the existing arc retaining dam, the present invention first provides a slit arc retaining dam. To solve the design problem of the slit arc retaining dam, the present invention defines the relative flow velocity coefficient of debris flow on the slit arc retaining dam, which represents the ratio of the flow velocity behind the debris flow dam to the flow velocity in front of the dam. The measurement method of this coefficient is to use parameters such as the opening width, median particle size of debris flow, and dam width obtained from on-site investigations, and calculate this coefficient in two cases. The present invention also provides a method for measuring the maximum impact force of debris flow on a slit arc retaining dam, which is determined by calculating according to the formula using parameters such as the Froude number, debris flow density, debris flow channel inclination angle, and flow depth in front of the dam obtained from on-site investigations. It solves the problem of measuring the maximum impact force of debris flow on each opening unit of a single-opening slit arc retaining dam or a multi-opening slit arc retaining dam. The present invention can guide the design of slit arc retaining dams.

Description

Technical Field

[0001] The present invention relates to an engineering measurement method, and particularly to a method for measuring the characteristics of debris flow passing over a dam of a gap-shaped arc-shaped retaining dam, belonging to the fields of mountain disaster prevention and control, engineering surveying, and engineering structure design. Background Art

[0002] Retaining dams are the most important engineering means for debris flow prevention and control, and also the engineering means with the longest history of use for people to control the mountain disaster environment. In long-term engineering practice, debris flow retaining dams have evolved from early traditional closed solid retaining dams to permeable retaining dams. The latter can better meet the design and construction objectives of debris flow retaining dams for intercepting debris flow, raising the erosion datum of the gully bed, and silting back to slow down the longitudinal slope of the local gully bed, and further achieve environmental governance objectives such as suppressing the formation of debris flow or reducing the occurrence frequency and scale of debris flow outbreaks. According to different permeable opening structures, permeable retaining dams can be divided into different types. The gap dam is a permeable retaining dam with one or several vertical strip-shaped openings in the middle and lower parts of the dam body. Whether it is a closed solid retaining dam or a permeable retaining dam with various forms, the common feature is that the impact surface of the retaining dam is designed as a vertical structure, that is, they all belong to "vertical retaining dams". During the process of being impacted by debris flow, the position of the dam foundation of the vertical retaining dam bears a large impact force, which is extremely likely to cause stress concentration at this position and lead to local impact damage.

[0003] The prior art (Wang Dongpo et al., Research on the dynamic response of debris flow impacting an arc-shaped retaining dam, Rock and Soil Mechanics, December 2020) discloses an arc-shaped retaining dam scheme, which optimizes the dam foundation structure of the vertical retaining dam into an arc shape. On the one hand, this optimization enhances the local strength at the dam foundation position, and on the other hand, it guides the kinetic energy of debris flow to be converted into potential energy and frictional heat energy through the arc surface of the dam foundation, so as to achieve the purpose of reducing the impact energy of debris flow on the dam, and finally realize the prevention and control objectives of reducing the risk of retaining dam failure and effectively preventing debris flow disasters. This literature also conducts theoretical calculation research on debris flow impacting an arc-shaped retaining dam based on the conservation of momentum and energy, and provides a method for calculating the impact force of debris flow on the arc-shaped retaining dam.

[0004] The above-mentioned arc-shaped retaining dam is essentially a solid dam. Although there are improvements in the safety performance against impact, it still retains the inherent disadvantages of solid dams. For example, solid dams only have the function of intercepting debris flow and cannot regulate debris flow, resulting in a series of problems such as being easily filled up during actual operation and losing the retaining effect on subsequent debris flow. Summary of the Invention

[0005] The purpose of the present invention is to provide a new debris flow retaining dam scheme on the basis of combining the existing arc-shaped retaining dam and the gap dam in view of the deficiencies of the prior art, and further provide a method for measuring important design parameters in the design of this new retaining dam.

[0006] To achieve the above object, the present invention first provides a slit arc retaining dam. The slit arc retaining dam is a permeable retaining dam, combining the characteristics of a slit dam and an arc dam: (1) The upstream flow-facing surface of the dam foundation (i.e., the lower part of the debris flow impact surface) is designed as an arc (arc radius R), giving play to the technical advantages of existing arc retaining dams such as strong foundation and energy dissipation; (2) One or more vertical strip openings are provided in the middle and lower parts of the dam body, giving play to the technical advantages of the slit dam in retaining debris and reducing water pressure through permeation.

[0007] The present invention further provides a technical solution for calculating the relative flow velocity coefficient of debris flow for the slit arc retaining dam, which is as follows:

[0008] A method for calculating the relative flow velocity coefficient of debris flow for a slit arc retaining dam, characterized in that: basic data is obtained through on-site investigation, and then the relative flow velocity coefficient of debris flow for the slit arc retaining dam is calculated according to Equation 1.

[0009]

[0010] In the formula, λ - the relative flow velocity coefficient of debris flow for the slit arc retaining dam.

[0011] B - the relative opening width of the slit arc retaining dam, determined by basic data.

[0012] d 50 - the median particle size of debris flow, in m, determined by basic data.

[0013] B 0 - the dam width, in m, determined by basic data.

[0014] The physical meaning of the relative flow velocity coefficient λ of debris flow for the slit arc retaining dam is the ratio of the flow velocity uf behind the dam to the flow velocity u 0 in front of the dam. When the debris flow passes through the slit arc retaining dam (i.e., over the dam), the dam opening becomes a cross-section that suddenly narrows between the upstream and downstream channels, resulting in a change in the debris flow field. Specifically, the cross-sectional width of the actual debris flow passing over the dam is greater than the opening width ( Figure 2 ). This change is reflected in the change in the debris flow velocity before and after the dam, and is characterized by the relative flow velocity coefficient λ. Due to the instantaneous change in the impact movement of the debris flow on the dam caused by the change in velocity, the determination of the relative flow velocity coefficient λ is an important variable for calculating multiple movement characteristic indexes during the process of debris flow passing over the dam. The prior art has not disclosed a technical solution for calculating the relative flow velocity coefficient λ of debris flow.

[0015] Since the relative flow velocity coefficient λ of debris flow is an important variable for calculating multiple movement characteristic indexes during the process of debris flow passing over the dam, the present invention also provides the following solution:

[0016] Application of the above method for calculating the relative flow velocity coefficient of debris flow in a slit-arc retaining dam to the measurement of the characteristics of debris flow passing over the dam.

[0017] Application of the above method for calculating the relative flow velocity coefficient of debris flow in a slit-arc retaining dam to the design of the slit-arc retaining dam.

[0018] Based on the previous research results, the present invention optimizes the characteristic index of debris flow passing over the dam as the impact force of debris flow on the dam, and provides a method for calculating the maximum impact force of debris flow on a slit-arc retaining dam. The scheme is as follows:

[0019] A method for calculating the maximum impact force of debris flow on a slit-arc retaining dam realized by using the above method for calculating the relative flow velocity coefficient of debris flow in a slit-arc retaining dam, which is characterized in that it is applicable to a slit-arc retaining dam with a single opening and an arc radius R = 2h 0 ~3h 0 where h 0 is the depth of debris flow 1 m in front of the dam; basic data is obtained through on-site investigation, and then the maximum impact force f of debris flow passing over the dam is calculated according to Equation 2 max ,

[0020]

[0021] In the formula, f max - the maximum impact force of debris flow passing over the slit-arc retaining dam,

[0022] Fr - Froude number, determined by basic data,

[0023] ρ - debris flow density, unit kg / m 3 , determined by basic data,

[0024] g - gravitational acceleration constant, unit m / s 2 ,

[0025] α - debris flow channel inclination angle, unit °, determined by basic data,

[0026] h 0 - the depth of debris flow in front of the debris flow dam, unit m, determined by basic data.

[0027] The above technical scheme for calculating the maximum impact force of debris flow is applicable to a slit-arc retaining dam with a single opening, and it is required that the arc radius R of the dam foundation is 2 to 3 times the depth h of debris flow in front of the dam 0 . The remaining specification parameters of the slit-arc retaining dam (such as the relationship between the opening height and the depth h of debris flow in front of the dam 0 ) can follow the general standards, practices, references, etc. of vertical slit dams in the prior art.

[0028] The basic principle of the above impact force measurement scheme is as follows:

[0029] (1) Establish a simplified research model for the movement of the debris flow impact gap arc retaining dam ( Figure 1 and Figure 2 ). In the simplified research model, α is the inclination angle of the debris flow channel (with the gravity component as the coordinate system), h j is the climbing height of the debris flow along the arc surface, the o-o section is the position section in front of the debris flow entering the gap arc retaining dam (u 0 and h 0 represent the flow velocity and flow depth of the debris flow passing through this section respectively, that is, the flow velocity and flow depth in front of the dam), the f-f section is the position section where the debris flow passes through the opening (u f and h f represent the flow velocity and flow depth of the debris flow passing through this section respectively, that is, the flow velocity and flow depth behind the dam), the j-j section is the position section where the debris flow climbs along the arc surface (u j and b j represent the flow velocity and flow depth of the debris flow passing through this section respectively), B 0 and B f are the dam width and the opening width respectively;

[0030] (2) Based on the simplified research model, establish the mass conservation equation (Equation 3) and the momentum conservation equation (Equation 4) for the climbing part of the debris flow entering the circular arc section (j-j) of the dam foundation;

[0031]

[0032] The left side term of Equation 3 is the mass of the debris flow passing through the control volume, and the right side term is the mass of the debris flow entering the control surface of the circular arc section. In the formula, ρ is the density of the debris flow; u is the flow velocity of the debris flow; t is the movement time of the debris flow; V j is the calculated control volume of the climbing part of the debris flow in the circular arc section (j-j); ∑j is the calculated control area of the climbing part of the debris flow entering the circular arc section (j-j); n is the normal vector of the control surface, and the direction is positive to the right.

[0033]

[0034] The first term on the left side of Equation 4 is the change of the momentum of the debris flow entering the climbing part of the circular arc section (j-j) with time, and the second term is the momentum flux passing through the control surface (j-j). The first term on the right side is the volume force of the debris flow entering the climbing part of the circular arc section (j-j), and the second term is the surface force of the control surface (j-j). In the formula, F Vj is the volume force of the debris flow entering the climbing part of the circular arc section (j-j), and F ∑j is the surface force of the control surface (j-j). Establish a description scheme for the four terms on the left and right, and then substitute it into Equation 4, then the maximum impact force of the debris flow (f max ) can be described as Equation 2.

[0035] (3) The above mass conservation equation (Equation 3) and momentum conservation equation (Equation 4) are both related to the velocity u of the debris flow in front of the dam. 0 and the velocity behind the dam u f Therefore, the velocity variation characteristics of debris flow over the dam are the key variables of the impact force f of the debris flow on the dam, f = f(u f ,u 0 ). By solving equation 3 and equation 4 together, we can obtain the maximum impact force f of the debris flow. max The maximum impact force f is determined by the expression max is the velocity behind the dam u f and the flow velocity u before the dam 0 The function of the ratio, The present invention defines this ratio as the relative velocity coefficient λ of the debris flow in the gap arc retaining dam,

[0036] The above-mentioned method for calculating the maximum impact force of debris flow on the gap arc retaining dam solves the problem of calculating the impact force of a single-opening gap dam. For a gap dam with multiple openings, when the openings are of the same specification and arranged evenly, each opening is a calculation unit, and the f calculated according to the formula max It is the maximum impact force of the debris flow over the dam in each opening unit.

[0037] The maximum impact force of debris flow passing through the dam is the most important indicator in the strength design of the retaining dam. The technical solution of the present invention can accurately quantify the impact force of debris flow on the gap arc retaining dam, thereby providing an important basis for the design of the retaining dam. At the same time, the impact force measurement technical solution of the present invention shows that for the gap arc retaining dam, the maximum impact force of the debris flow has nothing to do with the arc structure design at the dam foundation. This result can provide important technical guidance for the structural design of the gap arc retaining dam. Therefore, the present invention also provides the following solutions:

[0038] The invention discloses an application of the maximum impact force calculation method of debris flow passing through a gap arc retaining dam in the design of the gap arc retaining dam.

[0039] In the present invention, the on-site investigation includes various mapping, measurement, simulation test and testing of the mountain torrent mud-rock flow channel where the project is located, as well as the acquisition of historical disaster records and the acquisition of empirical data for reference.

[0040] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a gap arc retaining dam solution, which combines the structural features of the existing gap dam and arc dam. Test data show that the retaining dam structure can effectively reduce the impact force of debris flow on the dam, and play a good role in reducing the destructive impact of debris flow and protecting the prevention and control engineering structures. (2) The present invention defines the relative velocity coefficient α of the debris flow of the gap arc retaining dam, which is used to characterize the velocity u behind the debris flow dam. f and the flow velocity u before the dam 0The ratio is an effective tool for measuring the instantaneous change characteristics of the impact movement of debris flow on the slit-arc retaining dam, and is of great significance for the design of the slit-arc retaining dam. The present invention provides a technical solution for measuring this coefficient for the first time. (3) The present invention further provides a method for calculating the maximum impact force of debris flow on the slit-arc retaining dam, which solves the problem of calculating the maximum impact force of debris flow passing through the dam for each opening unit of a single-opening slit-arc retaining dam or a multi-opening slit-arc retaining dam. (4) The present invention simultaneously provides a method for calculating the relative flow velocity coefficient of debris flow on the slit-arc retaining dam and the application of the method for calculating the maximum impact force of debris flow on the slit-arc retaining dam in the design of the slit-arc retaining dam. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a calculation model of debris flow impacting a slit-arc retaining dam (side view).

[0042] Figure 2 is a calculation model of debris flow impacting a slit-arc retaining dam (top view).

[0043] Figure 3 is a schematic three-dimensional structure diagram of a slit-arc retaining dam in Embodiment 1.

[0044] Figure 4 is a schematic side view structure diagram of a slit-arc retaining dam in Embodiment 1.

[0045] Figure 5 is a schematic front view structure diagram of a slit-arc retaining dam in Embodiment 1.

[0046] Figure 6 Comparison of theoretical calculation values and test data.

[0047] The numerical marks in the drawings are respectively:

[0048] 1 arc structure 2 opening width 3 dam foundation 4 crown beam DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] The preferred embodiments of the present invention will be further described below with reference to the drawings.

[0050] Embodiment 1

[0051] An indoor physical model test is used to measure the maximum impact force of debris flow on the slit-arc retaining dam.

[0052] 1. Test device

[0053] The indoor model test uses a debris flow flume test system, which is a modification of the test system in the prior art (Wang Dongpo et al., Research on the dynamic response of debris flow impacting an arc retaining dam, Rock and Soil Mechanics, December 2020). The arc retaining dam installed at the end of the flume in this literature is replaced with a slit-arc retaining dam. The structure of the slit-arc retaining dam is as Figures 3 to 5as shown Figure 3 is a three-dimensional structural schematic diagram of the gap arc retaining dam Figure 4 is a side view structural schematic diagram of the gap arc retaining dam Figure 5 is a front view structural schematic diagram of the gap arc retaining dam. Dam width B 0 = 0.25m, number of openings n = 1, opening width B f = 0.06m, relative opening width B = B f / B 0 = 0.24

[0054] 2. Experimental design

[0055] Sampling the on-site debris flow source material, obtaining the particle size distribution curve through particle screening tests, and determining the median particle size d of the debris flow according to the particle size distribution curve 50 = 0.0075m; through on-site sampling and measurement, determining the debris flow density ρ = 1446 kg / m 3 ; during the experiment, keep the flume slope (channel inclination angle) a = 20°

[0056] 16 groups of experiments are carried out. The debris flow volume V for each group: for the 1st - 4th groups, 0.017 m 3 , for the 5th - 8th groups, 0.022 m 3 , for the 9th - 12th groups, 0.028 m 3 , for the 13th - 16th groups, 0.039 m 3 .

[0057] Sensors respectively collect the debris flow velocity u 0 in front of the dam, the flow depth h 0 in front of the dam, and the debris flow impact force f data. Calculate the relative velocity coefficient λ of the debris flow of the gap arc retaining dam for each group of experiments according to Equation 1, and calculate the maximum impact force f 2 of the debris flow passing through the dam of the gap arc retaining dam for each group of experiments according to Equation 2 (g = 9.8 m / s max ). The calculation of the Froude number Fr is based on the existing technology

[0058] The main parameter indicators and measurement result data of the experiment are as shown in Table 1 below

[0059] Table 1 Indoor physical model test data of the gap arc retaining dam

[0060]

[0061]

[0062] Result verification: Compare the theoretical calculated value of the maximum impact force with the experimental measurement data. The results are as Figure 6 . Figure 6It shows that there is good consistency between the theoretical value of the debris flow impact gap arc retaining dam obtained by the theoretical formula and the measured value in the experiment.

[0063] Comparative Example 1

[0064] Table 2 lists the data of the calculated maximum impact force and the measured maximum impact force in the same-condition experiment as in Table 1 without considering the relative flow velocity coefficient λ. The comparison between the data in Table 2 and Table 1 shows that, without considering the influence of the relative flow velocity coefficient λ defined in the technical solution of the present invention, the calculated maximum impact force f′ max has a large deviation from the measured result.

[0065] Table 2 Influence of not considering the relative flow velocity coefficient λ on the calculation result of the impact force

[0066]

[0067]

[0068] Comparative Example 2

[0069] Table 3 lists the experimental data under the same conditions as in Table 1, where the gap arc retaining dam used in the experimental system of Example 1 is replaced by the arc retaining dam used in the prior art (Wang Dongpo et al., Research on the dynamic response of debris flow impact arc retaining dam, Rock and Soil Mechanics, December 2020). The comparison between the data in Table 3 and Table 1 shows that adopting the gap arc retaining dam structure can significantly reduce the maximum impact force of the debris flow on the dam.

[0070] Table 1 Indoor physical model test data of the gap arc retaining dam

[0071]

Claims

1. Measuring method for relative flow velocity coefficient of debris flow in a slit-arc retaining dam, Characterized in that: Basic data are obtained through on-site investigation, and then the relative flow velocity coefficient of debris flow in the slit-arc retaining dam is calculated according to Equation 1, where λ is the relative flow velocity coefficient of debris flow in the slit-arc retaining dam, B is the relative opening width of the slit-arc retaining dam, which is determined by basic data, d 50 — Median particle size of debris flow, unit: m, basic data determined B 0 — Dam width, unit: m, determined by basic data.

2. Application of the measuring method for relative flow velocity coefficient of debris flow in a slit-arc retaining dam according to Claim 1 in measuring the characteristics index of debris flow passing over the slit-arc retaining dam.

3. Application of the measuring method for relative flow velocity coefficient of debris flow in a slit-arc retaining dam according to Claim 1 in the design of the slit-arc retaining dam.

4. Measuring method for maximum impact force of debris flow in a slit-arc retaining dam realized by using the measuring method for relative flow velocity coefficient of debris flow in a slit-arc retaining dam according to Claim 1, Characterized in that: Applicable to a single opening with an arc radius R = 2h 0 ~3h 0 of the gap arc retaining dam, where h 0 is the debris flow depth 1 m in front of the dam; basic data are obtained through on-site investigation, and then the maximum impact force f of the debris flow passing over the dam is calculated according to Equation 2 max , where f max — the maximum impact force of debris flow passing through the gap arc retaining dam Fr is the Froude number, which is determined by basic data, ρ—the density of debris flow, unit: kg / m 3 , basic data determined g—the gravitational acceleration constant, unit m / s 2 , α is the inclination angle of the debris flow channel, in degrees, which is determined by basic data h 0 — Flow depth in front of the debris flow dam, unit m, determined by basic data.

5. According to the measuring method for maximum impact force of debris flow according to Claim 4, Characterized in that: A gap arc retaining dam applicable to multiple openings with the same opening specifications and evenly arranged, f max is the maximum impact force of debris flow passing over the dam for each opening unit.

6. Application of the measuring method for maximum impact force of debris flow passing over the slit-arc retaining dam according to Claim 4 or 5 in the strength design of the slit-arc retaining dam.

7. According to the application according to Claim 6, Characterized in that: It is the strength design and / or structural design of the slit-arc retaining dam.

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