A calculation method for the impact force of debris flow on a retaining wall

Abstract

The present invention discloses a calculation method for the impact force of debris flow on a retaining wall, which solves the technical problem that the calculation of the impact force of debris flow in the prior art is not comprehensive and reasonable enough. The calculation method includes the following steps: Step 100, obtain the impact compressive stress coefficient and determine the action point of the resultant impact force; Step 200, calculate the distribution of the impact compressive stress according to the impact compressive stress coefficient; Step 300, calculate the effective impact action distance of the debris flow on the retaining wall along the channel length direction; Step 400, determine the index related to the viscosity of the debris flow material according to the impact compressive stress coefficient and the effective impact action distance; Step 500, determine the dimensionless correction coefficient related to the effective impact action distance and the index according to the effective impact action distance and the index; Step 600, determine the resultant impact force and correct it according to the dimensionless correction coefficient; Step 700, determine the linear distributed force of the impact force along the wall length direction and correct it according to the dimensionless correction coefficient.

Description

Technical Field

[0001] The present invention relates to the technical field of geological disaster prevention and control engineering, and more particularly, to a method for calculating the impact force of debris flow on a retaining wall. Background Art

[0002] Debris flow generally refers to a special flood in mountainous areas or other deep valleys and steep terrains, which is caused by heavy rain, heavy snow or other natural disasters, resulting in landslides and carrying a large amount of sediment and stones. A typical debris flow consists of a viscous mud slurry suspended with coarse solid debris and rich in silt and clay, and has a large impact force during the movement process.

[0003] In order to prevent and control debris flow disasters, retaining walls are usually set in debris flow channels (especially in the near gully mouth section). Therefore, how to reasonably design and construct retaining walls is of great significance in relevant prevention and control engineering practices. Among them, reasonably determining the impact pressure of debris flow on the retaining wall is one of the key technical links. However, due to the strong non-uniformity and non-linearity of the material composition and movement characteristics of debris flow, the impact force of debris flow on the retaining wall is also a complex non-linear problem.

[0004] In fact, the impact force of debris flow on the retaining wall includes three basic elements: the distribution pattern, the magnitude of the acting force, and the acting point of the resultant force. Strictly speaking, only when these three elements are determined can the impact force of debris flow on the retaining wall be comprehensively and reasonably determined. However, due to the complexity of such problems, previous related studies mainly focused on determining the resultant force of debris flow impact force, and rarely involved the study of the distribution of impact force along the wall height and the acting point of the resultant force. In particular, in engineering practice, the impact force of debris flow on the retaining wall is generally estimated approximately by experience, which has a certain blindness, resulting in unreasonable engineering design results of the retaining wall. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for calculating the impact force of debris flow on a retaining wall to solve the technical problem that the calculation of debris flow impact force in the prior art is not comprehensive and reasonable.

[0006] To achieve the above object, the present invention provides a method for calculating the impact force of debris flow on a retaining wall, and the technical solution is as follows:

[0007] A method for calculating the impact force of debris flow on a retaining wall includes the following steps:

[0008] Step 100, obtain the impact pressure stress coefficient along the height direction of the retaining wall, and determine the acting point of the resultant force of the impact force of debris flow on the retaining wall;

[0009] Step 200: Calculate the distribution of impact compressive stress along the height direction of the retaining wall according to the impact compressive stress coefficient;

[0010] Step 300: Calculate the effective impact action distance of the debris flow on the retaining wall along the channel length direction;

[0011] Step 400: Determine the index related to the viscosity of the debris flow material according to the impact compressive stress coefficient and the effective impact action distance;

[0012] Step 500: Determine the dimensionless correction coefficient related to the effective impact action distance and the index according to the effective impact action distance and the index;

[0013] Step 600: Determine the resultant force of the impact force of the debris flow on the retaining wall and correct it according to the dimensionless correction coefficient;

[0014] Step 700: Determine the linear distributed force of the impact force of the debris flow on the retaining wall along the wall length direction and correct it according to the dimensionless correction coefficient.

[0015] The outstanding advantages of a method for calculating the impact force of debris flow on a retaining wall of the present invention are as follows: (1) By calculating the distribution of impact compressive stress through the impact compressive stress coefficient, the present invention can form a quantitative characterization of the impact compressive stress distribution pattern. (2) The present invention uses the effective impact action distance to characterize the impact dynamic action of the debris flow on the wall within a certain length range behind the retaining wall, so as to fully consider the spatial effect of the debris flow impacting the retaining wall. (3) The present invention calculates the index that can characterize the viscosity of the debris flow material based on the impact compressive stress coefficient and the effective impact action distance, then calculates the dimensionless correction coefficient based on the effective impact action distance and the index, and uses the dimensionless correction coefficient to correct the calculation results of the resultant force of the impact force and the linear distributed force. It not only quantitatively characterizes the magnitude of the resultant force of the impact force, but also fully considers the comprehensive influence of relevant factors such as the debris flow material properties, debris flow kinematic properties, retaining wall geometric properties, and channel properties, making the calculation results more comprehensive and accurate.

[0016] In summary, the principle of the present invention is clear, the calculation process is simple and easy to operate, and the calculation results are relatively accurate. It can quantitatively determine the distribution pattern, resultant force magnitude, and action point of the debris flow impact force acting on the debris flow retaining wall, thereby providing a scientific and accurate basis for the engineering design of the debris flow retaining wall.

[0017] The following further describes the present invention in conjunction with the drawings and specific embodiments. The additional aspects and advantages of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0018] The accompanying drawings that form a part of the present invention are used to assist in understanding the present invention. The content provided in the accompanying drawings and the descriptions related thereto in the present invention can be used to explain the present invention, but do not constitute an undue limitation on the present invention. In the accompanying drawings:

[0019] Figure 1 It is a schematic diagram of debris flow, retaining wall, and channel related to the present invention.

[0020] Figure 2 It is a distribution diagram of impact compressive stress along the height direction of the retaining wall in an embodiment of the present invention.

[0021] Figure 3 It is a comparison diagram between the calculation result of the impact compressive stress coefficient and the observation result of the physical model test in an embodiment of the present invention. Detailed implementation manners

[0022] The present invention will be clearly and completely described below with reference to the accompanying drawings. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. Before describing the present invention with reference to the accompanying drawings, it should be particularly noted that:

[0023] The technical solutions and technical features provided in each part including the following description in the present invention can be combined with each other without conflict.

[0024] In addition, the embodiments of the present invention involved in the following description are usually only a part of the embodiments of the present invention, rather than all embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts should fall within the protection scope of the present invention.

[0025] Regarding the terms and units in the present invention. The terms "include", "have" and any variations thereof in the specification, claims and relevant parts of the present invention are intended to cover non-exclusive inclusion.

[0026] Figure 1 It is a schematic diagram of debris flow, retaining wall, and channel related to the present invention. The specific implementation manner of the calculation method of the impact force of the debris flow on the retaining wall shown in the present invention includes the following steps: Figure 1 The impact force of the debris flow on the retaining wall shown in the present invention is calculated by the following steps:

[0027] Step 100, obtain the impact compressive stress coefficient η along the height direction of the retaining wall, and determine the acting point of the resultant force F of the impact force of the debris flow on the retaining wall;

[0028] The actual meaning of the impact compressive stress coefficient η is η = σ / (γH), where σ is the impact compressive stress, γ is the debris flow density, and H is the wall height of the retaining wall. The centroid of the distribution diagram of the impact compressive stress coefficient η is taken as the action point of the resultant force F of the impact force; or, the action point of the resultant force F of the impact force is calculated according to the formula z a = 0.4H, where z a is the height of the action point of the resultant force F of the impact force from the bottom of the retaining wall, and H is the wall height of the retaining wall.

[0029] Step 200, calculate the distribution of the impact compressive stress σ along the height direction of the retaining wall according to the impact compressive stress coefficient η;

[0030] Step 300, calculate the effective impact action distance S of the debris flow on the retaining wall along the channel length direction;

[0031] Step 400, determine the index n related to the viscosity of the debris flow material according to the impact compressive stress coefficient η and the effective impact action distance S;

[0032] Step 500, determine the dimensionless correction coefficient ξ related to the effective impact action distance S and the index n according to the effective impact action distance S and the index n;

[0033] Step 600, determine the resultant force F of the impact force of the debris flow on the retaining wall and correct it according to the dimensionless correction coefficient ξ;

[0034] Step 700, determine the linear distributed force q of the impact force of the debris flow on the retaining wall along the wall length direction and correct it according to the dimensionless correction coefficient ξ;

[0035] Among them, in step 100, the distribution of the impact compressive stress coefficient η along the height direction of the retaining wall is obtained through experiments, and then a single-peak parabola expression is fitted to express the impact compressive stress coefficient η, which can accurately reflect the distribution of the impact compressive stress coefficient η along the height direction of the retaining wall. The calculation expression of the obtained impact compressive stress coefficient η is:

[0036]

[0037] In the formula, λ = z / H, z is the height of any point on the back of the retaining wall from the bottom of the wall, and H is the wall height of the retaining wall; e is the natural constant; a1, a2, and a3 are all fitting parameters.

[0038] The test is an indoor static physical model test of dilute debris flow. The geometric similarity ratio of the model to the prototype is 10:1, and the specific gravity similarity ratio is 1:1. The wall height of the model retaining wall is 15 cm, and the specific gravity of the model debris flow is 14.1 kN / m 3. The test results show that at the model retaining wall, different characteristics of impact accumulation are presented at different positions along the height direction of the wall. At the heights of 1.5 cm, 4.5 cm, 7.5 cm, 10.5 cm, and 13.5 cm from the bottom of the model retaining wall, the average impact compressive stress (for multiple groups of tests) on the retaining wall is 4.08 kPa, 8.51 kPa, 4.93 kPa, 3.48 kPa, and 1.59 kPa in sequence. By performing non-linear curve fitting on the measured results, a general calculation expression of this impact compressive stress coefficient η with three fitting parameters can be obtained.

[0039] In step 200, the calculation expression for calculating the impact compressive stress σ along the height direction of the retaining wall based on the proposed impact compressive stress coefficient η is:

[0040] σ = ρgHη

[0041] In the formula, ρ is the density of debris flow material; g is the acceleration due to gravity; H is the height of the retaining wall.

[0042] In step 300, the calculation expression for the effective impact distance S of the debris flow on the retaining wall along the channel length direction is:

[0043]

[0044] In the formula, v is the debris flow velocity; μ is the friction coefficient at the bottom of the channel at the location of the retaining wall; θ is the inclination angle of the channel at the location of the retaining wall.

[0045] The friction coefficient μ at the bottom of the channel at the location of the retaining wall can be obtained in various ways, such as through experimental methods or determined by empirical methods in the specifications based on the characteristics of debris flow materials; the debris flow velocity v can also be obtained in various ways, such as through numerical simulation methods (such as the commercial numerical simulation software RAMMS:DEBRIS FLOW) or empirical estimation methods in relevant specifications. Preferably, it can be determined according to the relevant algorithms in the "Code for Design of Debris Flow Control Engineering (T / CAGHP 021 - 2018)".

[0046] In step 400, according to the principle of equivalent resultant force, the calculation expression for the index n related to the viscosity of debris flow material is:

[0047]

[0048] In the formula, d is the depth of debris flow accumulation behind the retaining wall; lg represents the logarithmic function with base 10; d in dz is the differential symbol.

[0049] In step 500, the dimensionless correction coefficient ξ can comprehensively reflect the relevant main factors such as the material properties of debris flow, the kinematic properties of debris flow, the channel properties, and the geometric properties of the retaining wall, so that the calculation results of the resultant impact force F and the linear distributed force q are more comprehensive and accurate. The calculation expression of the dimensionless correction coefficient ξ is:

[0050]

[0051] In step 600, the calculation expression of the resultant impact force F corrected by the dimensionless correction coefficient ξ is:

[0052] F = ξρdwv 2

[0053] In the formula, w is the channel width or the retaining wall length at the position of the retaining wall.

[0054] In step 700, the calculation expression of the linear distributed force q corrected by the dimensionless correction coefficient ξ is:

[0055] q = ξρdv 2

[0056] The calculation formulas of the resultant impact force F and the linear distributed force q both include the dimensionless correction coefficient ξ, which can also comprehensively reflect the relevant main factors such as the material properties of debris flow, the kinematic properties of debris flow, the channel properties, and the geometric properties of the retaining wall, so as to provide an accurate basis for the engineering design of debris flow retaining walls.

[0057] The beneficial effects of the present invention are illustrated by the following embodiments.

[0058] For a debris flow in a certain mountainous area, a retaining wall is adopted at the gully mouth to prevent and control debris flow disasters. Through on-site investigation, tests and numerical simulation calculations, its basic parameters are obtained as follows: the debris flow material is dilute, the density of the debris flow material ρ = 1600 kg / m 3 , the debris flow velocity v = 4.5 m / s, the channel width or the retaining wall length w at the position of the retaining wall = 30 m, the depth of debris flow accumulation d behind the retaining wall = 4.48 m, the channel inclination angle θ at the position of the retaining wall = 30°, the bottom friction coefficient μ of the channel at the position of the retaining wall = 0.2679, and the height H of the retaining wall = 5.0 m.

[0059] Step 100: Take a1 = 9.5133, a2 = 27.5923, a3 = 0.4708, and calculate the impact pressure coefficient η along the height direction of the retaining wall:

[0060]

[0061] Step 200: Calculate the impact pressure σ along the height direction of the retaining wall:

[0062]

[0063] The distribution diagram of the impact compressive stress σ along the height direction of the retaining wall is as Figure 2 shown.

[0064] Step 300: Calculate the effective impact action distance S:

[0065]

[0066] Step 400: Calculate the index n related to the viscosity of debris flow material, n = 10.3406

[0067] Step 500: Calculate the dimensionless correction coefficient ξ = 5.5608

[0068] Step 600: Calculate the resultant force F of the impact force corrected by the dimensionless correction coefficient ξ = 24214.93 kN

[0069] Step 700: Calculate the linear distributed force q corrected by the dimensionless correction coefficient ξ = 807.16 kN / m

[0070] Figure 3 is the comparison diagram between the calculation result of the impact compressive stress coefficient η in the embodiment of the present invention and the observation result of the physical model test. As Figure 3 shown, the two are in good agreement. The goodness of fit of the distribution curve of the impact compressive stress coefficient η to the test observation result can reach 0.9356. It can be seen that the calculation method of the impact force of debris flow on the retaining wall of the present invention is reasonable and can provide a convenient and effective means for the engineering design of debris flow retaining walls.

[0071] Regarding the action point of the resultant force F of the impact force in Step 100, one determination method is: the action point of the resultant force F of the impact force on the retaining wall body is about 0.4H = 2.0 m above the bottom of the retaining wall. Or, according to Figure 3 the action point of the resultant force F determined by the centroid of the distribution diagram of the impact compressive stress coefficient η calculated according to the present invention shown is 0.401H = 2.005 m. It can be seen that the results of the two determination methods are almost the same.

[0072] At the same time, according to Figure 3 the observation result of the physical model test shown, the action point of the resultant force F of the impact force can be calculated accordingly to be about 0.431H = 2.155 m above the bottom of the retaining wall. It can be seen that the maximum error between the calculation result of the action point of the resultant force F of the method of the present invention and the observation result of the physical model test is about 8%, which belongs to the acceptable error range in engineering practice.

[0073] The above describes the relevant content of the present invention. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. Based on the above content of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

Claims

1. A calculation method for the impact force of debris flow on a retaining wall, characterized in that: It includes the following steps: Step 100: Obtain the impact pressure stress coefficient in the height direction of the retaining wall, and determine the acting point of the resultant force of the debris flow impact on the retaining wall; Step 200: Calculate the distribution of the impact pressure stress in the height direction of the retaining wall according to the impact pressure stress coefficient; Step 300: Calculate the effective impact action distance of the debris flow on the retaining wall body in the channel length direction; Step 400: Determine the index related to the viscosity of the debris flow material according to the impact pressure stress coefficient and the effective impact action distance; Step 500: Determine the dimensionless correction coefficient related to the effective impact action distance and the index according to the effective impact action distance and the index; Step 600: Determine the resultant force of the debris flow impact on the retaining wall body and correct it according to the dimensionless correction coefficient; Step 700: Determine the linear distributed force of the debris flow impact on the retaining wall body in the wall length direction and correct it according to the dimensionless correction coefficient.

2. The calculation method of the impact force of debris flow on the retaining wall according to claim 1, characterized in that: In Step 100, the calculation expression of the impact pressure stress coefficient is: In the formula, η is the impact pressure stress coefficient, and its actual meaning is η = σ / (γH), where σ is the impact pressure stress, γ is the debris flow density, and H is the height of the retaining wall body; λ = z / H, z is the height of any point on the retaining wall back from the wall bottom; e is the natural constant; a1, a2, and a3 are all fitting parameters.

3. The calculation method of the impact force of debris flow on the retaining wall according to claim 1, characterized in that: In Step 100, take the centroid of the impact pressure stress coefficient distribution diagram as the acting point of the resultant force of the impact; or, Calculate the acting point of the resultant impact force according to the formula z a = 0.4H, where z a is the height of the acting point of the resultant impact force from the bottom of the retaining wall, and H is the height of the retaining wall body.

4. The calculation method of the impact force of debris flow on a retaining wall according to claim 1, characterized in that: In Step 200, the calculation expression of the impact pressure stress is: σ = ρgHη In the formula, σ is the impact pressure stress; ρ is the density of the debris flow material; g is the acceleration due to gravity; H is the height of the retaining wall body; η is the impact pressure stress coefficient.

5. The calculation method of the impact force of debris flow on a retaining wall according to claim 1, characterized in that: In Step 300, the calculation expression of the effective impact action distance is: In the formula, S is the effective impact action distance; v is the debris flow velocity; g is the acceleration due to gravity; μ is the channel bottom friction coefficient at the retaining wall location; θ is the channel inclination angle at the retaining wall location.

6. The calculation method of the impact force of debris flow on the retaining wall according to claim 1, characterized in that: In Step 400, the calculation expression of the index related to the viscosity of the debris flow material is: In the formula, n is the index related to the viscosity of the debris flow material; g is the acceleration due to gravity; H is the height of the retaining wall body; S is the effective impact action distance; d is the depth of the debris flow accumulation behind the retaining wall; z is the height of any point on the retaining wall back from the wall bottom; ρ is the density of the debris flow material; lg represents the logarithmic function with base 10.

7. The calculation method of the impact force of debris flow on the retaining wall according to claim 1, characterized in that: In Step 500, the calculation expression of the dimensionless correction coefficient is: In the formula, ξ is the dimensionless correction coefficient; ρ is the density of the debris flow material; n is the index related to the viscosity of the debris flow material; S is the effective impact action distance; H is the height of the retaining wall body; v is the debris flow velocity.

8. The calculation method of the impact force of debris flow on a retaining wall according to claim 1, characterized in that: In Step 600, the calculation expression of the resultant force of the impact corrected by the dimensionless correction coefficient is: F = ξρdwv 2 In the formula, F is the resultant force of the impact; ξ is the dimensionless correction coefficient; ρ is the density of the debris flow material; d is the depth of the debris flow accumulation behind the retaining wall; w is the channel width or the retaining wall body length at the retaining wall location; v is the debris flow velocity.

9. The calculation method of the impact force of debris flow on the retaining wall according to claim 1, characterized in that: In Step 700, the calculation expression of the linear distributed force corrected by the dimensionless correction coefficient is: q = ξρdv 2 Wherein, q is the line distributed force; ξ is the dimensionless correction coefficient; ρ is the density of debris flow material; d is the accumulated depth of debris flow behind the retaining wall; v is the flow velocity of debris flow.

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