Method for calculating impact force of debris flow on retaining wall

Abstract

The invention discloses a method for calculating the impact force of debris flow on a retaining wall. The technical problem that in the prior art, calculation of the impact force of the debris flow is not comprehensive and reasonable enough is solved. The calculation method comprises the following steps: step 100, acquiring an impact pressure stress coefficient, and determining an action point of an impact force resultant force; step 200, calculating distribution of impact pressure stress according to the impact pressure stress coefficient; step 300, calculating the effective impact acting distance of debris flow on the wall body of the retaining wall in the length direction of the channel; step 400, determining an index related to the debris flow substance viscosity degree according to the impact pressure stress coefficient and the effective impact action distance; step 500, determining a dimensionless correction coefficient related to the effective impact acting distance and the index according to the effective impact acting distance and the index; step 600, determining the resultant force of the impact force and correcting the resultant force according to a dimensionless correction coefficient; and step 700, determining the linear distribution force of the impact force along the length direction of the wall body, and correcting according to the dimensionless correction coefficient.

Description

Technical Field

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

[0002] Debris flow generally refers to a special torrent of landslides caused by heavy rain, heavy snow or other natural disasters in mountainous areas or other areas with deep valleys and steep terrain, carrying a large amount of mud, sand and stones. A typical debris flow is composed of thick mud rich in silt and clay with coarse solid debris suspended in it, and has a great impact during movement.

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

[0004] In fact, the impact force of debris flow on retaining wall includes three basic elements: distribution pattern, force magnitude and point of action of resultant force. Strictly speaking, only when these three elements are determined can the impact force of debris flow on retaining wall be determined comprehensively and reasonably. However, in view of the complexity of such problems, previous related studies have mainly focused on determining the resultant force of debris flow impact force, while the distribution of impact force along the height of the wall and the point of action of resultant force are rarely studied. In particular, in engineering practice, the impact force of debris flow on retaining wall is generally estimated by empirical approximation, which is somewhat blind, resulting in unreasonable engineering design results of 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 a debris flow on a retaining wall, so as to solve the technical problem that the calculation of the debris flow impact force in the prior art is not comprehensive and reasonable enough.

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

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

[0008] Step 100, obtaining the impact compressive stress coefficient along the height direction of the retaining wall, and determining the point of action of the combined impact force of the debris flow on the retaining wall;

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

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

[0011] Step 400, determining an index related to the viscosity of debris flow materials according to the impact compressive stress coefficient and the effective impact action distance;

[0012] Step 500, determining a 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, determining the resultant impact force of the debris flow on the retaining wall and correcting it according to the dimensionless correction coefficient;

[0014] Step 700, determining the linear distribution force of the impact force of the debris flow on the retaining wall along the length direction of the wall and correcting it according to the dimensionless correction coefficient.

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

[0016] In summary, the present invention has clear principles, a simple and easy-to-operate calculation process, and relatively accurate calculation results. It can quantitatively determine the distribution pattern, resultant force, 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 present invention is further described below in conjunction with the accompanying drawings and specific embodiments. Additional aspects and advantages of the present invention will be partially given in the following description, partially become apparent from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of the present invention are used to assist in understanding the present invention. The contents provided in the drawings and their related descriptions in the present invention can be used to explain the present invention, but do not constitute improper limitations on the present invention. In the drawings:

[0019] Figure 1 It is a schematic diagram of the debris flow, retaining wall and ditch involved in the present invention.

[0020] Figure 2 This is a distribution diagram of the 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 of the calculation result of the impact compressive stress coefficient in the embodiment of the present invention and the observation result of the physical model test. DETAILED DESCRIPTION

[0022] The present invention is described clearly and completely below in conjunction with the accompanying drawings. A person skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention in conjunction with the accompanying drawings, it should be particularly noted that:

[0023] The technical solutions and technical features provided in each part of the present invention, including the following description, may be combined with each other if there is no conflict.

[0024] In addition, the embodiments of the present invention involved in the following description are generally only a part of the embodiments of the present invention, rather than all the embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0025] About the terms and units in the present invention: The terms "include", "have" and any variations thereof in the description and claims of the present invention and related parts are intended to cover non-exclusive inclusions.

[0026] Figure 1 The figure is a schematic diagram of the debris flow, retaining wall and channel involved in the present invention. Figure 1 The specific implementation method of the method for calculating the impact force of debris flow on the retaining wall shown includes the following steps:

[0027] Step 100, obtaining the impact compressive stress coefficient η along the height direction of the retaining wall, and determining the point of action of the combined impact force F 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 density of the debris flow, and H is the height of the retaining wall. The centroid of the distribution diagram of the impact compressive stress coefficient η is the point of action of the resultant impact force F; or, according to the formula z a = 0.4H to calculate the point of action of the resultant impact force F, where z a is the height from the point of action of the resultant impact force F to the bottom of the retaining wall, and H is the height of the retaining wall.

[0029] Step 200, calculating 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, calculating the effective impact distance S of the debris flow on the retaining wall along the length direction of the channel;

[0031] Step 400, determining an index n related to the viscosity of debris flow materials according to the impact pressure stress coefficient η and the effective impact action distance S;

[0032] Step 500, determining a 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, determining the resultant force F of the debris flow on the retaining wall and correcting it according to the dimensionless correction coefficient ξ;

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

[0035] 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] Where λ = z / H, z is the height from any point on the back of the retaining wall to the bottom of the wall, H is the height of the retaining wall; e is a natural constant; a1, a2, and a3 are all fitting parameters.

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

[0039] In step 200, the calculation expression for 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] Where ρ is the density of debris flow material; g is the acceleration of gravity; and H is the height of the retaining wall.

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

[0043]

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

[0045] The friction coefficient μ of the channel bottom at the retaining wall position can be obtained in a variety of ways, such as through experimental methods or by empirical methods in the specifications based on the characteristics of debris flow materials; the debris flow velocity v can also be obtained in a variety of ways, such as by numerical simulation methods (such as 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 "Design Specification for Debris Flow Prevention and Control Engineering (T / CAGHP 021-2018)".

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

[0047]

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

[0049] In step 500, the dimensionless correction coefficient ξ can fully reflect the material properties of the debris flow, the kinematic properties of the debris flow, the channel properties, the geometric properties of the retaining wall, and other related main factors, so that the calculation results of the impact force F and the linear distribution 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 impact force F corrected by the dimensionless correction coefficient ξ is:

[0052] F=ξρdwv 2

[0053] Where w is the channel width at the retaining wall or the length of the retaining wall.

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

[0055] q=ξρdv 2

[0056] The calculation formulas for the resultant impact force F and the linear distributed force q both include the dimensionless correction coefficient ξ, which can fully reflect the main factors related to the material properties of debris flow, the kinematic properties of debris flow, the channel properties, the geometric properties of the retaining wall, etc., thereby providing an accurate basis for the engineering design of debris flow retaining walls.

[0057] The beneficial effects of the present invention are described below by way of examples.

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

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

[0060]

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

[0062]

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

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

[0065]

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

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

[0068] Step 600: Calculate the impact force F=24214.93 kN after correction using the dimensionless correction coefficient ξ

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

[0070] Figure 3 : is a comparison chart of the calculated results of the impact pressure stress coefficient η in the embodiment of the present invention and the observed results of the physical model test. Figure 3 As shown, the two are well consistent, and the goodness of fit of the impact compressive stress coefficient η distribution curve to the experimental observation results 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 point of action of the resultant impact force F in step 100, one way to determine it is: the point of action of the resultant impact force F on the retaining wall is about 0.4H = 2.0m from the bottom of the retaining wall. Or, according to Figure 3 The point of action of the resultant impact force F determined by the centroid of the distribution diagram of the impact compressive stress coefficient η calculated by the present invention is 0.401H=2.005m. 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 According to the observation results of the physical model test shown in , the corresponding calculation shows that the height of the impact force F action point from the bottom of the retaining wall is about 0.431H=2.155m. It can be seen that the maximum error between the calculation result of the impact force F action point of the method of the present invention and the observation result of the physical model test is about 8%, which is within the acceptable error range in engineering practice.

[0073] The above is a description of the relevant contents of the present invention. A person skilled in the art will be able to implement the present invention based on these descriptions. Based on the above contents of the present invention, all other embodiments obtained by a person skilled in the art without creative work shall fall within the scope of protection of the present invention.

Claims

1. A method for calculating the impact force of debris flow on retaining wall, characterized in that: The following steps are involved: Step 100, obtaining the impact compressive stress coefficient along the height direction of the retaining wall, and determining the point of action of the combined impact force of the debris flow on the retaining wall; Step 200, calculating the distribution of the impact compressive stress along the height direction of the retaining wall according to the impact compressive stress coefficient; Step 300, calculating the effective impact distance of the debris flow on the retaining wall along the length direction of the channel; Step 400, determining an index related to the viscosity of debris flow materials according to the impact compressive stress coefficient and the effective impact action distance; Step 500, determining a 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, determining the resultant impact force of the debris flow on the retaining wall and correcting it according to the dimensionless correction coefficient; Step 700, determining the linear distribution force of the impact force of the debris flow on the retaining wall along the length direction of the wall and correcting it according to the dimensionless correction coefficient.

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

3. The method for calculating the impact force of a debris flow on a retaining wall according to claim 1, characterized in that: In step 100, the centroid of the impact compressive stress coefficient distribution diagram is used as the point of action of the resultant impact force; or, According to the formula z a =0.4H to calculate the point of action of the resultant impact force, where z a is the height from the point of action of the resultant impact force to the bottom of the retaining wall, and H is the height of the retaining wall.

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

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

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

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

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

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

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