Debris flow accumulation length calculation method

Abstract

The invention discloses a debris flow accumulation length calculation method, belongs to the technical field of debris flow motion analysis, and can solve the problems that an existing calculation method based on an empirical formula has relatively large limitation and relatively low calculation accuracy. The method comprises the steps that S1, friction force borne by a fluid unit on a preset array flow section of the debris flow on an accumulation area and the mass of the fluid unit are determined; s2, determining the acceleration of the preset array flow section on the accumulation area according to the friction force and the mass; and S3, determining the movement distance of the preset array flow section on the accumulation area according to the acceleration and the speed of the preset array flow section at the mountain exit, and determining the movement distance as the accumulation length of the debris flow. The method is used for calculating the accumulation length of the debris flow.

Description

Technical Field

[0001] The present invention relates to a method for calculating the deposition length of debris flow, belonging to the technical field of debris flow movement analysis. Background Art

[0002] Debris flow is a solid-liquid two-phase flow induced by factors such as rainfall, snowmelt, and dammed lake breach, usually developed in mountainous areas. Debris flow starts at a higher place on the mountain body, then erodes and scours along the gully, and finally deposits at the gentle part of the gully mouth, thus forming a deposition area with a relatively large area. The terrain of the deposition area is gentle and the area is large, including a large amount of available land, so there are often human settlements and activities. However, the suddenness of debris flow will cause great damage to humans and infrastructure in the deposition area. The movement distance of debris flow in the deposition area determines the deposition length of debris flow, and further determines the influence range of debris flow. Therefore, determining the movement distance and deposition length of debris flow is very important for ensuring the safety of humans and infrastructure in the deposition area.

[0003] The flow path of debris flow is often steep at the rear edge and gentle at the front edge. The deposition area is located at the end of the debris flow movement path and is one of the gentlest areas on the debris flow movement path. Debris flow continuously decelerates in the deposition area and finally stops. However, this deceleration process is affected by factors such as terrain, fluid characteristics, and bed roughness, and is difficult to be directly quantified. In the existing exploration and design specifications, empirical formulas are usually used to calculate the deposition length of debris flow. For example, in the "Design Code for Debris Flow Control Engineering (Trial)" (T / CAGHP 021-2018), the deposition length of a single debris flow is determined based on the empirical relationship between the fluid discharge, unit weight, and bed slope of the deposition area. However, this empirical relationship is often based on the parameter statistics of debris flow in a certain area or a certain type, with a limited applicable range and great limitations.

[0004] At the same time, due to the limitations of the empirical formula, the existing calculation method will also lead to inaccurate calculation results of the debris flow deposition length, affecting the disaster prevention and emergency rescue of debris flow. Therefore, it is necessary to optimize the calculation method of the debris flow deposition length to provide a more scientific theoretical basis for debris flow disaster prevention and emergency rescue. Summary of the Invention

[0005] The present invention provides a method for calculating the deposition length of debris flow, which can solve the problems that the existing calculation method based on empirical formula has great limitations and low calculation accuracy.

[0006] The present invention provides a method for calculating the deposition length of debris flow, and the method includes:

[0007] S1. Determine the friction force suffered by the fluid unit on the deposition area of the preset surge section of the debris flow and the mass of the fluid unit;

[0008] S2. Determine the acceleration of the preset debris flow segment on the accumulation area based on the frictional force and the mass.

[0009] S3. Determine the moving distance of the preset debris flow segment on the accumulation area based on the acceleration and the velocity of the preset debris flow segment at the outlet, and determine the moving distance as the accumulation length of the debris flow.

[0010] Optionally, in step S1, determining the frictional force on the fluid element on the preset debris flow segment in the accumulation area specifically includes:

[0011] Determine the frictional stress of the fluid element on the accumulation area based on the fluid parameters of the fluid element on the preset debris flow segment of the debris flow and the bottom bed parameters of the accumulation area.

[0012] Determine the frictional force on the fluid element on the accumulation area based on the frictional stress and the area of the fluid element.

[0013] Optionally, the fluid parameters include the density of the fluid element and the thickness of the overlying fluid; the bottom bed parameters include the cohesion and internal friction angle of the bottom bed material of the accumulation area, and the bottom bed slope of the accumulation area.

[0014] Optionally, determining the frictional stress of the fluid element on the accumulation area based on the fluid parameters of the fluid element on the preset debris flow segment of the debris flow and the bottom bed parameters of the accumulation area specifically includes:

[0015] Calculate the cosine value of the bottom bed slope of the accumulation area and the tangent value of the internal friction angle of the bottom bed material of the accumulation area.

[0016] Calculate the sum of the product of the density of the fluid element, the thickness of the overlying fluid of the fluid element, the cosine value, the tangent value, and the gravitational acceleration and the cohesion of the bottom bed material of the accumulation area to obtain the frictional stress of the fluid element on the accumulation area.

[0017] Optionally, determining the frictional force on the fluid element on the accumulation area based on the frictional stress and the area of the fluid element specifically includes:

[0018] Calculate the product of the frictional stress and the area of the fluid element to obtain the frictional force on the fluid element on the accumulation area.

[0019] Optionally, in step S1, determining the mass of the fluid element specifically includes:

[0020] Determine the mass of the fluid element based on the area, density, and thickness of the overlying fluid of the fluid element.

[0021] Optionally, determining the mass of the fluid unit according to the area, density and overlying fluid thickness of the fluid unit specifically includes:

[0022] Calculating the product of the acceleration due to gravity and the area, density and overlying fluid thickness of the fluid unit to obtain the mass of the fluid unit.

[0023] Optionally, S2 specifically includes:

[0024] Calculating the ratio of the frictional force to the mass to obtain the acceleration of the preset array flow section on the accumulation area.

[0025] Optionally, in S3, determining the movement distance of the preset array flow section on the accumulation area according to the acceleration and the velocity of the preset array flow section at the outlet specifically includes:

[0026] Calculating the square value of the velocity of the preset array flow section at the outlet and twice the acceleration;

[0027] Calculating the ratio of the square value to twice the value to obtain the movement distance of the preset array flow section on the accumulation area.

[0028] The beneficial effects that the present invention can produce include:

[0029] By analyzing the force state of the fluid unit on the preset array flow section of the debris flow, calculating the acceleration of the fluid unit according to the fluid parameters of the fluid unit and the bottom bed parameters of the accumulation area, and then combining the velocity of the preset array flow section at the outlet, the present invention determines the accumulation length of the debris flow. In this way, the accumulation length of the debris flow is calculated according to the actual movement process of the debris flow, without the need to calculate based on the existing empirical formula, thereby breaking through the limitations of the existing calculation method, improving the calculation accuracy, and being able to provide a more scientific theoretical basis for the prevention and control of debris flow disasters and emergency rescue. Description of the Drawings

[0030] Figure 1 is a flowchart of the method for calculating the accumulation length of the debris flow provided by the embodiment of the present invention;

[0031] Figure 2 is a schematic diagram of the movement of the debris flow on the accumulation area provided by the embodiment of the present invention;

[0032] Figure 3 is a schematic diagram of the force analysis of the fluid unit provided by the embodiment of the present invention.

[0033] Reference Signs:

[0034] 1. Debris flow; 2. Leading edge; 3. Accumulation area. Detailed Embodiment

[0035] The present invention will be described in detail below in conjunction with embodiments, but the present invention is not limited to these embodiments.

[0036] An embodiment of the present invention provides a method for calculating the accumulation length of debris flow, as Figure 1 shown, the method includes:

[0037] S1. Determine the frictional force exerted on the fluid unit on the preset surge flow section of debris flow 1 in the accumulation area 3 and the mass of the fluid unit;

[0038] S2. Determine the acceleration of the preset surge flow section in the accumulation area 3 according to the frictional force and the mass;

[0039] S3. Determine the moving distance of the preset surge flow section in the accumulation area 3 according to the acceleration of the preset surge flow section in the accumulation area 3 and the velocity of the preset surge flow section at the gully outlet, and determine the accumulation length of debris flow 1 according to the moving distance.

[0040] Specifically, as Figure 2 shown, in a debris flow 1, the potential energy of the leading head 2 is the largest and its moving distance is the farthest. By calculating the moving distance of the leading head 2 in the accumulation area 3, the accumulation length of the debris flow 1 in the accumulation area 3 can be obtained. Therefore, the preset surge flow section in this embodiment is the leading head 2 of the debris flow 1.

[0041] Specifically, as Figure 2 shown, during the movement of the leading head 2, the bed material in the accumulation area 3 exerts a resistance, that is, a frictional force, on the fluid of the leading head 2 in the opposite direction of its movement, thereby slowing down the movement speed of the leading head 2.

[0042] Specifically, the fluid unit is in contact with the bed of the accumulation area 3. In this embodiment, by calculating the frictional force exerted on the fluid unit in the accumulation area 3 and the mass of the fluid unit, the acceleration of the fluid unit is obtained, and the acceleration of the fluid unit is used as the acceleration of the preset surge flow section, that is, the leading head 2.

[0043] In this embodiment, the determination of the frictional force exerted on the fluid unit on the preset surge flow section of debris flow 1 in S1 can specifically be:

[0044] Determine the frictional resistance stress of the fluid unit in the accumulation area 3 according to the fluid parameters of the fluid unit on the preset surge flow section of debris flow 1 and the bed parameters of the accumulation area 3;

[0045] Determine the frictional force exerted on the fluid unit in the accumulation area 3 according to the frictional resistance stress and the area of the fluid unit.

[0046] In this embodiment, the determination of the frictional force exerted on the fluid unit in the accumulation area 3 according to the frictional resistance stress and the area of the fluid unit can specifically be:

[0047] Calculate the product of the frictional resistance stress and the area of the fluid element to obtain the frictional force exerted on the fluid element in the accumulation area 3.

[0048] Specifically, as Figure 3 shown, in this embodiment, a force analysis is performed on the fluid element, and the calculation formula for the frictional force exerted on the fluid element in the accumulation area 3 can be obtained as:

[0049] (1)

[0050] In formula (1), is the frictional force (kN) exerted on the fluid element in the accumulation area 3; is the frictional resistance stress (kPa) exerted by the bottom bed material of the accumulation area 3 on the fluid element; is the area of the fluid element (m 2 ); is the width (m) of the fluid element; is the length (m) of the fluid element.

[0051] Specifically, the fluid parameters of the fluid element may include the density of the fluid element and the thickness of the overlying fluid; the bottom bed parameters of the accumulation area 3 may include the cohesion and internal friction angle of the bottom bed material of the accumulation area 3, and the bottom bed slope of the accumulation area 3, and the bottom bed slope is the angle between the bottom bed and the horizontal plane.

[0052] Furthermore, the above-mentioned determination of the frictional resistance stress of the fluid element in the accumulation area 3 based on the fluid parameters of the fluid element on the preset surge section of the debris flow 1 and the bottom bed parameters of the accumulation area 3 can specifically be:

[0053] Calculate the cosine value of the bottom bed slope of the accumulation area 3 and the tangent value of the internal friction angle of the bottom bed material of the accumulation area 3;

[0054] Calculate the sum of the product of the density of the fluid element, the thickness of the overlying fluid of the fluid element, the above cosine value, the above tangent value, and the gravitational acceleration and the cohesion of the bottom bed material of the accumulation area 3 to obtain the frictional resistance stress of the fluid element in the accumulation area 3.

[0055] Specifically, according to the Coulomb resistance model in an infinite slope, The calculation formula of can be expressed as:

[0056] (2)

[0057] In formula (2), is the frictional resistance stress (kPa) exerted by the bottom bed material of the accumulation area 3 on the fluid element; is the cohesion (kPa) of the bottom bed material of the accumulation area 3; is the density of the fluid element (kg / m 3), i.e., the density of debris flow 1 (kg / m 3 ); is the acceleration due to gravity (N / kg); is the thickness of the overlying fluid of the fluid element (m), i.e., the thickness of the leading head 2 of debris flow 1 (m); is the bottom bed slope of the deposition area 3 (°); is the internal friction angle of the bottom bed material in the deposition area 3 (°).

[0058] Among them, , and can all be obtained through experiments; can be obtained by measuring the on-site situation of debris flow 1; in addition, since the movement distance of debris flow 1 in the deposition area 3 is relatively short, therefore, in this embodiment, the thickness attenuation of the leading head 2 of debris flow 1 on the deposition area 3 can be ignored, and the mud depth at the outfall is used to replace the thickness of the leading head 2 , so that the thickness can be obtained by measuring the cross-sectional mud depth at the outfall.

[0059] In this embodiment, S2 can specifically be:

[0060] Calculate the ratio of the frictional force acting on the fluid element in the deposition area 3 to the mass of the fluid element to obtain the acceleration of the preset array flow section in the deposition area 3.

[0061] Specifically, according to the force analysis of the fluid element, under the action of the frictional force, the fluid element will generate an acceleration opposite to its movement direction until its movement speed is 0. The calculation formula of this acceleration can be expressed as:

[0062] (3)

[0063] In formula (3), is the acceleration of the fluid element (m / s); is the frictional force acting on the fluid element in the deposition area 3 (kN); is the mass of the fluid element (kg).

[0064] In this embodiment, to determine the mass of the fluid element in S1, it can specifically be:

[0065] Determine the mass of the fluid element according to the area, density and overlying fluid thickness of the fluid element.

[0066] Furthermore, the above-mentioned determination of the mass of the fluid element according to the area, density and overlying fluid thickness of the fluid element can specifically be:

[0067] Calculate the product of the gravitational acceleration and the area, density, and overlying fluid thickness of the fluid element to obtain the mass of the fluid element.

[0068] Specifically, the calculation formula for the mass of the fluid element can be expressed as:

[0069] (4)

[0070] In formula (4), is the mass of the fluid element (kg); is the density of the fluid element (kg / m 3 ), that is, the density of debris flow 1 (kg / m 3 ); is the gravitational acceleration (N / kg); is the overlying fluid thickness of the fluid element (m), that is, the thickness of the leading edge 2 of debris flow 1 (m); is the area of the fluid element (m 2 ); is the width of the fluid element (m); is the length of the fluid element (m).

[0071] In this embodiment, the acceleration of the fluid element is calculated according to the above method, and the acceleration of the fluid element is used as the acceleration of the preset array flow section, that is, the leading edge 2 on the deposition area 3.

[0072] In this embodiment, in S3, the movement distance of the preset array flow section on the deposition area 3 is determined according to the acceleration of the preset array flow section on the deposition area 3 and the velocity of the preset array flow section at the gully outlet. Specifically, it can be:

[0073] Calculate the square value of the velocity of the preset array flow section at the gully outlet and twice the acceleration of the array flow section on the deposition area 3;

[0074] Calculate the ratio of the above square value and the above twice value to obtain the movement distance of the preset array flow section on the deposition area 3.

[0075] Specifically, the calculation formula for the movement distance of the preset array flow section on the deposition area 3 can be expressed as:

[0076] (5)

[0077] In formula (5), is the movement distance of the preset array flow section on the deposition area 3; is the velocity of the preset array flow section at the gully outlet, which can be calculated according to the formula in the "Code for Exploration of Debris Flow Disaster Prevention and Control Engineering" (DZ / T 0220 - 2006); is the acceleration of the fluid element (m / s), that is, the acceleration of the preset array flow section on the deposition area 3.

[0078] In this embodiment, by combining Equations (1) to (5), the calculation formula for the movement distance of the preset array flow segment on the accumulation area 3 can be further expressed as:

[0079] (6)

[0080] In Equation (6), is the movement distance of the preset array flow segment on the accumulation area 3; is the velocity of the preset array flow segment at the outlet; is the cohesion (kPa) of the bottom bed material in the accumulation area 3; is the density of the fluid element (kg / m 3 ), that is, the density of the debris flow 1 (kg / m 3 ); is the acceleration due to gravity (N / kg); is the thickness of the overlying fluid of the fluid element (m), that is, the thickness of the leading head 2 of the debris flow 1 (m); is the bottom bed slope of the accumulation area 3 (°); is the internal friction angle of the bottom bed material in the accumulation area 3 (°).

[0081] According to Equation (6), in this embodiment, , and can be obtained through experiments, and can be obtained through on-site measurement, and can be calculated according to the "Investigation Specification for Debris Flow Disaster Prevention and Control Engineering" (DZ / T 0220 - 2006). Then, by substituting the above parameters into Equation (6), the movement distance of the preset array flow segment, that is, the leading head 2, on the accumulation area 3 can be calculated, which greatly simplifies the calculation process and improves the calculation efficiency.

[0082] In this embodiment, the movement distance of the preset array flow segment on the accumulation area 3 is determined as the accumulation length of the debris flow 1.

[0083] The present invention calculates the acceleration of a fluid element by analyzing the force state of the fluid element on the preset surge section of the debris flow 1 and based on the fluid parameters of the fluid element and the bottom bed parameters of the deposition area 3, and then determines the deposition length of the debris flow 1 in combination with the velocity of the preset surge section at the gully mouth. In this way, the deposition length of the debris flow 1 is calculated according to its actual movement process without the need to calculate based on existing empirical formulas, thereby breaking through the limitations of the existing calculation methods, improving the calculation accuracy, and being able to provide a more scientific theoretical basis for the prevention and control of debris flow 1 disasters and emergency rescue. At the same time, the present invention conducts formula derivation based on the force state of the debris flow 1, with clear physical and mechanical concepts and a high degree of refinement of the formula, which is conducive to simplifying the calculation process and improving the calculation efficiency.

[0084] The above are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, makes some changes or modifications using the technical content disclosed above, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for calculating the length of debris flow accumulation, characterized in that: The method comprises: S1, determining the friction force exerted on the fluid unit on the preset array flow section of the debris flow in the accumulation area and the mass of the fluid unit; S2. determining the acceleration of the preset array flow segment on the accumulation area according to the friction force and the mass; S3. Determine the movement distance of the preset flow segment in the accumulation area according to the acceleration and the speed of the preset flow segment at the exit of the mountain, and determine the movement distance as the accumulation length of the debris flow.

2. The method according to claim 1, characterized in that The friction force exerted on the fluid unit in the preset array flow section of the debris flow in the accumulation area is determined in S1, specifically: Determining the friction stress of the fluid unit on the accumulation area according to the fluid parameters of the fluid unit on the preset array flow section of the debris flow and the bottom bed parameters of the accumulation area; The friction force exerted on the fluid unit on the accumulation area is determined according to the friction stress and the area of ​​the fluid unit.

3. The method according to claim 2, characterized in that The fluid parameters include the density of the fluid unit and the thickness of the overlying fluid; the bed parameters include the cohesion and internal friction angle of the bed material in the accumulation area, and the bed slope of the accumulation area.

4. The method according to claim 3, characterized in that The friction stress of the fluid unit on the accumulation area is determined according to the fluid parameters of the fluid unit on the preset array flow section of the debris flow and the bottom bed parameters of the accumulation area, specifically: Calculate the cosine value of the bottom slope of the accumulation area and the tangent value of the internal friction angle of the bottom material of the accumulation area; The density of the fluid unit, the thickness of the overlying fluid of the fluid unit, the product of the cosine value, the tangent value and the gravitational acceleration and the cohesion of the bottom bed material in the accumulation area are calculated to obtain the friction stress of the fluid unit on the accumulation area.

5. The method according to claim 2, characterized in that: The friction force exerted on the fluid unit on the accumulation area is determined according to the friction stress and the area of ​​the fluid unit, specifically: The product of the friction stress and the area of ​​the fluid unit is calculated to obtain the friction force exerted on the fluid unit on the accumulation area.

6. The method according to claim 3, characterized in that The mass of the fluid unit is determined in S1, specifically: The mass of the fluid unit is determined according to the area, density and overlying fluid thickness of the fluid unit.

7. The method according to claim 6, characterized in that The method of determining the mass of the fluid unit according to the area, density and thickness of the overlying fluid of the fluid unit is specifically as follows: The mass of the fluid unit is obtained by calculating the product of the gravitational acceleration and the area, density, and thickness of the overlying fluid of the fluid unit.

8. The method according to claim 1, characterized in that The S2 is specifically: The ratio of the friction force to the mass is calculated to obtain the acceleration of the preset array flow section on the accumulation area.

9. The method according to claim 1, characterized in that: In S3, the moving distance of the preset array flow segment in the accumulation area is determined according to the acceleration and the speed of the preset array flow segment at the exit of the mountain, specifically: Calculating the square value of the velocity of the preset array flow section at the exit of the mountain and the double value of the acceleration; The ratio of the square value to the double value is calculated to obtain the movement distance of the preset array flow segment on the accumulation area.

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