Calculation method for inverting vertical avalanche influence by using equivalent blasting

Abstract

The invention discloses a calculation method for inverting the influence of a vertical avalanche by using equivalent blasting. The calculation method comprises the following steps: measuring the slope area and volume of accumulated snow through an unmanned aerial vehicle and Arcscene; based on an overpressure failure theory, avalanche cloud blast propagation is regarded as explosion shock wave propagation, and an explosion explosive equivalent to avalanche and various calculation parameters are obtained; constructing a three-dimensional air explosion model, and carrying out numerical verification on the snow avalanche influence range; and based on an explosion overpressure expression and a reflection theory, proposing an influence formula corresponding to the drooping type avalanche, and obtaining an avalanche influence range. According to the calculation method for inverting the influence of the vertical avalanche by using the equivalent blasting, the diffusion range of an avalanche disaster can be ascertained, and a basis can be provided for design and construction of avalanche prevention and control measures of similar traffic engineering in alpine regions in China.

Description

Technical Field

[0001] The present invention relates to the technical field of avalanches, and in particular to a calculation method for using equivalent blasting to invert the influence of vertical avalanches. Background Art

[0002] With the successive implementation of major projects in the western region of China, a large number of tunnels and underground projects with construction environments of "high altitude, low temperature, and large temperature difference" have emerged. Due to human construction disturbances and natural factors, avalanche disasters will occur during this section of construction, resulting in accidents such as snow accumulation on the carriageway and snow burying vehicles. Therefore, the influencing factors and prevention of avalanches are particularly important.

[0003] Wang Yanlong qualitatively analyzed the causes, types, spatio-temporal distribution laws, and development characteristics of avalanches in "Research on Avalanches in China". Zhou Shiqiao demonstrated and screened four main factors for avalanche occurrence from a genetic perspective: snow cover thickness, weather, slope, and vegetation conditions, and proposed point and area avalanche hazard assessment criteria.

[0004] Subsequently, some scholars, based on avalanches on the plateau in the western region of China, quantitatively expressed the influence and control degree of each influencing factor on avalanche activities. Their proportions are 30.61% for climate and meteorology, 21.23% for topography and geomorphology, 20.26% for average altitude, slope aspect, surface curvature, and faults. At the same time, it is concluded that avalanches are mainly distributed in the altitude range of 4300 - 4900m, and the number of avalanches in this altitude range accounts for 64% of the total number.

[0005] In recent years, a large number of scholars have taken a certain western railway as the background, counted the situations of 130 glacial lakes, 70 wet snow avalanche points, and 4 avalanche areas along the route. On the basis of in-depth investigation of snow disasters (glacial lake outbursts, avalanches, glacial debris flows) and the severity of damage, a model of segmented mitigation countermeasures to the Sichuan-Tibet Expressway has been proposed, and the relationship between avalanche movement distance and snow cover thickness, average slope of the hillside, and snow density has been counted, obtaining that the area size and slope aspect differentiation of the avalanche formation area determine their activity frequency.

[0006] Regarding the research on avalanche protection measures in engineering construction, there are three methods: governance, resistance, and avoidance. McClung et al. linked the avalanche data of 76 locations with vegetation conditions and proposed a plan to change logging to control avalanches.

[0007] Cai Qiang proposed resistance measures such as open cut tunnels, windbreak walls, and shelter forests based on the FLUENT simulation of snowdrift on the snow accumulation at the tunnel entrance.

[0008] Wang Hua et al. obtained the avalanche diffusion distance by using the parametric mapping method, and proposed resistance measures such as snow protection shed tunnels, snow protection fences, and snow guiding based on the impact force of avalanches on the tunnel portal.

[0009] Wang Dong et al. set a special bridge with a certain safety height at the tunnel exit based on the avalanche landform conditions, the spatial conditions of the tunnel exit, and the distances of previous avalanches to avoid avalanches.

[0010] Regarding the simulation study of avalanches, Zhang Fucun et al. used remote sensing images and DEM data, calculated the water flow direction and the cumulative water flow concentration based on GIS, took the water flow path as the propagation path of avalanches, analyzed the impact of avalanches on the stability of ice lakes, and prevented the outbreak of ice lakes.

[0011] L Montrasio et al. simulated avalanches with sand and gravel, set obstacles of different sizes on their movement trajectories to measure the impact force, and at the same time, through the analysis of DEM, carried out good design and risk assessment.

[0012] Based on the research results of predecessors, it can be seen that the above research all focuses on slope avalanches and does not bring the propagation of explosion shock waves into the research on avalanche effects. Therefore, it is necessary to predict the effects of vertical avalanches by means of air explosion. Summary of the Invention

[0013] The purpose of the present invention is to provide a calculation method for inversely inferring the influence of vertical avalanches by equivalent blasting, which can find out the diffusion range and influence distance of avalanche disasters, and provide a basis for the design and construction of avalanche prevention measures for similar traffic projects in alpine regions of our country.

[0014] To achieve the above purpose, the present invention provides a calculation method for inversely inferring the influence of vertical avalanches by equivalent blasting, including the following steps:

[0015] Measure the slope area and volume of the snow cover through an unmanned aerial vehicle and Arcscene;

[0016] Based on the overpressure damage theory, regard the propagation of avalanche cloud air waves as the propagation of explosion shock waves, and obtain the equivalent explosive charge of the avalanche and various calculation parameters;

[0017] Construct a three-dimensional air explosion model to numerically verify the snow avalanche;

[0018] Based on the explosion overpressure expression and reflection theory, propose an influence formula corresponding to the vertical avalanche to obtain the influence range of the avalanche.

[0019] Preferably, use Arcscene to generate a 3D elevation model of the site and combine it with the on-site snow cover statistics, and calculate the snow volume according to the snow slope area measured by the unmanned aerial vehicle. The force expression of the snow cover is as follows:

[0020]

[0021] Wherein, T is the downward sliding force along the slope; N is the component force perpendicular to the slope; ρ is the snow density; h is the snow thickness; L is the snow length; α is the slope angle;

[0022] The generation of the sliding surface is closely related to the shear strength τ of the snow cover, and the expression is as follows:

[0023] τ = C + pf;

[0024] Wherein: τ is the shear strength of the snow cover; C is the cohesion of the snow cover; p is the normal pressure of the snow cover at the slope; f is the friction coefficient of the snow cover;

[0025] The calculation formula for the normal pressure of the snow cover at the slope is as follows:

[0026] P = N / L = ρhcosα.

[0027] Preferably, when the snow cover reaches a certain thickness, the critical condition for the generation of the sliding surface on the slope is that the downward sliding force along the sliding surface generated by its gravity is equal to the resistance:

[0028] T = τ·L;

[0029] The thickness of the sliding snow cover is the critical thickness for the generation of an avalanche. Calculate the critical thickness of the sliding snow cover:

[0030]

[0031] Wherein: h k is the critical thickness of the snow cover; g is the acceleration due to gravity.

[0032] Preferably, the propagation of the cloud and gas wave of the falling avalanche is equivalent to the propagation of the explosion shock wave. Correspondingly, the impact force of the avalanche is equivalent to the explosive charge and various calculation parameters. The steps are as follows: The propagation of the cloud and gas of the falling avalanche is equivalent to the propagation of the explosion shock wave. Correspondingly, the impact force of the avalanche is equivalent to the explosive charge and various calculation parameters. The steps are as follows:

[0033] When the snow cover falls to the accumulation area in free fall, according to the kinetic energy theorem, the expression is as follows:

[0034]

[0035] Wherein, H is the surface height difference at the snow cover; v is the instantaneous speed when contacting the ground; m is the mass of the snow cover;

[0036] Calculate the instantaneous impact force P' per unit area of the avalanche. The formula is as follows:

[0037] P' = Kρv 2 ;

[0038] Wherein, K is a constant, which is 3.0 when calculating the peak value of the impact force of the avalanche cloud and gas wave; ρ is the snow density;

[0039] In ANSYS LS-DYNA, the JWL state equation is expressed as the PV relationship, which is converted into the impact force generated by the total explosive of a single unit according to the magnitude of the total snow cloud air wave impact force:

[0040]

[0041] Where V is the avalanche volume; n is the volume corresponding to 1.2 g / cm 3 TNT explosive ratio; P cj The density is 1.2g / cm 3 The detonation pressure of TNT explosive is 1.0×10 4 MPa; V0 is the volume of TNT explosive, taken as 1.0m 3 .

[0042] Preferably, a three-dimensional air explosion model is constructed based on on-site geological survey data to perform numerical verification on snow avalanches:

[0043] A rectangular blast source of equivalent volume was used to simulate the air wave impact of the preceding avalanche. Because the avalanche formed by the following snow and the preceding snow repelled each other, a certain amount of snow was spread directly above the blast source to simulate this. The explosion was considered a fluid-solid coupling process in the simulation, with the air and explosives acting as fluids.

[0044] Based on the superposition of the avalanche reflected cloud wave and the incident vector, the influence formula corresponding to the vertical avalanche is proposed to obtain the avalanche impact range. The steps are as follows:

[0045] Drop-down impact type:

[0046]

[0047] The avalanche hazard is calculated using the above influence formula, where ρ is P′=Kρv 2 Medium snow density; P cj for The detonation pressure value of the medium explosive; α is Mid-slope angle; K is P′=Kρv 2 The constant in is 3; S is The area of the slope with medium snow cover; C is τ = C + pf, the cohesion of medium snow cover, which is taken as 350~450Pa; A, B, and C are all constants.

[0048] Therefore, the present invention adopts the above-mentioned calculation method of using equivalent blasting to invert the impact of vertical avalanches, which can explore the spread range of avalanche disasters and provide a basis for the design and construction of avalanche prevention and control measures for similar transportation projects in my country's high-altitude and cold regions.

[0049] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is the schematic diagram of the formation area principle of the falling avalanche in the embodiment of the calculation method for inversely inferring the influence of the falling avalanche by equivalent blasting according to the present invention;

[0051] Figure 2 It is the geographical feature map of the tunnel entrance in the embodiment of the calculation method for inversely inferring the influence of the falling avalanche by equivalent blasting according to the present invention;

[0052] Figure 3 It is the schematic diagram of the equivalence principle of avalanche and explosion overpressure in the embodiment of the calculation method for inversely inferring the influence of the falling avalanche by equivalent blasting according to the present invention;

[0053] Figure 4 It is the block diagram of the avalanche measurement value in the embodiment of the calculation method for inversely inferring the influence of the falling avalanche by equivalent blasting according to the present invention;

[0054] Figure 5 It is the schematic diagram of the three-dimensional air explosion model and boundary setting in the embodiment of the calculation method for inversely inferring the influence of the falling avalanche by equivalent blasting according to the present invention;

[0055] Figure 6 It is the schematic diagram of the vector superposition of the incident wave and the reflected wave in the embodiment of the calculation method for inversely inferring the influence of the falling avalanche by equivalent blasting according to the present invention;

[0056] Figure 7 It is the overpressure stress nephogram in the embodiment of the calculation method for inversely inferring the influence of the falling avalanche by equivalent blasting according to the present invention;

[0057] Figure 8 It is the schematic diagram of the change of the calculated overpressure peak value with the distance in the embodiment of the calculation method for inversely inferring the influence of the falling avalanche by equivalent blasting according to the present invention; Detailed implementation mode

[0058] The technical solution of the present invention will be further described below with reference to the drawings and embodiments.

[0059] Embodiment 1

[0060] Taking the avalanche above a certain cold region tunnel in Xinjiang as an example, the present invention provides a calculation method for inversely inferring the influence of the falling avalanche by equivalent blasting. According to the statistical data of the on-site temperature, snowfall, wind direction and wind speed, when the snow cover reaches the critical thickness, a sliding surface is generated, and a falling avalanche mainly in the form of smoky avalanche is formed. And the influence formula corresponding to the falling avalanche is proposed, which can calculate the avalanche hazard in a short time. This provides a theoretical support and practical basis for the prevention and control of avalanche disasters in major projects in alpine regions.

[0061] 1. Proposal and analysis of the falling avalanche

[0062] Currently, scholars categorize avalanches as smoke avalanches and surface avalanches, all based on the movement of snow on a slope. Based on the evolution of avalanches from multiple snow accumulations directly above a tunnel entrance in a cold region (over 800 meters above the entrance), the concept and characteristics of a vertical avalanche were proposed and analyzed. Based on force analysis of a specific snow accumulation and on-site drone measurements, the snow volume at that location was calculated, providing parameter support for subsequent numerical simulations.

[0063] 1.1 Snow conditions on site

[0064] The tunnel axis passes through a region of Xinjiang, characterized by steep mountains. The highest elevation is approximately 6,050 meters, with a maximum relative height difference of approximately 1,250 meters. Snow covers the area year-round above 4,600 meters. Annual precipitation is low, with large temperature variations, ranging from a low of -23.5°C to a high of 37.5°C, and an average annual temperature of 11°C. Wind speeds reach a maximum of 5.8 m / s, with an annual average of 0.4 m / s. Snowfall is heavy in the mountainous area, with an average of 6.6 days per year and a maximum winter snowfall of 23.3 mm. Arcscene was used to generate a 3D elevation model of the site based on DEM elevation data and satellite imagery. This model, combined with on-site snow accumulation statistics, mapped the topography and snow distribution at the tunnel entrance. A snowdrift with a slope greater than 55° was located 1,000 meters above the tunnel entrance. This snowdrift avalanches during the spring melt, when wind speeds are less than 0.7 m / s and humidity is greater than 94%. Field observations of the snowdrift were conducted, and the proposed calculation method was validated using the snowdrift avalanche locations.

[0065] 1.2 Characteristics and process analysis of vertical avalanches

[0066] The main factors influencing avalanches include human disturbance, snow depth, wind speed, slope gradient, and vegetation type and coverage. An analysis based on meteorological data at the avalanche location at the time of the avalanche and a map of the tunnel entrance revealed that the avalanche occurred in spring (a period characterized by large diurnal temperature differences and high humidity), and the slope of the avalanche initiation zone was greater than 55°. This reduced the cohesion of the snowpack, resulting in a layer within the snowpack that was weaker than the adjacent layers above and below it. This formed the weak layer (sliding surface), along which the snow slid to the base of the ridge.

[0067] Combined with the avalanche process collected from the scene, we can get Figure 1 Schematic diagram of the formation area of vertical avalanche, according to Figure 1 As can be seen, the location where the snow slides is called the starting zone. The upper layer of snow slides along the sliding surface to the cliff edge and falls vertically along the cliff face. After falling to the ground, it quickly spreads to the surrounding area like an explosion and causes overpressure damage to ground equipment. The cloud wave generated continues to decay along the ground to the farthest point. The starting point of the avalanche is the overpressure peak point. Because we have only studied avalanches that form along the slope surface and have not seen reports of this type of avalanche, this type of avalanche is called a drop avalanche. It can be seen that the characteristics of a drop avalanche are:

[0068] (1) It is sudden; (2) The snow accumulates vertically and falls to the ground; (3) The point where the snow accumulates vertically is the starting point of the avalanche formation and the peak overpressure point; (4) The point where the snow accumulates vertically is the main accumulation point of the snow after the avalanche occurs; (5) Compared with slope avalanches, the spread of vertical avalanches is a decay process without horizontal driving force.

[0069] To provide a basis for the numerical simulation parameters of subsequent avalanches, according to Figure 1 The schematic diagram of the formation area of vertical avalanches, the critical snow thickness is obtained by analyzing the forces acting on the snow, and based on the snow slope area measured by the drone, the volume of the snow at that location is calculated as follows:

[0070]

[0071] In the formula, T is the downward sliding force along the slope; N is the component force perpendicular to the slope; ρ is the snow density, and the density of fine snow to coarse snow is 220 - 350 (kg / m 3 ); h is the snow thickness (m); L is the snow length (m); α is the slope angle (°); The generation of the sliding surface is closely related to the shear strength τ of the snow, and the expression is as follows:

[0072] τ = C + pf (2)

[0073] In the formula: τ is the shear strength of the snow (Pa); C is the cohesion of the snow, which is 350 - 450 (Pa); p is the normal pressure of the snow at the slope (Pa); f is the friction coefficient of the snow.

[0074] The calculation formula for the normal pressure of the snow at the slope is as follows:

[0075]

[0076] When the snow reaches a certain thickness, the critical condition for the generation of the sliding surface on the slope is that the downward sliding force along the sliding surface generated by its gravity is equal to the resistance:

[0077] T = τ·L (4)

[0078] The corresponding sliding snow thickness is the critical thickness for the generation of the avalanche. Based on this, the equations are solved simultaneously to obtain the critical thickness of the sliding snow:

[0079]

[0080] In the formula: h k is the critical snow thickness (m); g is the acceleration due to gravity, taking 9.8 (m / s 2 ).

[0081] According to Figure 2From the geographical feature map of the tunnel entrance, it can be seen that the slope of the hillside at the avalanche location is 25 - 35°. Considering the most unfavorable situation and taking the tunnel net width (10.5 m) as a reference, the critical thickness at the avalanche location is obtained as 1.98 m after correction by drone measurement. After the avalanche occurred at this location, taking the tunnel net width as a reference, the slope area of the snow accumulation was measured using a drone and Arcscene, and the measured slope area S of the snow accumulation is approximately 150 m 2 ; Assume that the volume of the sliding snow is the snow slope area S × the critical snow thickness h k , and the obtained V is 297 m 3 , for the specific snow slope area, critical thickness and volume at this location, see Table 1

[0082] Table 1 Parameters of snow accumulation at this location

[0083] Snow accumulation <![CDATA[S(m 2 )]]> <![CDATA[h k (m)]]> <![CDATA[V(m 3 )]]> 2 150 1.98 297

[0084] 2. Idea of explosion inversion of falling avalanche

[0085] The avalanche form at this location above the tunnel is all falling avalanche. Combining Figure 1 the formation characteristics of the falling avalanche and Figure 3 the equivalent principle of avalanche and explosion overpressure, it can be seen that the moving area of the falling avalanche can be regarded as free-fall motion. When the avalanche falls to the ground accumulation area, it makes the ground rise into the air, generating a powerful avalanche cloud air wave, causing large-scale impact damage, similar to the detonation of explosives. The ground accumulation area can be regarded as the explosion source; the ground is damaged by the overpressure PS of the avalanche cloud air wave and the negative pressure PS - caused by the air pressure drop when the avalanche passes through. It is mainly damaged by the avalanche overpressure, which is the same as the overpressure damage theory of explosion propagation in the air. The propagation of the avalanche cloud air wave can be regarded as the propagation of the explosion shock wave

[0086] According to the above idea, the corresponding explosive parameters are solved as follows

[0087] Assume that the process of snow accumulation falling to the accumulation area is free-fall. According to the kinetic energy theorem, the expression is as follows

[0088]

[0089] In the formula, H is the surface elevation difference at the snow accumulation location (m); v is the instantaneous speed when contacting the ground (m / s); m is the mass of the snow accumulation (kg);

[0090] Calculate the instantaneous impact force P′ per unit area of the avalanche. The formula is as follows

[0091] P′ = Kρv 2 (7)

[0092] In the formula, K is a constant, which is 3 when calculating the peak impact force of the avalanche cloud air wave, and ρ is the snow density (kg / m 3 )

[0093] In ANSYS-LS-DYNA, the JWL state equation is expressed as the PV relationship, which is converted into the impact force generated by the total explosive of a single unit according to the magnitude of the total snow cloud air wave impact force:

[0094]

[0095] Where V is the avalanche volume, which is assumed to be equal to the snow volume on the slope; n is the volume corresponding to 1.2 g / cm 3 TNT explosive ratio; P cj The density is 1.2g / cm 3 The detonation pressure of TNT explosive is 1.0×10 4 MPa; V0 is the volume of TNT explosive, taken as 1.0m 3 The density of explosives and various parameters corresponding to the snow accumulation at this location are solved by combining formulas (6), (7), and (8), as shown in Table 2. The parameters of rock and air are shown in Table 3.

[0096] Table 2 Snow density and parameters of explosives

[0097]

[0098] Table 3 Rock and air parameters

[0099]

[0100]

[0101] 3. Numerical verification of avalanche impact range

[0102] 3.1 On-site avalanche statistics

[0103] According to the actual avalanche situation at the scene, the avalanche path was observed by drone, and the terrain calculation was performed with Arcscene software to obtain the avalanche range S at that location. The range was statistically plotted into a box plot and compared with the calculated value in the following step (3.2 Establishing a three-dimensional air explosion model). Figure 4 shown by Figure 4 It can be seen that the avalanche location has a small box shape, with an outlier number of impact ranges, indicating that it was not affected by the corresponding construction equipment. The maximum impact distance of the avalanche location is 709m, the average is 679m, and the median is 667m. The average is close to the median, reflecting that it is less affected by external factors and has greater reference value.

[0104] 3.2 Establishing a three-dimensional air explosion model

[0105] Based on the on-site geological survey report, a three-dimensional numerical model is established:

[0106] The unit value is cm-us-g-1x1011Pa. *MAT_SOIL_CONCRETE defines the snow cover layer within the top 1 m of the ground surface, and *MAT_JOHNSON_HOLMQUIST_CONCRETE defines the permafrost layer with a size of 800 m × 1000 m beneath the snow cover layer. Taking the X direction as the tunnel excavation direction, the corresponding rock stratum is Grade Ⅳ surrounding rock; *MAT_HIGH_EXPLOSIVE_BUR defines the explosion source. The air wave impact of the avalanche in the front is regarded as a cuboid explosion source with an equivalent volume. The avalanche formed by the snow in the back and the snow in the front has a repulsive reaction. Therefore, a layer of snow is laid flat directly above the explosion source for simulation. The explosion is regarded as a fluid-structure interaction process in the simulation. Air and explosives are fluids, and the corresponding air volume is 800 m × 1250 m × 1000 m; the three-dimensional air explosion model after meshing is as Figure 5 shown. *ELEMENT_SOLID defines solid elements, with a total of 829,193 elements and 868,474 nodes; the boundary setting of the three-dimensional air explosion model is as Figure 5 shown. *BOUNDATY_UON_REFLECTING defines the Ⅰ-Ⅴ plane as a non-reflecting boundary and the Ⅵ-Ⅶ plane as a free boundary.

[0107] 3.3 Numerical Verification Based on Overpressure Stress

[0108] For the incident shock wave generated during the explosion, when facing ridges, buildings, etc., they are regarded as plane rigid walls, thus generating normal reflection, regular oblique reflection, and Mach reflection. Without considering secondary reflection, the incident shock wave generated by the falling avalanche impacts the ridge head-on, and the corresponding reflection is mainly normal reflection. Under the condition of instant high pressure, the reflected wave and the incident wave do not show a superposition effect within a short distance. Subsequently, in the air, as the distance increases, the reflected wave and the incident wave show vector superposition, which is the superposition of effective stresses. The incident shock wave of the falling avalanche is affected by the air distance and produces a superposition effect, as Figure 6 shown. The incident waveform generated by the explosion source and the reflected waveform generated by the ridge enter the air surface successively in the form of propagation within the high-pressure surface. After propagating to a certain distance, the waveforms are respectively reduced to stress waveforms. As the propagation distance increases, the incident waveform and the reflected waveform show vector superposition.

[0109] Extract the overpressure stress diagram of the ground snow cover layer during the explosion process, as Figure 7 (a) shown; due to the fluid-structure interaction calculation method adopted by LS-DYNA, the air Part is selected separately to obtain the air compression trend during the explosion process, as Figure 7 (b) shown. It can be seen that the stress wave is gradually spreading outwards. Due to the influence of the snow in the back process, the air is subjected to a pressure peak along the X-axis (horizontal plane), which is similar to the ground diffusion form of the falling avalanche.

[0110] The avalanche damage is mainly caused by the peak overpressure of the avalanche impact on the ground surface. Therefore, the peak overpressure of the ground surface at every 10 m in the calculation results is extracted, as shown in Figure 8 the change of the peak overpressure with distance. As can be seen from Figure 8 it, the overpressure and the influence range of the avalanche at this location show a decreasing trend. The overpressure value drops sharply within 100 m. Due to the disappearance of the counteracting effect of the snow in the later stage on the avalanche impact force of the snow in the front stage, there is a phenomenon of a slowdown zone near 110 m from the avalanche location. As the distance increases, the avalanche shock wave breaks away from the high-pressure environment, and the vector superposition of the incident wave and the reflected wave of the avalanche occurs. Near the 300 m location, there is a sharp increase in the overpressure value of the avalanche at this location, and the superposition effect is completed at 410 m. Research shows that in the case of corresponding shelters, the "Safety Regulations for Blasting" (GB6722-2014) states that overpressure within 0.01 MPa does not cause health effects. Therefore, △Psum≦0.01 MPa is regarded as the safe area, and the influence range corresponding to △Psum = 0.01 MPa of this avalanche is extracted, which is 720 m.

[0111] Due to the obstruction of construction equipment and other factors at the site, it is more reasonable to compare the maximum value in the measured value with the calculated value. According to the above steps (calculated in step 3.3), the comparison between the measured maximum value of the avalanche influence distance and the calculated value in the above steps (step 3.2) is obtained, as shown in Table 4. It can be seen from Table 4 that since the air is regarded as uniform and static in the numerical simulation, and the corresponding air region is regarded as an infinite range, the characteristics of the explosion wave in the model are only related to the explosion distance and time; in the avalanche, the air is dynamic and affected by the wind direction, air pressure and stones at that time, resulting in a residual difference of -11 between the measured value and the calculated value of the avalanche position influence distance; the residual difference of this avalanche accounts for 1.6% of the measured value, which is less than 10%, indicating that the calculation results are in good agreement with the measured results and the calculation method is feasible.

[0112] Table 4 Measured value, calculated value and residual difference of avalanche influence distance

[0113] Avalanche Measured value (m) Calculated value (m) Residual Residual / Measured value (%) - 709 720 -11 1.6

[0114] 4. Analogy of the influence formula of the falling avalanche

[0115] 4.1 Explosion overpressure expression and reflection theory

[0116] When explosives explode in the air, a shock wave is generated, which is a high-energy and short-time propagation process. The peak overpressure corresponding to the shock wave decreases with distance and drops below the standard atmospheric pressure. According to the "Safety Regulations for Blasting" GB6722-2014, the overpressure is defined as:

[0117]

[0118] In the formula: ΔP is the overpressure (MPa); me is the corresponding mass of TNT explosive (kg); x is the distance from the explosion source (m).

[0119] 4.2 Vertical avalanche impact

[0120] For a falling avalanche, its kinetic energy, parallel to the ground, mainly comes from the instantaneous impact force of the snow falling to the accumulation point and the reflected impact force generated by the ridge. However, the expression of the explosive overpressure does not take into account the reflection theory. When the incident wave faces a plane rigid wall, the reflected wave generated is positively correlated with the magnitude of the incident wave. For weak waves, the acoustic approximation holds true, and the reflected overpressure is twice the incident overpressure. For strong waves, the reflected wave overpressure is 8 times the incident overpressure. Therefore, based on the expression of the explosive overpressure, the overpressure value of the cloud air wave of the falling avalanche is obtained as:

[0121] ΔP sum =9ΔP (10)

[0122] Where ΔP sum is the overpressure value of vertical avalanche, which takes into account the combined effects of incident and reflected waves.

[0123] According to the corresponding TNT density in Table 1, the avalanche overpressure is verified by combining the empirical formula of overpressure of explosion in air, and the formulas (9) and (10) are solved simultaneously. sum =0.01MPa corresponding to the impact range data, the calculated value of the avalanche position is 787m. The data are tabulated and compared with the field measured values (Table 5).

[0124] Table 5 Measured values, calculated values and residuals of avalanche impact distance

[0125] Avalanche Measured value (m) Calculated value (m) Residual Residual / Measured value (%) - 709 787 -78 11.0

[0126] Based on the empirical formula of the Safety Regulations for Blasting GB6722-2014, and considering vector superposition, equations (9) and (10) are combined to obtain equation (11); the instantaneous impact force of snow falling onto the accumulation area is regarded as the peak value of the explosion overpressure ΔP sum And the TNT explosives are converted into explosive mass m in equal proportions e , see formula (12); Formula (6), (11), and (12) are combined to obtain the relationship between the surface height difference H at the snow accumulation area and the avalanche impact distance x, see formula (13):

[0127]

[0128]

[0129]

[0130] According to formula (13), the avalanche impact distance x is not only related to the surface height difference H at the snow accumulation site, but also to the explosive ratio coefficient n. The relationship between the explosive ratio coefficient n and the various parameters of snow accumulation can be obtained by combining formulas (5) and (8), as shown in formula (14). Substituting formula (14) into the expression of Hn, the relationship between the avalanche impact distance x and the various parameters of snow accumulation can be obtained, as shown in formula (15):

[0131]

[0132]

[0133] Where: ρ is the snow density (kg / m 3 );P cj is the detonation pressure of the explosive in formula (8); α is the slope angle (°) in formula (1); K is the constant in formula (7), which is 3; S is the snow slope area in formula (5); C is the snow cohesion in formula (2), which is 350-450 (Pa); A, B, and C are all constants, which are 3780, 137.6519, and 4.1749, respectively, where H, S, and α are field measurement parameters.

[0134] Falling avalanches are sudden, and the most reliable and feasible prevention design plan must be made in a short time in the project. Otherwise, it will cause serious harm to life safety and construction equipment. Therefore, this formula can calculate the avalanche hazard in a short time, providing a corresponding theoretical basis for the design plan, which is of great significance for preventing such disasters.

[0135] Therefore, the present invention adopts the above-mentioned calculation method of using equivalent blasting to invert the impact of vertical avalanches, which can explore the spread range of avalanche disasters and provide a basis for the design and construction of avalanche prevention and control measures for similar transportation projects in my country's high-altitude and cold regions.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A calculation method for using equivalent blasting to invert the influence of a falling avalanche, characterized in that, It includes the following steps: Measure the slope area and volume of the snow cover by drones and Arcscene; Based on the overpressure damage theory, regard the propagation of the avalanche cloud air wave as the propagation of an explosive shock wave, and obtain the equivalent explosive charge of the avalanche and various calculation parameters; Construct a three-dimensional air explosion model to numerically verify the snow avalanche; Based on the explosion overpressure expression and reflection theory, propose an influence formula for the corresponding vertical-falling avalanche to obtain the influence range of the avalanche; 2. The method for calculating the impact of a falling avalanche using equivalent blasting inversion according to claim 1 is characterized in that: Use Arcscene to generate a 3D elevation model of the site and combine it with the on-site snow cover statistics, and calculate the snow volume according to the snow slope area measured by the drone. The force expression of the snow cover is as follows: In the formula, T is the downward sliding force along the slope; N is the component force perpendicular to the slope; ρ is the snow density; h is the snow thickness; L is the snow length; α is the slope angle; The generation of the sliding surface is closely related to the shear strength τ of the snow cover, and the expression is as follows: τ = C + pf; In the formula: τ is the shear strength of the snow cover; C is the cohesion of the snow cover; p is the normal pressure of the snow cover at the slope; f is the friction coefficient of the snow cover; The calculation formula for the normal pressure of the snow cover at the slope is as follows:

3. The calculation method for inverting the impact of a falling avalanche using equivalent blasting according to claim 2 is characterized in that: When the snow cover reaches a certain thickness, the critical condition for the generation of the sliding surface on the slope is that the downward sliding force along the sliding surface generated by its gravity is equal to the resistance: T = τ·L; The sliding snow thickness is the critical thickness for the generation of the avalanche. Calculate the critical thickness of the sliding snow: where: h k is the critical thickness of snow cover; g is the acceleration due to gravity.

4. The method for calculating the impact of a falling avalanche using equivalent blasting inversion according to claim 1, characterized in that: The propagation of the cloud air wave of the vertical-falling avalanche is equivalent to the propagation of an explosive shock wave. Correspondingly, the impact force of the avalanche is equivalent to the explosive charge and various calculation parameters. The steps are as follows: The cloud propagation of the vertical-falling avalanche is equivalent to the propagation of an explosive shock wave. Correspondingly, the impact force of the avalanche is equivalent to the explosive charge and various calculation parameters. The steps are as follows: When the snow cover falls to the accumulation area, it is a free fall. According to the kinetic energy theorem, the expression is as follows: In the formula, H is the surface elevation difference of the snow cover; v is the instantaneous speed when contacting the ground; m is the mass of the snow cover; Calculate the instantaneous impact force P' per unit area of the avalanche. The formula is as follows: P′ = Kρv 2 ; In the formula, K is a constant, which is 3 when calculating the peak value of the impact force of the avalanche cloud air wave; ρ is the snow density; In ANSYS LS-DYNA, the JWL equation of state represents the P-V relationship. Convert the total impact force of the snow avalanche cloud air wave into the impact force generated by the total explosive of a single unit: Wherein, V is the avalanche volume; n is the TNT explosive proportion corresponding to 1.2 g / cm 3 ; P cj is the detonation pressure value of TNT explosive with a density of 1.2 g / cm 3 , taking 1.0×10 4 MPa; V0 is the volume of TNT explosive, taking 1.0 m 3 .

5. A calculation method for using equivalent blasting inversion to influence the falling avalanche according to claim 1, characterized in that Construct a three-dimensional air explosion model according to the on-site geological exploration data to numerically verify the snow avalanche: Use a cuboid explosive source with an equivalent volume to simulate the air wave impact of the front-stage avalanche. Since the avalanche formed by the snow in the rear stage repels the avalanche in the front stage, lay a certain thickness of snow cover flat directly above the explosive source for simulation; The explosion is regarded as a fluid-structure coupling process in the simulation, and air and explosives are fluids; Based on the explosion overpressure expression and reflection theory, propose an influence formula for the corresponding vertical-falling avalanche to obtain the avalanche influence range. The steps are as follows: Vertical-falling influence formula: Calculate the avalanche hazard by the above influence formula, where ρ is the snow density in P′=Kρv 2 ; P cj is the detonation pressure value of the explosive in; α is the slope angle in; K is the constant in P′=Kρv 2 , taking 3.0; S is the snow-covered slope area in; C is the snow cohesion in τ=C+pf, taking 350.0~450.0Pa; A, B, and C are all constants.

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