Ice-water phase change considered frozen soil roadbed thaw collapse and melting disc evolution discrete element simulation method

Abstract

The invention discloses a frozen soil roadbed thaw collapse and thawing tray evolution discrete element simulation method considering ice-water phase change. The method comprises the following steps: step 1, acquiring frozen soil roadbed parameters; 2, constructing a frozen earth embankment discrete element model; 3, setting material contact parameters; 4, setting a temperature boundary; step 5, thermodynamic coupling of the frozen soil roadbed, including heat transfer and ice-water phase change; step 6, thaw settlement; 7, recording particle distribution; and step 8, melting disc evolution. The device can simulate the heat transfer process of heat from the surface layer of the asphalt pavement to the interior of the permafrost embankment in the sun irradiation process. In the ice-water phase change process, when the heated temperature of ice particles exceeds zero DEG C, the ice particles are melted into water, the bearing capacity of the roadbed is greatly reduced, the thaw collapse of the frozen soil highway roadbed is caused, different influences of a sunny slope and a shady slope on settlement of different monitoring points along an embankment can be calculated, the evolution process of a melting disc in permafrost is simulated, and the method has very high universality.

Description

Technical Field

[0001] The invention relates to the technical field of numerical simulation of geotechnical disciplines, and in particular to a discrete element simulation method for thawing settlement of frozen soil roadbed and evolution of thaw plate taking into account ice-water phase change. Background Art

[0002] With the popularization of computer technology, more and more researchers use numerical simulation methods to study the physical and mechanical properties of rock and soil materials with discrete characteristics. Compared with the shortcomings of laboratory experiments such as long time consumption, high personnel requirements and high costs, numerical simulation methods can significantly reduce manpower and time costs. Therefore, numerical simulation methods are increasingly used in geotechnical engineering.

[0003] The finite element method is often used to study the temperature field changes of frozen soil embankments, but the thawing deformation of frozen soil is a complex physical process involving temperature changes, water migration, and changes in the freeze-thaw state of the soil. The conventional finite element method uses the method of derivation of formulas, which cannot solve the coupling of multiple physical fields (such as temperature field, water field, and mechanical field) during the thawing process of frozen soil embankments. In addition, the determination of the freeze-thaw interface in actual simulations usually relies on experience and assumptions, which to a certain extent affects the accuracy of the simulation results. Finally, the finite element method is difficult to characterize complex physical processes such as ice-soil contact and ice-water phase change. Therefore, there are certain principle defects in using the finite element method to simulate the thawing of frozen soil embankments. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a discrete element simulation method for thawing settlement of frozen soil roadbed and evolution of melting plate considering ice-water phase change, which simulates the process of heat transfer from the surface of asphalt pavement to the inside of permafrost embankment during solar irradiation. Due to the ice-water phase change process, when the temperature of ice particles exceeds zero degrees, they will melt into water, greatly reducing the bearing capacity of the roadbed, resulting in thawing settlement of frozen soil roadbed. At the same time, this method can calculate the different effects of sunny slopes and shady slopes on the settlement of different monitoring points along the embankment, and simulate the evolution of the melting plate in permafrost, and has high popularity.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A discrete element simulation method for thawing settlement of frozen soil roadbed and evolution of thaw plate considering ice-water phase change includes the following steps.

[0007] Step 1: Collection of frozen soil roadbed parameters: Determine the actual frozen soil roadbed that needs to be monitored for thaw settlement, and collect the actual frozen soil roadbed parameters; the frozen soil roadbed parameters include the geometric structure parameters of the frozen soil layer, the composition and proportion parameters of the frozen soil layer materials, the geometric structure parameters of the roadbed, and the composition and proportion parameters of the roadbed materials.

[0008] Step 2, construct a discrete element model of the frozen soil embankment: Based on the frozen soil roadbed parameters collected in step 1, use discrete element software to construct a discrete element model of the frozen soil embankment with the same geometric structure and material composition as the actual frozen soil roadbed; at this time, the discrete element model of the frozen soil embankment is composed of particles of various materials; among which the frozen soil layer contains soil particles and ice particles.

[0009] Step 3: Set material contact parameters: For the discrete element model of frozen soil embankment constructed in step 2, set the contact model and parameters of different material particles.

[0010] Step 4: Set the temperature boundary: Set the initial temperature of all particles in the frozen soil layer in the discrete element model of the frozen soil embankment constructed in step 2, and set the surface temperature boundary of the discrete element model of the frozen soil embankment according to the peripheral solar radiation temperature of the actual frozen soil roadbed.

[0011] Step 5: thermal coupling of frozen soil roadbed, specifically including the following steps:

[0012] Step 5-1, heat transfer: According to the surface temperature boundary set in step 4, heat is transferred from the outermost particles of the frozen soil embankment discrete element model to the inner particles in sequence, thereby obtaining the temperature value of each particle in the frozen soil embankment discrete element model at the current moment.

[0013] Step 5-2, ice-water phase change: When the temperature of an ice particle A in the frozen soil layer reaches 0°C, the material properties of ice particle A are changed to water.

[0014] Step 6, thawing and settling: After the ice-water phase change, the ice particles melt into water particles. Compared with the ice particles, the volume of water particles decreases, and the overlapping area between water particles and adjacent particles increases, thereby reducing the total volume of the frozen soil layer, and the corresponding particles will sink downward.

[0015] Step 7: Record particle distribution: record the displacement distribution of the set particles in the discrete element model of the frozen soil embankment at the end of the current time step.

[0016] In step 2, the initial shapes of soil particles and ice particles are set to irregular shapes; in step 6, the initial shape of water particles is set to spherical.

[0017] In step 1, the actual frozen soil roadbed has a shady slope and a sunny slope; in step 4, the surface temperature boundary includes the shady slope surface temperature boundary, the sunny slope temperature boundary and the road surface temperature boundary.

[0018] The initial temperature of all particles in the frozen soil layer is set to -5°C; the surface temperature boundary of the shady slope, the road surface temperature boundary and the sunny slope temperature boundary increase successively and are all greater than 0°C.

[0019] The method further includes step 8, melt disk evolution: M time steps are set, and steps 5 to 7 are repeated for each time step, so as to obtain the displacement distribution evolution of the set particles arranged in time sequence.

[0020] In step 6, the volume of the water particles is one tenth smaller than the volume of the ice particles.

[0021] In step 7, the particles are set to be soil particles, ice particles, and water particles.

[0022] In step 6, several monitoring points are set for the discrete element model of the frozen soil embankment, and the thaw settlement value of each monitoring point is obtained, which can be used to study the thaw settlement curves at different locations.

[0023] The number of monitoring points is six, two on the shoulder, two at the toe of the slope, and two in the center of the road.

[0024] In step 5-1, assume that there are N contacting particles D around particle C. Particle C and all particles D form a heat source network. Each particle in the heat source network is regarded as a heat reservoir. The center of mass of each particle D is connected to the center of mass of particle C through a virtual heat pipe. The output thermal power of each virtual heat pipe to particle C is recorded as Qp. Then the temperature value of particle C at the current moment is The calculation formula is obtained by the following heat conduction equation:

[0025]

[0026] in:

[0027]

[0028] In the formula, represents the total thermal power of N virtual heat pipes; Q v represents the heat source intensity of particle C; m represents the mass of particle C; C v represents the specific heat of particle C at a set volume; ΔT represents the temperature difference between the two reservoirs at both ends of the virtual heat pipe; η represents the thermal resistance of the virtual heat pipe per unit length; l p Represents the length of the virtual heat pipe.

[0029] The present invention has the following beneficial effects:

[0030] 1. The present invention uses the discrete element method to simulate the thawing and settlement process of permafrost embankments. Compared with the finite element method, it can simulate the contact behavior between different bulk materials and has a natural advantage in simulating geotechnical engineering problems. The present invention uses the discrete element method to simulate the thawing and settlement process of permafrost embankments.

[0031] 2. The present invention converts the heat-absorbing ice particles into water. Due to the reduction of water modulus, it cannot provide sufficient foundation bearing capacity, resulting in settlement of the overlying roadbed.

[0032] 3. The present invention can be used to simulate the yin-yang slope effect by setting different temperature boundaries.

[0033] 4. The present invention can show the development trend of the melting plate of frozen soil roadbed by displaying the distribution of ice particles and water particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The schematic diagram of the ice-water phase change principle in the present invention is shown; wherein (a) is a schematic diagram showing the contact between ice particles and soil particles before the phase change; and (b) is a schematic diagram showing the contact between water particles and soil particles after the phase change.

[0035] Figure 2 The schematic diagram of the displacement field change of the frozen soil roadbed during the thawing and settlement process of the present invention is shown; wherein, Figures (a) to (d) respectively represent the initial time step and the schematic diagram of the thawing and settlement displacement field change of three time steps in chronological order.

[0036] Figure 3 The schematic diagram of the evolution process of the melting plate of the frozen soil roadbed during the thawing and settling process of the present invention is shown; wherein, Figures (a) to (d) respectively represent the initial time step and the schematic diagram of the melting plate of three time steps in chronological order.

[0037] Among them are: 1. Soil particles; 2. Ice particles; 3. Water particles. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific preferred embodiments.

[0039] In the description of the present invention, it should be understood that the terms "left side", "right side", "upper part", "lower part" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second" and the like do not indicate the importance of the components, and therefore cannot be understood as limiting the present invention. The specific dimensions used in this embodiment are only for illustrating the technical solution, and do not limit the scope of protection of the present invention.

[0040] like Figure 1 As shown, a discrete element simulation method for thawing settlement of frozen soil roadbed and evolution of melting plate considering ice-water phase change includes the following steps.

[0041] Step 1: Collection of frozen soil roadbed parameters: Determine the actual frozen soil roadbed that needs to be monitored for thaw settlement, and collect the actual frozen soil roadbed parameters; the frozen soil roadbed parameters include the geometric structure parameters of the frozen soil layer, the composition and proportion parameters of the frozen soil layer materials, the geometric structure parameters of the roadbed, and the composition and proportion parameters of the roadbed materials.

[0042] In this embodiment, the actual frozen soil roadbed preferably has a shady slope and a sunny slope.

[0043] Step 2, construct a discrete element model of the frozen soil embankment: Based on the frozen soil roadbed parameters collected in step 1, use discrete element software to construct a discrete element model of the frozen soil embankment with the same geometric structure and material composition as the actual frozen soil roadbed; at this time, the discrete element model of the frozen soil embankment is composed of particles of various materials; among which the frozen soil layer contains soil particles and ice particles.

[0044] In this embodiment, a two-dimensional model of a frozen soil embankment is established according to the geometric shape of the frozen soil roadbed. In this example, an asphalt pavement with a height of 2.0m and a top width of 9.6m is used. Each earth shoulder is 7.0m and the slope ratio is 1:1.5. The shady slope is on the right, and the sunny slope is on the left by default. There are three layers of structure inside the embankment, including asphalt, gravel and granular soil, with thicknesses of 0.4m, 0.6m and 1.0m respectively. There are two layers of soil underground, namely 1.0m thick molten soil and 7.0m thick frozen soil. When we study the effect of embankment size on thawing settlement, the geometric dimensions of the embankment may change.

[0045] The initial shapes of the soil particles and ice particles are preferably set as follows Figure 1 The irregular shape shown in Figure (a).

[0046] Step 3: Set material contact parameters: For the discrete element model of frozen soil embankment constructed in step 2, set the contact model and parameters of different material particles.

[0047] Step 4: Set the temperature boundary: Set the initial temperature of all particles in the frozen soil layer in the discrete element model of the frozen soil embankment constructed in step 2, and set the surface temperature boundary of the discrete element model of the frozen soil embankment according to the peripheral solar radiation temperature of the actual frozen soil roadbed.

[0048] The surface temperature boundary includes the shady slope surface temperature boundary, the sunny slope temperature boundary and the road surface temperature boundary; among them, the shady slope surface temperature boundary, the road surface temperature boundary and the sunny slope temperature boundary increase in sequence and are all greater than 0°C.

[0049] In this embodiment, the temperature boundary of the highway embankment model is set on the outermost particles, including the asphalt pavement, shoulders and ground, and these particles are all above zero degrees Celsius due to solar radiation. Due to heat absorption, the default temperature boundary of the asphalt pavement is set to 30.0 degrees Celsius. The temperature boundary of the shoulders on both sides is lower than the temperature boundary of the asphalt pavement, but the default temperature is slightly different due to the consideration of the sunny and shady slopes. The temperature of the sunny slope is set to 10.0 degrees Celsius, and the temperature of the shady slope is set to 5.0 degrees Celsius. The temperature boundary of the ground is lower than the temperature boundary of the shoulder. The bottom temperature boundary of the embankment is located in the permafrost layer. According to the literature, the initial temperature of the frozen soil is set to -5.0 degrees Celsius. When heat is transferred from the pavement, the temperature of the ground soil will increase.

[0050] Step 5: thermal-mechanical coupling of frozen soil roadbed, specifically including the following steps.

[0051] Step 5-1, heat transfer: According to the surface temperature boundary set in step 4, heat is transferred from the outermost particles of the frozen soil embankment discrete element model to the inner particles in sequence, thereby obtaining the temperature value of each particle in the frozen soil embankment discrete element model at the current moment.

[0052] Assume that there are N contacting particles D around particle C. Particle C and all particles D form a heat source network. Each particle in the heat source network is regarded as a heat reservoir. The center of mass of each particle D is connected to the center of mass of particle C through a virtual heat pipe. The output heat power of each virtual heat pipe to particle C is recorded as Qp. Then the temperature value of particle C at the current moment is The calculation formula is obtained by the following heat conduction equation:

[0053]

[0054] in:

[0055]

[0056] In the formula, represents the total thermal power of N virtual heat pipes; Q v represents the heat source intensity of particle C; m represents the mass of particle C; C v represents the specific heat of particle C at a set volume; ΔT represents the temperature difference between the two reservoirs at both ends of the virtual heat pipe; η represents the thermal resistance of the virtual heat pipe per unit length; l p Represents the length of the virtual heat pipe.

[0057] The calculation formula of the thermal resistance η per unit length of the virtual heat pipe is preferably:

[0058]

[0059] Where n represents the porosity of the frozen soil layer; k represents the macroscopic electric and thermal coefficient of the frozen soil layer; V b Indicates the particle volume.

[0060] Step 5-2, ice-water phase change: When the temperature of an ice particle A in the frozen soil layer reaches 0°C, the material properties of ice particle A are changed to water.

[0061] like Figure 1 As shown in (a), frozen soil is initially set as an ice-soil-air (vide) three-phase medium. Ice exists in the form of solid particles below zero degrees Celsius. The overlap between ice-ice particles or ice-soil particles is small. Heat is transferred through the contact between ice-ice particles or ice-soil particles. The heat transfer efficiency of air is very low and is not considered in this paper. In addition, in this thermodynamic model, the radius of the soil particles is not affected by temperature changes.

[0062] Step 6, melting and settling: The initial shape of the water particles is set as follows Figure 1 The sphere shown in (b) in the figure; when the ice-water phase transition occurs, the ice particles melt into water particles; the volume of water particles decreases compared to ice particles, and the overlap area between water particles and adjacent particles increases, thereby reducing the total volume of the frozen soil layer by one tenth. At the same time, the Young's modulus of water particles decreases compared to ice particles, which means that there may be significant overlap with adjacent soil or ice particles. Due to the overlap between water and soil particles, the total volume of the frozen soil medium decreases, and the corresponding particles will sink downward.

[0063] Furthermore, several monitoring points are set for the discrete element model of frozen soil embankment, and the thaw settlement value of each monitoring point is obtained, which can be used to study the thaw settlement curves at different locations, such as Figure 2 shown.

[0064] In this embodiment, the number of monitoring points is preferably six, two on the road shoulder, two at the foot of the slope (at the foot of the shady slope and the foot of the sunny slope respectively), and two at the center of the road.

[0065] Step 7: Record particle distribution: record the displacement distribution of the set particles in the discrete element model of the frozen soil embankment at the end of the current time step.

[0066] The above-mentioned set particles are preferably soil particles, ice particles and water particles.

[0067] Step 8, melt disk evolution: set M time steps, and repeat steps 5 to 7 for each time step, so as to obtain the displacement distribution evolution of the set particles arranged in time order, such as Figure 3 shown.

[0068] The present invention can simulate the process of heat transfer from the surface of the asphalt pavement to the inside of the permafrost embankment during solar irradiation. Due to the ice-water phase transition process, when the ice particles are heated to a temperature above zero, they will melt into water, greatly reducing the bearing capacity of the roadbed, resulting in the thawing and settlement of the frozen roadbed. At the same time, the method can calculate the different effects of sunny and shady slopes on the settlement of different monitoring points along the embankment, and simulate the evolution of the melting plate in the permafrost. The present invention has a unique idea, simple code writing, and high popularity.

[0069] The preferred embodiments of the present invention are described in detail above; however, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all belong to the protection scope of the present invention.

Claims

1. A discrete element simulation method for frozen soil roadbed thaw settlement and melt plate evolution considering ice-water phase change, characterized by: The steps include: Step 1: Collection of frozen soil roadbed parameters: Determine the actual frozen soil roadbed that needs to be monitored for thawing settlement, and collect the actual frozen soil roadbed parameters; the frozen soil roadbed parameters include the geometric structure parameters of the frozen soil layer, the composition and proportion parameters of the frozen soil layer materials, the geometric structure parameters of the roadbed, and the composition and proportion parameters of the roadbed materials; Step 2, constructing a discrete element model of frozen soil embankment: Based on the frozen soil roadbed parameters collected in step 1, using discrete element software, a discrete element model of frozen soil embankment with the same geometric structure and material composition as the actual frozen soil roadbed is constructed; at this time, the discrete element model of frozen soil embankment is composed of particles of various materials; wherein the frozen soil layer contains soil particles and ice particles; Step 3, setting material contact parameters: for the frozen soil embankment discrete element model constructed in step 2, setting the contact model and parameters of different material particles; Step 4, setting temperature boundary: setting initial temperature for all particles of the frozen soil layer in the discrete element model of the frozen soil embankment constructed in step 2, and setting the surface temperature boundary of the discrete element model of the frozen soil embankment according to the peripheral solar radiation temperature of the actual frozen soil roadbed; Step 5: thermal coupling of frozen soil roadbed, specifically including the following steps: Step 5-1, heat transfer: according to the surface temperature boundary set in step 4, heat is transferred from the outermost particles of the frozen soil embankment discrete element model to the inner particles in sequence, thereby obtaining the temperature value of each particle in the frozen soil embankment discrete element model at the current moment; Step 5-2, ice-water phase transition: When the temperature of an ice particle A in the frozen soil layer reaches 0°C, the material property of the ice particle A is changed to water; Step 6, melting and settling: After the ice-water phase change, the ice particles melt into water particles; the volume of water particles is smaller than that of ice particles, and the overlapping area between water particles and adjacent particles increases, thereby reducing the total volume of the frozen soil layer, and the corresponding particles will settle downward; Step 7: Record particle distribution: record the displacement distribution of the set particles in the discrete element model of the frozen soil embankment at the end of the current time step.

2. The discrete element simulation method for frozen soil roadbed thaw settlement and melt plate evolution considering ice-water phase change according to claim 1 is characterized by: In step 2, the initial shapes of soil particles and ice particles are set to irregular shapes; in step 6, the initial shape of water particles is set to spherical.

3. The discrete element simulation method for thawing settlement of frozen soil roadbed and evolution of melting plate considering ice-water phase change according to claim 1 is characterized by: In step 1, the actual frozen soil roadbed has a shady slope and a sunny slope; in step 4, the surface temperature boundary includes the shady slope surface temperature boundary, the sunny slope temperature boundary and the road surface temperature boundary.

4. The discrete element simulation method for frozen soil roadbed thaw settlement and melt plate evolution considering ice-water phase change according to claim 3 is characterized by: The initial temperature of all particles in the frozen soil layer is set to -5°C; the surface temperature boundary of the shady slope, the temperature boundary of the sunny slope and the road surface temperature boundary increase successively and are all greater than 0°C.

5. The discrete element simulation method for frozen soil roadbed thaw settlement and melt plate evolution considering ice-water phase change according to claim 1 is characterized by: The method further includes step 8, melt disk evolution: M time steps are set, and steps 5 to 7 are repeated for each time step, so as to obtain the displacement distribution evolution of the set particles arranged in time sequence.

6. The discrete element simulation method for frozen soil roadbed thaw settlement and melt plate evolution considering ice-water phase change according to claim 1 is characterized by: In step 6, the volume of the water particles is one tenth smaller than the volume of the ice particles.

7. The discrete element simulation method for frozen soil roadbed thaw settlement and melt plate evolution considering ice-water phase change according to claim 1 is characterized by: In step 7, the particles are set to be soil particles, ice particles, and water particles.

8. The discrete element simulation method for frozen soil roadbed thaw settlement and melt plate evolution considering ice-water phase change according to claim 1 is characterized by: In step 6, several monitoring points are set for the discrete element model of the frozen soil embankment, and the thaw settlement value of each monitoring point is obtained, which can be used to study the thaw settlement curves at different locations.

9. The discrete element simulation method for frozen soil roadbed thaw settlement and melt plate evolution considering ice-water phase change according to claim 8 is characterized by: The number of monitoring points is six, two on the shoulder, two at the toe of the slope, and two in the center of the road.

10. The discrete element simulation method for frozen soil roadbed thaw settlement and melt plate evolution considering ice-water phase change according to claim 1 is characterized by: In step 5-1, assume that there are N contacting particles D around particle C. Particle C and all particles D form a heat source network. Each particle in the heat source network is regarded as a heat reservoir. The center of mass of each particle D is connected to the center of mass of particle C through a virtual heat pipe. The output thermal power of each virtual heat pipe to particle C is recorded as Qp. Then the temperature value of particle C at the current moment is The calculation formula is obtained by the following heat conduction equation: in: In the formula, represents the total thermal power of N virtual heat pipes; Q v represents the heat source intensity of particle C; m represents the mass of particle C; C v represents the specific heat of particle C at a set volume; ΔT represents the temperature difference between the two reservoirs at both ends of the virtual heat pipe; η represents the thermal resistance of the virtual heat pipe per unit length; l p Represents the length of the virtual heat pipe.

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