A method for analyzing channel frost heave damage

Abstract

The invention discloses a channel frost heave damage analysis method, comprising the following steps: obtaining environmental cooling conditions, obtaining frozen soil channel material parameters, establishing a frozen soil channel finite element model and analyzing the cause of frost heave damage by using the finite element model; the invention adopts large-scale commercial multi-physics field coupling analysis software COMSOL to establish a typical cross-section frost heave finite element model of a frozen soil channel based on water-heat-force coupling, and designs three comparative working conditions of winter daily minimum temperature, daily average temperature, and typical annual and monthly average temperature, analyzes the channel foundation soil frost heave and lining stress law and the channel frost heave characteristics under different cooling conditions, realizes accurate and effective analysis of channel frost heave damage, so as to obtain the root cause of frost heave damage, and is convenient for providing important reference and theoretical basis for subsequent channel frost heave prevention and control work.

Description

Technical Field

[0001] The invention relates to the technical field of frost heave damage analysis, and in particular to a channel frost heave damage analysis method. Background Art

[0002] In recent years, with the rapid development of my country's northwest region, the number of canal projects has also increased. Among them, concrete panel rockfill dams have been widely used due to their high safety, good stability and simple construction. However, due to the influence of permafrost, canal buildings in permafrost areas are often damaged by freeze-thaw cycles, posing a major safety hazard to canal construction in cold areas. In order to ensure the structural safety of the built canal sections in the canal project and the smooth construction of the projects to be built, it is necessary to conduct frost heave damage analysis on the canal buildings.

[0003] Frost heave damage in canals is caused by the expansion of the frozen canal foundation soil, which supports the lining. The following conditions must be met for the expansion of the frozen canal foundation soil: continuous negative temperature conditions in cold climate zones; the presence of free water and capillary water in the soil, and unobstructed water supply channels; frozen and weathered soil surfaces; and the physical and mechanical properties of the soil itself, including the particle composition and mineral components of the soil. Among the above three conditions, the presence of free water and capillary water in the soil is a prerequisite and a necessary condition for frost heave to occur.

[0004] Most of the existing channel frost heave damage analysis methods have cumbersome steps and complex operations, and do not take into account the frost heave of the channel foundation soil and the stress law of the lining under different cooling conditions, resulting in the inability to accurately and effectively analyze the causes of channel frost heave damage, thereby failing to ensure the structural safety of the built channel sections in the canal system project, and causing the construction of the project to be built to be hindered. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to propose a channel frost heave damage analysis method to solve the problems that the existing channel frost heave damage analysis method has cumbersome steps, complex operation and cannot accurately and effectively analyze the causes of channel frost heave damage.

[0006] In order to achieve the purpose of the present invention, the present invention is implemented by the following technical scheme: a channel frost heave damage analysis method, comprising the following steps:

[0007] Step 1: Obtain the daily minimum temperature, daily average temperature and historical typical winter monthly average temperature in different time periods in the area where the frozen soil channel is located as environmental cooling conditions;

[0008] Step 2: Obtain the mechanical parameters of each phase of frozen soil channel concrete, the basic parameters of frozen soil channel base soil, and the thermodynamic and mechanical parameters of frozen-thawed soil as the material parameters of the frozen soil channel;

[0009] Step 3: First, measure the geometric dimensions of the frozen soil channel section, then take the midpoint of the channel bottom lining as the origin of the overall coordinates of the model, and combine the environmental cooling conditions and material parameters to establish a water-heat-force three-field coupling model of the frozen soil channel as the finite element model of the frozen soil channel section. Then, mesh the finite element model, and then determine the boundary conditions and initial conditions of the finite element model. Finally, use the transient analysis method to calculate the freezing situation of the frozen soil channel and set the calculation load of the finite element model.

[0010] Step 4: First, obtain the surface convection heat transfer coefficient of the shady slope of the right bank of the frozen soil channel and the convection heat transfer coefficient of the sunny slope and the channel bottom of the left bank of the frozen soil channel as the temperature field boundary of the model, and then substitute the temperature field boundary into the finite element model, and use the finite element model to perform coupled verification calculations on the frozen soil channel section to realize the calculation and analysis of the frost heave damage of the channel.

[0011] A further improvement is that in step 1, the daily average temperature is taken as the average of the daily maximum temperature and the daily minimum temperature, and the daily maximum temperature, the minimum temperature and the monthly average temperature are all queried through the official website of the National Meteorological Administration.

[0012] Further improvement lies in that: in the step 2, the mechanical parameters of each phase of concrete include density, elastic modulus, Poisson's ratio, thermal conductivity and volume specific heat capacity, the basic parameters include dry density, saturated moisture content, residual moisture content and saturated permeability, and the thermodynamic and mechanical parameters of freeze-thaw soil include thermal conductivity, volume specific heat capacity, elastic modulus and Poisson's ratio.

[0013] Further improvements are as follows: in step three, the water-heat-force three-field coupling model is established using the large-scale commercial multi-physics field coupling analysis software COMSOL, the finite element model uses the quadrilateral mapping grid method to divide the units, and the base soil adjacent to the channel is meshed.

[0014] Further improvements are as follows: in step three, when determining the boundary conditions of the finite element model, the bottom boundary and the left and right side boundaries of the model are constrained by directional hinge supports, and the upper surface of the model uses the second-class thermodynamic boundary conditions to describe the heat exchange process between the base soil and the atmospheric environment. The other parts of the model are all adiabatic and water-proof boundaries.

[0015] A further improvement is that the second type of boundary condition is defined as:

[0016] q l =h c (T ext -T)

[0017] In the formula, q l is the heat flux in the normal direction outside the boundary, T ext and T are the ambient temperature and boundary temperature respectively, h c is the convective heat transfer coefficient.

[0018] Further improvements are as follows: in the step three, when determining the initial conditions of the finite element model, it is assumed that the consolidation and settlement of the base soil are completed before freezing in winter. The ground stress balance method is used in the calculation to obtain the initial stress distribution under the condition of no self-weight deformation. The initial temperature of the model takes the daily average temperature, and the initial moisture content is combined with the geological survey results. The moisture content of each elevation of the left and right banks is calculated by the mathematical average method. Then, the initial moisture content distribution of the left and right banks of the channel is obtained by linear interpolation. The initial moisture content of the base soil below the channel bottom takes the average of the moisture contents of the lowest measuring points on the left and right banks.

[0019] A further improvement is that the elevation water content calculation formula is:

[0020]

[0021] In the formula, w 0i is the initial water content at elevation i, wif and wiuf are the water contents of the frozen layer and unfrozen layer at elevation i, respectively, and dif and diuf are the sampling thicknesses of the frozen layer and unfrozen layer at elevation i, respectively.

[0022] The beneficial effects of the present invention are as follows: the present invention adopts the large-scale commercial multi-physics field coupling analysis software COMSOL to establish a finite element model of frost heave of a typical cross-section of a frozen soil channel based on water-heat-force coupling, and designs three comparative working conditions of the winter daily minimum temperature, the daily average temperature, and the typical annual and monthly average temperature. The frost heave of the channel foundation soil and the stress law of the lining, as well as the frost heave characteristics of the channel under different cooling conditions are analyzed, so as to achieve accurate and effective analysis of the frost heave damage of the channel, and obtain the root cause of the frost heave damage, so as to provide important reference and theoretical basis for subsequent channel frost heave prevention and control work, so as to ensure the structural safety of the built channel sections in the canal system engineering and the smooth construction of the projects to be built. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0024] Figure 1 It is a schematic flow chart of the method of the present invention;

[0025] Figure 2 is a mesh diagram of a finite element model of the present invention;

[0026] Figure 3 is a schematic diagram of the freezing depth process calculated by different convective heat transfer coefficients in an embodiment of the present invention;

[0027] Figure 4 Schematic diagram of the relationship between the convective heat transfer coefficient and the calculated maximum freezing depth in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] See also Figure 1 , Figure 2 , Figure 3 , Figure 4 This embodiment provides a channel frost heave damage analysis method, comprising the following steps:

[0030] The National Meteorological Administration’s official website was used to query and select the daily minimum temperature and daily average temperature from November 1, 2020 to January 15, 2021, the minimum temperature from November 1, 2019 to January 15, 2020, and the historical typical winter monthly average temperature as environmental cooling conditions to analyze and study the frost heave characteristics of the canal section. The daily average temperature was taken as the average of the daily maximum and minimum temperatures.

[0031] The mechanical parameters of each phase of frozen soil channel concrete, the basic parameters of frozen soil channel base soil, and the thermodynamic and mechanical parameters of frozen-thaw soil are obtained as the material parameters of frozen soil channels. The mechanical parameters of each phase of concrete include the density of 2400kg / m 3 , elastic modulus 28GPa, Poisson's ratio 0.167, thermal conductivity 1.28W / (m·℃) and volume specific heat capacity 2.328J / (m 3 ·℃), the basic parameters of frozen soil channel foundation soil include dry density, saturated moisture content, residual moisture content and saturated permeability, as shown in Table 1 below, and the thermodynamic and mechanical parameters of frozen-thaw soil include thermal conductivity, volume specific heat capacity, elastic modulus and Poisson's ratio, as shown in Table 2 below;

[0032] First, the geometric dimensions of the frozen soil channel section were measured, and then the midpoint of the channel bottom lining was taken as the origin of the overall coordinate system of the model. The channel section was extended 3m on both sides as the left and right boundaries of the model, and 5m below the channel bottom was taken as the lower boundary of the model. The large-scale commercial multi-physics field coupling analysis software COMSOL was used in combination with the environmental cooling conditions and material parameters to establish a water-heat-force three-field coupling model of the frozen soil channel. As the finite element model of the frozen soil channel section, the finite element model used the quadrilateral mapping grid method to divide the units, with a total of 8224 units. The grid of the base soil adjacent to the channel was encrypted, and the maximum unit size was about 2.5cm. Then the finite element model was meshed. The mesh diagram of the finite element model is shown in the figure. Figure 2 As shown, the boundary conditions and initial conditions of the finite element model are then determined. When determining the boundary conditions of the finite element model, the bottom boundary and the left and right boundaries of the model are constrained by directional hinge supports, and the upper surface of the model uses the second-class thermodynamic boundary conditions to describe the heat exchange process between the base soil and the atmospheric environment. The second-class boundary conditions are defined as:

[0033] q l =h c (T ext -T)

[0034] In the formula, q l is the heat flux in the normal direction outside the boundary, T ext and T are the ambient temperature and boundary temperature respectively, h c is the convection heat transfer coefficient, and the rest of the model is adiabatic and water-proof. Finally, the transient analysis method is used to calculate the freezing of the frozen soil channel and set the calculation load of the finite element model.

[0035] When calculating the model, it is assumed that the foundation soil has been consolidated and settled before freezing in winter. The ground stress balance method is used to obtain the initial stress distribution under the condition of no self-weight deformation.

[0036] The initial temperature of the model is the daily average temperature on November 1, 2020. The initial water content is combined with the geological survey results, and the water content of each elevation on the left and right banks is calculated by the mathematical average method, that is,

[0037]

[0038] In the formula, w 0i is the initial water content at elevation i, wif and wiuf are the water contents of the frozen layer and the unfrozen layer at elevation i, respectively, and dif and diuf are the sampling thicknesses of the frozen layer and the unfrozen layer at elevation i, respectively;

[0039] The calculated moisture content of each elevation point on the left and right banks is shown in Table 3 below. The initial moisture content distribution (i.e., initial moisture field) of the left and right banks can be obtained by linear interpolation. The initial moisture content of the base soil below the channel bottom is the average of the moisture content of the lowest measuring point on the left and right banks, i.e., 27.55%;

[0040] First, the surface convection heat transfer coefficient of the foundation soil on the shady slope of the right bank of the frozen soil channel and the convection heat transfer coefficient between the sunny slope of the left bank of the frozen soil channel and the channel bottom are obtained as the temperature field boundary of the model. Then, the temperature field boundary is substituted into the finite element model, and the finite element model is used to perform coupled verification calculations on the frozen soil channel section to realize the calculation and analysis of the frost heave damage of the channel.

[0041] To calculate the convective heat transfer coefficient h c The reasonable value of h is established to establish a one-dimensional soil-water-heat coupling model in the vertical direction. c and the law of changes in freezing depth;

[0042] The calculation model takes a soil depth of 5m, the initial temperature is defined as 16℃, the initial moisture content is the moisture content of the unfrozen layer 0.6m from the foot of the right bank slope, that is, 39.2%, and the ambient temperature is the daily minimum temperature from November 1, 2020 to January 15, 2021. The calculation results of the convective heat transfer coefficient are shown in Figure 3 and Figure 4 The calculation results show that the convective heat transfer coefficient h c The larger the value, the faster the freezing depth develops, and the convective heat transfer coefficient h c It is basically linearly related to the maximum calculated freezing depth;

[0043] The results of geological survey section excavation show:

[0044] Channel top surface: 0.3m below the ground surface is not frozen;

[0045] Slope section: The vertical slope thickness of the frozen layer in the section 4.8 to 1.9 m from the toe of the channel bottom slope is 0.20 to 0.22 m; the vertical slope thickness of the frozen layer in the section 1.9 to 1.3 m from the toe of the channel bottom slope is 0.22 to 0.24 m, of which the section 1.4 to 1.5 m from the toe of the channel bottom slope is the width of the clay layer on the slope; the vertical slope thickness of the frozen layer in the section 1.3 to 0.6 m from the toe of the channel bottom slope is 0.24 to 0.30 m.

[0046] Therefore, combined with the results of geological exploration, Figure 4 The convective heat transfer coefficient between the right bank soil and the ambient temperature ranges from 7.5 to 28 W / (m 2 ℃), and the freezing depth on the right bank is basically distributed linearly from the bottom to the top of the channel. Therefore, in this review calculation, the convective heat transfer coefficient of the shady slope foundation soil is approximately linearly distributed. Through the two-dimensional water-thermal coupling calculation of the channel, h is selected to meet the geological survey freezing depth. c The equation is:

[0047] h c (y) = 28 (1-0.26y)

[0048] In the formula, y is the coordinate axis with vertical upward as positive, and y=0 corresponds to the elevation of the channel bottom plate surface.

[0049] According to 3.1.4 of the Code for Design of Canal Engineering for Frost Heave Resistance, the correction factor ψ d , can be calculated according to the dimension of the project site and the direction of the building axis as follows:

[0050] ψ d =α+(1-α)ψ i

[0051] In the formula, ψ i It is the correction coefficient of sunshine and shade degree in a certain part of a typical section (channel direction NS, bottom width and depth ratio B / H=1.0, slope ratio m=1.0), and α is the correction coefficient.

[0052] The right bank convection heat transfer coefficient h c The calculation formula is used to obtain the convective heat transfer coefficient h for the middle of the right bank corresponding to the channel height y = 1.35m. c,右岸中 =18.172W / (m 2 ℃), combined with shady and sunny slopes and channel bottom ψ d The relative proportional relationship of the left bank sun slope gives the convective heat transfer coefficient h c,左岸 =6.36W / (m 2 ℃), the convection heat transfer coefficient at the bottom of the channel is h c,渠底 =14.45W / (m2℃).

[0053] Table 1

[0054]

[0055] Table 2

[0056] Thermal conductivity λ Volumetric specific heat capacity Cv Elastic modulus E Poisson's ratio Unfrozen soil 1.54 <![CDATA[5.9×10 6 ]]> <![CDATA[1.5×10 7 ]]> 0.330 frozen soil 2.40 <![CDATA[4.3×10 6 ]]> <![CDATA[4.6×10 7 ]]> 0.373

[0057] Table 3

[0058]

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A channel frost heave damage analysis method, characterized in that: The following steps are involved: Step 1: Obtain the daily minimum temperature, daily average temperature and historical typical winter monthly average temperature in different time periods in the area where the frozen soil channel is located as environmental cooling conditions; Step 2: Obtain the mechanical parameters of each phase of frozen soil channel concrete, the basic parameters of frozen soil channel base soil, and the thermodynamic and mechanical parameters of frozen-thawed soil as the material parameters of the frozen soil channel; Step 3: First measure the geometric dimensions of the frozen soil channel section, then take the midpoint of the channel bottom lining as the origin of the overall coordinate system of the model, and combine the environmental cooling conditions and material parameters to establish a water-heat-force three-field coupling model of the frozen soil channel as the finite element model of the frozen soil channel section. Then, the finite element model is meshed, and then the boundary conditions and initial conditions of the finite element model are determined. Finally, the transient analysis method is used to calculate the freezing situation of the frozen soil channel and set the calculation load of the finite element model. When determining the boundary conditions of the finite element model, the bottom boundary and the left and right boundaries of the model are constrained by directional hinge supports. The upper surface of the model uses the second-class thermodynamic boundary conditions to describe the heat exchange process between the base soil and the atmospheric environment. The other parts of the model are adiabatic and water-proof boundaries. The second-class boundary conditions are defined as: q l =h c (T ext -T) In the formula, q l is the heat flux in the normal direction outside the boundary, T ext and T are the ambient temperature and boundary temperature respectively, h c is the convective heat transfer coefficient; Step 4: First, obtain the surface convection heat transfer coefficient of the shady slope of the right bank of the frozen soil channel and the convection heat transfer coefficient of the sunny slope and the channel bottom of the left bank of the frozen soil channel as the temperature field boundary of the model, and then substitute the temperature field boundary into the finite element model, and use the finite element model to perform coupled verification calculations on the frozen soil channel section to realize the calculation and analysis of the frost heave damage of the channel.

2. A channel frost heave damage analysis method according to claim 1, characterized in that: In the step 1, the daily average temperature is taken as the average of the daily maximum temperature and the daily minimum temperature, and the daily maximum temperature, the minimum temperature and the monthly average temperature are all queried through the official website of the National Meteorological Administration.

3. A channel frost heave damage analysis method according to claim 1, characterized in that: In the step 2, the mechanical parameters of each phase of concrete include density, elastic modulus, Poisson's ratio, thermal conductivity and volume specific heat capacity, the basic parameters include dry density, saturated moisture content, residual moisture content and saturated permeability, and the thermodynamic and mechanical parameters of freeze-thaw soil include thermal conductivity, volume specific heat capacity, elastic modulus and Poisson's ratio.

4. A channel frost heave damage analysis method according to claim 1, characterized in that: In the step three, the water-heat-force three-field coupling model is established using the large-scale commercial multi-physics field coupling analysis software COMSOL, the finite element model uses a quadrilateral mapping grid method to divide the units, and the base soil adjacent to the channel is meshed.

5. A channel frost heave damage analysis method according to claim 1, characterized in that: In the step three, when determining the initial conditions of the finite element model, it is assumed that the consolidation and settlement of the base soil are completed before freezing in winter. The ground stress balance method is used in the calculation to obtain the initial stress distribution under the condition of no self-weight deformation. The initial temperature of the model takes the daily average temperature. The initial moisture content is combined with the geological survey results. The moisture content of each elevation of the left and right banks is calculated by the mathematical average method. Then, the initial moisture content distribution of the left and right banks of the channel is obtained by linear interpolation. The initial moisture content of the base soil below the channel bottom takes the average of the moisture contents of the lowest measuring points on the left and right banks.

6. A channel frost heave damage analysis method according to claim 5, characterized in that: The elevation water content calculation formula is: In the formula, w 0i is the initial water content at elevation i, w if and w iuf are the water contents of the frozen layer and the unfrozen layer at elevation i, respectively, and d if and d iuf are the sampling thickness of the frozen layer and the unfrozen layer at elevation i, respectively.

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