Frost heaving control method based on cold source temperature dynamic adjustment

Abstract

The invention provides a frost heaving control method based on cold source temperature dynamic adjustment. The frost heaving control method comprises the following steps that 1, the influence of temperature evolution on driving force is analyzed; 1.1, the migration driving force of the thin film water is obtained; step 1.2, influence of temperature rise on migration driving force; step 2, analyzing freeze-thaw hysteresis of segregated ice; step 2.1, setting formation conditions of segregation ice; step 2.2, determining melting conditions of segregation ice; step 3, analyzing a water insulation mechanism of segregated ice; step 3.1, calculating a conversion relation between pressure-suction stress; step 3.2, influence of temperature rise on surface adsorption force; 4, discovering a segregation expansion control mechanism; step 4.1, influence of temperature evolution of a warm end of segregated ice on frost heaving; and step 4.2, a frost heaving control model of segregated ice is established. In order to solve the problem that frost heaving diseases are difficult to prevent and control in the stratum freezing process, frost heaving control mechanism research on frozen soil is carried out.

Description

Technical Field

[0001] The invention relates to the technical field of artificial ground freezing construction method, and in particular to a frost heave control method based on dynamic regulation of cold source temperature. Background Art

[0002] Ground freezing is a special ground reinforcement method. Due to its excellent water-proofing, strong adaptability, flexible support, easy control, and low environmental disturbance, it is very suitable for loose and unstable alluvial layers, fractured water-bearing rock layers, soft mudstone, and rock layers with extremely high water content and water pressure. However, the artificial freezing method changes the original temperature field of the formation, which will cause frost heave deformation within a certain range [4]. Frost heave mainly includes in-situ frost heave, which causes a volume increase of 9.05% due to the in-situ water phase transformation into ice, and segregation frost heave, which causes a volume increase of 109.05% due to the continuous migration of pore water and external replenishment water to the freezing front. Among them, water migration is the main cause of frost heave. Excessive frost heave will cause relative displacement of particles, resulting in an increase in soil volume and an increase in formation pressure, causing serious damage to underground structures, adjacent pipelines, and surface buildings or structures, bringing huge losses and adverse effects to the national economy. How to reduce the excessive frost heave caused by "artificial freezing construction technology" has become one of the world's difficult problems in underground engineering construction.

[0003] Given that frozen soil materials belong to a four-phase system of soil-water-ice-air, they are very sensitive to water and heat conditions, and their physical and mechanical properties are very unstable. In addition, they are affected by different engineering geology, hydrogeology, climate and other factors, making the actual frost heave problem more complicated. So far, there is no theoretical model that can comprehensively and reasonably reveal all frost heave phenomena. Due to the lack of sufficient theoretical support, the current frost heave prevention and control methods only start from the five major elements of soil, water, pressure, temperature and salt content, and improve the physical and mechanical properties of frozen soil, or provide auxiliary facilities to isolate water and heat, so as to inhibit the migration of water in the freezing process and achieve the purpose of controlling frost heave. However, the above methods are all passive and additional frost heave prevention and control technologies, which not only have poor economic benefits and large carbon emissions, but also fail to meet the technical requirements of green, clean, stable and efficient. Summary of the invention

[0004] The purpose of the present invention is to provide a frost heave control method based on dynamic adjustment of cold source temperature. This method aims at the problem that frost heave disease is difficult to prevent and control during ground freezing, and studies the frost heave control mechanism of frozen soil. This method has important theoretical value and practical significance for ensuring the safety of artificial freezing project construction and reducing frost heave disease.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A frost heave control method based on dynamic adjustment of cold source temperature comprises the following steps:

[0007] Step 1, analyzing the impact of temperature evolution on driving force;

[0008] Step 1.1, driving force for migration of film water;

[0009] Step 1.2, the effect of temperature rise on the migration driving force;

[0010] Step 2, analyzing the freeze-thaw hysteresis of the condensed ice;

[0011] Step 2.1, formation conditions of condensed ice;

[0012] Step 2.2, melting conditions of condensed ice;

[0013] Step 3, analyzing the water-isolating mechanism of condensed ice;

[0014] Step 3.1, conversion relationship between pressure and suction stress;

[0015] Step 3.2, the effect of temperature rise on surface adsorption;

[0016] Step 4, discover the control mechanism of frost heave;

[0017] Step 4.1, the effect of the temperature evolution of the warm end of the condensed ice on frost heave;

[0018] Step 4.2, frost heave control model of condensed ice.

[0019] Furthermore, in the above-mentioned frost heave control method based on dynamic adjustment of cold source temperature, in step 1.1, under the action of the virtual electric field force, the film water is adsorbed on the surface of the particle and forms a diffuse double electric layer. At this time, the film water generates hydraulic pressure along the surface normal direction:

[0020]

[0021] In equation (1): P L is the hydraulic pressure distribution; a is the coefficient; v L is the specific volume of water; y is the normal distance from the particle surface; α is the power;

[0022] From formula (1), we can see that the hydraulic pressure is related to the distance from the particle surface, that is, the closer to the surface, the greater the hydraulic pressure. When y = h, we get:

[0023]

[0024] In equation (2): h is the film thickness; P Lh is the hydraulic pressure distribution when the film thickness is h;

[0025] When the thin film water gradually freezes along the thickness direction, the water molecules in the ice crystals lose their dipole properties and are no longer adsorbed by the electric field, causing the hydraulic pressure of the thin liquid layer to decrease. The corresponding distribution is: PL -P Lh , freezing causes uneven changes in film thickness, inducing a hydraulic pressure difference between the thick film and the thin film; according to the principle of fluid dynamics, the hydraulic pressure difference is:

[0026] P Ld =P L -(P L -P Lh )=P Lh Equation (3)

[0027] In equation (3): P Ld It is the hydraulic driving force, driving water molecules to migrate from the thick film to the thin film. At the same time, as water molecules continue to migrate to the thin part, aggregate and change phase, ice crystals in the thin part grow rapidly and ice pressure increases. Given that ice pressure, hydraulic pressure and interface pressure in the thin part maintain stress balance on the curved ice-water interface, that is:

[0028]

[0029] In equation (4): P S is the ice pressure; SL is the ice-water interfacial tension; R is the effective radius; is the average curvature, which is positive toward the liquid layer side; is the interface pressure, that is, the equivalent pressure generated by the interface tension; P Ly In order to eliminate the influence of interface pressure, the ice pressure P S The actual hydraulic pressure delivered to the diaphragm;

[0030] Hydraulic Ly The increase of reduces the pressure difference between the thick film and the thin film; combined with equation (3), it can be seen that the hydraulic driving force is reduced to:

[0031]

[0032] From equation (5), we can see that P Ly Derived from ice pressure P S , minus the interface pressure The influence of ice pressure P S The actual hydraulic pressure transmitted to the membrane; combined with equation (3), it can be seen that the hydraulic driving force P Ld for:

[0033]

[0034] From equation (6), we can see that as the ice pressure P S increases, the hydraulic pressure difference between the thick film and the thin film gradually decreases; when the hydraulic pressure P Ly Growth to P Lh When the hydraulic driving force P LdApproaching 0 indicates that thermodynamic equilibrium has been reached, at which point water migration stops; the theoretical ice pressure in equilibrium is:

[0035]

[0036] In equation (7): P S0 is the theoretical ice pressure under equilibrium state; L is the latent heat of melting of water, which can be taken as 3.34×10 9 cm 2 / s 2 ; T is the surface temperature of the soil matrix; v S is the specific volume of ice; T A is the absolute freezing temperature of pure water, which can be taken as 273.15K; combined with equation (6), it can be seen that the hydraulic pressure equation under equilibrium state is:

[0037] P Ly =P Lh Equation (8)

[0038] Substituting equations (7) and (8) into equation (4), we can obtain the stress equilibrium relationship between ice pressure, hydraulic pressure and interface pressure at the curved ice-water interface under equilibrium state:

[0039]

[0040] Substituting equation (9) into equation (6), we can obtain:

[0041]

[0042] Combining equation (6), equation (7), and equation (10), we get:

[0043]

[0044] From equation (11), it can be seen that the driving force of water migration can be expressed by either hydraulic pressure difference or ice pressure difference.

[0045] Furthermore, in the above-mentioned frost heave control method based on dynamic adjustment of cold source temperature, in step 1.2, when the surface temperature T of the soil matrix rises uniformly by ΔT, the temperature variable after the temperature increase is T', then:

[0046] T'=T+ΔT Equation (12)

[0047] Substituting equation (12) into equation (7), we can obtain the theoretical ice pressure equation after heating, namely:

[0048]

[0049] From equation (13), we can see that as the temperature increases, the theoretical ice pressure decreases linearly. In addition, the film thickness gradually increases with the temperature. When the temperature rises by +ΔT, the film thickness increases from h to h(T), and the hydraulic pressure distribution at the film is: P L -P Lh(T) , the hydraulic driving force after heating is:

[0050]

[0051] In equation (14): P Ld ' is the hydraulic driving force after heating; P S ' is the actual ice pressure after heating;

[0052] From equation (14), we can see that when the temperature rises by +ΔT, the theoretical ice pressure P S0 ' shows a linear decreasing trend, the actual ice pressure decreases from P S Development to P S '.

[0053] Furthermore, in the above-mentioned frost heave control method based on dynamic adjustment of cold source temperature, in step 2.1, when the actual ice pressure in the frozen edge is greater than or equal to the sum of the overburden pressure and the separation pressure, a new ice lens is generated, that is:

[0054] P S1 ≥P OB +P sep Equation (15)

[0055] In equation (15): P S1 is the ice pressure distribution before the formation of condensed ice; P OB is the overburden pressure; P sep is the separation pressure;

[0056] According to the frost heave test, the ice pressure P S1 The rate of change with temperature is 1.1MPa / ℃; while the theoretical ice pressure P S0 The rate of change with temperature is 1.124MPa / ℃. Therefore, before the formation of fractional ice, the actual ice pressure is equal to the theoretical ice pressure. Based on this, the critical conditions for the formation of fractional ice can be obtained:

[0057]

[0058] In equation (16): T s is the segregation-freezing temperature;

[0059] Transforming equation (16), we can get the condensation-freezing temperature T s The governing equation is:

[0060]

[0061] In addition, after the formation of segregated ice, the discontinuous ice lens will develop into a continuous segregated ice layer, which needs to bear all the overlying loads alone. However, at the moment of segregated ice formation, the ice pressure at its warm end will drop rapidly from the sum of the overlying pressure and the separation pressure to the overlying pressure, that is:

[0062] P S2 =P OB Equation (18)

[0063] In equation (18): P S2 is the ice pressure distribution after the formation of condensed ice; according to the above analysis, the mechanical distribution model before and after the formation of condensed ice can be obtained, and the hydraulic driving force after the formation of condensed ice is:

[0064]

[0065] Furthermore, in the above-mentioned frost heave control method based on dynamic adjustment of cold source temperature, in step 2.2, according to the pressure melting test, the fitting equation between the overburden pressure and the melting temperature is:

[0066]

[0067] In equation (20): T sm is the melting temperature of condensed ice.

[0068] Furthermore, in the above-mentioned frost heave control method based on dynamic adjustment of cold source temperature, in step 3.1, the generalized Clapeyron equation is introduced, namely:

[0069]

[0070] In equation (21): P Lb is the surface adsorption force; ρ L is the density of water; ρ S is the density of ice; changing equation (21) yields:

[0071]

[0072] In equation (22): v L is the specific volume of water; v S is the specific volume of ice; and v L =1 / ρ L 、v S =1 / ρ S ;P SU is the theoretical suction force under equilibrium state; λ is the pressure-suction variable conversion coefficient, and λ=-v S / v L =-1.09.

[0073] Furthermore, in the above-mentioned frost heave control method based on dynamic adjustment of cold source temperature, in step 3.2, the theoretical suction force P is found to be SU It remains unchanged before and after the formation of condensed ice, that is:

[0074]

[0075] In equation (23): P SU1 P is the theoretical suction force before the formation of condensed ice; SU2 It is the theoretical suction force after condensation ice is formed.

[0076] The substrate surface temperature is raised uniformly by +ΔT, and the theoretical suction force P of the warm end of the condensed ice after the temperature rises SU2 'for:

[0077]

[0078] In equation (24): P SU2 ' is the theoretical suction after heating;

[0079] The theoretical suction force at the warm end of the condensed ice decreases linearly with the increase of temperature. After the condensed ice is formed, it bears all the overburden pressure alone, and the overburden pressure has nothing to do with the temperature. We can get:

[0080] P S2 =P S2 '=P OB Equation (25)

[0081] In equation (25): P S2 ' is the ice pressure distribution after the formation of condensed ice and heating.

[0082] Combining equations (22), (24) and (25), we can obtain the surface adsorption force of the warm end of the decondensed ice after heating:

[0083]

[0084] In equation (26): P Lb ' is the surface adsorption force after heating.

[0085] Furthermore, in the above-mentioned frost heave control method based on dynamic adjustment of cold source temperature, in step 3.3, as the temperature rise amplitude +ΔT increases, the adsorption force P of the warm end surface of the condensed ice increases. Lb 'gradually decreases. Let the state where the driving force of the warm end migration of the condensed ice is equal to zero be the critical state, and the corresponding temperature be the critical temperature, then:

[0086] T s '=T s +ΔT=T s,cr Equation (27)

[0087] In equation (27): T s,cr is the critical temperature at which the migration driving force is zero.

[0088] Substituting equation (27) into equation (26), we can obtain:

[0089]

[0090] According to equation (28), the critical temperature equation can be obtained:

[0091]

[0092] From equation (29), we can see that the critical temperature T s,cr Mainly affected by the overburden pressure P OB Control, combined with equation (27) and equation (29), the temperature rise equation can be obtained:

[0093]

[0094] Furthermore, in the above-mentioned frost heave control method based on dynamic adjustment of cold source temperature, in step 4.1, the size and distribution of the characteristic temperature can be given by combining equations (17), (20) and (29); and the formation, growth, water isolation and melting trends of the condensed ice can be judged by combining the corresponding relationship between the actual temperature of the warm end of the condensed ice and the characteristic temperature.

[0095] Furthermore, in the above-mentioned frost heave control method based on dynamic adjustment of cold source temperature, in step 4.2, the temperature of the warm end of the condensed ice is adjusted so that the temperature of the warm end of the condensed ice is maintained in the stop development zone, which can effectively control the development of frost heave, and a frost heave control model is constructed accordingly.

[0096] It can be seen from the analysis that the present invention discloses a frost heave control method based on dynamic regulation of cold source temperature. This method aims at the problem that frost heave disease is difficult to prevent and control during ground freezing, and carries out research on the frost heave control mechanism of frozen soil. First, according to the basic principles of thermodynamics, the thermodynamic regulation mechanism of the driving force of water migration is analyzed; secondly, according to the formation and development mechanism of segregated ice, the formation, melting and water-insulating model of segregated ice is constructed, and the zone where segregated ice stops developing is determined; and according to the dynamic regulation of cold source temperature, the control mechanism of segregated frost heave is revealed. Finally, the correctness of the mechanism is verified by experiments. The study shows that: 1. By slightly increasing the temperature, the migration driving force can be weakened and water migration can be inhibited; 2. There is a freeze-thaw hysteresis interval between the formation temperature and the melting temperature of segregated ice; 3. When the temperature is slightly increased within the freeze-thaw hysteresis interval, segregated ice exhibits water-insulating characteristics, neither growing nor melting; 4. Adjusting the cold source temperature to make segregated ice become water-insulating ice can effectively control frost heave. In short, the above research has important theoretical value and practical significance for ensuring the safety of artificial freezing engineering construction and reducing frost heave disease. BRIEF DESCRIPTION OF THE DRAWINGS

[0097] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them:

[0098] Figure 1 The present invention is a flowchart of a frost heave control method according to an embodiment of the present invention.

[0099] Figure 2 This is a diagram of a water migration driving force model according to an embodiment of the present invention.

[0100] Figure 3 FIG. 1 is a diagram showing the effect of temperature rise on the driving force of water migration according to an embodiment of the present invention.

[0101] Figure 4 FIG. 1 is a diagram showing the formation mechanism and force distribution of condensed ice according to an embodiment of the present invention.

[0102] Figure 5 FIG. 4 is a diagram showing the relationship between pressure-suction stress distribution according to an embodiment of the present invention.

[0103] Figure 6 FIG. 1 is a diagram showing the effect of temperature rise on the adsorption force of the warm end surface of condensed ice according to an embodiment of the present invention.

[0104] Figure 7 FIG. 1 is a diagram showing the relationship between the actual temperature of condensed ice and the characteristic temperature according to an embodiment of the present invention.

[0105] Figure 8 This is a diagram of a frost heave control model for condensed ice according to an embodiment of the present invention. DETAILED DESCRIPTION

[0106] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments. Each example is provided by way of explanation of the present invention and does not limit the present invention. In fact, it will be clear to those skilled in the art that modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. For example, a feature shown or described as a part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desired that the present invention encompasses such modifications and variations within the scope of the appended claims and their equivalents.

[0107] like Figures 1 to 8 As shown, according to an embodiment of the present invention, a frost heave control method based on dynamic adjustment of cold source temperature is provided, such as Figure 1 As shown, the following steps are included:

[0108] Step 1: Analyze the impact of temperature evolution on driving force.

[0109] Step 1.1, Driving force for migration of thin film water.

[0110] According to the thin film water theory, there are negative charges on the surface of particles, forming a virtual electric field. Under the action of the virtual electric field force, the thin film water is adsorbed on the surface of the particles and forms a diffuse double electric layer. At this time, the thin film water generates hydraulic pressure along the surface normal direction:

[0111]

[0112] In equation (1): P L is the hydraulic pressure distribution; a is the coefficient; v L is the specific volume of water; y is the normal distance from the particle surface; α is the power.

[0113] From formula (1), we can see that the hydraulic pressure is related to the distance from the particle surface, that is, the closer to the surface, the greater the hydraulic pressure. When y = h, we get:

[0114]

[0115] In equation (2): h is the film thickness; P Lh is the hydraulic pressure distribution when the film thickness is h.

[0116] When the thin film water gradually freezes along the thickness direction, the water molecules in the ice crystals lose their dipole properties and are no longer adsorbed by the electric field, causing the hydraulic pressure of the thin liquid layer to decrease. The corresponding distribution is: P L -P Lh ,like Figure 1 As shown:

[0117] Depend on Figure 2 It can be seen that freezing causes uneven changes in film thickness, inducing a hydraulic pressure difference between the thick film and the thin film. According to the principle of fluid dynamics, the hydraulic pressure difference is:

[0118] P Ld =P L -(P L -P Lh )=P Lh Equation (3)

[0119] In equation (3): P Ld It is the hydraulic driving force, driving water molecules to migrate from the thick film to the thin film. At the same time, as water molecules continue to migrate to the thin part, gather and change phase, the ice crystals in the thin part grow rapidly and the ice pressure increases. Given that the ice pressure, hydraulic pressure and interface pressure in the thin part maintain stress balance on the curved ice-water interface, that is:

[0120]

[0121] In equation (4): P S is the ice pressure; SL is the ice-water interfacial tension; R is the effective radius; is the average curvature, which is positive toward the liquid layer side; is the interface pressure, that is, the equivalent pressure generated by the interface tension; P Ly In order to eliminate the influence of interface pressure, the ice pressure P S The actual hydraulic pressure delivered to the diaphragm.

[0122] Depend on Figure 2 It can be seen that hydraulic P Ly The increase of reduces the pressure difference between the thick film and the thin film. Combined with equation (3), it can be seen that the hydraulic driving force is reduced to:

[0123]

[0124] From equation (5), we can see that P Ly Derived from ice pressure P S , minus the interface pressure The influence of ice pressure P S The actual hydraulic pressure transmitted to the diaphragm. Combined with equation (3), it can be seen that the hydraulic driving force P Ld for:

[0125]

[0126] From equation (6), we can see that as the ice pressure P S As the hydraulic pressure P increases, the hydraulic pressure difference between the thick film and the thin film gradually decreases. Ly Growth to P Lh When the hydraulic driving force P Ld Approaching 0 indicates that thermodynamic equilibrium has been reached, at which point water migration stops. The theoretical ice pressure in equilibrium is:

[0127]

[0128] In equation (7): P S0 is the theoretical ice pressure under equilibrium state; L is the latent heat of melting of water, which can be taken as 3.34×10 9 cm 2 / s 2 ; T is the surface temperature of the soil matrix (the matrix represents solid materials such as soil particles); v S is the specific volume of ice; T A is the absolute freezing temperature of pure water, which can be taken as 273.15 K. Combining equation (6), it can be seen that the hydraulic pressure equation under equilibrium state is:

[0129] P Ly =P Lh Equation (8)

[0130] Substituting equations (7) and (8) into equation (4), we can obtain the stress equilibrium relationship between ice pressure, hydraulic pressure and interface pressure at the curved ice-water interface under equilibrium state:

[0131]

[0132] Substituting equation (9) into equation (6), we can obtain:

[0133]

[0134] Combining equation (6), equation (7), and equation (10), we get:

[0135]

[0136] It can be seen from equation (11) that the driving force of water migration can be expressed by hydraulic pressure difference or ice pressure difference, but both represent the difference between the theoretical pressure in equilibrium state and the actual pressure in non-equilibrium state. In addition, the migration driving force is independent of boundary conditions or interface pressure and has wide applicability.

[0137] Step 1.2, the effect of temperature rise on the migration driving force.

[0138] According to the above analysis, on the basis of the water migration driving force model, the influence of temperature change on migration driving force is considered, such as Figure 3 shown.

[0139] exist Figure 3 h(T) is the thickness of the film after heating; other physical quantities are indicated by a semicolon after heating. For example, T' is the temperature variable after heating, P Ld ' is the hydraulic driving force after heating; P S ' is the actual ice pressure after heating; P S0 ' is the theoretical ice pressure after heating.

[0140] Assumption: When the surface temperature T of the soil matrix rises uniformly by ΔT, the temperature variable after the temperature rise is T', then:

[0141] T'=T+ΔT Equation (12)

[0142] Substituting equation (12) into equation (7), we can obtain the theoretical ice pressure equation after heating, namely:

[0143]

[0144] From equation (13), we can see that as the temperature increases, the theoretical ice pressure decreases linearly. In addition, the film thickness gradually increases with the temperature. Assume that when the temperature rises by +ΔT, the film thickness increases from h to h(T), then the hydraulic pressure distribution at the film is: P L -P Lh(T), the hydraulic driving force after heating is:

[0145]

[0146] In equation (14): P Ld ' is the hydraulic driving force after heating; P S ' is the actual ice pressure after heating.

[0147] From equation (14), we can see that when the temperature rises by +ΔT, the theoretical ice pressure P S0 ' shows a linear decreasing trend, the actual ice pressure decreases from P S Development to P S '; Since the growth of ice crystals is inhibited after warming, there are two development situations of actual ice pressure: (1) P S 'gradually decreases; (2) after heating, P S 'Remains unchanged. Given that the difference between theoretical ice pressure and actual ice pressure determines the driving force of water migration and dominates the path and direction of water migration, the law of actual ice pressure changes after warming is crucial for the study of the subsequent water migration mechanism.

[0148] According to the composition and structure of frozen soil, ice crystals in frozen soil are mainly pore ice and segregated ice. For porous ice, according to the freeze-thaw hysteresis effect of porous ice, the pore ice pressure gradually decreases with the increase of temperature. When the ice pressure drops to half of the capillary pressure (the pressure when pore ice is formed), the actual ice pressure is equal to the interface pressure; if the temperature continues to rise at this time, the actual ice pressure will be less than the interface pressure and will be melted by pressure. Therefore, with a slight increase in temperature, the actual ice pressure in the pores gradually decreases, and eventually the pressure melts to zero. For segregated ice, since its formation and melting conditions are different from those of porous ice, there are currently few related studies; therefore, whether segregated ice has freeze-thaw hysteresis and whether a slight increase in temperature can reduce the actual ice pressure will be analyzed in detail in subsequent steps.

[0149] Step 2, analyzing the freeze-thaw hysteresis of the condensed ice;

[0150] Step 2.1, formation conditions of condensed ice;

[0151] When the actual ice pressure in the frozen edge is greater than or equal to the sum of the overburden pressure and the separation pressure, a new ice lens is generated, that is:

[0152] P S1 ≥P OB +P sep Equation (15)

[0153] In equation (15): P S1 is the ice pressure distribution before the formation of condensed ice; P OB is the overburden pressure; P sep For separation pressure.

[0154] According to the frost heave test, the ice pressure P S1 The rate of change with temperature is 1.1MPa / ℃; while the theoretical ice pressure P S0 The rate of change with temperature is 1.124MPa / ℃, so it is assumed that before the formation of fractional ice, the actual ice pressure is equal to the theoretical ice pressure. Based on this, the critical conditions for the formation of fractional ice can be obtained:

[0155]

[0156] In equation (16): T s is the decomposition-freezing temperature.

[0157] Transforming equation (16), we can get the condensation-freezing temperature T s The governing equation is:

[0158]

[0159] In addition, after the formation of segregated ice, the discontinuous ice lens will develop into a continuous segregated ice layer, which needs to bear all the overburden loads alone. However, at the moment of segregated ice formation, the ice pressure at its warm end will drop rapidly from the sum of the overburden pressure and the separation pressure to the overburden pressure, that is:

[0160] P S2 =P OB Equation (18)

[0161] In equation (18): P S2 is the ice pressure distribution after the formation of condensed ice. Based on the above analysis, the mechanical distribution model before and after the formation of condensed ice can be obtained, as follows: Figure 4 As shown, in Figure 4 In the figure, curve I is the ice pressure distribution before the formation of the condensed ice; curve II is the ice pressure distribution after the formation of the condensed ice; T f is the freezing front temperature, which is 0°C. Figure 4 It can be seen that the hydraulic driving force after the formation of condensed ice is:

[0162]

[0163] Combined with equation (19), it can be seen that there is stress release before and after the formation of segregated ice, which causes the hydraulic driving force at the warm end to increase instantly, and eventually tends to the difference between the theoretical ice pressure corresponding to the segregation-freezing temperature Ts and the overlying pressure.

[0164] Step 2.2, melting conditions of condensed ice.

[0165] Since the condensed ice is layered ice, its curvature tends to be infinite, so it is not affected by the interface effect; but it needs to bear all external loads alone, so it is subject to external pressure melting. The greater the overburden pressure, the lower the melting temperature of the volume ice. Based on the pressure melting test, the fitting equation between the overburden pressure and the melting temperature is given:

[0166]

[0167] In equation (20): T sm is the melting temperature of condensed ice.

[0168] From equation (20), it can be seen that the melting temperature of the condensed ice is inversely proportional to the overlying pressure. Combined with equation (17), it can be seen that the formation temperature of the condensed ice T s Far below the melting temperature T sm Therefore, as long as the condensation temperature is maintained within the temperature range [T s , T sm ], the condensed ice always remains in a crystalline state.

[0169] From this we can see that segregated ice also has freeze-thaw hysteresis, but its freeze-thaw hysteresis mechanism is different from that of porous ice.

[0170] Step 3: Analyze the water-isolating mechanism of condensed ice.

[0171] Step 3.1, conversion relationship between compressive and suction stresses.

[0172] The above analysis only explains the effect of temperature rise on hydraulic driving force from the perspective of hydraulic drive; in fact, the real driving force for water migration is surface adsorption force. In order to clarify the relationship between hydraulic driving force and surface adsorption force, the generalized Clapeyron equation is introduced, namely:

[0173]

[0174] In equation (21): P Lb is the surface adsorption force; ρ L is the density of water; ρ S is the density of ice. Changing equation (21) yields:

[0175]

[0176] In equation (22): v L is the specific volume of water; v S is the specific volume of ice; and v L =1 / ρ L 、v S =1 / ρ S ;P SU is the theoretical suction force under equilibrium state; λ is the pressure-suction variable conversion coefficient, and λ=-v S / v L =-1.09.

[0177] From equation (22), we can see that the transformation between surface adsorption force and migration driving force satisfies the generalized Clapeyron equation and conforms to the pressure-absorption variable substitution. Since the surface adsorption force is a negative pressure, it is difficult to construct a physical and mechanical model. However, the hydraulic drive model and the pressure-absorption conversion relationship can be used to explain the mechanism of water migration and segregation, and the pressure-absorption stress distribution relationship is given accordingly. Figure 5 .

[0178] Depend on Figure 5 It can be seen that the film water is simultaneously subjected to the theoretical suction force P during the freezing process. SU and the actual ice pressure P S Working together, the surface adsorption force P Lb , driving the water to migrate from the thick film to the thin film; when the actual ice pressure P S Theoretical ice pressure P in equilibrium state S0 When the surface adsorption force P Lb or migration driving force P Ld At the same time, it tends to zero and moisture migration stops.

[0179] Step 3.2, the effect of temperature rise on surface adsorption.

[0180] Combination Figure 5 The distribution law of theoretical suction in the freezing edge area is known, and it is found that the theoretical suction P SU It remains unchanged before and after the formation of condensed ice, that is:

[0181]

[0182] In equation (23): P SU1 P is the theoretical suction force before the formation of condensed ice; SU2 It is the theoretical suction force after condensation ice is formed.

[0183] The substrate surface temperature is raised uniformly by +ΔT, and the theoretical suction force P of the warm end of the condensed ice after the temperature rises SU2 'for:

[0184]

[0185] In equation (24): P SU2 ' is the theoretical suction after heating, the distribution of the above variables can be seen in Figure 6 :

[0186] Depend on Figure 6 It can be seen that the theoretical suction force at the warm end of the condensed ice decreases linearly with the increase of temperature. Considering that the condensed ice bears all the overburden pressure alone after it is formed, and the overburden pressure has nothing to do with the temperature, we can get:

[0187] P S2 =P S2 '=P OB Equation (25)

[0188] In equation (25): P S2 ' is the ice pressure distribution after the formation of condensed ice and heating.

[0189] Combining equations (22), (24) and (25), we can obtain the surface adsorption force of the warm end of the decondensed ice after heating:

[0190]

[0191] In equation (26): P Lb ' is the surface adsorption force after heating. From equation (26), it can be seen that once the condensed ice is formed, as long as the temperature continues to rise, the surface adsorption force on the warm end will decrease linearly.

[0192] Step 3.3, separate the water-isolating properties of condensed ice.

[0193] Depend on Figure 6 It can be seen that as the temperature rise amplitude +ΔT continues to increase, the adsorption force P on the warm end of the condensed ice Lb 'gradually decreases. Let the state where the driving force of the warm end migration of the condensed ice is equal to zero be the critical state, and the corresponding temperature be the critical temperature, then:

[0194] T s '=T s +ΔT=T s,cr Equation (27)

[0195] In equation (27): T s,cr is the critical temperature at which the migration driving force is zero.

[0196] Substituting equation (27) into equation (26), we can obtain:

[0197]

[0198] According to equation (28), the critical temperature equation can be obtained:

[0199]

[0200] From equation (29), we know that the critical temperature T s,cr Mainly affected by the overburden pressure P OB Control, that is, the greater the overburden pressure, the lower the corresponding critical temperature. Combining equation (27) and equation (29), the temperature rise amplitude equation can be obtained:

[0201]

[0202] From equation (30), we can see that in the critical state, the temperature rise amplitude ΔT is mainly affected by the separation pressure P sepcontrol, that is, the smaller the separation pressure, the smaller the temperature rise required to reach the critical state. Therefore, when other conditions remain unchanged, the P OB / P sep The larger the ratio, the more conducive it is to frost heave control.

[0203] In summary, after the formation of condensed ice, as long as the warm end of the condensed ice is slightly heated, the surface adsorption force can be quickly reduced; when the temperature is increased from T s Up to T s,cr When the surface adsorption force approaches zero, the water migration stops. In addition, due to the critical temperature of ice separation T s,cr Much lower than the melting temperature T sm Therefore, the temperature of the condensed ice is in the range [T s,cr , T sm ], it neither grows nor melts, showing a water-isolating property, so it can be defined as the zone where the development of condensed ice stops. At this time, the condensed ice can effectively block the migration of water and inhibit the development of frost heave.

[0204] In short, the idea of ​​controlling frost heave by curbing the development of condensed ice through "temperature control" is theoretically feasible.

[0205] Step 4: Discover the control mechanism of frost heave.

[0206] Step 4.1, the effect of temperature evolution of the warm end of the condensed ice on frost heave.

[0207] Through the above analysis of the whole process of separation ice formation → growth → water isolation (stop growth) → melting, the characteristic temperature corresponding to each stage of separation ice can be determined, such as: separation ice formation temperature T s , critical temperature T s,cr , melting temperature T sm , and the freezing front temperature T f wait.

[0208] Combining equation (17), equation (20) and equation (29), the size and distribution of characteristic temperature can be given, see Figure 7 (a).

[0209] In addition, according to equation (26), after the formation of condensed ice, if the temperature is reduced by -ΔT, the surface adsorption force P Lb ' grows linearly, so the temperature below the decomposition-freezing temperature T s The range of driving force growth is defined as the driving force growth zone; if the temperature is increased by +ΔT, the surface adsorption force P Lb 'decreases linearly, so the temperature above the segregation-freezing temperature T s The interval is defined as the driving force decline zone. Combined with the zone where the development of condensation ice stops [T s,cr , T sm], it can be seen that if the temperature continues to rise, the condensed ice will show water-isolating properties, which can block water migration and inhibit the development of frost heave. If the temperature continues to rise, the condensed ice will be compressed and melted, resulting in melting and sinking.

[0210] Combined with the above correspondence between the actual temperature of the warm end of the condensed ice and the characteristic temperature, the formation, growth, water isolation (stop growth) and melting trend of the condensed ice can be directly judged. Figure 7 (b).

[0211] according to Figure 7 The relationship between the warm end temperature of the condensed ice and the characteristic temperature in (b) can predict the growth and development of the condensed ice. For example, when the condensed ice is formed, its warm end temperature is T s ; At this time, the frost heave increases rapidly with the decrease of temperature -ΔT, and increases slowly with the increase of temperature +ΔT; when the temperature increases from T s Up to T s,cr When the condensation ice enters the stop development zone [T s,cr , T sm ], then it stops growing; when it starts from T s,cr Up to T sm When the condensed ice enters the melting and settling zone [T sm , T f ], the frost heave will begin to decrease. If the temperature of the condensed ice is lowered by -ΔT again, the condensed ice will return to the stop growth zone, and the frost heave will remain unchanged; when the temperature drops to the critical temperature T s,cr When the temperature of the warm end of the condensation ice is maintained at the stop development zone [T s,cr , T sm ] is the key to controlling the development of frost heave.

[0212] Step 4.2, frost heave control model of condensed ice.

[0213] According to the cold structure of frozen soil, the growth and development of condensed ice plays a leading role in frost heave. Therefore, it is only necessary to adjust the temperature of the warm end of condensed ice to keep the temperature of the warm end of condensed ice in the stop growth zone [T s,cr , T sm ], the development of frost heave can be effectively controlled, and a frost heave control model is constructed based on this. Figure 8 .

[0214] Depend on Figure 8 It can be seen that after the condensed ice is formed, the heat source temperature T w Keep it unchanged and slightly increase the temperature of the cold source: T c,1 →T c,2 ; Causes the freezing edge temperature to rise slightly by +ΔT, and the temperature distribution in the freezing edge area will change from OT to O'-T', and the corresponding temperature at the warm end of the condensed ice will rise to: T s →T s'. The analysis found that as long as T s 'Stay in the zone where the condensation ice stops developing [T s,cr , T sm ], the warm end of the condensed ice will lose its ability to absorb water and become water-insulating ice, which can effectively control frost heave.

[0215] In summary, it can be seen that the purpose of controlling expansion can be achieved by forcing the condensed ice to enter the stop growth zone through temperature recovery and utilizing the water-isolating properties of the condensed ice. This method can effectively control frost heave by only slightly controlling the temperature, which meets the current green, clean, stable and efficient technical requirements. It also provides a feasible technical route for ensuring the safety of artificial freezing construction, reducing frost heave diseases, and expanding artificial freezing technology in the field of refined construction.

[0216] By utilizing the warming and water-isolating properties of the condensed ice layer, the condensed ice is forced into a stop-growth zone, thereby achieving the purpose of controlling expansion.

[0217] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0218] A frost heave control method based on dynamic regulation of cold source temperature is proposed. This method aims to solve the problem that frost heave disease is difficult to prevent and control during ground freezing, and studies the frost heave control mechanism of frozen soil. Firstly, according to the basic principles of thermodynamics, the thermodynamic regulation mechanism of the water migration driving force is analyzed; secondly, according to the formation and development mechanism of segregated ice, the segregated ice formation, melting and water-insulating model is constructed, and the segregated ice stop development zone is determined; and according to the dynamic regulation of cold source temperature, the segregated frost heave control mechanism is revealed. Finally, the correctness of the mechanism is verified by experiments. The study shows that: 1. The migration driving force can be weakened and water migration can be inhibited by a small temperature increase; 2. There is a freeze-thaw hysteresis interval between the formation temperature and the melting temperature of segregated ice; 3. When the temperature is slightly increased within the freeze-thaw hysteresis interval, the segregated ice exhibits water-insulating characteristics, neither growing nor melting; 4. Adjusting the cold source temperature to make the segregated ice become water-insulating ice can effectively control frost heave. In short, the above research has important theoretical value and practical significance for ensuring the safety of artificial freezing engineering construction and reducing frost heave disease.

[0219] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A frost heave control method based on dynamic adjustment of cold source temperature, characterized in that: The steps include: Step 1, analyze the impact of temperature evolution on driving force; Step 1.1, driving force for migration of film water; Step 1.2, the effect of temperature rise on the migration driving force; Step 2, analyzing the freeze-thaw hysteresis of the condensed ice; Step 2.1, formation conditions of condensed ice; Step 2.2, melting conditions of condensed ice; Step 3, analyzing the water-isolating mechanism of condensed ice; Step 3.1, conversion relationship between pressure and suction stress; Step 3.2, the effect of temperature rise on surface adsorption; Step 4, discover the control mechanism of frost heave; Step 4.1, the effect of the temperature evolution of the warm end of the condensed ice on frost heave; Step 4.2, frost heave control model of condensed ice.

2. The frost heave control method based on dynamic adjustment of cold source temperature according to claim 1 is characterized in that: In step 1.1, under the action of the virtual electric field force, the film water is adsorbed on the particle surface and forms a diffuse double electric layer. At this time, the film water generates hydraulic pressure along the surface normal direction: In equation (1): P L is the hydraulic pressure distribution; a is the coefficient; v L is the specific volume of water; y is the normal distance from the particle surface; α is the power; From formula (1), we can see that the hydraulic pressure is related to the distance from the particle surface, that is, the closer to the surface, the greater the hydraulic pressure. When y = h, we get: In equation (2): h is the film thickness; P Lh is the hydraulic pressure distribution when the film thickness is h; When the thin film water gradually freezes along the thickness direction, the water molecules in the ice crystals lose their dipole properties and are no longer adsorbed by the electric field, causing the hydraulic pressure of the thin liquid layer to decrease. The corresponding distribution is: P L -P Lh , freezing causes uneven changes in film thickness, inducing a hydraulic pressure difference between the thick film and the thin film; According to the principles of fluid dynamics, the hydraulic pressure difference is: P Ld =P L -(P L -P Lh )=P Lh Equation (3) In equation (3): P Ld It is the hydraulic driving force, driving water molecules to migrate from the thick film to the thin film. At the same time, as water molecules continue to migrate to the thin part, aggregate and change phase, ice crystals in the thin part grow rapidly and ice pressure increases. Given that ice pressure, hydraulic pressure and interface pressure in the thin part maintain stress balance on the curved ice-water interface, that is: In equation (4): P S is the ice pressure; SL is the ice-water interfacial tension; R is the effective radius; K is the average curvature, which is positive toward the liquid layer side; is the interface pressure, that is, the equivalent pressure generated by the interface tension; P Ly In order to eliminate the influence of interface pressure, the ice pressure P S The actual hydraulic pressure delivered to the diaphragm; Hydraulic Ly The increase of reduces the pressure difference between the thick film and the thin film; combined with equation (3), it can be seen that the hydraulic driving force is reduced to: From equation (5), we can see that P Ly Derived from ice pressure P S , minus the interface pressure The influence of ice pressure P S The actual hydraulic pressure transmitted to the membrane; combined with equation (3), it can be seen that the hydraulic driving force P Ld for: From equation (6), we can see that as the ice pressure P S increases, the hydraulic pressure difference between the thick film and the thin film gradually decreases; when the hydraulic pressure P Ly Growth to P Lh When the hydraulic driving force P Ld Approaching 0 indicates that thermodynamic equilibrium has been reached, at which point water migration stops; the theoretical ice pressure in equilibrium is: In equation (7): P S0 is the theoretical ice pressure under equilibrium state; L is the latent heat of melting of water, which can be taken as 3.34×10 9 cm 2 / s 2 ; T is the surface temperature of the soil matrix; v S is the ice specific volume; T A is the absolute freezing temperature of pure water, which can be taken as 273.15K; combined with equation (6), it can be seen that the hydraulic pressure equation under equilibrium state is: P Ly =P Lh Equation (8) Substituting equations (7) and (8) into equation (4), we can obtain the stress equilibrium relationship between ice pressure, hydraulic pressure and interface pressure at the curved ice-water interface under equilibrium state: Substituting equation (9) into equation (6), we can obtain: Combining equation (6), equation (7), and equation (10), we get: From equation (11), it can be seen that the driving force of water migration can be expressed by either hydraulic pressure difference or ice pressure difference.

3. The frost heave control method based on dynamic adjustment of cold source temperature according to claim 2 is characterized in that: In step 1.2, when the surface temperature T of the soil matrix rises uniformly by ΔT, the temperature variable after the temperature rise is T', then: T'=T+ΔT Equation (12) Substituting equation (12) into equation (7), we can obtain the theoretical ice pressure equation after heating, namely: From equation (13), we can see that as the temperature increases, the theoretical ice pressure decreases linearly. In addition, the film thickness gradually increases with the temperature. When the temperature rises by +ΔT, the film thickness increases from h to h(T), and the hydraulic pressure distribution at the film is: P L -P Lh(T) , the hydraulic driving force after heating is: In equation (14): P Ld ' is the hydraulic driving force after heating; P S ' is the actual ice pressure after heating; From equation (14), we can see that when the temperature rises by +ΔT, the theoretical ice pressure P S0 ' shows a linear decreasing trend, the actual ice pressure decreases from P S Development to P S '.

4. The frost heave control method based on dynamic adjustment of cold source temperature according to claim 1 is characterized in that: In step 2.1, when the actual ice pressure in the frozen edge is greater than or equal to the sum of the overlying pressure and the separation pressure, a new ice lens is generated, that is: P S1 ≥P OB +P sep Equation (15) In equation (15): P S1 is the ice pressure distribution before the formation of condensed ice; P OB is the overburden pressure; P sep is the separation pressure; According to the frost heave test, the ice pressure P S1 The rate of change with temperature is 1.1MPa / ℃; while the theoretical ice pressure P S0 The rate of change with temperature is 1.124MPa / ℃. Therefore, before the formation of fractional ice, the actual ice pressure is equal to the theoretical ice pressure. Based on this, the critical conditions for the formation of fractional ice can be obtained: In equation (16): T s is the segregation-freezing temperature; Transforming equation (16), we can get the condensation-freezing temperature T s The governing equation is: In addition, after the formation of segregated ice, the discontinuous ice lens will develop into a continuous segregated ice layer, which needs to bear all the overlying loads alone. However, at the moment of segregated ice formation, the ice pressure at its warm end will drop rapidly from the sum of the overlying pressure and the separation pressure to the overlying pressure, that is: P S2 =P OB Equation (18) In equation (18): P S2 is the ice pressure distribution after the formation of condensed ice; according to the above analysis, the mechanical distribution model before and after the formation of condensed ice can be obtained, and the hydraulic driving force after the formation of condensed ice is:

5. The frost heave control method based on dynamic adjustment of cold source temperature according to claim 1 is characterized in that: In step 2.2, according to the pressure melting test, the fitting equation between the overburden pressure and the melting temperature is: In equation (20): T sm is the melting temperature of condensed ice.

6. The frost heave control method based on dynamic adjustment of cold source temperature according to claim 4 is characterized in that: In step 3.1, the generalized Clapeyron equation is introduced, namely: In equation (21): P Lb is the surface adsorption force; ρ L is the density of water; ρ S is the density of ice; changing equation (21) yields: In equation (22): v L is the specific volume of water; v S is the specific volume of ice; and v L =1 / ρ L 、v S =1 / ρ S ;P SU is the theoretical suction force under equilibrium state; λ is the pressure-suction variable conversion coefficient, and λ=-v S / v L =-1.

09.

7. The frost heave control method based on dynamic adjustment of cold source temperature according to claim 6 is characterized in that: In step 3.2, the theoretical suction force P is found SU It remains unchanged before and after the formation of condensed ice, that is: In equation (23): P SU1 P is the theoretical suction force before the formation of condensed ice; SU2 It is the theoretical suction force after condensation ice is formed. The substrate surface temperature is raised uniformly by +ΔT, and the theoretical suction force P of the warm end of the condensed ice after the temperature rises SU2 'for: In equation (24): P SU2 ' is the theoretical suction after heating; The theoretical suction force at the warm end of the condensed ice decreases linearly with the increase of temperature. After the condensed ice is formed, it bears all the overburden pressure alone, and the overburden pressure has nothing to do with the temperature. We can get: P S2 =P S2 '=P OB Equation (25) In equation (25): P S2 ' is the ice pressure distribution after the formation of condensed ice and heating. Combining equations (22), (24) and (25), we can obtain the surface adsorption force of the warm end of the decondensed ice after heating: In equation (26): P Lb ' is the surface adsorption force after heating.

8. The frost heave control method based on dynamic adjustment of cold source temperature according to claim 7 is characterized in that: In step 3.3, as the temperature rise amplitude +ΔT increases, the adsorption force P on the warm end surface of the condensed ice Lb 'gradually decreases. Let the state where the driving force of the warm end migration of the condensed ice is equal to zero be the critical state, and the corresponding temperature be the critical temperature, then: T s '=T s +ΔT=T s,cr Equation (27) In equation (27): T s,cr is the critical temperature at which the migration driving force is zero. Substituting equation (27) into equation (26), we can obtain: According to equation (28), the critical temperature equation can be obtained: From equation (29), we know that the critical temperature T s,cr Mainly affected by the overburden pressure P OB Control, combined with equation (27) and equation (29), the temperature rise equation can be obtained:

9. The frost heave control method based on dynamic adjustment of cold source temperature according to claim 8, characterized in that: In step 4.1, by combining equation (17), equation (20) and equation (29), the magnitude and distribution of the characteristic temperature can be given; Based on the corresponding relationship between the actual temperature of the warm end of the condensed ice and the characteristic temperature, the formation, growth, water isolation and melting trends of the condensed ice can be judged.

10. The frost heave control method based on dynamic adjustment of cold source temperature according to claim 1, characterized in that: In step 4.2, the temperature of the warm end of the condensed ice is adjusted so that the temperature of the warm end of the condensed ice is maintained in the stop development zone, which can effectively control the development of frost heave, and a frost heave control model is constructed accordingly.

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