Experimental Analysis and Characterization Method for Fatigue Cracking of Solidified Soil Base Layers Applicable to Arid Regions

Abstract

The present invention discloses a test analysis and characterization method for fatigue cracking of solidified soil base in arid regions. Considering that the main cause of fatigue cracking of base materials is local plastic deformation inside the materials, a set of direct tension cyclic loading test methods with controlled strain and multi-level strain levels is designed. At the same time, in order to effectively characterize the fatigue cracking damage degree of solidified soil materials in arid regions, based on the energy-mechanics method, a method for solving damage density is given, thereby effectively characterizing the fatigue cracking performance and evolution trend of solidified soil materials under dry conditions. The present invention solves the problems of large workload, long time consumption of the previous solidified soil fatigue test methods, and the inability to simulate the fatigue cracking of the solidified soil base structure under direct tension. At the same time, based on the mechanical theory foundation, a damage characterization method for solidified soil under dry conditions is given from the level of the fatigue cracking mechanism of materials, providing a basis and guidance for the compatibility of solidified soil materials and the design of solidified soil road structures.

Description

Technical Field

[0001] The present invention relates to a method for testing and evaluating the performance of road materials, and particularly to a method for testing, analyzing and characterizing the fatigue cracking performance of solidified soil base course materials in arid regions, belonging to the field of road engineering. Background Art

[0002] The soil solidification technology was first proposed by European and American countries and introduced into China in the 1990s. In recent years, with the in-depth research on soil solidification technology, more and more new solidifying agents have been developed and applied, which has greatly improved the performance of solidified soil. At the same time, with the acceleration of China's urbanization process, more and more construction waste soil and drilling sludge and other waste soils are piled up everywhere, making it difficult to be digested and treated in time, which has a certain impact on the urban environment and safety. Therefore, under the policy of the state's strong support for resource recycling and the realization of circular economy, more and more solidified soil materials are used in the construction of the base course or sub-base course of low-grade highways and urban roads. However, for solidified soil materials, when applied to the base course or sub-base course, they often bear large tensile stresses under traffic loads. Especially in arid and semi-arid regions, solidified soil under dry conditions is more likely to exhibit the characteristics of brittle materials and fatigue cracking, which will reduce the overall performance of the road and seriously affect the service life. Therefore, it is necessary to focus on the tensile fatigue cracking performance of solidified soil materials under dry conditions and propose relevant test analysis and characterization methods.

[0003] How to design the tensile fatigue cracking performance test of solidified soil materials and propose a characterization method that can truly reflect the tensile fatigue cracking performance of solidified soil base courses is of great significance for guiding the durability design of raw materials and pavement structures. At present, the fatigue cracking performance of solidified soil materials in China mostly adopts the dynamic periodic compressive stress load mode of applying Havesine wave at three points for testing. The test mainly makes standard beam specimens and indirectly evaluates the direct tensile fatigue cracking performance of materials by simulating the fatigue state of materials under bending and tension forces. Finally, relevant fatigue life prediction equations are obtained through regression analysis. This test method not only has a large workload, but also is time-consuming and consumptive of materials. The most important thing is that this test analysis method still belongs to the category of indirect tensile fatigue tests, and the true state of the fatigue cracking performance of materials in the direct tensile state cannot be directly reflected. Moreover, the prediction equations are mostly based on statistical analysis, which is greatly affected by test operations and lacks certain theoretical support, and it is difficult to characterize the damage evolution of fatigue cracking of solidified soil base course materials from the fatigue cracking mechanism level. Summary of the Invention

[0004] The object of the present invention is to propose a test method that can effectively analyze and evaluate the fatigue cracking performance of solidified soil materials in arid regions under direct tension, and propose a set of analysis and characterization methods based on energy-mechanics theory that can reflect the fatigue cracking mechanism of dry solidified soil materials. It solves the problems of large workload, time-consuming and material-consuming of previous test methods, and that the model equations are mostly based on regression analysis and cannot effectively reflect the fatigue damage of solidified soil materials from the theoretical and mechanism levels.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A test analysis and characterization method for fatigue cracking of solidified soil base courses in arid regions, specifically including the following steps:

[0007] Manufacture soil into solidified soil specimens and conduct direct tension cyclic tests to obtain the parameters of the direct tension cyclic tests, including the stress amplitude σ0, the absolute value σ of the downward offset of the standard half-sine wave in the stress, the strain amplitude ε0, and the phase angle c , under different strain loading cycles

[0008] Solve to obtain the corresponding damage density based on the parameters of the obtained direct tension cyclic tests, and use the damage density to characterize the fatigue cracking damage degree of the solidified soil base courses in arid regions. Furthermore, analyze the fatigue cracking performance of the solidified soil base courses in arid regions through the evolution trend of the damage density under different loading cycles;

[0009] Among them, the damage density represents the damage cracking degree of the material, and is defined as:

[0010]

[0011] In the formula, A is the total cross-sectional area of the solidified soil specimen, A t is the area of the solidified soil particles on the cross-section of the specimen, S c is the area of pores and cracks on the cross-section of the solidified soil specimen, is the true stress amplitude. In the non-damaged state, at this time S c is equal to the initial porosity of the material; in the damaged state, in the formula, V is the external volume of the solidified soil specimen; V t is the volume occupied by the internal soil particle skeleton structure of the solidified soil specimen, DSE A is the apparent dissipated strain energy, is the true phase angle, and is obtained by back-calculation through ; |E *| is the true complex modulus of the material. Under the loading condition of the same strain level, the true complex modulus of the material is the same for different loading cycles. Therefore, for the damaged state, the true stress amplitude corresponding to N = 0 at the beginning of the damage test of the material is used. Calculated as:

[0012] S c is the pore and crack area of the cross-section of the solidified soil specimen. S c at N = 0 is the initial porosity of the material; σ 00 is the stress amplitude at N = 0.

[0013] Furthermore, in the direct tensile cyclic test, the RDT test is carried out on the same specimen with multiple strain levels. The time interval between every two consecutive strain level tests is 20 minutes. The strain level gradually increases from low to high, and it is ensured that the initial loading strain level is in the non-damaged state of the material.

[0014] Furthermore, in the direct tensile cyclic test, the strain control mode is adopted, the strain loading adopts the sine wave mode, and the loading frequency is 1 Hz.

[0015] Furthermore, in the first controlled strain RDT test, the maximum axial strain is generally controlled at 50 με or below 50 με. After that, each strain level increases by 10 με in turn until the damaged state is reached.

[0016] Furthermore, the complex modulus |E * | of the material is determined by probability statistical analysis whether it changes with the loading cycle and the strain level. According to the change of |E * |, the damage stage of the material is determined: if the complex modulus |E * | of the material does not change with the increase of the load cycle times, then the material is in the non-damaged state under the corresponding strain level; if the complex modulus |E * | of the material changes, then the material is in the damaged state under the corresponding strain level.

[0017] Generally, the complex modulus under each loading cycle can be obtained by solving.

[0018] Furthermore, in the damaged state, the solution process of the true complex modulus |E * | of the material is specifically as follows:

[0019] Based on the parameters of the direct tensile cyclic test obtained in the damaged state, including the stress amplitude σ0 under different loading cycles, the absolute value σ c of the downward offset of the standard half-sine wave in the stress and the phase angle The stress amplitude σ0 fitting curve, the absolute value σ of the downward shift of the standard half-sine wave in the surface stress, and the phase angle fitting curve under the damaged state are respectively obtained by fitting with a power function. c The fitting curve, and the phase angle The fitting curve;

[0020] Based on the obtained fitting curves, the stress amplitude σ when N = 0 under the damaged state, the absolute value σ of the downward shift of the standard half-sine wave in the stress, and the phase angle 00 are obtained. c0 And the phase angle

[0021] Calculate the true stress amplitude when N = 0, the apparent dissipated strain energy , and the apparent recoverable strain energy and the phase angle The phase angle

[0022]

[0023]

[0024]

[0025]

[0026] Finally, calculate the true complex modulus of the material when N = 0, which characterizes the true complex modulus of the material under different loading cycles in the damaged state:

[0027] The beneficial effects of the present invention are as follows:

[0028] The present invention proposes a performance test analysis method that can effectively analyze and evaluate the performance of dry-cured soil materials under tensile fatigue loads. By designing a set of direct tensile cyclic tests (RDT) with controlled strain to conduct multi-level strain level loading tests on the same specimen to analyze the anti-fatigue cracking performance of dry-cured soil, compared with previous fatigue tests, it can better simulate the fatigue tensile failure process of the plastic region materials inside the cured soil base layer, so that the test results can more directly reflect the road performance of the materials.

[0029] Based on the test results, the present invention proposes a set of methods for solving the mechanical and performance parameters of dry-cured soil materials based on the energy-mechanics method, and uses the damage density to characterize the damage degree of the cured soil materials. This is different from the previous analysis models based on statistical significance, and can better reflect the damage failure degree of dry-cured soil materials under tensile fatigue loads from the perspective of the fatigue cracking mechanism, so as to better characterize the fatigue damage evolution process of the materials, making the material selection and evaluation more effective and representative.

[0030] The present invention solves the problems of large workload, long time consumption of the conventional curing soil fatigue test method, and the inability to simulate the fatigue cracking of the curing soil base structure under direct tension. At the same time, based on the mechanical theory, a damage characterization method for curing soil under dry conditions is given from the perspective of the fatigue cracking mechanism of materials, providing a basis and guidance for the compatibility of curing soil materials and the design of curing soil road structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of the RDT test loading at multiple strain levels of the present invention;

[0032] Figure 2 is a schematic diagram of the material damage determination curve of the present invention;

[0033] Figure 3 is a schematic diagram of the solution result of the material damage density of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] The test analysis method and theoretical solution process of the present invention will be further described below in conjunction with the drawings and specific embodiments:

[0035] An experimental analysis and characterization method for the fatigue cracking of a dry curing soil base mainly includes experimental steps and analysis steps:

[0036] (1) The experimental steps are to make the soil into a curing soil specimen, cure it to the age and then naturally dry it before performing a direct tension cyclic test to obtain the parameters of the direct tension cyclic test, specifically including the following sub-steps:

[0037] (1.1) Specimen production and curing; The raw materials of the curing soil specimen include soil materials, curing agents, water, etc. The specimen is a cylindrical specimen with a diameter of 70 mm and a height of 140 mm. The specimen is formed according to the geotechnical test procedures, and the compaction degree is controlled at 95%. The curing time is 28 days. After curing to the age, it is first preliminarily dried in the natural environment and then placed in an oven for drying at a low temperature.

[0038] (1.2) Installation of the test device; The loading instrument used for the tensile fatigue test is a universal material testing machine (UTM). The test tensile method adopts the direct tensile test method, and the specimen deformation is measured by two axial linear displacement sensors (LVDTs) with an external length of 70 mm. The linear displacement sensor is an external magnetic adsorption type sensor.

[0039] (1.3) Test method and process;

[0040] To study the fatigue cracking behavior of solidified soil base courses, a set of direct tension cyclic tests (RDT) with controlled strain was designed in this embodiment. Among them, the strain loading adopted a sine wave mode, and the loading frequency was 1 Hz. The experimental process was to conduct RDT tests at multiple strain levels on the same specimen, as Figure 1 shown. In Figure 1 , the strain loading adopted a sine wave mode, and the loading frequency was 1 Hz. The experimental process was to conduct RDT tests at multiple strain levels on the same specimen. To ensure that the deformation caused by the previous loading was fully recovered, the time interval between every two consecutive RDT tests was 20 minutes. In the first controlled strain RDT test, the maximum axial strain was generally controlled at 50 με or below to ensure that the deformation of the solidified soil was in the non-damaged area, and the number of loading cycles was set to 200 times. In the second controlled strain RDT test, the strain level was increased by 10 με in sequence, that is, the maximum axial strain in the second test was 10 με larger than that in the first test, and the number of loading cycles was still set to 200 times. Until the damage critical point was determined, in the damage stage, the number of loading cycles was set to 5000 times. The test loading and analysis process is as follows:

[0041] ① In the first controlled strain RDT test, the maximum axial strain was controlled at 50 με to ensure that the deformation of the solidified soil was in the non-damaged area, and the number of loading cycles was set to 200 times.

[0042] ② After the first-stage load was applied, wait for 20 min before applying the next strain level. The strain level was increased by 10 με in sequence, that is, in the second controlled strain RDT test, the maximum axial strain was controlled at 60 με, and the number of loading cycles was still set to 200 times.

[0043] ③ Analyze the test data to determine the magnitude of the complex modulus |E * |, and determine whether it changes with the loading cycle and strain level through probabilistic statistical analysis, and then determine the damage stage of the material according to the change situation. During the RDT test with controlled strain, as the strain level increases, the material deformation may be in the non-damaged area or the damaged area, specifically as Figure 2 shown. The division of the damage stage and the non-damaged stage of the solidified soil material can be determined by analyzing the change of |E * |, and the specific determination method is as follows:

[0044] Judging the non-damaged area: When the material is in the non-linear elastic stage (such as from point O to point A in Figure 2 ), as the number of load cycles increases, the |E * | of the material will not change, but as the strain level increases, the |E * | of the material will change.

[0045] Determine the damage zone: When the material is in the damage stage (such as from point A to point B in Figure 2 ), as the number of load cycles increases, the |E * | of the material will change.

[0046] Determine the damage critical point: Define the demarcation point A between the non-damaged zone and the damaged zone as the damage critical point. Before the critical point (section OA), the deformation of the material can be fully recovered under any stress level, but after the critical point (section AB), damage occurs inside the material, resulting in non-recoverable plastic deformation, that is, permanent deformation, as shown in O-C in Figure 2 .

[0047] ④ Repeat the test procedures of ①-③, and load the subsequent strain levels in this way in sequence until the damage critical point is determined.

[0048] ⑤ After determining the damage critical point, conduct the damage test loading. The damage test loading is to set the strain level to a strain value greater than the damage critical point, and then conduct the RDT test. Its loading method is the same as before, and the loading cycle is set to 5000 times.

[0049] (2) The analysis step is to solve the parameters suitable for characterizing the fatigue cracking of the solidified soil base in arid areas based on the parameters obtained from the direct tensile cyclic test, that is, the damage density. In order to reflect the fatigue damage process of the material from the perspective of the fatigue cracking mechanism of the solidified soil, a set of methods for solving the mechanical and performance parameters of the solidified soil material based on the energy mechanics method is established. The specific process is as follows:

[0050] ① Expression of stress and strain

[0051] In the RDT test with controlled strain, the axial strain is controlled to be a standard sine wave shape (the axial strain is positive), and the applied stress is also an offset sine wave load. Therefore, a mathematical model can be used to represent the stress-strain change process of the material. The stress expression form is shown in Equation 1, and the strain expression form is shown in Equation 2:

[0052] σ = σ0[1 - cos(ωt)] - σ c (1)

[0053]

[0054] Where: σ is the stress inside the material at time t; σ0 is the stress amplitude; ω is the angular velocity, a parameter related to the loading frequency; σ c is the absolute value of the downward offset of the standard half-sine wave; t is the loading time. ε is the strain magnitude corresponding to the material at time t; ε0 is the strain amplitude, and φ is the phase angle.

[0055] ② Determination of the complex modulus and the damage critical point

[0056] After obtaining the test data, fitting analysis is carried out to obtain the magnitude of the complex modulus |E * |, and |E * | can be calculated according to Equation 3. After obtaining |E * judge the damage state according to step (1.3), and finally determine the damage critical point.

[0057]

[0058] ③ Energy solution formula

[0059] When a material is subjected to a force, its internal energy will change accordingly. In the fatigue cracking analysis based on the energy-mechanics method, the solution of energy is very important for the establishment of the subsequent model. Therefore, it is necessary to solve the energy change of the material during the RDT test through a certain method, which includes the cumulative dissipated strain energy (DSE) and the recoverable strain energy (RSE). The calculation formulas for DSE and RSE can be expressed as follows respectively:

[0060]

[0061]

[0062] In the formula, DSE is the cumulative dissipated strain energy; RSE is the recoverable strain energy; π is the pi.

[0063] ④ Establishment of the energy balance equation

[0064] The energy balance equation is a key step in the energy-mechanics method. By establishing the energy balance equation, the related parameters such as the apparent stress and energy can be related to the related parameters such as the true stress and energy inside the material, which is the theoretical basis for solving the change magnitude of the damage density of the solidified soil material in the later stage. The energy balance equation includes the dissipated strain energy balance equation and the recoverable strain energy balance equation, as shown in Equations 6 and 7 specifically:

[0065] DSE A V = DSE T V t (6)

[0066] RSE A V = RSE T V t (7) In the formula: DSE A is the apparent dissipated strain energy; DSE T is the true dissipated strain energy; RSE A is the apparent recoverable strain energy; RSE T is the true recoverable strain energy; V is the external volume of the solidified soil specimen; Vt It is the volume occupied by the internal soil particle skeleton structure of the solidified soil specimen.

[0067] ⑤ Expression of true stress and strain

[0068] When the solidified soil material in arid areas is subjected to a certain load, the forms of its true stress-strain and apparent stress-strain are the same. That is to say, in the RDT test with controlled strain, the mathematical expressions of true stress, true strain, apparent stress, and apparent strain all satisfy Equations 1 and 2. Therefore, the mathematical expressions of the true stress and true strain inside the solidified soil material are as shown in Equations 8 and 9:

[0069]

[0070]

[0071] Where:

[0072]

[0073] In the formula, σ T is the true stress corresponding to the load application time of t; is the true stress amplitude; is the absolute value of the downward offset of the standard half-sine wave in the true stress. ε T is the true strain corresponding to the load application time of t; is the true strain amplitude; is the phase angle in the true strain. E * is the true complex modulus of the material.

[0074] ⑥ Solution of true stress and strain under non-destructive conditions

[0075] For apparent stress and apparent strain, they can be directly obtained by fitting and analyzing the test results of the RDT test. However, for the solution of true stress and true strain, due to the existence of variables such as pores and crack areas, certain methods need to be adopted for step-by-step solution. Therefore, on the basis of the previous energy balance equation, the mechanical balance equation of the material is further introduced, thus developing a solution method for the relevant parameters of true stress, strain, and damage density of the material based on the energy-mechanics method.

[0076] When the material is subjected to an external force, there is a certain relationship between the apparent stress and the true stress, which can be expressed by the balance equation 11:

[0077]

[0078] A t =(A - S c ) (12)

[0079] According to Equation 11-12, Equations 13 and 14 can be analyzed and obtained as follows:

[0080]

[0081]

[0082] The relevant parameters of the true stress can be solved from Equations 13 and 14 and as shown in the following equation:

[0083]

[0084]

[0085] In the formula: A t is the area of the solidified soil particles on the cross-section of the specimen; A is the entire cross-sectional area of the specimen; S c is the area of pores and cracks on the cross-section of the specimen.

[0086] When the material is in a non-damaged state, S c is the initial porosity of the material. Therefore, the relevant parameters of the true stress of the material can be directly obtained through the relevant parameters of the apparent stress.

[0087] ⑦ Solving the true performance parameters of the material

[0088] In order to further solve the true stress-strain parameters of the material under damaged conditions, the true performance parameters of the material are required. To solve the true performance of the material, two energy balance equations, Equation 6 and Equation 7, are needed. In these two energy balance equations, the expressions of the apparent / true dissipated strain energy and the apparent / true recoverable strain energy are as shown in Equations 4 and 5, and the specific expressions are as follows:

[0089]

[0090]

[0091]

[0092]

[0093] Substituting Equation 19 and Equation 20 into Equation 6 and Equation 7 respectively, we can get:

[0094]

[0095]

[0096] Dividing the left and right sides of Equation 21 and Equation 22 respectively, we can get Equation 23:

[0097]

[0098] Further substituting Equation 15 and Equation 16 into Equation 23 gives Equation 24:

[0099]

[0100] In Equation 24, DSE A , RSE A , σ0 and σ c are quantities related to the apparent stress and can be obtained by processing and analyzing the RDT test data of the controlled strain. Therefore, the only unknown φ T can be calculated by back-calculating from Equation 24.

[0101] After obtaining φ T , it is still necessary to further solve the complex modulus |E * | of the corresponding real material, and the process is as follows:

[0102] Substituting Equation 10 into Equation 21 gives Equation 25:

[0103]

[0104] Substituting Equation 15 into Equation 25 and solving for the complex modulus |E * |:

[0105]

[0106] For the real performance parameters of the solidified soil material under non-destructive conditions, they can be directly obtained from Equation 24 and Equation 26. However, for the damaged conditions, since S c includes the damaged cracking area of the material, it is an unknown quantity. To obtain the real performance parameters of the material under damaged conditions, other methods need to be used for further solution, and the specific process is as follows:

[0107] 1) Use Equation 1 and Equation 2 to perform fitting analysis on the stress-strain terms in the RDT test results under damaged conditions to obtain the apparent stress-strain related parameters σ0, σ c , ε0,

[0108] 2) Plot σ0 corresponding to different cycles in the graph and use the power function σ0 = aN b + c to perform fitting analysis on the data points to obtain the optimal fitting curve, thereby obtaining the relevant fitting equation.

[0109] 3) When N = 0, the apparent stress amplitude σ 00 corresponding to the start of the damage test of the material can be obtained from the fitting equation in step 2), that is, σ 00= c. When N = 0, it indicates that the material has not been damaged yet. Therefore, the internal cracking area of the solidified soil is 0 at this time, that is, S c is the initial pore area of the material, which is a known parameter.

[0110] 4) Repeat the process in 2)-3) to obtain σ c , the value of σ corresponding to N = 0; then calculate the corresponding equivalent apparent energy DSE c0 and at this time according to Equations 17 and 18; and then calculate the true damage phase angle of the material according to Equation 24 A and RSE A ;

[0111] 5) Substitute the value of σ 00 into Equation 15 to calculate the true stress amplitude corresponding to the start of the damage test Then substitute into Equation 26 to obtain the true damage complex modulus |E * | of the solidified soil at this strain level.

[0112] ⑧ Solving the true stress and strain of the material under damaged conditions

[0113] The true performance parameters |E * | and of the material at the time of damage can be indirectly obtained through the method in ⑦. Also, according to the characteristics of the true performance parameters of the material, it can be known that under the loading condition of the same strain level, the material performance parameters corresponding to different cycles are the same. Therefore, using the obtained material performance parameters |E * | and can further calculate the true stress magnitudes corresponding to different cycles of the material under the load of this strain level ( and ). The specific solution process is as follows:

[0114] Substitute |E * | and into Equation 25 to obtain

[0115]

[0116] Then, according to Equations 15 and 16,

[0117]

[0118] In order to characterize the damage degree of solidified soil materials under direct tensile fatigue loading conditions, in this embodiment, the ratio of the area of pores and cracks in the material to the total area is used to define the fatigue cracking damage degree of the solidified soil base in arid areas, which is expressed as the damage density.

[0119]

[0120] In the formula: is the description index of the damage degree of the solidified soil specimen - the damage density; A t is the area of the solidified soil particles on the cross-section of the specimen; A is the entire cross-sectional area of the specimen; S c is the area of pores and cracks on the cross-section of the specimen.

[0121] The area of pores and cracks in the material changes with the fatigue cracking of the material, which can effectively characterize the fatigue cracking degree of the solidified soil base in arid areas. Combining the multi-level strain loading test data and the above theoretical solution process, σ0 and corresponding to different cycles can be obtained, and thus the damage evolution process of the solidified soil material with the change of the loading cycle can be obtained.

[0122] Next, in order to adopt the above test analysis and characterization methods, a specific embodiment of the test analysis of the direct tensile fatigue cracking performance of dry solidified soil materials is given:

[0123] Direct tensile fatigue cracking test of lime soil: In this embodiment, the soil source selected is the soft soil obtained from subway excavation, the lime content is 9%, and the compaction degree is controlled at 95%. The specimens are prepared by the static pressure forming method under the condition of the optimum moisture content of 18%. The specific test steps are as follows:

[0124] (1) Specimen production: Use a customized cylindrical mold to make the specimen size the same as that of the specimen in the present invention, which is a cylindrical specimen with a diameter of Φ70mm and a height of 140mm. First, mix the soft soil passing through a 4.75cm sieve hole after drying with lime and water evenly, weigh the materials according to the optimum moisture content and the maximum dry density at a compaction degree of 95%, and use a universal testing machine for static pressure forming. After 24 hours of forming, remove the mold, put it in a bag and place it in a standard curing room for curing. When the curing time reaches 28 days, take it out, then place it indoors to air dry naturally for three days, and then place it in an oven at 50 degrees for drying for use.

[0125] (2) Specimen centering and bonding: Bond the specimen with the upper and lower two tensile joints through a strong adhesive. During the bonding process, it is necessary to ensure good centering. The centering and bonding can be carried out by using relevant installation devices, and the bonding curing time should be greater than 24 hours.

[0126] (3) Iron natural color cylindrical nuts: Bond 4 iron natural color cylindrical nuts to the specified positions on the surface of the solidified soil using a strong adhesive. To ensure the accuracy of the bonding positions of the iron natural color cylindrical nuts, a special centering and installation bonding device can be used for auxiliary bonding, and the bonding curing time should also be greater than 24 hours.

[0127] Installation of the specimen onto the UTM testing machine: Use a tensile adapter fixture to install the well-centered and bonded solidified soil specimen onto the upper and lower joints of the UTM testing machine. Among them, the tensile joint, the tensile adapter fixture, and the connection between the tensile adapter fixture and the upper and lower joints of the UTM testing machine are connected by nuts and threaded rods.

[0128] (4) Installation of external magnetic adsorption type axial displacement sensors: Adsorb two external magnetic adsorption sensors to the 4 iron natural color cylindrical nuts. The two external magnetic adsorption type axial displacement sensors are distributed at 180°, and the monitoring range is the deformation of the specimen in the 35 - 105 mm section.

[0129] (5) Preparation and start of the test program: Prepare the test program according to the direct tensile cyclic RDT test process for controlling strain proposed in the present invention. After determining parameters such as the loading of each strain level and the frequency, start the test. The loading procedure of the experiment is as described above.

[0130] (6) Fitting analysis of stress-strain data: After obtaining the relevant test data, perform post-processing, and perform fitting analysis on the stress-strain data at each cycle under each strain level through formulas (1) and (2) to obtain the relevant parameters of stress-strain.

[0131] (7) Determination of the damage critical point: Calculate the magnitude of the complex modulus |E * | corresponding to different cycles at a certain strain level using formula (3), and determine the damage critical point A of the material according to the damage determination method.

[0132] (8) Loading test under damaged conditions: After determining the damage critical point, perform strain level loading under damaged conditions, and the loading cycle is 5000 times.

[0133] (9) Solving the fatigue cracking damage density: Determine the relevant mechanical parameters and performance parameters of the material according to the set of solution methods and processes based on the energy-mechanics method proposed in step (2) of the present invention. Finally, based on the multi-level strain loading data and the above theoretical solution results, the magnitude of the damage density under different cycle conditions can be obtained, as Figure 3 shown.

[0134] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or variations derived therefrom still fall within the protection scope of the present invention.

Claims

1. A test analysis and characterization method for fatigue cracking of solidified soil base in arid areas, characterized by: Specifically, the following steps are included: The soil is made into solidified soil specimens and a direct tension cyclic test is carried out to obtain the parameters of the direct tension cyclic test, including the stress amplitude σ0, the absolute value σ of the downward shift of the standard half-sine wave in the stress, the strain amplitude ε0 and the phase angle under different strain loading cycles c , the strain amplitude ε0 and the phase angle Based on the parameters obtained from the direct tension cyclic test, the corresponding damage density is solved, and the damage density is used to characterize the fatigue cracking damage degree of the solidified soil base layer in arid areas. Furthermore, the fatigue cracking performance of the solidified soil base layer in arid areas is analyzed through the evolution trend of the damage density under different loading cycles. Among them, the damage density represents the degree of damage cracking of the material, and is defined as: Where A is the total cross-sectional area of the solidified soil specimen, A t is the area of solidified soil particles on the cross section of the specimen, S c is the pore and crack area of the cross section of the solidified soil specimen, is the true stress amplitude, in the non-destructive state, At this time S c is equal to the initial porosity of the material; in the lossy state, Where V is the apparent volume of the solidified soil specimen; V t is the volume occupied by the soil particle skeleton structure inside the solidified soil specimen, DSE A is the apparent dissipated strain energy, is the true phase angle, Obtained by inverse calculation; |E *T | is the true complex modulus of the material. Under the same strain level loading conditions, the true complex modulus of the material under different loading cycles is the same. Therefore, for the lossy state, the true stress amplitude corresponding to the material at the beginning of the damage test, that is, when N = 0, is used. Calculation results: S c is the pore and crack area of the cross section of the solidified soil specimen. When N=0, S c is the initial porosity of the material; σ 00 is the stress amplitude when N=0.

2. The method according to claim 1, wherein In the direct tension cyclic test, the RDT test is carried out on the same specimen with multiple strain levels. The time interval between every two consecutive strain level tests is 20 minutes. The strain level gradually increases from low to high, and it is ensured that the initial loading strain level is in the non-damaged state of the material.

3. The method according to claim 2, wherein In the direct tension cyclic test, the strain control mode is adopted for loading, and the sine wave mode is used for strain loading with a loading frequency of 1 Hz.

4. The method according to claim 2, wherein In the first controlled strain RDT test, the maximum axial strain is generally controlled at 50 με or below 50 με. After that, each strain level is increased by 10 με in turn until the damage state is reached.

5. The method according to claim 1, characterized in that Determine the complex modulus of the material |E through probability statistical analysis * |Whether it changes with the loading cycle and strain level, according to |E * |Changes in the material damage stage: If the complex modulus of the material |E increases with the number of load cycles, * | will not change, then the material is in a lossless state at the corresponding strain level; if the complex modulus of the material |E increases with the number of load cycles * |will change, then the material is in a lossy state at the corresponding strain level.

6. The method according to claim 1, characterized in that Under the lossy state, the solution process of the true complex modulus |E *T | is specifically as follows: Based on the parameters obtained from the direct tension cyclic test under the damaged state, including the stress amplitude σ0 and the absolute value σ of the downward offset of the standard half-sine wave in the stress under different loading cycles c and the phase angle The fitting curves of the stress amplitude σ0, the absolute value σ of the downward offset of the standard half-sine wave in the stress, and the phase angle c under the damaged state are respectively obtained by fitting with power functions ; Based on the obtained fitting curve, the stress amplitude σ when N = 0 in the lossy state is obtained 00 , the absolute value of the downward deviation of the standard half-sine wave in stress σ c0 and phase angle Calculate the true stress amplitude at N = 0 Apparent dissipated strain energy and apparent recoverable strain energy True phase angle Finally, calculate the true complex modulus of the material when N = 0, which characterizes the true complex modulus of the material under different loading cycles in the lossy state:

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