Method for estimating dynamic elastic modulus of basalt fiber cement silty soil for roadbed in seasonal frozen region

Abstract

The invention discloses a basalt fiber cement silty soil dynamic elastic modulus estimation method for a subgrade in a seasonal frozen region, which comprises the following specific steps: preparing a sample, performing a freeze-thaw cycle test on the sample, then performing a graded loading dynamic triaxial test to obtain dynamic stress and dynamic strain of a soil body under different confining pressures, drawing a hysteretic curve, and estimating the dynamic elastic modulus of basalt fiber cement silty soil on the basis of a Hardin-Drnevich hyperbola model. The maximum dynamic elastic modulus and the final dynamic stress amplitude of the sample are obtained, reference dynamic strain is introduced, and the normalized secant dynamic elastic modulus is obtained; based on a nonlinear least square method, statistical analysis is carried out on test data under the action of different confining pressures and freezing and thawing cycle times, and a pre-estimation model representing correlation between the maximum dynamic elastic modulus and the final dynamic stress amplitude and the confining pressures and the freezing and thawing cycle action times is obtained; through nonlinear regression analysis, obtaining a prediction model of the maximum dynamic elastic modulus and the final dynamic stress amplitude considering the confining pressure and the freeze-thaw cycle effect, and further obtaining a normalized secant dynamic elastic modulus; the method improves the estimation efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of road engineering, and particularly relates to a basalt fiber cement silt soil dynamic modulus prediction method for subgrade in a seasonal frozen region. BACKGROUND

[0002] The transportation infrastructure network in China is becoming increasingly perfect, and the total mileage of the comprehensive transportation network has broken through 6 million kilometers, among which, the mileage of the second-grade and above-grade highways is 702,400 kilometers, the mileage of the expressways is 161,000 kilometers, and the operation mileage of the railways is 146,000 kilometers, among which, the mileage of the high-speed railways is 38,000 kilometers, and the comprehensive transportation channels of the ten verticals and ten horizontals are basically connected. China has proposed the goal of basically building a transportation power by 2035, and is gradually promoting the construction of the national comprehensive three-dimensional transportation network. With the increase in the number of transportation construction projects, more poor soil bodies with engineering properties in special areas will be encountered in the projects. Among them, the seasonal frozen soil region is a special region widely distributed in China, and the area accounts for more than half of the total land area of China, so the frozen soil engineering problems will inevitably be encountered in the road engineering construction. The northeast region belongs to a typical seasonal frozen region, and the silt soil is a poor subgrade filler commonly existing in the northwest region of Jilin Province, and has low natural moisture content, significant capillary action, poor water stability, and low strength. The traditional soil solidifying agent mainly includes cement and lime, and has the disadvantages of low efficiency, high energy consumption, and heavy pollution. The basalt fiber is a kind of high-performance inorganic green and environmentally-friendly fiber material, and its application conforms to the principle of the green transformation and safe development of the modern comprehensive transportation system development plan of the 14th Five-Year Plan, and is helpful to the implementation of the carbon peak and carbon neutralization goals. Meanwhile, compared with other fibers, the basalt fiber has the excellent properties of high tensile strength, good chemical stability, high temperature resistance, and acid and alkali corrosion resistance. The basalt fiber can effectively improve the brittle failure of the cement soil and improve the ductility of the soil body, and meanwhile, the basalt fiber cement soil has good anti-freeze-thaw stability. The basalt fiber cement silt soil as the road material will be subjected to the dynamic load of automobiles and the like during the service period, and under the freeze-thaw cycle action, the roadbed deformation and other road diseases are easily caused, and the road service life and driving safety are affected. Therefore, under the background of protecting the environment and energy saving and emission reduction, the research on the dynamic properties of the basalt fiber cement silt soil for the subgrade in the seasonal frozen region has important practical significance, and can provide reliable reference basis for the design and construction of the subgrade in the seasonal frozen region.

[0003] The dynamic properties of the subgrade soil are the main reference basis for the design of the subgrade, at present, most scholars mainly focus on the research on the change law of the dynamic stress-dynamic strain relationship, the dynamic elastic modulus, and the cumulative plastic deformation of the soil under the dynamic load, but the systematic research on the dynamic properties of the basalt fiber cement composite modified subgrade filler under the dynamic load is still insufficient, and the research considering the influence of the special geographical environment factors in the seasonal frozen region is rarely reported.

[0004] In his paper, "Research on Mechanical Properties and Design Methods of Solidified Silt Subgrade under Cyclic Traffic Loads," Zhang Xiaobin systematically studied the effects of factors such as curing agent dosage, curing age, initial moisture content, and test confining pressure on the dynamic stress-strain, dynamic elastic modulus, and damping ratio characteristics of cement- and high-performance curing agents-solidified silt through cyclic triaxial tests with progressively increasing dynamic stress amplitudes. Simultaneously, based on the influence of each factor on the maximum dynamic elastic modulus, a predictive model for the maximum dynamic elastic modulus of solidified silt was established. However, the predictive model for the maximum dynamic elastic modulus of solidified silt studied in this paper did not consider the influence of freeze-thaw cycles, and the curing agent used was traditional cement, which reduced the applicability and accuracy of the model.

[0005] Chinese patent CN117078080A discloses a rapid evaluation method for the dynamic elastic modulus and compaction degree of roadbed based on an improved PFWD (Power Factor Dynamics Theory). This method establishes optimal regression equations for dynamic elastic modulus and compaction degree, and calculates the required compaction degree and dynamic elastic modulus based on field measured data of dynamic elastic modulus and compaction degree, respectively, using the optimal regression equations to evaluate road construction quality with dual indicators, thus improving efficiency and accuracy. However, this patent does not consider the influence of external environmental conditions on dynamic elastic modulus and compaction degree, and cannot accurately predict the dynamic elastic modulus of soil under different stress conditions of repeated cyclic loading. Summary of the Invention

[0006] In view of the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide a method for predicting the dynamic elastic modulus of basalt fiber cement silt used in roadbeds in seasonally frozen areas. This method considers the influence of confining pressure and the number of freeze-thaw cycles on the dynamic characteristics of basalt fiber cement silt used in roadbeds in seasonally frozen areas. Based on the Hardin-Drnevich hyperbolic model, through nonlinear least squares method and nonlinear regression analysis, a prediction model for the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber cement silt under the combined influence of confining pressure and freeze-thaw cycles is established, which greatly improves the prediction efficiency and solves the problems of limited consideration of freeze-thaw cycle effects and complex and time-consuming prediction process in existing prediction methods.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for predicting the dynamic elastic modulus of basalt fiber-cement silt soil used in roadbeds in seasonally frozen zones, the method comprising the following steps: S1: Prepare the specimens and conduct freeze-thaw cycle tests on the cured specimens with different numbers of freeze-thaw cycles; S2: Perform staged loading dynamic triaxial tests on the samples after freeze-thaw cycles to obtain the dynamic stress of the soil under different confining pressures. and dynamic strain ,draw — The hysteresis curve, with its slope defined as the dynamic elastic modulus. , ; S3: fitting the relationship between and based on Hardin-Drnevich hyperbolic model, , where a, b are fitting parameters, the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber cement silt are obtained, , , , , ; S4: based on the nonlinear least squares method, statistical analysis is carried out on the test data under the action of different confining pressures and freeze-thaw cycle times, and the estimation model of the maximum dynamic elastic modulus and the final dynamic stress amplitude related to confining pressure and freeze-thaw cycle times of basalt fiber cement silt is obtained; S5: based on the estimation model obtained in step S4, through nonlinear regression analysis, the estimation model of the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber cement silt under the combined action of confining pressure and freeze-thaw cycle is obtained; S6: based on the estimation model obtained in step S5, the confining pressure and freeze-thaw cycle times required by the environmental condition factor are brought in, and the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber cement silt under the combined action of confining pressure and freeze-thaw cycle are obtained, and then the normalized dynamic elastic modulus is obtained.

[0008] Further, the step S1 specifically comprises the following steps: S11: add water to the silt to prepare soil samples with a set moisture content; S12: mix cement and basalt fiber into the soil sample; S13: prepare m parallel samples for each group of mix proportions using impact molding; S14: wrap the prepared samples with plastic wrap and place them in a curing room for curing; S15: perform freeze-thaw cycle tests on the cured samples with different freeze-thaw cycle times.

[0009] Further, in step S12, record the cement content, basalt fiber content, and basalt fiber length. The cement content is the percentage of cement mass to the total mass of dry silt, and the basalt fiber content is the percentage of fiber mass to the total mass of cement and dry silt.

[0010] Further, in step S13, in the impact molding process, a layered method is adopted, and the surface of the previous layer of soil is roughened before placing the next layer of soil.

[0011] Further, in step S14, the prepared sample is wrapped with a preservative film and placed in a curing room for curing for 14 days, with a temperature of 20±2 ℃ and a relative humidity of greater than 95%.

[0012] Further, in step S15, the selection of the temperature of the freeze-thaw cycle test needs to investigate the negative temperature extreme value of the project location in the past ten years, and combined with the strength change characteristics of the soil body under low temperature conditions, the test freezing temperature is selected, the absolute value of the melting positive temperature and the freezing negative temperature is equal, the freezing and melting time is set to 24 h, and the freeze-thaw cycle number is set to 0, 1, 3, 6 and 10 times in turn in the form of increasing difference.

[0013] Further, in step S2, the sample after freeze-thaw cycle is subjected to graded loading dynamic triaxial test, and the waveform of the dynamic triaxial test is half-sine wave; the axial dynamic load frequency is set to 1 Hz; the confining pressure selected for the dynamic triaxial test is 20 kPa, 50 kPa and 80 kPa; and during the test, first, a confining pressure of 30 kPa is applied to the sample for 1000 times of preloading, after the preloading is completed, the selected confining pressure is used to perform graded loading with an incremental gradient of 40 kPa, and each level of load is vibrated for 12 times.

[0014] Further, in step S4, the maximum dynamic elastic modulus of basalt fiber cement silt related to the confining pressure is estimated model, since the confining pressure is related to the atmospheric pressure, the atmospheric pressure is considered during data processing, and the atmospheric pressure P a is set to 101 kPa.

[0015] Further, in step S5, the expression of the estimated model of the maximum dynamic elastic modulus of basalt fiber cement silt under the combined influence of confining pressure and freeze-thaw cycle , the final dynamic stress amplitude ; ; In the formula: , are parameters of and under the combined influence of confining pressure and freeze-thaw cycle, and , and are respectively the confining pressure and the number of freeze-thaw cycles a prediction model of the maximum dynamic elastic modulus and the final dynamic stress amplitude.

[0016] Compared with the prior art, the application has the advantages and beneficial effects that: (1) The application studies the dynamic stress-dynamic strain relationship, the normalized dynamic elastic modulus, the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber cement silt under the action of different confining pressures and different freeze-thaw cycle numbers; at the same time, based on the Hardin-Drnevich hyperbolic curve model, a prediction model of the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber cement silt considering the influence of confining pressure and freeze-thaw cycle is established through nonlinear least squares method and nonlinear regression analysis, which provides a quantitative basis for the dynamic property analysis of basalt fiber cement silt for subgrade in the seasonal frozen region and provides a reliable reference for the design and construction of the project.

[0017] (2) Based on the prediction model obtained by the application, the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber cement silt can be obtained by bringing the required environmental condition factors of confining pressure and freeze-thaw cycle number, which is close to the actual test value, and then the normalized dynamic elastic modulus is obtained, which provides an efficient and reliable method for the characterization of the dynamic performance of basalt fiber cement silt subgrade in the seasonal frozen region.

[0018] (3) The prediction method provided by the application greatly improves the prediction efficiency and solves the problems of limited consideration of the freeze-thaw cycle effect and complex and time-consuming prediction process of the existing prediction method. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0020] Figure 1 The multi-stage axial load loading mode.

[0021] Figure 2 The dynamic stress-dynamic strain relationship curve of basalt fiber cement silt under the action of 6 freeze-thaw cycles under different confining pressures.

[0022] Figure 3 The dynamic stress-dynamic strain relationship curve of basalt fiber cement silt under the action of different freeze-thaw cycle numbers under a confining pressure of 50 kPa.

[0023] Figure 4The test value and fitting curve of the relationship between the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber cement silt under 6 freeze-thaw cycles and confining pressure.

[0024] Figure 5 The test value and fitting curve of the relationship between the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber cement silt under 50 kPa confining pressure and freeze-thaw cycle times.

[0025] Figure 6 The relationship curve of the normalized secant dynamic elastic modulus and dynamic strain of basalt fiber cement silt under different confining pressures and 6 freeze-thaw cycles.

[0026] Figure 7 The relationship curve of the normalized secant dynamic elastic modulus and dynamic strain of basalt fiber cement silt under different freeze-thaw cycle times and 50 kPa confining pressure.

[0027] Figure 8 The comparison chart of the test value and fitting value of the final dynamic stress amplitude of basalt fiber cement silt under different confining pressures and freeze-thaw cycle times.

[0028] Figure 9 The comparison chart of the test value and fitting value of the maximum dynamic elastic modulus of basalt fiber cement silt under different confining pressures and freeze-thaw cycle times. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0030] The embodiment of the present application provides a method for estimating the dynamic elastic modulus of basalt fiber cement silt for subgrade in a seasonal freezing region, which specifically comprises the following steps: S1: cylindrical samples with a cement content of 2%, a fiber content of 0.2%, and a fiber length of 12 mm are prepared by impact molding, and m parallel samples are prepared at the same time. The prepared samples are wrapped with preservative film and then placed in a curing room for curing for 14 days. The cured samples are subjected to 0-10 freeze-thaw cycles. S2: the samples after freeze-thaw cycles are subjected to a graded loading dynamic triaxial test to obtain the dynamic stress and dynamic strain of the soil body under different confining pressures. ​​S3: Based on the Hardin-Drnevich hyperbolic model, the maximum dynamic elastic modulus of basalt fiber-cemented silt was obtained. and final dynamic stress amplitude Introducing reference dynamic strain The normalized secant dynamic elastic modulus of basalt fiber cement silt was obtained. The specific analysis process is as follows: Drawing dynamic stress Dynamic strain Hysteresis curve, and the slope of the hysteresis curve is defined as the dynamic elastic modulus. : (1) Fitting with Hardin-Drnevich hyperbolic model and The relationship between them can be represented as: (2) Solving equations (1) and (2) simultaneously yields equation (3): (3) In particular, in formula (3) When, we get equation (4); when in equation (2) Then, we get equation (5): (4) (5) In the formula: This is the maximum dynamic elastic modulus, in MPa. This represents the final dynamic stress amplitude.

[0031] Introducing reference dynamic strain Its expression is equation (6): (6) Combining equations (3), (4), and (6), we can obtain the expression for the normalized secant dynamic elastic modulus as follows: (7) In the formula: This is the normalized secant dynamic elastic modulus.

[0032] In particular, the dynamic elastic moduli analyzed in this invention are all normalized secant dynamic elastic moduli.

[0033] S4: Based on the nonlinear least squares method, statistical analysis was performed on the experimental data under different confining pressures and freeze-thaw cycles to obtain the maximum dynamic elastic modulus characterizing basalt fiber-cement silt. and final dynamic stress amplitude The estimation model related to confining pressure and freeze-thaw cycle times; S5: Based on the estimation model obtained in step S4, through nonlinear regression analysis, the estimation model of the maximum dynamic elastic modulus of basalt fiber cement silt under the combined influence of confining pressure and freeze-thaw cycles is obtained and the final dynamic stress amplitude , and the effectiveness of the model is verified; S6: Based on the estimation model obtained in step S5, the confining pressure and freeze-thaw cycle times required environmental condition factors are brought in to obtain the maximum dynamic elastic modulus and final dynamic stress amplitude of basalt fiber cement silt under the combined influence of confining pressure and freeze-thaw cycles, and then the normalized secant dynamic elastic modulus is obtained.

[0034] Specifically, in this embodiment, the widely distributed silt for subgrade in Songyuan City, Jilin Province is used as the raw material, according to the previous research, the optimal dosage of 2% of 42.5 grade ordinary Portland cement (P.O 42.5) is selected for soil treatment, and the basic physical parameters of cement soil are shown in Table 1; The chopped basalt fiber produced by Jilin Huayang New Composite Material Co., Ltd. is used as the modification material, and the basic physical and mechanical parameters are shown in Table 2.

[0035] Table 1 Basic physical parameters of cement soil liquid limit w L (%)]]> plastic limit w P (%)]]> plasticity index I P (%)]]> Optimum moisture content limit w opt (%)]]> Maximum dry density ρ d max ( g / cm 3 )]] 25.6 17.6 8.9 9.69 2.042 Table 2 Basic properties of basalt fiber Fiber type Diameter (μm) Density (g / cm 3 ) Tensile strength (MPa) Elastic modulus (GPa) Melting point (°C) Monofilament 7 ~ 15 2.63 3000 ~ 4800 91 ~ 110 1050 The following will introduce in detail the estimation method of dynamic elastic modulus of basalt fiber cement silt for subgrade in seasonal frozen region, which specifically includes the following steps: S1: According to the specific requirements of “Highway Geotechnical Test Specification” JTG 3430-2020, the sample preparation is carried out, first, a proper amount of water is added to the silt and mechanically stirred, then placed in a sealed container for 8 hours to make the internal moisture evenly distributed. Then, cement and basalt fiber are mixed into the prepared silt and water is added to the optimum moisture content of 9.69%, and mechanically stirred for 10 min; The cement content is 2%, the basalt fiber content is 0.2%, and the basalt fiber length is 12 mm, wherein the cement content is the percentage of cement mass to the total mass of dry silt, the fiber content is the percentage of fiber mass to the total mass of cement and dry silt, and three parallel samples are prepared for each group. The sample is prepared into a cylindrical sample with a height of 100 mm, a diameter of 50 mm and a compaction degree of more than 96% by impact molding. During preparation, the maximum dry density is 2.042 g / cm 3According to the requirements of the standard, the sample was layered and impacted, and the surface of the previous layer was roughened before placing the next layer of soil. After preparation, the sample was wrapped in plastic wrap and placed in a curing room with a temperature of 20 ± 2 ℃ and a relative humidity of more than 95% according to the "Highway Engineering Inorganic Stabilized Material Test Standard" JTG E51-2009 for 14 days. Subsequently, the cured sample was subjected to 0, 1, 3, 6, and 10 freeze-thaw cycle tests, respectively. The specific test scheme is shown in Table 3.

[0036] Table 3 Test Scheme Cement content (%) Fiber content (%) Fiber length (mm) Curing time (days) Freeze-thaw cycle number 2 0.2 12 14 0，1，3，6，10 S2: Dynamic triaxial test was conducted using a multifunctional servo dynamic static triaxial tester produced by Germany Wille Company to obtain the dynamic stress and dynamic strain of the sample under different confining pressures and different freeze-thaw cycle numbers. The dynamic static triaxial tester has a circulating cold bath system, a full-automatic numerical control and data acquisition system, a maximum axial load of 25 kN, a confining pressure control range of 0 ~ 2 MPa, a test frequency range of 0 ~ 10 Hz, a maximum axial displacement of 100 mm, a temperature control range of -20 ℃ ~ 60 ℃, and can load different waveforms such as half-sine wave and sine wave. The loading mode of dynamic load during the test simulates the automobile load. Through field testing, it is known that the dynamic stress waveform in the roadbed under the action of automobile load is approximately half-sine wave, therefore, a half-sine wave as shown in Figure 1 is applied during the test, and the axial stress of the dynamic load is ; wherein represents the axial stress of the i 1st load, represents the stress increment of the i 1st load relative to the i- 1st load, represents the confining pressure. The speed of the highway automobile is generally 40 ~ 60 km / h, so the axial dynamic load frequency is set to 1 Hz. During the test, 30 kPa confining pressure is first applied to the sample for 1000 pre-loads, and after the pre-load is completed, the loading mode shown in Table 4 is used, the load is increased by 40 kPa gradient, each load vibrates 12 times, and the axial dynamic strain under different dynamic stress is tested.

[0037] Table 4 Dynamic Stress Amplitude Loading Scheme

[0038] Figure 2 ​The dynamic stress-strain curves of basalt fiber-cement silt under different confining pressures during six freeze-thaw cycles show that under low confining pressure, the dynamic stress-strain curve is relatively flat, while it becomes steeper with increasing confining pressure. This indicates that under the same strain level, the greater the confining pressure, the greater the dynamic stress the soil can withstand. Under the same stress level, the greater the confining pressure, the smaller the dynamic strain of the soil, indicating that the soil's load-bearing capacity increases with increasing confining pressure. Figure 3 The dynamic stress-strain curves of basalt fiber cement silt under different freeze-thaw cycles at a confining pressure of 50 kPa show that the dynamic stress-strain curve is relatively steep before freezing and thawing. As the number of freeze-thaw cycles increases, the curve gradually flattens, indicating that under the same stress level, freeze-thaw cycles increase soil deformation. After 6 freeze-thaw cycles, the soil can withstand the minimum load for the same deformation, indicating that the soil strength is at its lowest under 6 freeze-thaw cycles, representing the most unfavorable stress state. Therefore, the mechanical properties under 6 freeze-thaw cycles can be used as a construction reference.

[0039] S3: Based on the Hardin-Drnevich hyperbolic model, the maximum dynamic elastic modulus of basalt fiber-cemented silt was obtained. and final dynamic stress amplitude Introducing reference dynamic strain The normalized secant dynamic elastic modulus of basalt fiber cement silt was obtained. The specific analysis process is as follows: Drawing dynamic stress Dynamic strain Hysteresis curve, and the slope of the hysteresis curve is defined as the dynamic elastic modulus. : (1) Fitting with Hardin-Drnevich hyperbolic model and The relationship between them can be represented as: (2) Solving equations (1) and (2) simultaneously yields equation (3): (3) In particular, in formula (3) When, we get equation (4); when in equation (2) Then, we get equation (5): (4) (5) In the formula: This is the maximum dynamic elastic modulus, in MPa. This represents the final dynamic stress amplitude.

[0040] Introducing reference dynamic strain Its expression is equation (6): (6) Combining equations (3), (4), and (6), we can obtain the expression for the normalized secant dynamic elastic modulus as follows: (7) In the formula: This is the normalized secant dynamic elastic modulus.

[0041] Depend on Figure 2 and Figure 3 It can be seen that the nonlinear characteristics of the dynamic stress-strain relationship curve of soil under dynamic load are very significant. The Hardin-Drnevich hyperbola model of equation (2) is used to fit the dynamic stress-strain data of soil under different confining pressure conditions after freeze-thaw cycles. The fitting effect is good, and the dynamic constitutive relationship model parameters shown in Table 5 are obtained.

[0042] Table 5. Triaxial test conditions and fitting parameters for dynamic stress-strain curves.

[0043] By using equations (4) and (5) and combining them with Table 5, the maximum dynamic elastic modulus of basalt fiber cement silt can be obtained under different confining pressures and different freeze-thaw cycles. and final dynamic stress amplitude .Depend on Figure 4 The experimental values ​​and fitted curves of the relationship between the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber-reinforced cement silt and confining pressure after six freeze-thaw cycles show that both the maximum dynamic elastic modulus and the final dynamic stress amplitude increase with increasing confining pressure. The increase in the maximum dynamic elastic modulus with increasing confining pressure is due to the cement-soil skeleton structure generated by the hydration reaction significantly enhancing soil strength, and the bridging effect of the fibers effectively enhancing soil stiffness. The increase in the final dynamic stress amplitude is due to the good toughness and high tensile strength of the fibers, which improve the ductility of the cement-soil and enhance its bearing capacity. Figure 5The test values and fitting curves of the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber cement silt under 50 kPa confining pressure and different freeze-thaw cycle times show that both the maximum dynamic elastic modulus and the final dynamic stress amplitude decrease with the increase of freeze-thaw cycle times, the maximum decrease of the maximum dynamic elastic modulus is 44.96% after freeze-thaw cycles, and the maximum decrease of the final dynamic stress amplitude is 31.45%. The decrease of the maximum dynamic elastic modulus and the final dynamic stress amplitude after freeze-thaw cycles is because the water migration in the soil caused by freeze-thaw cycles leads to the weakening of the inter-particle bonding capacity, and the partial breakage or pull-out of the fibers.

[0044] Reference dynamic strain The normalized secant dynamic elastic modulus of basalt fiber cement silt under different confining pressures and different freeze-thaw cycle times is obtained by formula (7) . The normalized secant dynamic elastic modulus of basalt fiber cement silt under different confining pressures and different freeze-thaw cycle times is obtained by formula (7) Figure 6 The normalized secant dynamic elastic modulus of basalt fiber cement silt under different confining pressures and different freeze-thaw cycle times is obtained by formula (7) Figure 7 The normalized secant dynamic elastic modulus of basalt fiber cement silt under different confining pressures and different freeze-thaw cycle times is obtained by formula (7)

[0045] S4: Based on the nonlinear least squares method, the test data under different confining pressures and freeze-thaw cycle times are statistically analyzed to obtain the predictive models of the maximum dynamic elastic modulus and the final dynamic stress amplitude related to the confining pressure and the freeze-thaw cycle time: (7) (8) (9) (10) wherein: Emax is the maximum dynamic elastic modulus, unit MPa; P is the confining pressure, unit kPa; P a P0 is the atmospheric pressure, usually 101 kPa (since the confining pressure is related to the atmospheric pressure, the atmospheric pressure will affect the confining pressure and thus the data, so the atmospheric pressure is considered in data processing); σf is the final dynamic stress amplitude, unit MPa; N is the number of freeze-thaw cycles.

[0046] S5: Considering that the confining pressure and the number of freeze-thaw cycles both affect the maximum dynamic elastic modulus and the final dynamic stress amplitude, the maximum dynamic elastic modulus and the final dynamic stress amplitude can be represented by equations (11) and (12): (11) (12) wherein: , are parameters of Emax and σf under the joint influence of the confining pressure and the number of freeze-thaw cycles (the parameter values are obtained by regression analysis), and are the prediction models of the maximum dynamic elastic modulus and the final dynamic stress amplitude based on the confining pressure and the number of freeze-thaw cycles. and , and are the prediction models of the maximum dynamic elastic modulus and the final dynamic stress amplitude based on the confining pressure and the number of freeze-thaw cycles.

[0047] Based on equations (7)-(12), regression analysis is performed on the test data to obtain the prediction models of the maximum dynamic elastic modulus and the final dynamic stress of basalt fiber cement silt under the joint influence of the confining pressure and the number of freeze-thaw cycles: (13) (14) In order to verify the rationality and effectiveness of the established models, the comparison chart of the test values and the fitted values of the final dynamic stress amplitude and the maximum dynamic elastic modulus of basalt fiber cement silt under the influence of different confining pressures and different numbers of freeze-thaw cycles is drawn, as shown in Figure 8 , 9 It can be seen from Figure 8 and Figure 9 that the fitted values are approximately equal to the test values, the fitting effect is good, and the effectiveness of the prediction model is verified.

[0048] S6: Based on the estimated model obtained in step S5, the required environmental condition factors confining pressure and freeze-thaw cycle times are brought in, so as to obtain the maximum dynamic elastic modulus and the final dynamic stress amplitude of the basalt fiber cement silt under the combined influence of confining pressure and freeze-thaw cycles, and then obtain the normalized dynamic elastic modulus.

[0049] Each of the embodiments in the specification is described in a relevant manner, and the same and similar parts between the embodiments can be referred to each other. Each embodiment focuses on the difference from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the part of the method embodiment.

[0050] The above only describes the preferred embodiments of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for predicting the dynamic elastic modulus of basalt fiber cement silt soil used in roadbeds in seasonally frozen areas, characterized in that... The method includes the following steps: S1: Prepare the specimens and conduct freeze-thaw cycle tests on the cured specimens with different numbers of freeze-thaw cycles; S2: Perform staged loading dynamic triaxial tests on the samples after freeze-thaw cycles to obtain the dynamic stress of the soil under different confining pressures. and dynamic strain ,draw — The hysteresis curve, with its slope defined as the dynamic elastic modulus. , ; S3: Fitting based on Hardin-Drnevich hyperbolic model and The relationship between them Where a and b are fitting parameters, the maximum dynamic elastic modulus of basalt fiber cement silt is obtained. and final dynamic stress amplitude Introducing reference dynamic strain , The normalized secant dynamic elastic modulus of basalt fiber cement silt was obtained. , ; S4: Based on the nonlinear least squares method, statistical analysis was performed on the experimental data under different confining pressures and freeze-thaw cycles to obtain the maximum dynamic elastic modulus characterizing basalt fiber-cement silt. and final dynamic stress amplitude Prediction models related to confining pressure and number of freeze-thaw cycles; S5: Based on the predicted model obtained in step S4, the maximum dynamic elastic modulus of basalt fiber cement silt under the combined effects of confining pressure and freeze-thaw cycles is obtained through nonlinear regression analysis. and final dynamic stress amplitude The prediction model; S6: Based on the prediction model obtained in step S5, the maximum dynamic elastic modulus and the final dynamic stress amplitude of basalt fiber cement silt under the combined influence of confining pressure and freeze-thaw cycle can be obtained by substituting the required environmental conditions, confining pressure and freeze-thaw cycle number. Then, the normalized secant dynamic elastic modulus can be obtained.

2. The method for predicting the dynamic elastic modulus of basalt fiber cement silt soil for roadbeds in seasonally frozen areas according to claim 1, characterized in that, Step S1 specifically includes the following steps: S11: Add water to silty sand to prepare a soil sample with a set moisture content; S12: Incorporate cement and basalt fiber into the soil sample; S13: For each mix proportion, m parallel samples are prepared by impact molding; S14: Wrap the prepared sample in plastic wrap and place it in the curing room for curing; S15: Conduct freeze-thaw cycle tests on the cured specimens with different numbers of freeze-thaw cycles.

3. The method for predicting the dynamic elastic modulus of basalt fiber cement silt soil for roadbeds in seasonally frozen areas according to claim 2, characterized in that, In step S12, the cement content, basalt fiber content, and basalt fiber length are recorded. The cement content is the percentage of cement mass to the total mass of dry sand, and the basalt fiber content is the percentage of fiber mass to the total mass of cement and dry sand.

4. The method for predicting the dynamic elastic modulus of basalt fiber cement silt soil for roadbeds in seasonally frozen areas according to claim 2, characterized in that, In step S13, a layered method is used in the impact molding process, and the surface of the upper layer of soil is roughened before the next layer of soil is placed.

5. The method for predicting the dynamic elastic modulus of basalt fiber cement silt soil for roadbeds in seasonally frozen areas according to claim 2, characterized in that, In step S14, the prepared sample is wrapped in plastic wrap and placed in a curing room for 14 days. The curing conditions are a temperature of 20±2 ℃ and a relative humidity of more than 95%.

6. The method for predicting the dynamic elastic modulus of basalt fiber cement silt soil for roadbeds in seasonally frozen areas according to claim 2, characterized in that, In step S15, the selection of the freeze-thaw cycle test temperature requires investigation of the extreme negative temperature values ​​of the project site over the past ten years, and in combination with the soil strength change characteristics under low temperature conditions, the test freezing temperature is selected, the absolute values ​​of the thawing positive temperature and the freezing negative temperature are equal, the freezing and thawing time are both set to 24 h, and the number of freeze-thaw cycles is set to 0, 1, 3, 6 and 10 times in a progressively increasing manner.

7. The method for predicting the dynamic elastic modulus of basalt fiber cement silt soil for roadbeds in seasonally frozen areas according to claim 2, characterized in that, In step S2, the specimen after freeze-thaw cycles is subjected to a graded loading dynamic triaxial test. The waveform applied in the dynamic triaxial test is a half-sine wave. The axial dynamic load frequency is set to 1 Hz. The confining pressures selected for the dynamic triaxial test are 20 kPa, 50 kPa and 80 kPa. During the test, a confining pressure of 30 kPa is first applied to the specimen for 1000 pre-loading cycles. After the pre-loading is completed, the selected confining pressure is used to perform graded loading with an increment of 40 kPa. Each load level vibrates 12 times.

8. The method for predicting the dynamic elastic modulus of basalt fiber cement silt soil for roadbeds in seasonally frozen areas according to claim 2, characterized in that, In step S4, the maximum dynamic elastic modulus of basalt fiber cement silt is constructed. When using prediction models related to confining pressure, since confining pressure is related to atmospheric pressure, atmospheric pressure is considered during data processing. P a The setting is 101 kPa.

9. The method for predicting the dynamic elastic modulus of basalt fiber cement silt soil for roadbeds in seasonally frozen areas according to claim 2, characterized in that, In step S5, the maximum dynamic elastic modulus of basalt fiber cement silt soil under the combined effects of confining pressure and freeze-thaw cycles is determined. Final dynamic stress amplitude The expression for the prediction model is: ； ； In the formula: , Under the combined effects of confining pressure and freeze-thaw cycles and The parameters, and , and They are based on confining pressure and number of freeze-thaw cycles A model for predicting the maximum dynamic elastic modulus and the final dynamic stress amplitude.

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