CN117421860A - Unified characterization method for multi-type shear curve of roadbed soil under complex conditions - Google Patents

Abstract

The invention discloses a unified characterization method for multi-type shear curves of subgrade soil under complex conditions, including: designing a monotonic loading of subgrade soil that can fully cover the subgrade soil and possibly consider moisture content, compaction, confining pressure, and shear rate. Test plan, and through experiments, the shear curves of the subgrade soil under different working conditions were obtained, and the influence characteristics of each factor on the shear curve of the subgrade soil were clarified; based on the shear curves under different working conditions, a unified description of the complex conditions of the subgrade soil was proposed. Mathematical models of three types of shear curves: strain hardening, strain stabilization, and strain softening; use test data under different working conditions to fit the established mathematical model, obtain model parameters under different working conditions, and establish model parameters and Multivariate and multiform functional relationships among moisture content, compaction, confining pressure, and shear rate; through established mathematical models and multivariate functional relationships, different types of shear curves of subgrade soil under complex conditions are characterized, improving calculation efficiency and convergence. sex.

Description

Unified characterization method for multi-type shear curves of subgrade soil under complex conditions

Technical field

The invention belongs to the technical field of road engineering and relates to a unified representation method of multi-type shear curves of subgrade soil under complex conditions.

Background technique

Under the influence of complex environments and external loads, the weakening of soil shear resistance leads to unsteady accumulation of permanent strain in the roadbed, slope instability and collapse, and excessive settlement and deformation. As a result, the roadbed as the foundation of the road fails to perform its due role. Due to its solid and durable properties, it has caused many diseases such as rutting and cracking in the road structure, seriously affecting the stability and safety of road transportation. From the perspective of origin, subgrade diseases are caused by the weakening of the shear resistance of the subgrade soil, and the shear curve is the basis and source of analyzing the shear resistance of the subgrade soil. Due to the complex environment and stress state of the subgrade soil and the different shear speeds caused by the speed of construction, the shear curve of the subgrade soil shows three types: strain hardening, strain stability, and strain softening under different working conditions. Its reasonable and effective characterization is an important issue that continues to concern the field of road engineering.

Research on the stress-strain normalization characteristics of silt soil under freeze-thaw cycles (Chang Dan, et al. Geomechanics, 2015, 36(12): 3500-3505+3515.) Based on the traditional Duncan-Zhang model, the Soil proposed a normalized description method of the strain hardening curve that can only consider the effects of freeze-thaw cycles and confining pressure, but cannot take into account the moisture content, compaction degree and shear rate caused by subgrade humidification and different filling rates. influence, and the proposed model is not suitable for strain softening curves. If you need to describe the softening curve, you must use other models, resulting in the use of multiple expressions to describe different types of shear curves separately. At this time, different types of expressions are embedded When performing numerical calculations on various finite element calculation platforms, existing methods need to first determine the deformation type of the soil based on the stress state of the soil, and then select different expressions to simulate different types of soil based on the set judgment criteria. The deformation curve of It is easy to stop passively due to lack of convergence. Mechanical properties and stress-strain normalization of Yanji expansive rocks under dry-wet-freeze-thaw cycles (Zeng Zhixiong, et al. Rock and Soil Mechanics, 2018, 39(08): 2895-2904.) A method considering freezing was proposed for expansive soils. This method is a normalized description method for three types of shear curves: strain hardening, strain stabilization, and strain softening affected by melt cycles and confining pressure. However, it does not consider the effects of moisture content, compaction, and shear rate. At the same time, the confinement during the test is not considered. The pressure level is basically between 200 and 400kPa, which is far from the low confining stress state of the subgrade. The results obtained have good guidance for high confining pressure scenarios such as foundations, and are very different from the actual engineering characteristics of the subgrade. , and the expansion rock cannot be used to fill the roadbed, resulting in the existing technology being unsuitable for characterizing the three types of shear curves of strain hardening, strain stabilization, and strain softening of the roadbed soil. The Chinese invention patent with application number 202310004989.2 discloses a red clay hardening curve that can only consider the effects of confining pressure, fiber content and length. The effects on moisture content, compaction, shear rate and the usability of the strain softening curve are missing. The stress-strain relationship of frozen sand soil and the nonlinear Mohr strength criterion (Lai Yuanming, et al. Transactions of Rock Mechanics and Engineering, 2007, 187(8): 1612-1617.) have disclosed that they can simultaneously describe the strain hardening and strain stability of frozen soil. , three types of strain softening shear curve models, but it is still unable to uniformly characterize the shear curves under different moisture contents, compaction degrees, and shear rates. In view of the current problem that it is not possible to simultaneously describe the three types of shear curves of strain hardening, strain stabilization, and strain softening of subgrade soil under different moisture content, compaction degree, confining pressure, and shear rate, it is urgent to develop a multi-dimensional shear curve for subgrade soil under complex conditions. A unified characterization method for type shear curves.

Contents of the invention

In order to achieve the above objectives, the present invention provides a unified characterization method for multi-type shear curves of subgrade soil under complex conditions, solving the problem that currently there is no way to simultaneously describe the strain of subgrade soil under different moisture content, compaction degree, confining pressure and shear rate. Problems with three types of shear curves: hardening, strain stabilization, and strain softening.

In order to solve the above technical problems, the technical solution adopted by the present invention is a unified characterization method of multi-type shear curves of subgrade soil under complex conditions, which includes the following steps:

Step S1: Design a monotonic loading test plan for subgrade soil that can fully cover the subgrade soil, taking into account moisture content, compaction degree, confining pressure, and shear rate, and obtain different working conditions through experiments, that is, different moisture content, compaction degree, confining pressure, and shear rate. The shear curve of subgrade soil under pressure and shear rate, and the influence characteristics of moisture content, compaction degree, confining pressure, and shear rate on the shear curve of subgrade soil respectively;

Step S2: Based on the shear curves under different working conditions obtained in step S1, propose a mathematical model that can uniformly describe the three types of shear curves: strain hardening, strain stabilization, and strain softening under complex conditions of subgrade soil;

Step S3: Use the test data under different working conditions in step S1 to fit the mathematical model established in step S2, obtain the model parameters under different working conditions, and establish the relationship between the model parameters and the moisture content, compaction degree, confining pressure, Multivariate and multi-form functional relationships among factors such as shear rate;

Step S4: Characterize the three types of shear curves of strain hardening, strain stability, and strain softening of the subgrade soil under complex conditions such as different moisture contents, compaction degrees, and confining pressures through the mathematical model and multivariate functional relationships established in steps S2 to S3.

Further, step S2 proposes a mathematical model as shown in the following formula that can uniformly describe the three types of shear curves: strain hardening, strain stabilization, and strain softening under complex conditions of subgrade soil:

Among them: σ is the axial stress; ε is the axial strain; p, q, and k are model parameters.

Further, step S3 establishes a multivariate functional relationship between the model parameters p, q, k and moisture content, compaction degree, and confining pressure as shown in the following formula:

Among them, w is the moisture content, OMC is the optimal moisture content, K is the compaction degree, and σ ₃ is the confining pressure.

Further, in step S1:

In the monotonic loading test plan of subgrade soil, the moisture content levels are selected as 1.0OMC, 1.2OMC, 1.4OMC, and 1.6OMC, the compaction level is selected as 87%, 90%, 93%, and 96%, and the confining pressure The levels are selected as 30kPa, 60kPa, 90kPa, and 120kPa, and the shear rate levels are selected as 0.50%min ^-1 , 0.70%min ^-1 , 0.85%min ^-1 and 1.00%min ^-1 . The designed monotonic loading test plan See table below:

Group No compactness(%) Moisture content/OMC Shear rate (%min ^-1 ) Confining pressure (kPa) 1 96 1.0 0.70 30, 60, 90, 120 2 93 1.0 0.70 30, 60, 90, 120 3 90 1.0 0.70 30, 60, 90, 120 4 87 1.0 0.70 30, 60, 90, 120 5 96 1.2 0.70 30, 60, 90, 120 6 96 1.4 0.70 30, 60, 90, 120 7 96 1.6 0.70 30, 60, 90, 120 8 96 1.2 0.50 30, 60, 90, 120 9 96 1.2 0.85 30, 60, 90, 120 10 96 1.2 1.00 30, 60, 90, 120

;

The monotonic loading test adopts a non-consolidation and non-drainage method, and the loading is stopped when the axial strain reaches 15%.

Further, in step S3, the mathematical model established in step S2 is fitted using the test data under different working conditions in step S1. The planning solving function in Matlab data analysis is used during fitting. When the coefficient of determination reaches the maximum value Fitting ends.

The beneficial effects of the present invention are:

1. Seizing the commonality of different types of shear curves under different working conditions, it is proposed to use straight lines to describe the linear elastic stage of the shear curve, use hyperbola to describe the plastic part of the shear curve, and use the constant part to adjust the adaptability to a unified description. The mathematical model of three types of shear curves of strain hardening, strain stabilization and strain softening of subgrade soil can describe different types of shear curves of subgrade soil using only one unified expression, without the need to judge the deformation type of subgrade soil in advance. , and the model parameters have clear meaning and are easy to obtain, which greatly improves the calculation efficiency and calculation convergence, and saves calculation time in the analysis of practical problems such as subgrade deformation analysis, slope safety factor, etc.; the shear under subgrade scenarios was discovered The rate has little effect on the soil shear curve. Experiments have proved that the shear rate variable can be ignored when establishing the shear curve model, which reasonably reduces the influencing factors of the model and improves the prediction efficiency; moreover, the establishment of The relationship equation between the parameters p, q, k of the unified shear curve model and the moisture content, compaction degree, and confining pressure is established, and the corresponding working conditions can be quickly obtained according to the physical state and stress state of the subgrade soil. The shear curve under different moisture content, compaction degree, confining pressure, and shear rate has not been able to describe the three types of shear curves of subgrade soil at the same time: strain hardening, strain stability, and strain softening. It is an urgent need to obtain the shear curve. The soil shear curve and a series of shear resistance performance indicators obtained from the shear curve provide obvious engineering convenience for engineering disasters and participating units and have high practical value;

2. The designed test plan is completely based on the actual scenario of the subgrade. In particular, the confining pressure level is set to 30kPa, 60kPa, 90kPa, and 120kPa according to the low confining pressure characteristics of the subgrade, which avoids the existing technology to conduct tests at high confining pressure levels. The obtained phenomena, conclusions, and models are used to analyze incompatibility of subgrade soil shear deformation due to different actual characteristics. This avoids large deviations in guiding subgrade engineering using technologies obtained under high confining pressure conditions;

3. A test plan was designed that can fully cover the factors affecting the shear curve of the subgrade soil. This plan comprehensively considered the effects of moisture content, compaction, confining pressure, and shear rate, and reduced the number of soil samples during the test to 40. One can reveal the influence of different factors, avoiding the huge test volume of 4×4×4×4=256 specimens in the four-factor and four-level comprehensive test, greatly reducing the tedious process of sample preparation and reducing the cost. The difficulty of the monotonic shear test shortens the test time and improves the research efficiency.

Description of the drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a flow chart of the unified characterization method of multi-type shear curves of subgrade soil under complex conditions in this embodiment.

Figure 2 is a test flow chart of the unified characterization method of multi-type shear curves of subgrade soil under complex conditions in this embodiment.

Figure 3 shows the shear curves of subgrade soil specimens under different moisture contents and different confining pressures.

Figure 4 shows the shear curves of subgrade soil specimens under different compaction degrees and different confining pressures.

Figure 5 is the shear curve of the subgrade soil specimen under different shear rates and different confining pressures.

Figure 6 shows the variation pattern of parameter p of the unified shear curve model with moisture content, compaction degree, and confining pressure.

Figure 7 shows the variation pattern of parameter q of the unified shear curve model with moisture content, compaction degree, and confining pressure.

Figure 8 shows the variation pattern of parameter k of the unified shear curve model with moisture content, compaction degree, and confining pressure.

Figure 9 is the prediction effect of the multivariate functional relationship between the parameters p, q, and k of the shear curve unified model.

Figure 10 is the verification result of the multivariate functional relationship of the parameters p, q, and k of the shear curve unified model.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Example 1

The embodiment of the present invention provides a unified characterization method for multi-type shear curves of subgrade soil under complex conditions, as shown in Figure 1, specifically following the following steps S1 to S4.

Step S1: Design a monotonic loading test plan for subgrade soil that can fully cover the subgrade soil, taking into account moisture content, compaction degree, confining pressure, and shear rate, and obtain different working conditions through experiments, that is, different moisture content, compaction degree, confining pressure, and shear rate. The shear curve of subgrade soil under pressure and shear rate, and the influence characteristics of each factor (moisture content, compaction degree, confining pressure, shear rate) on the shear curve of subgrade soil respectively:

According to the equilibrium state of the roadbed moisture, based on the equilibrium moisture content and considering the fact that the roadbed humidity increases under humidification, the moisture content levels are selected as 1.0OMC, 1.2OMC, 1.0OMC, 1.2OMC, 1.4OMC, 1.6OMC; according to the zoning requirements of 96%, 94%, and 93% during roadbed filling and considering the attenuation of compaction during the service period, the compaction level is selected as 87%, 90%, 93%, 96 %; considering that the filling height of the roadbed is generally around 6m in most cases, the confining pressure levels are selected as 30kPa, 60kPa, 90kPa, and 120kPa based on 20kPa per meter; the shear rate levels are selected as 0.50% min ^-1 and 0.70 %min ^-1 , 0.85%min ^-1 and 1.00%min ^-1 to cover possible loading rates in the subgrade;

The maximum dry density and optimal moisture content (OMC) of the subgrade soil were determined based on the results of the compaction test. A split membrane tool was used to statically press the specimen under the universal hydraulic testing machine to obtain the specimen with the target compaction degree and moisture content. The specimen was statically pressed After being placed for 2 days, a monotonic loading test was carried out in accordance with Table 1 in a non-consolidated and non-drained manner. The loading was stopped when the axial strain reached 15%, and the influence of various factors on the shear curve was analyzed based on the shear curve test results. Among them, 1 Groups ∼4 analyze the influence of compaction, groups 1, 5-7 analyze the influence of moisture content, groups 5, 8-10 analyze the influence of shear rate, and the influence of confining pressure can be reflected in each group.

Table 1 Monotonous loading test plan table

Group No compactness(%) Moisture content/OMC Shear rate (%min ^-1 ) Confining pressure (kPa) 1 96 1.0 0.70 30, 60, 90, 120 2 93 1.0 0.70 30, 60, 90, 120 3 90 1.0 0.70 30, 60, 90, 120 4 87 1.0 0.70 30, 60, 90, 120 5 96 1.2 0.70 30, 60, 90, 120 6 96 1.4 0.70 30, 60, 90, 120 7 96 1.6 0.70 30, 60, 90, 120 8 96 1.2 0.50 30, 60, 90, 120 9 96 1.2 0.85 30, 60, 90, 120 10 96 1.2 1.00 30, 60, 90, 120

Step S2: Based on the shear curves under different working conditions obtained in step S1, propose a mathematical model that can uniformly describe the three types of shear curves: strain hardening, strain stabilization, and strain softening under complex conditions of subgrade soil;

Step S3: Use the test data under different working conditions in step S1 to fit the mathematical model established in step S2, obtain the model parameters under different working conditions, and establish the relationship between the model parameters and the moisture content, compaction degree, confining pressure, Multivariate and multi-form functional relationships among factors such as shear rate;

Step S4: Use the mathematical model and multivariate functional relationships established in steps S2 to S3 to characterize the three types of shear curves of strain hardening, strain stabilization, and strain softening of the subgrade soil under complex conditions such as different moisture contents, compaction degrees, and confining pressures:

By substituting any moisture content, compaction degree and confining pressure into the multivariate functional relationship between the model parameters p, q, k established in step S3 and moisture content, compaction degree and confining pressure, any moisture content, compaction degree can be obtained , the model parameters p, q, and k under the combination of confining pressure, so that the mathematical model proposed in step S2 can be used to characterize the three types of shear curves of strain hardening, strain stabilization, and strain softening of the subgrade soil under complex conditions.

Example 2

This embodiment provides a unified characterization method for multi-type shear curves of subgrade soil under complex conditions, including the following steps:

Taking the low liquid limit clay taken from Changsha, Hunan as an example, its basic physical parameters are shown in Table 2. From the liquid limit <50% and the plasticity index <26, it can be seen that the test soil sample selected in the embodiment is qualified roadbed fill soil.

Table 2 Basic physical parameters of soil samples

Step S1: Design a monotonic loading test plan for subgrade soil that can fully cover the subgrade soil, taking into account moisture content, compaction degree, confining pressure, and shear rate, and obtain different working conditions through experiments, that is, different moisture content, compaction degree, confining pressure, and shear rate. The shear curve of subgrade soil under pressure and shear rate, and the influence characteristics of various factors (moisture content, compaction degree, confining pressure, shear rate) on the shear curve of subgrade soil are clarified:

According to the compaction test results, it is determined that the maximum dry density of the subgrade soil is 1.71g·cm ^-3 and the optimal moisture content (OMC) is 14.2%; the test plan refers to step S1 of Example 1: select the moisture content level of the test soil sample Set as 1.0OMC, 1.2OMC, 1.4OMC, 1.6OMC; the compaction level of the test soil sample is selected as 87%, 90%, 93%, 96%; the test confining pressure level is selected as 30kPa, 60kPa, 90kPa, 120kPa; select the shear rate levels as 0.50%min ^-1 , 0.70%min ^-1 , 0.85%min ^-1 and 1.00%min ^-1 ; use a split membrane tool to divide into 5 layers under the universal hydraulic testing machine Static pressure was used to obtain the test piece at the target compaction degree and moisture content. After the piece was completed, it was sealed with plastic wrap and left to stand for 2 days. Then, it was used in the Triaxial-100/14 triaxial system produced by the Italian WF company to use non-consolidation and non-drainage. Carry out a monotonic loading test according to Table 1. The main steps in the test process are shown in Figure 2. Stop loading when the axial strain reaches 15%. Groups 1 to 4 analyze the impact of compaction, 1, 5 to 7 Groups 5, 8 to 10 analyze the influence of shear rate. The influence of confining pressure can be reflected in each group: the shear curves of test soil samples under different moisture contents and different confining pressures are shown in Figure 3. As shown, Figure 3 (a) is the shear curve of subgrade soil specimens with different moisture contents under the confining pressure of 30kPa, and Figure 3 (b) is the shear curve of the subgrade soil specimens with different moisture contents under the confining pressure of 60kPa. Figure 3 (c) is the shear curve of subgrade soil specimens with different moisture contents under the confining pressure of 90kPa. Figure 3 (d) is the shear curve of the subgrade soil specimens with different moisture contents under the confining pressure of 120kPa. Analysis diagram 3 It can be seen that the moisture content and confining pressure have a significant impact on the shear curve. When the moisture content and confining pressure change, not only the numerical value of the shear curve changes, but the type of the curve also changes. Strain hardening and strain stability appear under different working conditions. , three types of strain softening; the shear curves of test soil samples under different compaction degrees and different confining pressures are shown in Figure 4. Figure 4 (a) shows the shear curves of subgrade soil specimens with different compaction degrees under 30kPa confining pressure. Shear curve, Figure 4 (b) is the shear curve of subgrade soil specimens with different compaction degrees under 60kPa confining pressure, Figure 4 (c) is the shear curve of subgrade soil specimens with different compaction degrees under 90kPa confining pressure. Shear curve, (d) in Figure 4 is the shear curve of subgrade soil specimens with different compaction degrees under 120kPa confining pressure. The same analysis as shown in 4 shows that the compaction degree also has a significant impact on the shear curve; different shear The shear curves of test soil samples under different confining pressures and rates are shown in Figure 5. Figure 5(a) shows the shear curves of subgrade soil specimens with different shear rates under 30kPa confining pressure. Figure 5(b) It is the shear curve of the subgrade soil specimen with different shear rates under the confining pressure of 60kPa. Figure 5(c) is the shear curve of the subgrade soil specimen with different shear rates under the confining pressure of 90kPa. Figure 5(d) These are the shear curves of subgrade soil specimens with different shear rates under 120kPa confining pressure. It can be found that the change in shear rate does not affect the type and value of the shear curve, and the test curves under different shear rates are relatively consistent;

Step S2: Based on the shear curves under different working conditions obtained in step S1, propose a mathematical model that can uniformly describe the three types of shear curves: strain hardening, strain stabilization, and strain softening under complex conditions of subgrade soil:

From the shear curve test results under different working conditions shown in Figure 3, Figure 4, and Figure 5 in step S1, it can be seen that although the types of the three types of strain hardening, strain stable, and strain softening curves are obviously different, regardless of the strain hardening, strain stable Both strain softening curves have a linear elastic part and a plastic part. Based on this commonality, a straight line is used to describe the linear elastic stage of the shear curve, a hyperbola is used to describe the plastic part of the shear curve, and a constant part is used to adjust the adaptability of the model. The following is proposed The mathematical model shown in the formula can uniformly describe the three types of shear curves: strain hardening, strain stabilization, and strain softening under complex conditions of subgrade soil:

Among them: σ is the axial stress; ε is the axial strain; p, q, and k are model parameters, which can be obtained through monotonic loading test results;

Step S3: Use the test data under different working conditions in step S1 to fit the mathematical model established in step S2, obtain the model parameters under different working conditions, and establish the relationship between the model parameters and the moisture content, compaction degree, confining pressure, Multivariate and multi-form functional relationships among factors such as shear rate:

Use the test data under different working conditions in step S1 to fit the mathematical model established in step S2. The planning and solving function in Matlab data analysis is used during fitting. When the coefficient of determination reaches the maximum value, the fitting ends and the fitting result See Table 3;

Table 3 Parameter statistics table of the shear curve unified model

Then, based on the results in Table 3, we analyze the evolution rules of the model parameters p, q, and k with each influencing factor. The results are shown in Figures 6 to 8. Figure 6 (a) to (c) correspond to the parameter p with each influencing factor. The changing rules of moisture content, compaction degree, and confining pressure, Figure 7(a)~(c) correspond to the changing rules of parameter q with moisture content, compaction degree, and confining pressure, Figure 8(a)~(c) ) corresponds to the variation pattern of parameter k with moisture content, compaction degree, and confining pressure. In order to ensure the rigor and completeness of the model establishment, the parameters of the 40 working conditions shown in Table 3 are used independently in two parts: the first part selects 32 working conditions to establish the following model, and the second part selects the remaining 8 working conditions. It is used to verify the rationality and accuracy of the proposed unified characterization method of multi-type shear curves of subgrade soil under complex conditions. Since the test results in step S1 clearly show that the shear rate has little effect on the shear curve, the shear rate is no longer used as an influencing factor. Specifically, it can be seen from Figure 6 that the parameter p changes exponentially with the degree of compaction, logarithmically with the ratio of the actual moisture content to the optimal moisture content, and changes exponentially with the confining pressure; as can be seen from Figure 7, the parameter q changes linearly with the degree of compaction, changes exponentially with the ratio of the actual moisture content to the optimal moisture content, and changes logarithmically with the confining pressure. As can be seen from Figure 8, parameter k changes exponentially with the degree of compaction. It changes exponentially with the ratio of actual moisture content and optimal moisture content, and changes with a power function type with confining pressure. Furthermore, corresponding description forms were selected respectively, and a multivariate functional relationship as shown in the following formula was established between the parameters p, q, k of the unified shear curve model and the moisture content, compaction degree, and confining pressure (taking into account the magnitude reasons The model parameters in the functional relationship are appropriately amplified):

Among them, w is the moisture content, OMC is the optimal moisture content, K is the compaction degree, and σ ₃ is the confining pressure;

The accuracy of the multivariate functional relationship between model parameters p, q, and k is shown in Figure 9. Figure 9 (a) to (c) correspond to the actual values of parameters 10 ² × p, parameter 10 ⁵ × q, and parameter 10 ³ × k. The correlation result between the value and the predicted value, where N is the number of working conditions used, that is, the number of sample points for modeling. From R ² are both greater than 0.9, we know that the prediction accuracy of the multivariate function relationship of parameters p, q, k is very high;

Step S4: Use the mathematical model and multivariate functional relationships established in steps S2 to S3 to characterize the three types of shear curves of strain hardening, strain stabilization, and strain softening of the subgrade soil under complex conditions such as different moisture contents, compaction degrees, and confining pressures:

The monotonic loading test plan designed in step S1 has a total of 40 working conditions, and in step S3, 32 working conditions have been used when establishing the multivariate functional relationship of model parameters p, q, k. In order to verify the proposed unified model of shear curve As well as the rationality and accuracy of the multivariate functional relationship of the model parameters p, q, k, the moisture content, compaction degree, and confining pressure in the remaining eight working conditions are substituted into the multivariate functional relationship established in step S3 to obtain the corresponding The model parameters p, q, and k are then substituted into the mathematical model of the shear curve proposed in step S2 to obtain the shear curve calculation results corresponding to the eight working conditions. The comparison between the calculated values and the measured values is shown in Figure 10, Figure 10 (a) to (h) correspond to the comparison results between the calculated values and the measured values corresponding to the verification working conditions 1 to 8. The dotted lines represent the calculated values of the shear curve, and the hollow points represent the measured values of the shear curve. It can be It can be seen that the calculated values of the three types of curves of strain softening, strain hardening, and strain stabilization are highly consistent with the measured values, which proves that the unified characterization method of multi-type shear curves of subgrade soil under complex conditions proposed in this embodiment can accurately predict the shear curves of subgrade soil under complex conditions. The shear curve of the subgrade soil is uniformly and accurately described.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims (5)

1. The unified characterization method of the road foundation soil multi-type shear curve under the complex condition is characterized by comprising the following steps:

step S1: designing a possible roadbed earth monotone loading test scheme capable of comprehensively covering roadbed earth by taking the water content, compactness, confining pressure and shearing rate into consideration, obtaining shearing curves of roadbed earth under different working conditions, namely different water content, compactness, confining pressure and shearing rate, and determining the influence characteristics of the water content, compactness, confining pressure and shearing rate on the roadbed earth shearing curves respectively;

step S2: based on the shearing curves under different working conditions obtained in the step S1, a mathematical model capable of uniformly describing three types of shearing curves of strain hardening, strain stabilization and strain softening under complex conditions of roadbed soil is provided;

step S3: fitting the mathematical model established in the step S2 by using the test data under different working conditions in the step S1 to obtain model parameters under different working conditions, and establishing a multi-element and multi-form functional relation between the model parameters and factors of water content, compactness, confining pressure and shear rate;

step S4: and (3) representing three types of shear curves of road foundation soil strain hardening, strain stabilization and strain softening under complex conditions of different water contents, compactness and confining pressure by the mathematical model and the multivariate functional relation established in the steps (S2) to (S3).

2. The unified characterization method of the multi-type shear curve of the roadbed under the complex condition according to claim 1, wherein the step S2 is characterized in that a mathematical model capable of describing three types of shear curves of strain hardening, strain stabilization and strain softening under the complex condition of the roadbed is provided as shown in the following formula:

wherein: sigma is the axial stress; epsilon is the axial strain; p, q, k are model parameters.

3. The unified characterization method of the road foundation soil multi-type shearing curve under the complex condition according to claim 2, wherein the step S3 is characterized in that a multi-functional relation between model parameters p, q and k and water content, compactness and confining pressure is established, wherein the multi-functional relation is shown in the following formula:

wherein w is water content, OMC is optimal water content, K is compactness, sigma ₃ Is confining pressure.

4. A method for uniformly characterizing a multi-type shear curve of a roadbed under a complex condition according to any one of claims 1 to 3, wherein in step S1:

in the roadbed soil monotonous loading test scheme, the water content level is selected to be 1.0OMC, 1.2OMC, 1.4OMC and 1.6OMC, the compactness level is selected to be 87%, 90%, 93% and 96%, the confining pressure level is selected to be 30kPa, 60kPa, 90kPa and 120kPa, and the shearing rate level is selected to be 0.50% min ^-1 、0.70％min ^-1 、0.85％min ^-1 1.00% min ^-1 The designed monotonic loading test scheme is shown in the following table:

group number Degree of compaction (%) Water content/OMC Shear rate (% min) ^-1 ) Confining pressure (kPa) 1 96 1.0 0.70 30、60、90、120 2 93 1.0 0.70 30、60、90、120 3 90 1.0 0.70 30、60、90、120 4 87 1.0 0.70 30、60、90、120 5 96 1.2 0.70 30、60、90、120 6 96 1.4 0.70 30、60、90、120 7 96 1.6 0.70 30、60、90、120 8 96 1.2 0.50 30、60、90、120 9 96 1.2 0.85 30、60、90、120 10 96 1.2 1.00 30、60、90、120

；

The monotone loading test adopts a mode of non-consolidation and non-drainage, and the loading is stopped when the axial strain reaches 15%.

5. The unified characterization method of the multi-type shear curve of the roadbed under the complex conditions according to any one of claims 1 to 3, wherein in the step S3, the mathematical model established in the step S2 is fitted by using the test data under different working conditions in the step S1, a planning and solving function in Matlab data analysis is adopted during fitting, and the fitting is ended when the coefficient is determined to reach the maximum value.