A method for determining soil properties to assess the long-term stability of port structure foundations

Abstract

This invention relates to the field of port engineering structure technology, specifically to a method for determining soil property indicators to assess the long-term stability of port engineering structure foundations, comprising the following steps: S1, conducting indoor triaxial creep tests: performing triaxial consolidated undrained compression tests and creep tests under three different confining pressures; S2, processing creep test data: calculating the actual axial strain; S3, determining the long-term yield stress: obtaining the yield stress at different times under each confining pressure, and then fitting the result to obtain the long-term yield stress under each confining pressure; S4, calculating the long-term shear strength index: taking the average of the long-term cohesion and long-term internal friction angle calculated in each group as the final long-term shear strength index; S5, assessing the long-term stability of the port engineering structure foundation: calculating the long-term bearing capacity of the foundation and comparing it with the short-term bearing capacity to assess the long-term stability of the port engineering structure foundation. This invention significantly improves the accuracy of stability analysis and the reliability of safety assessment of port engineering structures under long-term service conditions.

Description

Technical Field

[0001] This invention relates to the field of port engineering structure technology, and in particular to a method for determining soil properties to assess the long-term stability of port engineering structure foundations. Background Technology

[0002] my country is a major port country, and the large-scale construction of port projects in recent years has played an important role in economic development and industrial structure optimization. my country has accumulated rich experience and advanced port construction technology in port engineering construction. However, there are still some cases of port instability. Among them, the foundation soil on which the port engineering structure depends has significant creep characteristics, which leads to a gradual decrease in its long-term shear strength. This is one of the important factors causing the instability of port structures. Therefore, it is of great significance to determine the long-term shear strength index of the soil to evaluate the long-term stability of the foundation of port engineering structures.

[0003] Currently, the isochronous curve inflection point method of deviatoric stress-axial strain is widely used in triaxial creep tests as the mainstream technique for determining the long-term strength of soil. This technique analyzes the inflection point position of the deviatoric stress-axial strain curve at different loading times to determine the yield stress at each time point, and further extrapolates to obtain the long-term yield stress, which is then equated to the long-term failure deviatoric stress of the soil. However, in triaxial compression tests of soil, the yield stress and the failure deviatoric stress are fundamentally different in physical sense: the yield stress reflects the critical point at which the soil transitions from an elastic state to a plastic state, while the failure deviatoric stress represents the stress level at which irreversible failure occurs in the soil at a specific time scale. Existing techniques do not clearly distinguish between the two, leading to conceptual confusion and inconsistent evaluation standards when calculating the long-term shear strength index of soil, affecting the accurate assessment of the long-term strength characteristics of soil, and consequently affecting the reliable acquisition of long-term shear strength index in engineering. Therefore, it is urgent to propose a method for determining the long-term shear strength index of soil based on the yield stress of the isochronous curve, thereby providing a more reliable technical foundation for the long-term stability analysis of port and engineering structure foundations. Summary of the Invention

[0004] This invention provides a method for determining soil properties to assess the long-term stability of port structure foundations, which solves the problems of confusion between yield stress and failure deviatoric stress, inconsistent strength assessment standards, and biased assessment results in the prior art, and provides an effective means for assessing the long-term stability of port structure foundations.

[0005] A method for determining soil properties to assess the long-term stability of port engineering structure foundations includes the following steps:

[0006] S1. Conduct indoor triaxial creep test: Select undisturbed soil samples representing the foundation of the port structure and conduct triaxial consolidated undrained compression test and creep test under three different confining pressures. The creep test adopts graded loading, and the deviatoric stress of each grade is kept constant for no less than 3 days.

[0007] S2, Processing creep test data: Convert the axial strain-time curve of the whole process into the axial strain-time curve of each stage of deviatoric stress loading separately, and calculate the actual axial strain by considering the axial strain at the beginning of loading and the effect of the previous stage of creep.

[0008] S3, Determine the long-term yield stress: Select different time points under each confining pressure to draw the deviatoric stress-axial strain isochronous curve, use the tangent method to determine the yield point, obtain the yield stress at different times under each confining pressure, and then fit to obtain the long-term yield stress under each confining pressure.

[0009] S4, Calculate the long-term shear strength index: Substitute the long-term yield stress under each confining pressure as the long-term shear strength of the soil into the Mohr-Coulomb strength theory. For any two confining pressures, a set of long-term cohesion and long-term internal friction angle can be calculated. Take the average value of the long-term cohesion and long-term internal friction angle calculated in each set as the final long-term shear strength index.

[0010] S5. Assess the long-term stability of the foundation of port engineering structures: Calculate the long-term bearing capacity of the foundation based on the long-term shear strength index and compare it with the short-term bearing capacity to assess the long-term stability of the foundation of port engineering structures.

[0011] Optionally, conducting the indoor triaxial creep test in S1 includes:

[0012] S11, Soil sample preparation: Select representative undisturbed soil from the foundation of the port structure, minimize disturbance during storage and transportation, and use a soil cutter to prepare the undisturbed soil into cylindrical samples.

[0013] S12, Conventional triaxial compression test: Consolidated undrained triaxial compression test is carried out under three different confining pressure conditions (the confining pressure is determined according to the overburden pressure at the corresponding depth of the undisturbed soil) to obtain the deviatoric stress of failure under each confining pressure. If there is a peak point in the deviatoric stress-axial strain curve, the peak stress is taken as the deviatoric stress of failure. If there is no peak point, the deviatoric stress when the axial strain is 15% is taken as the deviatoric stress of failure.

[0014] S13, Triaxial creep test setup: The creep test is conducted under the same three confining pressure conditions as the conventional triaxial compression test, using consolidation undrained conditions and graded loading.

[0015] S14, Loading scheme: The number of graded loading stages shall not be less than 5. The loading rate of each stage of deviatoric stress shall be consistent with that of the conventional triaxial compression test. After reaching the set deviatoric stress, it shall be kept constant. The deviatoric stress of each stage shall be kept constant for no less than 3 days.

[0016] Optionally, the creep test data in S2 includes:

[0017] S21, Obtain the full-process curve: After the creep test is completed, obtain the step-time full-process curve of axial strain under graded loading conditions;

[0018] S22, Curve Conversion: The entire process curve is segmented according to each stage of deviatoric stress loading and converted into axial strain-time curves under each stage of deviatoric stress loading.

[0019] S23, Initial Axial Strain Correction: For each stage of deviatoric stress loading, the axial strain corresponding to the time when the set deviatoric stress is reached is taken as the initial axial strain value of that stage.

[0020] S24, Correction for the influence of the previous stage: Calculate the axial strain growth rate at the end of the creep stage of the previous stage, and extend it to the next stage according to the rate. Shift the axial strain curve extended to the next stage upward as a whole to reflect the axial strain generated during the next stage of loading, so as to reflect the continuity of the previous stage.

[0021] S25, Calculation of actual axial strain: By comparing the previous stage curve after extension and translation with the current stage curve, the difference is calculated as the actual axial strain of this stage;

[0022] S26, Curve Translation and Synthesis: The actual axial strain at each level is translated to the left to its respective initial axial strain position, and the actual axial strain at each time moment is accumulated based on the initial axial strain value to obtain the corrected axial strain-time curves at each level.

[0023] Optionally, determining the long-term yield stress in S3 includes:

[0024] S31, Extracting graded loading curves: Based on the results of processing creep test data, obtain the axial strain-time curves under different levels of deviatoric stress;

[0025] S32, Constructing the deviatoric stress-axial strain isochronous curve: Select multiple different times under each confining pressure, extract the axial strain and corresponding deviatoric stress at different times under each confining pressure, and plot the deviatoric stress-axial strain isochronous curve at the corresponding time under each confining pressure.

[0026] S33, Determine the yield point location: For each isochronous curve, the yield point is determined using the tangent method. This involves linearly fitting the low-stress segment (zero point and the first two stress levels) and the high-stress segment (the last three stress levels). The intersection of the two fitted lines is the yield point at that time point, and the corresponding deviatoric stress is denoted as the yield stress. ;

[0027] S34, Plot the yield stress-time curve: Plot the yield stress at different time points under each confining pressure. The yield stress-time curve was plotted and linearly fitted in a logarithmic time coordinate system to obtain the time-varying law of yield stress under each confining pressure.

[0028] S35, Determine the long-term yield stress: Based on the yield stress-time curve under each confining pressure, select the yield stress value corresponding to the long-term acting time (100 years) as the long-term yield stress of the soil under each confining pressure. .

[0029] Optionally, the parameters for calculating long-term shear strength in S4 include:

[0030] S41, Set the yield stress to the shear strength: Calculate the long-term yield stress under each confining pressure. As the long-term shear strength of the soil under the corresponding confining pressure ;

[0031] S42, Establish the Mohr-Coulomb strength relationship: Based on the Mohr-Coulomb strength theory, establish the relationship between long-term shear strength, long-term shear strength index and confining pressure;

[0032] S43, Calculate the long-term internal friction angle: Select any two confining pressure conditions, subtract their corresponding long-term shear strengths, and calculate the difference. And solve for the long-term internal friction angle. ;

[0033] S44, Calculate long-term cohesion: based on the solved long-term internal friction angle. Calculate the long-term cohesion under any two confining pressures. ;

[0034] S45, Determine the final index: Calculate the three sets of long-term internal friction angles. and long-term cohesion The average value was taken as the final long-term shear strength index.

[0035] Optionally, the relationship between the long-term shear strength and the confining pressure is expressed as:

[0036] ;

[0037] in, For long-term shear strength, For confining pressure, For long-term cohesion, This is the long-term internal friction angle.

[0038] Optionally, the difference Represented as:

[0039] ;

[0040] in, Let be the difference between the long-term shear strength under the higher confining pressure and the long-term shear strength under the lower confining pressure, for any two confining pressures. It represents the difference between the high and low confining pressures under any two confining pressures.

[0041] The beneficial effects of this invention are:

[0042] This invention utilizes the yield stress information from the isochronous curves of deviatoric stress-axial strain in triaxial creep tests, taking the yield stress at each loading time point as the corresponding soil shear strength. Therefore, under a unified strength evaluation standard, it proposes a scientific, accurate, and practical method for determining the long-term shear strength of soil, and derives a more reliable long-term shear strength index based on this method. This method not only has clear physical significance and good rationality at the theoretical level, but also demonstrates significant advantages in engineering applications. It effectively solves problems in existing technologies such as the confusion between yield stress and failure deviatoric stress, inconsistent strength evaluation standards, and biased evaluation results, thereby significantly improving the accuracy of stability analysis and the reliability of safety assessment of port and harbor structure foundations under long-term service conditions. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the axial strain-time curve of an embodiment of the present invention;

[0045] Figure 2 This is a schematic diagram of data processing according to an embodiment of the present invention;

[0046] Figure 3 This is a schematic diagram of the axial strain-time curves under different loading conditions according to an embodiment of the present invention;

[0047] Figure 4 A schematic diagram of the isochronous curves of deviatoric stress-axial strain in an embodiment of the present invention;

[0048] Figure 5 This is a schematic diagram of the isochronous curves of deviatoric stress-axial strain in an embodiment of the present invention;

[0049] Figure 6 This is a schematic diagram of the yield stress-time logarithmic curve of an embodiment of the present invention;

[0050] Figure 7 This is a schematic diagram illustrating the calculation of the long-term strength index in an embodiment of the present invention;

[0051] Figure 8 This is a schematic diagram of the determination method according to an embodiment of the present invention;

[0052] Figure 9 This is a graph showing the axial strain-time curve under a confining pressure of 100 kPa, according to an embodiment of the present invention.

[0053] Figure 10 This is a graph showing the axial strain-time curves under different loading conditions according to an embodiment of the present invention;

[0054] Figure 11 This is a diagram of the isochronous curves of deviatoric stress-axial strain in an embodiment of the present invention;

[0055] Figure 12 This is a logarithmic yield stress-time curve of an embodiment of the present invention;

[0056] Figure 13 This is a schematic diagram of the cross-section of the high-pile wharf-bank slope according to an embodiment of the present invention. Detailed Implementation

[0057] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0058] It should be noted that the use of terms such as "an embodiment," "an embodiment," "an exemplary embodiment," and "some embodiments" in the specification indicates that the described embodiment may include a specific feature, structure, or characteristic, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments (whether explicitly described or not) should be within the knowledge of those skilled in the art.

[0059] Generally, terms can be understood at least partly from their use in context. For example, depending at least partly on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in a singular sense, or a combination of features, structures, or characteristics in a plural sense. Additionally, the term "based on" can be understood not necessarily to convey an exclusive set of factors, but rather, alternatively, depending at least partly on the context, to allow for the presence of other factors that are not necessarily explicitly described.

[0060] like Figures 1-13 As shown, a method for determining soil properties to assess the long-term stability of port structure foundations includes the following steps:

[0061] (1) Conduct indoor triaxial creep tests:

[0062] The test soil should ideally be undisturbed soil representative of the port engineering structure foundation. Disturbance to the undisturbed soil should be minimized during storage and transportation. The undisturbed soil sample is cut into a cylindrical shape using a soil cutter for triaxial creep testing. Before the triaxial creep test, three conventional triaxial consolidated undrained compression tests are conducted under different confining pressures to determine the failure deviatoric stress of the undisturbed soil sample under different confining pressures. The confining pressure can be determined based on the overburden pressure at the corresponding depth of the undisturbed soil. When the deviatoric stress-axial strain curve has a peak point, the failure deviatoric stress is taken as the peak stress; when the deviatoric stress-axial strain curve does not have a peak point, the failure deviatoric stress is taken as the deviatoric stress at 15% of the axial strain.

[0063] The creep test is conducted under the same three confining pressures as the conventional triaxial compression test, using a consolidated undrained and graded loading method. The number of loading stages should not be less than 5, and the constant time of each deviatoric stress should not be less than 3 days. The loading rate of each deviatoric stress should be the same as the loading rate of the conventional triaxial compression test to determine the failure deviatoric stress, and the deviatoric stress should be kept constant after reaching the set deviatoric stress of each stage.

[0064] (2) Processing creep test data:

[0065] After the creep test is completed, a "stepped" axial strain-time curve can be obtained, such as... Figure 1 As shown, the axial strain-time curves obtained from staged loading are processed and converted into axial strain-time curves for each stage of deviatoric stress. During the conversion, the axial strain generated when each stage is loaded to a constant deviatoric stress must be considered, along with the influence of the previous stage's creep on the next stage's creep. When considering the axial strain generated when each stage is loaded to a constant deviatoric stress, the axial strain at the set deviatoric stress of each stage is taken as the initial axial strain of that stage. When considering the influence of the previous stage's creep on the next stage's creep, the axial strain growth rate at the end of the previous stage's creep test can be calculated. This rate is then extended to the next stage's axial strain-time curve, and the axial strain generated during the next stage's loading process is shifted upwards. The difference between the current stage's axial strain and the axial strain after the shift in the next stage's axial strain-time curve is calculated as the actual axial strain of that stage. After calculating the actual axial strain of each stage, each stage is shifted to the left to the position of its initial axial strain. The actual axial strain of that stage at different times is then added to the initial axial strain of each stage. A schematic diagram of the data processing is shown below. Figure 2 As shown.

[0066] (3) Determine the long-term yield stress:

[0067] Using the above data processing method, the axial strain-time curves for each level of deviatoric stress are obtained, as follows: Figure 3 As shown in the figure. The axial strain-time curves of each level of deviatoric stress are processed, and the axial strain and corresponding deviatoric stress at different times are selected to obtain the deviatoric stress-axial strain curves at different times, i.e., the deviatoric stress-axial strain isochronous curves. A schematic diagram of the deviatoric stress-axial strain isochronous curves is shown in the figure. Figure 4 As shown, the schematic diagram of the obtained isochronous curve of deviatoric stress-axial strain is as follows. Figure 5 As shown.

[0068] The yield point of the deviatoric stress-axial strain curve at different times is determined. The location of the yield point can be determined using the tangent method. Linear fitting is performed on low stress level points (such as the zero point and the first two stress levels) and high stress level points (such as the last three stress levels) at different times. The intersection of the two lines is defined as the yield point, and the deviatoric stress corresponding to the yield point is the yield stress of the soil at different times. By plotting the yield stress-time curve, a linear fit can be performed on the logarithmic coordinate system of yield stress-time to obtain the time-varying law of yield stress. The yield stress over a long period (e.g., 100 years) can be taken as the long-term yield stress. ,like Figure 6 As shown.

[0069] (4) Calculate the long-term shear strength index:

[0070] Based on the triaxial creep test results under three different confining pressures, deviatoric stress-axial strain isochronous curves were plotted under the three different confining pressures, and the yield stress under the three different confining pressures was obtained. The time-varying pattern determines the long-term yield stress under each confining pressure. The long-term yield stress under three different confining pressures As the long-term shear strength of soil under its respective confining pressure Substituting the long-term shear strength index—long-term cohesion—into the Mohr-Coulomb strength theory. and long-term internal friction angle A schematic diagram for calculating long-term shear strength parameters is shown below. Figure 7 As shown.

[0071] When calculating the long-term shear strength index, the relationship between long-term shear strength, long-term shear strength index, and confining pressure can be obtained according to the Mohr-Coulomb strength theory:

[0072] (1)

[0073] In equation (1), For long-term shear strength, the long-term yield stress obtained in the experiment is used. , For confining pressure, For long-term cohesion, This is the long-term internal friction angle.

[0074] Subtracting the long-term shear strength under different confining pressures yields:

[0075] (2)

[0076] In equation (2), Let be the difference between the long-term shear strength under high confining pressure and the long-term shear strength under low confining pressure for any two confining pressures. Let be the difference between the high and low confining pressures under any two confining pressures, with the other variables being the same as in equation (1). The long-term internal friction angle can be solved using equation (2). Substituting into equation (1) can determine the corresponding long-term cohesion. Three sets of long-term shear strength indices can be obtained under three confining pressures. The average of the three sets of long-term shear strength indices yields the final long-term shear strength index—long-term cohesion. and long-term internal friction angle .

[0077] (5) Assess the long-term stability of the foundation of the port structure:

[0078] Based on the long-term shear strength index obtained in step (4), the long-term cohesion is used. and long-term internal friction angle The long-term bearing capacity of the foundation of the port structure is calculated, and the long-term bearing capacity is compared and analyzed with the short-term bearing capacity to evaluate the long-term stability of the foundation of the port structure.

[0079] The invention will now be explained in detail through a series of practical experiments and examples, consisting of five steps:

[0080] (1) Conduct indoor triaxial creep tests:

[0081] The undisturbed soil used in this experiment was taken from marine soil near a port in my country. The soil was taken from 11.0 m below the mud surface. The basic physical properties of the undisturbed soil are shown in Table 1.

[0082] Table 1 Physical properties and mechanical parameters of undisturbed marine soil

[0083]

[0084] Three confining pressures were selected based on the depth of the undisturbed soil samples: 50 kPa, 100 kPa, and 150 kPa. Consolidated undrained triaxial compression tests were conducted on the undisturbed soil samples, yielding failure deviatoric stresses of 92 kPa, 174 kPa, and 219 kPa under the confining pressures of 50 kPa, 100 kPa, and 150 kPa, respectively. Consolidated undrained triaxial creep tests were then conducted on the undisturbed soil samples under the three confining pressures. A staged loading method was used, with the ratio of the deviatoric stress increment to the failure deviatoric stress being 0.15 times. A total of five loading stages were performed, with each stage's deviatoric stress held constant for 72 hours. The loading rate for each deviatoric stress stage was the same as in the triaxial compression test, and the deviatoric stress was kept constant after reaching the set deviatoric stress at each stage.

[0085] (2) Processing creep test data:

[0086] The axial strain-time curves were obtained according to the creep test method. The axial strain-time curve for a confining pressure of 100 kPa is shown below. Figure 9 As shown. The axial strain-time curves for the entire process are processed to obtain the axial strain-time curves under different loading conditions, as shown below. Figure 10 As shown. The process considers the axial strain generated when each stage of loading is applied to a constant deviatoric stress, and also takes into account the influence of the creep of the previous stage on the creep of the next stage.

[0087] (3) Determine the long-term yield stress:

[0088] Based on the axial strain-time curves under separate loading conditions, isochronous curves of deviatoric stress-axial strain were plotted at 0 h, 4 h, 12 h, 24 h, 36 h, 48 h, and 72 h. Figure 11 As shown. Linear fitting is performed on low-stress levels (zero point and the first two stress levels) and high-stress levels (the last three stress levels). The intersection of the two lines is defined as the yield point, and the deviatoric stress corresponding to the yield point is the yield stress of the soil at different times. Plot the logarithmic yield stress-time curves under different confining pressures to determine the long-term yield stress under different confining pressures, such as... Figure 12 As shown.

[0089] (4) Determination of long-term shear strength index:

[0090] Based on the long-term yield stress under three different confining pressures, three sets of long-term shear strength indices can be obtained through equations (1) and (2). The average of the three sets of long-term shear strength indices is taken as the final determined long-term shear strength index—long-term cohesion. and long-term internal friction angle The long-term cohesion was calculated. The long-term internal friction angle is 6.0 kPa. The value is 21.3°, and the calculation results are shown in Table 2.

[0091] Table 2 Calculation of Long-Term Shear Strength Parameters

[0092]

[0093] (5) Assess the long-term stability of the foundation of the port structure:

[0094] This paper uses a high-pile wharf as an example to illustrate the method of assessing the long-term stability of port structure foundations using long-term shear strength indices. A finite element model of the high-pile wharf-slope is established. The strength reduction method is used to calculate the safety factor using both short-term and long-term shear strength indices, thereby assessing the long-term stability of the foundation. The high-pile wharf is built on silty clay, and the wharf structure material is C40 concrete. The model material parameters are shown in Table 3, and the cross-section of the high-pile wharf-slope is shown in Table 3. Figure 13 As shown.

[0095] Table 3 Model Material Parameters

[0096]

[0097] When the calculation based on slope strength reduction fails to meet the convergence condition, the slope is considered unstable, and the strength reduction factor is used as the slope safety factor. Using short-term shear strength indices, the safety factor for the high-pile wharf slope is calculated to be 1.31. However, when using long-term shear strength indices, the model fails to converge, indicating instability of the high-pile wharf and a slope safety factor dropping below 1.00, demonstrating reduced long-term stability. Therefore, long-term shear strength indices must be used to analyze and make accurate judgments when assessing the long-term stability of port structure foundations.

[0098] The above results demonstrate the necessity of accurately determining the long-term shear strength index of soil for assessing the long-term stability of port structure foundations, highlighting the significance of this invention.

[0099] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, and procedures are not described in detail.

[0100] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for determining soil property indicators to assess the long-term stability of port engineering structure foundations, characterized in that, Includes the following steps: S1. Conduct indoor triaxial creep test: Select undisturbed soil samples representing the foundation of the port structure and conduct triaxial consolidated undrained compression test and creep test under three different confining pressures. Use graded loading, and keep the deviatoric stress constant for no less than 3 days at each stage. S2, Processing creep test data: Convert the axial strain-time curve of the whole process into the axial strain-time curve of each stage of deviatoric stress loading separately, and calculate the actual axial strain by considering the axial strain at the beginning of loading and the effect of the previous stage of creep. S3, Determine the long-term yield stress: Select different time points under each confining pressure to draw the deviatoric stress-axial strain isochronous curve, use the tangent method to determine the yield point, obtain the yield stress at different times under each confining pressure, and then fit to obtain the long-term yield stress under each confining pressure. S4, Calculate the long-term shear strength index: Substitute the long-term yield stress under each confining pressure as the long-term shear strength of the soil into the Mohr-Coulomb strength theory. For any two confining pressures, a set of long-term cohesion and long-term internal friction angle can be calculated. Take the average value of the long-term cohesion and long-term internal friction angle calculated in each set as the final long-term shear strength index. S5, Assess the long-term stability of the foundation of port engineering structures: Calculate the long-term bearing capacity of the foundation based on the long-term shear strength index and compare it with the short-term bearing capacity to assess the long-term stability of the foundation of port engineering structures. The determination of the long-term yield stress in S3 includes: S31, Extracting graded loading curves: Based on the results of processing creep test data, obtain the axial strain-time curves under different levels of deviatoric stress; S32, Constructing the deviatoric stress-axial strain isochronous curve: Select multiple different times under each confining pressure, extract the axial strain and corresponding deviatoric stress at different times under each confining pressure, and plot the deviatoric stress-axial strain isochronous curve at the corresponding time under each confining pressure. S33, Determine the yield point location: For each isochronous curve, the yield point is determined using the tangent method, including linear fitting of the low-stress and high-stress segments respectively. The intersection of the two fitted lines is the yield point at that time point, and the corresponding deviatoric stress is denoted as the yield stress. ; S34, Plot the yield stress-time curve: Plot the yield stress at different time points under each confining pressure. The yield stress-time curve was plotted and linearly fitted in a logarithmic time coordinate system to obtain the time-varying law of yield stress under each confining pressure. S35, Determine the long-term yield stress: Based on the yield stress-time curves under each confining pressure, select the yield stress value corresponding to the long-term action time as the long-term yield stress of the soil under each confining pressure. ; The parameters for calculating long-term shear strength in S4 include: S41, Set the yield stress to the shear strength: Calculate the long-term yield stress under each confining pressure. As the long-term shear strength of the soil under the corresponding confining pressure ; S42, Establish the Mohr-Coulomb strength relationship: Based on the Mohr-Coulomb strength theory, establish the relationship between long-term shear strength, long-term shear strength index and confining pressure; S43, Calculate the long-term internal friction angle: Select any two confining pressure conditions, subtract their corresponding long-term shear strengths, and calculate the difference. And solve for the long-term internal friction angle. ; S44, Calculate long-term cohesion: based on the solved long-term internal friction angle. Calculate the long-term cohesion under any two confining pressures. ; S45, Determine the final index: Calculate the three sets of long-term internal friction angles. and long-term cohesion The average value was taken as the final long-term shear strength index.

2. The method for determining soil properties for assessing the long-term stability of port engineering structure foundations according to claim 1, characterized in that, The indoor triaxial creep test in S1 includes: S11, Soil sample preparation: Select representative undisturbed soil from the foundation of the port structure, minimize disturbance during storage and transportation, and use a soil cutter to prepare the undisturbed soil into cylindrical samples. S12, Conventional triaxial compression test: Consolidated undrained triaxial compression test is carried out under three different confining pressures to obtain the deviatoric stress of failure under each confining pressure. If there is a peak point in the deviatoric stress-axial strain curve, the peak stress is taken as the deviatoric stress of failure. If there is no peak point, the deviatoric stress when the axial strain is 15% is taken as the deviatoric stress of failure. S13, Triaxial creep test setup: The creep test is conducted under the same three confining pressure conditions as the conventional triaxial compression test, using consolidation undrained conditions and graded loading. S14, Loading scheme: The number of graded loading stages shall not be less than 5. The loading rate of each stage of deviatoric stress shall be consistent with that of the conventional triaxial compression test. After reaching the set deviatoric stress, it shall be kept constant. The deviatoric stress of each stage shall be kept constant for no less than 3 days.

3. The method for determining soil properties for assessing the long-term stability of port engineering structure foundations according to claim 2, characterized in that, The creep test data in S2 includes: S21, Obtain the full-process curve: After the creep test is completed, obtain the step-time full-process curve of axial strain under graded loading conditions; S22, Curve Conversion: The entire process curve is segmented according to each stage of deviatoric stress loading and converted into axial strain-time curves under each stage of deviatoric stress loading. S23, Initial Axial Strain Correction: For each stage of deviatoric stress loading, the axial strain corresponding to the time when the set deviatoric stress is reached is taken as the initial axial strain value of that stage. S24, Correction for the influence of the previous stage: Calculate the axial strain growth rate at the end of the creep stage of the previous stage, and extend it to the next stage according to the rate. Shift the axial strain curve extended to the next stage upward as a whole to reflect the axial strain generated during the next stage of loading, so as to reflect the continuity of the previous stage. S25, Calculation of actual axial strain: By comparing the previous stage curve after extension and translation with the current stage curve, the difference is calculated as the actual axial strain of this stage; S26, Curve Translation and Synthesis: The actual axial strain at each level is translated to the left to its respective initial axial strain position, and the actual axial strain at each time moment is accumulated based on the initial axial strain value to obtain the corrected axial strain-time curves at each level.

4. The method for determining soil properties for assessing the long-term stability of port engineering structure foundations according to claim 1, characterized in that, The relationship between the long-term shear strength, the long-term shear strength index, and the confining pressure is expressed as follows: ； in, For long-term shear strength, For confining pressure, For long-term cohesion, This is the long-term internal friction angle.

5. The method for determining soil properties for assessing the long-term stability of port engineering structure foundations according to claim 4, characterized in that, The difference Represented as: ； in, Let be the difference between the long-term shear strength under high confining pressure and the long-term shear strength under low confining pressure for any two confining pressures. It represents the difference between the high confining pressure and the low confining pressure under any two confining pressures.

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