Method for evaluating stability of microorganism modified seabed foundation
Through the stability evaluation method of microbial modified seabed foundations, the stability coefficient is calculated using experiments and regression equations, the problem of difficulty in evaluating the stability of seabed foundations is solved, and the stability prediction and evaluation of seabed foundations in complex environments is achieved.
Patent Information
- Application Number
- CN202411901485.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-23
- Publication Date
- 2025-04-15
AI Technical Summary
The stability of seabed foundations is difficult to effectively evaluate under extreme environments and complex geological conditions. Especially in calcified sand seabed foundations, whether the stability of microorganisms after reinforcement can remain stable under complex stress conditions requires systematic evaluation.
A stability evaluation method for microbial modified seabed foundation was adopted, and the stability coefficient S was calculated and combined with the bulk strain relationship was established through microbial reinforcement test, normal biased stress drainage shear test, stress path curve analysis and regression equation.
This method can predict the development process of instability damage of microbial modified seabed foundations, provide scientific stability assessment, ensure the stability of seabed foundations in complex environments, and avoid structural instability.
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Figure CN119824960A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of marine engineering technology, and in particular to a stability evaluation method for a microbial modified seabed foundation. Background Art
[0002] The stability of the seabed foundation where the offshore new energy project infrastructure is located is very important, as it affects the safe and long-term operation of the supporting infrastructure of the offshore new energy project on the seabed. The extreme environment and complex geological conditions on the seabed, such as uneven soil, active geological processes, and strong currents and waves, may affect the stability of the seabed foundation where the new energy project infrastructure is located. In particular, the seabed foundation with poor geology is prone to breakage and dissolution when subjected to mechanical disturbance or environmental influences. These properties may lead to a decrease in the bearing capacity of the soil, and in severe cases, lead to instability of structures such as offshore wind turbines and photovoltaics.
[0003] In order to ensure the stability of the seabed foundation in areas with poor geological conditions, the seabed foundation needs to be modified and reinforced. Microbial induced calcium carbonate precipitation (MICP) technology is a reinforcement method jointly developed by the fields of geotechnical engineering and bioengineering. It is a green and environmentally friendly reinforcement technology that effectively improves soil strength and inhibits soil liquefaction damage. This technology is different from traditional reinforcement methods, which are often accompanied by high energy consumption and serious environmental pollution problems. MICP technology relies on specific microorganisms to combine with positively charged ions in nutrient solution through their metabolic processes to form a variety of mineral precipitates. Therefore, using microorganisms to reinforce the seabed foundation around infrastructure is an environmentally friendly and sustainable soil reinforcement solution.
[0004] For calcareous sand seabed foundation, due to the porous surface of calcareous sand particles and irregular shapes, the stability is poor. Whether the calcareous sand seabed foundation reinforced by microorganisms can serve stably under the complex stress conditions of the seabed requires a systematic evaluation of its stability. Summary of the invention
[0005] The purpose of the present invention is to provide a stability evaluation method for a microbially modified seabed foundation, which can predict and scientifically evaluate the development process of instability and destruction of the microbially modified seabed foundation, and provide an effective reference and evaluation basis for its stability evaluation.
[0006] As conceived above, the technical solution adopted by the present invention is:
[0007] A stability evaluation method for a microbial modified seabed foundation comprises: step 1: conducting a microbial reinforcement test on the calcareous sand seabed soil in the tested sea area, grouping the soil according to the number of reinforcements and the overlying deadweight pressure, wherein the number of reinforcements is a positive integer greater than or equal to 1; step 2: conducting a constant deviator stress drained shear test on each group of reinforced soil based on a standard path triaxial system; step 3: based on the test results of step 2, drawing a stress path curve for each group of soil with the effective average principal stress as the ordinate and the deviator stress as the abscissa, and determining the reinforcement failure line and crack development line of the soil on the stress path curve; the reinforcement failure line is a straight line passing through point D and point A, point D is the failure point of the reinforced seabed, and point A is the overlying load loading point of the seabed; the crack development line is a straight line passing through point C and point A, and point C is the starting point for the development of seabed cracks; step 4: for each group of soil, The failure line and the crack development line are fitted to obtain the function expressions of the reinforcement failure line and the crack development line. Based on the two expressions, the slope ki of the crack development line is divided by the slope kc of the reinforcement failure line to obtain the stability coefficient S = ki / kc of the calcareous sand seabed soil after microbial modification in the experiment; Step 5: For multiple groups of soils with the same number of reinforcements and different overlying deadweight pressures, the regression equation of the slope ki of the crack development line and the overlying deadweight pressure P is obtained, and the regression equation of the slope kc of the reinforcement failure line and the overlying deadweight pressure P is obtained; Step 6: According to the number of reinforcements in the actual project, the corresponding regression equation in step 5 is selected, and the overlying deadweight pressure in the actual project is substituted into the regression equation to predict the slope ki of the crack development line and the slope kc of the reinforcement failure line, and then the two slopes are divided to obtain the stability coefficient S of the calcareous sand seabed foundation after microbial modification in the actual project.
[0008] Preferably, based on the constant deviator stress drained shear test in step 2, the volume strain ε of each group of soil after reinforcement when the axial strain reaches 25% is obtained, and for multiple groups of soil with the same number of reinforcements and different overlying self-weight pressures, the functional relationship between the volume strain ε and the overlying self-weight pressure P is obtained.
[0009] Preferably, according to the number of reinforcements in the actual project, the functional relationship between the corresponding volume strain ε and the overlying deadweight pressure P is selected, and the overlying deadweight pressure in the actual project is substituted into the functional relationship to obtain the corresponding volume strain ε, and the volume strain ε is compared with the set volume strain value ε0 to determine whether the microbial reinforcement of the seabed meets the engineering reinforcement requirements.
[0010] Preferably, for the microbial modified calcareous sand seabed soil reinforced twice, the functional relationship between the volume strain ε and the overlying self-weight pressure P is ε=1.98788ln(P)-0.4957; for the microbial modified calcareous sand seabed soil reinforced four times, the functional relationship between the volume strain ε and the overlying self-weight pressure P is ε=0.9932ln(P)+3.9535.
[0011] Preferably, when the number of reinforcement times in an actual project is 2 and the overlying deadweight pressure is 125 kPa, the volume strain ε=1.98788ln(125)-0.4957=9.1%.
[0012] Preferably, the microbial reinforced seabed is divided into three stability levels in combination with the stability coefficient S and the volume strain ε; when the stability coefficient S is less than or equal to the engineering requirement coefficient and the volume strain ε is greater than or equal to the set volume strain value, the stability level is level I; when the stability coefficient S is less than or equal to the engineering requirement coefficient and the volume strain ε is less than the set volume strain value, or, the stability coefficient S is greater than the engineering requirement coefficient and the volume strain ε is greater than or equal to the set volume strain value, the stability level is level II; when the stability coefficient S is greater than the engineering requirement coefficient and the volume strain ε is less than the set volume strain value, the stability level is level III.
[0013] Preferably, the calcareous sand seabed corresponds to different overlying deadweight pressures at different depths, and the calculation formula for the overlying deadweight pressure is P=γ′h1+ρgh2; wherein P represents the overlying deadweight pressure; γ′ is the average buoyant weight of the overlying soil layer; ρ is the density of water; h1 is the thickness of the soil layer below the seabed; and h2 is the depth of seawater.
[0014] Preferably, in step 5, for the microbially modified calcareous sand seabed soil reinforced twice, the regression equation of the slope ki of the crack development line and the overlying self-weight pressure P is ki=0.0045P-1.604, and the regression equation of the slope kc of the reinforcement failure line and the overlying self-weight pressure P is kc=0.0043P-1.465.
[0015] Preferably, in step 6, when the number of reinforcement times in the actual project is 2 and the overlying self-weight pressure is 125 kPa, the slope of the crack development line ki = -1.0415, the slope of the reinforcement failure line kc = -0.9275, and the two slopes are divided to obtain the stability coefficient S = 1.123 of the calcareous sand seabed foundation after microbial modification in the actual project.
[0016] Preferably, in step 5, for the microbially modified calcareous sand seabed soil reinforced 4 times, the regression equation of the slope ki of the crack development line and the overlying self-weight pressure P is ki=0.0022P-1.636, and the regression equation of the slope kc of the reinforcement failure line and the overlying self-weight pressure P is kc=0.0023P-1.561.
[0017] Beneficial effects of the present invention:
[0018] The stability evaluation method of the microbial modified seabed foundation proposed in the present invention improves the strength and density of the calcareous sand after microbial reinforcement. The more times of reinforcement, the higher the strength and density of the seabed soil. When evaluating the stability, the influence of the number of reinforcements and the overlying deadweight pressure on the reinforcement effect is considered, so it is more in line with the actual working conditions. By determining the reinforcement failure line and crack development line of the soil on the stress path curve, and taking the quotient of the slopes of the two as the stability coefficient, this calculation method omits the complicated area calculation in the traditional evaluation and is more suitable for engineering applications. For multiple groups of soils with the same number of reinforcements and different overburden self-weight pressures, the regression equations of the slope ki of the crack development line and the overburden self-weight pressure P are obtained, and the regression equations of the slope kc of the reinforcement failure line and the overburden self-weight pressure P are obtained. In actual engineering, the corresponding regression equation can be directly selected according to the number of reinforcements, and the overburden self-weight pressure in the actual engineering is substituted into the regression equation to predict the slope ki of the crack development line and the slope kc of the reinforcement failure line. Then, the two slopes are divided to obtain the stability coefficient S of the calcareous sand seabed foundation after microbial modification in the actual engineering, which is convenient for application to engineering practice. The comprehensive evaluation of seabed stability is achieved by characterizing with quantitative indicators and combining different performance indicators of microbial modified seabed foundations under different reinforcement times and overburden self-weight pressures. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 is a schematic diagram of a stress path curve provided in this embodiment;
[0020] Figure 2 is a schematic diagram of the reinforcement failure line and crack development line of the reinforcement twice provided in this embodiment;
[0021] Figure 3 is a schematic diagram of the reinforcement failure line and crack development line after four reinforcements provided in this embodiment;
[0022] Figure 4 Schematic diagram of the relationship between volume strain and overlying deadweight pressure provided in this embodiment. DETAILED DESCRIPTION
[0023] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.
[0024] See also Figures 1 to 4 , this embodiment provides a stability evaluation method for a microbial modified seabed foundation, which is used to evaluate the stability of a seabed foundation reinforced by microorganisms.
[0025] The stability evaluation method of the microbial modified seabed foundation includes: step 1: conducting a microbial reinforcement test on the calcareous sand seabed soil in the tested sea area, and grouping the soil according to the number of reinforcements and the overlying deadweight pressure, and the number of reinforcements is a positive integer greater than or equal to 1; step 2: based on the standard path triaxial system, conducting a constant deviator stress drained shear test on each group of reinforced soil; step 3: based on the test results of step 2, a stress path curve is drawn for each group of soil with the effective average principal stress as the ordinate and the deviator stress as the abscissa, and the reinforcement failure line and crack development line of the soil are determined on the stress path curve; the reinforcement failure line is a straight line passing through point D and point A, point D is the failure point of the reinforced seabed, and point A is the overlying load loading point of the seabed; the crack development line is a straight line passing through point C and point A, and point C is the starting point for the development of seabed cracks; step 4: for each group of soil, the reinforcement failure line is a straight line passing through point C and point A, and point C is the starting point for the development of seabed cracks; The reinforcement failure line and the crack development line are fitted to obtain the functional expressions of the reinforcement failure line and the crack development line. Based on the two expressions, the slope ki of the crack development line is divided by the slope kc of the reinforcement failure line to obtain the stability coefficient S = ki / kc of the calcareous sand seabed soil after microbial modification in the experiment; Step 5: For multiple groups of soils with the same number of reinforcements and different overlying deadweight pressures, the regression equation of the slope ki of the crack development line and the overlying deadweight pressure P is obtained, and the regression equation of the slope kc of the reinforcement failure line and the overlying deadweight pressure P is obtained; Step 6: According to the number of reinforcements in the actual project, the corresponding regression equation in step 5 is selected, and the overlying deadweight pressure in the actual project is substituted into the regression equation to predict the slope ki of the crack development line and the slope kc of the reinforcement failure line, and then the two slopes are divided to obtain the stability coefficient S of the calcareous sand seabed foundation after microbial modification in the actual project.
[0026] For the seabed foundation reinforced by microorganisms, the strength and density of the reinforced calcareous sand are improved. The more times of reinforcement, the higher the strength and density of the seabed soil will be. When evaluating the stability, the influence of the number of reinforcements and the overlying deadweight pressure on the reinforcement effect is considered, so it is more in line with the actual working conditions. By determining the reinforcement failure line and crack development line of the soil on the stress path curve, and taking the quotient of the slopes of the two as the stability coefficient, this calculation method omits the complex area calculation in the traditional evaluation and is more suitable for engineering applications. For multiple groups of soils with the same number of reinforcements and different overburden self-weight pressures, the regression equations of the slope ki of the crack development line and the overburden self-weight pressure P are obtained, and the regression equations of the slope kc of the reinforcement failure line and the overburden self-weight pressure P are obtained. In actual engineering, the corresponding regression equation can be directly selected according to the number of reinforcements, and the overburden self-weight pressure in the actual engineering is substituted into the regression equation to predict the slope ki of the crack development line and the slope kc of the reinforcement failure line. Then, the two slopes are divided to obtain the stability coefficient S of the calcareous sand seabed foundation after microbial modification in the actual engineering, which is convenient for application to engineering practice. The comprehensive evaluation of seabed stability is achieved by characterizing with quantitative indicators and combining different performance indicators of microbial modified seabed foundations under different reinforcement times and overburden self-weight pressures.
[0027] In step 1, multiple groups of soil can be selected according to actual needs, and the soil can be grouped according to the number of reinforcements and the overburden self-weight pressure. The calcareous sand seabed at different depths corresponds to different overburden self-weight pressures, and the calculation formula for the overburden self-weight pressure is P = γ′h1 + ρgh2; where P represents the overburden self-weight pressure; γ′ is the average buoyancy of the overburden soil layer; ρ is the density of water; h1 is the thickness of the soil layer below the seabed; and h2 is the depth of seawater.
[0028] In this embodiment, a total of 10 groups of soil bodies are selected, of which 5 groups of soil bodies are reinforced twice, and the corresponding overlying self-weight pressures are 50kPa, 100kPa, 150kPa, 200kPa and 250kPa respectively; the other 5 groups of soil bodies are reinforced 4 times, and the corresponding overlying self-weight pressures are 50kPa, 100kPa, 150kPa, 200kPa and 250kPa respectively.
[0029] In step 3, if Figure 1 As shown in the figure, point A is the loading point of the seabed overburden load, point B is the completion point of the shear load loading, point C is the starting point of the seabed crack development, and point D is the failure point of the reinforced seabed. The coordinates of each point are obtained in the test with the effective average principal stress as the ordinate and the deviator stress as the abscissa.
[0030] The reinforcement failure line is a straight line passing through points D and A, and the crack development line is a straight line passing through points C and A. Under different reinforcement times, different overlying deadweight pressures correspond to different stress path curves, and the corresponding reinforcement failure lines and crack development lines are also different.
[0031] Since the coordinates of points A, C, and D are all known, it is easy to obtain the functional expressions of the reinforcement failure line and the crack development line in step 4. Based on the two expressions, the slope ki of the crack development line is divided by the slope kc of the reinforcement failure line to obtain the stability coefficient S = ki / kc of the calcareous sand seabed soil after microbial modification in the experiment; this calculation method omits the complicated area calculation in traditional evaluation and is more suitable for engineering applications.
[0032] In step 5, for the microbial modified calcareous sand seabed soil with two reinforcement times, the regression equation of the slope ki of the crack development line and the overlying self-weight pressure P is ki = 0.0045P-1.604, and the regression equation of the slope kc of the reinforcement failure line and the overlying self-weight pressure P is kc = 0.0043P-1.465. Figure 2 As shown in the figure, for the five groups of soils reinforced twice, with the increase of the overlying deadweight pressure, the slope ki of the crack development line gradually increases, and the slope kc of the reinforcement failure line gradually increases. The point values obtained from the five groups of soils are fitted to obtain the corresponding regression equation.
[0033] For the microbial modified calcareous sand seabed soil with four reinforcement times, the regression equation of the slope ki of the crack development line and the overlying self-weight pressure P is ki = 0.0022P-1.636, and the regression equation of the slope kc of the reinforcement failure line and the overlying self-weight pressure P is kc = 0.0023P-1.561. Figure 3 As shown in the figure, for the five groups of soils reinforced four times, with the increase of the overlying deadweight pressure, the slope ki of the crack development line gradually increases, and the slope kc of the reinforcement failure line gradually increases. The point values obtained from the five groups of soils are fitted to obtain the corresponding regression equation.
[0034] In step 6, when the number of reinforcements in the actual project is 2 and the overlying deadweight pressure is 125 kPa, the slope of the crack development line is ki = -1.0415, and the slope of the reinforcement failure line is kc = -0.9275. Dividing the two slopes, the stability coefficient S = 1.123 of the calcareous sand seabed foundation after microbial modification in the actual project is obtained.
[0035] For example, if the difference between the stability coefficient and the engineering requirement coefficient S0 is within the set range, it means that the microbial reinforcement is effective and meets the requirements, and the seabed bearing capacity can meet the engineering needs; if the difference between the stability coefficient and the engineering requirement coefficient S0 is not within the set range, it means that the engineering needs cannot be met.
[0036] Based on the constant deviator stress drained shear test in step 2, the volume strain ε of each group of reinforced soils when the axial strain reaches 25% is obtained. For multiple groups of soils with the same number of reinforcements and different overlying deadweight pressures, the functional relationship between the volume strain ε and the overlying deadweight pressure P is obtained. When the axial strain of the soil reaches 25%, it is considered that the seabed collapses and becomes unstable under the action of the overlying structure. The volume strain ε at this time is the volume strain of the seabed instability. Through the functional relationship between the volume strain ε and the overlying deadweight pressure P, the volume strain of the seabed when it collapses and becomes unstable is predicted according to different overlying deadweight pressures. Since it does not involve specific time, the instability of the seabed can be predicted only by monitoring the volume strain, which is more practical in engineering applications.
[0037] According to the number of reinforcements in actual projects, the functional relationship between the corresponding volume strain ε and the overlying deadweight pressure P is selected, and the overlying deadweight pressure in the actual project is substituted into the functional relationship to obtain the corresponding volume strain ε. The volume strain ε is compared with the set volume strain value ε0 to determine whether the microbial reinforcement seabed meets the engineering reinforcement requirements.
[0038] like Figure 4 As shown in the figure, for the microbial modified calcareous sand seabed soil with two reinforcement times, the functional relationship between the volume strain ε and the overlying self-weight pressure P is ε=1.98788ln(P)-0.4957; for the microbial modified calcareous sand seabed soil with four reinforcement times, the functional relationship between the volume strain ε and the overlying self-weight pressure P is ε=0.9932ln(P)+3.9535.
[0039] When the number of reinforcements in actual engineering is 2 and the overlying deadweight pressure is 125 kPa, the volume strain ε=1.98788ln(125)-0.4957=9.1%.
[0040] As shown in the comprehensive evaluation table of stability levels in Table 1 below, the microbial reinforced seabed is divided into three stability levels by combining the stability coefficient S and the volume strain ε.
[0041] Stability level Volume strain ε is less than ε0 Volume strain ε is greater than or equal to ε0 Stability coefficient S is less than or equal to S0 II I Stability coefficient S is greater than S0 III II
[0042] When the stability coefficient S is less than or equal to the engineering requirement coefficient S0 and the body strain ε is greater than or equal to the set body strain value εO, the stability level is level I; when the stability coefficient S is less than or equal to the engineering requirement coefficient S0 and the body strain ε is less than the set body strain value ε0, or, the stability coefficient S is greater than the engineering requirement coefficient S0 and the body strain ε is greater than or equal to the set body strain value ε0, the stability level is level II; when the stability coefficient S is greater than the engineering requirement coefficient S0 and the body strain ε is less than the set body strain value ε0, the stability level is level III.
[0043] By combining the stability coefficient of microbial modification with the volume strain, a comprehensive grade evaluation of the reinforcement effect is conducted to determine whether the reinforcement effect meets the requirements. A stability grade of I indicates that the reinforced seabed is very stable and is suitable for engineering needs with a water depth of more than 1000m or a durability of more than 100 years. A stability grade of II indicates that the reinforced seabed is relatively stable and is suitable for engineering needs with a water depth of less than 1000m or a durability of 50-100 years. A stability grade of III indicates that the reinforced seabed is unstable and cannot meet engineering needs.
[0044] The above embodiments are only to illustrate the basic principles and characteristics of the present invention. The present invention is not limited by the above embodiments. Without departing from the spirit and scope of the present invention, the present invention may be subject to various changes and modifications, which are within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.
Claims
1. A method for evaluating the stability of a microbial modified seabed foundation, characterized in that: include: Step 1: Conduct a microbial reinforcement test on the calcareous sand seabed soil in the test area, and group the soil according to the number of reinforcements and the overlying deadweight pressure. The number of reinforcements is a positive integer greater than or equal to 1; Step 2: Based on the standard path triaxial system, a constant deviator stress drained shear test is performed on each group of reinforced soils; Step 3: Based on the test results of step 2, a stress path curve is drawn for each soil group with the effective average principal stress as the ordinate and the deviator stress as the abscissa, and the reinforcement failure line and crack development line of the soil are determined on the stress path curve; The reinforcement failure line is a straight line passing through point D and point A, point D is the failure point of the reinforced seabed, and point A is the loading point of the seabed overburden load; The crack development line is a straight line passing through point C and point A, and point C is the starting point of the seabed crack development; Step 4: For each group of soil, the reinforcement failure line and the crack development line are fitted to obtain the functional expressions of the reinforcement failure line and the crack development line. Based on the two expressions, the slope ki of the crack development line is divided by the slope kc of the reinforcement failure line to obtain the stability coefficient S = ki / kc of the calcareous sand seabed soil after microbial modification in the experiment; Step 5: For multiple groups of soils with the same number of reinforcements and different overlying deadweight pressures, obtain the regression equation of the slope ki of the crack development line and the overlying deadweight pressure P, and obtain the regression equation of the slope kc of the reinforcement failure line and the overlying deadweight pressure P; Step 6: Select the regression equation corresponding to step 5 according to the number of reinforcements in the actual project, and substitute the overlying deadweight pressure in the actual project into the regression equation to predict the slope ki of the crack development line and the slope kc of the reinforcement failure line. Then divide the two slopes to obtain the stability coefficient S of the calcareous sand seabed foundation after microbial modification in the actual project.
2. The method for evaluating the stability of a microbial modified seabed foundation according to claim 1, characterized in that: Based on the constant deviator stress drained shear test in step 2, the volume strain ε of each group of soil after reinforcement when the axial strain reaches 25% is obtained. For multiple groups of soil with the same number of reinforcements and different overlying self-weight pressures, the functional relationship between the volume strain ε and the overlying self-weight pressure P is obtained.
3. The method for evaluating the stability of a microbial modified seabed foundation according to claim 2, characterized in that: According to the number of reinforcements in actual projects, the functional relationship between the corresponding volume strain ε and the overlying deadweight pressure P is selected, and the overlying deadweight pressure in the actual project is substituted into the functional relationship to obtain the corresponding volume strain ε. The volume strain ε is compared with the set volume strain value ε0 to determine whether the microbial reinforcement seabed meets the engineering reinforcement requirements.
4. The method for evaluating the stability of a microbial modified seabed foundation according to claim 3, characterized in that: For the microbial modified calcareous sand seabed soil with two reinforcement times, the functional relationship between the volume strain ε and the overlying deadweight pressure P is ε=1.98788ln(P)-0.4957; For the microbially modified calcareous sand seabed soil reinforced four times, the functional relationship between the volume strain ε and the overlying deadweight pressure P is ε=0.9932ln(P)+3.9535.
5. The method for evaluating the stability of a microbial modified seabed foundation according to claim 4, characterized in that: When the number of reinforcements in actual engineering is 2 and the overlying deadweight pressure is 125 kPa, the volume strain ε=1.98788ln(125)-0.4957=9.1%.
6. The method for evaluating the stability of a microbial modified seabed foundation according to claim 2, characterized in that: Combining the stability coefficient S and the volume strain ε, the microbial reinforced seabed is divided into three stability levels; When the stability coefficient S is less than or equal to the engineering requirement coefficient and the volume strain ε is greater than or equal to the set volume strain value, the stability level is level I; When the stability coefficient S is less than or equal to the engineering requirement coefficient and the body strain ε is less than the set body strain value, or the stability coefficient S is greater than the engineering requirement coefficient and the body strain ε is greater than or equal to the set body strain value, the stability level is II; When the stability coefficient S is greater than the engineering requirement coefficient and the volume strain ε is less than the set volume strain value, the stability level is III.
7. The method for evaluating the stability of a microbial modified seabed foundation according to claim 1, characterized in that: The calcareous sand seabed at different depths corresponds to different overlying deadweight pressures. The calculation formula for the overlying deadweight pressure is P=γ′h1+ρgh2; where P represents the overlying deadweight pressure; γ′ is the average buoyant weight of the overlying soil layer; ρ is the density of water; h1 is the thickness of the soil layer below the seabed; and h2 is the depth of seawater.
8. The method for evaluating the stability of a microbial modified seabed foundation according to any one of claims 1 to 7, characterized in that: In step 5, for the microbially modified calcareous sand seabed soil reinforced twice, the regression equation of the slope ki of the crack development line and the overlying self-weight pressure P is ki=0.0045P-1.604, and the regression equation of the slope kc of the reinforcement failure line and the overlying self-weight pressure P is kc=0.0043P-1.
465.
9. The method for evaluating the stability of a microbial modified seabed foundation according to claim 8, characterized in that: In step 6, when the number of reinforcements in the actual project is 2 and the overlying deadweight pressure is 125 kPa, the slope of the crack development line is ki = -1.0415, and the slope of the reinforcement failure line is kc = -0.9275. Dividing the two slopes, the stability coefficient S = 1.123 of the calcareous sand seabed foundation after microbial modification in the actual project is obtained.
10. The method for evaluating the stability of a microbial modified seabed foundation according to any one of claims 1 to 7, characterized in that: In step 5, for the microbially modified calcareous sand seabed soil that has been reinforced four times, the regression equation between the slope ki of the crack development line and the overlying self-weight pressure P is ki=0.0022P-1.636, and the regression equation between the slope kc of the reinforcement failure line and the overlying self-weight pressure P is kc=0.0023P-1.561.