Soft soil foundation pit uplift resistance stability analysis method for static liquefaction instability of confined water sand layer

Abstract

The invention discloses a soft soil foundation pit upheaval resistance stability analysis method for static liquefaction instability of a confined water sand layer, and belongs to the field of soft soil underground engineering. The soft soil foundation pit upheaval resistance stability analysis method comprises the steps that foundation pit geometric parameters, soil mass mechanical parameters and hydrogeological parameters are obtained; monitoring the second-order work change of a soil body through a consolidation undrained triaxial shear test, and when the second-order work is converted from a positive value to a negative value, judging that the confined water sand layer has a static liquefaction instability risk; based on the corrected limit equilibrium theory, an anti-upheaval stability calculation model considering the static liquefaction weakening effect is constructed, and the foundation pit safety coefficient is calculated through strength reduction iteration; and stage treatment is executed according to the foundation pit safety coefficient threshold value. Scientific basis is provided for formulating a reasonable supporting structure form and a construction process, and potential safety hazards caused by neglecting the liquefaction effect in a traditional method are effectively avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of soft soil underground engineering, and in particular relates to a soft soil foundation pit anti-uplift stability analysis method for static liquefaction instability of a confined water-sand layer. Background Art

[0002] In deep foundation pit projects in soft soil areas, the existing technology generally uses the pressure balance method for anti-uplift stability analysis. This method, based on the principle of static equilibrium between the deadweight of the soil at the bottom of the pit and the pressure of the confined water, determines the safety factor by calculating the ratio of the soil's resistance to the buoyancy. By simplifying the soil mechanics model and incorporating basic parameters such as the pit geometry, soil density, and pore water pressure, it enables rapid stability assessment. Under conventional ground conditions, it offers the advantages of clear concepts and simple calculations.

[0003] However, the existing pressure balance method has significant defects: first, it does not consider the static liquefaction instability mechanism of the confined water-sand layer, and ignores the sudden drop in shear strength of the soil due to energy dissipation imbalance during triaxial shear; second, it is unable to quantify the progressive failure effect of the pit bottom induced by liquefaction, resulting in inaccurate assessment of the reduction of the soil lateral pressure coefficient and the strength weakening effect; third, there are systematic deviations in the calculation of the safety factor. Especially under complex working conditions with high-head confined sand layers, the traditional method is difficult to truly reflect the actual safety reserve of the foundation pit because it does not couple the liquefaction judgment criterion with the progressive failure model. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention proposes a soft soil foundation pit anti-uplift stability analysis method for static liquefaction instability of confined water-sand layer, so as to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a method for analyzing the anti-uplift stability of a soft soil foundation pit in response to static liquefaction instability of a confined water-sand layer, comprising:

[0006] Obtain foundation pit geometric parameters, soil mechanical parameters and hydrogeological parameters;

[0007] Based on the foundation pit geometric parameters, soil mechanical parameters, and hydrogeological parameters, a consolidated undrained triaxial shear test is performed to monitor the change in the soil's second-order work. When the second-order work changes from a positive value to a negative value, it is determined that the confined water-sand layer is at risk of static liquefaction instability.

[0008] Based on the modified limit equilibrium theory, a calculation model for anti-uplift stability considering the static liquefaction weakening effect is constructed, and the safety factor of the foundation pit is calculated through strength reduction iteration.

[0009] Gradual processing is performed according to the foundation pit safety factor threshold; if the foundation pit safety factor is ≥1, construction is allowed; if the foundation pit safety factor is <1, the excavation depth is adjusted, base reinforcement or liquefaction suppression measures are implemented, and the process is re-executed until the safety standards are met.

[0010] Preferably, the foundation pit geometric parameters include foundation pit length and foundation pit width;

[0011] The soil mechanical parameters include static earth pressure coefficient, passive earth pressure coefficient, effective cohesion, and internal friction angle;

[0012] The hydrogeological parameters include pore water pressure and the distance from the pit bottom to the calculation point.

[0013] Preferably, the process of monitoring the change of the second-order work of soil through the consolidated undrained triaxial shear test includes:

[0014] Real-time monitoring of axial stress, radial stress and strain rate through consolidated undrained triaxial shear test;

[0015] A second-order work dynamic curve is calculated according to the axial stress, the radial stress, and the strain rate, and static liquefaction instability determination is triggered when the axial strain meets a critical strain threshold.

[0016] Preferably, the critical strain threshold value ranges from 1% to 3%.

[0017] Preferably, the formula for constructing the anti-heave stability calculation model considering the static liquefaction weakening effect includes:

[0018] Calculation method of reduced lateral pressure coefficient:

[0019]

[0020] The safety factor calculation formula is:

[0021]

[0022] Among them, B2 is the width of the foundation pit; K p,SSR , K 0,SSR is the reduced lateral pressure coefficient; γ sat is the saturated weight of soil above the confined water layer; z is the distance from the pit bottom to the calculation point; c' and are the effective cohesion and internal friction angle of soil, respectively; p w is the water pressure of the confined aquifer; D is the burial depth of the retaining structure above the top surface of the confined aquifer; t is the distance from the top surface of the confined aquifer to the bottom of the retaining structure.

[0023] Preferably, adjusting the excavation depth includes:

[0024] Dynamically reduce layered excavation thickness based on real-time monitoring data;

[0025] Re-obtain soil parameters and iteratively calculate the foundation pit safety factor until the foundation pit safety factor is ≥1.

[0026] Preferably, the substrate reinforcement includes any one of the following measures:

[0027] High-pressure jet grouting piles are used to form a composite foundation;

[0028] Injecting nano-silicate slurry to improve sand layers;

[0029] Verify the parameters of the reinforced soil through lateral pressure test or static penetration test.

[0030] Preferably, the liquefaction suppression measures include any of the following operations:

[0031] Lay out a dewatering well system to lower the pressure head to 0.5-1.0m below the bottom of the sand layer;

[0032] Add underground continuous walls to prevent the expansion of the liquefaction area.

[0033] In a second aspect, the present invention further discloses a computer-readable storage medium having a computer program stored thereon, which implements the steps of the method described in the first aspect when executed by a processor.

[0034] In a third aspect, the present invention further discloses a computer program product, comprising a computer program, which implements the steps of the method described in the first aspect when executed by a processor.

[0035] Compared with the prior art, the present invention has the following advantages and technical effects:

[0036] The present invention provides a soft soil foundation pit anti-uplift stability analysis method for static liquefaction instability of a confined water-sand layer, comprising: first, obtaining foundation pit geometric parameters, soil mechanical parameters and hydrogeological parameters; second, based on the foundation pit geometric parameters, soil mechanical parameters and hydrogeological parameters, monitoring the change of the second-order work of the soil through a consolidation undrained triaxial shear test, and when the second-order work changes from a positive value to a negative value, it is determined that the confined water-sand layer has a risk of static liquefaction instability; then, based on the modified limit equilibrium theory, constructing an anti-uplift stability calculation model considering the static liquefaction weakening effect, and iteratively calculating the foundation pit safety factor through strength reduction; finally, performing graded processing according to the foundation pit safety factor threshold; if the foundation pit safety factor is ≥1, construction is allowed; if the foundation pit safety factor is <1, adjusting the excavation depth, implementing base reinforcement or liquefaction suppression measures, and re-execution until the safety standard is met.

[0037] The method of the present invention fully considers the mechanism of the anti-uplift stability of the confined water-sand layer under static liquefaction conditions on the bottom of the foundation pit, makes up for the defect of the traditional pressure balance method that ignores such influence, accurately reflects the influence of the static liquefaction of the confined water-sand layer on the uplift stability of the foundation pit, thereby significantly improving the accuracy of stability analysis.

[0038] The present invention systematically introduces the liquefaction judgment criterion and the progressive failure model, so that the calculation results are closer to the actual engineering stress characteristics than the traditional method, improves the calculation reliability of the anti-uplift safety factor, improves the accuracy of the judgment of the actual safety factor, and improves the credibility of the design parameters.

[0039] The anti-uplift stability analysis of foundation pits using the method of the present invention can identify in advance the adverse working conditions that may be caused by liquefaction, provide a scientific basis for formulating reasonable support structure forms and construction processes, enhance the scientificity and controllability of the deep foundation pit design stage, and effectively avoid the safety hazards caused by traditional methods that ignore the liquefaction effect.

[0040] The present invention is not only applicable to conventional soft soil layers, but also can adapt to stability analysis under complex geological conditions such as pressurized water-sand layers, and has a wide range of applicability and engineering practical value.

[0041] Through in-depth analysis of the liquefaction-inducing mechanism and anti-heave process, the present invention helps to formulate more targeted engineering monitoring and emergency measures, and improve the safety and controllability of the entire foundation pit construction process from the source. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0043] Figure 1 This is a flow chart of an analysis of the anti-uplift stability of a foundation pit for static liquefaction instability of a confined water-sand layer according to an embodiment of the present invention;

[0044] Figure 2 Schematic diagram of stress-strain curve of static liquefaction instability of confined sand layer in triaxial isotropic consolidation undrained shear test according to an embodiment of the present invention;

[0045] Figure 3 This is a diagram showing the variation of the second-order work of static liquefaction instability triggered by a confined water-sand layer according to an embodiment of the present invention, wherein the critical instability point is marked as the point where the axial strain ε is 3.74%;

[0046] Figure 4 A schematic diagram of a foundation pit anti-uplift force balance model according to an embodiment of the present invention, including a foundation pit cross-section and soil layer distribution;

[0047] Figure 5 Schematic diagram of a hierarchical assessment model for foundation pit construction safety based on the static liquefaction instability characteristics of confined water-sand layers according to an embodiment of the present invention;

[0048] Among them, 1. Surface fill layer; 2. Clay layer; 3. Foundation pit retaining structure; 4. Pressure-bearing water-bearing sand layer; 5. Deep clay layer; 6. Foundation pit bottom; 7. Real-time monitoring system; 8. Base reinforcement; 9. Finite element three-dimensional simulation; 10. Pressure head; 11. Bottom of aquiclude; 12. Pore pressure of aquiclude; 13. Foundation pit excavation boundary. DETAILED DESCRIPTION

[0049] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0050] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0051] Example 1

[0052] like Figure 1 As shown, this embodiment provides a method for analyzing the anti-uplift stability of a soft soil foundation pit for static liquefaction instability of a confined water-sand layer, including:

[0053] Step 1: Obtain foundation pit geometric parameters, soil mechanical parameters and hydrogeological parameters;

[0054] The foundation pit length B1, foundation pit width B2, static earth pressure coefficient K0, passive earth pressure coefficient K p , pore water pressure u, distance z from the pit bottom to the calculation point, effective cohesion c' and internal friction angle of the soil

[0055] Extract key parameters based on geological survey report and foundation pit design documents, including foundation pit geometric dimensions (foundation pit length B1, foundation pit width B2), soil mechanical properties (effective cohesion c' and internal friction angle ), static earth pressure coefficient K0, passive earth pressure coefficient K p , pore water pressure u, and the distance z from the pit bottom to the calculation point are used to construct the initial parameter system for foundation pit stability analysis.

[0056] Specifically, the static earth pressure coefficient K0 reflects the proportional relationship between the horizontal earth pressure and the vertical earth pressure generated by the deadweight of the soil in its natural state; the passive earth pressure coefficient K pIt describes the ratio between the passive earth pressure and the vertical earth pressure generated when the soil is subjected to external compression (such as displacement of the foundation pit support structure).

[0057] In addition, the pore water pressure u, as the pressure borne by the pore water in the soil, directly affects the effective stress state of the soil, and thus affects the shear strength and stability of the soil.

[0058] After determining the above basic parameters, we must also pay attention to the vertical distance z from the pit bottom to the specific calculation point. This distance is important for calculating the stress state and deformation characteristics of the soil at that point. At the same time, the effective cohesion c' and internal friction angle of the soil are As two key indicators of soil shear strength, they directly determine the shear failure characteristics and overall stability of the soil.

[0059] After the above parameters are extracted, cross-validation is required to ensure data consistency. For example, the in-situ test data in the geological survey report is compared with the laboratory calibration results. If the deviation exceeds 5%, recalibration is required.

[0060] Step 2: Based on the foundation pit geometric parameters, soil mechanical parameters, and hydrogeological parameters, a consolidated undrained triaxial shear test is performed to monitor the change in the soil's second-order work. When the second-order work changes from a positive value to a negative value, it is determined that the confined water-sand layer is at risk of static liquefaction instability.

[0061] Furthermore, static liquefaction instability judgment:

[0062] Calculate and determine whether the confined water-sand layer is in a state of static liquefaction instability. Obtain the stress-strain response curve of the saturated sand through a consolidated undrained triaxial shear test. Combined with the second-order work principle, dynamically monitor the evolution of the second-order work during loading. If the second-order work changes from positive to negative under a specific stress path, the confined water-sand layer is determined to be at risk of static liquefaction instability and needs to be included in the subsequent stability analysis model.

[0063] Specifically, in order to predict static liquefaction, the present invention constructs a set of static liquefaction instability judgment criteria for soil materials based on the second-order work principle. Based on the principle of conservation of energy, it is pointed out that in the process of soil stress, if there is a certain loading path that causes the second-order work (that is, the increment of work with the further change of strain) to become negative, it indicates that the sand may experience static liquefaction instability under this specific stress path, resulting in a sharp drop in shear strength. This reflects the deformation response of the soil under stress. If and only if there is a non-zero strain increment, if the second-order work becomes negative, it indicates that the soil is in an unstable state and there is a risk of static liquefaction.

[0064] In actual engineering, the above theoretical formula can be used to determine the following steps for static liquefaction identification of confined sand layers. The specific implementation process is as follows:

[0065] (1) Soil sample preparation and testing: Collect representative soil samples from the foundation pit bearing sand layer (such as Figure 2 As shown in the figure, saturated sand samples were prepared and consolidated undrained triaxial shear tests were carried out. The confining pressure σ'3 and axial loading rate were controlled, and the axial stress σ'1 and axial strain ε were monitored in real time. a and pore water pressure u.

[0066] (2) Second-order work calculation and analysis: Based on the test data, the instantaneous value of the second-order work during loading is calculated and W2-axial strain ε is plotted. a Curve (such as Figure 3 If W2 < 0 at a certain strain stage, it is determined that the sand has undergone static liquefaction instability.

[0067] (3) Parameter correction: When static liquefaction is triggered, the shear strength of the sand layer is significantly weakened, and the corrected internal friction angle corresponding to the static liquefaction instability triggering state needs to be used. Replace the original parameters to conservatively evaluate the anti-uplift stability and ensure the overall safety of the foundation pit.

[0068] Case data of instability of confined water-sand layer Figure 3 As shown, it can be seen that when the axial strain ε a When W2 is >3.74%, it turns from positive to negative, indicating that static liquefaction instability is triggered. At this time, the corrected internal friction angle The shear strength is reduced by about 33%, which significantly affects the safety factor calculation results.

[0069] Step 3: Based on the modified limit equilibrium theory, a calculation model for anti-uplift stability considering the static liquefaction weakening effect is constructed, and the foundation pit safety factor is calculated through strength reduction iteration;

[0070] Furthermore, based on the modified limit equilibrium theory, considering the weakening effect of soil shear strength caused by static liquefaction, an anti-uplift stability calculation model was constructed to derive the foundation pit safety factor F s The analytical expression of is obtained. Through numerical simulation and multi-condition parameter sensitivity analysis, the adaptability of the analytical method to complex hydrogeological conditions is verified.

[0071] like Figure 4 As shown in the figure, in order to more comprehensively evaluate the response of the soil layer under external loads, the anti-heave safety factor F of the foundation pit will be calculated based on the overall force balance and strength reduction principle. s , the anti-heave soil is regarded as a continuous medium, and it is assumed that the soil satisfies the static equilibrium condition in the critical state. At this time, the shear strength F τ , the total weight of the foundation pit soil G and the pressure water pressure P are in balance. τ If +G is insufficient to resist P, the foundation pit is at risk of instability due to heave, and appropriate reinforcement measures need to be taken to improve its stability.

[0072] To simplify the analysis and ensure the practicality of the results, the pore-water pressure is calculated as if the phreatic level within the pit is located at the bottom surface. To further simplify the calculation, it is assumed that there is no vertical seepage between the confined aquifer and the aquitard. Based on this assumption, it can be inferred that the confined water pressure has no direct impact on the pore-water pressure distribution in the aquitard. Therefore, the pore-water pressure within the confined sand layer can be calculated as hydrostatic pressure, which depends solely on water depth and water density. The effect of seepage on pore pressure caused by the difference in phreatic level between the inside and outside of the foundation pit can be ignored.

[0073] Furthermore, the anti-uplift safety factor is calculated based on the strength reduction principle. Based on the strength reduction principle, the reduction factor F is introduced. r The effective shear strength parameters c' and Make corrections and construct the critical state equation. Increase F gradually through iteration method. r , when the left side of the equation is equal to zero, the corresponding F r That is the safety factor F s Under the plane strain assumption (the pit length B1 approaches infinity), the three-dimensional stress state can be simplified to a two-dimensional problem, significantly reducing the computational complexity. According to the definition of limit in mathematics, the term can be simplified to Unreduced side pressure coefficient K p , K0, the safety factor calculation formula can be rewritten as:

[0074]

[0075] On the reduced side pressure coefficient K p When K0 is 0.0000, the safety factor expression can be further simplified to Equation (2), which combines integral operations to quantify the contribution of shear strength and confined water pressure within different depth ranges. Under certain conditions, the shear strength of the soil will gradually decrease with the increase of external load. In this case, it is necessary to reduce the lateral pressure coefficient accordingly to reflect the strength weakening effect. The safety factor calculation formula can be rewritten as:

[0076]

[0077] Among them, B2 is the width of the foundation pit; K p,SSR , K 0,SSR is the reduced lateral pressure coefficient; γ sat is the saturated weight of soil above the confined water layer; z is the distance from the pit bottom to the calculation point; c' and are the effective cohesion and internal friction angle of soil, respectively; p w is the water pressure of the confined aquifer; D is the depth of the retaining structure above the top of the confined aquifer; t is the distance from the top of the confined aquifer to the bottom of the retaining structure. If the retaining structure enters the confined aquifer, take t = 0.

[0078] The calculation method of the reduced lateral pressure coefficient is shown in formulas (3) and (4):

[0079]

[0080] Step 4: Perform graded processing according to the foundation pit safety factor threshold; if the foundation pit safety factor is ≥1, construction is allowed; if the foundation pit safety factor is <1, adjust the excavation depth, implement base reinforcement or liquefaction suppression measures, and re-execute until the safety standards are met.

[0081] Furthermore, based on the foundation pit anti-uplift safety factor F calculated in step 3, s , and evaluate the safety of foundation pit against uplift.

[0082] like Figure 5 As shown in the figure, a schematic diagram of the hierarchical assessment model for foundation pit construction safety based on the static liquefaction instability characteristics of the confined water-bearing sand layer is shown. The entire model consists of the surface fill layer 1, the clay layer 2, the confined water-bearing sand layer 4 and the deep clay layer 5 from top to bottom, forming a typical layered geological structure of a deep foundation pit in a soft soil area.

[0083] The surface fill layer 1 and the underlying clay layer 2 together form the overburden that must be penetrated during the initial excavation phase. The clay layer 2 serves both as a cover and a load transfer mechanism, directly underlying the pit bottom 6. Its physical and mechanical properties significantly influence the pit bottom's stability against uplift. The pit retaining structure 3 extends from the surface to the clay layer 2 and beyond, penetrating the overburden and sealing the pit excavation boundary 13. This supports the soil and provides water and pressure control.

[0084] The pressurized water-bearing sand layer 4 located below the pit bottom is the key location for static liquefaction instability. There is a significant pressurized water head 10 in its pores. This water head may be uploaded to the pit bottom area through seepage, forming an upward buoyancy force on the pit bottom, inducing liquefaction and causing uplift damage.

[0085] Beneath the confined aquifer 4 lies a deep clay layer 5, which has a stable structure and low permeability. Together with the confined aquifer 4, it forms the boundary of the hydrostatic pressure system. The interface between the confined aquifer 4 and the deep clay layer 5 is defined as the aquiclude bottom surface 11. The aquiclude pore pressure 12 within this aquiclude reflects the actual hydrostatic state of the region. This pore pressure parameter, a key input for liquefaction triggering criteria, plays a key role in foundation pit anti-heave stability analysis and is dynamically collected via the deployed real-time monitoring system 7.

[0086] The real-time monitoring system 7 is arranged around the retaining structure and the pit bottom, and integrates multiple types of sensor elements such as inclinometers and pore pressure gauges to achieve continuous tracking of key indicators such as displacement, pore pressure, and settlement during the excavation process of the foundation pit. This helps to compare actual working conditions with simulation prediction results and ensure construction safety.

[0087] The base reinforcement 8 is set between the pit bottom and the pressure-bearing layer. It uses high-pressure rotary spraying, deep mixing and other reinforcement technologies to reinforce the weakened soil layer to improve its shear strength, reduce permeability and effectively curb the development of liquefaction.

[0088] Furthermore, to accurately analyze foundation pit stability under complex geological structures and construction conditions, the present invention incorporates finite element three-dimensional simulations9, combining liquefaction criteria with an anti-uplift model to achieve refined simulation calculations of the pit's safety status under the influence of pressurized water-sand layers. The simulation strictly defines the excavation boundaries13 and dynamically analyzes the evolution of soil layers, water pressure, and support responses throughout the entire space, ensuring that the calculated safety factor is representative of the engineering and physically reasonable.

[0089] Specifically, through the safety factor F s Threshold value is used to evaluate the safety of foundation pit and conduct subsequent treatment. s When the value is ≥1, the foundation pit is judged to meet the anti-uplift stability requirements and normal construction is allowed. That is, there is no risk of uplift damage during the excavation process, and the project progress can continue. At the same time, a real-time monitoring system (such as an inclinometer and pore water pressure gauge) is used to continuously monitor the foundation pit stability to ensure the dynamic safety of the foundation pit.

[0090] When F s If the value is <1, the excavation depth is too deep, meaning the current excavation depth has exceeded the limit of its anti-heave stability. The excavation depth poses a potential risk of heave failure and does not meet the anti-heave safety and stability requirements, requiring immediate engineering intervention. A graded approach is adopted, including optimizing excavation depth, strengthening the base, or implementing liquefaction suppression measures. Iterative calculations and experimental verification ensure that the improved excavation meets safety standards. This method significantly improves the stability assessment accuracy of soft soil excavations containing confined water-sand layers by coupling the static liquefaction instability mechanism with an anti-heave analysis model, providing scientific assurance for engineering safety.

[0091] If F s <1, indicating that the excavation depth of the foundation pit does not meet the safety and stability requirements for anti-uplift, which can be addressed through a multi-dimensional processing strategy:

[0092] Method 1: Optimize the layered excavation plan, recollect parameters and perform iterative calculations, dynamically adjust the excavation depth, and repeat steps 2 to 4 based on the modified excavation depth until the anti-uplift safety and stability requirements of the excavation are met.

[0093] Specifically, the thickness of layered excavation is dynamically adjusted based on real-time monitoring data (such as soil displacement and pore water pressure changes), and the excavation depth is reduced in stages. For example, the original single-layer excavation thickness can be adjusted from 5m to 3m, and excavated layer by layer in three times. After each layer is excavated, construction is suspended, soil parameters are re-collected, and F is iteratively calculated. s , until it recovers above the safety threshold.

[0094] Method 2: Reinforce the bottom of the foundation pit using high-pressure jet grouting, grouting, or soil replacement to increase the bearing capacity of the base, and verify the improved soil parameters through in-situ testing. After reinforcement is completed, measure the strength parameters of the reinforced rock and soil, and repeat steps 2 to 4 until the foundation pit meets the safety and stability requirements for anti-uplift.

[0095] Specifically, if adjusting the excavation depth still fails to meet stability requirements, base reinforcement techniques are necessary. Strengthen the base through grouting, composite foundations, or lateral restraint techniques. For example, high-pressure jet grouting piles or nanosilicate slurry can be used to improve the sand layer to form a composite foundation. The effectiveness of the reinforcement can be verified by measuring the cone tip resistance and lateral friction resistance of the improved soil through static penetration tests (CPTs).

[0096] Method 3: If static liquefaction instability occurs in the confined water-sand layer, methods such as dewatering wells to reduce the confined water head or injecting nanosilicate slurry to fill the sand layer's pores can be used to improve soil properties and suppress static liquefaction potential. After improvements are made, triaxial testing and safety factor calculations must be repeated until the pit meets the safety and stability requirements for anti-uplift.

[0097] Specifically, to address the risk of static liquefaction, active suppression measures need to be taken: deploy a deep well dewatering system (well spacing of 10 to 15 meters, and well depth penetrating the confined water sand layer by 2 to 3 meters), and through staged pumping, reduce the confined water head to 0.5 to 1.0 meters below the bottom of the sand layer to reduce the pore water pressure; underground continuous walls can also be added to suppress liquefaction potential.

[0098] At the same time, combined with parameter sensitivity analysis, the safety factor F s Soil weight γ sat , internal friction angle and the robustness of pore water pressure u, ensuring the applicability of the method under complex geological conditions.

[0099] In order to verify the effectiveness of the treatment scheme, it is necessary to establish a three-dimensional seepage-stress coupling model in combination with finite element software (such as PLAXIS), simulate the stress-strain response of the reinforced foundation pit, and obtain the displacement field and pore water pressure distribution of the foundation pit under the combined action of graded excavation and dewatering, and extract the maximum vertical displacement δ v and safety factor F s Compare the deviation between theoretical calculation and numerical results (usually less than 5%).

[0100] Example 2

[0101] This embodiment further discloses a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method described in the first embodiment are implemented.

[0102] Example 3

[0103] This embodiment further discloses a computer program product, including a computer program, which implements the steps of the method described in the first embodiment when executed by a processor.

[0104] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for analyzing the anti-uplift stability of soft soil foundation pits for static liquefaction instability of confined water-sand layers, characterized by: The following steps are involved: Obtain foundation pit geometric parameters, soil mechanical parameters and hydrogeological parameters; Based on the foundation pit geometric parameters, soil mechanical parameters, and hydrogeological parameters, a consolidated undrained triaxial shear test is performed to monitor the change in the soil's second-order work. When the second-order work changes from a positive value to a negative value, it is determined that the confined water-sand layer is at risk of static liquefaction instability. Based on the modified limit equilibrium theory, a calculation model for anti-uplift stability considering the static liquefaction weakening effect is constructed, and the safety factor of the foundation pit is calculated through strength reduction iteration. Gradual processing is performed according to the foundation pit safety factor threshold; if the foundation pit safety factor is ≥1, construction is allowed; if the foundation pit safety factor is <1, the excavation depth is adjusted, base reinforcement or liquefaction suppression measures are implemented, and the process is re-executed until the safety standards are met.

2. The method according to claim 1, characterized in that The geometric parameters of the foundation pit include the length and width of the foundation pit; The soil mechanical parameters include static earth pressure coefficient, passive earth pressure coefficient, effective cohesion, and internal friction angle; The hydrogeological parameters include pore water pressure and the distance from the pit bottom to the calculation point.

3. The method according to claim 1, characterized in that The process of monitoring the change of the second-order work of soil through the consolidated undrained triaxial shear test includes: Real-time monitoring of axial stress, radial stress and strain rate through consolidated undrained triaxial shear test; A second-order work dynamic curve is calculated according to the axial stress, the radial stress, and the strain rate, and static liquefaction instability determination is triggered when the axial strain meets a critical strain threshold.

4. The method according to claim 3, characterized in that The critical strain threshold value ranges from 1% to 3%.

5. The method according to claim 1, wherein The formula for constructing the anti-heave stability calculation model considering the static liquefaction weakening effect includes: Calculation method of reduced lateral pressure coefficient: The safety factor calculation formula is: Among them, B2 is the width of the foundation pit; K p,SSR , K 0,SSR is the reduced lateral pressure coefficient; γ sat is the saturated weight of soil above the confined water layer; z is the distance from the pit bottom to the calculation point; c' and are the effective cohesion and internal friction angle of soil, respectively; p w is the water pressure of the confined aquifer; D is the burial depth of the retaining structure above the top surface of the confined aquifer; t is the distance from the top surface of the confined aquifer to the bottom of the retaining structure.

6. The method according to claim 1, wherein Adjusting the excavation depth includes: Dynamically reduce layered excavation thickness based on real-time monitoring data; Re-obtain soil parameters and iteratively calculate the foundation pit safety factor until the foundation pit safety factor is ≥1.

7. The method according to claim 1, characterized in that The base reinforcement includes any of the following measures: Use high-pressure jet grouting piles to form a composite foundation; Injecting nano-silicate slurry to improve sand layers; Verify the parameters of the reinforced soil through lateral pressure test or static penetration test.

8. The method according to claim 1, characterized in that Measures to suppress liquefaction include any of the following operations: Lay out a dewatering well system to lower the pressure head to 0.5-1.0m below the bottom of the sand layer; Add underground continuous walls to prevent the expansion of the liquefaction area.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

10. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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