A comprehensive soil saturation model and a test method for critical saturation intervals

Abstract

This invention discloses a comprehensive soil saturation model and a critical saturation interval test method, comprising: step S1, constructing a large-scale model test system; step S2, setting up a monitoring system; step S3, data acquisition; step S4, establishing a comprehensive saturation dynamic model; step S5, determining the critical saturation interval; and step S6, qualitatively analyzing the distribution of the unsaturated zone. This invention, through large-scale model tests and a comprehensive saturation dynamic calculation model, achieves for the first time continuous monitoring of soil saturation throughout the entire vacuum preloading process, revealing the complete evolution law of saturation gradually decreasing from a saturated state.

Description

Technical Field

[0001] This invention belongs to the field of soft soil foundation treatment technology in geotechnical engineering, specifically a comprehensive soil saturation model and a test method for critical saturation intervals. Background Technology

[0002] With the expansion of port and waterway scale and the progress of urban renewal, a large amount of dredged soil is generated annually that needs to be treated. This dredged soil often has characteristics such as high water content and high compressibility. Vacuum preloading has become the most commonly used method for reinforcing such dredged ultra-soft soil foundations. In previous studies, scholars often believed that the soil under vacuum preloading was saturated. For example, the paper "The Mechanism Difference between Vacuum Preloading and Vacuum Wellpoint Dewatering for Soft Soil Treatment" argues that the saturation state of the soil is one of the key differences between the two. However, some scholars hold the opposite view, believing that the soil is unsaturated, and thus discuss the water transport mechanism based on the relevant theories of unsaturated soil. To this end, some scholars have studied the saturation state of vacuum preloaded soil at a single moment, suggesting that during the gradual drainage of soil from a fully saturated state, gas will appear in the gaps between soil particles after the pore water is discharged. When the pore gas increases to a certain amount and becomes interconnected, the stress state of the soil changes, and the soil begins to transition from a saturated state to an unsaturated state, which will change its stress and force transmission mechanism. However, due to the lack of experimental methods and the differences in soil properties, it is still impossible to determine the boundary between a saturated and unsaturated state of soil. Based on experience, the "Building Standards for Collapsible Loess Areas" suggests using 85% as the cutoff value for saturation.

[0003] In summary, the core defect of existing technologies is that they can only obtain soil saturation at a single moment and cannot know the complete law of saturation development over time. Currently, the only method to obtain soil saturation is the sampling and drying method, which involves taking a ring sampler in the field or model, drying it, and then calculating the saturation. This method has the following fundamental limitations: (1) Destructive sampling: Each sampling will disturb the soil, making it impossible to repeat the measurement at the same location. (2) Single moment: It can only represent the saturation state at the sampling moment and cannot obtain the continuous change process. (3) Spatial dispersion: Due to the limitation of the number of sampling points, it is difficult to fully reflect the saturation distribution. (4) No retrospective: Once the saturation change during the consolidation process misses the sampling time node, it cannot be traced back.

[0004] Therefore, despite substantial research achievements in vacuum preloading technology, no study to date has been able to reveal the complete evolution of saturation over time during soil consolidation. This gap prevents researchers from accurately determining the timing and rate of unsaturation zone formation and development, and from identifying the critical saturation level for different soil types to enter a mechanically unsaturated state. In engineering practice, the empirical value of 85%, derived from the specifications for collapsible loess, can only be used. However, numerous studies have shown that the critical saturation levels vary significantly among different soil types, with the critical value for high-fine-particle-content mudstone potentially being much higher than 85%.

[0005] Existing experimental methods have certain limitations. Some researchers have tried to study the saturation problem through indoor model tests, but existing model tests have the following problems: (1) The drainage volume cannot be accurately measured in the field, so it is impossible to establish a quantitative relationship between drainage volume and saturation. (2) In small-scale model tests (such as 60 cm side length), the surface settlement is greatly affected by the boundary effect, and the drainage volume measurement error is also relatively large, making it difficult to support the accurate calculation of saturation.

[0006] Therefore, due to limitations in experimental methods and monitoring means, it has long been impossible to obtain continuous change data of saturation during consolidation, let alone reveal its temporal evolution law, and thus provide a comprehensive soil saturation model and a test method for critical saturation intervals. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, this invention provides a comprehensive soil saturation model and a critical saturation interval test method. Through large-scale model tests and a comprehensive saturation dynamic calculation model, it achieves continuous monitoring of soil saturation throughout the entire vacuum preloading process for the first time, revealing the complete evolution law of saturation gradually decreasing from a saturated state.

[0008] The technical solution to achieve the above objectives is: A comprehensive soil saturation model and a test method for the critical saturation range, comprising: Step S1: Construct a large-scale model test system: Construct a test pool with a horizontal cross-section side length ≥2.0m and an initial soil sample thickness ≥1.5m, inject slurry to the designed thickness, and record the initial total mass, moisture content, thickness and bottom area after static stabilization. Step S2, setting up the monitoring system: Vertical drainage boards are arranged in the soil sample at intervals of 50-80cm. At least one shallow and one deep pore pressure gauge are buried between the drainage boards. ≥4 settlement monitoring points are set on the surface of the soil sample. A drainage volume measuring device with an accuracy of 0.1kg is set at the outlet of the drainage pipe. A vacuum gauge is set under the sealing membrane. Step S3, Data Acquisition: Monitor and collect the settlement data at four settlement monitoring points in real time, and take the average value as the average surface settlement. Accumulated drainage volume is collected through a drainage volume metering device. The vacuum level under the membrane was collected using a vacuum gauge. ; Step S4: Establish a dynamic model for comprehensive saturation: Based on the assumptions of incompressible soil particles and initial complete saturation, establish a dynamic calculation model for comprehensive saturation to obtain the time-series curve of comprehensive saturation. In order to obtain the temporal evolution law of saturation; Step S5, determine the critical saturation range: based on the comprehensive saturation time series curve. By combining the depth cross-analysis of pore pressure dissipation anomalies, the occurrence of unsaturated regions is verified and the critical saturation range is determined. Step S6, Qualitative analysis of the distribution of unsaturated areas: Based on cross-analysis of monitoring data, the distribution pattern of unsaturated areas is determined to be funnel-shaped and expanding outward and downward from the center of the drainage board, and an intuitive physical image of the development process of unsaturated areas is provided.

[0009] Preferably, in step S1, the test tank is constructed of brick, and the dimensions of the test tank meet the following requirements: Length and width ≥ 2.4m, height ≥ 1.9m, with the bottom 1m buried below the ground surface; Arrange a 4×4 row drainage board array with the edge ≥0.3m from the pool wall; Two sets of pore pressure gauges, one shallow and one deep, were installed. The shallow layer is 0.2-0.5 m deep, and the deep layer is 0.8-1.2 m deep.

[0010] Preferably, in step S3, the average surface settlement is monitored and recorded in real time. Cumulative drainage and membrane vacuum Data from the start of vacuum loading to the end of the experiment were sampled at a frequency of no less than once per day.

[0011] Preferably, in step S4, a dynamic calculation model for comprehensive saturation is established based on the following physical assumptions: Soil particles are incompressible; the volume of soil particles during consolidation... Remain unchanged; The soil is initially fully saturated, and the initial total pore volume is... equal to the initial water volume ; Calculate any time using the following formula Overall saturation : ; ; In the formula, For a moment The volume of water, For any time The total pore volume, This represents the total mass of water in the initial soil mass, calculated from the initial total mass and initial water content. For cumulative drainage volume, The density of water, The horizontal cross-sectional area of ​​the test pool is... For a moment The average surface settlement; By obtaining the complete curve of the continuous change of soil comprehensive saturation over time throughout the entire vacuum preloading process. This reveals the entire process of saturation gradually decreasing from the initial saturation state.

[0012] Preferably, in step S5, the comprehensive saturation time-series curve obtained in step three is used as the basis. By combining the analysis of pore pressure dissipation values, characteristic saturation values ​​that characterize the soil state transformation are extracted. The pore pressure dissipation value is equal to the difference between the initial hydrostatic pressure and the pore pressure measurement value at a certain moment at the measuring point. Plot the curves of pore pressure dissipation values ​​in deep and shallow layers over time, and perform depth cross-analysis. Verification of the occurrence of the unsaturated region: Compare drainage settlement calculated from drainage volume Compared with the measured surface settlement ; when When the volume of water discharged is greater than the volume of soil compressed, it means that some pore water was discharged and left uncompressed pores, confirming the existence of an unsaturated zone. This verification does not rely on any additional sampling and is based entirely on cross-analysis of monitoring data. Determining the critical saturation range: Observe the pore pressure dissipation values ​​of deep and shallow layers and Relationship; Under saturated conditions, the deep pore pressure dissipation value should be greater than that of the shallow layer; When an unsaturated zone appears in the soil and extends to shallow measuring points, the capillary negative pressure in the shallow soil begins to superimpose the measured pore pressure, resulting in a "reversal" phenomenon where the shallow pore pressure dissipation value is greater than the deep pore pressure dissipation value. Record the start time of the reversal. Read the corresponding overall saturation , is defined as the upper limit of the critical saturation range of the soil; When an unsaturated zone appears in the soil and extends to the deep measuring point, the capillary negative pressure in the deep soil is superimposed on the measured pore pressure, resulting in the deep pore pressure dissipation value being greater than the shallow pore pressure dissipation value again. Record the start time of the reversal. Read the corresponding overall saturation , is defined as the lower limit of the critical saturation range of the soil.

[0013] Preferably, in step S5, for dredged fill mud with a fine particle content of <0.005 mm >40% and an initial moisture content >150%, the critical saturation range is 89%-92%.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1) This invention, through large-scale model tests and a comprehensive dynamic saturation calculation model, has for the first time realized continuous monitoring of soil saturation throughout the entire vacuum preloading process, revealing the complete evolution law of saturation gradually decreasing from the saturated state, and filling a long-standing technical gap in this field; 2) The large-scale model (side length ≥ 2.0 m, thickness ≥ 1.5 m) used in this invention overcomes the dual difficulties of being unable to measure drainage volume on site, small model settlement, and large drainage measurement error. This size selection enables the cumulative accuracy of drainage volume to reach 0.1 kg and the relative error of settlement measurement to be controlled within 5%, providing a reliable data basis for accurate saturation calculation. 3) This invention not only proposes a method for calculating saturation, but more importantly, it conducts in-depth cross-analysis of multi-source monitoring data such as drainage volume, settlement volume, and pore pressure dissipation values ​​in deep and shallow layers. Specifically, it verifies the occurrence of unsaturated zones by comparing drainage settlement volume with measured settlement volume, and objectively determines the critical saturation range by the reversal phenomenon of pore pressure dissipation in deep and shallow layers. This approach of multi-parameter joint analysis goes far beyond the simple listing of conventional monitoring data. 4) This invention utilizes the physical phenomenon of pore pressure dissipation and reversal to determine the critical saturation range, avoiding the subjectivity and blindness of traditional empirical values. For slurry with high fine particle content, it provides a range of 89%-92%, which is significantly higher than the traditional empirical value of 85%, providing a scientific basis for the refined control of vacuum pre-compression process. 5) The monitoring parameters (drainage volume, settlement volume, and pore pressure value) on which this invention is based are all routine monitoring items in vacuum preloading engineering. No special equipment is required. The calculation model is simple and intuitive, and is suitable for indoor model tests and field engineering applications. Attached Figure Description

[0015] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of a soil comprehensive saturation model and a critical saturation interval test method according to the present invention; Figure 2 This is a schematic diagram of the large-scale model test device in an embodiment of the present invention; Figure 3 This is a plan view of the monitoring points (drainage board, pore pressure gauge, settlement marker) in the experiment according to an embodiment of the present invention; Figure 4 This is a graph showing the overall saturation changing over time in an embodiment of the present invention; Figure 5 This is a comparison curve of drainage settlement and measured settlement in an embodiment of the present invention; Figure 6 This is a time-series comparison chart of shallow and deep pore pressure dissipation values ​​and overall saturation in an embodiment of the present invention; Figure 7 This is a qualitative schematic diagram of the funnel-shaped distribution in the unsaturated region in an embodiment of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] like Figure 1 As shown, a soil comprehensive saturation model and critical saturation interval test method include: Step S1: Construct a large-scale model test system: Construct a test pool with a horizontal cross-section side length ≥2.0m and an initial soil sample thickness ≥1.5m, inject slurry to the designed thickness, and record the initial total mass, moisture content, thickness and bottom area after static stabilization.

[0018] In this embodiment, the test tank is constructed of brick, and its dimensions meet the following requirements: Length and width ≥ 2.4m, height ≥ 1.9m, with the bottom 1m buried below the ground surface; Arrange a 4×4 row drainage board array with the edge ≥0.3m from the pool wall; Two sets of pore pressure gauges, one shallow and one deep, were installed. The shallow layer is 0.2-0.5 m deep, and the deep layer is 0.8-1.2 m deep.

[0019] The large-scale model test system of this size can control the relative error of surface settlement measurement within 5% and the cumulative measurement accuracy of drainage volume up to 0.1 kg, providing a reliable data basis for subsequent saturation calculation.

[0020] Step S2, setting up the monitoring system: Vertical drainage boards are arranged in the soil sample at intervals of 50-80cm. At least one shallow and one deep pore pressure gauge are buried between the drainage boards. ≥4 settlement monitoring points are set on the surface of the soil sample. A drainage volume measuring device with an accuracy of 0.1kg is set at the outlet of the drainage pipe. A vacuum gauge is set under the sealing membrane.

[0021] Step S3, Data Acquisition: Monitor and collect the settlement data at four settlement monitoring points in real time, and take the average value as the average surface settlement. Accumulated drainage volume is collected through a drainage volume metering device. The vacuum level under the membrane was collected using a vacuum gauge. .

[0022] In this embodiment, the average surface settlement is monitored and recorded in real time. Cumulative drainage and membrane vacuum Data from the start of vacuum loading to the end of the experiment were sampled at a frequency of no less than once per day.

[0023] Step S4: Establish a dynamic model for comprehensive saturation: Based on the assumptions of incompressible soil particles and initial complete saturation, establish a dynamic calculation model for comprehensive saturation to obtain the time-series curve of comprehensive saturation. This allows us to obtain the temporal evolution law of saturation.

[0024] In this embodiment, a dynamic calculation model for comprehensive saturation is established based on the following physical assumptions: Soil particles are incompressible; the volume of soil particles during consolidation... Remain unchanged; The soil is initially fully saturated, and the initial total pore volume is... equal to the initial water volume ; Calculate any time using the following formula Overall saturation : ; ; In the formula, For a moment The volume of water, For any time The total pore volume, This represents the total mass of water in the initial soil mass, calculated from the initial total mass and initial water content. For cumulative drainage volume, The density of water, The horizontal cross-sectional area of ​​the test pool is... For a moment The average surface settlement; By obtaining the complete curve of the continuous change of soil comprehensive saturation over time throughout the entire vacuum preloading process. This reveals the entire process of saturation gradually decreasing from the initial saturation state.

[0025] Step S5, determine the critical saturation range: based on the comprehensive saturation time series curve. By combining the depth cross-analysis of pore pressure dissipation anomalies, the occurrence of unsaturated regions was verified and the critical saturation range was determined.

[0026] In this embodiment, the time series curve of the comprehensive saturation obtained in step three is used. By combining the analysis of pore pressure dissipation values, characteristic saturation values ​​that characterize the soil state transformation are extracted. The pore pressure dissipation value is equal to the difference between the initial hydrostatic pressure and the pore pressure measurement value at a certain moment at the measuring point. Plot the curves of pore pressure dissipation values ​​in deep and shallow layers over time, and perform depth cross-analysis. Verification of the occurrence of the unsaturated region: Compare drainage settlement calculated from drainage volume Compared with the measured surface settlement ; when When the volume of water discharged is greater than the volume of soil compressed, it means that some pore water was discharged and left uncompressed pores, confirming the existence of an unsaturated zone. This verification does not rely on any additional sampling and is based entirely on cross-analysis of monitoring data. Determining the critical saturation range: Observe the pore pressure dissipation values ​​of deep and shallow layers and Relationship; Under saturated conditions, the deep pore pressure dissipation value should be greater than that of the shallow layer; When an unsaturated zone appears in the soil and extends to shallow measuring points, the capillary negative pressure in the shallow soil begins to superimpose the measured pore pressure, resulting in a "reversal" phenomenon where the shallow pore pressure dissipation value is greater than the deep pore pressure dissipation value. Record the start time of the reversal. Read the corresponding overall saturation , is defined as the upper limit of the critical saturation range of the soil; When an unsaturated zone appears in the soil and extends to the deep measuring point, the capillary negative pressure in the deep soil is superimposed on the measured pore pressure, resulting in the deep pore pressure dissipation value being greater than the shallow pore pressure dissipation value again. Record the start time of the reversal. Read the corresponding overall saturation , is defined as the lower limit of the critical saturation range of the soil.

[0027] In the embodiments, for dredged fill mud with a particle size <0.005 mm content >40% and an initial moisture content >150%, the critical saturation range is 89%-92%.

[0028] Step S6, Qualitative analysis of the distribution of unsaturated areas: Based on cross-analysis of monitoring data, the distribution pattern of unsaturated areas is determined to be funnel-shaped and expanding outward and downward from the center of the drainage board, and an intuitive physical image of the development process of unsaturated areas is provided.

[0029] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. 1. Construct a large-scale model test system The test tank is a brick structure, measuring 2.4 m × 2.4 m × 1.9 m in length, width, and height, with the bottom 1 m buried underground. The tank bottom and walls were plastered and leveled. The test tank's planar area is A = 5.76 m². 2 .

[0030] The test soil sample was taken from a dredging and reclamation project in Wenzhou, Zhejiang Province, and was characterized by high water content and high fine particle content. Initial physical properties: water content 180%, density 1198 kg / m³ 3 The liquid limit was 46.7%, the plastic limit was 20.6%, the fine particle content (<0.005 mm) was 50%, and the particle content (<0.075 mm) was 99%. After 15 days of natural settling, the soil sample was 1.67 m thick. The initial total mass was 11530 kg, including 7410 kg of water and 4120 kg of soil particles. The initial water volume was 7.41 m³. 3 The initial soil particle volume was 2.21 m³. 3 .

[0031] 2. Deploy a monitoring system according to Figure 2 and Figure 3 Arrangement: 16 plastic drainage boards are arranged in 4 rows and 4 columns, spaced 60 cm apart, with the edge drainage boards 30 cm from the pool wall. Shallow pore manometers (0.4 m deep) and deep pore manometers (1.0 m deep) are embedded between the drainage boards. Four settlement gauges are set on the surface, and the average value is taken. The drainage pipe outlet is connected to a water vapor separator and a weighing device, with a weighing accuracy of 0.1 kg for the drainage volume. A vacuum gauge is installed under the sealing membrane.

[0032] 3. Vacuum loading The loading gradient was 20 kPa → 40 kPa → 80 kPa, and the experiment lasted for a total of 108 days. The vacuum gauge threshold was ±2 kPa, and the vacuum level was automatically controlled. The loading gradient could be adjusted according to the soil properties.

[0033] 4. Data Collection Daily records are kept of cumulative drainage, average surface settlement, shallow pore pressure, deep pore pressure, and vacuum under the membrane.

[0034] 5. Comprehensive saturation calculation and time series pattern acquisition Calculate the overall saturation at each time point using the formula in step three. , drawn as Figure 4 The curve shown. Results show: the first 10 days =100%, maintaining saturation; then Gradually decrease; at the end of the experiment =80.5%. After the experiment, the average saturation of the drying method at the 24 ring sample points was 81.7%, which was consistent with the model calculation results, verifying the reliability of the calculation model.

[0035] 6. In-depth cross-analysis (1) Verification of the occurrence of unsaturated zone: Calculate drainage settlement , with measured settlement Comparison drawing as follows Figure 5 As shown. The results showed that the two were basically the same in the early stages of the experiment; after about 10 days, Start greater than At the end of the experiment = 0.740 m, = 0.606 m, a difference of 22%. The volume of water discharged is greater than the volume of soil compressed, proving that the pores were not compressed and filled after some of the pore water was discharged, that is, an unsaturated zone appeared.

[0036] (2) Determination of the critical saturation range: Calculate the pore pressure dissipation value and plot as shown in the figure. Figure 6 As shown in the figure, during the first 60 days of the test, the deep pore pressure dissipation value was greater than that of the shallow layer, consistent with the characteristics of saturated soil. Around day 65, the shallow pore pressure dissipation value began to exceed that of the deep layer, indicating a "reversal." The overall saturation at the start of this reversal was approximately 92%. Around day 90, the reversal ended, and the deep pore pressure dissipation value again exceeded that of the shallow layer, corresponding to an overall saturation of approximately 89%.

[0037] Based on the above analysis, the critical saturation range of the slurry in this experiment is determined to be 89%-92%.

[0038] 7. Qualitative Morphological Analysis of the Unsaturated Region Based on the physical mechanism of preferential drainage around the drainage board, and combined with the results of cross-analysis of monitoring data, the distribution pattern of the unsaturated zone, centered on the drainage board, extends outward and downward in a funnel shape. Figure 7 As shown.

[0039] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A comprehensive soil saturation model and a test method for critical saturation intervals, characterized in that, include: Step S1: Construct a large-scale model test system: Construct a test pool with a horizontal cross-section side length ≥2.0m and an initial soil sample thickness ≥1.5m, inject slurry to the designed thickness, and record the initial total mass, moisture content, thickness and bottom area after static stabilization. Step S2, setting up the monitoring system: Vertical drainage boards are arranged in the soil sample at intervals of 50-80cm. At least one shallow and one deep pore pressure gauge are buried between the drainage boards. ≥4 settlement monitoring points are set on the surface of the soil sample. A drainage volume measuring device with an accuracy of 0.1kg is set at the outlet of the drainage pipe. A vacuum gauge is set under the sealing membrane. Step S3, Data Acquisition: Monitor and collect the settlement data at four settlement monitoring points in real time, and take the average value as the average surface settlement. Accumulated drainage volume is collected through a drainage volume metering device. The vacuum level under the membrane was collected using a vacuum gauge. ; Step S4: Establish a dynamic model for comprehensive saturation: Based on the assumptions of incompressible soil particles and initial complete saturation, establish a dynamic calculation model for comprehensive saturation to obtain the time-series curve of comprehensive saturation. In order to obtain the temporal evolution law of saturation; Step S5, determine the critical saturation range: based on the comprehensive saturation time series curve. By combining the depth cross-analysis of pore pressure dissipation anomalies, the occurrence of unsaturated regions is verified and the critical saturation range is determined. Step S6, Qualitative analysis of the distribution of unsaturated areas: Based on cross-analysis of monitoring data, the distribution pattern of unsaturated areas is determined to be funnel-shaped and expanding outward and downward from the center of the drainage board, and an intuitive physical image of the development process of unsaturated areas is provided.

2. The soil comprehensive saturation model and critical saturation interval test method according to claim 1, characterized in that, In step S1, the test tank adopts a brick structure, and the dimensions of the test tank meet the following requirements: Length and width ≥ 2.4m, height ≥ 1.9m, with the bottom 1m buried below the ground surface; Arrange a 4×4 row drainage board array with the edge ≥0.3m from the pool wall; Two sets of pore pressure gauges, one shallow and one deep, were installed. The shallow layer is 0.2-0.5 m deep, and the deep layer is 0.8-1.2 m deep.

3. The soil comprehensive saturation model and critical saturation interval test method according to claim 1, characterized in that, In step S3, the average surface settlement is monitored and recorded in real time. Cumulative drainage and membrane vacuum Data from the start of vacuum loading to the end of the experiment were sampled at a frequency of no less than once per day.

4. The soil comprehensive saturation model and critical saturation interval test method according to claim 3, characterized in that, In step S4, a dynamic calculation model for comprehensive saturation is established based on the following physical assumptions: Soil particles are incompressible; the volume of soil particles during consolidation... Remain unchanged; The soil is initially fully saturated, and the initial total pore volume is... equal to the initial water volume ; Calculate any time using the following formula Overall saturation : ； ； In the formula, For a moment The volume of water, For any time The total pore volume, This represents the total mass of water in the initial soil mass, calculated from the initial total mass and initial water content. For cumulative drainage volume, The density of water, The horizontal cross-sectional area of ​​the test pool is... For a moment The average surface settlement; By obtaining the complete curve of the continuous change of soil comprehensive saturation over time throughout the entire vacuum preloading process. This reveals the entire process of how saturation gradually decreases from the initial saturation state.

5. The soil comprehensive saturation model and critical saturation interval test method according to claim 4, characterized in that, In step S5, the comprehensive saturation time-series curve obtained in step three is used as a basis. By combining the analysis of pore pressure dissipation values, characteristic saturation values ​​that characterize the soil state transformation are extracted. The pore pressure dissipation value is equal to the difference between the initial hydrostatic pressure and the pore pressure measurement value at a certain moment at the measuring point. Plot the curves of pore pressure dissipation values ​​in deep and shallow layers over time, and perform depth cross-analysis. Verification of the occurrence of the unsaturated region: Compare drainage settlement calculated from drainage volume Compared with the measured surface settlement ; when When the volume of water discharged is greater than the volume of soil compressed, it means that some pore water was discharged and left uncompressed pores, confirming the existence of an unsaturated zone. This verification does not rely on any additional sampling and is based entirely on cross-analysis of monitoring data. Determining the critical saturation range: Observe the pore pressure dissipation values ​​of deep and shallow layers and Relationship; Under saturated conditions, the deep pore pressure dissipation value should be greater than that of the shallow layer; When an unsaturated zone appears in the soil and extends to shallow measuring points, the capillary negative pressure in the shallow soil begins to superimpose the measured pore pressure, resulting in a "reversal" phenomenon where the shallow pore pressure dissipation value is greater than the deep pore pressure dissipation value. Record the start time of the reversal. Read the corresponding overall saturation , is defined as the upper limit of the critical saturation range of the soil; When an unsaturated zone appears in the soil and extends to the deep measuring point, the capillary negative pressure in the deep soil is superimposed on the measured pore pressure, resulting in the deep pore pressure dissipation value being greater than the shallow pore pressure dissipation value again. Record the start time of the reversal. Read the corresponding overall saturation , is defined as the lower limit of the critical saturation range of the soil.

6. The soil comprehensive saturation model and critical saturation interval test method according to claim 5, characterized in that, In step S5, for dredged fill mud with a fine particle content of <0.005 mm >40% and an initial moisture content >150%, the critical saturation range is 89%-92%.

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