Loess collapsible foundation disposal method based on porosity dynamic monitoring

Abstract

The invention relates to the technical field of foundation treatment, in particular to a loess collapsible foundation treatment method based on porosity dynamic monitoring, which comprises the following steps: carrying out initial investigation on a loess collapsible foundation to obtain an initial investigation result, including the soil particle specific gravity, the moisture content, the density, the initial porosity and the collapsibility coefficient of foundation loess; according to the initial investigation result, a foundation treatment scheme is designed, and the scheme comprises determination of the treatment depth, the treatment range and a selected treatment method; foundation treatment is conducted according to the scheme, and in the foundation treatment process, the change of the loess porosity is monitored in real time through a porosity monitoring device; and according to the real-time monitoring data of the porosity, a foundation treatment scheme is adjusted or additional treatment measures are taken until the foundation porosity reaches a preset range and the foundation meets design requirements. The dynamic change of the loess porosity can be monitored in real time, foundation treatment measures can be adjusted in time according to the change of the porosity, and the loess collapsible foundation treatment effect and reliability can be improved.

Description

Technical Field

[0001] This invention relates to the technical field of foundation treatment, and in particular to a method for treating loess collapsible foundations based on dynamic monitoring of porosity. Background Technology

[0002] The collapsibility of loess refers to the characteristic of loess that, when soaked in water under certain pressure, its soil structure rapidly breaks down, resulting in significant additional settlement. Loess is widely distributed in my country, with large areas found in more than 10 provinces and regions, including Gansu, Shaanxi, Ningxia, and Qinghai, covering an area of ​​approximately 635,000 square kilometers, or about 6.6% of the country's land area. Collapsible loess accounts for about three-quarters of this area. The presence of collapsible loess poses numerous challenges to engineering construction, such as significant settlement, cracking, and even collapse of buildings.

[0003] Currently, commonly used methods for treating collapsible loess foundations both domestically and internationally include dynamic compaction, cushion layer method, lime-soil compaction method, chemical reinforcement method, and pre-soaking method. However, these methods do not fully consider the dynamic changes in loess porosity during the foundation treatment process. The collapsibility of loess is closely related to its porosity; high natural porosity is one of the important reasons for loess collapse. During foundation treatment, the porosity of loess changes with the implementation of various treatment measures, and this change directly affects the effectiveness of the foundation treatment and the stability of the foundation. Summary of the Invention

[0004] This invention provides a method for treating loess collapsible foundations based on dynamic porosity monitoring, which helps to improve the effectiveness and reliability of treatment for loess collapsible foundations and can effectively solve the problems in the background art.

[0005] This invention provides a method for treating loess collapsible foundations based on dynamic porosity monitoring, comprising:

[0006] An initial investigation was conducted on the loess collapsible foundation to obtain initial investigation results, including the specific gravity of soil particles, water content, density, initial porosity, and collapsibility coefficient of the foundation loess. Based on the initial investigation results, a foundation treatment plan was designed, including determining the treatment depth, treatment range, and selected treatment methods.

[0007] According to the plan, the foundation treatment was carried out. During the foundation treatment process, a porosity monitoring device was used to monitor the changes in the porosity of the loess in real time.

[0008] Based on real-time monitoring data of porosity, adjust the foundation treatment plan or take additional treatment measures until the foundation porosity reaches the predetermined range and the foundation meets the design requirements.

[0009] In one possible design, the porosity monitoring device is a fiber optic grating sensor pre-embedded in the loess foundation, which calculates the porosity by measuring the wavelength change of the fiber optic grating.

[0010] In one possible design, the treatment methods selected include, but are not limited to, one or a combination of compaction, tamping, pre-soaking, lime-soil pile, and cement-soil pile methods.

[0011] In one possible design, when porosity monitoring results show that the porosity decreases too slowly, the compaction or tamping intensity is increased, or the number of treatments is increased.

[0012] In one possible design, if porosity monitoring results indicate that a rapid decrease in porosity may lead to soil structural damage, the treatment process can be slowed down, or measures can be taken to reinforce the soil.

[0013] In one possible design, when using the pre-soaking method, the water injection volume and injection time are adjusted according to the change in porosity to ensure uniform subsidence of the foundation and that the porosity reaches the expected target.

[0014] In one possible design, after the treatment is completed, the porosity is continuously monitored for a period of time, and if abnormal changes in porosity occur, remedial measures are taken in a timely manner.

[0015] In one possible design, the porosity within a predetermined range is determined through theoretical calculations and field tests based on the foundation design requirements and the engineering characteristics of loess.

[0016] In one possible design, the thickness of the collapsible loess layer, the load on the building, and the stability requirements of the foundation are taken into account when determining the treatment depth.

[0017] In one possible design, the foundation form, size, and the influence of the surrounding environment of the building are considered when determining the scope of treatment.

[0018] The technical solution of this invention can achieve the following technical effects:

[0019] This invention introduces dynamic porosity monitoring during the treatment of loess collapsible foundations, enabling flexible adjustments to treatment strategies based on real-time porosity changes. When porosity decreases too slowly, treatment intensity or frequency can be increased to ensure efficiency. Conversely, when porosity decreases too rapidly, potentially causing soil structural damage, the process can be slowed or the soil reinforced to avoid potential engineering hazards. In specific treatments such as pre-soaking, the injection volume and timing can be precisely controlled based on porosity changes to ensure uniform foundation settlement. This dynamic adjustment mechanism significantly improves the targeting and effectiveness of foundation treatment, reducing the risk of later settlement due to insufficient treatment or resource waste caused by overtreatment. Furthermore, continuous monitoring after treatment can promptly detect porosity anomalies, providing dual protection for long-term foundation stability, enhancing the reliability of loess collapsible foundation treatment, reducing the incidence of engineering accidents, and extending the service life of buildings. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart illustrating the method for treating loess collapsible foundations based on dynamic porosity monitoring in this invention. Detailed Implementation

[0022] This application will now be described with reference to the accompanying drawings.

[0023] like Figure 1 As shown, the present invention provides a method for treating loess collapsible foundations based on dynamic porosity monitoring, which specifically includes the following steps:

[0024] Step S1: Conduct an initial investigation of the loess collapsible foundation and obtain the initial investigation results, including the specific gravity of soil particles, water content, density, initial porosity, and collapsibility coefficient of the loess foundation.

[0025] Step S2: Based on the initial survey results, design a foundation treatment plan, which includes determining the treatment depth, treatment range, and selected treatment methods.

[0026] Step S3: Perform foundation treatment according to the plan. During the foundation treatment process, use a porosity monitoring device to monitor the changes in loess porosity in real time.

[0027] Step S4: Based on the real-time monitoring data of porosity, adjust the foundation treatment plan or take additional treatment measures until the foundation porosity reaches the predetermined range and the foundation meets the design requirements.

[0028] In this embodiment, by conducting an initial survey of the loess collapsible foundation and obtaining key parameters such as initial porosity, accurate basic data can be provided for the design of the foundation treatment scheme, ensuring that the scheme is consistent with the actual foundation conditions from the outset and avoiding scheme deviations due to insufficient information. By using a porosity monitoring device to monitor the changes in loess porosity in real time during the foundation treatment process, the dynamic progress of the foundation treatment can be grasped in a timely manner, providing a direct basis for judging the treatment effect. By adjusting the foundation treatment scheme or taking additional treatment measures based on the real-time porosity monitoring data, dynamic optimization of the foundation treatment can be achieved, avoiding problems such as incomplete or over-treatment due to the solidification of the scheme. By ensuring that the foundation porosity reaches the predetermined range and the foundation meets the design requirements, the effect and reliability of the loess collapsible foundation treatment can be improved, reducing the risk of settlement, cracking, or even collapse of buildings due to foundation problems, extending the service life of buildings, and also saving the cost of later maintenance and reinforcement.

[0029] In some embodiments of the present invention, the initial exploration is the foundation of the entire foundation treatment process, aiming to accurately obtain various key parameters of the foundation loess and provide a reliable basis for subsequent design. The layout of the exploration boreholes should be scientific and reasonable. The determination of the borehole spacing needs to take into account factors such as site size, geological complexity, and project importance. Specifically, it can be carried out in the following ways:

[0030] Site size: For small sites, such as those less than 5,000 square meters, the geological conditions are relatively easy to grasp due to the smaller area, so the borehole spacing can be appropriately reduced, generally controlled at 10-15 meters. Since small sites may have local geological anomalies, denser boreholes can capture these details more accurately. For large sites, such as those greater than 20,000 square meters, using too small a borehole spacing would significantly increase the exploration cost and workload. The borehole spacing can be widened to 20-30 meters, which can cover the entire site while controlling costs while ensuring exploration results. For medium-sized sites, with an area between 5,000 and 20,000 square meters, the borehole spacing can be set at 15-20 meters, achieving a balance between economy and accuracy.

[0031] Geological complexity: When geological conditions are simple, such as when the loess layer is evenly distributed, there are no obvious interlayers, and the collapsibility changes gently, the borehole spacing can be appropriately increased, such as using a borehole spacing of 20 meters; however, when geological conditions are complex, with faults, karst caves, and alternating layers of different soil properties, the borehole spacing must be reduced to thoroughly investigate these complex geological phenomena, and the borehole spacing can be reduced to 5-10 meters; for areas with large differences in collapsibility, such as some areas with strong collapsibility and some areas with weak collapsibility, the borehole spacing can be set at 10-15 meters to accurately delineate areas with different collapsibility levels.

[0032] Project Importance Level: For important projects, such as high-rise buildings and large bridges, the stability and safety requirements of the foundation are extremely high, requiring more detailed geological survey data. Therefore, the drilling spacing should be smaller, and the drilling spacing can be set at 10-15 meters to ensure a comprehensive and accurate understanding of the foundation conditions. For general projects, such as low-rise civil buildings, the drilling spacing can be appropriately widened to 15-25 meters.

[0033] In addition, relevant geological exploration specifications and standards can be consulted, which provide clear guidance on borehole spacing under different conditions. In practice, the initial borehole spacing can be determined according to the specifications and then adjusted according to the specific site conditions. For example, the specifications stipulate that the borehole spacing for medium-sized sites with medium geological conditions is 15-20 meters. If local geological anomalies are found in the site, the borehole spacing can be appropriately increased in that area, reducing the spacing to about 10 meters, in order to obtain more detailed geological information.

[0034] By comprehensively considering the above factors, the spacing of exploration boreholes can be determined scientifically and rationally.

[0035] The determination of borehole depth needs to comprehensively consider the estimated thickness of the collapsible loess layer, site geological conditions, project type, and specification requirements to ensure that the borehole can penetrate the entire collapsible loess layer and reserve sufficient safety depth to cope with geological uncertainties. Specifically, it can be determined as follows:

[0036] Estimated thickness of collapsible loess layer: Based on regional geological data or simple exploration methods such as excavation and probing, it is estimated that there is a collapsible loess layer in the site. The preliminary exploration borehole depth should exceed the estimated thickness. For example, if the estimated thickness of the collapsible loess layer is about 5 meters, in order to ensure that the soil layer can be completely revealed, the borehole depth can be initially set at 7-8 meters to avoid failure to penetrate the collapsible loess layer due to estimation errors.

[0037] Site geological conditions: The thickness of collapsible loess layers varies considerably across different geomorphic units such as loess plateaus, ridges, and mounds. For sites with flat terrain and simple geological structures, the thickness of collapsible loess layers is relatively stable, and the preliminary exploration borehole depth can be determined based on existing surrounding survey data. For example, in a loess plateau site, surrounding survey data shows that the average thickness of collapsible loess layers is 12 meters, and the preliminary exploration borehole depth can be set at 14-15 meters. However, for sites with significant topographic relief and geological structures such as faults or ancient river channels, the thickness of collapsible loess layers may change abruptly. In such cases, the borehole depth needs to be appropriately increased. For example, near suspected fault zones, the borehole depth can be increased by 5-8 meters compared to the estimated thickness of collapsible loess layers to investigate the impact of the structure on the soil layer distribution.

[0038] Project Type: For large-scale projects such as airports and highways, due to the large site area and complex load distribution, preliminary exploration needs to provide a more comprehensive understanding of the soil layer distribution, and the drilling depth should be relatively deep. For example, in the preliminary exploration of an international airport site, considering the load requirements of the runway and terminal building, the drilling depth is set at 20-25 meters to reveal any possible deep collapsible loess layers or other unfavorable soil layers. For small-scale projects, such as small factories, the drilling depth can be appropriately reduced, such as set at 10-15 meters.

[0039] Standards require that the depth of preliminary exploration boreholes be specified in standards such as the "Building Standard for Collapsible Loess Areas". For example, for general buildings, the depth of preliminary exploration boreholes should be greater than the depth of the foundation compressible layer and should not be less than 10 meters; for important buildings, the borehole depth should be even greater. In practice, the depth should be determined in combination with the standard requirements and the actual site conditions. For example, if the standard stipulates that the depth of preliminary exploration boreholes for a certain type of site should not be less than 15 meters, and the estimated thickness of the collapsible loess layer is 12 meters, then the borehole depth can be set at 15-18 meters.

[0040] By taking all the above factors into account, the drilling depth for preliminary exploration can be reasonably determined.

[0041] Based on the borehole spacing and depth, the exploration boreholes are arranged. When obtaining undisturbed soil samples using professional core sampling equipment, it is crucial to ensure that the soil samples are undisturbed and well-sealed during collection and transportation. In the laboratory, standard geotechnical testing methods are used to determine various parameters; among them, the specific gravity of soil particles, G... s The specific gravity bottle method can be used to accurately measure the mass and volume of the soil sample under different conditions and calculate it according to relevant formulas; the moisture content ω can be calculated using the drying method, by drying the soil sample in an oven at 105-110℃ to constant weight and calculating it based on the change in mass of the soil sample before and after drying; the density ρ can be calculated using the ring sampler method, by taking a soil sample with a ring sampler, weighing the total mass of the ring sample and the ring sample, subtracting the mass of the ring sampler, and then dividing by the volume of the ring sampler. These parameters can be used to calculate the density using formulas. Calculate the initial void ratio e0, and then use the formula The initial porosity n0 is obtained; at the same time, parameters such as the collapsibility coefficient can be determined through indoor collapsibility tests.

[0042] In some embodiments of the present invention, based on detailed data obtained from the initial survey, a targeted foundation treatment scheme needs to be designed, taking into account factors such as the type of building, the magnitude of the load, and the foundation type. If the project is a high-rise commercial building using a raft foundation, due to its large load, the bearing capacity and stability requirements of the foundation are extremely high. Considering the large thickness of the collapsible loess layer, a combined treatment method of compaction and pre-soaking can be adopted after comprehensive evaluation. The treatment depth should penetrate the collapsible loess layer, with a certain safety thickness reserved to cope with possible uncertainties. For example, if the thickness of the collapsible loess layer on site is 10 meters, the treatment depth can be determined to be 12 meters. The determination of the treatment range should be sufficient. Taking into account the foundation form and size of the building, as well as the influence of the surrounding environment, for example, the raft foundation size of a high-rise commercial building is 50 meters × 80 meters. To ensure the effectiveness and stability of the foundation treatment, the treatment range can be determined to extend 5 meters outward from the foundation edge, that is, the treatment range is 60 meters × 90 meters. When using the compaction method, lime-soil compaction piles can be selected. The selection of pile diameter should be determined comprehensively based on factors such as site soil conditions and treatment effect requirements. The determination of pile spacing needs to be optimized through theoretical calculations and field tests. When using the pre-soaking method, the soaking holes should be reasonably arranged according to the site area and the estimated water injection volume to ensure that water can permeate evenly into the loess within the entire treatment depth range.

[0043] In some embodiments of the present invention, in order to comprehensively and accurately monitor porosity changes within the foundation treatment area, fiber optic grating sensors need to be arranged according to a reasonable grid spacing. At the center of each grid, a hole is drilled to a suitable depth using professional drilling equipment. This depth should be sufficient to effectively monitor porosity changes in the main treatment area and is generally slightly less than the treatment depth. For example, if the treatment depth is 12 meters, the drilling depth can be set to 10 meters. After the fiber optic grating sensor is slowly placed into the hole, fine sand is filled around the sensor to ensure close contact between the sensor and the soil, thereby enabling accurate sensing of soil stress changes. The fiber optic grating sensor is connected to a data acquisition instrument via optical fiber. The data acquisition instrument collects the wavelength data of the sensor in real time and transmits the data to a computer for processing. The fiber optic grating sensor operates based on the fiber-optic elastic-optic effect. When the porosity of loess changes, the stress exerted by the soil on the optical fiber changes, causing a wavelength shift in the fiber optic grating. By measuring the wavelength change Δλ of the fiber optic grating, and using the wavelength-porosity calibration relationship n = f(Δλ) established in the laboratory through simulated loading experiments, the loess porosity can be calculated in real time. In actual foundation treatment, by measuring the wavelength change Δλ in real time and substituting it into this function, the real-time porosity n can be obtained. The porosity data is then transmitted to the data processing center in real time, enabling continuous and accurate monitoring of porosity.

[0044] In some embodiments of the present invention, during the pre-soaking stage, the porosity monitored in real time gradually increases as the water injection time progresses. When the porosity increase rate is too slow, measures need to be taken to accelerate the water infiltration rate to achieve the expected porosity change. This can be achieved by increasing the water injection pressure and water injection volume. Assuming the initial water injection pressure is 0.2 MPa and the water injection volume is 100 cubic meters per hour, and monitoring shows that the porosity increase rate is not as expected, calculations and analysis show that the water injection pressure can be increased to 0.3 MPa and the water injection volume can be increased to 130 cubic meters per hour. At the same time, if the porosity increases to a certain extent and then no longer changes significantly, it may be due to blockage of some immersion holes. In this case, the immersion holes need to be cleaned and unblocked in time, which can be done by using high-pressure water gun flushing or other methods to ensure the normal operation of the pre-soaking method. During the construction of lime-soil compaction piles, if the porosity decreases too slowly, it indicates that the compaction effect is not ideal. The number of compaction cycles can be appropriately increased; for example, if the original design required four cycles, it can be increased to six to enhance the compaction effect and promote a decrease in porosity. If the porosity decreases too quickly, it may lead to localized soil damage. In this case, the construction speed of the lime-soil compaction piles should be adjusted, and the pile driving frequency should be reduced, such as from 10 piles per hour to 6 piles per hour. An appropriate amount of cement should be added to the soil between the piles for reinforcement. The amount of cement added can be determined based on field tests, generally 5%-10% of the soil mass between the piles, to ensure soil structural stability and keep the porosity change within a reasonable range.

[0045] In some embodiments of the present invention, after the foundation treatment is completed, a comprehensive and rigorous evaluation of the treatment effect must be carried out. The bearing capacity of the foundation is tested through on-site load tests, using a slow-maintaining load method, loading to twice or even higher than the design load to fully verify whether the foundation bearing capacity meets the requirements. Assuming the design load is 500 kPa, the load is gradually increased to 1000 kPa in the on-site load test, and the foundation settlement is observed. Simultaneously, dynamic penetration tests are conducted to evaluate the foundation treatment effect by detecting the compaction of the foundation soil. Based on the dynamic penetration test indicators, such as the number of blows, it can be determined whether the compaction degree of the foundation soil has reached the expected level. Furthermore, after the foundation treatment is completed, the actual engineering conditions are considered... Establish a period for continuous monitoring of porosity, such as 6 months. During these 6 months, closely monitor whether the porosity remains stable within the predetermined range determined by theoretical calculations and field tests. Assuming that the predetermined porosity range is determined to be 0.3-0.35 through theoretical calculations and field tests, if abnormal changes occur in the porosity during subsequent monitoring, such as an increase in porosity exceeding the threshold of 0.03 determined based on actual engineering conditions and experience, it indicates that there may be potential problems with the foundation. Remedial measures should be taken in a timely manner, such as re-compacting the local area or using grouting reinforcement. Cement grout can be used as the grouting material. The grouting pressure and grouting volume should be determined through tests based on the site conditions to ensure that the stability and bearing capacity of the foundation always meet the engineering requirements.

[0046] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for treating loess collapsible foundations based on dynamic porosity monitoring, characterized in that, include: An initial investigation was conducted on the loess collapsible foundation to obtain initial investigation results, including the specific gravity of soil particles, water content, density, initial porosity, and collapsibility coefficient of the loess foundation. Based on the initial survey results, a foundation treatment plan is designed, which includes determining the treatment depth, treatment range, and selected treatment methods; The foundation treatment is carried out according to the above scheme. During the foundation treatment process, a porosity monitoring device is used to monitor the changes in the porosity of the loess in real time. Based on real-time monitoring data of porosity, adjust the foundation treatment plan or take additional treatment measures until the foundation porosity reaches the predetermined range and the foundation meets the design requirements.

2. The method for treating loess collapsible foundations based on dynamic porosity monitoring according to claim 1, characterized in that, The porosity monitoring device is a fiber optic grating sensor pre-embedded in the loess foundation, which calculates porosity by measuring the wavelength change of the fiber optic grating.

3. The method for treating loess collapsible foundations based on dynamic porosity monitoring according to claim 1, characterized in that, The selected treatment methods include, but are not limited to, one or more combinations of compaction, tamping, pre-soaking, lime-soil pile, and cement-soil pile methods.

4. The method for treating loess collapsible foundations based on dynamic porosity monitoring according to claim 1, characterized in that, When porosity monitoring results show that the porosity decreases too slowly, increase the compaction or tamping intensity, or increase the number of treatments.

5. The method for treating loess collapsible foundations based on dynamic porosity monitoring according to claim 1, characterized in that, When porosity monitoring results indicate that a rapid decrease in porosity may lead to soil structural damage, the treatment process should be slowed down, or measures should be taken to reinforce the soil.

6. The method for treating loess collapsible foundations based on dynamic porosity monitoring according to claim 1, characterized in that, When using the pre-soaking method, the water injection volume and injection time are adjusted according to the changes in porosity to ensure uniform subsidence of the foundation and that the porosity reaches the expected target.

7. The method for treating loess collapsible foundations based on dynamic porosity monitoring according to claim 1, characterized in that, After the treatment is completed, the porosity should be continuously monitored for a period of time. If any abnormal changes occur in the porosity, remedial measures should be taken in a timely manner.

8. The method for treating loess collapsible foundations based on dynamic porosity monitoring according to claim 1, characterized in that, The porosity within the predetermined range is determined through theoretical calculations and field tests based on the foundation design requirements and the engineering characteristics of loess.

9. The method for treating loess collapsible foundations based on dynamic porosity monitoring according to claim 1, characterized in that, When determining the treatment depth, the thickness of the collapsible loess layer, the load of the building, and the stability requirements of the foundation should be considered.

10. The method for treating loess collapsible foundations based on dynamic porosity monitoring according to claim 1, characterized in that, When determining the scope of treatment, the building's foundation type, size, and the impact of the surrounding environment should be considered.

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