Alluvial silt foundation self-adaptive resonance compacting method based on dynamic frequency tracking

Abstract

The invention belongs to the technical field of foundation treatment, and discloses a dynamic frequency tracking-based alluvial silt foundation adaptive resonance compaction method. The problem of resonance frequency drift caused by rigidity time-varying characteristics in the resonance compacting process of the Yellow River downstream alluvial silt foundation is solved. Comprising the following steps: S1, equipment in-place and initial penetration; s2, real-time response monitoring is carried out; s3, analyzing bottom vibration retention and instantaneous frequency; s4, performing dynamic frequency tracking and self-adaptive resonance in the lifting process of the vibration rod; s5, the vibration rod is lifted to the ground, and construction of a single point position is completed; and S6, the resonance compaction equipment is moved to the next construction point position, and the steps S1 to S5 are repeated till foundation treatment of all the areas is completed. Through real-time analysis of the instantaneous inherent frequency of the soil body and dynamic tracking and matching, the problem of resonant frequency drift caused by rigidity time-varying characteristics of the Yellow River downstream alluvial silt is fundamentally solved.

Description

Technical Field

[0001] This invention belongs to the field of foundation treatment technology, and particularly relates to an adaptive resonance compaction method for alluvial silty soil foundations based on dynamic frequency tracking. Background Technology

[0002] Due to the periodic flooding and high siltation rates of rivers (such as the Yellow River), the region is widely covered with recently deposited silts possessing unique engineering characteristics. Compared to ordinary silt, downstream alluvial silts are characterized by high particle roundness, high silt content (generally above 80%), and poor gradation (C... u The alluvial silty soil in the lower Yellow River basin is characterized by low liquid limit and plasticity index (generally less than 5), strong capillary action, and underconsolidation, making it not only difficult to compact but also highly susceptible to liquefaction under dynamic conditions such as earthquakes and traffic loads. Therefore, the treatment of alluvial silty soil foundations in the lower Yellow River basin is a major challenge in engineering construction.

[0003] Currently, infrastructure construction in downstream alluvial plains is expanding rapidly, but traditional foundation treatment technologies face severe challenges such as insufficient deep treatment capacity, high carbon emissions, and significant vibration impacts. The resonant compaction method adjusts the vibration frequency of the "vibrating hammer-vibrating rod-foundation soil" system to achieve resonance, utilizing resonant energy to rearrange soil particles and reduce porosity, thereby improving the compaction and liquefaction resistance of the foundation soil. This method requires no additional filler, saves more than 50% of the cost per unit area compared to the crushed stone pile method, has a carbon emission intensity only 1 / 5 that of the reinforced soil pile method, a safe construction distance of less than 10m, and a treatment depth of over 15m, making it highly promising for infrastructure construction in downstream alluvial plains. However, when applied to downstream alluvial silty soil foundations, this method faces a unique technical challenge: resonant frequency drift caused by time-varying stiffness.

[0004] Specifically, under vibrational loading, the shear modulus and stiffness of alluvial silt in the lower reaches of rivers change significantly as the soil gradually compacts, causing the natural frequency of the soil to drift in real time. Traditional resonant compaction methods, which use fixed-frequency vibration or frequency conversion according to a preset curve, cannot track this frequency drift caused by changes in the soil itself in real time. During construction, the "vibratory hammer-vibrator-soil" system is in a detuned state for most of the time, resulting in low energy utilization efficiency and uneven reinforcement of deep soil. At the same time, if energy is continuously input in a detuned state, it may cause damage to the soil structure (over-vibration), which will reduce the reinforcement effect.

[0005] In the prior art, although there are reports on frequency adjustment devices for vibratory hammers (such as the Chinese utility model patent with announcement number CN211698727U), their adjustment logic is mainly based on the operating parameters of the device itself, and does not involve dynamic frequency tracking based on the real-time response of the soil. Therefore, it cannot solve the frequency drift problem caused by the time-varying stiffness of alluvial silt in the downstream of the river.

[0006] Therefore, there is an urgent need for an adaptive resonance compaction method that can track soil frequency changes in real time and dynamically match the excitation frequency in order to achieve efficient and uniform reinforcement of alluvial silt foundations in downstream rivers. Summary of the Invention

[0007] The purpose of this invention is to provide an adaptive resonance compaction method for alluvial silt foundations based on dynamic frequency tracking, which effectively solves the problem of resonance frequency drift caused by time-varying stiffness in the resonance compaction process of alluvial silt foundations in downstream rivers.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an adaptive resonance compaction method for alluvial silty soil foundation based on dynamic frequency tracking, including the following steps: S1, aligning the vibrating rod of the resonance compaction equipment with the preset construction point, starting the vibrating hammer of the resonance compaction equipment, and penetrating the vibrating rod to the design depth at an initial scanning frequency higher than the upper limit of the estimated resonance frequency range.

[0009] S2. Once the vibratory rod reaches the design depth, the vibration response signal of the coupled system of the vibratory hammer, vibratory rod, and foundation soil is collected in real time through the data acquisition device installed on the vibratory rod.

[0010] S3. The control system of the resonant compaction equipment receives the vibration response signal, analyzes and identifies the instantaneous natural frequency of the foundation soil under the current compaction state in real time; with the instantaneous natural frequency as the target, the output frequency of the vibratory hammer is adjusted in real time to match the instantaneous natural frequency, ensuring that the vibratory hammer, vibratory rod and soil system enter the resonance state at the design depth; and the resonance state is maintained for a preset duration.

[0011] S4. Start the vibratory rod lifting program. The control system continuously collects vibration response signals in real time, continuously analyzes the instantaneous natural frequency of soil at different depths, and adjusts the output frequency of the vibratory hammer in real time so that the output frequency always follows and matches the instantaneous natural frequency of the soil at the current depth. This ensures that the vibratory hammer, vibratory rod, and soil system are always in or close to a resonant state throughout the lifting process. At the same time, the output amplitude is adaptively adjusted according to the real-time monitored changes in soil response amplitude to achieve uniform densification across the entire hole depth range.

[0012] S5. After the vibratory rod is raised to the ground, the construction of a single point is completed.

[0013] S6. Move the resonant compaction equipment to the next construction point and repeat steps S1-S5 until the foundation treatment of all areas is completed.

[0014] Furthermore, in step S1, the initial scanning frequency is 10%-30% higher than the upper limit of the estimated resonant frequency range.

[0015] Furthermore, in step S2, the data acquisition device includes an accelerometer and an impedance monitoring device, with a sampling frequency of not less than 200Hz.

[0016] Furthermore, the vibration response signal includes at least one of the following: the acceleration response signal of the vibrating rod, the vibration energy dissipation rate, and the vibration rod impedance change signal.

[0017] Furthermore, in steps S3 and S4, the instantaneous natural frequency is analyzed based on the fast Fourier transform spectrum analysis or peak search of the amplitude-frequency characteristic curve of the vibrating rod acceleration response signal; a sliding time window algorithm is used to process the continuous signal in real time, with a time window length of 0.5-2s.

[0018] Furthermore, in step S3, the preset duration of bottom vibration is 1-5 minutes.

[0019] Furthermore, in step S4, the vibratory rod lifting speed is controlled at 1.0-2.0 m / min.

[0020] Furthermore, in step S4, the specific method of adaptive adjustment is as follows: real-time monitoring of the vibration rod acceleration amplitude; when the acceleration amplitude shows a continuous downward trend or reaches the amplitude threshold corresponding to the preset density, the amplitude is automatically reduced or the output power is reduced.

[0021] Furthermore, the construction sites are arranged in a quincunx or square grid, with a spacing of 1.5-3.0m between adjacent construction sites.

[0022] Furthermore, it is applicable to treating alluvial silty soil foundations in the lower reaches of the Yellow River.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are: (1) Dynamic resonance matching throughout the entire process: The present invention fundamentally solves the problem of frequency drift caused by the time-varying stiffness of alluvial silt in the downstream of the river by analyzing the instantaneous natural frequency of the soil in real time and dynamically tracking and matching it. Compared with the traditional fixed-frequency resonance method, the technical solution of the present invention ensures that the "vibratory hammer-vibrating rod-soil" system is always in or close to the optimal resonance state throughout the entire construction process (including the bottom vibration stage and the lifting stage), and the effective reinforcement range is increased by 38%-56%.

[0024] (2) Uniform densification: During the lifting process, the present invention continuously performs dynamic frequency tracking to ensure that the soil at each depth can be densified in a resonant state, overcoming the problems of energy attenuation with depth and uneven reinforcement effect in traditional methods. The density of the treated soil is uniformly distributed along the depth direction, and the coefficient of variation of the standard penetration test blow count is reduced by more than 30%.

[0025] (3) Soil adaptive protection: The present invention uses the real-time response of the soil as the basis for adjustment. When the soil is close to the compaction state, the control system automatically senses and reduces energy input according to the change in acceleration amplitude, thus avoiding soil structure damage caused by frequency detuning or excessive vibration for a long time in traditional methods.

[0026] (4) Intelligent closed-loop control and energy saving and environmental protection: The present invention constructs a complete closed-loop control system of "real-time monitoring → instantaneous analysis → dynamic tracking → adaptive regulation", which does not require manual intervention, and the construction quality is stable and reliable, and is suitable for large-scale engineering applications. Due to the significant improvement in energy utilization efficiency, the energy consumption per unit volume of soil is reduced by 15%-25%; at the same time, due to the avoidance of excessive vibration and energy waste, the vibration impact on the surrounding environment is significantly reduced. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the method flow of the present invention.

[0028] Figure 2 This is a schematic diagram illustrating the dynamic frequency tracking principle of the present invention.

[0029] Figure 3 This is a comparison chart of the standard penetration test (SPT) blow count distribution curves along the depth of the present invention with those of the traditional fixed-frequency resonance method and the preset variable-frequency resonance method. Detailed Implementation

[0030] This invention provides an adaptive resonance compaction method for alluvial silty soil foundations based on dynamic frequency tracking. This method ensures that the "vibrator-soil" system remains in or near a resonant state throughout the compaction process, achieving efficient energy utilization and uniform soil densification. Notably, this invention is applicable to alluvial silty soil foundations with a depth of up to 25m, unlike surface vibration compaction.

[0031] like Figure 1 As shown, the process includes the following steps: S1, equipment placement and initial penetration.

[0032] Align the vibratory rod of the resonant compaction equipment with the preset construction point, start the vibratory hammer of the resonant compaction equipment, and drive the vibratory rod into the design depth at an initial scanning frequency higher than the upper limit of the estimated resonant frequency range.

[0033] The initial scanning frequency puts the "vibratory hammer-vibrator-soil" system in a non-resonant state, avoiding excessive vibration during penetration that could lead to premature energy dissipation. Simultaneously, high-frequency vibration reduces penetration resistance. The initial scanning frequency is 10%-30% higher than the upper limit of the estimated resonance frequency range; the specific value is determined based on site geological conditions and vibrator type.

[0034] S2, Real-time response monitoring.

[0035] Once the vibratory rod reaches the designed depth, the vibration response signal of the "vibratory hammer-vibratory rod-foundation soil" coupled system is collected in real time through a data acquisition device installed on the vibratory rod.

[0036] The data acquisition device includes an accelerometer and an impedance monitoring device, with a sampling frequency of no less than 200Hz to ensure the real-time performance and accuracy of instantaneous frequency analysis.

[0037] The vibration response signal includes at least one of the following: the acceleration response signal of the vibrating rod, the vibration energy dissipation rate, and the vibration rod impedance change signal.

[0038] S3, Bottom Vibration and Instantaneous Frequency Analysis.

[0039] The control system of the resonant compaction equipment receives the vibration response signal, analyzes and identifies the instantaneous natural frequency of the foundation soil under the current compaction state in real time; with the instantaneous natural frequency as the target, the output frequency of the vibratory hammer is adjusted in real time to match the instantaneous natural frequency, ensuring that the "vibratory hammer-vibrating rod-soil" system enters the resonance state at the design depth; the resonance state is maintained for a preset duration to densify deep soil (depth between 10m and 25m, which is a depth that is difficult to handle by conventional methods such as dynamic compaction; of course, this method is also applicable to soil with a depth of less than 10m).

[0040] The preset duration of bottom vibration is 1-5 minutes, and the specific duration is determined through field tests based on the site geological conditions and design compaction requirements.

[0041] S4. Dynamic frequency tracking and adaptive resonance during the vibratory rod lifting process.

[0042] Start the vibratory bar lifting program, and control the vibratory bar lifting speed at 1.0-2.0 m / min to ensure that there is enough time to fully densify the foundation soil during the lifting process.

[0043] During the vibratory bar lifting process, the control system continuously collects vibration response signals in real time, continuously analyzes the instantaneous natural frequencies of soil at different depths, and adjusts the output frequency of the vibratory hammer in real time so that the output frequency always follows and matches the instantaneous natural frequency of the soil at the current depth. This ensures that the "vibratory hammer-vibratory bar-soil" system is always in or close to a resonant state throughout the lifting process. At the same time, based on the real-time monitored changes in soil response amplitude, the output amplitude is adaptively adjusted to achieve uniform densification across the entire hole depth range.

[0044] During the vibratory boom lifting process, the output frequency of the vibratory hammer always follows and matches the instantaneous natural frequency of the soil at the current depth. This frequency exhibits a dynamic variation with depth. Assume the output frequency of the vibratory hammer is... The instantaneous natural frequency of the soil obtained through real-time analysis is The absolute deviation between the two : ;when When the frequency is ≤±0.5Hz, the system is considered to be in optimal resonance state; when... When the frequency is within the range of ±0.5Hz to ±1.0Hz, the system is considered to be approaching its optimal resonance state; when... When the frequency is greater than ±1.0Hz, the system is determined to be detuned, and frequency tracking closed-loop adjustment is immediately initiated.

[0045] In step S4, the adaptive adjustment is specifically implemented by real-time monitoring of the vibration amplitude. When the acceleration amplitude shows a continuous decreasing trend or reaches the amplitude threshold corresponding to the preset compaction degree, it is determined that the soil is close to a compacted state, and the amplitude is automatically reduced or the output power is lowered. The amplitude threshold is preset based on previous tests or empirical values.

[0046] Figure 2 This demonstrates the dynamic frequency tracking principle of the present invention. The figure shows the frequency change pattern throughout the entire process from penetration, vibration retention, to boosting. Figure 2 As shown, the alluvial silt of the lower Yellow River exhibits significant time-varying stiffness during vibration compaction: as the soil gradually compacts, its shear modulus and stiffness increase significantly, causing the natural frequency of the soil to rise in real time. Traditional fixed-frequency resonance methods cannot track this change, resulting in the soil being in a detuned state for most of the construction process.

[0047] S5. After the vibratory rod is raised to the ground, the construction of a single point is completed.

[0048] S6. Loop through the points until the foundation treatment of all areas is completed.

[0049] Move the resonant compaction equipment to the next construction point and repeat steps S1-S5 until the foundation treatment of the entire area is completed. The construction points are arranged in a quincunx or square grid, with a spacing of 1.5-3.0m between adjacent construction points, depending on the design requirements.

[0050] In steps S3 and S4, the instantaneous natural frequency is analyzed based on the fast Fourier transform spectrum analysis or peak search of the amplitude-frequency characteristic curve of the vibrating rod acceleration response signal; a sliding time window algorithm is used to process the continuous signal in real time, and the time window length is preferably 0.5-2s.

[0051] The analysis of the instantaneous natural frequency of soil in this invention is performed synchronously and in real time with the construction process. The core principle is to accurately identify the true natural frequency of the soil from the vibration response of the "vibratory hammer-vibrator-soil" coupled system, providing a control target for dynamic frequency tracking. The analysis of the instantaneous natural frequency of soil is implemented according to the following core process: ① Preprocessing the collected vibration rod acceleration response signal to remove interference; ② Using a 0.5-2s sliding time window to process the signal in segments in real time; ③ Performing FFT spectrum analysis on each segment to obtain the amplitude-frequency characteristic curve; ④ Eliminating the frequency interference of the equipment itself, locking the frequency corresponding to the peak value within the effective frequency range of the soil, which is the current instantaneous natural frequency of the soil.

[0052] The analysis of the instantaneous natural frequency of the soil includes the following steps: (1) Effective signal acquisition: The axial acceleration sensor installed on the vibrating rod is used to collect the vibration acceleration signal at the contact end between the vibrating rod and the soil in real time. The sampling frequency is not less than 200Hz, and the collected signal is synchronously transmitted to the equipment control system. (2) Signal preprocessing: The original acceleration signal is subjected to basic interference removal processing; firstly, the DC component and low frequency trend term in the signal are removed to eliminate the signal drift caused by the penetration and lifting of the vibrating rod; secondly, the effective signal of 10-30Hz is retained by bandpass filtering to filter out high frequency noise and low frequency mechanical vibration interference in the construction environment, so as to provide an effective data source for subsequent analysis. (3) Real-time framing with sliding time window: The continuous signal after preprocessing is segmented by a sliding time window. The time window length is 0.5-2s, and the windows slide continuously with a 50% overlap rate. Each slide outputs a segment of effective signal to be analyzed to ensure real-time tracking of soil frequency changes and avoid missed detection. (4) Spectrum analysis and peak extraction: For each segment of effective signal after frame division, perform Fast Fourier Transform (FFT) spectrum analysis to obtain the amplitude-frequency characteristic curve of the signal segment; search for the peak point in the curve, and the frequency corresponding to the peak point is the main resonance frequency of the coupled system. (5) Accurate identification of instantaneous natural frequency of soil: The true natural frequency of soil is locked from the main resonance frequency of the coupling system. The judgment rules are as follows: ① Equipment frequency elimination: Before formal construction, the natural frequency range of the vibrating hammer and vibrating rod is pre-calibrated by the equipment's no-vibration sweep frequency test. The peak value in the range is permanently eliminated in the spectrum analysis to eliminate the vibration interference of the equipment itself; ② Effective range locking: For the engineering characteristics of alluvial silt in the lower reaches of the Yellow River, the natural frequency of the soil in the whole state from loose to dense is in the range of 15-25Hz. Only the effective peak value is searched in this range; ② Validity verification: The locked peak value must be the maximum amplitude peak value in the effective range, and the deviation from the soil frequency analyzed in the previous frame does not exceed ±2Hz. It conforms to the characteristics of gradual change of soil stiffness and continuous frequency drift, avoiding sudden interference and misjudgment; The frequency corresponding to the peak value that meets the above rules is the instantaneous natural frequency of the soil in the current dense state. ⑥ Real-time output of results: After each frame of signal is analyzed, the instantaneous natural frequency of the soil is immediately output to the equipment control system. The control system adjusts the output frequency of the vibratory hammer in real time based on this as the target, so as to realize the dynamic tracking of the resonance state.

[0053] When the excitation frequency of the vibratory hammer matches the natural frequency of the soil at the site, the "vibratory hammer-vibrating rod-foundation soil" system enters a resonant state, and the transmission efficiency of vibration energy to the foundation soil reaches its peak. At this time, the vibration acceleration of the soil monitored on the ground will show a global significant peak. The excitation frequency corresponding to this peak is the true reference resonant frequency of the soil at the site. Using this as the core reference, all preset values ​​in this invention are calibrated. This is an in-situ, non-destructive, and reproducible method that fully conforms to the real geological conditions of the alluvial silt site downstream of the river. It solves the problems of large deviations between indoor tests and field geological conditions and the lack of site-specificity of preset values.

[0054] The method for determining the true reference resonant frequency of the soil is as follows: (1) Before formal construction, select no less than 3 representative test pile locations at the construction site and conduct pre-penetration calibration tests: At the test pile locations, 0.5m, 1.0m, and 1.5m radially, 3 sets of vertical vibration acceleration sensors are symmetrically arranged. The sensor sampling frequency is not less than 200Hz, and the data is collected synchronously with the data acquisition device on the vibrating rod; (2) Start the vibrating hammer and adopt a linear sweep frequency mode of 10-30Hz (sweep frequency rate 0.2Hz / s). Simultaneously, the vibrating rod is driven into the design depth at a uniform speed. The real-time output frequency of the vibrating hammer and the ground vibration response data are recorded synchronously throughout the process. When the average vibration acceleration of the 3 sets of monitoring points reaches a global peak at a certain excitation frequency, the frequency is determined to be the reference resonant frequency of the soil at the site.

[0055] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0056] Example 1: This example focuses on the treatment of alluvial silty soil foundation in the lower reaches of the Yellow River. The site is located at DZ. Geological surveys show that the silt content is 85%, the natural void ratio is 0.85, the moisture content is 32%, the groundwater level is 0.5m deep, and the site is classified as severely liquefiable. The design requires a standard penetration test (SPT) blow count of no less than 10 after treatment to eliminate liquefaction potential.

[0057] The foundation treatment is carried out using the adaptive resonance compaction method for alluvial silt foundation based on dynamic frequency tracking provided by the present invention. The specific steps are as follows: (1) Preliminary test to determine the estimated frequency range: Before formal construction, a representative area is selected for on-site excitation test to determine the natural frequency range of the soil in the site as 16-22Hz.

[0058] (2) Equipment placement and initial penetration: An XY-100 type resonant compaction device was used, with a vibratory rod diameter of 0.35m and a length of 20m. The vibratory rod was aligned with the preset construction point, and the vibratory hammer was started at an initial scanning frequency of 26.4Hz (20% higher than the upper limit of the estimated resonant frequency range), and the vibratory rod was penetrated at a uniform speed to the designed depth of 16m. Monitoring during the penetration process showed that the vibration acceleration amplitude was low, indicating that the system was in a non-resonant state.

[0059] (3) Real-time response monitoring: After the vibrating rod reaches the design depth, the vibration acceleration signal is collected in real time by the acceleration sensor (sampling frequency 200Hz) installed on the vibrating rod.

[0060] (4) Bottom Vibration and Dynamic Frequency Tracking: The control system receives the acceleration signal and performs a fast Fourier transform using a 1-second sliding time window to analyze the instantaneous natural frequency of the soil in real time. The initial analytical value is 17.5Hz. The control system uses this frequency as the target and adjusts the output frequency of the vibratory hammer to 17.5Hz. At this time, a significant increase in the acceleration amplitude is detected, indicating that the system has entered the resonance state. As the vibration continues, the instantaneous natural frequency gradually rises. The control system tracks and adjusts the output frequency in real time to maintain the resonance state. The vibration duration is set to 2 minutes, and the instantaneous natural frequency rises to 22.0Hz at the end.

[0061] (5) Adaptive Resonance During Vibratory Rod Lifting: The vibratory rod lifting program is initiated, and the lifting speed is controlled at 1.0 m / min. During the lifting process, the control system continuously collects acceleration signals, continuously analyzes the instantaneous natural frequencies of the soil at different depths, and adjusts the output frequency in real time to follow the changes. Monitoring data shows that during the lifting process from a depth of 10 m to the ground, the instantaneous natural frequency varies between 19-23 Hz, and the output frequency always matches it, maintaining a high acceleration amplitude. At the same time, the acceleration amplitude is monitored in real time. When a decreasing trend in the amplitude is detected, the control system automatically reduces the amplitude by about 15% to prevent excessive vibration from causing damage to the soil structure.

[0062] (6) Raise the vibratory rod to the ground: After the vibratory rod is raised to the ground, the construction of a single point is completed. The total construction time for a single point is about 20 minutes.

[0063] (7) Point cycle: The points are arranged in a quincunx pattern with a spacing of 1.8m, and all 64 points are constructed in sequence.

[0064] The treatment effect of this embodiment was tested as follows: Standard penetration test (SPT) and static cone penetration test (PCT) were conducted 14 days after construction. The results showed that the average SPT blow count before treatment was 5 blows, which increased to 18-21 blows after treatment, with a coefficient of variation of 0.12; the average cone tip resistance of the static cone penetration test increased from 2.5 MPa before treatment to 8.2 MPa; according to the specification, the liquefaction potential improved from "severe liquefaction" to "non-liquefaction"; core sampling showed that the soil was dense and uniform.

[0065] Example 2: This example addresses the treatment of alluvial silty soil foundations in the lower reaches of the Yellow River. The site is located at DY. Geological surveys show that the silt content is 80%, the natural void ratio is 0.92, the moisture content is 34%, the groundwater level is at a depth of 0.5m, and the site is classified as severely liquefiable. The design requires a standard penetration test (SPT) blow count of no less than 10 after treatment to eliminate liquefaction potential.

[0066] The foundation treatment is carried out using the adaptive resonance compaction method for alluvial silt foundation based on dynamic frequency tracking provided by the present invention. The specific steps are as follows: (1) Preliminary test to determine the estimated frequency range: Before formal construction, a representative area is selected for on-site excitation test to determine the natural frequency range of the soil in the site as 18-23Hz.

[0067] (2) Equipment placement and initial penetration: An XY-100 type resonant compaction device was used, with a vibratory rod diameter of 0.35m and a length of 20m. The vibratory rod was aligned with the preset construction point, and the vibratory hammer was started at an initial scanning frequency of 25.76Hz (12% higher than the upper limit of the estimated resonant frequency range), and the vibratory rod was penetrated at a uniform speed to the designed depth of 16m. Monitoring during the penetration process showed that the vibration acceleration amplitude was low, indicating that the system was in a non-resonant state.

[0068] (3) Real-time response monitoring: After the vibrating rod reaches the design depth, the vibration acceleration signal is collected in real time by the acceleration sensor (sampling frequency 200Hz) installed on the vibrating rod.

[0069] (4) Bottom Vibration and Dynamic Frequency Tracking: The control system receives the acceleration signal and performs a fast Fourier transform using a 1-second sliding time window to analyze the instantaneous natural frequency of the soil in real time. The initial analytical value is 18Hz. The control system uses this frequency as the target and adjusts the output frequency of the vibratory hammer to 18Hz. At this time, a significant increase in the acceleration amplitude is detected, indicating that the system has entered the resonance state. As the vibration continues, the instantaneous natural frequency gradually rises. The control system tracks and adjusts the output frequency in real time to maintain the resonance state. The vibration duration is determined to be 2 minutes based on field tests. At the end, the instantaneous natural frequency rises to 22.5Hz.

[0070] (5) Adaptive Resonance During Vibratory Rod Lifting: The vibratory rod lifting program is initiated, and the lifting speed is controlled at 1.5 m / min. During the lifting process, the control system continuously collects acceleration signals, continuously analyzes the instantaneous natural frequencies of the soil at different depths, and adjusts the output frequency in real time to follow the changes. Monitoring data shows that during the lifting process from a depth of 10 m to the ground, the instantaneous natural frequency varies between 20-23 Hz, and the output frequency always matches it, maintaining a high acceleration amplitude. At the same time, the acceleration amplitude is monitored in real time. When a 5% decrease in acceleration amplitude is detected, the control system automatically reduces the amplitude by 20% to prevent excessive vibration from damaging the soil structure.

[0071] (6) Raise the vibratory rod to the ground: After the vibratory rod is raised to the ground, the construction of a single point is completed. The total construction time for a single point is about 25 minutes.

[0072] (7) Point cycle: The points are arranged in a quincunx pattern with a spacing of 1.6m, and all 100 points are constructed in sequence.

[0073] The treatment effect of this embodiment was tested as follows: Standard penetration test and static cone penetration test were carried out 14 days after the completion of construction. The results showed that the number of standard penetration test blows increased from 4-6 blows before treatment to 16-19 blows, with a coefficient of variation of 0.10; the average resistance of the cone tip of the static cone penetration test increased from 2.3 MPa before treatment to 7.6 MPa; the liquefaction potential was completely eliminated, and the reinforcement effect was good.

[0074] Comparative Example 1: The test site for this comparative example is the same as that for Example 1. The foundation treatment method used is the traditional fixed-frequency resonance method, and the output frequency (vibration frequency) of the vibrating hammer is fixed at 20Hz.

[0075] Comparative Example 2: The test site for this comparative example is the same as that for Example 1. The foundation treatment method used is the preset frequency conversion resonance method, and the output frequency (vibration frequency) of the vibratory hammer increases from 18Hz to 23Hz according to the preset curve.

[0076] The treatment effect testing method for both Comparative Example 1 and Comparative Example 2 was as follows: a standard penetration test was conducted 14 days after construction was completed. The comparison results of the treatment effects of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Table 1 and... Figure 3 As shown, the results indicate that the adaptive resonance compaction method for alluvial silt foundations based on dynamic frequency tracking of the present invention used in Example 1 is significantly superior to the traditional methods of Comparative Example 1 and Comparative Example 2 in terms of reinforcement effect (the higher the SPT blow count, the better the soil reinforcement effect), uniformity, effective reinforcement range, and energy saving.

[0077] Table 1. Treatment effects of different foundation treatment methods In summary, this invention fundamentally solves the frequency drift problem caused by the time-varying stiffness of alluvial silt in downstream rivers by real-time analysis of the soil's instantaneous natural frequency and dynamic tracking and matching. Compared with traditional fixed-frequency resonance methods, the technical solution of this invention ensures that the "vibratory hammer-vibrator-soil" system remains in or approaches the optimal resonance state throughout the entire construction process (including the bottom vibration stage and the lifting stage), effectively increasing the reinforcement range by 38%-56%.

[0078] This invention continuously tracks the dynamic frequency during the lifting process to ensure that the soil at each depth is densified in a resonant state, overcoming the problems of energy attenuation with depth and uneven reinforcement effect in traditional methods. After treatment, the soil density is uniformly distributed along the depth direction, and the coefficient of variation of the standard penetration test blow count is reduced by more than 30%.

[0079] This invention constructs a complete closed-loop control system of "real-time monitoring → instantaneous analysis → dynamic tracking → adaptive adjustment," requiring no manual intervention, ensuring stable and reliable construction quality, and suitable for large-scale engineering applications. Due to a significant improvement in energy utilization efficiency, energy consumption per unit volume of soil is reduced by 15%-25%; simultaneously, by avoiding excessive vibration and energy waste, the vibration impact on the surrounding environment is significantly reduced.

[0080] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. An adaptive resonance compaction method for alluvial silty soil foundations based on dynamic frequency tracking, characterized in that, Includes the following steps: S1. Align the vibratory rod of the resonant compaction equipment with the preset construction point, start the vibratory hammer of the resonant compaction equipment, and drive the vibratory rod into the design depth at an initial scanning frequency higher than the upper limit of the estimated resonant frequency range. S2. When the vibratory rod reaches the design depth, the vibration response signal of the coupling system of the vibratory hammer, vibratory rod and foundation soil is collected in real time through the data acquisition device set on the vibratory rod. S3. The control system of the resonant compaction equipment receives the vibration response signal, analyzes and identifies the instantaneous natural frequency of the foundation soil under the current compaction state in real time; with the instantaneous natural frequency as the target, the output frequency of the vibratory hammer is adjusted in real time to match the instantaneous natural frequency, ensuring that the vibratory hammer, vibratory rod and soil system enter the resonant state at the design depth; and the resonant state is maintained for a preset duration. S4. Start the vibratory rod lifting program. The control system continuously collects vibration response signals in real time, continuously analyzes the instantaneous natural frequency of soil at different depths, and adjusts the output frequency of the vibratory hammer in real time so that the output frequency always follows and matches the instantaneous natural frequency of the soil at the current depth. This ensures that the vibratory hammer, vibratory rod, and soil system are always in or close to a resonant state throughout the lifting process. At the same time, the output amplitude is adaptively adjusted according to the real-time monitored changes in soil response amplitude to achieve uniform densification across the entire hole depth range. S5. After the vibratory rod is raised to the ground, the construction of a single point is completed; S6. Move the resonant compaction equipment to the next construction point and repeat steps S1-S5 until the foundation treatment of all areas is completed.

2. The adaptive resonance compaction method for alluvial silty soil foundation based on dynamic frequency tracking according to claim 1, characterized in that, In step S1, the initial scanning frequency is 10%-30% higher than the upper limit of the estimated resonant frequency range.

3. The adaptive resonance compaction method for alluvial silty soil foundation based on dynamic frequency tracking according to claim 1, characterized in that, In step S2, the data acquisition device includes an accelerometer and an impedance monitoring device, and the sampling frequency is not less than 200Hz.

4. The adaptive resonance compaction method for alluvial silty soil foundation based on dynamic frequency tracking according to claim 1, characterized in that, The vibration response signal includes at least one of the following: the acceleration response signal of the vibrating rod, the vibration energy dissipation rate, and the vibration rod impedance change signal.

5. The adaptive resonance compaction method for alluvial silty soil foundation based on dynamic frequency tracking according to claim 3 or 4, characterized in that, In steps S3 and S4, the instantaneous natural frequency is analyzed based on the fast Fourier transform spectrum analysis of the vibration rod acceleration response signal or the peak search of the amplitude-frequency characteristic curve; a sliding time window algorithm is used to process the continuous signal in real time, with a time window length of 0.5-2s.

6. The adaptive resonance compaction method for alluvial silty soil foundation based on dynamic frequency tracking according to claim 1, characterized in that, In step S3, the preset duration of bottom vibration is 1-5 minutes.

7. The adaptive resonance compaction method for alluvial silty soil foundation based on dynamic frequency tracking according to claim 1, characterized in that, In step S4, the vibratory rod lifting speed is controlled at 1.0-2.0 m / min.

8. The adaptive resonance compaction method for alluvial silty soil foundation based on dynamic frequency tracking according to claim 1, characterized in that, In step S4, the specific method of adaptive adjustment is as follows: real-time monitoring of the vibration rod acceleration amplitude; when the acceleration amplitude shows a continuous downward trend or reaches the amplitude threshold corresponding to the preset density, the amplitude is automatically reduced or the output power is reduced.

9. The adaptive resonance compaction method for alluvial silty soil foundation based on dynamic frequency tracking according to claim 1, characterized in that, The construction sites are arranged in a quincunx or square grid, with a spacing of 1.5-3.0m between adjacent construction sites.

10. The adaptive resonance compaction method for alluvial silty soil foundation based on dynamic frequency tracking according to claim 1, characterized in that, Suitable for treating alluvial silt foundations in the lower reaches of the Yellow River.

Images