Method for determining soft foundation reinforcement vibroflotation construction parameters

Abstract

The invention relates to the technical field of civil engineering, in particular to a soft foundation reinforcement vibroflotation construction parameter determination method, which comprises the following steps of: presetting multi-dimensional parameter combinations such as vibroflotation spacing and point distribution mode, dividing equal-area test area construction, and synchronously monitoring dynamic response parameters such as soil pore water pressure and horizontal displacement; after construction, indexes such as the standard penetration stroke number and the foundation bearing capacity are detected; and carrying out parameter sensitivity analysis in combination with an extended Duck-Prager model, locking high-sensitivity parameters such as an internal friction angle, screening an optimal parameter combination through a weighted scoring method, and outputting final parameters after the optimal parameter combination is confirmed to reach the standard through engineering verification. The method gets rid of experience dependence, parameter determination is scientific and accurate, the bearing capacity of the reinforced foundation reaches 158 kPa, the standard penetration number is increased, compared with a traditional method, the construction efficiency is improved, the cost is reduced, the liquefaction risk can be effectively eliminated, and the method is suitable for complex soft foundation treatment such as hydraulic reclamation.

Description

Technical Field

[0001] This invention relates to the field of civil engineering technology, specifically to a method for determining the parameters of vibratory compaction construction for soft foundation reinforcement. Background Technology

[0002] With the rapid development of marine resources and the construction of coastal cities, land reclamation projects are increasing. The resulting soft soil foundations are characterized by high water content, low strength, high compressibility, and underconsolidation, requiring reinforcement to meet engineering load-bearing requirements. Vibro-compaction has become a commonly used technique for soft soil foundation reinforcement due to its convenient construction, low cost, and significant reinforcement effect. Its core principle is to use the vibration of a vibro-compactor and the action of high-pressure water jetting to liquefy the soil, rearrange and compact the particles, and improve the foundation's bearing capacity and resistance to liquefaction.

[0003] However, existing methods for determining vibro-compaction construction parameters for soft soil reinforcement rely heavily on engineering experience and on-site trial and error, resulting in a high degree of arbitrariness and a lack of systematic experimental design and numerical simulation. This leads to low construction efficiency and high costs. Furthermore, the influence of vibro-compaction parameters (such as spacing, placement method, power, and load frequency) is unclear, and parameter sensitivity analysis has not been conducted for the characteristics of dredged sand, making it difficult to accurately optimize key parameters. At the same time, monitoring indicators are limited, and the dynamic response of the soil and reinforcement effect indicators are not collected simultaneously, making it impossible to comprehensively evaluate the rationality of the parameters. Numerical simulation is disconnected from on-site testing, and existing models do not fully consider the elasto-plastic characteristics of dredged sand, resulting in a lack of theoretical support for parameter optimization.

[0004] The aforementioned problems lead to unstable vibro-compaction reinforcement effects, frequent occurrences of insufficient improvement in foundation bearing capacity and excessive settlement, limiting the application of vibro-compaction technology in complex soft soil foundation treatment. Therefore, developing a systematic method for determining vibro-compaction construction parameters that integrates experimental design, numerical simulation, parameter sensitivity analysis, and engineering verification has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned deficiencies and problems, this invention provides a method for determining vibratory compaction construction parameters for soft soil foundation reinforcement. By combining experiments and numerical simulations, the influence of key parameters is clarified, enabling optimized selection of vibratory compaction construction parameters and ensuring the effectiveness of soft soil foundation reinforcement.

[0006] The solution adopted by this invention to solve its technical problem is: a method for determining the parameters of vibratory compaction construction for soft soil foundation reinforcement, comprising the following steps: (1) Preset combination of vibratory compaction construction parameters, including vibratory compaction spacing, layout method, vibratory compaction power, construction process and vibration load parameters; (2) Divide the test areas into multiple test areas of equal area and carry out vibratory compaction construction according to the preset parameter combination; (3) During the construction process, the dynamic response parameters of the soil are monitored simultaneously, and the foundation reinforcement effect index is tested after construction; (4) Based on monitoring data and reinforcement effect indicators, parameter sensitivity analysis is conducted using numerical models to select the optimal combination of construction parameters; (5) Verify the optimal combination of construction parameters in engineering, and output the final construction parameters after confirming that the design requirements are met.

[0007] Furthermore, the preset range of the vibration spacing in step (1) is 2m to 3m, the vibration power is 100kW to 130kW, the layout method includes equilateral triangle arrangement and square arrangement, the construction process includes vibration direct insertion process and vibration reverse insertion process, and the vibration load parameters include peak load of 300kN to 800kN and vibration frequency of 4Hz to 24Hz.

[0008] Furthermore, the area of ​​the test area mentioned in step (2) is 500m², the vibratory compaction reinforcement depth is 8m to 9m during construction, the vibration time at the bottom of the hole is 1min, and the vibration is left for 30s every 1m when the vibratory compactor is lifted.

[0009] Furthermore, the dynamic response parameters of the soil in step (3) include pore water pressure, horizontal displacement, vertical settlement, surface vibration velocity and surface vibration acceleration; the reinforcement effect indicators include standard penetration test blow count, foundation bearing capacity, dry density, compaction degree and settlement.

[0010] Furthermore, the numerical model described in step (4) is an extended Druck-Prager model. The parameter sensitivity analysis focuses on the internal friction angle β, shear dilatation angle ψ, cohesion C and elastic modulus E in the model, and selects β, ψ and C as highly sensitive parameters for key optimization.

[0011] Furthermore, the optimal combination of construction parameters in step (4) satisfies the following: the vibratory spacing is 2.5m, the layout is an equilateral triangle, the vibratory power is 100kW~130kW, the construction process adopts the vibratory direct insertion process, and the vibration frequency is 16Hz.

[0012] Furthermore, the criteria for judging the engineering verification in step (5) are: foundation bearing capacity ≥150kPa, standard penetration test blow count increased by ≥40% compared with before construction, dry density ≥1.70g / cm³, and compaction degree ≥0.90.

[0013] Furthermore, the standard penetration test (SPT) blow count is performed at the vibratory impact hole position, the midpoint of the line connecting the holes, and the centroid of the layout, and the average value of multiple test results is taken; the settlement measurement is performed for different layout methods, and the settlement of the equilateral triangle layout is ≥27% higher than that of the square layout.

[0014] The beneficial effects of this invention are: This invention solves the problems of existing methods relying on engineering experience and having strong blind trial-and-error in the field by using a closed-loop technical solution that combines multi-dimensional parameter combinations for zonal testing with synchronous monitoring, numerical simulation, parameter sensitivity analysis, and engineering verification. By using an extended Druck-Prager model to lock in highly sensitive parameters such as the internal friction angle β, shear dilatation angle ψ, and cohesion C, and combining the weighted scoring method to screen the optimal parameter combination, the influence law of key parameters such as vibration spacing and point layout is clarified. This makes parameter optimization no longer dependent on subjective experience, but based on quantitative data and theoretical support, which greatly improves the scientificity and accuracy of parameter determination. This invention achieves a comprehensive assessment of the rationality of parameters by simultaneously monitoring dynamic soil response parameters such as pore water pressure and horizontal displacement, as well as reinforcement effect indicators such as SPT blow count and foundation bearing capacity. Engineering verification results show that after construction using the optimal parameter combination (2.5m vibratory compaction spacing, equilateral triangular layout, vibratory direct insertion process, 16Hz vibration frequency, etc.), the average foundation bearing capacity reaches 158kPa, an increase of 23.4% compared to the traditional empirical method; the SPT blow count increases by 69.7%, far exceeding the design requirement of 40%, and effectively eliminates the risk of sand liquefaction; dry density and compaction degree both meet design standards, and the settlement uniformity deviation does not exceed 5%, completely solving the problems of unstable reinforcement effect and excessive settlement in traditional methods, ensuring reliable soft soil foundation reinforcement quality. Attached Figure Description

[0015] Figure 1 This is a schematic diagram showing the distribution of the test areas; Figure 2 This is a schematic diagram of the equilateral triangle vibratory impact and standard penetration test hole positions; Figure 3 This is a schematic diagram of the square vibratory impact test and standard penetration test hole locations; Figure 4 The yield trajectory diagram for the linear Drucker-Prager model; Figure 5 This is a plastic potential surface plot for the linear Drucker-Prager model; Figure 6 A comparison chart of standard penetration test (SPT) hit counts in different areas; Figure 7 This is a PS curve of the foundation bearing capacity. Figure 8 For parameter sensitivity analysis curves; Figure 9 This is a graph showing the relationship between horizontal displacement and distance. Detailed Implementation

[0016] The following section uses the Xiamen Daxiaodeng land reclamation project as an example, along with related information. Figure 1-9 The specific embodiments of the present invention will be described in detail below. This embodiment is only used to explain the present invention and is not intended to limit the scope of protection of the present invention.

[0017] Example 1: This example provides a complete process for determining the parameters of vibratory compaction construction for soft foundation reinforcement.

[0018] 1. Preparation of test site and equipment Site conditions: The test site is located in the Xiamen Daxiaodeng land reclamation project, a large-scale hydraulic reclamation project with a total area of ​​9.81 km². The test area is 3000 m² (divided into 6 500 m² zones, such as...). Figure 1 (As shown). The foundation soil of the site is distributed from top to bottom as follows: ① gravelly sand, ② silt, ③ silty clay, ④ medium sand, and ⑤ marine clay.

[0019]

[0020] Construction equipment: ZCQ-100 (100kW, excitation force 190kN, amplitude 8mm, speed 1460r / min) and ZCQ-130 (130kW, excitation force 220kN, amplitude 10mm, speed 1480r / min) vibratory compactors; QUY55 crawler crane; 80-50-250 high-pressure water pump; 500kW generator.

[0021] Monitoring equipment includes: pore water pressure sensor, horizontal displacement meter, vertical settlement observation instrument, surface vibration velocity sensor, and surface vibration acceleration sensor; testing equipment includes standard penetration test apparatus, plate load test apparatus, and ring cutter density meter.

[0022] Numerical simulation equipment: Finite element analysis software is used to construct an elastic-plastic model of soil based on the extended Druck-Prager model. The extended DP model contains multiple material parameters, all of which are obtained from triaxial consolidated drained tests. Each test parameter is meaningful and can be implemented in the finite element software.

[0023] The yield function of the linear DP model is: , in, , In the formula: q is the equivalent deviatoric stress, and q can be replaced by t. The above formula can reflect the influence of the principal stress on the model to a certain extent; β is the angle value corresponding to the yield surface; k is the ratio of triaxial tensile strength to triaxial compressive strength; d represents the intercept of the yield surface, and its magnitude is the distance from the linear function to the t value. When the yield surface is a linear function, its yield trajectory is as follows: Figure 4 As shown; The plastic potential surface of the linear DP model is shown below. Figure 5 Its function is: , In the formula: y¢ is the plastic potential surface angle. Since the plastic potential surface of the model is different from the yield function, only non-associated flow rules can be used for calculation.

[0024] The final model parameters are as follows: elastic modulus of dredged sand 20 MPa, internal friction angle β = 30°, dilatation angle ψ = 10°, cohesion C = 17300 kPa, and Poisson's ratio 0.3.

[0025] 2. Step (1): Preset combination of vibratory compaction construction parameters Based on the site soil characteristics and engineering experience, the preset construction parameters cover five categories: vibratory compaction spacing, vibratory compaction power, placement method, construction technology, and vibration load parameters. The preset vibratory compaction spacing ranges from 2m to 3m; the vibratory compaction power is selected from two specifications: 100kW and 130kW; the placement method includes two types: equilateral triangle and square arrangement, as detailed below. Figure 2 and Figure 3 As shown; Vibratory compaction method: single-machine vibratory compaction or dual-machine resonance; Construction process is divided into vibratory direct insertion process (construction is completed by one sinking and lifting) and vibratory reverse insertion process (secondary sinking and reinforcement after one sinking); Among the vibration load parameters, the peak load covers five levels: 300kN, 400kN, 500kN, 600kN, and 800kN, and the vibration frequency covers six levels: 4Hz, 8Hz, 12Hz, 16Hz, 20Hz, and 24Hz.

[0026] 3. Step (2): Divide the test area and carry out construction. Test area division and parameter allocation: The 3000m² test site was divided into six test areas (Ⅰ, Ⅳ, Ⅱ, Ⅴ, Ⅲ, VI) with equal area. Each test area was constructed independently using different parameter combinations. For example, Zone Ⅰ used 100kW vibratory power, 2m vibratory spacing, square layout, single-machine vibratory impact, vibratory direct insertion process, 400kN peak load, and 12Hz vibration frequency; Zone Ⅱ used 100kW vibratory power, 2.5m vibratory spacing, equilateral triangle layout, dual-machine resonance, vibratory direct insertion process, 500kN peak load, and 16Hz vibration frequency. The remaining zones were allocated according to the preset parameter combinations to ensure that all different combinations of preset parameters were covered.

[0027] Construction Process: First, the site is leveled, debris is cleared from the test area, and a leveling instrument is used to ensure the surface slope does not exceed 0.5%, providing a flat foundation for subsequent construction. Next, the points are laid out. According to the pre-set layout, a total station is used to accurately locate each vibratory compaction point, with the point deviation controlled within 5cm to ensure uniformity of the layout. During vibratory compaction, a crawler crane suspends the vibratory compactor to the designated point. The high-pressure water pump and vibratory compactor are started, and the vibratory compactor is lowered to the designed depth of 8-9m at a sinking speed of 0.025m / s. After reaching the designed depth, vibration is maintained at the bottom of the hole for 1 minute. Then, the vibratory compactor is lifted at a uniform speed, maintaining vibration for 30 seconds every 1m, until the vibratory compactor is raised to the ground and the equipment is shut down. Throughout the construction process, the verticality control system of the crane ensures that the vertical deviation of the vibratory compactor does not exceed 1%, and the sinking and lifting speeds remain uniform and stable to avoid affecting the reinforcement effect due to equipment tilting or speed fluctuations.

[0028] 4. Step (3): Monitoring and Detection Dynamic Response Monitoring: Throughout the entire vibro-compaction process, sensors pre-embedded at different depths and locations within the soil are used to synchronously collect dynamic response parameters of the soil. Pore water pressure sensors are embedded at the interfaces and intermediate positions of each soil layer to capture the changes in pore water pressure during vibration in real time. Horizontal displacement gauges and vertical settlement observation instruments are deployed at different distances around the vibro-compaction points to monitor the horizontal and vertical displacement changes of the soil. Surface vibration velocity sensors and acceleration sensors are placed on the surface of the test area to record the velocity and acceleration changes during vibration propagation. All data collected by the sensors are transmitted to the controller in real time to ensure full traceability of the soil response during construction.

[0029] Reinforcement effect testing: 28 days after the completion of vibro-compaction construction, a comprehensive reinforcement effect test was conducted on each test area. Standard penetration test (SPT) blow count (N63.5) was tested by drilling holes at the vibratory punching hole location, the midpoint of the line connecting the holes, and the centroid of the test point. The test was conducted once every 1m depth, and each test point was tested three times. The average of the three test results was taken as the SPT blow count for that point. The bearing capacity of the foundation was tested using a 1m² square bearing plate for plate load testing, with 10 loading levels, each level having a load capacity of 30kPa, and a maximum load value of 300kPa. Load-settlement (PS) curves were plotted (e.g., ...). Figure 7 As shown in the figure, the load corresponding to the settlement-to-bearing plate width ratio (s / b) of 0.01 to 0.015 is taken as the characteristic value of the foundation bearing capacity; Dry density and compaction degree were tested using the ring cutter method. Samples were taken at three depths in each test area: 0–0.4 m, 0.4–0.8 m, and 0.8–1.0 m. Each group of samples was tested twice in parallel, and the average value was taken as the dry density at that depth. The compaction degree was calculated based on the maximum dry density of 1.88 g / cm³. Settlement was measured by leveling the difference in ground elevation before and after construction in the test area. Ten observation points were evenly set up in each test area, and the average elevation difference of the ten observation points was taken as the settlement of the test area. For sandy soil at a depth of 20m below the ground surface, the standard penetration test (SPT) threshold for liquefaction can be calculated using the following formula: , Where: N cr The critical value for determining whether liquefaction has occurred; N0 is the baseline value for determining whether liquefaction has occurred; d s The depth (m) of the test for each soil layer; d w Where is the groundwater level depth (m); FC is the percentage content of clay particles in the soil. Calculate the critical value using the above formula, and compare it with the standard penetration test (SPT) blow count after the test to determine the degree of liquefaction elimination.

[0030] 5. Step (4): Numerical simulation and parameter selection Numerical Model Establishment: Based on the extended Druck-Prager model, a cylindrical soil model was constructed using finite element software. The model has a radius of 12.5m and a depth of 20m. The soil is modeled as an Eulerian solid, with a 2m high empty Eulerian solid at the surface to accommodate the flow space requirements after soil deformation. The vibratory compactor is modeled as a Lagrange solid, consisting of a cylinder and a conical apex. The cylinder is 10m long and 750mm in diameter, using steel material parameters of 7850kg / cm³ density, Poisson's ratio 0.3, and elastic modulus 200Gpa. Eight-node hexahedral elements were used for the soil, and four-node tetrahedral elements were used for the vibratory compactor. The model contains a total of 312,255 nodes and 260,011 elements. The model boundary conditions were set as follows: the horizontal velocity constraint on the outer surface of the soil was 0, and the vertical velocity constraint at the bottom was 0. The vibratory compactor was subjected to a horizontal vibration load and a settlement velocity of 0.025m / s, consistent with the on-site construction parameters. The contact between the soil and the vibratory compactor is set as a universal contact, with the tangential direction using the Mohr-Coulumb friction model and defined as "penalty", and the normal direction set as hard contact property to ensure the realism of the contact behavior during the simulation.

[0031] Parameter sensitivity analysis: During the numerical simulation, with other model parameters fixed, parameter reduction and incremental analyses were performed on the internal friction angle β, dilatation angle ψ, cohesion C, and elastic modulus E in the extended Druck-Prager model. Only one parameter was changed at a time, and the rate of change of horizontal displacement at a distance of 1m from the vibratory impact point was calculated when the vibratory impactor subsided by 4m. The analysis results in the table below show that changes in the internal friction angle β, dilatation angle ψ, and cohesion C resulted in horizontal displacement changes ranging from ±11% to ±24%, while changes in the elastic modulus E resulted in horizontal displacement changes ranging from ±1.3% to ±1.9%. Therefore, β, ψ, and C were identified as highly sensitive parameters and will be the focus of subsequent parameter optimization.

[0032]

[0033] Optimal Parameter Selection: Combining on-site monitoring data and numerical simulation results, a weighted scoring method was used to select the optimal parameter combination. The weights were allocated as follows: reinforcement effect 60%, construction efficiency 30%, and cost 10%. By comparing the scoring results of different parameter combinations, the optimal parameter combination was finally determined. With a vibratory impact spacing of 2.5m, the standard penetration test (SPT) blow count at this spacing increased by 14.70% and 20.56% compared to spacings of 2m and 3m, respectively. The equilateral triangle layout resulted in a 27% increase in settlement compared to a square layout. The vibration power is selected from 100kW to 130kW to control energy consumption while ensuring the reinforcement effect; The construction process adopts the vibratory direct insertion process, which reduces the settlement by only 4.2% compared to the vibratory reverse insertion process, but reduces the construction cost by 20%, making it more economical. The vibration frequency is 16Hz. At this frequency, the ground acceleration tends to be stable, and the reinforcement range is the largest and the uniformity is the best.

[0034] 6. Step (5): Engineering Verification Verification area: An independent area of ​​294,140 m² in the Xiamen Daxiaodeng land reclamation project was selected as the verification area. The geological conditions of this area are consistent with those of the test area. Vibro-compaction construction was carried out using the optimal parameter combination selected in step (4).

[0035] Verification Results: After the project verification was completed, a comprehensive inspection was conducted on the verification area. The results showed that: The average bearing capacity of the foundation reaches 158 kPa, which meets the design requirement of ≥150 kPa. The average number of blows in the standard penetration test (SPT) was 15.2 before construction and increased to 25.8 after construction, an increase of 69.7%, far exceeding the ≥40% judgment standard. The average dry density is 1.72 g / cm³, which meets the requirement of ≥1.70 g / cm³; The average compaction degree was 0.92, meeting the qualified standard of ≥0.90; The average settlement was 58.6 cm, and the uniformity deviation of settlement within the area did not exceed 5%, with no local settlement exceeding the standard.

[0036] Verification results show that the combination of construction parameters determined by the method of this invention can stably achieve the reinforcement effect of soft soil foundation, fully meeting the requirements of engineering design and subsequent construction. Example

[0037] To verify the superiority of the method of the present invention, a control group (traditional empirical parameter method) and an experimental group (the method of the present invention) were set up, and the comparison results are as follows:

[0038] The comparative results show that the parameters determined by the method of the present invention are superior to the traditional empirical method in terms of reinforcement effect, construction efficiency and cost control.

[0039] The above description is only a preferred embodiment of the present invention and does not limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the parameters of vibratory compaction construction for soft soil foundation reinforcement, characterized in that, Includes the following steps: (1) Preset combination of vibratory compaction construction parameters, including vibratory compaction spacing, layout method, vibratory compaction power, construction process and vibration load parameters; (2) Divide the test areas into multiple test areas of equal area and carry out vibratory compaction construction according to the preset parameter combination; (3) During the construction process, the dynamic response parameters of the soil are monitored simultaneously, and the foundation reinforcement effect index is tested after construction; (4) Based on monitoring data and reinforcement effect indicators, parameter sensitivity analysis is conducted using numerical models to select the optimal combination of construction parameters; (5) Verify the optimal combination of construction parameters in engineering, and output the final construction parameters after confirming that the design requirements are met.

2. The method for determining the parameters of vibratory compaction construction for soft soil foundation reinforcement according to claim 1, characterized in that, The preset range of the vibration spacing in step (1) is 2m to 3m, the vibration power is 100kW to 130kW, the layout method includes equilateral triangle arrangement and square arrangement, the construction process includes vibration direct insertion process and vibration reverse insertion process, and the vibration load parameters include peak load of 300kN to 800kN and vibration frequency of 4Hz to 24Hz.

3. The method for determining the parameters of vibratory compaction construction for soft soil foundation reinforcement according to claim 1, characterized in that, The area of ​​the test area mentioned in step (2) is 500m². The vibratory compaction reinforcement depth is 8m to 9m during construction. The vibration time at the bottom of the hole is 1min. When the vibratory compactor is lifted, the vibration is left for 30s every 1m.

4. The method for determining the parameters of vibratory compaction construction for soft soil foundation reinforcement according to claim 1, characterized in that, The dynamic response parameters of the soil in step (3) include pore water pressure, horizontal displacement, vertical settlement, surface vibration velocity and surface vibration acceleration; the reinforcement effect indicators include standard penetration test blow count, foundation bearing capacity, dry density, compaction degree and settlement.

5. The method for determining the parameters of vibratory compaction construction for soft soil foundation reinforcement according to claim 1, characterized in that, The numerical model described in step (4) is the extended Druck-Prager model. The parameter sensitivity analysis focuses on the internal friction angle β, shear dilatation angle ψ, cohesion C and elastic modulus E in the model. β, ψ and C are selected as highly sensitive parameters for key optimization.

6. The method for determining the parameters of vibratory compaction construction for soft soil foundation reinforcement according to claim 1, characterized in that, The optimal combination of construction parameters in step (4) satisfies the following: the vibratory spacing is 2.5m, the layout is an equilateral triangle, the vibratory power is 100kW~130kW, the construction process adopts the vibratory direct insertion process, and the vibration frequency is 16Hz.

7. The method for determining the parameters of vibratory compaction construction for soft soil foundation reinforcement according to claim 1, characterized in that, The criteria for engineering verification in step (5) are: foundation bearing capacity ≥150kPa, standard penetration test blow count increased by ≥40% compared with before construction, dry density ≥1.70g / cm³, and compaction degree ≥0.

90.

8. The method for determining the parameters of vibratory compaction construction for soft soil foundation reinforcement according to claim 4, characterized in that, The standard penetration test blow count is performed at the vibratory impact hole position, the midpoint of the line connecting the holes, and the centroid of the layout, and the average value of multiple test results is taken; the settlement measurement is performed for different layout methods, and the settlement of the equilateral triangle layout is ≥27% higher than that of the square layout.

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