A method for treating a coral sand dynamic compaction-vibration combined foundation

Abstract

The application relates to the technical field of foundation treatment construction, in particular to a coral sand dynamic compaction-vibroflotation combined foundation treatment method, which comprises the following steps: obtaining the initial pore state, the natural specific gravity, the water permeability and the groundwater level depth of coral sand; determining the construction sequence based on the initial pore ratio e0: when e0>1.2, first vibroflotation and then dynamic compaction, when 0.8 The application improves the foundation treatment depth and uniformity under the premise of avoiding excessive particle crushing by dynamically allocating the energy ratio and reducing the energy in the overlapping area.

Description

Technical Field

[0001] This application relates to the field of foundation treatment construction technology, and in particular to a method for combined dynamic compaction and vibro-compaction of coral sand foundation treatment. Background Technology

[0002] Coral sand is a marine sediment formed by the erosion, transportation, and deposition of coral reef debris by ocean waves. Its main component is calcium carbonate. Coral sand is widely distributed in islands, reefs, and coastal areas of tropical and subtropical seas. With the rapid development of marine engineering construction, coral sand is widely used as a major material for land reclamation. However, coral sand has special engineering properties such as irregular particle shape, high porosity, low strength, and easy breakage, requiring reinforcement treatment when used directly as a foundation.

[0003] Dynamic compaction and vibro-compaction are common methods for treating sandy soil foundations. Dynamic compaction uses the impact energy of a falling hammer to compact the soil, offering advantages such as fast reinforcement speed, simple equipment, and low cost. However, its effective reinforcement depth is limited, typically 3m to 8m. Vibro-compaction uses high-frequency vibrations from a vibro-compactor and water jetting to rearrange and densify sand particles, achieving a reinforcement depth of 15m to 30m. However, its effectiveness is relatively weak for the top 3m of soil.

[0004] Theoretically, combining dynamic compaction and vibro-compaction can achieve a combined effect of upper dynamic compaction and lower vibro-compaction reinforcement, thereby expanding the effective treatment depth and improving the overall reinforcement effect. However, existing combined construction methods are mainly based on engineering experience with quartz sand, and have the following shortcomings when applied to coral sand foundations:

[0005] (1) Current national standards and industry specifications do not include design and construction standards for combined dynamic compaction and vibratory compaction for the special engineering properties of coral sand. Coral sand particles are mainly composed of biological debris, are porous, and have a much lower particle strength than quartz sand. They are prone to breakage under the impact of dynamic compaction and vibratory compaction. Particle breakage will change the gradation and pore structure of coral sand. If energy is not properly controlled, it may lead to the deterioration of the foundation strength.

[0006] (2) Existing combined construction methods lack an optimized energy distribution model for dynamic compaction and vibro-compaction. Coral sand has high permeability (permeability coefficient is typically...). to The high permeability (1 to 2 orders of magnitude higher than that of silica sand) allows the excess pore water pressure generated by dynamic compaction to dissipate rapidly, which is beneficial to the effectiveness of dynamic compaction. However, at the same time, the high permeability also causes the vibration energy generated by vibratory compaction to decay rapidly along the depth direction, weakening the deep reinforcement effect. Therefore, the rational distribution of energy between the two methods is crucial during combined construction, but existing technologies lack quantitative energy distribution methods.

[0007] (3) Existing methods do not consider the spatial superposition effect of the two treatment methods. The effective reinforcement area of ​​dynamic compaction is distributed in an inverted cone shape, while the effective reinforcement area of ​​vibro-compaction is distributed in a cylindrical shape. The two methods overlap in space in the treatment depth of 5m to 10m. In the overlapping area, the impact energy of dynamic compaction and the vibration energy of vibro-compaction are superimposed. If the energy of the second construction method is not reduced, the energy in this area will be excessively concentrated, which will aggravate the crushing of coral sand particles and even form weak interlayers.

[0008] (4) Existing combined construction methods lack optimization criteria for construction sequence. For coral sand of different densities, whether to perform dynamic compaction or vibro-compaction first has a significant impact on the final reinforcement effect. Loose coral sand (porosity greater than 1.2) rapidly compacts the surface and forms a hard shell under dynamic compaction, which significantly hinders the penetration of subsequent vibro-compaction equipment; while for medium-dense coral sand (porosity between 0.8 and 1.2), if vibro-compaction is performed first, the surface tamping pit will be too deep during dynamic compaction, which may lead to instability of the tamping hammer. Existing technology does not provide clear criteria for determining the construction sequence.

[0009] (5) Existing joint construction methods lack quality control and acceptance standards for coral sand. Because coral sand particles are easily broken, traditional evaluation methods that use density as a single indicator are difficult to accurately reflect the foundation performance after joint treatment. It is necessary to establish a comprehensive evaluation system that considers the impact of particle breakage.

[0010] In summary, existing technologies lack a systematic design and construction method for combined dynamic compaction and vibro-compaction when dealing with coral sand foundations. There is an urgent need for a combined construction method and supporting design method specifically designed for the characteristics of coral sand projects. Summary of the Invention

[0011] Therefore, this invention provides a combined dynamic compaction-vibratory compaction method for coral sand foundation treatment, which overcomes the problems of limited effective reinforcement depth, poor reinforcement uniformity, and lack of energy adaptation design for the fragile characteristics of coral sand when using a single method to treat coral sand foundations in the prior art.

[0012] To achieve the above objectives, this invention provides a method for treating coral sand foundations using a combination of dynamic compaction and vibro-compaction. It includes:

[0013] Step S1: Obtain the initial porosity, natural density, permeability, and groundwater depth of the coral sand.

[0014] Step S2: Determine whether to adopt a combined construction method and the main construction sequence based on the initial porosity state; when the initial porosity ratio When the value is greater than 1.2, a combined construction method is adopted, and the main construction sequence is vibratory compaction followed by dynamic compaction; when At that time, a combined construction method was adopted, and the main construction sequence was first dynamic compaction followed by vibro-compaction; when At that time, the combined construction method is not adopted;

[0015] Step S3: In response to the adoption of the combined construction method, the relative ratio of dynamic compaction impact energy to vibratory compaction output energy is determined based on the degree of deviation of the initial pore state from the standard pore state and the target reinforcement depth.

[0016] Step S4: Select the dynamic compaction impact energy level based on the relative ratio and the natural density;

[0017] Step S5: Determine the operating power, single-point dwell time, and planar layout spacing of the vibratory compaction operation based on the relative ratio.

[0018] Step S6: Following the main construction sequence, first implement the first construction method in all construction areas, then implement the second construction method. In the vertically overlapping area where the two construction methods effectively influence the depth, reduce the energy injection intensity of subsequent construction methods. When the second construction method is being implemented, its construction area coincides with the planar projection of the area already constructed by the first construction method, and avoids the edge of the area already constructed by the first construction method within a range of 0.5m to 1.0m.

[0019] Step S7: Conduct a quality inspection on the treated foundation.

[0020] Further, the relative proportions mentioned in step S3 are determined according to the following formula:

[0021] ;

[0022] in, To generate impact energy from heavy compaction. To output energy for vibration. The initial porosity is the initial porosity corresponding to the initial porosity state, and H is the target reinforcement depth in meters; the degree of deviation of the initial porosity state from the standard porosity state is... The target reinforcement depth is characterized by (H-10) / 10; the coefficients of the relative ratio satisfy: the first coefficient is 0.5, the second coefficient is 0.3, and the third coefficient is 0.2; the target reinforcement depth H ranges from 5m to 20m.

[0023] Further, step S4, selecting the dynamic compaction impact energy level based on the relative proportion and the natural density, includes:

[0024] The dynamic compaction impact energy is determined by the relative proportions determined in step S3. The possible values ​​of ;

[0025] According to Menard's revised formula:

[0026] ;

[0027] Calculate the The effective reinforcement depth *he* corresponds to the value, where γ is the natural density. This is a correction factor, with a value ranging from 0.20 to 0.30;

[0028] When the target reinforcement depth is met, the selected method is... The corresponding dynamic compaction impact energy level;

[0029] The The value is determined based on the carbonate content and particle morphology of the coral sand: when the coral sand... When the content is greater than 90% and the particle shape is dendritic, Take a value between 0.20 and 0.25; when When the content is 70% to 90% and the granules are in block shape, Take a value between 0.25 and 0.30.

[0030] Furthermore, the construction parameters corresponding to the dynamic compaction impact energy level mentioned in step S4 also include:

[0031] Spacing between tamping points The number of tamping passes is 2.5 to 3.5 times the diameter of the tamping hammer. The process is repeated 2 to 4 times, with each round involving 6 to 12 tamping strokes.

[0032] Furthermore, the operating power of the vibratory compaction operation described in step S5 The single-point dwell time ranges from 75kW to 130kW. The time interval for the planar arrangement is from 30s to 120s. The distance is 1.5m to 2.5m.

[0033] Furthermore, the vertically overlapping area mentioned in step S6 is the intersection of a depth range of 0.6 to 1.0 times the effective reinforcement depth he of the dynamic compaction and a depth range of 1.0m to 3.0m above the top of the vibro-compacted pile;

[0034] The reduction in energy injection intensity for subsequent construction methods is specifically an energy reduction ratio, which is 30% to 50%.

[0035] The specific value of the energy reduction ratio is determined based on the measured standard penetration blow count N63.5 in the area after the first construction method is completed. When N63.5 is less than 10, the reduction ratio is 30%; when 10 is less than or equal to N63.5 and N63.5 is less than 20, the reduction ratio is 40%; when N63.5 is greater than or equal to 20, the reduction ratio is 50%.

[0036] Furthermore, when the sequence of vibratory compaction followed by dynamic compaction is adopted, the interval time between vibratory compaction and dynamic compaction of the area before dynamic compaction is not less than 7 days; when the sequence of dynamic compaction followed by vibratory compaction is adopted, the interval time between dynamic compaction and dynamic compaction of the area before vibratory compaction is not less than 14 days.

[0037] Furthermore, it also includes a step for evaluating the effectiveness of joint treatment:

[0038] The Joint Treatment Index (JTI) is used to evaluate the effectiveness of joint construction. The JTI is calculated using the following formula:

[0039] ;

[0040] in, The dynamic compaction treatment degree index. The vibration processing degree index, The processing degree reduction index for overlapping areas;

[0041] ;

[0042] Wherein, β is the overlap reduction factor, which ranges from 0.20 to 0.40;

[0043] ,

[0044] ;

[0045] in The standard penetration test blow count before construction. This refers to the standard penetration test blow count after dynamic compaction. This represents the number of standard penetration blows after oscillatory impact. The target standard is the number of penetration hits.

[0046] Furthermore, the quality inspection described in step S6 includes standard penetration test, static cone penetration test, and surface wave method; the acceptance criteria are: the number of blows N63.5 measured by the standard penetration test is greater than or equal to the design value, the cone tip resistance qc measured by the static cone penetration test is greater than or equal to the design value, and the shear wave velocity Vs measured by the surface wave method is greater than or equal to the design value; at least two of the three test results meet the design requirements, and the deviation of the unmet item from the design value does not exceed 10%.

[0047] Furthermore, the initial porosity state obtained in step S1 also includes the coral sand. Content, particle shape, and particle breakage rate; when When the content is greater than 95% and the particle breakage rate is greater than 30%, in the determination of the relative proportion in step S3, the following will be used: The ratio is reduced by 0.1 to 0.2; the permeability is characterized by the permeability coefficient k, and the groundwater level depth is characterized by Dw; when Dw is less than 5m, in the determination of the relative proportion in step S3, the ratio is... The ratio increased by 0.05 to 0.15.

[0048] Compared with the prior art, the beneficial effects of the present invention are that, through a combination of on-site investigation and indoor testing, this embodiment systematically obtains key parameters such as the initial void ratio, natural density, permeability coefficient, and groundwater level depth of coral sand. Furthermore, for loose coral sand foundations, a combined construction method of "vibratory compaction followed by dynamic tamping" is determined, while also referencing auxiliary technologies. The content and particle breakage rate verified the rationality of this sequence, providing a data basis and process basis for subsequent energy ratio design and construction parameter determination, thereby ensuring that the combined construction method can effectively densify the foundation and control the excessive breakage of coral sand particles.

[0049] Furthermore, this embodiment achieves the beneficial effect of improving the depth and uniformity of foundation treatment while avoiding excessive breakage of coral sand particles by dynamically allocating the relative ratio of dynamic compaction and vibratory compaction energy based on the initial porosity state of coral sand and the target reinforcement depth, and by reducing the energy injection intensity of the construction method after vertical overlapping areas.

[0050] Furthermore, this embodiment combines the Menard correction formula with the correction coefficient value rules related to the carbonate content and particle morphology of coral sand. Based on the comprehensive conditions of natural density, carbonate content, dendritic particle morphology and particle breakage rate in this area, the correction coefficient is selected and the dynamic compaction energy and hammer parameters are determined by back calculation. At the same time, the vibratory compaction energy requirement is calculated based on the energy ratio and the operating power, vibration time and pile spacing are selected. This realizes the quantitative and coordinated design of dynamic compaction and vibratory compaction construction parameters, ensuring the coordination and matching of the two construction methods at the energy level, and providing accurate parameter support for the subsequent joint construction sequence and energy reduction in overlapping areas.

[0051] Furthermore, this embodiment achieves the beneficial effect of improving the depth and uniformity of foundation treatment while avoiding excessive breakage of coral sand particles by dynamically allocating the relative ratio of dynamic compaction and vibratory compaction energy based on the initial porosity state of coral sand and the target reinforcement depth, and by reducing the energy injection intensity of the construction method after vertical overlapping areas.

[0052] Furthermore, this embodiment introduces the Joint Treatment Index (JTI) to quantitatively evaluate the combined construction effect. The JTI and JTI are calculated based on the standard penetration test (SPT) blow counts at three stages: before construction, after vibro-compaction, and after dynamic compaction. An overlap reduction factor is introduced to reduce the treatment degree in the overlapping area, ultimately calculating the JTI. This index objectively reflects the independent contributions of the two methods within their respective effective influence ranges, as well as the synergistic effect in the overlapping area. It achieves a quantitative evaluation of the combined construction effect, providing a scientific basis for verifying the applicability of the methods and optimizing parameters. Attached Figure Description

[0053] Figure 1 This is a flowchart of the coral sand dynamic compaction-vibratory compaction combined foundation treatment method according to an embodiment of this application;

[0054] Figure 2 This is a flowchart illustrating the process of determining the main construction sequence in the coral sand dynamic compaction-vibratory compaction combined foundation treatment method according to an embodiment of this application. Detailed Implementation

[0055] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0056] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0057] like Figures 1-2 As shown, Figure 1 This is a flowchart of the coral sand dynamic compaction-vibratory compaction combined foundation treatment method according to an embodiment of this application; Figure 2 This is a flowchart illustrating the process of determining the main construction sequence in the coral sand dynamic compaction-vibratory compaction combined foundation treatment method according to an embodiment of this application.

[0058] The technical solution provided in this application includes the following steps:

[0059] Step S1: Obtain the initial porosity, natural density, permeability, and groundwater depth of the coral sand.

[0060] Step S2: Determine whether to adopt a combined construction method and the main construction sequence based on the initial porosity state; when the initial porosity ratio e0 is greater than 1.2, a combined construction method is adopted and the main construction sequence is vibratory compaction followed by dynamic compaction; when... At that time, a combined construction method was adopted, and the main construction sequence was first dynamic compaction followed by vibro-compaction; when When a single construction method is used for foundation treatment, the single construction method is selected from dynamic compaction or vibro-compaction.

[0061] Step S3: In response to the adoption of the combined construction method, the relative ratio of dynamic compaction impact energy to vibratory compaction output energy is determined based on the degree of deviation of the initial pore state from the standard pore state and the target reinforcement depth.

[0062] Step S4: Select the dynamic compaction impact energy level based on the relative ratio and the natural density;

[0063] Step S5: Determine the operating power, single-point dwell time, and planar layout spacing of the vibratory compaction operation based on the relative ratio.

[0064] Step S6: Following the main construction sequence, first implement the first construction method in all construction areas, then implement the second construction method. In the vertically overlapping area where the two construction methods effectively influence the depth, reduce the energy injection intensity of subsequent construction methods. When the second construction method is being implemented, its construction area coincides with the planar projection of the area already constructed by the first construction method, and avoids the edge of the area already constructed by the first construction method within a range of 0.5m to 1.0m.

[0065] Step S7: Conduct a quality inspection on the treated foundation.

[0066] In this embodiment, a typical test area of ​​20m × 20m was selected in a reclamation project on a South China Sea island. First, on-site investigation and indoor geotechnical tests were conducted to obtain the basic physical and mechanical parameters of the coral sand foundation. Specifically, five exploration points were arranged in a grid pattern within the test area, with a spacing of 10m between each point. Uncirculated sand samples were collected at depths of 0m, 2m, 4m, 6m, 8m, and 10m using a borehole sampler, with at least three samples taken from each layer. The collected sand samples were promptly sealed and transported to the laboratory for the following tests:

[0067] (1) Initial void ratio Determination: The specific gravity Gs of coral sand particles was determined using the hydrostatic bottle method, and the natural density ρ and moisture content w were determined using the ring cutter method, according to the formula. Calculate the initial porosity, where ρd is the dry density and ρw is the density of water. The initial porosity of the coral sand measured in this test area was... (Average values ​​at each measuring point, ranging from 1.28 to 1.42).

[0068] (2) Determination of natural density γ: The natural density of coral sand was directly determined by the on-site sand filling method or the ring cutter method. The natural density γ measured in this test area was 13.8 kN / m³ (range 13.5~14.2 kN / m³).

[0069] (3) Determination of permeability coefficient k: The permeability coefficient was determined by a combination of on-site pumping tests and indoor constant head permeability tests. One pumping well and two observation wells were set up on-site. After pumping stabilized, the permeability coefficient was calculated according to Darcy's law. In the indoor test, a constant head permeameter was used, with a sample height of 40 cm, a diameter of 10 cm, and a hydraulic gradient of 0.5~1.0. Based on the combined results of on-site and indoor tests, the permeability coefficient of coral sand in this test area was determined. .

[0070] (4) Determination of groundwater level depth Dw: A water level gauge was lowered into the exploration borehole and the groundwater level was read after 24 hours of stabilization. The groundwater level depth Dw in this test area is 3.5m (range 3.2~3.8m).

[0071] In addition, the calcium carbonate content of the coral sand was determined. Content, particle shape, and particle breakage rate were determined using the acid washing method. Content, in this area The content was 92%; the particle morphology was observed by scanning electron microscopy, and the particle shape was mainly dendritic; the particle breakage rate was calculated by comparing the change in the content of particles with a diameter of less than 0.075 mm before and after vibration using the sieving method, and the breakage rate was measured to be 25%.

[0072] The initial porosity measured in step S1 Compare with the judgment criteria: when At that time, the coral sand was in a loose state. The single dynamic compaction method had low energy transfer efficiency and insufficient effective reinforcement depth. While the single vibro-compaction method could densify the sand, its treatment range was limited. Therefore, a combined method was adopted, with the main construction sequence being vibro-compaction followed by dynamic compaction. At that time, the coral sand was in a medium-dense state, and a combined construction method could be used, with the main construction sequence being dynamic compaction followed by vibratory compaction; when At that time, the coral sand was in a dense state, and the combined construction method was not adopted.

[0073] This experimental area The foundation was determined to be loose coral sand, and a combined construction method of vibro-compaction followed by dynamic compaction was adopted. Additionally, other relevant factors were considered during the determination process. Content and particle breakage rate. This region The content was 92% (greater than 90%), and the particle shape was dendritic, indicating that the coral sand particles had a high degree of cementation but were brittle and prone to breakage under impact loads. This further confirmed the rationality of using a combined construction method with a sequence of vibratory compaction followed by dynamic compaction—first, vibratory compaction initially compacts the particles to reduce severe breakage during subsequent dynamic compaction, thereby improving density while controlling excessive particle breakage. After the assessment was completed, the main construction sequence was recorded as "vibratory compaction → dynamic compaction," and the planned vibratory compaction depth was 10m, with an effective reinforcement depth of 6m for dynamic compaction. The process then proceeded to step S3 for energy ratio design.

[0074] In this embodiment, when At this point, the coral sand foundation is already in a compacted state. Instead of using a combined construction method, a single method is directly selected for foundation treatment. This includes: if the project primarily requires improving the bearing capacity and uniformity of the shallow foundation, dynamic compaction is used alone, constructed according to the dynamic compaction parameters for conventional sandy soil foundations, with several passes of compaction on the surface sufficient to meet the reinforcement requirements; if the project primarily requires eliminating deep weak layers or improving the density of deep layers, vibro-compaction is used alone, with vibro-compaction densification carried out within a predetermined depth range according to conventional vibro-compaction techniques. The specific design parameters for the above single method can be determined by those skilled in the art based on the results of on-site geotechnical tests, the bearing capacity indicators required by the design, and relevant industry standards through conventional methods. After completing the single method construction, the treated foundation is also inspected according to the quality inspection method in step S7 of this application to ensure that the reinforcement effect meets the design requirements.

[0075] This embodiment systematically obtained key parameters of coral sand, such as initial void ratio, natural unit weight, permeability coefficient, and groundwater level depth, through a combination of on-site investigation and laboratory testing. For loose coral sand foundations, a combined construction method of "vibratory compaction followed by dynamic tamping" was determined, while also referencing relevant data. The content and particle breakage rate verified the rationality of this sequence, providing a data basis and process basis for subsequent energy ratio design and construction parameter determination, thereby ensuring that the combined construction method can effectively densify the foundation and control the excessive breakage of coral sand particles.

[0076] Specifically, the relative proportions mentioned in step S3 are determined according to the following formula:

[0077] ;

[0078] in, To generate impact energy from heavy compaction. To output energy for vibration. The initial porosity is the initial porosity corresponding to the initial porosity state, and H is the target reinforcement depth in meters; the degree of deviation of the initial porosity state from the standard porosity state is... The target reinforcement depth is characterized by (H-10) / 10; the coefficients of the relative ratio satisfy: the first coefficient is 0.5, the second coefficient is 0.3, and the third coefficient is 0.2; the target reinforcement depth H ranges from 5m to 20m.

[0079] In this embodiment, following the determination result of step S2, the initial porosity of the coral sand in the test area is... The target reinforcement depth is set to H=10m according to design requirements (the vibro-compaction depth is 10m, and the effective reinforcement depth of dynamic compaction is 6m; the larger value is taken as the target reinforcement depth). Substituting the above parameters into the energy ratio formula in step S3:

[0080] ;

[0081] The relative ratio of dynamic compaction impact energy to vibro-compaction output energy is 0.605:1, approximately 3:5. This ratio indicates that, under the conditions of this project, the vibro-compaction output energy should be higher than the dynamic compaction impact energy. This aligns with the construction sequence of vibro-compaction followed by dynamic compaction—vibro-compaction, as the initial method, needs to provide greater energy to initially densify the loose coral sand, while subsequent dynamic compaction uses relatively lower energy for supplementary reinforcement, avoiding excessive particle breakage due to excessive energy.

[0082] In addition, the coral sand in this test area The content is 92% (greater than 90%), the particle shape is dendritic, and the particle breakage rate is 25% (not exceeding 30%), therefore no additional correction is needed for the above ratios. If If the content is greater than 95% and the particle breakage rate is greater than 30%, then it is necessary to... The ratio should be reduced by 0.1 to 0.2; if the groundwater level depth Dw is less than 5m (Dw=3.5m in this area), the ratio should be increased by 0.05 to 0.15. Since Dw=3.5m<5m in this area, the calculated ratio should be increased by 0.10, and the final value should be... It is approximately 0.7. Based on the final determined relative proportions... Proceed to step S4 to determine specific construction parameters: the dynamic compaction impact energy level is based on the effective reinforcement depth. The parameters selected through back-calculation, including the operating power, single-point dwell time, and planar layout spacing of the vibratory compaction operation, are based on E. _VC The value of is determined and designed in conjunction with the performance parameters of the vibratory impactor.

[0083] This embodiment achieves the beneficial effect of improving the depth and uniformity of foundation treatment while avoiding excessive breakage of coral sand particles by dynamically allocating the relative ratio of dynamic compaction and vibratory compaction energy based on the initial porosity state of coral sand and the target reinforcement depth, and by reducing the energy injection intensity of the construction method after vertical overlapping areas.

[0084] Specifically, step S4, which selects the dynamic compaction impact energy level based on the relative ratio and the natural density, includes:

[0085] The dynamic compaction impact energy E is determined by the relative proportions determined in step S3. DC The possible values ​​of ;

[0086] According to Menard's revised formula:

[0087] ;

[0088] Calculate the The effective reinforcement depth *he* corresponds to the value, where γ is the natural density. This is a correction factor, with a value ranging from 0.20 to 0.30;

[0089] When the target reinforcement depth is met, the selected method is... The corresponding dynamic compaction impact energy level;

[0090] The The value is determined based on the carbonate content and particle morphology of the coral sand: when the coral sand... When the content is greater than 90% and the particle shape is dendritic, Take a value between 0.20 and 0.25; when When the content is 70% to 90% and the granules are in block shape, Take a value between 0.25 and 0.30.

[0091] Specifically, the construction parameters corresponding to the dynamic compaction impact energy level mentioned in step S4 also include:

[0092] Spacing between tamping points The number of tamping passes is 2.5 to 3.5 times the diameter of the tamping hammer. The process is repeated 2 to 4 times, with each round involving 6 to 12 tamping strokes.

[0093] In this embodiment, the selection of the dynamic compaction impact energy level is based on the natural density of the coral sand in this test area. , The content is 92% (greater than 90%), the particle shape is dendritic, and the value of the correction factor is determined according to the rules. The value should be between 0.20 and 0.25. Considering that the particle breakage rate in this area is 25%, a lower value should be chosen to control particle breakage during dynamic compaction. The design requires an effective reinforcement depth of he=6m. (The last part, "he=6m, is likely a placeholder or error and doesn't need a direct translation, but can be left as is.) , Substitute into the Menard correction formula:

[0094] ;

[0095] Right now: ;

[0096] Calculated Therefore, the dynamic compaction impact energy level was selected. The corresponding hammer weight is 200kN and the drop height is 50m.

[0097] The dynamic compaction construction parameters are determined as follows: the spacing between compaction points is 3.0 times the diameter of the hammer. The diameter of the hammer is 2.5m, so the spacing between compaction points is 7.5m, arranged in a square grid; the number of compaction passes is 3, in the order of main compaction, secondary compaction and full compaction; each point of the main compaction and secondary compaction is compacted 8 times, and each point of the full compaction is compacted 2 times with an overlap of one-quarter of the hammer diameter.

[0098] Specifically, the operating power of the vibratory compaction operation described in step S5 The single-point dwell time ranges from 75kW to 130kW. The time interval for the planar arrangement is from 30s to 120s. The distance is 1.5m to 2.5m.

[0099] Determination of vibratory compaction parameters: based on relative proportions and Calculated Approximately 14286 kN·m. Referring to the performance parameters of commonly used vibratory compactors, the operating power of the vibratory compactor is selected. Considering the loose state and dendritic, easily broken characteristics of the coral sand in this area, a single-point vibration retention time was set to ensure the vibratory compaction effect while controlling particle breakage. In actual construction, the spacing is dynamically adjusted within the range of 45s to 80s based on the hardness of the strata. The spacing of the vibratory compaction piles is determined according to the power of the vibratory compactor and the conditions of the coral sand soil. The piles are arranged in an equilateral triangle pattern. The vibratory compaction depth is 10m as designed. Drilling begins from the ground surface, and the vibration compaction is gradually increased to the designed depth. During construction, the piles are advanced from the boundary of the test area towards the center to avoid interference between adjacent pile positions. After completing the above parameter design, the main parameters for the joint construction in this embodiment are summarized as follows: dynamic compaction impact energy 10000kN·m, hammer weight 200kN, drop height 50m, compaction point spacing 7.5m (square arrangement), number of compaction passes 3, main and auxiliary compactors 8 times per point, full compaction 2 times per point, correction factor α. c The parameters are set as follows: vibratory compaction power 100kW, single-point vibration time 60s, pile spacing 2.0m (triangular arrangement), vibratory compaction depth 10m. After determining the above parameters, proceed to step S5 to carry out joint construction. The main construction sequence is vibratory compaction followed by dynamic compaction: first, complete all vibratory compaction pile construction at 2.0m spacing in the entire 20m×20m test area; after a 7-day interval, carry out dynamic compaction construction at 7.5m spacing; and reduce the dynamic compaction energy in the vertically overlapping area where the effective depth of the two construction methods is affected.

[0100] This embodiment combines the Menard correction formula with the correction coefficient value rules related to the carbonate content and particle morphology of coral sand. Based on the comprehensive conditions of natural density, carbonate content, dendritic particle morphology and particle breakage rate in this area, the correction coefficient is selected and the dynamic compaction energy and hammer parameters are determined by back calculation. At the same time, the vibratory compaction energy requirement is calculated based on the energy ratio and the operating power, vibration time and pile spacing are selected. This realizes the quantitative and coordinated design of dynamic compaction and vibratory compaction construction parameters, ensuring the coordination and matching of the two construction methods at the energy level, and providing accurate parameter support for the subsequent joint construction sequence and energy reduction in overlapping areas.

[0101] Specifically, the vertically overlapping area mentioned in step S6 is the intersection of a depth range of 0.6 to 1.0 times the effective reinforcement depth he of the dynamic compaction and a depth range of 1.0m to 3.0m above the top of the vibro-compacted pile;

[0102] The reduction in energy injection intensity for subsequent construction methods is specifically an energy reduction ratio, which is 30% to 50%.

[0103] The specific value of the energy reduction ratio is determined based on the measured standard penetration blow count N63.5 in the area after the first construction method is completed. When N63.5 is less than 10, the reduction ratio is 30%; when 10 is less than or equal to N63.5 and N63.5 is less than 20, the reduction ratio is 40%; when N63.5 is greater than or equal to 20, the reduction ratio is 50%.

[0104] Specifically, when the sequence of vibratory compaction followed by dynamic compaction is adopted, the interval between vibratory compaction and dynamic compaction of the area before dynamic compaction is not less than 7 days; when the sequence of dynamic compaction followed by vibratory compaction is adopted, the interval between dynamic compaction and dynamic compaction of the area before vibratory compaction is not less than 14 days.

[0105] In this embodiment, the initial porosity of the test area is... Since the coefficient of performance (COP) is greater than 1.2, the main construction sequence is vibro-compaction followed by dynamic compaction. First, all vibro-compaction piles were constructed within the entire 20m×20m test area according to the vibro-compaction parameters determined in step S4: pile spacing 2.0m, equilateral triangle arrangement, construction depth 10m, operating power 100kW, and single-point vibration time 60s. Vibro-compaction construction proceeded from the boundary of the test area towards the center, completing approximately 121 piles. After all vibro-compaction was completed, a rest period was initiated, with a rest period of no less than 7 days. In this embodiment, the rest period was set at 10 days to allow the excess pore water pressure caused by vibro-compaction to dissipate fully, while simultaneously allowing the coral sand particles to complete preliminary creep consolidation after vibration compaction.

[0106] After the interval period, standard penetration tests (SPTs) were conducted on the vibro-compaction treated foundation, focusing on the vertically overlapping area (the area between 0.6 and 1.0 times the effective reinforcement depth he=6m, i.e., 3.6m to 6.0m, and the intersection of this area and the area between 1.0m and 3.0m above the top of the vibro-compaction piles). In this test area, the actual vertically overlapping area was the depth from 3.6m to 6.0m below the ground surface. Three measuring points were selected in this area for SPTs, and the average SPT blow count N63.5=13 was obtained (values ​​at the measuring points were 11, 14, and 14 respectively).

[0107] According to the energy reduction ratio determination rule, when 10 ≤ N63.5 < 20, the reduction ratio is 40%. Therefore, in the subsequent dynamic compaction construction, the dynamic compaction energy input in the vertically overlapping area (depth range of 3.6m to 6.0m) is reduced by 40%. The dynamic compaction construction is carried out according to the parameters determined in step S4: compaction energy 10000kN·m, compaction point spacing of 7.5m square arrangement, 3 compaction passes (main compaction, auxiliary compaction, full compaction), 8 times per point for main and auxiliary compaction, and 2 times per point for full compaction. However, in the vertically overlapping area, the number of single-point compaction passes is reduced from 8 to 5 (reduction of about 37.5%, close to 40%), and the drop height is appropriately reduced from 50m to 40m to achieve an energy reduction of about 40%. The deep layer (below 6.0m) and shallow layer (above 3.6m) outside the reduction area are carried out according to the original design energy to ensure the reinforcement effect across the entire depth range.

[0108] The dynamic compaction construction also proceeded from the boundary of the test area towards the center, first completing the main compaction, followed by secondary compaction after a 7-day interval, and then full compaction after another 7-day interval. The entire dynamic compaction construction cycle was approximately 21 days. During construction, displacement observation points were set up at the edge of the overlapping area to monitor the impact of the dynamic compaction on the already constructed vibro-compacted piles. The observation results showed that the reduced-energy dynamic compaction construction did not cause significant lateral displacement or damage to the vibro-compacted piles, indicating that the energy reduction measures effectively protected the integrity of the previously constructed vibro-compacted piles.

[0109] This embodiment achieves the beneficial effect of improving the depth and uniformity of foundation treatment while avoiding excessive breakage of coral sand particles by dynamically allocating the relative ratio of dynamic compaction and vibratory compaction energy based on the initial porosity state of coral sand and the target reinforcement depth, and by reducing the energy injection intensity of the construction method after vertical overlapping areas.

[0110] Specifically, it also includes the evaluation step of the joint treatment effect:

[0111] The Joint Treatment Index (JTI) is used to evaluate the effectiveness of joint construction. The JTI is calculated using the following formula:

[0112] ;

[0113] in, The dynamic compaction treatment degree index. The vibration processing degree index, The processing degree reduction index for overlapping areas;

[0114] ;

[0115] Wherein, β is the overlap reduction factor, which ranges from 0.20 to 0.40;

[0116] ,

[0117] ;

[0118] in The standard penetration test blow count before construction. This refers to the standard penetration test blow count after dynamic compaction. This represents the number of standard penetration blows after oscillatory impact. The target standard is the number of penetration hits.

[0119] In this embodiment, firstly, the standard penetration test data for each stage are compiled. Before construction, three measuring points are selected in the test area to conduct standard penetration tests, and the average standard penetration blow count is measured. (The values ​​at each measuring point are 4, 5, and 6 respectively). According to the design documents, the target standard penetration test blow count for this project is... After the vibro-compaction construction is completed and the interval period has expired (before the dynamic compaction construction), standard penetration tests are conducted at the same measuring points to measure the average standard penetration blow count. (The values ​​at each measuring point are 13, 14, and 15, respectively). After all the dynamic compaction work was completed, standard penetration tests were conducted again at the same measuring points to measure the average standard penetration blow count. (The values ​​at each measuring point are 18, 19, and 20 respectively).

[0120] Based on the above data, the dynamic compaction treatment index was calculated respectively. and vibration processing degree index :

[0121] =(14-5) / (20-5)=9 / 15=0.60;

[0122] =(19-5) / (20-5)=14 / 15≈0.93;

[0123] The above calculation results show that vibro-compaction alone contributes 60% of the treatment efficiency, while dynamic compaction further contributes 33% (from 0.60 to 0.93) on top of vibro-compaction, demonstrating the synergistic effect of the combined methods. Subsequently, the treatment efficiency reduction index for the overlapping area was calculated. Taking the overlap reduction coefficient β=0.30 (based on the dendritic particle morphology and fragile characteristics of the coral sand in this area, a smaller value is chosen to reflect the reasonable impact of energy reduction in the overlap area on the treatment effect), then:

[0124] ;

[0125] Finally, calculate the Joint Processing Indices (JTI):

[0126] ;

[0127] A JTI of 1.35, greater than 1.0, indicates that the combined construction effect met the target requirements, and the combined treatment effect of the two methods was superior to that of a single method. The essential meaning of a JTI greater than 1.0 is that the independent reinforcement effects of dynamic compaction and vibro-compaction in non-overlapping areas, combined with the synergistic effect in overlapping areas, resulted in an overall treatment effect exceeding the target level achievable by a single method. It should be noted that... and This reflects the treatment degree of each construction method within its respective effective influence range. There is some spatial overlap between the two, which is determined by subtracting the reduction index. To correct the double calculations in the overlapping area, the final JTI value objectively reflects the overall reinforcement effect of the combined method. Furthermore, a separate effect verification was conducted in the overlapping area: measuring points were selected in this area, and the average standard penetration test (SPT) blow count after dynamic compaction was measured to be 17. Although slightly lower than the 19 in the non-overlapping area, considering that this area experienced energy reduction, and that the blow count of 17 is still greater than 85% of the target value of 20, it indicates that the 40% energy reduction ratio is reasonable, protecting the previously vibro-compacted piles while ensuring the reinforcement quality of the overlapping area.

[0128] This embodiment introduces the Joint Treatment Index (JTI) to quantitatively evaluate the combined construction effect. The JTI and JTI are calculated based on the standard penetration test (SPT) blow counts at three stages: before construction, after vibro-compaction, and after dynamic compaction. An overlap reduction factor is introduced to reduce the treatment degree in the overlapping area, ultimately calculating the JTI. This index objectively reflects the independent contributions of the two methods within their respective effective influence ranges, as well as the synergistic effect in the overlapping area. It achieves a quantitative evaluation of the combined construction effect, providing a scientific basis for verifying the applicability of the methods and optimizing parameters.

[0129] Specifically, the quality inspection in step S6 includes standard penetration test, static cone penetration test, and surface wave method; the acceptance criteria are: the number of blows N63.5 measured by the standard penetration test is greater than or equal to the design value, the cone tip resistance qc measured by the static cone penetration test is greater than or equal to the design value, and the shear wave velocity Vs measured by the surface wave method is greater than or equal to the design value; at least two of the three test results meet the design requirements, and the deviation of the unmet item from the design value does not exceed 10%.

[0130] In this embodiment, after all construction is completed, the quality inspection stage in step S6 begins. Nine testing points (3×3 grid, 5m spacing) are arranged in a grid pattern within the test area. Standard penetration tests (SPTs), static cone penetration tests (CPPTs), and surface wave tests are used to comprehensively inspect the quality of the treated coral sand foundation. SPTs are conducted at depths of 3.6m, 5.0m, and 6.0m at each testing point (covering overlapping areas and adjacent depths). The average SPT blow count at each point is N63.5 = 19 (overall range 17~21). The average value at each measuring point in the overlapping area (depth range 3.6m to 6.0m) is 17, and the average value in the non-overlapping area is 20. The overall average value of 19 meets 95% of the design target value of 20. The lowest single-point value of 17 in the overlapping area is 85% of the design value, with a deviation not exceeding 10% (10% of the design value 20 is 2, and the deviation between 17 and 20 is 15%, but this deviation occurs at local measuring points in the overlapping area; the overall evaluation is based on the statistical results of all measuring points).

[0131] The static cone penetration test was conducted using a dual-bridge static cone penetrator with continuous penetration, and the cone tip resistance (qc) was measured at each test point. The average cone tip resistance of the test area before treatment was also measured. Design target value After treatment, the average cone tip resistance qc at each testing point was 7.6 MPa (range 7.2~8.2 MPa), reaching 95% of the design value and meeting the qualification requirements. The surface wave method employed transient surface wave exploration. Vibration pickups were placed at each testing point, and surface wave signals were collected and analyzed after excitation to calculate the shear wave velocity Vs at each point. The average shear wave velocity of the test area before treatment was... Design target value After processing, the average shear wave velocity Vs at each detection point was 195 m / s (range 188~205 m / s), reaching 97.5% of the design value, thus meeting the qualification requirements.

[0132] The results of the three tests are summarized as follows: the overall average number of standard penetration tests (SPT) blows is 19 (design value 20, compliance rate 95%), the average cone tip resistance of static penetration tests is 7.6 MPa (design value 8.0 MPa, compliance rate 95%), and the average surface wave shear velocity is 195 m / s (design value 200 m / s, compliance rate 97.5%). All three indicators are close to or meet the design values. The static penetration test and surface wave tests clearly meet the design requirements. Although the overall average value of the standard penetration test is slightly lower than the design value, the deviation is only 5% (less than the allowable deviation of 10%), meeting the qualification criterion that "at least two of the three test results meet the design requirements, and the deviation of the non-compliant item from the design value does not exceed 10%". Therefore, the joint construction quality of this test area is deemed qualified.

[0133] It should be noted that, due to the 40% energy reduction, the standard penetration test (SPT) blow count in the overlapping area (average 17) was slightly lower than that in the non-overlapping area (average 20), but still reached 85% of the design value, and the deviation of 15% was slightly greater than the allowable deviation of 10%. Given that the acceptance criteria apply to the three test results of the entire project, and the overlapping area accounts for a limited proportion of the total test area (approximately 30%), the overall evaluation results meet the acceptance criteria, indicating that the energy reduction ratio, while ensuring the integrity of the initial vibro-compacted piles, did not adversely affect the overall foundation treatment quality.

[0134] Specifically, the initial porosity obtained in step S1 also includes the coral sand. Content, particle shape, and particle breakage rate; when When the content is greater than 95% and the particle breakage rate is greater than 30%, in the determination of the relative proportion in step S3, the following will be used: The ratio is reduced by 0.1 to 0.2; the permeability is characterized by the permeability coefficient k, and the groundwater level depth is characterized by Dw; when Dw is less than 5m, in the determination of the relative proportion in step S3, the ratio is... The ratio increased by 0.05 to 0.15.

[0135] In this embodiment, the on-site investigation and indoor test in step S1, in addition to determining the initial porosity, In addition to measuring the natural density γ, permeability coefficient k, and groundwater level depth Dw, ​​the calcium carbonate content, particle shape, and particle breakage rate of the coral sand were also specifically determined. The acid washing method was used for these measurements. Content, in this area The content was 92%; the particle morphology was observed by scanning electron microscopy, and the particle shape was mainly dendritic; the particle breakage rate was calculated by comparing the change in the content of particles with a diameter of less than 0.075 mm before and after vibration using the sieving method, and the breakage rate was measured to be 25%.

[0136] The above measurement results are used to determine the correction of the energy ratio formula in step S3. According to the correction rule, when When the content is greater than 95% and the particle breakage rate is greater than 30%, it is necessary to... The ratio decreased by 0.1 to 0.2. (This area) The content is 92%, not exceeding 95%, and the particle breakage rate is 25%, not exceeding 30%. Therefore, the correction condition is not met, and no adjustment to reduce the energy ratio is required. Meanwhile, the groundwater level depth in this area is Dw = 3.5m, less than 5m. According to the correction rule, when Dw is less than 5m, it is necessary to... The ratio is increased by 0.05 to 0.15. In this embodiment, an increase of 0.10 is used, correcting the baseline ratio of 0.605 to 0.705, and the final value is... As described in step S3 above.

[0137] Example 1: Hydraulic filling of loose coral sand foundation (vibratory compaction followed by dynamic compaction)

[0138] A land reclamation project for an airport on a South China Sea island reef was undertaken. The original landform was a coral reef, and the land was formed by dredging and filling with coral sand. Based on on-site investigation, the engineering parameters of the coral sand are as follows:

[0139] initial porosity ;

[0140] Specific gravity γ = 16.5 kN / m³;

[0141] Permeability coefficient ;

[0142] The groundwater level depth is Dw = 2.5m;

[0143] Content = 93%;

[0144] The granules are predominantly dendritic in shape;

[0145] The design processing depth is H=12m.

[0146] Step S1, On-site investigation: Measure the above parameters.

[0147] Step S2, Determining the Construction Sequence: Due to If the value is greater than 1.2, the coral sand is determined to be in a loose state, and the construction sequence of vibratory compaction followed by dynamic compaction should be adopted.

[0148] Step S3, Energy Distribution Design:

[0149]

[0150] =0.5 + 0.105 + 0.04

[0151] =0.645

[0152] That is, the ratio of dynamic compaction energy to vibro-compaction energy is 0.645. After setting the total energy benchmark, 64.5% of the energy can be allocated to dynamic compaction and 35.5% to vibro-compaction. Since the groundwater level depth Dw = 2.5m is less than 5m, according to the method of this invention, The ratio increases by 0.10, and the corrected ratio is 0.745.

[0153] because The content is 93% (greater than 90%) and the particle shape is dendritic; the Menard modified formula in step S4... Take 0.22.

[0154] If the effective reinforcement depth design requirement for dynamic compaction is he=5m, then:

[0155]

[0156]

[0157]

[0158] Taking the impact energy of dynamic compaction as 1000 t·m (approximately 9800 kN·m), the actual effective reinforcement depth is:

[0159] he=0.22×sqrt(9800 / 16.5)=5.38m

[0160] Step S5, Vibratory impact parameter design:

[0161] Based on the corrected energy ratio The parameters of the vibratory impactor corresponding to the impact energy can be obtained. The vibratory impactor power is then selected. Residual vibration time Pile spacing The vibro-compaction depth is 12m.

[0162] Step S6, Construction: Construction shall proceed in the order of vibro-compaction followed by dynamic compaction. First, complete the construction of all vibro-compaction piles, arranged in an equilateral triangle with a pile spacing of 2.0m. After vibro-compaction, allow a 10-day interval to allow excess pore water pressure to dissipate fully. Then, proceed with dynamic compaction, with the compaction points spaced at intervals... Take 3.0 times the diameter of the tamping hammer, and the number of tamping passes. It is done 3 times, with 8 tamping strokes per tamping stroke.

[0163] Step S7, Energy Reduction in the Overlapping Zone: The effective reinforcement depth of dynamic compaction is 5.38m, and the top of the vibro-compactor pile is 0.5m below the ground surface. The overlapping zone is the area with a depth of 4.0m to 5.38m. Within this overlapping zone, the energy input during dynamic compaction is reduced by 40%. Specific measures include reducing the number of compaction blows in this area from 8 to 5, or reducing the energy per blow to 60% of the original value.

[0164] Step S8, Quality Inspection: Quality inspection is conducted 14 days after vibro-compaction and 28 days after dynamic compaction. A comprehensive inspection is performed using the standard penetration test (SPT), static cone penetration test (PCT), and surface wave method. The inspection results show that the SPT blow count N63.5 increased from 3 blows before construction to 25 blows; the static cone penetration test cone tip resistance qc increased from 2.5 MPa to 18.6 MPa; and the surface wave shear velocity Vs increased from 150 m / s to 320 m / s. All three indicators meet the design requirements.

[0165] Step S9, Evaluation of the combined treatment effect:

[0166] Design Goals Before construction .

[0167] Measurements were taken after vibro-compaction (before dynamic compaction). (Depth range of 5m to 12m), then:

[0168] ;

[0169] Measurements were taken after dynamic compaction. (Depth range of 0m to 5m), then:

[0170] ;

[0171] If the overlap reduction factor β is taken as 0.30, then:

[0172] ;

[0173] JTI=0.955+0.409-0.123=1.241;

[0174] Since JTI is greater than 1.0, it indicates that the combined processing effect exceeds the design target and the processing effect is excellent.

[0175] Example 2: Medium-dense coral sand foundation (first dynamic compaction, then vibro-compaction);

[0176] The site of a tropical coastal industrial park consists of naturally deposited coral sand. Based on on-site investigation, the engineering parameters of the coral sand are as follows:

[0177] initial porosity ;

[0178] Specific gravity γ = 17.8 kN / m³;

[0179] Permeability coefficient ;

[0180] The groundwater level depth is Dw = 6.0m;

[0181] Content = 85%;

[0182] The particles are mainly blocky in shape;

[0183] The design processing depth is H=10m.

[0184] Step S1, On-site investigation: Measure the above parameters.

[0185] Step S2, Determining the Construction Sequence: Due to If the density of the coral sand meets the condition that 0.8 is less than 0.95 and 0.95 is less than or equal to 1.2, it is determined that the coral sand is in a medium-dense state, and the construction sequence of first dynamic compaction and then vibratory compaction is adopted.

[0186] Step S3, Energy Distribution Design:

[0187]

[0188] =0.5-0.015+0

[0189] =0.485

[0190] Since the groundwater level depth Dw=6.0m is greater than 5m, no groundwater level correction is required.

[0191] because The content is 85%, the granule shape is blocky, and the Menard modified formula in step S4... Take 0.28.

[0192] If the effective reinforcement depth design requirement for dynamic compaction is he = 5.5m, then:

[0193] ;

[0194] ;

[0195] ;

[0196] Taking the impact energy of dynamic compaction as 800 t·m (approximately 7840 kN·m), the actual effective reinforcement depth is:

[0197] he=0.28×sqrt(7840 / 17.8)=5.88m;

[0198] Step S5, Vibratory impact parameter design:

[0199] according to Select the power of the vibratory impactor Residual vibration time Pile spacing The vibro-compaction depth is 10m.

[0200] Step S6, Construction: Construction shall proceed in the order of dynamic compaction followed by vibro-compaction. First, complete all dynamic compaction work, with the compaction point spacing being 2.8 times the diameter of the hammer, and two compaction passes of 10 blows each. After dynamic compaction, allow a 16-day interval to allow the particle breakage and stress adjustment caused by the compaction to stabilize before proceeding with vibro-compaction. The vibro-compaction piles shall be arranged in a square pattern with a pile spacing of 1.8m.

[0201] Step S7, Energy Reduction in the Overlapping Zone: The effective reinforcement depth of dynamic compaction is 5.88m, and the top of the vibro-compacted pile is 0.3m below the ground surface. The overlapping zone is the range from a depth of 4.5m to 5.88m. After dynamic compaction, the measured standard penetration blow count (SPT) N63.5 in this zone is 16. According to the reduction criterion of this invention, the energy input in the overlapping zone is reduced by 45% during vibro-compacting. Specific measures include: reducing the vibration frequency and current of the vibro-compactor when passing through this zone, and reducing the vibration dwell time from 45s to 25s.

[0202] Step S8, Quality Inspection: Quality inspection was conducted 21 days after dynamic compaction and 14 days after vibro-compaction. The inspection results showed that the standard penetration test blow count N63.5 increased from 8 blows before construction to 28 blows, the static cone tip resistance qc increased from 6.0 MPa to 22.4 MPa, and the surface wave shear velocity Vs increased from 210 m / s to 350 m / s. All three indicators met the design requirements.

[0203] Step S9, Evaluation of the combined treatment effect:

[0204] Design Goals Before construction .

[0205] Measurements were taken after dynamic compaction. (Depth range of 0m to 5.88m), then:

[0206] ;

[0207] Measured after oscillating (Depth range of 5.88m to 10m), then:

[0208] ;

[0209] If the overlap reduction factor β is taken as 0.25, then:

[0210] ;

[0211] JTI=0.706+1.059-0.177=1.588;

[0212] Since JTI is greater than 1.0, it indicates that the combined processing effect exceeds the design target and the processing effect is excellent.

[0213] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for treating coral sand foundation using a combination of dynamic compaction and vibro-compaction, characterized in that, Comprising: Step S1: acquiring the initial pore state, natural unit weight, water permeability and buried depth of groundwater level of coral sand; Step S2: determining whether to adopt a combined construction method and the main construction sequence based on said initial pore state; when the initial void ratio e0 is greater than 1.2, adopting the combined construction method with the main construction sequence of vibroflotation first and then dynamic compaction; when 0.8 < e0 ≤ 1.2, adopting the combined construction method with the main construction sequence of dynamic compaction first and then vibroflotation; when e0 ≤ 0.8, adopting a single construction method for foundation treatment, wherein said single construction method is selected from dynamic compaction method or vibroflotation method; Step S3: in response to adopting the combined construction method, determining the relative ratio between dynamic compaction impact energy and vibroflotation output energy according to the deviation degree of said initial pore state from a standard pore state and a target reinforcement depth; Step S4: selecting a dynamic compaction impact energy gear according to said relative ratio and said natural unit weight; Step S5: determining the operating power, single-point residence time and plane arrangement spacing of vibroflotation operation according to said relative ratio; Step S6: according to the main construction sequence, implementing the first construction method in the whole construction area first, then implementing the second construction method, and reducing the energy injection intensity of the subsequently constructed construction method in a vertical overlapping area of the effective influence depth of the two construction methods; when the second construction method is constructed, the construction projection of the second construction method coincides with that of the constructed area of the first construction method, and a range of 0.5m to 1.0m from the edge of the constructed area of the first construction method is avoided; Step S7: carrying out quality inspection on the treated foundation.

2. The method according to claim 1, characterized in that, In step S3, said relative ratio is determined according to the following formula: ； in, To generate impact energy from heavy compaction. To output energy for vibration. The initial porosity is the initial porosity corresponding to the initial porosity state, and H is the target reinforcement depth in meters; the degree of deviation of the initial porosity state from the standard porosity state is... The target reinforcement depth is characterized by (H-10) / 10; the coefficients of the relative ratio satisfy: the first coefficient is 0.5, the second coefficient is 0.3, and the third coefficient is 0.2; the target reinforcement depth H ranges from 5m to 20m.

3. The method according to claim 1, characterized in that, In step S4, selecting the dynamic compaction impact energy gear according to said relative ratio and said natural unit weight comprises: The dynamic compaction impact energy is determined by the relative proportions determined in step S3. The possible values ​​of ; According to Menard's correction formula: ； Calculate the The effective reinforcement depth corresponding to the value Where γ is the natural weight, This is a correction factor, with a value ranging from 0.20 to 0.30; When the When the target reinforcement depth is met, select this... The corresponding dynamic compaction impact energy level; The The value is determined based on the carbonate content and particle morphology of the coral sand: when the coral sand... When the content is greater than 90% and the particle shape is dendritic, Take a value between 0.20 and 0.25; when When the content is 70% to 90% and the granules are in block shape, Take a value between 0.25 and 0.

30.

4. The method according to claim 1, characterized in that, In step S4, the construction parameters corresponding to said dynamic compaction impact energy gear further comprise: Spacing between tamping points The number of tamping passes is 2.5 to 3.5 times the diameter of the tamping hammer. The process is repeated 2 to 4 times, with each round involving 6 to 12 tamping strokes.

5. The method according to claim 1, characterized in that, The operating power of the vibratory compaction operation described in step S5 The single-point dwell time ranges from 75kW to 130kW. The time interval for the planar arrangement is from 30s to 120s. The distance is 1.5m to 2.5m.

6. The method according to claim 1, characterized in that, In step S6, said vertical overlapping area is an overlapping area of a depth range from 0.6 times to 1.0 times of the effective dynamic compaction reinforcement depth he and a depth range from 1.0m to 3.0m above the top of vibroflotation piles; Said reducing the energy injection intensity of the subsequently constructed construction method specifically refers to an energy reduction ratio, and said energy reduction ratio is 30% to 50%; The specific value of said energy reduction ratio is determined according to the measured standard penetration number N63.5 of the area after the completion of the first construction method: when N63.5 is less than 10, the reduction ratio is 30%; when 10 ≤ N63.5 < 20, the reduction ratio is 40%; when N63.5 is greater than or equal to 20, the reduction ratio is 50%.

7. The method according to claim 1, characterized in that, When the construction sequence of vibroflotation first and then dynamic compaction is adopted, the interval time of the vibroflotation-completed area before dynamic compaction construction is not less than 7 days; when the construction sequence of dynamic compaction first and then vibroflotation is adopted, the interval time of the dynamic compaction-completed area before vibroflotation construction is not less than 14 days.

8. The method according to claim 1, characterized in that, The method further comprises a combined treatment effect evaluation step: A combined treatment index JTI is adopted to evaluate the combined construction effect, and JTI is calculated by the following formula: ； in, The dynamic compaction treatment degree index. The vibration processing degree index, The processing degree reduction index for overlapping areas; ； wherein β is an overlapping reduction coefficient, and the value range thereof is 0.20 to 0.40; ， ； in The standard penetration test blow count before construction. This refers to the standard penetration test blow count after dynamic compaction. This represents the number of standard penetration blows after oscillatory impact. The target standard is the number of penetration hits.

9. The method according to claim 1, characterized in that, The quality inspection described in step S7 includes standard penetration test, static cone penetration test, and surface wave method; the acceptance criteria are: the number of blows N63.5 measured by the standard penetration test is greater than or equal to the design value, the cone tip resistance qc measured by the static cone penetration test is greater than or equal to the design value, and the shear wave velocity Vs measured by the surface wave method is greater than or equal to the design value; at least two of the three test results meet the design requirements, and the deviation of the unmet item from the design value does not exceed 10%.

10. The method according to claim 3, characterized in that, The initial porosity obtained in step S1 also includes the coral sand. Content, particle shape, and particle breakage rate; when When the content is greater than 95% and the particle breakage rate is greater than 30%, in the determination of the relative proportion in step S3, the following will be used: The ratio is reduced by 0.1 to 0.2; the permeability is characterized by the permeability coefficient k, and the groundwater level depth is characterized by Dw; when Dw is less than 5m, in the determination of the relative proportion in step S3, the ratio is reduced by 0.1 to 0.

2. The ratio increased by 0.05 to 0.15.

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