Method for combined treatment of dredged sludge conditioning agent and vacuum preloading

Abstract

The present application relates to a kind of dredging sludge modifier and vacuum preloading combined processing method, in particular to the technical field of dredging sludge vacuum preloading, the dredging sludge modifier and vacuum preloading combined processing method include: according to the permeability coefficient K h , volume compression coefficient m v And the maximum radius r smax Of dredging sludge jam area, establish layered gradient PVD arrangement model;After each layer PVD installation is completed, inject rice hull ash and slag composite solidification composition into dredging sludge;According to the layered gradient PVD arrangement model, the vacuum negative pressure P0=80kPa~100kPa is applied in surface layer, the vacuum negative pressure P0=60kPa~80kPa is applied in middle layer, the vacuum negative pressure P0=40kPa~60kPa is applied in bottom layer, and real-time monitoring of each layer's excess pore water pressure u h ;Adjust vacuum negative pressure value, so that the difference of each layer's consolidation degree does not exceed 5%.The present application is by layered gradient PVD arrangement, rice hull ash and slag composite solidification composition pulse injection and vacuum pressure dynamic regulation, and the overall consolidation speed is improved by 40%, and the jam effect is reduced by 50%.

Description

Technical Field

[0001] This invention relates to the field of vacuum preloading technology for dredged sludge, and particularly to a combined treatment method for dredged sludge conditioning agent and vacuum preloading. Background Technology

[0002] Current vacuum preloading technology for dredged sludge generally relies on empirical methods to set vacuum pressure, which is difficult to adapt to the complex and variable permeability characteristics of sludge, resulting in significant clogging effects and low consolidation efficiency. In standardized construction, the uniform spacing of plastic drainage boards (PVD) and the uniform application of vacuum negative pressure easily cause a sharp drop in the permeability coefficient of the surface clogging zone, hindering the dissipation of deep pore water, resulting in a consolidation degree difference of more than 15% and a resource waste rate exceeding 20%. Existing mathematical models often ignore the dynamic expansion of clogging zones and the stratified seepage characteristics, and the solidifying agent components are loose with limited permeability regulation effects, often requiring secondary treatment in engineering projects and extending the construction period by 30% to 50%. Summary of the Invention

[0003] The main objective of this invention is to propose a combined treatment method for dredged sludge conditioning agent and vacuum preloading, which aims to adapt to the complex and ever-changing permeability characteristics of sludge, improve construction efficiency, and save construction costs.

[0004] To achieve the above objectives, the present invention proposes a combined treatment method for dredged sludge conditioning agent and vacuum preloading, wherein the combined treatment method for dredged sludge conditioning agent and vacuum preloading includes: Based on the permeability coefficient K of the dredged silt h Volume compressibility factor m v and the maximum radius r of the siltation area smax A layered gradient PVD layout model was established; the dredged silt layer was divided into at least three longitudinal layers, with the PVD spacing of the surface layer being 0.3m to 0.5m, the PVD spacing of the middle layer being 0.6m to 0.8m, and the PVD spacing of the bottom layer being 0.9m to 1.2m. After each layer of PVD is installed, a rice husk ash and carbide slag composite curing composition is injected into the dredged sludge; the rice husk ash and carbide slag composite curing composition includes, by weight, 30-50 parts of rice husk ash, 20-40 parts of carbide slag, 5-10 parts of calcium chloride, and 3-8 parts of polyacrylamide. According to the layered gradient PVD arrangement model, the vacuum negative pressure P0 = 80 kPa ~ 100 kPa is applied to the surface layer, the vacuum negative pressure P0 = 60 kPa ~ 80 kPa to the middle layer, and the vacuum negative pressure P0 = 40 kPa ~ 60 kPa to the bottom layer. The excess pore water pressure u of each layer is monitored in real time. h ; Adjust the vacuum negative pressure value so that the difference in the degree of consolidation of each layer does not exceed 5%.

[0005] In one embodiment, the permeability coefficient K of the dredged silt is... h Volume compressibility factor m v and the maximum radius r of the siltation area smax The steps for establishing a hierarchical gradient PVD layout model include: Based on the permeability coefficient K of dredged silt h Given the permeability coefficient K0 of the non-clogging zone, calculate the attenuation coefficient K2 of the clogging zone for each layer (0.4–0.8), and determine the radius of the clogging zone for each layer using a formula to ensure the permeability of the surface layer. smax ≤0.15 m, the r of the middle layer smax ≤0.25 m, the r of the bottom layer smax ≤0.35 m; The formula is: .

[0006] In one embodiment, the step of injecting a rice husk ash-carbide slag composite curing composition into the dredged sludge after each layer of PVD installation includes: After each PVD layer is installed, a rice husk ash calcium carbide slag composite solidification composition is injected into the dredged sludge. The injection amount of the rice husk ash calcium carbide slag composite solidification composition is 20-30 kg per cubic meter of dredged sludge. The injection method is to inject in three pulses along the PVD axis, with an interval of 12-24 hours between each injection.

[0007] In one embodiment, the rice husk ash in the rice husk ash-carbide slag composite curing composition has a particle size ≤0.075mm, a calcium-to-magnesium ratio of carbide slag ≥3:1, calcium chloride is in anhydrous granular form, and the molecular weight of polyacrylamide is 8 million to 12 million.

[0008] In one embodiment, according to the layered gradient PVD arrangement model, a vacuum negative pressure P0 = 80 kPa to 100 kPa is applied to the surface layer, a vacuum negative pressure P0 = 60 kPa to 80 kPa is applied to the middle layer, and a vacuum negative pressure P0 = 40 kPa to 60 kPa is applied to the bottom layer. The excess pore water pressure u of each layer is monitored in real time. h The steps include: A continuous suction mode is used for the surface layer, and a vacuum negative pressure P0 = 80kPa~100kPa is applied to the surface layer. Intermittent suction mode is used in the middle layer stratification, and the vacuum negative pressure P0 in the middle layer stratification is 60kPa~80kPa; A low-frequency pulse suction mode was used in the bottom layer, with a vacuum negative pressure P0 of 40 kPa to 60 kPa in the bottom layer, and the excess pore water pressure u in each layer was monitored in real time. h .

[0009] In one embodiment, the step of adjusting the vacuum negative pressure value so that the difference in the degree of consolidation of each layer does not exceed 5% includes: According to the formula: 1-

[0010] The degree of consolidation of each layer is calculated in real time. When the difference in the degree of consolidation between adjacent layers is greater than 5%, it is determined according to the following:

[0011] Increase the vacuum negative pressure value for low-consolidation stratification by 5% to 10% of the current value.

[0012] In one embodiment, according to the layered gradient PVD arrangement model, a vacuum negative pressure P0 = 80 kPa to 100 kPa is applied to the surface layer, a vacuum negative pressure P0 = 60 kPa to 80 kPa is applied to the middle layer, and a vacuum negative pressure P0 = 40 kPa to 60 kPa is applied to the bottom layer. The excess pore water pressure u of each layer is monitored in real time. h The steps include: A vacuum negative pressure system was used based on the aforementioned layered gradient PVD arrangement model. Vacuum negative pressure P0 = 80 kPa–100 kPa was applied to the surface layer, P0 = 60 kPa–80 kPa to the middle layer, and P0 = 40 kPa–60 kPa to the bottom layer. The excess pore water pressure u in each layer was monitored in real time. h The vacuum negative pressure system includes three independent vacuum pump groups. Each pump group is connected to the adjacent pump group through a pressure balancing valve. The opening threshold of the balancing valve is ≥5 kPa of the pressure difference between adjacent layers, and the pumping rate of the pump group is related to the permeability coefficient k of the layer. h Proportional.

[0013] In one embodiment, the exhaust end of the three-stage independent vacuum pump group is connected to a gas-water separation device. The separated water is reinjected into the outer edge of the PVD-affected zone of the bottom layer through a guide pipe. The reinjection flow rate is 10% to 15% of the pumping flow rate.

[0014] In one embodiment, the surface-layered PVD uses a diamond-shaped grid arrangement with a node spacing of 0.3m to 0.5m; the middle-layered PVD uses a rectangular grid arrangement with an aspect ratio of 1:1.5; and the bottom-layered PVD uses a radial arrangement with a radiation angle of 30° to 45°, and the grid density is related to the permeability coefficient k of the layer. h Inversely proportional.

[0015] In one embodiment, after the step of adjusting the vacuum negative pressure value to ensure that the difference in the degree of consolidation of each layer does not exceed 5%, the method further includes: The dredged sludge was subjected to secondary conditioning. The conditioning agent was a mixed solution of sodium silicate and aluminum sulfate with a mass ratio of 1:2. The spraying rate was 5 L / m² to 8 L / m². After spraying, the sludge was allowed to stand for 48 hours.

[0016] The technical solution of this invention, through layered gradient PVD arrangement, pulse injection of a rice husk ash and carbide slag composite solidification composition, and dynamic control of vacuum pressure, increases the overall consolidation speed by 40% and reduces the clogging effect by 50%. Examples show that applying pressure from the surface to the bottom layer (90 kPa / 70 kPa / 50 kPa) combined with a rhomboid-radial grid arrangement ensures that the difference in consolidation degree between each layer is stable at ≤5%; the solidification composition (40 parts rice husk ash and 30 parts carbide slag) can increase the permeability coefficient of the non-clogging area to 1.5 × 10⁻⁶. -8 m / s, shortening the construction period by 30%. After secondary conditioning of sodium silicate-aluminum sulfate, the 28-day unconfined compressive strength is ≥200 kPa, the porosity is reduced by 35%, and the project cost is reduced by more than 25%. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of an embodiment of the combined treatment method of dredged sludge conditioner and vacuum preloading provided by the present invention. Figure 2 This is an example of a vacuum preloading calculation model for the present invention; Figure 3 This is an example of the influence of the maximum radius of the sludge zone on the degree of consolidation in this invention. Figure 4 This is an example of the effect of the attenuation coefficient of the sludge zone on the degree of consolidation in this invention; Figure 5 This is an example of the effect of the clogging coefficient on the degree of consolidation in this invention; Figure 6 The results of the influence of the maximum volume compressibility coefficient of dredged silt on the degree of consolidation are shown in the example of this invention. Figure 7 This is an example of the effect of the radius of influence of the plastic drainage board on the degree of consolidation in this invention; Figure 8 The results illustrate the influence of the permeability coefficient on the degree of consolidation in the non-clogging area of ​​dredged sludge, as exemplified by this invention.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0022] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0023] Please see Figure 1 In one embodiment of the present invention, the method for combined treatment of dredged sludge conditioning agent and vacuum preloading includes: Step S10, based on the permeability coefficient K of the dredged silt h Volume compressibility factor m v and the maximum radius r of the siltation area smax A layered gradient PVD layout model was established; the dredged silt layer was divided into at least three longitudinal layers, with the PVD spacing of the surface layer being 0.3m to 0.5m, the PVD spacing of the middle layer being 0.6m to 0.8m, and the PVD spacing of the bottom layer being 0.9m to 1.2m. Step S20: After each layer of PVD is installed, a rice husk ash and carbide slag composite curing composition is injected into the dredged sludge; the rice husk ash and carbide slag composite curing composition includes, by mass parts: 30-50 parts rice husk ash, 20-40 parts carbide slag, 5-10 parts calcium chloride, and 3-8 parts polyacrylamide. Step S30: According to the layered gradient PVD arrangement model, apply a vacuum negative pressure P0 = 80kPa~100kPa to the surface layer, a vacuum negative pressure P0 = 60kPa~80kPa to the middle layer, and a vacuum negative pressure P0 = 40kPa~60kPa to the bottom layer, and monitor the excess pore water pressure u of each layer in real time. h ; Step S40: Adjust the vacuum negative pressure value so that the difference in the degree of consolidation of each layer does not exceed 5%.

[0024] Specifically, based on the permeability coefficient, volume compressibility coefficient, and maximum radius of the clogging zone of the dredged sludge, a layered gradient PVD layout model was established, dividing the dredged sludge layer into at least three longitudinal layers; the PVD spacing for the surface layer was 0.3–0.5 m, for the middle layer it was 0.6–0.8 m, and for the bottom layer it was 0.9–1.2 m. m; After each layer of PVD installation is completed, a composite solidification composition of rice husk ash and carbide slag is injected into the dredged sludge. The composition comprises, by mass, 30-50 parts rice husk ash, 20-40 parts carbide slag, 5-10 parts calcium chloride, and 3-8 parts polyacrylamide. According to the layered gradient PVD arrangement model, a vacuum negative pressure P0 = 80kPa-100kPa is applied to the surface layer, P0 = 60kPa-80kPa to the middle layer, and P0 = 40kPa-60kPa to the bottom layer, and the excess pore water pressure of each layer is monitored in real time. Based on the real-time monitoring data, the vacuum negative pressure value is dynamically adjusted through the radial consolidation equation to ensure that the difference in the degree of consolidation of each layer does not exceed 5%. The core steps of the layered gradient PVD arrangement are defined, and the clogging effect is suppressed by the layered pressure and the injection of the solidification composition, and a dynamic adjustment mechanism is introduced to ensure the uniformity of consolidation.

[0025] The technical solution provided by this invention, through layered gradient PVD arrangement, pulse injection of the rice husk ash and carbide slag composite solidification composition, and dynamic control of vacuum pressure, increases the overall consolidation speed by 40% and reduces the clogging effect by 50%. Examples show that applying pressure from the surface to the bottom layer (90 kPa / 70 kPa / 50 kPa) combined with a rhomboid-radial grid arrangement ensures that the difference in consolidation degree between each layer is stable at ≤5%; the solidification composition (40 parts rice husk ash and 30 parts carbide slag) can increase the permeability coefficient of the non-clogging area to 1.5 × 10⁻⁶. -8m / s, shortening the construction period by 30%. After secondary conditioning of sodium silicate-aluminum sulfate, the 28-day unconfined compressive strength is ≥200kPa, the porosity is reduced by 35%, and the project cost is reduced by more than 25%.

[0026] In one embodiment, the permeability coefficient K of the dredged silt is... h Volume compressibility factor m v and the maximum radius r of the siltation area smax The steps for establishing a hierarchical gradient PVD layout model include: Based on the permeability coefficient K of dredged silt h Given the permeability coefficient K0 of the non-clogging zone, calculate the attenuation coefficient K2 of the clogging zone for each layer (0.4–0.8), and determine the radius of the clogging zone for each layer using a formula to ensure the permeability of the surface layer. smax ≤0.15 m, the r of the middle layer smax ≤0.25 m, the r of the bottom layer smax ≤0.35 m; the formula is: The calculation methods for key parameters in the layered model are further defined, and the seepage path is optimized by controlling the radius of the siltation zone at different depths.

[0027] In one embodiment, the step of injecting a rice husk ash-carbide slag composite curing composition into the dredged sludge after each layer of PVD installation includes: After each layer of PVD is installed, a composite solidification composition of rice husk ash and carbide slag is injected into the dredged sludge. The injection amount of the rice husk ash and carbide slag composite solidification composition is 20-30 kg per cubic meter of dredged sludge, and the injection method is three pulse injections along the PVD axis, with an interval of 12-24 hours between each injection. The injection amount and method of the composition are limited, and the pulse injection enhances the permeability coefficient adjustment effect and avoids local clogging.

[0028] In one embodiment, the rice husk ash in the rice husk ash-carbide slag composite curing composition has a particle size ≤0.075mm, a calcium-to-magnesium ratio of ≥3:1 for the carbide slag, anhydrous granular calcium chloride, and a molecular weight of 8 million to 12 million for the polyacrylamide. Refining the physical parameters of the composition ensures that its interaction with the sludge particles effectively reduces the clogging coefficient.

[0029] In one embodiment, according to the layered gradient PVD arrangement model, a vacuum negative pressure P0 = 80 kPa to 100 kPa is applied to the surface layer, a vacuum negative pressure P0 = 60 kPa to 80 kPa is applied to the middle layer, and a vacuum negative pressure P0 = 40 kPa to 60 kPa is applied to the bottom layer. The excess pore water pressure u of each layer is monitored in real time. h The steps include: A continuous suction mode is used for the surface layer, and a vacuum negative pressure P0 = 80kPa~100kPa is applied to the surface layer. Intermittent suction mode is used in the middle layer stratification, and the vacuum negative pressure P0 in the middle layer stratification is 60kPa~80kPa; A low-frequency pulse suction mode was used in the bottom layer, with a vacuum negative pressure P0 of 40 kPa to 60 kPa in the bottom layer, and the excess pore water pressure u in each layer was monitored in real time. h .

[0030] Specifically, the surface layer uses a continuous suction mode, the middle layer uses an intermittent suction mode (suction for 30 minutes / 10-minute interval), and the bottom layer uses a low-frequency pulse suction mode (frequency ≤ 0.1 Hz). Different suction modes are adapted to the permeability characteristics of each layer, reducing the rate of blockage formation.

[0031] In one embodiment, the step of adjusting the vacuum negative pressure value so that the difference in the degree of consolidation of each layer does not exceed 5% includes: According to the formula: 1-

[0032] The degree of consolidation of each layer is calculated in real time. When the difference in the degree of consolidation between adjacent layers is greater than 5%, it is determined according to the following:

[0033] Increase the vacuum negative pressure value for low-consolidation stratification by 5% to 10% of the current value.

[0034] Specifically, the degree of consolidation of each layer is calculated in real time. When the difference in the degree of consolidation between adjacent layers is greater than 5%, the vacuum negative pressure value of the layer with the lower degree of consolidation is automatically increased by 5% to 10% of the current value. An automated feedback mechanism is introduced to optimize the vacuum pressure distribution in real time through equations.

[0035] In one embodiment, according to the layered gradient PVD arrangement model, a vacuum negative pressure P0 = 80 kPa to 100 kPa is applied to the surface layer, a vacuum negative pressure P0 = 60 kPa to 80 kPa is applied to the middle layer, and a vacuum negative pressure P0 = 40 kPa to 60 kPa is applied to the bottom layer. The excess pore water pressure u of each layer is monitored in real time. h The steps include: A vacuum negative pressure system was used based on the aforementioned layered gradient PVD arrangement model. Vacuum negative pressure P0 = 80 kPa–100 kPa was applied to the surface layer, P0 = 60 kPa–80 kPa to the middle layer, and P0 = 40 kPa–60 kPa to the bottom layer. The excess pore water pressure u in each layer was monitored in real time. hThe vacuum negative pressure system includes three independent vacuum pump groups. Each pump group is connected to the adjacent pump group through a pressure balancing valve. The opening threshold of the balancing valve is ≥5 kPa of the pressure difference between adjacent layers, and the pumping rate of the pump group is related to the permeability coefficient k of the layer. h Proportional.

[0036] Specifically, the vacuum negative pressure system includes a multi-stage vacuum pump group, with each pump group independently controlling one layer. The pump groups are connected by a pressure balancing valve, and the opening threshold of the balancing valve is a pressure difference between adjacent layers ≥ 5 kPa. The hardware system supports independent control of each layer, ensuring the accuracy of dynamic pressure adjustment.

[0037] In one embodiment, the exhaust end of the three-stage independent vacuum pump group is connected to a gas-water separation device. The separated water is reinjected into the outer edge of the PVD-affected zone of the bottom layer through a guide pipe. The reinjection flow rate is 10% to 15% of the pumping flow rate.

[0038] In one embodiment, the surface-layered PVD uses a diamond-shaped grid arrangement with a node spacing of 0.3m to 0.5m; the middle-layered PVD uses a rectangular grid arrangement with an aspect ratio of 1:1.5; and the bottom-layered PVD uses a radial arrangement with a radiation angle of 30° to 45°, and the grid density is related to the permeability coefficient k of the layer. h The permeability coefficients of the layers are inversely proportional. The surface layer of PVD uses a diamond grid arrangement, the middle layer uses a rectangular grid arrangement, and the bottom layer uses a radial arrangement. The grid density is inversely proportional to the permeability coefficient of each layer. Different arrangement forms are adapted to the seepage characteristics of each layer, further suppressing the clogging effect.

[0039] In one embodiment, after the step of adjusting the vacuum negative pressure value to ensure that the difference in the degree of consolidation of each layer does not exceed 5%, the method further includes: The dredged sludge was subjected to secondary conditioning. The conditioning agent was a mixed solution of sodium silicate and aluminum sulfate with a mass ratio of 1:2. The spraying rate was 5 L / m² to 8 L / m². After spraying, the sludge was allowed to stand for 48 hours.

[0040] Ultimately, conditioning enhances soil stability and prevents subsequent siltation and rebound.

[0041] In some confirmatory embodiments, the method of the present invention may be performed according to the following procedure: Establish as Figure 2 The theoretical model for vacuum preloading calculation considering the clogging effect is shown. The vacuum negative pressure applied to the top of the plastic drainage board (illustrated using PVD in the following text) is p0, which decreases linearly along the depth with an attenuation coefficient of k1. The vacuum negative pressure at the end position is... The treatment depth of PVD, i.e., the thickness of the dredged sludge, is... H The PVD permeability coefficient, equivalent drainage radius, and influence zone radius are k, respectively. wr w and r h Under vacuum pressure, pore water in the dredged sludge within the PVD's influence area will radially seep into the PVD. During this process, fine particles will also migrate towards the PVD under vacuum pressure, thus forming a clogging zone around the PVD. Because the vacuum level decreases vertically, the size of the clogging zone also decreases with depth. For simplicity, it is assumed that the radius of the clogging zone is determined by the surface position. Linearly decrease to the end position The attenuation coefficient is k2, and the radius of the sludge zone at any depth is... Due to the clogging effect, the radial permeability coefficient in the clogging zone is smaller than that in the non-clogging zone, and the permeability coefficient decreases further closer to the PVD. The permeability coefficient at any location can be represented by... This indicates that the area surrounding the clogging zone is a non-clogging zone with a radial permeability coefficient of k. h .

[0042] The following basic assumptions are made during the analysis: Assumption 1: The soil has no lateral deformation, and the vertical deformation at any point at the same depth is equal; Assumption 2: Considering only radial seepage, seepage under negative pressure conditions obeys Darcy's law; Assumption 3: The area below the calculation depth and outside the radius of influence of the vertical drainage board is an impermeable area; Assumption 4: The vertical drainage board, the silted-up area, and the non-silted-up area are the same in all properties except for their permeability coefficients; Assumption 5: The vacuum level decreases linearly along the vertical direction, and the extent of the blockage zone decreases linearly along the depth.

[0043] Based on the above assumptions, the radial consolidation equation for dredged silt under vacuum preloading is expressed as:

[0044] In the formula: and These represent the vertical strain and volume compressibility coefficient of the dredged silt, respectively. t represents the average excess pore pressure at any depth within the PVD influence range when only radial seepage is considered.

[0045] according to Figure 2 The vacuum degree at any depth can be expressed as:

[0046] The radius of the sludge zone at any depth can be expressed as:

[0047] Assume the permeability coefficient of the clogging zone is determined by k in the non-clogging zone. hIf the permeability coefficient decreases linearly along the radial direction to near the PVD location (k0), then the permeability coefficient at any location in the clogging zone can be expressed as:

[0048] In the formula: This represents the minimum permeability coefficient of the silted-up area. .

[0049] The boundary conditions are as follows: At the outer boundary of the PVD-affected zone, we have:

[0050] The excess pore pressure on the contact surface between PVD and the clogging zone is equal, that is:

[0051] The excess pore pressure is equal at the contact surface between the clogging zone and the non-clogging zone, that is:

[0052] In the formula: , and These represent the excess pore pressure in PVD, the clogging zone, and the non-clogging zone, respectively.

[0053] At the top of PVD:

[0054] At the bottom of PVD:

[0055] In some specific implementation processes, Darcy's law states that the radial seepage flow rate through a cylindrical surface of radius r and thickness dz in time dt is:

[0056] In the formula: Let be the radial seepage flow rate of the soil, and k be the permeability coefficient. It should be noted that k here is a general term, and the permeability coefficient varies in different locations within the silted-up zone and in non-silted-up zones. The soil weight, This refers to the excess pore water pressure on the cylindrical surface. .

[0057] During time dt, the radius is from r to The volume change of a soil mass with thickness dz is:

[0058] Based on the fact that radial seepage flow is equal to the change in soil volume, we can conclude that:

[0059] for The silted-up area within the range, equation It can be written as:

[0060] And for The non-clogging area within the range, equation It can be written as:

[0061] At the interface between PVD and the clogging area, i.e. At point dz, the amount of water that seeps into the PVD through the cylindrical surface of thickness dt in time dt is:

[0062] The upward water flow increment within this thickness range of PVD can be expressed as:

[0063] In the formula: This refers to the water permeability of PVD.

[0064] Since the amount of water seeping into the PVD from the soil is equal to the increase in water flow upwards from the PVD, therefore:

[0065] From the equation and boundary condition equations and The excess pore water pressure at the contact surface between the clogging zone and the PVD layer can be calculated as follows:

[0066] In the formula: ; , where is the well diameter ratio.

[0067] For equation Integrating both sides, we get:

[0068] Solve the equation and combined with equations We can obtain:

[0069] Similarly, for the equation Integrating both sides, we get:

[0070] Solve the equation and combined with equations and We can obtain:

[0071] The average excess pore water pressure at a certain depth in dredged silt can be expressed as:

[0072] Equation , and, Substitute into the equation From this, we can obtain:

[0073] Because n 2 The values ​​are relatively large; therefore, for simplicity, higher-order terms are ignored. It can be approximated as:

[0074] According to the equation , It can be further written in the following form:

[0075] In the formula: As a time factor, it can be expressed as:

[0076] Furthermore, the average radial degree of consolidation can be obtained as follows: 1-

[0077] In the formula: , and Corresponding to the initial time, time t, and infinity respectively value.

[0078] Overall average degree of consolidation of dredged sludge within the PVD treatment depth range It can be represented as:

[0079] The influence of the maximum radius of the silted-up area on the degree of soil consolidation is as follows: Figure 3As shown, after the application of vacuum negative pressure, the degree of consolidation of the soil gradually increases over time, and the rate of increase gradually slows down, indicating that the soil consolidation rate gradually decreases. During the vacuum preloading process of dredged sludge, the permeability coefficient of the sludge-clogging zone formed around the PVD is significantly smaller than that of the surrounding non-sludge-clogging zone, leading to a slower pore water seepage rate. Therefore, as the maximum radius of the sludge-clogging zone increases, the degree of soil consolidation gradually decreases over the same period, indicating that the soil consolidation rate gradually slows down. Furthermore, in the initial stage of consolidation, the slope of the consolidation degree curve decreases significantly with the increase of the maximum radius of the sludge-clogging zone, indicating that the influence of the maximum radius of the sludge-clogging zone on the soil consolidation rate is more pronounced in the initial stage of consolidation. For example, when the consolidation time is 25 days, the degrees of consolidation corresponding to the increase in the maximum radius of the sludge-clogging zone from 5 cm to 15 cm are 59.91%, 42.46%, 33.43%, 27.91%, and 24.16%, respectively. When the consolidation time is 100 days, the degree of consolidation corresponding to the maximum siltation zone radius of 5 cm is 97.32%, and the soil has basically been consolidated. However, at this time, the degree of consolidation corresponding to the maximum siltation zone radius of 15 cm is only 66.56%, indicating that the siltation effect during the vacuum preloading process of the dredged silt site will significantly affect the treatment effect. In actual engineering, appropriate measures should be taken to minimize the siltation effect.

[0080] The effect of the attenuation coefficient of the silted area on the degree of soil consolidation is as follows: Figure 4 As shown, an attenuation coefficient of 1 means that the radii of the bottom and top of the clogging zone are the same. As the attenuation coefficient of the clogging zone increases, the degree of consolidation corresponding to the same time period gradually decreases. In the initial stage of consolidation, the attenuation coefficient has a relatively small impact on the degree of soil consolidation; however, as time increases, the influence of the attenuation coefficient of the clogging zone gradually becomes significant. When the consolidation time is 100 days, as the attenuation coefficient increases from 0.2 to 1, the degree of consolidation decreases from 89.37% to 72.52%. A larger attenuation coefficient indicates a smaller difference between the minimum and maximum radii of the clogging zone, meaning a larger average radius of the entire clogging zone, and a greater impact on soil consolidation.

[0081] The effect of the siltation coefficient on the degree of soil consolidation is as follows: Figure 5 As shown, the soil consolidation degree curves corresponding to different siltation coefficients exhibit similar trends over time. However, as the siltation coefficient increases, the soil consolidation degree decreases at the same time, but the rate of decrease gradually slows down. For example, when the consolidation time is 100 days, the consolidation degrees are 84.76%, 80.05%, 75.41%, 72.80%, and 71.01% respectively when the siltation coefficient increases from 50 to 400. This is because as the siltation coefficient increases, the permeability coefficient of the silted area decreases, leading to a slower dissipation of excess pore water pressure in the silted area and a slower consolidation rate.

[0082] The effect of the volume compressibility coefficient of dredged silt on the degree of soil consolidation is as follows: Figure 6As shown, with the increase of the volumetric compressibility coefficient of dredged silt, the degree of consolidation of the soil gradually decreases in the same time period. Furthermore, the rate of decrease decreases gradually in the initial stage of consolidation, while the rate of decrease gradually increases in the later stage. This indicates that with the increase of the volumetric compressibility coefficient, the consolidation rate of dredged silt gradually decreases, and the decrease is more pronounced in the initial stage of consolidation.

[0083] The effect of PVD influence radius on soil consolidation degree is as follows: Figure 7 As shown, a smaller PVD influence radius means a denser PVD array, resulting in a steeper slope of the consolidation degree curve in the initial consolidation phase and a faster consolidation speed. For example, with an influence radius of 0.3 m, the consolidation degree reaches 99.19% after 100 days, indicating complete consolidation. At the same time, the consolidation degree corresponding to an influence radius of 0.7 m is only 54.44%, a significant difference. Therefore, in practical engineering, the consolidation speed can be increased by appropriately reducing the PVD spacing. Furthermore, at this point, the consolidation degree corresponding to an influence radius of 0.4 m also reaches 92.56%, with little difference in treatment effect compared to the 0.3 m influence radius. Therefore, from an engineering cost perspective, PVD arrays should not be deployed too densely.

[0084] The effect of permeability coefficient on soil consolidation in non-clogging areas of dredged silt is as follows: Figure 8 As shown, with the increase of the permeability coefficient in the non-clogging area of ​​the dredged sludge, the soil consolidation rate increases significantly, but the rate of increase gradually slows down. For example, when the consolidation time is 100 days, the soil consolidation degree is 33.23%, 55.39%, 70.18%, 80.05%, and 98.19% when the permeability coefficient increases from 2.5×10⁻⁹ m / s to 1.25×10⁻⁸ m / s, respectively. Based on the analysis results, adding appropriate amounts of non-polluting ionic salts to the dredged sludge during the sludge discharge process to condition the sludge and increase its permeability coefficient is of great significance for accelerating the vacuum preloading process and saving construction time and costs.

[0085] Based on the examples provided above and in conjunction with Figures 2 to 8In the verification embodiment of this invention, it is evident that the siltation effect significantly impacts the consolidation rate of dredged sludge under vacuum preloading. As the maximum radius and attenuation coefficient of the siltation zone increase, the area of ​​the siltation zone expands, and the soil consolidation rate decreases. The impact of the siltation effect should be considered in practical engineering. A larger siltation coefficient results in a smaller permeability coefficient in the siltation zone, slower dissipation of excess pore pressure, and a slower consolidation rate of the dredged sludge. As the volume compressibility coefficient of the dredged sludge increases, the consolidation rate gradually decreases. A smaller PVD influence radius leads to a faster consolidation rate. Therefore, in practical engineering, the consolidation rate can be improved by appropriately reducing the PVD spacing. However, after reaching a certain threshold, further reducing the PVD spacing has limited effect on improving the consolidation rate. The permeability coefficient of the non-siltation zone of the dredged sludge significantly affects the consolidation rate. As the permeability coefficient of the non-siltation zone increases, the consolidation rate significantly increases. Therefore, in practical engineering, conditioning the dredged sludge during the sludge discharge process can be considered to increase the permeability coefficient, which is instructive for shortening the vacuum preloading period.

[0086] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for combined treatment of dredged sludge with a conditioning agent and vacuum preloading, characterized in that, The combined treatment method of dredged sludge conditioning agent and vacuum precompression includes: Based on the permeability coefficient K of the dredged silt h Volume compressibility factor m v and the maximum radius r of the siltation area smax A layered gradient PVD layout model was established; the dredged silt layer was divided into at least three longitudinal layers, with the PVD spacing of the surface layer being 0.3m to 0.5m, the PVD spacing of the middle layer being 0.6m to 0.8m, and the PVD spacing of the bottom layer being 0.9m to 1.2m. After each layer of PVD is installed, a rice husk ash and carbide slag composite curing composition is injected into the dredged sludge; the rice husk ash and carbide slag composite curing composition includes, by weight, 30-50 parts of rice husk ash, 20-40 parts of carbide slag, 5-10 parts of calcium chloride, and 3-8 parts of polyacrylamide. According to the layered gradient PVD arrangement model, the vacuum negative pressure P0 = 80 kPa ~ 100 kPa is applied to the surface layer, the vacuum negative pressure P0 = 60 kPa ~ 80 kPa to the middle layer, and the vacuum negative pressure P0 = 40 kPa ~ 60 kPa to the bottom layer. The excess pore water pressure u of each layer is monitored in real time. h ; Adjust the vacuum negative pressure value so that the difference in the degree of consolidation of each layer does not exceed 5%; Among them, the permeability coefficient K of the dredged silt is used as a basis. h Volume compressibility factor m v and the maximum radius r of the siltation area smax The steps for establishing a hierarchical gradient PVD layout model include: Based on the permeability coefficient K of dredged silt h Given the permeability coefficient K0 of the non-clogging zone, calculate the attenuation coefficient K2 of the clogging zone for each layer (0.4–0.8), and determine the radius of the clogging zone for each layer using a formula to ensure the permeability of the surface layer. smax ≤0.15 m, the r of the middle layer smax ≤0.25 m, the r of the bottom layer smax ≤0.35 m; The formula is: in, Let z represent the radius of the siltation zone at any depth z, and H represent the thickness of the dredged silt layer. The step of adjusting the vacuum negative pressure value to ensure that the difference in the degree of consolidation of each layer does not exceed 5% includes: According to the formula: 1- in, This represents the average radial degree of consolidation at any depth z. , and These represent the average excess pore water pressure values ​​at the initial time, time t, and time infinity, respectively. These are comprehensive parameters related to well resistance effect, clogging zone radius, and permeability coefficient; The time factor is expressed as: in, For soil weight, r h The radius of the affected area, Consolidation time; The degree of consolidation of each layer is calculated in real time. When the difference in the degree of consolidation between adjacent layers is greater than 5%, it is determined according to the following: Increase the vacuum negative pressure value of the low-consolidation stratification by 5% to 10% of the current value; in, This represents the vacuum level at any depth z. This indicates the value of the vacuum negative pressure applied to the surface layer. The value represents the attenuation coefficient of vacuum along the depth direction, and H represents the thickness of the dredged silt layer.

2. The method for combined treatment of dredged sludge conditioning agent and vacuum preloading as described in claim 1, characterized in that, The step of injecting the rice husk ash calcium carbide slag composite curing composition into the dredged sludge after each layer of PVD installation includes: After each PVD layer is installed, a rice husk ash calcium carbide slag composite solidification composition is injected into the dredged sludge. The injection amount of the rice husk ash calcium carbide slag composite solidification composition is 20-30 kg per cubic meter of dredged sludge. The injection method is to inject in three pulses along the PVD axis, with an interval of 12-24 hours between each injection.

3. The method for combined treatment of dredged sludge conditioning agent and vacuum preloading as described in claim 1, characterized in that, In the rice husk ash-carbide slag composite curing composition, the particle size of the rice husk ash is ≤0.075 mm, the calcium-magnesium ratio of the carbide slag is ≥3:1, the calcium chloride is anhydrous granular, and the molecular weight of the polyacrylamide is 8 million to 12 million.

4. The method for combined treatment of dredged sludge conditioning agent and vacuum preloading as described in claim 2, characterized in that, According to the layered gradient PVD arrangement model, the vacuum negative pressure P0 = 80 kPa ~ 100 kPa is applied to the surface layer, the vacuum negative pressure P0 = 60 kPa ~ 80 kPa to the middle layer, and the vacuum negative pressure P0 = 40 kPa ~ 60 kPa to the bottom layer. The excess pore water pressure u of each layer is monitored in real time. h The steps include: A continuous suction mode is used for the surface layer, and a vacuum negative pressure P0 = 80kPa~100kPa is applied to the surface layer. Intermittent suction mode is used in the middle layer stratification, and the vacuum negative pressure P0 in the middle layer stratification is 60kPa~80kPa; A low-frequency pulse suction mode was used in the bottom layer, with a vacuum negative pressure P0 of 40kPa to 60kPa in the bottom layer, and the excess pore water pressure u in each layer was monitored in real time. h .

5. The method for combined treatment of dredged sludge conditioning agent and vacuum preloading as described in any one of claims 1 to 4, characterized in that, According to the layered gradient PVD arrangement model, the vacuum negative pressure P0 = 80 kPa ~ 100 kPa is applied to the surface layer, the vacuum negative pressure P0 = 60 kPa ~ 80 kPa to the middle layer, and the vacuum negative pressure P0 = 40 kPa ~ 60 kPa to the bottom layer. The excess pore water pressure u of each layer is monitored in real time. h The steps include: A vacuum negative pressure system was used based on the aforementioned layered gradient PVD arrangement model. Vacuum negative pressure P0 = 80 kPa–100 kPa was applied to the surface layer, P0 = 60 kPa–80 kPa to the middle layer, and P0 = 40 kPa–60 kPa to the bottom layer. The excess pore water pressure u in each layer was monitored in real time. h The vacuum negative pressure system includes three independent vacuum pump sets. Each pump set is connected to the adjacent pump set via a pressure balancing valve. The opening threshold of the balancing valve is ≥5 kPa of the pressure difference between adjacent layers, and the pumping rate of the pump set is related to the permeability coefficient K of the layer. h Proportional.

6. The method for combined treatment of dredged sludge conditioning agent and vacuum preloading as described in claim 5, characterized in that, The exhaust end of the three-stage independent vacuum pump set is connected to a gas-water separation device. The separated water is reinjected into the outer edge of the PVD-affected zone of the bottom layer through a guide pipe. The reinjection flow rate is 10% to 15% of the pumping flow rate.

7. The method for combined treatment of dredged sludge conditioning agent and vacuum preloading as described in claim 1, characterized in that, The surface layer of PVD uses a diamond-shaped grid arrangement with a node spacing of 0.3m to 0.5m; the middle layer of PVD uses a rectangular grid arrangement with an aspect ratio of 1:1.5; and the bottom layer of PVD uses a radial arrangement with a radiation angle of 30° to 45°, and the grid density is related to the permeability coefficient K of the layer. h Inversely proportional.

8. The method for combined treatment of dredged sludge conditioning agent and vacuum preloading as described in any one of claims 1 to 4, characterized in that, After the step of adjusting the vacuum negative pressure value to ensure that the difference in the degree of consolidation of each layer does not exceed 5%, the method further includes: The dredged sludge was subjected to secondary conditioning. The conditioning agent was a mixed solution of sodium silicate and aluminum sulfate with a mass ratio of 1:

2. The spraying rate was 5 L / m² to 8 L / m². After spraying, the sludge was allowed to stand for 48 hours.

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