Old pressing construction method for dredged soil roadbed filler

Abstract

The invention discloses an aging and pressing construction method for dredged soil roadbed filler, the core process of the aging and pressing construction method comprises three-time crushing, two-stage compaction and aging and multi-stage rolling compaction, the reaction between a curing material and dredged soil is promoted through stepped regulation and control (from wopt + 10-12% to wopt + 5-7%) of the water content and aging maintenance of a closed hard shell layer, and the curing effect of the dredged soil is improved. The compaction degree of the improved soil in the subsequent rolling process is improved, and the final compaction degree can reach 88%-92%. According to the method, efficient synergistic utilization of the dredged soil and the industrial solid waste is achieved, the process adaptability is high, construction can be conducted under the wet condition, the unconfined compressive strength of the obtained filler within 28 days can reach 2.5 MPa or above, and remarkable social, economic and environment-friendly benefits are achieved.

Description

Technical Field

[0001] This invention relates to geotechnical engineering technology and the resource utilization of solid waste, specifically to a compaction construction method for dredged soil roadbed fill. Background Technology

[0002] Dredging projects in my country's rivers, lakes, and seas generate massive amounts of dredged soil annually, which has a high natural moisture content, low strength, and is difficult to treat and dispose of. At the same time, large quantities of industrial solid waste, such as calcium carbide slag, steel slag, and flue gas desulfurization gypsum, accumulate, posing a significant environmental challenge.

[0003] In existing technologies, traditional cementitious materials such as cement and lime are often used to solidify dredged soil, or the simple compaction process of traditional roadbeds is applied to the construction of improved soil. These methods generally have the following defects: First, they fail to fully consider the special engineering behavior of improved soil with high moisture content and high viscosity during the compaction process, which can easily lead to problems such as difficulty in compaction, insufficient compaction degree, and large post-construction settlement in a "slightly wet" state; Second, the solidifying agent is mainly cement, which is costly and fails to make full use of bulk industrial solid waste; Third, the construction process is disconnected from the material properties, ignoring the synergistic relationship between moisture content evolution, solidification reaction process and compaction energy input, resulting in slow strength development and poor controllability of construction quality.

[0004] Therefore, developing a complete set of technologies that can precisely control the construction process and deeply match the special solid waste base filler is of great engineering value and environmental significance for promoting the synergistic resource utilization of dredged soil and industrial solid waste, and solving the problem of roadbed construction under wet conditions. Summary of the Invention

[0005] To address the problem of poor construction quality of dredged soil as roadbed material, this invention provides a compaction construction method for dredged soil roadbed filler. By precisely controlling the moisture content, reaction process, and compaction state in a step-by-step manner, it ensures high-quality and high-efficiency roadbed construction even under unfavorable moisture conditions.

[0006] To achieve the above objectives, the present invention provides a method for compaction construction of dredged soil roadbed fill material, comprising the following steps: S1. Adjust the moisture content of the dredged soil to 10%-12% above its optimum moisture content (w_opt+10-12%), and then perform initial crushing of the soil to ensure that the soil is initially uniform. S2. Add carbide slag to the pretreated soil and mix it. Then, use a road roller to statically compact the soil to form the first dense hard shell layer on the surface. This hard shell layer can inhibit the disorderly evaporation of moisture from the lower layers. Subsequently, the soil is piled up and aged for no less than 12 hours. During this process, the carbide slag rapidly absorbs water and undergoes preliminary cementation. Its effective component, Ca(OH)2, quickly dissociates into Ca upon contact with water. 2+ With OH- On the one hand, it consumes free water and reduces the soil moisture content; on the other hand, it increases the pH value of the system, creating an alkaline environment for the subsequent alkaline activation of the slag. After aging, the overall soil moisture content should be reduced to 8%-10% above the optimum moisture content of the dredged soil to achieve initial stability. S3. Secondary crushing of the soil that has undergone primary aging to break up hardening; S4. Add calcium carbide slag, blast furnace slag, and desulfurization gypsum, with calcium carbide slag providing Ca. 2+ In an alkaline environment, slag (S95 grade and above) undergoes depolymerization and recombination to form hydrated calcium silicate (CSH) gel, which constitutes the main structural component. Desulfurization gypsum provides SO4. 2- With the active aluminum phase and Ca in the slag 2+ The reaction produces ettringite (AFt), which fills the pores and enhances the compactness. The three components form an 'alkali-activated-sulfate-activated' composite cementing system. After mixing, the mixture is statically pressed again to form a second, more tightly sealed hard shell layer. Then, a second aging process of no less than 12 hours is carried out. Under the action of the sealed hard shell layer, moisture migration is restricted, and the system is in a constant humidity state. This is conducive to the full ion exchange and cementing reaction between the slag and desulfurized gypsum, improving the early structural stability and providing a uniform material state for the final rolling. S5. The soil that has undergone the second aging process is subjected to final crushing and mixing to break down the hard crust, mix the soil and solidifier more evenly, and restore the soil to a uniform and loose construction state, while ensuring that the moisture content is evenly distributed at 5%-7% above the optimum moisture content of the dredged soil. S6. Improved soil treated with S5 is loosely laid and subjected to static compaction, low-amplitude light vibration, high-amplitude strong vibration, low-amplitude light vibration, and static compaction. S7. Immediately after compaction, cover with geotextile or plastic film for at least 7 days of heat preservation and moisture retention. During this period, vehicle traffic is strictly prohibited.

[0007] Preferably, the mass ratio of carbide slag in step S2 to that in step S4 is 1:(1-1.2).

[0008] Specifically, compared to 100 parts of dredged dry soil, the total amount of carbide slag used is 6-9 parts, the amount of slag used is 2-4 parts, and the amount of desulfurized gypsum used is 1-2 parts.

[0009] The slag is preferably S95 grade or higher granulated blast furnace slag powder; the effective Ca(OH)2 content in the carbide slag should not be less than 60%; the desulfurization gypsum is a by-product of flue gas desulfurization, and its main component is calcium sulfate dihydrate (CaSO4·2H2O). The above ratio utilizes the carbide slag to provide alkalinity and calcium source, the slag to provide a silica-alumina framework, and the desulfurization gypsum to introduce sulfates, forming a complementary reaction pathway: the carbide slag activates the slag activity, and the slag hydration products and the ettringite derived from the desulfurization gypsum intertwine and symbiotically form a dense network in the pores, thereby achieving synergistic enhancement in strength, water stability, and volume stability.

[0010] Specifically, in steps S2 and S4, an 18-22 ton steel wheel roller is used to perform static compaction 2-3 times.

[0011] Specifically, the crushing in steps S1 and S3 is carried out using a rotary tiller, and the mixing in steps S4 and S5 is carried out using a road mixer.

[0012] Specifically, in step S6, static compaction is performed 2-3 times using a 10-12 ton roller; low amplitude light vibration is performed 1-2 times using an 18-22 ton roller with an excitation force of 100-200kN; and high amplitude strong vibration is performed 1-2 times using an 18-22 ton roller with an excitation force of 400-500kN, compacting from the edge of the roadbed towards the center.

[0013] Furthermore, during low-amplitude, light-vibration compaction, the wheel tracks overlap by 1 / 4 to 1 / 3.

[0014] Furthermore, during high-amplitude, high-vibration compaction, the speed is increased by 10%-15% per pass.

[0015] Specifically, in step S6, the compaction degree after rolling is controlled at 88%-92%.

[0016] Through the above technical solution, the present invention achieves the following beneficial effects: 1. Outstanding resource utilization and environmental benefits: The formula is composed entirely of industrial solid waste, realizing the large-scale and high-value synergistic utilization of dredged soil, carbide slag, mine slag, and desulfurization gypsum, reducing raw material costs and environmental impact.

[0017] 2. Strong technological innovation and deep synergy: The pioneering "two-stage compaction and aging" process is the core innovation. By adding materials in stages, forming a closed hard shell layer twice and aging it deeply, the unfavorable "wet" conditions in traditional construction are cleverly transformed into favorable factors that promote the deep hydration reaction of cementitious materials, thus improving the difficulty of compacting improved soil and the insufficient strength development under wet conditions.

[0018] 3. High controllability and applicability in construction: By implementing precise, step-by-step control of moisture content—from initial pretreatment (w_opt + 10-12%) to primary aging (w_opt + 8-10%) to final compaction (w_opt + 5-7%)—precise management of the entire construction process is achieved. This method essentially eliminates the time-consuming and weather-dependent deep drying stage of traditional processes, making it particularly suitable for rainy areas, areas with high groundwater levels, or projects with tight schedules. It is expected to shorten the construction period by more than 30%.

[0019] 4. Excellent and reliable finished product performance: Combining a multi-stage refined energy input compaction process, a high compaction degree of 88%-92% can be stably achieved under the optimized slightly moist conditions mentioned above. Experiments show that, using the optimized mix ratio B and this process, the resulting subgrade fill material can achieve an unconfined compressive strength of over 2.5 MPa after 28 days, a bearing capacity ratio (CBR) of over 108%, and a water stability coefficient of 0.85, far exceeding the design requirements for first-class highway subgrades. Attached Figure Description

[0020] Figure 1 This is a flowchart of the pressing construction process of the present invention. Detailed Implementation

[0021] The specific embodiments of the present invention will be described in detail below with reference to examples. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0022] The raw materials and testing methods used in the following embodiments are as follows: Dredged soil: taken from a river channel, with a natural water content of about 55%, liquid limit of 44.4%, plastic limit of 19.4%, and plasticity index of 25.

[0023] Industrial solid waste: carbide slag (Ca(OH)2 content ≥65%), S95 grade granulated blast furnace slag powder, flue gas desulfurization gypsum.

[0024] Testing standards: All mix design and performance tests were conducted in accordance with the "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG 3441-2024).

[0025] Example 1 In this embodiment, the percentages of each component in the composite curing agent relative to the dry dredged soil are as follows: 7.5% carbide slag, 3% blast furnace slag, and 1.5% desulfurized gypsum. The optimal moisture content of the improved soil is 27.1%.

[0026] like Figure 1 As shown, the refined compaction construction method for dredged soil roadbed fill is as follows: S1. Initial Crushing and Pretreatment: The dredged soil is turned over and crushed to uniformly adjust its moisture content to 37%-39%. Then, a rotary tiller is used to perform initial crushing of the soil to ensure that the soil is initially uniform.

[0027] S2. Primary Mixing and Compaction Aging: Add approximately 50% of the total amount of carbide slag from the composite curing agent to the pretreated soil and mix using a rotary tiller. Then, use an 18-ton steel wheel roller to statically compact the soil twice, followed by 14 hours of composting and aging. After this stage, the overall moisture content of the soil should drop to 35%-37%, achieving initial stability.

[0028] S3. Secondary crushing: Use a rotary tiller to crush the soil that has been aged for one stage, and break up the compaction.

[0029] S4. Secondary mixing and compaction aging: Add all remaining composite curing agent (including remaining carbide slag, all slag, and desulfurized gypsum), and use a road mixer for thorough and uniform final mixing. After mixing, perform static compaction twice more, followed by a second aging process of 15 hours.

[0030] S5. Final Crushing and Conditioning: Use a road mixer to perform final crushing and final mixing on the deeply aged soil, while ensuring that the moisture content is evenly distributed within the ideal compaction range of 32%-34%.

[0031] S6. Multi-stage progressive vibratory compaction: The loose layer thickness of the improved soil treated by S5 is strictly controlled at 20-25cm. A five-stage progressive compaction process is adopted: ① Passes 1-2: Static compaction with a 12-ton roller for stabilization; ② Passes 3-4: Light vibration with an 18-ton roller at low amplitude (excitation force 150kN) to reconstruct the particle skeleton; ③ Passes 5-6: Strong vibration with an 18-ton roller at high amplitude (excitation force 450kN) for compaction; ④ Passes 7-8: Light vibration to homogenize the structure and eliminate stress concentration; ⑤ Passes 9-10: Static compaction to seal the layer and eliminate wheel tracks. Through this process, the final compaction degree should be controlled at 91%.

[0032] S7. Curing: Immediately after compaction, cover with geotextile or plastic film for at least 7 days for heat preservation and moisture retention curing. During this period, vehicle traffic is strictly prohibited.

[0033] Performance: 28-day unconfined compressive strength is approximately 2.6 MPa, CBR is 110%, and water stability coefficient is approximately 0.81.

[0034] Example 2 In this embodiment, the percentages of each component in the composite curing agent relative to the dry dredged soil are: 6% carbide slag, 2% blast furnace slag, and 1% desulfurized gypsum. The optimal moisture content of the improved soil is 26.2%.

[0035] like Figure 1As shown, the refined compaction construction method for dredged soil roadbed fill is as follows: S1. Initial Crushing and Pretreatment: The dredged soil is turned over and crushed to uniformly adjust its moisture content to 36%-38% above its optimum moisture content. Then, a rotary tiller is used to perform initial crushing of the soil to ensure that the soil is initially uniform.

[0036] S2. Primary mixing and compaction aging: Approximately 45% of the total amount of carbide slag from the composite curing agent was added to the pretreated soil, and it was mixed using a rotary tiller. Then, an 18-ton steel wheel roller was used for static compaction twice, followed by 12 hours of composting and aging. After this stage, the overall soil moisture content dropped to 35%-36%, achieving initial stability.

[0037] S3. Secondary crushing: Use a rotary tiller to crush the soil that has been aged for one stage, and break up the compaction.

[0038] S4. Secondary mixing and compaction aging: Add all remaining composite curing agent (including remaining carbide slag, all slag, and desulfurized gypsum), and use a road mixer for thorough and uniform final mixing. After mixing, perform static compaction three times, followed by a second aging process of 12 hours.

[0039] S5. Final Crushing and Conditioning: Use a road mixer to perform final crushing and final mixing on the deeply aged soil, while ensuring that the moisture content is evenly distributed within the ideal compaction range of 33%-35%.

[0040] S6. Multi-stage progressive vibratory compaction: The loose layer thickness of the improved soil treated by S5 is strictly controlled at 20-25cm. A five-stage progressive compaction process is adopted: ① Passes 1-2: Static compaction with a 12-ton roller for stabilization; ② Passes 3-4: Light vibration with an 18-ton roller at low amplitude (excitation force 100kN) to reconstruct the particle skeleton; ③ Passes 5-6: Strong vibration with an 18-ton roller at high amplitude (excitation force 400kN) for compaction; ④ Passes 7-8: Light vibration to homogenize the structure and eliminate stress concentration; ⑤ Passes 9-10: Static compaction to seal the layer and eliminate wheel tracks. Through this process, the final compaction degree should be controlled at 88%.

[0041] S7. Curing: Immediately after compaction, cover with geotextile or plastic film for at least 7 days for heat preservation and moisture retention curing. During this period, vehicle traffic is strictly prohibited.

[0042] Performance: 28-day unconfined compressive strength is approximately 2.4 MPa, CBR is 108%, and water stability coefficient is approximately 0.78.

[0043] Example 3 In this embodiment, the percentages of each component in the composite curing agent relative to the dry dredged soil are: 9% carbide slag, 4% blast furnace slag, and 2% desulfurized gypsum. The optimal moisture content of the improved soil is 27.9%.

[0044] like Figure 1 As shown, the refined compaction construction method for dredged soil roadbed fill is as follows: S1. Initial Crushing and Pretreatment: The dredged soil is turned over and crushed to uniformly adjust its moisture content to 38%-40%. Then, a rotary tiller is used to perform initial crushing of the soil to ensure that the soil is initially uniform.

[0045] S2. Primary Mixing and Compaction Aging: Add approximately 50% of the total amount of carbide slag from the composite curing agent to the pretreated soil and mix using a rotary tiller. Then, use an 18-ton steel wheel roller to statically compact the soil twice, followed by 13 hours of composting and aging. After this stage, the overall moisture content of the soil should drop to 36%-38%, achieving initial stability.

[0046] S3. Secondary crushing: Use a rotary tiller to crush the soil that has been aged for one stage, and break up the compaction.

[0047] S4. Secondary mixing and compaction aging: Add all remaining composite curing agent (including remaining carbide slag, all slag, and desulfurized gypsum), and use a road mixer for thorough and uniform final mixing. After mixing, perform static compaction three times, followed by a second aging process of 16 hours.

[0048] S5. Final Crushing and Conditioning: Use a road mixer to perform final crushing and final mixing on the deeply aged soil, while ensuring that the moisture content is evenly distributed within the ideal compaction range of 32%-33%.

[0049] S6. Multi-stage progressive vibratory compaction: The loose layer thickness of the improved soil treated by S5 is strictly controlled at 20-25cm. A five-stage progressive compaction process is adopted: ① Passes 1-2: Static compaction with a 12-ton roller for stabilization; ② Passes 3-4: Light vibration with an 18-ton roller at low amplitude (excitation force 200kN) to reconstruct the particle skeleton; ③ Passes 5-6: Strong vibration with an 18-ton roller at high amplitude (excitation force 500kN) for compaction; ④ Passes 7-8: Light vibration to homogenize the structure and eliminate stress concentration; ⑤ Passes 9-10: Static compaction to seal the layer and eliminate wheel tracks. Through this process, the final compaction degree should be precisely controlled at 92%.

[0050] S7. Curing: Immediately after compaction, cover with geotextile or plastic film for at least 7 days for heat preservation and moisture retention curing. During this period, vehicle traffic is strictly prohibited.

[0051] Performance: 28-day unconfined compressive strength is approximately 2.7 MPa, CBR is 130%, and water stability coefficient is approximately 0.85.

[0052] Comparative Example 1 (Conventional Construction Process) Other conditions are the same as in Example 1. The dredged soil is turned over and crushed to uniformly adjust its moisture content to 30%-31%. It is then mixed and added in one go, and the conventional process of "one pass of static compaction + four passes of vibratory rolling" is used. The compaction degree after compaction is 94%, and the moisture content is 26-28%.

[0053] Performance: 28-day unconfined compressive strength is approximately 2.8 MPa, CBR is 114%, and water stability coefficient is approximately 0.77.

[0054] Comparative Example 2 (Conventional construction methods were used under slightly damp conditions) Other conditions are the same as in Example 1. Under similar slightly moist conditions, the materials were mixed in one go, and the conventional process of "one pass of static compaction + four passes of vibratory rolling" was used. The compaction degree after compaction was only 84%-85%.

[0055] Performance: The unconfined compressive strength after 28 days is only about 1.4 MPa, the CBR is 62%, and the water stability coefficient is about 0.62.

[0056] Comparative Example 3 (Single Carbide Slag Improvement) In this embodiment, the percentage of each component in the composite curing agent relative to the dry dredged soil is as follows: carbide slag 12%. The optimal moisture content of the improved soil is 27.8%. Construction is carried out under similar slightly moist conditions, with other conditions the same as in Example 1.

[0057] Performance: The unconfined compressive strength after 28 days is only about 1.1 MPa, the CBR is 65%, and the water stability coefficient is about 0.68.

[0058] The performance data from the examples and comparative examples show that: Using the composite curing agent formulation and the matching refined curing construction method provided by this invention, the key indicators of the improved soil, such as unconfined compressive strength, California bearing ratio (CBR), and water stability coefficient, can all meet or exceed the relevant specifications for first-class highway subgrade materials.

[0059] As can be seen from the comparative examples and Comparative Example 1, the "staged addition, compaction aging, and progressive rolling" process provided by this invention allows for direct construction under conditions of relatively high initial moisture content (slightly moist), avoiding the prolonged excessive drying required by traditional processes. Under this advantage, the unconfined compressive strength and CBR value of the obtained improved soil are still close to those of conventional methods, while the water stability coefficient is significantly better. This proves that this refined process can effectively promote the solidification reaction, forming a more stable and uniform structure, thereby comprehensively improving the long-term durability and engineering applicability of the improved soil.

[0060] A direct comparison between Example 1 and Comparative Example 2 shows that, under similar initial slightly moist conditions, the performance indicators (strength, CBR, water stability) obtained using the process of this invention are far superior to those of Comparative Example 2, which uses a conventional one-time admixture and compaction process. This fully demonstrates that the refined compaction construction method is key to solving the technical problem of high natural moisture content in dredged soil, making direct compaction difficult.

[0061] The performance data (strength 1.1 MPa, CBR 65%, water stability 0.68) of Comparative Example 3 (single calcium carbide slag modification) are significantly lower than those of Example 1, which uses the same process but a composite curing agent. This comparison demonstrates that the curing and modification effect of a single lime (calcium carbide slag) is limited; while the composite system of the present invention, by introducing slag powder and desulfurized gypsum, stimulates a more active cementitious reaction in the alkaline environment provided by calcium carbide slag, producing a significant synergistic enhancement effect, and comprehensively and fundamentally improving the mechanical properties and water stability of the material.

[0062] The process of this invention creates and utilizes a "hard shell layer" for deep aging under "slightly moist" conditions, repeatedly crushes the uniform soil, and progressively compacts to optimize particle arrangement. It successfully achieves a high degree of compaction under high moisture content conditions. With the pore-filling effect of ettringite and the particle cementing effect of hydrated calcium silicate, it achieves excellent road mechanical properties, far exceeding those of traditional processes.

[0063] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0064] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0065] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for compaction construction of dredged soil roadbed fill, characterized in that, Includes the following steps: S1. Adjust the moisture content of the dredged soil to 10%-12% above its optimum moisture content, and then perform initial crushing of the soil. S2. Add carbide slag to the pretreated soil and mix it. Then, use a road roller to statically compact the soil to form the first dense hard shell layer on the surface. After that, allow it to sit and age for no less than 12 hours until the overall moisture content of the soil should drop to 8%-10% above the optimum moisture content of the dredged soil. S3. Secondary crushing of the soil that has undergone primary aging; S4. Add carbide slag, slag and desulfurized gypsum, mix and press statically again to form the second hard shell layer, and then carry out a second aging for no less than 12 hours. S5. Perform final crushing and mixing on the soil that has undergone the second aging process to restore the soil to a uniform and loose state for construction, while ensuring that the moisture content is evenly distributed at 5%-7% above the optimum moisture content of the dredged soil; S6. Improved soil treated with S5 is loosely laid and subjected to static compaction, low-amplitude light vibration, high-amplitude strong vibration, low-amplitude light vibration, and static compaction. S7. After rolling and molding, perform heat preservation and moisture retention maintenance for no less than 7 days.

2. The pressing construction method according to claim 1, characterized in that, The mass ratio of carbide slag in step S2 to that in step S4 is 1:(1-1.2).

3. The pressing construction method according to claim 2, characterized in that, Compared to 100 parts of dredged dry soil, the total amount of calcium carbide slag used is 6-9 parts, the amount of slag used is 2-4 parts, and the amount of desulfurized gypsum used is 1-2 parts.

4. The pressing construction method according to claim 3, characterized in that, The slag is S95 grade or above granulated blast furnace slag powder; the Ca(OH)2 content in the carbide slag is not less than 60%.

5. The pressing construction method according to claim 1, characterized in that, In steps S2 and S4, a 18-22 ton steel wheel roller is used to perform static compaction 2-3 times.

6. The pressing construction method according to claim 1, characterized in that, The crushing in steps S1 and S3 is done using a rotary tiller, and the mixing in steps S4 and S5 is done using a road mixer.

7. The pressing construction method according to claim 1, characterized in that, In step S6, static compaction is performed 2-3 times using a 10-12 ton roller; low amplitude light vibration is performed 1-2 times using an 18-22 ton roller with an excitation force of 100-200kN; and high amplitude strong vibration is performed 1-2 times using an 18-22 ton roller with an excitation force of 400-500kN, compacting from the edge of the roadbed towards the center.

8. The pressing construction method according to claim 7, characterized in that, When compacting with low amplitude and light vibration, the wheel tracks overlap by 1 / 4 to 1 / 3.

9. The pressing construction method according to claim 7, characterized in that, When using high-amplitude, high-intensity compaction, increase the speed by 10%-15% per pass.

10. The pressing construction method according to claim 1, characterized in that, In step S6, the compaction degree after rolling is controlled at 88%-92%.

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