Improved construction method of sand filling roadbed

Abstract

This invention discloses an improved construction method for a hydraulically filled sand subgrade. The construction method includes the following steps: surface clearing and temporary drainage; soft soil treatment; gabion cofferdam construction; first layer of hydraulically filled sand construction; first layer of edging soil construction; second layer of hydraulically filled sand construction; geogrid laying and subgrade layered filling construction and acceptance; and subgrade slope protection and subgrade drainage construction and acceptance. This invention, through process restructuring, reduces repeated earth cofferdam construction and excavation, and sand cofferdam construction, significantly improving construction efficiency and shortening the construction period. The pre-constructed and stabilized edging soil has higher stability and superior drainage and sand-blocking effects compared to temporary cofferdams, further eliminating potential quality hazards. Without repeated disturbance to the main sand filling structure and with unified construction planning, the subgrade stability is significantly enhanced, and the bearing capacity is improved. Compared to the original process, it saves a significant amount of equipment and labor time, resulting in significantly reduced construction costs and outstanding economic benefits.

Description

Technical Field

[0001] This invention relates to the field of roadbed construction technology, and in particular to a method for constructing a modified structured hydraulic fill roadbed. Background Technology

[0002] Hydraulic fill sand roadbeds have advantages such as convenient material sourcing, lower project costs, and convenient construction, making them widely used in large-scale projects such as highway subgrades and port terminals. However, the traditional construction techniques for hydraulic fill sand roadbeds currently have many prominent drawbacks, severely restricting construction efficiency, project quality, and cost control, as follows:

[0003] 1. The temporary cofferdam process is cumbersome and results in significant time loss: In traditional dredged sand roadbed construction, temporary cofferdams need to be erected in layers, including earth cofferdams, sandbag cofferdams, or sand cofferdams. After each layer of dredged sand is completed, the original temporary cofferdam needs to be dismantled and a new cofferdam needs to be erected for the next layer of dredged sand. The repeated filling and excavation process of temporary cofferdams is cumbersome, which not only increases the input of a lot of manpower and machinery, but also causes an additional 2-3 days of construction time loss for each layer of dredged sand, resulting in low overall construction efficiency.

[0004] 2. Poor stability of the retaining structure and prominent leakage risks: Traditional temporary cofferdams are mostly constructed by manually stacking sandbags or temporarily piling up soil and sand, resulting in poor overall stability and weak resistance to lateral pressure, which easily leads to problems such as slippage and collapse. At the same time, the seepage prevention and sand blocking measures of temporary cofferdams are not perfect, which can easily lead to the loss of fine sand particles in the dredged sand, which not only wastes resources but also increases the differential settlement of the roadbed in the later stage, affecting the bearing capacity of the roadbed.

[0005] 3. Poor coordination of retaining structures and obvious connection risks: In traditional processes, the construction of temporary cofferdams and permanent edging soil is independent of each other. Due to repeated excavation and disturbance in traditional construction processes, gaps, voids, and relative slippage are likely to occur at the connection between the two, resulting in insufficient lateral stability of the roadbed and potential quality risks such as slope collapse and leakage in the later stages.

[0006] While existing technologies employ gabions as protective structures and geotextiles as filtration materials, these solutions are primarily used for riverbank protection and slope protection. They fail to address the specific characteristics of layered filling and drainage / sand control requirements of dredged sand roadbeds, and do not involve precise design for gabion mesh size, filler particle size, and geotextile parameters. Furthermore, existing technologies lack a collaborative construction system, making it impossible to simultaneously address the multiple pain points of traditional construction methods, such as long construction periods, poor stability, inadequate drainage and sand control, and high costs.

[0007] Therefore, there is an urgent need to develop a construction method for hydraulic filling roadbed that features reasonable process reconstruction, stable support, excellent drainage and sand control effects, high construction efficiency, and controllable costs, in order to overcome the shortcomings of existing technologies and meet the large-scale, high-quality construction needs of large-scale projects. Summary of the Invention

[0008] To address the aforementioned shortcomings of existing technologies, this invention provides an improved method for constructing a dredged sand-filled roadbed. Through process restructuring, it reduces repeated earthen cofferdam construction and excavation, as well as sand cofferdam construction, significantly improving construction efficiency and shortening the construction period. The pre-constructed and stabilized edge soil exhibits higher stability and superior drainage and sand-blocking effects compared to temporary cofferdams, further eliminating potential quality risks. The absence of repeated disturbance to the main sand-filling structure and unified construction planning significantly enhance roadbed stability and improve bearing capacity. Compared to the original process, it saves substantial amounts of equipment and labor, resulting in significant cost reduction and outstanding economic benefits. Furthermore, it enables the recycling and utilization of waste materials from the quarry, promoting environmental friendliness and improving resource utilization.

[0009] To achieve the above objectives, this application provides a construction method for an improved structural hydraulic fill sand roadbed, the construction method comprising the following steps: S1. Surface clearing and temporary drainage; S2, soft soil treatment; S3, Construction of gabion cofferdam; S4. Construction of the first layer of dredged sand; S5. Construction of the first layer of edging soil; S6, Second layer of dredged sand filling construction; S7. Construction and acceptance of geogrid laying and subgrade layer filling; S8. Construction and acceptance of subgrade slope protection and subgrade drainage; During the construction of S3, the geotextile for the roadbed and the inner side of the cofferdam of S3.1 is laid simultaneously; during the construction of S5, the geotextile and plastic film for the inner side of the edging soil of S5.1 are laid simultaneously; between S6 and S7, S5, S5.1 and S6 are repeated, and the construction is carried out in a cycle until the bottom of the roadbed is reached.

[0010] In S1, the surface cleaning and temporary drainage include the following steps: A comprehensive cleanup of the area within the roadbed construction zone shall be carried out. The cleanup materials include weeds, debris, loose soil, and humus. The cleanup depth shall be determined based on the actual geological conditions on site, but shall not be less than 20cm. After the cleanup is completed, the base shall be initially leveled and compacted. After the cleanup is completed, the project shall be submitted to the supervisor for acceptance. After the cleanup is completed, temporary drainage ditches shall be excavated in conjunction with the permanent drainage locations, and plastic film shall be laid to protect the drainage ditches.

[0011] In S2, soft foundation processing includes the following steps: Based on the survey data, a soft soil foundation treatment process was adopted, which includes replacing the soft soil foundation with graded sand and gravel or cement mixing piles to reinforce the soft soil foundation and ensure that the treatment results meet the design requirements.

[0012] In S3, the construction of gabion cofferdams includes the following steps: First, the base of the gabion cofferdam is leveled and compacted to ensure that the bearing capacity of the base meets the requirements. The material usage is calculated according to the construction schedule, including galvanized gabion cages, filler stones, threaded steel anchor bars, and binding wire. The galvanized gabion cage mesh size is 8×10cm or 6×8cm, and the cage size is 1×1×2m. The filler stones are selected from strongly weathered to moderately weathered quarry waste with a hard texture, strength ≥20MPa, and a particle size of 10-30cm. The mud content of the quarry waste is no more than 5%. Then, the gabion cages are assembled and fixed. The joints of the cages are firmly bound with binding wire at intervals ≤20cm to ensure no looseness or gaps at the joints. The cages are placed neatly, and their axis and elevation conform to the layout requirements. Line requirements: Secure the gabion cage at the bottom with threaded steel anchor bars to prevent displacement during filling and after construction. The anchor point spacing should be 1.5-2m. Then, fill with riprap using a loader, filling the cage in layers with each layer being 30-40cm thick. Place the riprap gently during filling to avoid damaging the cage. Ensure the riprap filling is full, filling any gaps with small-diameter gravel to ensure no voids inside the cage, with a filling density ≥95%. Adjust the verticality of the cage during filling to prevent tilting. Finally, seal the cage. After filling the top with riprap, tidy the edges to ensure a regular shape. Then, secure the top cover with binding wire, ensuring the binding spacing matches the joints to prevent riprap from falling off.

[0013] The construction of geotextile laying on the S3.1 roadbed and inner side of the cofferdam includes the following steps: Before laying, clean the roadbed and inner slope of the cofferdam, remove sharp debris and stones, ensure the slope is smooth, and avoid puncturing the geotextile; the reverse permeability geotextile is laid on the top of the original ground and the inner side of the gabion cofferdam after the soft soil treatment and leveling and compaction are completed. The geotextile material selection requirements are a basis weight of not less than 400g / ㎡, an equivalent pore size of 0.08~0.12mm, and a vertical permeability coefficient of 1×10 - ²~1×10 - ³cm / s, tensile strength not less than 15kN / m, CBR puncture resistance not less than 3.5kN, overlap width not less than 30cm, and fixed with U-shaped nails or geotextile-specific nails every 50-80cm; the geotextile is laid all the way to the top of the gabion cofferdam and compacted, and the fabric surface must be tightly attached to the gabion at the contact point between the inner side and the gabion cofferdam.

[0014] In S4, the first layer of dredged sand filling includes the following steps: Sand blowing equipment is used to blow sand that meets the design requirements into the roadbed area. During the blowing process, the mud content and organic matter content of the sand are controlled and blown in layers. The blowing thickness is carried out according to the design requirements. After the blowing is completed, the test is carried out.

[0015] In S5, the construction of the first layer of edging soil includes the following steps: Select qualified native soil and improve it with quicklime. Fill the edges of the dredged sand layer at the designed positions on both sides. During the filling process, spread and compact the soil in layers, control the spreading thickness and compaction degree, and ensure that the slope meets the design requirements. There is no risk of collapse or sliding. After the edge soil is constructed to the design elevation, the geotextile and plastic film on the inner side of the S6.1 edge soil are laid. During the S5.1 construction, first clean the inner surface of the edging soil to ensure it is flat and smooth. Then lay the geotextile and plastic film. The plastic film thickness should be no less than 1.0 mm, the geotextile weight should be no less than 300 g / m², the equivalent pore size should be 0.10–0.15 mm, and the vertical permeability coefficient should be 1 × 10⁻⁶. - ²~1×10 - ³cm / s; The geotextile and plastic film are laid in the direction of the blown sand filling, following the principle of upstream fabric pressing down on downstream fabric. The overlap width of the geotextile is not less than 30cm, and the overlap is fixed with U-shaped nails or special nails every 50-80cm. The top of the geotextile is compacted to ensure tight adhesion, no wrinkles, and no gaps. The geotextile is on the inside and the plastic film is on the outside, with tight adhesion and standardized overlap. The overlap width of the plastic film is not less than 20cm, and the overlap is compacted and sealed to prevent water seepage. After laying, check to confirm that there is no damage or omissions.

[0016] The edging soil adopts a trapezoidal cross section with an inner slope ratio of 1:1.0, an outer slope ratio of 1:1.5, and a top width of 2.5m. The edging soil is made of 4% improved lime soil with a compaction degree of not less than 95%. The top width of the edging soil is 250cm + 50cm. The bottom layer width is calculated based on the slope ratios on both sides. The thickness of the layered filling after compaction is 20cm to 40cm. Based on the centerline and edgeline of the roadbed, use Beidou or GPS to locate and mark the outer boundary of the edging soil; select silty clay or loam free of impurities, humus, and frozen soil, and control the moisture content within ±2% of the optimum moisture content; select Grade III or higher quicklime powder; use centralized mixing method to mix the materials, mix the edging soil and quicklime powder evenly, ensure the uniformity of mixing meets the requirements, with no clumps of edging soil or lime lumps, and uniform color; transport the mixed materials to the construction site in a timely manner after mixing. The mixed lime-improved soil is spread to the designated area using a loader. The spreading thickness is controlled according to the designed layer thickness. During the spreading process, the surface is leveled to ensure that the spreading width and thickness are uniform. After spreading, a road roller is used to compact the soil. The compaction sequence is from both sides to the middle, from slow to fast, and from weak to strong. The compaction speed is controlled at 2-3 km / h. The number of compaction passes is no less than four, until the compaction degree meets the design requirements. If springiness or peeling occurs, the soil is promptly mixed, locally lime is added, and then the soil is re-compacted.

[0017] The construction method for the second layer of dredged sand in S6 is the same as that for the first layer of dredged sand in S4. After S6, the construction of the edging soil, the laying of geotextile and plastic film on the inner side of the edging soil, and the construction of dredged sand are repeated in sequence until the bottom elevation of the subgrade structure is reached.

[0018] In S7, the construction and acceptance of geogrid laying and subgrade layer filling includes the following steps: First, clean the bottom of the roadbed to ensure it is flat and clean. Then, lay bidirectional geogrids that meet the design specifications. The overlap width of the bidirectional geogrids should not be less than 20cm. The overlaps should be firmly fixed with U-shaped nails. The roadbed should be laid flat and without wrinkles. Next, the roadbed structure should be filled in layers. Select fill materials that meet the design requirements, spread and compact them in layers, and control the thickness, compaction degree and moisture content of each layer. After each layer is filled, conduct quality inspection. After all filling is completed, conduct acceptance.

[0019] In S8, the construction and acceptance of subgrade slope protection and subgrade drainage include the following steps: In accordance with design requirements, slope protection is carried out on both sides of the roadbed to ensure slope stability and prevent rainwater erosion. At the same time, the roadbed drainage system is constructed according to the design plan to ensure smooth drainage and avoid water accumulation on the roadbed that could affect its stability. During construction, the dimensions, slope, and construction quality of the protection and drainage facilities are controlled. After all construction is completed, a final acceptance inspection is conducted. Once the inspection is passed, the entire roadbed construction process is completed.

[0020] Compared with the prior art, the above-conceptual technical solution conceived in this application has the following beneficial effects: 1. Significantly improved construction efficiency and shortened construction period: The traditional process of layered construction and dismantling of temporary cofferdams is eliminated, and the construction period for each layer of dredging can be reduced by 5-7 days, resulting in an overall construction period reduction of 25% to 33%.

[0021] 2. Excellent drainage and sand-blocking effect, completely eliminating potential quality problems: The 60×80mm mesh gabion and 400g / ㎡ special drainage and sand-blocking geotextile form a double-layer protection system of rigid material blocking and flexible water filtration, which effectively avoids sand loss during construction; the composite seepage prevention and drainage structure of plastic film and geotextile on the inner side of the edging soil further blocks the leakage path and completely eliminates the quality problems such as leakage and settlement in traditional construction.

[0022] 3. Significantly enhanced roadbed stability and improved bearing capacity: The gabion cofferdam and the layered edging soil form a synergistic support system, making the roadbed an integrated stress structure. This effectively avoids the hidden dangers of slippage and voids at the weak connection between the temporary cofferdam and the edging soil, which are subject to repeated disturbances. It significantly improves the lateral stability and overall bearing capacity of the roadbed, meeting the requirements of large-scale projects.

[0023] 4. Significantly reduced construction costs and outstanding economic benefits: The gabion cofferdam filling material uses strong to moderately weathered waste material from the quarry, eliminating the need for additional stone procurement and reducing the labor, machinery, and material inputs for the dismantling and construction of temporary cofferdams, resulting in a 16%-21% reduction in overall construction costs.

[0024] 5. Green and environmentally friendly, improving resource utilization: Fully utilize waste materials from quarry mining as gabion filling materials, reduce waste material stockpiling and disposal costs, and achieve resource recycling; in line with the engineering concepts of green construction, energy conservation and environmental protection. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in this 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 for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart of the main construction steps of the present invention.

[0027] Figure 2 This is a flowchart of the construction steps of a conventional process used in comparison with the present invention.

[0028] Figure 3 This is a schematic diagram of the main structure of the present invention.

[0029] Figure 4 This is a schematic diagram of a conventional process used in comparison with the present invention.

[0030] Figure 5 This is a schematic diagram showing the result after step 4 of the present invention is completed.

[0031] Figure 6 This is a schematic diagram showing the result after step 6 of the present invention is completed.

[0032] Figure 7 This is a frontal schematic diagram of the anchor bar location of the gabion structure of the present invention.

[0033] Figure 8 This is a side view of the anchor bar location of the gabion structure of the present invention.

[0034] Figure 9 This is a schematic diagram of the conventional process used in comparison with the present invention to complete step 4.

[0035] Figure 10 This is a schematic diagram of the conventional process used in comparison with the present invention to complete step 6.

[0036] Figure 11 This is a schematic diagram of the conventional process used in comparison with the present invention to complete step 8.

[0037] Figure label: 1. Original ground after clearing and compaction; 2. Sandbag cofferdam; 3. Main body of the dredged sand roadbed; 4. Edge soil; 5. Roadbed structure; 6. Drainage ditch; 7. Gabion cofferdam; 8. Earth cofferdam; 9. Sand cofferdam; 10. Geogrid; 11. Geotextile; 12. Plastic film; 13. Soft soil treatment; 14. Threaded steel anchor bars; 15. Binding wire. Detailed Implementation

[0038] To more clearly illustrate the purpose, technical solution, and beneficial effects of this application, a further detailed description of this application is provided below in conjunction with illustrations and specific embodiments. It should be specifically noted that the specific embodiments described below are only for illustrating the technical content of this application and do not constitute a limitation on the scope of protection of this application.

[0039] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0040] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection via an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0041] Example 1: See Figure 3 An improved structure for dredged sand roadbed includes a soft soil treatment 13 located under the roadbed structure, a geotextile 11 located at the bottom layer of the roadbed structure, a dredged sand roadbed body 3 located above the geotextile 11, a gabion cofferdam 7 located outside the first layer of dredged sand roadbed, a geotextile 11 located inside the gabion cofferdam 7, a trapezoidal edging soil 4 located outside the dredged sand roadbed body, a geotextile 11 and a plastic film 12 located inside the edging soil 4, a bidirectional geogrid 10 located at the top of the dredged sand roadbed body 3 and the edging soil 4, a roadbed structure 5 located at the top of the geogrid, and a drainage ditch 6 located on both sides of the roadbed that combines permanent and temporary structures.

[0042] The gabion cofferdam 7 serves as a lateral support for the first layer of dredged sand roadbed 3; the geotextile 11 inside the gabion cofferdam 7 plays a role in blocking sand and draining water during the first layer of dredged sand filling; the trapezoidal edging soil 4 serves as a lateral support for the subsequent layers of dredged sand roadbed 3, forming a complete support system of gabion cofferdam and layered edging soil; the edging soil 4 is layered according to the construction thickness of the dredged sand roadbed 3, with each layer having a trapezoidal cross section and inner and outer slope ratios of 1:1.0 and 1:1.5 respectively, and is compacted in layers, which has higher stability than temporary cofferdams; the reverse seepage geotextile 11 and plastic film 12 inside the edging soil 4 protect the stability of the edging soil during the dredged sand filling process.

[0043] Example 2: Based on Example 1, see Figure 1 The construction method includes the following steps: S1. Surface clearing and temporary drainage; S2, soft soil treatment; S3, Construction of gabion cofferdam; S4. Construction of the first layer of dredged sand; S5. Construction of the first layer of edging soil; S6, Second layer of dredged sand filling construction; S7. Construction and acceptance of geogrid laying and subgrade layer filling; S8. Construction and acceptance of subgrade slope protection and subgrade drainage; During the construction of S3, the geotextile for the roadbed and the inner side of the cofferdam of S3.1 is laid simultaneously; during the construction of S5, the geotextile and plastic film for the inner side of the edging soil of S5.1 are laid simultaneously; between S6 and S7, S5, S5.1 and S6 are repeated, and the construction is carried out in a cycle until the bottom of the roadbed is reached.

[0044] The specific procedures are as follows: First, carry out surface clearing and temporary drainage construction on S1. Thoroughly clean up weeds, debris, loose soil, humus, etc. within the roadbed construction area. The cleaning depth is determined according to the actual geological conditions on site and should not be less than 20cm. After cleaning, the base is initially leveled and compacted to form the original ground 1 after surface clearing and compaction, which lays the foundation for subsequent procedures. After the surface clearing is completed, report to the supervisor for acceptance. After the surface clearing is completed, excavate drainage ditch 6 in conjunction with the permanent drainage location and adopt preliminary protective measures such as laying plastic film. After the surface clearing and temporary drainage are completed, proceed to the next procedure.

[0045] Next, the construction of S2 soft soil treatment 13 will be carried out. For the soft soil section on site, the corresponding soft soil treatment technology will be adopted based on the survey data, such as replacement with graded sand and gravel, cement mixing piles, etc., to reinforce the soft soil foundation and ensure that the treatment results meet the design requirements. During the treatment process, key parameters such as the mixing speed of the mixing piles and the amount of cementitious materials will be strictly controlled. After the treatment is completed and the test is qualified, the construction of S3 gabion cofferdam 7 will be carried out.

[0046] S3 gabion cofferdam 7 construction stage, see Figure 5 First, the base of the cofferdam is leveled and compacted. Then, galvanized gabion cages are assembled. The joints are secured with 15mm gabion wire, and the cages are arranged neatly and fixed to prevent displacement. The cages are filled with rubble in layers to ensure full filling without voids. After filling, the cages are covered and secured. This ensures the overall stability of the cofferdam and meets the needs of temporary support and water blocking.

[0047] join Figure 7 , 8 According to the design location of gabion cofferdam 7, the site was cleared and leveled, and a bearing capacity test was conducted to ensure that the foundation bearing capacity was ≥120kPa. Temporary drainage facilities were also installed to prevent water accumulation in the construction area. Then, materials were prepared, and the material usage was calculated according to the construction schedule. This included galvanized gabion cages (using galvanized low-carbon steel wire that meets the specifications, with a mesh size of 8×10cm or 6×8cm, and a cage size of 1×1×2m. After arrival, the thickness of the galvanized layer and the uniformity of the mesh were checked, and unqualified materials were strictly prohibited from use), filler stones (using hard, strong ≥20MPa, and 10-30cm particle size strongly weathered to moderately weathered quarry waste, with surface soil and debris cleaned in advance, neatly stacked, and rainproof measures taken. The mud content of the quarry waste should not exceed 5%), threaded steel anchor bars 14, and binding wire 15, etc. Next, the gabion cages are assembled and secured. The joints are firmly bound with gabion binding wire, with a binding spacing of ≤20cm, ensuring no looseness or gaps at the joints. The gabions are placed neatly, with their axes and elevations meeting the layout requirements. 14mm threaded steel anchor bars are used to secure the bottom of the gabions to prevent displacement during filling and after construction. The fixing points are spaced 1.5-2m apart to ensure the gabions are stable. Then, the gabions are filled with rubble. A loader is used for collection, and an excavator fills the gabions in layers, each layer 30-40cm thick. The rubble is placed gently during filling to avoid damaging the gabions. The filling must be full, with gaps filled with small-diameter crushed stone to ensure no voids inside the gabions, and a filling density ≥95%. The verticality of the gabions is adjusted promptly during filling to prevent tilting. Finally, after sealing the cage and filling the top with pebbles, tidy up the edges of the cage to ensure that the cage is in a regular shape. Then, use gabion binding wire to secure the top cover of the cage firmly, with the binding spacing consistent with the splicing points to prevent the pebbles from falling off.

[0048] During the construction of gabion cofferdam 7, the laying of geotextile 11 on the S3.1 roadbed was carried out simultaneously, followed by the laying of geotextile 11 on the inner side of the cofferdam. Geotextile 11 was laid on the top of the original ground after soft soil treatment, leveling, and compaction, and on the inner side of gabion cofferdam 7. The geotextile 11 material was required to have a basis weight of not less than 400 g / m², an equivalent pore size of 0.08–0.12 mm, and a vertical permeability coefficient of 1 × 10⁻⁶. - ²~1×10 -The tensile strength is not less than 15kN / m, and the puncture resistance of CBR is not less than 3.5kN. The overlap width of geotextile 11 should be ≥30cm on horizontal and slope surfaces. For overlap fixing, use U-shaped nails or geotextile-specific nails every 50-80cm, ensuring a tight overlap without curling edges or gaps. Geotextile 11 is laid up to the top of the gabion cofferdam 7, and is secured by backfilling and compaction or by pressing with stones. At the contact point between the inner side and the gabion, the fabric surface must be tightly adhered to the gabion, without any gaps or wrinkles.

[0049] S4 First Layer Hydrated Sand 3 Construction Stage, see Figure 5 Specialized sand blowing equipment is used to blow sand that meets the design requirements into the roadbed area. During the blowing process, the mud content and organic matter content of the sand are controlled. The blowing is carried out in layers, and the blowing thickness is in accordance with the design requirements. After the blowing is completed, the test is carried out. After passing the test, the construction of the first layer of S5 edging soil 4 is carried out.

[0050] When constructing the first layer of S5 edge soil 4, refer to Figure 6 The selected subgrade soil is improved with quicklime, with a specific lime mixing ratio of 4%. The actual ratio should be adjusted according to the test section results. The filling is carried out at the designed positions on both sides of the dredged sand layer. During the filling process, it is spread and compacted in layers, and the spreading thickness and compaction degree are controlled. The slope of the side slope meets the design requirements and there is no risk of collapse or sliding. The edging soil 4 is overfilled by 50cm on the outside of the roadbed to ensure the rolling quality and facilitate subsequent slope finishing. After the edging soil 4 is constructed to the design elevation, the geotextile 11 and plastic film 12 on the inside of the S5.1 edging soil 4 are laid.

[0051] Specifically, the edging soil 4 adopts a trapezoidal cross-section, with an inner slope ratio of 1:1.0 and an outer slope ratio of 1:1.5, and a top width of 2.5m. The edging soil 4 uses 4% improved lime-soil, with a compaction degree of not less than 95%. The top width of the edging soil is 250cm + 50cm (over-width filling). The bottom layer width is calculated based on the slope ratios on both sides, and the layered filling thickness is 20cm after compaction. According to the roadbed centerline and edge line, the outer boundary of the edging soil 4 is located using Beidou or GPS, and marked with white lime to ensure accurate positioning. The subgrade soil is selected as silty clay or loam free of impurities, humus, and frozen soil, with the moisture content controlled within ±2% of the optimum moisture content; the lime is selected as Grade III or above quicklime powder. The materials are mixed using a centralized mixing method, uniformly mixing the subgrade soil and quicklime powder, ensuring the mixing uniformity meets the requirements, with no subgrade lumps or lime clumps, and a consistent color. After mixing, it is transported to the construction site in a timely manner, or the road mixing method can be used directly. The mixed lime-improved soil is spread to the designated area using a loader. The spreading thickness is controlled according to the designed layer thickness. During spreading, the surface is leveled to ensure uniform spreading width and thickness. After spreading, a road roller is immediately used for compaction. The compaction sequence is from both sides to the middle, from slow to fast, and from weak to strong, with the compaction speed controlled at 2-3 km / h. The number of compaction passes is no less than 4 times until the compaction degree meets the design requirements. If springiness or peeling occurs, the soil is promptly mixed, locally lime is added, and then compacted again. After compaction, the compaction degree is tested promptly. Only after the test is passed can the next layer be constructed.

[0052] During the construction of S5.1, please refer to... Figure 6 First, clean the inner surface of the edging soil 4 to ensure it is flat and smooth. Then, lay the geotextile 11 and plastic film 12, with the geotextile 11 on the inside and the plastic film 12 on the outside, ensuring they are tightly fitted and overlapped correctly. The overlap width of the plastic film 12 should be no less than 20cm, and the overlap should be compacted and sealed to prevent water seepage. After laying, check to confirm that there is no damage or omissions, ensuring the anti-erosion and anti-seepage effect of the inner side of the edging soil 4, and providing protection for the next layer of dredged sand 3.

[0053] The inner side of the edging soil 4 is laid with a composite structure of plastic film 12 and geotextile 11. The thickness of plastic film 12 is not less than 1.0 mm, the geotextile basis weight is not less than 300 g / m², the equivalent pore size is 0.10~0.15 mm, and the vertical permeability coefficient is 1×10⁻⁶. - ²~1×10 -³cm / s. The laying direction is from upstream to downstream, with the upstream layer overlapping the downstream layer. Geotextile 11 and plastic film 12 are laid in the direction of the dredged sand filling, following the principle of upstream layer overlapping downstream layer. The overlap width of geotextile 11 should not be less than 30cm, and the overlap should be fixed with U-shaped nails or special nails every 50-80cm. The top of geotextile 11 needs to be compacted to ensure a tight fit, no wrinkles, and no gaps. Geotextile 11 is on the inside, and plastic film 12 is on the outside water-facing side, with a tight fit and standardized overlap. The overlap width of plastic film 12 should not be less than 20cm, and the overlap should be compacted and sealed to prevent water seepage. After laying, check to confirm that there is no damage or omissions.

[0054] Then, the construction cycle begins, with the second layer of dredged sand, the second layer of edging soil, and the laying of geotextile and plastic film on the inner side of the edging soil being carried out sequentially upwards. The construction process is repeated. After each layer of dredged sand, edging soil 4, and impermeable layer is completed, a quality inspection is required. Only after passing the inspection can the next layer be constructed. This cycle is repeated until the main body of the dredged sand subgrade 3 and the edging soil 4 are constructed to the bottom design elevation of the subgrade structure 5, thus completing the construction of the subgrade main structure.

[0055] After the cyclic construction is completed, the construction and acceptance of the S7 bidirectional geogrid 10 and the subgrade structure 5 in layers will be carried out. First, the bottom of the subgrade will be cleaned to ensure it is flat and clean. The bidirectional geogrid 10 that meets the design specifications will be laid, with an overlap width of not less than 20cm. The overlaps will be firmly fixed with U-shaped nails, and the laying will be flat and wrinkle-free. Then, the subgrade structure 5 will be filled in layers, using fill material that meets the design requirements. Each layer will be spread and compacted, and the thickness, compaction degree, and moisture content of each layer will be controlled. After each layer is filled, a quality inspection will be carried out. After all filling is completed, a comprehensive acceptance will be organized. After the acceptance is qualified, the subsequent procedures will begin.

[0056] Finally, the construction and acceptance of the S10 roadbed slope protection and permanent drainage ditch 6 were carried out. The roadbed slope protection, in accordance with design requirements, involved protective treatment of both sides of the roadbed slopes, such as masonry revetment and grass planting to ensure slope stability and prevent rainwater erosion. Simultaneously, the roadbed drainage system was constructed according to the design plan to ensure smooth drainage and prevent water accumulation from affecting stability. During construction, the dimensions, slope, and construction quality of the protection and drainage facilities were strictly controlled. After all construction was completed, a final acceptance inspection was conducted. Upon successful acceptance, the entire roadbed construction process was completed.

[0057] Specifically, in this embodiment, the construction of the main body 3 of the dredged sand roadbed is carried out in layers, with each layer having a dredged sand thickness of about 1.0m. Seven days before the start of the construction of each layer of the main body 3 of the dredged sand roadbed, the construction of the corresponding layer of edging soil 4 needs to be organized and completed. The construction of the edging soil 4 adopts layered compaction, with each layer having a compaction thickness of no more than 20cm.

[0058] The traditional dredged sand filling construction process is as follows: (See...) Figure 2, 4 For sections 9, 10, and 11, first construct the earthen cofferdam 8, then lay the plastic film 12 inside, followed by sand filling, and then excavate the earthen cofferdam 8. See below. Figure 10 First, construct the sandbag cofferdam 2, then construct the first layer of sand cofferdam 9 as a retaining structure for subsequent dredged sand filling. Next, lay the plastic film 12 inside the sand cofferdam 9, then carry out the dredged sand filling, and finally construct the outer edging soil 4 of the sand cofferdam 9. See [link to relevant documentation]. Figure 4 Then, the second layer of sand cofferdam 9 is constructed as a retaining structure for subsequent dredged sand filling. Next, the inner plastic film 12 of the sand cofferdam 9 is laid, followed by dredged sand filling. Then, the outer edge soil 4 of the sand cofferdam 9 is constructed. Then, the third layer of sand cofferdam 9 is constructed as a retaining structure for subsequent dredged sand filling. Next, the inner plastic film of the sand cofferdam 9 is laid, followed by dredged sand filling. This cycle continues until the bottom of the roadbed is reached.

[0059] The sand-filling construction process of this invention is as follows: See Figure 1 , 3 First, construct the gabion cofferdam 7, then lay the geotextile 11 and plastic film 12, then carry out the dredged sand filling construction, then construct the first layer of edge soil 4, then carry out the dredged sand filling 3, then construct the second layer of edge soil 4, then carry out the dredged sand filling 4, then construct the third layer of edge soil 4, then carry out the dredged sand filling construction, and so on until the bottom of the roadbed.

[0060] In this method, the edging soil 4 serves as both a permanent protective structure for the roadbed and a replacement for the traditional temporary cofferdam, acting as a lateral support structure for the next layer of dredged sand, forming an integrated closed loop that combines permanent and temporary structures. This eliminates the layered construction and dismantling process of the temporary cofferdam in the traditional process, greatly simplifying the construction process and shortening the construction period.

[0061] From a construction period perspective, the main drawback of traditional methods is the time-consuming repetitive processes. Each layer requires the construction of cofferdams, laying of geomembranes, backfilling, and edging, with a single cycle taking approximately 15-20 days. Cofferdam dismantling requires careful handling to avoid disturbing the already formed backfill sand, adding an extra 1-2 days per layer and necessitating repeated measurement and control. The complex workflow, involving multiple trades working simultaneously including cofferdam construction, backfilling, geomembranes, and edging, results in long waiting times for acceptance.

[0062] The technological advantages of this application are that it not only eliminates redundant procedures and completely eliminates the steps of cofferdam demolition and new cofferdam construction, but also compresses the single-cycle cycle to 10-14 days, shortening it by approximately 30%. Furthermore, the pre-construction of the edging soil (4th layer) is completed 7 days ahead of schedule, operating in a continuous flow with the dredged sand filling (3rd layer) process, eliminating additional waiting time. In terms of overall construction period calculation, taking 4 layers of dredged filling as an example, the traditional process requires approximately 60-80 days, while the process of this application requires approximately 40-50 days, shortening the overall construction period by 25%-33%. Analyzing construction costs, the traditional process is more expensive. Its temporary structure costs, including earth cofferdam (8th layer), sand cofferdam (9th layer), sandbag cofferdam (2nd layer), labor, and machinery, account for approximately 12%-15% of the total cost; cofferdam demolition costs account for approximately 4%-6% of the total cost; in addition, there are repair costs, as cofferdam demolition easily disturbs the roadbed, and subsequent repair and reinforcement costs account for approximately 3%-5% of the total cost. The process cost of this application is significantly reduced. It eliminates the need for repeated construction and dismantling of temporary earthen cofferdams 8 and saves the construction of sand cofferdams 9. It only increases the cost of edge soil 4, which is a small amount of edge soil material cost, accounting for about 3% to 5% of the total cost. However, its function replaces the temporary cofferdam, offsetting the cost of cofferdam materials and dismantling. In terms of comprehensive cost calculation, the process of this invention can reduce the direct engineering cost by 16% to 21% compared with the traditional process, while also reducing the later maintenance cost.

[0063] This application is applicable to roadbed construction requiring large-scale dredged sand filling. It has the following advantages: Improved construction efficiency and significantly shortened construction period: The elimination of the layered construction and dismantling process of temporary cofferdams saves 5-7 days of construction time per layer of dredged filling, resulting in an overall construction period reduction of 25%~33%. Excellent drainage and sand control effect, eliminating potential quality hazards: 60×80mm mesh gabions and 400g / ㎡ drainage and sand control geotextile form a rigid material retaining and flexible water filtration system to prevent sand loss; the inner side of the edging soil 4 adopts a composite seepage prevention structure of plastic film 12 and geotextile 11 to block the seepage path and completely eliminate the risks of leakage and settlement.

[0064] Enhanced roadbed stability and improved bearing capacity: The gabion cofferdam 7 and the layered edging soil 4 form a synergistic retaining structure, creating an integrated stress structure that avoids slippage and voiding caused by repeated disturbances, significantly improving lateral stability and overall bearing capacity.

[0065] Construction costs are reduced and economic benefits are significant: the gabion filling material uses strongly to moderately weathered waste material from the quarry, eliminating the need for additional procurement; the investment in dismantling and rebuilding temporary cofferdams is eliminated, resulting in a 16%-21% reduction in overall construction costs. Utilizing quarry waste as gabion filling material reduces the costs of waste stockpiling and disposal, aligning with the concept of green construction.

[0066] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0067] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A construction method for an improved structure of hydraulically filled sand roadbed, characterized in that: The construction method includes the following steps: S1. Surface clearing and temporary drainage; S2, soft soil treatment; S3, Construction of gabion cofferdam; S4. Construction of the first layer of dredged sand; S5. Construction of the first layer of edging soil; S6, Second layer of dredged sand filling construction; S7. Construction and acceptance of geogrid laying and subgrade layer filling; S8. Construction and acceptance of subgrade slope protection and subgrade drainage; During the construction of S3, the geotextile for the roadbed and the inner side of the cofferdam of S3.1 is laid simultaneously; during the construction of S5, the geotextile and plastic film for the inner side of the edging soil of S5.1 are laid simultaneously; between S6 and S7, S5, S5.1 and S6 are repeated, and the construction is carried out in a cycle until the bottom of the roadbed is reached.

2. The improved structural dredged sand subgrade construction method according to claim 1, characterized in that: In S1, the surface cleaning and temporary drainage include the following steps: The cleaning of the roadbed construction area shall be carried out in a comprehensive manner. The cleaning materials include weeds, debris, loose soil and humus. The cleaning depth shall be determined according to the actual geological conditions on site and shall not be less than 20cm. After the cleaning is completed, the base shall be initially leveled and compacted. After the surface cleaning is completed, the supervisor shall be notified for acceptance. After the surface cleaning is completed, a temporary drainage ditch (6) shall be excavated in conjunction with the permanent drainage location. The drainage ditch (6) shall be covered with plastic film for protection.

3. The improved structural dredged sand subgrade construction method according to claim 1, characterized in that: In S2, soft foundation processing includes the following steps: Based on the survey data, a soft soil foundation treatment process was adopted, which includes replacing the soft soil foundation with graded sand and gravel or cement mixing piles to reinforce the soft soil foundation and ensure that the treatment results meet the design requirements.

4. The improved structural hydraulic filling sand roadbed construction method according to claim 1, characterized in that: In S3, the construction of gabion cofferdams includes the following steps: First, the base of the gabion cofferdam is leveled and compacted to ensure that the bearing capacity of the base meets the requirements. The material usage is calculated according to the construction progress, including galvanized gabion cages, filling stones, threaded steel anchor bars (14) and binding wire (15). The mesh size of the galvanized gabion cage is 8×10cm or 6×8cm, and the cage size is 1×1×2m. The filling stones are selected from the waste quarry of strongly weathered to moderately weathered material with hard texture, strength ≥20MPa, and particle size of 10-30cm. The mud content of the waste quarry is not greater than 5%. Then, the cages are assembled and fixed. The joints of the cages are firmly tied with binding wire (15), and the binding spacing is ≤20cm to ensure that there is no looseness or gaps at the joints. The cages are placed neatly, and the axis and elevation are consistent with the requirements. The requirements for laying the line are as follows:

1. Use threaded steel anchor bars (14) to fix the bottom of the gabion to prevent the gabion from shifting during filling and after construction. The spacing between fixing points is 1.5-2m. Then fill the gabion with rubble. Use a loader to collect and transport the gabion in layers. The filling thickness of each layer is 30-40cm. Place the rubble gently during filling to avoid damaging the gabion. Fill the gabion with rubble and fill the gaps with small-diameter crushed stone to ensure that there are no voids in the gabion. The filling density is ≥95%. Adjust the verticality of the gabion in time during the filling process to avoid tilting. Finally, complete the gabion capping. After the rubble is filled to the top of the gabion, tidy up the edge of the gabion to ensure that the gabion is in a regular shape. Then use binding wire (15) to firmly bind the top cap of the gabion. The binding spacing is consistent with the splicing point to prevent the rubble from falling off. The construction of S3.1 roadbed and inner side of cofferdam geotextile (11) includes the following steps: Before laying, clean the roadbed and inner side slope of the cofferdam, remove sharp debris and stones, ensure the slope is smooth, and avoid puncturing the geotextile (11); the reverse seepage geotextile (11) is laid on the top of the original ground after the soft foundation treatment and leveling and compaction and on the inner side of the gabion cofferdam (7). The geotextile material selection requirements are a weight of not less than 400g / ㎡, an equivalent pore size of 0.08~0.12mm, and a vertical permeability coefficient of 1×10 - ²~1×10 - ³cm / s, tensile strength not less than 15kN / m, CBR puncture resistance not less than 3.5kN, overlap width not less than 30cm, and fixed with U-shaped nails or geotextile-specific nails every 50-80cm; geotextile (11) is laid all the way to the top of the gabion cofferdam (7) and compacted, and the fabric surface is required to be tightly attached to the gabion at the contact point between the inner side and the gabion cofferdam (7).

5. The improved structural hydraulic filling sand roadbed construction method according to claim 1, characterized in that: In S4, the first layer of dredged sand filling includes the following steps: Sand blowing equipment is used to blow sand that meets the design requirements into the roadbed area. During the blowing process, the mud content and organic matter content of the sand are controlled and blown in layers. The blowing thickness is carried out according to the design requirements. After the blowing is completed, the test is carried out.

6. The improved structural hydraulic filling sand roadbed construction method according to claim 1, characterized in that: In S5, the construction of the first layer of edging soil includes the following steps: Select qualified plain soil and improve it with quicklime. Fill the edges of the dredged sand layer at the designed positions on both sides. During the filling process, spread and compact the soil in layers, control the spreading thickness and compaction degree, and ensure that the slope meets the design requirements. There is no risk of collapse or sliding. After the edge soil (4) is constructed to the design elevation, the geotextile (11) and plastic film (12) on the inner side of the edge soil (4) of S6.1 are laid. During the construction of S5.1, first clean the inner surface of the edging soil (4) to ensure it is flat and smooth. Then lay the geotextile (11) and plastic film (12). The thickness of the plastic film (12) shall not be less than 1.0 mm, the weight of the geotextile (11) shall not be less than 300 g / m², the equivalent pore size shall be 0.10-0.15 mm, and the vertical permeability coefficient shall be 1×10⁻⁶. - ²~1×10 - ³cm / s; The geotextile (11) and plastic film (12) are laid in the direction of the blown sand filling, following the principle of the upstream fabric pressing the downstream fabric. The overlap width of the geotextile (11) is not less than 30cm, and the overlap is fixed with U-shaped nails or special nails every 50-80cm. The top of the geotextile (11) is compacted to ensure that it is tightly attached, without wrinkles or gaps. The geotextile (11) is on the inside and the plastic film (12) is on the outside, with tight fit and standardized overlap. The overlap width of the plastic film (12) is not less than 20cm, and the overlap is compacted and sealed to prevent water seepage. After the laying is completed, check to confirm that there is no damage or omissions.

7. A construction method for an improved structural hydraulic fill sand roadbed according to claim 1 or 6, characterized in that: The edging soil (4) adopts a trapezoidal cross section with an inner slope ratio of 1:1.0, an outer slope ratio of 1:1.5, and a top width of 2.5m; the edging soil (4) adopts 4% improved lime soil with a compaction degree of not less than 95%; the top width of the edging soil is 250cm+50cm, the bottom layer width is calculated according to the slope ratio on both sides, and the layered filling thickness is 20cm~40cm after compaction; According to the centerline and edgeline of the roadbed, use Beidou or GPS to locate the outer boundary range of the edging soil (4) and mark it; the soil should be silty clay or loam without impurities, humus, or frozen soil, and the moisture content should be controlled at the optimum moisture content ±2%; the lime should be grade III or above quicklime powder; the material mixing adopts a centralized mixing method, and the soil and quicklime powder are mixed evenly. The mixing uniformity meets the requirements, there are no soil lumps or lime clumps, the color is consistent, and the mixture is transported to the construction site in time after mixing. The mixed lime-improved soil is spread to the designated area using a loader. The spreading thickness is controlled according to the designed layer thickness. During the spreading process, the surface is leveled to ensure that the spreading width and thickness are uniform. After spreading, a road roller is used to compact the soil. The compaction sequence is from both sides to the middle, from slow to fast, and from weak to strong. The compaction speed is controlled at 2-3 km / h. The number of compaction passes is no less than four, until the compaction degree meets the design requirements. If springiness or peeling occurs, the soil is promptly mixed, locally lime is added, and then the soil is re-compacted.

8. A construction method for an improved structural hydraulic fill sand roadbed according to claim 1 or 6, characterized in that: The construction method for the second layer of dredged sand in S6 is the same as that for the first layer of dredged sand in S4. After S6, the construction of the edging soil, the laying of geotextile and plastic film on the inner side of the edging soil, and the construction of dredged sand are repeated in sequence until the bottom elevation of the roadbed is reached.

9. A construction method for an improved structural hydraulic fill sand roadbed according to claim 1 or 6, characterized in that: In S7, the construction and acceptance of geogrid laying and subgrade layer filling includes the following steps: First, clean the bottom of the roadbed to ensure it is flat and clean. Lay a bidirectional geogrid (10) that meets the design specifications. The overlap width of the bidirectional geogrid (10) should not be less than 20cm. The overlap should be fixed firmly with U-shaped nails. The roadbed should be laid flat and without wrinkles. Then, the roadbed structure (5) should be filled in layers. Select fill material that meets the design requirements, spread and compact it in layers, control the thickness, compaction and moisture content of each layer, conduct quality inspection after each layer is filled, and conduct acceptance after all filling is completed.

10. The improved structural hydraulic filling sand roadbed construction method according to claim 1, characterized in that: In S8, the construction and acceptance of subgrade slope protection and subgrade drainage include the following steps: In accordance with design requirements, slope protection is carried out on both sides of the roadbed to ensure slope stability and prevent rainwater erosion. At the same time, the roadbed drainage system is constructed according to the design plan to ensure smooth drainage and avoid water accumulation on the roadbed that could affect its stability. During construction, the dimensions, slope, and construction quality of the protection and drainage facilities are controlled. After all construction is completed, a final acceptance inspection is conducted. Once the inspection is passed, the entire roadbed construction process is completed.

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