A large-thickness collapsible loess roadbed structure in a seasonal freezing region and a construction method thereof

Abstract

The application discloses a seasonal frozen region large-thickness collapsible loess roadbed structure and a construction method thereof, and belongs to the technical field of collapsible loess roadbed structures.The seasonal frozen region large-thickness collapsible loess roadbed structure comprises a water storage pool, a main drain pipe, a pressure water injection pump, an isolation plate, a support, a sleeve, an upper water injection pipe, a secondary drain pipe, a bottom plate, a support base, a cover plate, a support leg, a water-soaked pit, the sleeve, a lower water injection pipe, a flow rate controller, a clamping groove and a clamping seat; the water injection system of the application adopts a novel sleeve and a water injection pipe; when pre-soaking, the water injection pipe is prone to be blocked; the method of the sleeve plus the water injection pipe is adopted to realize double protection, so that the water injection pipe is not prone to be blocked during water injection; the support, the cover plate, the sleeve, the bottom plate and the isolation plate form an integrated structure; when the soil body is pre-soaked and collapsed, according to engineering conditions, the bottom plate can be loaded to accelerate the collapse efficiency and simultaneously treat the collapsibility of the shallow soil body; the cover plate on the sleeve can prevent sundries from entering the sleeve and affecting construction.

Description

Technical Field

[0001] This invention belongs to the field of collapsible loess technology, and specifically relates to a roadbed structure for thick collapsible loess in seasonally frozen areas and its construction method. Background Technology

[0002] Collapsible loess is an unsaturated, undercompressed soil with large pores and vertical joints. Under natural humidity, it has low compressibility and high strength, but when it is soaked in water, the soil strength decreases significantly. The resulting collapsible deformation is an unstable deformation with large settlement and fast settlement speed, which is very harmful to engineering construction.

[0003] Seasonally frozen soil regions, or seasonally frozen areas for short, experience periodic freeze-thaw cycles in their soil surface during seasonal changes. Because water expands when it freezes, and roadbeds are laid directly on this soil layer and contain a large amount of moisture, excessive moisture within the roadbed can easily lead to frost heave, causing cracking and damage. When the frozen soil at the base of the roadbed melts, it can easily cause roadbed collapse. Therefore, roads in seasonally frozen areas frequently suffer damage during these cyclical freeze-thaw cycles, drastically reducing their service life. Currently, most roadbeds in seasonally frozen soil regions have insufficient water removal capacity, and groundwater replenishes upwards during the cold season, easily causing frost heave. In the warm season, the melting surface ice cannot infiltrate, leading to frost heave. Both situations cause significant damage to the roadbed and pavement. In existing countermeasures, conventional roadbeds are mostly paved with waterproof materials, and a few use drainage materials. However, roadbeds using drainage materials cannot fully drain water from the roadbed, and their durability is relatively insufficient. Therefore, an effective and durable drainage material and roadbed construction method are particularly important.

[0004] Thick, collapsible loess sites refer to loess areas with a thickness greater than 15m and strong self-weight collapsibility. In recent years, with the development of infrastructure construction in collapsible loess areas of my country, construction land has become increasingly scarce, forcing many large-scale engineering projects to be built on thick, collapsible loess sites. Existing mature methods for treating collapsible loess foundations generally only eliminate the collapsibility of the foundation soil 10-15m below the foundation. To ensure that the treated foundation is technically advanced and economically reasonable, new and effective methods for treating thick, collapsible loess foundations should be researched.

[0005] Commonly used methods for treating collapsible loess foundations include dynamic compaction, subgrade layering, compaction piles, chemical reinforcement, and pre-soaking. Chemical reinforcement involves injecting a sodium silicate solution into the foundation soil. Through a chemical reaction, it generates cementing substances or activates the surface of soil particles, causing them to solidify at the contact points, thus strengthening the bonds between soil particles and improving the soil's mechanical strength. Currently, the injection volume of sodium silicate solution is mostly adjusted based on past experience. However, the judgment of the injection volume is not accurate enough. Too much injection will not further improve the soil's mechanical strength due to saturation, resulting in wasted chemical solution and significantly increased treatment costs. Too little injection will lead to insufficient soil mechanical strength, affecting the quality of improvement for collapsible loess subgrades. This causes significant inconvenience in the improvement of collapsible loess subgrades, making it difficult to guarantee the quality of the improvement. Dynamic compaction involves using a heavy hammer to compact collapsible loess areas, increasing the strength and stability of the loess itself. However, this method does not improve the characteristics of collapsible loess, and problems such as subsidence and flow still exist over time, damaging road surfaces. The lime-soil compaction pile method suffers from low strength, poor cohesion, and poor waterproofing. The subbase method is generally suitable for smaller buildings; it increases construction costs for larger buildings. Pre-soaking is effective for treating collapsible loess foundations, but its construction cycle is long, and the soaking rate is slow. The pre-soaking stage requires drilling deep into the loess to insert the injection pipe, which traditional ramming equipment cannot achieve, thus failing to meet the needs of loess foundation treatment. Furthermore, the pre-soaking method cannot be carried out in seasonally frozen areas.

[0006] Currently, the main methods for preventing and controlling frost damage to roadbeds are: replacement and waterproofing. Replacement involves replacing frost-susceptible soil with non-frost-susceptible soil during roadbed construction. While this method is a reliable measure for controlling frost damage, it has a long construction period. Furthermore, the amount of non-frost-susceptible soil required for replacement is enormous, making it difficult to guarantee sufficient soil sources along the roadbed route, thus limiting its practical application. Replacement also generates a large amount of waste soil, leading to significant environmental damage. Waterproofing involves installing a waterproof layer in the roadbed, primarily made of various waterproof materials such as geomembranes and geotextiles. However, during actual construction, both geomembranes and geotextiles inevitably suffer various forms of damage, resulting in ineffective waterproofing and poor engineering performance.

[0007] Existing geocell systems have the following problems: 1. When filling existing geocells, the stress on adjacent cells shifts, causing deformation and affecting the quality of the filling material. 2. Geocells need to be fully expanded for maximum utilization during use, requiring significant pulling force, which makes the ground strips at the connection points prone to breakage. 3. The tensile force generated by the geocell sheets is almost entirely concentrated on the pin shaft, resulting in excessive stress on a single component.

[0008] For the reasons mentioned above, it is necessary to propose a new subgrade structure and construction method for thick collapsible loess in seasonally frozen areas to solve the problem of periodic freeze-thaw phenomena in the pavement of thick collapsible loess subgrades in seasonally frozen areas. Summary of the Invention

[0009] This invention provides a roadbed and pavement structure for thick collapsible loess in seasonally frozen areas and its construction method, which can solve the problem of periodic freeze-thaw phenomena in roadbeds and pavements for thick collapsible loess in seasonally frozen areas.

[0010] To solve the above problems, the technical solution provided by the present invention is as follows:

[0011] This invention proposes a roadbed structure for thick collapsible loess in a seasonally frozen area, which includes a saturation pit (16) and a water storage tank (1) located on the ground surface (7). The bottom of the saturation pit (16) is provided with a bottom plate (9), and an isolation plate (4) is arranged around the saturation pit (16). The isolation plate (4) and the bottom plate (9) are fixedly connected to form a whole that can be loaded. Multiple water injection holes are provided inside the saturation pit (16).

[0012] The water storage tank (1) is connected to a main drain pipe (2) on the right side. A pressure water pump (3) is installed on the main drain pipe (2). The main drain pipe (2) is located in the middle of the immersion pit (16). Multiple secondary drain pipes are alternately arranged on both sides of the main drain pipe (2). Each secondary drain pipe is connected to an upper water injection pipe (7). Each upper water injection pipe (7) is equipped with a bracket (5) corresponding to the bottom plate (9). A flow rate controller (7-2) is installed on the upper water injection pipe (7). The upper water injection pipe (7) is connected to a lower water injection pipe (7-4). A sleeve (6) is fitted on the lower water injection pipe (7-4). A cover plate (12) is provided on the sleeve (6). Each lower water injection pipe (7-4) and its sleeve (6) are located in a water injection hole. The diameter of the water injection hole is larger than the diameter of the sleeve (6). The sleeve (6) passes through the bottom plate (9).

[0013] The sleeve (6) has a drain hole (6-2) on its side, and a filter screen (6-3) is installed on the drain hole (6-2). A drill bit (6-4) is installed at the bottom of the sleeve (6). The surface of the lower water injection pipe (7-4) is provided with the same drain hole (6-2) and filter screen (6-3) as the surface of the sleeve (6). The sleeve (6) has a slot (6-6) and a seat (6-7) installed inside. The seat (6-7) is connected to an electric heating tube (6-1). The upper end of the sleeve (6) has a first round hole (6-5). The side bolt (5-1) of the bracket (5) passes through the first round hole (6-5) and the second round hole (14) on the support leg (13) at the bottom of the cover plate (12) so that the sleeve (6) is fixedly connected to the bracket (5).

[0014] The surface of the cover plate (12) is provided with a water injection hole (7-3) and a fixing hole (7-5) through which the heating tube (6-1) and the card holder (6-7) pass. The shape of the fixing hole (7-5) is the same as the outline of the heating tube (6-1) and the card holder (6-7). The side bolt (5-1) of the bracket (5) passes through the third round hole (15) on the base plate (9) to fix the isolation plate (4), the base plate (9), the bracket (5), and the cover plate (12) together.

[0015] According to an optional embodiment of the present invention, the multiple secondary drainage pipes include a first drainage pipe (8) and a second drainage pipe (10) arranged alternately at intervals. Each first drainage pipe (8) is connected to 3 upper water injection pipes (7), and each second drainage pipe (10) is connected to 2 upper water injection pipes (7). The water consumption of the first drainage pipe (8) is greater than the water consumption of the second drainage pipe (10).

[0016] According to an optional embodiment of the present invention, both ends of the upper water injection pipe (7) are provided with threads (7-1), and both ends of the upper water injection pipe (7) are respectively connected to the secondary drain pipe and the lower water injection pipe (7-4) through threads (7-1).

[0017] According to an optional embodiment of the present invention, a support (11) is provided on the side of the immersion pit (16) away from the water storage tank (1), and the support (11) is used to support the main drain pipe (2).

[0018] According to an optional embodiment of the present invention, the base plate (9) is a steel plate.

[0019] According to an optional embodiment of the present invention, a pre-soaking treatment layer (18) is provided in the immersion pit (16), and waterproof curtains (19) are provided on the left and right sides of the pre-soaking treatment layer (18). A lignin fiber treatment layer (20), a modified asphalt surface layer (24), and a three-dimensional geocell (25) are laid on the pre-soaking treatment layer (18). The three-dimensional geocell (25) is composed of a cell (28) and a ribbed steel bar (29). The cell (28) has water-permeable holes (30) on the front and rear sides of the middle part. The connecting parts on the left and right sides of the water-permeable holes (30) have retaining rings (31). The retaining rings (31) and the ribbed steel bar (29) are used together.

[0020] A large sand and gravel layer (21) is laid on top of the lignin fiber treatment layer (20), and a crushed stone layer (22) is laid on top of the large sand and gravel layer (21). A 3:7 lime-soil connecting layer (26) is laid at the junction of the lignin fiber treatment layer (20), the large sand and gravel layer (21), and the crushed stone layer (22). The function of the 3:7 lime-soil connecting layer (26) is to provide multi-layer insulation and seepage prevention, so as to avoid water accumulation inside and freeze-thaw in winter. Drainage ditches (27) are set on the left and right sides of the waterproof curtain (19), and waterproof geotextile treatment layers (32) are set on both slope protection layers of the pre-soaked water treatment layer (18).

[0021] This invention also provides a construction method for a thick collapsible loess subgrade structure in a seasonally frozen region, implemented using a thick collapsible loess subgrade structure as described in the above embodiments, characterized in that the construction method includes:

[0022] Step S1: Based on the survey data and design requirements, determine the treatment depth and scope for completely or partially eliminating loess foundation subsidence. Then confirm the immersion depth and the size of the immersion test pit. The base plate thickness is determined through rough calculation. Different component sizes are used for different working conditions; large-diameter sleeves are selected for large-scale projects, and small-diameter sleeves for small-scale projects. The specific details are determined based on the needs of the construction site. First, calculate the weight of the sleeve, support, and cover plate, simplify it to a surface load, and then estimate the steel plate thickness using the steel plate thickness calculation formula to avoid steel waste and reduce costs.

[0023] Step S2: Determine the layout of the water injection holes, calculate the volume of the wetted loess and the amount of water to be injected based on the required treatment depth and radius, and determine the location of the water injection holes.

[0024] Step S3: Drill the water injection hole according to the existing process. After the water injection hole is drilled, insert the sleeve into the water injection hole. The diameter of the water injection hole is slightly larger than the sleeve. The sleeve provides support to prevent the hole wall from collapsing. A drill bit is installed at the lower end of the sleeve. Drainage holes are provided around the sleeve, and filter screens are installed on the drainage holes. A slot and a seat are installed on the inner side of the sleeve. The seat is connected to the heating element, and the heating element is electrically connected to the water storage tank. The water storage tank can be powered by a generator or solar panels. After completing the above steps, place the base plate on the sleeve. The round hole at the lower end of the support aligns with the opening in the wooden board. The round holes are aligned and connected with bolts. The round holes at the top of the bracket are bolted to the round holes at the top of the sleeve. The bolts pass through the round holes at the top of the bracket, the first round hole at the top of the sleeve, and the second round hole of the support leg on the cover plate. Then, a water-resistant plate is installed around the immersion pit to avoid affecting the soil on both sides of the road. This method improves the immersion efficiency within the treatment area. The water-resistant plate is bolted to the plate on the ground, thus fixing the water-resistant plate, base plate, sleeve, bracket, and cover plate together. All of the above structures require anti-corrosion and anti-rust treatment to achieve the effect of reusable steel components. Water-based anti-corrosion coating application: First, surface treatment is performed, cleaning and treating the steel structure surface to remove dust, grease, rust, and other contaminants. Surface treatment methods such as sandblasting, polishing, or brushing can be used to ensure a clean, smooth surface and good adhesion. Then, a primer is applied, selecting a primer product suitable for water-based anti-corrosion coatings. Typically, the primer needs to be applied quickly after surface preparation to prevent new contaminants from adhering. Next, an intermediate coating is applied. After the primer is completely dry, one or more layers of water-based anti-corrosion coating are applied as an intermediate coating. Finally, a topcoat is applied, consisting of a water-based anti-corrosion coating, which provides final anti-corrosion protection and decorative effect.

[0025] Step S4: Connect the water injection pipe and inject water through the reservoir. Operate the water injection device to continuously immerse the foundation in water and observe the collapsibility deformation until the foundation is saturated and the collapsibility is eliminated. The immersion time is stopped when the collapsibility deformation stabilizes. The standard for stable collapsibility deformation is that the average collapsibility amount in the last 5 days is less than 1 mm / d. When the thickness of the collapsible loess layer being treated is greater than 20 m, the standard for stable settlement is that the average collapsibility amount in the last 5 days is less than 2 mm / d. Insert the lower water injection pipe into the sleeve through the water injection hole on the cover plate. Inside the cylinder, the lower water injection pipe and the upper water injection pipe are connected by threads, and the upper water injection pipe is also connected by threads to the upper drain pipe. A flow rate controller is installed on the water injection pipe. When water is injected, the calculated water consumption varies due to different hole depths. The flow rate controller can be used to adjust different rates to achieve the estimated water consumption and reduce water waste. The lower water injection pipe has a drain hole and filter screen similar to the sleeve. The lower water injection pipe extends out of the water injection hole on the cover plate for easy connection with the upper water injection pipe.

[0026] Step S5: After the water supply is stopped, the water injection pipe can be disassembled, the lower water injection pipe can be pulled out, and water can be pumped out to start the water level drop. The drainage consolidation and settlement should be observed. After the settlement is stable, proceed to the next step.

[0027] Step S6: Remove the drainage pipe. If a load has been applied, remove the load first, then remove the heating element, sleeve, support, base plate, isolation plate, and drainage device in sequence. After pre-soaking, test the bearing capacity of the foundation according to the construction requirements to determine whether pile foundation construction is necessary. If the bearing capacity is high after pre-soaking, fill and compact the duct with crushed stone, sand, etc. If the bearing capacity is low, then carry out pile foundation construction. Since the collapsibility of the shallow and deep layers has been completely eliminated, water-proofing and drainage measures can now be taken for the roadbed. Lay out and level the site, mark the filling range of the cement cushion layer, determine the position of the water-stop curtain on both sides of the roadbed, and construct the water-stop curtain along the outer side of the two slope toes of the roadbed according to the existing construction process: construct the jet grouting pile water-stop curtain.

[0028] Step S7: After the water-stop curtain is completed, level the foundation and pour concrete in layers with a thickness of more than 1 meter. Before pouring each layer, place geocells and fix them with ribbed steel bars through the clamps. The layer thickness is 20-50cm. When pouring each layer, remove the laitance, weak concrete layer and loose stones from the pouring surface and expose the coarse aggregate evenly. Before pouring the upper layer of concrete, wash the surface of the concrete with pressurized water to remove dirt and fully moisten it, but there should be no water. For non-pumped and low-flow concrete, grouting measures should be taken when pouring the upper layer of concrete.

[0029] Step S8: After the roadbed is laid, waterproof geotextile is laid on the slope and then compacted with soil to prevent water seepage on the slope. Drainage ditches are set on both sides of the roadbed.

[0030] Step S9, final acceptance.

[0031] According to an optional embodiment of the present invention, step S4 further includes: if construction is carried out in winter, adding antifreeze to the water during water injection, with ethylene glycol as the antifreeze agent.

[0032] According to an optional embodiment of the present invention, step S6, constructing the water-stop curtain, includes: firstly, constructing 3-4 rows of jet grouting piles, all of which are arranged in a quincunx pattern, i.e., one jet grouting pile in the middle row is surrounded by four jet grouting piles from other rows, with adjacent jet grouting piles arranged tangentially; then, filling the spaces between the jet grouting piles with inter-pile soil, ensuring that the permeability coefficient of the jet grouting pile water-stop curtain is less than 10. 7cm / s; or, construct a compaction pile water-stop curtain. First, construct 3-4 rows of compaction piles, all arranged in a staggered pattern, i.e., one compaction pile in the middle row is surrounded by four compaction piles from other rows, with adjacent compaction piles tangentially arranged. Then, fill the spaces between the compaction piles with inter-pile soil. The lower end of the compaction pile water-stop curtain penetrates the lower limit of collapsible loess, and the permeability coefficient of the compaction pile water-stop curtain is less than 10. 7 cm / s.

[0033] According to an optional embodiment of the present invention, step S7 further includes: adding an antifreeze agent to the concrete to synthesize modified concrete, wherein the antifreeze agent includes an air-entraining agent, a porous material and a hydrophobic material, wherein the air-entraining agent includes polysiloxane; the porous material includes one or a combination of two of zeolite and diatomite; and the hydrophobic material includes one or a combination of more than two of stearic acid, calcium stearate and paraffin.

[0034] Beneficial effects:

[0035] (1) When using the pre-soaking method, the present invention adopts a new type of sleeve with a drainage hole and a filter screen on the drainage hole. A drill bit is installed under the sleeve. The sleeve can provide support to prevent the hole wall from collapsing. During the pre-soaking and settling, the sleeve can provide weight and the drill bit can better prevent the foundation from sinking due to its own weight.

[0036] (2) The sleeve in this invention is equipped with an upper water injection pipe and a lower water injection pipe. The lower water injection pipe also has holes and a filter screen similar to those on the sleeve. During pre-soaking, the existing water injection pipe is prone to clogging. This invention uses a sleeve plus a water injection pipe for double protection, making it less likely to clog the water injection pipe during water injection. Even if clogging occurs, the outer sleeve will clog first, making it easier to observe the phenomenon. At this time, the worker can shut off the water injection in time and take appropriate measures.

[0037] (3) In this invention, the sleeve, base plate, and isolation plate are bolted together to form a whole. When the soil experiences pre-immersion collapse, the drill bit on the sleeve can reduce the frictional resistance of the soil, allowing the self-weight generated by the integrated structure to accelerate the collapse of the soil. The self-weight generated by the integrated structure can treat the shallow soil. Furthermore, depending on the project conditions, it can be loaded on the base plate to accelerate the collapse efficiency and simultaneously address the collapsibility of the shallow soil. The cover plate on the sleeve can prevent debris from entering the sleeve and affecting construction. Due to uneven collapse caused by immersion rate or other factors, the duct may become skewed, affecting immersion efficiency and the calculation of water consumption. The integrated structure can effectively avoid this situation. This integrated structure can be disassembled and reused, saving resources. Diversification is achieved in the selection of loading materials; for example, soil, machinery, or other items can be selected, simply by placing them evenly on the base plate.

[0038] (4) The sleeve of the present invention is provided with a slot and a seat. The seat is connected to the heating tube. This structure is used in conjunction with antifreeze to enable construction in winter. During construction, the heating tube is used to melt the frozen soil layer first, and then the antifreeze is used for pre-soaking. After the heating tube is used up, it can be pulled out through the slot to achieve the effect of recycling.

[0039] (5) The water injection holes of this invention are arranged using shallow and deep holes. Since each hole produces a droplet-shaped distribution of water after immersion, inserting the shallow hole can accelerate the immersion efficiency of the soil after water injection. It can also increase the distance between two deep holes, thereby reducing the number of holes, reducing construction costs, and allowing for a variety of subsequent construction schemes. For example, shallow holes can be constructed using shallow compaction piles or crushed stone piles, while deep holes can be constructed using rotary drilling or jet grouting, thus eliminating the need for re-drilling and saving resources. After pre-immersion, roadbed construction is carried out. Based on the test of the foundation bearing capacity, it is determined whether pile foundation construction is required. If pile foundation construction is required, the above method can be used. If not, crushed stone can be directly filled and compacted.

[0040] (6) The water injection pipe of the present invention is equipped with a flow rate controller, which makes it easy to control the drainage volume and adjust the water resources to achieve the purpose of saving water resources.

[0041] (7) The roadbed structure of the present invention adopts a two-layer modified concrete structure. The layout is as follows: one layer is laid under the surface layer and one layer is laid on the foundation. The two modified concrete layers are located and have different thicknesses. The upper concrete layer is mainly used to support and resist shear force and shoving deformation. The lower concrete layer and the lignin fiber treatment layer serve as an antifreeze cushion layer. The concrete and antifreeze agent are integrated, which can provide good antifreeze performance, strength and stability, and can effectively reduce roadbed deformation.

[0042] (8) The modified concrete of this invention uses a novel geocell. The geocell has channels for water permeability, and there are retaining rings on both sides of the channels. The retaining rings and ribbed steel bars are used together. When filling the existing geocell, the stress on adjacent cells will shift and deform, affecting the filling quality of the geocell. Adjusting the size of the geocell with ribbed steel bars and fixing the geocell can effectively avoid this situation. When using the geocell, it needs to be unfolded as much as possible to maximize its utilization, so a lot of force is required to pull it. This makes the ground strip at the connection buckle very easy to break. When using it, it is not necessary to pull it to the maximum extent at first. After pulling it to a certain extent, the retaining rings are used to fix and adjust the geocell. In addition, the insertion of steel bars also solves the problem that the tensile force generated by the geocell sheet is almost entirely concentrated in the pin part, and the stress on a single component is too large. Moreover, the structure is simple to operate.

[0043] (9) The loess subgrade structure of the present invention has multi-layer insulation and seepage prevention measures. A 3:7 lime-soil connecting layer is laid at the interface of each layer to prevent seepage and keep warm, reducing the impact of freeze-thaw cycles on the subgrade in winter. The multi-layer connecting layer can improve the shear strength and displacement deformation capacity of the interface. The multi-layer anti-freeze measures, the anti-freeze cushion layer, the lignin fiber treatment layer, and the modified concrete all have a good anti-freeze effect and reduce the damage to the subgrade in winter. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments or prior art, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a top view of a thick collapsible loess subgrade structure in a seasonally frozen area, provided as an embodiment of this application.

[0046] Figure 2 This is a cross-sectional schematic diagram of a thick collapsible loess subgrade structure in a seasonally frozen area, provided as an embodiment of this application.

[0047] Figure 3 A schematic diagram of a sleeve structure for a thick collapsible loess subgrade in a seasonally frozen area, provided as an embodiment of this application.

[0048] Figure 4 This is a top view schematic diagram of a sleeve structure for a thick collapsible loess subgrade in a seasonally frozen area, provided as an embodiment of this application.

[0049] Figure 5 This is a schematic diagram of a support structure for a thick collapsible loess subgrade in a seasonally frozen area, provided as an embodiment of this application.

[0050] Figure 6 This is a schematic diagram of the base plate structure of a thick collapsible loess subgrade in a seasonally frozen area, provided as an embodiment of this application.

[0051] Figure 7 This is a schematic diagram of a cover plate structure for a thick collapsible loess subgrade in a seasonally frozen area, provided as an embodiment of this application.

[0052] Figure 8 This is a schematic diagram of the upper water injection pipe structure of a thick collapsible loess subgrade in a seasonally frozen area, provided as an embodiment of this application.

[0053] Figure 9 This is a schematic diagram of the structure within the pre-soaking water treatment layer of a thick collapsible loess subgrade structure in a seasonally frozen area, provided as an embodiment of this application.

[0054] Figure 10 This is a schematic diagram of a pre-soaked subgrade structure for a thick collapsible loess subgrade in a seasonally frozen area, provided as an embodiment of this application.

[0055] Figure 11 This is a detailed diagram of a geocell structure for a thick collapsible loess subgrade in a seasonally frozen region, provided as an embodiment of this application.

[0056] Figure 12 This application provides a rough estimation parameter for the thickness of the sleeve bottom plate of a thick collapsible loess subgrade structure in a seasonally frozen area. Detailed Implementation

[0057] The technical solutions of the embodiments of this application 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 this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0058] like Figure 1 and Figure 2 As shown, this embodiment of the invention provides a roadbed structure for thick collapsible loess in a seasonally frozen region. This roadbed structure includes a immersion pit 16 and a water storage tank 1 located on the ground surface. The size of the immersion pit 16 is excavated according to site conditions. A bottom plate 9 is provided at the bottom of the immersion pit 16, and isolation plates 4 are arranged around the immersion pit 16, with the isolation plates 4 fixedly connected to the bottom plate 9 to form a single unit capable of bearing loads. Multiple water injection holes are provided inside the immersion pit 16. Figure 12 As shown, the thickness of the base plate is determined by rough calculation. Different component sizes are used for different working conditions. Large-scale projects select large-diameter sleeves, while small-scale projects select small-diameter sleeves. The specific situation is determined according to the needs of the construction site. First, the weight of the sleeve, bracket, and cover plate is calculated and simplified into surface load. Then, the steel plate thickness can be estimated according to the steel plate thickness calculation formula to avoid steel waste and reduce costs.

[0059] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7As shown, a main drain pipe 2 is connected to the right side of the water storage tank 1. A pressure water injection pump 3 is installed on the main drain pipe 2, and the main drain pipe 2 is located in the middle of the immersion pit 16. Multiple secondary drain pipes are alternately arranged on both sides of the main drain pipe 2, and an upper water injection pipe 7 is connected to the bottom of each secondary drain pipe. Specifically, the multiple secondary drain pipes include a first drain pipe 8 and a second drain pipe 10 that are alternately arranged at intervals. In this embodiment, each first drain pipe 8 is connected to 3 upper water injection pipes 7, and each second drain pipe 10 is connected to 2 upper water injection pipes 7. The water consumption of the first drain pipe 8 is greater than that of the second drain pipe 10.

[0060] Each upper water injection pipe 7 has a bracket 5 installed at the position corresponding to the base plate 9. A flow rate controller 7-2 is installed on the upper water injection pipe 7. The flow rate controller 7-2 is configured with different water flow rates. According to the calculated water volume, when water is injected, the flow rate of the first drain pipe 8 is greater than that of the second drain pipe 10, and the water volume required by the first drain pipe 8 is greater than that required by the second drain pipe 10.

[0061] The upper water injection pipe 7 is connected to the lower water injection pipe 7-4. A sleeve 6 is fitted onto the lower water injection pipe 7-4, and a cover plate 12 is installed on the sleeve 6. Each lower water injection pipe 7-4 and its sleeve 6 are located in a water injection hole. The diameter of the water injection hole is slightly larger than the diameter of the sleeve 6, and the sleeve 6 passes through the base plate 9. The multiple water injection holes are arranged in a rectangular pattern, with one shallow hole sandwiched among four deep holes.

[0062] The sleeve 6 has a drain hole 6-2 on its side, and a filter screen 6-3 is installed on the drain hole 6-2. A drill bit 6-4 is installed at the bottom of the sleeve 6. The surface of the lower water inlet pipe 7-4 is provided with the same drain hole 6-2 and filter screen 6-3 as the surface of the sleeve 6. The inner side of the sleeve 6 is provided with a slot 6-6 and a seat 6-7. The seat 6-7 is fixedly connected to the heating element 6-1. The upper end of the sleeve 6 has a first round hole 6-5. The side bolt 5-1 of the bracket 5 passes through the first round hole 6-5 and the second round hole 14 on the support leg 13 at the bottom of the cover plate 12 to fix the sleeve 6 to the bracket 5.

[0063] The surface of the cover plate 12 is provided with a water injection hole 7-3 and a fixing hole 7-5 through which the heating element 6-1 and the card holder 6-7 pass. The shape of the fixing hole 7-5 is the same as the outline of the heating element 6-1 and the card holder 6-7. The side bolt 5-1 of the bracket 5 passes through the third round hole 15 on the base plate 9 to fix the isolation plate 4, the base plate 9, the bracket 5, and the cover plate 12.

[0064] like Figure 8As shown, both ends of the upper water injection pipe 7 are equipped with threads 7-1, and the two ends of the upper water injection pipe 7 are connected to the secondary drainage pipe and the lower water injection pipe 7-4 respectively through threads 7-1. A support 11 is provided on the side of the immersion pit 16 away from the water storage tank 1, and the support 11 is used to support the main drainage pipe 2. The base plate 9 is a steel plate.

[0065] like Figure 9 , Figure 10 and Figure 11 As shown, after the pre-soaking treatment is completed, the bearing capacity of the foundation soil is tested according to the project requirements to determine whether pile foundation construction is required. If the bearing capacity is high after pre-soaking treatment, the ducts can be filled and compacted with crushed stone, sand, etc. If the bearing capacity is low, pile foundation construction is carried out. A pre-soaking treatment layer 18 is set in the soaking pit 16, and waterproof curtains 19 are set on the left and right sides of the pre-soaking treatment layer 18. A lignin fiber treatment layer 20, a modified concrete layer 23, a modified asphalt surface layer 24, and geocells 25 are laid on the pre-soaking treatment layer 18.

[0066] A modified concrete layer 23 is also laid under the modified asphalt surface layer 24. The modified concrete layer 23 is mainly used to support and resist shear and shoving deformation. The geocell 25 and the structure it forms have the characteristics of strong lateral confinement and high stiffness. The lower concrete layer and the lignin fiber treatment layer 20 serve as an anti-freeze cushion layer, which can provide good anti-freeze heave performance, strength and stability, and can effectively reduce roadbed deformation.

[0067] The three-dimensional geocell 25 is composed of a cell 28 and ribbed steel bars 29. The cell 28 has permeable holes 30 on both the front and rear sides of the middle part, and the connecting parts on the left and right sides of the permeable holes 30 have retaining rings 31. The retaining rings 31 and the ribbed steel bars 29 are used together. The circular structure formed by the three-dimensional geocell 25 is a detailed structure.

[0068] When filling existing geocells, the stress on adjacent cells shifts, causing deformation and affecting the quality of the filling material. This invention uses ribbed steel bars to adjust the size of the cells and fix them in place, effectively avoiding this problem. Geocells need to be fully expanded for maximum utilization during use, requiring significant pulling force. This makes the ground strips at the connection points prone to breakage. Furthermore, this invention solves the problem of almost all the tensile force generated by the cell panels being concentrated on the pin shaft, resulting in excessive stress on a single component. The corresponding structure of this invention is also simple to operate.

[0069] A large sand and gravel layer 21 is laid on top of the lignin fiber treatment layer 20, and a crushed stone layer 22 is laid on top of the large sand and gravel layer 21. A 3:7 lime-soil connecting layer 26 is laid at the junction of the lignin fiber treatment layer 20, the large sand and gravel layer 21 and the crushed stone layer 22. The function of the 3:7 lime-soil connecting layer 26 is to provide multi-layer insulation and seepage prevention, so as to avoid water accumulation inside and freeze-thaw in winter. Drainage ditches 27 are set on the left and right sides of the waterproof curtain 19. Both slope protection layers of the pre-impregnated water treatment layer 18 are equipped with waterproof geotextile treatment layers 32.

[0070] This invention also provides a construction method for a thick collapsible loess subgrade structure in a seasonally frozen region, which is implemented using a thick collapsible loess subgrade structure in a seasonally frozen region as described in the above embodiments. The construction method includes:

[0071] Step S1: Based on the survey data and design requirements, determine the treatment depth and scope for completely or partially eliminating loess foundation subsidence, and then confirm the immersion depth and immersion test pit dimensions. The base plate thickness is determined through rough calculation. Different component sizes are used for different working conditions; large-diameter sleeves are selected for large-scale projects, and small-diameter sleeves are selected for small-scale projects. The specific situation is determined according to the needs of the construction site. First, calculate the weight of the sleeve, support, and cover plate, simplify it into surface load, and then estimate the steel plate thickness using the steel plate thickness calculation formula to avoid steel waste and reduce costs.

[0072] Step S2: Determine the layout of the water injection holes. Based on the required treatment depth and radius, calculate the volume of the wetted loess and the amount of water to be injected, and determine the location of the water injection holes.

[0073] Step S3: Drill water injection holes according to existing technology. The depth of the water injection holes varies, with a shallow hole inserted between every four deep holes, and the depth difference is 4 to 6 meters. Since each hole will produce a water droplet-shaped distribution after water is injected, inserting the shallow hole can accelerate the water absorption efficiency of the soil after water injection. It can also increase the distance between two deep holes, thereby reducing the number of holes, reducing construction costs, and allowing for more diverse choices of subsequent construction methods. For example, shallow holes can be constructed using shallow compaction piles or crushed stone piles, while deep holes can be constructed using rotary drilling or jet grouting, thus eliminating the need for re-drilling and saving resources.

[0074] After the water injection hole is completed, the sleeve is placed into the water injection hole. The diameter of the water injection hole is slightly larger than that of the sleeve. The sleeve can provide support and prevent the hole wall from collapsing. A drill bit is installed at the lower end of the sleeve. Drainage holes are set around the sleeve, and filter screens are installed on the drainage holes. The filter screens can prevent the surrounding soil from clogging the drainage holes during the water injection process, thus reducing the water injection efficiency. The inner side of the sleeve is equipped with a slot and a seat. The seat connects to the heating element, which is electrically connected to the water storage tank. The water storage tank can be powered by a generator or solar panels. The heating element is used to thaw the frozen soil layer during construction in seasonally frozen areas and to prevent freezing during water injection, allowing the pre-soaking method to be carried out in winter. Depending on the soil freezing conditions, 1 to 6 heating elements can be installed, and the temperature can be controlled within a reasonable range. The heating element is electrically connected to the water storage tank, which can be powered by a generator or solar panels. After use, the heating element can be removed by sliding between the slot and the seat, enabling effective recycling and repair. The step of installing the heating element can be skipped during summer construction.

[0075] After completing the above steps, place the base plate on the sleeve, aligning the round hole at the lower end of the bracket with the round hole on the wooden board, and connect them with bolts. Connect the round hole at the upper end of the bracket with the round hole at the upper end of the sleeve using bolts. The bolts pass through the round hole at the upper end of the bracket, the first round hole at the upper end of the sleeve, and the second round hole of the support leg on the cover plate. Then, install a water-resistant plate around the immersion pit to avoid affecting the soil on both sides of the road. This method improves the immersion efficiency within the treatment area. The water-resistant plate is bolted to the plate on the ground, thus fixing the water-resistant plate, base plate, sleeve, bracket, and cover plate. All the above structural components must undergo anti-corrosion and anti-rust treatment to achieve the effect of reusable steel components. Water-based anti-corrosion coating application: First, perform surface treatment, cleaning and treating the steel structure surface to remove dust, grease, rust, and other contaminants. Surface treatment can be performed using methods such as sandblasting, polishing, or brushing to ensure a clean, smooth surface and good adhesion. Then, apply a primer, selecting a primer product suitable for water-based anti-corrosion coatings. Typically, a primer should be applied quickly after surface preparation to prevent the adhesion of new contaminants. This is followed by an intermediate coat; after the primer is completely dry, one or more layers of water-based anti-corrosion coating are applied. Finally, a topcoat of water-based anti-corrosion coating is applied, providing final anti-corrosion protection and a decorative finish.

[0076] In this design, the drainage holes around the sleeve and the first circular hole at the top of the sleeve, along with multiple heating elements, are preferably not aligned vertically to avoid obstructing the holes and affecting connection and drainage efficiency. The overall structural function of this thick, collapsible loess subgrade in the seasonally frozen zone is as follows: 1. When soil subsidence occurs, the drill bit on the sleeve reduces the soil's frictional resistance, allowing the self-weight of the integrated structure to accelerate soil subsidence. The self-weight of the integral plate can treat shallow soil layers. Furthermore, depending on the project requirements, additional loads can be placed on the base plate to accelerate subsidence efficiency and simultaneously address the collapsibility of shallow soil layers. The cover plate on the sleeve prevents debris from entering and affecting construction. 2. Due to uneven subsidence caused by varying immersion rates or other factors, the channels may become skewed, affecting immersion efficiency and water consumption calculations. The integral structure effectively avoids this. 3. It can be disassembled and reused, saving resources. 4. Various types of loads can be selected; for example, soil, machinery, or other items can be chosen, simply placed evenly on the base plate. The thickness of the base plate is determined by rough calculation. Different component sizes are used for different working conditions. Large-scale projects use large-diameter sleeves, while small-scale projects use small-diameter sleeves. The specific situation is determined according to the needs of the construction site. First, the weight of the sleeve, support, and cover plate is calculated and simplified into surface load. Then, the steel plate thickness can be estimated according to the steel plate thickness calculation formula to avoid steel waste and reduce costs.

[0077] Step S4: Connect the water injection pipe and inject water through the reservoir. Operate the water injection device to continuously immerse the foundation in water and observe the collapsibility deformation until the foundation is saturated and the collapsibility is eliminated. The immersion time is stopped when the collapsibility deformation stabilizes. The standard for stable collapsibility deformation is that the average collapsibility amount in the last 5 days is less than 1 mm / d. When the thickness of the collapsible loess layer being treated is greater than 20 m, the standard for stable settlement is that the average collapsibility amount in the last 5 days is less than 2 mm / d. Insert the lower water injection pipe into the sleeve through the water injection hole on the cover plate. Inside the cylinder, the lower water injection pipe and the upper water injection pipe are connected by threads, and the upper water injection pipe is also connected by threads to the upper drain pipe. A flow rate controller is installed on the water injection pipe. When water is injected, the calculated water consumption varies due to different hole depths. The flow rate controller can be used to adjust different rates to achieve the estimated water consumption and reduce water waste. The lower water injection pipe has a drain hole and filter screen similar to the sleeve. The lower water injection pipe extends out of the water injection hole on the cover plate for easy connection with the upper water injection pipe.

[0078] Water flows sequentially through the main drain pipe, pressure pump, secondary drain pipe, upper injection pipe, lower injection pipe, and sleeve. The advantage of the lower injection pipe not contacting the soil is: 1. The filter screens on the sleeve and drain pipe provide double protection, preventing clogging of the lower injection hole and thus avoiding damage to the entire system. 2. In case of clogging, the outer sleeve will clog first, making the phenomenon easier to observe. Workers can then promptly shut off the water supply and take appropriate measures.

[0079] Step S5: After the water supply is stopped, the water injection pipe can be disassembled, the lower water injection pipe can be pulled out, and water can be pumped out to start the water discharge. The drainage consolidation and settlement can be observed. After the settlement is stable, proceed to the next step.

[0080] Step S6: Remove the drainage pipe. If a load has been placed, remove the load first, then remove the heating element, sleeve, support, base plate, isolation plate, and drainage device in sequence. After pre-soaking, test the bearing capacity of the foundation according to the construction requirements to determine whether pile foundation construction is required. If the bearing capacity is high after pre-soaking, fill and compact the duct with crushed stone, sand, etc. If the bearing capacity is low, carry out pile foundation construction. Since the collapsibility of the shallow and deep layers has been completely eliminated, water-proofing and drainage measures can now be taken for the roadbed. Lay out and level the site, mark the filling range of the cement cushion layer, determine the position of the water-stop curtain on both sides of the roadbed, and construct the water-stop curtain along the outer side of the two slope toes of the roadbed according to the existing construction process: construct the jet grouting pile water-stop curtain.

[0081] Step S7: After the water-stop curtain is completed, level the foundation and pour concrete in layers with a thickness of more than 1 meter. Before pouring each layer, place geocells and fix them with ribbed steel bars through the clamps. The layer thickness is 20-50cm. When pouring each layer, remove the laitance, weak concrete layer and loose stones from the pouring surface and expose the coarse aggregate evenly. Before pouring the upper layer of concrete, use pressurized water to wash the surface of the concrete to remove dirt and fully moisten it, but there should be no water. For non-pumped and low-flow concrete, grouting measures should be taken when pouring the upper layer of concrete.

[0082] Step S8: After the roadbed is laid, waterproof geotextile is laid on the slope and then compacted with soil to prevent water seepage on the slope. Drainage ditches are set on both sides of the roadbed.

[0083] Step S9, final acceptance.

[0084] Preferably, step S4 further includes: if construction is carried out in winter, adding antifreeze to the water during water injection, with ethylene glycol as the antifreeze agent. Ethylene glycol as an antifreeze agent has advantages such as high flash point, low volatility, wide availability of raw materials, and low price, therefore ethylene glycol is used as the antifreeze agent.

[0085] Preferably, step S6, constructing the water-stop curtain, includes: first, constructing 3-4 rows of jet grouting piles, all arranged in a quincunx pattern, i.e., one jet grouting pile in the middle row is surrounded by four jet grouting piles from other rows, with adjacent jet grouting piles tangentially arranged; then, filling the spaces between the jet grouting piles with inter-pile soil, ensuring the permeability coefficient of the jet grouting water-stop curtain is less than 10. 7cm / s; or, construct a compaction pile water-stop curtain. First, construct 3-4 rows of compaction piles, all arranged in a staggered pattern, i.e., one compaction pile in the middle row is surrounded by four compaction piles from other rows, with adjacent compaction piles tangentially arranged. Then, fill the spaces between the compaction piles with inter-pile soil. The lower end of the compaction pile water-stop curtain penetrates the lower limit of collapsible loess, and the permeability coefficient of the compaction pile water-stop curtain is less than 10. 7 cm / s.

[0086] Preferably, step S7 further includes: adding an antifreeze agent to the concrete to synthesize modified concrete, wherein the antifreeze agent includes an air-entraining agent, a porous material and a hydrophobic material, wherein the air-entraining agent includes polysiloxane; the porous material includes one or a combination of two of zeolite and diatomite; and the hydrophobic material includes one or a combination of more than two of stearic acid, calcium stearate and paraffin.

[0087] The amount of antifreeze agent used is 0.5-1% of the weight of the cementitious materials in the building materials. The lignin fiber amendment layer is prepared according to the following mass ratio principle: lignin fiber accounts for 0.5-1.0%, and loess accounts for 99.0-99.5%, with the loess being crushed and sieved before use. The lignin fiber is a high-molecular polymer material processed from cotton pulp, with strong water control; in its free state, it can absorb 15-20 times its own weight in water. The lignin fiber length is 0.5-1.5 mm, the average diameter is 30-50 μm, the moisture content is less than 5%, and the ash content is 14-18%. After the modified concrete layer is completed, construction surveying and layout are carried out, the roadbed cross-section is checked, pre-construction review and testing are conducted, and a test section is filled to determine the optimal roadbed compaction scheme. The loose paving coefficient is determined based on site conditions, and layered filling is performed. During filling, the "section flow method" is followed, with horizontal layering across the entire width laterally and horizontally in the longitudinal direction. Filling begins from the bottom layer and proceeds upwards in the following order: lignin fiber treated layer—3:7 lime-soil bonding layer—large gravel layer—3:7 lime-soil bonding layer—crushed stone layer—3:7 lime-soil bonding layer—modified concrete layer—3:7 lime-soil bonding layer—modified asphalt concrete layer. The paving area of ​​each layer is calculated based on the loose paving thickness, and the stockpile size is determined. The filling should be carried out in layers with a density of ≤30cm and ≥10cm, starting from the bottom up. The same type of fill material should be used for the entire width of each horizontal layer, and the cumulative compaction thickness of each type of fill material should not be less than 50cm. When using crushed stone or rock fill, the maximum compaction thickness of each layer should not exceed 35cm, and the minimum layer thickness should not be less than 10cm. Construction lines should be laid out for each layer, marking the centerline and edge lines. To ensure effective compaction at the edges of the fill layers, the roadbed on both sides should be widened by 30-50cm during filling. The filling should be carried out in horizontal layers along the entire width of the cross-section, with a 3:7 lime-soil connecting layer between each layer for seepage prevention and insulation.Bulldozing is used to evenly pave the basic road surface across the entire width. After one initial static compaction with a smooth-drum roller, the surface elevation reaches the loose paving thickness determined in the test section, followed by two more compactions with a smooth-drum roller. A measurement section is set every 20m longitudinally, with 2-4 measuring points per section. The coarse and fine materials in each paving layer should be evenly distributed. Vibratory compaction: The moisture content of the filler is controlled within the range of 2% as determined by heavy compaction tests. If the moisture content exceeds 2%, it should be dried or watered and mixed promptly. When the filler is within the optimal moisture content control range, compaction can begin. A roller is used, moving parallel to the road surface, compacting from both sides to the middle, following the steps of static compaction, weak vibration, and strong vibration. The initial compaction speed of the roller is 2-3 km / h, and the maximum initial compaction speed should not exceed [a certain value]. The compaction speed is 3-4.5 km / h for the secondary compaction and no more than 5 km / h for the final compaction. The compaction speed is 3-6 km / h for the final compaction and no more than 6 km / h for the final compaction. Construction joints are overlapped during compaction. For straight sections, compaction proceeds from both sides towards the middle, and for curved sections, compaction proceeds from the inside to the outside, in a longitudinal advancing and retreating manner. The transverse wheel tracks overlap by no less than 40 cm, and the longitudinal overlap between two adjacent sections is no less than 2.0 m. The joints of the upper and lower fill layers are staggered by no less than 3 m. Finishing and shaping: Finishing is carried out simultaneously with the paving and compaction of each fill layer to ensure that the fill slope is neat and smooth. The compaction equipment moves to the edge, and the slope is compacted every 0.9-1.5 m of fill. After the roadbed is filled, the slope is finished according to the design, excess fill is removed, and the slope is tamped. Modified asphalt concrete construction: Restore the centerline on the accepted base course (during bottom and surface layer construction). Measure the horizontality by driving stakes every 5-10 meters at a distance of 0.3-0.5m outside the edge line, establish a baseline, draw the edge line, and determine the loose paving coefficient, construction process, machinery allocation, personnel organization, number of compaction passes, and check the compaction degree, asphalt content, aggregate gradation, and various Marshall technical indicators of the asphalt mixture. Add antifreeze to the asphalt mixture during mixing. Select 1-2 high-density asphalt concrete pavers with automatically adjustable paving thickness and leveling devices, heated vibrating screeds, and good operating conditions, based on the road width. The bottom, middle, and surface layers are constructed using the line-following method, while the surface layer is constructed using the drag-bar method. The paver travels evenly, with its speed matching the mixing plant's output to ensure uniform and uninterrupted paving. Do not arbitrarily change speed during paving; minimize interruptions. The paving temperature of asphalt concrete should be adjusted according to air temperature changes, and should be checked and recorded continuously during the paving process. The screed of the paver should be heated before paving. When using a two- or three-paver tiered approach, the distance between adjacent pavers should be controlled at 10–30 meters. The tracks of the two pavers should overlap by 5–10 cm. During paving, the paving quality should be checked continuously, and any segregation, missing material at edges, or other issues should be manually replenished or replaced promptly. The elevation and paving thickness should be checked continuously during paving, and the operator should be notified immediately.In areas where pavers cannot operate, manual paving will be used with the approval of the supervising engineer. Two double-drum, double-vibrating rollers will be used, closely following the paver, for 4-6 passes of combined compaction. Final compaction: 1-2 passes of static compaction with double-drum, double-vibrating rollers. For corners and edges that cannot be compacted by the roller, vibratory tampers will be used to compact the mixture. Compaction will be carried out longitudinally from the lower edge to the higher edge at the specified speed. The overlap width between adjacent compacted sections should be greater than 30cm. Joint treatment: During construction, a 20-30cm wide section of the paved mixture will be left uncompacted as an elevation reference for the subsequent paving. The subsequent paving will be completed immediately, and the joint will be compacted across the joint to remove any traces. When hot jointing is not possible for half-width construction, manual planing or cutting will be used to straighten the joint. Before paving the other half, the edges must be cleaned and a small amount of tack coat asphalt applied. When paving, overlap the new layer by 5-10cm. After paving, manually remove the mixture. During compaction, first drive on the already compacted road surface and compact the new layer for 10-15cm, then compact the new part, extending another 10-15cm beyond the already compacted road surface to fully compact the joint tightly. Treatment of transverse joints: First, use a 3m straightedge to check the end flatness. If it does not meet the requirements, cut it clean perpendicular to the road centerline. After cleaning, apply a tack coat of asphalt to the end and then continue paving. Adjust the reserved height during paving. After the paving layer at the joint is completed, check the flatness again with a 3m straightedge and immediately treat it manually. For transverse joint compaction, first use a double-drum, double-vibration roller. During compaction, the roller should be positioned on the already compacted mixture layer, extending 15cm into the new layer. Then, move the roller 15-20cm towards the new mixture with each pass until it is entirely on the new layer, then switch to longitudinal compaction.

[0088] A thick collapsible loess subgrade structure and its construction method in seasonally frozen areas have the following advantages:

[0089] Multi-layered frost protection, including an frost-resistant cushion layer, a lignin fiber treatment layer, and modified concrete, all contribute to effective frost resistance and reduce roadbed damage in winter. A new type of sleeve is employed, providing support to prevent borehole wall collapse and offering weight during pre-soaking and settlement, allowing the drill bit to better facilitate ground subsidence under its own weight.

[0090] The water injection system employs a new type of sleeve and injection pipe. During pre-immersion, the injection pipe is prone to clogging. The sleeve combined with the injection pipe provides double protection, reducing the likelihood of clogging during injection. Even if clogging does occur, the outer sleeve will clog first, making the phenomenon easier to observe. Workers can then promptly shut off the water injection and take appropriate measures. The sleeve, base plate, and isolation plate form an integrated structure. When soil pre-immersion collapse occurs, the drill bit on the sleeve reduces the soil's frictional resistance, allowing the self-weight of the integrated structure to accelerate soil collapse. The self-weight of the integrated structure can treat shallow soil layers. Furthermore, depending on the project requirements, additional loads can be placed on the base plate to accelerate collapse efficiency and simultaneously address the collapsibility of shallow soil layers. The cover plate on the sleeve prevents debris from entering and affecting construction. Uneven collapse due to immersion rate or other factors may cause the borehole to become misaligned, affecting immersion efficiency and calculated water consumption. The integrated structure effectively avoids this. This integrated structure can be disassembled and reused, conserving resources.

[0091] The construction scheme offers diverse options, with borehole layout employing both shallow and deep methods. For example, shallow boreholes can utilize shallow compaction piles or crushed stone piles, while deeper boreholes can be constructed using rotary drilling or jet grouting. This eliminates the need for repeated drilling, saving resources. After pre-soaking, roadbed construction proceeds. Based on the bearing capacity testing of the foundation, a decision is made regarding whether pile foundation construction is necessary. If pile foundation construction is required, the methods described above can be followed; otherwise, crushed stone can be directly filled and compacted. Various loading conditions are available. Utilizing an integrated system of sleeves, base plates, and isolation plates, soil, machinery, or other materials can be selected, simply placed evenly on the base plate.

[0092] Each component is easy to disassemble and assemble, and resources can be recycled, saving resources and costs. A flow rate controller is installed on the water injection pipe to easily control the drainage volume and adjust water resources to achieve water conservation. The new sleeve is equipped with slots and seats, with the seats connected to the heating element. This structure, used in conjunction with antifreeze, enables construction in winter. During construction, the heating element is first used to thaw the frozen soil, followed by pre-soaking with antifreeze. After use, the heating element can be pulled out through the slots, achieving a recycling effect.

[0093] Adding antifreeze agents to concrete improves the frost resistance of the roadbed. A new type of geocell is used inside the modified concrete. The geocell has channels for water permeability, and retaining rings on both sides of the channels. These retaining rings are used in conjunction with ribbed steel bars. In existing geocells, when filling the interior, the stress on adjacent cells shifts, causing deformation and affecting the quality of the filling. Using ribbed steel bars to adjust the size and fix the cells effectively avoids this problem. When using geocells, they need to be unfolded as much as possible to maximize utilization, which requires a lot of force to pull. This makes the ground strips at the connection points very prone to breakage. During use, it is not necessary to unfold them to their maximum extent initially. After stretching them to a certain degree, the ribbed steel bars are used to fix and adjust the cells through the retaining rings. In addition, the insertion of the steel bars solves the problem of the tensile force generated by the cell sheets being almost entirely concentrated at the pin shaft, resulting in excessive stress on a single component. Furthermore, this structure is simple to operate.

[0094] This loess roadbed structure incorporates multiple layers of insulation and seepage prevention measures. A 3:7 lime-soil bonding layer is laid at the interface of each layer, serving as both a seepage prevention and insulation measure. This reduces the impact of freeze-thaw cycles in winter, and the multiple bonding layers enhance the interface shear strength and shoving deformation capacity. The multiple frost-resistant measures, including the frost-resistant cushion layer, the lignin fiber treatment layer, and the modified concrete, all contribute effectively to frost resistance and reduce roadbed damage in winter.

[0095] The loess roadbed structure has good drainage, seepage prevention, heat preservation and frost resistance. The large sand and gravel layer and the crushed stone layer play a drainage role, the 3:7 lime-soil connecting layer has a good heat preservation and seepage prevention effect, the water-stop curtain can block the exchange of water layers inside and outside the roadbed, and the frost-resistant cushion layer, the lignin fiber treatment layer and the modified concrete layer have a good frost resistance effect.

[0096] In summary, although the present invention has been disclosed above with reference to preferred embodiments, the above preferred embodiments are not intended to limit the present invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope defined in the claims.

Claims

1. A roadbed structure for thick collapsible loess in a seasonally frozen region, characterized in that, It includes a immersion pit (16) and a water storage tank (1) located on the ground surface (7). The bottom of the immersion pit (16) is provided with a bottom plate (9). The immersion pit (16) is surrounded by an isolation plate (4), and the isolation plate (4) is fixedly connected to the bottom plate (9) to form a whole that can be stacked. The immersion pit (16) is provided with multiple water injection holes. The water storage tank (1) is connected to a main drain pipe (2) on the right side. A pressure water pump (3) is installed on the main drain pipe (2). The main drain pipe (2) is located in the middle of the immersion pit (16). Multiple secondary drain pipes are alternately arranged on both sides of the main drain pipe (2). Each secondary drain pipe is connected to an upper water injection pipe (7). Each upper water injection pipe (7) is equipped with a bracket (5) corresponding to the bottom plate (9). A flow rate controller (7-2) is installed on the upper water injection pipe (7). The upper water injection pipe (7) is connected to a lower water injection pipe (7-4). A sleeve (6) is fitted on the lower water injection pipe (7-4). A cover plate (12) is provided on the sleeve (6). Each lower water injection pipe (7-4) and its sleeve (6) are located in a water injection hole. The diameter of the water injection hole is larger than the diameter of the sleeve (6). The sleeve (6) passes through the bottom plate (9). The sleeve (6) has a drain hole (6-2) on its side, and a filter screen (6-3) is installed on the drain hole (6-2). A drill bit (6-4) is installed at the bottom of the sleeve (6). The surface of the lower water injection pipe (7-4) is provided with the same drain hole (6-2) and filter screen (6-3) as the surface of the sleeve (6). The sleeve (6) has a slot (6-6) and a seat (6-7) installed on its inner side. The seat (6-7) is connected to an electric heating tube (6-1). The upper end of the sleeve (6) has a first round hole (6-5). The side bolt (5-1) of the bracket (5) passes through the first round hole (6-5) and the second round hole (14) on the support leg (13) at the bottom of the cover plate (12) so that the sleeve (6) is fixedly connected to the bracket (5). The surface of the cover plate (12) is provided with a water injection hole (7-3) and a fixing hole (7-5) through which the heating pipe (6-1) and the card holder (6-7) pass. The shape of the fixing hole (7-5) is the same as the outline of the heating pipe (6-1) and the card holder (6-7). The side bolt (5-1) of the bracket (5) passes through the third round hole (15) on the base plate (9) to fix the isolation plate (4), the base plate (9), the bracket (5), the sleeve (6), and the cover plate (12) in place. The immersion pit (16) is provided with a pre-immersion treatment layer (18), and waterproof curtains (19) are provided on the left and right sides of the pre-immersion treatment layer (18). A lignin fiber treatment layer (20), a modified asphalt surface layer (24), and a three-dimensional geocell (25) are laid on the pre-immersion treatment layer (18). The three-dimensional geocell (25) is composed of a cell (28) and a ribbed steel bar (29). The cell (28) has water-permeable holes (30) on the front and back sides of the middle part. The connecting parts of the water-permeable holes (30) on the left and right sides have retaining rings (31). The retaining rings (31) and the ribbed steel bar (29) are used together. A large sand and gravel layer (21) is laid on top of the lignin fiber treatment layer (20), and a crushed stone layer (22) is laid on top of the large sand and gravel layer (21). A 3:7 lime-soil connecting layer (26) is laid at the junction of the lignin fiber treatment layer (20), the large sand and gravel layer (21), and the crushed stone layer (22). The function of the 3:7 lime-soil connecting layer (26) is to provide multi-layer insulation and seepage prevention, avoiding water accumulation inside and freeze-thaw in winter. Drainage ditches (27) are set on the left and right sides of the waterproof curtain (19), and waterproof geotextile treatment layers (32) are set on both slope protection layers of the pre-soaked water treatment layer (18).

2. The roadbed structure of thick collapsible loess in a seasonally frozen area according to claim 1, characterized in that, The multiple drainage pipes include a first drainage pipe (8) and a second drainage pipe (10) that are alternately arranged at intervals. Each first drainage pipe (8) is connected to 3 upper water injection pipes (7), and each second drainage pipe (10) is connected to 2 upper water injection pipes (7). The water consumption of the first drainage pipe (8) is greater than that of the second drainage pipe (10).

3. The roadbed structure for thick collapsible loess in a seasonally frozen zone according to claim 1, characterized in that, The upper water injection pipe (7) is provided with threads (7-1) at both ends. The two ends of the upper water injection pipe (7) are respectively connected to the secondary drainage pipe and the lower water injection pipe (7-4) through threads (7-1).

4. The roadbed structure of thick collapsible loess in a seasonally frozen area according to claim 1, characterized in that, A support (11) is provided on the side of the immersion pit (16) away from the water storage tank (1), and the support (11) is used to support the main drainage pipe (2).

5. A roadbed structure for thick collapsible loess in a seasonally frozen zone according to claim 1, characterized in that, The base plate (9) is a steel plate.

6. A construction method for a thick collapsible loess subgrade structure in a seasonally frozen zone, implemented using the thick collapsible loess subgrade structure described in any one of claims 1 to 5, characterized in that... The construction method includes: Step S1: Based on the survey data and design requirements, determine the treatment depth and range for completely or partially eliminating the subsidence of the loess foundation, and then confirm the immersion depth and the size of the immersion test pit; the thickness of the bottom plate is determined by rough calculation. Different component sizes are used for different working conditions. Large-scale projects select large-diameter sleeves, and small-scale projects select small-diameter sleeves. The specific situation is determined according to the needs of the construction site; first, calculate the weight of the sleeve, support, and cover plate, simplify it into surface load, and then estimate the steel plate thickness according to the steel plate thickness calculation formula to achieve the purpose of saving steel. Step S2: Determine the layout of the water injection holes, calculate the volume of the wetted loess and the amount of water to be injected based on the required depth and radius, and determine the location of the water injection holes. Step S3: Drill the water injection hole according to the existing process; after the water injection hole is drilled, place the sleeve into the water injection hole. The diameter of the water injection hole is slightly larger than the sleeve. The sleeve can provide support and prevent the hole wall from collapsing. A drill bit is set at the lower end of the sleeve. Drainage holes are set around the sleeve, and filter screens are set on the drainage holes. A slot and a seat are installed on the inner side of the sleeve. The seat is connected to the electric heating tube, and the electric heating tube is electrically connected to the water storage tank. The water storage tank is powered by a generator or solar panel; after completing the above steps, place the base plate on the sleeve, and the lower end of the support... The round holes are aligned with the round holes on the wooden board and connected with bolts. The round holes at the top of the bracket are bolted to the round holes at the top of the sleeve. The bolts pass through the round holes at the top of the bracket, the first round hole at the top of the sleeve, and the second round hole of the support leg on the cover plate. Then, a water-proof plate is installed around the immersion pit to avoid affecting the soil on both sides of the road. The water-proof plate is bolted to the bottom plate, so that the water-proof plate, bottom plate, sleeve, bracket, and cover plate are fixedly connected. All of the above structures need to be treated for corrosion prevention and rust prevention to achieve the recycling of steel components. Step S4: Connect the water injection pipe and inject water through the reservoir. Operate the water injection device to continuously immerse the foundation in water and observe the collapse deformation until the foundation is saturated and the collapse is eliminated. Stop the immersion time based on the stability of the collapse deformation. The standard for stable collapse deformation is that the average collapse amount in the last 5 days is less than 1 mm / d. When the thickness of the collapsible loess layer is greater than 20 m, the standard for stable settlement is that the average collapse amount in the last 5 days is less than 2 mm / d. Insert the lower water injection pipe into the sleeve through the water injection hole on the cover plate. The lower water injection pipe is threaded to the upper water injection pipe, and the upper water injection pipe is threaded to the upper drainage pipe. The water injection pipe is equipped with a flow rate controller. When water is injected, the calculated water consumption varies due to different hole depths. The flow rate controller is used to adjust different rates to achieve the estimated water consumption and reduce water waste. The lower water injection pipe has a drainage hole and a filter screen. The lower water injection pipe extends out of the water injection hole on the cover plate for easy connection with the upper water injection pipe. Step S5: After the water supply is stopped, disassemble the water injection pipe, pull out the lower water injection pipe, and use a water pump to pump water to start the water discharge. Observe the drainage consolidation and settlement. Proceed to the next step after the settlement has stabilized. Step S6: Remove the drainage pipe. If a load has been applied, remove the load first, then remove the heating element, sleeve, support, base plate, isolation plate, and drainage device in sequence. After pre-soaking, test the bearing capacity of the foundation according to the construction requirements to determine whether pile foundation construction is necessary. If the bearing capacity is high after pre-soaking, fill and compact the duct with crushed stone and gravel. If the bearing capacity is low, carry out pile foundation construction. Since the collapsibility of the shallow and deep layers has been completely eliminated, water-proofing and drainage measures can now be taken for the roadbed. Lay out and level the site to mark the filling range of the cement cushion layer. Determine the position of the water-stop curtain on both sides of the roadbed. Construct the water-stop curtain along the outer side of the two slope toes of the roadbed according to the existing construction process: construct the jet grouting pile water-stop curtain. Step S7: After the water-stop curtain is completed, level the foundation and pour concrete in layers with a thickness of more than 1 meter. Before pouring each layer, place geocells and fix them with ribbed steel bars through the clamps. The layer thickness is 20-50cm. When pouring each layer, remove the laitance, weak concrete layer and loose stones from the pouring surface and expose the coarse aggregate evenly. Before pouring the upper layer of concrete, wash the surface of the concrete with pressurized water to remove dirt and fully moisten it, but there should be no water. For non-pumped and low-flow concrete, grouting measures should be taken when pouring the upper layer of concrete. Step S8: After the roadbed is laid, waterproof geotextile is laid on the slope and then compacted with soil to prevent water seepage on the slope. Drainage ditches are set on both sides of the roadbed. Step S9, final acceptance.

7. The construction method for a thick collapsible loess subgrade structure in a seasonally frozen zone according to claim 6, characterized in that, Step S3 also includes: the steel structure base plate, water-proof plate, sleeve, bracket, and cover plate need to be treated for corrosion and rust prevention, using water-based anti-corrosion coatings: First, surface treatment is carried out, cleaning and treating the steel structure surface to remove dust, grease, rust, and other contaminants; surface treatment is performed using sandblasting, polishing, or brushing methods to ensure the surface is clean, smooth, and provides good adhesion; then, a primer is applied, selecting a suitable primer product for the water-based anti-corrosion coating, which needs to be applied quickly after surface preparation to prevent new contaminants from adhering; then, an intermediate coating is applied, after the primer is completely dry, one or more layers of the intermediate coating of water-based anti-corrosion coating are applied; finally, a topcoat is applied, applying the topcoat of water-based anti-corrosion coating, which provides final anti-corrosion protection and decorative effect.

8. A construction method for a thick collapsible loess subgrade structure in a seasonally frozen zone according to claim 6, characterized in that, Step S4 also includes: if construction is carried out in winter, add antifreeze to the water during water injection, with ethylene glycol as the antifreeze agent.

9. A construction method for a thick collapsible loess subgrade structure in a seasonally frozen zone according to claim 6, characterized in that, Step S6, constructing the water-stop curtain, includes: first, constructing 3-4 rows of jet grouting piles, all arranged in a quincunx pattern, i.e., one jet grouting pile in the middle row surrounded by four jet grouting piles from other rows, with adjacent jet grouting piles tangentially arranged; then, filling the spaces between the jet grouting piles with inter-pile soil. The permeability coefficient of the jet grouting pile water-stop curtain is less than 10. 7 cm / s; or, construct a compaction pile water-stop curtain. First, construct 3-4 rows of compaction piles, all arranged in a staggered pattern, i.e., one compaction pile in the middle row is surrounded by four compaction piles from other rows, with adjacent compaction piles tangentially arranged. Then, fill the spaces between the compaction piles with inter-pile soil. The lower end of the compaction pile water-stop curtain penetrates the lower limit of collapsible loess, and the permeability coefficient of the compaction pile water-stop curtain is less than 10. 7 cm / s.

10. A construction method for a thick collapsible loess subgrade structure in a seasonally frozen zone according to claim 6, characterized in that, Step S7 also includes: adding an antifreeze agent to the concrete to synthesize modified concrete. The antifreeze agent includes an air-entraining agent, a porous material, and a hydrophobic material. The air-entraining agent includes polysiloxane. The porous material includes one or a combination of two of zeolite and diatomite. The hydrophobic material includes one or a combination of more than two of stearic acid, calcium stearate, and paraffin.

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