A kind of cold region tunnel anti-frost heaving structure based on frozen soil replacement

Abstract

The application provides a cold region tunnel anti-frost heaving structure based on frozen soil replacement, which comprises a frozen soil replacement area arranged outside a tunnel lining, a plurality of sand and stone filler bags are stacked in the frozen soil replacement area, and the sand and stone filler bags are connected into an integral whole through solidified cement-based slurry. The sand and stone filler bag comprises a polymer film bag and concrete stones solidified in the polymer film bag. The application completely blocks the interaction between the soil outside the tunnel lining and external moisture and temperature, and eliminates the core condition (water-ice phase change volume expansion) of frost heaving. The application adopts a broken grading filler system to realize active cutting of capillary water paths, directional reconstruction of pore structures and multi-stage dissipation of frost heaving energy through coupling of particle size breaks and function enhancement, so that the frost heaving rate is significantly reduced, and the application has high permeability and frost resistance and durability, and is particularly suitable for lining invert and side wall backfill areas of railway, highway and water conservancy tunnels which are seriously affected by frost heaving soil.

Description

Technical Field

[0001] This application relates to the field of tunnel protection technology, and in particular to a frost-resistant structure for cold-region tunnels based on permafrost replacement. Background Technology

[0002] 1. Brief description of existing technical solutions:

[0003] In the construction and operation of tunnels in high-altitude, cold regions, tunnel frost damage is a significant problem. With the arrival of winter, the temperature of the surrounding rock in the tunnel rapidly drops below 0°C. At this time, unfrozen water in the surrounding rock freezes into ice, expanding in volume and generating frost heave force. This exerts enormous pressure on the tunnel structure, leading to cracking and deformation of the walls, arch, and foundation.

[0004] For the prevention and control of tunnel frost damage, the main treatment methods at present are insulation, drainage, heating and replacement. (1) Insulation usually uses passive insulation materials such as polyurethane foam and insulation board to isolate the outside low temperature and reduce the freezing of the surrounding rock. However, its long-term performance is easily affected by freeze-thaw cycles. After the material absorbs water, the thermal conductivity increases and the insulation effect decreases year by year. At the same time, the insulation layer only delays heat exchange and cannot prevent the transmission of frost heave force. Moreover, the insulation efficiency decreases significantly in the extreme low temperature environment at high altitude. (2) Drainage involves laying waterproof board between the lining and the surrounding rock and burying drainage pipes in the circumferential and longitudinal gaps between the initial support and the secondary lining. However, traditional drainage pipes are prone to failure due to ice blockage, which leads to the inability to drain water from the surrounding rock and aggravates frost heave. The joints of the waterproof board are prone to cracking due to frost heave, forming leakage channels and accelerating structural damage after freeze-thaw cycles. In addition, factors such as tunnel length, air temperature, wind direction and slope need to be considered. Combined with long-term temperature monitoring data, different drainage measures need to be set for different temperature ranges, which is very troublesome. (3) Heating methods use heat to prevent freezing, but active heating technologies such as electric heating or ground source heat pumps consume a lot of energy and face problems such as unstable power supply and difficult equipment maintenance in high-altitude areas; local heating can easily cause uneven temperature gradients, leading to thermal stress concentration and inducing lining cracking. (4) Replacement methods replace the soil and rock materials around the tunnel that are prone to frost heave with materials with good frost resistance, such as coarse-grained soil and gravel, to reduce the source of frost heave and thus reduce the damage of frost heave to the tunnel structure. Replacement methods are the "fundamental solution" for frost resistance in cold-region tunnels. By replacing materials, the risk of frost heave is reduced from the root. However, if the replacement range or material selection is inappropriate, it may lead to a decrease in the bearing capacity of the surrounding rock or new drainage problems.

[0005] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Utility Model Content

[0006] The purpose of this application is to provide a frost-resistant tunnel structure for cold regions based on permafrost replacement, which eliminates the source of frost heave, avoids the generation of frost heave force from the root, improves structural stability, and reduces operating costs and maintenance difficulty, so as to solve or alleviate the problems existing in the prior art.

[0007] To achieve the above objectives, this application provides the following technical solution:

[0008] A frost heave-resistant structure for cold-region tunnels based on frozen soil replacement includes a frozen soil replacement zone set outside the tunnel lining. The frozen soil replacement zone is filled with a plurality of sand and gravel packing bags stacked together and connected to each other by a solidified cement-based grout. The sand and gravel packing bags include a polymer membrane bag and concrete aggregate solidified inside the polymer membrane bag.

[0009] Furthermore, the thickness of the frozen soil replacement zone is 45cm-55cm.

[0010] Furthermore, the height of the permafrost replacement zone is more than two-thirds of the tunnel height.

[0011] In one embodiment, the polymer film bag comprises a high-density polyethylene (HDPE) film bag, the HDPE film bag having a thickness of 1.0-3.0 mm.

[0012] In one embodiment, the polymer film bag includes a high-density polyethylene (HDPE) film bag and a mesh bag fitted over the HDPE film bag.

[0013] In a preferred embodiment, the polymer film bag has a double-layer structure, with the inner layer being a high-density polyethylene (HDPE) base film and the outer layer being a composite antifreeze and tear-resistant polyester fiber mesh; the composite antifreeze and tear-resistant polyester fiber mesh includes a polyester fiber mesh body and a coating applied to its surface to improve freeze-thaw cycle performance; the coating thickness is 20-30 μm.

[0014] Furthermore, the concrete aggregate is formed by the solidification of a mixture of sand and gravel filler and cement slurry, wherein the sand and gravel filler is a mixture of coarse aggregate, medium sand and fine sand.

[0015] Furthermore, the coarse aggregate has a particle size range of 10-50 mm, the medium sand has a particle size range of 2-5 mm, and the fine sand has a particle size range of 0.1-0.3 mm.

[0016] Furthermore, the coarse aggregate is selected from angular basalt crushed stone, with a needle-like and flaky particle content of <12% and a crushed surface ratio of ≥70%.

[0017] Furthermore, a waterproof layer is provided between the tunnel lining and the frozen soil replacement zone, and a moisture-proof layer is provided on the inner surface of the tunnel lining.

[0018] Compared with the closest prior art, the technical solution of this application has the following beneficial effects:

[0019] This application completely blocks the interaction between the soil surrounding the tunnel lining (partially or entirely replaced by sand and gravel filler bags) and external moisture and temperature through polymer membrane bags, eliminating the core condition for frost heave (volume expansion during water-ice phase change). This application employs a graded filler system that couples particle size distribution with functional enhancement to actively cut off capillary water pathways, directionally reconstruct pore structure, and dissipate frost heave energy at multiple stages, significantly reducing the frost heave rate. It also possesses high permeability and freeze-thaw resistance, making it particularly suitable for the backfill areas of the lining arches and sidewalls in railway, highway, and hydraulic tunnels severely affected by frost-susceptible soil. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein:

[0021] Figure 1 This is a structural schematic diagram of an embodiment of the present utility model.

[0022] Figure 2 This is a schematic diagram of the structure of the sand and gravel filler bag according to an embodiment of the present invention.

[0023] Explanation of reference numerals in the attached figures:

[0024] 1-Frozen soil replacement zone, 2-Sand and gravel filler bag, 3-Waterproof layer, 4-Tunnel lining, 21-Concrete aggregate, 22-Inner layer, 23-Outer layer, 24-Filling grouting seal. Detailed Implementation

[0025] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present application without departing from the scope or spirit thereof. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present application encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing embodiments of this disclosure only and is not intended to limit this disclosure.

[0027] In the description of this application, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and do not require that this application be constructed and operated in a specific orientation, and therefore should not be construed as limiting this application. The terms "connected," "linked," and "set up" used in this application should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; direct connections or indirect connections through intermediate components; wired connections, radio connections, or wireless communication signal connections. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0028] like Figures 1-2 As shown, a frost-resistant tunnel structure for cold regions based on frozen soil replacement includes a frozen soil replacement zone 1 set outside the tunnel lining 4. The frozen soil replacement zone 1 is filled with a plurality of sand and gravel filler bags 2, which are connected to each other by a solidified cement-based grout. The sand and gravel filler bags 2 include a polymer membrane bag and concrete aggregate 21 solidified inside the polymer membrane bag.

[0029] Furthermore, such as Figure 1 As shown, a waterproof layer 3 is provided between the tunnel lining 4 and the frozen soil replacement zone 1, and a moisture-proof layer is provided on the inner surface of the tunnel lining 4. The waterproof layer 3 and the moisture-proof layer are provided according to conventional tunnel construction methods; the waterproof layer 3 in a tunnel is generally a waterproof membrane, and the moisture-proof layer is a highly dense coating. Furthermore, as... Figure 1 As shown, the thickness of the frozen soil replacement zone 1 is 45cm-55cm, and the height of the frozen soil replacement zone 1 is more than two-thirds of the tunnel height. Preferably, to reduce the amount of work, the height of the frozen soil replacement zone 1 is 2 / 3 of the tunnel height, and it is not necessary to completely replace it. To avoid disturbing the original soil bearing area, the thickness range of the frozen soil replacement zone 1 is limited to a 50cm annular band on the outer side of the tunnel lining 4.

[0030] Furthermore, to address the varying sizes of frozen soil replacement zones 1, during the design phase, standard dimensions of polymer membrane bags were customized based on the tunnel cross-section, primarily determined by the tunnel cross-section shape and the length of the construction section. A 15-20cm overlap allowance was reserved based on the unfolded perimeter of the excavation outline of frozen soil replacement zone 1. This overlap allowance refers to the dimensional redundancy reserved in the prefabrication design phase to compensate for manufacturing errors, construction deformation, and curvature deformation; it is a fundamental manufacturing parameter for a single membrane bag. Additionally, an expansion of 5%-15% was added for sections with different curvatures, such as the arch and sidewalls, to compensate for bending deformation.

[0031] In one embodiment, such as Figure 2As shown, the polymer membrane bag has a double-layer composite membrane structure. The inner layer 22 is a high-density polyethylene (HDPE) base film, and the outer layer 23 is a composite antifreeze and tear-resistant polyester fiber mesh. The composite antifreeze and tear-resistant polyester fiber mesh includes a polyester fiber mesh body and a coating applied to its surface to improve freeze-thaw cycle resistance. The recommended mesh size of the polyester fiber mesh body is 25mm×25mm-30mm×30mm. The coating thickness is 20-30μm, and the coating material is silicone resin (Dow Chemical, model SILASTIC). ® 590) and nano silica (Evonik Degussa, model AEROSIL) ® The composite coating has an average particle size of 20-30 nm for nano-silica; the mass ratio of organosilicon resin to nano-silica in the coating is (2.8-3.2):1. The high-density polyethylene (HDPE) membrane bags in this embodiment and the following two embodiments require high tensile strength and must meet the environmental requirements of tunnels in cold regions. For example, HDPE geomembrane from Shandong Dezhou Guangying New Material Co., Ltd., item number DF-1001, can be used, which has high tensile strength and can be used in environments ranging from -70℃ to 110℃. Mechanical properties of a single sand and gravel filler bag 2 using the double-layer composite membrane structure of this embodiment were tested. The peak compressive strength was 18.6 MPa and the elastic modulus was 2.35 GPa, which are 4.4 times and 3.5 times that of undisturbed frost-susceptible soil, respectively. The cohesion was 45 kPa and the comprehensive shear capacity (internal friction angle 38.5°) was 1.8 times that of traditional sand replacement. After 100 freeze-thaw cycles, the compressive strength of the sand and gravel packing bag 2 remained at 91%, while that of the traditional material was only 63%. The traditional material refers to the continuously graded sand and gravel packing used in the conventional replacement method for preventing frost damage in tunnels in cold regions.

[0032] In another embodiment, the polymer film bag has a single-layer structure and is a high-density polyethylene (HDPE) film bag with a thickness of 1.0-3.0 mm (e.g., 1 mm, 1.5 mm, 1.7 mm, 2 mm, 2.5 mm, 2.8 mm). Preferably, in this embodiment, the outer surface of the high-density polyethylene (HDPE) film bag is coated with a coating to improve its resistance to freeze-thaw cycles.

[0033] In another embodiment, the polymer membrane bag has a double-layer structure, comprising a high-density polyethylene (HDPE) membrane bag and a mesh bag fitted over the HDPE membrane bag. The mesh bag is also required to meet the environmental requirements of cold-region tunnels and can be selected from existing mesh bags, such as nylon mesh bags or polyester fiber mesh. Preferably, in this embodiment, the outer surface of the HDPE membrane bag is coated with a coating to improve its resistance to freeze-thaw cycles.

[0034] Furthermore, the polymer membrane bag is provided with a filler injection port, which is vented after filling and then sealed by heat fusion. Figure 2 The diagram schematically illustrates the grouting seal 24 after closure; the vacuum level inside the membrane bag after venting is recommended to be 80%-90%. The empty polymer membrane bag unfolds into a rectangle and can be folded or rolled into a roll during transportation for easy transport and filling. The filling rate of the sand and gravel filler inside the polymer membrane bag is 85%-95% (by volume) to ensure density and avoid over-compression. Excessive compression may lead to aggregate structure damage and functional deterioration due to overfilling or excessive compaction. After filling, the polymer membrane bag has a flat, near-cylindrical shape (similar to the effect of filling common sandbags), matching the tunnel contour.

[0035] Furthermore, the concrete aggregate 21 is formed by the solidification of a mixture of sand and gravel filler and cement slurry, wherein the sand and gravel filler is a mixture of coarse aggregate, medium sand, and fine sand. Based on the requirements for frost heave resistance and rapid drainage of the replacement layer in polar permafrost tunnels, the polymer membrane bag filling material uses a discontinuously graded basalt sand and gravel mixture as the sand and gravel filler. The discontinuously graded system forms a three-level synergistic structure of "skeleton support - pore drainage - fine particle stabilization" by precisely controlling the proportion and spatial distribution of particles of different sizes. Its gradation design and performance parameters are as follows:

[0036] ① Coarse aggregate, particle size 10-50mm: angular basalt crushed stone is selected, accounting for 40%-45% of the weight of sand and gravel filler. 5-10mm particles are removed to form the main skeleton gap; particles >50mm are dynamically screened out by a drum screener to avoid puncture of the membrane bag, and the content of needle-shaped and flaky particles is controlled to <12%, and the proportion of crushed surface is ≥70%.

[0037] ② Medium sand, particle size 2-5mm: Natural river sand or manufactured sand is selected, accounting for 25%-30% of the weight of sand and gravel filler. The particle size is strictly limited to the range of 2-5mm. 0.3-2mm particles are removed to block capillary water migration.

[0038] ③ Fine sand layer, particle size 0.1-0.3mm: Quartz sand is selected, accounting for 25%-30% of the weight of sand and gravel filler, with a silica content ≥95%, forming a 0.3-2mm double-break zone with the medium sand layer.

[0039] To investigate the frost heave suppression effect of discontinuous graded fillers, a closed-system frost heave test (-20℃ constant temperature for 48 hours, moisture content 15%) was conducted. The results showed that the frost heave rate of discontinuous graded sand and gravel fillers was only 0.38%, the frost heave force was 12.5 kPa, and no ice lens formation was observed. In the comparative test, the frost heave rate of traditional continuous graded sand and gravel reached 4.72%, the frost heave force was 153.6 kPa, and a 2.1 mm thick ice layer appeared.

[0040] This invention utilizes a multi-layered, graded, and segmented design to effectively suppress frost heave. Its core principle lies in actively cutting off the moisture migration path and reconstructing the system's pore structure. Coarse aggregate forms a large-pore, rigid skeleton as a framework layer, blocking the continuous rise of capillary water. Medium sand acts as a control layer, and its dual-segment design with the fine sand layer disrupts the continuity of the capillary water film. Simultaneously, hydrophobic fine particles reduce the driving force for ice crystal growth. This structure forces moisture to return through a permeability coefficient abrupt change and absorbs frost heave stress through the elastic deformation of the skeleton, thereby reducing the frost heave rate.

[0041] The construction process of this utility model is as follows:

[0042] (1) Identification of frost-susceptible soil and design of replacement depth.

[0043] A three-dimensional model of the base frozen soil was generated by cross-scanning with dual-frequency ground-penetrating radar to identify the distribution range and depth of frost-susceptible soil; the frost-susceptible sensitive area was located; and core samples were taken at 10m intervals to determine the thickness and content of the frost-susceptible soil layer.

[0044] (2) Customized polymer film bags.

[0045] The standard dimensions of the polymer membrane bag are customized according to the tunnel cross-section, with the longitudinal length matching the construction section, and the membrane bag thickness is precisely controlled. This polymer membrane bag maintains extremely high elongation at break even in frigid environments and effectively resists frost heave deformation after being filled with sand and gravel to replace the filler.

[0046] (3) Preparation and filling of graded sand and gravel filler.

[0047] After weighing coarse aggregate, medium sand, and fine sand according to the specified proportions and removing impurities, cement slurry is added and mixed in stages using a forced mixer. First, the coarse aggregate and some of the medium sand are mixed, then the fine sand and the remaining medium sand are added, ensuring a uniform mixture without lumps. When filling the polymer membrane bags, a chute is used to buffer the material flow and control the height. The bags are filled in stages from one end, and compacted by patting and vibration to ensure uniform filling. After filling, the surface is covered with a waterproof cloth and left to stand for 1 hour. Finally, the venting is vented and the filler injection port is sealed by heat fusion. A water spray test is performed to check for leaks at the seams of the polymer membrane bags to prevent segregation of the sand and gravel filler. The polymer membrane bags have high longitudinal tensile strength and high elongation at break. The vibration compaction process forms a stress buffer network in the coarse aggregate layer, effectively preventing penetration of the polymer membrane bags by the sand and gravel filler during filling and handling. The polymer membrane bags are equipped with filler injection ports, which are sealed by heat fusion after filling.

[0048] (4) Frozen soil replacement construction.

[0049] First, based on the tunnel design cross-section, a certain over-excavation range is reserved in the frozen soil replacement zone 1 in advance to facilitate replacement construction; the over-excavation is carried out simultaneously with the main tunnel excavation, forming the tunnel in one go to avoid secondary excavation; after the tunnel excavation is completed, the frozen soil replacement zone 1 on the outer side of the lining is excavated, the slope of the excavation face is controlled, and quick-setting cement mortar is sprayed on the slope to prevent collapse. High-moisture-content frost-susceptible soil is removed first, while low-sensitivity undisturbed soil is retained; temporary steel arch support is required for every 1m increase in excavation depth. Subsequently, with the tunnel axis as the center, a ring-shaped frozen soil zone is excavated radially outward, advancing in three stepped layers: upper, middle, and lower; the excavation depth of each layer does not exceed 2m, and a 30cm thick layer of frozen soil can be reserved as temporary support; the excavation face is cooled in a timely manner to inhibit the warming of the frozen soil.

[0050] Then, based on the depth of the replacement in the frozen soil area, a water-stop curtain is formed around the replacement area, and temporary steel supports are erected to stabilize the stratum. Using an airbag jacking system in conjunction with lubricant, the sand and gravel packing bags 2 filled in step (3) are precisely pressed into the replacement area to ensure that they match the original design outline. The overlap width of adjacent sand and gravel packing bags 2 is ≥30cm. The overlap width is the actual overlap size between adjacent membrane bags during the construction and installation stage. After the sand and gravel packing bags 2 are in place, ultrafine cement-based grout is injected through the reserved grouting pipe to strengthen the contact surface between the sand and gravel packing bags 2. After the grout strength reaches the standard, the temporary support is removed, and convergence measuring points are set up simultaneously to monitor the deformation rate.

[0051] Compared to traditional methods such as drainage, insulation, and heating, which only delay frost heave, this application directly cuts off the transmission path of frost heave force, avoiding instability, cracking, and road surface heave caused by the accumulation of frost heave stress in the lining. Traditional technologies passively address frost heave through "water blocking, insulation, and energy consumption," while this application reconstructs the permafrost environment through a direct replacement active intervention mechanism. It eliminates dual frost heave sources by actively wrapping the graded filler with polymer membrane bags. The polymer membrane bags, through a closed replacement process, operate only within a pre-set over-excavation zone, limiting the heat impact range to a certain area outside the replacement zone, reducing thermal disturbance to the fragmented undisturbed soil, and maximizing the mechanical stability of the undisturbed permafrost. Furthermore, as a physical isolation layer, the polymer membrane bags' nano-modified coating can block moisture migration, allowing the sand and gravel filler bag 2 to deform in tandem with the surrounding permafrost, reducing the efficiency of frost heave stress transmission and effectively suppressing the risk of circumferential cracking in the tunnel lining 4.

[0052] This invention addresses the long-standing problem of lining cracking caused by frost-susceptible soil in tunnel engineering in high-altitude, cold regions. It is particularly suitable for the backfill areas of the lining arch and sidewalls in railway, highway, and hydraulic tunnels severely affected by frost-susceptible soil. The sand and gravel filler bag 2 of this invention can also be used for replacing frozen soil at the bottom of tunnels, solving problems such as track bed heave and invert arch instability.

[0053] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A frost-resistant tunnel structure for cold regions based on frozen soil replacement, comprising a frozen soil replacement zone (1) located outside the tunnel lining (4), characterized in that: The frozen soil replacement zone (1) is filled with several sand and gravel packing bags (2), which are connected to each other by solidified cement-based slurry; the sand and gravel packing bags (2) include polymer membrane bags and concrete stones (21) solidified in the polymer membrane bags.

2. The frost-resistant tunnel structure for cold regions based on permafrost replacement according to claim 1, characterized in that: The thickness of the frozen soil replacement zone (1) is 45cm-55cm.

3. The frost-resistant tunnel structure for cold regions based on frozen soil replacement according to claim 1, characterized in that: The height of the frozen soil replacement zone (1) is more than two-thirds of the tunnel height.

4. The frost-resistant tunnel structure for cold regions based on frozen soil replacement according to claim 1, characterized in that: The polymer film bag includes a high-density polyethylene film bag, and the thickness of the high-density polyethylene film bag is 1.0-3.0 mm.

5. The frost-resistant tunnel structure for cold regions based on frozen soil replacement according to claim 1, characterized in that: The polymer film bag includes a high-density polyethylene film bag and a mesh bag fitted over the high-density polyethylene film bag.

6. The frost-resistant tunnel structure for cold regions based on frozen soil replacement according to claim 1, characterized in that: The polymer membrane bag has a double-layer structure, with the inner layer (22) being a high-density polyethylene base film and the outer layer (23) being a composite antifreeze and tear-resistant polyester fiber mesh; the composite antifreeze and tear-resistant polyester fiber mesh includes a polyester fiber mesh body and a coating applied to its surface to improve the antifreeze-thaw cycle performance; the coating thickness is 20-30μm.

7. The frost-resistant tunnel structure for cold regions based on frozen soil replacement according to claim 1, characterized in that: A waterproof layer (3) is provided between the tunnel lining (4) and the frozen soil replacement zone (1), and a moisture-proof layer is provided on the inner surface of the tunnel lining (4).

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