Method for preventing tunnel portal lining cracking induced by pot cover effect

Abstract

The invention discloses a method for preventing tunnel portal lining cracking induced by the pot cover effect, and relates to the technical field of geotechnical engineering. A designed axial symmetry arc-shaped hydrophobic vapor-proof structure is laid between a tunnel lining and a surrounding stratum, the structure comprises upper-layer perforated closed geotechnical cloth, lower-layer closed geotechnical cloth and middle interlayer silty sand, and blind ditches are formed in the two sides of the structure to dredge accumulated water. In addition, air curtain equipment driven by solar energy and wind energy is installed at the tunnel portal so as to prevent external cold air from entering the tunnel portal, and therefore the temperature difference influence is eliminated. The method can effectively prevent soil layer or rock layer water vapor from migrating to the surface of the tunnel portal lining. Concrete frost heaving and cracking caused by the hydrothermal coupling effect caused by the pot cover effect are avoided, and the strength and stability of the lining structure are ensured. Therefore, the influence of the pot cover effect on tunnel portal lining cracking is eliminated from the source, and tunnel lining engineering disasters caused by the pot cover effect can be effectively prevented and controlled.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to a method for preventing and controlling "pot cover effect"-induced cracking of tunnel opening lining. Background Art

[0002] The "pot lid effect" refers to the phenomenon that, driven by the temperature gradient, water vapor in deep, enclosed soil migrates from warm areas to cold areas and condenses or sublimates, resulting in an increase in the moisture content of shallow soil. This phenomenon is particularly significant in high-latitude seasonal frozen soil areas such as Northwest and Northeast my country. These areas account for about 54% of my country's land area. The climate is dry, cold, and rainy, with sufficient sunshine and dry and windy weather. In addition, the groundwater level is deep and the temperature difference between day and night is large, which can easily cause the "pot lid effect."

[0003] Most of my country's tunnels are located in seasonally frozen soil areas. During construction or operation, tunnel portal lining cracks in winter and leakage during the spring thaw period occur frequently, and the trend is increasing year by year, seriously threatening the tunnel structure and train operation safety. Tunnel excavation destroys the original thermodynamic equilibrium and forms a new thermodynamic system. The temperature difference between the cold air at the tunnel portal and the warm area of ​​the surrounding strata drives the water vapor in the soil or rock layer to migrate to the lining surface, and significantly increases the water content of the area after condensation or sublimation. Under the action of seasonal freeze-thaw cycles, the "pot lid effect" water accumulation will cause different degrees of frost heave force on the upper and inner parts of the lining, and long-term freeze-thaw cycles will eventually cause serious damage to the lining. Therefore, preventing moisture from invading the lining and blocking cold air from entering the tunnel are the two key technologies to solve the problem of lining cracking.

[0004] Traditional protective measures are mainly focused on the lining body, such as adding secondary lining or pasting insulation materials. However, the problem of lining cracking or leakage has not been fundamentally solved, and there is a lack of in-depth analysis of the damage mechanism and specific prevention and control measures. The construction of tunnels in cold regions will continue to increase, and the problem of lining cracking in tunnel portals in seasonally frozen soil areas needs to be solved urgently. In this context, the present invention addresses the defects of the prior art, makes full use of the climatic characteristics of seasonally frozen soil areas, and proposes a method for preventing and controlling the "pot lid effect" that induces cracking of tunnel portal linings. This method not only provides a scientific basis for solving tunnel lining diseases, but also brings potential value for improving driving safety and social and economic benefits. Summary of the invention

[0005] The present invention provides a method for preventing and controlling cracking of tunnel portal lining induced by the "pot lid effect", aiming to solve the problems raised in the background technology. The method aims at preventing engineering disasters such as frost heave cracking and water leakage of tunnel portal lining induced by the "pot lid effect", and ensures the strength and stability of the tunnel lining structure through effective technical means. In addition, the method has the significant advantages of low maintenance cost and convenient construction.

[0006] To achieve the above objectives, the present invention provides a method for preventing and controlling the "pot cover effect"-induced cracking of the tunnel opening lining, comprising the following steps:

[0007] Step S1, according to the size of the excavated tunnel opening, a hydrophobic steam isolation structure is set between the lining and the surrounding strata, the slope of the structure is consistent with the designed tunnel lining slope, forming an arc-shaped axisymmetric structure with a high middle and low sides;

[0008] Step S2: construct a lining layer below the hydrophobic vapor barrier structure, and apply two asphalt adhesive layers between the structural layer and the lining layer. Referring to the design elevation of the road surface in the tunnel, set blind ditches in the low-lying areas on both sides of the silty sand layer, fill the blind ditches with gravel, and connect them to external drainage facilities at certain intervals.

[0009] Step S3, repeating the local unit arrangement scheme of steps S1-S2 until the entire tunnel entrance area is covered;

[0010] Step S4: Extend a rectangular structure higher than the tunnel on both sides of the tunnel entrance, and install air curtain equipment on the ceiling. Air curtain equipment can also be appropriately added on both sides according to the actual tunnel size to ensure that the air curtain wall completely covers the tunnel entrance. The equipment is powered by external photovoltaic panels and wind generators, and is driven by solar energy and wind energy.

[0011] Preferably, the thickness of the lower geotextile of the hydrophobic vapor barrier structure in step S1 is 0.3 cm, and no water permeable holes are provided; the thickness of the upper geotextile is 0.3 cm, the diameter of the water permeable holes is 2 cm, and the center distance between adjacent water permeable holes is 30 cm.

[0012] Preferably, the asphalt tack layer in step S2 has a thickness of 0.2 cm, and the silty sand layer has a thickness of 4 cm.

[0013] Preferably, the structure in step S4 is 1m higher than the tunnel and 2m long; air curtain equipment is installed at the entrance and exit of the tunnel.

[0014] Therefore, the present invention proposes a method for preventing and controlling the cracking of the tunnel entrance lining caused by the "pot lid effect". By adopting a hydrophobic vapor barrier structure of double-layer geotextile sandwiched with silty sand, a significant hydrophobic vapor barrier effect is achieved. Combined with air curtain technology, this scheme forms a new method combining dredging and blocking. It fundamentally prevents and controls the cracking of the lining caused by the "pot lid effect". This method is simple to construct, safe and stable, and has significant economic advantages.

[0015] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1It is a structural arrangement diagram of the present invention for preventing and controlling the "pot cover effect" from inducing cracking of the tunnel opening lining;

[0017] Figure 2 This is the AA section of the tunnel portal lining;

[0018] Figure 3 It is a plan view of the upper part of the hydrophobic vapor barrier structure;

[0019] Figure 4 It is the operation flow chart of air curtain equipment;

[0020] Description of the drawings: 10. Air curtain equipment; 11. Wind turbine; 12. Tunnel portal lining; 13. Blind ditch; 14 Silty sand; 15. Photovoltaic panels; 16. Air curtain wall; 17. Upper geotextile; 18. Lower geotextile; 19. Structure; 20. External cold air; 21. Hydrophobic vapor barrier structure; 22. Water-permeable holes; 23. Geotextile without holes; 24. Controller; 25. Battery; 26. Inverter. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0022] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0023] Example

[0024] See also Figure 1-4, the present invention provides a method for preventing and controlling the "pot lid effect" that induces cracks in the tunnel entrance lining, and relates to the field of geotechnical engineering technology. The method is performed by laying an axisymmetric arc-shaped hydrophobic vapor barrier structure between the tunnel lining and the surrounding strata. The structure consists of an upper layer of open-pored closed geotextile, a middle layer of silty sand and a lower layer of closed geotextile, and blind ditches are set on both sides to drain the accumulated water. In addition, making full use of the local climate characteristics of sufficient sunshine and high winds, an air curtain device driven by solar energy and wind energy is installed at the tunnel entrance to block cold air from entering the tunnel and eliminate the influence of temperature differences. Specifically comprising the following steps:

[0025] Step S1: According to the excavated tunnel opening, a water-repellent vapor barrier structure 21 is set around the tunnel, and its slope is consistent with the designed tunnel lining 12 to form an enclosing structure, such as Figure 1 The thickness of the lower geotextile 18 of the hydrophobic vapor barrier structure in step S1 is 0.3 cm and has no water permeable holes; the thickness of the upper geotextile 17 is 0.3 cm, the diameter of its water permeable holes 22 is 2 cm, and the center distance between adjacent water permeable holes is 30 cm. Figure 3 shown.

[0026] Step S2: construct a lining layer below the hydrophobic vapor barrier structure, and apply two layers of asphalt adhesive layers between the structural layer and the lining layer. Set blind ditches 13 in the low-lying areas on both sides of the silty sand layer 14 flush with the road surface to ensure that all the upper seepage water is discharged into the ditch, and waterproof treatment is done between the blind ditch and the lower hydrophobic vapor barrier structure. Fill the blind ditch with gravel and connect it to external drainage facilities at a certain interval; the thickness of the asphalt adhesive layer in step S2 is 0.2 cm, and the laying thickness of the silty sand is 4 cm.

[0027] Step S3, repeat the local unit arrangement scheme of steps S1-S2 until the entire tunnel entrance area is covered.

[0028] Step S4: Extend a rectangular structure 19 about 1m higher than the tunnel at the tunnel entrances on both sides, with a horizontal length of 2m. Figure 2 As shown. And install the top blowing air curtain equipment 10, or according to the actual tunnel size, add the side blowing air curtain equipment on both sides to ensure that the air curtain wall completely covers the tunnel, such as Figure 1 The electric energy of the air curtain device is provided by the photovoltaic panel 15 and the wind turbine 11, and is stored in the battery 25 through the controller 24, which can be used as an off-grid backup power supply, and then boosted by the inverter 26 to drive the air curtain device 10 to operate. Figure 4 As shown. A wind curtain wall with a significant temperature difference from the outside of the tunnel is formed, such as a hot air curtain in winter, which effectively isolates the low-temperature air outside the tunnel. In step S4, air curtain equipment is installed at the entrance and exit of the tunnel.

[0029] The present invention can effectively solve the problem of "pot lid effect" water vapor migration damaging the tunnel entrance lining, which not only dredges the water accumulation on the lining, but also prevents deep water vapor from migrating to the lining surface, thus ensuring the strength and structural integrity of the tunnel lining. At the same time, the air curtain equipment blocks the external cold air from entering the tunnel, eliminates the influence of temperature difference, and effectively avoids lining cracking, water seepage and other disasters caused by long-term freeze-thaw cycles.

[0030] Therefore, the present invention adopts the above-mentioned method for preventing and controlling the "pot lid effect"-induced cracking of the tunnel entrance lining. By adopting a hydrophobic vapor barrier structure of double-layer geotextile sandwiched with silty sand, it has both the functions of stable hydrophobicity and water vapor barrier; combined with air curtain technology, it prevents and controls the tunnel entrance lining engineering disasters caused by the "pot lid effect" from the root. In addition, this method reveals the occurrence mechanism of tunnel entrance lining disasters in seasonal frozen soil areas, and effectively uses clean and environmentally friendly energy to provide electricity for the air curtain equipment. It has the advantages of low construction cost, safety, high efficiency, economy and environmental protection, and provides a practical engineering solution.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preventing and controlling the "pot cover effect" from inducing cracking of the tunnel opening lining, characterized in that The following steps are involved: Step S1, according to the size of the excavated tunnel opening, a hydrophobic steam isolation structure is set between the lining and the surrounding strata, the slope of the structure is consistent with the designed tunnel lining slope, forming an arc-shaped axisymmetric structure with a high middle and low sides; Step S2, referring to the designed elevation of the road surface in the tunnel, blind ditches are set at the lower positions on both sides of the silty sand layer, the blind ditches are filled with gravel, and are connected to external drainage facilities at certain intervals; Step S3, repeating the local unit arrangement scheme of steps S1-S2 until the entire tunnel entrance area is covered; Step S4: Extend a rectangular structure higher than the tunnel outward from the tunnel entrance, and install an air curtain device on the top. According to the actual tunnel size, air curtain equipment can be appropriately added on both sides to ensure that the air curtain wall completely covers the tunnel entrance. The air curtain equipment is powered by external photovoltaic panels and wind turbines, and is driven by solar and wind energy to form a wind curtain with a significant temperature difference from the outside of the tunnel (such as a hot air curtain in winter).

2. A method for preventing and controlling "pot cover effect"-induced cracking of tunnel opening lining according to claim 1, characterized in that: The hydrophobic vapor barrier structure in step S1 comprises two layers of geotextiles and a middle silty sand interlayer, wherein: the thickness of the lower geotextile is 0.3 cm and no water permeable holes are provided; the thickness of the upper geotextile is 0.3 cm, the diameter of its water permeable holes is 2 cm, and the center distance between adjacent water permeable holes is 30 cm.

3. The method for preventing and controlling the "pot cover effect"-induced cracking of the tunnel opening lining according to claim 2, characterized in that: The laying thickness of the silty sand layer in step S2 is 4 cm.

4. The method for preventing and controlling the "pot cover effect"-induced cracking of the tunnel opening lining according to claim 1, characterized in that: The structure in step S4 is about 1m higher than the tunnel, has a horizontal length of 2m, and air curtain equipment is installed at the entrance and exit of the tunnel.

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