A sectional variable-thickness spraying heat preservation construction method and structure for cold region tunnels

Abstract

This invention relates to the field of antifreeze and insulation construction technology for tunnels in cold regions, and discloses a method and structure for segmented variable-thickness spray insulation construction in cold regions. The method involves acquiring the ambient temperature outside the tunnel, the longitudinal ambient temperature of the tunnel, and the radial temperature of the surrounding rock; establishing a transient water-heat coupling model to determine the insulation protection length and the design thickness of each insulation segment, ensuring that the design thickness decreases from the tunnel entrance towards the tunnel depth; performing base treatment and interface reinforcement on the inner surface of the secondary lining of the tunnel; forming a spray insulation layer according to the design thickness of each insulation segment; and creating a thickness gradient transition section between adjacent insulation segments; reserving a groove for installing electric heating tape in the insulation segment near the tunnel entrance and laying a self-regulating electric heating tape; and setting an enhanced protective layer and a fireproof surface layer on the surface of the spray insulation layer. This invention enables the insulation thickness to match the longitudinal antifreeze requirements of the tunnel, improving the reliability of antifreeze and reducing the use of unnecessary insulation materials.

Description

Technical Field

[0001] This invention relates to the field of antifreeze and insulation construction technology for tunnels in cold regions, specifically a method and structure for segmented variable thickness spray insulation construction in tunnels in cold regions. Background Technology

[0002] Tunnels in cold regions are affected by factors such as periodic low temperatures outside the tunnel, cold air intrusion at the tunnel entrance, water content in the surrounding rock, and water-ice phase transition during operation. This can easily lead to sub-zero temperatures in the secondary lining and surrounding rock, causing frost damage such as water seepage freezing, lining frost heave cracking, ice buildup, and road surface icing. To reduce the impact of low temperatures on tunnel structure and operational safety, current technologies typically include an insulation layer inside the secondary lining. This reduces heat exchange between the tunnel's internal air and the secondary lining, minimizing the transfer of low temperatures to the surrounding rock. Existing insulation layers are mainly constructed using methods such as prefabricated insulation board bonding, mechanical anchoring, or on-site spraying. The length and thickness of the insulation layer are usually determined based on the lowest temperature in the tunnel site area, engineering experience, and safety margins.

[0003] However, the degree to which cold-region tunnels are affected by low external temperatures varies along the tunnel's longitudinal direction. Typically, the temperature variation is larger near the tunnel entrance and gradually decreases towards the tunnel's depth. Current technologies often employ a uniform insulation thickness throughout the entire insulation area, or simply divide the tunnel into pre-set fixed segments. This fails to determine the insulation requirements at each location based on the actual changes in longitudinal atmospheric temperature, radial temperature of the surrounding rock, and temperature of the secondary lining. This can easily lead to insufficient insulation near the tunnel entrance, while excessive insulation material is applied in the deeper parts of the tunnel, making it difficult to balance frost protection reliability with efficient insulation material utilization. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method and structure for segmented variable-thickness spray insulation construction in cold-region tunnels, solving the problem that existing cold-region tunnel insulation construction methods, which use uniform insulation thickness or simple fixed segments, are difficult to match with the longitudinal cold impact of the tunnel.

[0005] To achieve the above objectives, the present invention provides a method for segmented variable-thickness spray insulation construction in tunnels in cold regions, comprising the following steps:

[0006] S1. Determine the insulation protection range and insulation zone parameters, including:

[0007] S101. Obtain the ambient temperature outside the tunnel, the longitudinal ambient temperature of the tunnel, and the radial temperature of the surrounding rock, establish a transient water-heat coupling model, determine the insulation length based on the transient water-heat coupling model, and divide the insulation range into at least four insulation zones.

[0008] S102. Adjust the simulated insulation layer thickness segment by segment based on the criterion that the intermediate temperature of the secondary lining is not lower than 0℃. For insulation sections that meet the criterion before reaching the preset maximum spraying thickness, determine the design thickness based on the simulated insulation layer thickness that meets the criterion. For insulation sections that do not meet the criterion after reaching the preset maximum spraying thickness, determine them as insulation sections near the tunnel entrance. Set the preset maximum spraying thickness as the design thickness of the insulation sections near the tunnel entrance. Determine the arrangement parameters of the self-regulating electric heating tape based on the criterion that the intermediate temperature of the secondary lining is not lower than 0℃ after laying the self-regulating electric heating tape, so that the design thickness of each insulation section decreases from the tunnel entrance to the tunnel depth.

[0009] S2. Clean the inner surface of the secondary lining of the tunnel within the insulation range, seal or drain the cracks and seepage points to form a sprayed base layer without standing water.

[0010] S3. Apply an interface treatment agent to the surface of the sprayed base layer and cure it until the surface of the interface treatment agent is dry to the touch to form an interface reinforcement layer.

[0011] S4. Use a two-component high-pressure spraying device to preheat the A and B components of the sprayed insulation material, and heat the delivery pipeline and spray gun to complete the test spraying inspection of the sprayed insulation material.

[0012] S5. According to the design thickness of each insulation section, a sprayed insulation layer is formed by single-pass spraying or multiple-pass spraying. A thickness gradient transition section is formed at the junction of two adjacent insulation sections, so that the thickness of the sprayed insulation layer continuously changes from the design thickness of the thicker insulation section to the design thickness of the thinner insulation section within the thickness gradient transition section. An electric heating cable installation groove is reserved during the spraying process of the insulation section near the opening.

[0013] S6. The surface of the cured sprayed insulation layer is trimmed, and an enhanced protective layer and a fireproof surface layer are formed sequentially on the surface of the trimmed sprayed insulation layer.

[0014] S7. Lay a self-regulating electric heating cable in the electric heating cable installation groove, and fill the electric heating cable installation groove with heat-conducting material and seal the groove opening.

[0015] Furthermore, the insulation section includes a first insulation section, a second insulation section, a third insulation section, and a fourth insulation section;

[0016] The first insulation section is located within 0 to 50 meters from the tunnel entrance, and the designed thickness of the first insulation section is 7 to 10 cm.

[0017] The second insulation section is located 50 to 200 meters from the tunnel entrance, and the design thickness of the second insulation section is 6 to 8 cm.

[0018] The third insulation section is located within a range of 200 to 500 meters from the tunnel entrance, and the designed thickness of the third insulation section is 3 to 5 cm.

[0019] The fourth insulation section is the range from 500m from the tunnel entrance to the end of the insulation protection length, and the design thickness of the fourth insulation section is 2-3cm.

[0020] The design thickness of the first insulation section, the second insulation section, the third insulation section, and the fourth insulation section are selected in a progressively decreasing manner within their respective ranges.

[0021] Furthermore, in step S101, at least eight longitudinal monitoring sections are set from the tunnel entrance to the tunnel depth direction. The longitudinal monitoring sections are respectively set at the tunnel entrance and at positions 10m, 50m, 100m, 200m, 500m, 1000m and 1500m away from the tunnel entrance.

[0022] Each longitudinal monitoring section is provided with at least five radial temperature monitoring points along the surrounding rock. The radial temperature monitoring points are respectively located at different depths on the inner surface of the secondary lining of the tunnel, the outer surface of the initial support, and the outer side of the initial support.

[0023] Further, in step S101, the empirically calculated value of the thermal insulation length is obtained based on the average temperature of the coldest month at the tunnel entrance, and the model-calculated value of the thermal insulation length is obtained based on the transient water-heat coupling model. The larger of the empirically calculated value and the model-calculated value is determined as the thermal insulation length.

[0024] In step S102, the simulated insulation layer thickness corresponding to each insulation section is adjusted according to the preset thickness step size; for insulation sections that ensure the intermediate temperature of the secondary lining is not lower than 0°C before reaching the preset maximum spraying thickness, the sum of the minimum simulated insulation layer thickness that meets this condition and the thickness safety margin is determined as the design thickness; for insulation sections that still cannot ensure the intermediate temperature of the secondary lining is not lower than 0°C after reaching the preset maximum spraying thickness, they are determined as the insulation section near the opening, and the arrangement parameters of the self-regulating electric heating tape are determined based on the criterion that the intermediate temperature of the secondary lining is not lower than 0°C after the self-regulating electric heating tape is laid.

[0025] Furthermore, the transient water-thermal coupling model includes at least the surrounding rock, initial support, secondary tunnel lining, air zone inside the tunnel, and simulated insulation layer.

[0026] The transient water-thermal coupling model simulates the intermediate temperature of the secondary lining at different longitudinal positions during the design freezing period, based on at least the thermal properties of the surrounding rock, the water-bearing state parameters of the surrounding rock, the thermal properties of the initial support, the thermal properties of the secondary lining of the tunnel, the thermal properties of the sprayed insulation material, the atmospheric temperature outside the tunnel, and the longitudinal atmospheric temperature of the tunnel.

[0027] Furthermore, in step S2, the floating dust, oil stains and loose attachments on the inner surface of the secondary lining of the tunnel are removed, the cracks are sealed with grouting material, and the seepage points are grouted to stop the water or drain it, so that the sprayed base layer is free of standing water and the moisture content does not exceed 8%.

[0028] Further, in step S3, the interface treatment agent is a silane coupling agent modified acrylate emulsion, and the coating amount of the interface treatment agent is 150-200 g / m².

[0029] Furthermore, the sprayed insulation material is a commercially available two-component sprayed polyurethane material, which is mixed under high pressure, sprayed and foamed to form a modified rigid polyurethane closed-cell foam.

[0030] The modified rigid polyurethane closed-cell foam has a thermal conductivity of not more than 0.020 W / (m·℃), a closed-cell rate of not less than 95%, a molding density of 35-45 kg / m³, a compressive strength of not less than 200 kPa, a volumetric water absorption rate of not more than 3%, and an oxygen index of not less than 30%.

[0031] Further, in step S4, the preheating temperature of component A is 30-40°C, the preheating temperature of component B is 25-35°C, the heating temperature of the delivery pipeline is 35-45°C, the heating temperature of the spray gun is 40-50°C, the spraying pressure is 8-12 MPa, the spraying flow rate is 3-6 kg / min, and the volume ratio of component A to component B is 1:1.05-1.20.

[0032] Furthermore, in step S5, when the sprayed insulation layer is formed by multiple spraying passes, the spray gun directions of adjacent spraying passes are arranged in an intersecting manner, the distance between the spray gun and the inner surface of the tunnel secondary lining is 400-600mm, the spray gun speed is 0.3-0.5m / s, and the overlap width between adjacent spraying passes is 80-120mm.

[0033] Furthermore, the length of the thickness gradient transition section is not less than 3m. Within the thickness gradient transition section, the gun speed is continuously adjusted from the gun speed corresponding to the thicker insulation section to the gun speed corresponding to the thinner insulation section, so that the thickness of the sprayed insulation layer continuously decreases.

[0034] Further, in step S5, a mold strip is positioned on the surface of the first layer of sprayed coating in the near-end insulation section of the opening, so that the subsequent sprayed coating covers both sides of the mold strip. After the sprayed insulation layer has cured, the mold strip is removed to form the electric heating cable installation groove.

[0035] Further, in step S6, a polymer crack-resistant mortar is applied to the surface of the sprayed insulation layer, and an alkali-resistant glass fiber mesh is embedded in the polymer crack-resistant mortar, so that the polymer crack-resistant mortar and the alkali-resistant glass fiber mesh together form the reinforced protective layer; a fire-retardant coating is applied to the surface of the reinforced protective layer to form the fire-resistant surface layer.

[0036] Furthermore, in step S7, the self-regulating heating cable is continuously laid along the circumference of the tunnel, and the distance between adjacent self-regulating heating cables along the longitudinal direction of the tunnel is no more than 500mm.

[0037] Thermally conductive silicone grease is filled on the outside of the self-regulating electric heating cable, and the mounting groove of the electric heating cable is sealed with silicone sealant.

[0038] A segmented variable thickness sprayed insulation structure for tunnels in cold regions includes an interface reinforcement layer, a sprayed insulation layer, a reinforced protective layer, and a fireproof surface layer, which are sequentially arranged from the inner surface of the secondary lining of the tunnel towards the tunnel clearance.

[0039] The interface enhancement layer is a film formed by curing a silane coupling agent-modified acrylate emulsion.

[0040] The sprayed insulation layer is a modified rigid polyurethane closed-cell foam layer. The sprayed insulation layer is divided into at least four insulation sections along the longitudinal direction of the tunnel, and the thickness of each insulation section decreases from the tunnel entrance to the depth of the tunnel.

[0041] A thickness gradient transition section is provided between two adjacent insulation sections, and the thickness of the sprayed insulation layer changes continuously within the thickness gradient transition section.

[0042] The reinforced protective layer includes a polymer crack-resistant mortar layer and an alkali-resistant glass fiber mesh embedded in the polymer crack-resistant mortar layer.

[0043] The fireproof surface layer is a fireproof coating layer applied to the surface of the reinforced protective layer.

[0044] At least one of the insulation sections near the tunnel entrance is a near-entrance insulation section, and the thickness of the near-entrance insulation section is not less than the thickness of the other insulation sections; the near-entrance insulation section is provided with an electric heating cable installation groove embedded in the sprayed insulation layer, the electric heating cable installation groove does not penetrate the sprayed insulation layer, so that a continuous sprayed insulation layer is maintained between the bottom of the electric heating cable installation groove and the interface reinforcement layer.

[0045] Furthermore, the insulation section includes a first insulation section 0-50m from the tunnel entrance with a thickness of 7-10cm, a second insulation section 50-200m from the tunnel entrance with a thickness of 6-8cm, a third insulation section 200-500m from the tunnel entrance with a thickness of 3-5cm, and a fourth insulation section extending from 500m from the tunnel entrance to the depth of the sprayed insulation layer with a thickness of 2-3cm.

[0046] The thickness of the first insulation section, the second insulation section, the third insulation section, and the fourth insulation section decreases progressively, and the length of the thickness transition section is not less than 3m.

[0047] Furthermore, the thickness of the interface reinforcement layer is 0.1–0.3 mm, the thickness of the reinforcement protective layer is 4–6 mm, and the thickness of the fireproof surface layer is 0.3–0.5 mm.

[0048] Furthermore, the electric heating cable installation groove is provided with a self-regulating electric heating cable, a thermally conductive silicone grease layer, and a silicone sealant layer.

[0049] The self-regulating heating cable extends continuously along the circumference of the tunnel, and the distance between adjacent self-regulating heating cables along the longitudinal direction of the tunnel is no more than 500mm.

[0050] The thermally conductive silicone grease layer covers the self-regulating heating cable, and the silicone sealant layer seals the opening of the heating cable mounting groove.

[0051] This invention provides a method and structure for segmented variable-thickness spray insulation construction in tunnels in cold regions. It offers the following advantages:

[0052] 1. This invention obtains the ambient temperature outside the tunnel, the longitudinal ambient temperature of the tunnel, and the radial temperature of the surrounding rock. It determines the insulation length using a transient water-thermal coupling model and determines the design thickness of each insulation section based on the criterion that the intermediate temperature of the secondary lining is not lower than 0℃, ensuring that the thickness of the sprayed insulation layer decreases from the tunnel entrance towards the tunnel depth. This allows for the configuration of appropriate insulation thicknesses to address different cold-affected areas near the tunnel entrance and in the tunnel depth, improving the reliability of anti-freezing near the entrance while reducing the use of unnecessary insulation materials in the tunnel depth, thus achieving a balance between anti-freezing effectiveness and material utilization.

[0053] 2. The present invention sets a thickness gradient transition section at the junction of two adjacent insulation sections, and by continuously adjusting the gun speed, the design thickness of the sprayed insulation layer is continuously changed from the design thickness of the thicker insulation section to the design thickness of the thinner insulation section. This avoids the formation of abrupt steps between adjacent insulation sections, reduces the possibility of sudden changes in local thermal resistance and stress concentration in the outer protective structure, and improves the stability of the sprayed insulation structure under temperature cycling.

[0054] 3. In the process of spraying the insulation layer near the tunnel entrance, this invention utilizes mold strips to form an electric heating cable installation groove embedded within the sprayed insulation layer but not penetrating it. After the sprayed insulation layer cures, the self-regulating electric heating cable is laid within the installation groove, ensuring a continuous sprayed insulation layer between the bottom of the groove and the interface reinforcement layer. When the sprayed insulation layer alone is insufficient to meet the anti-freezing requirements near the tunnel entrance, the self-regulating electric heating cable can compensate for heat in localized low-temperature areas while reducing heat loss from the heating cable to the tunnel clearance side, thus improving the reliability of anti-freezing under extreme low-temperature conditions.

[0055] 4. This invention uses on-site spraying to form a modified rigid polyurethane closed-cell foam layer on the inner surface of the tunnel secondary lining. The sprayed material can foam and form according to the shape of the inner surface of the tunnel secondary lining, and the interface reinforcement layer improves the bonding stability between the sprayed insulation layer and the tunnel secondary lining, reducing thermal bridges and voids caused by gaps in the splicing joints of prefabricated insulation boards and insufficient local bonding.

[0056] 5. The present invention provides an enhanced protective layer on the surface of the sprayed insulation layer, consisting of a polymer crack-resistant mortar layer and an alkali-resistant glass fiber mesh, and provides a fireproof surface layer on the surface of the enhanced protective layer. This can provide crack resistance, impact resistance and fire protection for the sprayed insulation layer, reduce the damage to the sprayed insulation layer caused by airflow, vibration, temperature cycling and external collisions in the tunnel operating environment, and extend the service life of the sprayed insulation structure. Attached Figure Description

[0057] Figure 1 This is a flowchart of the method for segmented variable thickness spray insulation construction in cold-region tunnels according to the present invention;

[0058] Figure 2 This is a cross-sectional schematic diagram of the segmented variable thickness spray insulation structure for cold-region tunnels according to the present invention, and a partial enlarged view of the near end of the tunnel entrance.

[0059] Figure 3 This is a schematic diagram of the segmented variable thickness arrangement of the sprayed insulation layer along the longitudinal direction of the tunnel according to the present invention.

[0060] The components include: 1. secondary tunnel lining; 2. interface reinforcement layer; 3. sprayed insulation layer; 4. reinforced protective layer; and 5. fireproof surface layer. Detailed Implementation

[0061] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Adaptive adjustments made by those skilled in the art to certain construction parameters based on the climate conditions, tunnel cross-sectional dimensions, surrounding rock type, lining structure, and groundwater conditions of the tunnel location without departing from the concept of the present invention should all be included within the scope of protection of the present invention.

[0062] In this embodiment, "tunnel longitudinal direction" refers to the direction extending from the tunnel entrance into the tunnel depth; "tunnel circumferential direction" refers to the direction extending along the tunnel cross-sectional outline; "intermediate temperature of secondary lining" refers to the lowest temperature at the middle position of the secondary lining 1 along its thickness direction during the design freezing period; "insulation protection length" refers to the length of the sprayed insulation layer 3 required to be installed along the tunnel longitudinal direction from the tunnel entrance; "insulation section near the tunnel entrance" refers to the insulation section most significantly affected by low temperatures and cold wind intrusion from outside the tunnel, where passive insulation alone may not meet the anti-freezing requirements. "Preset maximum spraying thickness" refers to the upper limit of the single-sided spraying thickness predetermined based on the tunnel clearance limit, the stability of the sprayed insulation layer, and the engineering economy; in this embodiment, it is preferably 10cm.

[0063] The preset maximum coating thickness is not solely determined by the anti-freezing temperature requirement. As the thickness of the sprayed insulation layer increases, the material usage and weight also increase. The unevenness of the tunnel secondary lining surface and the interlayer differences caused by multiple coatings also have a greater impact on the stability of the sprayed insulation layer. Simultaneously, the thickness of the sprayed insulation layer is also constrained by tunnel clearance limits and the utilization rate of engineering materials. Therefore, when the simulated insulation layer thickness reaches the preset maximum coating thickness but still cannot ensure that the intermediate temperature of the secondary lining is not lower than 0℃, the thickness of the sprayed insulation layer is no longer increased. Instead, a self-regulating heating cable is used to compensate for the remaining heat demand, thus switching between passive insulation and active heat replenishment.

[0064] For tunnels that are connected to the external environment at both ends, the insulation length can be determined starting from each of the two tunnel entrances. When the insulation areas at both ends overlap, the overlapping area should be constructed according to the design thickness corresponding to the less unfavorable end.

[0065] Implementation Method 1

[0066] like Figure 1 As shown in the figure, this embodiment provides a method for segmented variable thickness spray insulation construction in tunnels in cold regions, including the following steps.

[0067] S1. Determination of thermal insulation protection range and thermal insulation zone parameters

[0068] S101. Temperature data acquisition, model establishment, and thermal insulation zone division.

[0069] First, obtain the atmospheric temperature outside the tunnel, the longitudinal atmospheric temperature of the tunnel, and the radial temperature of the surrounding rock.

[0070] Multiple longitudinal monitoring sections are set up from the tunnel entrance to the tunnel depth. Preferably, at least eight longitudinal monitoring sections are set up, located at the tunnel entrance and at positions 10m, 50m, 100m, 200m, 500m, 1000m and 1500m from the tunnel entrance.

[0071] When the tunnel length is less than 1500m, the longitudinal monitoring sections located outside the thermal insulation protection range should be reduced according to the actual tunnel length, but longitudinal monitoring sections should be set at the tunnel entrance, the pre-set zone boundary, and the location where the temperature tends to be stable.

[0072] At least five radial temperature monitoring points are set along the surrounding rock at each longitudinal monitoring section. The radial temperature monitoring points are set at different depths on the inner surface of the secondary lining 1, the outer surface of the initial support, and the outer side of the initial support. Preferably, the three radial temperature monitoring points on the outer side of the initial support are located at distances of 60cm, 120cm, and 180cm from the outer surface of the initial support, respectively.

[0073] Each temperature monitoring point uses a temperature sensor capable of meeting the low-temperature environment requirements of cold regions. The temperature sensor is connected to a data acquisition unit, which collects temperature data at preset time intervals. The preset time interval can be set from 10 minutes to 60 minutes.

[0074] To improve the reliability of temperature boundary fitting and model verification, the monitoring period should preferably cover at least one complete freezing period; where conditions permit, the monitoring period should cover a full year. For newly constructed tunnels that are not yet in operation, an initial temperature boundary can also be established by combining historical temperature data from nearby meteorological stations, short-term on-site monitoring data from the tunnel site, and monitoring data from similar tunnels, and then corrected based on measured data during subsequent construction or operation.

[0075] Based on the monitoring results of each longitudinal monitoring section, the lowest longitudinal temperature distribution of the tunnel and the radial temperature variation of the surrounding rock during the design freezing period are obtained. The longitudinal temperature of the tunnel can be fitted using a cosine function, exponential function, or piecewise function; it is not required that all tunnels satisfy the same fixed function form.

[0076] Subsequently, a transient water-thermal coupling model was established. The transient water-thermal coupling model includes at least the surrounding rock, initial support, secondary tunnel lining 1, air zone inside the tunnel, and the proposed sprayed insulation layer 3.

[0077] The parameters input to the transient water-thermal coupling model must include at least:

[0078] The parameters include: surrounding rock density, specific heat capacity, thermal conductivity, porosity, saturated water content, residual water content, water diffusion parameters, water infiltration parameters, latent heat of water-ice phase change, thermal properties of initial support, thermal properties of tunnel secondary lining 1, and thermal properties of sprayed insulation material.

[0079] The heat transfer process in the transient water-heat coupling model includes heat conduction between the surrounding rock, initial support, tunnel secondary lining 1 and sprayed insulation layer 3, convective heat transfer between air inside the tunnel and the tunnel wall, and phase change heat effect caused by freezing or melting of pore water in the surrounding rock; the moisture migration process includes the migration of pore water in the surrounding rock caused by the influence of water content gradient and temperature gradient.

[0080] In this embodiment, the transient water-heat coupling model uses temperature field control equations and moisture field control equations to describe the heat transfer, moisture migration and water-ice phase transition process in the surrounding rock.

[0081] The governing equation for the temperature field is:

[0082] ;

[0083] The governing equation for the moisture field is:

[0084] ;

[0085] In the formula, ρ is the density of the rock mass; C(θ) is the equivalent heat capacity of the water-bearing rock mass; T is the temperature; λ(θ) is the equivalent thermal conductivity; and L is the latent heat of water-ice phase change. The density of ice; This represents the saturated moisture content. denoted as residual water content; B(T) is the solid-liquid ratio function characterizing the change of the solid-liquid phase ratio of pore water with temperature; S is the relative saturation. Let be the density of water; D(S) be the water diffusion coefficient; and k(S) be the permeability coefficient function.

[0086] During model solving, a finer mesh was set within a 2m radius of the sprayed insulation layer, the secondary tunnel lining, and its outer side, ensuring that the sprayed insulation layer had at least four mesh elements along its thickness. An adaptive time step was used for transient calculations, with an initial time step of 1 hour and a maximum time step of 6 hours. The calculations were performed when the residuals of the temperature field and relative saturation field between two adjacent iterations were no greater than 1 × 10⁻⁶. ⁻5 The current time step is then determined to be converged.

[0087] The external temperature boundary of the model is determined based on the monitoring results of the external atmospheric temperature; the internal temperature boundary of the tunnel is determined based on the longitudinal atmospheric temperature of the tunnel at different longitudinal monitoring sections; the external boundary of the model is set as a constant temperature boundary or an adiabatic boundary; the initial temperature of the model is determined based on the measured surrounding rock temperature before construction.

[0088] After the model is established, the simulated temperature of the secondary tunnel lining is compared with the temperature monitoring results. When the deviation between the simulation results and the monitoring results exceeds the preset allowable deviation, the thermal conductivity of the surrounding rock, the convective heat transfer coefficient, the moisture migration parameter, or the boundary temperature fitting parameter are adjusted until the simulation results meet the preset allowable deviation.

[0089] The freezing depth for on-site monitoring is determined based on the lowest temperature of each radial temperature monitoring point within the same longitudinal monitoring section. When the lowest temperatures of two adjacent radial temperature monitoring points are located on both sides of 0℃, linear interpolation is performed on the two adjacent radial temperature monitoring points to obtain the 0℃ isothermal position, and the radial distance from the 0℃ isothermal position to the outer surface of the initial support is determined as the freezing depth for on-site monitoring.

[0090] In one embodiment, the preset allowable deviation is that the absolute value of the difference between the simulated temperature and the measured temperature is not greater than 1.0℃, or the relative error between the simulated value and the measured value of the freezing depth is not greater than 10%.

[0091] The insulation length was determined through empirical calculations and a transient water-heat coupling model.

[0092] The thermal insulation length calculated empirically is:

[0093] ;

[0094] In the formula:

[0095] The insulation length is calculated empirically and is expressed in meters.

[0096] The average temperature of the coldest month at the tunnel entrance, in °C. <0.

[0097] A transient water-heat coupling model was used to simulate the lowest temperature of the secondary lining 1 of the tunnel at different longitudinal positions when no sprayed insulation layer 3 was installed. The position where the secondary lining 1 of the tunnel no longer experienced negative temperatures was determined as the end of the insulation protection calculated by the model, and the calculated values ​​were obtained. .

[0098] The larger value between the empirically calculated value and the model-calculated value is determined as the insulation design length, i.e.:

[0099] ;

[0100] In the formula, y is the final determined insulation length.

[0101] The method of taking the larger value described above is used to reserve a safety margin for the insulation length. When long-term field monitoring data is available and the model has been fully calibrated, the insulation length can also be determined directly using the model's calculated value.

[0102] After determining the length of the insulation protection, the insulation protection area is divided into at least four insulation zones.

[0103] In a preferred embodiment, the thermal insulation section includes:

[0104] The first insulation section is located within a range of 0 to 50 meters from the tunnel entrance;

[0105] The second insulation section is located within a range of 50 to 200 meters from the tunnel entrance;

[0106] The third insulation section is located within a range of 200 to 500 meters from the tunnel entrance;

[0107] The fourth insulation section is located from 500m from the tunnel entrance to the end of the insulation protection length.

[0108] When the insulation length is greater than 1000m and the target insulation thickness changes significantly after 500m from the tunnel entrance, the fourth insulation section can be further divided into two or more insulation sections.

[0109] S102. Determination of design thickness and self-regulating heating cable arrangement parameters.

[0110] The design thickness of each insulation section is determined segment by segment using a transient water-thermal coupling model.

[0111] Specifically, simulated insulation layers are set in the model areas corresponding to each insulation section. Starting from a preset initial thickness, the thickness of the simulated insulation layer is increased in preset thickness steps of 5mm or 10mm, and the lowest temperature at the middle position along the thickness direction of the secondary lining 1 of the tunnel during the design freezing period is simulated. When the intermediate temperature of the secondary lining at all calculated sections within the corresponding insulation section is not lower than 0℃, the current simulated insulation layer thickness is determined to meet the anti-freezing requirements.

[0112] For insulation sections that meet the antifreeze requirements before the simulated insulation layer thickness reaches the preset maximum spraying thickness, select the minimum simulated insulation layer thickness that meets the antifreeze requirements, and increase the thickness safety margin according to the allowable construction deviation to obtain the design thickness of the corresponding insulation section.

[0113] The thickness safety margin can be determined based on the accuracy of the spraying equipment, the surface flatness of the secondary lining of the tunnel, and the temperature monitoring error, and is preferably 5 to 10 mm.

[0114] The design thickness of the first insulation section is 7-10cm, the design thickness of the second insulation section is 6-8cm, the design thickness of the third insulation section is 3-5cm, and the design thickness of the fourth insulation section is 2-3cm.

[0115] The design thickness of each insulation section is selected within the corresponding range by gradually decreasing from the tunnel entrance to the depth of the tunnel.

[0116] For insulation sections where the intermediate temperature of the secondary lining is below 0℃ even after the simulated insulation layer thickness reaches the preset maximum spraying thickness, these sections are designated as the near-end insulation sections of the opening, and the preset maximum spraying thickness is designated as the design thickness of the near-end insulation sections of the opening. Subsequently, self-regulating heating cables are installed in the model, and the rated power and longitudinal spacing of the self-regulating heating cables are adjusted for recalculation until the intermediate temperature of the secondary lining in each calculated section of the near-end insulation section of the opening is not lower than 0℃ after the self-regulating heating cables are installed. The corresponding rated power and longitudinal spacing are then designated as the layout parameters of the self-regulating heating cables.

[0117] S2, Spraying the base layer treatment

[0118] Inspect the inner surface of the secondary lining 1 of the tunnel within the insulation protection range and record the location of cracks, construction joints, seepage points, oil stains, laitance and loose attachments.

[0119] Remove loose dust, oil, slurry, and other loose attachments from the inner surface of the secondary lining 1 of the tunnel. For oily areas, use an alkaline cleaning agent to clean them, and then use clean water to remove any remaining cleaning agent. For loose or sandy areas, use a grinding machine to grind them until the stable base layer is exposed.

[0120] Cracks wider than 0.3 mm were sealed with epoxy resin grout. Cracks no wider than 0.3 mm but with water seepage were also sealed.

[0121] For seepage points and construction joints, grouting or drainage treatment should be used to stop the seepage or to divert the water. When grouting is used to stop the seepage, polyurethane grouting materials or other grouting materials suitable for sealing tunnel seepage can be used; when drainage is used, the seepage water should be guided to the tunnel drainage system.

[0122] After the base treatment, the inner surface of the secondary lining 1 of the tunnel should be free of standing water. Spot checks should be conducted using a base moisture content testing device to ensure the base moisture content does not exceed 8%.

[0123] Finally, a high-pressure air gun or industrial vacuum cleaner is used to remove dust from the surface of the base layer, forming a spray base layer that is free of standing water, floating dust, and loose attachments.

[0124] S3, Interface Enhancement Processing

[0125] An interface treatment agent is uniformly applied to the surface of the substrate. The interface treatment agent is a silane coupling agent modified acrylic emulsion.

[0126] The interface treatment agent can penetrate into the surface pores of the secondary tunnel lining 1 and form an interface reinforcement layer 2 after curing, so as to improve the bonding stability between the sprayed insulation layer 3 and the secondary tunnel lining 1.

[0127] The application rate of the interface treatment agent is 150–200 g / m². Apply the agent by roller coating, brush coating, or low-pressure spraying to avoid missed areas and localized liquid accumulation.

[0128] After the interface treatment agent is applied, allow it to cure naturally until the surface is dry to the touch.

[0129] When the ambient temperature is 5-15℃, the curing time shall not be less than 3 hours; when the ambient temperature is greater than 15℃ but not higher than 30℃, the curing time shall not be less than 2 hours.

[0130] In low-temperature or high-humidity environments, the condition for proceeding to the next process is based on the actual touch-dry state of the interface treatment agent, not just the curing time.

[0131] S4. Preparation of spraying equipment and parameter setting

[0132] The insulation layer 3 is applied using a two-component high-pressure spraying system. The two-component high-pressure spraying system includes an A-component storage unit, a B-component storage unit, a material preheating unit, a metering and conveying unit, a heat-tracing conveying pipeline, and spray guns.

[0133] The sprayed insulation material uses commercially available two-component sprayed polyurethane material, which includes component A and component B. Component A and component B are mixed under high pressure, sprayed and foamed and cured to form modified rigid polyurethane closed-cell foam.

[0134] Commercially available two-component sprayable polyurethane materials should be able to form modified rigid polyurethane closed-cell foam that meets the following performance requirements: thermal conductivity not greater than 0.020 W / (m·℃), closed-cell rate not less than 95%, molding density of 35~45 kg / m³, compressive strength not less than 200 kPa, volumetric water absorption not greater than 3%, and oxygen index not less than 30%.

[0135] Before spraying, preheat component A to 30-40°C, preheat component B to 25-35°C, set the heating temperature of the heat tracing pipeline to 35-45°C, and set the heating temperature of the spray gun to 40-50°C.

[0136] The spraying pressure is set to 8–12 MPa, the spraying flow rate is set to 3–6 kg / min, and the volume ratio of component A to component B is set to 1:1.05–1.20.

[0137] Before formal spraying, conduct test spraying on waste slabs or non-construction areas of the tunnel. After test spraying, check the mixing state, foaming state, surface drying time, cell uniformity, and surface condition of the material.

[0138] If uneven color, soft bubbles, brittle bubbles, shrinkage, continuous large pores, or persistent stickiness are observed in the test spray layer, check the metering ratio of component A to component B, material temperature, spraying pressure, and spray gun mixing components. After eliminating the abnormalities, re-test spray.

[0139] After the test spray layer has foamed evenly, with fine pores and is no longer sticky to the touch, the formal spraying can begin.

[0140] S5, Segmented Variable Thickness Spraying Application

[0141] Spraying is preferably carried out from the end furthest from the tunnel entrance toward the tunnel entrance, but the direction of construction can be adjusted according to equipment layout, traffic organization, and construction ventilation conditions.

[0142] According to the design thickness of each insulation section, the sprayed insulation layer 3 is formed by single-coat or multi-coat spraying.

[0143] The distance between the spray gun and the inner surface of the secondary lining 1 of the tunnel should be 400-600mm, the gun travel speed should be 0.3-0.5m / s, and the overlap width between adjacent spray lines should be 80-120mm.

[0144] For insulation sections with a design thickness of 2 to 3 cm, a single coat of spraying can be used to form the sprayed insulation layer 3; for insulation sections with a design thickness greater than 3 cm, multiple coats of spraying can be used to form the sprayed insulation layer 3.

[0145] When using multiple coats, apply the next coat only after the previous coat has reached a non-sticky state to the touch. The spray gun should be moved alternately between adjacent coats. For example, the first coat should be applied longitudinally along the tunnel, the second coat circumferentially along the tunnel, and subsequent coats should alternate between longitudinal and circumferential directions.

[0146] Cross-spraying staggers the overlap positions between different spray rows to reduce the possibility of continuous weak areas forming.

[0147] After each preset construction area is completed, the thickness of the sprayed insulation layer 3 is tested. In the wet film state, a thickness gauge can be used for testing; after curing, core drilling or ultrasonic thickness measurement can be used for verification.

[0148] When the thickness detected is less than the design thickness of the corresponding insulation section, additional spraying is carried out in the area with insufficient thickness; when the local thickness is significantly greater than the design thickness and affects the tunnel clearance, surface repair is carried out after the sprayed insulation layer 3 has cured.

[0149] A thickness gradient transition section shall be set at the junction of two adjacent insulation sections. The length of the thickness gradient transition section shall not be less than 3m.

[0150] The sprayed insulation layer 3 in the thickness gradient transition section continuously changes from the design thickness of the thicker insulation section to the design thickness of the thinner insulation section, thereby avoiding the formation of abrupt thickness steps between adjacent insulation sections.

[0151] When forming a thickness gradient transition section, while keeping the spray flow rate, the distance between the spray gun and the inner surface of the tunnel secondary lining 1 and the overlap width of adjacent spray lines basically stable, the gun speed is gradually increased along the direction from the thicker insulation section to the thinner insulation section.

[0152] Under the condition that the spraying flow rate, the distance between the spray gun and the inner surface of the secondary lining 1 of the tunnel and the overlap width of adjacent spraying rows are basically stable, the amount of sprayed insulation material received per unit area decreases as the speed of the spray gun increases, thereby causing the sprayed insulation layer 3 to be continuously thinned along the thickness transition section.

[0153] When using manual spraying, multiple position marks can be set within the thickness gradient transition section, and the gun speed can be adjusted in stages according to the position marks, so that the thickness change after the staged adjustment approximates the continuous change.

[0154] When using automatic spraying equipment, a gun speed control curve is generated based on the starting thickness, ending thickness, and length of the thickness gradient transition section, so that the gun speed continuously changes from the gun speed corresponding to the thicker insulation section to the gun speed corresponding to the thinner insulation section.

[0155] During the construction of the insulation section near the tunnel entrance, after the first coat of sprayed material reaches a non-sticky state to the touch, mold strips are positioned on the surface of the first coat. The mold strips are continuously arranged along the circumference of the tunnel, and the spacing between adjacent mold strips along the longitudinal direction of the tunnel is no more than 500mm.

[0156] The mold strip is preferably made of heat-resistant silicone material, and its cross-section can be rectangular, trapezoidal, or rectangular with rounded corners. The cross-sectional dimensions of the mold strip are determined based on the dimensions of the self-regulating electric heating tape and the required thermal conductivity filling space.

[0157] When applying the subsequent coating layer, ensure that the coating material covers both sides of the mold strip, and avoid completely covering the side of the mold strip facing the tunnel clearance.

[0158] After the sprayed insulation layer 3 has cured, the mold strip is removed to form the electric heating cable installation groove. The electric heating cable installation groove does not penetrate the sprayed insulation layer 3 to ensure that the self-regulating electric heating cable and the secondary lining 1 of the tunnel retain continuous sprayed insulation material.

[0159] By placing the self-regulating heating cable in a cable tracing groove embedded within the sprayed insulation layer 3, the sprayed insulation layer 3 can block heat loss from the self-regulating heating cable towards the tunnel clearance side. The thermally conductive silicone grease reduces the contact thermal resistance between the self-regulating heating cable and the groove wall, facilitating heat transfer along the sprayed insulation layer 3 around the cable tracing groove. The cable tracing groove does not penetrate the sprayed insulation layer 3, maintaining a continuous sprayed insulation layer between the groove bottom and the interface reinforcement layer 2. This prevents the cable tracing groove from directly penetrating the tunnel secondary lining 1 and creating localized weak points in insulation.

[0160] S6. Surface finishing and protective construction

[0161] After the sprayed insulation layer 3 has fully cured, use a hot wire cutter or other trimming tools suitable for rigid polyurethane foam to remove any protruding parts from the surface.

[0162] Use a 2m straightedge to check the surface flatness of the sprayed insulation layer 3, and ensure that the surface flatness deviation is no more than 5mm.

[0163] Temporary shielding strips are installed at the opening of the electric heat tracing cable installation trough to prevent the subsequent reinforcement protective layer 4 and fireproof surface layer 5 from sealing the electric heat tracing cable installation trough.

[0164] Apply the first layer of polymer crack-resistant mortar to the surface of the repaired sprayed insulation layer 3, and press the alkali-resistant glass fiber mesh into the first layer of polymer crack-resistant mortar before the first layer of polymer crack-resistant mortar has cured.

[0165] The overlap width between adjacent strips of alkali-resistant fiberglass mesh shall not be less than 100mm.

[0166] After the first layer of polymer crack-resistant mortar has initially set, apply the second layer of polymer crack-resistant mortar so that the first and second layers of polymer crack-resistant mortar together form a polymer crack-resistant mortar layer.

[0167] The polymer-resistant crack-resistant mortar layer and the alkali-resistant glass fiber mesh embedded in the polymer-resistant crack-resistant mortar layer together constitute the reinforcing protective layer 4. The total thickness of the reinforcing protective layer 4 is 4-6 mm.

[0168] After the reinforced protective layer 4 has been cured for no less than 7 days, a fire-retardant coating is applied to the surface of the reinforced protective layer 4 to form a fire-retardant surface layer 5. The fire-retardant surface layer 5 preferably uses a fire-retardant coating with a combustion performance of not less than Class A, and the thickness of the fire-retardant surface layer 5 is 0.3 to 0.5 mm.

[0169] After the fireproof surface layer 5 is completed, remove the temporary shielding strip set at the opening of the electric heating cable installation trough to keep the electric heating cable installation trough open.

[0170] S7, Electric heating tape construction

[0171] Self-regulating heating cables are laid in the cable tracing installation trench. The self-regulating heating cables extend continuously along the circumference of the tunnel, and the distance between adjacent self-regulating heating cables along the longitudinal direction of the tunnel is no more than 500mm.

[0172] Self-regulating heating cables can be fixed in the heating cable installation groove using fixing clips or heat-resistant adhesive dots.

[0173] Thermally conductive silicone grease is filled between the self-regulating electric heating cable and the wall of the electric heating cable installation groove to form a thermally conductive silicone grease layer covering the self-regulating electric heating cable.

[0174] The thermally conductive silicone grease layer is used to reduce the contact thermal resistance between the self-regulating electric heating cable and the sprayed insulation layer 3, and to ensure that the heat generated by the self-regulating electric heating cable is evenly transferred along the electric heating cable installation groove.

[0175] Silicone sealant is filled on the outside of the thermally conductive silicone grease layer to form a silicone sealant layer that seals the groove of the electric heating cable installation channel.

[0176] The self-regulating heating cable is connected to the temperature controller. The temperature detection end of the temperature controller is set on the surface of the secondary lining 1 of the tunnel in the first insulation section or on the side of the sprayed insulation layer 3 near the secondary lining 1 of the tunnel.

[0177] When the temperature detected by the temperature sensor drops to the start-up temperature, the temperature controller connects the self-regulating heating cable; when the temperature rises to the stop temperature, the temperature controller disconnects the self-regulating heating cable.

[0178] The start-up temperature can be set to 1–3℃, and the stop temperature can be set to 6–10℃. The start-up and stop temperatures are determined based on the extreme minimum air temperature at the tunnel location, the design thickness of the sprayed insulation layer 3, and the degree of cold air intrusion at the tunnel entrance.

[0179] Implementation Method 2

[0180] like Figure 2 and Figure 3 As shown, this embodiment provides a segmented variable thickness sprayed insulation structure for cold-region tunnels formed using the above-described construction method.

[0181] The segmented variable thickness sprayed insulation structure for tunnels in cold regions includes an interface reinforcement layer 2, a sprayed insulation layer 3, a reinforced protective layer 4, and a fireproof surface layer 5, which are sequentially arranged from the inner surface of the secondary lining 1 of the tunnel towards the tunnel clearance.

[0182] The interface reinforcement layer 2 is a film formed by curing an acrylic emulsion modified with a silane coupling agent. The interface reinforcement layer 2 continuously covers the inner surface of the secondary tunnel lining 1, and the thickness of the interface reinforcement layer 2 is 0.1-0.3 mm.

[0183] The sprayed insulation layer 3 is a modified rigid polyurethane closed-cell foam layer. The sprayed insulation layer 3 is in direct contact with the interface reinforcement layer 2 and extends continuously along the inner surface of the tunnel secondary lining 1, thereby reducing the gaps formed by the splicing of prefabricated insulation panels.

[0184] The sprayed insulation layer 3 is divided into at least four insulation sections along the longitudinal direction of the tunnel, and the thickness of each insulation section decreases from the tunnel entrance to the depth of the tunnel.

[0185] In a preferred configuration, the sprayed insulation layer 3 includes a first insulation section, a second insulation section, a third insulation section, and a fourth insulation section.

[0186] The first insulation section is 0-50m from the tunnel entrance and has a thickness of 7-10cm; the second insulation section is 50-200m from the tunnel entrance and has a thickness of 6-8cm; the third insulation section is 200-500m from the tunnel entrance and has a thickness of 3-5cm; the fourth insulation section extends from 500m from the tunnel entrance to the depth of the sprayed insulation layer 3 and has a thickness of 2-3cm.

[0187] A thickness gradient transition section is provided between two adjacent insulation sections. The length of the thickness gradient transition section is not less than 3m, and the thickness of the sprayed insulation layer 3 changes continuously within the thickness gradient transition section.

[0188] The reinforced protective layer 4 includes a polymer crack-resistant mortar layer and an alkali-resistant glass fiber mesh embedded in the polymer crack-resistant mortar layer.

[0189] The fireproof surface layer 5 is installed on the side of the reinforced protective layer 4 facing the tunnel clearance.

[0190] At least one insulation section near the tunnel entrance is designated as the near-entrance insulation section. In this embodiment, the first insulation section is the near-entrance insulation section, and the thickness of the first insulation section is not less than the thickness of the other insulation sections. The first insulation section is provided with multiple electric heating cable installation slots embedded in the sprayed insulation layer 3. The electric heating cable installation slots extend circumferentially along the tunnel, and the distance between adjacent electric heating cable installation slots along the longitudinal direction of the tunnel is not greater than 500mm.

[0191] The electric heating cable installation trough does not penetrate the sprayed insulation layer 3, so that a continuous sprayed insulation layer is maintained between the bottom of the electric heating cable installation trough and the interface reinforcement layer 2; the electric heating cable installation trough is provided with a self-regulating electric heating cable, a thermally conductive silicone grease layer and a silicone sealant layer. The thermally conductive silicone grease layer covers the self-regulating electric heating cable, and the silicone sealant layer seals the opening of the electric heating cable installation trough.

[0192] Example 1

[0193] This embodiment uses a cold-region tunnel on a highway in Liaoning Province as an example to illustrate the specific implementation process of the present invention.

[0194] The tunnel is a split tunnel, with each tunnel exceeding 5500m in length. The average annual temperature in the tunnel site area is approximately 6.5℃, with an extreme minimum temperature of approximately -38℃, and the sub-zero temperature period lasts from October to April of the following year.

[0195] Longitudinal monitoring sections were set up at the tunnel entrance and at locations 10m, 50m, 100m, 200m, 500m, 1000m, and 1500m from the tunnel entrance. Each longitudinal monitoring section was equipped with monitoring points for the inner surface temperature of the secondary lining, the outer surface temperature of the initial support, and the surrounding rock temperature at locations 60cm, 120cm, and 180cm outside the initial support.

[0196] After 12 months of continuous monitoring, the results showed that the temperature variation inside the tunnel decreased with increasing distance from the tunnel entrance, and the temperature variation decreased significantly after 500m from the tunnel entrance; the temperature of the surrounding rock tended to stabilize with increasing radial depth from the tunnel wall.

[0197] A three-dimensional transient water-thermal coupling model was established. The calculation area of ​​the model is 1600m along the longitudinal direction of the tunnel, and the calculation range of the rock outside the tunnel cross section is 60m×60m.

[0198] In the model, the density of the surrounding rock is taken as 1800 kg / m³, the thermal conductivity of the surrounding rock is taken as 1.85 W / (m·℃), and the specific heat capacity of the surrounding rock is taken as 840 J / (kg·℃); the density of the secondary lining 1 of the tunnel is taken as 2400 kg / m³, and the thermal conductivity is taken as 1.81 W / (m·℃).

[0199] The external temperature is used as the periodic temperature boundary outside the tunnel, and the longitudinal atmospheric temperature of the tunnel at each longitudinal monitoring section is used as the internal temperature boundary inside the tunnel. The model parameters are then corrected based on the radial temperature monitoring results of the surrounding rock.

[0200] Based on the lowest temperature at each radial temperature monitoring point, linear interpolation is performed on adjacent radial temperature monitoring points located on both sides of 0℃ to obtain the field monitoring freezing depth. The relative error between the freezing depth calculated by the model and the field monitoring freezing depth is less than 9%, indicating that the model can be used to determine the length and design thickness of the thermal insulation protection.

[0201] The average temperature of the coldest month at the tunnel entrance is about -14℃. The insulation length calculated according to the empirical formula is about 762m, and the insulation length calculated by the transient water-heat coupling model is 1000m. Therefore, the larger value of 1000m is determined as the insulation length.

[0202] The insulation protection area is divided into four insulation zones.

[0203] The first insulation section is located 0-50m from the tunnel entrance, with a designed thickness of 10cm; the second insulation section is located 50-200m from the tunnel entrance, with a designed thickness of 6cm; the third insulation section is located 200-500m from the tunnel entrance, with a designed thickness of 4cm; and the fourth insulation section is located 500-1000m from the tunnel entrance, with a designed thickness of 2cm.

[0204] Transient water-heat coupling model calculations show that even after increasing the simulated insulation layer thickness of the first insulation section to the preset maximum spraying thickness of 10cm, there are still locations where the intermediate temperature of the secondary lining is below 0℃. Therefore, the first insulation section is determined as the insulation section near the opening, its design thickness is set to 10cm, and a self-regulating electric heating cable is installed. By adjusting the rated power and longitudinal spacing of the self-regulating electric heating cable, the intermediate temperature of the secondary lining at each calculated section in the first insulation section is not lower than 0℃ when the rated power is 15W / m and the longitudinal spacing is 500mm.

[0205] During construction, the inner surface of the secondary lining 1 of the tunnel was first inspected. Any water seepage points were sealed with polyurethane grout, and cracks wider than 0.3 mm were sealed with epoxy resin.

[0206] After cleaning the base layer, the moisture content was sampled and tested. The moisture content of the base layer was 5.8% to 7.6%, and there was no visible water on the surface.

[0207] A silane coupling agent modified acrylic emulsion was coated on the surface of the sprayed substrate at a coating amount of 175 g / m², and cured for 3 hours at an ambient temperature of approximately 15°C to form an interface reinforcement layer 2.

[0208] The two-component high-pressure spraying equipment was used for construction. The preheating temperature of component A was set to 35℃, the preheating temperature of component B was set to 28℃, the temperature of the heat tracing pipeline was set to 40℃, the spray gun temperature was set to 45℃, the spraying pressure was set to 9.5MPa, the spraying flow rate was set to 4.5kg / min, and the volume ratio of component A to component B was set to 1:1.15.

[0209] The fourth insulation section uses a single-coat spray to form a 2cm thick sprayed insulation layer 3.

[0210] The third insulation section uses two coats of spraying, each with a target thickness of 2cm, and the spray gun directions of adjacent coats are set to cross each other.

[0211] The second insulation section uses two coats of spraying, each with a target thickness of 3cm, and the spray gun directions of adjacent coats are set to cross.

[0212] The first insulation section is coated with three layers of spray, with a target thickness of 33-34 mm for each layer.

[0213] After the first coat of the first insulation section reaches a non-sticky state, heat-resistant silicone mold strips with a cross-sectional size of 8mm×12mm are positioned along the tunnel circumferentially, with adjacent mold strips spaced 500mm apart along the tunnel longitudinal direction.

[0214] The second and third coats of spray coating cover both sides of the mold strip. After the third layer of insulation has cured, the mold strip is removed, forming the installation groove for the electric heating cable.

[0215] A thickness gradient transition section with a length of 3m is set between the first insulation section and the second insulation section, between the second insulation section and the third insulation section, and between the third insulation section and the fourth insulation section.

[0216] Within the thickness gradient transition section, by gradually changing the gun speed, the thickness of the sprayed insulation layer 3 is continuously changed from the design thickness of the adjacent thicker insulation section to the design thickness of the thinner insulation section.

[0217] Thickness was randomly checked after the spraying was completed. The measured average thickness of the first insulation section was 100.5 mm, the measured average thickness of the second insulation section was 61.0 mm, the measured average thickness of the third insulation section was 41.2 mm, and the measured average thickness of the fourth insulation section was 20.8 mm.

[0218] After the thermal insulation layer 3 has cured for 24 hours, surface finishing is performed. The maximum flatness deviation after finishing is 4mm.

[0219] An enhanced protective layer 4 with a total thickness of approximately 5 mm is formed on the surface of the sprayed insulation layer 3, and a fireproof surface layer 5 with a thickness of approximately 0.4 mm is formed after the enhanced protective layer 4 has been cured for 7 days.

[0220] A self-regulating heating cable with a rated power of 15W / m is laid inside the heating cable installation groove. The outside of the self-regulating heating cable is filled with thermally conductive silicone grease to form a thermally conductive silicone grease layer, and the groove opening is sealed with silicone sealant to form a silicone sealant layer.

[0221] The temperature controller's start-up temperature is set to 2℃, and its stop temperature is set to 8℃.

[0222] After construction, core drilling tests were conducted. The density of the sprayed insulation layer 3 was 36-42 kg / m³, the thermal conductivity of each core sample was no greater than 0.020 W / (m·℃), and the pull-out bond strength was 0.14-0.21 MPa.

[0223] During the first freezing period after construction, under the condition that the extreme temperature outside the tunnel was about -35℃, the intermediate temperature of the secondary lining in each insulation section was maintained above 0℃, and no cracking or leakage expansion of the secondary lining 1 of the tunnel was found due to freezing.

[0224] Example 2

[0225] This example uses a tunnel in a cold region with an extreme minimum temperature of approximately -42°C and an average temperature of approximately -22°C in the coldest month as an example.

[0226] The insulation length calculated based on empirical formulas is approximately 1001m, while the insulation length calculated by the transient water-heat coupling model is 1200m. Therefore, the larger value of 1200m is determined as the insulation length.

[0227] Based on the intermediate temperature of the secondary lining at different longitudinal positions, the insulation protection range is divided into five insulation zones.

[0228] The first insulation section is the area from 0 to 50m from the tunnel entrance, with a designed thickness of 10cm, and is equipped with a self-regulating electric heating cable.

[0229] The second insulation section is located 50 to 200 meters from the tunnel entrance, with a designed thickness of 8 cm.

[0230] The third insulation section is located 200 to 500 meters from the tunnel entrance, with a designed thickness of 6 cm.

[0231] The fourth insulation section is located 500-800m from the tunnel entrance, with a designed thickness of 4cm.

[0232] The fifth insulation section is located 800-1200m from the tunnel entrance, with a designed thickness of 2cm.

[0233] Each adjacent insulation section is provided with a thickness gradient transition section with a length of not less than 3m.

[0234] The thermal conductivity of the sprayed insulation material used in this embodiment is 0.018 W / (m·℃). The other steps, such as substrate treatment, interface reinforcement treatment, preparation of spraying equipment, segmented variable thickness spraying, construction of reinforced protective layer 4, construction of fireproof surface layer 5, and construction of self-regulating electric heating cable, are the same as in embodiment one.

[0235] Temperature monitoring was conducted during the first freezing period after construction. Under the condition that the extreme temperature outside the tunnel was about -42℃, the intermediate temperature of the secondary lining in each insulation section remained above 0℃.

[0236] This embodiment illustrates that the insulation sections of the present invention are not limited to four. When the tunnel insulation length is long or the temperature change along the tunnel longitudinal direction is large, the number of insulation sections can be further increased based on no less than four insulation sections, so that the thickness of the sprayed insulation layer 3 matches the tunnel longitudinal anti-freezing requirements.

[0237] The above are merely preferred embodiments of the present invention. The number of insulation sections, the longitudinal range of each insulation section, and the design thickness should be determined based on the temperature monitoring results of the specific tunnel and the calculation results of the transient water-heat coupling model, and should not be construed as being limited to the values ​​listed in the embodiments.

Claims

1. A sectional variable-thickness spraying heat preservation construction method for cold region tunnels, characterized in that, Includes the following steps: S1. Determine the insulation protection range and insulation zone parameters, including: S101. Obtain the ambient temperature outside the tunnel, the longitudinal ambient temperature of the tunnel, and the radial temperature of the surrounding rock, establish a transient water-heat coupling model, determine the insulation length based on the transient water-heat coupling model, and divide the insulation range into at least four insulation zones. S102. Adjust the simulated insulation layer thickness segment by segment based on the criterion that the intermediate temperature of the secondary lining is not lower than 0℃. For insulation sections that meet the criterion before reaching the preset maximum spraying thickness, determine the design thickness based on the simulated insulation layer thickness that meets the criterion. For insulation sections that do not meet the criterion after reaching the preset maximum spraying thickness, determine them as insulation sections near the tunnel entrance. Set the preset maximum spraying thickness as the design thickness of the insulation sections near the tunnel entrance. Determine the arrangement parameters of the self-regulating electric heating tape based on the criterion that the intermediate temperature of the secondary lining is not lower than 0℃ after laying the self-regulating electric heating tape, so that the design thickness of each insulation section decreases from the tunnel entrance to the tunnel depth. S2. Clean the inner surface of the secondary lining of the tunnel within the insulation range, seal or drain the cracks and seepage points to form a sprayed base layer without standing water. S3. Apply an interface treatment agent to the surface of the sprayed base layer and cure it until the surface of the interface treatment agent is dry to the touch to form an interface reinforcement layer. S4. Use a two-component high-pressure spraying device to preheat the A and B components of the sprayed insulation material, and heat the delivery pipeline and spray gun to complete the test spraying inspection of the sprayed insulation material. S5. According to the design thickness of each insulation section, a sprayed insulation layer is formed by single-pass spraying or multiple-pass spraying. A thickness gradient transition section is formed at the junction of two adjacent insulation sections, so that the thickness of the sprayed insulation layer continuously changes from the design thickness of the thicker insulation section to the design thickness of the thinner insulation section within the thickness gradient transition section. An electric heating cable installation groove is reserved during the spraying process of the insulation section near the opening. S6. The surface of the cured sprayed insulation layer is trimmed, and an enhanced protective layer and a fireproof surface layer are formed sequentially on the surface of the trimmed sprayed insulation layer. S7. Lay a self-regulating electric heating cable in the electric heating cable installation groove, and fill the electric heating cable installation groove with heat-conducting material and seal the groove opening.

2. The cold region tunnel sectional variable thickness spray and apply thermal insulation construction method according to claim 1, characterized in that, The insulation section includes: The first insulation section is located 0-50m from the tunnel entrance, and the design thickness of the first insulation section is 7-10cm. The second insulation section is located 50 to 200 meters from the tunnel entrance, and its design thickness is 6 to 8 cm. The third insulation section is located 200 to 500 meters from the tunnel entrance, and the design thickness of the third insulation section is 3 to 5 cm. The fourth insulation section, located 500m from the tunnel entrance to the end of the insulation length, has a design thickness of 2-3cm. The design thickness of the first insulation section, the second insulation section, the third insulation section, and the fourth insulation section are selected in a progressively decreasing manner within their respective ranges.

3. The method for segmented variable thickness spray insulation construction of tunnels in cold regions according to claim 1, characterized in that, In step S101, at least eight longitudinal monitoring sections are set from the tunnel entrance to the tunnel depth. The longitudinal monitoring sections are set at the tunnel entrance and at positions 10m, 50m, 100m, 200m, 500m, 1000m and 1500m away from the tunnel entrance. Each longitudinal monitoring section is set with at least five radial temperature monitoring points along the surrounding rock. The radial temperature monitoring points are set at different depths on the inner surface of the secondary lining, the outer surface of the initial support and the outer side of the initial support.

4. The method for segmented variable thickness spray insulation construction of tunnels in cold regions according to claim 1, characterized in that, In step S101, the empirically calculated value of the insulation length is obtained based on the average temperature of the coldest month at the tunnel entrance, and the model-calculated value of the insulation length is obtained based on the transient water-thermal coupling model. The larger of the empirically calculated value and the model-calculated value is determined as the insulation length. The transient water-thermal coupling model simulates at least the heat conduction of the surrounding rock, the migration of pore water in the surrounding rock, and the water-ice phase change process. In step S102, the simulated insulation layer thickness corresponding to each insulation section is adjusted according to a preset thickness step. For insulation sections where the intermediate temperature of the secondary lining is not lower than 0°C before reaching the preset maximum spraying thickness, the sum of the minimum simulated insulation layer thickness that meets this condition and the thickness safety margin is determined as the design thickness. For the insulation section near the tunnel entrance, the rated power and longitudinal spacing of the self-regulating electric heating tape are determined based on the criterion that the intermediate temperature of the secondary lining is not lower than 0°C after the self-regulating electric heating tape is laid.

5. The method for segmented variable thickness spray insulation construction of tunnels in cold regions according to claim 1, characterized in that, The sprayed insulation material is modified rigid polyurethane closed-cell foam, which has a thermal conductivity of no more than 0.020 W / (m·℃), a closed-cell rate of no less than 95%, a molding density of 35-45 kg / m³, a compressive strength of no less than 200 kPa, a volumetric water absorption rate of no more than 3%, and an oxygen index of no less than 30%. In step S4, the preheating temperature of component A is 30-40℃, the preheating temperature of component B is 25-35℃, the heating temperature of the conveying pipeline is 35-45℃, the heating temperature of the spray gun is 40-50℃, the spraying pressure is 8-12 MPa, the spraying flow rate is 3-6 kg / min, and the volume ratio of component A to component B is 1:1.05-1.

20.

6. The method for segmented variable thickness spray insulation construction of tunnels in cold regions according to claim 1, characterized in that, In step S5, when the sprayed insulation layer is formed by multiple spraying passes, the spray gun directions of adjacent spraying passes are arranged in an intersecting manner. The distance between the spray gun and the inner surface of the tunnel secondary lining is 400-600mm, the spray gun speed is 0.3-0.5m / s, and the overlap width between adjacent spraying passes is 80-120mm. The length of the thickness gradient transition section is not less than 3m. Within the thickness gradient transition section, the spray gun speed is continuously adjusted from the spray gun speed corresponding to the thicker insulation section to the spray gun speed corresponding to the thinner insulation section.

7. The method for segmented variable thickness spray insulation construction of tunnels in cold regions according to claim 1, characterized in that, In step S5, a mold strip is positioned on the surface of the first layer of sprayed coating in the near-end insulation section of the tunnel opening, so that the subsequent sprayed coating covers both sides of the mold strip. After the sprayed insulation layer is cured, the mold strip is removed to form the electric heating cable installation groove. In step S7, the self-regulating electric heating cable is continuously laid along the circumference of the tunnel, and the spacing between adjacent self-regulating electric heating cables along the longitudinal direction of the tunnel is no more than 500mm. Thermally conductive silicone grease is filled on the outside of the self-regulating electric heating cable, and the electric heating cable installation groove is sealed with silicone sealant.

8. A segmented variable thickness spray insulation structure for tunnels in cold regions, characterized in that, It includes an interface reinforcement layer, a sprayed insulation layer, a reinforced protective layer, and a fireproof surface layer, which are sequentially arranged from the inner surface of the secondary tunnel lining towards the tunnel clearance direction; The interface reinforcement layer is a film layer formed by curing a silane coupling agent-modified acrylate emulsion; The sprayed insulation layer is a modified rigid polyurethane closed-cell foam layer. The sprayed insulation layer is divided into at least four insulation sections along the longitudinal direction of the tunnel. The thickness of each insulation section decreases from the tunnel entrance to the depth of the tunnel. There is a thickness transition section between two adjacent insulation sections. The thickness of the sprayed insulation layer changes continuously within the thickness transition section. The reinforced protective layer includes a polymer crack-resistant mortar layer and an alkali-resistant glass fiber mesh embedded in the polymer crack-resistant mortar layer; The fireproof surface layer is a fireproof coating layer applied to the surface of the reinforced protective layer; At least one of the insulation sections near the tunnel entrance is a near-entrance insulation section, and the thickness of the near-entrance insulation section is not less than the thickness of the other insulation sections; the near-entrance insulation section is provided with an electric heating cable installation groove embedded in the sprayed insulation layer, the electric heating cable installation groove does not penetrate the sprayed insulation layer, so that a continuous sprayed insulation layer is maintained between the bottom of the electric heating cable installation groove and the interface reinforcement layer.

9. The segmented variable thickness spray insulation structure for cold-region tunnels according to claim 8, characterized in that, The insulation sections include a first insulation section with a thickness of 7-10cm located 0-50m from the tunnel entrance, a second insulation section with a thickness of 6-8cm located 50-200m from the tunnel entrance, a third insulation section with a thickness of 3-5cm located 200-500m from the tunnel entrance, and a fourth insulation section with a thickness of 2-3cm extending from 500m from the tunnel entrance to the depth of the sprayed insulation layer. The thickness of the first, second, third, and fourth insulation sections decreases progressively, and the length of the thickness transition section is not less than 3m.

10. The segmented variable thickness spray insulation structure for cold-region tunnels according to claim 8, characterized in that, The electric heating cable installation groove is provided with a self-regulating electric heating cable, which extends continuously along the circumference of the tunnel, and the distance between adjacent self-regulating electric heating cables along the longitudinal direction of the tunnel is no more than 500mm; the electric heating cable installation groove is also provided with a thermally conductive silicone grease layer covering the self-regulating electric heating cable and a silicone sealant layer sealing the groove opening of the electric heating cable installation groove.

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