Real-time control calculation method for heat preservation of the closed hole opening with silica fume-lined concrete

Abstract

The present invention provides a real-time control calculation method for the insulation of the closed opening of silica fume lining concrete, which is conducive to more optimized control of the temperature cracks of the silica fume lining concrete in the Longluowei section. Through on-site internal temperature observation and simple and rapid calculation, the internal and external temperature difference control and the insulation design of the closed opening are carried out in real time, and the insulation of the closed opening is implemented in a timely manner. The real-time control calculation method for the insulation of the closed opening of silica fume lining concrete includes: Step 1. Obtain the temperature crack control data of the silica fume lining concrete of the flood discharge tunnel; Step 2. Calculate the allowable internal and external temperature difference 【△T nw 】 of the silica fume lining concrete of the flood discharge tunnel; Step 3. Real-time monitor and analyze the internal temperature observation information of the silica fume lining concrete to obtain the monitored value of the internal and external temperature difference; Step 4. Compare the allowable internal and external temperature difference 【△T nw 】 with the monitored value, and based on the comparison result, analyze in real time and reasonably take the insulation measures for closing the tunnel opening.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete temperature crack control, and specifically relates to a real-time control calculation method for the thermal insulation of the closed opening of silica fume lining concrete. Background Art

[0002] According to the "Design Specification for Temperature Control of Concrete Dams" (NB / T 35092-2017), the internal and external temperature difference refers to the difference between the highest temperature inside the concrete and the surface temperature of the concrete. The internal and external temperature difference is an important parameter for concrete temperature crack control. Due to the differences in the hydration processes of concretes with different structures and different admixtures such as silica fume, there will be significant differences in the internal and external temperature differences of the concrete.

[0003] To improve the abrasion resistance of the concrete in the high-flow velocity area of the dragon tail section of the spillway tunnel ( Figure 1 ), silica fume (admixture) is often added, and the thermal, mechanical, abrasion resistance, construction and other properties of the concrete have changed significantly. In particular, the early shrinkage deformation performance is relatively large, and early surface cracks are likely to occur. For example, Figure 2 For the silica fume concrete of the side wall of the dragon tail section of the Baihetan spillway tunnel, due to the relatively large early internal and external temperature difference resulting in relatively large surface temperature stress, and due to the reasons such as the failure to timely close the opening for thermal insulation and good moisture conservation, turtle-back-shaped microcracks occurred on the concrete surface in the early stage. Although the microcracks healed and closed after the later-stage strengthening of maintenance and thermal insulation, it also caused micro-damage, affecting the strength and durability of the concrete.

[0004] Lining is an inevitable structure for the dragon tail section of the spillway tunnel ( Figure 3 ). There are no regulations and standards for controlling the internal and external temperature difference of lining concrete in the relevant code articles of hydraulic tunnels and structural concrete. For the section from the closed thermal insulation door to the opening, the surface thermal insulation design calculation can be carried out according to the mass concrete such as the dam (although the current calculation using the finite element method, difference method, etc. is complex, and a large number of physical and mechanical, thermal performance tests of concrete are required). However, for the silica fume concrete lining in the dragon tail section of the tunnel, since the temperature variation in the tunnel is relatively smaller than that of the natural environment, surface covering or wrapping thermal insulation will not be adopted, so there has been no research on the control or design calculation of the internal and external temperature difference of the lining concrete in the tunnel so far, let alone the control standard and the design method of control measures. However, like mass concrete, the internal and external temperature difference is still an important factor causing temperature cracks, and the lining structure has a small thickness, and the surface geometric temperature gradient generated by the internal and external temperature difference is particularly large, which is the main reason for the generation of early surface cracks. The temperature control measures such as water cooling not only need to reduce the highest internal temperature but also need to reduce the internal and external temperature difference. Moreover, due to the differences in the hydration processes of concretes with different structures and different admixtures such as silica fume, there will be significant differences in the internal and external temperature differences of the concrete.

[0005] Therefore, for the silica fume lining concrete of the Longluowei section, it is urgent to conduct research on the internal and external temperature differences, and propose a control standard for the allowable internal and external temperature differences that is simple, highly accurate, and can be quickly calculated, so that construction personnel can conduct real-time control of the internal and external temperature differences and design the thermal insulation of the closed tunnel entrance through on-site internal temperature observation and simple and quick calculation. Summary of the Invention

[0006] The purpose of the present invention is to provide a real-time control calculation method for the thermal insulation of the closed tunnel entrance of silica fume lining concrete, which is conducive to more optimized control of the temperature cracks of silica fume lining concrete in the Longluowei section. Through on-site internal temperature observation and simple and quick calculation, real-time control of the internal and external temperature differences and design of the thermal insulation of the closed tunnel entrance are carried out, and the thermal insulation of the closed tunnel entrance is implemented in a timely manner.

[0007] In order to achieve the above purpose, the present invention adopts the following solutions:

[0008] As Figure 4 shown, the present invention provides a real-time control calculation method for the thermal insulation of the closed tunnel entrance of silica fume lining concrete, which is characterized by including the following steps:

[0009] Step 1. Obtain the temperature crack control data of the silica fume lining concrete of the flood discharge tunnel;

[0010] Step 2. Calculate the allowable internal and external temperature difference

△T nw

[0011]

△T nw

[0012] In the formula: β is the silica fume content. For example, when the content is 5%, β = 0.05; H is the thickness (m) of the silica fume lining concrete structure; L is the length (m) of the longest side of the lining structure section. When the side wall height is greater than the joint length, the side wall height (m) is taken; C is the strength grade (MPa) of the silica fume lining concrete at the 90-day design age. For example, if C 90 40, then C = 40; T a is the in-tunnel air temperature value (°C) during the concrete pouring period; E is the surrounding rock deformation modulus (GPa); it must be pointed out that when the strength grade designed for the 28-day age of the lining concrete is used, it needs to be converted to the strength grade designed for the 90-day age according to the specifications; if hanging curtain thermal insulation is adopted during the construction period, resulting in an increase in the air temperature in the underground cavern, then T a should adopt the increased in-tunnel air temperature;

[0013] Step 3. Real-time monitor and analyze the internal temperature observation information of the silica fume lining concrete to obtain the monitored value of the internal and external temperature difference;

[0014] Step 4. Compare the allowable internal and external temperature difference [ΔT nw with the monitored value, and based on the comparison result, analyze in real time and reasonably adopt heat preservation measures for closing the tunnel portal.

[0015] For the length L of the longest side of the lining structure section in Step 2, taking Figure 7 as an example for further supplementary description: For the flood discharge tunnel of Baihetan Hydropower Station, the joint length is 12 m. First, pour the side wall to the straight height of the bottom bedrock of 13.2 m (see the left side wall, from the top to the construction joint, and from the bottom to the bedrock, height = 12 m + 1.2 m = 13.2 m), which is greater than the joint length. At this time, take L = 13.2 m. For the diversion tunnel of Baihetan, the joint length is 15 m. Similarly Figure 7 pour the side wall first, then the side wall height of 13.2 m is less than the joint length, and L should be taken as the joint length, L = 15 m.

[0016] Preferably, the real-time control calculation method for heat preservation of the silica fume lining concrete for closing the tunnel portal provided by the present invention may further have the following characteristics: In Step 1, the temperature crack control data of the silica fume lining concrete of the flood discharge tunnel obtained includes: the general situation of the flood discharge tunnel project, hydrological and meteorological information data, and the technical requirements for temperature control design of the silica fume lining concrete.

[0017] Preferably, the real-time control calculation method for heat preservation of the silica fume lining concrete for closing the tunnel portal provided by the present invention may further have the following characteristics: Step 3 includes the following sub-steps:

[0018] Step 3.1 Monitor the internal temperature through the temperature sensor installed at the center of the silica fume lining concrete.

[0019] Step 3.2 Analyze the internal temperature observation data of the silica fume lining concrete to determine the internal maximum temperature T max ;

[0020] Step 3.3 Calculate the monitored value of the internal and external temperature difference of the silica fume lining concrete:

[0021] ΔT nw = T max - T a (Formula 2)

[0022] Since the lining concrete in the tunnel will not be covered for heat preservation, and the surface concrete temperature drops rapidly to reach the tunnel air temperature, the surface concrete temperature is approximately taken as the tunnel air temperature, that is, the tunnel air temperature T a during the concrete pouring period. The internal and external temperature difference calculated in this way is slightly on the high side, and it is safe to control with this calculated value.

[0023] Preferably, the real-time control calculation method for heat preservation of the silica fume lining concrete for closing the tunnel portal provided by the present invention may further have the following characteristics: Step 4 includes the following sub-steps:

[0024] Step 4.1 Compare and analyze the internal and external temperature difference △T nw Whether it exceeds the allowable value [△T nw ;

[0025] Step 4.2 If △T nw ≤ [△T nw , no heat preservation measures are required; if △T nw > [△T nw , then close the opening for heat preservation.

[0026] Preferably, the real-time control calculation method for heat preservation of the silica fume-lined concrete closed opening provided by the present invention may further have the following characteristics: In step 4.2, if [△T nw < △T nw ≤ [△T nw + 2.0 °C, then adopt a simple curtain hanging method to close the opening for heat preservation; if △T nw > [△T nw + 2.0 °C, then adopt a strict method to close the opening for heat preservation.

[0027] Preferably, the real-time control calculation method for heat preservation of the silica fume-lined concrete closed opening provided by the present invention may further have the following characteristics: As Figure 5 shown, the simple curtain hanging method to close the opening for heat preservation refers to a method of closing the opening by using a thin geotextile, plastic film, etc. to cover the opening in a hanging manner, and the combination between each strip / block is not tight, there are ventilation leaks or gaps;

[0028] As Figure 6 shown, the strict method to close the opening for heat preservation refers to a method of closing the opening by using a thick heat preservation quilt, cotton felt, etc. to strictly fix and seal the whole opening, and the closed structure forms a whole without ventilation gaps.

[0029] In addition, the reliability of the (formula 1) for calculating the allowable internal and external temperature difference [△T nw of the silica fume-lined concrete in the dragon's tail section in step 2 above is verified as follows: Taking the dragon's tail section project of a large domestic flood discharge tunnel as an example, the temperature and temperature stress simulation calculations of 111 schemes of lining concrete with different silica fume contents, different thicknesses, and different strength grades in the side walls of the horseshoe-shaped section in the dragon's tail section under different temperature control measures are carried out by using the three-dimensional finite element method, and the internal and external temperature differences of 60 schemes with a crack resistance safety factor greater than 1.0 are sorted out and listed in Table 1, and then these data are statistically analyzed; the crack resistance safety factors corresponding to the internal and external temperature differences of these 60 schemes are all greater than 1.0, which verifies that as long as the internal and external temperature difference of the silica fume concrete in the lining structure does not exceed the calculated value of (formula 1), no surface temperature cracks will occur.

[0030] Table 1 Simulation calculation results of the internal and external temperature differences of the silica fume-lined concrete in the side walls of the horseshoe-shaped section

[0031]

[0032]

[0033] Note: The concrete strength values in the table are the grade values at 90-day age. For example, 60 corresponds to C 90 60.

[0034] Functions and Effects of the Invention

[0035] The real-time control calculation method for heat preservation of the silica fume-lined concrete closed portal of the present invention first proposes a scientific method for calculating the allowable internal and external temperature difference. Considering the influence of factors such as silica fume content, lining structure size, concrete strength, surrounding rock deformation modulus, and in-cave air temperature during the pouring period on the allowable internal and external temperature difference, it can scientifically calculate the allowable internal and external temperature difference of silica fume concrete with high precision. Then, the monitored value of the internal and external temperature difference is compared with the allowable value in real time to determine the heat preservation measures for closing the portal in the low-temperature season, and the internal and external temperature difference is controlled in real time to effectively prevent early surface cracks. It is especially applicable to the silica fume-lined concrete in the long tail drop section. Description of the Drawings

[0036] Figure 1 It is the spillway bucket spillway discharge diagram of the outlet of the long tail drop section of the flood discharge tunnel related to the present invention. Among them, (a) is a photo of the flood discharge and flow-through of the Xiluodu flood discharge tunnel, and (b) is a photo of the flood discharge and flow-through of the Baihetan flood discharge tunnel;

[0037] Figure 2 It is the early-stage turtle-back-shaped fine crack diagram of the silica fume-lined concrete of the side wall of the long tail drop section of the Baihetan flood discharge tunnel related to the present invention;

[0038] Figure 3 It is the cross-sectional diagram of the circular-arch straight-wall type lining structure of the hydraulic tunnel related to the present invention (unit: m);

[0039] Figure 4 It is the flow chart of the real-time control calculation method for heat preservation of the silica fume-lined concrete closed portal (only showing one round of calculation and comparison process);

[0040] Figure 5 It is the schematic diagram of the heat preservation structure for simple heat preservation of the closed portal and prevention of cross ventilation in winter related to the present invention;

[0041] Figure 6 It is the schematic diagram of the strict heat preservation structure for closing the portal of the Baihetan flood discharge tunnel related to the present invention;

[0042] Figure 7 It is the cross-sectional diagram of the 1.2m-thick lining structure of the long tail drop section of the Baihetan flood discharge tunnel related to the present invention;

[0043] Figure 8This is the cross-sectional view of the lining structure with a thickness of 1.5 m at the dragon's tail of the spillway tunnel of Baihetan Hydropower Station, which is related to the present invention. Specific embodiments

[0044] The following will take the silica fume lining concrete of the dragon's tail lining structure of the spillway tunnel project of Baihetan Hydropower Station as an example in combination with the drawings, and elaborate in detail on the specific implementation plan of the real-time control calculation method for the thermal insulation of the silica fume lining concrete closed opening involved in the present invention.

[0045] <Temperature control data of the lining concrete of the spillway tunnel project of Baihetan Hydropower Station>

[0046] The installed capacity of Baihetan Hydropower Station is 16,000 MW, which is the second largest hydropower station in the world (second only to the Three Gorges). The hub project consists of main buildings such as a barrage, a flood discharge and energy dissipation structure, and a water intake and power generation system. The flood discharge facilities include 6 surface outlets, 7 deep outlets of the dam, and 3 spillway tunnels on the left bank. The 3 spillway tunnels are arranged on the left bank and adopt the form of unpressurized spillway tunnels. They are all composed of an intake (gate chamber), an unpressurized gentle slope section, a dragon's tail section, and an outlet flip bucket. The reverse arcs of the dragon's tails of the 1# and 2# spillway tunnels are directly connected to the flip bucket. Due to topographical conditions, the end of the reverse arc of the 3# tunnel is connected to a horizontal section with a slope of 8%, and then connected to the outlet flip bucket.

[0047] The tunnel section of the spillway tunnel includes the unpressurized section and the dragon's tail section of the spillway tunnel, both of which are in the shape of a horseshoe cross-section. According to characteristics such as lining thickness and surrounding rock, they are divided into four basic lining types with thicknesses of 1.0 m, 1.2 m, 1.5 m, and 2.5 m. The design allowable maximum temperature of the lining concrete of the spillway tunnel is shown in Table 2.

[0048] Table 2 Allowable maximum temperature during the construction period of the lining concrete of the spillway tunnel Unit: °C

[0049]

[0050]

[0051] During the whole process of concrete pouring and curing, temperature control of the concrete is carried out to avoid concrete cracking. The design requirements for temperature control measures include:

[0052] (1) Optimize the concrete mix ratio and improve the crack resistance of the concrete.

[0053] (2) Reasonably arrange the concrete construction procedures and construction progress, and strive to improve the construction management level.

[0054] (3) Control the maximum internal temperature of concrete. Effective measures include reducing the concrete pouring temperature, reducing the heat rise of cementitious materials hydration, and initial water circulation, etc. For the water circulation cooling time, it is required that the concrete surface temperature reaches the tunnel air temperature, generally 10 - 20 days. Control the lining concrete pouring temperature, which is 20°C from April to September; and 18°C from October to March of the following year. The concrete transportation tools should have heat insulation and sunshade measures to shorten the exposure time of concrete to the sun and reduce the temperature rise during the concrete transportation and pouring process. Try to avoid pouring concrete during high-temperature periods, and make full use of the low-temperature seasons and the periods with low temperatures in the early morning, evening and night for pouring.

[0055] <Example 1> Pouring the 1.2m-thick silica fume lining concrete at the dragon's tail of the flood discharge tunnel in the low-temperature season, closing the tunnel entrance for heat preservation and real-time control

[0056] For the silica fume lining concrete at the dragon's tail of the flood discharge tunnel, in the surrounding rock area of Class Ⅲ1, the deformation modulus E of the surrounding rock is 15GPa, the lining thickness is 1.2m, the section is horseshoe-shaped, and generally a circumferential construction joint is set every 12m along the axis of the flood discharge tunnel (due to the curve descent of the dragon's tail section, the lengths of each structural section are inconsistent, and the specific lengths can be seen in the structural section calculation). The bottom slab and side walls of the lining structure are C 90 60 low-heat concrete, and the crown is C 90 30 low-heat concrete, with 5% silica fume added, as Figure 7 shown. The concrete is poured in 3 stages: first the side walls, then the crown, and finally the bottom slab. The basic temperature control data is the same as above. It is maintained with normal-temperature tap water for 90 days, and water circulation cooling is used to control the internal temperature of the concrete.

[0057] According to the above temperature control data, the construction unit plans to take temperature control measures for pouring: pour at about 16°C in the low-temperature season, cool with river water at T w = about 15°C for 10 days, and the formwork removal time t m = 3 days. For the air temperature in the tunnel, based on the monitoring data of the air temperature in the diversion tunnel, the annual average air temperature is 14 - 26°C without the condition of closing the tunnel entrance for heat preservation.

[0058] Taking the 51st unit of the 3# flood discharge tunnel of Baihetan as an example for real-time control. The 3# flood discharge tunnel of Baihetan is constructed by the 5th Bureau of Hydropower Engineering Group Co., Ltd. The 51st unit of the 3# flood discharge tunnel has a stake number of 2 + 089.27 - 2 + 098.24m, a lining thickness of 1.2m, a side wall height of 13.06m, a joint length of 8.97m, C 90 60 low-heat concrete, and the surrounding rock of Class Ⅲ1 has E = 15GPa. The concrete pouring started at 11:10 on March 15, 2019 and was completed at 19:30 on March 16. The measured air temperature in the tunnel is 20.3°C, the pouring temperature is 16.4°C, and it is cooled with water at 14.6°C for 19 days. A thermometer is installed at the center of the lining, and the measured maximum internal temperature is 36.81°C.

[0059] AsFigure 4 As shown in the figure, the real-time control calculation method for the heat preservation of the siliceous powder-lined concrete closed tunnel entrance provided in this embodiment includes the following contents:

[0060] Step 1. Analyze the data on temperature crack control of the siliceous powder-lined concrete in the dragon's tail drop section of the flood discharge tunnel. Since the flood discharge tunnel of the Baihetan Hydropower Station is a Class 1 building and the maximum water flow velocity reaches nearly 50 m / s, temperature control and crack prevention of the lined concrete are very important. According to the design requirements, effective measures including water cooling need to be taken for temperature control.

[0061] Step 2. Calculate the allowable internal and external temperature difference

△T nw

△T nw

[0062] Step 3. Real-time monitor and analyze the internal temperature observation data of the siliceous powder-lined concrete, including:

[0063] Step 3.1 Install thermometers at the center of the siliceous powder-lined concrete to monitor the internal temperature. For relevant technologies, refer to relevant specifications. The temperature monitoring results are as described above.

[0064] Step 3.2 Analyze the internal temperature observation data of the siliceous powder-lined concrete to determine the internal maximum temperature T max ; According to the measured results, T max = 36.81 °C.

[0065] Step 3.3 Calculate the internal and external temperature difference of the siliceous powder-lined concrete. The monitored value of the internal and external temperature difference is obtained by calculating with (Formula 2): △T nw = T max - T a = 36.81 - 20.3 = 16.51 °C.

[0066] Step 4. Real-time analyze and reasonably take heat preservation measures for closing the tunnel entrance. Since the measured internal temperature value (monitoring value) of the siliceous powder-lined concrete △T nw = 16.51 °C, which is less than the allowable value

△T nw

[0067] Furthermore, since

△T nw

△T nw

[0068] <Example 2> Real-time control of insulation for sealing the openings during the casting of 1.5 m thick silica fume lining concrete at the dragon's tail section of the flood discharge tunnel in summer

[0069] For the silica fume lining concrete at the dragon's tail section of the flood discharge tunnel, the surrounding rock deformation modulus E = 12 GPa in the surrounding rock area of Class Ⅲ2, with a 1.5 m thick lining, horseshoe-shaped cross-section, and circumferential construction joints are set every 12 m along the axis of the flood discharge tunnel. The bottom slab and side walls of the lining structure are C 90 60 low-heat concrete, and the top arch is C 90 30 low-heat concrete, with 5% silica fume added, as Figure 8 shown. The concrete is cast in 3 stages: first the side walls, then the top arch, and finally the bottom slab. The basic temperature control data is the same as above. Moisture curing is carried out with normal temperature tap water for 90 d, and water cooling is used to control the internal temperature of the concrete.

[0070] According to the above temperature control data, the construction unit plans to take temperature control measures for casting: casting at 18 °C in summer, water cooling with 22 °C river water for 20 d, and the form removal time t m = 3 d. The air temperature in the tunnel, based on the monitoring data of the air temperature in the diversion tunnel, has an annual average temperature of 14 - 26 °C under the condition of no insulation for sealing the openings.

[0071] Taking the 54th unit of the No. 1 flood discharge tunnel of Baihetan as an example for real-time control. The flood discharge tunnel of Baihetan is constructed by the 5th Bureau of Hydropower Engineering Group. The 54th unit of the No. 1 flood discharge tunnel has a stake number of 2 + 308.00 - 2 + 317.00 m, a lining thickness of 1.5 m, a side wall height of 13.5 m, a joint length of 9.0 m, C 90 60 low-heat concrete, and the surrounding rock of Class Ⅲ2 has E = 12 GPa. The concrete casting started at 00:10 on August 1, 2019, and was completed at 04:30 on August 5. The measured air temperature in the tunnel is 26.7 °C, the casting temperature is 16.3 °C, and water cooling is carried out with 14.9 °C water for 29 d. Thermometers are installed at the center of the lining, and the measured maximum internal temperature is 38.31 °C.

[0072] As Figure 4 shown, the real-time control calculation method for insulation of silica fume lining concrete with sealed openings provided in this embodiment includes the following content:

[0073] Step 1. Analyze the temperature crack control data of the silica fume lining concrete at the dragon's tail section of the flood discharge tunnel. Since the flood discharge tunnel of Baihetan Hydropower Station is a Class 1 building, the maximum water flow velocity reaches nearly 50 m / s, and temperature control and crack prevention of the lining concrete are very important. According to the design requirements, effective measures including water cooling are needed for temperature control.

[0074] Step 2. Calculate the allowable internal and external temperature difference

△Tnw

△T nw

[0075] Step 3. Monitor and analyze the internal temperature observation data of silica fume lining concrete in real time, including:

[0076] Step 3.1 Install thermometers at the center of the silica fume lining concrete to monitor the internal temperature. For relevant technologies, refer to relevant specifications. The actual temperature control results are as described above.

[0077] Step 3.2 Analyze the internal temperature observation data of silica fume lining concrete to determine the internal maximum temperature T max . According to the actual measurement results, T max = 38.31°C.

[0078] Step 3.3 Calculate the temperature difference between the inside and outside of the silica fume lining concrete. The monitored value of the temperature difference between the inside and outside is obtained by calculating with (Formula 2): △T nw = T max - T a = 38.31 - 26.7 = 11.61°C.

[0079] Step 4. Analyze in real time and reasonably take heat preservation measures for closing the tunnel entrance. Since the calculated △T nw = 11.61°C for the internal temperature of the measured silica fume lining concrete, which is greater than

△T nw

[0080] Furthermore, because △T nw = 11.61°C, which is only 0.36°C greater than

△T nw

[0081] Based on the above calculation and analysis, for pouring 1.5m thick long tail silica fume lining concrete of the structure in summer, the temperature inside the tunnel is high and the measured temperature difference between the inside and outside of the concrete is small (only 0.36°C greater than the allowable value), only Figure 5 simple heat preservation measures for closing the tunnel entrance are required. For pouring 1.2m thick long tail silica fume lining concrete in low temperature seasons, the temperature inside the tunnel is low and the measured temperature difference between the inside and outside of the concrete is large, and Figure 6 strict heat preservation measures for closing the tunnel entrance are required. Based on the comprehensive calculation results, for pouring the long tail silica fume lining concrete of the flood discharge tunnel, it is advisable to take strict heat preservation measures for closing the tunnel entrance throughout the year.

[0082] In actual engineering, for the placement of silica fume lining concrete in the dragon drop - tail section (i.e., the outlet) of the spillway tunnel of Baihetan Hydropower Station, considering the temperature control in the non - pressure section, heat preservation for closing the tunnel outlet, and the requirement of preventing cross - ventilation, strict heat - preservation measures for closing the tunnel outlet are adopted throughout the year at the tunnel outlet. As a result, the maximum internal temperature of the concrete and the maximum internal - surface temperature difference are both significantly reduced, and the temperature in the tunnel in winter is increased. The measured minimum temperature in the tunnel at the outlet section in winter is above 16°C. After adopting the heat - preservation measures for closing the tunnel outlet, the effect of no temperature cracks in the lining concrete is achieved (for the control effect of temperature and temperature cracks, see "Theory and Application of Temperature Crack Control in Lining Concrete of Hydraulic Tunnels" written by Duan Yahui, Fan Qixiang, etc. (China Water & Power Press, October 2021)). This verifies that the above - calculated analysis results are consistent with the actual engineering situation. Figure 6 The above - mentioned embodiments are merely illustrative examples of the technical solutions of the present invention. The real - time control calculation method for heat preservation of closing the tunnel outlet of the silica fume lining concrete involved in the present invention is not limited only to the content described in the above embodiments, but is subject to the scope defined by the claims. Any modification, supplement, or equivalent replacement made by those skilled in the art of the present invention based on this embodiment is within the scope protected by the claims of the present invention.

[0083] The above - mentioned embodiments are merely illustrative examples of the technical solutions of the present invention. The real - time control calculation method for heat preservation of closing the tunnel outlet of the silica fume lining concrete involved in the present invention is not limited only to the content described in the above embodiments, but is subject to the scope defined by the claims. Any modification, supplement, or equivalent replacement made by those skilled in the art of the present invention based on this embodiment is within the scope protected by the claims of the present invention.

Claims

1. A real-time control method for heat preservation of a concrete closed hole with a silica powder lining, characterized in that, It includes the following steps: Step 1. Obtain the information on controlling the temperature cracks of the silica fume lining concrete in the flood discharge tunnel; Step 2. Calculate the allowable internal and external temperature difference 【△T nw 】 of the silica fume lining concrete of the flood discharge tunnel according to the obtained data: 【△T nw 】 = 47.32β - 64.44H / L - 0.25C - 0.69T a - 0.12E + 0.19H×C + 33.81 (Formula 1) In the formula: β is the content of silica fume; H is the thickness of the concrete structure lined with silica fume; L is the length of the longest side of the lined structure segment, and when the height of the side wall is greater than the joint length, the height of the side wall is taken; C is the strength grade of the silica fume lined concrete at the design age of 90d; T a is the in - tunnel air temperature value during the concrete pouring period; E is the deformation modulus of the surrounding rock; Step 3. Monitor and analyze the internal temperature observation information of the silica fume lining concrete in real time to obtain the monitored value of the temperature difference between the inside and outside; Step 4. Compare the allowable internal and external temperature difference [△T nw with the monitored value, and based on the comparison result, analyze in real time and reasonably take heat preservation measures for closing the tunnel portal.

2. The real-time control method for heat preservation of the closed opening of the silica fume lining concrete according to claim 1, characterized in that: Among them, In step 1, the information on controlling the temperature cracks of the silica fume lining concrete in the flood discharge tunnel obtained includes: the general situation of the flood discharge tunnel project, the hydrological and meteorological information, and the technical requirements for temperature control design of the silica fume lining concrete.

3. The real-time control method for heat preservation of the closed opening of the silica fume lining concrete according to claim 1, characterized in that: Among them, Step 3 includes the following sub-steps: Step 3.1 Monitor the internal temperature through the temperature sensors installed at the center of the silica fume lining concrete; Step 3.2 Analyze the internal temperature observation data of the silica fume-lined concrete to determine the maximum internal temperature T max ; Step 3.3 Calculate the monitored value of the temperature difference between the inside and outside of the silica fume lining concrete; △T nw =T max -T a (Formula 2) Since the lining concrete in the tunnel will not be covered for heat preservation, and the surface concrete temperature drops rapidly to reach the air temperature in the tunnel, the surface concrete temperature is approximately taken as the air temperature in the tunnel, that is, the air temperature T in the tunnel during the concrete pouring period a .

4. The real-time control method for heat preservation of the closed opening of the silica fume lining concrete according to claim 1, characterized in that: Among them, Step 4 includes the following sub-steps: Step 4.1 Compare and analyze the internal and external temperature difference △T nw Whether it exceeds the allowable value [△T nw ; Step 4.2 If ΔT nw ≤ 【ΔT nw 】, no heat preservation measures are required; if ΔT nw > 【ΔT nw 】, the opening is sealed for heat preservation.

5. The real-time control method for heat preservation of the closed opening of the silica fume lining concrete according to claim 4, characterized in that: Among them, In step 4.2, if nw 】 < △T nw ≤ nw 】 + 2.0 °C, then simple curtain hanging is adopted to seal the opening for heat preservation; if △T nw > nw 】 + 2.0 °C, then strict sealing of the opening is adopted for heat preservation.

6. The real-time control method for heat preservation of the closed opening of the silica fume lining concrete according to claim 5, characterized in that: Among them, The simple curtain hanging for heat preservation of the closed opening refers to the way of closing the opening by using geotextiles and plastic films with small thicknesses and covering the opening in a hanging manner. The combination between each strip / block is not tight, and there are ventilation holes or gaps; The strict heat preservation of the closed opening refers to the way of closing the opening by using thick heat preservation quilts and cotton felts and strictly fixing and sealing the whole opening. The closed structure forms a whole and there is no ventilation gap.

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