Ventilation pre-cooling method for lining cracking prevention of high-temperature water working tunnel

Abstract

The invention discloses a ventilation pre-cooling method for preventing cracking of a lining of a high-temperature water working tunnel, which is characterized in that ventilation pre-cooling (the temperature is controlled to be 15-25 DEG C) is carried out before and after lining pouring, and operation water temperature optimization (the temperature is not lower than 15 DEG C) is combined, so that the tensile stress of the lining is effectively reduced (the reduction amplitude is 30-85%), and cracking is prevented. The method is high in adaptability, parameters can be adjusted according to engineering conditions, the durability of the high-ground-temperature tunnel lining is remarkably improved, and the method is suitable for the field of water conservancy projects.

Description

Technical Field

[0001] This invention relates to the field of hydraulic engineering tunnel construction technology, specifically to a ventilation and pre-cooling method for preventing cracking of the lining of high-temperature hydraulic tunnels. Background Technology

[0003] Due to the release of heat of hydration and changes in temperature gradient, the concrete lining of high-temperature tunnels is prone to tensile stress, which can lead to cracking. Conventional crack prevention measures (such as reducing the pouring temperature) have limited effectiveness. Furthermore, existing technologies lack a systematic crack prevention scheme that combines ventilation pre-cooling and optimized operating water temperature for high-temperature environments, making it difficult to effectively control the tensile stress in the lining. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a ventilation pre-cooling method for crack prevention of lining in high-temperature hydraulic tunnels. This ventilation pre-cooling method reduces the initial temperature and maximum temperature rise of the lining concrete by ventilation pre-cooling, thereby reducing tensile stress in the later cooling stage.

[0006] A ventilation and pre-cooling method for crack prevention in the lining of high-temperature hydraulic tunnels, characterized by comprising the following steps: Before the tunnel lining concrete is poured, S1 ventilates and pre-cools the tunnel interior and shallow surrounding rock to form a low-temperature surrounding rock zone. S2 controls the ventilation temperature within the range of 15℃-25℃, which can reduce the tensile stress by 30%-85% after water is introduced; When the S3 tunnel is in operation with water, the operating water temperature should be no lower than 15℃; this can further reduce the temperature difference between the exposed side of the lining and the water temperature, and reduce tensile stress.

[0007] S4 ventilation and pre-cooling will continue until the day the tunnel begins water operation.

[0008] Preferably, the ventilation temperature is 20℃-25℃.

[0009] Preferably, the operating water temperature is 15℃-20℃.

[0010] Preferably, when the initial ground temperature of the surrounding rock is 40℃-60℃, the ventilation temperature is controlled below 25℃ to meet the crack prevention requirements.

[0011] Preferably, the ambient temperature inside the cave during the ventilation and pre-cooling stage is lower than the ambient temperature inside the cave when it is not ventilated.

[0012] Preferably, the duration of the aforementioned ventilation and pre-cooling is from the start of the tunnel chamber pre-cooling stage to the end of the tunnel operation period water supply.

[0013] Preferably, when the tunnel diameter is 6m and the lining thickness is 40cm, the ventilation temperature is controlled at 15℃-25℃ and the operating water temperature is controlled at 5℃-20℃, the tensile stress reduction of the lining is ≥30%.

[0014] Preferably, the focus of temperature control and crack prevention before water is introduced into the tunnel is the side of the lining surrounding rock, and the focus of temperature control and crack prevention after water is introduced is the side of the lining exposed to the air.

[0015] Preferably, when the ventilation temperature is ≤25℃, the maximum tensile stress reduction at each position of the lining after the tunnel is filled with water is ≥30%, and all of them are less than the axial tensile strength of C30 concrete at 180 days of age, which is 2.7MPa.

[0016] Preferably, when the ventilation temperature is 15℃, the operating water temperature should be 5℃ to meet the lining crack prevention requirements; when the ventilation temperature is 25℃, the operating water temperature should be ≥15℃ to meet the lining crack prevention requirements.

[0017] The working mechanism of this invention is as follows: ventilation and pre-cooling form a low-temperature surrounding rock zone, which reduces the temperature difference between concrete and surrounding rock, and optimizes the operating water temperature, thereby reducing the maximum temperature rise caused by hydration heat and the temperature drop after water flow, which helps to reduce tensile stress. Attached Figure Description

[0019] Figure 1 These are the maximum tensile stress curves of the lining structure under different ventilation temperatures before water is introduced; Figure 2 These are the maximum tensile stress curves of the lining structure under different ventilation temperatures after water is supplied; Figure 3 These are curves showing the maximum tensile stress reduction of the lining structure under different ventilation temperatures after water is supplied. Figure 4 The tensile stress at typical locations of the lining structure under different operating water temperatures before water supply (without ventilation pre-cooling measures) at a ventilation temperature of 30℃. Figure 5 The tensile stress at typical locations of the lining structure under different operating water temperatures before water is introduced, at a ventilation temperature of 30℃ (with ventilation and pre-cooling measures taken). Figure 6 The tensile stress at typical locations of the lining structure under different operating water temperatures after water is introduced at a ventilation temperature of 30℃ (without ventilation pre-cooling measures). Figure 7 This refers to the tensile stress at typical locations of the lining structure under different operating water temperatures at different stages after water is introduced at a ventilation temperature of 30℃ (with ventilation and pre-cooling measures taken). Figure 8 This is the curve showing the maximum tensile stress reduction of the lining structure when the ventilation temperature is 30℃. Figure 9 The maximum tensile stress curves of the lining structure under different water temperatures during different operating periods before water supply, with a ventilation temperature of 25℃. Figure 10 The maximum tensile stress curves of the lining structure under different water temperatures during different operating periods after water is introduced at a ventilation temperature of 25℃. Figure 11 The curves show the maximum tensile stress reduction of the lining structure under different operating water temperatures after water is introduced at a ventilation temperature of 25℃. Figure 12 The maximum tensile stress curves of the lining structure under different operating water temperatures before water supply, with a ventilation temperature of 20℃; Figure 13 The maximum tensile stress curves of the lining structure under different water temperatures during different operating periods after water is introduced at a ventilation temperature of 20℃. Figure 14 The curves show the maximum tensile stress reduction of the lining structure under different operating water temperatures after water is introduced at a ventilation temperature of 20℃. Figure 15 The maximum tensile stress curves of the lining structure under different water temperatures during different operating periods before water supply, with a ventilation temperature of 15℃. Figure 16 The maximum tensile stress curves of the lining structure under different water temperatures during different operating periods after water is introduced at a ventilation temperature of 15℃. Figure 17 It is the curve showing the maximum tensile stress reduction of the lining structure under different operating water temperatures after water is introduced at a ventilation temperature of 15℃. Detailed Implementation

[0021] The specific embodiments of the present invention will now be described in conjunction with the accompanying drawings. The advantages and features of the present invention will become clearer from the following description.

[0022] It should be noted that the embodiments of the present invention are preferred for implementation but are not intended to limit the invention in any way. The technical features or combinations of technical features described in the embodiments of the present invention should not be considered isolated; they can be combined with each other to achieve better technical effects. The scope of the preferred embodiments of the present invention may also include other implementations, and this should be understood by those skilled in the art to which the embodiments of the present invention pertain.

[0023] The present invention provides a ventilation and pre-cooling method for preventing cracking in the lining of high-temperature hydraulic tunnels, comprising the following steps: Before the tunnel lining concrete is poured, S1 ventilates and pre-cools the tunnel interior and shallow surrounding rock to form a low-temperature surrounding rock zone. S2 controls the ventilation temperature within the range of 15℃-25℃, which can reduce tensile stress by 30%-85% after water is introduced; the optimal ventilation temperature is 20℃-25℃.

[0024] When the S3 tunnel is in operation with water, the operating water temperature should be no lower than 15℃. This can further reduce the temperature difference between the exposed side of the lining and the water temperature, and reduce tensile stress. The optimal operating water temperature is 15℃-20℃.

[0025] S4 ventilation and pre-cooling will continue until the start of tunnel water supply operation. Specifically, the duration of ventilation and pre-cooling is from the start of the tunnel chamber pre-cooling stage to the end of the tunnel operation period water supply.

[0026] When the ventilation temperature is 15℃, the operating water temperature should be 5℃ to meet the requirements for lining crack prevention; when the ventilation temperature is 25℃, the operating water temperature should be ≥15℃ to meet the requirements for lining crack prevention.

[0027] The present invention uses ventilation and pre-cooling to form a low-temperature surrounding rock zone, which reduces the temperature difference between concrete and surrounding rock, and optimizes the operating water temperature, thereby reducing the maximum temperature rise caused by hydration heat and the temperature drop after water flow, which helps to reduce tensile stress. To verify the effect of the above technical solution of the present invention, specific verification examples are as follows.

[0028] I. The Influence of Ventilation Temperature on Tensile Stress Using the controlled variable method, the tunnel diameter was taken as 6m, the lining thickness as 40cm, the ambient temperature inside the tunnel before ventilation as 40℃, the water temperature during operation as 15℃, and the initial ground temperature of the surrounding rock as 60℃. Ventilation temperatures were taken as 15℃, 20℃, 25℃, and 30℃ respectively. The tensile stress on the lining structure under different ventilation temperatures was calculated to determine its impact on the ventilation pre-cooling effect.

[0029] The maximum tensile stress values ​​at typical locations of the lining structure under different ventilation temperatures, calculated by finite element method, are shown in Tables 1-1 and 1-2 below. To more intuitively summarize the patterns, curves showing the maximum tensile stress values ​​and their decrease before and after tunnel water flow under different ventilation temperatures are plotted using the data in the tables. Figure 1 , 2 and Figure 3 As shown in the table and the series of curves in the graph: (1) After the tunnel is filled with water, as the ventilation temperature decreases, the tensile stress value at each typical location of the lining structure gradually decreases. This indicates that within a certain range, the lower the ventilation temperature, the better the anti-cracking effect on the lining structure. Compared with no ventilation, the decrease in tensile stress value gradually increases. When the ventilation temperature is greater than or equal to 30℃, the tensile stress value of the lining structure gradually decreases from the inside to the outside. When the ventilation temperature is less than or equal to 25℃, the tensile stress value of the lining structure gradually increases from the inside to the outside. The reason is that when the ventilation temperature is high, the ambient temperature inside the tunnel is also high. The temperature difference between the lining free side and the water temperature during operation is large, resulting in a large temperature gradient. As the ventilation temperature decreases, the temperature difference between the lining free side and the water temperature during operation decreases, while the temperature difference between the lining surrounding rock side and the surrounding rock increases, causing the tensile stress value of the surrounding rock side to exceed that of the free side.

[0030] (2) When the ventilation is pre-cooled to 30°C, the maximum tensile stress of the lining structure after water is supplied is greater than the axial tensile strength of C30 concrete at 180 days, which will cause cracking. When the ventilation is pre-cooled to 25°C or below, the maximum tensile stress of the lining before and after water supply to the tunnel is less than the tensile strength of the concrete at the corresponding age, which will not cause cracking. Therefore, when the tunnel diameter is 6m and the lining thickness is 40cm, the optimal ventilation temperature range for crack resistance is 25°C to 30°C.

[0031] Table 1-1 Maximum tensile stress values ​​of tunnel lining under different ventilation temperatures before water flow (Unit: MPa) Table 1-2 Maximum tensile stress values ​​of tunnel lining under different ventilation temperatures after water supply (Unit: MPa) II. The Influence of Water Temperature on Tensile Stress During Operation Using the controlled variable method, the tunnel diameter was taken as 6m, the lining thickness as 40cm, the initial ground temperature of the surrounding rock as 60℃, the ambient temperature inside the tunnel before ventilation as 40℃, and the water temperatures during operation as 5℃, 10℃, 15℃, and 20℃, respectively. The tensile stress on the lining structure under different water temperatures during operation was calculated to determine the degree of influence on the ventilation and pre-cooling effect.

[0032] To eliminate the influence of ventilation temperature, the ventilation temperature was set to 30℃, 25℃, 20℃ and 15℃, and the relationship between the operating water temperature and the ventilation pre-cooling crack prevention effect under each condition was studied.

[0033] (1) The effect of water temperature during operation when the ventilation temperature is 30℃ Tables 2-1 and 2-2 show the maximum tensile stress values ​​at typical locations of the lining structure under different water temperatures during different operating periods, in both unventilated and ventilated pre-cooled conditions to 30℃. To more intuitively summarize the patterns, curves depicting the maximum tensile stress values ​​and their reduction before and after tunnel water flow at different operating water temperatures are plotted using the data in the tables. Figure 4-7 and Figure 8 As shown in the table and the series of curves in the graph: (1) Before the tunnel is filled with water, the stress value of the lining structure does not change with the water temperature during operation because there is no water temperature. After the tunnel is filled with water, as the water temperature during operation increases, the maximum tensile stress value at each typical location of the lining structure gradually decreases regardless of whether ventilation and pre-cooling measures are taken. Compared with no ventilation, the maximum tensile stress value decreases gradually after ventilation and pre-cooling measures are taken. This indicates that when other factors are the same, the maximum tensile stress on the lining is smaller when the water temperature during tunnel operation is higher. Therefore, water should be filled when the local temperature is higher as much as possible.

[0034] (2) After ventilation and pre-cooling to 30℃, the maximum tensile stress of the lining under different operating water temperatures before the tunnel is filled with water is 0.94MPa, which is much less than the axial tensile strength of C30 concrete at 180 days old and will not cause cracking. After the water is filled with water, the maximum tensile stress on the free side of the lining is above 3.3MPa when the operating water temperature is 5℃, 10℃ and 15℃ respectively, which is greater than the tensile strength of concrete and does not meet the requirements for crack prevention of the lining. When the operating water temperature is 20℃, the tensile stress at each position of the lining is less than the tensile strength of concrete and meets the requirements for crack prevention of the lining.

[0035] Table 2-1 Maximum tensile stress values ​​of tunnel lining under different operating temperatures before water supply (Unit: MPa) Table 2-2 Maximum tensile stress values ​​of tunnel lining under different operating temperatures before water supply (Unit: MPa) (2) The effect of water temperature during operation when the ventilation temperature is 25℃ Tables 2-3 and 2-4 show the maximum tensile stress values ​​at typical locations of the lining structure under different water temperatures during different operating periods, in the cases of no ventilation and ventilation pre-cooling to 25℃. To more intuitively summarize the patterns, curves showing the maximum tensile stress values ​​and their reduction before and after tunnel water flow at different operating water temperatures were plotted using the data in the tables. Figure 9 , 10 and Figure 11 As shown in the table and the series of curves in the graph: (1) After the tunnel is filled with water, as the water temperature increases during operation, the maximum tensile stress value of the lining decreases by at least 23% and at most over 60%.

[0036] (2) When the lining is pre-cooled to 25℃ and the water temperature during operation is 5℃ and 10℃ respectively, the maximum tensile stress on the free side of the lining is above 3.4MPa, which is greater than the tensile strength of concrete and does not meet the requirements for crack prevention of the lining. When the water temperature during operation is 15℃ and 20℃, the tensile stress at each position of the lining is less than the tensile strength of concrete and meets the requirements for crack prevention of the lining.

[0037] Table 2-3 Maximum tensile stress values ​​of tunnel lining under different operating temperatures before water supply (Unit: MPa) Table 2-4 Maximum tensile stress values ​​of tunnel lining under different water temperatures during different operating periods after water supply (Unit: MPa) (3) The effect of water temperature during operation when the ventilation temperature is 20℃ Tables 2-5 and 2-6 show the maximum tensile stress values ​​at typical locations of the lining structure under different water temperatures during different operating periods, in the cases of no ventilation and ventilation pre-cooling to 20℃. To more intuitively summarize the patterns, curves showing the maximum tensile stress values ​​and their reduction before and after tunnel water flow at different operating water temperatures were plotted using the data in the tables. Figure 12 , 13 and Figure 14 As shown in the table and the series of curves in the graph: (1) After the tunnel is filled with water, as the water temperature increases during operation, the maximum tensile stress value of the lining decreases by at least 30% and at most close to 80%.

[0038] (2) When the lining is pre-cooled to 20℃ and the water temperature during operation is 5℃, the maximum tensile stress on the free side of the lining is above 3.5MPa, which is greater than the tensile strength of concrete and does not meet the requirements for crack prevention of the lining. When the water temperature during operation is 10℃, 15℃ and 20℃, the tensile stress at each position of the lining is less than the tensile strength of concrete and meets the requirements for crack prevention of the lining.

[0039] Table 2-5 Maximum tensile stress values ​​of tunnel lining under different operating temperatures before water supply (Unit: MPa) Table 2-6 Maximum tensile stress values ​​of tunnel lining under different operating temperatures after water supply (Unit: MPa) (4) The effect of water temperature during operation when the ventilation temperature is 15℃ Tables 2-7 and 2-8 show the maximum tensile stress values ​​at typical locations of the lining structure under different water temperatures during different operating periods, in the cases of no ventilation and ventilation pre-cooling to 15℃. To more intuitively summarize the patterns, curves showing the maximum tensile stress values ​​and their reduction before and after tunnel water flow at different operating water temperatures were plotted using the data in the tables. Figure 15 , 16 and Figure 17 As shown in the table and the series of curves in the graph: (1) After the tunnel is filled with water, as the water temperature increases during operation, the maximum tensile stress value of the lining decreases by at least 40% and at most over 80%.

[0040] (2) When the ventilation pre-cooling is set to 15℃, and the water temperature during operation is 5℃, 10℃, 15℃ and 20℃ respectively, the tensile stress on the free side of the lining is less than the tensile strength of the concrete, which meets the requirements for crack prevention of the lining.

[0041] Table 2-7 Maximum tensile stress values ​​of tunnel lining under different operating temperatures before water supply (Unit: MPa) Table 2-8 Maximum tensile stress values ​​of tunnel lining under different water temperatures during different operating periods after water supply (Unit: MPa) (III) The inventiveness of this invention This invention breaks through the limitations of traditional crack prevention by combining ventilation pre-cooling to reduce initial temperature rise with coordinated adjustment of operating water temperature: ventilation pre-cooling forms a low-temperature surrounding rock zone, reducing the maximum temperature rise of hydration heat and the cooling range of water flow; coordinated optimization of ventilation temperature and operating water temperature enables flexible parameter adaptation to different engineering conditions; tensile stress reduction is up to 85%, which is significantly better than conventional measures.

[0042] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A ventilation and pre-cooling method for preventing cracking in the lining of high-temperature hydraulic tunnels, characterized in that, Includes the following steps: Before the tunnel lining concrete is poured, S1 ventilates and pre-cools the tunnel interior and shallow surrounding rock to form a low-temperature surrounding rock zone. S2 controls the ventilation temperature within the range of 15℃-25℃; When the S3 tunnel is being emptied of water, the operating water temperature should be no lower than 15℃. S4 ventilation and pre-cooling will continue until the day the tunnel begins water operation.

2. The method according to claim 1, characterized in that, The ventilation temperature is 20℃-25℃.

3. The method according to claim 1, characterized in that, The operating water temperature is 15℃-20℃.

4. The method according to claim 1, characterized in that, When the initial ground temperature of the surrounding rock is 40℃-60℃, the ventilation temperature should be controlled below 25℃ to meet the crack prevention requirements.

5. The method according to claim 1, characterized in that, The temperature inside the cave during the ventilation and pre-cooling stage is lower than the temperature inside the cave when it is not ventilated.

6. The method according to claim 1, characterized in that, The duration of the ventilation pre-cooling is from the start of the tunnel chamber pre-cooling stage to the end of the tunnel operation period when water is supplied.

7. The method according to claim 1, characterized in that, When the tunnel diameter is 6m and the lining thickness is 40cm, the ventilation temperature is controlled at 15℃-25℃ and the operating water temperature is controlled at 5℃-20℃, and the tensile stress reduction of the lining is ≥30%.

8. The method according to claim 1, characterized in that, Before water is introduced into the tunnel, the focus of temperature control and crack prevention is on the side of the lining surrounding rock; after water is introduced, the focus of temperature control and crack prevention is on the side of the lining exposed to the air.

9. The method according to claim 1, characterized in that, When the ventilation temperature is ≤25℃, the maximum tensile stress reduction at each position of the lining after the tunnel is filled with water is ≥30%, and all of them are less than the axial tensile strength of C30 concrete at 180 days of age, which is 2.7MPa.

10. The method according to claim 1, characterized in that, When the ventilation temperature is 15℃, the operating water temperature should be 5℃ to meet the requirements for lining crack prevention; when the ventilation temperature is 25℃, the operating water temperature should be ≥15℃ to meet the requirements for lining crack prevention.

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