The design of 10 air-cushion surge tanks already built in Norway generally follows the relevant design guidelines for unlined tunnels. The three air-cushion surge tanks of the self-built Yili Hydropower Station, Xiaotiandu Hydropower Station and the Mudu Hydropower Station under construction in China. The layout design is benevolent and wise. In fact, reasonable layout of the air cushion type surge chamber is of great significance for ensuring the safe, reliable and economic operation of the air chamber and water curtain. Based on the design of 12 air-cushion surge chambers in 9 projects in Norway and 3 projects in China, the paper discusses and summarizes the control conditions affecting the position selection of air cushion surge chambers, air cushion surge chambers and waterway elevation layout. The relationship of the relationship, the traffic inspection hole, the air compressor room and other auxiliary caverns, the shape of the air chamber and the layout of the water curtain are expected to be discussed with experts in this field.
1 Several control conditions affecting the position selection of the air cushion type surge chamber 1. The ground stress condition The ground stress condition is the necessary condition that must be satisfied when the position of the air cushion type surge tank is selected. It is generally called the minimum principal stress criterion, that is, the minimum. The main ground stress should be greater than the maximum internal water pressure and maximum gas pressure of the air cushion type surge tank. More specifically, the normal pressure in the joints in the rock should be greater than the maximum pressure and water pressure in the surge chamber.
The key to the problem is whether the representative value of the maximum internal water pressure or maximum gas pressure is based on the dynamic pressure or the maximum pressure under dynamic conditions, or the corresponding value under static conditions. 5å€çš„安全系数。 The minimum principal stress should be considered to be greater than the maximum hydrodynamic pressure or dynamic gas pressure, and a safety factor of 1. 4 ~ 1.6 times. After studying the data of several projects in Norway, it is considered that the above design ideas are inappropriate or even incorrect. As a result of this, the optional range of the position of the surge tank is too strictly limited, and it is possible to make the position selection in the vicinity of the unfavorable structure, which adversely affects the safe operation of the surge tank, such as a wooden seat cushion type. The special design of the surge chamber.
The safety factor of the Norwegian experience is that the minimum principal stress should be greater than the maximum static internal water pressure or the corresponding maximum gas pressure under normal operating conditions, while considering a safety factor of not less than 1.2. The reason is that the calculation results of the air cushion type pressure regulating chamber should ensure that the maximum dynamic water pressure or the corresponding gas pressure does not exceed 15% to 20% under normal operation. According to the actual situation in China, the minimum principal stress criterion can be clearly defined as the minimum. The main ground stress is not less than the maximum dynamic water pressure or the corresponding gas pressure, but the maximum dynamic water pressure should take into account the possible error between the hydraulic calculation and the actual operation. Because the duration of the hydrodynamic pressure is short, even if the minimum main geostress is less than the maximum dynamic pressure or water curtain pressure, there will be no air pressure or hydraulic fracturing. The maximum pressure of the water curtain should be suitable according to the maximum dynamic pressure of the air chamber. .
The test of ground stress should be based on the hydraulic fracturing method, which is closer to the actual working condition of the pressure tunnel than the stress relieving method, and the effectiveness of the large-scale rock mass test. The value of the earth stress should have a concept of the overall range, and should not be limited to the local position of the air cushion type pressure regulating chamber. When the local stress conditions cannot meet the geostress criterion, the three-dimensional finite element regression analysis of the ground stress field is carried out by the measured values, and the minimum principal stress value is reasonably determined.
5M Pa的压压。 The pressure of the water curtain is 4. 5M Pa, the pressure of the air pressure of the pressure chamber is 0. 5M Pa overpressure. The total pressure of the two groups is 5. 2~11. 9M. The pressure is 5. 2~11. 9M The singularity of the pressure of the pressure of 4. 3 ~ 7. 3M Pa, the minimum of the pressure of the pressure of the test. The pressure value is 4. 3 M Pa, which is less than the maximum static air pressure. Group D tests were conducted in the surge chamber tunnel.至5. 0M Pa. The pressure of the pressure is 4. 5 ~ 5. 0M Pa.
Since the local minimum pressure water pressure (minimum ground stress) obtained by the test cannot meet the requirement of more than 1.2 times the maximum static air pressure of 414 M Pa, considering that the ground stress should work as a whole within a certain range, For the results of the measuring point, the minimum principal stress value is considered at 517 M Pa and is used as the design basis for the pressure regulating chamber and water curtain.
1. 2 Geological structure conditions The choice of the location of the surge chamber should pay great attention to the impact of unfavorable geological structures. It is generally required to select an air cushion type surge chamber with high rock strength (hard rock), relatively complete rock mass and good stability of the cavern, avoiding large unfavorable geological structures and karst development areas. In order to make the rock mass have better impermeability, the surrounding rock should be selected and the surrounding rock should be the main part, and the area where the crack is developed should be avoided as much as possible. The mass of the rock mass itself and the surrounding rock mass do not have to be too high, but the outer part should have at least 50-100 m complete area rock mass to close the air leakage and water leakage. Especially within the range of 50 m, it is not suitable to have large faults, joint fractures and other unfavorable structures. When these structures are vertical tunnels and the inclination angle is steep, the conditions are more unfavorable. It will not only form water leakage, air leakage passage, but also cause hydraulic fracture and damage due to the effective stress of the structural surface after water seepage.
1. 3 anti-seepage conditions and groundwater level conditions of rock mass (1) Impermeability of rock mass The permeability of rock mass is an important indicator for determining the leakage and leakage of rock mass in the cave wall, especially when the air leakage is large. It will directly increase the operating cost and even affect the normal operation of the air cushion type surge chamber, and have to re-infiltrate the anti-seepage reinforcement or increase the water curtain measures. As far as possible, the air-permeable surge chamber arrangement should be selected for the rock mass with weak permeability. The design of several air-cushion surge chambers in China requires the permeability of the rock mass of the cave wall to be less than 1. 0 L u, and Norway has been built. Compared with the engineering, the standard is low, and it is worthwhile to further explore the criteria for the permeability of the wall.
It can be seen that the permeability of the surrounding rock of most air-cushioning surge chambers is much lower than that of 1 L u. Kvilldal and Tafjord have large water permeability, and the gas leakage during operation is serious. The water curtain is added in the trapping treatment scheme. The measures, O sa air cushion type pressure chamber has a water permeability of nearly 1 L u. During the operation, the air leakage is unacceptable compared with the air compressor capacity. It has to be shut down after 8 months of operation of the power station. Torpa permeability coefficient Larger, lower groundwater level, the first time in the design to actively consider the setting of the water curtain.
The ratio of pore water pressure to air pressure in the surge chamber of Kvilldal Hydropower Plant is 0.6. Starting in 1981, the air cushion pressure is 4M Pa, and the gas leakage after operation reaches 240 N. m 3 h, which is not allowed. Air leakage, after a water curtain was set up and put into operation in 1983, the air leakage phenomenon was completely eliminated.
The ratio of the pore water pressure to the air pressure of the surrounding rock of the Tafjord power station is only 0. 48~0. 56, and the operation is started in 1982. The pressure of the pressure chamber is between 6.5 and 7.77M Pa. Chamber leakage, air leakage 150 N. m 3 h. Although it is smaller than the Kvilldal power station, the air pressure equipment of the power station is limited, and it is difficult to make the surge chamber work effectively. Therefore, between 1982 and 1990, the power station of the power station was completely Filled with water, it is ineffective. At the beginning, there was a grout repair work, but it failed to work, and then had to add a water curtain.
Osa power station air cushion type surge tank, although effective cement grouting and chemical grouting were carried out during construction, and spray anchor support was used at the top of the tunnel, but about 900 N. m 3 h of air leakage occurred shortly after operation. Compared with the available air compressor capacity of 2 320 N. m 3 h, it is unacceptable, so it has to be shut down for maintenance after 8 months of operation. The air leakage treatment took 3 months. The project consists of 6 800 m drilling, 36 t of cement and 5 500 L of chemical grouting. The grouting is concentrated in the severe leakage. After the trapping process, the air leakage is stable at 80 N. m 3 h. Although this is still the highest value of all operating air cushion surge chambers, the air compressor can fully meet the needs of air cushion operation.
Relatively speaking, although the air-cushion surge chambers of several power stations in China are located in rock masses with high rock strength such as granite, the permeability of rock mass is much higher than that of Norway due to the development of unfavorable geological phenomena such as fissures and sandstone captive bodies. Engineering, although the permeability of most rock masses is less than 1L u, which meets the standard of general waterproof curtains, but the permeability of rock mass may reach 100 times of water permeability, and grouting of air-cushion surrounding rock is still necessary. The standard of grouting should also be improved accordingly. The author believes that it should not be at least greater than 0.1 L u.
(2) The choice of the position of the groundwater level air cushion type surge chamber should take into account the groundwater level of the surrounding mountain. If the natural groundwater pressure is higher than the air cushion pressure, the groundwater pressure gradient toward the air cushion is positive during operation, which can reduce or even avoid air leakage, thereby reducing the air-cushion anti-seepage treatment engineering volume and the air compressor operation. cost.
If the natural groundwater level at the location of the proposed air cushion surge tank is lower than the highest gas pressure head, or the natural groundwater situation is unclear, when the rock mass permeability is large, engineering measures are taken to control the gas in the air cushion type. Leakage is very necessary. On the one hand, solid wall grouting measures can be used to reduce the water permeability of the surrounding rock to below 0.1 L u or even lower. Such a treatment scheme may cost a lot, as long as the construction quality is a little overlooked, it may be abandoned. In terms of the need to set up a water curtain, artificially generate the necessary water pressure to solve the problem of air leakage.
(3) The hydraulic gradient between the rock masses requires a certain airfront surface due to the arrangement of the construction channel and other caverns around the air cushion type surge tank. The presence of the air surface shortens the length of the high-pressure water flow and the gas permeation channel, and increases the hydraulic gradient or pressure gradient between the rock masses. This is very unfavorable for controlling the air leakage, and even hydraulic fracturing and pressure 劈 occur. Crack damage, the diameter of the permeation should be increased as much as possible. According to the trapping and reinforcement of the air cushion in the one-in-one air cushion and combined with the design experience of China's high-pressure tunnel, the hydraulic gradient should be about 3~5 according to the integrity and water permeability of the surrounding rock. When the requirements are not met, the reinforced concrete lining should be used to strengthen the joint grouting to extend the permeability.
1. 4 Adjustment guarantee The minimum horizontal distance from the air-cushion pressure regulating room to the workshop shall be not less than the requirement of the length of the steel lining section of the high-pressure unlined tunnel, which depends not only on the geological conditions, but also on the size and orientation of the water head and the plant. Norwegian experience, generally taking 12% to 20% of the static head. In the existing and under construction projects, the air-cushion pressure regulating room of the Tafjord power station is closest to the factory building, the distance from the turbine is only 150 m, and most of the other is 350-680 m. There are 3 projects with more than 1 000 m and the built maximum of 1 300 m.
The air cushion type surge chamber should be as close as possible to the turbine to improve the maintenance effect, but the minimum distance should take into account the layout of the plant and the impact on the safety of the plant after the crash, and ensure the safety requirements of impermeability. The maximum limit distance should be determined based on the adjustment calculation.
2 The relationship between the position of the air cushion type pressure regulating chamber and the layout of the water channel elevation When the air cushion type pressure regulating chamber scheme is adopted, the water diversion tunnel generally adopts a gentle slope arrangement (commonly known as a slope to the bottom), which is more reasonable and economical. This arrangement eliminates the need for a long high-pressure shaft or inclined well on the downstream diversion channel of the conventional surge tank scheme, which increases the buried depth of the tunnel, and is more conducive to the use of unlined tunnels to reduce the amount of tunnel lining work; It can be placed as close as possible to the plant, which is beneficial to the reflection of water shock waves, which can reduce the water hammer pressure and increase the stability of the unit, which is beneficial to the operation of the power station. On the other hand, the longitudinal slope of the tunnel can basically be consistent with the river along the river, greatly shortening the routine. The surge chamber scheme greatly reduces or even avoids the adverse impact on environmental damage due to the uphill road required for the construction of the surge tank and the low-pressure section tunnel, so that some sensitive problems that restrict the construction of hydropower projects have been solved.
However, due to the limitations of design experience and construction technology, as well as the requirements of surrounding rock quality, ground stress conditions, construction traffic conditions, etc., there are also many arrangements for using slow slope tunnels and their subsequent pressure inclined wells or shafts, especially When building a high-head power station in the early days of a country.
The Yili Hydropower Station is the second cascade hydropower station of the Huoxi River, a tributary of the Minjiang River in Sichuan. It is located at the lower reaches of the Shuiniujia Hydropower Station. The 10 km diversion tunnel and underground powerhouse are located on the right bank of the Huoxi River. There are 2 sets of power stations installed, with a total installed capacity of 130MW. The maximum head of the power station is 474. 14m, the minimum head is 439. 95 m, and the maximum power reference flow is 33. 16 m 3 s.
Since the one-inch air cushion type pressure regulating chamber is the first air cushion type surge tank in China, considering that the diversion tunnel adopts the "one slope to the bottom" arrangement, about 80% of the tunnel is a high pressure tunnel section, and the corresponding air cushion type The maximum pressure of the surge tank will exceed 500 m. In addition, the geological conditions along the long high-pressure tunnel are unclear. There are many unforeseen factors in the construction and future operation of the power station, and the construction period is tight. It is not appropriate to make major adjustments for each construction hole. Therefore, from a safe point of view, the diversion tunnel from the one-in-one air-cushioning surge tank scheme does not adopt the “one slope to the bottom†arrangement, but uses the vertical concentrated pressure lower hole line in front of the air cushion type surge chamber. An air cushion type pressure regulating chamber is disposed on the middle flat section between the segment and the lower flat section. The total length of the low-pressure section of the diversion tunnel is about 8 600 m, the total height difference is about 40 m, the average longitudinal slope of the tunnel is about 0.45%, the first-level shaft height before the surge tank is about 260 m, and the height difference of the downstream secondary shaft is about 150 m. The static head of the lower flat section is about 484 m. The static head of the air cushion type pressure regulating chamber and the middle section of the diversion tunnel is about 337 m.
The air cushion type surge tank of Sim a hydropower station was designed in 1973. The maximum head of the power station is 1 152 m. Considering the design experience of the air cushion type pressure regulating chamber at that time, the diversion tunnel does not use the slope of the average slope of 1:9. The water head reaches a layout of 780m. The actual scheme adopted is a 1:14 gentle slope diversion tunnel plus a high-pressure inclined well arrangement of nearly 600 m water head. The air cushion type surge chamber is arranged above the left side of the gentle slope diversion tunnel. The head of the air cushion chamber is about 490 m, and the distance from the turbine About 1 300 m. The first unit of the Kvilldal Hydropower Station was put into operation in December 1981. It was also installed in a gentle slope tunnel section with an air cushion type pressure regulating chamber, followed by four pressure inclined shaft layout schemes with a height difference of about 90 m.
The U lset hydropower station was put into operation in February 1985. The air cushion type pressure regulating chamber was set on the gentle slope section of 5 ,, and the pressure inclined shaft with a height difference of 70 m was connected at 262 m after the pressure regulation chamber. Other power stations with air-cushion surge chambers are equipped with gentle slope layout schemes, typically equipped with hydropower stations such as Jukla, Oksla, Osa, Torpa, Xiaotiandu and Muzu. Xiaotiandu Hydropower Station is located on the Vas River in Kangding County, Sichuan Province. The upstream is the Mugecuo Scenic Area. The 318 National Road passes along the river. The diversion power generation system is located on the right bank of the Vas River. There are 3 underground installations with a total installed capacity of 240MW. Design the hair head 392. 5 m, the maximum power generation reference flow of the power station 77. 7 m 3 s.
The diversion tunnel adopts an average longitudinal slope of 5.6% of “one slope to the bottom†layout type, and a connection pipe and an air cushion type surge chamber are connected at about 490 m upstream of the turbine. The total length of the diversion tunnel is about 6 182m, the section of the 100-450 m head is about 5,000 m, the horizontal depth of the pressure tunnel is generally 500-800 m, and the vertical depth is 300-750 m. It meets the requirements of the Norwegian guidelines for unlined tunnels. Covering the thickness, most of the hole sections are not lining structure or spray anchor structure.
The air-cushion surrounding rock of the surge chamber is plagiogranite and granodiorite, which is mainly composed of surrounding rocks. The horizontal buried depth is 450-500 m, and the vertical buried depth is 435-500 m. The hydraulic fracturing method is the smallest measured rock mass. The main ground stress is 7. 88~10. 12M Pa, which is greater than the maximum pressure in the pressure regulating chamber.
The pressure regulating chamber chooses to avoid the contact zone between the plagiogranite and the diorite developed by the two fractures and the crushing zone. The closest distance from the contact zone is about 200 m. The air cushion type pressure regulating chamber is located on the right side of the diversion tunnel, and the design size It is 156 m×9. 6 m×15. 5 m (length×width×height), and the water cushion in the gas chamber is 3 m deep. The air chamber and the diversion tunnel are connected by a shaft, and the top of the air chamber is provided with a gate hole type of 8 m wide. The water curtain chamber, the bottom plate is 15 m above the top of the gas chamber, the water curtain pressure is 4.25 M Pa, and the water curtain hole depth is 35 to 60 m.
The air pressure type pressure regulating chamber has a design gas pressure of 3.75 M Pa, a maximum air pressure of 4.35 M Pa, a minimum air pressure of 3.35 M Pa, and a design gas volume of 18 048 m 3 . The Muzuo Hydropower Station is the third cascade hydropower station of the Huoxi River, a tributary of the Minjiang River in Sichuan. It is located at the lower reaches of the Ziyi Hydropower Station. The diversion tunnel and underground powerhouse of about 12 km are located on the left bank of the Huoxi River. 2 sets of power station installed, the total installed capacity is 100MW. The maximum head of the power station is 289. 01m, the minimum head is 261. 75 m, the rated head is 262. 7 m, and the maximum power reference flow is 43. 02 m 3 s.
The diversion tunnel adopts a longitudinal slope of 1.5% to 5.5% of the "slow slope to the bottom" layout type, and the air cushion type surge chamber is about 300 m away from the turbine. The surrounding rock is tuffaceous biotite granulite, saturated and compressive. The strength is greater than 100M Pa. The designed air pressure of the initial air cushion type pressure regulating chamber is 2190 M Pa, the maximum gas pressure is 3.63M Pa, and the minimum principal stress of the rock mass measured by hydraulic fracturing method is б3 = 5.37M Pa, air cushion type The surrounding rock of the pressure chamber is mainly of type, and its minimum depth is about 250 m, which meets the Norwegian guidelines. Since the initial air-cushioning surge chamber is located next to the upstream crushing zone J1, the special review requires that the position and axis of the surge tank be adjusted according to the geological conditions revealed after the construction excavation.
3 Air cushion type pressure regulating room traffic inspection hole, air compressor room and other auxiliary caverns are arranged. After the position of the air cushion type surge tank is determined, the layout of the traffic tunnel, maintenance tunnel, air compressor room and plug position of the surge tank is reasonable. Whether or not the layout of the water curtain room is reasonable or not is related to the success or failure of the air cushion type pressure regulating room. When China began to build the air cushion type pressure regulating chamber, it was insufficiently recognized in this aspect, which was proved by later operational practice. Although the Norwegian experts did not have any theory and experience on the layout design of the auxiliary caverns and water curtains, they did not pay attention to this issue when they consulted the company. This may not necessarily involve the invited experts in the Norwegian air cushion. The design of the surge chamber is related to experts who have not studied the layout design. The Norwegian air-cushioning surge room layout design follows the correct concept, and although these concepts have not been summarized, it runs through eight air-cushion surge chambers already built in Norway.
O ksla hydropower station, the maximum hydrostatic air cushion pressure of the air cushion type surge chamber is 4. 4M Pa, the air chamber is arranged on the right side of the diversion tunnel, the traffic tunnel and the air compressor room are arranged on the left side of the tunnel, and the junction of the traffic tunnel and the diversion tunnel is adopted. The open steel pipe with telescopic joints is blocked, and the only auxiliary cavern traffic tunnel has a minimum distance of 100 m from the air chamber.
B rattset hydropower station, the maximum hydrostatic air cushion pressure of the air cushion type pressure regulating chamber is 2. 5M Pa, the air chamber is arranged on the left side of the diversion tunnel, the traffic tunnel and the air compressor room are arranged on the right side of the tunnel, and the connection between the traffic tunnel and the diversion tunnel is adopted. The installed concrete plug is blocked, and the only auxiliary tunnel traffic hole has a minimum distance of 150 m from the air chamber.
The maximum air cushion pressure of the U lset air cushion type pressure chamber is 2. 8M Pa. The construction traffic tunnel, the maintenance tunnel and the observation hole are all used in the horizontal hole 260 m away from the downstream of the air chamber, and the steel gate is closed during the operation period. Kvilldal Hydropower Station, the maximum cushion pressure of the air cushion type surge tank is 4. 1M Pa, and the maximum design pressure of the water curtain at the later stage is 5. 1M Pa. The air chamber is arranged on the left side of the diversion tunnel, and there are no other auxiliary caverns in the range of more than 300m. And the temporary surface, the transportation traffic tunnel inlet and the air compressor room during the construction period are located on the downstream side of the last pressure manifold.
At the Torpa hydropower station, the maximum cushion pressure of the air cushion type surge chamber is 414 M Pa, and the maximum design pressure of the water curtain is 4. 9 M Pa. The air chamber is arranged on the left side of the diversion tunnel, and there are no other auxiliary caverns and temporary planes in the vicinity of 200 m. The only one of the auxiliary caverns during the construction period is located on the left side of the tunnel, and the air compressor room is placed in the traffic hole outside the plug.
Summarizing the layout experience of the Norwegian air cushion type surge chamber, there are three main points: First, the auxiliary caverns are as small as possible, and the airfront surface of the cavern is as far as possible from the air chamber; second, the air chamber and traffic tunnel, air pressure The chambers such as the machine room are arranged as far as possible on both sides of the tunnel; the third is that the hydraulic gradient or pressure gradient of the air chamber to the air surface is generally between 1 and 5. The hydraulic gradient depends on the integrity and permeability of the rock mass. The arrangement of the auxiliary caverns should minimize the hydraulic gradient between the rock masses to reduce the leakage and leakage; the auxiliary caverns and air chambers are arranged separately on both sides of the diversion tunnel. Due to the barrier of the high pressure water in the tunnel itself, the groundwater level around the air chamber is raised, and the leakage of gas into the air space in the gas chamber is blocked.
Comparing the design of the air cushion type surge chamber in China from Yili and Xiaotiandu, there are tunnel traffic tunnels, water curtain chamber traffic tunnels, air cushion traffic tunnels, and ground exploration caves. The empty surface is located on the left side of the tunnel, the shortest diameter of the water curtain hole is only about 30 m, and the shortest diameter of the gas chamber is only 40 m, compared with 3.23 M Pa of design gas pressure and 3.73 M Pa. The design pressure of the water curtain, the hydraulic gradient is obviously difficult to meet the requirements. In the initial operation, a large amount of water leakage and air leakage are inevitable. In the consultation of the reinforcement scheme, the concrete lining and consolidation grouting range of several traffic passages were proposed, and the depth of high-pressure consolidation grouting was deepened to 8-10 m, and the lining range was controlled according to the actual seepage diameter of not less than 100 m. To try to make the water curtain hole around the area, in the stable seepage period, to maintain a higher groundwater level.
The layout of the auxiliary caverns of the Xiaotiandu project has similar problems as the ones in the same place. The specific layout design still needs to wait for the test of actual operation.
4 plenum shape and water curtain layout design The shape of the air chamber has a strip shape, a return type, a V type and the like, which mainly depends on the size and geological conditions of the air cushion chamber, so as to reduce leakage and stability of the chamber. in principle. The axis of the strip-shaped air cushion is generally oblique to the tunnel. In addition to the Kvilldal and Torpa air-cushioning pressure regulating outdoor, the air cushion type pressure regulating chambers at home and abroad are mostly arranged in a strip shape. The layout of the water curtain, Kvilldal and Tafjord were later rebuilt. There is no special water curtain room. The high pressure water is injected into the surrounding rock body of the gas chamber through the steel pipe to form a water curtain. The Torpa air cushion type pressure regulating chamber is the first design. The water curtain project is considered. The water curtain room is designed in the upper part of the middle of the return type air chamber. It is a dome-shaped barrel with a diameter of 5-6 m. The bottom of the water curtain gallery is 10 m above the top of the air cushion. The air chamber is sealed with a concrete plug, and the water curtain covers the entire top of the surge tank and the side wall.
The water curtain room layout design of China's related projects is completely different from that of Torpa. The water curtain corridor parallel to the air cushion type has a large volume space. When the water curtain chamber is filled with water, when the pressure difference between the air cushion type and the water curtain chamber is large. The rock mass between the two is easily broken down, and its structure has a disadvantageous side. It is worthy of further research and improvement in the future. Torpa's water curtain room layout is the main type worth learning.
5 points of experience (1) The choice of the position of the air cushion type surge chamber and the layout design of the auxiliary caverns and water curtain chambers are the key to the success of the air cushion type surge tank.
(2) The minimum principal stress shall be greater than the maximum hydrodynamic pressure or dynamic gas pressure, and the safety factor of 1. 4 to 1.6 times is too conservative. The minimum principal stress shall be greater than the maximum hydrodynamic pressure or not less than 1. The maximum hydrostatic pressure of 2.
(3) The gas chamber should have a complete rock mass with a thickness of at least 50-100 m, especially within a range of 50 m. It is not advisable to have large faults, joint fracture zones and other unfavorable structures to close the air leakage and water leakage.
(4) The percolation standard of the surrounding rock of the air-cushioning pressure regulating chamber is to be improved, and the water permeability of the surrounding rock after the grouting should be at least not greater than 0.1 L u.
(5) The diversion tunnel adopting the air cushion type surge chamber scheme should adopt the layout of “slow slope to the bottom†as much as possible.
(6) The number of auxiliary caverns should be minimized, and the airspace of the cavern should be as far as possible from the air cushion type. The hydraulic gradient or pressure gradient of the air cushion to the air surface should be less than 5, preferably less than 3; The pressure chambers, traffic tunnels, air compressor rooms and other caverns are placed on both sides of the tunnel as much as possible.
(7) The space volume of the water curtain chamber should be minimized to avoid adverse consequences of the rock mass structure between the water curtain chamber and the air cushion type.
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