Lining-free ecological energy dissipation tunnel and design method thereof

Abstract

The invention provides a lining-free ecological energy dissipation tunnel and a design method thereof. The tunnel is provided with an irregular inner surface. The irregular inner surface is formed by surrounding rock blasting construction or formed by surrounding rock blasting construction and shotcrete-anchor supporting measures after surrounding rock blasting construction. The design method comprises the following steps: acquiring tunnel related basic data; a plurality of roughness calculation values are prepared, the water flow velocity in the tunnel is calculated repeatedly, and the roughness calculation value, corresponding to the water flow velocity in the tunnel, in the multiple roughness calculation values is selected as the design roughness of the tunnel when the water flow velocity in the tunnel is smaller than or equal to and closest to the set flow velocity; and the unevenness of the tunnel is calculated based on the design roughness, and blasting construction and shotcrete anchor supporting of the tunnel are conducted according to the unevenness. According to the method, manual roughening is conducted on the tunnel through the irregular excavation face formed through high-strength surrounding rock blasting construction, the flow speed of water flow in the tunnel is controlled, the on-way energy dissipation effect is obvious, the reinforced concrete lining engineering amount is greatly reduced, the outlet energy dissipater scale is reduced, and engineering investment is saved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydraulic engineering design, and particularly relates to an ecological energy dissipation tunnel without lining and a design method thereof. BACKGROUND

[0002] The karst valley region in China has a wide distribution, and the main stratum lithology is carbonate rock, which is a frequent flood disaster area and an ecologically fragile region.

[0003] The flood drainage tunnel is an important infrastructure for flood control and drainage in the karst valley region. The newly-built flood drainage tunnel mainly discharges the flood in the basin to other rivers. Some water conservancy flood drainage tunnels have a large water head difference between the upstream and downstream, and the length of the tunnel is limited, resulting in a large water flow gradient, high flow velocity, complex hydraulic conditions, and prominent energy dissipation problems of the flood drainage tunnel. Since the outlet river channel of most tunnels is narrow, effective energy dissipation measures need to be taken at the end of the tunnel to avoid the discharged flood from impacting the mountain, thereby causing safety hazards. Generally, according to the topographic and geological conditions, the pick-up energy dissipation or the bottom flow energy dissipation is used at the tunnel outlet. The bottom flow energy dissipation has the advantages of stable flow state, good energy dissipation effect, strong adaptability to geological conditions and tail water level changes, and slight discharge atomization, and can adapt to different water heads of high, medium and low. However, the bottom flow energy dissipation pool has a large geometric size and high cost, and is not suitable for setting in some narrow valley regions. Since the pick-up energy dissipation structure is simple, when the downstream geological conditions of the discharge structure are good, the pick-up energy dissipation is more economical and reasonable to fully utilize the anti-erosion capacity of the downstream river channel. In recent decades, the pick-up energy dissipation has been widely used in high and medium water head discharge structures. The pick-up water tongue is broken in the air due to the drag and entrainment of the atmosphere, and splashing and atomization are generated when colliding with the downstream water body. Therefore, the atomization influence of the pick-up energy dissipation must be considered in the overall layout of the structure. In some narrow valley regions, the large flow velocity at the tunnel outlet causes a large pick-up distance and serious atomization, which may affect the stability of the mountain.

[0004] To reduce the flow velocity at the tunnel outlet, the energy dissipation structure can be arranged in the tunnel. The tunnel energy dissipation structure is arranged inside the water tunnel to artificially create large turbulent rolling to convert part of the water flow energy into heat energy, so as to reduce the outlet energy of the water flow, reduce the investment of the energy dissipation structure, and optimize the layout of the water conservancy structure. The tunnel energy dissipation structure is often arranged in the project of converting the diversion tunnel into a flood discharge tunnel, and the existing types include the following: the energy dissipation well, the vortex type energy dissipation structure, the tunnel energy dissipation pool, the orifice plate and the tunnel plug.

[0005] The flood discharge tunnel generally has a large height difference between the inlet and outlet, and has conditions for arranging the stilling well, the rotational flow energy dissipator and the in-hole stilling basin. However, the above energy dissipators need to excavate a large-sized underground chamber, have high requirements on the geological conditions, have complex structures, and have large engineering investment. The orifice plate energy dissipator has simple structure and high energy dissipation rate, but cavitation is prone to occur at the sharp edge of the orifice plate ring, the surface of the orifice plate needs to be protected by special materials, the orifice plate itself is subjected to large water flow impact force, the stability of the orifice plate itself is difficult to guarantee, and high water fins are prone to occur at the outlet of the orifice plate, affecting the flow safety. The plug-type energy dissipator has simple shape and structure, and has been used in the reconstruction of the diversion tunnel into the flood discharge tunnel in some hydropower stations. However, in the reconstruction of the diversion tunnel into the flood discharge tunnel, the outlet of the diversion tunnel is low and is in a submerged state, the static water pressure at the position of the plug is very large, and it is necessary to reduce the ratio of the plug hole to the original diversion tunnel water area as much as possible, so as to improve the energy dissipation efficiency, and at the same time ensure that there is enough positive pressure in the plug to avoid cavitation and cavitation.

[0006] A Chinese invention patent with the application number CN201910465430.3 discloses a diversion tunnel plug energy dissipation structure and its arrangement method. The main method of the patent is to set several stages of plug structures including plugs and water release holes in the diversion tunnel to segmentally reduce the water flow energy and reduce the outlet flow velocity. However, the method has a relatively complex structure, and additional structures such as shear anchor rods and air vents may increase the maintenance cost.

[0007] A Chinese invention application with the application number CN202410336270.3 discloses a continuous diffusion type bucket flow energy dissipation structure. The method uses continuously changing bucket flow angles to diffuse the water flow in the air, enhance the energy dissipation effect and reduce the impact on the riverbed bottom. However, the bucket flow structure is relatively complex and has large construction difficulty, which increases the operation and maintenance cost.

[0008] A Chinese utility model patent with the application number CN202320335189.4 discloses a diversion tunnel outlet energy dissipation structure. The patent uses two-stage energy dissipation to arrange the energy dissipation piers and energy dissipation banks to reduce the scouring of the water flow on the downstream, and uses the trapezoidal cross-section energy dissipation piers and the integral pouring structure to enhance the stability. However, the method has a complex structure, and the specific size usually needs to be determined through a hydraulic model test, which does not have universality.

[0009] A Chinese utility model patent with the application number CN201921098040.9 discloses a flood discharge energy dissipation structure for high flow rate non-pressure tunnels. The patent uses the combination of sudden expansion drop banks, diffusion type twisted surface discharge grooves and trapezoidal cross-section stilling basins to improve the water flow state and improve the energy dissipation efficiency. However, the construction precision requirement is high, and the maintenance difficulty is large. SUMMARY

[0010] In order to overcome the above technical deficiencies, the purpose of the present application is to provide an unlined ecological energy dissipation tunnel and a design method thereof, which solves the problem of the safety hazard caused by the discharged flood impacting the mountain, and has the advantages of low cost, low construction difficulty, simple maintenance and the like.

[0011] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: An unlined ecological energy dissipation tunnel, the tunnel is a flood discharge tunnel, comprising a tunnel body, and the tunnel body has an irregular inner surface for energy dissipation.

[0012] As a preferred scheme, the roughness of the tunnel is 0.015-0.04, the roughness of the tunnel is increased through the irregular inner surface, so as to reduce the water flow speed in the tunnel and achieve the effect of energy dissipation.

[0013] As a preferred scheme, the surrounding rock saturated compressive strength of the tunnel is ≥30MPa, and only sufficient surrounding rock strength can ensure the structural stability of the tunnel without lining, and meet the impact resistance requirement.

[0014] As a preferred scheme, the irregular inner surface is an irregular excavation surface formed by blasting construction of the surrounding rock, or an irregular inner surface formed by blasting construction of the surrounding rock and anchor shotcrete support measures after the blasting construction of the surrounding rock.

[0015] Further, the tunnel body is a non-lining structure or only has anchor shotcrete lining.

[0016] As a preferred scheme, a bucket flow energy dissipater is arranged at the outlet of the tunnel body.

[0017] Further, the bucket flow energy dissipater is a bucket flow nose sill arranged at the tail of the tunnel body.

[0018] The present application also provides a design method of the above-mentioned unlined ecological energy dissipation tunnel, and the special process comprises the following steps: 1) obtaining tunnel-related basic data; 2) preparing a plurality of roughness calculation values, repeatedly calculating the water flow speed in the tunnel based on the design discharge flow of the tunnel and the roughness calculation values, and selecting the roughness calculation value corresponding to the water flow speed in the tunnel being less than or equal to and closest to the set flow speed in the plurality of roughness calculation values as the design roughness of the tunnel; the water flow speed in the tunnel is the maximum flow speed in the tunnel; 3) calculating the unevenness of the tunnel based on the design roughness, and performing blasting construction and anchor shotcrete support of the tunnel according to the unevenness.

[0019] As a preferred scheme, in step 1), the basic data comprises the location and elevation of the inlet and outlet of the tunnel, the cross-sectional size, the longitudinal slope, and the design discharge flow under the design flood control standard.

[0020] Furthermore, the designed discharge flow rate is determined based on hydrological planning; the tunnel inlet and outlet locations, elevations, and longitudinal slopes are determined based on hydrological, topographical, geological, existing dikes, buildings, important infrastructure, and three-zone three-line data, taking into account topographical and geological conditions and surrounding limiting factors.

[0021] As a preferred embodiment, in step 2), the set flow velocity is the allowable erosion velocity of the surrounding rock of the tunnel.

[0022] Furthermore, the set flow rate is 7~9 m / s.

[0023] Furthermore, the set flow rate is 8 m / s.

[0024] As a preferred embodiment, in step 2), the formula for calculating the water flow velocity inside the tunnel is as follows:

[0025] In the formula, v is the flow velocity (m / s); R is the hydraulic radius (m); i is the longitudinal slope of the tunnel; and n is the roughness coefficient of the tunnel.

[0026] As a preferred embodiment, the roughness of the tunnel is 0.015 to 0.04.

[0027] Furthermore, the method for determining the roughness calculation value includes starting with the roughness when using the full lining scheme and gradually increasing it at a set calculation interval; the calculation interval is 0.001~0.01, determined according to the actual engineering accuracy. That is, the roughness calculation value includes n0, n0+Δn, n0+2Δn, n0+3Δn, ..., where n0 is the roughness when using the full lining scheme, and Δn is the calculation interval, which is 0.001~0.01.

[0028] Furthermore, the tunnel has a shotcrete lining; the roughness of the tunnel with the shotcrete lining is 0.02 to 0.04.

[0029] As a preferred embodiment, in step 3), the formula for calculating the unevenness is as follows:

[0030] In the formula, △ represents the unevenness inside the tunnel, in meters (m); D represents the tunnel diameter, in meters (m); R represents the hydraulic radius, in meters (m); and g represents the acceleration due to gravity, in meters per second (m / s²). 2 n is the roughness coefficient; a = The value is K s This represents the equivalent roughness of the tunnel.

[0031] As a preferred embodiment, the design method further includes the following steps: 4) determine whether the tunnel exit has the condition of flip flow energy dissipation, if yes, then multiple flip flow water tongue water surface exit angles theta are proposed for multiple trial calculations, the flip flow water tongue water surface exit angle theta which will not cause scouring impact on the bank and the opposite bank is obtained, and based on the flip flow water tongue water surface exit angle theta, the flip flow energy dissipation structure is designed.

[0032] As a preferred solution, the flip flow energy dissipation structure is a flip flow bucket; and the flip flow water tongue water surface exit angle theta is 10-20 degrees.

[0033] Compared with the prior art, the beneficial effects of the present application are: The present application provides a kind of ecological energy dissipation tunnel with lining-free for hard rock mountain area and its design method, solves the problem of safety hazard caused by discharging flood to impact mountain, with the advantages of low cost, low construction difficulty, simple maintenance, etc.

[0034] The present application reduces the flow velocity in the tunnel by setting ecological energy dissipation structure, thereby reducing the outlet flow velocity of the tunnel, and on this basis, the flip flow energy dissipation structure is set at the tail of the tunnel, which can effectively solve the problem of excessive flip distance and serious atomization caused by large outlet flow velocity of the tunnel.

[0035] The present application provides a kind of ecological energy dissipation tunnel with lining-free and its design method, which proposes the energy dissipation design concept of converting water flow kinetic energy into heat energy by increasing the roughness of the tunnel, and artificially roughening the tunnel by using irregular excavation surface formed by high-strength surrounding rock blasting construction, which has obvious effect on controlling water flow velocity in the tunnel and energy dissipation along the way, greatly reduces the amount of reinforced concrete lining, and effectively saves engineering investment. At the same time, due to the reduction of outlet flow velocity of the tunnel, the size of outlet energy dissipation structure is reduced, the layout of energy dissipation structure is simplified, the land occupation of outlet of flood discharge tunnel is reduced, and the impact on local vegetation and soil erosion is reduced. The method provides a new design idea and scheme for controlling outlet water flow pattern of flood discharge tunnel with high water head, short distance and high-strength surrounding rock. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings from the structures shown in the drawings without creating any creative labor.

[0037] Figure 1 It is a schematic diagram of tunnel outlet flip flow energy dissipation; Figure 2 It is a typical section diagram of tunnel lining-free; Figure 3 It is a roughness and flow velocity relationship curve table; Figure 4A table of flow rate versus pick-up distance.

[0038] The purposes, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0040] Embodiment 1 As shown in Figure 1 and Figure 2 An unlined ecological energy dissipation tunnel of the present application is a city gate-shaped tunnel, and the surrounding rock of the tunnel has a saturated compressive strength of ≥30 MPa. The tunnel comprises a tunnel body, and the tunnel body has an irregular inner surface for energy dissipation. The irregular inner surface is an irregular excavation surface formed after blasting of the surrounding rock or an irregular inner surface formed by the blasting of the surrounding rock and the subsequent shotcrete and anchor support measures, i.e., the tunnel body is a structure without lining or only has an anchor shot lining; the roughness of the tunnel is 0.015-0.04; and the roughness of the tunnel with an anchor shot lining is 0.02-0.04.

[0041] A pick-up energy dissipator is arranged at the outlet of the tunnel body; and the pick-up energy dissipator is a pick-up nose sill arranged at the tail of the tunnel body.

[0042] The height difference between the inlet and the outlet of the tunnel is 100-110 m, the longitudinal slope of the tunnel floor i is 3%-4%, and the length of the tunnel is ≤3 km.

[0043] Embodiment 2 A design method of the unlined ecological energy dissipation tunnel in Embodiment 1 comprises the following steps: 1) Obtain the relevant basic data of the tunnel; the basic data includes the location and elevation of the inlet and outlet of the tunnel, the size of the main section, the longitudinal slope, and the design discharge under the design flood control standard.

[0044] According to the calculation results of hydrology, hydraulic engineering and other professionals, determine the design discharge under the design flood control standard of the tunnel.

[0045] Collect the boundary condition data of the inlet and outlet area of the tunnel, including hydrology, topography, geology, existing embankments, houses, important infrastructure, three-zone three-line data, etc. According to the topographic and geological conditions, surrounding limiting factors, the location, elevation, section size, and longitudinal slope of the inlet and outlet of the tunnel are determined.

[0046] 2) A plurality of roughness calculation values are prepared, and based on the basic data of the tunnel and the roughness calculation values, the water flow velocity in the tunnel is repeatedly calculated to obtain the roughness calculation value when the water flow velocity in the tunnel is less than or equal to and closest to the set flow velocity as the design roughness of the tunnel. The roughness calculation value of the tunnel ranges from 0.015 to 0.04. The roughness of the tunnel with anchor shot lining ranges from 0.02 to 0.04, and preferably ranges from 0.03 to 0.035. The set flow velocity is the permissible erosion-resistant flow velocity of the tunnel, which is 7-9 m / s, and preferably 8 m / s.

[0047] The preparation process of the roughness calculation value is to gradually increase the roughness calculation value at a set calculation interval starting from the roughness when the full lining scheme is adopted. The calculation interval is 0.001-0.01, and preferably 0.005. That is, the roughness calculation value includes n0, n0+△n, n0+2△n, n0+3△n,..., wherein n0 is the roughness when the full lining scheme is adopted, and△n is the calculation interval.

[0048] 3) The tunnel irregularity is calculated based on the design roughness, and the blasting construction and anchor shot support of the tunnel are performed according to the irregularity.

[0049] The tunnel hydraulics calculation is performed considering the full lining of the tunnel to determine the water flow velocity in the tunnel.

[0050] Through the tunnel hydraulics calculation, the relationship between the tunnel roughness n and the water flow velocity v is obtained, and the relationship between the roughness n and the irregularity△ in the tunnel is further analyzed. The preliminary roughness n is substituted into the Xiecai formula and the Manning formula to calculate the corresponding flow velocity v, and further, the Modi formula is introduced to calculate the relationship between the corresponding along-path water head loss coefficient λ and the equivalent roughness K s . In addition, in the tunnel construction process, the irregularity△ and the equivalent roughness K s have a close relationship, and the specific calculation process is as follows: According to the preliminary tunnel roughness n, the Xiecai formula and the Manning formula are introduced to calculate the flow velocity . The calculation shows that the water flow velocity in the tunnel is inversely proportional to the tunnel roughness , and increasing the roughness can reduce the flow velocity, and the calculation expression is as follows: (Equation 1) (Equation 2) From equation 2, we have: = (Equation 3) The Xiecai formula is introduced as follows: (Equation 4) wherein i= , equation 3 is substituted into equation 4 to obtain (Formula five) That is: C= (Formula six) Manning formula is introduced: (Formula seven) Formula six and formula seven are combined, that is

[0051] That is: (Formula eight) Formula seven is brought into formula four, that is: (Formula nine) Further, Moddy formula is introduced, and it is calculated that the tunnel roughness n is proportional to lgK s , and the calculation expression is as follows: Moddy formula is introduced: (Formula ten) Formula ten is brought into formula eight, that is: (Formula eleven) Further, the tunnel unevenness△ is inversely calculated, and according to the measurement, generally . Assuming , it is calculated that the equivalent roughness K s is proportional to the unevenness△, and the specific calculation formula is as follows:

[0052] That is:

[0053] In the formula, R is the hydraulic radius (m), R=A / χ; A is the water area in the tunnel, m 2 ; χ is the water wet perimeter in the tunnel, m; C is the Chezai coefficient, m 3 ; n is the tunnel roughness; h f is the head loss along the way, m; v is the flow velocity in the tunnel, m / s; Q is the design flow of the tunnel, Q=A·v, m 3 / s; D is the diameter of the tunnel, m; i is the longitudinal slope of the tunnel; λ is the head loss coefficient along the way; K s is the equivalent roughness of the tunnel;△ is the unevenness in the tunnel, m; l is the length of the tunnel, m.

[0054] That is, the calculation formula of the flow velocity in the tunnel is as follows:

[0055] In the formula, v is the flow velocity, m / s; R is the hydraulic radius, m; i is the longitudinal slope of the tunnel; n is the tunnel roughness.

[0056] The calculation formula of unevenness is as follows:

[0057] In the formula, △ is the unevenness in the tunnel, m; D is the tunnel diameter, m; R is the hydraulic radius, m; g is the gravity acceleration, m / s 2 ; n is the tunnel roughness.

[0058] 4) Determine whether the tunnel outlet has the condition of flip energy dissipation, if yes, then multiple flip nappe water surface exit angles θ are determined for multiple trial calculations, the flip nappe water surface exit angle θ which does not cause scouring impact on the bank and the opposite bank is obtained, and based on the flip nappe water surface exit angle θ, a flip energy dissipation work is designed. The flip energy dissipation work is a flip bucket; the flip nappe water surface exit angle θ is 10-20°.

[0059] The flood drainage tunnel mostly belongs to a high water head, short distance, high strength surrounding rock type flood discharge tunnel, the energy dissipation problem is prominent, appropriate measures should be taken to reduce the scale of the energy dissipation work, simplify the layout of the energy dissipation work, reduce large excavation and large filling, reduce water and soil loss and impact on local vegetation, and at the same time, reduce the engineering investment, so as to achieve economy, rationality and safety. The energy dissipation setting of the flood drainage tunnel in A Village is used to further illustrate the content of the present application.

[0060] The inlet of the flood drainage tunnel in A Village is located at the lowest part of the karst valley in A Village, and the outlet is located on the right bank of B River, the flood drainage tunnel and the design method thereof are used for tunnel energy dissipation setting, and the specific method is as follows: 1) Obtain the related basic data of the tunnel; The total length of the tunnel is about 2.64 km, the height difference between the inlet and the outlet of the tunnel is 104 m, the longitudinal slope of the tunnel bottom plate is i=3.88%, the cross section of the tunnel is a city gate shape, the bottom width is 4 m, the hole height is 4.5 m, and the designed discharge flow is 101.04 m / s. The surrounding rock of the tunnel is limestone and limestone intercalated with shale, the rock mass is relatively complete, the structure is not developed, the surrounding rock is mainly of class II and III, and the surrounding rock strength is 30-55 MPa. The tunnel belongs to a high water head, short distance, high strength surrounding rock type flood discharge tunnel, due to the narrow river channel at the outlet of the tunnel, effective energy dissipation measures need to be taken at the end of the tunnel to avoid the discharged flood water impacting the opposite bank mountain, and causing safety hazards. The water head greater than 100 m can be called high water head; there is no fixed requirement for short distance, and for water conveyance engineering, less than 10 km is short distance.

[0061] Combined with the overall layout of the tunnel and the natural conditions of the downstream river channel, the following design principles are determined when designing the energy dissipation of the flood discharge tunnel: ① Avoid the direct impact of the flood discharge water on the left bank of River B under the condition of 10-year design flood; ② The top of the tunnel is the diversion channel of the C Reservoir Power Station, and the arrangement of the energy dissipation facilities should ensure that the diversion channel is not deformed or damaged; ③ Reduce the scale of the energy dissipation works as much as possible, reduce the engineering quantity, and save investment; ④ While reducing the scale of the energy dissipation works, simplify the arrangement of the energy dissipation works, reduce the land occupation of the outlet of the flood discharge tunnel, and reduce the water and soil loss and the impact on the local vegetation.

[0062] Energy dissipation scheme study Since the diversion channel of the C Reservoir Power Station at the top of the tunnel is only 15 m away from the bottom plate of the tunnel outlet, arranging an in-tunnel stilling basin at the end of the tunnel will inevitably raise the height of the tunnel top, which may have an adverse impact on the upper structures. In addition, the excavation and support of the in-tunnel stilling basin will require a large amount of engineering. If an out-tunnel stilling basin is arranged, the elevation of the tunnel outlet needs to be lowered, which will not only increase the energy dissipation head and thus the scale of the energy dissipation works, but also cause large-scale destruction of the vegetation at the outlet and water and soil loss, which is not conducive to the local ecology.

[0063] Based on the energy dissipation design principles and the good resistance to erosion and abrasion of the limestone at the outlet of the flood discharge tunnel, the energy dissipation mode at the outlet of the flood discharge tunnel can adopt the flip bucket energy dissipation, and the calculation formula of the flip bucket energy dissipation water tongue flip distance is as follows:

[0064] In the formula, L is the flip distance, m; v1 is the water surface flow velocity at the nose dam crest, m / s; θ is the water surface exit angle of the flip bucket water tongue; h1 is the vertical water depth at the crest of the dam, m; and h2 is the height difference from the crest of the dam to the river bed, m. If the scour pit has been formed, it can be calculated to the pit bottom.

[0065] As can be seen from the formula, the flip distance is related to the water surface flow velocity v1 at the nose dam crest, the water surface exit angle θ of the flip bucket water tongue, and other factors, among which the flow velocity v1 has the greatest impact. Therefore, reducing the flow velocity in the flood discharge tunnel is an important means to reduce the water discharge flip distance.

[0066] Since the tunnel has a certain slope, referring to the theory of uniform flow in open channels, the tunnel is a long and straight prism type down slope, and the bottom plate longitudinal slope i remains unchanged for about 2.58 km in length. The water flow pattern in the tunnel is uniform flow. According to the calculation formula of uniform flow in open channels, the flow velocity in the open channel is controlled by the factors of the hydraulic radius R, the bottom plate longitudinal slope i, and the Chezy coefficient C, while n is the roughness of the tunnel, and C is inversely proportional to n.

[0067] In summary, in order to avoid the direct impact of the flood discharge water on the opposite bank, the flow velocity in the flood discharge tunnel needs to be controlled, and an important means is to increase the roughness of the tunnel to increase the along-path head loss and achieve the effect of along-path energy dissipation in the tunnel.

[0068] 2) A plurality of roughness calculation values are prepared, and based on the design discharge of the tunnel and the roughness calculation values, the flow velocity in the tunnel is repeatedly calculated to obtain the roughness when the flow velocity in the tunnel is closest to the set flow velocity in each scheme, that is, the design roughness of the tunnel, and the flow velocity in the tunnel corresponding to the roughness is less than or equal to the set flow velocity. According to the actual project, the set flow velocity is set to 8 m / s.

[0069] Based on the design discharge of the tunnel, the flow velocity of the main section of the tunnel and the outlet of the tunnel is determined when the full lining scheme is adopted. As shown in Table 1, when the full lining scheme is adopted, the roughness of the tunnel is 0.015, at this time, the flow velocity v in the tunnel is 13 m / s, which is greater than 8 m / s.

[0070] Adjust the roughness of the tunnel for trial calculation until the flow velocity in the tunnel is closest to the set flow velocity, and the flow velocity in the tunnel is less than or equal to the set flow velocity, and obtain the roughness at this time as the design roughness of the tunnel. The roughness of the tunnel is gradually increased by 0.005 intervals for multiple trial calculations. The trial calculation results are shown in Table 1 and Figure 3 .

[0071] According to the tunnel arrangement, the longitudinal slope i of the tunnel floor is 3.88%. For the high-strength limestone tunnel section, the ecological combination energy dissipation without lining is adopted, that is, for type II and III, under the condition of ensuring the stability and safety of the tunnel itself, only the initial anchor spraying support measures are taken, the irregular excavation surface formed by blasting is maintained, and the roughness of the tunnel water passage section is increased. According to the uniform flow formula of open channel, the flow pattern of the tunnel is calculated multiple times. When the ecological combination energy dissipation without lining is adopted in the tunnel, when n=0.03, the flow velocity is reduced to 59% of the flow velocity of the full-section lining, which is lower than 8 m / s and closest to 8 m / s.

[0072] Table 1: Tunnel flow velocity calculation results under different roughness conditions

[0073] 3) Based on the roughness of the tunnel, the roughness of the tunnel is calculated, and the construction of the tunnel is carried out according to the roughness. Through the reverse calculation, the roughness of the tunnel is 0.3 m. The final size of the tunnel is shown in Table 2.

[0074] Table 2: Tunnel flow passage section

[0075] As shown in Table 2, the standard section size of the tunnel is 4 m x 4.5 m (width x height), and the maximum flow velocity in the tunnel is 7.61 m / s, which is less than the allowable impact flow velocity 8 m / s of the anchor shot lining tunnel.

[0076] 4) It is determined that the tunnel outlet has the condition of flip energy dissipation, a flip nose is arranged at the tail of the tunnel, the initial flip water tongue water surface emission angle θ is calculated, and the flip distance L and the impact pit depth T are calculated.

[0077] Based on the pick distance L and the scour pit depth T, it is determined whether the energy dissipation causes scouring effect on the bank and the opposite bank. If not, the water surface ejection angle θ of the pick flow nappe is determined as the current calculation water surface ejection angle θ of the pick flow nappe. If yes, the water surface ejection angle θ of the pick flow nappe is adjusted. Through repeated trial calculation, the water surface ejection angle θ of the pick flow nappe which does not cause scouring effect on the bank and the opposite bank is obtained, and based on the water surface ejection angle θ of the pick flow nappe, the pick flow bucket is designed.

[0078] Through repeated trial calculation, the water surface ejection angle θ of the pick flow nappe which does not cause scouring effect on the bank and the opposite bank is obtained, and based on the water surface ejection angle θ of the pick flow nappe, the pick flow bucket is designed. Figure 4 As shown in Tables 3 and Figure 4 , when the roughness is 0.03 and the water surface ejection angle θ of the pick flow nappe is 15°, the corresponding water nappe distance L is 14.59 m, which does not cause adverse effects on the upper structure and the opposite bank. Through this scheme, the pick distance of the tunnel outlet pick flow energy dissipation design is shortened from the opposite bank to the tunnel outlet side riverbed to the river center range, which greatly reduces the scouring of the surrounding rock during flood discharge and ensures the safe operation of the flood discharge tunnel.

[0079] Table 3: Water nappe distance calculation results of different flow velocities in the tunnel when the water surface ejection angle θ of the pick flow nappe is 15°

[0080] Through calculation, the elevation of the pick flow bucket top is 715.00 m, the vertical direction water depth of the pick flow bucket end is 2.62 m, and the water surface velocity of the pick flow bucket top is 9.65 m / s. The pick distance is estimated according to the continuous pick bucket, and the water nappe distance formula and the maximum water cushion depth calculation formula of the scour pit are used according to the specification. The calculation results are shown in Table 4. In the formula, T is the water cushion thickness, which is calculated from the water surface to the pit bottom, m; k is the scouring coefficient, which is determined according to the joint fissure and bedrock structure characteristics; and Z is the water level difference between the upstream and downstream, m.

[0081] Table 4: Pick distance calculation results under the design flood frequency

[0082] As can be seen from the data in Table 4, under the 10-year condition, the tunnel discharge water pick distance is only 14.59 m, the scour pit depth is 3.04 m, and the water nappe is located on the right bank of the river, effectively eliminating the scouring of the pick flow energy dissipation on the opposite bank, and the flow pattern is as shown in Figure 1 .

[0083] The flood discharge tunnel of the project has been put into operation. According to the feedback from the operation unit, the inspection results during the flood discharge process of the flood discharge tunnel show that the design scheme effectively controls the kinetic energy of the water flow, and the discharged water flow still falls on the right bank bedrock of B river during flood discharge, without causing adverse effects on the B river bed and the left bank. The tunnel operates well, and the outlet river section is not obviously scoured.

[0084] The tunnel roughness is improved and the water flow velocity in the tunnel is reduced by the innovative tunnel ecological combination energy dissipation technology, the irregular excavation surface formed by high strength surrounding rock blasting construction is used to artificially increase the roughness of the tunnel, the water flow velocity in the tunnel is controlled, the energy dissipation effect along the tunnel is obvious, the amount of reinforced concrete lining engineering is greatly reduced, the engineering investment is effectively saved, and a new design idea and scheme are provided for the method for controlling the water flow state at the outlet of the flood discharge tunnel with high water head, short distance and high strength surrounding rock.

[0085] The above examples are only examples of the technical solutions of the present application. The tunnel section partition static excavation method involved in the present application is not limited to the content described in the above examples, but is subject to the scope defined in the claims. Any modification or supplement or equivalent replacement made by the person skilled in the art on the basis of the examples is within the scope claimed by the claims of the present application.

Claims

1. A lining-free ecological energy dissipation tunnel, the tunnel comprising a tunnel body, characterized in that: The tunnel body has an irregular inner surface for energy dissipation; the saturated compressive strength of the surrounding rock of the tunnel is ≥30MPa.

2. The lining-free ecological energy dissipation tunnel according to claim 1, characterized in that: The roughness of the tunnel is 0.015 to 0.

04.

3. The lining-free ecological energy dissipation tunnel according to claim 1, characterized in that: The irregular inner surface is an irregular excavation face formed by surrounding rock blasting construction, or an irregular inner surface formed by surrounding rock blasting construction and subsequent shotcrete and anchor support measures.

4. The lining-free ecological energy dissipation tunnel according to claim 1, characterized in that: A flow dissipation structure is installed at the exit of the tunnel body.

5. The lining-free ecological energy dissipation tunnel according to claim 4, characterized in that: The flow dissipation device is a flow nose sill, which is installed at the tail of the tunnel body.

6. The design method for the lining-free ecological energy dissipation tunnel according to any one of claims 1 to 5, characterized in that: Includes the following steps: 1) Obtain basic information related to the tunnel; 2) Draft multiple roughness calculation values. Based on the design discharge flow rate of the tunnel and the roughness calculation values, repeatedly calculate the water flow velocity inside the tunnel. Select the roughness calculation value that corresponds to the water flow velocity inside the tunnel being less than or equal to and closest to the set flow velocity from among the multiple roughness calculation values ​​as the design roughness of the tunnel. 3) Calculate the tunnel roughness based on the design roughness, and carry out tunnel blasting construction and shotcrete support according to the roughness.

7. The design method according to claim 6, characterized in that: In step 2), the method for determining the roughness calculation value includes starting with the roughness when using the full lining scheme and gradually increasing it at a set calculation interval; the calculation interval is 0.001~0.01; the set flow velocity is the allowable erosion velocity of the surrounding rock of the tunnel.

8. The design method according to claim 7, characterized in that: The set flow rate is 7~9 m / s.

9. The design method according to claim 6, characterized in that: In step 2), the formula for calculating the water flow velocity inside the tunnel is as follows: In the formula, v is the flow velocity (m / s); R is the hydraulic radius (m); i is the longitudinal slope of the tunnel; and n is the roughness coefficient of the tunnel.

10. The design method according to claim 6, characterized in that: In step 3), the formula for calculating the unevenness is as follows: In the formula, △ represents the unevenness inside the tunnel, in meters (m); D represents the tunnel diameter, in meters (m); R represents the hydraulic radius, in meters (m); and g represents the acceleration due to gravity, in meters per second (m / s²). 2 n is the roughness coefficient; a = The value is K s This represents the equivalent roughness of the tunnel.

11. The design method according to any one of claims 6 to 10, characterized in that: The design method further includes the following steps: 4) Determine whether the tunnel outlet has the conditions for jet flow energy dissipation. If so, propose multiple jet flow tongue water surface exit angles θ and perform multiple trial calculations to obtain the jet flow tongue water surface exit angle θ that will not cause scouring impact on the local bank and the opposite bank. Based on the jet flow tongue water surface exit angle θ, design the jet flow energy dissipation structure.

12. The design method according to claim 11, characterized in that: The energy dissipator is a flow-lifting nose sill; the water jet exit angle θ of the flow-lifting water tongue is 10~20°.

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