Arch dam flood discharge and energy dissipation structure

Abstract

The invention provides an arch dam flood discharge and energy dissipation structure, and relates to the technical field of water conservancy and hydropower. The structure comprises a plunge pool and an auxiliary dam, the plunge pool adopts a concrete bottom plate, and the plunge pool is symmetrically arranged along a flood discharge center line of an arch dam; the cross section of the plunge pool is in a compound trapezoid shape, and a reinforced concrete lining protection structure is adopted. Concrete apron blocks are arranged at the bottom of the plunge pool, and water stop pieces are arranged between the concrete apron blocks; an impermeable layer and a drainage gallery are arranged at the bottom of the concrete apron; and a dam foundation of the secondary dam is provided with an anti-seepage curtain. While flood discharge and energy dissipation are achieved, scouring of the bottom of the plunge pool is reduced, direct impact on a riverbed is relieved, and the safety of the arch dam is guaranteed. The impermeable layer and the drainage gallery are arranged at the bottom of the concrete apron, so that closed pumping and drainage measures are taken for the apron, and the anti-floating stability of the apron can meet the stability requirement under the normal operation condition and the overhaul condition. And the seepage-proofing curtain is arranged on the dam foundation of the secondary dam, so that the seepage flow of the water body is greatly reduced, and the uplift pressure is reduced.

Description

Technical Field

[0001] The present disclosure relates to the technical field of water conservancy and hydropower, and in particular to an arch dam flood discharge and energy dissipation structure. Background Art

[0002] When an arch dam releases floodwater, water flows down from the towering crest or spillway at high speed, generating immense kinetic energy. This high-speed flow carries enormous energy, potentially hollowing out the dam foundation or the rock mass along its banks, severely eroding the riverbed and threatening the overall stability of the dam. It can also cause cracking or failure of structures like aprons and stilling basins, increasing repair costs. Therefore, ensuring arch dam safety while dissipating energy through flood discharge is a key research topic in this field. Summary of the Invention

[0003] The present disclosure aims to solve one of the technical problems in the related art at least to a certain extent.

[0004] To this end, the first embodiment of the present disclosure proposes an arch dam flood discharge and energy dissipation structure, comprising a water cushion pond and a secondary dam sequentially arranged downstream of the arch dam; the water cushion pond adopts a concrete bottom plate, and the water cushion pond is symmetrically arranged along the flood discharge centerline of the arch dam;

[0005] The cross section of the water cushion pond is a compound trapezoid, and the water cushion pond adopts a reinforced concrete lining structure;

[0006] A concrete guardrail is provided at the bottom of the water cushion pond, the concrete guardrail is anchored to the rock foundation by anchor piles, and copper water stop plates are provided between the concrete guardrail blocks;

[0007] An anti-seepage layer is provided at the bottom of the concrete apron to form a closed area, and a drainage corridor is provided in the closed area;

[0008] The second dam is a concrete gravity dam;

[0009] The dam foundation of the second dam is provided with an anti-seepage curtain, which is respectively connected with the curtains on both sides of the second dam and the foundation anti-seepage curtain of the arch dam, together forming a closed anti-seepage system of the water cushion pond.

[0010] In some embodiments of the present disclosure, the anti-seepage layer includes curtain grouting or concrete anti-seepage wall.

[0011] In some embodiments of the present disclosure, a drainage network is laid at the interface between the bottom of the concrete apron and the bedrock, leading into the drainage corridor.

[0012] In some embodiments of the present disclosure, the drainage corridor includes at least three drainage corridors extending transversely to the river, and at least two drainage corridors arranged longitudinally along the toe of the slope protection.

[0013] In some embodiments of the present disclosure, the thickness of the concrete slabs on both sides of the plunge pool is negatively correlated with the elevation of the slopes on both sides.

[0014] In some embodiments of the present disclosure, the upstream slope ratio of the second dam is 1:0.6, and the downstream slope ratio is 1:0.8.

[0015] In some embodiments of the present disclosure, a hydropower station is provided upstream of the arch dam, and the dam top elevation of the second dam is higher than the full tail water level of the generator set of the hydropower station.

[0016] In some embodiments of the present disclosure, a main drainage hole is provided on the upstream side of the anti-seepage curtain, and a secondary drainage hole is provided in the drainage corridor on the upstream side of the dam foundation of the second dam.

[0017] The arch dam flood discharge and energy dissipation structure provided by the present disclosure can reduce the scouring of the bottom of the water cushion pond while achieving flood discharge and energy dissipation, alleviate the direct impact on the riverbed, and ensure the safety of the arch dam. An anti-seepage layer and a drainage corridor are set at the bottom of the concrete apron to take closed pumping and drainage measures for the apron, so that the anti-floating stability of the apron can meet the stability requirements under both design and maintenance conditions. In addition, the anti-seepage curtains set on the dam foundation, which are respectively connected to the curtains on both sides of the second dam and the foundation anti-seepage curtains of the arch dam, greatly reduce the seepage volume of the water body, thereby reducing the uplift pressure and ensuring the stability of the dam foundation.

[0018] Additional aspects and advantages of the present disclosure will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or additional aspects and advantages of the present disclosure will become apparent and readily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0020] Figure 1 A plan view of the plunge pool provided in an embodiment of the present disclosure;

[0021] Figure 2 A longitudinal cross-sectional view of a plunge pool provided in an embodiment of the present disclosure;

[0022] Figure 3 A cross-sectional view of a plunge pool provided in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0023] The following describes in detail embodiments of the present disclosure, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present disclosure, and should not be construed as limiting the present disclosure.

[0024] The arch dam flood discharge and energy dissipation structure proposed in this disclosure includes a plunge pool and a secondary dam, located downstream of the arch dam. The secondary dam provides maintenance conditions for the plunge pool and prevents the downstream overburden, sediment, and other debris from flowing back into the plunge pool, causing wear and tear. Maintenance and construction should be scheduled during the dry season. The plunge pool has a concrete base and is symmetrically arranged along the arch dam's centerline. Figure 1 This is a plan view of the plunge pool provided in the embodiment of the present disclosure. Figure 1 As shown in the figure, the pad pond is arranged symmetrically along the discharge center line of the arch dam.

[0025] The energy dissipation factors of a plunge pool mainly include the distance of the incident water flow and the depth of the scouring pit.

[0026] The calculation formula for surface orifice drop flow is as follows:

[0027] L d =2.3q 0.54 Z 0.19

[0028] t d =0.6q 0.44 Z 0.34

[0029] t k =kq 0.5 .5H 0.25

[0030] The calculation formula for deep hole flow is as follows:

[0031]

[0032] Where, v1 is the water velocity at the top of the bank (m / s);

[0033] ——Weir face velocity coefficient, which can be initially estimated to be 0.95;

[0034] H0 - height difference between reservoir water level and sill top (m);

[0035] h1——average water depth normal to the top of the bank (m);

[0036] θ——the angle of the nose bridge (°);

[0037] L - water tongue throw (m), which is the horizontal distance from the embankment to the intersection of the outer edge of the water tongue and the downstream water surface;

[0038] h2 - height difference between the top of the bank and the downstream water surface (m);

[0039] β - water tongue entry angle (°), the angle between the outer edge of the water tongue and the downstream water surface;

[0040] t k——Water cushion depth from the downstream water surface to the deepest point of the scour pit (m);

[0041] k——bedrock scour coefficient, adopted according to bedrock characteristics;

[0042] q - single width flow rate at the embankment (m 3 / s·m);

[0043] H - upstream and downstream water level difference (m);

[0044] T——maximum scouring pit depth (m), the depth from the riverbed to the pit bottom;

[0045] H2 - downstream water depth (m);

[0046] L – Horizontal distance from the embankment to the deepest point of the scour (m).

[0047] Z – height difference from nose sill to riverbed (m).

[0048] t d ——Water cushion depth upstream of the water tongue drop point (m)

[0049] Taking a certain plunge pool as an example, the calculation results of the span and maximum scouring depth of the surface holes at various flow rates when the plunge pool is not protected are shown in Table 1, and the calculation results of the span and maximum scouring depth of the deep holes are shown in Table 2.

[0050] Table 1

[0051]

[0052]

[0053] Table 2

[0054]

[0055] The calculation results in Tables 1 and 2 show that the bottom of the cushion pond has a certain degree of scouring under natural conditions, and the maximum depth of the scouring pit reaches 22.0m. Therefore, in order to ensure the safety of the dam, in the embodiment disclosed in this disclosure, the cushion pond adopts a concrete bottom plate. According to the bedrock conditions, the elevation of the cushion pond bottom plate is taken as 2118.0m. The concrete scouring coefficient is taken as 0.75 based on the lower limit of the hard and intact bedrock. After calculation, under various levels of discharge, the required maximum water cushion thickness is 35m, which is less than the downstream water depth of the corresponding working condition, and the concrete bottom plate is not scoured. Model tests show that the maximum impact pressure of the cushion pond bottom plate in this example is 10.43×9.81kPa, which is less than the impact dynamic water pressure control parameter of the flat floor cushion pond of similar projects of 15×9.81kPa. The cushion depth of the cushion pond is sufficient, and the stability of the bottom plate is guaranteed.

[0056] The cross section of the water cushion pond is a compound trapezoid, and the water cushion pond adopts a reinforced concrete lining structure. Figure 2A longitudinal cross-sectional view of a plunge pool provided in an embodiment of the present disclosure is shown. Figure 3 This is a cross-sectional view of a plunge pond provided in an embodiment of the present disclosure. In some embodiments of the present disclosure, the thickness of the concrete slabs on both sides of the plunge pond is negatively correlated with the elevation of the slope. This means that, given the impact of forces at different elevations, the higher the elevation, the thinner the concrete slabs. As an example, the concrete slabs on both sides of the plunge pond below an elevation of 2375.00m are 3m thick, and between 2375.00m and 2415.00m, the concrete slabs are 0.8m thick.

[0057] A concrete apron is installed at the bottom of the plunge pond. Anchored to the rock foundation with anchor piles, copper waterstops are installed between the concrete apron blocks to prevent water leakage. As an example, a 4-meter-thick concrete apron can be installed at the bottom of the pond, anchored to the bedrock with 4C36@3m×3m anchor piles, with a depth of 7.5m. The apron top is 59 meters wide across the river, with each block approximately 15 meters long along the river and 15 / 14 meters wide across the river. Two copper waterstops are installed between the blocks.

[0058] The bottom of the concrete apron is provided with an anti-seepage layer, such as curtain grouting or a concrete anti-seepage wall, to form a closed area. A drainage corridor is provided in the closed area, and closed pumping measures are taken for the apron to ensure the anti-floating stability of the apron. Optionally, in some embodiments, a drainage network is laid at the interface between the bottom of the concrete apron and the bedrock below the apron, which leads into the drainage corridor. The drainage corridor can include at least three drainage corridors in the transverse direction of the river, with a spacing of 100m, and at least two drainage corridors arranged longitudinally along the toe of the slope protection (i.e., one drainage corridor is arranged longitudinally along the toe of the slope protection).

[0059] In order to verify the effectiveness of the concrete apron structure, the ultimate bearing capacity limit state calculation can be performed. The effect function and resistance function of the apron anti-floating stability calculation are as follows:

[0060] S(·)=γ Q2 Q2+γ Q3 Q3

[0061] R(·)=γ G1 G1+γ Q1 Q1+γ G2 G2

[0062] Among them, G1 is the standard value of the tank's deadweight, kN, G1 = γ c ZA;

[0063] γG1——tank weight partial coefficient;

[0064] G2——standard value of effective weight of anchor foundation, kN;

[0065] γG2——partial coefficient of effective deadweight of anchored foundation;

[0066] Q1——standard value of the average pressure on the top surface of the guardrail, kN, Q1=p tr A;

[0067] γQ1——the time-averaged pressure partial coefficient of the top surface of the guardrail;

[0068] Q2——standard value of pulsating pressure on the top surface of the guardrail, kN, Q2=β m p fr A;

[0069] γQ2——partial coefficient of pulsating pressure on the top surface of the guardrail;

[0070] Q3——Standard value of uplift pressure on the bottom of the apron (including seepage pressure and buoyancy), kN;

[0071] γQ 31 ——Partial coefficient of seepage pressure on the bottom of the apron;

[0072] γQ 32 ——partial coefficient of buoyancy of the bottom surface of the apron;

[0073] γQ 33 — partial coefficient of uplift pressure on the bottom surface of the apron (not distinguishing between seepage pressure and buoyancy);

[0074] γ c ——Concrete density of the apron, kN / m 3 ;

[0075] p tr ——Representative value of average pressure during tank protection, kN / m 2 ;

[0076] p fr ——Representative value of pulsating pressure of guard tank, kN / m 2 ;

[0077] β m ——area averaging coefficient;

[0078] A——Calculated area of the tank, m 2 ;

[0079] Z——thickness of the tank guard, m.

[0080] The design situation and maintenance situation are selected to calculate the anti-floating stability of the apron. The load combinations of the design situation and maintenance situation are shown in Table 3.

[0081] Table 3

[0082]

[0083]

[0084] The cushion pond apron is assumed to be 4m thick, with individual sections measuring 15m x 14m. It is anchored to the bedrock using 4C36@3m x 3m anchor piles, with a depth of 7.5m. The concrete bulk density of the apron is 24kN / m, the anchoring bedrock bulk density is 25kN / m, and the water bulk density is 9.8kN / m. Under the design scenario, a 1% flood discharge (including power station water diversion) is applied, with the cushion pond water level approximately 2360.00m and the downstream water level of Erdao Dam 2358.68m. Under the maintenance scenario, a 10% flood discharge (including power station water diversion) during the dry season is applied, with the cushion pond empty and the downstream water level of Erdao Dam 2350.69m. The calculations consider both pumping and non-pumping conditions. The uplift pressure coefficient is assumed to be 1.0 under the non-pumping condition and 0.25 under the pumping condition. The results of the apron anti-floating stability calculations are shown in Table 4.

[0085] Table 4

[0086]

[0087] It can be seen from Table 4 that the anti-floating stability of the apron under the conditions of pumping and drainage can meet the requirements. Therefore, the embodiment of the present disclosure adopts closed pumping and drainage measures for the apron (i.e., the anti-seepage layer and drainage corridor at the bottom of the apron) to ensure the anti-floating stability of the apron.

[0088] The Erdao Dam is a concrete gravity dam with a simple structure and well-defined load-bearing characteristics. Optionally, in some embodiments, the upstream slope ratio of the Erdao Dam can be set to 1:0.6, and the downstream slope ratio can be set to 1:0.8. A hydropower station is located upstream of the arch dam, and the crest elevation of the Erdao Dam is higher than the full tailwater level of the hydropower station's turbines. Furthermore, in some embodiments, the crest elevation of the Erdao Dam must not only be higher than the full tailwater level of the hydropower station's turbines, but also higher than the downstream water level of a 10% flood during the dry season.

[0089] The foundation of Erdao Dam is equipped with an anti-seepage curtain (i.e. grouting around the apron or in the foundation rock to form an anti-seepage barrier and reduce the amount of seepage). The anti-seepage curtain is connected to the curtains on both sides of Erdao Dam and the foundation anti-seepage curtain of the arch dam, forming a closed anti-seepage system of water cushion ponds to prevent the apron from floating or becoming unstable due to excessive water pressure at the bottom, and to avoid problems such as piping and softening of the foundation soil or rock formations due to seepage, which can extend the service life of the apron and reduce maintenance costs.

[0090] Concrete plunge pools are used downstream of the dam to dissipate energy, arranged symmetrically along the centerline of the flood discharge. The top elevation of the plunge pool slab was set at 2,314 meters based on bedrock conditions. Calculations show that at all discharge levels, the maximum span is approximately 200 meters, the free hydraulic jump after entry is approximately 110 meters, and the forced hydraulic jump is approximately 85 meters. This results in a plunge pool bottom length of 300 meters. A secondary dam is installed at the end of the plunge pool, with a base elevation of 2,310.00 meters and a crest elevation of 2,352.00 meters. Tests have shown that under all characteristic operating conditions, the ejected water entering the plunge pool forms a submerged hydraulic jump. The downstream flow of the secondary dam flows smoothly, ensuring sufficient energy dissipation.

[0091] A hydropower station is calibrated to have a flood peak flow of 12,000 m / s, a downstream water level of approximately 2,363 m, a head of approximately 175 m, and a total flood discharge capacity of approximately 20,000 MW. The bottom of the energy dissipation zone is approximately 300 m long, and the total water volume in the energy dissipation zone is approximately 1.5 million m 3 The energy dissipation rate per unit water body is about 13.3kW / m 3 The energy dissipation rate per unit water body of the plunge pool is lower than that of the Baihetan and Laxiwa projects, and is within the existing engineering technology level. It can be seen that the arch dam flood discharge and energy dissipation structure arrangement proposed in the embodiment of the present disclosure is appropriate.

[0092] In some embodiments, the anti-sliding stability and stress of the arch dam's flood discharge and energy dissipation structure can be verified, and the ultimate bearing capacity limit state calculation of the dam body can be performed according to the "Specifications for the Design of Concrete Gravity Dams" (NB / T35026-2022), including the strength calculation of the dam body and the dam foundation, and the anti-sliding stability calculation of the contact surface between the dam body and the dam foundation. The riverbed dam section is selected for calculation. Under the completed working condition, the Erdao Dam only considers the gravity load of the dam body concrete; under normal operating conditions, the upstream and downstream of the Erdao Dam are subject to similar water heads. The water level inside the water cushion pond is relatively high and is calculated according to the top elevation of 2352.00m. The downstream side is calculated according to the normal water storage level of the downstream cascade hydropower station at 2345.0m. Under maintenance conditions, the water cushion pond is emptied, and the Erdao Dam is subjected to the unidirectional water load on the downstream side and is calculated according to the 10% flood level of 2350.69m during the dry season (supported by the downstream cascade hydropower station). In accordance with the requirements of the specifications, the stress and stability conditions of Erdao Dam under completed conditions, normal operating conditions and maintenance conditions were recalculated.

[0093] Under various calculation conditions, the stress and stability calculation results of the dam body along the foundation surface are shown in Table 5 - Stability and Stress Results of the Second Dam Foundation Surface.

[0094] Table 5

[0095]

[0096] As shown in Table 5, under various calculation conditions, the compressive strength of the dam toe and the anti-sliding stability along the foundation surface of each dam section of Erdao Dam meet the regulatory requirements that the resistance is greater than the effect of the action. Under the long-term combined action of the normal serviceability limit state, no tensile stress appears in the vertical stress at the dam heel under any working condition.

[0097] By implementing the embodiments of the present disclosure, it is possible to reduce scouring of the bottom of the cushion pond while achieving flood discharge and energy dissipation, alleviate direct impacts on the riverbed, and ensure the safety of the arch dam. An anti-seepage layer and drainage corridor are set at the bottom of the concrete apron to take closed pumping and drainage measures for the apron, so that the anti-floating stability of the apron can meet the stability requirements under both design and maintenance conditions. In addition, the anti-seepage curtains set on the dam foundation, which are connected to the curtains on both sides of the second dam and the foundation anti-seepage curtains of the arch dam, can greatly reduce the seepage volume of the water body, thereby reducing the uplift pressure and ensuring the stability of the dam foundation.

[0098] In the descriptions of the aforementioned embodiments, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are mutually inconsistent.

[0099] Although the embodiments of the present disclosure have been shown and described above, it is understood that the above embodiments are illustrative and are not to be construed as limitations on the present disclosure. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present disclosure.

Claims

1. An arch dam flood discharge and energy dissipation structure, comprising a plunge pool and a secondary dam arranged in sequence downstream of the arch dam, characterized in that: The water cushion pond adopts a concrete bottom plate, and the water cushion pond is symmetrically arranged along the flood discharge center line of the arch dam; The cross section of the water cushion pond is a compound trapezoid, and the water cushion pond adopts a reinforced concrete lining structure; A concrete guardrail is provided at the bottom of the water cushion pond, the concrete guardrail is anchored to the rock foundation by anchor piles, and water stop plates are provided between the concrete guardrail blocks; An anti-seepage layer is provided at the bottom of the concrete apron to form a closed area, and a drainage corridor is provided in the closed area; The second dam is a concrete gravity dam; The dam foundation of the second dam is provided with an anti-seepage curtain, which is respectively connected with the curtains on both sides of the second dam and the foundation anti-seepage curtain of the arch dam, together forming a closed anti-seepage system of the water cushion pond.

2. The arch dam flood discharge and energy dissipation structure according to claim 1, characterized in that: The anti-seepage layer includes curtain grouting or concrete anti-seepage wall.

3. The arch dam flood discharge and energy dissipation structure according to claim 1, characterized in that: A drainage network is laid at the interface between the bottom of the concrete apron and the bedrock, leading into the drainage gallery.

4. The arch dam flood discharge and energy dissipation structure according to claim 3, characterized in that: The drainage corridors include at least three drainage corridors in the transverse direction of the river and at least two drainage corridors arranged longitudinally along the foot of the slope protection.

5. The arch dam flood discharge and energy dissipation structure according to claim 1, characterized in that: The thickness of the concrete slabs on both sides of the water cushion pond is negatively correlated with the elevation of the slopes on both sides.

6. The arch dam flood discharge and energy dissipation structure according to claim 1, characterized in that: The upstream slope ratio of the Erdao Dam is 1:0.6, and the downstream slope ratio is 1:0.

8.

7. The arch dam flood discharge and energy dissipation structure according to claim 1, characterized in that: A hydropower station is provided upstream of the arch dam, and the dam crest elevation of the second dam is higher than the full tail water level of the generating units of the hydropower station.

8. The arch dam flood discharge and energy dissipation structure according to claim 1, characterized in that: A main drainage hole is provided on the upstream side of the anti-seepage curtain, and a secondary drainage hole is provided in the drainage corridor on the upstream side of the dam foundation of the second dam.

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