A middle-low earth-rock dam overtop protection drainage structure and a design method thereof

Abstract

The application discloses a kind of middle-low earth-rock dam overtop protection drainage structure and its design method, the middle-low earth-rock dam overtop protection drainage structure includes dam crest drainage structure, downstream slope surface drainage structure and dam foot drainage energy dissipation structure sequentially arranged from top to bottom along dam cross section, wherein dam crest drainage structure is used to converge part of overtop flow;Downstream slope surface drainage structure is used to accept the overtop flow converged by the dam crest drainage structure, and further guides, collects and dissipates the flow overtop to downstream slope surface;Dam foot drainage energy dissipation structure is used to dissipate the flow of downstream slope surface drainage structure and discharge it.The application comprehensively considers the concentration of overtop scour flow, drainage, dissipation and has better overtop protection effect.

Description

Technical Field

[0001] This invention relates to overtopping protection structures for earth-rock dams, specifically to an overtopping protection diversion and drainage structure for medium-low earth-rock dams and its design method. Background Technology

[0002] The flood control standards for medium and low-level earth-rock dams in my country are generally low, with the design flood control standard for small (1) type reservoirs being only once every 10 to 50 years. In recent years, climate change has intensified, and flood events exceeding the standard have occurred frequently. Due to the weak erosion resistance of the soil material in earth-rock dams, they are easily damaged or even collapse when subjected to floods exceeding the standard. The existing overtopping protection structures of earth-rock dams mainly adopt rigid or flexible revetments with full coverage, mainly considering increasing the seepage prevention and erosion resistance of the dam surface. The main structural forms include concrete slab slope protection, concrete blocks, gabions, etc. The structure has a single function. After the earth-rock dam revetment is subjected to the erosion and seepage of the high-speed water flow overtopping, the revetment and the bottom material of the dam slope below the revetment are often eroded and damaged, thus affecting the overall protection effect. Summary of the Invention

[0003] Purpose of the invention: The first purpose of the invention is to provide a better overtopping protection and drainage structure for medium and low earth-rock dams, which is suitable for medium and low earth-rock dams with a dam height not exceeding 30m; the second purpose of the invention is to provide a design method for the overtopping protection and drainage structure for medium and low earth-rock dams.

[0004] Technical solution: The overtopping protection, diversion and drainage structure for medium and low earth-rock dams described in this invention includes:

[0005] The dam crest drainage structure is used to constrict part of the overflowing water flow.

[0006] The downstream slope diversion and drainage structure is used to receive the overflow water flow converging from the dam crest diversion and drainage structure, and further guide, collect, and dissipate the water flow overflowing onto the downstream slope.

[0007] In addition, a drainage and energy dissipation structure at the dam toe is used to dissipate energy from the incoming flow from the downstream slope drainage structure and discharge it.

[0008] Compared to traditional dam crest protection structures, the dam crest diversion and drainage structure adds a diversion function, enabling the dam crest to provide partial water flow capacity. This allows it to work in conjunction with subsequent drainage structures to form a diversion, drainage, and energy dissipation system. By utilizing the dam crest diversion and drainage structure to appropriately constrict the overtopping flow and direct it to the downstream slope diversion and drainage structure, approximately 40% of the overtopping flow can be reduced from directly scouring the dam crest and slope, thereby preventing or mitigating overtopping scouring damage.

[0009] The downstream slope surface diversion and drainage structure serves as an emergency channel when the dam overflows, collecting and quickly discharging the overflowing water. By guiding the water flow, it enhances the slope's drainage capacity and increases the slope's energy dissipation function, thereby reducing the direct scouring of the dam slope and toe by the overflowing water. It can also serve as a slope drainage system during daily operation.

[0010] Earth-rock dams generally do not have scour prevention measures at the dam toe, but scour prevention measures at the dam toe are a key link in overtopping protection. They can effectively prevent scour damage to the dam toe under high water head and large flow rate, and further prevent the damage from developing into the dam body. Therefore, drainage and energy dissipation structures at the dam toe are necessary for overtopping protection.

[0011] This invention comprehensively considers the centralized guidance, discharge, and energy dissipation of overtopping scour flow. In the event of overtopping caused by above-standard floods or other unforeseen events, it can guide the overtopping flow to automatically and rapidly drain, dissipating energy during the drainage process. This achieves a good overtopping protection effect for earth-rock dams, realizing the goal of "overtopping without collapse" or "overtopping with slow collapse." This overtopping protection and drainage structure can also be used as a conventional drainage structure for dams.

[0012] Furthermore, the dam crest diversion and drainage structure includes a wave wall located on the upstream side of the dam crest, with a fan-shaped symmetrical diversion channel on the top of the wave wall, and a guide wall with a trumpet-shaped inlet in front of the diversion channel; a longitudinal drainage ditch is installed on both the upstream and downstream sides of the dam crest, and a transverse drainage ditch is installed behind the diversion channel and below the dam crest road, with the transverse drainage ditch connected to the two longitudinal drainage ditches on the dam crest.

[0013] Furthermore, the main direction of the diversion channel is directed to the intersection of the central main channel section and the downstream side of the dam crest. The maximum semi-central angle of the main direction of the channel is less than 15°. The channel depth is 0.3~0.5m, the total net width of a single diversion channel is 2.0~4.0m, and the longitudinal spacing between the diversion channels is 10~30m.

[0014] The guide wall is 0.2~0.3m thick, with its top elevation level with the top of the wave wall, its bottom connected to the wave wall base, and its upstream extension extending 1.0~1.2m beyond the wave wall surface.

[0015] Furthermore, the longitudinal drainage ditch on the dam crest adopts a U-shaped or rectangular cross-section, with a width of 0.3~0.5m and a depth the same as the transverse drainage ditch on the dam crest, with the bottom slope converging towards the transverse drainage ditch on the dam crest;

[0016] The transverse drainage ditch on the dam crest corresponds one-to-one with the diversion channel, adopting a double U-shaped or trapezoidal cross section. The total width of the cross section surface is 3.0~4.5m, the slope ratio of the trapezoidal cross section is 1:0.8~1:1.25, the bottom slope is downstream, and the slope is 0.01~0.02.

[0017] Furthermore, the bottom of the transverse drainage ditch on the dam crest is equipped with an energy-dissipating skirt, which is lined with stainless steel and has a surface decorated with plum blossom-shaped umbrella-shaped comb teeth.

[0018] Furthermore, the downstream slope drainage structure includes a downstream slope transverse drainage ditch connected to the transverse drainage ditch on the dam crest. The downstream slope of the dam is provided with a fish-scale-shaped interlocking block revetment that has the functions of diversion and energy dissipation. The fish-scale-shaped interlocking block revetment is constructed by dry-machining fish-scale-shaped interlocking blocks. The fish-scale-shaped interlocking blocks are composed of an I-shaped self-locking base and a guide sill. The guide sill is a round-headed pier type, and the angle between it and the horizontal axis of the plane of the I-shaped self-locking base is 20~30°.

[0019] The dam slope is reinforced with fish-scale interlocking blocks. During low-flow overtopping scour, the block can effectively guide all water flow to the downstream transverse drainage ditch for rapid drainage. During high-flow scour, it can also act as an energy dissipation sill to reduce the scouring effect of overtopping on the dam toe while guiding the water flow. Compared to traditional slope protection structures, fish-scale interlocking blocks offer both flow diversion and energy dissipation capabilities, significantly enhancing slope protection. They also offer advantages such as ease of construction and successful post-disaster repair.

[0020] Furthermore, assuming that the overflow flow passing through the slope guide sill is decomposed into the guiding flow along the guide sill and the overflow flow over the guide sill, and the overflow flow is estimated according to the weir flow formula, by simultaneously solving the continuity equation, energy equation, momentum equation and weir flow formula, the slope flow distribution, conductivity coefficient and energy dissipation coefficient can be approximately obtained:

[0021] (1)

[0022] (2)

[0023] (3)

[0024] In equations (1) to (3), Q is the overflow flow rate; i is the horizontal row number of the fish-scale lock block, counted as n rows; The flow rate of the drainage ditch at the i-th row of lock block slope guide sill; The flow rate is guided by the flow guide. To divert overflow flow; The water depth in front of the diversion sill; This refers to the width of the slope for flow. ρ is the velocity coefficient; g is the acceleration due to gravity; This is the total head difference from the front of the diversion sill to the top of the previous row of diversion sills; The slope angle; The density of water; The overflow velocity vector of the guide sill; The velocity vector of the flow guided by the guide sill; The vector of the reaction force of the entire locking block on the water flow; The height of the guide sill; The slope conductivity coefficient; The slope energy dissipation coefficient; The total head of the slope starting from the dam toe;

[0025] The slope flow distribution is calculated step by step using equation (1), and the slope diversion coefficient and energy dissipation coefficient are calculated using equations (2) and (3), respectively.

[0026] Furthermore, the dam toe drainage and energy dissipation structure includes a riprap anti-scour channel arranged along the entire length of the downstream slope toe of the dam, which also serves as a longitudinal drainage ditch.

[0027] Furthermore, both the top drainage structure and the downstream slope drainage structure are covered with anti-scouring crushed stone cushion layer to prevent the overflow water from seeping down along the interface between the drainage structure and the dam body, thereby reducing the scouring of the foundation dam body below the drainage structure.

[0028] In the above technical solution, the diversion channel on the dam crest is arranged symmetrically in a fan shape. During high-flow overtopping, the diversion channel guides the water flow to the air for energy dissipation through aerial collision. During low-flow overtopping, the energy-dissipating skirts at the bottom of the transverse drainage ditch on the dam crest dissipate the energy of the water flow. The fish-scale-shaped interlocking block slope protection on the dam slope can also serve as a stilling sill, and the riprap anti-scour channel at the dam toe also has an energy dissipation function. Through multiple energy dissipation structures, the scouring and damage caused by the overtopping water flow to the dam crest, slope, and toe can be effectively reduced.

[0029] The design method for the overtopping protection, diversion, and drainage structure of a medium-low earth-rock dam as described in this invention includes:

[0030] (1) Determine the design flood process exceeding the standard;

[0031] (2) Based on the peak flow of the flood exceeding the standard and the length of the dam axis, determine the initial diversion channel depth and the total net width of the single-hole diversion channel, determine the longitudinal spacing of the diversion channels, and calculate the discharge capacity of the single-hole diversion channel;

[0032] (3) Perform reservoir discharge and flood control calculations under conditions of floods exceeding the standard. If the discharge capacity of the diversion channel meets the requirement that the reservoir water level does not exceed the top elevation of the wave wall during the flood discharge process, proceed to the next step; otherwise, return to step (2) to adjust the depth and total net width of the diversion channel, prioritizing the increase of the total net width of the channel.

[0033] (4) Determine the layout of the guide wall and the surface width of the transverse drainage ditch on the dam top based on the width of the single-hole diversion channel. The surface width of the transverse drainage ditch on the dam top shall be ≥ the total width of the single-hole diversion channel.

[0034] (5) Determine the cross-sectional dimensions of the transverse drainage ditch on the dam crest based on the maximum discharge capacity of the diversion channel calculated in the flood control calculation, so as to meet the discharge capacity requirements of the diversion channel;

[0035] (6) Based on the surface width of the transverse drainage ditch on the dam crest, determine the corresponding width of the longitudinal drainage ditch on the dam crest. The depth of the longitudinal drainage ditch on the dam crest is the same as that of the transverse drainage ditch on the dam crest.

[0036] (7) The downstream slope transverse drainage ditch is connected to the dam crest transverse drainage ditch, with conventional layout and the same cross-sectional dimensions as the dam crest transverse drainage ditch;

[0037] (8) Determine the depth of the rockfill anti-scour trench at the dam toe and the particle size of the boulders based on the energy dissipation and anti-scour calculation.

[0038] The principle of this invention is as follows:

[0039] By combining the dam crest drainage structure with the dam slope energy dissipation fish-scale interlocking block revetment, the erosion prevention effect of the concentrated drainage structure and multiple energy dissipation measures reduces the uncertain erosion damage of the overtopping water flow to the dam crest, dam slope, and dam toe, improves the overall reliability of the protective structure, and achieves the goal of enhancing the overtopping erosion protection capacity of the earth-rock dam.

[0040] Compared with conventional earth-rock dam slope protection structures, this invention has the advantages of strong centralized drainage capacity at the top of the slope, less scouring of the slope and dam toe, and good protection effect of the slope structure at the top of the slope. It is applicable to both existing and newly built dams, is easy to construct, and is easy to repair after disasters.

[0041] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention comprehensively considers the centralized guidance, discharge and energy dissipation of the floodwater flow, and has a better flood protection effect. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of a medium-low earth-rock dam overtopping protection diversion and drainage structure provided in an embodiment of this application;

[0043] Figure 2 yes Figure 1 A schematic diagram of the cross-section;

[0044] Figure 3 yes Figure 1 Top view;

[0045] Figure 4 This is a schematic diagram of the dam crest diversion and drainage structure in an embodiment of this application;

[0046] Figure 5 This is a schematic diagram of the fish-scale type locking block slope protection structure in the embodiments of this application. Detailed Implementation

[0047] The invention will now be further described with reference to the accompanying drawings.

[0048] Appendix Figures 1 to 5 The accompanying figure labels are as follows:

[0049] 1. Dam body; 2. Dam crest road; 3. Wave wall; 4. Diversion channel; 5. Guide wall; 6. Longitudinal drainage ditch on dam crest; 7. Transverse drainage ditch on dam crest; 8. Transverse drainage ditch on downstream slope; 9. Fish scale type interlocking block slope protection; 10. Rockfill anti-scour channel; 11. Energy dissipation skirt; 12. Anti-scour crushed stone cushion layer; 13. Steel mesh cover plate.

[0050] like Figures 1 to 3 As shown in the figure, a medium-low earth-rock dam overtopping protection diversion and drainage structure is provided in an embodiment of this application. The medium-low earth-rock dam body 1 has a dam slope and a dam crest, wherein a dam crest road 2 is provided on the dam crest, and the dam crest road 2 adopts an asphalt concrete pavement or a reinforced concrete slab pavement.

[0051] The overtopping protection and drainage structure of the medium-low earth-rock dam includes a dam crest drainage structure, a downstream slope drainage structure, and a dam toe drainage and energy dissipation structure arranged sequentially from top to bottom along the dam cross section. The dam crest drainage structure is used to constrict part of the overtopping flow; the downstream slope drainage structure is used to receive the overtopping flow constricted by the dam crest drainage structure and further guide, collect, and dissipate the flow that overflows onto the downstream slope; the dam toe drainage and energy dissipation structure is used to dissipate the energy of the flow coming from the downstream slope drainage structure and discharge it.

[0052] The following sections will provide a detailed introduction to the dam crest diversion and drainage structure, the downstream slope diversion and drainage structure, and the dam toe drainage and energy dissipation structure.

[0053] Combination Figure 4 The dam crest drainage structure includes a reinforced concrete wave wall 3 located on the upstream side of the dam crest. A fan-shaped, symmetrically arranged diversion channel 4 is formed at the top of the wave wall 3, and a guide wall 5 with a funnel-shaped inlet is installed in front of the diversion channel 4. A longitudinal drainage ditch 6 is installed along the entire length of the dam crest on both the upstream and downstream sides. A transverse drainage ditch 7 is installed behind the diversion channel 4 and below the dam crest road 2. The transverse drainage ditch 7 is connected to the two longitudinal drainage ditches 6, allowing water flow from the longitudinal drainage ditches 6 to converge into the transverse drainage ditch 7. The transverse drainage ditch 7 corresponds one-to-one with the diversion channel 4, with its bottom slope facing downstream. An energy-dissipating skirt 11 is installed at the bottom of the transverse drainage ditch 7. The energy-dissipating skirt 11 is lined with stainless steel and has a surface with round nail-like teeth arranged in a staggered pattern with a spacing of 0.1m. The longitudinal drainage ditch 6 and the transverse drainage ditch 7 are covered with a steel mesh cover plate 13.

[0054] In this embodiment, the main direction of the diversion channel 4 is directed to the intersection of the middle main channel section and the downstream side of the dam crest. The maximum half-center angle of the main direction of the channel is less than 15°. The bottom elevation of the channel should meet the design requirements of the flood control superelevation of the dam crest. The channel depth is 0.3~0.5m. The total net width of a single diversion channel 4 is 2.0~4.0m. The longitudinal spacing of the diversion channels 4 is 10~30m, which is determined according to the drainage requirements.

[0055] The guide wall 5 is located upstream of the wave wall 3 and smoothly connects to the outer edge of the diversion channel 4. The wall thickness is 0.2~0.3m, the top elevation is level with the top of the wave wall 3, the bottom of the wall connects to the base of the wave wall 3, and the upstream extends 1.0~1.2m beyond the surface of the wave wall 3.

[0056] The longitudinal drainage ditch 6 on the dam crest is a concrete structure with a U-shaped or rectangular cross-section, a width of 0.3~0.5m, a depth the same as the transverse drainage ditch 7 on the dam crest, a bottom slope of 0.001, and converges towards the transverse drainage ditch 7 on the dam crest.

[0057] The transverse drainage ditch 7 on the dam crest is a concrete structure with a double U-shaped or trapezoidal cross section. The total width of the cross section is 3.0~4.5m, the slope ratio of the trapezoidal cross section is 1:0.8~1:1.25, and the depth is determined according to the drainage requirements. The bottom slope is downstream with a slope of 0.01~0.02.

[0058] The downstream slope drainage structure includes a downstream slope transverse drainage ditch 8 connected to the transverse drainage ditch 7 at the dam crest, and a fish-scale-shaped interlocking block revetment 9 with diversion and energy dissipation functions on the downstream slope of the dam, combined with... Figure 5 The fish-scale lock block slope protection 9 is constructed by dry-machining fish-scale lock blocks. The fish-scale lock blocks consist of an I-shaped self-locking base and a flow guide sill, which is a round-headed pier type.

[0059] Assuming that the overflow flow passes through the slope guide sill, it is decomposed into the guide flow along the guide sill and the overflow flow over the guide sill. The overflow flow rate is estimated according to the weir flow formula. By solving the continuity equation, energy equation, momentum equation and weir flow formula simultaneously, the slope flow distribution, conductivity coefficient and energy dissipation coefficient can be approximately obtained.

[0060] (1)

[0061] (2)

[0062] (3)

[0063] In equations (1) to (3), Q is the overflow flow rate; i is the horizontal row number of the fish-scale lock block, counted as n rows; The flow rate of the drainage ditch at the i-th row of lock block slope guide sill; The flow rate is guided by the flow guide. To divert overflow flow; The water depth in front of the diversion sill; This refers to the width of the slope for flow. ρ is the velocity coefficient; g is the acceleration due to gravity; This is the total head difference from the front of the diversion sill to the top of the previous row of diversion sills; The slope angle; The density of water; The overflow velocity vector of the guide sill; The velocity vector of the flow guided by the guide sill; The vector of the reaction force of the entire locking block on the water flow; The height of the guide sill; The slope conductivity coefficient; The slope energy dissipation coefficient; The total head of the slope starting from the dam toe;

[0064] The slope flow distribution is calculated step by step using equation (1), and the slope diversion coefficient and energy dissipation coefficient are calculated using equations (2) and (3), respectively.

[0065] In this embodiment, the downstream slope transverse drainage ditch 8 is a concrete structure with a conventional layout and a U-shaped or trapezoidal cross section. The outer contour dimensions of the cross section are the same as those of the transverse drainage ditch 7 on the dam crest.

[0066] The fish-scale locking block is a concrete structure. The dimensions of the I-shaped self-locking base are 80cm×80cm×15cm (length×width×thickness), and the dimensions of the guide sill are 80cm×16cm×15cm (length×width×thickness). The angle between the guide sill and the horizontal axis of the I-shaped self-locking base is 20~30°.

[0067] In addition, a layer of anti-scouring crushed stone cushion 12 composed of coarse gravel aggregate is laid at the bottom of both the dam crest diversion and drainage structure and the downstream slope diversion and drainage structure.

[0068] The dam toe drainage and energy dissipation structure includes a riprap scour channel 10 arranged along the entire length of the downstream slope toe of the dam. The riprap scour channel 10 also serves as a longitudinal drainage ditch. In this embodiment, the riprap scour channel 10 has a trapezoidal cross-section, with a slope adapted to the dam slope, a depth of 1.0~2.0m, and is filled with riprap.

[0069] When a medium-low earth-rock dam encounters a sudden event such as a flood exceeding the standard level, if the reservoir water level does not exceed the top of the wave wall 3, the reservoir water exceeding the bottom elevation of the diversion channel 4 will be all collected and guided through the diversion channel 4 by the guide wall 5. If the reservoir water level further exceeds the top of the wave wall 3 and overtopping occurs, the guide wall 5 will directly guide 30% to 40% of the overtopping water flow through the diversion channel 4. At low flow rates, the water flows along the wave wall 3 into the longitudinal drainage ditch 6 on the upstream side of the dam crest and then into the transverse drainage ditch 7 on the dam crest. At high flow rates, the water flows outward, collide and dissipate energy in the air, and then directly into the transverse drainage ditch 7 on the dam crest. The remaining overtopping water flowing down the dam slope is guided by the fish-scale-shaped interlocking block slope protection 9, dissipates energy, and then converges into the transverse drainage ditch 8 on the downstream slope. Finally, it is discharged downstream after dissipating energy through the riprap anti-scour channel 10 at the dam toe. The overflowing water is quickly discharged after being constricted, and will not completely scour the dam crest and slope. The overflowing water dissipates energy at the dam crest, slope and toe, thus comprehensively enhancing the dam's overtopping drainage and protection capabilities.

[0070] A comparative test was conducted between the overtopping protection diversion and drainage structure of the earth-rock dam provided in the embodiments of this application and an overtopping protection structure without diversion. The test results show that the present invention enables the main water flow of the overtopping to be discharged through the diversion and drainage structure and dissipates energy through the dam top, dam slope and dam toe, which greatly reduces the scouring of the downstream slope and dam toe of the earth-rock dam during overtopping and significantly improves the overtopping protection capacity of the earth-rock dam.

[0071] This application also provides a design method for a flood control and drainage structure for a medium-low earth-rock dam, which specifically includes the following steps:

[0072] (1) Determine the design flood process exceeding the standard;

[0073] (2) Based on the peak flow of the super-standard flood and the length of the dam axis, the initial diversion channel 4 is proposed to have a groove depth and a total net width of the single-hole diversion channel 4. The longitudinal spacing of the diversion channels 4 is determined, with a groove depth of 0.3~0.5m, a total net width of 2.0~4.0m for a single diversion channel, and a longitudinal spacing of 10~30m for the diversion channels. The discharge capacity of the single-hole diversion channel 4 is calculated. The bottom elevation of the diversion channel 4 should meet the design requirements for the superelevation of the dam crest for flood control.

[0074] (3) Perform reservoir discharge and flood control calculations under conditions of floods exceeding the standard. If the discharge capacity of the diversion channel 4 meets the requirement that the reservoir water level does not exceed the top elevation of the wave wall 3 during the flood discharge process, proceed to the next step. If it does not meet the requirement, return to step (2) and adjust the depth and total net width of the diversion channel 4, prioritizing the increase of the total net width of the channel.

[0075] (4) Based on the slot width of the single-hole diversion channel 4, determine the layout of the guide wall 5, the surface width of the transverse drainage ditch 7 on the top of the dam, the thickness of the guide wall 5 is 0.2~0.3m, the upstream extension of the wave wall 3 is 1.0~1.2m, and the surface width of the transverse drainage ditch 7 on the top of the dam is ≥ the total width of the single-hole diversion channel 4;

[0076] (5) Based on the maximum discharge flow of the diversion channel 4 calculated by flood control, determine the cross-sectional dimensions of the transverse drainage ditch 7 on the top of the dam to meet the discharge requirements of the diversion channel 4. The total width of the cross-section is 3.0~4.5m, the slope ratio of the trapezoidal cross-section is 1:0.8~1:1.25, the depth is determined according to the drainage requirements, the bottom slope is downstream, and the slope is 0.01~0.02.

[0077] (6) Based on the surface width of the transverse drainage ditch 7 on the dam crest, determine the width of the longitudinal drainage ditch 6 on the dam crest, which is 0.3~0.5m wide and has the same depth as the transverse drainage ditch 7 on the dam crest, with a bottom slope of 0.001 and concentrating towards the transverse drainage ditch 7 on the dam crest;

[0078] (7) The downstream slope transverse drainage ditch 8 is connected to the dam crest transverse drainage ditch 7. It is conventionally arranged and its cross-sectional dimensions are the same as those of the dam crest transverse drainage ditch 7.

[0079] (8) Determine the depth of the rockfill anti-scour trench at the dam toe based on the energy dissipation and anti-scour calculation. The depth is 1.0~2.0m, and the particle size of the boulders is determined to be 10~30cm.

Claims

1. A flood control and drainage structure for overtopping protection of medium-low earth-rock dams, characterized in that, include: The dam crest drainage structure is used to constrict part of the overflowing water flow. The downstream slope diversion and drainage structure is used to receive the overflow water flow confined by the dam crest diversion and drainage structure, and further guide, collect and dissipate the water flow that overflows onto the downstream slope. In addition, a drainage and energy dissipation structure at the dam toe is used to dissipate energy from the flow coming from the downstream slope drainage structure and discharge it. The dam crest drainage structure includes a wave wall (3) located on the upstream side of the dam crest, a fan-shaped symmetrical diversion channel (4) on the top of the wave wall (3), and a guide wall (5) with a trumpet-shaped inlet in front of the diversion channel (4); a longitudinal drainage ditch (6) is laid along the upstream and downstream sides of the dam crest, and a transverse drainage ditch (7) is laid behind the diversion channel (4) and below the dam crest road (2), and the transverse drainage ditch (7) is connected to the two longitudinal drainage ditches (6); an energy dissipation skirt (11) is provided at the bottom of the transverse drainage ditch (7), the energy dissipation skirt (11) is lined with stainless steel, and the surface is arranged with plum blossom-shaped umbrella-shaped comb teeth; The downstream slope drainage structure includes a downstream slope transverse drainage ditch (8) connected to the transverse drainage ditch (7) at the top of the dam. The downstream slope of the dam is equipped with a fish-scale-shaped interlocking block slope protection (9) with the functions of diversion and energy dissipation. The fish-scale-shaped interlocking block slope protection (9) is constructed by dry-machining fish-scale-shaped interlocking blocks. The fish-scale-shaped interlocking blocks are composed of an I-shaped self-locking base and a guide sill. The guide sill is a round-headed pier type, and the angle between the guide sill and the horizontal axis of the I-shaped self-locking base is 20~30°. When the slope is scourged by a small flow, the fish-scale-shaped interlocking block slope protection (9) can guide all the water flow on the slope to the downstream slope transverse drainage ditch for rapid drainage. When the slope is scourged by a large flow, the fish-scale-shaped interlocking block slope protection (9) can guide the water flow while also serving as an energy dissipation sill for bottom flow energy dissipation, reducing the scouring of the dam toe by the overtopping water flow. The drainage and energy dissipation structure at the dam toe includes a riprap anti-scour channel (10) arranged along the entire length of the downstream slope toe of the dam. The riprap anti-scour channel (10) also serves as a longitudinal drainage ditch.

2. The overtopping protection, diversion, and drainage structure for medium-low earth-rock dams according to claim 1, characterized in that, The main direction of the diversion channel (4) is to the intersection of the middle main channel section and the downstream side of the dam crest. The maximum half-center angle of the main direction of the channel is less than 15°. The channel depth is 0.3~0.5m. The total net width of a single diversion channel (4) is 2.0~4.0m. The longitudinal spacing of the diversion channels (4) is 10~30m. The guide wall (5) has a wall thickness of 0.2~0.3m, its top elevation is level with the top of the wave wall (3), its bottom is connected to the base of the wave wall (3), and its upstream extends 1.0~1.2m beyond the surface of the wave wall (3).

3. The overtopping protection, diversion, and drainage structure for medium-low earth-rock dams according to claim 1, characterized in that, The longitudinal drainage ditch (6) on the top of the dam adopts a U-shaped or rectangular cross section with a width of 0.3~0.5m and a depth the same as the transverse drainage ditch (7) on the top of the dam. The bottom slope is concentrated towards the transverse drainage ditch (7) on the top of the dam. The transverse drainage ditch (7) on the top of the dam corresponds one-to-one with the diversion channel (4), adopting a double U-shaped or trapezoidal cross section. The total width of the cross section surface is 3.0~4.5m, the slope ratio of the trapezoidal cross section is 1:0.8~1:1.25, the bottom slope is downstream, and the slope is 0.01~0.

02.

4. The overtopping protection, diversion, and drainage structure for medium-low earth-rock dams according to claim 1, characterized in that, Assuming that the overflow flow passes through the slope guide sill, it is decomposed into the guide flow along the guide sill and the overflow flow over the guide sill. The overflow flow rate is estimated according to the weir flow formula. By solving the continuity equation, energy equation, momentum equation and weir flow formula simultaneously, the slope flow distribution, conductivity coefficient and energy dissipation coefficient can be approximately obtained. ； ； ； Mode to middle, Top traffic; The fish-scale shaped lock blocks are numbered horizontally, counting... Row; For the first Flow rate of drainage ditch at the slope guide sill of the lock block revetment; The flow rate is directed to the flow guide. To divert overflow flow; The water depth in front of the diversion sill; This refers to the width of the slope for flow. The velocity coefficient; It is the acceleration due to gravity; This is the total head difference from the front of the diversion sill to the top of the previous row of diversion sills; The slope angle; The density of water; The overflow velocity vector of the guide sill; The velocity vector of the flow guided by the guide sill; The vector of the overall reaction force of the locking block on the water flow; The height of the guide sill; The slope conductivity coefficient; The slope energy dissipation coefficient; The total head of the slope starting from the dam toe; Slope water flow distribution is given by formula The slope diversion coefficient and energy dissipation coefficient are calculated step by step from the formulas. and calculate.

5. The overtopping protection and drainage structure for medium-low earth-rock dams according to claim 1, characterized in that, Both the top diversion and drainage structure and the downstream slope diversion and drainage structure are covered with anti-scouring crushed stone cushion layer (12).

6. A design method for a flood control and drainage structure for a medium-low earth-rock dam as described in claim 1, characterized in that, include: S1: Determine the design flood process exceeding the standard; S2: Based on the peak flow of the super-standard flood and the length of the dam axis, the initial diversion channel (4) opening depth and the total net width of the single-hole diversion channel (4) are determined, the longitudinal spacing of the diversion channel (4) is determined, and the discharge capacity of the single-hole diversion channel (4) is calculated. S3: Under the condition of flood exceeding the standard, the reservoir discharge and flood regulation calculation is carried out. If the discharge capacity of the diversion channel (4) meets the requirement that the reservoir water level does not exceed the top elevation of the wave wall (3) during the flood discharge process, proceed to the next step; otherwise, return to step S2 to adjust the trench depth and total net width of the diversion channel (4), and give priority to increasing the total net width of the trench. S4: Based on the slot width of the single-hole diversion channel (4), determine the layout of the guide wall (5) and the surface width of the transverse drainage ditch (7) on the top of the dam. The surface width of the transverse drainage ditch (7) on the top of the dam is greater than or equal to the total width of the single-hole diversion channel (4). S5: Based on the flood control calculation of the maximum discharge flow of the diversion channel (4), determine the cross-sectional dimensions of the transverse drainage ditch (7) on the top of the dam to meet the discharge requirements of the diversion channel (4); S6: Based on the surface width of the transverse drainage ditch (7) on the dam crest, determine the width of the longitudinal drainage ditch (6) on the dam crest accordingly. The depth of the longitudinal drainage ditch (6) on the dam crest is the same as that of the transverse drainage ditch (7) on the dam crest. S7: The downstream slope transverse drainage ditch (8) is connected to the dam crest transverse drainage ditch (7), with a conventional layout and the same cross-sectional dimensions as the dam crest transverse drainage ditch (7); S8: Determine the depth of the rockfill anti-scour trench (10) at the dam toe based on the energy dissipation and anti-scour calculation, and determine the particle size of the boulders.

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