A composite drainage and seepage system and method for use in power plant valley ash disposal sites

Abstract

This invention belongs to the field of flood drainage and seepage technology for valley ash dumps. It proposes a composite flood drainage and seepage system and method for use in power plant valley ash dumps. The invention includes a drainage ditch set along the direction from the flood control dam towards the initial dam of the ash dump. The drainage ditch includes a flood drainage culvert at the bottom of the ash dump, a seepage ditch and a flood drainage ditch located above the flood drainage culvert. The bottoms of the seepage ditch and the flood drainage ditch share a common pool wall with the upper part of the flood drainage culvert. The adjacent side walls of the seepage ditch and the flood drainage ditch also share a common pool wall. This effectively reduces the foundation treatment area and land occupation, as well as the amount of steel reinforcement and concrete used, thus lowering the project cost. Simultaneously, the flood drainage ditch has an opening at its upper part and a cover plate placement groove. A seepage pipe is installed at the end of the drainage ditch away from the flood control dam. This system is suitable not only for flood drainage and seepage when upstream floodwaters flow into the ash dump along the slopes of both banks, but also for flood drainage and seepage under conditions of high rainfall.

Description

Technical Field

[0001] This invention belongs to the field of flood drainage and seepage technology in valley ash fields, and particularly relates to a composite flood drainage and seepage system and method applied to valley ash fields of power plants. Background Technology

[0002] For dry ash disposal sites in valleys of power plants, flood control dams are often built at the top of the ash disposal site to prevent upstream floodwaters from entering. For floodwaters that the dams cannot contain, some of the floodwaters will flow along the slopes on both sides of the valley into the ash disposal site. In this case, a drainage system is needed to discharge the floodwaters downstream. The design of drainage culverts within the ash disposal site is quite complex, requiring consideration of various operating conditions, such as the dam being built but not yet storing ash, the dam being built and storing ash, and the ash disposal site being closed after storage.

[0003] The inventors discovered that the current flood drainage and seepage system for dry ash dumps in power plant valleys involves the independent installation of flood drainage culverts, drainage shafts, and seepage systems at different locations for different operating conditions. Correspondingly, the flood control dam drainage system, the ash dump internal drainage system, and the ash dump internal seepage system are all independently set up and constructed separately. The entire construction process for the ash dump flood drainage and seepage system is labor-intensive, occupies a large area, and requires a high amount of steel and concrete, resulting in high costs. Furthermore, the current ash dump flood drainage and seepage system only considers the water flow from upstream floodwaters along the slopes of both banks into the ash dump, neglecting the drainage and seepage issues during rainfall. Especially under conditions of heavy rainfall, the current flood drainage and seepage system is ineffective. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a composite drainage and seepage system and method for use in power plant valley ash disposal sites. The bottom of the seepage ditch and the bottom of the flood drainage ditch share a common pool wall with the upper part of the flood drainage culvert. Adjacent side walls of the seepage ditch and the flood drainage ditch also share a common pool wall. This effectively reduces the scope of foundation treatment and land occupation, as well as the amount of steel reinforcement and concrete used, thereby lowering project costs and improving construction efficiency. The flood drainage ditch has an opening at the top and is equipped with a cover plate placement groove. A seepage pipe is located at the end of the drainage ditch furthest from the flood control dam. The open drainage ditch meets the requirements for timely flood discharge during rainfall and allows for seepage through the seepage pipe after the drainage ditch is covered. This system is suitable not only for flood drainage when upstream floodwaters flow into the ash disposal site along the slopes on both banks, but also for flood drainage needs under conditions of heavy rainfall.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a composite flood drainage and infiltration system for use in ash disposal sites in power plant valleys, employing the following technical solution:

[0006] A composite flood discharge and seepage system for use in a power plant valley ash field includes a drainage ditch set along the direction of the flood control dam toward the initial dam of the ash field, a flood discharge shaft set at the end of the drainage ditch near the flood control dam, and a seepage pipe set at the end of the drainage ditch away from the flood control dam.

[0007] The drainage ditch includes a flood discharge culvert located at the bottom of the ash field, a seepage ditch and a flood discharge ditch located above the flood discharge culvert; the flood discharge ditch has an opening at the top and is provided with a cover plate placement groove; the flood discharge shaft is connected to the flood discharge ditch, and the seepage pipe is connected to the seepage ditch; the bottom of the seepage ditch and the bottom of the flood discharge ditch share a pool wall with the upper part of the flood discharge culvert, and the adjacent side walls of the seepage ditch and the flood discharge ditch share a pool wall.

[0008] Furthermore, the cross-section of the drainage ditch along its vertical length is rectangular, and the lower end of the drainage ditch is provided with the flood discharge culvert, while the upper end is provided with the seepage drainage ditch and the flood discharge ditch.

[0009] Furthermore, one end of the flood discharge culvert is located upstream of the flood control dam, and the other end is located downstream of the initial dam of the ash field.

[0010] Furthermore, one end of the drainage ditch is located downstream of the flood control dam, and the other end opens downstream of the initial dam of the ash field.

[0011] Furthermore, one end of the drainage ditch is located within the ash field, and the other end opens downstream of the initial dam of the ash field.

[0012] Furthermore, the drainage ditch is equipped with multiple flood discharge shafts at one end near the flood control dam, and multiple seepage pipes are installed at the other end near the initial dam of the ash field.

[0013] Furthermore, a cover plate is installed in the cover plate placement groove, and cement mortar is applied to the cover plate.

[0014] Furthermore, the drainage shaft includes multiple shaft units, which are connected by connecting clips.

[0015] Furthermore, the drainage pipe has multiple drainage holes, and the outer wall of the drainage holes is wrapped with geotextile; the upper part of the drainage ditch has multiple drainage holes, and the drainage ditch is also covered with geotextile.

[0016] To achieve the above objectives, in a second aspect, the present invention also provides a composite flood discharge and seepage drainage method applied to ash disposal sites in power plant valleys, employing the following technical solution:

[0017] A composite flood discharge and seepage method for power plant valley ash disposal sites employs the composite flood discharge and seepage system for power plant valley ash disposal sites as described in the first aspect, comprising: floodwater upstream of the flood control dam is discharged to the downstream of the initial dam of the ash disposal site through the flood discharge box culvert; when floodwater upstream of the flood control dam flows into the ash disposal site along the slopes on both sides, or when rainfall occurs in the ash disposal site, floodwater is discharged through the opening at the top of the flood discharge ditch; after ash begins to accumulate in the ash disposal site, the opening of the flood discharge ditch is covered with a cover plate, and floodwater enters the flood discharge ditch through the flood discharge shaft for flood discharge, and seepage is carried out through the seepage pipe and the seepage ditch.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The present invention discloses a drainage ditch installed along the direction from the flood control dam towards the initial dam of the ash field. The drainage ditch includes a flood discharge culvert at the bottom of the ash field, a seepage ditch and a flood discharge ditch located above the flood discharge culvert. The bottom of the seepage ditch and the bottom of the flood discharge ditch share a pool wall with the upper part of the flood discharge culvert. The adjacent side walls of the seepage ditch and the flood discharge ditch also share a pool wall. This effectively reduces the foundation treatment area and land occupation, as well as the amount of steel reinforcement and concrete used, thereby reducing the project cost. It meets the requirement of simultaneous construction of the flood control dam flood discharge system, the ash field flood discharge system, and the ash field seepage system, simplifies the formwork system, and improves construction efficiency. At the same time, the flood discharge ditch has an opening at the top and is equipped with a cover plate placement groove. A seepage pipe is installed at the end of the drainage ditch away from the flood control dam. The open flood discharge ditch meets the requirements of timely flood discharge during rainfall and allows for seepage through the seepage pipe after the flood discharge ditch is covered. It is not only suitable for flood discharge and seepage when upstream floods flow into the ash field along the slopes on both sides, but also meets the flood discharge and seepage requirements under conditions of large rainfall.

[0020] The flood drainage shaft in this invention adopts a modular snap-fit ​​connection structure, which facilitates modular installation on site and makes on-site construction and operation very convenient, avoiding the waste of manpower and material resources caused by multiple on-site pouring.

[0021] This invention features a composite drainage structure in the ash field, consisting of horizontally arranged drainage ditches and vertically arranged drainage pipes wrapped with geotextile. The horizontal sections are constructed of reinforced concrete, while the vertical sections utilize perforated pipes with drainage holes. This design avoids the use of traditional single steel pipes and PVC plastic pipes, ensuring both the drainage of ash water and effective connection between the vertical perforated pipes and the concrete. It also enables modular installation and avoids the risk of leakage through dams, as is common in traditional structures. Attached Figure Description

[0022] The accompanying drawings, which form part of this embodiment, are used to provide a further understanding of this embodiment. The illustrative embodiments and their descriptions are used to explain this embodiment and do not constitute an improper limitation of this embodiment.

[0023] Figure 1This is a gray field plan view of Embodiment 1 of the present invention;

[0024] Figure 2 This is a cross-sectional view of the gray field in Embodiment 1 of the present invention;

[0025] Figure 3 This is the case of no ash in Embodiment 1 of the present invention. Figure 2 Cross-sectional view at point AA;

[0026] Figure 4 In the case of ash storage as described in Embodiment 1 of the present invention Figure 2 Cross-sectional view at point AA;

[0027] Figure 5 In the case of ash storage as described in Embodiment 1 of the present invention Figure 2 Cross-sectional view at point BB;

[0028] Figure 6 As in Embodiment 1 of the present invention Figure 2 Cross-sectional view at point C;

[0029] Figure 7 This is a schematic diagram of the flood discharge shaft structure in Embodiment 1 of the present invention;

[0030] Among them, 1. Drainage ditch; 101. Flood discharge box culvert; 102. Flood discharge ditch; 103. Drainage ditch; 104. Cover plate placement groove; 2. Flood discharge shaft; 201. Shaft unit; 202. Connecting buckle; 3. Drainage pipe; 301. Drainage hole; 302. Geotextile; 4. Flood control dam; 5. Initial dam of ash field; 6. Cover plate. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0033] Example 1:

[0034] For dry ash disposal sites in valleys of power plants, if the upstream drainage area is large and the flood volume is significant, a flood control dam needs to be constructed upstream of the ash disposal site to intercept and store floodwaters, preventing floods from entering the site. Floodwaters intercepted by the dam can be diverted downstream to the downstream ash disposal site via circular drainage culverts, or discharged through spillways or spillways. For floodwaters that the dam cannot intercept, some will flow along the slopes on both sides into the ash disposal site. This portion of the floodwater also requires a drainage system to discharge it downstream. The design of drainage culverts within the ash disposal site is complex, requiring consideration of various operating conditions, such as the dam being built but not yet storing ash, the dam being built and storing ash, and the ash disposal site being closed after storage.

[0035] Before ash storage, a flood discharge culvert is installed at the lowest point inside the ash storage area. This culvert is an open concrete structure, allowing floodwaters from both banks to flow into the ditch and drain downstream. During ash storage, as ash accumulates and occupies the internal space, the flood discharge culvert needs to be covered and sealed with precast slabs to prevent ash from entering. At this point, a perforated flood discharge shaft is required to guide floodwaters flowing into the ash storage area into the drainage culvert. After ash storage is completed and the ash storage area is closed, the ash storage area needs to be sealed when it reaches the design elevation. The perforated opening of the flood discharge shaft is then closed. Floodwaters flowing into the ash storage area then drain through the top of the shaft into the flood discharge culvert and drain downstream.

[0036] As described in the background section, current power plant valley dry ash disposal site flood drainage and seepage systems employ separate flood drainage culverts, drainage shafts, and seepage systems at different locations for different operating conditions. Correspondingly, the flood control dam drainage system, the ash disposal site flood drainage system, and the ash disposal site seepage system are also independently designed and constructed. The entire construction process of the ash disposal site flood drainage and seepage system involves a large workload, occupies a large area, and requires high quantities of steel reinforcement and concrete, resulting in high costs. The entire ash disposal site flood drainage and seepage system is complex, requiring consideration of various structural types, leading to significant engineering work and foundation treatment costs. Furthermore, previous ash disposal site designs did not consider seepage prevention measures for rainwater infiltration into the ash disposal site. However, in areas with high rainfall, frequent rainfall can lead to saturation of the ash within the ash disposal site, reducing the shear strength and internal friction angle of the ash, which is highly detrimental to the slope stability of the dam. Additionally, if floodwater is not drained promptly during heavy rains, the water level within the ash disposal site can rise significantly. Therefore, effective flood drainage and seepage prevention measures are necessary during rainfall.

[0037] Regarding at least one of the above problems, such as Figure 1 As shown, this embodiment provides a composite flood discharge and seepage system for a power plant valley ash field, including a drainage ditch 1, a flood discharge shaft 2, a seepage pipe 3, and a cover plate 6; it is assumed that there is a flood control dam 4 upstream of the ash field and an initial dam 5 for the ash field is constructed downstream.

[0038] Optional, such as Figure 1and Figure 2 As shown, the drainage ditch 1 is set along the direction of the flood control dam 4 toward the initial dam 5 of the ash field. The flood discharge shaft 2 is set at the end of the drainage ditch 1 near the flood control dam 4, and the seepage pipe 3 is set at the end of the drainage ditch 1 away from the flood control dam 4. It can be understood that the flood discharge shaft 2 is set upstream of the ash field, and the seepage pipe 3 is set downstream of the ash field.

[0039] like Figure 3 As shown, the drainage ditch 1 includes a flood discharge box culvert 101 located at the bottom of the ash field, a seepage ditch 103 and a flood discharge ditch 102 located above the flood discharge box culvert 101; the flood discharge ditch 102 has an opening at the top and is provided with a cover plate placement groove 104; the flood discharge shaft 2 is connected to the flood discharge ditch 102, and the seepage pipe 3 is connected to the seepage ditch 103; the bottom of the seepage ditch 103 and the bottom of the flood discharge ditch 102 share a pool wall with the upper part of the flood discharge box culvert 101, and the adjacent side walls of the seepage ditch 103 and the flood discharge ditch 102 share a pool wall.

[0040] Specifically, the bottom of the drainage ditch 103 and the bottom of the flood drainage ditch 102 share a pool wall with the upper part of the flood drainage culvert 101. The adjacent side walls of the drainage ditch 103 and the flood drainage ditch 102 share a pool wall, which effectively reduces the foundation treatment area and land occupation, as well as the amount of steel bars and concrete used, thus reducing the project cost. It meets the requirements for simultaneous construction of the flood control dam drainage system, the ash field flood drainage system, and the ash field seepage system, simplifies the formwork system, and improves construction efficiency. At the same time, the flood drainage ditch 102 has an opening at the top and is equipped with a cover plate placement groove 104. The seepage pipe 3 is installed at the end of the drainage ditch 1 away from the flood control dam 4. The open flood drainage ditch 102 meets the requirements for timely flood discharge during rainfall and can achieve the purpose of seepage through the seepage pipe 3 after the flood drainage ditch 102 is covered. It is not only suitable for flood discharge and seepage when upstream floods flow into the ash field along the slopes on both sides, but also meets the flood discharge and seepage requirements under conditions of large rainfall.

[0041] In some embodiments, such as Figure 3 , Figure 5 and Figure 6 As shown, the cross-section of the drainage ditch 1 along its vertical length is rectangular, for example, in... Figure 2At sections AA, BB, and CC, the lower end of the drainage ditch 1 is provided with the flood discharge box culvert 101, and the upper end is provided with the seepage drainage ditch 103 and the flood discharge ditch 102. Optionally, the drainage ditch 1 adopts a concrete rectangular structure, and the flood discharge box culvert 101, the seepage drainage ditch 103, and the flood discharge ditch 102 are set as an integrated structure, which reduces the amount of excavation work in the ash field, reduces the space occupation, and reduces the amount of construction materials such as concrete used, thereby reducing costs.

[0042] In some embodiments, such as Figure 2 As shown, one end of the flood discharge culvert 101 is located upstream of the flood control dam 4, and the other end is located downstream of the initial dam 5 of the ash field, used to discharge floodwater upstream of the flood control dam 4 to the downstream of the initial dam 5 of the ash field. One end of the flood discharge ditch 102 is located downstream of the flood control dam 4, and the other end is located downstream of the initial dam 5 of the ash field, used to discharge floodwater in the ash field to the downstream of the initial dam 5 of the ash field; a cover plate 6 is installed in the cover plate placement groove 104, and cement mortar is applied to the cover plate 6. One end of the seepage drainage ditch 103 is located in the ash field, and the other end is located downstream of the initial dam 5 of the ash field, used for seepage drainage from the ash field.

[0043] In some embodiments, the drainage ditch 1 is provided with a plurality of flood discharge shafts 2 at one end near the flood control dam 4, and a plurality of seepage pipes 3 are provided at one end near the initial dam 5 of the ash field; the provision of a plurality of flood discharge shafts 2 and a plurality of seepage pipes 3 can adapt to flood discharge and seepage at different water levels and rainfall, thereby improving flexibility and stability.

[0044] In some embodiments, such as Figure 7 As shown, the drainage shaft 2 includes multiple shaft units 201, which are connected by connecting clips 202. Optionally, the shaft unit 201 can be multiple prefabricated concrete pipes, and the connecting clips 202 can be implemented in a sleeved form, for example, by setting an annular stepped insertion hole on the lower concrete pipe and a protruding insertion part on the upper concrete pipe.

[0045] In some embodiments, such as Figure 5As shown, the drainage pipe 3 has multiple drainage holes 301, and the outer wall of the drainage holes 301 is wrapped with geotextile 302; the upper part of the drainage ditch 103 is provided with multiple drainage holes, and the drainage ditch 103 is also covered with geotextile. The horizontally arranged drainage ditch 103 and the vertically arranged drainage pipe 3 in the ash field are wrapped with geotextile to form a composite drainage structure of the ash field. The horizontal section adopts a reinforced concrete structure, and the vertical section adopts a perforated pipe structure with drainage holes, avoiding the traditional single steel pipe and PVC plastic pipe. This ensures that the ash water is drained away and that the vertical perforated pipe is effectively connected to the concrete, realizing modular installation and avoiding the risk of water leakage through the dam in the traditional structure.

[0046] For valley ash disposal sites, the flood discharge system is relatively complex, consisting of three parts: a flood control dam discharge system, an internal ash disposal site discharge system, and an internal ash disposal site infiltration system. Based on this, some embodiments provide a composite flood control and infiltration system for valley ash disposal sites, including a flood discharge culvert 101, a flood discharge ditch 102 located within the ash disposal site, a flood discharge shaft 2, an infiltration ditch 103 located within the ash disposal site, and infiltration pipes 3, etc. The flood discharge culvert 101 adopts a concrete rectangular structure, discharging floodwaters from above the flood control dam 4 downstream of the initial dam 5 of the ash disposal site, preventing them from entering the ash disposal site and thus avoiding backflow. The drainage ditch 102 discharges floodwaters flowing into the ash disposal site downstream of the initial dam. The drainage ditch 102 can be constructed with cast-in-place concrete walls and a base. When no ash is stored in the ash disposal site, it has an open structure to drain floodwaters. Once ash begins to accumulate in the site, a concrete cover 6 is placed on top of the drainage ditch 102 and sealed with cement mortar to prevent ash from entering. At this time, floodwaters from the ash disposal site are discharged into the drainage ditch 102 through the drainage shaft 2. When the ash pile surface is higher than the drainage ditch 102, the drainage shaft 2 discharges the floodwaters collected in the ash disposal site into the drainage ditch 102 and then away. The drainage shaft 2 adopts a modular snap-fit ​​connection structure, facilitating on-site modular installation and making on-site construction and operation extremely convenient. The horizontally arranged drainage ditch 103 and the vertically arranged drainage pipe 3 within the ash field are covered with geotextile 302, forming a composite drainage structure for the ash field. This structure removes seepage water from the ash body. The horizontal dam-crossing area utilizes a cast-in-place reinforced concrete structure. Optionally, the drainage pipe 3 can be a PVC perforated pipe structure with drainage holes 301, avoiding the use of traditional single steel pipes and PVC plastic pipes. This ensures both the removal of ash water and effective connection between the vertical perforated pipe and the concrete, enabling modular installation and avoiding the risk of leakage from the cast-in-place concrete structure crossing the dam. The flood discharge culvert 101, the flood discharge ditch 102, and the drainage ditch 103 are connected by sharing a common pool wall or bottom slab, reducing land occupation, the amount of reinforced concrete used, foundation treatment costs, and overall construction costs.

[0047] Example 2:

[0048] This embodiment provides a composite flood discharge and seepage method for a power plant valley ash field, employing the composite flood discharge and seepage system for a power plant valley ash field as described in Embodiment 1. The system includes: floodwater upstream of the flood control dam 4 is discharged through the flood discharge box culvert 101 to the downstream of the initial dam 5 of the ash field; when floodwater upstream of the flood control dam 4 flows into the ash field along the slopes on both sides, or when rainfall occurs in the ash field, floodwater is discharged through the opening at the top of the flood discharge ditch 102; after ash begins to accumulate in the ash field, the opening of the flood discharge ditch 102 is covered with a cover plate, and floodwater enters the flood discharge ditch 102 through the flood discharge shaft 2 for drainage, and seepage occurs through the seepage pipe 3 and the seepage ditch 103.

[0049] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A composite flood drainage and seepage system applied to a power plant valley ash disposal site, characterized in that, It includes a drainage ditch set along the flood control dam towards the initial dam of the ash field, a flood discharge shaft set at the end of the drainage ditch near the flood control dam, and a seepage pipe set at the end of the drainage ditch away from the flood control dam. The drainage ditch includes a flood discharge culvert located at the bottom of the ash field, a seepage ditch and a flood discharge ditch located above the flood discharge culvert; the flood discharge ditch has an opening at the top and is provided with a cover plate placement groove; the flood discharge shaft is connected to the flood discharge ditch, and the seepage pipe is connected to the seepage ditch; the bottom of the seepage ditch and the bottom of the flood discharge ditch share a pool wall with the upper part of the flood discharge culvert, and the adjacent side walls of the seepage ditch and the flood discharge ditch share a pool wall; One end of the flood discharge box culvert is located upstream of the flood control dam, and the other end is located downstream of the initial dam of the ash field. One end of the drainage ditch is located downstream of the flood control dam, and the other end opens downstream of the initial dam of the ash field. One end of the drainage ditch is located within the ash field, and the other end opens downstream of the initial dam of the ash field.

2. The composite flood drainage and seepage system applied to a power plant valley ash disposal site as described in claim 1, characterized in that, The drainage ditch has a rectangular cross-section along its vertical length. The lower end of the drainage ditch is equipped with the flood discharge culvert, and the upper end is equipped with the seepage drainage ditch and the flood discharge ditch.

3. The composite flood drainage and seepage system applied to a power plant valley ash disposal site as described in claim 1, characterized in that, The drainage ditch is equipped with multiple flood discharge shafts at one end near the flood control dam, and multiple seepage pipes are installed at the other end near the initial dam of the ash field.

4. The composite flood drainage and seepage system applied to a power plant valley ash disposal site as described in claim 1, characterized in that, A cover plate is installed in the cover plate placement groove, and cement mortar is applied to the cover plate.

5. A composite flood drainage and seepage system applied to a power plant valley ash disposal site as described in claim 1, characterized in that, The drainage shaft comprises multiple shaft units, which are connected by connecting clips.

6. A composite flood drainage and seepage system applied to a power plant valley ash disposal site as described in claim 1, characterized in that, The drainage pipe has multiple drainage holes, and the outer wall of the drainage holes is wrapped with geotextile; the upper part of the drainage ditch has multiple drainage holes, and the drainage ditch is covered with geotextile.

7. A composite flood drainage and seepage method applied to ash disposal sites in valleys of power plants, characterized in that, The composite flood discharge and seepage system applied to the valley ash field of a power plant as described in any one of claims 1-6 is adopted, comprising: floodwater upstream of the flood control dam is discharged to the downstream of the initial dam of the ash field through the flood discharge box culvert; when floodwater upstream of the flood control dam flows into the interior of the ash field along the slopes on both sides, or when rainfall occurs in the ash field, floodwater is discharged through the opening at the top of the flood discharge ditch; when ash begins to accumulate in the ash field, the opening of the flood discharge ditch is covered with a cover plate, and floodwater enters the flood discharge ditch through the flood discharge shaft for flood discharge, and seepage is carried out through the seepage pipe and the seepage ditch.

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