Ladder type drainage groove arrangement method for accelerating dam-break of dammed lake and improving discharge efficiency

Abstract

The application discloses a kind of stepped drainage groove arrangement methods for accelerating dammed lake breaching and improving discharge efficiency.It includes the following steps,step one: excavate drainage groove in dammed body pass or relatively low concave natural part,with the goal of smaller excavation engineering quantity,as high as possible flow efficiency and combining dammed body material structure composition,confirm the structure form of drainage groove cross section and longitudinal section;Step two: vertically excavate drainage groove at the midpoint of drainage groove downstream side at equal intervals,form vertical ladder with gradually increasing vertical height until connected to dammed body downstream dam slope.The application has the advantages of effectively shortening dammed lake storage time,lowering dammed lake storage capacity,discharging dammed lake storage flood safely and quickly,lowering dammed lake maximum water level and breaching flood peak,thus more greatly reducing reservoir area inundation loss and downstream breaching damage.

Description

Technical Field

[0001] This invention relates to a method for arranging stepped diversion channels to accelerate the breaching of landslide dams and improve discharge efficiency. Background Technology

[0002] Landslide-dammed lakes, a major natural disaster in high mountain and canyon areas, are natural lakes formed by landslides, collapses, or debris flows caused by dynamic geological processes such as heavy rainfall and earthquakes, which block natural river channels. The solid deposits that roll down into the river channel from landslides or collapses become the landslide dam. The landslide dam obstructs the natural river channel, blocking its normal flow and creating an extreme imbalance in discharge between the upstream and downstream sides. This can easily lead to a continuous rise in the water level of the landslide-dammed lake reservoir, or even cause the dam to overflow and breach, resulting in an abnormal outburst flood peak that seriously endangers the lives and property of people along the river.

[0003] For high-risk landslide dammed lakes, the most widely used and effective engineering measure is the diversion channel hazard mitigation technology. This involves longitudinally excavating a trapezoidal cross-section diversion channel at the top of the landslide dam to lower the water level of the dam and reduce the reservoir capacity of the landslide dam. By utilizing the floodwaters overflowing the dam, the dam is gradually eroded and scourded, prompting the landslide dam to release its stored floodwaters gradually. This effectively reduces the inundation losses in the landslide dam reservoir area and the damage caused by downstream breach floods. However, the process of a landslide dam breach is complex: in the early stages of a landslide dam breach, the overflow flow from the diversion channel is relatively small, far lower than the inflow into the reservoir. As a result, the water level in the reservoir continues to rise and the reservoir capacity continues to increase, which can easily lead to inundation losses in the reservoir area. During the headward erosion stage of the landslide dam, the flow velocity of the overflow gradually increases and continuously cuts and erodes the downstream slope of the dam body, forming a multi-level, undulating steep slope along the way, until the multiple steep slopes converge and merge to form a larger drop slope. In the rapid development stage of the landslide dam breach, the overflow flow rises rapidly, even far exceeding the inflow into the reservoir. The water level in the reservoir continues to drop, and the breach flood peak can easily cause damage along the downstream river section.

[0004] In response to the typical development process of high-risk landslide dammed lakes, the engineering community generally lacks effective engineering measures to control the development process of landslide dammed lakes. Once the conventional trapezoidal cross-section diversion channel overflows, the overflowing water can only be allowed to overflow freely, that is, the water level of the landslide dammed lake is allowed to rise slowly and gradually. The overflowing water moves longitudinally along the diversion channel to the downstream slope of the landslide dam, causing the landslide dam to form a headward steep slope, resulting in the gradual collapse of the landslide dam. This process is time-consuming, has low discharge efficiency, and may even account for 70-80% of the overall landslide dammed lake collapse development process. During this stage, the water level of the landslide dammed lake continues to rise (the inflow is much higher than the overflow flow), the water storage capacity continues to increase, and the water storage time is long. Therefore, when the landslide dam breaks, it is very easy to form a large outburst flood peak. Currently, the engineering community mainly adopts the type of diversion channel with a gentle front and a steep rear slope, as well as the type of diversion channel with a vertical steep sill. The aim is to accelerate the early discharge of the diversion channel and shorten the water storage time of the landslide dammed lake. For example, the longitudinal slope of the diversion channel of Tangjiashan landslide dammed lake is 0.006 in the range of 0+00 to 0+326m, 0.24 in the range of 0+326 to 0+444m, and 0.16 in the range of 0+444 to 0+550m. Although variable-slope diversion channels can locally increase the flow velocity of the overburden, in the early stages of a landslide dam break, the overburden in the diversion channel is shallow, or even flows close to the bottom slope of the channel. The flow velocity is low, and the sand-carrying capacity is weak. Therefore, the kinetic energy loss of the overburden in the diversion channel is large due to frictional resistance, and the velocity increase effect is not significant. It is impossible to quickly increase the flow velocity of the overburden and to quickly discharge the floodwater stored in the landslide dam. Similar to variable-slope diversion channels, vertical steep-sill diversion channels can locally increase the flow velocity of the overburden, but only locally at the vertical steep sill, and the effect of increasing the flow velocity varies significantly with the height of the vertical steep sill.

[0005] Therefore, it is necessary to develop a method for arranging diversion channels to accelerate the breaching of landslide dams and improve the efficiency of discharge. Summary of the Invention

[0006] The purpose of this invention is to provide a stepped diversion channel arrangement method that accelerates the breach of a landslide dam and improves the discharge efficiency. This method can effectively shorten the water storage time of the landslide dam, reduce the water storage capacity of the landslide dam, safely and quickly discharge the floodwater stored in the landslide dam, reduce the maximum water level of the landslide dam and the breach flood peak, thereby minimizing the inundation losses in the reservoir area and the damage caused by the breach downstream. This invention solves the engineering problems of low discharge efficiency and long water storage time in current landslide dam diversion channels, which lead to high water levels in the landslide dam reservoir, large water storage capacity, severe inundation losses in the reservoir area and damage caused by the breach downstream.

[0007] To achieve the above objectives, the technical solution of the present invention is: a method for arranging diversion channels to accelerate the breaching of landslide dams and improve discharge efficiency, characterized by comprising the following steps:

[0008] Step 1: Excavate a diversion channel at the pass of the landslide dam or a relatively low-lying natural location. The goal is to minimize the amount of excavation work, maximize the flow efficiency, and take into account the material structure of the landslide dam. Determine the cross-sectional and longitudinal structural forms of the diversion channel.

[0009] Step 2: Divide the diversion channel longitudinally into two equal parts. On the downstream side of the midpoint of the diversion channel, excavate the diversion channel vertically at equal intervals to form a vertical step with gradually increasing vertical height until it connects to the downstream slope of the landslide dam.

[0010] In the above technical solution, in step two, the maximum height of the vertical steps is less than or equal to 5m;

[0011] The height difference between adjacent vertical steps is equal or less than 1m, and the longitudinal spacing is 20 to 50m.

[0012] In the above technical solution, when the reservoir capacity of the landslide dam reaches 0.1 billion m³... 3 Material structure composition of the landslide dam D 50 When the diameter is ≥200mm, the cross-section of the diversion channel can be deep and narrow, that is, the transverse width of the bottom of the diversion channel is maintained at 3 to 5m, the transverse slope ratio on both sides of the diversion channel is 1:0.8 to 1:1.2, the longitudinal slope of the diversion channel maintains the original natural river channel longitudinal slope, and vertical steps with gradually increasing height can be excavated every 20 to 30m in the downstream area from the midpoint of the diversion channel, with the maximum height of the vertical steps ≤5m, until it connects to the downstream slope of the landslide dam.

[0013] In the above technical solution, when the reservoir capacity of the landslide dam reaches 0.1 billion m³... 3 Material structure composition of the landslide dam D 50 When the diameter is ≤200mm, the diversion channel of the landslide dam can adopt a wide and gentle cross section, that is, the transverse width of the bottom of the diversion channel is maintained at 5 to 8m, the transverse slope ratio on both sides of the diversion channel is 1:1.2 to 1:2.0, the longitudinal slope of the diversion channel is maintained at the original natural river channel, and vertical steps with gradually increasing height are excavated every 30 to 50m downstream of the midpoint of the diversion channel, with the maximum height of the vertical steps ≤5m, until they connect to the downstream slope of the landslide dam.

[0014] Compared to traditional trapezoidal diversion channels, the stepped diversion channel arrangement method mentioned in this invention, which accelerates the breaching of landslide dams and improves discharge efficiency, has the following main advantages:

[0015] (1) By utilizing the potential energy conversion of free water drop in vertical steps, the flow velocity of the overflowing water along the top of the breach can be effectively increased in the initial stage of the breach, which accelerates the erosion of the bottom slope of the diversion channel, causing the source steep slope to appear faster and improving the discharge efficiency of the diversion channel.

[0016] (2) Shorten the water storage time of the landslide dammed lake in the initial stage of the breach, reduce the water storage capacity of the landslide dammed lake, reduce the flood peak of the landslide dammed lake breach, and avoid greater flooding losses and breach damage;

[0017] This invention is mainly used for emergency response to high-risk landslide-dammed lakes in the field of mountain torrents and geological disasters, especially for giant landslide-dammed lakes formed by landslides or debris flows blocking natural river channels in high mountain and canyon areas. The method of this invention is extremely beneficial to improving the discharge efficiency of diversion channels, shortening the water storage time of landslide-dammed lakes, avoiding greater inundation losses in upstream reservoir areas and greater flood damage along downstream banks, and facilitating subsequent emergency response to landslide-dammed lakes, thus having good social benefits. Attached Figure Description

[0018] Figure 1 A three-dimensional structural diagram of an existing conventional diversion channel (including an existing conventional trapezoidal cross-section diversion channel and a variable slope diversion channel with a gentle front and steep rear).

[0019] Figure 2 A three-dimensional structural schematic diagram of the stepped drainage channel of the present invention.

[0020] Figure 3 This is a schematic diagram of the deep and narrow cross-section drainage channel in this invention.

[0021] Figure 4 This is a schematic diagram of the structure of the wide and gentle cross-section drainage channel in this invention.

[0022] Figure 5 This is a schematic diagram of the longitudinal cross-sectional structure of the drainage channel in this invention.

[0023] exist Figure 5 In the diagram, i0 represents the longitudinal slope of the original natural riverbed; L represents the length of the excavation platform; h o ,h1……h n The following are the vertical steep slope heights, which can be set to h according to the actual situation. n =1m,h n-1 =2m,h n-2 =3m……h o =5m.

[0024] In the diagram, 1-diversion channel slope, 2-diversion channel bottom slope, 3-diversion channel, 4-original natural riverbed, 5-upstream slope of the landslide dam, 6-top of the landslide dam, and 7-downstream slope of the landslide dam. Detailed Implementation

[0025] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, these descriptions do not constitute a limitation of the present invention and are merely illustrative. The advantages of the present invention will become clearer and easier to understand through this description.

[0026] The basic principle of the stepped diversion channel arrangement method for improving discharge efficiency described in this invention is: by utilizing the natural drop of the vertical steep slope, the gravitational potential energy of the overtopping water in the diversion channel is converted into kinetic energy in the early stage of the landslide dam breach, thereby locally increasing the flow velocity of the overtopping water, improving the discharge efficiency of the diversion channel in the early stage of the landslide dam breach, shortening the water storage time of the landslide dam and reducing the reservoir capacity of the landslide dam, thereby reducing the maximum water level of the landslide dam and the peak of the breach. The stepped diversion channel proposed in this invention forces the overtopping water to fall freely at the vertical steps along the course during the early stages of a landslide dam breach, achieving local potential energy conversion at multiple steps, rapidly increasing the flow velocity of the overtopping water, and using the free water drop to accelerate the erosion of the bottom slope of the diversion channel, forming a larger drop and accelerating the formation of the headwaters slope. This effectively shortens the water storage time of the landslide dam, improves the discharge efficiency of the diversion channel, accelerates the overtopping breach of the landslide dam, and further reduces the storage capacity of the landslide dam and the peak of the breach flood. It overcomes the problem of existing variable slope diversion channels having large frictional losses of the kinetic energy of the overtopping water, and the flow velocity increase effect is not obvious, making it impossible to quickly increase the flow velocity of the overtopping water and achieve rapid discharge of floodwater stored in the landslide dam.

[0027] Referring to the attached diagram, a method for arranging stepped diversion channels to accelerate the breaching of a landslide dam and improve discharge efficiency includes the following steps:

[0028] Step 1: Excavate a diversion channel at the pass of the landslide dam or a relatively low-lying natural location. The goal is to minimize the amount of excavation work, maximize the flow efficiency, and take into account the material structure of the landslide dam. Determine the cross-sectional and longitudinal structural forms of the diversion channel.

[0029] Step 2: Divide the diversion channel longitudinally into two equal parts. On the downstream side of the midpoint of the diversion channel, excavate the diversion channel vertically at equal intervals to form a vertical step with gradually increasing vertical height until it connects to the downstream slope of the landslide dam.

[0030] Within the limited emergency response window for landslide dammed lakes, to improve the efficiency of emergency response construction and avoid excessively increasing the amount of excavation work, the original longitudinal slope of the diversion channel should be maintained to transition to the downstream slope of the landslide dam (e.g., ...). Figure 2 , Figure 5 (As shown).

[0031] Furthermore, in step two, to ensure the stability of the vertical steps themselves and prevent them from collapsing, the maximum height of the vertical steps is less than or equal to 5m; the heights of adjacent vertical steps are equal or less than 1m, and the longitudinal spacing is 20 to 50m.

[0032] Furthermore, the optimization of the cross-sectional and longitudinal structure of the diversion channel is aimed at the reservoir capacity and material composition of the landslide dam; when the reservoir capacity of the landslide dam reaches 0.1 billion m³... 3 The landslide dam is mainly composed of boulders or isolated rocks (material structure composition D). 50When the diameter is ≥200mm, meaning the boulders or isolated rocks can provide structural support and the dam itself has high stability, the cross-section of the diversion channel can be deep and narrow (e.g., Figure 3 As shown), the bottom transverse width of the diversion channel is maintained at 3-5m, the transverse slope ratio on both sides of the diversion channel is 1:0.8-1:1.2, and the longitudinal slope of the diversion channel maintains the original natural river channel gradient. Downstream from the midpoint of the diversion channel, vertical steps of gradually increasing height can be excavated every 20-30m. To ensure the stability of the vertical steps and prevent collapse, the maximum height of the vertical steps is ≤5m, until they connect to the downstream slope of the landslide dam (e.g., ...). Figure 5 (As shown).

[0033] Furthermore, when the reservoir capacity of the landslide dam reaches 0.1 billion m³... 3 The landslide dam is mainly composed of gravel, sand, or soil (material composition D). 50 When the diameter of the landslide dam is ≤200mm, the stability of the landslide dam itself is relatively weak. The overtopping water flow can easily erode the landslide dam too quickly, causing it to collapse instantly. In this case, the diversion channel of the landslide dam lake can adopt a wide and gentle cross section (such as...). Figure 4 As shown), the bottom transverse width of the diversion channel is maintained at 5-8m, the transverse slope ratio on both sides of the diversion channel is 1:1.2-1:2.0, and the longitudinal slope of the diversion channel maintains the original natural river channel gradient. Downstream from the midpoint of the diversion channel, vertical steps of gradually increasing height are excavated every 30-50m. To ensure the stability of the vertical steps and prevent collapse, the maximum height of the vertical steep slope is ≤5m, until it connects to the downstream slope of the landslide dam (e.g., Figure 5 (As shown).

[0034] The diversion channel arrangement method for accelerating the breach of a landslide dam and improving the discharge efficiency described in this invention is a stepped diversion channel arrangement structure, in which the vertical steps are set on the downstream side of the midpoint of the diversion channel and are connected to the downstream slope of the landslide dam.

[0035] There are multiple vertical steps; these multiple vertical steps are evenly spaced, and their vertical height increases from top to bottom (e.g., ...). Figure 5 (As shown).

[0036] Example

[0037] The present invention will now be described in detail using an example of its application in a landslide dammed lake to arrange a stepped diversion channel, accelerate the dammed lake's collapse, and improve the discharge efficiency. This example will also provide guidance for applying the present invention to other landslide dammed lakes for the same purpose of arranging diversion channels, accelerating the dammed lake's collapse, and improving the discharge efficiency.

[0038] In this embodiment, the landslide dam of a certain landslide-dammed lake is tongue-shaped and lies across the main river channel, with a maximum storage capacity of 770 million cubic meters. 3The landslide dam has a width of 300m across the river, with a longitudinal length of 195m at the top and 300m at the bottom, and a vertical height of 96m at the pass. The slope of the upstream and downstream slopes of the dam is approximately 1:2. The landslide dam is mainly composed of gravel and angular gravel, mixed with some boulders. The soil-to-rock ratio observed on-site is 8:2 to 7:3, with a high content of fine particles, classifying it as a soil-rock type landslide dam. The boulders are mainly 0.2 to 0.5m in size, with occasional boulders reaching 1m in diameter, and the largest boulder is about 3m in diameter. During the emergency response, on-site sampling of the landslide dam's material composition and particle size analysis showed that the landslide dam was mainly composed of angular gravel, accounting for 45.9% to 51.6%, followed by sand and gravel, accounting for 20.8% to 21.9%, and then gravel, accounting for 17.8% to 21.4%. Overall, D 50 It is approximately 4.39 mm.

[0039] The flooding of the upstream reservoir of the landslide dam affected more than 1,700 people, and the downstream floodwaters affected four cities and prefectures, impacting a population of up to 107,000.

[0040] This embodiment utilizes the diversion channel arrangement method described in this invention for accelerating the breach of a landslide dam and improving discharge efficiency. The specific method is as follows:

[0041] Step 1: Excavate a diversion channel at the pass of the landslide dam or a relatively low-lying natural location. The goal is to minimize the amount of excavation work, maximize the flow efficiency, and take into account the material structure of the landslide dam. Determine the cross-sectional and longitudinal structural forms of the diversion channel.

[0042] In this embodiment, given the large reservoir capacity of the landslide dammed lake and the fact that the dammed body is mainly composed of fine particles, D 50 With a thickness of only 4.39 mm, at the right bank pass of the landslide dam, a wide and gentle diversion channel with a top width of 42 m, a bottom width of 3 m, and a maximum excavation depth of 15 m was formed by continuous manual and mechanical excavation. The total longitudinal length of the diversion channel is 220 m, and the slope ratio on both sides is 1:1.3.

[0043] Step 2: To improve the discharge efficiency of the diversion channel and accelerate the discharge, a vertical stepped diversion channel is excavated from the downstream side of the midpoint of the diversion channel. The length L of the stepped excavation platform is 40m, and the vertical height h of the steps from upstream to downstream gradually increases from 1m to 5m until it smoothly transitions to the downstream slope of the landslide dam.

[0044] Conclusion: Compared with existing technologies (conventional trapezoidal cross-section diversion channel, and variable slope diversion channel with gentle front and steep rear), this embodiment uses the method of the present invention, which reduces the water storage capacity of the landslide dammed lake and accelerates the discharge of the diversion channel, thus quickly and effectively alleviating the danger of the landslide dammed lake.

[0045] All other unspecified parts belong to the prior art.

Claims

1. A method for arranging stepped diversion channels to accelerate the breaching of a landslide dam and improve the discharge efficiency, characterized in that: Includes the following steps, Step 1: Excavate a diversion channel at the pass of the landslide dam or a relatively low-lying natural location, and determine the cross-sectional and longitudinal structural forms of the diversion channel based on the material composition of the landslide dam. When the reservoir capacity of the landslide dammed lake reaches 0.1 billion m³ 3 The landslide dam is mainly composed of boulders or isolated rocks. 50 When the diameter is ≥200mm, the cross-section of the diversion channel adopts a deep and narrow type, that is, the transverse width of the bottom of the diversion channel is maintained at 3 to 5m, and the transverse slope ratio of both sides of the diversion channel is 1:0.8 to 1:1.

2. When the reservoir capacity of the landslide dammed lake reaches 0.1 billion m³ 3 The landslide dam is mainly composed of materials such as gravel, sand, or soil. 50 When the diameter is ≤200mm, the diversion channel of the landslide dammed lake adopts a wide and gentle cross section, that is, the transverse width of the bottom of the diversion channel is maintained at 5 to 8m, and the transverse slope ratio of both sides of the diversion channel is 1:1.2 to 1:2.0; The longitudinal slope of the diversion channel is maintained in accordance with the original natural river channel. Step 2: Divide the diversion channel longitudinally into two equal parts. On the downstream side of the midpoint of the diversion channel, excavate the diversion channel vertically at equal intervals to form a vertical step with gradually increasing vertical height until it connects to the downstream slope of the landslide dam.

2. The method for arranging stepped diversion channels to accelerate the breaching of landslide dams and improve discharge efficiency according to claim 1, characterized in that: In step two, the maximum height of the vertical steps is less than or equal to 5m; the heights of adjacent vertical steps are equal or differ by 1m, and the longitudinal spacing is 20 to 50m.

3. The method for arranging stepped diversion channels to accelerate the breaching of landslide dams and improve discharge efficiency according to claim 1, characterized in that: When the reservoir capacity of the landslide dammed lake reaches 0.1 billion m³ 3 Material structure composition of the landslide dam D 50 When the diameter is ≥200mm, vertical steps with gradually increasing height are arranged in the downstream area from the midpoint of the diversion channel at intervals of 20 to 30m, with the maximum height of the vertical steps being less than or equal to 5m.

4. The method for arranging stepped diversion channels to accelerate the breaching of landslide dams and improve discharge efficiency according to claim 1, characterized in that: When the reservoir capacity of the landslide dammed lake reaches 0.1 billion m³ 3 Material structure composition of the landslide dam D 50 When the diameter is ≤200mm, vertical steps with gradually increasing height are excavated in the downstream area of ​​the diversion channel at intervals of 30 to 50m, with the maximum height of the vertical steps being less than or equal to 5m.

Images