Debris flow fan ecological and geotechnical measures coordinated siltation prevention system

Abstract

The present invention discloses a debris flow accumulation fan ecological and geotechnical measures coordinated siltation prevention system. The system organically integrates two types of geotechnical and ecological measures, and arranges them in three dimensions within the debris flow ground flow area and the impact height spatial area. Along the siltation prevention movement direction, three sections are arranged in sequence: geotechnical measures section, ecological geotechnical combined measures section, and ecological measures section. In each section, the system utilizes the selection of measures type and its structural characteristics to produce three-layer blocking effects on the debris flow in sequence, namely, counter-energy dissipation and diversion and peak cutting, ground resistance increase and spatial graded blocking, and ground resistance increase and siltation prevention. The technology aims to synergistically integrate the prevention and control effects of geotechnical and ecological measures, enhance the natural ecological recovery capacity of the siltation prevention system, extend the system's operating service life, and eliminate the hidden dangers of secondary disasters. The optimized ecological geotechnical combined measures section adopts a phased construction method that matches spatial arrangement with dynamic time to ensure the stable and organic combination of the two measures. The invention also provides a design and calculation model for the blocking height of structures within the system.

Description

Technical Field

[0001] The present invention relates to a debris flow disaster prevention project, in particular to a siltation prevention project at the downstream outlet of a river channel, and belongs to the fields of water conservancy engineering, debris flow blocking and prevention engineering technology, and mountain environment management technology. Background Art

[0002] The key principles for debris flow prevention and control in mountainous areas are "stabilization, interception, drainage, and stoppage." "Stoppage" refers to the process of slowing down and stopping debris flows through step-by-step interception and resistance-enhancing measures implemented on natural accumulation fans after they have moved along the channel to the downstream gentle slopes or exit areas. In theory, for debris flow control that has already begun, regardless of the locally adapted mud disaster prevention and control strategies and engineering measures, ultimately stopping the flow is essential to achieve the disaster prevention goal.

[0003] According to the current "Code for the Design of Debris Flow Prevention and Control Projects" (TCAGHP 021-2018), silt retention projects are a sub-project for debris flow prevention and control. These projects must be located on gentle slopes downstream of river channels or in open areas at their outlets. These are typically located in the alluvial fan zone at the outlet of a small watershed, where mountainous areas are often densely populated and where available space is relatively limited. Therefore, within this limited space, debris flows must be prevented from directly impacting the alluvial fan, while excessive construction of structures that would otherwise occupy land or cause excessive deflection of debris flows is essential. Balancing these two objectives—maximizing the use of the alluvial fan's land space and maximizing its debris flow-stopping function—is the primary technical challenge for silt retention projects, especially those on alluvial fans.

[0004] In the long-term practice of mountain disaster environmental management, early geotechnical measures have gradually revealed drawbacks: they are incompatible with the ecological restoration of the surrounding environment. In particular, geotechnical measures are detrimental to the self-recovery function of the mountain environment, inherent in its biodiversity. Consequently, the concept of ecological measures has begun to be incorporated into debris flow prevention and control systems. Existing ecological measures are primarily used in environmental management projects for debris flow stabilization, drainage, and interception, and are rarely used in siltation control projects.

[0005] The prior art CN2022106653788 discloses a water-stone separation and expansion-type debris flow silt retention field technology. It utilizes the terrain to sequentially set up a solid phase barrier, a first-level solid-liquid separation expansion part, a second-level solid-liquid separation expansion part, and sediment deposition along the flow direction of the debris flow. It performs a silt retention design for the solid and liquid phases in the debris flow, and performs silt retention and expansion according to the flow rate of the debris flow, thereby achieving the purpose of adjustable silt retention field volume. The main defects of this technical solution are: First, there are many facilities, which occupy the silt retention space; second, the ecological measures use plum blossom piles to arrange the circular gabions with trees planted, which limits the function of the trees themselves in transforming the environment. The role of trees in the entire technical solution is more like a landscape. Third, the overall layout is a multi-section walkway. If the length of the silt retention space is insufficient, the functions of each section are difficult to achieve, so there are certain requirements for the terrain. Summary of the Invention

[0006] The purpose of the present invention is to address the deficiencies of the existing technology and provide a technical solution for stopping siltation in debris flow accumulation fans, which can integrate geotechnical measures with ecological measures, and give full play to the role of vegetation in transforming and repairing the environment while achieving effective siltation.

[0007] To achieve the above objectives, the present invention provides a debris flow fan ecological and geotechnical measures coordinated siltation prevention system, and its technical solution is as follows.

[0008] A debris flow accumulation fan ecological and geotechnical measures coordinated siltation prevention system, including x The geotechnical measures section, ecological geotechnical combined measures section, and ecological measures section are arranged;

[0009] The diversion pier is arranged in the upstream area of the geotechnical measures section, and the geotechnical retaining net is arranged in the downstream area. The geotechnical retaining nets are arranged in a basket shape with the basket mouth facing the diversion pier; the diversion pier is located in the middle of the upstream area, which is a steel-concrete column pier with a fan-shaped cross-section, a head narrower than the tail, and the head facing the entrance of the accumulation fan; the geotechnical retaining net arranged in a basket shape includes three parts, which are respectively located at the rear and two side rear positions of the diversion pier. The mesh surface of the geotechnical retaining net at the rear position faces the diversion pier, and the mesh surface of the geotechnical retaining net at the side rear position faces the diversion direction on both sides of the diversion pier; the vertical distance between the downstream end pile of the side rear position geotechnical retaining net and the geotechnical retaining net at the rear position is 1.23mm. d 1>0;

[0010] The ecological geotechnical combination measures section along x Multiple rows of ecological barriers are arranged in a certain direction. The ecological barriers in each row are arranged in a certain direction and the front and back rows are staggered. The height of each row of ecological barriers is along the same direction. x Direction down, aperture along x The direction is lowered and reduced, and shrubs and grasses are arranged at the bottom of the bed;

[0011] The geotechnical barrier net or ecological barrier net is a pile-and-net structure, with a protective net stretched between the piles. The piles of the geotechnical barrier net are steel-concrete piles, and the piles of the ecological barrier net are trees.

[0012] The ecological measures section has shrubs scattered around and grass planted between the shrubs.

[0013] The above-mentioned debris flow accumulation fan ecological and geotechnical measures coordinated siltation prevention system of the present invention integrates and utilizes the two major types of geotechnical measures and ecological measures in debris flow prevention engineering measures, and arranges them in three dimensions within the debris flow movement space. In the debris flow ground flow area, shrubs and herbs are used to change the ground roughness characteristics, adjust the debris flow siltation dynamics and flow state changes; in the debris flow impact height space area, with the accumulation fan siltation direction as the axis, a gradual arrangement method combining two measures independently and crosswise is adopted to block and reduce the debris flow impact kinetic energy in sections and reduce the siltation range. Through the three-dimensional arrangement, the siltation prevention capacity of the debris flow accumulation fan siltation prevention system and the environmental self-repairing capacity are improved.

[0014] The present invention further provides an optimization scheme for the above-mentioned debris flow fan ecological and geotechnical measures coordinated siltation prevention system technical solution. The following optimization schemes can be implemented separately or simultaneously under the premise of no conflict.

[0015] Optimization 1. Blocking height of structures H Design optimization. The structures in the system are a general term for diversion piers or rock and soil retaining nets or ecological retaining nets. The height of the structure is H Diversion pier height H 11 , Height of rock and soil barrier net H 12 , Height of ecological barrier net H 21 The blocking height of the structure H Not less than the model design value calculated using formula 1 H d .

[0016] Formula 1

[0017] Where, H d - Model design value of structure height, unit: m, ε -Structure diversion stress coefficient, dimensionless, F r - Froude number of debris flow at the structure, dimensionless; g - Gravitational acceleration constant, unit m / s 2 The remaining parameters are determined based on the engineering basic data of the accretion fan desilting system, including: U - Debris flow velocity at the structure, unit: m / s, φ - The bottom friction angle of debris flow when it moves on the accumulation fan, unit: °, h - Depth of debris flow at the structure, unit: m, I - Natural slope of the alluvial fan, unit: °.

[0018] Furthermore, in the geotechnical barrier or ecological barrier H d In the design, the debris flow velocity U Determined according to formula 2.

[0019] Formula 2

[0020] Where, n -1 - The resistance coefficient of debris flow at the structure is dimensionless. The remaining parameters are determined based on the basic engineering data of the accumulation fan siltation system, including: w s - Debris flow solid particle concentration, dimensionless, d 2mm - The percentage of particles with a diameter less than 2 mm in the full-size particle distribution curve of debris flow, %.

[0021] Furthermore, in the geotechnical barrier or ecological barrier H d In the design, the depth of debris flow h Determined according to formula 3.

[0022] Formula 3

[0023] All parameters in the formula are determined based on the basic engineering data of the accumulation fan desilting system, including: h α - Depth of debris flow at the entrance section of the accumulation fan, unit: m, L x - The vertical distance between the structure and the entrance section of the accumulation fan, in meters. For the rock and soil retaining net, L x The distance between the downstream end pile and the inlet section of the accumulation fan is taken as the value. L - Length of the accumulation fan, in meters.

[0024] Optimization 2. Optimization of the diversion pier. The cross section of the diversion pier is disc-shaped cam, with the curvature of the head greater than the curvature of the tail. Furthermore, the diversion pier is generally designed with the central axis l Symmetrical, with the sides and center axis l Angle θ =15°~35°.

[0025] Optimize the width of the protective net of the rock and soil barrier net wn12 Design optimization. w n12 Determine according to formula 4, where a 112 Is the length of the arc chord at the tail of the diversion pier. If the tail of the diversion pier is not bilaterally symmetrical, a 112 The average value of the arc chord length can be obtained.

[0026] Formula 4

[0027] Optimization 4: Blocking height of single-row ecological barrier net H 21 Design optimization. Single row ecological barrier net blocking height H 21 Determine according to formula 7, the total width of the single row ecological barrier net protection net w n21 Determined according to formula 8.

[0028] Formula 7

[0029] Formula 8

[0030] Where, δ - Single-row design ecological transmittance, value ranges from 0 to 1, λ - Single-row design total interception rate, value ranges from 0.3 to 0.5; other values are determined based on basic engineering data: H b,i - Stake tree species during the debris flow recurrence period i Corresponding diameter at breast height H b , unit m, W j - Width of the accumulation fan at the horizontal line of the ecological barrier net, unit: m.

[0031] Optimization 5. Optimize the length and distance distribution of each section. The length of the geotechnical measures section should not be less than 2 / 5 L , the length of the ecological geotechnical combined measures section is not less than 2 / 5 L The front end of the diversion pier head is not less than 1 / 10 of the distance from the inlet section of the accumulation fan L .

[0032] Optimization 6. Optimization of the layout process of ecological geotechnical combination measures. Since the organic and stable combination of ecological measures and geotechnical measures takes time, the ecological geotechnical combination measure section is laid out in stages: in the first stage, the ecological barrier net in the early stage of construction is constructed using the original trees, transplanted trees or planted trees. The preset protection net is tensioned according to the anti-impact and anti-pullout mechanical properties of the tree piles, and an auxiliary protection net is arranged in front of each row of ecological barrier nets. Shrubs dominated by herbs are arranged at the bottom of the bed of the ecological geotechnical combination measure section, and energy dissipation piers are dispersed in the shrubs and grasses; in the second stage, from the time the shrubs and grasses mature, the energy dissipation piers are removed in batches, and shrubs and grasses are replanted in the original position of the energy dissipation piers to increase the proportion of shrubs in the shrubs and grasses; in the third stage, when 80% of the tree piles of the ecological barrier net grow to the design specifications, the auxiliary protection nets are removed in batches, and shrubs and grasses are replanted in the original position of the auxiliary protection net piles. The protection net is tensioned between the tree piles that have grown to the design specifications, and the preset protection net is removed to maintain the shrubs and grasses as the dominant position; the height of the auxiliary protection net is not less than the height of the protection net of the ecological barrier net in the rear row

[0033] The field investigation referred to in this technology includes various geological surveys, reconnaissance, mapping, and measurement work at the alluvial fan site at the outlet of the river channel where the project is located, as well as existing simulation experiments, testing experiments, observation experiments, and analysis experiments in the field, as well as the acquisition of historical disaster records, relevant technical specifications, and empirical methods and data acquisition for reference. The data obtained from the field investigation is collectively referred to as the basic engineering data of this technical solution.

[0034] Compared with the existing technology, the beneficial effects of the present invention are as follows: (1) In the design of the debris flow fan siltation prevention system, the planning of engineering measures is prone to conflicts in at least the following aspects: first, the number of engineering measures is insufficient, and the debris flow cannot be effectively stopped; second, the large number of engineering measures occupies limited siltation prevention space, reducing the utilization efficiency of the siltation prevention system; and finally, compared with other types of debris flow prevention and control engineering areas, the natural ecological restoration of the siltation prevention site is more difficult. Based on this, the present invention provides a technical solution for the debris flow fan siltation prevention engineering system that integrates geotechnical engineering measures and ecological engineering measures and has hierarchical and systematic characteristics. Along the direction of movement of the debris flow into the debris flow fan, the technical solution arranges three control measure sections: geotechnical measure section, ecological geotechnical combined measure section, and ecological measure section. In each section, by comprehensively utilizing the selection of measure types and their structural design, the system produces three-level blocking effects on the debris flow: hedging and dissipating energy and diverting peaks, increasing ground resistance and spatial graded blocking, and increasing ground resistance and stopping siltation. The ultimate goal of the system design is to maximize the different functions of the limited number of construction measures in the siltation prevention system, and to increase the proportion of ecological measures in the siltation prevention system of the alluvial fan under the premise of meeting the "stop" prevention and control requirements, enhance the natural ecological recovery capacity of the system, extend the service life of the siltation prevention system, and eliminate the hidden dangers of secondary disasters. (2) Regarding the design of the blocking height of each structure in the siltation prevention system, the present invention provides a blocking height design method, which is based on the principle of debris flow dynamics and a mathematical calculation model that comprehensively considers the two major factors of debris flow movement characteristics and the natural morphology of the alluvial fan. It is scientific and rigorous. (3) Compared with other types of debris flow prevention and control engineering measures, in the siltation prevention system, due to the limitation of the proportion of siltation prevention space, the types and number of ecological engineering measures that can be introduced are very limited. For this purpose, the present invention designs an ecological geotechnical combination measure section construction method that matches the spatial arrangement of engineering measures with dynamic time. It is divided into three basic stages, with progressive ground resistance enhancement and spatial blocking arrangement measures arranged before and after. Through the comprehensive use of means such as process adjustment of shrub and grass species structure, process increase and decrease of auxiliary protection nets and energy dissipation piers, while finally completing the layout of the ecological geotechnical combination measures section, the stable and organic combination of geotechnical measures and ecological measures in the section is ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the debris flow fan ecological and geotechnical measures coordinated siltation prevention system.

[0036] Figure 2 It is a schematic diagram of several fan-shaped expansion shapes of the diversion pier cross section.

[0037] Figure 3 Schematic diagram of the structure of geotechnical retaining net and ecological retaining net, (a) geotechnical retaining net, (b) ecological retaining net.

[0038] Figure 4It is a schematic diagram of the meaning of some parameters in the geotechnical measures section.

[0039] The numbers in the accompanying drawings are:

[0040] 1. Geotechnical measures section; 11. Diversion pier; 111. Head; 112. Tail; 113. Side; 114. Prestressed member; 12. Geotechnical retaining net; 12a. Rear geotechnical retaining net; 12b. Side and rear geotechnical retaining net; 121. Downstream end pile; 2. Ecological geotechnical combined measures section; 21. Ecological retaining net; 22. Shrubs and grass; 3. Ecological measures section. DETAILED DESCRIPTION

[0041] The preferred embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0042] Example 1

[0043] like Figures 1 to 4 As shown in the figure, a debris flow prevention system was designed in a certain alluvial fan by coordinating ecological and geotechnical measures.

[0044] 1. On-site investigation to obtain basic data

[0045] Conduct on-site investigations to obtain basic engineering data. Combining the investigation data with debris flow prevention and control regulations, determine that the maximum mud depth of a debris flow at the entrance of the accumulation fan with a certain recurrence period (assuming a 100-year return period) is 5 meters. Obtain the growth curve of local suitable trees and determine the tree height at breast height corresponding to a debris flow recurrence period of 100 years. h i=100 =6.5m, diameter at breast height d i=100 =1.2m.

[0046] Table 1 Main engineering basic data of the accumulative fan desilting system

[0047]

[0048] 2. Overall layout of the siltation prevention system

[0049] Figure 1 It is a schematic diagram of the structure of the debris flow fan ecological and geotechnical measures coordinated siltation prevention system.

[0050] Debris flow fan ecological and geotechnical measures coordinated siltation prevention system, including the flow direction along the debris flow inlet x The layout includes geotechnical measures section 1, ecological geotechnical combined measures section 2, and ecological measures section 3.

[0051] The diversion pier 11 is arranged in the upstream area of the geotechnical measures section 1, and the geotechnical retaining net 12 is arranged in the downstream area. The geotechnical retaining net 12 is arranged in a basket shape with the basket mouth facing the diversion pier 11; the diversion pier 11 is located in the middle of the upstream area, is a steel-concrete columnar pier, and the cross section is fan-shaped. The head 111 is narrower than the tail 112, and the head 111 faces the entrance of the accumulation fan; the geotechnical retaining net 12 arranged in a basket shape includes three parts, which are respectively located at the rear and two rear sides of the diversion pier 11. The mesh surface of the rear geotechnical retaining net 12a faces the diversion pier 11, and the mesh surfaces of the side and rear geotechnical retaining net 12b face the diversion directions on both sides of the diversion pier 11; the downstream end pile 121 of the side and rear geotechnical retaining net 12b is vertically spaced from the rear geotechnical retaining net 12a. d 1>0.

[0052] Figure 2 It is a schematic diagram of several fan-shaped expansion shapes of the diversion pier cross section.

[0053] To enhance performance, a prestressed member 114 may be installed on the flow-facing surface of the head 111 .

[0054] Ecological geotechnical combined measures section 2 along x Multiple rows of ecological barriers 21 are arranged at a distance in the direction of the road, and the ecological barriers 21 in each row are arranged at a distance and the front and rear rows are staggered. The height of each row of ecological barriers 21 is along the direction of the road. x Direction down, aperture along x The direction is lowered and reduced, and shrubs and grasses 22 are arranged at the bottom of the bed.

[0055] Figure 3 Schematic diagram of the structure of geotechnical retaining net and ecological retaining net, (a) geotechnical retaining net, (b) ecological retaining net.

[0056] The geotechnical retaining net 12 or the ecological retaining net 21 is a pile-and-net structure, with a protective net stretched between the piles. The piles of the geotechnical retaining net 12 are steel-concrete piles, and the piles of the ecological retaining net 21 are trees.

[0057] Ecological measures section 3: shrubs are scattered and grass is planted between the shrubs.

[0058] In this example, the length of geotechnical measures section 1 is 2 / 5 L The distance between the front end of the diversion pier 11 head 111 and the inlet section of the accumulation fan is α length l 11a Not less than 1 / 10 L The length of the ecological geotechnical combined measures section 2 is 2 / 5 L , arrange three rows of ecological barriers 21. The length of ecological measure section 3 is 1 / 5 L .

[0059] Table 2 Location of each structure and related parameters

[0060]

[0061] 3. Main parameter design

[0062] Figure 4 It is a schematic diagram of the meaning of some parameters in the geotechnical measures section.

[0063] 3.1 Parameter design of diversion pier 11

[0064] Determine the parameters of diversion pier 11 based on the engineering basic data obtained from the on-site investigation, including the flow depth h 11 , flow rate U 11 , calculate the model design value according to formula 1 H d . Blocking height H 11 Not less than H d In this example, the diversion pier 11 has a blocking height of H 11 = H d .

[0065] In this example, the cross section of the diversion pier 11 is specifically designed to be a disc-shaped cam, with the central axis l Symmetrical, with side 113 and central axis l Angle θ =30°, the contour line of the head 111 or the tail 112 is a 180° elliptical curve. a 111 , chord-center distance b 111 , tail arc chord length 112 a 112 , chord-center distance b 112 , respectively determined according to the model of formula 5 and formula 6. In the formula, γ - The coefficient of the diversion pier's anti-overturning width is dimensionless and is determined based on the project requirements or is 1 / 20 to 1 / 30. w α - The cross-sectional width of the accumulation fan entrance, in meters, shall be determined based on basic engineering data.

[0066] Formula 5

[0067] Formula 6

[0068] The coefficient of the anti-overturning width of the diversion pier in this example γ =1 / 25. γ 、 w α=80m Substitute into equations 5 and 6 to determine the four design parameters of the head 111 and the tail 112: a 111 =3.2 m, b 111 =1.8 m, a 112 =6.4 m, b 112 =3.2 m.

[0069] 3.2 Parameter design of geotechnical retaining net 12

[0070] The side and rear rock and soil retaining net 12b and the center axis l Angle β =30°~60°, distance d 1 is 2* a 112 , the downstream end pile 121 and the center axis l Vertical distance of extension line d 2 is 2* a 112 .

[0071] The specifications of the geotechnical retaining nets 12 distributed on the side and rear of the diversion pier 11 are the same. The design value of the model is calculated according to the model of formula 1 using the same method as the design of the diversion pier 11. H d , where flow depth h 12 , flow rate U 12 The measurement point is the location of the pile 121 at the downstream end of the rock and soil barrier 12 in the side and rear direction. H 12 Not less than H d .

[0072] according to H 12 and a 112 , calculate and determine the width of the protective net (referred to as the net width) according to formula 4 w n12 .

[0073] The ground height and underground depth of the rock and soil barrier 12 piles are designed according to the specifications of the protective net above them in accordance with conventional methods. The other parameters are designed according to the blocking performance to meet the characteristic particle size of the accumulation fan debris flow. d n Standard design. Including, pile diameter according to characteristic particle size d n Impact load design, the aperture of the protective net is based on the characteristic particle size d nPass-through design.

[0074] In this example, the rock retaining net 12 has a retaining height of H 12 = H d , the height of steel-concrete pile is designed to be 1.2* H 12 、Underground burial depth is 0.5*1.2* H 12 , pile diameter is 2* d 80 , the aperture of the protective net is d 80 =0.3m. Angle β =45°.

[0075] 3.3 Parameter design of ecological barrier net 21

[0076] According to the engineering basic data obtained from the on-site investigation, the parameters of each row of ecological barrier nets 21, including flow depth, h 21 , flow rate U 21 , calculate the model design value according to formula 1 H d Then adopt the optimization scheme and determine the height of each row of barriers according to formula 7 H 21 During the phased construction process, the auxiliary protection net 22 height H 22 Not less than the blocking height of the rear ecological blocking net 21 (i.e. the height of the protective net) H 21 .

[0077] along x direction, δ The values decrease step by step to achieve segmented interception and balanced siltation of debris flow solid matter.

[0078] According to formula 8, the total width of the protective net of a single row of ecological barrier net 21 (referred to as the total net width) is: w n21 The total interception rate λ of a single row design refers to the width of the accumulation fan of a single row of ecological interception net 21 at its horizontal line. W j The λ value of each row is determined within the range of values. It can be determined based on the conditions of a single row or a comprehensive value considering the conditions of the front and rear rows. Generally, within the range of values, the λ value varies with the total number of rows of the ecological barrier network. N decreases with the increase of .

[0079] Table 3 Total width of ecological barrier network

[0080]

[0081] Each row of ecological barrier net 21 is determined in the total network width w n21 After that, the number of ecological barriers 21 is n 21 The width of each ecological barrier net 21 can be determined relatively flexibly based on field conditions, in conjunction with design specifications for debris flow prevention projects or existing technologies. Generally, the following should be met: uniform arrangement of each row of ecological barrier nets 21, uniform width specifications, and uniform spacing between each row. The staggered arrangement of front and rear rows of ecological barrier nets 21 should ensure effective staggering, meaning that the rear row of ecological barrier nets 21 fills the gap between the front rows.

[0082] For the ecological barrier net 21, when designing the tree stake specifications, the ground height of the stake corresponds to the tree's DBH height, and the stake diameter corresponds to the tree's DBH diameter, both of which are calculated based on the growth curve of the tree species during the designed debris flow recurrence period. i In this example, the design specifications for tree stakes are as follows: the height of the stakes from the ground is the height of the diameter at breast height of a 20-year-old fir tree. h i=100 =6.5m, the diameter of the pile is the diameter at breast height d i=100 =1.2m.

[0083] The aperture of each row of ecological barrier nets 21 is selected according to the barrier performance to meet the characteristic particle size of the accumulation fan debris flow. d n Standard design and characteristic particle size of geotechnical retaining net 12 d n In this example, the aperture design standards for the three rows of ecological barrier nets 21 are as follows: d 60 =0.12m, d 40 =0.08 m, d 20 =0.02 m.

[0084] 4. Phased layout planning of ecological geotechnical combined measures section 2

[0085] The key to the ecological-geotechnical combined measures section 2 is the stable and organic combination of ecological measures and geotechnical measures, which requires sufficient construction time.

[0086] In the first phase, the initial ecological barrier net 21 will be constructed using existing, transplanted, or planted trees. Pre-tensioned protective nets will be deployed based on the impact and pullout resistance of the tree stakes. Auxiliary protective nets will be placed in front of each row of ecological barrier nets 21. A herbaceous shrubbery 22 will be placed underneath, with energy dissipation piers dispersed within the shrubbery 22. The specifications of the pre-tensioned protective nets and the tensioned structural parameters will be determined based on the impact and pullout resistance of the tree stakes. The height of the auxiliary protective nets should be no less than that of the ecological barrier net 21 in the row behind them.

[0087] In the second phase, once the shrubs and grasses 22 mature, the energy dissipation piers will be removed in batches and replanted in their original locations to increase the proportion of shrubs within the shrubs and grasses 22. The timing of energy dissipation pier removal will be determined based on the roughness characteristics of the bed around the piers.

[0088] In the third phase, once 80% of the tree stakes in the ecological barrier net 21 have grown to their design specifications, the auxiliary netting will be removed in batches. Shrubs and grasses 22 will be replanted in their place. Protective netting will be stretched between tree stakes that have reached their design specifications. The pre-installed netting will be removed, maintaining a predominantly shrub-based structure within the ecological barrier net 21. The timing of the auxiliary netting's removal will be determined based on the subsequent growth of the tree stakes. Once the tree stakes have reached their design specifications and the ecological barrier net 21's protective netting has been stretched, it can be removed.

[0089] Example 2

[0090] The design parameters of the debris flow fan ecological and geotechnical measures coordinated siltation prevention system in Example 1 are recalculated. The difference is that the design values of the model are calculated according to the formula 1 for each structure. H d When the workload of determining the independent variables of the model of formula 1 directly from the basic data is reduced, the model of formula 2 and formula 3 is introduced to complete the H d Value calculation.

[0091] For structures, separate the structure from the entrance section of the accumulation fan. α The vertical distance (abbreviated as section) α Vertical separation L x , entrance section α mud depth h α =2m, L = 1200m Substitute into the model in formula 3 to calculate the debris flow depth at the structure h ;Will h 、 I =8°, d 2mm =25%, w s =0.5758Substitute into the model in formula 2 to calculate the resistance coefficient of debris flow at the structuren -1 Debris flow velocity U ; g, U, h 、 I, φ =30ºSubstitute into the model in formula 1 and calculate the structure H d (Table 4).

[0092] For the geotechnical retaining net 12, according to H 12 and a 112 , and then recalculate according to formula 4 w n12 ,have w n12 =max(2.4*1.27,2*6.4)=12.8 m.

[0093] For ecological barrier network 21 according to H d 、 δ 、 H b,i Then recalculate the height of each row of barriers according to formula 7 H 21 (Table 4).

[0094] Table 4 Partial data of each structure

[0095]

Claims

1. A debris flow fan ecological and geotechnical synergistic siltation prevention system, characterized by: Including the direction of flow along the entrance of debris flow x The geotechnical measures section (1), ecological geotechnical combined measures section (2), and ecological measures section (3) are arranged; The geotechnical measures section (1) is provided with a diversion pier (11) in the upstream area and a geotechnical retaining net (12) in the downstream area. The geotechnical retaining net (12) is arranged in a basket shape with its opening facing the diversion pier (11). The diversion pier (11) is located in the middle of the upstream area and is a steel-concrete columnar pier with a fan-shaped cross section. The head (111) is narrower than the tail (112), and the head (111) faces the entrance of the accumulation fan. The geotechnical retaining net (12) arranged in a basket shape includes three parts, which are respectively located at the rear position and two side rear positions of the diversion pier (11). The rear position geotechnical retaining net (12a) faces the diversion pier (11), and the side rear position geotechnical retaining net (12b) faces the diversion direction on both sides of the diversion pier (11). The vertical distance between the downstream end pile (121) of the side rear position geotechnical retaining net (12b) and the rear position geotechnical retaining net (12a) is 100%. d 1>0; The ecological geotechnical combined measures section (2) along x Multiple rows of ecological barrier nets (21) are arranged at intervals in the direction, and the ecological barrier nets (21) in each row are arranged at intervals and the front and rear rows are staggered. The height of each row of ecological barrier nets (21) is along the x Direction down, aperture along x The direction is lowered and reduced, and shrubs and grasses are arranged at the bottom of the bed (22); The rock and soil retaining net (12) or the ecological retaining net (21) is a pile-and-net structure, with a protective net stretched between the piles. The piles of the rock and soil retaining net (12) are steel-concrete piles, and the piles of the ecological retaining net (21) are trees. The ecological measures section (3) is to arrange bushes in a dispersed manner and plant grass between the bushes.

2. The debris flow fan ecological and geotechnical measures coordinated siltation prevention system according to claim 1 is characterized by: The blocking height of the structure H Not less than the model design value calculated using formula 1 H d The structure is a diversion pier (11) or a rock and soil retaining net (12) or an ecological retaining net (21), and the retaining height of the structure is H are the heights of the diversion pier (11) H 11 、Geotechnical retaining net (12) Height of protective net H 12 、Ecological barrier net (21) Protection net height H 21 , Formula 1 Where, H d - Model design value of structure height, in m, U - Debris flow velocity at the structure, in m / s, determined based on basic engineering data. g - Gravitational acceleration constant, unit: m / s 2 , ε -Structure diversion stress coefficient, dimensionless, F r - Froude number of debris flow at the structure, dimensionless, φ - The bottom friction angle of debris flow when it moves in the accumulation fan, unit is °, determined according to the basic engineering data. h - Depth of debris flow at the structure, in meters, determined based on basic engineering data. I - The natural slope of the accumulation fan, in degrees, is determined based on basic engineering data.

3. The debris flow fan ecological and geotechnical measures coordinated siltation prevention system according to claim 2 is characterized by: The rock and soil barrier net (12) or ecological barrier net (21) H d In the design, the debris flow velocity U Determine according to formula 2, Formula 2 Where, n -1 - Resistance coefficient of debris flow at the structure, dimensionless, w s - Debris flow solid particle concentration, dimensionless, determined based on engineering basic data, d 2mm - The percentage of particles with a diameter less than 2 mm in the full-size particle distribution curve of debris flow, %, is determined based on basic engineering data.

4. The debris flow fan ecological and geotechnical measures coordinated siltation prevention system according to claim 3 is characterized by: The rock and soil barrier net (12) or ecological barrier net (21) H d In the design, the depth of debris flow h Determine according to formula 3, Formula 3 Where, h α - Depth of debris flow at the entrance section of the accumulation fan, in meters, determined based on basic engineering data. L x - The vertical distance between the structure and the entrance section of the accumulation fan, in meters, for the geotechnical retaining net (12), L x The distance between the downstream end pile (121) and the inlet section of the accumulation fan is determined based on the basic engineering data. L - Accumulation fan length, in meters, is determined based on basic engineering data.

5. The debris flow fan ecological and geotechnical measures coordinated siltation prevention system according to any one of claims 1 to 4, characterized in that: The cross section of the diversion pier (11) is in the shape of a disc cam, and the curvature of the head (111) is greater than the curvature of the tail (112); the width of the protective net of the rock and soil retaining net (12) is w n12 Determine according to formula 4, Formula 4 Where, a 112 - Length of the arc chord of the tail (112), in meters.

6. The debris flow fan ecological and geotechnical measures coordinated siltation prevention system according to claim 5 is characterized by: The cross section of the diversion pier (11) is centered on the axis l Symmetrical, with the side (113) and the central axis l Angle θ =15°~35°, length of arc chord of head (111) a 111 , chord-center distance b 111 , the tail (112) arc chord length a 112 , chord-center distance b 112 , respectively determined according to formula 5 and formula 6, Formula 5 Formula 6 Where, γ - The coefficient of the diversion pier's anti-overturning width is dimensionless and is determined based on the project requirements or can be set at 1 / 20 to 1 / 30. w α - Cross-sectional width of the accumulation fan entrance, in meters, determined based on basic engineering data; The side and rear azimuth rock and soil retaining net (12b) is aligned with the central axis l Angle β =30°~60°, the distance d 1 for 2 a 112 , the downstream end pile (121) is aligned with the central axis l Vertical distance of extension line d 2 for 2 a 112 .

7. The debris flow fan ecological and geotechnical measures coordinated siltation prevention system according to any one of claims 1 to 4, characterized in that: Single row ecological barrier net (21) barrier height H 21 According to formula 7, the total width of the protection net of a single row of ecological barrier net (21) is determined as follows: w n21 Determine according to formula 8, Formula 7 Formula 8 Where, δ - Single row design ecological transmittance, ranging from 0 to 1, H b,i - Stake tree species during the debris flow recurrence period i Corresponding diameter at breast height H b , unit m, determined according to basic engineering data, λ - total blocking rate of single-row design, ranging from 0.3 to 0.5, W j - The width of the accumulation fan at the horizontal line where the ecological barrier net (21) is located, in meters, is determined based on the basic data of the project.

8. The debris flow fan ecological and geotechnical measures coordinated siltation prevention system according to any one of claims 1 to 4, characterized in that: The length of the geotechnical measures section (1) is not less than 2 / 5 L , Ecological geotechnical combined measures section (2) length not less than 2 / 5 L The distance between the front end of the head (111) of the diversion pier (11) and the inlet section of the accumulation fan is not less than 1 / 10 L A prestressed component (114) is installed on the flow-facing surface of the head (111).

9. The debris flow fan ecological and geotechnical measures coordinated siltation prevention system according to any one of claims 1 to 4, characterized in that: The blocking performance of the rock and soil blocking net (12) is determined according to the characteristic particle size of the debris flow in the accumulation fan. d 80 Design, the blocking performance of each row of ecological barrier nets (21) is d 80 On a decreasing basis.

10. The debris flow fan ecological and geotechnical measures coordinated siltation prevention system according to any one of claims 1 to 4, characterized in that: The ecological rock and soil combination measure section (2) is laid out in stages: in the first stage, the ecological barrier net (21) is constructed in the early stage using the original trees or transplanted trees or planted trees, and the preset protection net is stretched according to the anti-impact and anti-pullout mechanical properties of the tree piles. Auxiliary protection nets are arranged in front of each row of ecological barrier nets (21), and shrubs (22) dominated by herbs are arranged at the bottom of the bed of the ecological rock and soil combination measure section (2), and energy dissipation piers are dispersedly arranged in the shrubs (22); in the second stage, from the maturity of the shrubs (22), the energy dissipation piers are moved in batches. In addition to the energy dissipation piers, shrubs and grasses (22) are replanted in the original position of the energy dissipation piers to increase the proportion of shrubs in the shrubs and grasses (22); in the third stage, after 80% of the tree piles of the ecological barrier net (21) have grown to the design specifications, the auxiliary protection nets are removed in batches, and shrubs and grasses (22) are replanted in the original position of the auxiliary protection net piles. The protection nets are stretched between the tree piles that have grown to the design specifications, and the preset protection nets are removed to maintain the shrubs and grasses (22) as the dominant shrub; the height of the auxiliary protection net is not less than the height of the protection net of the ecological barrier net (21) behind it.

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