Cylindrical pier anti-scouring device suitable for unidirectional flow

Abstract

The cylindrical bridge pier anti-scouring device comprises a cylindrical bridge pier arranged in a river channel, a plurality of flow guide sheets are arranged around the cylindrical bridge pier in an up-down parallel mode at equal intervals, and the flow guide sheets are oval flow guide sheets fixed to the cylindrical bridge pier. The long-axis ends of the oval flow guide sheets face the river water flow direction, and the distance width between the outer side vertexes of the oval sheets in the long-axis direction and the pier face is 3-4 times of the distance width between the outer side vertexes of the oval sheets in the short-axis direction and the pier face. According to the anti-scour device provided by the invention, a group of parallel flow guide sheets are mounted on the cylindrical pier, so that three-dimensional flow near the pier can be effectively converted into planar two-dimensional flow, vortex generation is reduced, hydrodynamic conditions for scour of a riverbed can be obviously reduced, scour around the pier is obviously reduced, and the safety performance of a bridge is improved; and the pier scouring protection cost is greatly reduced, the market application prospect is wide, and the social and economic benefits are huge.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of anti-scour of river-crossing piers, and in particular to an anti-scour device for cylindrical piers suitable for unidirectional flow. BACKGROUND

[0002] China is a big country of bridges, and the total number of highway bridges has exceeded 1.1 million by 2024. However, the problem of water damage seriously threatens the safety and durability of river-crossing bridges. Studies have shown that water damage is one of the main factors leading to bridge damage. According to incomplete statistics, among the 102 damaged bridges in China from 2007 to 2015, 44 were caused by water damage, accounting for 43.1%. The main technical means to solve the problem of pier scour at present is to estimate the local scour range and maximum scour depth of the pier first, and then to protect the bridge foundation accordingly, that is, to admit that pier scour is inevitable and to take passive protection. This passive protection method is large in engineering quantity, high in cost, and cannot fundamentally solve the problem of pier scour. Whether it is possible to find a protective measure to prevent or at least significantly slow down pier scour, improve the safety performance of bridges, and reduce the protection cost is a major technical problem that needs to be solved in the protection of pier scour.

[0003] Pier scour is mainly caused by the complex flow around the pier. The flow field around the pier presents a complex three-dimensional structure, and its hydrodynamic characteristics are mainly composed of the following three parts: 1) the water flow forms two jets after being blocked on the pier face, among which the upward jet produces surface cyclone, and the downward jet directly scours the riverbed; 2) the downward jet and the incoming flow superimpose near the bed surface to form a horseshoe vortex structure, which scours the riverbed; 3) the boundary layer separates on both sides of the pier tail, and then a tail vortex is generated, which scours the riverbed. This complex flow field characteristic is the core mechanism leading to local scour of the pier and is also a problem that needs to be solved in the design of protection.

[0004] At present, the pier scour protection technology can be mainly divided into passive protection and active protection.

[0005] The technical route of passive protection is: first, admit that pier scour is inevitable, then predict the scour pit range and maximum possible scour depth of the pier by experiment or numerical simulation or empirical formula, and then protect the riverbed around the pier by increasing the pier depth, expanding the pier foundation volume, throwing stones, stone cage sinking, concrete mold bag, etc. to avoid the scour of the bed surface around the pier. Although the passive protection technology is relatively mature, it is large in engineering quantity, poor in integrity, high in investment, and high in maintenance cost in the later period. Under the action of long-term scouring of clear water or short duration and high intensity of flood scouring, the riverbed outside the pier protection range may be scoured and cut down obviously, leading to the overall collapse of the protection structure and threatening the safety of the bridge.

[0006] The main technical approach of active protection is to minimize scour near bridge piers. This is achieved by altering the flow field structure around the piers, weakening the scouring effect of downward jets and eddies on the riverbed, thereby effectively reducing localized scour around the piers and lowering investment in protective engineering. Typical active protection technologies include horizontal retaining rings, pier joints, pier-front piles, foundation caissons, and embedded sand retainers. While these active protection measures offer some scour prevention, they still face several challenges and problems. 1. Some applications have limitations: For example, horizontal retaining rings only physically isolate the bed sediment from the water flow. Although they can prevent the downstream water flow in front of the pier from scouring the bed sediment, once the riverbed itself is scourted down, the retaining ring becomes suspended and cannot play its anti-scour role. Horizontal retaining rings are effective in protecting piers on non-scour riverbeds, but are not suitable for scour-prone riverbeds.

[0007] 2. Some designs are complex, difficult to construct, and costly: For example, the installation of foundation caissons and buried sand retaining barriers requires underwater construction or large equipment, which is difficult to carry out, costly, and difficult to maintain. Furthermore, measures such as pier openings and front-pier piles significantly alter the normal bridge design, making the hydrodynamic conditions near the piers more complex, increasing construction costs and difficulty.

[0008] To address the above issues, there is an urgent need to develop an anti-scour device suitable for cylindrical bridge piers that can effectively mitigate pier scour, improve bridge safety performance, is relatively simple to construct, and has low cost. Summary of the Invention

[0009] The purpose of this invention is to provide a cylindrical bridge pier anti-scour device suitable for unidirectional flow, which can effectively transform three-dimensional flow into two-dimensional planar flow and reduce the generation of eddies; it can reduce the pier burial depth, reduce the base volume, reduce the protection range of the bed surface near the pier, improve the safety performance of the bridge, reduce the engineering cost, and at the same time, it can effectively solve the problem of difficult later maintenance.

[0010] To achieve the above objectives, the present invention provides a scour prevention device for cylindrical bridge piers suitable for unidirectional flow, comprising a cylindrical bridge pier placed in a river channel, wherein multiple flow-guiding thin plates are arranged parallel to each other and at equal intervals around the cylindrical bridge pier, with at least one flow-guiding thin plate remaining below the riverbed surface and at least three plates remaining above the riverbed surface. The flow-guiding thin plates are elliptical flow-guiding thin plates fixed to the cylindrical bridge pier, with one end of the major axis of the elliptical flow-guiding thin plate facing the direction of the river flow. The distance between the outer vertex of the major axis of the elliptical flow-guiding thin plate and the bridge pier surface is 3 to 4 times the distance between the outer vertex of the minor axis of the elliptical flow-guiding thin plate and the bridge pier surface. The distance between the outer vertex of the major axis of the elliptical flow-guiding thin plate and the bridge pier surface is 1 / 4 to 1 / 2 times the diameter of the cylindrical bridge pier. The distance between the upper and lower flow-guiding thin plates is 1 / 4 to 1 / 2 the diameter of the cylindrical bridge pier.

[0011] The solution further includes: two of the multiple guide sheets are below the riverbed surface, and four are above the riverbed surface.

[0012] A further aspect of the solution is that the multiple flow-guiding sheets are arranged horizontally parallel to each other and at equal intervals.

[0013] A further aspect of the solution is that the flow-guiding sheet is a stainless steel sheet or an acrylic sheet.

[0014] A further step in the solution is that the flow-guiding sheet is fixed to the cylindrical bridge pier by anchor bolts.

[0015] This invention has the following effects and application value: (1) This invention involves installing a set of parallel flow-guiding plates on a cylindrical bridge pier, which can transform the strong three-dimensional flow and eddies near the pier into an approximately planar two-dimensional flow, significantly reducing the vertical downward flow's scouring effect on the riverbed and the eddies' erosion effect on the riverbed. This invention can reduce the pier's burial depth, reduce the pier's base volume, reduce the pier's protection range, and lower the project investment cost; this invention can significantly enhance the safety of the pier, reduce bridge damage, and extend the bridge's service life; the working principle of this invention is clear, the device itself has a small load, low cost, quick and convenient construction, and low subsequent maintenance cost.

[0016] (2) This invention is applicable to the scour protection of newly built bridge piers, as well as the compensatory protection of the scour of existing bridge piers, and is even more applicable to the scour protection of offshore wind power pile foundations, with broad prospects for promotion.

[0017] The invention will be further explained in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0018] Figure 1 A schematic diagram illustrating the erosion of a cylindrical bridge pier; Figure 2 This is a schematic diagram of the planar structure of the present invention; Figure 3 This is a schematic diagram of the front structure of the present invention; Figure 4 This is a schematic diagram of the anchor bolt connector of the present invention; Figure 5 This is a comparison chart showing the depth and extent of scour pits on bridge piers with and without the installation of guide plates. Detailed Implementation

[0019] Figure 1The illustration vividly depicts the different turbulent states formed by the scouring of cylindrical bridge piers by water flow. The main driving force for the scouring of bridge piers comes from the strong three-dimensional flow and eddies near the bridge piers. First, when the water flow encounters the obstruction of the bridge pier, it forms a vertically downward velocity component that directly scours the riverbed. Second, because the vertically downward velocity and the velocity along the direction of water flow are squeezed by the bridge pier and subjected to shape resistance, they form strong turbulence and eddies, thus scouring the riverbed.

[0020] To change the turbulent state of the water flow near the bridge piers, such as Figure 2 , Figure 3 and Figure 4 As shown in the figure, this embodiment provides an anti-scouring device for cylindrical bridge piers suitable for unidirectional flow, comprising a cylindrical bridge pier 1 placed in a river channel, wherein: multiple flow-guiding thin plates 2 are arranged parallel to each other and at equal intervals around the cylindrical bridge pier, with at least one flow-guiding thin plate remaining below the riverbed surface and at least three thin plates remaining above the riverbed surface. The flow-guiding thin plates are elliptical flow-guiding thin plates fixed on the cylindrical bridge pier, with one end of the major axis of the elliptical flow-guiding thin plate facing the direction 3 of the river flow. The distance B between the outer vertex 201 of the elliptical flow-guiding thin plate in the direction of the major axis and the bridge pier surface 101 is 3 to 4 times the distance b between the outer vertex 202 of the elliptical flow-guiding thin plate in the direction of the minor axis and the bridge pier surface. Furthermore, the distance B between the outer vertex 201 of the elliptical flow-guiding thin plate in the direction of the major axis and the bridge pier surface is 1 / 4 to 1 / 2 times the diameter D of the cylindrical bridge pier, and the distance h between the upper and lower flow-guiding thin plates is 1 / 4 to 1 / 2 the diameter of the cylindrical bridge pier.

[0021] Specifically: Two of the multiple flow-guiding sheets are below the riverbed surface, and four are above the riverbed surface. Furthermore: the multiple flow-guiding sheets are horizontally parallel to each other and equally spaced.

[0022] The flow-guiding sheet is made of stainless steel or plexiglass, and the stainless steel or plexiglass sheet is of uniform thickness and as thin as possible so as not to deform or vibrate under the action of water flow. For ease of installation, the flow-guiding sheet can be designed as two semi-elliptical rings.

[0023] The flow-guiding sheet is fixed to the cylindrical pier by anchor bolts 3. The anchor bolts 3 are bolts made of stainless steel or hot-dip galvanized high-strength bolts. Figure 4 As shown, the fixing connectors are positioned and drilled around the bridge piers, with 5-6 holes evenly spaced around each pier. After injecting colloid into the holes, bolts are inserted, and a high-strength connection is formed after curing. Perforated steel plates are fixed to the anchor bolts, and the flow-guiding sheets are fixed to the perforated steel plates.

[0024] During operation, the guide vanes are fixed to the bridge piers via fasteners, with the longer protruding portion facing the direction of the incoming flow. As the water approaches the piers, the parallel vanes installed on the piers act as guides, significantly reducing the vertically downward velocity component and transforming the three-dimensional flow into a two-dimensional planar flow. This significantly reduces the direct scouring of the riverbed by the downward jet. Simultaneously, the guide vanes near the riverbed help to maintain a laminar flow state on both sides and at the tail of the piers, reducing turbulence, eddies, and spiral flows, thereby mitigating the scouring effect of eddies on the riverbed. This is the working principle of the guide vanes in preventing pier scouring.

[0025] The scour-prevention effect of the flow-guiding plates: The scour-prevention effect of the flow-guiding plates has been verified through experiments. In the experiment, the pier height H was 20cm and the diameter D was 4cm. A total of 6 flow-guiding plates were installed in parallel on the pier, 2 below the bed surface and 4 above the bed surface. The main parameters of the flow-guiding plates were B=2cm, b=0.5cm, and h=2cm. For ease of comparison, while ensuring that the flow between the piers did not interfere with each other, the flow-guiding plates were installed on the left pier of the test flume, while no flow-guiding plates were installed on the right pier. Four flow conditions were applied in the experiment, with flow rates of 15L / s, 20L / s, 25L / s, and 30L / s; the bed sand particle size was 0.8~1.0mm. After the scour stabilized, the scour changes near the piers were observed.

[0026] The test results are as follows Figure 5 As shown, under different flow conditions, the scour depth and range of the pier equipped with the guide plate (left side) are significantly smaller than those of the pier without the guide plate (right side). Obvious scour pits appear on the upstream side of the pier without the guide plate, and the greater the flow rate, the deeper and larger the scour pits become. When the flow rate is 30 L / s, the scour around the pier is very intense, even threatening the stability of the pier. In contrast, no obvious scour pits appear on the upstream side of the pier equipped with the guide plate. Scour pits only appear on the upstream side when the flow rate reaches 30 L / s, but these are significantly smaller than those without the guide plate. This experimental result demonstrates that the guide plate can effectively improve the flow field structure around the pier, transforming strong three-dimensional flow into approximately two-dimensional flow, reducing vertically downward jets and eddies around the pier, thus playing a significant role in scour prevention. These experimental results can provide important theoretical and technical basis for the scour prevention design of cylindrical piers.

Claims

1. A scour prevention device for cylindrical bridge piers suitable for unidirectional flow, comprising cylindrical bridge piers placed in a river channel, characterized in that, Multiple flow-guiding thin plates are arranged parallel to each other and at equal intervals around the cylindrical pier. At least one flow-guiding thin plate is retained below the riverbed surface, and at least three are above the riverbed surface. The flow-guiding thin plates are elliptical flow-guiding thin plates fixed to the cylindrical pier. One end of the major axis of the elliptical flow-guiding thin plate faces the direction of the river flow. The distance between the outer vertex of the major axis of the elliptical flow-guiding thin plate and the pier surface is 3 to 4 times the distance between the outer vertex of the minor axis of the elliptical flow-guiding thin plate and the pier surface. The distance between the outer vertex of the major axis of the elliptical flow-guiding thin plate and the pier surface is 1 / 4 to 1 / 2 times the diameter of the cylindrical pier. The distance between the vertical flow-guiding thin plates is 1 / 4 to 1 / 2 the diameter of the cylindrical pier.

2. The anti-scouring device for cylindrical bridge piers according to claim 1, characterized in that, The multiple guide plates consist of two plates below the riverbed surface and four plates above the riverbed surface.

3. The anti-scouring device for cylindrical bridge piers according to claim 1, characterized in that, The multiple flow-guiding thin plates are horizontally parallel to each other and equally spaced.

4. The anti-scouring device for cylindrical bridge piers according to claim 1, characterized in that, The flow guide sheet is a stainless steel sheet or an acrylic sheet.

5. The anti-scouring device for cylindrical bridge piers according to claim 1, characterized in that, The flow-guiding sheet is fixed to the cylindrical pier by anchor bolts.

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