WO2021253824A1

WO2021253824A1 - Bridge pier scour protection method combining concave normal surface of revolution and particle material

Info

Publication number: WO2021253824A1
Application number: PCT/CN2021/072817
Authority: WO
Inventors: 孙志林; 董海洋; 孙逸之
Original assignee: 浙江大学
Priority date: 2021-01-12
Filing date: 2021-01-20
Publication date: 2021-12-23
Also published as: CN215562387U

Abstract

A bridge pier scour protection method combining a concave normal surface of revolution and a particle material. The method is used for protection against pier foundation scour in a sea-crossing or river-crossing beam bridge. When a scour pit in the local region surrounding the bottom of a bridge pier or a bridge column reaches a set depth, a concave normal surface-of-revolution protective structure is laid out, and a particle material of a specific thickness is laid out in the interior of the concave normal surface-of-revolution protective structure. The present protection method organically combines the defense against underscour water flow by a normal surface structure in a scour pit with the weakening of horseshoe vortexes by a particle material layer. The normal surface structure is mainly used to defend against underscour water flow in front of a pier, and the particle material layer is able to weaken horseshoe vortexes around the pier. During bridge use, the present protection system is able to decrease underscour flow and the energy of horseshoe vortexes around bridge piers and reduce local scour, thus having an effective protective effect on bridge pier foundations and being effective for protecting the foundations of partially-submerged constructions.

Description

Bridge pier scour protection method combined with concave rotating normal surface and bulk particles

Technical field

The invention belongs to the field of partial scour protection of bridge foundations, and in particular relates to a bridge pier scour protection method combining a concave rotating normal curved surface and a bulk body.

Background technique

The local scour around the piers of cross-sea (river) bridges has a great impact on the safety of the bridge foundation and is the main cause of bridge damage. Bridge collapses caused by local scour around the piers accounted for more than half of the total. Therefore, it is very important to effectively and adequately protect the local scour of the bridge piers.

There are three reasons for the local scour of the bridge piers by water flow: (1) The blocking of the bridge piers causes the surrounding flow velocity to increase, which means that when the flow encounters obstacles, the cross-sectional area of the water passing through decreases, causing the local flow velocity to increase, and the bed surface is scoured by sediment. Pit; (2) Downflushing water flow erodes the bed surface, mainly refers to the forward flow of water hitting the bridge piers to form a downwashing water flow, which produces a strong erosion effect on the bed surface; (3) Horseshoe vortex scouring, mainly refers to when the water flow bypasses obstacles The formed horseshoe-shaped vortex swept away part of the sand around the pier.

The local scour protection measures of bridge piers are mainly divided into two categories: (1) Active protection. To reduce the scouring energy of the water flow on the piers, that is, to weaken the downflow and the horseshoe vortex flow in the scouring process of the water flow. Measures such as enlarging the foundation plane of the piers or setting foot guards are usually adopted to reduce the scouring energy of the water flow. (2) Passive protection. To improve the anti-scouring ability of the bottom bed near the bridge pier, usually by throwing rocks or twisting the king block around the foundation of the bridge pier, in an attempt to improve the anti-scouring ability of the bridge pier.

Existing protection measures have disadvantages such as high cost, poor protection effect, and inability to effectively resist typhoon storm surges and other disastrous marine environments. The active protection measures that expand the top surface of the pier foundation can resist the downwashing flow under normal currents. However, under extreme hydrodynamic environments, the bed surface is severely scoured and descends, causing the pier foundation to be completely exposed on the bed surface, thus facing the bridge pier foundation. A stronger downwash is formed on the stream surface, which leads to more serious local scour. The opening of the pier body can weaken the strength of the horseshoe-shaped vortex. If there are more openings, the strength of the pier will be lowered. If there are few openings, the effect will be poor. The openings may also be blocked by floating objects. When the flow direction of the bridge pier is inconsistent with the direction of the opening due to rotating flow or mainstream swing, the opening of the seam will lose its protective effect.

Ripple protection has always been the most widely used form of passive protection for large and medium-sized bridge piers. It has disadvantages such as enhanced eddy current, poor protection effect, large operation and maintenance costs and workload. Especially under the action of extreme hydrodynamic force, a strong vortex is formed around the riprap, which intensifies the erosion of the vortex on the bed surface. Not only does it fail to protect, it may even have the opposite effect.

Summary of the invention

In view of the shortcomings of the prior art, the present invention proposes a method for protecting bridge piers from erosion by combining a concave rotating normal surface with granular bodies. The specific technical solutions are as follows:

A method for pier scour protection combined with a concave rotating normal surface and bulk particles. The method is used to protect the foundation scour of bridge piers across the sea or river. When the local scour pits around the bottom of the pier or bridge pile reach a set depth , Lay a concave rotating normal surface protection structure, and pave a specific thickness of granular body inside the rotating normal surface protection structure.

Further, the normal curved protection structure is a section of rotating normal curved shell with a thickness of a. The point of intersection between the center of the pier and the unwashed river bed plane is the origin, the water flow direction is the positive direction of the x-axis, and the horizontal plane is perpendicular to the The direction of the water flow is the y-axis, and the pier axis downward is the positive direction of the z-axis, then the inner surface of the normal curved shell is a curved surface that satisfies the following equation:

Among them, x, y, z are the coordinates of the points on the inner surface of the normal curved shell, and l is the gap distance between the inner surface of the normal curved shell and the surface of the pier after the normal curved shell is sleeved on the pier; σ is the scouring pit The range-related variance value, h ₀ is the distance from the upper part of the normal curved shell to the bed surface. The bottom of the normal curved surface is located at mh _b below the bed surface, where h _b is the depth of the maximum erosion pit, m=0.7～0.9.

Further, the ratio λ of the thickness Δh of the granular body layer to the maximum depth h _b of the scour pit satisfies the following conditions:

Among them, G'is the equivalent gravity of the granular particles; F _w is the water flow force; μ is the friction coefficient of the scouring pit bed surface; L is the length of the scouring pit; Angle, ρ _w is the water density.

Further, the normal curved surface protection structure further includes a cylindrical sleeve-shaped base inserted into the river bed for fixing the normal curved shell, the thickness of which is the same as that of the normal curved shell, and the inner surface of the base meets the following requirements relation:

Further, a = 0.1 to 0.3 m, and h _c = 1 to 2 m.

Furthermore, the particle size d of the granular particles is 3 to 5 times the initial particle size of the sediment under the extreme velocity of the local natural conditions.

The beneficial effects of the present invention are as follows:

The main cause of local scouring around the bridge piers is the downwash and the horseshoe vortex. The protection system of the present invention organically combines the normal curved surface structure in the scour pit to resist downwashing water flow with the weakened horseshoe-shaped vortex of the granular body layer. The normal curved surface structure is mainly used to resist the downwashing current in front of the pier, and the granular body layer can reduce the bridge pier. Horseshoe vortex around. The protection system can reduce the energy of downwashing and horseshoe vortex around the pier during the use of the bridge, reduce local scour, and effectively protect the foundation of the pier.

Description of the drawings

Figure 1 is a diagram of the force on the granular body on the slope;

Figure 2 is a side view of the local scour protection around the bridge pier combined with a concave normal curved surface and granular body.

Figure 3 is a top view of the local scour protection around the bridge pier combined with the concave rotating normal surface and the granular body.

detailed description

The following describes the present invention in detail based on the accompanying drawings and preferred embodiments. The purpose and effects of the present invention will become more apparent. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention.

First, introduce the force of the granular body in the pier scour pit. As shown in Figure 1, the force of the granular particles on the surface of the scouring pit can be simplified as: gravity, bed resistance, buoyancy, and water flow.

Granular body weight:

buoyancy:

Effective gravity: G'=GF _T

Hydrodynamics:

A is the waterfront area:

C _D is the thrust coefficient;

River bed resistance: f ₁ -the friction force that the particles receive at the bottom of the scour pit

f ₂ -The friction force of the particles on the slope of the scouring pit

d is the diameter of the granular body; u is the water flow velocity; ρ is the density of the granular body; ρ _w is the water density; g is the acceleration of gravity, which is taken as 9.8N/kg.

According to the field observation data of the cross-sea bridge, in the strait and estuary environment dominated by tides, the length of the scour pits before and after the pier is basically the same, and the angle between the slopes of the scour pits of the front and rear ends and the horizontal direction is also roughly the same, as shown in Figure 2, which is the invention The pier scour protection device combined with the concave rotating normal curved surface protection structure and the granular body. When the local scour pit around the bottom of the pier or bridge pile reaches the set depth, the concave rotating normal curved surface protection structure is laid and the rotating normal surface is rotated. A specific thickness of granular material is laid inside the surface protection structure. The rotating normal curved surface protection structure is a section of rotating normal curved shell with a thickness of a. The following specifically introduces the shape of the pier scour protection device.

Further, the normal curved surface protection structure is a section of a rotating normal curved shell with a thickness of a, the bottom of the normal curved surface is located mh _b below the bed surface, and h _b is the maximum erosion pit depth, m=0.7-0.9. Taking the point of intersection between the center of the pier and the plane of the unwashed river bed as the origin, the direction of water flow is the positive direction of the x-axis, the horizontal plane perpendicular to the direction of the water flow is the y-axis, and the pier axis downward is the positive direction of the z-axis, then the normal surface The inner surface of the shell is a curved surface that satisfies the following equation:

After the scouring pit is formed, the normal curved structure is sunk into the scouring pit. Due to its own weight, the structure will compact the silt in the pit and fix it on the surface of the scouring pit.

Furthermore, in order to enable the rotating normal curved surface protection structure to be firmly fixed, a section of cylindrical sleeve-shaped base is continuously provided at the lower end of the rotating normal curved surface protection structure, and inserted vertically downward into the deposition layer, thereby rotating the normal curved surface The protective structure is fixed on the river bed at the bottom of the scour pit. The normal curved surface protection structure also includes a cylindrical sleeve-shaped base inserted in the river bed for fixing the normal curved shell, the thickness of which is the same as that of the normal curved shell, and the inner surface of the cylindrical sleeve-shaped base satisfies the following relationship:

When the base is set, h _c is the depth at which the rotating normal curved protection structure is inserted into the bottom of the river bed. Further, a = 0.1 to 0.3 m, and h _c = 1 to 2 m.

Figure 3 is a top view of the protective structure and granular bodies. The particle size d and thickness Δh of the laid granular material are determined by the calculation method of the starting flow velocity of the granular material slope and the force analysis of the granular material on the normal curved surface to play the most effective protective effect. On the one hand, the particle size d and laying thickness Δh of the granular body ensure that the granular body will not be moved out of the scouring pit, and on the other hand, it can avoid the abrasion of the structure by the granular body. There is a certain gap between the normal curved structure and the bridge pier to avoid impact force on the bridge pier. Therefore, the thickness of the granular body layer is determined in the following way:

If it is ensured that the particles will not be washed away from the protective structure, it should be satisfied: before the granular particles are washed to the edge of the normal curved protective structure, the speed should be reduced to zero and fall back to the bottom of the scour pit, that is, the water flow and buoyancy are positive. The sum of work is less than the sum of negative work done by gravity and surface resistance. In addition, suppose the original maximum scouring depth is h _b , the water flow velocity u, the bridge pier diameter is D, and μ is the resistance coefficient of the scouring pit granular layer surface. The thickness of the laid granular layer is Δh=λh _b , the particle size is d, and the water flow velocity under extreme hydrodynamic conditions is u ₂ . That is, W _Fw + W _FT ≤ W _G + W _f

Organize, get:

Preferably, the particle size of the granular particles used is 3 to 5 times the initial particle size of the sediment under the extreme flow velocity under local natural conditions (without bridge construction).

The pier scour protection device with the combination of the concave normal curved surface and the granular body of the present invention is laid in the local scour pit around the bridge pier, and uses the granular body gap to eliminate vortex and the movement of the granular body on the slope to consume the vortex energy to reduce the surrounding area of the bridge pier. The turbulence of the water flow and the strength of the horseshoe vortex reduce the erosion effect of the horseshoe vortex on the bridge pier and its protective structure. The gap between the granular bodies can reduce the wake vortex around the bridge piers and effectively absorb the horseshoe vortex energy; at the same time, the granular bodies will move diagonally away from the pier along the normal curved surface under the action of downwashing current, and then fall back under the action of gravity. Converting the kinetic energy of the water flow into the kinetic energy and potential energy of the granular body can further consume the energy of the downwash and the horseshoe vortex. The weight of the granular layer increases, and the normal curved surface structure compacts the sediment below it, which helps to maintain the stability of the protective structure.

For other wading buildings, the corresponding curved structures and granular bodies can be designed with reference to the protection method provided by the present invention. The present invention has a guiding effect on the erosion protection of the foundation of wading buildings.

Those of ordinary skill in the art can understand that the above descriptions are only preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, for those skilled in the art, they can still The technical solutions recorded in the foregoing examples are modified, or some of the technical features are equivalently replaced. All modifications and equivalent substitutions made within the spirit and principle of the invention shall be included in the scope of protection of the invention.

Claims

A method for scouring protection of bridge piers combined with a concave rotating normal surface and bulk particles is characterized in that the method is used for the protection of the scouring of the bridge pier foundations of cross-sea or river-crossing bridges. After setting the depth, lay a concave rotating normal surface protection structure, and pave a specific thickness of granular body inside the rotating normal surface protection structure. The bottom of the normal curved surface is located at mh b below the bed surface, where h b is the depth of the maximum erosion pit, m=0.7～0.9.
The pier scour protection method combined with a concave rotating normal curved surface and granular body according to claim 1, wherein the normal curved surface protection structure is a section of rotating normal curved shell with a thickness of a. The point of intersection between the center of and the unwashed river bed plane is the origin, the direction of the water flow is the positive x-axis direction, the horizontal plane perpendicular to the direction of the water flow is the y-axis, and the axis of the bridge pier downwards is the positive z-axis direction, then the normal curved shell The inner surface of is a curved surface that satisfies the following equation:

Among them, x, y, z are the coordinates of the points on the inner surface of the normal curved shell, and l is the gap distance between the inner surface of the normal curved shell and the surface of the pier after the normal curved shell is sleeved on the pier; σ is the scouring pit The range-related variance value, h 0 is the distance from the upper part of the normal curved shell to the bed surface.
The method for protecting bridge piers against erosion by combining a concave rotating normal surface with granular bodies according to claim 2, wherein the ratio λ of the thickness of the granular body layer Δh to the maximum depth of the scouring pit h b satisfies the following conditions:

Effective gravity of granular particles: G'=GF T

Granular body weight:

buoyancy:

Hydrodynamics:
A is the waterfront area:
C D is the thrust coefficient;

Among them, F w is the water flow force; μ is the friction coefficient of the scouring pit bed surface; L is the length of the scouring pit; α, β are the angles between the slope and the horizontal plane before and after the scouring pit, and ρ w is the water density.
The pier scour protection method combined with a concave rotating normal curved surface and granular bodies according to claim 3, wherein the normal curved surface protection structure further comprises inserting into a river bed for fixing the normal curved shell The thickness of the cylindrical sleeve-shaped base is the same as that of the normal curved shell, and the inner surface of the base satisfies the following relationship:

h c is the height of the cylindrical sleeve-shaped base.
The method for scouring protection of bridge piers combined with a concave rotating normal surface and granular bodies according to claim 4, characterized in that a = 0.1 to 0.3 m, and h c = 1 to 2 m.
According to claim 4, the method for protecting bridge pier erosion by combining a concave rotating normal surface with bulk particles is characterized in that the particle size d of the bulk particles is 3% of the initial particle size of the sediment under the action of extreme flow velocity under local natural conditions. ~ 5 times.