WO2024052259A1 - Sensor for detecting scour - Google Patents

Abstract

A sensor for detecting scour comprises a body adapted to be partially buried adjacent a submerged structure in a region of a riverbed expected to suffer from scour, a plurality of vertically spaced flexible fins extending from a downstream side of the body, said fins incorporating fibre Bragg gratings or other electrical based movement sensors, wherein, once a respective fin is uncovered due to the action of scour, movement of the respective fin due to vortices created by water flowing around the body to which the fin is attached is detected by the movement sensors embedded in the fin, thereby provided an indicated of the progression of the scour.

Description

Sensor for Detecting Scour

FIELD OF THE INVENTION

This invention relates to a sensor for detecting scour adjacent submerged structures.

BACKGROUND OF THE INVENTION

Scour is defined as the excavation and removal of material from the bed and banks of streams, rivers and marine environments as a result of the erosive action of flowing water. The erosion of sediment by scour at the base of bridge piers, abutments and other underwater structures is a major problem in civil engineering. Scour of bridge foundations in particular is a major cause of bridge instability and collapse. The high profile failure of the Malahide railway viaduct in Dublin was caused by foundation scour. While scour can occur slowly over time, flood events can cause rapid scouring, to the point of structure failure.

It is therefore desirable to provide a real time monitoring system to monitor scour adjacent submerged structures, and in particular bridge foundations.

Existing techniques for determining/monitoring scour include using a buried float coupled to a switch to that detects when the buried float become uncovered by scour, optical/sonar devices to measure depth in the expected location of scour adjacent a submerged structure, and the measurement of strain on buried rods, whereby bending of the rods once uncovered and exposed to the flow of water is detected by strain gauges. Other methods include the attachment of sensors to the bridge structure above water to detect global damage which may be an indicator of scour.

One known method of scour monitoring is to use a single use device including a float, possibly tethered to a switch, buried in a region of the bed or bank likely to experience scour, said float rising towards the surface when the action of scour causes the device to become uncovered and the float released. However, such single use devices cannot provide continuous monitoring of the progression of scour and typically require expensive installation and they give no indication of the maximum scour depth reached.

Other measuring systems use reflected optical, acoustic or electromagnetic signals to measure depth or obtain a geophysical profile of the river bed. However, such systems are expensive, cannot provide continuous monitoring and are difficult to use in harsh weather conditions and flooding. The initial calibration of such systems can also be problematic. In order to determine the properties of the surrounding material, a calibration of the sensors are required, so that the complex data output can be interpreted correctly. This typically involves expensive set up and ongoing costly testing of riverbed soil samples in a lab. When in operation, it is difficult to verify if the sensors are working correctly or if they are giving false readings of their surroundings. The effect of metal objects, which are often found under bridges, such as discarded bicycles, shopping trolleys and other debris, may also have an impact on the sensitivity of such sensors. Furthermore, such sensors may not work in salt water or brackish environments, limiting them to freshwater locations only.

It is also known to provide embedded sensors, for example elongate rods, incorporating strain gauges to detect induced bending of the sensor as it becomes partially exposed due to scour. Such devices have the benefit of being cheap and easy to fabricate and can perform well in monitoring the development of scour over time. However, they can be sensitive to vibrations due to flowing water or traffic excitation of the adjacent structure (e.g. a bridge) and may give false readings.

The ability to withstand debris damage in a natural river setting is also a major hurdle for real-time scour monitoring devices is the greatest hurdle. The effects of debris giving false readings or affecting the performance of the devices such as float based devices are well known. Many of these devices have an inability to provide real time data on the scour progression during a high flow event nor provide text alerts to asset owners. SUMMARY OF THE INVENTION

According to the present invention there is provided a sensor for detecting scour comprises a body adapted to be partially buried adjacent a submerged structure in a region of a riverbed expected to suffer from scour, a plurality of vertically spaced flexible fins extending from a downstream side of the body, said fins incorporating one or more sensors to detect movement, such as fibre Bragg gratings, strain gauges, crack gauges or similar, wherein, once a respective fin is uncovered due to the action of scour, movement of the respective fin due to vortices created by water flowing around the body to which the fin is attached is detected by the respective sensors, thereby provided an indication of the progression of the scour.

Preferably said body comprises a vertically arranged post adapted to be at buried in the riverbed. Said body may comprise a metal box section post. Said body may made from stainless steel. Electronic components of the sensor may be housed within the post. Said body may include a flat face on an upstream side thereof to encourage the formation of oscillating vortices on a downstream side of the body.

Each fin is preferably made from an elastomeric polymer having fibre Bragg gratings or other electrical based movement sensors embedded therein.

BRIEF DESCRIPTION OF THE DRAWINGS

A scour sensor in accordance with an embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a scour sensor in accordance with an embodiment of the present invention; and

Figures 2 to 4 illustrate the scour sensor of Figure 1 in use.

DETAILED DESCRIPTION OF THE DRAWINGS As illustrated in the drawings, a scour sensor 1 in accordance with an embodiment of the present invention comprises a substantially rigid body 2 in the form of a post adapted to be partially buried adjacent a submerged structure, such as a bridge support 10, in a region of a riverbed expected to suffer from scour, a plurality of vertically spaced flexible polymeric fins 4,6,8 extending from a downstream side of the body 2, said fins incorporating fibre Bragg gratings or electrical based movement sensors embedded therein or applied thereto, wherein, once a respective fin is uncovered due to the action of scour “S”, movement of the respective fin 4,6,8 due to vortices created by water flowing around the body 2 to which the fin 4,6,8 is attached is detected by the movement sensors embedded in the fin, thereby provided an indication of the progression of the scour. Preferably an upstream side of the body 2 is defined by a substantially flat surface 3 arranged to extend transverse to the expected direction of water flow.

The sensor 1 can measure the progression of scouring in real time of riverbed material using the principal of vortex shedding of flowing water around a bluff body (i.e. around the post 2).

Scouring is the leading cause of bridge failure worldwide and bridges over water represent over 50% of the total bridge stock in Northern Ireland. Currently scouring is recorded if found during a routine scheduled bridge inspection or as a special inspection should a specific concern be raised about a bridge site. There are limited options for measuring scouring during the scour event, as by its nature they tend to be high flow situations when operatives are unable to safely assess/ measure the scour extents. As the high flow subsides, suspended material tends to in-fill the scouring thus potentially masking the true extents and severity. Often this means that the maximum scour experienced at a structure is not known or its likely response to future scouring events. This has been seen in some recent high profile bridge failures across the UK and Ireland.

A scour sensor in accordance with the present invention can reliably measure the presence of scouring near a bridge support in a river environment and provide early warning of scouring events in order to allow proactive response by the asset owner. This can help inform the asset owner on the structural stability of the bridge during high flow events and whether corrective action could be considered or closing the structure in the interests of public safety.

During the development of the sensor, a number of measurement methods were evaluated to attempt to identify the initial development scour within the sensor, including strain, bending, temperature and pressure measurements. In each case the methods were discounted due to unsuitability for harsh environmental conditions or vulnerability to false readings due to debris in the river.

The action of inserting a non-stream lined obstruction in flowing water results in oscillating vortices on the downstream side of the object. This novel approach of artificially producing such oscillating vortices on a downstream side of a post by means of flexible fins extending from said downstream side of the post to identify water flow in a scour hole provides a straightforward means of alerting asset owners to a scour event.

The bluff body/post 2 and rubber fins 4,6,8 may be geometrically optimised to force movement in the fin even at water low flow rate. The sensor exploits the generation of vortices downstream of the body 2 by using said rubber fins 4,6,8 embedded with movement sensors, such as Fibre Bragg Grating sensors (FBG), whereby the fins move with these vortices and such movement is detected by the movement sensors. The signals from the movement sensors may be received by electronics within the body adapted to translate the sensed movement of the or each fin into a signal output, for example on a digital display. The signals may be recorded over time to provide a record of the progression of scour. Wireless transmission means may be provided for transmitting data from the movement sensors to a remote location, such as to a mobile telephone.

When the fins 4,6,8 are buried, there is no movement registered in the fins. Should one or more of the fins 4,6,8 become exposed through the action of scouring, the flow of water around the body 2 and over the respective fin causes the exposed fin or fins to move and said movement is registered by the sensor. Should material in-fill the scour hole and burry the exposed fin or fins again, such fin will no longer move with the flow of water and will cease to register a response. This allows for a determination of the real time scour depth at the sensor location which is not dependant on any initial calibration of soil conditions.

The sensor 1 may be installed at areas known to be at risk of scour and to a depth at which trigger alerts can be linked in order to inform the asset owner if the scouring is posing a risk to the foundations of the structure.

The flow rate for a pre-determined movement of the or each fin may be established by testing to establish a correlation between the magnitude of change in flow rate and the initial occurrence of the scour event, thereby determining a link between flow rate and scour.

A scour senor in accordance with the present invention does not try to identify scour through changing structural performance of the bridge. Rather the scour sensor is installed in the river bed to identify the scour event before it causes damage to the bridge. The scour sensor may provide a real time record of scouring and infill events which is a limitation to many of the other more established methods employed to date.

Once installed, the scour sensor may track the progression of scour and provide advanced warnings of early scour events, thus allowing bridge asset owner to arrange for proactive measures to be deployed to prevent catastrophic damage to structures or enact emergency response plans (such as temporary road closures) in the interests of public safety.

A scour sensor in accordance with the present invention is relatively simple in its approach to output. If a fin is exposed to flow it will oscillate and provide a signal to indicate it is exposed. Once it is infilled and the fin stops moving, the signal stops. This does not require careful calibration of the soil conditions around it or ongoing calibration. Operatives carrying out scheduled bridge inspections with minimal training could verify if a sensor fin 4,6,8 of the scour sensor 1 is exposed or buried and compare that to a simple digital output showing ‘flow’ or ‘no flow’.

As the scour sensor does not rely on the dielectric properties of the surroundings it is unaffected by metal objects present or salt water environments meaning it can be deployed in any water environment.

The body 2 of the scour sensor may comprise a stainless steel box section post providing a robust defence against waterborne debris damage, such as floating trees during a flood event. The exposed rubber fins 4,6,8 attached to and extending from the post 2 are flexible enough to take impact damage and deflect back to shape without permanent damage. The movement sensors embedded in the fins 4,6,8 may be electrically connected to circuitry safely housed within the steel box section post 2 to minimise potential for damage.

The scour sensor 1 can be provide real time output on the development and infilling of scour and can allow for set trigger levels alert to inform asset owners that action may need to be taken at vulnerable structures. This sensor setup is not limited to fresh water environments as it is unaffected by salty marine water or metal debris which could be potentially found at these sites. There is less calibration required for setting up the sensors on site as they work on the principal of ‘Flow = exposed’ or ‘ No Flow = buried’ and as such are easier to interpret and check by bridge asset owners.

The invention is not limited to the embodiment described herein but can be amended or modified without departing from the scope of the present invention as defined by the appended claims.

Claims

1. A sensor for detecting scour comprises a body adapted to be partially buried adjacent a submerged structure in a region of a riverbed expected to suffer from scour, a plurality of vertically spaced flexible fins extending from a downstream side of the body, said fins incorporating movement sensors, wherein, once a respective fin is uncovered due to the action of scour, movement of the respective fin due to vortices created by water flowing around the body to which the fin is attached is detected by said movement sensors, thereby provided an indicated of the progression of the scour.

2. A sensor as claimed in claim 1 , wherein said movement sensors comprise fibre Bragg gratings or other electrical based movement sensors embedded within said fins.

3. A sensor as claimed in claim 1 , wherein said movement sensors comprise one or more strain gauges, crack gauges or other sensors capable of detecting movement of the respective fin.

4. A sensor as claimed in any preceding claim, wherein each fin is made from an elastomeric polymer having said movement sensors embedded therein.

5. A sensor as claimed in any preceding claim, wherein said body comprises a vertically arranged post adapted to be at buried in the riverbed.

6. A sensor as claimed in claim 5, wherein said body comprises a metal box section post.

7. A sensor as claimed in claim 6, wherein said body is made from stainless steel.

8. A sensor as claimed in any preceding claim, wherein electronic components of the sensor are housed within the post.

9. A sensor as claimed in any preceding claim, wherein the body includes a flat face on an upstream side thereof.