Portable Scour Monitoring Equipment (2004) / Chapter Skim
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Pages 5-40
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From page 5... ...
A search of various computer literature data bases did not identify many references on portable scour monitoring. Databases searched included the following: • The TRB TRIS, • The National Science Foundation, • The American Geophysical Union Water Resources Research, • The American Geophysical Union Earth and Space Index, • ASCE Publications, and • USGS Publications.
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From page 6... ...
Physical probes refer to any type of device that extends the reach of the inspector, the most common being sounding poles and sounding weights (1)
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From page 7... ...
to a remotely controlled articulated arm. Hand-held probes or arms are not generally useable at flood flow conditions.
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From page 8... ...
Tethered floats are a low-cost approach that has been used with some success during flood flow conditions. Various float designs have been proposed and used to varying degrees for scour measurements, typically to deploy a sonar transducer.
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From page 9... ...
The rapid changes and improvements in GPS technology, along with reduced cost, make this technology increasingly viable for portable scour measurements. For example, various manufacturers have a survey-grade, waterproof GPS receiver with a built-in antenna, memory, battery, and radio.
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From page 10... ...
FEASIBLE ALTERNATIVES The objective of this research was to develop improvements and/or alternatives to existing portable scour monitoring equipment and techniques for measuring stream bed elevations at bridge foundations during flood conditions. Under flood conditions, the velocity of flow, sediment transport, and air entrainment can be high; debris loading can be a problem; and various different bridge geometries will be 10 encountered by the inspector attempting to make these measurements.
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From page 11... ...
If a commercially available articulated crane from another industry, such as the construction materials industry, could be adapted for scour monitoring applications, a lower cost device might be possible. A towed acquisition vehicle, similar to that used in the offshore industry might be a viable approach for positioning a sensor when the device can be controlled from a boat upstream of the bridge or possibly using a crane off the bridge deck.
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From page 12... ...
However, the scour measurement can be referenced to the water surface elevation or a reference elevation on the bridge deck, with the GPS data used only for horizontal position. Therefore, if a local DPGS signal is available (e.g., from the NDGPS network or some other source)
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From page 13... ...
Ideally, the software would not only automate the data collection process, but also provide immediate access to the results, which could include a cross section plot or bathymetric map. PROTOTYPE DEVELOPMENT AND LIMITED TESTING Minnesota Boom Original Design Minnesota DOT developed an innovative boom and sounding weight system for scour depth measurements using a boom truck and a custom-fabricated winch setup.
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From page 14... ...
The final modification related to the readout from the wire rope counter. Initially, a speedometer cable was used to relocate the mechanical readouts of the wire rope counters to the instrument box on the flatbed.
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From page 15... ...
15 H Figure 6. Dimensioned drawing of Minnesota style winch.
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From page 16... ...
Application of winch concept on a nonarticulated crane.
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From page 17... ...
Mounting the Twinscope™ transducer for field testing.
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From page 18... ...
There are various manufacturers of articulated arm cranes. The first step in the investigation of feasible alternatives for use in a scour monitoring application was to contact various dealers across the country to obtain specific design and cost information.
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From page 19... ...
For purposes of scour monitoring, with no substantial weight being transported on the truck bed, a rear mount seemed advantageous. Based on the reach of the PK4501C crane, mounted with an offset to the center of the truck, the PK4501C has the capability to reach 21.25 ft (6.5 m)
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From page 20... ...
20 Figure 17. Reach below the bridge deck with the PK4501C crane on a Ford F-450 truck.
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From page 21... ...
An articulated crane provides a very stable platform to deploy scour measurement devices, but does not provide any positioning information without the addition of other sensors to track the movement of the crane. Therefore, a critical part of the articulated crane research was to develop a methodology to track the location of the end of the crane in a real-time mode as the crane was being operated.
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From page 22... ...
A computer with two serial ports was used to process the data from each data logger, sent as serial data strings. Knowing the rotation of the crane and the rotator, the deflection angles of the crane arm and rotator, and the extension of the crane arm 22 allowed geometrically calculating the position in space of the end of the rotator relative to the center pivot of the crane where it was mounted to the truck bed.
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From page 23... ...
To provide a serial data string, pulse counters were added to the wheel to register electronically the distance traveled. Scour Measurement Devices As developed, the instrumented, articulated crane could be used to position various scour measurement devices, both directly from the end of the crane and from cable-suspended methods using the winches.
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From page 24... ...
A third version was built with the rotation point moved forward, as well as being built with a longer extension that provide more reach with the crane arm and less chance of submerging the rotator and instrument box at the end of the crane (Figure 29)
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From page 25... ...
An accurate location of the sonar measurement could be calculated knowing the position of the end of the rotator, the length of the framework, the distance to the water surface, and the angle of the rotator. Cable-suspended operations with a sonar installed in a sounding weight were also tested.
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From page 26... ...
Low-Cost GPS Available GPS Receivers Research on low-cost GPS receivers was completed to evaluate their ability to provide position information for the truck and/or other related scour measurement technologies. Although GPS technology can provide accurate position information and has been used in scour measurement applications, its high cost and lack of ease of use limits its widespread application.
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From page 27... ...
A data string can also be output to a laptop using in-house software. Cost of the receiver and data logger are approximately $9,500.
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From page 28... ...
Although the GPS satellite constellation is described as being 28 in geosynchronous orbit, suggesting that the satellite coverage should not change with time, there are issues related to the time of measurement. GPS satellite orbits consist of 24 satellites that orbit the earth twice in a 24-hour period.
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From page 29... ...
as viewed looking up at the satellite orbits from Fort Collins, Colorado. Figure 38.
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From page 30... ...
Four programs were created: one for direct sonar measurements with the articulated arm, one for use with the kneeboard deployed on a rigid frame, one for direct probing, and one for cable-suspended operations. All programs produce an x,y,z data file that can be read by CAESAR (Cataloging and Expert Evaluation of Scour Risk and River Stability)
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From page 31... ...
Within the software, these coordinates were converted to "bridge" 31 coordinates, as defined by the profile line for the bridge. The profile line is a station-elevation line on the bridge plans, typically along the centerline of the bridge deck.
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From page 32... ...
DETAILED FIELD TESTING Objective The objective of detailed field testing was to evaluate the performance of the articulated arm truck at various sites, representing a range of bridge and site conditions with the assistance and/or cooperation of at least two local or state transportation agencies. The purpose of this testing was to validate the performance of the prototype devices and/or procedures under real-world conditions, as implemented by highway personnel.
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From page 33... ...
State River Bridge Date Colorado Colorado River I-70 near Debeque March 14 & 26, 2002 Alabama Heron Bay State Highway 193 April 3, 2002 Chickasaw Creek State Highway 213 April 3, 2002 Little Lagoon Pass State Highway 180 April 4, 2002 Minnesota Minnesota River State Trunk Highway 93 May 13, 2002 Wisconsin Wisconsin River State Trunk Highway 80 May 14, 2002 Missouri Grand River U.S. Highway 24 May 17, 2002 Indiana White River State Highway 61 May 22, 2002 Idaho Snake River Ferry Butte June 4, 2002 Shelley June 4, 2002 TABLE 5 Locations and dates of detailed field testing
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From page 34... ...
11 <2000 No No Medium Heron Bay at SH 193 NA <3 <100 No No Low Chickasaw Creek at SH 213 NA <3 <100 No No Low Little Lagoon Pass at SH 180 NA 3 <100 No No Low Minnesota River at STH93 7,460 cfs at USGS Gage 05330000 (20 mi upstream) <3 <500 No No Low Wisconsin River At STH80 22,900 cfs at USGS Gage 05407000 (located at bridge)
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From page 35... ...
Figure 41 shows the bridge from the upstream side, with Pier 2 on the right side where the articulated arm truck is parked. Flow conditions between Pier 2 and the right abutment are shown in Figure 42.
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From page 36... ...
extension on the end of the articulated arm and the ability of the fin to swivel freely and track the current on its own. This was also the first field test of a cross-section measurement by driving the truck with the castors down.
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From page 37... ...
and was found to track the current and remain in a steady position, which had been a problem with earlier versions of the modified sounding weight. Idaho Bridges Two bridges on the Snake River were visited near Blackfoot, Idaho.
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From page 38... ...
Arc measurements were made at the upstream side of the piers at both bridges, supplemented by kneeboard measurements at Ferry Butte and a cross section at West Shelley. High-velocity and turbulent conditions existed near the piers (Figure 55)
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From page 39... ...
The basic bridge geometry was included, using information provided on the bridge plans. At this location, both arc measurements in front of the piers and a cross section measurement were taken.
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From page 40... ...
Figure 57. Typical results obtained with the articulated arm.
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