Channel stability at a bridge crossing depends on the stream system.
Natural and man-made disturbances may result in changes in sediment load and flow dynamics resulting in adverse changes in the stream channel at the bridge crossing. Scour can occur any time there is a natural or man-made structure, such as a pier, in a moving body of water.
In significant cases, such as a large storm event, flowing water approaching a pier will cause the water to move back and down, pushing the soil in the water away from the pier and creating a deep hole. Once this happens, it can expose the pier pilings. A pier piling is typically placed 100-150 ft into the earth under the water and is typically made up of steel sheet pilings or concrete columns. They are capped with a concrete encasement at the top of the pile for protection from exposure to the water.
Exposure to the steel sheet piles in the water will cause corrosion and is a threat to the piers if scour is not treated. Corrosion causes deterioration of the piling, undermining the substructure of bascule piers, causing the pier to shift or lean. This shift will cause the bridge to move, thus creating bridge failure and in worst cases, a collapse.
Each pier is holding up a certain amount of load pressure. If the soil loosens around the steel pipe supporting a single pier, load pressure is lost, placing additional load pressure on the other piers. This will cause the concrete to crack, which could again lead to bridge failure.
“Anytime you have a large storm event, a high frequency of large storm events or you have a high velocity of water flow at a bridge crossing, you should perform an evaluation to determine if scour protection is required,” said Kim Rivera, P.E., of Jones Edmunds and Associates Inc., the design engineer for the project. “This can help avoid potential future bridge failures.”
NASA Kennedy Space Center (KSC) in Cape Canaveral, Fla., battled scour problems around each bascule pier of four bridges throughout the KSC’s channel and fender systems.
An underwater inspection was completed around all of the bascule and approach piers of the four bridges: The main entrance bridges to KSC in the Indian River, Banana River Bridge, Jay Jay Railroad Bridge and the Haulover Canal Bridge.
Two bridges in the large body of water in the Indian River provide the main public entrances into KSC and as such carry the largest amount of public vehicle traffic.
The Jay Jay Railroad Bridge dealt with the same water flow as the main entrance bridges because it was located in the Indian River as well. This bridge was strictly used for railcars.
The bridge in the Banana River was much smaller and was located in a smaller body of water. This bridge allowed no public traffic because it was for NASA and Cape Canaveral Air Force Station use only.
The Haulover Canal Bridge, connecting the Indian River to Mosquito Lagoon and the Jay Jay Railroad Bridge, was located in a narrower body of water, where water rushes through rapidly, creating deep scour pockets around the bascule piers.
All of the bridges and their piers were evaluated for potential scour by performing hydraulic modeling to predict scour depth. Large scour was predicted around the bascule piers of each bridge when tested during a 100-year and 500-year storm. What originally started out as a study quickly turned into a design to install scour protection.
Positioning and anchoring the scour protection system was challenging because the project involved installing the geosynthetic revetment system at depths of approximately 20 ft, amid high water velocities, with limited overhead clearance and poor visibility in the water. Narrow channels, strong currents and deep scour pockets demanded dredge-and-fill maneuvers or anchoring systems for slopes greater than 2-to-1.
Trying to place material underwater and get a specified thickness of material in adverse conditions can be difficult.
Three applications were evaluated when trying to find the best solution for NASA’s KSC bridge scour problems: bank and shore rubble riprap, articulated concrete blocks and marine mattresses.
Riprap is made up of larger stones that vary in size, 1-3 ft in diameter. Its 3.6-ft thickness would have required excessive channel dredging to ensure the required U.S. Army Corps of Engineers’ (USACE) approved depth of minus 18 ft.
Riprap was first considered because it is the most common method used for bridge scour protection. It has a simple installation method and is a readily available product. The scour protection already in place at Haulover Canal was riprap, so it was thought to be easier to place additional riprap to the current protection system already in place. However, riprap would have required more dredging of the soil to maintain the USACE’s approved surface depth.
The articulated concrete block option was much more expensive and more technical in design. The blocks are honeycomb-shaped, so each block had to fit just right under the water, which would have been very challenging. It also couldn’t be custom designed to fit the bridges’ fender systems, which was an important factor to consider when comparing scour-protection systems.
The marine mattresses were a less expensive option than the concrete blocks and only required 1-ft-thick mats, so not as much dredging was required in order to meet the minus 18-ft depth requirement. Less material also was used and was therefore more environmentally friendly.
In the end, NASA selected Tensar’s Triton Marine Mattress System for its challenging subaqueous scour protection project.
Leaning on mattresses
The marine mattresses were selected for their constructability, adaptability and durability in a challenging, submarine environment. Also, the coastal and waterway revetment system was much more cost-effective than the alternatives.
The mattresses were made up of uniaxial geogrids, which are manufactured using select grades of copolymer (high-density polyethylene [HDPE] and polypropylene [PP]) resins that are highly oriented and resist elongation (creep) when subjected to high tensile loads for long periods of time. Polymeric geogrids provide high resistance to installation damage and long-term chemical or biological degradation. With this geogrid, the mattresses had the strength and flexibility to armor the bridge piers without damaging them.
NASA and Jones Edmunds and Associates also selected the reinforcement systems because the units could be locally constructed and customized on shore prior to installation and could be conformed around fenders or circular piers.
In high-flow conditions, the marine mattresses tend to be very stable. Trying to place material underwater and get a specified thickness of material in adverse conditions is always difficult. Having a unit like the marine mattresses that goes in as a discreet size that can be positioned using GPS ensures the contractor and engineer know that what was specified is actually what was installed.
Six inches of bedding stone was laid down first at the bottom of the piers for leveling purposes. Bedding stones are small pebbles, so the shipping costs were much less than for the 300 lb of the limestone riprap. Lastly, the mattresses were assembled and placed using cranes by the piers.
The government appreciated the fact that an efficient bridge-scour protection was achieved at less than half the thickness of riprap and that mattresses are much easier to remove than riprap, a factor that also minimized the transition from surrounding grades. The government had to consider this, given the potential for future bridge-replacement projects.
During the KSC project, 1,281 marine mattresses were utilized with the geosynthetic revetment systems at depths of approximately 20 ft amid strong currents and with limited overhead clearance using GPS. Even in the most demanding conditions, the mattresses had the strength and flexibility to armor the bridge piers without damaging them.
Due to the capability of customizing, depending on the pier, different sized mattresses were used. All were 5 ft wide and they varied in length, 10-20 ft long.
“Currently the bridges are in good condition, and the mattresses are still intact,” Rivera said. “No problems or damages have been reported.” R&B
The S 43 SX Concrete Pump is the latest of 16 Schwing boom pumps available in North America, featuring the RZ boom, which combines functions of the Roll and Fold and Z-type booms. The boom consists of five sections, with a 270° Z-fold at the tip for increased maneuverability. With an unfolded height of 28 ft 6 in., the machine is ideal for low overhead situations. Super X Outriggers set up quickly for a compact pouring platform close to the pouring area. The Generation 3 concrete pump generates up to 213 cu yd per hour.
Computer chips are the brains within the redesigned Smart electric concrete pokers from Atlas Copco. They achieve sufficient concrete vibration in half the time of previous models; the radius of action is approximately 12 times the diameter of the poker itself. A new aluminum housing protects all three models—the 40, 48 and 56—and makes them 30% lighter. The Smart concrete pokers are easy to use, usable with an average 120-volt power supply for “plug-and-poke” efficiency. All models come standard with 32.8 ft of cable and 16.4 ft of hose for maneuverability around the jobsite.
CAN do anything
Gomaco has expanded the number of offerings compatible with its G+ Connect CAN-based network, which now includes the GHP-2800 slipform paver. The network employs a closed-loop control system governing a machine’s electronics and hydraulics, interacting directly with valves and sensors for improved performance. The system reacts with the push of a button or turn of a dial. A 6.5-in. flat-panel screen displays all critical machine information, including paving speed, percentage of drive, steering and grade information, among other items. Detailed fault histories are also available instantly.
Reinventing a classic
Users might not recognize the 2013 editions of Terex’s line of front-discharge mixer trucks, thanks to a wide array of improvements. Maneuverability is enhanced by a new steering system that allows the steering wheel to turn farther for a tighter turning radius; the revamped suspension also provides a smoother ride. The cab received much attention from Terex engineers, who made it larger and included hanging foot pedals, a new door hatch and brighter LED lighting. On the maintenance side, bolt-on roller trunnions make for easier roller-position adjustment.
Twice the power
Not one but two 23-hp, Tier IV-compliant engines now power the Terex Bid-Well 4800 paver. One exclusively controls machine function and movement; the other provides dedicated power to the paving carriage. Other highlights include a new skewable power crown adjuster, which can be mounted in-line on a straight paver or positioned on the frame at the skew for easier adjustments at extended paving widths. A new fogging system offers independently adjustable and removable spray nozzles, which can be adapted for wind, mix conditions or any other specifications.
Scare away debris
Weighing in at just 14 lb, CS Unitec’s Model 194.C405 handheld pneumatic scarifier gives users an alternative to small-area shot-blasting for cleaning and preparing surfaces. The unit effectively and aggressively removes alkyds, adhesives, lead-based paints, mastics and coatings corrosion from a range of steel and concrete substrates, sporting a 4-in. cutting width. Pairing it with a dust collection system further improves its ability to remove hazardous materials. Combining it with the optional 3M Heavy-duty Rotopeen captive shot flaps helps the unit to remove light paint and rust.
Addition by subtraction
The engineers at Power Pavers adapted the frame of the SF-2700 paver to create the new SF-1700, reducing both the engine size and the main frame width. Able to pave up to 24 ft across, the SF-1700 was designed for two-pass paving when one pass would be less economical. A pair of heavy-duty track systems with 12-in.-wide, triple-grouser steel track pads guide the machine, which can be controlled automatically or manually. Other features include a 160-hp, Tier III-compliant Cummins engine; spread auger and tamper bar; and 12 Wyco vibrators.
Stringless and digital
Power Curbers now offers stringless pouring technology with the 5700-C curb-and-gutter machine. This means that no string line is left behind when concrete is poured. Machine control has also advanced, now accomplished via the MOBA digital control system, which can interface with 3-D or GPS controls from a wide array of suppliers. Single-lane pouring is standard on the 5700-C, with dual-side pouring available as well. The new Cummins engine is quieter and more fuel efficient.
Keeping the right angle
MBW focuses on maintaining a perpendicular angle between the output shaft and blade arms on its walk-behind power trowels, which prevents the machines from wobbling. This is achieved through heavier bearings, output shafts, gears, spiders and blade arms. The handles, while adjustable, are also 6 in. longer than the average trowel for increased stability. Available sizes include 24, 36 and 46 in.
A 44-hp Kubota turbo diesel engine powers Allen Engineering’s new RS844 Roller Screed, a ride-on, spinning tube paver model. The paving tube itself is 8 in., providing 25% more surface contact. Standard features include: a drive tube and paving tube scrapers to eliminate concrete buildup; emergency kill switches on both ends of the machine and operator panel; and four lights on the front and back of the machine. Optional features include: a powered spray system for retardant application; a hydraulic up/down dolly jack system; and a tow bar so the RS844 can be moved with a pickup truck.
For contractors on small or remote jobsites, the RexCon Mobile 5 portable batch plant will keep the concrete flowing. The pouring system is made up of a 225 barrel storage silo and gravity-fed cement surge hopper. When the hopper is full, any excess cement flows back into the silo for recirculation later; at any one time, two loads are always ready for batching. A single-trailer configuration is standard, with the option for a front-end loader setup; no crane is required. The low-profile aggregate bin allows more than 16 cu yd of storage capacity for material loading.
Swing into action
The SmartLeg Swing Leg System is one of the highlights of G&Z’s redesigned S850SL mid-size slipform paver. Now operators can adjust the angle of the swing leg on the fly while automatically keeping the crawler track straight ahead. This makes it easier to get around any track line obstacles without stopping. Handling also is improved by the AccuSteer Slew Drive Track Control System, which replaces steering cylinders with slew drives for improved maneuverability; each track can be independently rotated in nearly a full circle. The JC Extender System allows major changes to tractor width in less than an hour.
Higher and wider
Curb Fox has expanded the area that can be covered in one pass by its 5000T-HD slipform paver, so that operators can now pave flat sections up to 10 ft wide and barriers up to 39 in. high. In the offset position, the machine also can tackle large curb-and-gutter sections up to 39 in. wide. Stability and traction have improved thanks to a 50% weight increase from heavier tracks, but still sports a turning radius down to 2 ft. The average paving speed on 8-ft-wide pavement is 10 ft per minute.
A three-phase induction motor operating at 180 Hz drives Denver Concrete Vibrator’s line of high-cycle vibrators for consistent vibration at any depth. The entire lineup is ideally suited for large-scale projects thanks to a force output of up to 2,000 lb. Available head sizes range from 1.75 in. up to 3 in. Handling hose lengths are made to order, with a sectional handling hose available for easy adjustment on the jobsite.
The Eagle Crusher UltraMax 1200-25CC is a portable concrete plant specifically designed to withstand the challenges of rebar-laden concrete thanks to its solid-steel, three-bar rotor. A 5-ft x 16-ft double-deck screen allows the machine to produce two cubical spec products simultaneously for greater efficiency. Eagle Crusher offers both electric- and diesel-powered models.