Mitigating Bridge Approach and Departure Slab Settlement Issues with UDI
Twenty-five years ago, in 1995, studies revealed that of the 600,000 bridges in use in the United States, 150,000 had settlement issues at the bridge approach and departure ramps. At that time, this was a $100 million problem each year for highway and transportation officials across the country.
In the years since, the problem has become even more pronounced, with older bridge assets under siege from the forces of settlement as well as the best intentions of engineers and contractors still holding on to outdated methods of mitigation.
Settled Bridge Approach and Departure Slabs Endanger Drivers
For drivers, early settlement at a bridge approach might manifest itself as a pronounced “bump” upon entering the bridge. A song might skip or maybe a little coffee gets spilled. But as the settlement progresses, serious safety issues are presented for drivers, many of whom are completely unprepared for the adrenaline rush that accompanies the temporary loss of control upon entrance onto or exit off of a seriously settled bridge abutment. Bridges like these present a serious safety issue, and the only ones who don’t mind are probably the owners of the local front-end alignment shop.
The severity of the elevation difference between the bridge approach and the deck determines the degree of danger present for drivers. From a transportation department’s point of view, bridge settlement issues can be the face of larger public perception challenges, with citizens pointing to dangerous bridge ramps as an indication of overall department effectiveness. In some cases, faulty bridge approach and departure ramps have resulted in costly litigation that have seriously compromised already-tight budgets.
The solution to bridge settlement problems, therefore, must always seek to reduce the size of the “bump” at approach and departure ramps, and it must do this in an economical manner that provides enough flexibility to address a wide variety of site-specific variables.
Providing a Safe Transition Between Road and Bridge
Simply stated, the approach slab provides a transition between the roadway pavement system and the bridge. In this capacity, the approach slab acts as an intermediate bridge to span the portion of embankment directly behind the bridge abutment, which was excavated during construction of the abutment. It is understood that this area is traditionally difficult to compact during construction and is therefore prone to settlement.
The approach slab bridges the gap between the rigid abutment and the undisturbed embankment beyond the area excavated during construction. Even on new construction projects, it is typical for there to be some settlement below the bridge ramp, even with diligent compaction. In these cases, just like in older bridge installations, the pavement end of the approach slab may settle, creating an uneven transition onto the bridge.
Important Bridge Integrity Consequences
While driver safety is always of paramount importance, the structural integrity of the bridge is also a major consideration for highway officials. Left uncorrected, settled approach and departure slabs cause undue impact upon the bridge, especially from trucks.
Over time, these impacts can have catastrophic effects on longitudinal members, imparting stresses for which they were not designed, and significantly weakening them. In these cases, the causes of a momentary catastrophic bridge failure can be traced back to years of improper stress loading on the bridge.
Therefore, it is easy to understand that smooth bridge approaches deliver much more than just driver comfort and safety.
Bridge Maintenance with URETEK Deep Injection® (UDI)
When bridge approach and departure slab settlement has become a priority for state highway officials, URETEK offers proven solutions. As mentioned above, loose, poorly compacted foundation soils, or erosion from water penetration can result in a rough ride when approaching or leaving bridges. Furthermore, the bridge structure itself is also placed under stress from the impact loading experienced when cars and trucks pound on and off the bridge.
Fortunately, loose, poorly compacted foundation soils are our specialty. URETEK has extensive experience with this type of work and a long list of completed projects, many of which will likely match the particular circumstances you face with bridge settlement in your area. Our experience will assure you that we have the specific solution you need to restore the smooth flow of traffic onto and off of your bridge.
Local DOT’s Rely on UDI to Keep Traffic Moving
Beginning in 1989, with the introduction of URETEK Deep Injection® (UDI), our trusted pavement preservation method has been relied upon by state DOT officials all across the country. In every climate, they depend on UDI to stabilize soils, fill voids, and most importantly, maintain smooth and level bridge approach and departure slabs.
UDI involves the injection of structural polymer into base and subgrade soils to increase their load bearing capacity. This is achieved by injecting the polymer through small holes drilled directly through the pavement structure to depths determined by site-specific analysis. URETEK’s proprietary high-density polyurethane foam (HDPF) polymer material flows easily into voids and weak zones within the soil mass below. Then, through a controlled chemical reaction, the expanding polymer compacts surrounding soils, increasing their load bearing capacity. The composite material quickly cures into a strong, dimensionally stable, environmentally inert, non-toxic, and water-resistant geo-material that provides years of reliable service.
Trusted Vendor for Bridge Maintenance Programs
For over 30 years, URETEK has been a trusted, reliable partner for DOT officials and prime contractors intent on maintaining critical pavement systems. With increasing traffic loads across the country, the need for reliability and trust has never been more important than it is today. With its rapid response and crew scheduling that takes advantage of overnight and off-peak hours, URETEK is the vendor most prepared to complete bridge approach and departure slab maintenance tasks without severely impacting traffic.
When we arrive, our crews get right to work on a site-specific repair or maintenance solution that quickly mitigates weak soil issues and extends the reliable working life of important bridges. Best of all, our zero-excavation solution means the work is completed in days, not weeks or months. When the job involves stabilizing base and subbase soils and restoring critical pavement systems to their optimal functional state, nobody does it better, or faster, than URETEK.
Contact URETEK today to learn more about our speedy pavement maintenance and repair solutions that keep budgets in line while assuring many more years of reliable service from bridges.
Also, see our case studies to learn more about how our UDI application has successfully worked to extend the life of bridges across the country.