U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
In June 2002, the Federal Highway Administration (FHWA), in a joint effort with the American Association of State Highway and Transportation Officials (AASHTO), organized a geotechnical engineering scan tour of Europe. Its purpose was to identify and evaluate innovative European technology for accelerated construction and rehabilitation of bridge and embankment foundations. The scan team also explored opportunities for cooperative research and development and implementation of accelerated construction technology.
The scan team evaluated the following technologies for accelerated construction and/ or rehabilitation:
The geotechnical scan team members included both geotechnical and structural (bridge design) engineers representing Federal, State, academic, and private industry sectors. Team members were invited to participate on the basis of their positions as leaders in the development and implementation of new technologies. The team met with technical and industry leaders in Sweden, Finland, the United Kingdom, Germany, Italy, and Belgium to acquire detailed design and construction information for possible application in the United States. To effectively evaluate the equipment and techniques that may be used for accelerating construction, approximately 50 percent of the scan team’s activities were devoted to viewing physical demonstrations of the technologies and methodologies in Sweden, the Netherlands, Germany, Italy, and Belgium. Team members also conducted interviews, including case study briefings, with contractors and equipment manufacturers.
The team identified 30 technologies and up to 15 processes that offer a potential for accelerating construction and rehabilitation of bridge and embankment foundations. Many of the technologies also offer a potential for cost savings and, in a majority of the cases, an improvement in the quality over current practice. This report includes complete tables with a relative ranking of all the technologies in terms of anticipated improvements in construction time, cost, and quality (located in chapter 6). The technologies that offer the greatest potential for success in terms of construction expediency and ease of implementation are summarized in the following sections.
Team members also gained insight on other, related construction practices in Europe that may benefit U.S. practice. In several European countries, the emphasis is on maintaining traffic during construction, which often dictates the construction procedures and has led to innovations in parallel bridge construction. Team members reviewed several projects in which the new bridge was constructed adjacent to the old bridge, foundation support was improved under the old bridge while maintaining traffic, then the new bridge was moved into final position by a specialized truck transporter (as shown in the example in figure 1) or by sliding. Traffic disruption was held to a minimum, for example, less than 72 hours in two cases. Another emphasis is on the reduction of noise (also a key issue in the United States), which drove the use of some of the technologies identified in the scan tour. Public relations plays an important role, and sometimes includes offers to relocate families during the construction period.
The overall goal of the scan trip is to implement technologies of best practice in the United States. With this perspective in mind, the team identified European technologies and methods to accelerate construction and devised new ways in which these technologies could be applied in both the United States and Europe. This process resulted in a vast and broad array of cross-applications of technologies, methods, and processes that was so large and complex that concise and effective communication of the scan team’s findings became a major concern. After much thought and discussion, the team strongly agreed that the findings should be presented in an easy-to-use tabular format that is organized around end users’ needs. The goal was to devise tables such that engineers could enter with a specific need, and quickly see a list of applicable scan findings along with important supplemental information about the use of a specific technology for their specific need. The following paragraphs summarize selected technologies highlighted by the team as having a high potential for accelerating construction while maintaining or improving both cost and quality.
For bridge foundation construction, the standard of practice in the United States for poor to marginal foundation conditions is driven piles or drilled shafts. Because of quality control/quality assurance (QC/QA) problems with auger-cast piling, auger-cast or continuous flight auger (CFA) piles are rarely used in U.S. bridge construction. CFA piles with automated computer control for monitoring installation and automated QC would appear to offer a rapid alternative to the current practice that could be easily implemented. Bored cased secant pile (CSP) techniques with automated computer control should also be evaluated as an alternate accelerated method that can provide both bridge support and excavation support in cut situations. For large projects with difficult drilling conditions and/or tight spaces, the use of a diaphragm wall constructed with a Hydro-MillTM offers a rapid construction method with low noise and low vibrations that could also be used to support large loads.
Figure 1. Example of rapid bridge replacement showing transport of new bridge with specialized lift (from Belgian presentation).For embankment foundation construction over soft, compressible soils, the Europeans are using column-supported embankments to accelerate construction instead of the classical method of using surcharge with or without wick drains. The approach is preferred because of its much shorter construction time, simplicity of QC, environmental friendliness, and its nonimpact on the performance of existing roadways, rail lines, and buildings.
Although this is a familiar technology in the United States, it is often associated with high cost and difficult access problems. However, advances in pile and geosynthetic bridging platform technology identified on this tour convinced the scan team that column-supported embankments is an attractive method for accelerated construction and should be explored as a viable alternative for most soft ground projects.
The team also identified new technology for the stabilization of the upper 10 to 16 ft (3 to 5 m) of soil materials through either mass mixing or rapid impact compaction that may also hold some promise in constructing foundation support mats with and without deep foundation systems.
Several technologies evaluated on the tour offer the potential to accelerate placement and compaction of fill for construction of the embankment itself, while maintaining or improving cost and quality. Lightweight fills have been used in the United States to a limited extent to reduce placement and surcharge time in soft soil conditions. The frequency of this use in Europe appears to be increasing (it is almost routine). Expanding its use in the United States should increase availability and decrease cost, making lightweight fills such as geofoam an attractive alternative to surcharge fills, and also should accelerate construction. The rate of embankment construction could also be significantly increased through the use of high-energy impact, rolling compactors and rapid impact hydraulic hammer compactors, both of which appear to provide a much greater depth of compaction, allowing for placement of thicker fills. Another promising technology application is the use of instrumentation on the compaction equipment to measure dynamic modulus in real time, which can be used for improving compaction uniformity and effective compaction effort. Most importantly, the ability of instrumented compaction equipment to provide 100 percent QC coverage should allow the use of performance-based approaches to specifications, leading to the effective implementation of warrantees and guarantees for both earthworks and pavements (as is currently the practice in Europe).
Rapid construction alternatives to conventional bridge retaining wall construction (i.e., using sheeting and shoring with cast-in-place walls) were identified that could be easily implemented. These technologies include bored CSP techniques and continuous diaphragm walls, both of which are applicable for the retaining wall as well as the support of the bridge. These methods can provide considerable speed and cost savings where (1) access space is limited (widening projects); (2) sound walls will be attached to the top of the retaining wall; and (3) difficult drilling is anticipated. In addition, both methods produce low noise and low vibrations, which could significantly increase their production because such equipment could be operated for a greater number of hours during a day than conventional equipment.
The team agreed that the scan tour findings with the greatest potential for accelerated construction are processes and approaches used in the development of projects or in project control. The common theme among all of these processes is simplicity through sophistication.
Practically all of the equipment and construction methods employ real-time automated installation control and documentation. These systems monitor, measure, control, and document critical aspects of the technology and, thereby, allow for rapid construction without compromising quality. In fact, in most cases they improve quality. In addition to faster installation, these technologies and methods accelerate construction by reducing or eliminating QC methods that are intrusive to the construction process. Another extremely important aspect of these methods is that they have allowed the realization and implementation of rational performance specifications and warrantee/guarantee requirements.
We also observed the simplicity through sophistication approach being applied to construction materials. Specifically, one of the most exciting finds of the trip was the common usage of self-compacting concrete (SCC) in Sweden. SCC is not a new technology, but SCC research, development, and implementation to the highly advanced level of common usage is a new achievement.
By using advanced SCC technology, Sweden is able to pour concrete in intricate forms and/or dense reinforcement situations significantly faster, using far fewer workers, and smaller pumps, while still achieving superior quality. SCC should lead to a longer life via superior coverage of reinforcement and low permeability. It provides significant benefits when post tension or other ductwork is present. Since vibration is not needed, ductwork cannot be pushed out of alignment or crushed, thereby avoiding costly and time-consuming field repairs. The scan team is working to utilize SCC in new ways not observed during the scan trip (e.g., the use of SCC in drilled shaft foundations in high seismic regions).
The scan team identified several other European Community (EC) standard processes that could lead to improvements in both construction rate and quality at a moderate cost, including:
The German Federal Highway Research Institute (BASt) presented a process to evaluate which method would provide optimum acceleration considering the total scope and integration with all phases of the project (i.e., how accelerated construction methods fit in with the critical path for project completion). This process is detailed in this report and will be used by the team as a model to help agencies identify opportunities and the optimum method for accelerated construction.
The overall goal of the scan trip is to implement technologies of best practice in the United States. With this objective clearly in mind, team members developed an implementation ranking using the following two-step process:
The technologies that were selected for immediate implementation action are
Many of the other technologies identified in the scan tour show great promise, but successful implementation requires a champion. In addition, given the diversity of the team members (contractor, consultant, Department of Transportation [DOT], Federal, geotechnical, and structural engineers), the ranking should be an excellent indicator of the accelerated technologies preferences of the highway construction community as a whole.
The above list is not necessarily a ranking of technologies with the greatest technical potential for accelerating construction. Instead, it is a list of European accelerated construction technologies with the greatest potential for implementation in the United States. This type of focused selection should ensure that our resources are focused and not diluted. Plans for implementation of all potentially beneficial technologies are detailed in this report.
At the end of the tour, team members reviewed an implementation plan, which consisted of:
A Scan Technology Implementation Plan team was organized to develop a request for seed funding to assist in the implementation efforts for specific, high-priority technologies. The complete implementation program is detailed in this report.
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