Innovative Technology for Accelerated Construction of Bridge and Embankment Foundations in Europe

Chapter Six: Major Findings

The team identified 30 technologies and up to 15 processes that offer a potential for accelerating construction and rehabilitation of bridge and embankment foundations, which are listed in table 3. 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. Tables 4 through 8 summarize the technologies evaluated and rank them in terms of anticipated improvements in construction time, cost, and quality. The table in Appendix C lists web sites where additional information can be obtained for many of the technologies. The technologies that offer the greatest potential benefit clearly lead to recommended practices as outlined in the next section of this summary report.

Table 3. Technologies (a.) and Processes (b.) for Accelerated Construction of Bridge and Embankment Foundations

3a. List of Technologies:

1. Embankment on Columns
2. Lightweight Aggregates
3. Deep Mixing (Lime-Cement) Columns
4. Mass Stabilization
5. Geotextile-Encased Columns (GEC)
6. Rapid Impact Compaction (Building on Fills)
7. Vibro-Jet Sheet Pile Driving
8. Load Transfer Mat Concrete Slab
9. Load Transfer Mat – Caps and Geosynthetics
10. Automatic Controlled Variable Roller Compaction
11. Reinforced Soil Sound Barriers
12. Self-Drilling Hollow Bar Nails and Micropiling
13. Screw Piling
14. Combined Soil Stabilization (CSV) System
15. Accelerated Site Investigation
16. Continuous Flight Auger (CFA) Piles
17. Bored Piling – Cased Secant Piles (CSP)
18. Berlin Wall (Micropile Wall)
19. Continuous Diaphragm Walls (CDW)
20. Hydro-Millä Diaphragm Walls
21. Reinforced Protective Umbrella Method (RPUM) Glass-Reinforced Plastic Bar
22. Pretunneling
23. Micropiling Rod Carousels
24. Rock Saw
25. Computer Controlled Consolidation Grouting
26. Turbo-Jets
27. Horizontal Vacuum Consolidation
28. AuGeo™
29. Dynamic Stiffness Gauge
30. Higher Energy Compaction Impact Roller

3b. Processes and Approaches:

1. Public Relocation during Construction
2. Communication with the Public
3. Designer on Board during Construction
4. Contractor Involved in Design
5. Contractor/Designer QC/QA Required ISO 9000
6. Real-Time Lab Testing and Data Storage
7. Real-Time Design (e.g., ADECO-RS (Analysis of Controlled Deformation)
8. 10-Year Warranties/Insurance
9. Pile Load Test Program/Certification for Screw Piling (Recommendations)
10. Self-Compacting Concrete
11. Prefabricated Bridge Parts (Bayonet Pipe Pile Connection)
12. Moving Completed Bridges on Site
13. Automated GPR for Pavement
14. Maintenance-based Payment Procedure
15. Automated Control QC Documentation of Installation

BRIDGE FOUNDATIONS (TABLE 4)

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 QC/QA problems with auger cast piling, auger cast or CFA piles are rarely used in U.S. bridge construction. CFA piles with automated computer control and automated QC/QA would appear to offer a rapid alternative to the current practice that could be easily implemented. CSP piles should also be evaluated as an alternate accelerated method that can provide both bridge support and excavation support in cut situations. Both systems are limited in load support by the maximum diameter of piles that can be formed. 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.

EMBANKMENT FOUNDATIONS (TABLES 5 AND 6)

For embankment foundation construction over soft, compressible soils, the Europeans use column-supported embankments to accelerate construction over classically using a surcharge load with or without wick drains. Although this is familiar technology in the United States, it is often associated with high cost and difficult access. However, with some of the advances in pile technology (i.e., faster installation, lighter equipment, and lower cost) as identified on this tour, column-supported embankments are considered by the team as a much more attractive alternative that should be explored as a viable alternative for most soft ground projects.

An embankment mat support system may be required to spread the load over the foundation soil or piles, depending on the soil conditions, type of pile, and deep foundation spacing. Load-transfer mats constructed with geosynthetic reinforcements, and often combined with lightweight aggregates or geofoam, offer a viable solution, with the design methods supported by both U.S. and European practice. Stabilization of the upper 10 to 16 ft (3 to 5 m) of soil materials through either mass stabilization or rapid impact compaction may also hold some promise in constructing foundation support mats with and without deep foundation systems.

EMBANKMENT CONSTRUCTION (TABLE 7)

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 use in Europe appears to be increasing (almost routine). Increasing the use in the United States should expand availability and decrease cost, making lightweight fills such as geofoam an attractive alternative to surcharge fills, and 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 is the use of instrumentation on the compaction equipment to measure dynamic modulus, which can be used for improving compaction uniformity, effective compaction effort, and, potentially, compaction QC.

EARTH-RETENTION SYSTEMS (TABLE 8)

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. The technologies include bored CSPs and CDWs, both of which can be used for the retaining wall as well as the support of the bridge. Both methods can be used on sites where difficult drilling is anticipated, and both methods produce low noise and low vibrations.

PROCESSES AND APPROACHES

The scan team agrees that the scan findings with the greatest potential for accelerated construction are the processes and approaches listed at the bottom of each of the tables. The common theme among all of these processes is simplicity through sophistication.

Practically all of the equipment and construction methods presented in tables 4 through 8 employ real-time automated installation control and documentation. These systems monitor, measure, control, and document critical aspects of their 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.

The scan team 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 SCC in Sweden. SCC is not a new technology, but SCC research, development, and implementation to such a 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, with fewer workers, less dependence on worker skills, smaller pumps, and higher quality. SCC should lead to a longer life via superior coverage of reinforcement and very low permeability. It provides significant benefits when post-tensioning or other ductwork is present. Since vibration is not needed, ductwork cannot be pushed out of alignment or damaged.

Several other European Community (EC) standard processes were also identified that could lead to both improvements in construction rate and quality at a moderate cost, including (1) requiring the contractor and designer to have a QC/QA program modeled after the ISO 9000 series process, and (2) increasing requirements for computer automated equipment control and requiring generated data to be provided as part of the QC program. 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) was presented by the BASt. This process could be used as a model to help agencies identify opportunities and the optimum method for accelerated construction.