U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
The last visit of the study tour was to Belgium on June 27 and 28, 2002, where the program consisted of formal and informal meetings and presentations at several locations. On the first day, the scan team met with representatives of the Ministry of Transport, Flemish Geotechnics Division, in Zwijnaarde. Activities included:
On June 28, the team met with representatives of the Belgian Building Research Institute (BBRI) at its facilities in Limelette for presentations and discussions. BBRI activities included:
Figure 20. Screw pile test site at the Belgian Building Research Institute (BBRI).
Figure 21. Bridge canal project visit in Strepy, showing: (a) canal bridge under construction and (b) aerial view of project, including boat elevator.
A significant amount of work has been done in Belgium on screw piles, which are friction piles for embankments, retaining walls, and light structures. A variety of systems were presented, and results from comparative studies were shown. An interesting project was presented in which two bridges were replaced within an 82-hour traffic-disruption period by constructing the replacement bridges near the old bridges on site, demolishing the old bridges, and then moving the new bridges into position on wheeled transport platforms. Two recent geotechnical developments that were presented included the use of underwater horizontal vacuum consolidation with horizontally installed drains and the use of vegetated geosynthetic-reinforced berms as sound barriers.
During the site visit to the rail project, the team observed the use of lime stabilization to allow marginal soils to be placed behind retaining walls and a berm with a geosynthetic-lined cap that is being used as a sound barrier and to retain contaminated construction waste. At the bridge canal site visit, presentations were given on two major features of the canal project: a 150-ft- (46-m-) wide, 1640-ft- (500-m-) long canal bridge to support the canal over a river valley containing two multilane roadways, and a very high ship elevator.
The following section provides a review of the accelerated construction methods identified in Belgium in relation to the amplifying questions.
Screw piles are rapidly emerging pile systems consisting of steel or concrete piles with either the tip or the entire pile formed in a helical screw shape that are literally screwed into the ground. Screw piles can also be cast in situ (e.g., CFA piles are a form of screw piles). This system provides low-capacity vertical and lateral earth support. The vertical capacity is lower than that of driven piles for most systems because the zone below the pile is not compacted. There are numerous types of piles, and the equipment for installation varies considerably (e.g., Fundex, Altas, Olivier, DeWaal, and Omega). The newer generation of screw piles includes displacement screw piles, precast screw piles, and tapered multihelic screw piles. The significant advantage of screw piles over driven piles is lower noise and vibration to the extent that the use of driven piles in Europe is decreasing, while the use of screw piles is increasing. Another advantage is relatively lightweight installation equipment. However, increased torque was identified as a recent advancement in improving capacity, which may result in heavier equipment requirements. These friction-type piles are used for embankments, light structures, and retaining walls, similar to applications of driven piles. Screw pile installation rates of up to 500 ft (150 m) per day can be achieved. Diameters range from 16 to 32 in (400 to 800 mm).
Specialized equipment is required for installing screw piles. Most of the equipment is patented, but a variety is available. Screw pile equipment is readily available in the United States. The process is not patented. Several empirical design methods are well established, most of which are based on CPT. Ongoing research will provide updated parameters for design. One disadvantage is that a uniform calibration test does not exist for screw piles. The performance is sensitive to installation skill, and load tests are required to confirm capacity. Screw pile installation is usually contracted (in the United States) on a linear footage basis.
The BBRI’s screw pile study is financed by the Belgian Federal Ministry of Economic Affairs. Systems manufacturers are also conducting internal research. Future developments are in the areas of improved pile tip soil interaction, improved shaft capacity, and casting the concrete for precast systems. Prof. van Impe suggests potential benefits in research on pile group capacities with pile tips located shallower than those determined from individual piles.
Lime stabilization clay was also presented to the scan team as an accelerated method of construction of embankments and fills behind retaining walls with marginal soils. This technique is a common practice in many regions of the United States. The ongoing research at the University of Ghent and BBRI could provide valuable information for extending the use of this technology. A final report of the BBRI field test study will be available.
Geotextile/sound barrier embankment is an innovative use of geotextile-reinforced mechanically stabilized earth (MSE) walls. MSE walls are already considered an accelerated construction method, and this extension of their use could increase application of this technology in the United States. The geosynthetic-reinforced walls at the Brussels airport were constructed berms with a vegetated face to provide a sound barrier. Marginal soils were used to construct the walls.
Underwater vacuum consolidation appears to be an innovative variation of vacuum consolidation, a standard technique that has been used in Belgium and the United States since about 1960. In the United States, its use has been limited because of higher costs than for classical surcharge methods. In vacuum consolidation, a stress is applied to soft soil through a vacuum to remove water. Normally, a large membrane is required to be placed over the surface. In the method presented in Belgium, the vacuum was applied through horizontal drains. Vertical drains could also be used. The technology could be used for dredge spoil, soft sites where access for placement of surcharge is not practical, underwater stabilization of soft soils, and for underwater slope stability improvement for underwater embankments as presented during the meeting in Belgium. This method avoids the construction of a surcharge load and is therefore faster than surcharging. However, it still is a slow process, as it requires the same amount of consolidation time as surcharging. The technique requires specialized, patented equipment. At this time the equipment is not available in the United States. The process is basically a standard vacuum consolidation and is not patented. Basic consolidation theory is used, with some accounting for strain-dependent soil properties (large strain theory). Measuring settlement and pore water pressure is used to control quality. Means and methods contracts are currently used to apply this technology with the requirements specified by the geotechnical engineer. The geotechnical engineer provides detailed methods and procedures for installation and monitoring. The scan team believes that specialized training would be required for technicians. This method has no impact on the environment. Research is ongoing at the University of Ghent using field data from offshore sites.
Similar to the prefabricated technology reviewed in Germany, a completed bridge was moved into its final position on a project in Belgium. On the Belgian project, two bridges were replaced by building new bridges adjacent to the old bridges. Within 82 hours, the old bridges were demolished, the new bridges were rolled into place, and the roadway was reconstructed and opened to traffic. Sand-cement mixture was used for backfill behind the abutment wall to reduce the lateral load on the bridge wall and to accelerate placement and construction. The width of the bridge wall was reduced from 3.3 ft to 1.3 ft (1 m to 0.4 m) to decrease the bridge load and allow it to be rolled into position. This technology was again primarily utilized to minimize disruption to traffic, as well as to save time. The application of this technology would depend on the site conditions and traffic control requirements. The scan team sees no impacts to the environment in using this technology.
A second accelerated bridge technology viewed in Belgium was the canal bridge constructed using a cast-on-site incremental launch construction method. The method was invented in Germany several decades ago, and has been used most commonly for bridges over deep ravines or valleys in the mountainous areas of Europe. This method eliminates the need for expensive and time-consuming temporary supports, and it allows on-site casting to occur year round (the bridge box segments are cast within an enclosed facility located at the bridge abutment). The application of this technology for construction of the canal bridge demonstrated accelerated construction solutions that are common to highway construction problems (i.e., speed of completion and noninterference with existing traffic). The bridge was completed nearly a year earlier than would have been possible with conventional construction, and without impact to the roadway below the bridge.
The status of limit state design in the context of Eurocode 7 was not reviewed during this portion of the scan tour.
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