U.S. Department of Transportation
Federal Highway Administration
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The first scan sessions took place in Sweden on June 17 and 18, 2002. The review involved formal meetings held at the Solna regional office of the Swedish National Road Administration (SNRA) with presentations by engineering and managerial transportation officials from the SNRA; an engineer from Konsult; two Finnish representatives from Finnish Road Enterprise; and a United Kingdom (U.K.) representative from the research group BRE, Centre for Ground Engineering and Remediation. Representatives from the private sector involved in the design, contracting, and construction sectors also joined in the discussions, including Skanska Teknik AB, Skanska Berg och Bro, Möbius, de neef Northern Europe, Hercules Grundläggning AB, and Tyrens. Presentations on the second day were held in the Södra Länken (Southern Link) exhibition room and focused on the Southern Link Road Construction project, which had used several innovative features to maintain traffic and to reduce public inconvenience (e.g., noise issues). The team also made field visits to several sites, including the Traneberg Bridge, a major bridge reconstruction project for which vehicle and rail traffic has to be maintained throughout the project (figure 4); a soil nailing project in which self-drilling and grouting nails are being used to stabilize a slope (figure 5); and several portions of the Southern Link Road Construction project in Stockholm, including a soil and rock tunnel section (figure 6).
In Sweden, several innovative technologies were presented, including mass stabilization, in which cement, fly ash, or blast furnace slag are mixed with the upper 10 to 16 ft (3 to 5 m) of poor soils (e.g., peat, mud, or soft clay) to provide a method for accelerated ground improvement. Advances in deep soil mixing, an emerging technology in the United States, were identified in terms of testing and equipment. Presentations highlighted the results of research carried out under the European Union (EU)–sponsored EuroSoilStab project for the development of design and construction methods to stabilize soft organic soils. In four of the countries involved in the study, full-scale field trials were completed, three using the dry method and one (in the United Kingdom) using the wet method. One of the contractors presented a cost comparison of deep soil mixing and other soil improvement technologies.
SCC is being used in Sweden for foundation construction and offers a potential to reduce noise generated from compaction as well as reduced construction time. A wire type rock saw is used to cut rock in lieu of blasting or line drilling, thereby limiting noise and vibration and speeding up construction. Reduction of noise was emphasized in several presentations. Public relations plays an important role, and sometimes includes offers to relocate families during the construction period.
The use of geotextile-encased columns, a German technology, was introduced as a fast method of soft soil stabilization (more details were provided during the German tour). A Dutch method for constructing piled embankments in very soft soils using plastic pipe filled with concrete was also briefly reviewed. In addition, developments in the use of self-drilling and self-grouting micropiles and nails were presented, and the nail technology was demonstrated during a site visit.
The United Kingdom's presentation reviewed the results of EuroSoilStab research carried out at BRE on deep mixing to stabilize organic soils and how it can help accelerate construction. In addition, relevant work to accelerate construction was presented on ground treatment (surcharging, dynamic compaction, and rapid impact compaction); soft ground foundation systems (vibro stone columns, vibro concrete columns, and deep soil mixing); building on fill; and driveability of steel sheet piles. The presentation concluded with a preview of an EU project called TOPIC, which is in progress, and an EU project about to start on the re-use of foundations. Information also was presented on vibro-jet sheet pile driving for rapid installation of temporary sheeting. Information on advancements in piles was offered, including on screw piles, which reportedly can be installed in one-third of the time required for auger-cast piles; piles that are tailored to match the soil type; and piles that minimize concrete requirements. Literature was provided on high-energy compaction using impact type, noncircular rollers.
The Finnish presentation provided several valuable accelerated construction technologies and complementary methodologies. Geotechnically, rapid automated site investigation methodology is being used in Finland. For example, new resistivity technology is being used to estimate water content and consolidation settlement in existing roadway embankments. With this technology and software, they are able to do a geophysical site investigation along with preliminary design, time, and cost calculations in a few days instead of the typical time of several months or more. In addition to being rapid, this methodology quickly locates and brings project focus/ resources to bear upon areas of the most importance with respect to project time lines, costs, and performance objectives. Consequently, project site investigations and designs are significantly faster, less costly, more cost-effective to construct, and have lower probabilities for delays and claims during the total project cycle.
Structurally, steel pipe piles are predominantly used in Finland to achieve rapid installation, especially in areas with boulders. To complement this rapid approach, they have developed a direct connection design detail that attaches the pile directly to the superstructure (steel, precast concrete, or cast-in-place bridge girders). This ingenious approach eliminates the pile cap, pier columns, and the pier cap. Literally, the construction of the entire substructure, excluding the piles, is eliminated, resulting in typical savings of between 10 and 15 percent of the entire bridge cost.
The following section reviews the accelerated construction methods identified in Sweden, the United Kingdom, and Finland in relation to the amplifying questions.
The mass stabilization technique was identified in Sweden as a method that saves time when compared with preloading (see figure 7). The technology came from Finland about 10 years ago. In the mass stabilization technique, the upper 10 to 16 ft (3 to 5 m) of the soft subgrade is mixed with a cement, fly ash, or blast furnace slag stabilizing agent over the entire surface area of a project. The stabilizing agent is typically applied at a rate of 30 to 40 lb/ft2 (150 to 200 kg/m2). At this rate, approximately 400 to 650 yd3 (300 to 500 m3) of soft soil can be stabilized per day. Mass stabilization projects performed to date show that settlements develop rapidly in stabilized peat and underlying unstabilized soils. This method does require specialized mixing equipment. The equipment is patented but the process is not. The availability of equipment in the United States is unknown, but it is possibly being used in the waste industry.
For design, the properties of the stabilized mass are determined on the basis of correlation with lab test data and local experience. The technique has worked well for peat, mud, and soft clay, but as previously indicated, is only effective for the upper 10 to 16 ft (3 to 5 m). Quality control (QC) and quality assurance (QA) are evaluated through the use of conventional geotechnical field measurements, including the cone penetration test (CPT) to determine the differences in permeability properties and to control homogeneity in the mass stabilized peat; standard column penetration test (SPT); column vane test; spectral analysis of surface waves (SASW) measurement; settlement; horizontal movement; and pore pressure measurements. The technique requires little training. Average equipment contractors and inspectors can be taught in a few days. Training is required to be able to determine the amount of stabilization agent (cement, fly ash, blast furnace slag) to mix, as well as types, properties, and volume of agents.
Some safety issues are associated with this technology, including transport of cement from the truck to the mixing machine. Using the current technology, cement can spread easily over the site (e.g., windblown) and can cause burns to the skin and eyes as well as breathing problems. This transfer process will have to be changed for U.S. implementation. In Sweden, the technology is contracted using a performance-based specification in which the contractor is responsible for the performance. The contractor provides a 5-year warranty. Performance is defined as the ability of the system to limit settlement, as measured initially on the basis of lab tests on the soil-cement mixture and in the long term on the basis of field monitoring. The University of Lund in Sweden is currently performing research on this technology. The technology has not been used in seismically active regions. Cold weather and freezing soil do not appear to affect the application, at least in the mass stabilization projects performed to date. The thermal conductivity of stabilized peat is of an order at which it can be expected to influence the frost penetration of the whole road structure. The measured thermal conductivity factors have been of an order of ~ = 0.2 to 0.6 W/Km, which corresponds to thermal conductivity of natural peats (Carlsten, 1988; Helenelund, 1980). This insulating effect can be taken into account at the frost dimensioning stage (Tielaitos, 1995).
Lime/cement columns (deep soil mixing) has been introduced in the United States; however, a significant amount of development work has been performed in Sweden. Much of the effort has gone into QC and QA, with some advances reported to the team on the rate of mixing and on in situ testing. Ongoing research on mixing energy, i.e., relating strength to mixing time (rotations), was presented. Deep soil mixing uses specialized, patented equipment, much of which is readily available in the United States. The process is not patented. A presentation was conducted on the analysis of composite ground using a mean strength method. The EuroSoilStab Consortium, headquartered at the Swedish Soil Stabilization Research Center of the Swedish Geotechnical Institute, has ongoing research projects on this subject.
Self-compacting concrete (SCC; also known as self-consolidating concrete) was identified as a rapid construction technique currently being used and evaluated in Sweden. Finnish and German representatives indicated that they also are using SCC in bridge construction. SCC is a special, fine grain, fluid concrete mix (similar to a mortar mix) that rapidly consolidates after placement to form a dense, high-strength concrete. Fluidifiers are used as admixtures to maintain the consistency of the mix. It has significant advantages: no vibration is required, the mix is very fluid, thereby flowing easily into tight areas, and segregation is not a problem. Main applications have been for structural components, such as facing units for tunnel linings, but the technology offers significant potential for use in deep foundations, such as drilled shafts. The technique does not require specialized equipment. Neither the equipment nor the process is patented, and the equipment is readily available in the United States. SCC is contracted in Sweden on a unit cost basis. Means and methods of applications are based on specification of mix design verification requirements and sampling and testing of concrete.
Geotextile-encased columns (GEC) consist of inserting continuous, seamless, high-strength geotextile tubes into soft soil with a mandrel and filling the tube with sand (or fine gravel) to form a column with a high bearing capacity. The application is similar to sand piles used in Japan and stone columns, which are widely used in the United States. It is suitable for soft soils and where high bearing capacity is desired. The method has been used for supporting new roadway embankments and large pavement areas on 15 ft (5 m) of soft peat material. Advantages of this system over stone columns include: (1) the column is confined in such a way that it does not intrude into the soft soil; (2) a consistent diameter is maintained by the geotextile tube; and (3) improved shear capacity is provided by the high strength of the geotextile and the confinement of the sand or gravel. The geotextile also provides a filter to prevent the intrusion of fines (and long-term loss of soil) while allowing water to pass. This significantly improves drainage and accelerates consolidation. Following classical consolidation theory with drainage improvements provided by the columns, consolidation rates on the order of 80 to 90 percent have been achieved within three months. The technique allows for rapid installation of the columns with minimum noise. Although this technique has not been used for seismic applications, such as stone columns and sand piles, it has potential for liquefaction mitigation. Weather is not a problem.
AuGeoä piling, a Dutch technology and a registered trademark of Geotechnics Holland BV, was also introduced in Sweden as a rapid, economical method for constructing column-supported embankments in very soft soils. This method consists of using a mandrel to push, vibrate, or drive a large-diameter plastic pipe through soft soil, then filling the pipe with concrete to form a column. QC uses conventional concrete sampling and testing. Load testing is performed to confirm performance. For design, the scan team believes that field measurements of spacing, diameter, and depth could easily be evaluated. The scan team also believes that only average pile equipment skills would be required. Contracts could be prepared on performance-based specification with concrete samples and testing performed by the owner for confirmation. Additional information will be solicited on this technology as part of the scan implementation program.
A rock saw a cable type saw, is an alternative to blasting for making rock cuts and shafts in rock. The technique does not appear to be any faster than blasting, as the rock saw requires predrilled holes for setup. However, the technology may still speed up construction by allowing for night construction in urban areas given its low noise and lack of vibration. The technique also results in a uniform, smooth cut, which reduces the noisy jackhammer dental work. The technique does require specialized equipment. However, we understand that neither the equipment nor the process is patented. The equipment is also readily available in the United States because it is commonly used in quarrying operations. A video demonstrating this technology was provided, as is listed in the bibliography section of this report (see Appendix C).
Rapid impact compaction, as indicated in the previous section, is a technique using a 5-ton, 1-meter drop hydraulic pile hammer to compact the soil, and was presented as an accelerated construction method by the United Kingdom’s representative from BRE. This technique basically uses a hydraulic piling hammer to drive a large foot into the ground. This technology eliminates excavation and allows for compaction of shallow layers up to 9 ft (3 m) thick. The technique was initially developed by the military for repair of bomb damage to airfields. (Reportedly, the U.S. Army Corps of Engineers also performed some initial work on this technology for rapid airfield repair.) The British are currently evaluating this technique for compaction of loose fills such as construction rubble, shallow refuse, industrial waste fills, or loosely placed dumped fill. The team also discussed use of the technique for increasing conventional lift thickness during embankment construction.
The technique may also have some application in densifying shallow, liquefiable layers to limited depths in seismic zones. Cost information was not available. The technique requires specialized equipment, but there does not appear to be a patent on the process or the equipment. The equipment is readily available in the United States, and no special training should be required to apply this technology. The scan team also believes that standard density testing could be used for quality control. Contracting could be performed on a performance-based specification with results measured by CPT tests before and after placement. The contractor is responsible for performance of method on the basis of testing results. Some noise and vibration issues may have to be addressed, similar to pile driving.
Vibro-jet sheet pile driving, currently being evaluated by the United Kingdom, combines vibratory pile driving with jetting procedures to significantly speed up sheet pile installation. This technique allows the effective installation of sheet piling through clays that are far too stiff for conventional impact or vibratory hammer methods. The team also noted that the jet conduits could be used after driving to grout the sheets in place and, thereby, eliminate any reduction in lateral fixity caused by the jetting process.
Jetting may reduce duration of vibratory driving. However, if spoil is undesirable, jetting may not be a viable option. The technique requires specialized equipment, but patents do not exist on the equipment or the process. The equipment is readily available in the United States. Design techniques for conventional sheet piles would apply; however, the use for axial loading capacity is unknown. QC would be based on field observations of the performance. Training would be required to operate a vibratory hammer. Calibration would be required to suit site conditions. As with conventional sheet pile installation, contracting could be performed on a performance-based specification. Usually sheet piling is temporary, so the contractor is solely responsible for performance.
Screw piles are also being used in the United Kingdom, with installation requiring one-third the time required for auger-cast piles. Advanced information was presented to a few of the scan team members in England prior to the tour. Two types of systems were discussed during the Swedish session, including: (1) D2A in which the hole size is matched to the soil type, and (2) Screwsol in which the concrete required to form the pile is minimized. Discussions included load testing and special training requirements for both techniques. Performance-based contracting is being used by the British for both pile types with the owner making measurements on the in-place piles. Significant information on this technology was presented during the Belgium tour, as is reviewed later in this report. Load testing special training is required.
The British are also evaluating the reuse of foundations as a method to accelerate construction. This technology eliminates time to replace foundations. Evaluation consists of load testing, field verification of existing foundations and their dimensions, and nondestructive tests for integrity and durability. This technology has also been used in the United States, and, like the British, we have found that a very special effort is required by the geotechnical engineer. Contracts are usually based on a time and materials basis.
The use of steel pipe piling, identified by Finland as its most common pile type, is based on the speed of driving through boulders. This piling method is common practice in the United States and is not necessarily a new accelerated construction method; however, because of its extensive use, Finland has also developed an innovative direct connection from the steel pipe piles to the superstructure. The elimination of a pile cap, pier column, and pier cap saves significant time during construction. The installation of the piles is conventional technology that is contracted on a performance basis based on blow counts. The connection is a standard detail requiring no special training. Noise and vibration potentially limit urban production, but the piles can be prebored to limit this problem.
Another advancement in Finland is the development of an automated rapid site investigation technique using resistivity. This is an extension of Finland’s work in evaluation of pavement systems, which combines resistivity and falling weight deflectometer (FWD) measurements. The Finnish are currently evaluating the use of resistivity profiles to rapidly estimate water content and consolidation settlement. This technology has significant potential to save time in preliminary geotechnical investigations and layout of final borings. A similar initiative is under way by the FHWA in the United States, and a cooperative effort could provide for a more rapid development.
SCC, as discussed in the previous section, was also identified by the team as a prefabricated technology with significant U.S. application potential. SCC requires no vibration and thus produces no noise and speeds up construction. The technology has been used successfully in Sweden over the past 4 years on more than 20 projects. For example, SCC was used in the concrete rock lining of the Södra Länken Tunnel Project, which the team visited. Based on the Swedish project experience, a 10 to 15 percent time and cost savings has been identified in addition to the positive impact on the work environment (i.e., low noise and vibration). Because of the low noise, this technology would also benefit nighttime construction. Specialized equipment is not needed, but new processes and skills are needed to handle the more fluid mix (e.g., workability test, pour rate, form pressure, and form design). Sweden does not have design requirements for earthquake, and thus has no experience in application in seismic regions. Special consideration for cold weather concrete placement may also be needed.
The direct connection of pipe piles to the bridge structure used by Finland, which was discussed in the previous section, is another prefabricated technology.
In relation to limit state design, the United Kingdom provided us with a special issue of Civil Engineering magazine on Eurocodes (November 2001, Volume 144, Special Issue Two), which contains an excellent overview of the development and current status of the Eurocodes, including Eurocode 7: Geotechnical Design. The information on Eurocode 7 is reproduced in Appendix E with permission of Civil Engineering, Thomas Telford publishers, as a follow-up to the previous 1999 geotechnical engineering practices tour.
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