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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.

Table 4. Bridge Foundation Systems, Equipment, and Ground Improvement Methods for Accelerated Construction and Rehabilitation on Poor Subgrades
Technology or Process Anticipated Accelerated Construction Performance Relative* Potential for Accelerated Construction Applicable Conditions for Accelerated Construction Relative Cost* Improvement in Quality* Design and Construction Issues* Comments
Settlement Reduction Equipment Mobility Soil Excavation Vibration & Noise
Base-line Technology for Comparison — Driven Piles and Drilled Shafts
Vibro-Jet of Sheet Pile Driving Speeds driving of sheet piles through layered soils M Same as conventional sheet piles L L L-M M Y M Bridge abutments with grouting through vibro-jet pipes
Self-Drilling Hollow Bar Nailing & Micro Piling Self-drilling and grouting for one-step installation H Difficult ground for drilling/driving L H M H N L Confined conditions with difficult ground for drilling or driving
Screw Piling Requires 1/3 the time of auger cast piles and lighter/smaller equipment. Similar to driven piles. L Relatively weak soil condition. Foundations with low vertical and lateral loads per pile. M L H H N L Auto control
Depth < 100 ft (30 m)
Nonartesian
Continuous Flight Auger Piles (CFA) Rapid pile installation for vertical or slight batter piles H Best in weak to medium soil M L H H Y M Use only with automated control and documentation. Not suitable for difficult drilling and obstructions.
Bored Piling — Cased Secant Pile (CSP) Rapid pile installation for vertical piles H Cut situations and temporary excavations M M L-M H Y L Casing assists in some soil conditions
Hydro-Mill™ Rapid excavation of wall with no mess. M Difficult drilling conditions, large loads M H H L Y M Use on large projects with difficult drilling conditions, large loads, low noise & vibrations, tight spaces

Applicable Process from Scan Tour:

  • Contractor/Designer QC/QA Required ISO 9000
  • Self-Compacting Concrete
  • Automated Control QC Documentation of Installation

* H, M, L = High, Moderate, Low; Y, N - Yes, No.

 

Table 5. Embankment Foundation Systems, Equipment, and Ground Improvement Methods for Accelerated Construction on Poor Subgrades
Technology or Process Anticipated Accelerated Construction Performance Relative* Potential for Accelerated Construction Applicable Conditions for Accelerated Construction Relative Cost* Improvement in Quality* Design and Construction Issues* Comments
Settlement Reduction Equipment Mobility Soil Excavation Vibration & Noise
Base-line Technology for Comparison — Surcharged Embankment on Poor Subgrade
Column-Supported Embankments Saves surcharge time; no surcharge required H Depth** < 120 ft H H H M to H Y & N M to H Newer piles and columns (e.g., GEC, CSV, CFA, AuGeo™, Screw Piles) may reduce cost
Deep Mixing (Lime-Cement) Columns Reduces surcharge requirements M Depth < 120 ft
Low organic
Nonartesian
M+ H M M N L Advances in QC, mixing, equipment, and uniformity
Mass Stabilization Saves time when compared with preloading M to H Depth < 25 ft
High organic
M M M H N L Effective for 10 to 16 ft (3 to 5 m) depth in peat, mud, or soft clay
Geotextile-Encased Columns (GEC) High bearing capacity, saves time required for surcharge, low noise M to H Depth < 60 ft
Nonartesian
M M M M N M 85% to 95% settlement in 3 months
Screw Piling Similar to driven piles, low noise & vibration H Depth < 100 ft
Nonartesian
H H H H N L Lower-capacity friction piles; variety of systems
Combined Soil Stabilization (CSV) System One-step installation of sand-cement columns M Depth < 50 ft
Nonartesian
H H M M N M Low weights, easily mobilized equipment
Continuous Flight Auger (CFA) Piles Rapid pile installation of vertical or slight batter piles H Depth < 120 ft
Nonartesian
H H H H Y M Installation rate up to 1600 ft (500 m) per day at low cost; not suitable for obstruction
Turbo-Jets Rapid vertical column for soil support M Depth < 110 ft M+ M+ M M N M Control appears better than jet grouting
AuGeo™ Fast piling system H Depth < 50 ft H? H H H N M Not presented, more information required
Horiz. Vacuum Consolidation Rapid consolidation without surcharge M Depth ? H H? L ? N L Potential technology; especially for hydraulic fill

Applicable Process from Scan Tour:

  • Contractor/Designer QC/QA Required ISO 9000
  • Automated Control QC Documentation of Installation

* H, M, L = High, Moderate, Low; Y, N - Yes, No.
** 1 ft = 0.3 m

 

Table 6. Embankment Mat Foundation Systems and Equipment for Accelerated Construction on Poor Subgrades or over Deep Foundations
Technology or Process Anticipated Accelerated Construction Performance Relative* Potential for Accelerated Construction Applicable Conditions for Accelerated Construction Relative Cost* Improvement in Quality* Comments
Base-line Technology for Comparison — Normal (possible staged) Fill Construction; Assumes Close Spacing and Arching for Piled Foundations
Load Transfer Mat — Geosynthetics No or reduced surcharge required H Close piles with soft tops M M For hard piles/ columns need to check punching shear; works well with soft piles
Light Aggregates Reduces or eliminates surcharge H Soft foundations M to H H Geofoam, flowable fill, etc.
Load Transfer Mat — Concrete Slab No surcharge required; could use prefab mats H Soft foundations H H Soft foundations — highest cost
Load Transfer Mat — Concrete Caps No surcharge required M Hard piles or columns that are closely spaced H M Requires hard piles/ columns that are closed spaced
Load Transfer Mat — Caps and Geosynthetics No or reduced surcharge required M Hard piles or columns with wide spacings M to H H Arching and spacing versus geosynthetic strength
Mass Stabilization Saves time when compared with preloading M Soft and/ or organic ground M to H M Works well for soft and/ or high organic soils
Automatic Controlled Variable Roller Compaction Speeds compaction eliminating wasted time. M Granular fill M H Compaction efficiency and uniformity improved; minimizes passes required

Applicable Process from Scan Tour:

  • Designer on Board during Construction
  • Contractor Involved in Design
  • Contractor/Designer QC/QA Required ISO 9000
  • Real-Time Lab Testing and Data Storage
  • Real-Time Design (for example: Analysis of Controlled Deformation [ADECO-RS])
  • 10-Year Warranties/Insurance

* H, M, L = High, Moderate, Low

 

Table 7. Embankment Construction Equipment and Methods for Accelerated Construction
Technology or Process Anticipated Accelerated Construction Performance Relative* Potential for Accelerated Construction Applicable Conditions for Accelerated Construction Relative Cost* Improvement in Quality* Comments
Base-line Technology for Comparison — Normal (possible staged) Fill Construction; Assumes Close Spacing and Arching for Piled Foundations
Light Aggregates Reduces or eliminates surcharge M-H Poor/ soft foundations M to H H Geofoam, flowable fill, etc.
Rapid Impact Compaction Building with thick fills and rubble fills M Thick fills and rubble M L Currently used for building on rubble fills; quality of compaction needs evaluation
Automatic Controlled Variable Roller Compaction Speeds compaction eliminating wasted time plus rapid QC M All cases but best in granular fill M M Compaction efficiency and uniformity improved; minimizes passes required
Accelerated Site Investigation Large area rapid QC by using ground-probing radar or resistivity M Use of GPR or resistivity for QC. All cases. L L Works for all cases
Horizontally Vacuum Consolidation Rapid consolidation of soft soils and below water soils without surcharge M Hydraulic fill and dredge spoil L L Allows use of hydraulic fill and dredge spoil
Dynamic Stiffness Gauge Rapid QC, approximately 2 minutes per test L-M Sands and gravels, possible rock fill L L-M Works for granular soils
Higher Energy Compation Impact Roller Allows use of thicker fills L-M Thicker fills M L Quality of compaction needs evaluation

Applicable Process from Scan Tour:

  • Contractor/Designer QC/QA Required ISO 9000
  • Real-Time Lab Testing and Data Storage
  • 10-Year Warranties/Insurance
  • Auto Control QC Documentation of Installation

* H, M, L = High, Moderate, Low

 

Table 8. Innovative Earth-Retention Systems for Accelerated Construction and Rehabilitation.
Technology or Process Anticipated Accelerated Construction Performance Relative* Potential for Accelerated Construction Applicable Conditions for Accelerated Construction Relative Cost* Improvement in Quality* Design and Construction Issues* Comments
Settlement Reduction Equipment Mobility Soil Excavation Vibration & Noise
Base-line Technology for Comparison — Temporary Sheeting and Shoring with Cast-in-Place (CIP) Wall
Deep Mixing (Lime-Cement) Columns Stabilizes soil to allow excavation without sheeting and shoring M Soft soils in low organic, nonartesian conditions M M L-M M N L Wet method is not applicable in tight R/W conditions; requires CIP wall
Vibro-Jet of Sheet Pile Driving Speeds driving of sheet piles through layered soils H Same as conventional sheet piles M L L-M M Y M Quality can be improved with post-grouting
Self-Drilling Nails Self-drilling and grouting for one-step installation H Difficult ground for drilling/ driving M M M H N L Use for difficult drilling (cobbles & boulders)
Cased Secant Pile (CSP) Rapid vertical and lateral support M Cut situations M M L/ M H Y L Depressed section in weak ground
Berlin Wall (Micropile Wall) Lateral wall support with vertical capacity H Difficult ground for drilling/ driving M H M H Y L Used for difficult drilling (cobbles & boulders) above ground water
Continuous Diaphragm Walls (CDW) One-step excavation & concrete placement with minimum mess (no slurry) H Tight site conditions, low headroom H M H L Y L Limited to 33 ft (10 m), setup cost is high
Hydro-Mill™ Diaphragm Walls One-step excavation and slurry placement with minimum mess H Useful in difficult drilling conditions, i.e., cobbles and boulders M H H L Y M High mobilization costs, good control on alignment with automated control system
Turbo-Jets Rapid vertical columns with limited spoil M All soils M M M M Y-M M Control appears better than jet grouting. Does not work well where obstructions.

Applicable Process from Scan Tour:

  • Designer on Board during Construction
  • Contractor Involved in Design
  • Contractor/Designer QC/QA Required ISO 9000

* H, M, L = High, Moderate, Low; Y, N = Yes, No.

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