Increase Use of Spread Footings on Soils to Support Highway Bridges - PowerPoint PPT Presentation

2019 Midwest Geotechnical Conference Columbus, OH September 17-19 Increase Use of Spread Footings on Soils to Support Highway Bridges By: Dr. Naser Abu-Hejleh, P.E. FHWA Resource Center, Geo/Hydro Team Geotechnical Engineering Specialist

Spread Footings on Soils to Support Bridges Spread Footing Soil 2

Advantages of Spread Footings Cost/time savings in foundation design, construction and maintenance: • Simpler and more flexible design and construction • Use common materials, equipment, and labour • Construction: safer and fewer problems/claims • Maintenance: safer and less disruption to traffic • Address issues with using deep foundations 3

2007-2010 FHWA Surveys of State  Use and performance of bridges supported by spread footings  Selection of spread footings  Bridge tolerable settlement (covered later). Spread footing = Spread footings bearing on soils to support highway bridges 4

Distribution of State DOTs Use of Bridge Foundations Spread Footings Spread Footings Driven Drilled on Soils on Rock Piles Shafts 11.5 % 12.5 % 56.5 % 19.5 %  States with extensive use  States with no or limited use 5

States with Extensive Use of Spread Footings States Spread Footings (%) Deep Foundations (%) Soil Rock Driven Piles Drilled Shafts Northeast States Connecticut 50 25 20 5 Vermont 40 10 45 5 Massachusetts 35 15 20 27 New Hampshire 30 30 30 10 New York 30 15 47 3 New Jersey 30 20 40 5 Southwest States New Mexico 30 10 30 30 Nevada 25 3 18 54 Arizona 20 5 Northwest States Idaho 20 10 60 10 Oregon 20 10 60 10 6

States with No or Limited Use of Spread Footings No Use Limited Use (<10%) Midwest Iowa, Missouri Illinois, Indiana, Wisconsin, Minnesota, Ohio Northeast West Virginia Maine, Virginia, Maryland All States Southeast Texas, Arkansas Colorado, Utah Southwest Northwest South Dakota, Wyoming, Hawaii North Dakota FHWA Conclusion: Use of spread footings when appropriate is not considered by many State DOTs 7

States with No or Limited Use of Spread Footings. Why? • Due to “perceived obstacles.” • Not due to valid obstacles (i.e., scour) These states are missing an opportunity to save time and money by not considering spread footings Photo credit: Derrick Dasenbrock, MnDOT. Used with permission 8

FHWA Goals Promote the use of spread footings on soils to support highway bridges when appropriate. Per AASHTO/FHWA consider spread footings bearing on:  Competent natural soils  Improved natural soils  Engineered granular fills (embankment)  Engineered MSE fills (walls, embankments) 9

Reference to Achieve FHWA Goals https://www.fhwa.dot.gov/resourcecenter/teams/geohydraulics/spreadfootings.pdf 10

Approach Used in the FHWA Reference 1. Identify perceived obstacles in using spread footings 2. Develop:  Recommendations to address perceived obstacles  Guidance to implement the recommendations 11

9 Obstacles States Main Obstacles 1. Limited knowledge of good performance and successful use and selection of spread footings 2. Use of very conservative settlement analysis  Concern of excessive bridge settlement that are costly and difficult to repair 12

8 Recommendations to Address Perceived Obstacles 1. Deploy AASHTO/FHWA technical resources 2. Review FHWA surveys of State DOTs for use, performance, and selection of spread footing 3. Consider spread footing on granular/MSE fills and with semi-integral and integral abutments. 4. Consider load tests and instrumentation programs 5. Deploy adequate subsurface investigation, construction, and quality control procedures. 13

8 Recommendations to address Perceived Obstacles 6. Deploy a rational procedure for settlement analysis of bridges supported on spread footings bearing on soils 7. Develop a rational procedure to determine the LRFD design bearing resistances for spread footings 8. Based on previous recommendations, develop LRFD Guidance for:  Selection of spread footings, and  Design of spread footings 14

I. Use, Performance, and Selection of Spread Footings 1. Use and Performance of bridges supported by spread footings 2. Selection of spread footings 3. Bridge tolerable Settlement (Covered later) 15

Use and Performance of Bridges Supported by Spread Footings Northeast States State Soils Rocks Performance (%) (%) Connecticut 50 25 Good performance Vermont 40 10 Good performance Massachusetts 35 15 Good performance New Hampshire 30 20 Good performance New York 30 15 Good performance New Jersey 30 20 Good performance Delaware 13 4 Good performance Pennsylvania 10-20 45-55 Good performance Rhodes Island 10 Good performance Maine 5 31 Good performance Virginia 5 30 Good performance Maryland 2-4 Good performance West Virginia 0 20 No use 16

Use and Performance of Bridges Supported by Spread Footings Midwest States State Soils Rocks Use and Performance (%) (%) Michigan 10 5 Hundreds of bridges with spread footings were constructed (70% before 1980, reduced to 50% by 1990, and currently 10%). Their overall performance is adequate and as bridges with deep foundations. Illinois 5 10 Very limited use with MSE walls. To support piers with very hard tills and dense sand). No performance or movement problems with these bridges. Wisconsin 5 10 Roughly 75 bridges supported on stiff natural soils in the last 10 years. Very limited use with MSE walls. Mix use of abutment piling and spread footing piers. These bridges are performing well or as good as bridges with piles” Indiana 1 5 Recently allowed spread footers for median piers in the accelerate I-465 project. Considered with glacial tills, IGM’s and engineered fills and in process to allow them over MSE walls. There has been no visible evidence of excessive settlement.” Minnesota 7 2 Recently used spread footing in simple span bridges (at abutments only) on dense sand and gravel at a rate of around 4 bridges per year. “ Bridges appeared to be in fine shape and perform well.” Ohio 5 1 Since January, 1998 built 244 structures on spread footing on MSE walls and rocks. Currently use of spread footings on MSE walls is not permitted, and allowed with dense sand and in few cases with very stiff clays. Problems are not observed Missouri ? 5 No use/not allowed Iowa 0 0 17

Use and Performance of Bridges Supported by Spread Footings Southwest States State Soils Rocks Use and Performance (%) (%) New 30 10 Extensive use of spread footings on MSE walls (30 out of the 55 Mexico bridges in the I-25/I-40 interchange). Also, used on abutments on embankments, to support piers, for single and multi span “Performed well, better than deep foundations as there is no bridge bump.” Nevada 25 3 With all types of bridges. Not allowed on MSE fills. “No known Issues, they are performing well” Arizona 20 5 Success with spread footings on MSE walls. Performance is not reported, but expected to be OK California 5% (30% -50% in Significant savings. With any type of bridge. “ Performed very well, South California no indications of poor performance” Utah 8 5 Mostly single span bridges. Not allowed on MSE fills. “Performed well” Two bridges on MSE walls, 3 rd bridge on 2:1 approach embankment. Colorado 3 bridges Costly with MSE walls! “All three bridges are performing well” Texas 0 0 No use Kansas 0 - No use 18

Use and Performance of Bridges Supported by Spread Footings Northwest States State Soils Rocks Performance (%) (%) Idaho 20 10 “Not aware of any performance issues with spread footings” Oregon 20 10 “Not aware of any performance issues with spread footings” Washington 10 25 “Not aware of any performance issues with spread footings Nebraska 10 “Not aware of any performance issues with spread footings” Montana 10 5 “Not aware of any performance issues with spread footings” Wyoming 5 17 “Not aware of any performance issues with spread footings” Alaska 5 “Not aware of any performance issues with spread footings” Hawaii 7 2 “Not aware of any performance issues with spread footings” South Dakota 0 5 No use North Dakota 0 - No use 19

Reported Performance from Instrumented Bridges  Minnesota DOT. In recent projects:  Settlement < 1”  Use of spread footing is increasing (DB, CMGC)  Ohio DOT. 1990-2006, 54 bridges:  All bridges are in good conditions  Spread footing are viable option for supporting bridges  Colorado DOT. Founders/Meadows Bridge (1998): Excellent performance with no bridge bump problem  20

Summary: Use and Performance of Spread Footings to Support Bridges  Use of spread footings by states varies significantly (0 to 50%)  Significant use in the Northeast  Some states do not consider spread footings even when they are appropriate  Good performance and economical use reported by all states that used spread footings Conclusion: many states are missing an opportunity to save time and money by not considering spread footings when appropriate 21

Summary: Selection of Spread Footings on Soils to Support Bridges • States considered (see FHWA Reference for more details): • Type of foundation soils • Favorable and unfavorable conditions • Bridges supported on spread footings bearing on recommended soils and fills have been safely and economically constructed by State DOTs 22