LONG-TERM MOVEMENTS OF HIGHWAY BRIDGE APPROACH EMBANKMENTS AND PAVMENTS

Transcription

1 LONG-TERM MOVEMENTS OF HIGHWAY BRIDGE APPROACH EMBANKMENTS AND PAVMENTS Tommy C. Hopkins Research Engineer University of Kentucky Transportation Center Geotechnology 8 TH ANNUAL TECHNICAL FORUM GEOHAZARDS IN TRANSPORTATION IN THE APPALACHIAN REGION Geotechnology Charleston, WV 8/5-7/08 Geotechnology Charleston, WV 8/5-7/08 Florida

2 Causes and factors to consider Potential mitigation and design measures

3 CURRENT ICE AGE PERIOD Recent interglacial Periods Pre-Illinoian Illinoian Ice Sheet Wisconsin Ice Sheet (Pre-Gorian Period) Wisconsin Kentucky Ohio River No glaciers advanced into KY

4 Kentucky Geology Sedimentary Formations

5 Soils in Kentucky are residual (90% clays and silty clays) Depth to bedrock is generally shallow ---0 to 30 feet Exception: Along major streams and in far Western KY

6 (Interglacial Global Warming Period) Typical Situation in KY Bridge approach pavement ti is free to settle Bridge cannot settle Fill Soil Foundation Bedrock Piles

7 Research Studies Observation method: Examined several hundred bridges on Interstates and Parkways and noted attributes Detailed studies: Performed detailed studies at selected bridge sites Involving long-term measurements (1966 to 1978)

8 Selected Six Bridge Approach Sites Foundation Settlement Analysis Collected thin-walled tube samples Performed oedometer tests Estimated primary and secondary consolidation Installed settlement gages on foundation Measured magnitude and rate of primary and secondary consolidation and compared values to estimated values

9 Selected Six Bridge Approach Sites Collected thin-walled tube samples from foundation and embankment Performed consolidated-undrained d d i d triaxial i tests with pore pressure measurements Performed slope stability analysis factor of safety Installed Slope inclinometers to measure horizontal movements Installed points on approach pavements and measured settlements periodically

10 Factors to consider Lack of good compaction of backfill Dynamic loading Drainage of water from bridge and pavement into backfill Erosion (water) Primary and secondary consolidation of foundation soils Fill Soil Foundation Bedrock Slope Toe Rapid Drawdown Long-term creep settlement of embankment--fs is too low

11 CONCLUSION To minimize differential settlement between the bridge deck and approach pavement: Each factor listed in the previous slide must be considered Detailed subsurface and geotechnical studies will be required. Complex Problem..There are no magical solutions to this problem

12 Route 4, Parkers Mill Overpass, Fayette Co. F min = Settlement Gage

13 Approach Paving 1.5 ) Load (TSF) Approach Pavement Constucted Settlemen nt (in.) Measured Predicted Predicted Magnitude= 3.6 in Time (Days)

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15 Approach Embankment I 64 Bridge Across Bull Fork Creek (East End) (ft) Ele evation Bullfork Bridge Approach Embankment---Conglomertate of weathered, soft shale and hard durable rock, Ohio black shales; Bedfork, Borden shales; sandstones φ' = c' = 69 lbs/ft 0 Foundation φ' = 31 ; c' = Horizontal Distance (ft)

16 Depth (Ft t)) Resultant Movement (in.) Slope Inclinometer Measurements (Initial) To (9.6 years)

17 Eastern Approach Embankment Load (tons/ft 2 ) Construction Started August 1968 Bridge Approach Pavement Constructed 2 Set ttlement (in nches) Primary Predicted Observed Secondary Predicted Ultimate Settlement = 14 inches Time (days)

18 Western Approach Embankment Primary Predicted d Observed Secondary

19 Slope Stability: F = Eastern Approach Embankment Consolidated Undrained Triaxial Tests w/pp Measurements

20 Western Approach F min =

21 Eastern Approach Emb. (EBEE) Bullfork Creek Eastern Bridge Approach Embankment ch 0 Settlement of Approa Pavemen nt (inches) Approaches Constructed Outside Pavement Edge Projected Time (Days)

22 Western Approach Emb. (WBEE)

23 Booneville-Jackson Road (KY 30) Spread Footing 55 Rapid Foundation Consolidation

24 Embankment Creep Settlement Abu utmen nt Settl lement (in.) Monitored: 9 years Time (days)

25 I 64, Slate Creek, Bath County (Example of Erosion) Erosion o below abutment t and in front of Embankment Slope

26 Horizontal Movement (in.) Depth (ft) Resultant Movement (in.) Monitored: To or 8 years

27 Foundation Settlement

28 Approach Settlement of Pavement I 64, Slate Creek, Rowan Co.

29 I 64, Slate Creek, Bath County (Example of Erosion; low FS ) F min = 1.12 min

30 Example of Erosion of Embankment Toe US 68, Bridge Across Licking River, Nicholas Co. Southern Approach Emb. Failed During Construction Side-Hill Fill Berm Northern Approach

31 Example of Erosion of Embakment Toe Southern Approach

32 Embankment Toe Erosion

33 Method of Repair Shear Key and Berm

34 Shear Key and Berm Limestone in cut section

35 View Downstream

36 Example: Secondary Compression of Foundation I 24 bridges across Eddy Creek Lake Barkley (Early Construction ti Specified) F min =

37 Primary and Secondary Compression of Foundation ment L oad (TS SF) (in.) Lo oad (TS F) Settlem Primary Approach Paving Approach Paving Time (days) Time (days)

38 Primary and Secondary Compression of Foundation Settlem ment (in.) Load (TS SF) Approach Paving Time (days)

39 Settlem ment (in.) Load (TS SF) Primary and Secondary Compression of Foundation Approach Paving Time (days)

40 I 24, Eddy Creek ( ) views after 17 years Northern Entrance Approach Pavement Northern Exit Approach Pavement

41 Bluegrass Parkway Bridges Across Chaplin River (Low FS- failure) Western Approach Eastern Approach Western Approach Eastern Approach 50 Chaplin River 70

42 Scarp Slope Failure Exposed H-piles

43 Slope Inclinometer

44 Bluegrass Parkway: Eastern Settlement Patching

45 Eastern Approach F min = (Peak) F min = (Residual)

46 Bluegrass Parkway: Eastern Approach Horizontal Movement

47 3:1 3.5:1 Repair Method Eastern Approach 2:1 100 ft

48 Western Approach Repair Method F min = 1.17 (Peak) F min = 0.86 (Residual) 50 ft Decrease Slope; Relocate abutment

49 I 71 Bridges Across Kentucky River Settlement t Gages History doesn't repeat itself, but it does rhyme Mark Twain

50 Slope Stability Analysis I 71 Approach Embankment FS = 1.52

51 Primary and Secondary Compression of Foundation Primary Secondary

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53 ment (in.) 0 1 Secondary Foundation Compression Settle 2 Total Exit Appr roach Paving Time (days)

54 Primary and Secondary Compression of Foundation

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56 I 71 Bridges Across Kentucky River

57 I 71 Bridges Across Kentucky River

58 Effect of Compaction on Approach Embankment Stability and Settlement? Selected nine Kentucky Shales (talus piles at bases of shale roadway cuts). Performed compaction tests t on each shale using low-energy, standard, and modified compactive energies. Performed consolidated undrained triaxial tests with pore pressure measurements (specimens remolded to 100 % maximum dry density and optimum moisture content).

59 Potential Specs. Current Specs. bs/ft 3 ) Dry De ensity (l 140 Modified Standard Low-Energy Moisture Content (Percent)

60 Compaction Tests on Selected Kentucky Shales Ma aximum m Dry Density (lbs/ft 3 ) Modified (Potential Specs.) Standard (Current Specs.) Low Energy Optimum Moisture Content (%)

61 Triaxial Tests on Selected Kentucky Shales Modified Standard Low-Energy Shale φ ' Name Compaction T 189 φ ' (Degree s) Compaction T 99 Effective Compaction Stress Parameters c c c (lbs/ft 2 ) φ ' (Degree s) φ' (lbs/ft 2 ) (Degrees) (lbs/ft 2 ) New Albany Hance Drakes Nancy Osgood New Providence Kope Crab Orchard Newman

62 Embankment Material: New Providence Shale

63 Low-Energy φ' ' = c' = 40 psf Standard φ' ' = c' = 335 psf φ' = Modified c' = 1013 psf

64 Method for Estimating Embankment Creep Fill Settle ement (in.) Linear Time (days)

65 H ( ) ss= csshelog10 t ss/t c or H /H ss e c ss= = Coefficient of Embankment Creep log ( / t ) 10 tss c Hss He = = shear strain and secondary settlement of approach embankment (creep?) Height of approach embankment t c t = = time of placement of approach pavement ss time of significant shear strain and secondary compression of approach embankment---usually 10,000 days

66 Method for Estimating Embankment Creep C ss= Coefficient of Embankment Creep p( (?) F r = ratio of embankment height to factor of safety C ss = 47370F r ss C F r

67 = 47370Fr ss c c ss = slope of the settlement logarithm of time curve (coefficient) F r = ratio of the embankment height, H e e, to the long-term. factor of safety, F C = ss (. 5013log F )

68 Method for Estimating Embankment Creep F lt = minimum long-term factor of safety = (Low-energy compaction) (New Providence Shale) H = height of embankment = 98 ft, e H 98 e F r = = = 78.4 Flt t 800 days after start of construction (estimated value), ss t c 10,000 days (or 27.4 years)

69 EXAMPLE OF IMPROVING COMPACTION Low-Energy (F = 1.09) 98 (1.5013log ) in 10,000days H ss= 10 98ft log 10 = 20.4 in. ft 800days Standard d (F =1.42) H ss= 13.7 Modified (F= 1.91) H ss= 8.7

70 25 Embankment Creep Settlement (in.), H Hss STD Mod LE H ss = 23.1F Factor of Safety, F

71 Empirical Method of Estimating Time Rate of Primary Settlement T = T c

72 If time, T c, end of embankment construction is not known: End of emban nkment Construc ction, T c (Days) T Ht. of Embankment, H e (ft) = c H e

73 T T 100 c T T 100 = end of primary consolidation T c = end of embankment construction c c H e H e = height of embankment. H e T H )

74 c vfield = TH t = Coefficient i of Consolidation T = dimensionless Time parameter H = thickness of compressible Layer c vfield 2 2 = TH 1. 6H = H H e e

75 CONCLUSION To minimize differential settlement between the bridge deck and approach pavement: Each bridge site must be evaluated. Detailed subsurface and geotechnical studies will be required.

76 Lack of good compaction of backfill Dynamic loading Drainage of water from bridge and pavement into backfill Erosion (water) Primary and secondary consolidation of foundation soils Fill Soil Foundation Bedrock Slope Toe Rapid Drawdown Long-term creep settlement of embankment--fs is too low Complex Problem..There are no magical solutions to this problem

77 CONCLUSION AND RECOMMENDATIONS Each site must be evaluated. Detailed attention must be given to: Primary and secondary foundation compression Compaction energy considering using Modified Embankment creep /shear strain Lateral movements Erosion Detailed subsurface and geotechnical studies will be required.

78 CONCLUSION AND RECOMMENDATIONS Embankments on compressible foundations: Preconsolidate foundation with a surcharge fill Fine-grained soils use modify compaction Use wick drains or sand drain to speed up foundation settlement Removal of compressible foundation materials Lightweight Fill--slag slag, fly ash, cinders, geofoam etc..

79 CONCLUSION AND RECOMMENDATIONS Embankments: Construct with high shear strength material Specify early construction Completely break down shales