Abutment Design Example. Chris Byrum Doug Parmerlee

Transcription

1 Abutment Design Example Chris Byrum Doug Parmerlee

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4 Example Bridge

5 Evaluate Existing Test Hole Data Not much before 1940 MDOT Housel Soil Mechanics s ASTM SPT N-modified values

6 Evaluate Existing Test Hole Data Not much before 1940 MDOT Housel Soil Mechanics s ASTM SPT N-modified values

7 Evaluate Existing Test Hole Data Not much before 1940 MDOT Housel Soil Mechanics s ASTM SPT N-modified values

8 New Test Holes

9 In-Situ Vane-shear and 3 Shelby Tubes

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12 Design Shear Strength Profiles 4* Sc old MDOT Vane only Final Selection UC only Used for: Global Stability, Bearing Capacity, Piling Side Resistance, Pile Lateral..

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15 Used for Piling Tip Resistance

16 External Stability Task 1: Lateral Squeeze Task 2: Global Stability Task 3: Settlement Analyses Task 4:Bearing Capacity

17 LATERAL SQUEEZE ANALYSIS FS = 2*Cu + (4.14*Cu) gama*ds*tan(theta) H*gama Also used in the past H*gama < 3Cu, or 4Cu Where, Cu = Undrained shear strength of soft layer, psf Ds = Thickness of soft soil layer, ft gama = Unit weight of fill soil, psf theta = Angle of fill slope, degrees H = Height of fill, ft

18 Primary Shear

19 Secondary/Sympathy Shear

20 Edge of Recent Fill Laterally Squeezed Bulging Uplift Area

21 Previous Scenario H = 6 to 7 feet

22 Utility Contractor Adds Weight

23 Reaches F.S. = 1.0 Condition Road Centerline E.O.M.

24 Failure Backcalculation FS = 2*Cu + (4.14*Cu) gama*ds*tan(theta) H*gama Component 1 Component 2 FS Cu = 180 psf Ds = 30 ft For FS = 1 gama = 125 pcf 3*Cu = 540 theta = 45 degrees 4*Cu = 720 H = 6.5 ft gama*h = 812.5

25 Example Bridge

26 FS = 2*Cu + (4.14*Cu) gama*ds*tan(theta) H*gama Component 1 Component 2 FS Cu = 2100 psf Ds = 100 ft gama = 120 pcf 3*Cu = 6300 theta = 88 degrees 4*Cu = 8400 H = 46 ft gama*h = 5520 Cu FS Calculated F.S. Lateral Squeeze Abut. B Abut. A Undrained Shear strength, Cu, psf Where, Cu = Undrained shear strength of soft layer, psf Ds = Thickness of soft soil layer, ft gama = Unit weight of fill soil, psf theta = Angle of fill slope, degrees H = Height of fill, ft

27 Abutment A GLOBAL STABILITY ANALYSIS

28 Abutment A Set 2% strain force > 1.1 FS force

29 Abutment A Set ultimate force > 1.3 FS force

30 Abutment A Set Grid Limits > 1.54 FS force

31 Change in Plan Decided to add-a-span, use short pile-supported abutment, on 25+ feet of fill instead of the tall full-height abutment

32 Abutment A

33 Abutment B

34 Abutment B

35 Abutment B

36 Abutment B

37 ARE SPREAD FOOTINGS OK? Bearing Capacity

38 ARE SPREAD FOOTINGS OK? Bearing Capacity Factored B.C. = approx psf Approach Embankment Weight next to Abutment: Abut. A = 48*125 = 6000 psf not likely! Abut. B = 30 * 125 = 3750 psf maybe

39 ARE SPREAD FOOTINGS OK? Settlement Management Need to estimate settlement of footings caused by approach embankments And Footing pressures causing settlement serviceability-limit (1-inch and 1.5-inch limits) Pre-loads? Lightweight Fills? Pile Downdrag?

40 SETTLEMENT MANAGEMENT

41 SETTLEMENT MANAGEMENT

42 Elevation, ft Pressure, psf Groundwater Table Today s Condition P0, Overburden

43 615 Pressure, psf Lake Stanley Dry Period Elevation, ft 590 P0, Overburden Glacial Lake Stanley Groundwater Table 515

44 Elevation, ft Pressure, psf Pseudo-Pc P0, Overburden Preconsolidation Glacial Lake Stanley Pc Assumption Ice Weight on Hard Till 515

45 615 Pressure, psf Load Effects Elevation, ft P0, Overburden Glacial Lake Stanley Footing Pressure Pc Assumption P0 + DP

46 615 Pressure, psf Settlement, in Elevation, ft 590 P0, Overburden Glacial Lake Stanley Footing Pressure Pc Assumption P0 + DP Elevation, ft 590 Uc = 100% Uc = 75% Uc = 50% Uc = 25%

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48 SETTLEMENT MANAGEMENT

49 Wick Drains

50 Wick Drains

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52 Wick Drains

53 Example Bridge (5-20 years w/o wicks) 6 8 Settlement Estimates Soil Only, no footing pressures

54 Change in Plan Wick Drains Installed through Sand Drainage Layer

55 Change in Plan Pre-Load to this Elev. 7 (6 month wait for T90) Settlement Estimates

56 Change in Plan EPS Block H-Piles Less than 0.4 remains (ZERO Downdrag!!!!!) Settlement Estimates

57 Placement of EPS and Geogrid behind sheeting.

58 Example Bridge

59 Wick Drains Installed through Sand Drainage Layer

60 Pre-Load to Full Height (2 month wait) 7 Settlement Estimates

61 Remove Pre-Load, Piles, and Partial EPS EPS Block Est. Settlement =60% of all-sand pre-load

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64 Piling Analyses Axial Resistance Lateral Resistance: batter vs COM624P Bridge Approach Fill Settlement Downdrag Negative Skin Friction

65 Axial Capacity: Driven into Shale Rock With about 400 Kip Side Resistance 100+ kip Tip/Bottom Resistance HP14x73

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70 0.4 settlement

71 615 Pressure, psf " Settlement, in Elevation, ft 590 P0, Overburden Glacial Lake Stanley Footing Pressure Pc Assumption P0 + DP Elevation, ft 590 Uc = 100% Uc = 75% Uc = 50% Uc = 25% kip kip 350 kip 360 kip

72 615 Pressure, psf " 0.5" Settlement, in Elevation, ft 590 P0, Overburden Glacial Lake Stanley Footing Pressure Pc Assumption P0 + DP Elevation, ft 590 Uc = 100% Uc = 75% Uc = 50% Uc = 25% kip 250 kip kip 320 kip 340 kip 350 kip 355 kip 360 kip An extra 0.1 allowance for elastic pile shortening.

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74 For R ndr = 500 kip HP14x73, 25% settlement remaining: R n = (250/400) = kips Q p = 0.75(362.5) 220 = 52 kips/pile OUCH!!!! Drive 500 kip pile, only 52 kip available for bridge weight!!! NO GO!!

75 PDA with Dynamic Signal Matching Dynamic Static Rs = 400 kips R sdd = 250/400(DD) reduced side resistance during driving

76 615 Pressure, psf " 0.5" Settlement, in Elevation, ft 590 P0, Overburden Glacial Lake Stanley Footing Pressure Pc Assumption P0 + DP Elevation, ft 590 Uc = 100% Uc = 75% Uc = 50% Uc = 25% kip 250 kip kip 320 kip 340 kip 350 kip 355 kip 360 kip An extra 0.1 allowance for elastic pile shortening.

77 180 Pile Lateral Resistance COM624P LPILE Depth Below Footing, in Lateral Deflection, in Lateral Load 9-kip 15-kip 20-kip kip 30-kip

78 From LPILE Technical Manual

79 P = soil pressure V Q M W p From LPILE Technical Manual

80 List of Recs Given To Bridge Engineer Global Stability Settlement Amounts and Rates Spreads versus Deep Foundations Lateral Resistances Special Provisions/Materials Specifications Construction Considerations Water control Surface preparation Temporary Walls Vibrations Geotechnical Instrumentation needed?

81 Doug Parmerlee Overview of Abutment Design Concepts

82 Geotechnical Engineering During Construction

83 Geotechnical Field Monitoring Pile Axial Capacity Settlement Rates and Amounts Geosynthetics: Limits/Continuity/Splicing Lightweight Fills: Limits/Materials

84 PDA with Dynamic Signal Matching

85 Static Pile Load Tests

86 Soil Pore Pressure Dissipation

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89 Ancient Glacial Lake Beach on top of Grand Portal Point, Pictured Rocks Michigan s State Fossil: Mastodon M = EI d 2 z 2 dx