BRIDGE RESTORATION AND LANDSLIDE CORRECTION USING STRUCTURAL PIER AND GRADE BEAM

Transcription

1 BRIDGE RESTORATION AND LANDSLIDE CORRECTION USING STRUCTURAL PIER AND GRADE BEAM Swaminathan Srinivasan, P.E., M.ASCE H.C. Nutting/Terracon David Tomley, P.E., M.ASCE KZF Design Delivering Success for Clients

2 Project Location Lady Bug Point Bridge Over West Fork Lake Winton Woods Park

3 Site Vicinity Project Location

4 Presentation Outline Srinivasan (H.C. Nutting) Project Overview Geology & Subsurface Conditions Geotechnical Design Alternatives Value Engineering Solution Construction Tomley (KZF) Structural Aspects Srinivasan (H.C. Nutting) & Tomley (KZF) Summary & Questions

5 Bridge Structure & Pre-existing Topography Fill Placement Five-span bridge with composite precast concrete girders 2.5H: 1V spill-through abutments 15 ft. of fill placed along lakeshore Constantly flooded during wet seasons

6 Original Bridge Foundations Abutments Shallow Foundations Interior Piers Driven Piles

7 Landslide and Foundation Distress South Abutment Constructed in 1998 January south abutment and spill-through slope developed signs of distress and landslide movement The head scarp and tension cracks visible on the east and south sides of the bridge abutment Movements continued despite remedial repair (gravel filling)

8 Site Geology Geology Maps Review 100 Glacial Drift w/ Alluvial silt, sand and gravel, laminated silt and clay (lakebed deposits) Lakebed clays at the site susceptible to slope instability Glacial Map of Ohio Bedrock Interbedded Shale and Limestone of Grant Lake and Fairview Formation (Bellevue and Miamitown members)

9 Boring/Inclinometer Location Plan

10 Subsurface Profile at Bridge South Abutment Material Type (USCS) SPT N-Values (blows/ft) Average Thickness (ft.) Existing Fill (CL) Alluvial Clay (CL) Lakebed Fat Clay (CH) 5-8 (softmedium stiff) 8-15 (medium stiff-stiff) (stiff-very stiff) Lakebed Silty Clay (CL/CH) 2-8; less than 5, (very softmedium stiff) 80+

11 Monitoring of Slope Movement Cumulative Displacement Incremental Displacement

12 2007 Geotechnical Evaluation (by others) Possible contributing factors for distress abutment fill and bridge abutment loads (spread footing) dredging activities soft lakebed clay fluctuating water

13 Slope Stability Analysis (by others) Remedial Recommendation - a re-grading scheme Install multiple stabilization rock berms that extend beyond Interior Pier No. 1, to serve as toe buttress fill

14 Concerns with Re-grading Scheme Constructability Time of year Weather Cost Schedule permitting issues (USCOE) Post remediation lateral movement of abutment footing Needed excavations in front of the abutment footing may result in Loss of passive resistance May Undermine abutment foundation support Continued Settlement of Abutment Footing

15 Value Engineering Design Solutions Cantilevered soldier pile wall (single row) Tied back soldier pile wall Soldier pile wall with deadman system (Option 1) Ground improvement solutions Multiple rows of piers without grade beam Multiple rows of piers with grade beam (Option 2)

16 Value Engineering - Option 1 Deadman Piers Piers for vertical and lateral support

17 Value Engineering - Option 2 The owner preferred option

18 Design Approach Load Distribution along Length of Each Pier Landslide Forces Soil Arching Effect (S/D) Group Effects/Resistant Reduction from each individual pier Deflection Criteria at Pier Top Bridge Abutment Underpinning first Lateral support immediately in front of South Abutment Overall Stability of Corrected Slope Numerical Computer Modeling

19 Soil Arching Effect / Group Effect Two rows of piers, structurally tied to grade beams would restrain continued abutment lateral movements. Drilled shafts installed with large spacing are discrete structures rather than a continuous retaining wall. Pier clear spacing (S) to diameter (D) ratio of 2 was used here to include arching effects and due to abutment slope and constraints from the bridge superstructure. The long-term creep effect of cohesive soils were considered (over the time, stress relaxation and creep may reduce the arching mechanism) DRILLED SHAFT FOUNDATIONS FOR NOISE BARRIER WALLS AND SLOPE STABILIZATION - FHWA/OH-2002/038 BY ROBERT Y. LIANG Due to progressive settlement, bridge abutment underpinning was also necessary

20 Slope Stabilization Design Abutment Underpinning Bridge Abutment Underpinning Design Two drilled piers were used to underpin the abutment footing. Underpinning piers enabled access of construction equipment onto bridge deck to install the downslope stabilization piers excavation for grade beam system

21 Abutment Slope Stabilization Design Design procedure summary: determining landslide forces perform laterally loaded pier group analyses to optimize pier layout performing single pier lateral load analyses to optimize pier diameter, embedment, reinforcement, and estimate deflection

22 Calculate Landslide Forces using Analytical Method Wedge Analysis: 2000 psf (loads) on 2.5H:1V slope 0.65 ft. 17 ft.

23 Group Layout and Forces on Each Individual Pier GROUP 6.0 was used to determine the optimal pile embedment and group layout

24 LPILE Analyses for Each Individual Pier

25 Remedial Construction Delivering Success for Clients

26 Construction Sequence - Piers Remediation Timeline Closed in the Winter of 2007 Remedial system installed in spring The bridge was then re-opened in June 2008 Construction Sequence Close the bridge, and no traffic on the abutment and bridge decks. Install two underpinning piers and their hunches/knee brace supports beneath the abutment footing

27 Construction Sequence Grade Beams Install ten slope stabilization piers, including saw cutting bridge deck to allow the two middle pier installation Install first row pier hunches/knee brace supports beneath the abutment, and grade beams Install the remaining grade beams to complete pier group Use grade beams as reaction beams to raise the end span and cast a new pedestal. Restore the bridge abutment by hydrodemolition and concrete overlay, and repair the cut composite bridge decks, apply joint sealant, and then reopen the bridge.

28 Construction Completion

29 Winton Woods Structural

30 Bridge Approach

31 Walking/Riding Surface

32 Bridge Approach

33 Shaft Layout Plan

34 Beam Verification

35 Drilling

36 Side Support Shafts

37 Access

38 Temporary Access Path

39 Deck Removal

40 Structural Reinforcing & Grade Beams

41 Beam Jacking

42 Completed Bridge Underside

43 Completed Bridge Side View

44 Summary & Conclusions Aggressive structural remediation approach was utilized rather the initial passive buttress fill method The remedial approach continues to perform effectively The total cost of the bridge restoration and slope stabilization was less than $250,000 dollars Landslides are actually 3-D problems and may require 3-D analysis to model relatively large S/D ratio pier groups. Numerical methods such as PLAXIS 3D (finite element analysis) or FLAC 3D (finite difference analysis) can be used GROUP, SHAFT, and LPILE programs can be used for effective slope stabilization design An instrumentation monitoring program can be valuable

45 Acknowledgments Owner: Hamilton County Park District, Cincinnati, Ohio Foundation Contractor: Scherzinger Drilling, Cincinnati, Ohio General Contractor: Fred A. Nemann Company, Cincinnati, Ohio Geotechnical Engineer: H.C. Nutting, a Terracon Company, Cincinnati, Ohio Structural Engineer: KZF Design, Cincinnati, Ohio.

46 Questions??