COLUMBIA & COWLITZ RAILWAY BRIDGE #7 SPIN FIN PILES IN PRACTICE

Transcription

1 COLUMBIA & COWLITZ RAILWAY BRIDGE #7 SPIN FIN PILES IN PRACTICE Todd Nottingham, P.E. Peratrovich, Nottingham & Drage Inc. 811 First Avenue, Suite 260 Seattle, Washington, Phone: , Fax: Mike Hartley, P.E. Peratrovich, Nottingham & Drage Inc. 811 First Avenue, Suite 260 Seattle, Washington Phone: , Fax:

2 ABSTRACT COLUMBIA & COWLITZ BRIDGE #7 - SPIN FIN PILES IN PRACTICE The Columbia & Cowlitz Railway Bridge #7 was severely damaged by fire in the summer of 2001, effectively destroying 900-feet of the structure. The bridge was part of the railway line that transported a significant amount of Weyerhaeuser timber product. The loss of the bridge forced Weyerhaeuser to absorb alternate transportation costs and affected the employment of many; therefore, it was important to quickly repair the bridge. Weyerhaeuser solicited bids from a number of firms to reconstruct the bridge under a design/build scenario on November 2, with bids due November 30, The team of Hurlen Construction and Peratrovich, Nottingham & Drage, Inc. was selected and was awarded a contract on December 17, The bridge was substantially complete and allowed traffic on March 20, 2002, an elapsed time of just 93 days. The bridge structure crosses a paved county road, elevated approximately 35-feet above the ground and is on a curve and grade. Soil conditions at the site consisted of loose to medium dense alluvial deposits over bedrock at various depths. The pile foundation for the bridge utilized spin fin tips, which substantially increases both compressive and tensile strengths of the piles. The increased capacity allowed longer spans and fewer piles and simplified longitudinal load resistance, thus saving time and reducing costs for the project. Key words: Railroad, Bridge, Spin Fin Pile Word count: 2,866

3 COLUMBIA & COWLITZ BRIDGE #7 - SPIN FIN PILES IN PRACTICE INTRODUCTION Overview The original Columbia & Cowlitz Railway Bridge #7 consisted of a combination of steel and timber construction. A 700-foot timber trestle section of the bridge was entirely destroyed and another 200-feet of bridge was severely damaged during a fire in the summer of 2001 (figure I). The loss of the bridge significantly affected the operations of Weyerhaeuser Company who owns and operates the line which is used to transport wood products in the area. The need to replace the bridge became apparent relatively soon after the fire when alternate transportation means failed to provide a cost affective solution. Weyerhaeuser hired the design/build team of Hurlen Construction and Peratrovich, Nottingham & Drage, Inc. (PND) through a design/build bidding process to reconstruct the C&C Railway Bridge #7 (figure II). The team was selected from a group of other highly qualified teams because it offered several cost saving solutions and provided the most timely construction schedule. Following the bid process that lasted from November 2 to November 30, 2001, Weyerhaeuser proceeded to negotiate with Hurlen/PND to provide an accelerated schedule. On December 17, 2001, a notice to proceed was issued with a substantial completion requirement of March 20, 2002.

4 Structure Description The selected concept featured relatively long spans using rolled steel girders. The girders were supported by two pile moment frame bents that utilized the driven pile as the column. The 700- foot main bridge replacement was divided into three independent bridge sections with a central four-pile bent utilizing batter piles that resisted longitudinal loads (figure III & IV). An open deck with timber ties and standard rail sections completed the superstructure. Reduced project time and lower cost was achieved by minimizing the number of driven piles, reducing the number of field installed components, and maximizing the use of locally available and existing materials (piles and pile caps). The design of Bridge #7 followed AREMA (American Railway Engineering and Maintenance of Way Association) guidelines. Design loading included standard E80 live load, wind, seismic, impact, and longitudinal loads. This bridge, with a 14-degree horizontal curve, needed to resist a significant centrifugal loading component. The selected 50-foot girder spans were the maximum that could be achieved with the available rolled steel girders and still meet roadway and other clearances. The bridge girders along the curved section were kept straight, but were positioned to provide optimal load balancing between all girders.

5 Project Implementation Work began concurrently on preliminary design, surveys, geotechnical investigation, and material acquisition for long lead items. Close coordination between all parties was necessary. Thirty-inch diameter pipe piles were initially selected based upon the anticipated height of the bridge. A mill order was not possible because of the long lead time. Existing material was found and put on hold in sufficient quantity to match preliminary pile estimates. However, four different pile wall thicknesses and grades of steel were required to meet the anticipated demand. Heavier wall piles and higher grade materials were used on pile bents that were subject to higher loads such as the longitudinally braced bents. Thinner wall piles were used at shorter spans and end bents which were subject to smaller loads. Ordered pile lengths were established after the geotechnical investigation was completed with sufficient quantity reserved for overruns. Final completion of pile driving showed a 7% overrun based upon preliminary pile estimates. Surveyors were mobilized to the site upon notice to proceed and continued to work through the holiday season. A final topographic survey was completed in late December that provided enough information to perform detailed design. The survey effort identified a significant quantity and variety of utilities along the west side of the road that apparently extended outside of the right of way. Based upon the locates, it was determined that special pile spacing would be needed in that area. Pile locations were established in the field and potholes were dug (soil vacuumed out to expose utility without damage) to verify that utility conflicts were avoided. The pile bent configuration at bent 8 was designed to allow the pile cap to span the majority of the utilities with one pile actually threaded between a power line and a water line.

6 A field geotechnical investigation performed by PND was initiated and completed by December 23, The program consisted of drilling four holes across the proposed alignment. Variable conditions were encountered, but generally consisted of variable depths of sand and silt over bedrock. Bedrock depths in some areas were excessive and it was determined that the pile foundation would need to be designed as friction piles in most instances. The steel superstructure for the bridge required a mill rolling for the main girders that met grade and charpy requirements. The two largest domestically rolled beam shapes were picked to be used on the project. The largest, W40 x 324, was used to span the main roadway while the other W40 x 230 was used throughout the remaining bridge. The initial mill order for the girders was placed on December 15, 2001 for the estimated steel lengths and rolling scheduled on January 2, The steel was rolled and trucked to Jesse Engineering in Tacoma, Washington where it was fabricated and sub-assembled to ensure the desired curvature and fit-up were obtained. Field construction began on January 15, 2002, with completion of demolition of the damaged trestle bridge (figures V & VI) followed by pile driving. Piles were driven with an impact hammer to desired pile capacities. Spin-fin pile tips were utilized on piles that were subject to tension loads located at longitudinal force resisting bents (figure VII). Tie placement, rail installation (figure VIII), and completion of the superstructure all went smoothly and allowed the first train to cross the bridge on March 20, 2002 (figure IX).

7 SPIN FIN PILE General Highly loaded tensile capacity piles, often over 100-tons, are being used with a greater frequency and in more diverse applications. Conventional piles are often unable to resist these tension loads. An innovative pile dubbed the Spin Fin with tension characteristics superior to those of usual piles does not usually require increasing the pile length, or require heavier driving equipment. A spin fin pile is a pipe with steel fins welded at a batter, giving the pile a screw-like appearance and characteristics at the pile tip. Fins can be readily shop or field fabricated and attached. Because of their unique deformation characteristics, these piles allow substantial pile movement without catastrophic failure. The result is a more predictable and reliable tension pile. End bearing or pile compression is also markedly improved. Spin fin piles were originally utilized in 1984 for a bulkhead tension tieback for a coal loading system, following in-house testing of model piles in Subsequent full scale model testing under a grant from the State of Alaska and Federal Highway Administration ( Use of Spin Fin Piles for Increased Tension Capacity, unpublished report for the State of Alaska Department of Transportation and Public Facilities; Campbell, Christopherson, Nottingham, 1987) and Caltrans ( Colton Interchange Spin Fin Pile Tension Load Test; Nottingham, Unpublished, 1991) established initial design parameter for sandy and silty soils. Practical installation and testing in a variety of structures have progressed from 1984 with thousands of spin fin piles now in place.

8 Pile Configuration Spin-fin piles differ from conventional piles in tip configuration only. Spin-fin pile connection to substructure components must usually be made to develop the pile strength and to resist torsion. Strong details at this interface assure development of the redundant aspects (i.e. large overload and energy absorbing capacity) of the spin fin piles. Conventional interface details such as short concrete embedment or penetration through piles by footing reinforcing steel are not acceptable. Spin-Fin Pile Action Spin-fin piles develop strength in two primary ways. Basically, this strength is derived through the pile skin friction as is a conventional pile, plus modified end bearing on the projected fin area resulting from fin/soil interface. Figure X shows an idealized tension pile. A compression pile would act similarly, except end bearing and shaft friction would be reversed. End bearing is engaged when the pile attains maximum skin friction, usually after a short primarily elastic movement for tension piles. Typical load deflection curves are graphically described in figures XI and XII. As pile movement continues, spin fin piles continue to gain strength in comparison to smooth piles. P u = P O + P f = Pile ultimate capacity P f =(k f N+c) A e, Where:

9 P f = Pile ultimate frictional capacity k f = A constant N = Standard split-spoon value for soil strata c = Cohesion A e = Effective pile friction area P O = A O k O d e, Where: P O = Pile ultimate spin-fin capacity k O = A constant that varies for compressive or tensile capacity and soil types A O = Projected plan area of fins d e = Depth to fin layer Limited by maximum or minimum depth. Note: Minimum depth must be adequate to develop a conical soil mass with greater weight than the pile tension.

10 Pile Load Tests Spin fin pile load tests require some special features, specifically, the pile must be restrained against rotating. Since the pile drives with a rotating screw-like action, this characteristic must be resisted during testing to achieve accurate results. Tests generally follow ASTM Quick Load Tests Procedures, often times extended to failure. Testing has shown large strength gain by simply modifying the pipe pile tips with slanted steel plates. Results in similar soils show some variation due to fin size, pitch, length, and time elapsed to testing and driving, and other variables. Without going into lengthy discussion, the most critical spin fin characteristic is the guarantee of predictable performance. Conventional smooth friction pipe piles seem to fail rapidly once shaft friction resistance is exceeded and may even be extracted at decreasing load. On the other hand similar spin fin piles move with increasing load after frictional resistance is surpassed and seem to produce predictable failure patterns. The pile elastic limit should not be exceeded under operating conditions (i.e. no permanent set) which is normally less than the limit of the shaft friction or approximately ½-inch of load test deformation. However, unusual loads such as maximum contingency loads should not exceed pile resistance at some acceptable pile set such as 1-inch. Using this philosophy the structure will never exceed permanent set during operational conditions and will experience only limited deformation after contingency events.

11 Geotechnical Information The following discusses one driven pile that was installed at the Bridge #7 Bent 9 left vertical (Pile 9LV). This vertical pile was positioned in the middle third of the replacement trestle and was subject to various loadings that were significantly larger than other typical bents. A spin fin pile tip was installed on the pile (figure VII). Initial geotechnical work was completed in the early stages of the projects. Figure XIII shows a generalized soil profile and two partial drill logs adjacent to Pile 9LV. The logs indicated the near surface material to be soft clays and silts down to 20-feet. This is followed with a medium dense sand layer from 20 to 60-feet. A dense sand layer with gravel extends from 60-feet to bedrock which is greater than 130-feet below grade. Pile Loads Loads to Pile 9LV consist of various components including dead, live, longitudinal, and centrifugal. These loads are visually described in Figure III. These loads are combined as follows: Compression Primary: Secondary: Dead + Live = 330 kip Longitudinal = 250-kips

12 Tension Maximum tension load is minimal due to configuration for this pile with maximum anticipated tension load less than 50-kips. However, the adjacent batter pile (Pile 9LB) could see as much as 280-kips in tension. Pile Analysis As previously discussed, spin-fin pile capacity is derived from two components skin friction and a type of end bearing. Pile 9LV was driven with an initial length of 140-feet to an embedment of 130-feet. It is a 30- inch diameter pile with inch wall thickness equipped with an 8-plate spin fin. A pile driving log is shown in Figure XIV. The ultimate elastic skin friction component of the pile was estimated as follows: Depth Material properties Skin Friction 0-20 feet clay/silt C=500 psf 80-kips feet Sand friction = 30*25=750 psf 240 kips feet Sand/gravel friction = 35*25=875 psf 480-kips Total estimated skin friction 780-kips The estimated ultimate skin friction was confirmed after driving by two methods a modified ENR formula which estimated the pile capacity at 950-kips and also by a wave equation method which estimated the pile capacity at 900-kips.

13 The ultimate capacities for the pile for both tension and compression were calculated using the wave evaluation as the ultimate skin friction capacity, P f, and P o = A o K o D e for the bearing component. Ultimate Pile Compressive Capacity P UC = P OC + P f = 900+1,600 = 2,500 kips Ultimate Pile Tensile Capacity P UT = P Ot + P f = = 1,500 kips In hind sight, pile embedment depths could have been substantially reduced with estimated embedment 20 to 30 feet less than was actually installed for this pile. However, some conservatism was justified due to the speed of construction. CONCLUSION Bridge #7 has been in operation since March, Spin fin piles provided assurance that tensile and compressive capacities would be met on the project that standard smooth piles could not. The completed structure utilized a minimum number of piles that allowed for an accelerated construction schedule (figures XV & XVI).

14 REFERENCES 1. Nottingham, D., Spin Fin Pile Performance, International Conference on Design and Construction of Deep Foundations, Orlando, Florida December 6-8, 1994.

15 TABLES AND FIGURES Figures I. Original Bridge - Fire II. New Bridge III. Pile Cap 9 IV. Typical Batter Pile Bent V. Fire Damaged Bridge VI. Existing / Remaining Bridge VII. Spin Fin Pile Tip VIII. Steel Superstructure IX. First Crossing X. Pile Tension Load Action XI. Typical Compression Pile Test XII. Typical Comparative Repetitious Tension Pile Test XIII. Soil Profile XIV. Pile Driving Record XV. Product Crossing XVI. Finished Bridge

16 ORIGINAL BRIDGE FIRE FIGURE I

17 NEW BRIDGE FIGURE II

18 PILE CAP 9 FIGURE III

19 TYPICAL BATTER PILE BENT FIGURE IV

20 FIRE DAMAGED BRIDGE FIGURE V

21 EXISTING / REMAINING BRIDGE FIGURE VI

22 SPIN FIN PILE TIP FIGURE VII

23 STEEL SUPERSTRUCTURE FIGURE VIII

24 FIRST CROSSING FIGURE IX

25 PILE TENSION LOAD ACTION FIGURE X

26 TYPICAL COMPRESSION PILE TEST IN SAND FIGURE XI

27 TYPICAL COMPARATIVE REPITITIOUS TENSION PILE TEST FIGURE XII

28 SOIL PROFILE FIGURE XIII

29 Project: Columbia & Cowlitz Bridge #7 Project No: Pile Designation: 9LV Ground Elev.: +29-ft Pile Type: 30-Inch Diameter Tip Elev.: -101-ft Foreman: Terry McConnville Pile Wall Thickness: inches Cutoff Elev.: ft Vibratory Hammer Type: NA Pile Tip Type: Spin Fin Initial Length:140-ft Impact Hammer Type: ICE 120S Req. Comp. Cap.: 500-kips Final Length: 170-ft Rated Energy: 120,000 ft-lbs Req. Tensile Cap.: 100-kips Full Stroke: 12,000 10ft Penetration Blows/ Foot Blow/ Minute Est. Energy Pile Rotation Notes 1 to Soft driving not recorded to ft-kips 90 degree at 30-ft to ft-kip 180 degree at 70-ft Splice and redrive at 100-feet degree at 88-ft 100 to ft-kip ft-kip Reduced energy for final driving ft-kip ft-kip ft-kip ft-kip ft-kip final rotation not recorded PILE DRIVING RECORD (Condensed from original) FIGURE XIV

30 PRODUCT CROSSING FIGURE XV

31 FINISHED BRIDGE FIGURE XVI