FEATURE ARTICLE Old Bridge Prestressed Conc. Test Pile-1 New Bridge Steel Reinforcement LDOE Test Pile 0.4 to 1.0 (Tomlinson, 1970). The effective stress method (β-method) relates friction resistance to the effective overburden pressure (σ' ) and was first proposed by Burland (1973): β=f /σ'v v s , where β = effective stress coefficient. Many re- searchers (e.g., Clausen, 2005; Fellenius, 2015) reported the backcalculated values of β, which range from 0.15 to 0.35 for clays and from 0.30 to 0.90 for sands (Fellenius, 2015). The specific objectives of this study Project site, test piles, instrumentation and Statnamic testing Large Diameter Open End Piles for Rigolets Pass Bridge in Louisiana Open-end (OE) cylinder piles are widely used for bridge foundations construction, as they provide superior moment resis- tance and high axial capacity. Small diameter (14 in [356 mm] or less) OE piles are generally observed to plug early in the driving process and are thought to behave similar to closed-end piles. At larger diameters, however, OE piles usually “cut” through the soil instead of plugging, resulting in a column of soil within the pile whose height approaches the pile embed- ment depth. This transition to large diameter OE piles from prestressed concrete (PSC) and small diameter closed- end piles have brought to focus some of the gaps or inadequacies in current pile design procedures by the American Association of State Highway and Transportation officials (AASHTO) and American Petroleum Institute (API). Available research on large diameter OE (LDOE) cylinder piles mainly focuses on “plugging” and predicting pile capacity from CPT methods. However, very few full-scale field studies were conducted and reported on LDOE cylinder piles to examine their behavior during driving, load testing, soil setup process and predicting the axial capacity by total stress and effective stress methods. Test piles (TPs) are usually instru- mented with strain gauges to evaluate the load distribution along the pile length. Design parameters, such as the total stress adhesion factor (α) and the effective stress factor (β), are typically used to estimate the side resistance of the pile and can be back calculated from the measured load distribution of the instrumented pile. Not enough studies have been conducted to recommend α and β values for LDOE piles as the costs for the instrumentation and performing the load test are expensive. The adhesion factor is related to the undrained shear strength (S ) of clayey soils and can u be calculated from the method proposed by Tomlinson (1957): α=f /S , where f = unit side resistance and S = undrained shear strength. For cohesive soils, α ranges from s u u s Chris Nickel, P.E., Louisiana Department of Transportation and Development were to (a) instrument the test pile with strain gauges to measure the side and tip resistances separately during load testing, (b) perform the laboratory and in-situ testing to characterize the subsurface soil condition, (c) conduct load tests (i.e., static load testing [SLT], dynamic load testing [DLT] and Statnamic load testing [SNLT]) to measure the amount of setup with time, (d) calculate the rate of increase in pile resistance or setup, and (e) back-calculate the design parameters (α and β) for individual soil layers along the pile length. Project Description and Soil Conditions The project consisted of the construction of the new Rigolets Pass Bridge located in Orleans Parish along Route U.S. 90 in Chalmette, Louisiana, which is located northeast of New Orleans. The old bridge was damaged by Hurricane Katrina in August 2005 and required major repairs. To safely improve roadway and waterway traffic flow, a new two-lane high-rise structure was built west of the existing structure. Four test piles were driven along the bridge to perform the load tests and verify the design methodology. Subsurface Geotechnical Conditions: Laboratory and in-situ testing programs were performed to characterize the subsurface soil conditions at the locations of the test piles (TPs). Boreholes were drilled at the four TP locations and high- quality 3 in (7.6 cm) diameter Shelby tube AUTHORS Murad Y. Abu-Farsakh, Ph.D., P.E., Louisiana State University; Md. Nafiul Haque, Ph.D., Ardaman and Associates; and DEEP FOUNDATIONS • SEPT/OCT 2019 • 81
