Pile Setup, Dynamic Construction Control, and Load and Resistance Factor Design of Vertically-Loaded Steel H-Piles

摘要

Because of the mandate imposed by the Federal Highway Administration (FHWA) on the implementation of Load Resistance Factor Design (LRFD) in all new bridge projects initiated after October 1, 2007, research on developing the LRFD recommendations for pile foundations that reflect local soil conditions and construction experiences for the State of Iowa becomes essential. This research focuses on the most commonly used steel H-pile foundation. The research scope is to (1) characterize soil-pile responses under pile driving impact loads, and (2) understand how the generated information could be used to improve design and construction control of piles subjected to vertical loads in accordance with LRFD.It has been understood that efficiency of the pile foundation can be elevated, if the increase in pile resistance as a function of time (i.e., pile setup) can be quantified and incorporated into the LRFD. Because the current pile foundation practice involves different methods in designing and verifying pile performances, the resulting discrepancy of pile performances often causes an adjustment in pile specifications that incurs incremental construction costs, significant construction delays, and other associated scheduling issues. Although this research focuses on the most advanced dynamic analysis methods, such as Pile Driving Analyzer (PDA), Wave Equation Analysis Program (WEAP), and CAse Pile Wave Analysis Program (CAPWAP), the accuracy of these methods in estimating and verifying pile performances is highly dependent upon the input selection of dynamic soil parameters that have not been successfully quantified in terms of measured soil properties.To overcome these problems and due to the limited data available from the Iowa historical database (PILOT), ten full-scaled field tests on the steel H-piles (HP 250 y 63) were conducted in Iowa. Detailed in-situ soil investigations using the Standard Penetration Test (SPT) and the Cone Penetration Test (CPT) were completed near test piles. Push-in pressure cells were installed to measure total lateral earth and pore water pressures during the life stages of the test piles. Soil characterization and consolidation tests were performed. Pile responses during driving, at the end of driving (EOD), and at restrikes were monitored using PDA. PDA records were used in CAPWAP analysis to estimate the pile performances. In addition, hammer blow counts were recorded for WEAP analysis. After completing all restrikes, static load tests were performed to measure the pile resistance.The information collected from the tests provided both qualitative and quantitative studies of pile setup. Unlike the empirical pile setup methods found in the literature, analytical semi-empirical equations are developed in terms of soil coefficient of consolidation, SPT N-value, and pile radius to systematically quantify the pile setup. These proposed equations do not require the performance of pile restrikes or load tests; both are time consuming and expensive. The successful validation of these proposed equations provides confidence and accuracy in estimating setup for steel H-piles embedded in cohesive soils. For the similar study on large displacement piles, the results indicate that the proposed methods provide a better pile setup prediction for smaller diameter piles.Based on statistical evaluations performed on the available database, field tests, and sources found in the literature, it was determined that different uncertainties were associated with the estimations of the initial pile resistance at the EOD and pile setup resistance. To account for this difference, a procedure for incorporating the pile setup in LRFD was established by expanding the First Order Second Moment (FOSM) method, while maintaining the same target reliability level. The outcome of the research provides a methodology to determine resistance factors for both EOD and setup resistances based on any regional database. Therefore, the practical implementation of pile setup can now be included in a pile design, which has not been provided in the latest American Association of State Highway and Transportation Officials (AASHTO) Bridge Design Specifications.Combining the PILOT database with the field test results, regionally calibrated resistance factors for bridge deep foundations embedded in clay, sand, and mixed soil profiles were established for the dynamic analysis methods. This regional calibration generated higher resistance factors and improved the efficiency of pile performances when compared with those recommended by the latest AASHTO Bridge Design Specifications. Furthermore, using these calibrated results of the dynamic analysis methods that serve as the construction control methods, the resistance factors of the Iowa in-house method (Iowa Blue Book) that serves as the design method were enhanced through the development of a construction control procedure. Construction control consideration minimizes the discrepancy between design and field pile resistances, and integrates the construction control methods as part of the design process.An improved CAPWAP signal matching procedure was developed to provide a better quantification of the dynamic soil damping factor and quake value with respect to different soil properties along the shaft and at the toe of a pile. Correlation studies resulted in the development of several empirical equations for quantifying the dynamic soil parameters using the measured SPT N-value. In addition, the results reveal the influences of pile setup and pile installation on the dynamic soil parameters. The application of these estimated dynamic soil parameters was validated through the improvement of a CAPWAP signal match quality.