Date of Award

5-2013

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Department

Civil Engineering

Advisor

Thomas C. Sandford

Second Committee Member

Melissa Landon Maynard

Third Committee Member

William G. Davids

Abstract

The current pile capacity calculation methods suggested by the Federal Highway Administration (FHWA) and the Canadian Geotechnical Society (CGS) used by the Maine Department of Transportation (MaineDOT) are sometimes unreliable and can provide poor estimates of in situ pile capacities. This is particularly an issue in Maine, as the recommended skin friction equations were not formulated for low displacement steel H-piles driven through glacial tills. The soil conditions in the state can also provide erratic predictions for open and closed ended pipe piles. Additionally, the bearing capacity parameters needed in design require extensive sampling and bedrock unconfined compressive strength; however, MaineDOT does not typically measure these strengths and must rely on generalized and variable strength estimates.

The goal of the research provided in this thesis is to improve design efficiency and lead to more effective design methods for driven piles in Maine. The correlations generated from this project could lead to cost savings and could also prove beneficial to other departments of transportation in the region that encounter similar subsurface conditions in design.

The project was essentially conducted in two phases. In the first phase a database was generated which contained data from approximately 80 different projects and over 250 dynamic load tests. Its purpose is to allow MaineDOT designers to search for information about projects that could potentially aid them in the design process. They will be able to find information about the site, pile, driving system, and measured capacities for each pile in the database. The database also includes the capability to expand allowing the designers to add new projects to the database as they are completed.

The second phase of the project aimed to correlate the Case Pile Wave Analysis Program (CAPWAP) results for each test pile with design methods suggested by FHWA. Each layer providing resistance for the pile was categorized as either cohesive, granular, till, or bedrock. The contribution of each layer to the total pile capacity was estimated from in situ or laboratory testing. The cohesive layers were analyzed using the Alpha and Beta Methods, the granular layers were analyzed using the Nordlund and Meyerhof Methods as well as direct standard penetration test (SPT) correlations, and the bedrock layers were analyzed using the Intact Rock and CGS Methods.

This thesis demonstrates the effectiveness of the design methods at estimating side friction capacity, end bearing capacity, and total capacity for each pile. The MaineDOT typically performs CAPWAP analyses at end of driving and one day after driving, so the available data did not allow for significant trends in capacity with time to be formulated. Upon inspection of the results, it was apparent that the Meyerhof, Alpha, and Intact Rock Methods provided the estimates closest to the CAPWAP measured capacities. The Nordlund Method and CGS methods were observed to perform the worst at predicting the side and end bearing capacities respectively. It was also apparent that capacity estimates for closed ended pipe piles on bedrock were more erratic than other types of piles.

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